Regulation of exercise-stimulated glucose uptake in skeletal muscle

Differential expression of glucose metabolism-related genes and AMP-activated protein kinases in crop tissue of male and female pigeons (Columba livia domestica) during the incubation and chick-rearing periods

The objective of this study was to explore the carbohydrate contents of crop milk, insulin and glucose concentrations in serum and the expression patterns of AMP-activated protein kinases (AMPKs) and genes related to glucose metabolism in pigeon crops during the breeding period. Crop milk was collected from squabs of rearing Day 1 (R1) to R6. Contents of total sugar and reducing sugar increased to the maximum levels at R6 (p < 0.05). Forty-two pairs of adult pigeons were allotted to seven groups by different breeding stages, and their crops and serum were sampled. No significant differences were found in either insulin or glucose levels in serum. The glucose transporter 2 gene level was the greatest at R15 in females, whereas it was at R7 in males. However, sodium-dependent glucose transporters 1 expression in both sexes decreased from incubation Day 17 (I17) to R7. In females, glucokinase expression peaked at R1, and at R1 and R7 in males. Pyruvate kinase mRNA levels peaked at R7 in females and at R15 males. The mRNA abundance of fructose-1,6-bisphosphatase 1 in both sexes and glucose-6-phosphatase in females decreased after I10. While phosphoenolpyruvate carboxykinase 1 expression decreased after I17 (p < 0.05). Protein levels of AMPKα in crops were minimized at R1 (p < 0.05). In females, expression of AMPKα1 and AMPKα2 was inhibited at I17 and R1 (p < 0.05). In males, AMPKα1 expression was decreased at R7 (p < 0.05) and AMPKα2 was reduced at I10 and R1. pAMPK expression was the lowest at I17 in females, and it was at R7 and R25 in males. Conclusively, glycolysis in pigeon crops was enhanced during chick-rearing, while gluconeogenesis was significantly inhibited. The stability of the insulin level suggests that it was probably not involved in the regulation of glucose metabolism in crop tissues.

Free fatty acid impairs myogenic differentiation through AMPKα-miR-206 pathway

The activity of AMPKα is reduced in type-2 diabetes, and type-2 diabetes is associated with muscular atrophy. To date, there is little known about the mechanism by which FFA participates in muscular impairment. The purpose of the present study was to explore whether FFA damages myogenesis through AMPKα-HDAC4-miR-206 pathway. The results showed that 1mM FFA produced lipid accumulation, significantly impaired insulin signaling pathway and decreased myogenic differentiation of C2C12 myoblast cells. FFA reduced LKB1-AMPKα pathway; activation of AMPKα rescued the myogenic impairment caused by FFA (P < 0.05). AMPKα promoted myogenesis by regulating the expression of miR-206 through HDAC4 (P < 0.05); AMPKα affected cell cycle and cell proliferation to promote myogenesis by regulating miR-206 and miR-206's target gene - cyclin D1. In addition, AICAR and HDAC4 siRNA promoted myogenic differentiation compared with FFA group; however, this positive effect was significantly down-regulated after transfection of miR-206 inhibitor. In summary, AMPKα plays positive roles in myogenic differentiation and myogenesis, and FFA decreased myogenic differentiation and myotubes formation through AMPKα-HDAC4-miR-206 pathway.

Influence of exercise training on diabetic kidney disease: A brief physiological approach

IMPACT STATEMENT

Diabetic kidney disease (DKD) is associated with increased mortality in diabetic patients and has a negative impact on public health. The identification of potential therapies that help the management of DKD can contribute to the improvement of health and quality of life of patients. Thus, this paper is timely and relevant because, in addition to presenting a concise review of the pathogenesis and major pathophysiological mechanisms of DKD, it addresses the most recent findings on the impact of exercise training on this disease. Thus, since non-pharmacological interventions have gained increasing attention in the fight against chronic diseases, this paper appears as an important tool to increase knowledge and stimulate innovative research on the impact of exercise on kidney disease.

Role of Pro-inflammatory Cytokines in Regulation of Skeletal Muscle Metabolism: A Systematic Review

Background:

Metabolic pathways perturbations lead to skeletal muscular atrophy in the cachexia and sarcopenia due to increased catabolism. Pro-inflammatory cytokines induce the catabolic pathways that impair the muscle integrity and function. Hence, this review primarily concentrates on the effects of pro-inflammatory cytokines in regulation of skeletal muscle metabolism.

Objective:

This review will discuss the role of pro-inflammatory cytokines in skeletal muscles during muscle wasting conditions. Moreover, the coordination among the pro-inflammatory cytokines and their regulated molecular signaling pathways which increase the protein degradation will be discussed.

Results:

During normal conditions, pro-inflammatory cytokines are required to balance anabolism and catabolism and to maintain normal myogenesis process. However, during muscle wasting their enhanced expression leads to marked destructive metabolism in the skeletal muscles. Proinflammatory cytokines primarily exert their effects by increasing the expression of calpains and E3 ligases as well as of Nf-κB, required for protein breakdown and local inflammation. Proinflammatory cytokines also locally suppress the IGF-1and insulin functions, hence increase the FoxO activation and decrease the Akt function, the central point of carbohydrates lipid and protein metabolism.

Conclusion:

Current advancements have revealed that the muscle mass loss during skeletal muscular atrophy is multifactorial. Despite great efforts, not even a single FDA approved drug is available in the market. It indicates the well-organized coordination among the pro-inflammatory cytokines that need to be further understood and explored.

Study on the effect of CaMKKβ-mediated AMPK activation on the glycolysis and the quality of different altitude postmortem bovines longissimus muscle

This study investigated the activity of adenosine monophosphate-activated protein kinase (AMPK), glycolysis, and meat quality index in three altitude bovines during postmortem aging process. Local cattle (altitude:1,500 m), Gannan yak (3,000 m), and Yushu yak (4,500 m) postmortem Longissimus Dorsi (LD) muscle were used. Results indicated that CaCl₂ significantly increased the AMPK activity by increasing the calcium-regulated protein kinase kinase (CaMKKβ) activity. Besides, AMPK activation enhanced the activity of lactate dehydrogenase (LDH) and Ca²⁺ -ATPase and accelerated the rate of muscle maturation during postmortem aging. Moreover, the expression of HIF-1, PRKAA2, and GLUT4 genes in high-altitude Yushu yak was higher than that of low-altitude bovines. CaCl₂ activates AMPK by activating CaMKKβ cascade and accelerates postmortem glycolysis affecting the intramuscular environment, color, and muscle protein degradation to accelerate postmortem muscle maturation, suggesting that AMPK has essential effects on postmortem muscle glycolysis and quality, and can regulate muscle quality by regulating postmortem muscle AMPK activity. PRACTICAL APPLICATIONS: Insufficient postmortem glycolysis usually leads to DFD (dark, firm, and dry) meat. Beef have relatively high incidences of DFD meat, which has an unattractive dark color and causes significant loss to the meat industry. Therefore, AMPK, which can regulate postmortem glycolysis to affect meat quality, is a valid research target.

AMP-Activated Protein (AMPK) in Pathophysiology of Pregnancy Complications

Although the global maternal mortality ratio has been consistently reduced over time, in 2015, there were still 303,000 maternal deaths throughout the world, of which 99% occurred in developing countries. Understanding pathophysiology of pregnancy complications contributes to the proper prenatal care for the reduction of prenatal, perinatal and neonatal mortality and morbidity ratio. In this review, we focus on AMP-activated protein kinase (AMPK) as a regulator of pregnancy complications. AMPK is a serine/threonine kinase that is conserved within eukaryotes. It regulates the cellular and whole-body energy homeostasis under stress condition. The functions of AMPK are diverse, and the dysregulation of AMPK is known to correlate with many disorders such as cardiovascular disease, diabetes, inflammatory disease, and cancer. During pregnancy, AMPK is necessary for the proper placental differentiation, nutrient transportation, maternal and fetal energy homeostasis, and protection of the fetal membrane. Activators of AMPK such as 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR), resveratrol, and metformin restores pregnancy complications such as gestational diabetes mellitus (GDM), preeclampsia, intrauterine growth restriction, and preterm birth preclinically. We also discuss on the relationship between catechol-O-methyltransferase (COMT), an enzyme that metabolizes catechol, and AMPK during pregnancy. It is known that metformin cannot activate AMPK in COMT deficient mice, and that 2-methoxyestradiol (2-ME), a metabolite of COMT, recovers the AMPK activity, suggesting that COMT is a regulator of AMPK. These reports suggest the therapeutic use of AMPK activators for various pregnancy complications, however, careful analysis is required for the safe use of AMPK activators since AMPK activation could cause fetal malformation.

Comorbidity Analysis between Alzheimer's Disease and Type 2 Diabetes Mellitus (T2DM) Based on Shared Pathways and the Role of T2DM Drugs

Background:

Various studies suggest a comorbid association between Alzheimer’s disease (AD) and type 2 diabetes mellitus (T2DM) indicating that there could be shared underlying pathophysiological mechanisms.

Objective:

This study aims to systematically model relevant knowledge at the molecular level to find a mechanistic rationale explaining the existing comorbid association between AD and T2DM.

Method:

We have used a knowledge-based modeling approach to build two network models for AD and T2DM using Biological Expression Language (BEL), which is capable of capturing and representing causal and correlative relationships at both molecular and clinical levels from various knowledge resources.

Results:

Using comparative analysis, we have identified several putative “shared pathways”. We demonstrate, at a mechanistic level, how the insulin signaling pathway is related to other significant AD pathways such as the neurotrophin signaling pathway, PI3K/AKT signaling, MTOR signaling, and MAPK signaling and how these pathways do cross-talk with each other both in AD and T2DM. In addition, we present a mechanistic hypothesis that explains both favorable and adverse effects of the anti-diabetic drug metformin in AD.

Conclusion:

The two computable models introduced here provide a powerful framework to identify plausible mechanistic links shared between AD and T2DM and thereby identify targeted pathways for new therapeutics. Our approach can also be used to provide mechanistic answers to the question of why some T2DM treatments seem to increase the risk of AD.

Mechanical stress regulates insulin sensitivity through integrin-dependent control of insulin receptor localization

Kim et al. show that insulin signaling in Drosophila adipocytes is abolished in the absence of physical activity and mechanical stress. The insulin receptor and downstream components are recruited to the plasma membrane upon stress sensing mediated by integrins.

Insulin resistance, the failure to activate insulin signaling in the presence of ligand, leads to metabolic diseases, including type 2 diabetes. Physical activity and mechanical stress have been shown to protect against insulin resistance, but the molecular mechanisms remain unclear. Here, we address this relationship in the Drosophila larval fat body, an insulin-sensitive organ analogous to vertebrate adipose tissue and livers. We found that insulin signaling in Drosophila fat body cells is abolished in the absence of physical activity and mechanical stress even when excess insulin is present. Physical movement is required for insulin sensitivity in both intact larvae and fat bodies cultured ex vivo. Interestingly, the insulin receptor and other downstream components are recruited to the plasma membrane in response to mechanical stress, and this membrane localization is rapidly lost upon disruption of larval or tissue movement. Sensing of mechanical stimuli is mediated in part by integrins, whose activation is necessary and sufficient for mechanical stress-dependent insulin signaling. Insulin resistance develops naturally during the transition from the active larval stage to the immotile pupal stage, suggesting that regulation of insulin sensitivity by mechanical stress may help coordinate developmental programming with metabolism.

High, but not low, exercise volume shifts the balance of renin-angiotensin system toward ACE2/Mas receptor axis in skeletal muscle in obese rats

Metabolic syndrome is a cluster of metabolic risk factors that is linked to central obesity, elevated blood pressure, insulin resistance (IR), and dyslipidemia, where the renin-angiotensin system (RAS) may provide a link among them. This study aimed to evaluate volume exercise effects comparing low vs. high volume of chronic aerobic exercise on RAS axes in skeletal muscle in a diet-induced obesity (DIO) rat model. For this, male Wistar-Kyoto rats were fed a standard chow (SC) diet or a high-fat (HF) diet for 32 wk. Animals receiving the HF diet were randomly divided into low exercise volume (LEV, 150 min/wk) and high exercise volume (HEV, 300 min/wk) at the 20th week. After 12 wk of aerobic treadmill training, the body mass and composition, blood pressure, glucose and lipid metabolism, RAS axes, insulin signaling, and inflammatory pathway were performed. HEV slowed the body mass gain, reduced intra-abdominal fat pad and leptin levels, improved total and peripheral body composition and inflammatory cytokine, reduced angiotensin II type 1 receptor expression, and increased Mas receptor protein expression compared with the HF animals. Sedentary groups (SC and HF) presented lower time to exhaustion and maximal velocity compared with the LEV and HEV groups. Both exercise training groups showed reduced resting systolic blood pressure and heart rate, improved glucose tolerance, IR, insulin signaling, and lipid profile. We conclude that the HEV, but not LEV, shifted the balance of RAS toward the ACE2/Mas receptor axis in skeletal muscle, presenting protective effects against the DIO model.