Abstract
Severe obesity causes a state of adipose tissue hypoxia and low blood flow. Both human and rodent visceral adipose tissue have been shown to have low oxygen tension (~15mmHg PO2) and increased levels of hypoxia inducible factor alpha (Hif1α), a prominent transcription factor in response to hypoxic conditions. Hif1α has been shown to increase endothelin‐1 (ET‐1) levels at the transcriptional level in endothelial cells. Obesity is associated with high circulating levels of ET‐1, which plays an important role in energy metabolism and insulin signaling when acting on the ET‐1 type A and B receptors on adipocytes. Therefore, the goal of this study was to determine whether hypoxia increases ET‐1 expression in adipocytes via Hif1α and inhibits insulin signaling. We utilized 3T3‐L1 murine fibroblast (passage 3–4) differentiated into adipocyte like cells. Exposure of 3T3‐L1 adipocytes to hypoxia (5% O2) for 24 hours led to a significant 3‐fold increase in ET‐1 mRNA compared to normoxic control cells (21% O2). Associated with increased ET‐1, hypoxia reduced insulin mediated glucose uptake and glycerol release compared to normoxic cells (148.8±16.4 vs. 237.6±24.4 glucose, 83.17±0.6 vs. 93.22±2.8 glycerol percent of control). In a separate experiment, 6‐hour exposure of 3T3‐L1 adipocytes caused a significant increase in ET‐1 and Hif1α mRNA (25.5±2.5 vs. 77.5±7.09 ET‐1, 2117±235.5 vs. 5015±370.2 Hif1α copies/50ng of RNA). Inhibition of Hif1a with either IDF‐11774 (1,25, and 50uM) or GN 44028 (1,10,20 uM) resulted in a significant attenuation in ET‐1 mRNA in response to hypoxia (77.5±7.09 vs. 22.35±3.7 ET‐1, 5015±370.2 vs. 3569±223.5 Hif1α Copies/50ng of cDNA) in a dose dependent manner. These data suggest that a hypoxia promotes ET‐1 production in adipocytes via Hif1α and is associated with diminished insulin sensitivity, suggesting a potential mechanism by which adipose tissue hypoxia promotes insulin resistance in obese individuals.Support or Funding InformationR00HL127178, P206M104357
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