Neu1 sialidase interacts with perilipin 1 on lipid droplets and inhibits lipolysis in 3T3-L1 adipocytes.

Fatty acids are stored within adipocytes in lipid droplets (LDs) as triacylglycerol (TG), which is converted to free fatty acid (FFA) and glycerol via lipolysis. Increased plasma FFA levels in obesity are associated with several clinical conditions. We previously found that Neu1 activity is aberrant in the epididymal fat and liver of obese and diabetic mice. Here, we examined involvement of Neu1 in lipolysis in 3T3-L1 adipocytes. Small interfering RNA against Neu1 was introduced into adipocytes, and glycerol concentrations were measured in the culture medium. We then assessed the effects of Neu1 knockdown on lipolytic protein expression and phosphorylation, as well as interactions between perilipin 1 (Plin1) and hormone-sensitive lipase (HSL) after isoproterenol (IS) stimulation. Interactions between Neu1 and Plin1 were analyzed by immunoprecipitation and immunofluorescent imaging using adipocytes transfected with pCMV6-mNeu1-myc-DYKDDDDK (mNeu1DDK). Neu1 knockdown increased glycerol concentrations in culture media and Plin1 phosphorylation in whole lysates of IS-stimulated cells. Neu1 knockdown increased interaction between Plin1 and HSL after IS stimulation whereas that between Neu1 and Plin1 on LD observed under basal conditions was lost. These results suggest that Neu1 inhibits lipolysis induced by β-adrenergic stimulation in adipocytes via interactions with Plin1 on LD.