CARF (CDKN2AIP) regulates cellular fate in response to various stresses. However, its role in metabolic stress is unknown. We found that fatty livers from mice exhibit low CARF expression. Similarly, overloaded palmitate inhibited CARF expression in HepG2 cells, suggesting that excess fat-induced stress downregulates hepatic CARF. In agreement with this, silencing and overexpressing CARF resulted in higher and lower fat accumulation in HepG2 cells, respectively. Furthermore, CARF overexpression lowered the ectopic palmitate accumulation in HepG2 cells. We were interested in understanding the role of hepatic CARF and underlying mechanisms in the development of NAFLD. Mechanistically, transcriptome analysis revealed that endoplasmic reticulum (ER) stress and oxidative stress pathway genes significantly altered in the absence of CARF. IRE1α, GRP78, and CHOP, markers of ER stress, were increased, and the treatment with TUDCA, an ER stress inhibitor, attenuated fat accumulation in CARF-deficient cells. Moreover, silencing CARF caused a reduction of GPX3 and TRXND3, leading to oxidative stress and apoptotic cell death. Intriguingly, CARF overexpression in HFD-fed mice significantly decreased hepatic steatosis. Furthermore, overexpression of CARF ameliorated the aberrant ER function and oxidative stress caused by fat accumulation. Our results further demonstrated that overexpression of CARF alleviates HFD-induced insulin resistance assessed with ITT and GTT assay. Altogether, we conclude that excess fat-induced reduction of CARF dysregulates ER functions and lipid metabolism leading to hepatic steatosis.

In spite of the widespread use of electronic cigarettes, also known as e-cigarettes, and the proposed adverse cardiac effects of nicotine, the detrimental effects of e-cigarettes on the heart are not well known. This study examines the detrimental effects of e-cigarettes with nicotine at doses that yield circulating nicotine and cotinine in the ranges similar to the levels found in habitual smokers, and a high fat diet (HFD) on cardiac structure and function in a commonly used model of diet-induced obesity (DIO). C57BL/6J mice on an HFD were exposed to e-cigarette in the presence (2.4% nicotine) or absence (0% nicotine) of nicotine and saline aerosol for 12 weeks. Echocardiographic data demonstrated a decrease in left ventricular (LV) fractional shortening, LV ejection fraction, and velocity of circumferential fiber shortening (VCF) in mice treated with e-cigarette (2.4% nicotine) compared to e-cigarette (0% nicotine) or saline exposed mice. Cardiomyocytes (CMs) of mice treated with e-cigarette (2.4% nicotine) exhibited LV abnormalities, including lipid accumulation (ventricular steatosis), myofibrillar derangement and destruction, and mitochondrial hypertrophy, as revealed by transmission electron microscopy. The detrimental effects of e-cigarettes (2.4% nicotine) on cardiac structure and function was accompanied by increased oxidative stress, plasma free fatty acid levels, CM apoptosis, and inactivation of AMP-activated protein kinase and activation of its downstream target, acetyl-CoA-carboxylase. Our results indicate profound adverse effects of e-cigarettes (2.4% nicotine) on the heart in obese mice and raise questions about the safety of the nicotine e-cigarettes use.