College of Life Science/Institute of Molecular Medicine, Zhejiang Chinese Medical University, Hangzhou, 310053, Zhejiang, China.
College of Life Science, Zhejiang University, Hangzhou, 310058, Zhejiang, China.
Mol Cell Biochem. 2021 Aug;476(8):3163-3175. doi: 10.1007/s11010-021-04150-0. Epub 2021 Apr 17.
Nonalcoholic fatty liver disease (NAFLD) is related to elevated cytoplasmic calcium signaling in hepatocytes, which may be mediated by store-operated calcium channel (SOCC) and inositol triphosphate receptor (IP3R). However, the regulatory effect of calcium signaling on lipid accumulation and degeneration in hepatocytes and the underlying molecular mechanism remain unknown. Autophagy inhibition promotes lipid accumulation and steatosis in hepatocytes. However, the association between elevated calcium signaling and autophagy inhibition in hepatocytes and its effect on hepatocyte fatty lesions remain unclear. Here, we established a mouse hepatocyte fatty gradient model using oleic acid. SOCC and IP3R channel opening and cytoplasmic calcium levels gradually increased with the hepatocyte pimelosis degree, whereas autophagy gradually decreased. We also established an optimal oleic acid (OOA) hepatocyte model, observing significantly increased SOCC and IP3R channel opening and calcium influx alongside significantly decreased autophagy and aggravated cellular fatty lesion. Calcium channel blockers (CCBs) and calcium channel gene silencing reagents (CCGSRs), respectively, reversed these effects, indicating that elevated cytoplasmic calcium signaling promotes NAFLD occurrence and the development by inhibiting hepatocyte autophagy. In the OOA model, upregulated extracellular regulated protein kinases 1/2 (ERK1/2), which can be regulated by SOCC and IP3R proteins transient receptor potential canonical 1 (TRPC1)/IP3R with elevated cytoplasmic calcium signaling, over-inhibited forkhead/winged helix O (FOXO) signaling and over-activated mammalian target of rapamycin complex 1 (mTORC1) signaling. Over-inhibited FOXO signaling significantly downregulated autophagy-related gene 12, which inhibits autophagosome maturation, while over-activated mTORC1 signaling over-inactivated Unc-51 like autophagy activating kinase 1, which inhibits preautophagosome formation. CCBs and CCGSRs recovered autophagy by significantly downregulating ERK1/2 to block abnormal changes in FOXO and mTORC1 signaling. Our findings indicate that upregulated SOCC and IP3R channels and subsequent elevated cytoplasmic calcium signaling in hepatocyte fatty lesions inhibits hepatocyte autophagy through (TRPC1/IP3R)/ERK/(FOXO/mTORC1) signaling pathways, causes lipid accumulation and degeneration in hepatocytes, and promotes NAFLD occurrence and development.
非酒精性脂肪性肝病（NAFLD）与肝细胞细胞质钙信号升高有关，其可能由钙库操纵的钙通道（SOCC）和三磷酸肌醇受体（IP3R）介导。然而，钙信号对肝细胞脂质堆积和变性的调节作用及其潜在的分子机制尚不清楚。自噬抑制可促进肝细胞内脂质堆积和脂肪变性。然而，尚不清楚肝细胞内钙信号升高与自噬抑制的关系及其对肝细胞脂肪病变的影响。本研究采用油酸建立了小鼠肝细胞脂肪梯度模型。随着肝细胞脂肪变性程度的增加，SOCC 和 IP3R 通道开放以及细胞质钙离子水平逐渐升高，而自噬逐渐降低。我们还建立了一个优化的油酸（OOA）肝细胞模型，观察到 SOCC 和 IP3R 通道开放和钙内流显著增加，自噬显著减少，细胞脂肪病变加重。钙通道阻滞剂（CCBs）和钙通道基因沉默试剂（CCGSRs）分别逆转了这些作用，表明升高的细胞质钙信号通过抑制肝细胞自噬促进 NAFLD 的发生和发展。在 OOA 模型中，细胞外调节蛋白激酶 1/2（ERK1/2）被上调，该激酶可被 SOCC 和 IP3R 蛋白瞬时受体电位经典通道 1（TRPC1）/IP3R 调节，升高的细胞质钙信号可过度抑制叉头框/翼状螺旋 O（FOXO）信号并过度激活哺乳动物雷帕霉素靶蛋白复合物 1（mTORC1）信号。过度抑制 FOXO 信号显著下调自噬相关基因 12，该基因抑制自噬体成熟，而过激活的 mTORC1 信号过度抑制自噬激活激酶 1，该激酶抑制前自噬体形成。CCBs 和 CCGSRs 通过显著下调 ERK1/2 恢复自噬，从而阻断 FOXO 和 mTORC1 信号的异常变化。我们的研究结果表明，肝细胞脂肪病变中上调的 SOCC 和 IP3R 通道和随后升高的细胞质钙信号通过（TRPC1/IP3R）/ERK/（FOXO/mTORC1）信号通路抑制肝细胞自噬，导致肝细胞内脂质堆积和变性，并促进 NAFLD 的发生和发展。
