Insulin secretory granules (ISGs) mediate the regulated secretion of insulin. The basic machinery responsible for this regulated exocytosis consists of specific membrane proteins present both at the plasma membrane and on ISGs. The protein composition of ISGs thus dictates their release properties, yet the mechanisms controlling ISG budding from the trans-Golgi network (TGN), which partly determines this molecular composition, remain poorly understood. The cytosolic protein VSP41 was recently identified as a potential coat protein at the TGN involved in the formation of neuroendocrine/neuronal granules. To test whether this protein might contribute to ISG biogenesis, we have generated VPS41 KO Ins1 cells using CRISPR/Cas9. Loss of VPS41 leads to reduced cellular insulin content with a defect in regulated insulin secretion. We also find, using live-imaging and a pHluorin based reporter, that VPS41 KO cells exhibit less stimulated exocytotic events. At the cellular level, insulin appears to be retained in a perinuclear compartment, and cell fractionation and electron microscopy analysis further reveal a change in ISG protein composition and number. Finally, mice with a beta-cell specific deletion of VPS41 are glucose intolerant and display a defect in insulin secretion in response to glucose. Altogether our data suggest that VPS41 is an important player in the formation or maintenance of ISG.
C.H. Burns: None. B. Yau: None. M.A. Kebede: None. C.S. Asensio: None.
American Diabetes Association (1-17-JDF-064 to C.S.A.); National Institutes of Health (R15GM116096, R01GM124035)