Virginia Commonwealth University, Department of Biochemistry and Molecular Biology, VA, USA.
Virginia Commonwealth University, Department of Biochemistry and Molecular Biology, VA, USA.
Mol Metab. 2022 Aug;62:101523. doi: 10.1016/j.molmet.2022.101523. Epub 2022 Jun 6.
Men with non-alcoholic fatty liver disease (NAFLD) are more likely to progress to non-alcoholic steatohepatitis (NASH) and liver fibrosis than women. However, the underlying molecular mechanisms of this dimorphism is unclear. We have previously shown that mice with global deletion of SphK1, the enzyme that produces the bioactive sphingolipid metabolite sphingosine 1-phosphate (S1P), were protected from development of NASH. The aim of this study was to elucidate the role of hepatocyte-specific SphK1 in development of NASH and to compare its contribution to hepatosteatosis in male and female mice.
We assessed mouse livers in early-stage fibrosis induced by high fat feeding, using single harmonic generation microscopy, LC-MS/MS analysis of hydroxyproline levels, and expression of fibrosis markers. We identified an antifibrotic intercellular signaling mechanism by culturing primary mouse hepatocytes alongside, and in co-culture with, LX2 hepatic stellate cells.
We generated hepatocyte-specific SphK1 knockout mice (SphK1-hKO). Unlike the global knockout, SphK1-hKO male mice were not protected from diet-induced steatosis, inflammation, or fibrogenesis. In contrast, female SphK1-hKO mice were protected from inflammation. Surprisingly, however, in these female mice, there was a ∼10-fold increase in the fibrosis markers Col1α1 and 2-3 fold induction of alpha smooth muscle actin and the pro-fibrotic chemokine CCL5. Because increased fibrosis in female SphK1-hKO mice occurred despite an attenuated inflammatory response, we investigated the crosstalk between hepatocytes and hepatic stellate cells, central players in fibrosis. We found that estrogen stimulated release of S1P from female hepatocytes preventing TGFβ-induced expression of Col1α1 in HSCs via S1PR3.
The results revealed a novel pathway of estrogen-mediated cross-talk between hepatocytes and HSCs that may contribute to sex differences in NAFLD through an anti-fibrogenic function of the S1P/S1PR3 axis. This pathway is susceptible to pharmacologic manipulation, which may lead to novel therapeutic strategies.
非酒精性脂肪性肝病（NAFLD）男性患者比女性患者更易进展为非酒精性脂肪性肝炎（NASH）和肝纤维化。然而，这种性别二态性的潜在分子机制尚不清楚。我们之前的研究表明，SphK1 酶（产生生物活性鞘脂代谢物 1-磷酸鞘氨醇（S1P））的全球缺失可保护小鼠免于发生 NASH。本研究旨在阐明肝实质细胞特异性 SphK1 在 NASH 发生发展中的作用，并比较其在雄性和雌性小鼠肝脂肪变性中的作用。
我们使用单谐波产生显微镜、羟脯氨酸水平的 LC-MS/MS 分析以及纤维化标志物的表达，评估了高脂肪喂养诱导的早期纤维化小鼠的肝脏。我们通过培养原代小鼠肝细胞与 LX2 肝星状细胞共培养，鉴定了一种抗纤维化的细胞间信号转导机制。
我们生成了肝实质细胞特异性 SphK1 敲除小鼠（SphK1-hKO）。与全局敲除不同，SphK1-hKO 雄性小鼠不能预防饮食诱导的脂肪变性、炎症或纤维化。相反，SphK1-hKO 雌性小鼠则对炎症有保护作用。然而，令人惊讶的是，在这些雌性小鼠中，纤维化标志物 Col1α1 的表达增加了约 10 倍，α平滑肌肌动蛋白的表达增加了 2-3 倍，促纤维化趋化因子 CCL5 的表达也增加了。由于雌性 SphK1-hKO 小鼠的纤维化增加是在炎症反应减弱的情况下发生的，我们研究了在纤维化中起核心作用的肝细胞和肝星状细胞之间的串扰。我们发现，雌激素刺激了 S1P 从雌性肝细胞中的释放，通过 S1PR3 阻止了 TGFβ诱导的 HSCs 中 Col1α1 的表达。
这些结果揭示了雌激素介导的肝细胞与 HSCs 之间的新串扰途径，该途径可能通过 S1P/S1PR3 轴的抗纤维化功能导致 NAFLD 的性别差异。该途径易受药物干预，这可能为新的治疗策略提供依据。
