HHNS*6130 READING LIST - Winter 2009
January 13 -
GLYCOGEN METABOLISM (INCLUDING LIVER)
Work on skeletal muscle glycogen utilization was the first area in which the biochemical effects of muscle contraction were examined. This was facilitated by the re-introduction of the needle biopsy technique in the 1960’s for human research. This technique was not new as it had been used in the 1800s. The advance in the 1960’s was the additional use of a local aneasthetic, which had not been the case in the 1800’s.
The following papers are to be read (1), (2)(3)(4), (5)(6)
References (1), (2), and (4) are essentially historical background on which much of exercise metabolism was founded, while the latter 3 involve modern techniques for the study of glycogen. Treat Armstrong 1974 and Gollnick 1973 as “1 paper”
1. Armstrong RB, Saubert CWt, Sembrowich WL, Shepherd RE, and Gollnick PD. Glycogen depletion in rat skeletal muscle fibers at different intensities and durations of exercise. Pflugers Arch 352: 243-256, 1974.
2. Gollnick PD, Armstrong RB, Saubert CW, Sembrowich WL, Shepherd RE, and Saltin B. Glycogen depletion patterns in human skeletal muscle fibers during prolonged work. Pflugers Arch 344: 1-12, 1973.
3. Marchand I, Tarnopolsky M, Adamo KB, Bourgeois JM, Chorneyko K, and Graham TE. Quantitative assessment of human muscle glycogen granules size and number in subcellular locations during recovery from prolonged exercise. J Physiol 580: 617-628, 2007.
4. Nilsson LH and Hultman E. Liver glycogen in man--the effect of total starvation or a carbohydrate-poor diet followed by carbohydrate refeeding. Scand J Clin Lab Invest 32: 325-330, 1973.
5. Prats C, Cadefau JA, Cusso R, Qvortrup K, Nielsen JN, Wojtaszewski JF, Hardie DG, Stewart G, Hansen BF, and Ploug T. Phosphorylation-dependent translocation of glycogen synthase to a novel structure during glycogen resynthesis. J Biol Chem 280: 23165-23172, 2005.
6. Wilson RJ, Gusba JE, Robinson DL, and Graham TE. Glycogenin protein and mRNA expression in response to changing glycogen concentration in exercise and recovery. Am J Physiol Endocrinol Metab 292: E1815-1822, 2007.
_______________________________________________________________________________________________________
January 20 -
CARBOHYDRATE METABOLISM – BONEN
GLUCOSE TRANSPORT & SIGNALLING
BACKGROUND INFORMATION ON GLUCOSE TRANSPORT
Diabetes
Types of Diabetes
A). Insulin dependent diabetes mellitus (IDDM) = Type 1 = Juvenile diabetes
15% of all cases usually in young people < 30 years
B) Non-insulin dependent diabetes mellitus (NIDDM) = type 2 = maturity onset diabetes
Problem
IDDM or type 1 diabetes: pancreas produces no insulin, Rx: insulin injection
NIDDM or type 2 diabetes : in early stages there is lots of insulin, in fact insulin levels are very high because glucose is high and so pancreas secretes insulin. The problem therefore is at the level of disposal (i.e. some tissues are insulin resistant). In later stages insulin production is lowered by pancreas
Rx: in early stages (diet, exercise, weight loss, oral hypoglycemics).
later stages these (diet, exercise, weight loss, insulin)
PROBLEM IN NIDDM
some tissues are insulin resistant -- i.e. adipose tissue and muscle (muscle normally takes up 90% of a glucose load) by mass muscle is most NB
Site of the problem: Glucose enters cells via a facilitated transport system involving a transporter protein. In the past decade a family of GLUT isoforms (GLUT1-GLUT13) have been cloned. Some GLUTS are co-expressed in the same tissue (e.g GLUT1 and GLUT4 in muscle, heart, adipose tissue). Other GLUT transporters are expressed in a tissue specific manner.
All GLUT transporters exhibit tissue-specific and isoform-specific regulation. (i.e. cannot generalize).
The key transporter in muscle is believed to be GLUT-4. It is the “insulin-sensitive transporter”. GLUT4 is translocated by insulin from an intracellular site to the plasma membrane and also T-tubules in muscle. GLUT-1 has a “basal” function.
So the NIDDM problem is centered around this transporter protein GLUT-4: i.e. the number of GLUT4 proteins, the possible activity of the transporter, the translocation of the protein; the signalling of the protein to get it ready to translocate
Muscle |
Obese Zucker Rat (insulin resistant, GLUT4 normal) |
|---|---|
insulin ---> increase glucose transport contraction ---> increase glucose transport insulin +contraction ---> increase glucose transport additively |
Reduced glucose transport in presence of insulin but exhibits normal contraction induced glucose transport |
For background, it is highly recommended that you read the following reference to get an overview of insulin-stimulated glucose transport
Thong FSL, Dugani CB, and Klip A. Turning Signals On and Off: GLUT4 Traffic in the Insulin-Signaling Highway. Physiology ( Bethesda), 2006.
Have a look at Song et al for the time needed to induce insulin signalling optimally
Song XM, Ryder JW, Kawano Y, Chibalin A, Krook A, and Zierath JR. Muscle fiber type specificity in insulin signal transduction. Am J Physiol (Reg Int Comp Physiol) 277: R1690-E1696, 1999.
Assigned readings are (1), (2), (4)(3), and (5)
1. Alkhateeb H, Chabowski A, Glatz JF, Luiken J, and Bonen A. Two phases of palmitate-induced insulin resistance in skeletal muscle: impaired GLUT4 translocation is followed by a reduced GLUT4 intrinsic activity. Am J Physiol Endocrinol Metab 293: E783-E793, 2007.
2. Jorgensen SB, Viollet B, Andreelli F, Frosig C, Birk JB, Schjerling P, Vaulont S, Richter EA, and Wojtaszewski JF. Knockout of the alpha2 but not alpha1 5'-AMP-activated protein kinase isoform abolishes 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranosidebut not contraction-induced glucose uptake in skeletal muscle. J Biol Chem 279: 1070-1079, 2004.
3. Kramer HF, Taylor EB, Witczak CA, Fujii N, Hirshman MF, and Goodyear LJ. Calmodulin-binding domain of AS160 regulates contraction- but not insulin-stimulated glucose uptake in skeletal muscle. Diabetes 56: 2854-2862, 2007.
4. Kramer HF, Witczak CA, Taylor EB, Fujii N, Hirshman MF, and Goodyear LJ. AS160 regulates insulin- and contraction-stimulated glucose uptake in mouse skeletal muscle. J Biol Chem 281: 31478-31485, 2006.
5. Lemieux K, Han X-X, L. Dombrowski, Bonen A, and Marette A. The transferrin receptor defines two distinct contraction-responsive GLUT4 vesicle populations. Diabetes 49: 183-189, 2000.
_______________________________________________________________________________________________________
January 27 -
MITOCHONDRIAL TRANSCRIPTION FACTOR (PGC1)
PGC-1 BACKGROUND
Skeletal muscle insulin resistance is a cardinal feature of obesity and type 2 diabetes. Yet, it is well known that increasing physical activity can improve insulin sensitivity in obese individuals and those with type 2 diabetes, as well as in healthy individuals (cf (22,39,57,104,109). While the molecular bases of these of these prophylactic/therapeutic benefit are not well understood, the very recent discovery of a master metabolic molecule, peroxisome proliferator-activated receptor co-activator a (PGC-1) (103), may begin to unravel this mystery. PGC-1 co-activates transcription factors that induce gene transcription of a) mitochondrial enzymes involved with fatty acid oxidation (106,124), b) mitochondrial biogenesis (78,123) and the glucose transporter GLUT4 (91c). Importantly, these observations may begin to explain the molecular basis of the training-induced improvements in insulin sensitivity, since the molecular processes initiated via PGC-1, parallel almost exactly the processes induced by exercise training (cf (59)), including altered gene expression that may be expected to improve insulin sensitivity (106,124)
DISCOVERY AND SIGNIFICANCE OF PGC-1
PGC-1 discovery: It had been observed that antidiabetic thiazolidinediones, which activate the peroxisome proliferator-activated receptor (PPAR), promote the differentiation of brown adipose cells and their energy expenditure. But, it was also clear that simply activating PPAR failed to activate similar metabolic processes in different cell types (see (1,103,108) for discussions) This suggested that in some cells a co-activator was required to realize the full metabolic program that could be achieved by activating PPAR. This led directly to the cloning, in 1998, of a co-activator termed PPAR co-activator 1 (PGC-1) (103). This was renamed PGC-1 after the cloning, in 2002, of a homologue of PGC-1, termed PGC-1 (81a; see section 4). The docking of PGC-1 and PGC-1 to transcription factors, and thereby regulating these factors, is a newly identified type of biologic regulation. Spiegelman (123) has proposed that "working through a co-activator that can interact with multiple transcription factor families----- would allow coordination of many otherwise disparate transcriptional regulators into a program of whole-body physiology"(123).
PGC-1and its critical biologic role: PGC-1 is expressed in metabolically active tissues (liver, heart, kidney, white and brown adipose tissue and skeletal muscle (1)). Within a very short period of time it became evident that PGC-1 not only regulated the molecular program that resulted in adaptive (non-shivering) thermogenesis (103), but that PGC-1 also exerted profound effects on metabolism, by upregulating genes involved with hepatic gluconeogenesis (e.g. PEPCK, G-6-Pase) (58,106,124) and glucose transport (91c), and genes encoding enzymes involved with mitochondrial fatty acid oxidation (MCAD, M-CPT-1) and oxidative phosphorylation (i.e.citrate synthase, b and c subunits of F1-F0 ATP synthase, cytochrome c, cytochrome c oxidase subunits I, II, IV, Va, Vb) (78,79,118,123). Quite unexpectedly, PGC-1 also stimulated mitochondrial biogenesis (78,123) through induction of nuclear respiratory factors, NRF-1 and NRF-2, on the promoter for mitochondrial transcription factor A, a direct regulator of mitochondrial DNA replication and transcription (123). Yet, another surprise was that PGC-1 also converted glycolytic (type II) skeletal muscle fibers to oxidative (type I) skeletal muscle fibers that expressed more myoglobin and cytochrome c, and were more fatigue resistant (82). These muscle fiber type transformations appear to involve PGC-1 acting through calcium/calmodulin-dependent protein kinase (CaMKIV) activation (122), and through calcineurin activation and then co-activating the transcription factors Mef2c and Mdf2d (82).
POSSIBLE SIGNIFICANCE OF PGC-1
PGC-1 was cloned in 2002 (81a), and in the past 2 months PGC-1 isoforms (PGC-1-a and PGC-1-b) have been reported (91a). In humans and rodents PGC-1 isoforms are expressed predominantly in brown adipose tissue, brain, heart and skeletal muscle, important metabolic tissues characterized by their high mitochondrial content (91a). The PGC-1mRNA expression in heart is greater than in skeletal muscle in humans and rodents (91a), further suggesting an association between PGC-1 expression and mitochondrial density, and possibly the capacity for fatty acid oxidation, in these muscle tissues.
While PGC-1 has some similar effects when compared to PGC-1, there are also considerable difference in vitro and in vivo. Unlike PGC-1, PGC-1is not inducible in animals by cold temperature (91a, 81a) or forskolin treatment of brown adipose cells in culture (81a). There is contradictory evidence as to whether in liver both PGC-1 mRNA and PGC-1 mRNA are increased by fasting (81a,b), or whether fasting only increases PGC-1 mRNA (91a). PGC-1 only activates genes involved with fatty acid oxidation not hepatic gluconeogenesis (81a, b) While PGC-1 induced both mitochondrial biogenesis and mitochondrial proton leak, PGC-1 induced greater mitochondrial biogenesis than PGC-1 (91a, 110), but not proton leak (110). This suggest that PGC-1 could perhaps be more important in improving mitochondrial fatty acid oxidation, and thereby be more effective in improving insulin sensitivity.
SUMMARY
In ~5 years it has become evident that PGC-1 is a master integrator of complex metabolic programs, including a) mitochondrial biogenesis, b) gene expression of the glucose transporter GLUT4, enzymes of fatty acid oxidation and gluconeogenesis, and d) muscle fiber type transformation (58, 62, 78, 81a, 82, 91c, 106, 123, 124). The bulk of this evidence (>99%) has been derived in cell lines which are more easily transfected than mature mammalian tissues, although PGC-1 transgenic hearts demonstrate some similar responses (78). The recent discovery of PGC-1 (81a,91a) has complicated the understandings of the metabolic effects of the PGC-1 family of co-activators. Arguments can be made to support a key role for PGC-1 in muscle metabolism (81a), or no role at all (91a). PGC-1 and may induce different metabolic programs within the same tissue. Whether mature, mammalian skeletal muscle is affected similarly by PGC-1 and is not yet known.
(1)(3, 4)(2)(6)(5)
Background reading:
4. Handschin C and Spiegelman BM. Peroxisome proliferator-activated receptor gamma coactivator 1 coactivators, energy homeostasis, and metabolism. Endocr Rev 27: 728-735, 2006.
Required readings
1. Akimoto T, Pohnert SC, Li P, Zhang M, Gumbs C, Rosenberg PB, Williams RS, and Yan Z. Exercise stimulates Pgc-1alpha transcription in skeletal muscle through activation of the p38 MAPK pathway. J Biol Chem 280: 19587-19593, 2005.
2. Benton CR, Nickerson J, Lally J, Han X-X, Holloway GP, Glatz JFC, Luiken JJFP, Graham TE, Heikkila JJ, and Bonen A. Modest PGC-1a overexpression in muscle in vivo is sufficient to increase insulin sensitivity and palmitate oxidation in SS, not IMF, mitochondria. J Biol Chem in press, 2008.
3. Handschin C, Chin S, Li P, Liu F, Maratos-Flier E, Lebrasseur NK, Yan Z, and Spiegelman BM. Skeletal Muscle Fiber-type Switching, Exercise Intolerance, and Myopathy in PGC-1{alpha} Muscle-specific Knock-out Animals. J Biol Chem 282: 30014-30021, 2007.
5. Leone TC, Lehman JJ, Finck BN, Schaeffer PJ, Wende AR, Boudina S, Courtois M, Wozniak DF, Sambandam N, Bernal-Mizrachi C, Chen Z, Holloszy JO, Medeiros DM, Schmidt RE, Saffitz JE, Abel ED, Semenkovich CF, and Kelly DP. PGC-1alpha deficiency causes multi-system energy metabolic derangements: muscle dysfunction, abnormal weight control and hepatic steatosis. PLoS Biol 3: e101, 2005.
6. Wright DC, Han DH, Garcia-Roves PM, Geiger PC, Jones TE, and Holloszy JO. Exercise-induced mitochondrial biogenesis begins before the increase in muscle PGC-1alpha expression. J Biol Chem 282: 194-199, 2007.
_______________________________________________________________________________________________________
WEEK #5 - FEBRUARY 3
FAT METABOLISM – Regulation of Triacylglycerol (TG) Lipolysis and Mitochondrial Transport - Intro to Readings
In keeping with the recent research interest in the regulation of fat metabolism in skeletal muscle during exercise, we examine two steps that appear to be sites of regulation; triacylglycerol (TG) degradation and transport of long-chain fatty acids across the mitochondrial membranes.
The general reading articles address whether there really is any controversy about the role of intramuscular TG (IMTG) as an energy substrate for oxidative phosphorylation during exercise. While it is easy to estimate whole body fat oxidation rates it has not been easy to quantify the sources of the oxidized fat, even if we assume that most of the fat oxidation occurs in skeletal muscle during exercise. Both articles argue that despite the controversy, there is now evidence with the major techniques for estimating IMTG use during exercise that IMTG does in fact contribute substrate during low and moderate (even high, in trained individuals) exercise. The Kiens group continues to argue that the IMTG use is more pronounced in women, but other groups have not reported this gender difference. The first assigned paper (Stellingwerff) looks at IMTG use during exercise with three current techniques.
The second paper (Donsmark) summarizes information regarding the muscle version of the enzyme TG lipase (often called hormone-sensitive lipase, HSL), which is thought to play a regulatory role in IMTG lipolysis. The experiments with rodent skeletal muscle (supplementary reading) are more mechanistic than the article that tries to summarize much of the human work. Please see the accompanying diagram in the Roepstorff review paper that outlines the putative control of this enzyme. HSL can be activated by contractions and by epinephrine exposure although it is likely that contractile stimuli are dominant. The enzyme would be more aptly named, “contraction sensitive lipase” A major point, however, is that activation of HSL is only one step (of at least 3) in the complicated regulation of TG lipolysis in skeletal muscle during exercise.
The Zimmermann paper is a new development outlining the identification and characterization of a new protein and enzyme (adipose triglyceride lipase, ATGL) that appears to be able to degrade TG. Interestingly, diacylglcyerol (DG) is not a good substrate for this enzyme, suggesting that it may be responsible for TG degradation and HSL may handle DG lipolysis in cells. This may explain why previous in vitro work with HSL has always reported a much higher affinity of this enzyme for DG than TG. This paper also reports the presence of ATGL mRNA in heart and skeletal muscle. If this enzyme is present in skeletal muscle, it will revamp the way we interpret the previous HSL data and our understanding of the regulation of TG lipolysis during exercise. However, some time has passed and it has not been identified in skeletal muscle to date.
The final two studies assess the regulation of long-chain FA transport into the mitochondria via the carnitine - fatty acyltransferase (commonly referred to as CPT I) complex and the putative FA transport protein FAT/CD36. Dr. Will Winder proposed that malonyl-CoA (M-CoA), a potent inhibitor of CPT I activity, controlled the rate of FFA entry into the mitochondria in rat skeletal muscle. At rest, high M-CoA levels inhibited the enzyme and kept FFA transfer low. During exercise, the [M-CoA] decreased, releasing this inhibition and increasing FFA transport and ultimately oxidation. However, M-CoA does not fall in human skeletal muscle with exercise (or at least not much), suggesting that the regulation of CPT I and FFA transfer is more complex. There may be other regulators that activate CPT I, or M-CoA insensitive isoforms may exist, or other proteins may be involved in the process. The Bezaire paper outlines recent work in human skeletal muscle mitochondria and proposes a regulatory scheme. The Holloway paper examines these issues during 2 hours of exercise.
General Reading:
Required Reading:
Background reading:
Langfort, J., T. Ploug, J. Ihelmann, C. Holm and H. Galbo. Stimulation of hormone-sensitive lipase by contractions in rat skeletal muscle. Biochem. J. 351: 207-214, 2000.
Langfort, J., T. Ploug, J. Ihelmann, M. Saldo, C. Holm and H. Galbo. Expression of hormone-sensitive lipase and its regulation by adrenaline in skeletal muscle. Biochem. J. 340: 459-465, 1999.
Watt, M.J., G.J.F. Heigenhauser, and L.L. Spriet. Effects of dynamic exercise intensity on the activation of hormone-sensitive lipase in human skeletal muscle. J. Physiol. 547.1: 301-308, 2003
Starritt, E.C., R.A. Howlett, G.J.F. Heigenhauser, and L.L. Spriet. Sensitivity of CPT I activity to malonyl-CoA in trained and untrained human skeletal muscle. Am. J. Physiol. 278 (Endocrinol. Metab.): E462-E468, 2000.
Bezaire, V., G.J.F. Heigenhauser, and L.L. Spriet. Regulation of CPT I activity in intermyofibrillar and subsarcolemmal mitochondria from human and rat skeletal muscle. Am. J. Physiol. Endocrinol. Metab. 286:E85-E91, 2004.
Campbell, SE, NN Tandon, G Woldegiorgis, JJFP Luiken, JFC Glatz, and A Bonen. A novel function for fatty acid translocase (FAT)/CD36. J. Biol. Chem. 279: 36235-36241, 2004.
Velasco G., M.J. Geelen, T.G. del Pulgar, and M Guzmán. Malonyl-CoA-independent acute control of hepatic carnitine palmitoyltransferase I activity. Role of Ca2+/calmodulin-dependent protein kinase II and cytoskeletal components. J. Biol. Chem. 273: 21497-504, 1998.
Velasco G, T.G. del Pulgar, D. Carling, and M. Guzmán. Evidence that the AMP-activated protein kinase stimulates rat liver carnitine palmitoyltransferase I by phosphorylating cytoskeletal components. FEBS Lett. 439:317-20, 1998.
Kerner, J., and C. Hoppel. Fatty acid import into mitochondria. Biochim. Biophys. Acta. 1486: 1-17, 2000.
_______________________________________________________________________________________________________
WEEK # 6 – FEBRUARY 10
PLASMA MEMBRANE FATTY ACID TRANSPORT – Intro to Readings
The general review by Bonen and colleagues is provided as a balanced overview, outlining the arguments, both for and against, protein mediated transport of fatty acids across plasma membranes. This review will not be discussed in class, but should be read as it highlights the important findings of the papers to be discussed, as well as incorporates these findings within the broader context of the regulation of lipid metabolism during exercise and insulin resistance. If you feel you require additional background information several good general reviews are also provided in the supplementary reading list, as well as additional primary articles.
The readings for week 6 provide you with an overview of the evidence in support of a protein mediated process in the transport of fatty acids across the plasma membranes, as well as potential mechanisms regulating this key step in lipid metabolism under various metabolic states (basal, contraction and insulin stimulated). The first paper by Bonen and colleagues provides seminal data in support of protein mediated transport, including evidence of; 1) transport saturation kinetics, 2) competitive inhibition, 3) pharmacological inhibition, 4) fiber type differences, and 5) transport protein content ‘matching’ function. Make sure you understand why each of these arguments supports the notion of protein-mediated transport!
The second paper highlights the importance of regulating fatty acid transport into the muscle cell during conditions of increased metabolic demand. Prior to this publication, the increase in fatty acid oxidation during exercise was thought to result largely from the adipose tissue ‘releasing’ more FFA into the circulation, and as a result increasing the driving gradient, and subsequently passive transport, of free fatty acids (FFAs) into skeletal muscle. The paper by Bonen and colleagues alternatively suggests that the transport of FFAs into muscle during exercise increases as a result of a redistribution of fatty acid translocase (FAT/CD36) from an intracellular depot to the plasma membrane. Similar logic is reported in the third paper, emphasizing that the transport of FFAs into the skeletal muscle of obese and T2D individuals is increased as a result of a redistribution of FAT/CD36 to the plasma membrane. This data provides a potential mechanism for the observed increased intramuscular TAGs in obesity and T2D, which have been linked to attenuations in insulin signaling (although current wisdom suggestions that TAGs do not directly alter insulin signaling, and are probably a marker of altered lipid metabolism, and other more reactive lipid species (DAGs and ceramides) are probably the culprits).
The final 2 papers, by Bonen and colleagues and Clarke and colleagues, incorporate molecular approaches to alter (both increase and decrease) the expression of specific transport proteins to determine the functional consequences. Bonen et al., use a FAT/CD36 null mouse to show that by eliminating FAT/CD36 fatty acid uptake and subsequent metabolism is attenuated in the basal, insulin and AICAR stimulated states. These data further emphasis a central role for FAT/CD36. Clarke et al. use an alternative approach, and instead increase (rather than decrease) the expression of a specific fatty acid transport protein. These authors use a novel technique to over-express FABPpm, without altering the expression or distribution of FAT/CD36, and subsequently increase the rate of palmitate transport into giant sarcolemmal vesicles. These studies provide direct evidence to support the notion that both FAT/CD36 and FABPpm regulate plasma membrane fatty acid transport, although the manner in which this is accomplished remains unknown.
The papers discussed this week provide evidence in support of protein mediated fatty acid transport across the plasma membrane. However, it is important to remember that we currently do not know exactly how this is accomplished, as none of the putative transport proteins create a pore like traditional transporters (eg. GLUT4).
General Review:
Required Readings :
Supplementary Readings :
Bonen A, Campbell SE, Benton CR, Chabowski A, Coort SL, Han XX, Koonen DP, Glatz JF, and Luiken JJ. Regulation of fatty acid transport by fatty acid translocase/CD36. Proc Nutr Soc 63: 245-249, 2004.
Kiens B. Skeletal muscle lipid metabolism in exercise and insulin resistance. Physiol Rev 86: 205-243, 2006.
Koonen DP, Benton CR, Arumugam Y, Tandon NN, Calles-Escandon J, Glatz JF, Luiken JJ, and Bonen A. Different mechanisms can alter fatty acid transport when muscle contractile activity is chronically altered. Am J Physiol Endocrinol Metab 286: E1042-1049, 2004.
Koonen DP, Coumans WA, Arumugam Y, Bonen A, Glatz JF, and Luiken JJ. Giant membrane vesicles as a model to study cellular substrate uptake dissected from metabolism. Mol Cell Biochem 239: 121-130, 2002.
Koonen DP, Glatz JF, Bonen A, and Luiken JJ. Long-chain fatty acid uptake and FAT/CD36 translocation in heart and skeletal muscle. Biochim Biophys Acta 1736: 163-180, 2005.
_______________________________________________________________________________________________________
WEEK # 8 – FEBRUARY 24
MITOCHONDRIAL METABOLISM I - Intro to Readings
The general reviews by Meyer & Wiseman and Tonkonogi & Sahlin provide overviews of mitochondrial function and metabolic regulation in human skeletal muscle (the latter pdf is attached). These papers will not be discussed in class but should be read if you feel you need a review or introduction to these areas. Both are fairly plain language overviews meant for people interested in exercise science. If required, please review the processes that occur in the mitochondria in any biochemistry textbook.
The readings for the first mitochondrial metabolism week attempt to provide you with an overview of several issues relevant to mitochondrial metabolism. We start with a short review by David Wilson where he reminds us that the 3 major sets of inputs for oxidative ATP production are: 1) reducing equivalents (NADH, FADH 2), 2) free ADP and P i, and 3) O 2. The provision of these inputs to the electron transport chain (ETC) and the process of oxidative phosphorylation (OP) are required for optimal aerobic ATP resynthesis during exercise. However, there appears to be little direct regulation of the ETC and the processes of OP, other than altering the mitochondrial content. Instead, control is substrate level and therefore occurs upstream at the level of the provision of the raw materials for ATP synthesis; 1) moving the free ADP and P i from the cytosol, where ATP is degraded, back into the mitochondria, 2) control of the pathways associated with NADH production, and 3) the provision of O 2 to the mitochondria. He also points out that the cumulative stimulatory effect of these 3 groups of inputs will determine the rate of OP. For instance in mild hypoxia, a reduction in the partial pressure of O 2 in the mitochondria could be counterbalanced by an increase in the ADP and P i concentrations, such that the driving force for ATP resynthesis is maintained at the rate required to sustain movement during exercise.
The Walsh et al. paper then examines the possibility that factors related to the energy charge of the cell also play a role in the regulation of mitochondrial respiration. They examine combinations of ADP, phosphocreatine (PCr) and creatine and demonstrate that PCr and Cr can modulate the sensitivity of mitochondrial respiration to ADP.
The Dudley et al. paper demonstrates the importance of the training-induced increase in mitochondrial content (and ETC and OP capacity) for mitochondrial control. In short, smaller metabolic disturbances are needed at a given absolute power output following aerobic training to activate OP to the desired level to meet the demand for ATP. The authors argue that this is a function of the greater number of ETC’s and complex V’s in the trained muscle.
The final 2 papers examine attempts to determine which of the inputs for aerobic ATP production might be limiting in varying exercise situations – delivery of O 2 to the mitochondria and/or the inertia associated with activating many of the metabolic pathways that ultimately provide NADH. Both studies examine human skeletal muscle during exercise situations. Howlett at al. use a metabolic approach to study the transition from rest to exercise where aerobic metabolism takes a finite time to increase and reach the desired level of ATP synthesis as dictated by the power output. Is the increase in O 2 uptake dependent on O 2 delivery to the muscle or the provision of NADH at the onset of exercise? Richardson et al. altered the inspired O 2 concentration at constant barometric pressure to determine if the supply of O 2 limits the attainment on VO 2max during incremental knee kicking exercise.
General Review:
Meyer, R.A., and R.W. Wiseman. The metabolic systems: Control of ATP synthesis in skeletal muscle. In: ACSM’s Advanced Exercise Physiology. C.M. Tipton (ed). LWW, Baltimore, MD, 2006. pp. 370-384.
Tonkonogi M and Sahlin, K. Physical exercise and mitochondrial function in human skeletal muscle. Exerc Sport Sci Rev 30 (3): 129-137, 2002.
Required Reading :
Walsh B, Tonkonogi M, Soderlund K, Hultman E, Saks V and Sahlin K. The role of phosporylcreatine and creatine in the regulation of mitochondrial respiration in human skeletal muscle. J Physiol 537.3: 971-978, 2001.
Howlett RA, Heigenhauser GJF, Hultman E, Hollidge-Horvat MG, and Spriet LL. Effects of dichloroacetate infusion on human skeletal muscle metabolism at the onset of exercise. Am J Physiol Endocrinol Metab 277: 18-25, 1999.
Background reading :
Meyer/Foley – Ch. 18 in Handbook of Physiology – Section 12 – Exercise Bible, 1996!
Supplementary Reading :
Hansford, R.G. Role of calcium in respiratory control. Med. Sci. Sports. Exerc. 26: 44-51, 1994.
Erecinska, M., and D.F. Wilson. Regulation of cellular energy metabolism. J. Memb. Biol. 70: 1-14, 1982.
Balaban, R.S. Regulation of oxidative phosphorylation in the mammalian cell . Am. J. Physiol. 258 (Cell Physiol.): C377-C389, 1990.
Hogan, M, C.J. Roca, P.D. Wagner, and J.B. West. Limitation of maximal O 2 uptake and performance by acute hypoxia in dog muscle in situ. J. Appl. Physiol. 65:815-821, 1988.
Richardson, R.S. What governs skeletal muscle VO 2max? New Evidence. Med. Sci. Sports Exerc. 32: 100-107, 2000.
_______________________________________________________________________________________________________
WEEK # 9 – MARCH 3
MITOCHONDRIAL METABOLISM II - Intro to Readings
There has been a long-standing controversy regarding whether the availability of O 2 for oxidative metabolism is ever less than optimal. We examined whether this might occur at the onset of exercise last week. While there is general agreement that this should not be the case during low and moderate intensity, steady state, aerobic exercise, there are two exercise situations where this may not be the case:
1) power outputs approaching maximal oxygen uptake (80-100% VO 2max)
2) power outputs above VO 2max.
A related question is whether lactate production in muscle is therefore a function of sub-optimal O 2 availability and/or simply a consequence of increased glycolytic flux as exercise intensity increases. It could be that some lactate will always be produced just because the match between flux down the glycolytic pathway and the use of pyruvate by PDH in the mitochondria can never be perfect, and some pyruvate will always go to lactate (in other words several Rxs compete for pyruvate as a substrate). While measurements of muscle and blood lactate and even muscle lactate efflux are straightforward, it has been very difficult to measure the availability of O 2 at the mitochondria. The estimates of muscle lactate and O 2 availability are also complicated by the fact that they are average responses from different muscle fiber types.
Tissue O 2 availability is most often indirectly inferred from estimates of the mitochondrial redox state - the NAD/NADH ratio or oxidation/reduction state of various electron transport chain components (eg. a,a 3). Estimates during exercise which do not change or increase the NAD/NADH ratio are interpreted as evidence that O 2 is not limiting, while decreases in the NAD/NADH ratio (accumulations of NADH) suggest a limitation in the ability to oxidize NADH. The assumption here is that the major controllers of mitochondrial respiration during exercise are NADH, O 2 and ADP (or energy charge, ATP/ADP + P i ), and that ADP availability is high during exercise (as discussed last week). Therefore, an increase in NADH is interpreted to mean that O 2 must be limiting oxidative phosphorylation.
The initial three papers this week estimate the mitochondrial redox state with different techniques, with two of the methods producing very divergent results. The first paper examined the feasibility of measuring muscle oxygenation with NIRS in varying situations and this technique may not have the sensitivity to be used as a research tool (read the McCully paper also). Sahlin estimated the mitochondrial redox state with “whole muscle” measurements of NADH. Alternately, Graham and Saltin estimated mitochondrial NAD/NADH using the components of the glutamate dehydrogenase reaction during exercise, as this enzyme is exclusively mitochondrial and believed to be near-equilibrium. Their results and interpretations do not agree with the Sahlin work. An additional report which we don’t have time to read (Duhaylangsod et al. 1993) produced results similar to the Sahlin study. All three techniques appear to have problems and we await better technology to resolve this controversy.
We then examine two papers that try to determine whether lactate production is a consequence of an O 2 limitation or simply a by-product of increased glycolytic flux, or both? The Connett et al. paper examines the relationship between lactate release and intracellular pO 2 in working, red skeletal muscle and argues that lactate is produced in "fully aerobic" muscle. The Katz and Sahlin review presents their interpretations based on "whole muscle" [NADH] and they argue that muscle hypoxia is rampant.
General Reading:
Required Reading :
Supplementary Reading :
Duhaylangsod, F.G., J.A. Griebel, D.S. Bacon, W.G. Wolfe, and C.A. Piantadosi. Effects of muscle contraction on cytochrome a,a 3 redox state. J. Appl. Physiol. 75:790-797, 1993.
Stainsby, W.N., W.F. Brechue, D.M. O'Drobinak, and J.K. Barclay. Oxidation/Reduction state of cytochrome oxidase during repetitive contractions. J. Appl. Physiol. 67: 2158-2162, 1989.
Bhambhani, Y., S. Buckley, and T. Susaki. Muscle oxygenation trends during constant work rate cycle exercise in men and women. Med. Sci. Sports Exerc. 31:90-98, 1999.
Spriet, L.L., R.A. Howlett, and G.J.F. Heigenhauser. An enzymatic approach to lactate production in human skeletal muscle during exercise. Med. Sci. Sports Exerc. 32:756-763, 2000.
Hughson R.L., M.E. Tschakovsky, and M.E. Houston. Regulation of oxygen consumption at the onset of exercise. Exerc. Sport Sci. Rev. 29:129-133, 2001.
Richardson, R.S., L.J. Haseler, A.T. Nygren, S. Bluml, and L.R. Frank. Local perfusion and metabolic demand during exercise: a noninvasive MRI method of assessment. J. Appl. Physiol. 91:1845-1853, 2001.
_______________________________________________________________________________________________________
WEEK #10 - March 10, 2009
MITOCHONDRIA WITH OBESITY/AGING – Intro to Readings
The readings for week 11 provide you with an overview of the evidence pertaining to mitochondrial function with obesity and aging. While the majority of the papers discussed will center on insulin resistance, the review provided highlights the aging process to balance the information provided. Cross-sectional studies as well as ‘experimental’ approaches (high fat feeding and knock-out models) will provide information both for and against the notion that mitochondria participate in the etiology of insulin resistance.
The review by Huang and Hood focuses on mitochondrial function with aging, however the pertinent information also applies to insulin resistant states. The information presented in this review begins the process of understanding mitochondrial ‘function’ at two levels; 1) the whole muscle and 2) individual mitochondria. The whole muscle mitochondrial capacity is determined by both the content of mitochondria and the individual mitochondrial function. The review outlines the mechanisms that induce mitochondrial proliferation (content), and how these are perturbed with aging (again still pertinent to insulin resistant states). Information on oxidative damage is also provided as a mechanism that can alter individual mitochondrial function, this is discussed further in the primary paper by Kevin Short. This review will not be discussed in class, but should be read as it highlights important concepts that due to time constraints will not be covered. If you feel you require additional background information a good review is also provided in the supplementary reading list, as well as additional primary articles.
The first paper by Mogensen and colleagues provides data with isolated mitochondria indicating fatty acid oxidation is not impaired in patients with type 2 diabetes. The authors do report a reduction in pyruvate oxidation, and these findings should be integrated into the broader context of substrate oxidation and metabolic flexibility with insulin resistance. Limitations with the methodology used by Mogensen and colleagues should also be considered, which is why the second paper by Bousel and colleagues is discussed.
The third paper uses high fat feeding as a model to show that insulin resistance can develop in the presence of improvements in mitochondrial fatty acid oxidation (both content and intrinsic function-similar findings and methodologies are also used in the Garcia-Roves and Hancock papers listed in the supplementary reading). These findings argue against the notion that reductions in mitochondrial fatty acid oxidation are a necessary progression in the development of insulin resistance.
The forth paper by Koves and colleagues provides a novel theory of ‘incomplete’ fatty acid oxidation participating in the development of mitochondrial ‘dysfunction’ and insulin resistance. The authors argument is centered on the observations that high fat fed animals have higher levels of fatty acid derivatives within mitochondria, and higher ‘acid soluble fractions’ during oxidation measurements. The logic with this theory is that more fatty acids enter the mitochondria than oxidized, stressing the mitochondria. The authors also utilize pharmacological and knock-out studies to inhibit the entry of fatty acids into mitochondria and show a protective effect. These data should be considered in the context of exercise training, which increases mitochondrial stress and improves insulin sensitivity.
The last paper by Short and colleagues provides information on how mitochondria are altered during the aging process. The same concepts are discussed, including both mitochondrial content and function. However a particular focus in this paper is on DNA oxidation as a potential mechanism to reduce mitochondrial fatty acid oxidative capacity.
The papers discussed this week provide evidence both for and against the notion that alterations in mitochondrial substrate handling participates in the development of insulin resistance and the aging process. However, it is important to remember that these measurements are made under optimal conditions, and the in vivo environments may be different between healthy lean controls and insulin resistant states (eg. if malonyl-CoA levels are high fatty acid oxidation could be reduced despite maintained or increased mitochondrial content).
General Review:
Huang JH and Hood DA. Age-associated mitochondrial dysfunction in skeletal muscle: Contributing factors and suggestions for long-term interventions. IUBMB Life 61: 201-214, 2009.
Required Readings :
Mogensen M, Sahlin K, Fernstrom M, Glintborg D, Vind BF, Beck-Nielsen H, and Hojlund K. Mitochondrial respiration is decreased in skeletal muscle of patients with type 2 diabetes. Diabetes 56: 1592-1599, 2007.
Boushel R, Gnaiger E, Schjerling P, Skovbro M, Kraunsoe R, and Dela F. Patients with type 2 diabetes have normal mitochondrial function in skeletal muscle. Diabetologia 50: 790-796, 2007.
Turner N, Bruce CR, Beale SM, Hoehn KL, So T, Rolph MS, and Cooney GJ. Excess lipid availability increases mitochondrial fatty acid oxidative capacity in muscle: evidence against a role for reduced fatty acid oxidation in lipid-induced insulin resistance in rodents. Diabetes 56: 2085-2092, 2007.
Koves TR, Ussher JR, Noland RC, Slentz D, Mosedale M, Ilkayeva O, Bain J, Stevens R, Dyck JR, Newgard CB, Lopaschuk GD, and Muoio DM. Mitochondrial overload and incomplete fatty acid oxidation contribute to skeletal muscle insulin resistance. Cell Metab 7: 45-56, 2008.
Short KR, Bigelow ML, Kahl J, Singh R, Coenen-Schimke J, Raghavakaimal S, and Nair KS. Decline in skeletal muscle mitochondrial function with aging in humans. Proc Natl Acad Sci U S A 102: 5618-5623, 2005.
Supplementary Readings :
Holloway GP, Benton C, Mullen KL, Yoshida Y, Snook LA, Han XX, Glatz JF, Luiken JJ, Lally J, Dyck DJ, and Bonen A. In obese rat muscle transport of palmitate is increased and is channeled to triacylglycerol storage despite an increase in mitochondrial palmitate oxidation. Am J Physiol Endocrinol Metab, 2009. in press
Hancock CR, Han DH, Chen M, Terada S, Yasuda T, Wright DC, and Holloszy JO. High-fat diets cause insulin resistance despite an increase in muscle mitochondria. Proc Natl Acad Sci U S A 105: 7815-7820, 2008.
Garcia-Roves P, Huss JM, Han DH, Hancock CR, Iglesias-Gutierrez E, Chen M, and Holloszy JO. Raising plasma fatty acid concentration induces increased biogenesis of mitochondria in skeletal muscle. Proc Natl Acad Sci U S A 104: 10709-10713, 2007.
Holloway GP, Thrush AB, Heigenhauser GJ, Tandon NN, Dyck DJ, Bonen A, and Spriet LL. Skeletal muscle mitochondrial FAT/CD36 content and palmitate oxidation are not decreased in obese women. Am J Physiol Endocrinol Metab 292: E1782-1789, 2007.
Bandyopadhyay GK, Yu JG, Ofrecio J, and Olefsky JM. Increased malonyl-CoA levels in muscle from obese and type 2 diabetic subjects lead to decreased fatty acid oxidation and increased lipogenesis; thiazolidinedione treatment reverses these defects. Diabetes 55: 2277-2285, 2006.
Kiens B. Skeletal muscle lipid metabolism in exercise and insulin resistance. Physiol Rev 86: 205-243, 2006.
Ritov VB, Menshikova EV, He J, Ferrell RE, Goodpaster BH, and Kelley DE. Deficiency of subsarcolemmal mitochondria in obesity and type 2 diabetes. Diabetes 54: 8-14, 2005.
Kelley DE, He J, Menshikova EV, and Ritov VB. Dysfunction of mitochondria in human skeletal muscle in type 2 diabetes. Diabetes 51: 2944-2950, 2002.
_______________________________________________________________________________________________________
WEEK #11 – March 17, 2009
CARBOHYDRATE METABOLISM – Glycogenolysis (PHOS), Glycolysis (PFK) and PDH activity – Intro to Readings
The aim of the readings for this week is to understand the regulation of glycogenolysis, glycolysis and PDH activation and flux in human skeletal muscle during various intensities and modes of exercise. The research papers take an enzymatic approach to this problem concentrating on the key, non-equilibrium enzymes that appear to control flux rates in these pathways. I have given you overviews of the proposed regulation of PHOS, PFK and PDH and an overview of the glycolytic pathway with estimated flux rates at the onset of exercise at either 65% or ~250% VO 2 max. This information is combined with the knowledge gained in weeks 2 and 3 where you examined the regulation and uptake of exogenous carbohydrate into skeletal muscle and the regulation of liver and muscle glycogen metabolism.
The glycogenolytic/glycolytic pathway provides substrate for both aerobic (oxidative phosphorylation) and so-called anaerobic ATP resynthesis (substrate phosphorylation) and therefore experiences very different flux rates during "aerobic" exercise (0-100% VO 2 max) and "anaerobic" or sprint exercise (power outputs above that which elicits VO 2 max, >100% VO 2 max). In other words, the pathway serves two masters - the low to moderate flux rates of aerobic exercise (ATP mainly provided by oxidative phosphorylation) and the very high flux rates of anaerobic exercise (ATP mainly supplied by substrate phosphorylation). Naturally, the maximal enzyme activities of the enzymes in the pathway are a function of the latter. The pathways of aerobic exercise turn on during sprint exercise as well, but take 45-60 s to reach their max and even when the do, can’t provide more than about1/3 rd of the energy required during maximal sprinting.
The Howlett and Parolin papers examine the activity and regulation of PHOS and PDH at aerobic and sprint power outputs in human skeletal muscle, respectively. The approach used is to “trap” these two covalently regulated enzymes in their “more active and less active” forms and measure as many of the known or suspected regulators of these enzymes as possible, in an effort to explain their regulation. The Peters & Spriet paper examines the regulation of PFK in vitro and attempts to more closely simulate the conditions that exist in intact muscle cells. The purpose of the work was to explain how this enzyme stays active in the face of increasing acidity during intense exercise, when earlier in vitro results predicted total inhibition of the enzyme at the prevailing [H +] during intense contractions.
The final two papers incorporate molecular techniques and measurements of PDH kinase to examine the rapid up-regulation of PDK activity and therefore down-regulation of PDH activity and carbohydrate oxidation that occurs with long-term aerobic exercise and dietary manipulation.
The Peters et al. paper examined the chronic response of PDH to severe CHO restriction (and increase in fat intake). It examined the mechanisms that are available to decrease PDH activation over a longer time course (min to hours, as opposed to exercise – seconds to min) in the face of the CHO restriction in order to conserve the body’s CHO store. Measurements of PDK2 and 4 mRNA and protein, and total PDK activity have been made in human skeletal muscle.
The Watt et al. paper moves these changes to an even shorter domain – 4 hr of exercise at ~50% VO 2 max in well-trained cyclists. PDK activity increases without changes in total PDK protein, most likely by an alternate mechanism where existing PDK units are incorporated into the PDH complex. This is an even shorter mechanism for up-regulating the activity of an enzyme than making new protein.
WEEK # 11. CARBOHYDRATE METABOLISM – Regulation of Glycogenolysis and Glycolysis (including Pyruvate Dehydrogenase (PDH) activity)
Required Reading :
Parolin, M.L., A. Chesley, M.P. Matsos, L.L. Spriet, N.L. Jones, and G.J.F. Heigenhauser. Regulation of skeletal muscle glycogen phosphorylase and PDH during maximal intermittent exercise. Am. J. Physiol. 277 (Endocrinol. Metab.): E890-E900, 1999.
Background reading :
Connett, R.J., and K. Sahlin. Control of glycolysis and glycogen metabolism. In: Rowell, LB, and JT Shepherd (eds) Handbook of Physiology, American Physiological Society, Section 12: Exercise: Regulation and Integration of Multiple Systems. Oxford Univ. Press, New York, 1996. pp. 870-911.
Spriet, L.L., and G.J.F. Heigenhauser. Regulation of pyruvate dehydrogenase (PDH) activity in human skeletal muscle during exercise. Exerc Sport Sci Rev 30: 91-95, 2002.
Hargreaves, M. Skeletal muscle carbohydrate metabolism during exercise. In: Exercise Metabolism 2 nd Edition, Edited by M. Hargreaves and LL Spriet, Human Kinetics, Champ., IL, 2006, pp. 29-44.
Spriet, LL Anaerobic metabolism during exercise. In: Exercise Metabolism. 2 nd Edition, Edited by M. Hargreaves and LL Spriet, Human Kinetics, Champ., IL, 2006. pp. 7-28.
Hargreaves, M. The metabolic systems: Carbohydrate metabolism. In. ACSM’s Advanced exercise Physiology. CM Tipton (ed). LW&W, Baltimore, MD, 2006. pp. 385-395.
_______________________________________________________________________________________________________
WEEK #12– March 24, 2009
LACTATE METABOLISM – Intro to Readings
For almost 200 years! scientists have examined how exercise influence lactate levels in blood or muscle. The bulk of this work has been observational/descriptive. Lactate however is not merely a metabolic “dead-end”, it can be used as fuel to produce glucose by liver and kidney (gluconeogenesis), replenish glycogen within muscle (rates depend on species, low in mammals). As with other substrates the entry of lactate and other monocarboxylates is regulated by a family of MCTs with different affinities for monocarboxylates. To date 14 MCTs have been identified, but the metabolic roles for all have not been identified. We will discuss MCT1 and MCT4 in muscle.
As MCTs also are apparently present in mitochondria, a controversy has arisen as to whether mitochondria can directly oxidize lactate without first converting it to pyruvate. We will look at some of the evidence.
The first paper by Bonen and colleagues introduces the monocarboxylate transporters (MCT), and shows divergent responses in MCT1 and MCT4 following chronic low frequency stimulation. The data also suggests that MCT1 transports lactate out of the blood and into skeletal muscle, although the role of MCT4 cannot determined.
The paper by Brooks and colleagues uses isolated mitochondria to show that mitochondria directly oxidize lactate. Moreover, they show the presence of lactate dehydrogenase in the mitochondrial matrix, suggesting that mitochondria can convert lactate back to pyruvate, which subsequently would be oxidized. The papers by Rasmussen and Sahlin use similar methodology (isolated mitochondria), but conclude that mitochondria do not directly oxidize lactate, and argue that pyruvate is the only ‘entry’ point for oxidation of monocarboxylates. Additionally, Sahlin does not find the presence of LDH within mitochondria, and argue on a theoretical basis that LDH, even if present in mitochondria, would be rendered incapable of moving lactate to pyruvate because of the extremely high levels of NADH within mitochondria.
The last paper by Yoshida and colleagues re-visits the notion that mitochondria can directly oxidize lactate. However, this paper utilizes several additional experimental models (competitive inhibition, AICAR, cell fractionation) to show that mitochondria convert lactate to pyruvate in the cytsol prior to oxidation.
The papers discussed this week provide evidence both for and against the notion that mitochondria can directly oxidize lactate. However, to date independent verification of the data from Brooks’ laboratory has not been generated, and data is mounting to suggest mitochondria do not directly oxidize lactate. As pointed out in the review by Gladden, this does not diminish the importance of lactate as a cell-to-cell ‘shuttle’ of available fuel.
General Review:
Gladden JB. Lactate metabolism: a new paradigm for the third millennium. J Physiol 558: 5-30, 2004.
Required Readings :
Bonen A, Tonuchi M, Miskovic D, Heddle C, Heikkila JJ, and Halestrap AP. Isoform-specific regulation of the lactate transporters MCT1 and MCT4 by contractile activity. Am J Physiol Endocrinol Metab 279: E1131-E1138, 2000.
Brooks GA, Dubouchaud H, Brown M, Sicurello JP, and Butz CE. Role of mitochondrial lactate dehydrogenase and lactate oxidation in the intracellular lactate shuttle. Proc Natl Acad Sci U S A 96: 1129-1134, 1999.
Rasmussen HN, van Hall G, Rasmussen UF. Lactate dehydrogenase is not a mitochondrial enzyme in human and mouse vastus lateralis muscle. J Physiol. 541: 575-580, 2002.
Sahlin K, Fernstrom M, and Tonkonogi M. No evidence of an intracellular lactate shuttle in rat skeletal muscle. J Physiol 541: 569-574, 2002.
Yoshida Y, Holloway GP, Ljubicic V, Hatta H, Spriet LL, Hood DA and Bonen A. Negligible direct lactate oxidation in subsarcolemmal and intermyofibrillar mitochondria obtained from red and white rat skeletal muscle J. Physiol 582:1317-1335, 2007.
Supplementary Readings :
Benton CR, Yoshida Y, Lally J, Han XX, Hatta H, and Bonen A. PGC-1alpha increases skeletal muscle lactate uptake by increasing the expression of MCT1 but not MCT2 or MCT4. Physiol Genomics 35: 45-54, 2008.
Bonen A, Heynen M, and Hatta H. Distribution of monocarboxylate transporters MCT1-MCT8 in rat tissues and human skeletal muscle. Appl Physiol Nutr Metab 31: 31-39, 2006.
Burgomaster KA, Cermak NM, Phillips SM, Benton CR, Bonen A, and Gibala MJ. Divergent response of metabolite transport proteins in human skeletal muscle after sprint interval training and detraining. Am J Physiol Regul Integr Comp Physiol 292: R1970-1976, 2007.
Coles L, Litt J, Hatta H, and Bonen A. Exercise rapidly increases expression of the monocarboxylate transporters MCT1 and MCT4 in rat muscle. J Physiol 561: 253-261, 2004.
_______________________________________________________________________________________________________
WEEK #13 – March 31, 2009
BIOCHEMICAL AND MOLECULAR RESPONSES TO TRAINING - Intro to Readings
We add a week on training this year as the advent of molecular biology techniques has resulted in a renaissance of studies examining the molecular and biochemical responses to training. Specifically, what are the signals - and what is the time course of the molecular signals that activate the production of mitochondrial proteins, such that we see an increased capacity to oxidize carbohydrate and fat in 5-7 days in human subjects?
Please read one of the two review papers to get an idea of the events that occur with training.
We start off the required readings by examining one of the classic papers published by JO Holloszy who pioneered the studies that examined the effects of repetitive aerobic training in rats on skeletal muscle adaptations. This is followed by a study from Howie Green’s Laboratory in Waterloo from the 90’s looking at the progressive muscle adaptations in human subjects to 30 days of training.
The remaining three papers are contemporary papers using human subjects and alternate models of repetitive training (higher intensity and lower volume) to examine the metabolic adaptations to training. More importantly the molecular responses to training are examined that lead to the rapid changes in mitochondrial protein.
General Review:
Required Readings :
Perry, CGR, GP Holloway, GJF Heigenhauser, A Bonen and LL Spriet. Temporal transcriptional regulation of mitochondrial biogenesis during training in human skeletal muscle. Unpublished – Thesis work - 2009.
Supplementary Readings :
Hood, DA, and A Saleem. Exercise induced mitochondrial biogenesis in skeletal muscle. Nutr Metab Cardiovasc Dis 17: 332-337, 2007.
Holloszy, JO, L Oscai, LB Don, IJ and PA Mole. Mitochondrial citric acid cycle and related enzymes: adaptive response to exercise. Biochem Biophys Res Comm, 40, 1368-73, 1970.
Leblanc, PJ, SJ Peters, RJ Tunstall, D Cameron-Smith, and GJF Heigenhauser. Effects of aerobic training on pyruvate dehydrogenase and pyruvate dehydrogenase kinase in human skeletal muscle. J Physiol , 557, 559-70, 2004.
Mole, PA, LB Oscai, and JO Holloszy. Adaptation of muscle to exercise. Increase in levels of palmitoyl CoA synthetase, carnitine palmityltransferase, and palmityl CoA dehydrogenase, and in the capacity to oxidize fatty acids. J Clin Invest, 50, 2323-30, 1971.
Oscai, LB and JO Holloszy. Biochemical adaptations in muscle. II. Response of mitochondrial adenosine triphosphatase, creatine phosphokinase, and adenylate kinase activities in skeletal muscle to exercise. J Biol Chem, 246, 6968-72, 1971.
Saltin, B, and P Gollnick, P. (1983). Skeletal muscle adaptability: significance for metabolism and performance. In: L.D. Peachey, R.H. Adrian, and S.R. Geiger (eds.) Handbook of Physiology, Skeletal Muscle Bethesda: American Physiological Society, pp. 555-631.
Talanian, JL, SD Galloway, GJF, Heigenhauser, A Bonen and LL Spriet. Two weeks of high-intensity aerobic interval training increases the capacity for fat oxidation during exercise in women. J Appl Physiol , 102, 1439-47, 2007.