Local nitric oxide synthase inhibition reduces skeletal muscle glucose uptake but not capillary blood flow during in situ muscle contraction in rats

OBJECTIVE: We have previously shown in humans that local infusion of a nitric oxide synthase (NOS) inhibitor into the femoral artery attenuates the increase in leg glucose uptake during exercise without influencing total leg blood flow. However, rodent studies examining the effect of NOS inhibition on contraction-stimulated skeletal muscle glucose uptake have yielded contradictory results. This study examined the effect of local infusion of an NOS inhibitor on skeletal muscle glucose uptake (2-deoxyglucose) and capillary blood flow (contrast-enhanced ultrasound) during in situ contractions in rats.

RESEARCH DESIGN AND METHODS: Male hooded Wistar rats were anesthetized and one hindleg electrically stimulated to contract (2 Hz, 0.1 ms) for 30 min while the other leg rested. After 10 min, the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (arterial concentration of 5 µmol/l) or saline was infused into the epigastric artery of the contracting leg.

RESULTS: Local NOS inhibition had no effect on blood pressure, heart rate, or muscle contraction force. Contractions increased (P < 0.05) skeletal muscle NOS activity, and this was prevented by L-NAME infusion. NOS inhibition caused a modest significant (P < 0.05) attenuation of the increase in femoral blood flow during contractions, but importantly there was no effect on capillary recruitment. NOS inhibition attenuated (P < 0.05) the increase in contraction-stimulated skeletal muscle glucose uptake by ~35%, without affecting AMP-activated protein kinase (AMPK) activation.

CONCLUSIONS: NOS inhibition attenuated increases in skeletal muscle glucose uptake during contraction without influencing capillary recruitment, suggesting that NO is critical for part of the normal increase in skeletal muscle fiber glucose uptake during contraction.

Adiponectin decreases pyruvate dehydrogenase kinase 4 gene expression in obese- and diabetic derived

Aim: To investigate the effects of globular adiponectin (gAd) on gene expression and whether these effects are mediated through 3',5'-cyclic monophosphate-activated protein kinase in skeletal muscle myotubes obtained from lean, obese and obese diabetic individuals.

Methods: Rectus abdominus muscle biopsies were obtained from surgical patients to establish primary skeletal muscle cell cultures. Three distinct primary cell culture groups were established (lean, obese and obese diabetic; n = 7 in each group). Once differentiated, these cultures were then exposed to gAd or 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) for 6 h.

Results: Stimulation with gAd decreased pyruvate dehydrogenase kinase 4 (PDK4) gene expression in the obese and diabetic samples (p ≤ 0.05) and increased cytochrome c oxidase (COX) subunit 4 (COXIV) gene expression in the myotubes derived from lean individuals only (p < 0.05). AICAR treatment also decreased PDK4 gene expression in the obese- and diabetic-derived myotubes (p ≤ 0.05) and increased the gene expression of the mitochondrial gene, COXIII, in the lean-derived samples only (p < 0.05).

Conclusions: This study demonstrated distinct disparity between myotubes derived from lean compared with obese and obese diabetic individuals following gAd and AICAR treatment. Further understanding of the regulation of PDK4 in obese and diabetic skeletal muscle and its interaction with adiponectin signalling is required as this appears to be an important early molecular event in these disease states that may improve blood glucose control and metabolic flux.

Skeletal muscle fat metabolism during post-exercise recovery in humans

Recovery after prolonged or high-intensity exercise is characterised by a substantial increase in adipose tissue lipolysis, resulting in elevated rates of plasma-derived fat oxidation. Despite the large increase in circulating fatty acids (FAs) after exercise, only a small fraction of this is taken up by exercised muscle in the lower extremities. Indeed, the predominant fate of non-oxidised FAs derived from post-exercise lipolysis is reesteriflcation hi the liver. During recovery from endurance exercise, a number of changes also occur hi skeletal muscle that allow for a high metabolic priority towards glycogen resynthesis. Reducing muscle glycogen during exercise potentiates these effects, however the cellular and molecular mechanisms regulating substrate oxidation following exercise remain poorly defined. The broad arm of this thesis was to examine the regulation of fat metabolism during recovery from glycogen-lowering exercise hi the presence of altered fat and glucose availability. In study I, eight endurance-trained males completed a bout of exhaustive exercise followed by ingestion of carbohydrate (CHO)-rich meals (64-70% of energy from CHO) at 1, 4, and 7 h of recovery. Duplicate muscle biopsies were obtained at exhaustion and 3, 6 and 18 h of recovery. Despite the large intake of CHO during recovery (491 ± 28 g or 6.8 + 0.3 g • kg-1), respiratory exchange ratio values of 0.77 to 0.84 indicated a greater reliance on fat as an oxidative fuel. Intramuscular triacylglycerol (IMTG) content remained unchanged in the presence of elevated glucose and insulin levels during recovery , suggesting IMTG has a negligible role in contributing to the enhanced fat oxidation after exhaustive exercise. It appears that the partitioning of exogenous glucose towards glycogen resynthesis is of high metabolic priority during immediate post-exercise recovery, supported by the trend towards reduced pyruvate dehydrogenase (PDH) activity and increased fat oxidation. The effect of altering plasma FA availability during post-exercise recovery was examined in study II. Eight endurance-trained males performed three trials consisting of glycogen-lowering exercise, followed by infusion of either saline (CON), saline + nicotinic acid (NA) (LFA) or Intralipid and heparin (HFA). Muscle biopsies were obtained at the end of exercise (0 h) and at 3 and 6 h in recovery. Altering the availability of plasma FAs during recovery induced changes in whole-body fat oxidation that were unrelated to differences in skeletal muscle malonyl-CoA. Furthermore, fat oxidation and acetyl-CoA carboxylase (ACC) phosphorylation appear to be dissociated after exercise, suggesting mechanisms other than phosphorylation-mediated changes in ACC activity have an important role in regulating malonyl-CoA and fat metabolism in human skeletal muscle after exercise. Alternative mechanisms include citrate and long-chain fatty acyl-CoA mediated changes in ACC activity, or differences in malonyl-CoA decarboxylase (MCD) activity. Reducing plasma FA concentrations with NA attenuated the post-exercise increase in MCD and pyruvate dehydrogenase kinase 4 (PDK4) gene expression, suggesting that FAs and/or other factors induced by NA are involved hi the regulation of these genes. Despite marked changes hi plasma FA availability, no significant changes in IMTG concentration were detected, providing further evidence that plasma-derived FAs are the preferential fuel source contributing to the enhanced fat oxidation post-exercise during recovery. To further examine the effect of substrate availability after exercise, Study III investigated the regulation of fat metabolism during a 6 h recovery period with or without glucose infusion. Enhanced glucose availability significantly increased CHO oxidation compared with the fasted state, although no differences in whole-body fat oxidation were apparent. Consistent with the similar rates of fat metabolism, no difference hi AMPK or ACCβ phosphorylation were observed between trials. In addition, no significant treatment or time effects for IMTG concentration were detected during recovery. The large exercise-induced PDK4 gene expression was attenuated when plasma FAs were reduced during glucose infusion, supporting the hypothesis that PDK4 is responsive to sustained changes in lipid availability and/or changes in plasma insulin. Furthermore, the possibility exists that the suppression of PDK4 mRNA also reduced PDK activity and thus maintained PDH activity to account for the higher rates of CHO oxidation observed during glucose infusion compared with the control trial.

Exercise and skeletal muscle glucose transporter 4 expression: molecular mechanisms

1.      Skeletal muscle is a highly plastic tissue that has a remarkable ability to adapt to external demands, such as exercise. Many of these adaptations can be explained by changes in skeletal muscle gene expression. A single bout of exercise is sufficient to induce the expression of some metabolic genes. We have focused our attention on the regulation of glucose transporter isoform 4 (GLUT-4) expression in human skeletal muscle.

2.      Glucose transporter isoform 4 gene expression is increased immediately following a single bout of exercise, and the GLUT-4 enhancer factor (GEF) and myocyte enhancer factor 2 (MEF2) transcription factors are required for this response. Glucose transporter isoform enhancer factor and MEF2 DNA binding activities are increased following exercise, and the molecular mechanisms regulating MEF2 in exercising human skeletal muscle have also been examined.

3.      These studies find possible roles for histone deacetylase 5 (HDAC5), adenosine monophosphate–activated protein kinase (AMPK), peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α) and p38 mitogen-activated protein kinase (MAPK) in regulating MEF2 through a series of complex interactions potentially involving MEF2 repression, coactivation and phosphorylation.

4.      Given that MEF2 is a transcription factor required for many exercise responsive genes, it is possible that these mechanisms are responsible for regulating the expression of a variety of metabolic genes during exercise. These mechanisms could also provide targets for the treatment and management of metabolic disease states, such as obesity and type 2 diabetes, which are characterized by mitochondrial dysfunction and insulin resistance in skeletal muscle.

Effect of sex differences on human MEF2 regulation during endurance exercise

Women exhibit an enhanced capability for lipid metabolism during endurance exercise compared with men. The underlying regulatory mechanisms behind this sex-related difference are not well understood but may comprise signaling through a myocyte enhancer factor 2 (MEF2) regulatory pathway. The primary purpose of this study, therefore, was to investigate the protein signaling of MEF2 regulatory pathway components at rest and during 90 min of bicycling exercise at 60% VO2peak in healthy, moderately trained men (n = 8) and women (n = 9) to elucidate the potential role of these proteins in substrate utilization during exercise. A secondary purpose was to screen for mRNA expression of MEF2 isoforms and myogenic regulatory factor (MRF) family members of transcription factors at rest and during exercise. Muscle biopsies were obtained before and immediately after exercise. Nuclear AMP-activated protein kinase-{alpha} ({alpha}AMPK) Thr172 (P < 0.001), histone deacetylase 5 (HDAC5) Ser498 (P < 0.001), and MEF2 Thr (P < 0.01) phosphorylation increased with exercise. No significant sex differences were observed at rest or during exercise. At rest, no significant sex differences were observed in mRNA expression of the measured transcription factors. mRNA for transcription factors MyoD, myogenin, MRF4, MEF2A, MEF2C, MEF2D, and peroxisome proliferator-activated receptor-{gamma} coactivator 1{alpha} (PGC1{alpha}) were significantly upregulated by exercise. Of these, MEF2A mRNA increased 25% specifically in women (P < 0.05), whereas MEF2D mRNA tended to increase in men (P = 0.11). Although minor sex differences in mRNA expression were observed, the main finding of the present study was the implication of a joint signaling action of AMPK, HDAC5, and PGC1{alpha} on MEF2 in the immediate regulatory response to endurance exercise. This signaling response was independent of sex.

AMP-activated protein kinase regulates GLUT4 transcription by phosphorylating histone deacetylase 5

Objective: Insulin resistance associated with obesity and diabetes is ameliorated by specific overexpression of GLUT4 in skeletal muscle. The molecular mechanisms regulating skeletal muscle GLUT4 expression remain to be elucidated. The purpose of this study was to examine these mechanisms.

Research Design and Methods and Results: Here, we report that AMP-activated protein kinase (AMPK) regulates GLUT4 transcription through the histone deacetylase (HDAC)5 transcriptional repressor. Overexpression of HDAC5 represses GLUT4 reporter gene expression, and HDAC inhibition in human primary myotubes increases endogenous GLUT4 gene expression. In vitro kinase assays, site-directed mutagenesis, and site-specific phospho-antibodies establish AMPK as an HDAC5 kinase that targets S259 and S498. Constitutively active but not dominant-negative AMPK and 5-aminoimidazole-4-carboxamide-1-β-d-ribonucleoside (AICAR) treatment in human primary myotubes results in HDAC5 phosphorylation at S259 and S498, association with 14-3-3 isoforms, and H3 acetylation. This reduces HDAC5 association with the GLUT4 promoter, as assessed through chromatin immunoprecipitation assays and HDAC5 nuclear export, concomitant with increases in GLUT4 gene expression. Gene reporter assays also confirm that the HDAC5 S259 and S498 sites are required for AICAR induction of GLUT4 transcription.

Conclusions: These data reveal a signal transduction pathway linking cellular energy charge to gene transcription directed at restoring cellular and whole-body energy balance and provide new therapeutic targets for the treatment and management of insulin resistance and type 2 diabetes.

Normal hypertrophy accompanied by phosphoryation and activation of AMP-activated protein kinase α1 following overload in LKB1 knockout mice

The activation of the AMP-activated protein kinase (AMPK) and inhibition of the mammalian target of rapamycin complex 1 (mTORC1) is hypothesized to underlie the fact that muscle growth following resistance exercise is decreased by concurrent endurance exercise. To directly test this hypothesis, the capacity for muscle growth was determined in mice lacking the primary upstream kinase for AMPK in skeletal muscle, LKB1. Following either 1 or 4 weeks of overload, there was no difference in muscle growth between the wild type (wt) and LKB1−/− mice (1 week: wt, 38.8 ± 7.75%; LKB1−/−, 27.8 ± 12.98%; 4 week: wt, 75.8 ± 15.2%; LKB1−/−, 85.0 ± 22.6%). In spite of the fact that the LKB1 had been knocked out in skeletal muscle, the phosphorylation and activity of the α1 isoform of AMPK were markedly increased in both the wt and the LKB1−/− mice. To identify the upstream kinase(s) responsible, we studied potential upstream kinases other than LKB1. The activity of both Ca2+–calmodulin-dependent protein kinase kinase α(CaMKKα) (5.05 ± 0.86-fold) and CaMKKβ (10.1 ± 2.59-fold) increased in the overloaded muscles, and this correlated with their increased expression. Phosphorylation of TAK-1 also increased 10-fold following overload in both the wt and LKB1 mice. Even though the α1 isoform of AMPK was activated by overload, there were no increases in expression of mitochondrial proteins or GLUT4, indicating that the α1 isoform is not involved in these metabolic adaptations. The phosphorylation of TSC2, an upstream regulator of the TORC1 pathway, at the AMPK site (Ser1345) was increased in response to overload, and this was not affected by LKB1 deficiency. Taken together, these data suggest that the α1 isoform of AMPK is preferentially activated in skeletal muscle following overload in the absence of metabolic adaptations, suggesting that this isoform might be important in the regulation of growth but not metabolism.

Optimizing training adaptations by manipulating glycogen

For decades, glycogen has been recognized as a storage form of glucose within the liver and muscles. Only recently has a greater role for glycogen as a regulator of metabolic signalling been suggested. Glycogen either directly or indirectly regulates a number of signalling proteins, including the adenosine-5'-phosphate- (AMP-) activated protein kinase (AMPK) and p38 mitogen-activated protein kinase (MAPK). AMPK and p38 MAPK play a significant role in controlling the expression and activity of the peroxisome proliferator activated receptor γ coactivators (PGCs), respectively. The PGCs can directly increase muscle mitochondrial mass and endurance exercise performance. As low muscle glycogen is generally associated with greater activation of these pathways, the concept of training with low glycogen to maximize the physiological adaptations to endurance exercise is gaining acceptance in the scientific community. In this review, we evaluate the scientific basis for this philosophy and propose some practical applications of this philosophy for the general population as well as elite endurance athletes.

Intravenous AICAR administration reduces hepatic glucose output and inhibits whole body lipolysis in type 2 diabetic patients

Aims/hypothesis: The 5′-AMP-activated protein kinase (AMPK) pathway is intact in type 2 diabetic patients and is seen as a target for diabetes treatment. In this study, we aimed to assess the impact of the AMPK activator 5-aminoimidazole-4-carboxamide riboside (AICAR) on both glucose and fatty acid metabolism in vivo in type 2 diabetic patients.

Methods: Stable isotope methodology and blood and muscle biopsy sampling were applied to assess blood glucose and fatty acid kinetics following continuous i.v. infusion of AICAR (0.75 mg kg−1 min−1) and/or NaCl (0.9%) in ten male type 2 diabetic patients (age 64 ± 2 years; BMI 28 ± 1 kg/m2).
Results Plasma glucose rate of appearance (R a) was reduced following AICAR administration, while plasma glucose rate of disappearance (R d) was similar in the AICAR and control test. Consequently, blood glucose disposal (R d expressed as a percentage of R a) was increased following AICAR infusion (p < 0.001). Accordingly, a greater decline in plasma glucose concentration was observed following AICAR infusion (p < 0.001). Plasma NEFA R a and R d were both significantly reduced in response to AICAR infusion, and were accompanied by a significant decline in plasma NEFA concentration. Although AMPK phosphorylation in skeletal muscle was not increased, we observed a significant increase in acetyl-CoA carboxylase phosphorylation (p < 0.001).

Conclusions/interpretation: The i.v. administration of AICAR reduces hepatic glucose output, thereby lowering blood glucose concentrations in vivo in type 2 diabetic patients. Furthermore, AICAR administration stimulates hepatic fatty acid oxidation and/or inhibits whole body lipolysis, thereby reducing plasma NEFA concentration.

Exercise-induced histone modifications in human skeletal muscle

Skeletal muscle adaptations to exercise confer many of the health benefits of physical activity and occur partly through alterations in skeletal muscle gene expression. The exact mechanisms mediating altered skeletal muscle gene expression in response to exercise are unknown. However, in recent years, chromatin remodelling through epigenetic histone modifications has emerged as a key regulatory mechanism controlling gene expression in general. The purpose of this study was to examine the effect of exercise on global histone modifications that mediate chromatin remodelling and transcriptional activation in human skeletal muscle in response to exercise. In addition, we sought to examine the signalling mechanisms regulating these processes. Following 60 min of cycling, global histone 3 acetylation at lysine 9 and 14, a modification associated with transcriptional initiation, was unchanged from basal levels, but was increased at lysine 36, a site associated with transcriptional elongation. We examined the regulation of the class IIa histone deacetylases (HDACs), which are enzymes that suppress histone acetylation and have been implicated in the adaptations to exercise. While we found no evidence of proteasomal degradation of the class IIa HDACs, we found that HDAC4 and 5 were exported from the nucleus during exercise, thereby removing their transcriptional repressive function. We also observed activation of the AMP-activated protein kinase (AMPK) and the calcium–calmodulin-dependent protein kinase II (CaMKII) in response to exercise, which are two kinases that induce phosphorylation-dependent class IIa HDAC nuclear export. These data delineate a signalling pathway that might mediate skeletal muscle adaptations in response to exercise.

Acute signalling responses to intense endurance training commenced with low or normal muscle glycogen

We have previously demonstrated that well-trained subjects who completed a 3 week training programme in which selected high-intensity interval training (HIT) sessions were commenced with low muscle glycogen content increased the maximal activities of several oxidative enzymes that promote endurance adaptations to a greater extent than subjects who began all training sessions with normal glycogen levels. The aim of the present study was to investigate acute skeletal muscle signalling responses to a single bout of HIT commenced with low or normal muscle glycogen stores in an attempt to elucidate potential mechanism(s) that might underlie our previous observations. Six endurance-trained cyclists/triathletes performed a 100 min ride at ∼70% peak O₂ uptake (AT) on day 1 and HIT (8 × 5 min work bouts at maximal self-selected effort with 1 min rest) 24 h later (HIGH). Another six subjects, matched for fitness and training history, performed AT on day 1 then 1–2 h later, HIT (LOW). Muscle biopsies were taken before and after HIT. Muscle glycogen concentration was higher in HIGH versus LOW before the HIT (390 ± 28 versus 256 ± 67 μmol (g dry wt)⁻¹). After HIT, glycogen levels were reduced in both groups (P < 0.05) but HIGH was elevated compared with LOW (229 ± 29 versus 124 ± 41 μmol (g dry wt)−1; P < 0.05). Phosphorylation of 5'AMP-activated protein kinase (AMPK) increased after HIT, but the magnitude of increase was greater in LOW (P < 0.05). Despite the augmented AMPK response in LOW after HIT, selected downstream AMPK substrates were similar between groups. Phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) was unchanged for both groups before and after the HIT training sessions. We conclude that despite a greater activation AMPK phosphorylation when HIT was commenced with low compared with normal muscle glycogen availability, the localization and phosphorylation state of selected downstream targets of AMPK were similar in response to the two interventions.

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.