14-3-3zeta is required for PKA-dependent lipolysis in mature adipocytes
Altered hypertrophy and hyperplasia of adipocytes lie at the core of the development of obesity. We previously demonstrated that the molecular scaffold 14-3-3zeta (14-3-3ζ) had essential roles in adipogenesis. However, the contributions of 14-3-3ζ to mature adipocyte function are not known. 3T3-L1 cells and tamoxifen-inducible adipocyte-specific 14-3-3ζ knockout mice (adi14-3-3ζKO) models were used to examine the roles of 14-3-3ζ in lipolysis. siRNA-mediated knockdown of 14-3-3ζ impaired lipolysis in 3T3-L1 cells stimulated by the beta-adrenergic agonist isoproterenol (Iso), forskolin (an activator of adenylyl cyclase) and dibutyryl cAMP (dbcAMP). qPCR analyses revealed significant reductions in lipase transcript levels (Atgl and Hsl). Furthermore, reductions in the phosphorylated and total levels of PKA substrates such as HSL and CREB were detected in 14-3-3ζ-depleted 3T3-L1 lysates by immunoblotting. These findings were recapitulated in vivo, as reductions in phosphorylated and total HSL levels were detected in the gonadal adipose tissue of adi14-3-3ζKO mice. adi14-3-3ζKO mice and gonadal explants also displayed impaired lipolysis following i.p CL-316,243 (a beta-3 adrenergic agonist) injections and Iso treatment respectively. Interestingly, decreased 14-3-3ζ expression in 3T3-L1 cells and mice revealed reductions in characteristics of a mature adipocyte, such as Pparg, Lpl, and Fabp4 transcript levels, PPARγ levels, triglyceride content, and Oil Red O (ORO) incorporation. Collectively, these results demonstrate that 14-3-3ζ has essential roles in facilitating lipolysis and determining adipocyte maturity.
Lipase Adipocyte mature Lipolysis Mature adipocyte