Lack of cholesterol mobilization in islets of hormone-sensitive lipase deficient mice impairs insulin secretion.

The observations that hormone-sensitive lipase (HSL) is located in close association to insulin granules in beta-cells and that cholesterol ester hydrolase activity is completely blunted in islets of HSL null mice made us hypothesize that the role of HSL in beta-cells is to provide cholesterol for the exocytosis of insulin. To test this hypothesis, wild type (wt) and HSL null islets were depleted of plasma membrane cholesterol using methyl-beta-cyclodextrin (mbetacd). A significant reduction in insulin secretion from HSL null islets was observed whereas wt islets were unaffected. Using synaptosomal protein of 25kDa (SNAP-25) as indicator of cholesterol-rich microdomains, confocal microscopy was used to show that HSL null beta-cells treated with mbetacd contained fewer clusters than wt beta-cells. These results indicate that HSL plays an important role in insulin secretion by providing free cholesterol for the formation and maintenance of cholesterol-rich patches for docking of SNARE-proteins to the plasma membrane.