Author Report for: Watt MJNo contact information in database for Watt MJ
Keenan SN, De Nardo W, Lou J, Schittenhelm RB, Montgomery MK, Granneman JG, Hinde E, Watt MJ Ref: J Lipid Res, 62:100016, 2021 : PubMed ESTHER: Keenan_2021_J.Lipid.Res_62_100016 PubMedSearch: Keenan 2021 J.Lipid.Res 62 100016 PubMedID: 33334871 Abstract Perilipin 5 (PLIN5) is a lipid-droplet-associated protein that coordinates intracellular lipolysis in highly oxidative tissues and is thought to regulate lipid metabolism in response to phosphorylation by protein kinase A (PKA). We sought to identify PKA phosphorylation sites in PLIN5 and assess their functional relevance in cultured cells and the livers of mice. We detected phosphorylation on S155 and identified S155 as a functionally important site for lipid metabolism. Expression of phosphorylation-defective PLIN5 S155A in Plin5 null cells resulted in decreased rates of lipolysis and triglyceride-derived fatty acid oxidation. FLIM-FRET analysis of protein-protein interactions showed that PLIN5 S155 phosphorylation regulates PLIN5 interaction with adipose triglyceride lipase at the lipid droplet, but not with alpha-beta hydrolase domain-containing 5. Re-expression of PLIN5 S155A in the liver of Plin5 liver-specific null mice reduced lipolysis compared with wild-type PLIN5 re-expression, but was not associated with other changes in hepatic lipid metabolism. Furthermore, glycemic control was impaired in mice with expression of PLIN5 S155A compared with mice expressing PLIN5. Together, these studies demonstrate that PLIN5 S155 is required for PKA-mediated lipolysis and builds on the body of evidence demonstrating a critical role for PLIN5 in coordinating lipid and glucose metabolism. Title: An integrative systems genetic analysis of mammalian lipid metabolism Parker BL, Calkin AC, Seldin MM, Keating MF, Tarling EJ, Yang P, Moody SC, Liu Y, Zerenturk EJ and Drew BG <17 more author(s)> Parker BL, Calkin AC, Seldin MM, Keating MF, Tarling EJ, Yang P, Moody SC, Liu Y, Zerenturk EJ, Needham EJ, Miller ML, Clifford BL, Morand P, Watt MJ, Meex RCR, Peng KY, Lee R, Jayawardana K, Pan C, Mellett NA, Weir JM, Lazarus R, Lusis AJ, Meikle PJ, James DE, de Aguiar Vallim TQ, Drew BG (- 17) Ref: Nature, 567:187, 2019 : PubMed ESTHER: Parker_2019_Nature_567_187 PubMedSearch: Parker 2019 Nature 567 187 PubMedID: 30814737 Gene_locus related to this paper: human-ABHD1, mouse-abhd1 Abstract Dysregulation of lipid homeostasis is a precipitating event in the pathogenesis and progression of hepatosteatosis and metabolic syndrome. These conditions are highly prevalent in developed societies and currently have limited options for diagnostic and therapeutic intervention. Here, using a proteomic and lipidomic-wide systems genetic approach, we interrogated lipid regulatory networks in 107 genetically distinct mouse strains to reveal key insights into the control and network structure of mammalian lipid metabolism. These include the identification of plasma lipid signatures that predict pathological lipid abundance in the liver of mice and humans, defining subcellular localization and functionality of lipid-related proteins, and revealing functional protein and genetic variants that are predicted to modulate lipid abundance. Trans-omic analyses using these datasets facilitated the identification and validation of PSMD9 as a previously unknown lipid regulatory protein. Collectively, our study serves as a rich resource for probing mammalian lipid metabolism and provides opportunities for the discovery of therapeutic agents and biomarkers in the setting of hepatic lipotoxicity. Title: Triglyceride metabolism in exercising muscle Watt MJ, Cheng Y Ref: Biochimica & Biophysica Acta, 1862:1250, 2017 : PubMed ESTHER: Watt_2017_Biochim.Biophys.Acta_1862_1250 PubMedSearch: Watt 2017 Biochim.Biophys.Acta 1862 1250 PubMedID: 28652193 Abstract Triglycerides are stored within lipid droplets in skeletal muscle and can be hydrolyzed to produce fatty acids for energy production through beta-oxidation and oxidative phosphorylation. While there was some controversy regarding the quantitative importance of intramyocellular triglyceride (IMTG) as a metabolic substrate, recent advances in proton magnetic resonance spectroscopy and confocal microscopy support earlier tracer and biopsy studies demonstrating a substantial contribution of IMTG to energy production, particularly during moderate-intensity endurance exercise. This review provides an update on the understanding of IMTG utilization during exercise, with a focus on describing the key regulatory proteins that control IMTG breakdown and how these proteins respond to acute exercise and in the adaptation to exercise training. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink. Title: Integrated phenotypic and activity-based profiling links Ces3 to obesity and diabetes Dominguez E, Galmozzi A, Chang JW, Hsu KL, Pawlak J, Li W, Godio C, Thomas J, Partida D and Saez E <6 more author(s)> Dominguez E, Galmozzi A, Chang JW, Hsu KL, Pawlak J, Li W, Godio C, Thomas J, Partida D, Niessen S, O'Brien PE, Russell AP, Watt MJ, Nomura DK, Cravatt BF, Saez E (- 6) Ref: Nat Chemical Biology, 10:113, 2014 : PubMed ESTHER: Dominguez_2014_Nat.Chem.Biol_10_113 PubMedSearch: Dominguez 2014 Nat.Chem.Biol 10 113 PubMedID: 24362705 Gene_locus related to this paper: human-CES3, mouse-Ces1d Inhibitor(s) related to this paper: WWL229, WWL113 Abstract Phenotypic screening is making a comeback in drug discovery as the maturation of chemical proteomics methods has facilitated target identification for bioactive small molecules. A limitation of these approaches is that time-consuming genetic methods or other means are often required to determine the biologically relevant target (or targets) from among multiple protein-compound interactions that are typically detected. Here, we have combined phenotypic screening of a directed small-molecule library with competitive activity-based protein profiling to map and functionally characterize the targets of screening hits. Using this approach, we identify carboxylesterase 3 (Ces3, also known as Ces1d) as a primary molecular target of bioactive compounds that promote lipid storage in adipocytes. We further show that Ces3 activity is markedly elevated during adipocyte differentiation. Treatment of two mouse models of obesity-diabetes with a Ces3 inhibitor ameliorates multiple features of metabolic syndrome, illustrating the power of the described strategy to accelerate the identification and pharmacologic validation of new therapeutic targets. Title: Cellular localization and associations of the major lipolytic proteins in human skeletal muscle at rest and during exercise Mason RR, Meex RC, Russell AP, Canny BJ, Watt MJ Ref: PLoS ONE, 9:e103062, 2014 : PubMed ESTHER: Mason_2014_PLoS.One_9_e103062 PubMedSearch: Mason 2014 PLoS.One 9 e103062 PubMedID: 25054327 Abstract Lipolysis involves the sequential breakdown of fatty acids from triacylglycerol and is increased during energy stress such as exercise. Adipose triglyceride lipase (ATGL) is a key regulator of skeletal muscle lipolysis and perilipin (PLIN) 5 is postulated to be an important regulator of ATGL action of muscle lipolysis. Hence, we hypothesized that non-genomic regulation such as cellular localization and the interaction of these key proteins modulate muscle lipolysis during exercise. PLIN5, ATGL and CGI-58 were highly (>60%) colocated with Oil Red O (ORO) stained lipid droplets. PLIN5 was significantly colocated with ATGL, mitochondria and CGI-58, indicating a close association between the key lipolytic effectors in resting skeletal muscle. The colocation of the lipolytic proteins, their independent association with ORO and the PLIN5/ORO colocation were not altered after 60 min of moderate intensity exercise. Further experiments in cultured human myocytes showed that PLIN5 colocation with ORO or mitochondria is unaffected by pharmacological activation of lipolytic pathways. Together, these data suggest that the major lipolytic proteins are highly expressed at the lipid droplet and colocate in resting skeletal muscle, that their localization and interactions appear to remain unchanged during prolonged exercise, and, accordingly, that other post-translational mechanisms are likely regulators of skeletal muscle lipolysis. Title: Exercise training enhances white adipose tissue metabolism in rats selectively bred for low- or high-endurance running capacity Stephenson EJ, Lessard SJ, Rivas DA, Watt MJ, Yaspelkis BB, 3rd, Koch LG, Britton SL, Hawley JA Ref: American Journal of Physiology Endocrinol Metab, 305:E429, 2013 : PubMed ESTHER: Stephenson_2013_Am.J.Physiol.Endocrinol.Metab_305_E429 PubMedSearch: Stephenson 2013 Am.J.Physiol.Endocrinol.Metab 305 E429 PubMedID: 23757406 Abstract Impaired visceral white adipose tissue (WAT) metabolism has been implicated in the pathogenesis of several lifestyle-related disease states, with diminished expression of several WAT mitochondrial genes reported in both insulin-resistant humans and rodents. We have used rat models selectively bred for low- (LCR) or high-intrinsic running capacity (HCR) that present simultaneously with divergent metabolic phenotypes to test the hypothesis that oxidative enzyme expression is reduced in epididymal WAT from LCR animals. Based on this assumption, we further hypothesized that short-term exercise training (6 wk of treadmill running) would ameliorate this deficit. Approximately 22-wk-old rats (generation 22) were studied. In untrained rats, the abundance of mitochondrial respiratory complexes I-V, citrate synthase (CS), and PGC-1 was similar for both phenotypes, although CS activity was greater than 50% in HCR (P = 0.09). Exercise training increased CS activity in both phenotypes but did not alter mitochondrial protein content. Training increased the expression and phosphorylation of proteins with roles in beta-adrenergic signaling, including beta3-adrenergic receptor (16% increase in LCR; P < 0.05), NOR1 (24% decrease in LCR, 21% decrease in HCR; P < 0.05), phospho-ATGL (25% increase in HCR; P < 0.05), perilipin (25% increase in HCR; P < 0.05), CGI-58 (15% increase in LCR; P < 0.05), and GLUT4 (16% increase in HCR; P < 0.0001). A training effect was also observed for phospho-p38 MAPK (12% decrease in LCR, 20% decrease in HCR; P < 0.05) and phospho-JNK (29% increase in LCR, 20% increase in HCR; P < 0.05). We conclude that in the LCR-HCR model system, mitochondrial protein expression in WAT is not affected by intrinsic running capacity or exercise training. However, training does induce alterations in the activity and expression of several proteins that are essential to the intracellular regulation of WAT metabolism. Title: Adipose triglyceride lipase-null mice are resistant to high-fat diet-induced insulin resistance despite reduced energy expenditure and ectopic lipid accumulation Hoy AJ, Bruce CR, Turpin SM, Morris AJ, Febbraio MA, Watt MJ Ref: Endocrinology, 152:48, 2011 : PubMed ESTHER: Hoy_2011_Endocrinology_152_48 PubMedSearch: Hoy 2011 Endocrinology 152 48 PubMedID: 21106876 Abstract Adipose triglyceride lipase (ATGL) null (-/-) mice store vast amounts of triacylglycerol in key glucoregulatory tissues yet exhibit enhanced insulin sensitivity and glucose tolerance. The mechanisms underpinning these divergent observations are unknown but may relate to the reduced availability of circulating fatty acids. The aim of this study was to determine whether the enhancements in insulin stimulated glucose metabolism in ATGL-/- mice persist when challenged with a high-fat diet. ATGL-/- mice fed a low-fat diet exhibit improved whole-body insulin sensitivity and glucose tolerance compared with wild-type mice. Wild-type mice became hyperlipidemic and insulin-resistant when challenged with a high-fat diet (HFD, 60% fat) for 4 wk. ATGL-/- mice fed a HFD had elevated circulating fatty acids but had reduced fasting glycemia compared to pre-high-fat diet levels and were refractory to glucose intolerance and insulin resistance. This protection from high-fat diet-induced metabolic perturbations was associated with a preference for fatty acid utilization but reduced energy expenditure and no change in markers of mitochondrial capacity or density. The protection from high-fat diet-induced insulin resistance in ATGL-/- mice was due to increased cardiac and liver insulin-stimulated glucose clearance despite increased lipid content in these tissues. Additionally, there was no difference in skeletal muscle insulin-stimulated glucose disposal, but there was a reduction observed in brown adipose tissue. Overall, these results show that ATGL-/- mice are protected from HFD-induced insulin resistance and reveal a tissue specific disparity between lipid accumulation and insulin sensitivity. Title: Adipose triacylglycerol lipase is a major regulator of hepatic lipid metabolism but not insulin sensitivity in mice Turpin SM, Hoy AJ, Brown RD, Rudaz CG, Honeyman J, Matzaris M, Watt MJ Ref: Diabetologia, 54:146, 2011 : PubMed ESTHER: Turpin_2011_Diabetologia_54_146 PubMedSearch: Turpin 2011 Diabetologia 54 146 PubMedID: 20842343 Abstract AIMS/HYPOTHESIS: Hepatic steatosis is characterised by excessive triacylglycerol accumulation and is strongly associated with insulin resistance. An inability to efficiently mobilise liver triacylglycerol may be a key event mediating hepatic steatosis. Adipose triacylglycerol lipase (ATGL) is a key triacylglycerol lipase in the liver and we hypothesised that liver-specific overproduction of ATGL would reduce steatosis and enhance insulin action in obese rodents. METHODS: Studies of fatty acid metabolism were conducted in primary hepatocytes isolated from wild-type and Atgl (also known as Pnpla2)(-)(/)(-) mice. An ATGL adenovirus was utilised to overproduce ATGL in the livers of obese insulin-resistant C57Bl/6 mice (Ad-ATGL). Blood chemistry, hepatic lipid content and insulin sensitivity were assessed in mice. RESULTS: Triacylglycerol content was increased in Atgl(-)(/)(-) hepatocytes and was associated with increased fatty acid uptake and impaired fatty acid oxidation. ATGL adenovirus administration in obese mice increased the production of hepatic ATGL protein and reduced triacylglycerol, diacylglycerol and ceramide content in the liver. Overproduction of ATGL improved insulin signal transduction in the liver but did not affect fasting glycaemia or insulinaemia. Inflammatory signalling was not suppressed by ATGL overproduction. While ATGL overproduction increased plasma non-esterified fatty acids, neither lipid deposition nor insulin-stimulated glucose uptake were affected in skeletal muscle. CONCLUSIONS/INTERPRETATION: Liver ATGL overproduction decreases hepatic steatosis and mildly enhances liver insulin sensitivity. These effects are not sufficient to improve fasting glycaemia or insulinaemia in rodent obesity. Title: Triacylglycerol lipases and metabolic control: implications for health and disease Watt MJ, Spriet LL Ref: American Journal of Physiology Endocrinol Metab, 299:E162, 2010 : PubMed ESTHER: Watt_2010_Am.J.Physiol.Endocrinol.Metab_299_E162 PubMedSearch: Watt 2010 Am.J.Physiol.Endocrinol.Metab 299 E162 PubMedID: 20071561 Abstract Fatty acids derived from the hydrolysis of adipose tissue and skeletal muscle triacylglycerol (TG) are an important energy substrate at rest and during physical activity. This review outlines the identification of the new TG lipase, adipose triglyceride lipase, the current understanding of how cellular TG lipases are regulated, and the implications for understanding the integrated control of TG lipolysis. Furthermore, this review outlines recent advances that propose a "revised" role for TG lipases in cellular function, metabolic homeostasis, and disease prevention. Title: Triglyceride lipases alter fuel metabolism and mitochondrial gene expression Watt MJ Ref: Appl Physiol Nutr Metab, 34:340, 2009 : PubMed ESTHER: Watt_2009_Appl.Physiol.Nutr.Metab_34_340 PubMedSearch: Watt 2009 Appl.Physiol.Nutr.Metab 34 340 PubMedID: 19448696 Abstract Fatty acids derived from the hydrolysis of adipose tissue and skeletal muscle triacylglycerol (TG) are an important energy substrate at rest and during prolonged moderate-intensity exercise. Hormone sensitive lipase (HSL) was long considered to be the rate-limiting enzyme for adipocyte and skeletal muscle TG lipolysis. However, the understanding of TG lipolysis regulation was recently challenged by the finding that adipose TG lipase (ATGL) is the predominant TG lipase in adipose tissue and an important regulator of TG degradation in skeletal muscle. Thus, it is now proposed that ATGL and HSL regulate lipolysis in a serial manner, with ATGL cleaving the first fatty acid and HSL the second fatty acid of TG. Further to this biochemical evaluation, the generation and metabolic characterization of ATGL-/- and HSL-/- mice have revealed distinct phenotypes. ATGL-/- mice are obese, exhibit impaired thermogenesis, oxidize more carbohydrate, and die prematurely due to cardiac dysfunction. Studies in HSL-/- mice report defective beta-adrenergic stimulated lipolysis, protection against high-fat diet-induced obesity, and possible impairments in insulin secretion. This review outlines the current understanding of the cellular regulation of TG lipases, lipolytic regulation, and the functional implications of manipulating ATGL and HSL in vivo. Title: Regulation and function of triacylglycerol lipases in cellular metabolism Watt MJ, Steinberg GR Ref: Biochemical Journal, 414:313, 2008 : PubMed ESTHER: Watt_2008_Biochem.J_414_313 PubMedSearch: Watt 2008 Biochem.J 414 313 PubMedID: 18717647 Abstract The ability to store energy in the form of energy-dense TAG (triacylglycerol) and to mobilize these stores rapidly during times of low carbohydrate availability (fasting or famine) or during heightened metabolic demand (exercise or cold-stress) is a highly conserved process essential for survival. Today, in the presence of nutrient excess and sedentary lifestyles, the regulation of this pathway is viewed as an important therapeutic target for disease prevention, as elevated circulating fatty acids in obesity contribute to many aspects of the metabolic syndrome including hepatic steatosis, atherosclerosis and insulin resistance. In the present review, we discuss the metabolic regulation and function of TAG lipases with a focus on HSL (hormone-sensitive lipase), ATGL (adipose triacylglycerol lipase) and newly identified members of the lipolytic proteome. Title: Adipose triglyceride lipase regulation of skeletal muscle lipid metabolism and insulin responsiveness Watt MJ, van Denderen BJ, Castelli LA, Bruce CR, Hoy AJ, Kraegen EW, Macaulay L, Kemp BE Ref: Mol Endocrinol, 22:1200, 2008 : PubMed ESTHER: Watt_2008_Mol.Endocrinol_22_1200 PubMedSearch: Watt 2008 Mol.Endocrinol 22 1200 PubMedID: 18202145 Abstract Adipose triglyceride lipase (ATGL) is important for triglyceride (TG) metabolism in adipose tissue, and ATGL-null mice show increased adiposity. Given the apparent importance of ATGL in TG metabolism and the association of lipid deposition with insulin resistance, we examined the role of ATGL in regulating skeletal muscle lipid metabolism and insulin-stimulated glucose disposal. ATGL expression in myotubes was reduced by small interfering RNA and increased with a retrovirus encoding GFP-HA-ATGL. ATGL was also overexpressed in rats by in vivo electrotransfer. ATGL was down-regulated in skeletal muscle of obese, insulin-resistant mice and negatively correlated with intramyocellular TG levels. ATGL small interfering RNA in myotubes reduced TG hydrolase activity and increased TG content, whereas ATGL overexpression induced the reciprocal response, indicating that ATGL is an essential TG lipase in skeletal muscle. ATGL overexpression in myotubes increased the oxidation of fatty acid liberated from TG and diglyceride and ceramide contents. These responses in cells were largely recapitulated in rats overexpressing ATGL. When ATGL protein expression and TG hydrolase activity in obese, insulin-resistant rats were restored to levels observed in lean rats, TG content was reduced; however, the insulin resistance induced by the high-fat diet persisted. In conclusion, ATGL TG hydrolysis in skeletal muscle is a critical determinant of lipid metabolism and storage. Although ATGL content and TG hydrolase activity are decreased in obese, insulin-resistant phenotypes, overexpression does not rescue the condition, indicating reduced ATGL is unlikely to be a primary cause of obesity-associated insulin resistance. Title: Adipocyte triglyceride lipase expression in human obesity Steinberg GR, Kemp BE, Watt MJ Ref: American Journal of Physiology Endocrinol Metab, 293:E958, 2007 : PubMed ESTHER: Steinberg_2007_Am.J.Physiol.Endocrinol.Metab_293_E958 PubMedSearch: Steinberg 2007 Am.J.Physiol.Endocrinol.Metab 293 E958 PubMedID: 17609260 Abstract We have investigated the gene and protein expression of adipose triglyceride lipase (ATGL) and triglyceride (TG) lipase activity from subcutaneous and visceral adipose tissue of lean and obese subjects. Visceral and subcutaneous adipose tissue was obtained from 16 age-matched lean and obese subjects during abdominal surgery. Tissues were analyzed for mRNA expression of lipolytic enzymes by real-time quantitative PCR. ATGL protein content was assessed by Western blot and TG lipase activity by radiometric assessment. Subcutaneous and visceral adipose tissue of obese subjects had elevated mRNA expression of PNPLA2 (ATGL) and other lipases including PNPLA3, PNPLA4, CES1, and LYPLAL1 (P < 0.05). Surprisingly, ATGL protein expression and TG lipase activity were reduced in subcutaneous adipose tissue of obese subjects. Immunoprecipitation of ATGL reduced total TG lipase activity in adipose lysates by 70% in obese and 83% in lean subjects. No significant differences in the ATGL activator CGI-58 mRNA levels (ABHD5) were associated with obesity. These data demonstrate that ATGL is important for efficient TG lipase activity in humans. They also demonstrate reduced ATGL protein expression and TG lipase activity despite increased mRNA expression of ATGL and other novel lipolytic enzymes in obesity. The lack of correlation between ATGL protein content and in vitro TG lipase activity indicates that small decrements in ATGL protein expression are not responsible for the reduction in TG lipase activity observed here in obesity, and that posttranslational modifications may be important. Title: Adrenergic regulation of HSL serine phosphorylation and activity in human skeletal muscle during the onset of exercise Talanian JL, Tunstall RJ, Watt MJ, Duong M, Perry CG, Steinberg GR, Kemp BE, Heigenhauser GJ, Spriet LL Ref: American Journal of Physiology Regul Integr Comp Physiol, 291:R1094, 2006 : PubMed ESTHER: Talanian_2006_Am.J.Physiol.Regul.Integr.Comp.Physiol_291_R1094 PubMedSearch: Talanian 2006 Am.J.Physiol.Regul.Integr.Comp.Physiol 291 R1094 PubMedID: 16690773 Abstract Skeletal muscle hormone-sensitive lipase (HSL) activity is increased by contractions and increases in blood epinephrine (EPI) concentrations and cyclic AMP activation of the adrenergic pathway during prolonged exercise. To determine the importance of hormonal stimulation of HSL activity during the onset of moderate- and high-intensity exercise, nine men [age 24.3 +/- 1.2 yr, 80.8 +/- 5.0 kg, peak oxygen consumption (VO2 peak) 43.9 +/- 3.6 ml x kg(-1) x min(-1)] cycled for 1 min at approximately 65% VO2 peak, rested for 60 min, and cycled at approximately 90% VO2 peak for 1 min. Skeletal muscle biopsies were taken pre- and postexercise, and arterial blood was sampled throughout exercise. Arterial EPI increased (P < 0.05) postexercise at 65% (0.45 +/- 0.10 to 0.78 +/- 0.27 nM) and 90% VO2 peak (0.57 +/- 0.34 to 1.09 +/- 0.50 nM). HSL activity increased (P < 0.05) following 1 min of exercise at 65% VO2 peak [1.05 +/- 0.39 to 1.78 +/- 0.54 mmol x min(-1) x kg dry muscle (dm)(-1)] and 90% VO2 peak (1.07 +/- 0.24 to 1.91 +/- 0.62 mmol x min(-1) x kg dm(-1)). Cyclic AMP content also increased (P < 0.05) at both exercise intensities (65%: 1.52 +/- 0.67 to 2.75 +/- 1.12, 90%: 1.85 +/- 0.65 to 2.64 +/- 0.93 micromol/kg dm). HSL Ser660 phosphorylation (approximately 55% increase) and ERK1/2 phosphorylation ( approximately 33% increase) were augmented following exercise at both intensities, whereas HSL Ser563 and Ser565 phosphorylation were not different from rest. The results indicate that increases in arterial EPI concentration during the onset of moderate- and high-intensity exercise increase cyclic AMP content, which results in the phosphorylation of HSL Ser660. This adrenergic stimulation contributes to the increase in HSL activity that occurs in human skeletal muscle in the first minute of exercise at 65% and 90% VO2 peak. Title: Regulation of HSL serine phosphorylation in skeletal muscle and adipose tissue Watt MJ, Holmes AG, Pinnamaneni SK, Garnham AP, Steinberg GR, Kemp BE, Febbraio MA Ref: American Journal of Physiology Endocrinol Metab, 290:E500, 2006 : PubMed ESTHER: Watt_2006_Am.J.Physiol.Endocrinol.Metab_290_E500 PubMedSearch: Watt 2006 Am.J.Physiol.Endocrinol.Metab 290 E500 PubMedID: 16188906 Abstract Hormone-sensitive lipase (HSL) is important for the degradation of triacylglycerol in adipose and muscle tissue, but the tissue-specific regulation of this enzyme is not fully understood. We investigated the effects of adrenergic stimulation and AMPK activation in vitro and in circumstances where AMPK activity and catecholamines are physiologically elevated in humans in vivo (during physical exercise) on HSL activity and phosphorylation at Ser(563) and Ser(660), the PKA regulatory sites, and Ser(565), the AMPK regulatory site. In human experiments, skeletal muscle, subcutaneous adipose and venous blood samples were obtained before, at 15 and 90 min during, and 120 min after exercise. Skeletal muscle HSL activity was increased by approximately 80% at 15 min compared with rest and returned to resting rates at the cessation of and 120 min after exercise. Consistent with changes in plasma epinephrine, skeletal muscle HSL Ser(563) and Ser(660) phosphorylation were increased by 27% at 15 min (P < 0.05), remained elevated at 90 min, and returned to preexercise values postexercise. Skeletal muscle HSL Ser(565) phosphorylation and AMPK signaling were increased at 90 min during, and after, exercise. Phosphorylation of adipose tissue HSL paralleled changes in skeletal muscle in vivo, except HSL Ser(660) was elevated 80% in adipose compared with 35% in skeletal muscle during exercise. Studies in L6 myotubes and 3T3-L1 adipocytes revealed important tissue differences in the regulation of HSL. AMPK inhibited epinephrine-induced HSL activity in L6 myotubes and was associated with reduced HSL Ser(660) but not Ser(563) phosphorylation. HSL activity was reduced in L6 myotubes expressing constitutively active AMPK, confirming the inhibitory effects of AMPK on HSL activity. Conversely, in 3T3-L1 adipocytes, AMPK activation after epinephrine stimulation did not prevent HSL activity or glycerol release, which coincided with maintenance of HSL Ser(660) phosphorylation. Taken together, these data indicate that HSL activity is maintained in the face of AMPK activation as a result of elevated HSL Ser(660) phosphorylation in adipose tissue but not skeletal muscle. Title: Hormone-sensitive lipase is reduced in the adipose tissue of patients with type 2 diabetes mellitus: influence of IL-6 infusion Watt MJ, Carey AL, Wolsk-Petersen E, Kraemer FB, Pedersen BK, Febbraio MA Ref: Diabetologia, 48:105, 2005 : PubMed ESTHER: Watt_2005_Diabetologia_48_105 PubMedSearch: Watt 2005 Diabetologia 48 105 PubMedID: 15609025 Abstract AIMS/HYPOTHESIS: Type 2 diabetes mellitus is characterised by increased plasma NEFA and IL-6 concentrations, and IL-6 increases lipolysis in healthy men. We assessed the adipose tissue hormone-sensitive lipase (HSL) mRNA expression, protein expression and HSL activity in patients with type 2 diabetes mellitus, and determined the effect of IL-6 administration on these measures. Title: Effects of reduced free fatty acid availability on hormone-sensitive lipase activity in human skeletal muscle during aerobic exercise O'Neill M, Watt MJ, Heigenhauser GJ, Spriet LL Ref: J Appl Physiol (1985), 97:1938, 2004 : PubMed ESTHER: O'Neill_2004_J.Appl.Physiol.(1985)_97_1938 PubMedSearch: O'Neill 2004 J.Appl.Physiol.(1985) 97 1938 PubMedID: 15208282 Abstract Hormone-sensitive lipase (HSL) catalyzes the hydrolysis of intramuscular triacylglycerol (IMTG); however, its regulation in skeletal muscle is poorly understood. To examine the effects of reduced free fatty acid (FFA) availability on HSL activity in skeletal muscle during aerobic exercise, 11 trained men exercised at 55% maximal O2 uptake for 40 min after the ingestion of nicotinic acid (NA) or nothing (control). Muscle biopsies were taken at rest and 5, 20, and 40 min of exercise. Plasma FFA were suppressed (P < 0.05) in NA during exercise ( approximately 0.40 +/- 0.04 vs. approximately 0.07 +/- 0.01 mM). The respiratory exchange ratio (RER) was increased throughout exercise (0.020 + 0.008) after NA ingestion. However, the provision of energy from fat oxidation only decreased from 33% of the total in the control trial to 26% in the NA trial, suggesting increased IMTG oxidation in the NA trial. Mean HSL activity was 2.25 + 0.15 mmol x kg dry mass(-1) x min(-1) at rest and increased (P < 0.05) to 2.94 +/- 0.20 mmol x kg dry mass(-1) x min(-1) at 5 min in control. Contrary to the hypothesis, mean HSL was not activated to a greater extent in the NA trial during exercise (2.20 + 0.28 at rest to 2.88 + 0.21 mmol x kg dry mass(-1) x min(-1) at 5 min). No further HSL increases were observed at 20 or 40 min in both trials. There was variability in the response to NA ingestion, as some subjects experienced a large increase in RER and decrease in fat oxidation, whereas other subjects experienced no shift in RER and maintained fat oxidation despite the reduced FFA availability in the NA trial. However, even in these subjects, HSL activity was not further increased during the NA trial. In conclusion, reduced plasma FFA availability accompanied by increased epinephrine concentration did not further activate HSL beyond exercise alone. Title: Glucose ingestion blunts hormone-sensitive lipase activity in contracting human skeletal muscle Watt MJ, Krustrup P, Secher NH, Saltin B, Pedersen BK, Febbraio MA Ref: American Journal of Physiology Endocrinol Metab, 286:E144, 2004 : PubMed ESTHER: Watt_2004_Am.J.Physiol.Endocrinol.Metab_286_E144 PubMedSearch: Watt 2004 Am.J.Physiol.Endocrinol.Metab 286 E144 PubMedID: 14506077 Abstract To examine the effect of attenuated epinephrine and elevated insulin on intramuscular hormone sensitivity lipase activity (HSLa) during exercise, seven men performed 120 min of semirecumbent cycling (60% peak pulmonary oxygen uptake) on two occasions while ingesting either 250 ml of a 6.4% carbohydrate (GLU) or sweet placebo (CON) beverage at the onset of, and at 15 min intervals throughout, exercise. Muscle biopsies obtained before and immediately after exercise were analyzed for HSLa. Blood samples were simultaneously obtained from a brachial artery and a femoral vein before and during exercise, and leg blood flow was measured by thermodilution in the femoral vein. Net leg glycerol and lactate release and net leg glucose and free fatty acid (FFA) uptake were calculated from these measures. Insulin and epinephrine were also measured in arterial blood before and throughout exercise. During GLU, insulin was elevated (120 min: CON, 11.4 +/- 2.4, GLU, 35.3 +/- 6.9 pM, P < 0.05) and epinephrine suppressed (120 min: CON, 6.1 +/- 2.5, GLU, 2.1 +/- 0.9 nM; P < 0.05) compared with CON. Carbohydrate feeding also resulted in suppressed (P < 0.05) HSLa relative to CON (120 min: CON, 1.71 +/- 0.18, GLU, 1.27 +/- 0.16 mmol.min-1.kg dry mass-1). There were no differences in leg lactate or glycerol release when trials were compared, but leg FFA uptake was lower (120 min: CON, 0.29 +/- 0.06, GLU, 0.82 +/- 0.09 mmol/min) and leg glucose uptake higher (120 min: CON, 3.16 +/- 0.59, GLU, 1.37 +/- 0.37 mmol/min) in GLU compared with CON. These results demonstrate that circulating insulin and epinephrine play a role in HSLa in contracting skeletal muscle. Title: Beta-adrenergic stimulation of skeletal muscle HSL can be overridden by AMPK signaling Watt MJ, Steinberg GR, Chan S, Garnham A, Kemp BE, Febbraio MA Ref: FASEB Journal, 18:1445, 2004 : PubMed ESTHER: Watt_2004_FASEB.J_18_1445 PubMedSearch: Watt 2004 FASEB.J 18 1445 PubMedID: 15231718 Abstract Hormone-sensitive lipase (HSL), an important regulatory enzyme for triacylglycerol hydrolysis within skeletal muscle, is controlled by beta-adrenergic signaling as well as intrinsic factors related to contraction and energy turnover. In the current study, we tested the capacity of 5'AMP-activated protein kinase (AMPK) to suppress beta-adrenergic stimulation of HSL activity. Eight male subjects completed 60 min of cycle exercise at 70% VO2 peak on two occasions: either with normal (CON) or low (LG) pre-exercise muscle glycogen content, which is known to enhance exercise-induced AMPK activity. Muscle samples were obtained before and immediately after exercise. Pre-exercise glycogen averaged 375 +/- 35 and 163 +/- 27 mmol x kg(-1) dm for CON and LG, respectively. AMPK alpha-2 was not different between trials at rest and was increased (3.7-fold, P<0.05) by exercise during LG only. HSL activity did not differ between trials at rest and increased (0 min: 1.67 +/- 0.13; 60 min: 2.60 +/- 0.26 mmol x min(-1) x kg(-1) dm) in CON. The exercise-induced increase in HSL activity was attenuated by AMPK alpha-2 activation in LG. The attenuated HSL activity during LG occurred despite higher plasma epinephrine levels (60 min: CON, 1.96 +/- 0.29 vs LG, 4.25 +/- 0.60 nM, P<0.05) compared with CON. Despite the attenuated HSL activity in LG, IMTG was decreased by exercise (0 min: 27.1 +/- 2.0; 60 min: 22.5 +/- 2.0 mmol x kg(-1) dm, P<0.05), whereas no net reduction occurred in CON. To confirm the apparent effect of AMPK on HSL activity, we performed experiments in muscle cell culture. The epineprine-induced increase in HSL activity was totally attenuated (P<0.05) by AICAR administration in L6 myotubes. These data provide new evidence indicating that AMPK is a major regulator of skeletal muscle HSL activity that can override beta-adrenergic stimulation. However, the increased IMTG degradation in LG suggests factors other than HSL activity are important for IMTG degradation. | |||||||
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