Hepatic processing of Z variant α-1-antitrypsin alters ERAD capacity to regulate cholesterol biosynthesis in a zebrafish model
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ABSTRACT:
PROVIDER: PRJNA891244 | ENA |
REPOSITORIES: ENA
Dataset's files
| Action | DRS | |||
|---|---|---|---|---|
| SRR21930613_1.fastq.gz | Fastqsanger.gz | |||
| SRR21930613_2.fastq.gz | Fastqsanger.gz | |||
| SRR21930614_1.fastq.gz | Fastqsanger.gz | |||
| SRR21930614_2.fastq.gz | Fastqsanger.gz | |||
| SRR21930615_1.fastq.gz | Fastqsanger.gz |
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Project description:Homozygosity for the Z allele of α1-antitrypsin (ZAAT) predisposes affected individuals to developing liver disease as the serpin misfolds and forms insoluble polymers that accumulate in the endoplasmic reticulum (ER) of hepatocytes, resulting in gain-of-function hepatotoxicity. This prevents secretion of ZAAT leading to serum insufficiency. A zebrafish model expressing human ZAAT in the liver shows no signs of hepatic accumulation despite displaying serum insufficiency, suggesting defect in ZAAT secretion occurs independently of its tendency to accumulate in hepatocytes. In this study, global transcriptomic approach was used to identify pathways activated and operating in the ZAAT-expressing zebrafish liver. The analysis provided strong evidence of suppressed Srebp2-mediated cholesterol biosynthesis. qPCR confirms this observation in the human liver cell line stably expressing ZAAT. We proposed that the engagement of misfolded ZAAT by the ER-associated degradation (ERAD) system inhibits the turnover of Srebp2-repressing elements therefore hindering the activation of Srebp2.
2023-02-15 | GSE215899 | GEO
Project description:Homozygosity for the Z allele of α1-antitrypsin (ZAAT) predisposes affected individuals to developing liver disease as the serpin misfolds and forms insoluble polymers that accumulate in the endoplasmic reticulum (ER) of hepatocytes, resulting in gain-of-function hepatotoxicity. This prevents secretion of ZAAT leading to serum insufficiency. A zebrafish model expressing human ZAAT in the liver shows no signs of hepatic accumulation despite displaying serum insufficiency, suggesting defect in ZAAT secretion occurs independently of its tendency to accumulate in hepatocytes. In this study, proteomic and transcriptomic analysis of the ZAAT-expressing zebrafish liver provided strong evidence of suppressed Srebp2-mediated cholesterol biosynthesis. qPCR confirms this observation in the human liver cell line stably expressing ZAAT. We proposed that the engagement of misfolded ZAAT by the ER-associated degradation (ERAD) system inhibits the turnover of Srebp2-repressing elements therefore hindering the activation of Srebp2. Protein quality control factors was manipulated to dissect the intracellular processing of ZAAT further mechanistically. Ablation of erlec1 resulted in a further suppression in the cholesterol biosynthesis pathway, confirming a role of this ER lectin in targeting misfolded ZAAT to ERAD. Deletion of the two ER mannosidase I homologs in zebrafish enhanced ZAAT secretion without inducing hepatic accumulation. Together, the present study provides novel insights into hepatic ZAAT processing and suggest potential therapeutic targets to improve ZAAT secretion and alleviate serum insufficiency in this form of α1-antitrypsin disease.
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Project description:Impaired secretion of an essential blood coagulation factor fibrinogen leads to hepatic fibrinogen storage disease (HFSD), characterized by the presence of fibrinogen-positive inclusion bodies and hypofibrinogenemia. However, the molecular mechanisms underlying the biogenesis of fibrinogen in the endoplasmic reticulum (ER) remains unexplored. Here we uncovered a key role of SEL1L-HRD1 complex of ER-associated degradation (ERAD) in the formation of aberrant inclusion bodies, and the biogenesis of nascent fibrinogen protein complex in hepatocytes. Serendipitously, acute or chronic deficiency of SEL1L-HRD1 ERAD, but not UPR sensor IRE1α, in the hepatocytes led to the formation of hepatocellular inclusion bodies. Proteomics studies followed by biochemical assays revealed fibrinogen, not albumin or α1-antitrypsin, as a major component of the inclusion bodies. Degradation of misfolded endogenous fibrinogen Aα, Bβ, and γ chains by SEL1L-HRD1 ERAD was required for the formation of a functional fibrinogen complex in the ER. Providing clinical relevance of these findings, SEL1L-HRD1 ERAD indeed degraded and thereby attenuated the pathogenicity of a disease-causing fibrinogen γ mutant. Together, this study demonstrates an essential role of SEL1L-HRD1 ERAD in fibrinogen biogenesis and provides novel insights into the pathogenesis of protein-misfolding diseases.
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Project description:Sel1L is an adaptor protein for the E3 ligase Hrd1 involved in endoplasmic reticulum-associated degradation (ERAD). Its physiological importance in mammalian ERAD, however, remains to be established. Here, using the inducible Sel1L knockout mouse and cell models, we provide the first in vivo evidence that Sel1L is indispensable for Hrd1 stability, ER homeostasis and survival. Acute loss of Sel1L leads to premature death in adult mice within 3 weeks with profound pancreatic atrophy. Contrary to current belief, our data show that mammalian Sel1L is required for Hrd1 stability and ERAD function both in vitro and in vivo. Sel1L deficiency disturbs ER homeostasis, activates ER stress, attenuates translation and promotes cell death. Serendipitously, using biochemical approach coupled with mass spectrometry, we found that Sel1L deficiency causes the aggregation of both small and large ribosomal subunits. Thus, Sel1L is an indispensable component of mammalian ERAD and ER homeostasis, which is essential for protein translation, pancreatic function, cellular and organismal survival. Pancreas tissue of wild type and inducible Sel1L knockout mice were subjected to gene expression analysis.
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Project description:Intricate regulatory networks govern the net balance of cholesterol biosynthesis, uptake and efflux; however, the mechanisms surrounding cholesterol homeostasis remain incompletely understood. Here, we develop an integrative genomic strategy to detect regulators of LDLR activity and identify 250 genes whose knockdown affects LDL-cholesterol uptake and whose expression is modulated by intracellular cholesterol levels in human hepatic cells. From these hits, we focus on MMAB, an enzyme which catalyzes the conversion of vitamin B12 to adenosylcobalamin, and whose expression has previously been linked to altered levels of circulating cholesterol in humans. We demonstrate that hepatic levels of MMAB are modulated by dietary and cellular cholesterol levels through SREBP2, the master transcriptional regulator of cholesterol homeostasis. Knockdown of MMAB decreases intracellular cholesterol levels and augments SREBP2-mediated gene expression and LDL-cholesterol uptake in human and mouse hepatic cell lines. Reductions in total sterol content were attributed to increased intracellular levels of propionic and methylmalonic acid and subsequent inhibition of HMGCR activity and cholesterol biosynthesis. Moreover, mice treated with antisense inhibitors of MMAB display a significant reduction in hepatic HMGCR activity and hepatic sterol content and increased expression of SREBP2-mediated genes. Collectively, these findings reveal an unexpected role for the adenosylcobalamin pathway in regulating LDLR expression and identify MMAB as an additional control point by which cholesterol biosynthesis is regulated by its end product.
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