Cyclodextrin-Mediated Cholesterol Depletion Induces Adiponectin Secretion in 3T3-L1 Adipocytes

Adipocytes store a significant amount of cholesterol and triglycerides. However, whether cholesterol modulates adipocyte function remains largely unknown. We modulated the cholesterol level in adipocytes to examine its effect on the secretion of adiponectin, an important hormone specifically secreted by adipocytes. Treating differentiated 3T3-L1 adipocytes with 4 mM methyl-beta-cyclodextrin (M beta CD), a molecule with a high affinity for cholesterol, rapidly depleted cholesterol in adipocytes. Interestingly, M beta CD treatment increased adiponectin in the medium without affecting its intracellular level, suggesting a modulation of secretion. By contrast, cholesterol addition did not affect adiponectin secretion, suggesting that cholesterol-depletion-induced intracellular cholesterol trafficking, but not reduced cholesterol level, accounted for M beta CD-induced adiponectin secretion. M beta CD-induced adiponectin secretion was reduced after 10 mu g/mL U18666A treatment that suppressed cholesterol transport out of late endosomes/lysosomes. Depleting Niemann-Pick type C1 (NPC1) or NPC2 proteins, which mediate endosomal/lysosomal cholesterol export, consistently reduced M beta CD-induced adiponectin secretion. Furthermore, treatment with 1 mu M bafilomycin A1, which neutralized acidic endosomes/lysosomes, also attenuated M beta CD-induced adiponectin secretion. Finally, M beta CD treatment redistributed cellular adiponectin to lower-density fractions in sucrose gradient fractionation. Our results show that M beta CD-mediated cholesterol depletion elevates the secretion of adiponectin, highlighting the involvement of endosomes and lysosomes in adiponectin secretion in adipocytes.