Hypoxia in 3T3-L1 adipocytes suppresses adiponectin expression via the PERK and IRE1 unfolded protein response.

ABSTRACT

Adiponectin, an adipocytokine produced by adipocytes, functions as an anti-inflammatory and anti-apoptotic substance, while also enhancing insulin sensitivity. Patients or model animals with obesity or diabetes typically present attenuated expression of adiponectin. Moreover, obesity and diabetes are often accompanied with hypoxia in adipose tissue, which may result in endoplasmic reticulum (ER) stress as well as low expression of adiponectin. The purpose of this study was to investigate the specific role of the unfolded protein response (UPR) involved in the low expression of adiponectin induced by hypoxia. Subjecting 3T3-L1 adipocytes to hypoxia significantly reduced adiponectin expression and activated the PERK and IRE1 signaling pathways in a time-dependent manner. The ATF6 signaling pathway showed no obvious changes with hypoxia treatment under a similar time course. Moreover, the down-regulated expression of adiponectin induced by hypoxia was relieved once the PERK and IRE1 signaling pathways were suppressed by the inhibitors GSK2656157 and 4µ8C, respectively. Overall, these data demonstrate that hypoxia can suppress adiponectin expression and activate the PERK and IRE1 signaling pathways in differentiated adipocytes, and this two pathways are involved in the suppression of adiponectin expression induced by hypoxia.