Short-Term Hypoxia-Induced Inhibition of Adipogenesis and Enhancement of Insulin Sensitivity in 3T3-L1 Adipocytes

Abstract

Obesity is a risk factor of insulin resistance and metabolic disorders. Studies demonstrated that adipose tissue dysfunction may cause insulin resistance in obese individuals. Several pieces of evidence suggested that adipose tissues of obese individuals were in a low-oxygen status compared with the lean control. Other studies demonstrated that exercise re-arranged tissue blood flow, disposing cells to low oxygen concentration and increasing insulin sensitivity. According to the above findings, regulation of hypoxia on insulin sensitivity is still controversial. The purpose of the present study was to investigate the regulatory mechanism of hypoxia on adipogenesis and insulin sensitivity in 3T3-L1 dipocytes. To explore the effect of hypoxia on adipogenesis, 3T3-L1 preadipocytes were incubated in hypoxia status for 6 h in initial adipocyte differentiation. Differentiation efficiency was determined by intracellular triglyceride content measurement, oil red O staining of oil droplets, and expression of adipocyte lipidbinding protein (ALBP/aP2). Expressions of key transcriptional regulators, including those of preadipocyte factor-1 (pref-1), CCAAT/enhancer binding protein α (C/EBPα), and peroxisome proliferator-activated receptor-γ (PPARγ), were measured by immunoblotting. To investigate the effect of hypoxia on insulin sensitivity, differentiated 3T3-L1 adipocytes were preincubated in hypoxia status for 6 h, and then insulin-stimulated phosphorylation of insulin signaling pathways and glucose uptake were measured. To further elucidate the underlying mechanism, we clarify the involvement of hypoxia inducible factor-1α (HIF-1α) on hypoxia-regulated adipogenesis and insulin sensitivity by using HIF-1α inhibitor. Our results showed that hypoxia significantly decreased lipid accumulation and aP2 expression compared with normoxia control. Inhibitory effects of hypoxia on adipocyte differentiation were associated with increased pref-1 expression and decreased PPARγ expression. Hypoxia treatment increased insulinstimulated insulin receptor autophosphorylation and Akt phosphorylation and glucose uptake in 3T3-L1 adipocytes compared with normoxia control. Both hypoxia-inhibited adipogenesis and hypoxia-enhanced insulin sensitivity could be prevented by pretreatment with HIF-1α inhibitor, YC-1. In conclusion, short-term hypoxia suppressed adipogenesis and enhanced insulin sensitivity through HIF- 1α-dependent pathway in 3T3-L1 adipocytes.