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

Physiol Rep. 2017 Nov;5(21):e13493. doi: 10.14814/phy2.13493.


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.

Keywords: TIRF; Beta cell; SNAP25; STXBP1; Type 2 Diabetes; exocytosis; insulin secretion; microRNA; patch‐clamp.

MeSH terms

  • Animals
  • Cell Line
  • Diabetes Mellitus, Type 2 / metabolism*
  • Disease Models, Animal
  • Exocytosis
  • Humans
  • Insulin / metabolism*
  • Insulin Secretion
  • Insulin-Secreting Cells / metabolism
  • Islets of Langerhans / metabolism
  • MicroRNAs / metabolism*
  • Munc18 Proteins / metabolism
  • Rats
  • Synaptosomal-Associated Protein 25 / metabolism
  • Synaptotagmins / metabolism


  • Insulin
  • MIRN335 microRNA, human
  • MicroRNAs
  • Munc18 Proteins
  • Snap25 protein, rat
  • Stxbp1 protein, rat
  • Synaptosomal-Associated Protein 25
  • Syt11 protein, rat
  • Synaptotagmins