Background: NAFLD has become the most common chronic liver disease worldwide. Human antigen R (HuR), an RNA-binding protein, is an important post-transcriptional regulator. HuR has been reported as a key player in regulating lipid homeostasis in the liver and adipose tissues by using tissue-specific HuR knockout mice. However, the underlying mechanism by which hepatocyte-specific HuR regulates hepatic lipid metabolism under metabolic stress remains unclear and is the focus of this study. Methods: Hepatocyte-specific HuR deficient mice (HuR^hKO) and age-/gender-matched control mice, as well as long-noncoding RNA H19 knockout mice (H19^−/−), were fed a Western Diet plus sugar water (WDSW). Hepatic lipid accumulation, inflammation and fibrosis were examined by histology, RNA transcriptome analysis, qRT–PCR, and Western blot analysis. Bile acid composition was measured using LC–MS/MS. Results: Hepatocyte-specific deletion of HuR not only significantly increased hepatic lipid accumulation by modulating fatty acid synthesis and metabolism but also markedly induced inflammation by increasing immune cell infiltration and neutrophil activation under metabolic stress. In addition, hepatic deficiency of HuR disrupted bile acid homeostasis and enhanced liver fibrosis. Mechanistically, HuR is a repressor of H19 expression. Analysis of a recently published dataset (GSE143358) identified H19 as the top-upregulated gene in liver-specific HuR knockout mice. Similarly, hepatocyte-specific deficiency of HuR dramatically induced the expression of H19 and sphingosine-1 phosphate receptor 2 (S1PR2), but reduced the expression of sphingosine kinase 2 (SphK2). WDSW-induced hepatic lipid accumulation was alleviated in H19^−/− mice. Furthermore, the downregulation of H19 alleviated WDSW-induced NAFLD in HuR^hKO mice. Conclusions: HuR not only functions as an RNA binding protein to modulate post-transcriptional gene expression but also regulates H19 promoter activity. Hepatic HuR is an important regulator of hepatic lipid metabolism via modulating H19 expression.

Background: Sphingosine-1 phosphate (S1P) is a bioactive lipid molecule that modulates inflammation and hepatic lipid metabolism in MASLD, which affects 1 in 3 people and increases the risk of liver fibrosis and hepatic cancer. S1P can be generated by 2 isoforms of sphingosine kinase (SphK). SphK1 is well-studied in metabolic diseases. In contrast, SphK2 function is not well characterized. Both sphingolipid and redox metabolism dysregulation contribute to MASLD pathologic progression. While SphK2 localizes to both the nucleus and mitochondria, its specific role in early MASH is not well defined. Methods: This study examined SphK2 depletion effects on hepatic redox metabolism, mitochondrial function, and inflammation in a 16-week western diet plus sugar water (WDSW)-induced mouse model of early MASH. Results: WDSW-SphK2 ^−/− mice exhibit increased hepatic lipid accumulation and hepatic redox dysregulation. In addition, mitochondria-localized cholesterol and S1P precursors were increased. We traced SphK2 ^−/− -mediated mitochondrial electron transport chain impairment to respiratory complex-IV and found that decreased mitochondrial redox metabolism coincided with increased oxidase gene expression and oxylipin production. Consistent with this relationship, we observed pronounced increases in hepatic inflammatory gene expression, prostaglandin accumulation, and innate immune homing in WDSW-SphK2 ^−/− mice compared to WDSW-wild-type mice. Conclusions: These studies suggest SphK2-derived S1P maintains hepatic redox metabolism and describe the potential consequences of SphK2 depletion on proinflammatory gene expression, lipid mediator production, and immune infiltration in MASH progression.

We previously reported that two bile acid (BA) analogs, CamSA and CA-Quin, demonstrate potent anti-germination activity against Clostridioides difficile (C. difficile) spores, protecting rodents from C. difficile infections. Here, we further evaluated the impact of these analogs on the hepatic transcriptome and BA homeostasis in vivo by focusing BA profiles on the liver, feces, and chyme as well as the hepatic transcriptome after a 7-day treatment. The two compounds demonstrated similar impact on BA profiles among the three samples, with significantly increased BA excretion in feces. This change is aligned with significantly altered expression of genes involved in BA homeostasis in both liver and gut tissues. Also, both compounds increased levels of deconjugated BAs in the feces, possibly suggesting increased activity of gut microbiota. Fecal levels of anti-C. difficile germination chenodeoxycholic acid and pro-germination taurocholic acid are significantly increased and decreased by the treatments, respectively. The hepatic transcriptome showed limited difference in gene expression between the three groups, suggesting a minimal adverse impact of the two compounds on liver function. Overall, our study suggests that in vivo CamSA and CA-Quin treatment demonstrated safe and significantly altered BA homeostasis that inhibits C. difficle germination.

We previously reported that two bile acid (BA) analogs CamSA and CA-Quin demonstrate potent anti-germination activity against Clostridioides difficile (C. difficile) spores, protecting rodents from C. difficile infections. Here we further evaluated the impact of these analogs on the hepatic transcriptome and BA homeostasis in vivo by focusing BA profiles on the liver, feces, and chyme as well as hepatic transcriptome after a 7-day treatment. The two compounds demonstrated similar impact on BA profiles among the three samples, with significantly increased BA excretion in feces. This change is aligned with significantly altered expression of genes involved in BA homeostasis in both liver and gut tissues. Also, both compounds increased levels of unconjugated BAs in the feces, indicating an elevated activity of gut microbiota (GM). Notably, fecal levels of anti-c. difficile germination chenodeoxycholate and pro-germination taurocholate are significantly increased and decreased by the treatments, respectively. While hepatic transcriptome did not show significant toxicity, altered genes are enriched in pathways associated with GM activity and lipid metabolism. Overall, our study suggests that in vivo CamSA and CA-Quin treatment demonstrated minimal hepatoxicity but significantly altered BA homeostasis and potentially favorable improvement for GM profiles that together inhibit C. difficle germination.