Mitochondrial Cholesterol Metabolites in a Bile Acid Synthetic Pathway Drive Nonalcoholic Fatty Liver Disease: A Revised "Two-Hit" Hypothesis

HSDL2 links nutritional cues to bile acid and cholesterol homeostasis

In response to energy and nutrient shortage, the liver triggers several catabolic processes to promote survival. Despite recent progress, the precise molecular mechanisms regulating the hepatic adaptation to fasting remain incompletely characterized. Here, we report the identification of hydroxysteroid dehydrogenase-like 2 (HSDL2) as a mitochondrial protein highly induced by fasting. We show that the activation of PGC1α-PPARα and the inhibition of the PI3K-mTORC1 axis stimulate HSDL2 expression in hepatocytes. We found that HSDL2 depletion decreases cholesterol conversion to bile acids (BAs) and impairs FXR activity. HSDL2 knockdown also reduces mitochondrial respiration, fatty acid oxidation, and TCA cycle activity. Bioinformatics analyses revealed that hepatic Hsdl2 expression positively associates with the postprandial excursion of various BA species in mice. We show that liver-specific HSDL2 depletion affects BA metabolism and decreases circulating cholesterol levels upon refeeding. Overall, our report identifies HSDL2 as a fasting-induced mitochondrial protein that links nutritional signals to BAs and cholesterol homeostasis.

Larsucosterol: endogenous epigenetic regulator for treating chronic and acute liver diseases

Larsucosterol, a potent endogenous epigenetic regulator, has been reported to play a significant role in lipid metabolism, inflammatory responses, and cell survival. The administration of larsucosterol has demonstrated a reduction in lipid accumulation within hepatocytes and the attenuation of inflammatory responses induced by lipopolysaccharide (LPS) and TNFα in macrophages, alleviating LPS- and acetaminophen (ATMP)-induced multiple organ injury, and decreasing mortalities in animal models. Results from phase 1 and 2 clinical trials have shown that larsucosterol has potential as a biomedicine for the treatment of acute and chronic liver diseases. Recent evidence suggests that larsucosterol is a promising candidate for treating alcohol-associated hepatitis with positive results from a phase 2a clinical trial, and for metabolic dysfunction-associated steatohepatitis (MASH) from a phase 1b clinical trial. In this review, we present a culmination of our recent research efforts spanning two decades. We summarize the discovery, physiological and pharmacological mechanisms, and clinical applications of larsucosterol. Furthermore, we elucidate the pathophysiological pathways of metabolic dysfunction-associated steatotic liver diseases (MASLD), metabolic dysfunction-associated steatohepatitis (MASH), and acute liver injuries. A central focus of the review is the exploration of the therapeutic potential of larsucosterol in treating life-threatening conditions, including acetaminophen overdose, endotoxin shock, MASLD, MASH, hepatectomy, and alcoholic hepatitis.

Mitochondrial Dysfunction in Metabolic Dysfunction Fatty Liver Disease (MAFLD)

Nonalcoholic fatty liver disease (NAFLD) has become an increasingly common disease in Western countries and has become the major cause of liver cirrhosis or hepatocellular carcinoma (HCC) in addition to viral hepatitis in recent decades. Furthermore, studies have shown that NAFLD is inextricably linked to the development of extrahepatic diseases. However, there is currently no effective treatment to cure NAFLD. In addition, in 2020, NAFLD was renamed metabolic dysfunction fatty liver disease (MAFLD) to show that its pathogenesis is closely related to metabolic disorders. Recent studies have reported that the development of MAFLD is inextricably associated with mitochondrial dysfunction in hepatocytes and hepatic stellate cells (HSCs). Simultaneously, mitochondrial stress caused by structural and functional disorders stimulates the occurrence and accumulation of fat and lipo-toxicity in hepatocytes and HSCs. In addition, the interaction between mitochondrial dysfunction and the liver-gut axis has also become a new point during the development of MAFLD. In this review, we summarize the effects of several potential treatment strategies for MAFLD, including antioxidants, reagents, and intestinal microorganisms and metabolites.

Integration of Transcriptomics and Lipidomics Profiling to Reveal the Therapeutic Mechanism Underlying Ramulus mori (Sangzhi) Alkaloids for the Treatment of Liver Lipid Metabolic Disturbance in High-Fat-Diet/Streptozotocin-Induced Diabetic Mice

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disorder, with a global prevalence of 25%. Currently, there remains no approved therapy. Ramulus mori (Sangzhi) alkaloids (SZ-As), a novel natural medicine, have achieved comprehensive benefits in the treatment of type 2 diabetes; however, few studies have focused on its role in ameliorating hepatic lipid metabolic disturbance. Herein, the therapeutic effect and mechanism of SZ-As on a high-fat diet (HFD) combined with streptozotocin (STZ)-induced NAFLD mice were investigated via incorporating transcriptomics and lipidomics. SZ-As reduced body weight and hepatic lipid levels, restored pathological alternation and converted the blood biochemistry perturbations. SZ-A treatment also remarkedly inhibited lipogenesis and enhanced lipolysis, fatty acid oxidation and thermogenesis. Transcriptomics analysis confirmed that SZ-As mainly altered fatty acid oxidative metabolism and the TNF signaling pathway. SZ-As were further demonstrated to downregulate inflammatory factors and effectively ameliorate hepatic inflammation. Lipidomics analysis also suggested that SZ-As affected differential lipids including triglyceride (TG) and phosphatidylcholine (PC) expression, and the main metabolic pathways included glycerophospholipid, sphingomyelins and choline metabolism. Collectively, combined with transcriptomics and metabolomics data, it is suggested that SZ-As exert their therapeutic effect on NAFLD possibly through regulating lipid metabolism pathways (glycerophospholipid metabolism and choline metabolism) and increasing levels of PC and lysophosphatidylcholine (LPC) metabolites. This study provides the basis for more widespread clinical applications of SZ-As.