Histone modifications and skeletal muscle metabolic gene expression

1.      Skeletal muscle oxidative function and metabolic gene expression are co-ordinately downregulated in metabolic diseases such as insulin resistance, obesity and Type 2 diabetes. Altering skeletal muscle metabolic gene expression to favour enhanced energy expenditure is considered a potential therapy to combat these diseases.

2.      Histone deacetylases (HDACs) are chromatin-remodelling enzymes that repress gene expression. It has been shown that HDAC4 and 5 co-operatively regulate a number of genes involved in various aspects of metabolism. Understanding how HDACs are regulated provides insights into the mechanisms regulating skeletal muscle metabolic gene expression.

3.      Multiple kinases control phosphorylation-dependent nuclear export of HDACs, rendering them unable to repress transcription. We have found a major role for the AMP-activated protein kinase (AMPK) in response to energetic stress, yet metabolic gene expression is maintained in the absence of AMPK activity. Preliminary evidence suggests a potential role for protein kinase D, also a Class IIa HDAC kinase, in this response.

4.      The HDACs are also regulated by ubiquitin-mediated proteasomal degradation, although the exact mediators of this process have not been identified.

5.      Because HDACs appear to be critical regulators of skeletal muscle metabolic gene expression, HDAC inhibition could be an effective therapy to treat metabolic diseases.

6.      Together, these data show that HDAC4 and 5 are critical regulators of metabolic gene expression and that understanding their regulation could provide a number of points of intervention for therapies designed to treat metabolic diseases, such as insulin resistance, obesity and Type 2 diabetes.

N-Acetylcysteine infusion does not affect glucose disposal during prolonged moderate-intensity exercise in humans

There is evidence that reactive oxygen species (ROS) signalling is required for normal increases in glucose uptake during contraction of isolated mouse skeletal muscle, and that AMP-activated protein kinase (AMPK) is involved. The aim of this study was to determine whether ROS signalling is involved in the regulation of glucose disposal and AMPK activation during moderate-intensity exercise in humans. Nine healthy males completed 80 min of cycle ergometry at 62 ± 1 of peak oxygen consumption ( . A 6,6-2H-glucose tracer was infused at rest and during exercise, and in a double-blind randomised cross-over design, N-acetylcysteine (NAC) or saline (CON) was co-infused. NAC was infused at 125 mg kg?1h?1for 15 min and then at 25 mg kg?1h?1for 20 min before and throughout exercise. NAC infusion elevated plasma NAC and cysteine, and muscle NAC and cysteine concentrations during exercise. Although neither NAC infusion nor exercise significantly affected muscle reduced or oxidised glutathione (GSH or GSSG) concentration (P> 0.05), S-glutathionylation (an indicator of oxidative stress) of a protein band of ?270 kDa was increased ?3-fold with contraction and this increase was prevented by NAC infusion. Despite this, exercised-induced increases in tracer determined glucose disposal, plasma lactate, plasma non-esterified fatty acids (NEFAs), and decreases in plasma insulin were not affected by NAC infusion. In addition, skeletal muscle AMPK? and acetyl-CoA carboxylase-? (ACC?) phosphorylation increased during exercise by ?3- and ?6-fold (P< 0.05), respectively, and this was not affected by NAC infusion. Unlike findings in mouse muscle ex vivo, NAC does not attenuate skeletal muscle glucose disposal or AMPK activation during moderate-intensity exercise in humans.

Effect of L-arginine infusion on glucose disposal during exercise in humans

Purpose: We have previously shown that local infusion of a nitric oxide synthase (NOS) inhibitor attenuates increases in leg glucose uptake during exercise in humans. We have also shown that infusion of the NOS substrate, L-arginine (L-Arg), increases glucose clearance, although the mechanisms involved were not determined. A potential mechanism for NO-mediated glucose disposal is via interactions with NOS and the energy sensor AMPactivated protein kinase (AMPK). The aim of this study was to determine the mechanism(s) by which L-Arg infusion increases glucose disposal during exercise in humans by examining total NOS activity and AMPK signaling.

Methods: Seven males cycled for 120 min at 64% T 1% V˙ O2peak, during which the [6,6-2H]glucose tracer was infused. During the final 60 min of exercise, either saline alone (Control, CON), or saline containing L-Arg HCl (L-Arg, 30 g at 0.5 gIminj1) was coinfused in a double-blind, randomized, counterbalanced order.

Results: L-Arg increased the glucose rate of disappearance and glucose clearance rate during exercise; however, this was accompanied by a 150% increase in plasma insulin concentration from 65 to 75 min (P G 0.05) that remained significantly elevated until 90 min of exercise. Skeletal muscle AMPK signaling, nNOSK phosphorylation by AMPK, and total NOS activity increased to a similar extent in the two trials.

Conclusions: The increase in glucose disposal after L-Arg infusion during exercise is likely due to the significantly higher plasma insulin concentration.

Hedgehog partial agonism drives warburg-lie metabolism in muscle and brown fat

Diabetes, obesity, and cancer affect upward of 15% of the world’s population. Interestingly, all three diseases juxtapose dysregulated intracellular signaling with altered metabolic state. Exactly which genetic factors define stable metabolic set points in vivo remains poorly understood. Here, we show that hedgehog signaling rewires cellular metabolism. We identify a cilium-dependent Smo-Ca2+-Ampk axis that triggers rapid Warburg-like metabolic reprogramming within minutes of activation and is required for proper metabolic selectivity and flexibility. We show that Smo modulators can uncouple the Smo-Ampk axis from canonical signaling and identify cyclopamine as one of a new class of “selective partial agonists,” capable of concomitant inhibition of canonical and activation of noncanonical hedgehog signaling. Intriguingly, activation of the Smo-Ampk axis in vivo drives robust insulin-independent glucose uptake in muscle and brown adipose tissue. These data identify multiple noncanonical endpoints that are pivotal for rational design of hedgehog modulators and provide a new therapeutic avenue for obesity and diabetes.

Mitochondrial dysfunction has divergent, cell type-dependent effects on insulin action

The contribution of mitochondrial dysfunction to insulin resistance is a contentious issue in metabolic research. Recent evidence implicates mitochondrial dysfunction as contributing to multiple forms of insulin resistance. However, some models of mitochondrial dysfunction fail to induce insulin resistance, suggesting greater complexity describes mitochondrial regulation of insulin action. We report that mitochondrial dysfunction is not necessary for cellular models of insulin resistance. However, impairment of mitochondrial function is sufficient for insulin resistance in a cell type-dependent manner, with impaired mitochondrial function inducing insulin resistance in adipocytes, but having no effect, or insulin sensitising effects in hepatocytes. The mechanism of mitochondrial impairment was important in determining the impact on insulin action, but was independent of mitochondrial ROS production. These data can account for opposing findings on this issue and highlight the complexity of mitochondrial regulation of cell type-specific insulin action, which is not described by current reductionist paradigms.

Statin-induced increases in atrophy gene expression occur independently of changes in PGC1α protein and mitochondrial content

One serious side effect of statin drugs is skeletal muscle myopathy. Although the mechanism(s) responsible for statin myopathy remains to be fully determined, an increase in muscle atrophy gene expression and changes in mitochondrial content and/or function have been proposed to play a role. In this study, we examined the relationship between statin-induced expression of muscle atrophy genes, regulators of mitochondrial biogenesis, and markers of mitochondrial content in slow- (ST) and fast-twitch (FT) rat skeletal muscles. Male Sprague Dawley rats were treated with simvastatin (60 or 80 mg·kg(-1)·day(-1)) or vehicle control via oral gavage for 14 days. In the absence of overt muscle damage, simvastatin treatment induced an increase in atrogin-1, MuRF1 and myostatin mRNA expression; however, these were not associated with changes in peroxisome proliferator gamma co-activator 1 alpha (PGC-1α) protein or markers of mitochondrial content. Simvastatin did, however, increase neuronal nitric oxide synthase (nNOS), endothelial NOS (eNOS) and AMPK α-subunit protein expression, and tended to increase total NOS activity, in FT but not ST muscles. Furthermore, simvastatin induced a decrease in β-hydroxyacyl CoA dehydrogenase (β-HAD) activity only in FT muscles. These findings suggest that the statin-induced activation of muscle atrophy genes occurs independent of changes in PGC-1α protein and mitochondrial content. Moreover, muscle-specific increases in NOS expression and possibly NO production, and decreases in fatty acid oxidation, could contribute to the previously reported development of overt statin-induced muscle damage in FT muscles.

Long-term high-fat diet-induced obesity decreases the cardiac leptin receptor without apparent lipotoxicity

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Exercício físico na prevenção e no tratamento da síndrome metabólica: um modelo experimental com ratos

Pós-graduação em Ciências da Motricidade - IBRC

Biogênese mitocondrial e marcadores de estresse oxidativo em ratos treinados e suplementados com L-Arginina

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Efeitos do exercício físico de salto sobre as proteínas relacionadas à captação de glicose e via proteolítica dependente de ATP no músculo gastrocnêmio de ratos diabéticos induzidos por administração de aloxana

Pós-graduação em Fisioterapia - FCT

Preventive Effects of Chitosan Coacervate Whey Protein on Body Composition and Immunometabolic Aspect in Obese Mice

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Perivascular adipose tissue and vascular responses in healthy trained rats

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Decaffeinated green tea extract rich in epigallocatechin-3-gallate improves insulin resistance and metabolic profiles in normolipidic diet--but not high-fat diet-fed mice

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)