Transforming growth factor-β1 (TGF-β1) plays important roles in chronic liver diseases, including metabolic dysfunction–associated steatotic liver disease (MASLD). MASLD involves various biological processes including dysfunctional cholesterol metabolism and contributes to progression to metabolic dysfunction–associated steatohepatitis and hepatocellular carcinoma. However, the reciprocal regulation of TGF-β1 signaling and cholesterol metabolism in MASLD is yet unknown. Changes in transcription of genes associated with cholesterol metabolism were assessed by RNA sequencing of murine hepatocyte cell line (alpha mouse liver 12/AML12) and mouse primary hepatocytes treated with TGF-β1. Functional assays were performed on AML12 cells (untreated, TGF-β1 treated, or subjected to cholesterol enrichment [CE] or cholesterol depletion [CD]), and on mice injected with adenovirus-associated virus 8–control/TGF-β1. TGF-β1 inhibited messenger RNA expression of several cholesterol metabolism regulatory genes, including rate-limiting enzymes of cholesterol biosynthesis in AML12 cells, mouse primary hepatocytes, and adenovirus-associated virus–TGF-β1–treated mice. Total cholesterol levels and lipid droplet accumulation in AML12 cells and liver tissue also were reduced upon TGF-β1 treatment. Smad2/3 phosphorylation after 2 hours of TGF-β1 treatment persisted after CE or CD and was mildly increased after CD, whereas TGF-β1–mediated AKT phosphorylation (30 min) was inhibited by CE. Furthermore, CE protected AML12 cells from several effects mediated by 72 hours of incubation with TGF-β1, including epithelial–mesenchymal transition, actin polymerization, and apoptosis. CD mimicked the outcome of long-term TGF-β1 administration, an effect that was blocked by an inhibitor of the type I TGF-β receptor. In addition, the supernatant of CE- or CD-treated AML12 cells inhibited or promoted, respectively, the activation of LX-2 hepatic stellate cells. TGF-β1 inhibits cholesterol metabolism whereas cholesterol attenuates TGF-β1 downstream effects in hepatocytes.

中文翻译：

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TGF-β1 和胆固醇协调肝细胞命运、EMT 和 HSC 激活信号的相互作用

转化生长因子-β1 (TGF-β1) 在慢性肝病中发挥重要作用，包括代谢功能障碍相关的脂肪肝病 (MASLD)。 MASLD 涉及多种生物过程，包括胆固醇代谢功能障碍，并导致代谢功能障碍相关的脂肪性肝炎和肝细胞癌的进展。然而，MASLD 中 TGF-β1 信号传导和胆固醇代谢的相互调节尚不清楚。通过对小鼠肝细胞系（α小鼠肝脏 12/AML12）和用 TGF-β1 处理的小鼠原代肝细胞进行 RNA 测序来评估与胆固醇代谢相关的基因转录的变化。对 AML12 细胞（未经处理、TGF-β1 处理或进行胆固醇富集 [CE] 或胆固醇消耗 [CD]）以及注射腺病毒相关病毒 8-对照/TGF-β1 的小鼠进行功能测定。 TGF-β1 抑制多种胆固醇代谢调节基因的信使 RNA 表达，包括 AML12 细胞、小鼠原代肝细胞和腺病毒相关病毒 TGF-β1 处理小鼠中胆固醇生物合成的限速酶。 TGF-β1 治疗后，AML12 细胞和肝组织中的总胆固醇水平和脂滴积累也有所降低。 TGF-β1 处理 2 小时后，Smad2/3 磷酸化在 CE 或 CD 后持续存在，并在 CD 后轻度增加，而 TGF-β1 介导的 AKT 磷酸化（30 分钟）被 CE 抑制。此外，CE 保护 AML12 细胞免受 TGF-β1 孵育 72 小时介导的多种影响，包括上皮间质转化、肌动蛋白聚合和细胞凋亡。 CD 模仿了长期 TGF-β1 给药的结果，这种效果被 I 型 TGF-β 受体抑制剂阻断。此外，CE或CD处理的AML12细胞的上清液分别抑制或促进LX-2肝星状细胞的活化。 TGF-β1 抑制胆固醇代谢，而胆固醇则减弱肝细胞中 TGF-β1 下游的影响。