AMPKγ3 Controls Muscle Glucose Uptake in Recovery From Exercise to Recapture Energy Stores.

Exercise increases muscle glucose uptake independently of insulin signaling and represents a cornerstone for the prevention of metabolic disorders. Pharmacological activation of the exercise-responsive AMPK in skeletal muscle has been proven successful as a therapeutic approach to treat metabolic disorders by improving glucose homeostasis through the regulation of muscle glucose uptake. However, conflicting observations cloud the proposed role of AMPK as a necessary regulator of muscle glucose uptake during exercise. We show that glucose uptake increases in human skeletal muscle in the absence of AMPK activation during exercise and that exercise-stimulated AMPKγ3 activity strongly correlates to muscle glucose uptake in the postexercise period. In AMPKγ3-deficient mice, muscle glucose uptake is normally regulated during exercise and contractions but impaired in the recovery period from these stimuli. Impaired glucose uptake in recovery from exercise and contractions is associated with a lower glucose extraction, which can be explained by a diminished permeability to glucose and abundance of GLUT4 at the muscle plasma membrane. As a result, AMPKγ3 deficiency impairs muscle glycogen resynthesis following exercise. These results identify a physiological function of the AMPKγ3 complex in human and rodent skeletal muscle that regulates glucose uptake in recovery from exercise to recapture muscle energy stores. ARTICLE HIGHLIGHTS: Exercise-induced activation of AMPK in skeletal muscle has been proposed to regulate muscle glucose uptake in recovery from exercise. This study investigated whether the muscle-specific AMPKγ3-associated heterotrimeric complex was involved in regulating muscle glucose metabolism in recovery from exercise. The findings support that exercise-induced activation of the AMPKγ3 complex in human and mouse skeletal muscle enhances glucose uptake in recovery from exercise via increased translocation of GLUT4 to the plasma membrane. This work uncovers the physiological role of the AMPKγ3 complex in regulating muscle glucose uptake that favors replenishment of the muscle cellular energy stores.

Insulin Sensitization Following a Single Exercise Bout Is Uncoupled to Glycogen in Human Skeletal Muscle: A Meta-analysis of 13 Single-Center Human Studies.

Exercise profoundly influences glycemic control by enhancing muscle insulin sensitivity, thus promoting glucometabolic health. While prior glycogen breakdown so far has been deemed integral for muscle insulin sensitivity to be potentiated by exercise, the mechanisms underlying this phenomenon remain enigmatic. We have combined original data from 13 of our studies that investigated insulin action in skeletal muscle either under rested conditions or following a bout of one-legged knee extensor exercise in healthy young male individuals (n = 106). Insulin-stimulated glucose uptake was potentiated and occurred substantially faster in the prior contracted muscles. In this otherwise homogenous group of individuals, a remarkable biological diversity in the glucometabolic responses to insulin is apparent both in skeletal muscle and at the whole-body level. In contrast to the prevailing concept, our analyses reveal that insulin-stimulated muscle glucose uptake and the potentiation thereof by exercise are not associated with muscle glycogen synthase activity, muscle glycogen content, or degree of glycogen utilization during the preceding exercise bout. Our data further suggest that the phenomenon of improved insulin sensitivity in prior contracted muscle is not regulated in a homeostatic feedback manner from glycogen. Instead, we put forward the idea that this phenomenon is regulated by cellular allostatic mechanisms that elevate the muscle glycogen storage set point and enhance insulin sensitivity to promote the uptake of glucose toward faster glycogen resynthesis without development of glucose overload/toxicity or feedback inhibition.

Illumination of the Endogenous Insulin-Regulated TBC1D4 Interactome in Human Skeletal Muscle.

Insulin-stimulated muscle glucose uptake is a key process in glycemic control. This process depends on the redistribution of glucose transporters to the surface membrane, a process that involves regulatory proteins such as TBC1D1 and TBC1D4. Accordingly, a TBC1D4 loss-of-function mutation in human skeletal muscle is associated with an increased risk of type 2 diabetes, and observations from carriers of a TBC1D1 variant associate this protein to a severe obesity phenotype. Here, we identified interactors of the endogenous TBC1D4 protein in human skeletal muscle by an unbiased proteomics approach. We detected 76 proteins as candidate TBC1D4 interactors. The binding of 12 of these interactors was regulated by insulin, including proteins known to be involved in glucose metabolism (e.g., 14-3-3 proteins and α-actinin-4 [ACTN4]). TBC1D1 also coprecipitated with TBC1D4 and vice versa in both human and mouse skeletal muscle. This interaction was not regulated by insulin or exercise in young, healthy, lean individuals. Similarly, the exercise- and insulin-regulated phosphorylation of the TBC1D1-TBC1D4 complex was intact. In contrast, we observed an altered interaction as well as compromised insulin-stimulated phosphoregulation of the TBC1D1-TBC1D4 complex in muscle of obese individuals with type 2 diabetes. Altogether, we provide a repository of TBC1D4 interactors in human and mouse skeletal muscle that serve as potential regulators of TBC1D4 function and, thus, insulin-stimulated glucose uptake in human skeletal muscle.

Direct small molecule ADaM-site AMPK activators reveal an AMPKγ3-independent mechanism for blood glucose lowering.

OBJECTIVE: Skeletal muscle is an attractive target for blood glucose-lowering pharmacological interventions. Oral dosing of small molecule direct pan-activators of AMPK that bind to the allosteric drug and metabolite (ADaM) site, lowers blood glucose through effects in skeletal muscle. The molecular mechanisms responsible for this effect are not described in detail. This study aimed to illuminate the mechanisms by which ADaM-site activators of AMPK increase glucose uptake in skeletal muscle. Further, we investigated the consequence of co-stimulating muscles with two types of AMPK activators i.e., ADaM-site binding small molecules and the prodrug AICAR. METHODS: The effect of the ADaM-site binding small molecules (PF739 and 991), AICAR or co-stimulation with PF739 or 991 and AICAR on muscle glucose uptake was investigated ex vivo in m. extensor digitorum longus (EDL) excised from muscle-specific AMPKα1α2 as well as whole-body AMPKγ3-deficient mouse models. In vitro complex-specific AMPK activity was measured by immunoprecipitation and molecular signaling was assessed by western blotting in muscle lysate. To investigate the transferability of these studies, we treated diet-induced obese mice in vivo with PF739 and measured complex-specific AMPK activation in skeletal muscle. RESULTS: Incubation of skeletal muscle with PF739 or 991 increased skeletal muscle glucose uptake in a dose-dependent manner. Co-incubating PF739 or 991 with a maximal dose of AICAR increased glucose uptake to a greater extent than any of the treatments alone. Neither PF739 nor 991 increased AMPKα2ß2γ3 activity to the same extent as AICAR, while co-incubation led to potentiated effects on AMPKα2ß2γ3 activation. In muscle from AMPKγ3 KO mice, AICAR-stimulated glucose uptake was ablated. In contrast, the effect of PF739 or 991 on glucose uptake was not different between WT and AMPKγ3 KO muscles. In vivo PF739 treatment lowered blood glucose levels and increased muscle AMPKγ1-complex activity 2-fold, while AMPKα2ß2γ3 activity was not affected. CONCLUSIONS: ADaM-site binding AMPK activators increase glucose uptake independently of AMPKγ3. Co-incubation with PF739 or 991 and AICAR potentiates the effects on muscle glucose uptake and AMPK activation. In vivo, PF739 lowers blood glucose and selectively activates muscle AMPKγ1-complexes. Collectively, this suggests that pharmacological activation of AMPKγ1-containing complexes in skeletal muscle can increase glucose uptake and can lead to blood glucose lowering.

The insulin-sensitizing effect of a single exercise bout is similar in type I and type II human muscle fibres.

KEY POINTS: Rodent studies suggest muscle fibre type-specific insulin response in the recovery from exercise.  The current study investigates muscle fibre type-specific insulin action in the recovery from exercise in healthy subjects.  In type I and type II muscle fibres, key proteins in glucose metabolism are similarly regulated by insulin during recovery from exercise.  Our findings imply that both type I and type II muscle fibres contribute to the phenomenon of increased insulin sensitivity in the recovery from a single bout of exercise in humans. ABSTRACT: Human skeletal muscle consists of slow-twitch (type I) and fast-twitch (type II) muscle fibres. Muscle insulin action, regulating glucose uptake and metabolism, is improved following a single exercise bout. Rodent studies suggest that this phenomenon is confined to specific muscle fibre types. Whether this phenomenon is also confined to specific fibre types in humans has not been described. To investigate this, nine healthy men underwent a euglycaemic hyperinsulinaemic clamp (EHC) in the recovery from a single bout of one-legged knee-extensor exercise. Pools of type I and type II fibres were prepared from muscle biopsies taken in the rested and prior exercised leg before and after the EHC. AMPK γ3 and TBC1D4 - two key proteins regulating muscle insulin action following exercise - were higher expressed in type II than type I fibres. However, phosphor-regulation of TBC1D4 was similar between fibre types when related to the total amount of TBC1D4 protein. The activating dephosphorylation of glycogen synthase was also similar in the two fibre types. Thus, insulin-induced regulation of key proteins important for transport and intracellular flux of glucose towards glycogen storage in the recovery from exercise, does not differ between fibre types. In conclusion, the insulin-sensitizing effect of a single bout of exercise includes both type I and type II fibres in human skeletal muscle. This may be an important observation for future pharmacological strategies targeting muscle insulin sensitivity in humans.

Inducible deletion of skeletal muscle AMPKα reveals that AMPK is required for nucleotide balance but dispensable for muscle glucose uptake and fat oxidation during exercise.

OBJECTIVE: Evidence for AMP-activated protein kinase (AMPK)-mediated regulation of skeletal muscle metabolism during exercise is mainly based on transgenic mouse models with chronic (lifelong) disruption of AMPK function. Findings based on such models are potentially biased by secondary effects related to a chronic lack of AMPK function. To study the direct effect(s) of AMPK on muscle metabolism during exercise, we generated a new mouse model with inducible muscle-specific deletion of AMPKα catalytic subunits in adult mice. METHODS: Tamoxifen-inducible and muscle-specific AMPKα1/α2 double KO mice (AMPKα imdKO) were generated by using the Cre/loxP system, with the Cre under the control of the human skeletal muscle actin (HSA) promoter. RESULTS: During treadmill running at the same relative exercise intensity, AMPKα imdKO mice showed greater depletion of muscle ATP, which was associated with accumulation of the deamination product IMP. Muscle-specific deletion of AMPKα in adult mice promptly reduced maximal running speed and muscle glycogen content and was associated with reduced expression of UGP2, a key component of the glycogen synthesis pathway. Muscle mitochondrial respiration, whole-body substrate utilization, and muscle glucose uptake and fatty acid (FA) oxidation during muscle contractile activity remained unaffected by muscle-specific deletion of AMPKα subunits in adult mice. CONCLUSIONS: Inducible deletion of AMPKα subunits in adult mice reveals that AMPK is required for maintaining muscle ATP levels and nucleotide balance during exercise but is dispensable for regulating muscle glucose uptake, FA oxidation, and substrate utilization during exercise.

Extended versus limited arch replacement in acute Type A aortic dissection.

OBJECTIVES: The recommended extent of surgical resection and reconstruction of the arch in acute DeBakey Type I aortic dissection is an ongoing controversy. However, several recent reports indicate a trend towards a more extensive arch operation in several institutions. We have analysed the recent data from the International Registry of Acute Aortic Dissection to assess the choice of procedure over time and to evaluate the surgical outcome in a 'real-world' database. Our aim was to compare short- and mid-term outcomes of limited repairs versus complete arch surgery. METHODS: Of the 1241 patients included in the 'Interventional Cohort' of the International Registry of Acute Aortic Dissection from March 1996 to March 2015, 907 underwent ascending aortic or hemiarch replacement (Group A) and 334 had extended arch replacement (Group B). An extended resection was a surgeon's 'judgement call'. Logistic regression analysis, propensity-adjusted multivariable comparisons and Kaplan-Meier curves were used for analyses. RESULTS: Overall in-hospital mortality was 14.2% with no difference between groups (Group A 13.1%, Group B 17.1%). Coma/altered consciousness (odds ratio 3.16, 95% confidence interval 1.60-6.25, P = 0.001), hypotension, tamponade or shock (2.03, 1.11-3.73, P = 0.022) and any pulse deficit (1.92, 1.04-3.54, P = 0.038) were predictors of in-hospital mortality in a propensity score-adjusted multivariable analysis. Overall 5-year survival was 69.4% in the ascending group and 73.1% in the total arch group (P = 0.83 by Kaplan-Meier analysis). For survivors of the index hospitalization, the 5-year freedom from death, aortic rupture and reintervention were 71.1% in Group A and 76.4% in Group B (P = 0.54 by Kaplan-Meier analysis). CONCLUSIONS: Selective, or 'surgeon's choice', extended arch replacement had no discernible acute downside compared with less extensive surgery. Whether extended arch replacement improves the prognosis beyond 5 years remains to be settled.

The International Registry of Acute Aortic Dissections (IRAD) - experiences from the first 20 years.

An international collaboration on various aspects of acute aortic syndromes, IRAD or The International Registry of Acute Aortic Dissections, is celebrating its 20th anniversary this year (2016). In this paper, we present important lessons learned during these first 20 years.

Presentation, Diagnosis, and Outcomes of Acute Aortic Dissection: 17-Year Trends From the International Registry of Acute Aortic Dissection.

BACKGROUND: Diagnosis, treatment, and outcomes of acute aortic dissection (AAS) are changing. OBJECTIVES: This study examined 17-year trends in the presentation, diagnosis, and hospital outcomes of AAD from the International Registry of Acute Aortic Dissection (IRAD). METHODS: Data from 4,428 patients enrolled at 28 IRAD centers between December 26, 1995, and February 6, 2013, were analyzed. Patients were divided according to enrollment date into 6 equal groups and by AAD type: A (n = 2,952) or B (n = 1,476). RESULTS: There was no change in the presenting complaints of severe or worst-ever pain for type A and type B AAD (93% and 94%, respectively), nor in the incidence of chest pain (83% and 71%, respectively). Use of computed tomography (CT) for diagnosis of type A increased from 46% to 73% (p < 0.001). Surgical management for type A increased from 79% to 90% (p < 0.001). Endovascular management of type B increased from 7% to 31% (p < 0.001). Type A in-hospital mortality decreased significantly (31% to 22%; p < 0.001), as surgical mortality (25% to 18%; p = 0.003). There was no significant trend in in-hospital mortality in type B (from 12% to 14%). CONCLUSIONS: Presenting symptoms and physical findings of AAD have not changed significantly. Use of chest CT increased for type A. More patients in both groups were managed with interventional procedures: surgery in type A and endovascular therapy in type B. A significant decrease in overall in-hospital mortality was seen for type A but not for type B.

Extent of preoperative false lumen thrombosis does not influence long-term survival in patients with acute type A aortic dissection.

BACKGROUND: Partial thrombosis of the false lumen has been related to aortic growth, reoperations, and death in the chronic phase of type B and repaired type A aortic dissections. The impact of preoperative false lumen thrombosis has not been studied previously. We used data from a contemporary, multinational database on aortic dissections to evaluate whether different degrees of preoperative false lumen thrombosis influenced long-term prognosis. METHODS AND RESULTS: We examined the records of 522 patients with surgically treated acute type A aortic dissections who survived to discharge between 1996 and 2011. At the preoperative imaging, 414 (79.3%) patients had patent false lumens, 84 (16.1%) had partial thrombosis of the false lumen, and 24 (4.6%) had complete thrombosis of the false lumen. The annual median (interquartile range) aortic growth rates were 0.5 (-0.3 to 2.0) mm in the aortic arch, 2.0 (0.2 to 4.0) mm in the descending thoracic aorta, and similar regardless of the degree of false lumen thrombosis. The overall 5-year survival rate was 84.7%, and it was not influenced by false lumen thrombosis (P=0.86 by the log-rank test). Independent predictors of long-term mortality were age >70 years (hazard ratio [HR], 2.34; 95% confidence interval [CI], 1.20 to 4.56, P=0.012) and postoperative cerebrovascular accident, coma, and/or renal failure (HR, 2.62; 95% CI, 1.40 to 4.92, P=0.003). CONCLUSIONS: Patients with acute type A aortic dissection who survive to discharge have a favorable prognosis. Preoperative false lumen thrombosis does not influence long-term mortality, reintervention rates, or aortic growth.

Patients with type A acute aortic dissection presenting with major brain injury: should we operate on them?

OBJECTIVES: The management strategy remains controversial for patients presenting with type A acute aortic dissection with cerebrovascular accident or coma. The present study aimed to help guide surgeons treating these high-risk patients. METHODS: Of 1873 patients with type A acute aortic dissection enrolled in the International Registry for Acute Dissection, 87 (4.7%) presented with cerebrovascular accident and 54 (2.9%) with coma. The hospital and 5-year results were stratified by the presence and type of brain injury (no injury vs stroke vs coma) and management type (medical vs surgical). Independent predictors of short- and mid-term survival were identified. RESULTS: Presentation with shock, hypotension, or tamponade (46.8% vs 25.2%; P < .001) and arch vessel involvement (55.0% vs 36.1%; P < .001) was more likely in patients with brain injury. Surgical management was avoided more often in patients with coma (33.3%) or cerebrovascular accident (24.1%) than in those without brain injury (11.1%; P < .001). The overall hospital mortality was 22.7% without brain injury, 40.2% with cerebrovascular accident, and 63.0% with coma (P < .001). Mortality varied among the management types for both cerebrovascular accident (76.2% medical vs 27.0% surgical; P < .001) and coma (100% medical vs 44.4% surgical; P < .001). Postoperatively, cerebrovascular accident and coma resolved in 84.3% and 78.8% of cases, respectively. On logistic regression analysis, surgery was protective against mortality in patients presenting with brain injury (odds ratio 0.058; P < .001). The 5-year survival of patients presenting with cerebrovascular accident and coma was 23.8% and 0% after medical management versus 67.1% and 57.1% after surgery (log rank, P < .001), respectively. CONCLUSIONS: Brain injury at presentation adversely affects hospital survival of patients with type A acute aortic dissection. In the present observational study, the patients selected to undergo surgery demonstrated improved late survival and frequent reversal of neurologic deficits.