Journal Article

MiR‐335 overexpression impairs insulin secretion through defective priming of insulin vesicles

Ofori, Jones K., Salunkhe, Vishal A., Gandasi, Nikhil R., Eliasson, Lena, Andersson, Markus E., Barg, Sebastian, Esguerra, Jonathan L. S., Wendt, Anna, Salö, Sofia A., Hansson, Sofia

2017

Overview

MicroRNAs contribute to the maintenance of optimal cellular functions by fine‐tuning protein expression levels. In the pancreatic β‐cells, imbalances in the exocytotic machinery components lead to impaired insulin secretion and type 2 diabetes (T2D). We hypothesize that dysregulated miRNA expression exacerbates β‐cell dysfunction, and have earlier shown that islets from the diabetic GK‐rat model have increased expression of miRNAs, including miR‐335‐5p (miR‐335). Here, we aim to determine the specific role of miR‐335 during development of T2D, and the influence of this miRNA on glucose‐stimulated insulin secretion and Ca2+‐dependent exocytosis. We found that the expression of miR‐335 negatively correlated with secretion index in human islets of individuals with prediabetes. Overexpression of miR‐335 in human EndoC‐βH1 and in rat INS‐1 832/13 cells (OE335) resulted in decreased glucose‐stimulated insulin secretion, and OE335 cells showed concomitant reduction in three exocytotic proteins: SNAP25, Syntaxin‐binding protein 1 (STXBP1), and synaptotagmin 11 (SYT11). Single‐cell capacitance measurements, complemented with TIRF microscopy of the granule marker NPY‐mEGFP demonstrated a significant reduction in exocytosis in OE335 cells. The reduction was not associated with defective docking or decreased Ca2+ current. More likely, it is a direct consequence of impaired priming of already docked granules. Earlier reports have proposed reduced granular priming as the cause of reduced first‐phase insulin secretion during prediabetes. Here, we show a specific role of miR‐335 in regulating insulin secretion during this transition period. Moreover, we can conclude that miR‐335 has the capacity to modulate insulin secretion and Ca2+‐dependent exocytosis through effects on granular priming. Earlier reports have proposed reduced granular priming as the cause of reduced first‐phase insulin secretion during prediabetes. Here, we show a negative correlation between miR‐335 expression and insulin secretion index during this transition period. Moreover, overexpression of miR‐335 in β‐cells resulted in decreased glucose‐stimulated insulin secretion, reduced Ca2+‐dependent exocytosis through effects on granular priming, and concomitant reduction in three exocytotic proteins: SNAP25, Syntaxin‐binding protein 1 (STXBP1), and synaptotagmin 11 (SYT11). PM, plasma membrane; VDCC, voltage‐dependent calcium channel.

• Publisher: John Wiley & Sons, Inc,John Wiley and Sons Inc
• Subject: Animals / Basic Medicine / Beta cell / Beta cells / Calcium / Calcium currents / Capacitance / Cell and Molecular Biology / Cell Line / Cell- och molekylärbiologi / Clinical Medicine / Diabetes mellitus / Diabetes Mellitus, Type 2 - metabolism / Disease Models, Animal / Endocrine and Metabolic Conditons, Disorders and Treatments / Endocrinology and Diabetes / Endokrinologi och diabetes / Exocytosis / Glucose / Humans / Insulin / Insulin - metabolism / Insulin Secretion / Insulin-Secreting Cells - metabolism / Islets of Langerhans - metabolism / Klinisk medicin / Medical and Health Sciences / Medicin och hälsovetenskap / Medicinska och farmaceutiska grundvetenskaper / Metabolism and Regulation / microRNA / MicroRNAs - metabolism / miRNA / Munc18 Proteins - metabolism / Neuropeptide Y / Original Research / Pancreas / patch-clamp / Physiology / Rats / Rodents / Secretion / SNAP-25 protein / SNAP25 / STXBP1 / Synaptosomal-Associated Protein 25 - metabolism / Synaptotagmin / Synaptotagmins - metabolism / Syntaxin / TIRF / Type 2 Diabetes