Division of Endocrinology, Metabolism and Molecular Medicine, Department of Internal Medicine, Charles R. Drew University, Los Angeles, CA 90059, USA.
David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA.
Cells. 2023 Apr 1;12(7):1069. doi: 10.3390/cells12071069.
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.
CARF（CDKN2AIP）可响应各种应激调节细胞命运。然而，其在代谢应激中的作用尚不清楚。我们发现，脂肪性肝中的 CARF 表达水平较低。同样，过量的棕榈酸抑制了 HepG2 细胞中 CARF 的表达，提示过量脂肪诱导的应激下调了肝 CARF。与此一致，沉默和过表达 CARF 分别导致 HepG2 细胞中脂肪积累增加和减少。此外，CARF 的过表达降低了 HepG2 细胞中棕榈酸的异位积累。我们对了解肝 CARF 在 NAFLD 发展中的作用及其潜在机制很感兴趣。从机制上讲，转录组分析表明，缺乏 CARF 时内质网（ER）应激和氧化应激途径基因显著改变。内质网应激标志物 IRE1α、GRP78 和 CHOP 增加，用 ER 应激抑制剂 TUDCA 处理可减轻 CARF 缺陷细胞中的脂肪积累。此外，沉默 CARF 导致 GPX3 和 TRXND3 减少，导致氧化应激和细胞凋亡。有趣的是，高脂饮食喂养的小鼠中 CARF 的过表达显著减少了肝脂肪变性。此外，CARF 的过表达改善了脂肪积累引起的异常 ER 功能和氧化应激。我们的结果进一步表明，CARF 的过表达减轻了高脂饮食诱导的胰岛素抵抗，用 ITT 和 GTT 测定评估。总之，我们得出结论，过量脂肪诱导的 CARF 减少会导致 ER 功能和脂质代谢紊乱，从而导致肝脂肪变性。
