Hepatic processing of Z variant α-1-antitrypsin alters ERAD capacity to regulate cholesterol biosynthesis in a zebrafish model

ABSTRACT: 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.

INSTRUMENT(S): Orbitrap Fusion

ORGANISM(S): Danio Rerio (zebrafish) (brachydanio Rerio)

TISSUE(S): Liver

SUBMITTER: Ralf Schittenhelm  

LAB HEAD: Phillip I Bird

PROVIDER: PXD036830 | Pride | 2023-03-10

REPOSITORIES: Pride