Regulated renin release from 3T3-L1 adipocytes

Whereas adipose tissue possesses a local renin-angiotensin system, the synthesis and regulated release of renin has not been addressed. To that end, we utilized differentiating 3T3-L1 cells and analyzed renin expression and secretion. Renin mRNA expression and protein enzymatic activity were not detectable in preadipocytes. However, upon differentiation, renin mRNA and both intracellular and extracellular renin activity were upregulated. In differentiated adipocytes, forskolin treatment resulted in a 28-fold increase in renin mRNA, whereas TNFα treatment decreased renin mRNA fourfold. IL-6, insulin, and angiotensin (Ang) II were without effect. In contrast, forskolin and TNFα each increased renin protein secretion 12- and sevenfold, respectively. Although both forskolin and TNFα induce lipolysis in adipocytes, fatty acids, prostaglandin E₂, and lipopolysaccharide had no effect on renin mRNA or secretion. To evaluate the mechanism(s) by which forskolin and/or TNFα are able to regulate renin secretion, a general lipase inhibitor (E600) and PKA inhibitor (H89) were used. Both inhibitors attenuated forskolin-induced renin release, whereas they had no effect on TNFα-regulated secretion. In contrast, E600 potentiated forskolin-stimulated renin mRNA levels, whereas H89 had no effect. Neither inhibitor had any influence on TNFα regulation of renin mRNA. Relative to lean controls, renin expression was reduced 78% in the epididymal adipose tissue of obese male C57Bl/6J mice, consistent with TNFα-mediated downregulation of renin mRNA in the culture system. In conclusion, the expression and secretion of renin are regulated under a complex series of hormonal and metabolic determinants in mature 3T3-L1 adipocytes.