miR-9 Restricts Insulin Secretion by Targeting Rab34, Which Mediates Lysosomal Degradation of Proinsulin

Area of Science:

• Endocrinology
• Molecular Biology
• Cell Biology

Background:

• Insulin secretion is a critical vesicular transport process.
• Rab34 regulates intracellular vesicle transport, but its role in insulin secretion is unknown.
• MicroRNA-9 (miR-9) is implicated in type 2 diabetes.

Purpose of the Study:

• To investigate if miR-9 targets Rab34 to regulate insulin secretion in beta (β) cells.
• To elucidate the molecular mechanism underlying miR-9's regulation of insulin secretion via Rab34.

Main Methods:

• Utilized miR-9 mimics and inhibitors in Min6 cells.
• Employed dual-luciferase reporter gene assays to confirm miR-9 targeting of Rab34.
• Applied transmission electron microscopy and immunofluorescence microscopy to analyze insulin particles, proinsulin, and vesicle transport.

Main Results:

• Rab34 overexpression decreased insulin particles and promoted proinsulin degradation in β cells.
• Rab34 depletion increased proinsulin levels and enhanced insulin secretion.
• miR-9 overexpression inhibited insulin secretion, while miR-9 downregulation promoted it.
• Rab34 mediated insulin secretory vesicles towards autophagic degradation.

Conclusions:

• miR-9 inhibits insulin secretion by promoting Rab34 expression in β cells.
• Rab34 regulates insulin secretion through proinsulin degradation and autophagic pathways.
• This study reveals a novel mechanism for miR-9 in controlling insulin secretion.