Cardiac dysfunction in patients with liver cirrhosis is strongly associated with increased serum bile acid concentrations. Here we show that excess bile acids decrease fatty acid oxidation in cardiomyocytes and can cause heart dysfunction, a cardiac syndrome that we term Cholecardia. Fxr; Shp double knockout (DKO) mice, a model for bile acid overload, display cardiac hypertrophy, bradycardia, and exercise intolerance. In addition, DKO mice exhibit an impaired cardiac response to catecholamine challenge. Consistent with this decreased cardiac function, we show that elevated serum bile acids reduce cardiac fatty acid oxidation both in vivo and ex vivo. We find that increased bile acid levels suppress expression of Pgc1α, a key regulator of fatty acid metabolism, and that Pgc1α overexpression in cardiac cells was able to rescue the bile acid-mediated reduction in fatty acid oxidation genes. Importantly, intestinal bile acid sequestration with cholestyramine was sufficient to reverse the observed heart dysfunction in the DKO mice. Conclusions Overall, we propose that decreased Pgc1α expression contributes to the metabolic dysfunction in Cholecardia, and that reducing serum bile acid concentrations will be beneficial against metabolic and pathological changes in the heart.

Highlights Cell cycle, inflammation, and glucose homeostasis are some of the common pathways altered in a variety of liver disorders. Phase I and II metabolic genes are induced in Fxr −/− Shp −/− double knockouts (DKOs) and bile-acidfed control mice. Activation of xeno-sensor, constitutive androstane receptor (CAR), is observed in cholestasis. Inhibiting CAR activity in DKO mice exacerbates zoxazolamine-induced paralysis and acetaminophen-induced hepatotoxicity. A subset of patients with biliary atresia display increased expression of CAR target protein CYP2B6. Lay summary Transcriptomic analysis of diverse liver diseases revealed alterations in common and distinct pathways. Specifically, in cholestasis, we found that detoxification genes and their activity are increased. Thus, cholestatic patients may have an unintended consequence on drug metabolism and not only have a beneficial effect against liver toxicity, but also may require adjustments to their therapeutic dosage.

Regulation of RNA processing contributes profoundly to tissue development and physiology. Here, we report that serine-arginine-rich splicing factor 1 (SRSF1) is essential for hepatocyte function and survival. Although SRSF1 is mainly known for its many roles in mRNA metabolism, it is also crucial for maintaining genome stability. We show that acute liver damage in the setting of targeted SRSF1 deletion in mice is associated with the excessive formation of deleterious RNA–DNA hybrids (R-loops), which induce DNA damage. Combining hepatocyte-specific transcriptome, proteome, and RNA binding analyses, we demonstrate that widespread genotoxic stress following SRSF1 depletion results in global inhibition of mRNA transcription and protein synthesis, leading to impaired metabolism and trafficking of lipids. Lipid accumulation in SRSF1-deficient hepatocytes is followed by necroptotic cell death, inflammation, and fibrosis, resulting in NASH-like liver pathology. Importantly, SRSF1-depleted human liver cancer cells recapitulate this pathogenesis, illustrating a conserved and fundamental role for SRSF1 in preserving genome integrity and tissue homeostasis. Thus, our study uncovers how the accumulation of detrimental R-loops impedes hepatocellular gene expression, triggering metabolic derangements and liver damage.

Nuclear receptors farnesoid X receptor (FXR) and small heterodimer partner (SHP) are key regulators of metabolism. Here, we report a previously unknown function for the hepatic FXR-SHP axis in controlling protein N-linked glycosylation. Transcriptome analysis in liver-specific Fxr-Shp double knockout (LDKO) livers revealed induction of genes encoding enzymes in the N-glycosylation pathway, including Mgat5, Fut8, St3gal6, and St6gal1. FXR activation suppressed Mgat5, while Shp deletion induced St3gal6 and St6gal1. Increased percentages of core-fucosylated and triantennary glycan moieties were seen in LDKO livers, and proteins with the “hyperglycoforms” preferentially localized to exosomes and lysosomes. This up-regulation of N-glycosylation machinery was specific to the Golgi apparatus and not the endoplasmic reticulum. The increased glycan complexity in the LDKO correlated well with dilated unstacked Golgi ribbons and alterations in the secretion of albumin, cholesterol, and triglycerides. Our findings demonstrate a role for the FXR-SHP axis in maintaining glycoprotein diversity in the liver.

Regulation of RNA processing contributes profoundly to tissue development and physiology. Here, we report that serine-arginine-rich splicing factor 1 (SRSF1) is essential for hepatocyte function and survival. Although SRSF1 is mainly known for its many roles in mRNA metabolism, it is also crucial for maintaining genome stability. We show that acute liver damage in the setting of targeted SRSF1 deletion in mice is primarily mediated by the excessive formation of deleterious RNA–DNA hybrids (R-loops), which induce DNA damage. Combining hepatocyte-specific transcriptome, proteome, and RNA binding analyses, we demonstrate that widespread genotoxic stress following SRSF1 depletion results in global inhibition of mRNA transcription and protein synthesis, leading to impaired metabolism and trafficking of lipids. Lipid accumulation in SRSF1-deficient hepatocytes is followed by necroptotic cell death, inflammation, and fibrosis, resulting in NASH-like liver pathology. Importantly, SRSF1-depleted human liver cancer cells recapitulate this pathogenesis illustrating a conserved and fundamental role for SRSF1 in preserving genome integrity and tissue homeostasis. Thus, our study uncovers how accumulation of detrimental R-loops impedes hepatocellular gene expression, triggering metabolic derangements and liver failure.

Understanding the alterations in drug metabolism in different liver diseases is crucial for appropriate therapeutic intervention. We performed high-throughput RNA sequencing on various liver injury models, including cholestasis, diet-induced steatosis, and regeneration. Comparative liver transcriptome analysis revealed overlapping and distinct gene profiles among different liver diseases. Particularly, cholestatic livers displayed robust induction of drug metabolizing genes. This upregulation is not a generic hepatic stress response, as it was suppressed or unchanged in other models of liver diseases. Consistently, drug metabolic gene profiles were induced in a subset of biliary atresia patients, but not in individuals with hepatitis B or C viral infection, and alcoholic hepatitis. Further analysis revealed this induction was specific to genes regulated by nuclear receptor CAR (Constitutive Androstane Receptor). To test this, we challenged cholestatic mice with a paralytic agent, zoxazolamine. Compared to controls, these mice displayed significantly reduced paralysis time, reflecting increased drug metabolism, and this effect was lost upon inhibition of CAR. Thus, CAR activation can alter therapeutic efficacy of certain drugs in a subset of cholestatic individuals.

Nuclear receptor Farnesoid X Receptor (Fxr) and Small Heterodimer Partner (Shp) are key regulators of glucose, fat and bile acid homeostasis. As expected, liver-specific deletion of both Fxr and Shp (LDKO) sensitizes mice to bile acid excess. Surprisingly, high throughput RNA-sequencing analysis revealed increases in key glycosyltransferases involved in “decorating” various glycoproteins in LDKO livers. Remarkably, we were able to confirm increased glycan decoration and branching in LDKO livers using glycomics and glycoproteomics approaches. Further, electron microscopic analysis revealed disruption and dilation of Golgi network, which is consistent with aberrant glycosylation. LDKO mice were hypoglycemic, stored lower glycogen, indicating glucose being utilized to meet the increased glycosylation demand. Taken together, we uncover a novel role for hepatic Fxr-Shp axis in maintaining the glycosylation status of proteins in the liver.