Glucose sensing by skeletal myocytes couples nutrient signaling to systemic homeostasis. Mus musculus

Skeletal muscle is a major site of postprandial glucose disposal. Inadequate insulin action in this tissue contributes to hyperglycemia in type 1 and type 2 diabetes. While glucose is known to stimulate insulin secretion by pancreatic b cells, whether it directly engages nutrient-sensing pathways in skeletal muscle to regulate glucose metabolism remains largely unexplored. Here we identified the Baf60c-Deptor-AKT pathway as a target of muscle glucose sensing that augments insulin action in skeletal myocytes. Genetic activation of this pathway improves postprandial glucose disposal in mice, whereas the muscle-specific ablation impaired insulin action and led to glucose intolerance. Mechanistically, glucose triggers a rapid calcium response in myocytes that acts on the class IIa histone deacetylase HDAC5, leading to Baf60c induction and insulin-independent AKT activation. The pathway is engaged by the anti-diabetic drugs sulfonylureas, suggesting that its therapeutic activation may have beneficial effects on glycemic control in diabetes. We used microarrays to elucidate the role of of Baf60c in transcriptional regulation by glucose in skeletal myocytes. Overall design: C2C12 myoblasts were transduced with retroviruses expressing shRNAs targeting control or mouse Baf60c, differentiated into myotubes, and treated with 1 mM or 10 mM glucose for 12 h. Then cells were harvested for RNA isolation and microarray hybridization using Affymetrix Mouse Gene ST 2.1 Arrays. Two independent biological replicates for each treatment were included in this study.

骨骼肌是餐后葡萄糖清除的主要组织位点。该组织内胰岛素作用缺陷是1型与2型糖尿病患者出现高血糖的重要诱因。尽管已知葡萄糖可刺激胰腺β细胞（pancreatic β cells）分泌胰岛素，但葡萄糖是否可直接激活骨骼肌内的营养感知通路以调控葡萄糖代谢，目前仍未得到充分研究。
本研究鉴定出Baf60c-Deptor-AKT通路为骨骼肌葡萄糖感知的靶通路，可增强骨骼肌肌细胞的胰岛素应答功能。该通路的遗传激活可改善小鼠的餐后葡萄糖清除能力，而骨骼肌特异性敲除该通路则会削弱胰岛素作用并引发糖耐量异常。
从机制层面来看，葡萄糖可触发肌细胞内快速的钙信号应答，该应答作用于IIa类组蛋白去乙酰化酶HDAC5（class IIa histone deacetylase HDAC5），进而诱导Baf60c表达并激活不依赖胰岛素的AKT通路。该通路可被抗糖尿病药物磺酰脲类（sulfonylureas）靶向激活，提示对其进行治疗性激活或可改善糖尿病患者的血糖控制。
本研究利用微阵列芯片（microarrays）阐明了Baf60c在骨骼肌肌细胞中参与葡萄糖介导的转录调控的作用。
实验整体设计：将表达靶向对照或小鼠Baf60c的短发夹RNA（shRNAs）的逆转录病毒（retroviruses）转导至C2C12成肌细胞，诱导其分化为肌管后，分别用1 mM或10 mM葡萄糖处理12小时。随后收集细胞进行RNA提取，并使用Affymetrix小鼠基因ST 2.1芯片进行微阵列杂交。本研究中每个处理组均设置两个独立生物学重复。