Effects of mitochondrial uncoupling on adipocyte intracellular Ca2+ and lipid metabolism

Previous data from this laboratory demonstrate that increased intracellular Ca2+ ([Ca2+]i) coordinately regulates human and murine adipocyte lipid metabolism by stimulating lipogenesis and inhibiting lipolysis. However, recent data demonstrate metabolic uncoupling increases [Ca2+]i but inhibits lipogenesis by suppressing fatty acid synthase (FAS) activity. Accordingly, we have evaluated the interaction between mitochondrial uncoupling, adipocyte [Ca2+]i, and adipocyte lipid metabolism. Pretreatment of 3T3-L1 cells with mitochondrial uncouplers (DNP or FCCP) amplified the [Ca2+]i response to depolarization with KCl by 2-4 fold (p <0.001), while this increase was prevented by [Ca2+]i channel antagonism with lanthanum. Mitochondrial uncouplers caused rapid (within 4hr) dose-dependent inhibition of FAS activity (p <0.001), while lanthanum caused a further additive inhibition. The suppression of FAS activity induced by uncoupling was reversed by addition of ATP. Mitochondrial uncouplers increased FAS expression significantly while [Ca2+]i antagonism with lanthanum decreased FAS expression (P <0.001). In contrast, mitochondrial uncouplers independently inhibited basal and isoproterenol-stimulated lipolysis (20-40%, p <0.001), while this inhibition was fully reversed by lanthanum. Thus, mitochondrial uncoupling exerted short-term regulatory effects on adipocyte [Ca2+]i and lipogenic and lipolytic systems, serving to suppress lipolysis via a Ca2+ -dependent mechanism and FAS activity via a Ca2+-independent mechanism.