11b-HSD1 modulates LPS-induced innate immune responses in adipocytes by altering expression of pten

Abstract

Inhibition of 11b-hydroxysteroid dehydrogenase type 1 (11b-HSD1) represents a therapeutic target for treating hyperglycemia in type 2 diabetes. Here, we investigate the effects of 11b-HSD1 on the innate immune response of adipocytes to produce proinflammatory cytokines. The 11b-HSD1 inhibitor emodin, or 11b-HSD1-targeted small interfering RNA, dose dependently suppressed IL-6, IL-1b, and TNF-a expression in lipopolysaccharide-treated 3T3-L1 adipocytes. Inhibiting 11b-HSD1 also reduced phosphatase and tensin homologue (PTEN) expression, a negative regulator of phosphatidylinositol 3-kinase effects, whereas 1pM cortisone or dexamethasone induced IL-6 and PTEN levels. PTEN-targeted small interfering RNA decreased IL-6, IL-1b, and TNF-a without affecting 11b-HSD1 levels. Correspondingly, emodin increased phosphorylated protein kinase B (p-PKB) (Ser473) to PKB ratio but not p-PKB (Thr308) to PKB ratio. Emodin did not increase the p-PKB (Ser473) to PKB ratio when the rapamycin-insensitive companion of mTOR was depleted, further supporting the involvement of mammalian target of rapamycin complex 2 in PKB phosphorylation. Moreover, emodin suppressed phosphorylated inhibitor of kB a (p-IkBa) to IkBa ratio and reduced nuclear factor k B subunit p50 in the nuclear fraction. In contrast, 1pM cortisone or dexamethasone decreased p-PKB (Ser473) to PKB ratio, increased p-IkBa to IkBa ratio, and increased nuclear NF-kB subunit p50. Additionally, wortmannin had similar effects on IL-6, p-PKB (Ser473) to PKB ratio, and p-IkBa to IkBa ratio as 1pM cortisone or dexamethasone. Finally, emodin treatment of streptozotocin diabetic rats on a high-fat diet reduced levels of IL-6, PTEN, Cluster of Differentiation 68, and the ratio of p-IkBa to IkBa in visceral fat, indicating that our findings in vitro may also apply to visceral fat in vivo. Together, these results suggest that inhibiting 11b-HSD1 reduces lipopolysaccharide-induced proinflammatory innate immune responses in adipocytes by down-regulating PTEN expression, leading to activation of the PI3K/PKB pathway.