Mechanisms by which hepatocyte extracellular miRNAs mediate peripheral insulin sensitivity

肥胖引起的胰岛素抵抗是代谢综合征的主要决定因素，代谢综合征先于2型糖尿病的发展，因此是新出现的糖尿病流行背后的驱动力。目前的抗糖尿病治疗方法是可用的，但不足以控制大多数患者的疾病，并且对治疗糖尿病以预防发病率和死亡率的更好方法的大量未满足的医疗需求。我们最近的研究发现，肥胖诱导肝细胞外囊泡（EV） mirna分泌的动态变化，对胰岛素产生细胞和外周胰岛素敏感性产生深远影响。在肝细胞特异性Rab27KO小鼠中，肝脏细胞外mirna的缺失导致肥胖早期葡萄糖耐量和胰岛素敏感性受损。我们进一步证明，高脂饮食喂养4周（4周- hfd）诱导的肝脏EV mirna可以降低肥胖受体小鼠的胰岛素抵抗。此外，4周的hfd EV治疗显著提高了胰岛素水平

Obesity-induced insulin resistance is the major determinant of metabolic syndrome, which precedes the development of Type 2 diabetes mellitus and is thus the driving force behind the emerging diabetes epidemic. Current anti-diabetic therapeutics are available, but are inadequate to control the disease in most patients and there is a large unmet medical need for better methods of treating diabetes to prevent morbidity and mortality. Our recent work has led to the discovery that obesity induces a dynamic change in secretion of hepatic extracellular vesicle (EV) miRNAs that exert profound impacts on insulin producing cells and peripheral insulin sensitivity. Depletion of hepatic extracellular miRNAs in the hepatocyte-specific Rab27KO mice resulted in impaired glucose tolerance and insulin sensitivity at the early onset of obesity. We further demonstrated that 4wks high-fat diet feeding (4wks-HFD)-induced hepatic EV miRNAs can reduce the insulin resistance of obese recipient mice. In addition, the 4wks-HFD EV treatment significantly enhanced the insulin secretion and proliferation of beta cells in vitro and in vivo. By contrast, prolonged obesity induced secretion of pathogenic hepatocyte EV miRNAs that blunted insulin sensitivity of lean recipient WT mice. Consistently, the mice without hepatic extracellular miRNAs by knockout of hepatic Rab27 showed a reduction in insulin resistance after 16 weeks HFD feeding. miRNA-free EVs derived from YBX1KO hepatocytes had minimal effects on the metabolic phenotypes of recipient mice, suggesting miRNAs as key cargoes within these EVs. Using a novel thiouracil tagging method, we identified that miR-3075-5p, a highly enriched miRNAs in 4wks-HFD EVs, can be efficiently incorporated into target cells and improves cellular insulin responses through repressing Fa2h expression. In addition, the miR-434-3p-Map2k6 regulatory axis plays a critical role in promoting proinflammatory activation of macrophages, which can subsequently exacerbate tissue inflammation and insulin resistance. These results lead to the conclusion that hepatic EV miRNAs are important endocrine molecules regulating functions of insulin-producing and -targeting cells in obesity. This proposal sees to build on this newly identified hepatic EV miRNAs regulatory system to reveal the underlying cellular and molecular mechanisms of obesity-induced insulin resistance. We will further determine the mechanisms by which hepatic EV miRNAs modulate functions of beta cell and insulin sensitizing cells in response to obesity. With the proposed experiments, we will develop miR-3075-5p as an insulin sensitizer molecule and explore the pathogenic effect of miR-434-3p in obesity. This therapeutic strategy could be used for the treatment of obese patients with insulin resistance pre-diabetic state. This would lead to improved glycemic control adding a new component in our therapeutic armamentarium for the treatment of this widespread metabolic disease. Finally, using the thiouracil tagging method, we will identify the hepatic extracellular miRNAs in circulation as biomarkers predicting the insulin resistance state in obesity.