Abstract 1599: Exposure of Adipocytes to Tobacco Smoke Traps High Molecular Weight Adiponectin Intracellularly and Induces ER Stress: A Novel Mechanism for Hypoadiponectinemia in Smokers
Cigarette smoking has been associated with increased risk of type 2 diabetes mellitus (T2DM), but the underline mechanism is not clear. Smokers exhibit low levels of serum adiponectin (APN), an insulin-sensitizing adipokine. APN circulates as trimers, hexamers, and high molecular weight (HMW) multimeric isoforms. Peripheral insulin sensitivity is closely related to levels of HMW APN. We hypothesized that tobacco smoke might alter APN secretion or its isoform distribution. We found that exposure of mouse 3T3-L1 adipocytes to tobacco smoke extract (TSE) caused a time- and dose-dependent suppression of total APN secretion into medium, to 32.0%±2.4% of control after exposure to 1.5% TSE for 20h (P<0.001). Viability of the adipocytes was unaffected under our conditions. Conversely, TSE exposure trapped APN intracellularly, shown as increased total APN by immunoblot of adipocyte extracts, to 155±13% (p=0.013) of control. Similar phenomena were observed after TSE exposure of mouse visceral adipose explants. Most interestingly, we found that the decrease in APN in the medium after TSE exposure was mainly attributable to reduced secretion of HMW APN, while the intracellular HMW APN isoforms were increased. Assembly and secretion of HMW APN is influenced by thiol redox status in endoplasmic reticulum (ER), owing to the need to form intermolecular disulfide bonds. Here, we found that exposure of 3T3-L1 adipocytes to 1.5% TSE increased intracellular reactive oxidative species (ROS), as detected by DCF staining, and induced ER stress, shown by induction of C/EBO Homologous Protein (CHOP)/GADD153 on immunoblots. Pretreatment of 3T3-L1 adipocytes with N-acetylcysteine (NAC) decreased TSE-induced intracellular ROS accumulation and attenuated TSE-induced ER stress. Importantly, NAC treatment during TSE exposure restored APN secretion and decreased intracellular accumulation of APN. We conclude that TSE exposure traps HMW APN intracellularly, thereby blocking its secretion from adipocytes. Intracellular redox alterations and ER stress may play a role. These results provide a novel mechanism for hypoadiponectinemia, decreased peripheral insulin sensitivity, and increased risk of T2DM in smokers.