The regulatory α and β subunits of phosphorylase kinase directly interact with its substrate, glycogen phosphorylase

Leveraging genetic diversity to identify small molecules that reverse mouse skeletal muscle insulin resistance

Systems genetics has begun to tackle the complexity of insulin resistance by capitalising on computational advances to study high-diversity populations. 'Diversity Outbred in Australia (DOz)' is a population of genetically unique mice with profound metabolic heterogeneity. We leveraged this variance to explore skeletal muscle's contribution to whole-body insulin action through metabolic phenotyping and skeletal muscle proteomics of 215 DOz mice. Linear modelling identified 553 proteins that associated with whole-body insulin sensitivity (Matsuda Index) including regulators of endocytosis and muscle proteostasis. To enrich for causality, we refined this network by focusing on negatively associated, genetically regulated proteins, resulting in a 76-protein fingerprint of insulin resistance. We sought to perturb this network and restore insulin action with small molecules by integrating the Broad Institute Connectivity Map platform and in vitro assays of insulin action using the Prestwick chemical library. These complementary approaches identified the antibiotic thiostrepton as an insulin resistance reversal agent. Subsequent validation in ex vivo insulin-resistant mouse muscle and palmitate-induced insulin-resistant myotubes demonstrated potent insulin action restoration, potentially via upregulation of glycolysis. This work demonstrates the value of a drug-centric framework to validate systems-level analysis by identifying potential therapeutics for insulin resistance.

Aerobic exercise reduced the amount of CHRONO bound to BMAL1 and ameliorated glucose metabolic dysfunction in skeletal muscle of high-fat diet-fed mice

AIMS

The purpose of this study was to investigate the effects of aerobic exercise on the CHRONO-BMAL1 pathway and glucose metabolism in skeletal muscle of high-fat diet (HFD)-fed mice.

MAIN METHODS

Male C57BL/6J mice were randomly allocated into four groups: normal chow diet with control (NCD + CON), NCD with exercise (NCD + EXE), HFD with control (HFD + CON) and HFD with exercise (HFD + EXE). The NCD and HFD groups were respectively fed a diet of 10 % and 60 % kilocalories from fat for 12 weeks. During the dietary intervention, EXE groups were subjected to 70 % VO_2max intensity of treadmill exercise six times per week for 12 weeks. Body weight, energy intake, fat weight, serum lipid profiles, systemic glucose homeostasis, the amount of CHRONO bound to BMAL1, the enzymatic activity, mRNA and protein expression involved in glucose metabolism of skeletal muscle were measured.

KEY FINDINGS

The results showed that the 12-week HFD feeding without exercise induced weight gain, serum dyslipidemia and insulin resistance. Furthermore, HFD increased the amount of CHRONO bound to BMAL1 and repressed the glucose metabolism in skeletal muscle. However, aerobic exercise prevented weight gain, serum dyslipidemia and systemic insulin resistance in the HFD-fed mice. Meanwhile, aerobic exercise also decreased the amount of CHRONO bound to BMAL1 and increased the glucose uptake, glucose oxidation and glycogenesis in skeletal muscle of the HFD-fed mice.

SIGNIFICANCE

These data suggested that aerobic exercise could counterbalance CHRONO interacted with BMAL1 and prevent glucose metabolism dysfunction of skeletal muscle, and finally maintain whole-body insulin sensitivity in the HFD-fed mice.

Role of phosphorylation on characteristics of glycogen phosphorylase in lamb with different glycolytic rates post-mortem

The relationship between glycogen phosphorylase activity and phosphorylation levels in the longissimus thoracis muscle post-mortem was studied. Sixty lamb samples were collected at 0.5 h, 2 h, 6 h, 12 h, 24 h, 48 h, and 72 h post-mortem and divided into three groups (n = 6) with different glycolytic rates (fast, intermediate, and slow) according to the pH at 6 h post-mortem. The phosphorylation level and activity and expression of glycogen phosphorylase were determined. The results showed that the phosphorylation level and activity of glycogen phosphorylase in the slow pH decline group was lower than that in the fast pH decline group during 24 h post-mortem (P < .05). There was a significant positive correlation between the glycogen phosphorylase activity and the phosphorylation level. In conclusion, these data demonstrated that the glycogen phosphorylase activity in lambs was affected by phosphorylation levels and postmortem duration.