Project description:Liver injury is a core pathological process in the majority of liver diseases, yet the genetic factors predisposing individuals to its initiation and progression remain poorly understood. Here we show that asialoglycoprotein receptor 1 (ASGR1), a lectin specifically expressed in the liver, is downregulated in patients with liver fibrosis or cirrhosis and male mice with liver injury. ASGR1 deficiency exacerbates while its overexpression mitigates acetaminophen-induced acute and CCl4-induced chronic liver injuries in male mice. Mechanistically, ASGR1 binds to an endoplasmic reticulum stress mediator GP73 and facilitates its lysosomal degradation. ASGR1 depletion increases circulating GP73 levels and promotes the interaction between GP73 and BIP to activate endoplasmic reticulum stress, leading to liver injury. Neutralization of GP73 not only attenuates ASGR1 deficiency-induced liver injuries but also improves survival in mice received a lethal dose of acetaminophen. Collectively, these findings identify ASGR1 as a potential genetic determinant of susceptibility to liver injury and propose it as a therapeutic target for the treatment of liver injury.
Project description:The hepatic unfolded protein response (UPR) is an adaptive cellular response to endoplasmic reticulum stress that is important in the pathogenesis of many liver diseases. In this study, we utilized liver biopsies from patients after liver transplantation as a disease model to determine the transcriptional profile and hepatic UPR gene expression that is associated with liver injury and cholestasis.
Project description:A1AT deficiency is an autosomal not recessive disorder caused by mutations in the SERPINA1 gene. Individuals with the Z variant retain polymerised protein in the endoplasmic reticulum of hepatocytes, predisposing them to liver disease. This study primarily aimed to uncover the molecular mechanisms that link protein misfolding to liver injury. To that end, RNA was extracted from hepatocytes differentiated from hIPSCs carrying the Z variant and mutation-corrected hIPSCs (control). The second objective of the study was to benchmark the gene expression profile of both hIPSC-derived hepatocytes types to primary hepatocytes of wild type and a Z variant A1AT genotype.
Project description:Accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) lumen triggers unfolded protein response (UPR) for stress adaptation, the failure of which induces cell apoptosis and tissue/organ damage. The molecular switches underlying how the UPR selects for stress adaptation over apoptosis remain unknown. Here we discovered that accumulation of unfolded/misfolded proteins selectively induces N6-adenosine-methyltransferase-14 (METTL14) expression. METTL14 promotes CHOP mRNA decay through its 3’UTR N6-adenosine methylation (m6A) to inhibit its downstream pro-apoptotic target genes expression. UPR induces METTL14 expression through competing the HRD1-ERAD machinery to block METTL14 ubiquitination and degradation. Therefore, mice with liver-specific METTL14 deletion are highly susceptible to both acute pharmacological and alpha-1 antitrypsin (AAT) deficiency-induced ER proteotoxic stress and liver injury. Further hepatic CHOP deletion protects METTL14 knockout mice from ER stress-induced liver damage. Our study reveals a crosstalk between ER stress and mRNA m6A pathways, the ERm6A pathway, for ER stress adaptation to proteotoxicity.
Project description:The mechanism underlying the loss of normal liver tissues in liver cirrhosis, mainly hepatocytes, is not well-characterized. Endoplasmic reticulum (ER) stress-induced cell death has emerged as a potential mechanism for chronic liver diseases. We have previously demonstrated that cyclooxygenase-2 (COX-2) is closely related to the progress of liver cirrhosis. In this study, we aimed to verify whether hepatocytes COX-2 deficiency could protect liver injury via inducing ER stress in liver cirrhosis.
Project description:O-GlcNAcylation is a reversible post-translational modification controlled by the activity of two enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). In the liver, O-GlcNAcylation has emerged as an important regulatory mechanism underlying normal liver physiology and metabolic disease.To address whether OGT acts as a critical hepatic nutritional node, mice with a constitutive hepatocyte-specific deletion of OGT (OGTLKO) were generated.Analyses of 4-week-old OGTLKO mice revealed significant oxidative and endoplasmic reticulum stress, and DNA damage, together with inflammation and fibrosis, in the liver. Susceptibility to oxidative and endoplasmic reticulum stress- induced apoptosis was also elevated in OGTLKO hepatocytes. Although OGT expression was partially recovered in the liver of 8- week-old OGTLKO mice, hepatic injury and fibrosis were not rescued but rather worsened with time. Interestingly, weaning of OGTLKO mice on a ketogenic diet (low carbohydrate, high fat) fully prevented the hepatic alterations induced by OGT deletion, indicating that reduced carbohydrate intake protects an OGT-deficient liver. These findings pinpoint OGT as a key mediator of hepatocyte homeostasis and survival upon carbohydrate intake and validate OGTLKO mice as a valuable model for assessing therapeutical approaches of advanced liver fibrosis.
Project description:Endoplasmic reticulum stress is closely associated with the onset and progression of inflammatory bowel disease. ERdj5 is an endoplasmic reticulum-resident protein disulfide reductase that mediates the cleavage and degradation of misfolded proteins. Although ERdj5 expression is significantly higher in the colonic tissues of patients with inflammatory bowel disease than in healthy controls, its role in inflammatory bowel disease has not yet been reported. Hence, in the current study, we utilized ERdj5-knockout mice to investigate the potential roles of ERdj5 in inflammatory bowel disease. ERdj5 deficiency causes severe inflammation in mouse colitis models and weakens gut barrier function by increasing NF-κB-mediated inflammation. ERdj5 may not be indispensable for goblet cell function under steady-state conditions, while its deficiency induces goblet cell apoptosis under inflammatory stimuli.
Project description:A population genetic study identified that the asialoglycoprotein receptor 1 (ASGR1) mutation carriers had significantly lower non-HDL-c levels and reduced risks of cardiovascular diseases. However, the mechanism behind this phenomenon remained unclear. Here, we established Asgr1 knockout mice that represented a plasma lipid profile with significantly lower non-HDL-c and triglyceride caused by decreased secretion and increased uptake of VLDL/LDL. These two phenotypes were linked with the decreased expression of microsomal triglyceride transfer protein (MTTP) and proprotein convertase subtilisin/kexin type 9 (PCSK9), two key target genes of the sterol regulatory element-binding proteins (SREBPs). Furthermore, there were less nSREBPs on account of more SREBPs being trapped in endoplasmic reticulum, which was caused by an increased expression of insulin-induced gene 1 (INSIG1), an anchor of SREBPs. Logically, two rescue experiments were conducted in ASGR1 deficient condition. Both INSIG1 knockdown and ASGR1 rescue independently reversed the ASGR1-mutated phenotypes, restoring the SREBP signaling manifested by improved APOB secretion and reduced LDL uptake. Our observation demonstrated a novel axis of ASGR1-INSIG1-SREBPs regulating lipid hemostasis, and hypomorphic manipulation of ASGR1 leads to significant reduction of lipid content via less nSREBPs. It provides multiple potential targets, including ASGR, for lipid-lowering drug development.
Project description:Non-alcoholic fatty liver is the most common liver disease worldwide. Here, we show that the mitochondrial protein mitofusin 2 (Mfn2) protects against liver disease. Reduced Mfn2 expression was detected in liver biopsies from patients with non-alcoholic steatohepatitis (NASH). Moreover, reduced Mfn2 levels were detected in mouse models of steatosis or NASH, and its re-expression in a NASH mouse model ameliorated the disease. Liver-specific ablation of Mfn2 in mice provoked inflammation, triglyceride accumulation, fibrosis, and liver cancer. We demonstrate that Mfn2 binds phosphatidylserine (PS) and can specifically extract PS into membrane domains, favoring PS transfer to mitochondria and mitochondrial phosphatidylethanolamine (PE) synthesis. Consequently, hepatic Mfn2 deficiency reduces PS transfer and phospholipid synthesis, leading to endoplasmic reticulum (ER) stress and the development of a NASH-like phenotype and liver cancer. Ablation of Mfn2 in liver reveals that disruption of ER-mitochondrial PS transfer is a new mechanism involved in the development of liver disease.