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Pancreatic β-cell dysfunction caused by obesity can be associated with alterations in the levels of miRNAs. However, the role of miRNAs in such processes remains elusive. Here, we show that pancreatic islet miR-27a-5p, which is markedly increased in obese mice and impairs insulin secretion, is mainly delivered by visceral adipocyte–derived extracellular vesicles (EVs). Depleting miR-27a-5p significantly improved insulin secretion and glucose intolerance in db / db mice. Supporting the function of EV miR-27a-5p as a key pathogenic factor, intravenous injection of miR-27a-5p–containing EVs showed their distribution in mouse pancreatic islets. Tracing the injected adeno-associated virus (AAV)-miR-27a-5p (AAV-miR-27a) or AAV-FABP4-miR-27a-5p (AAV-FABP4-miR-27a) in visceral fat resulted in upregulating miR-27a-5p in EVs and serum and elicited mouse pancreatic β-cell dysfunction. Mechanistically, miR-27a-5p directly targeted L-type Ca2+ channel subtype CaV1.2 (Cacna1c) and reduced insulin secretion in β-cells. Overexpressing mouse CaV1.2 largely abolished the insulin secretion injury induced by miR-27a-5p. These findings reveal a causative role of EV miR-27a-5p in visceral adipocyte–mediated pancreatic β-cell dysfunction in obesity-associated type 2 diabetes mellitus. Article Highlights: miR-27a-5p expression in the islets is increased in obesity-associated diabetes mouse models. miR-27a-5p overexpression in β-cells impairs β-cell function in vitro and in vivo. Visceral adipocyte–derived extracellular vesicles and their cargo miR-27a-5p lead to β-cell insulin secretion injury and glucose intolerance by targeting L-type Ca2+ channel subtype CaV1.2. Blockage of visceral adipocyte extracellular vesicle miR-27a-5p expression improves β-cell insulin secretion and glucose tolerance in db / db mice. [ABSTRACT FROM AUTHOR]

Aim: To assess the expression and function of miR‐483‐5p in diabetic β cells. Methods: The expression of miR‐483‐5p was evaluated in the pancreatic islets of obesity mouse models by quantitative reverse transcription polymerase chain reaction. Dual‐luciferase activity, and western blotting assays, were utilized for miR‐483‐5p target gene verification. Mice with β cell‐specific miR‐483‐5p downregulation were studied under metabolic stress (i.e. a high‐fat diet) condition. Lineage tracing was used to determine β‐cell fate. Results: miR‐483‐5p increased in the islets of obese mouse models. Expression levels of miR‐483‐5p were significantly upregulated with the treatment of high glucose and palmitate, in both MIN6 cells and mouse islets. Overexpression of miR‐483‐5p in β cells results in impaired insulin secretion and β‐cell identity. Cell lineage‐specific analyses revealed that miR‐483‐5p overexpression deactivated β‐cell identity genes (insulin, Pdx1 and MafA) and derepressed β‐cell dedifferentiation (Ngn3) genes. miR‐483‐5p downregulation in β cells of high‐fat diet‐fed mice alleviated diabetes and improved glucose intolerance by enhancing insulin secretory capacity. These detrimental effects of miR‐483‐5p relied on its seed sequence recognition and repressed expression of its target genes Pdx1 and MafA, two crucial markers of β‐cell maturation. Conclusions: These findings indicate that the miR‐483‐5p–mediated reduction of mRNAs specifies β‐cell identity as a contributor to β‐cell dysfunction via the loss of cellular differentiation. [ABSTRACT FROM AUTHOR]