Abstract
Endoplasmic reticulum (ER) stress, which is defined as the accumulation of unfolded or misfolded proteins in the ER, triggers cellular dysfunction and eventually leads to cell death. In particular, excessive and prolonged ER stress is closely related with hepatic injury. Adiponectin, a hormone predominantly produced by adipose tissue, is known to possess potent hepatoprotective properties and exhibits a cytoprotective effect in response to chronic ER stress. However, the underlying mechanisms are not clearly understood. In the present study, we examined the protective effect of globular adiponectin (gAcrp) on tunicamycin-induced cell death and further investigated its potential underlying mechanisms in rat hepatocytes. Herein, we found that treatment with gAcrp inhibited tunicamycin-induced cell death, decreased lactate dehydrogenase release (marker of pyroptotic cell death), and suppressed caspase activation; clearly indicating that gAcrp protects liver cells from ER stress. Interestingly, gAcrp prevented the tunicamycin-induced activation of the inflammasome, a key platform involved in the production of inflammatory cytokines that induces pyroptosis, determined by suppression of interleukin-1β (IL-1β) maturation, apoptosis-associated speck-like protein containing a carboxy-terminal CARD (ASC) speck formation, and caspase-1 activation. Moreover, we showed that suppression of the inflammasome activation by gAcrp was mediated via modulation of reactive oxygen species (ROS) production, particularly inhibition of NADPH oxidase. In addition, inhibition of heme oxygenase-1 (HO-1) signaling by pretreatment with SnPP, a pharmacological inhibitor of HO-1, or transfection with an siRNA targeting HO-1, abrogated the protective effects of gAcrp against tunicamycin-induced cell death and abolished the suppressive effect on the inflammasome activation, demonstrating that HO-1 signaling plays a crucial role in the protective effect of gAcrp against tunicamycin-induced damage in liver cells. Taken together, these results indicate that gAcrp protects liver cells from ER stress by modulating inflammasomes activation, at least in part, via HO-1 signaling-dependent mechanisms.