Hyon, A. | Search bioRxiv

bioRxiv2022

The inositol-requiring enzyme 1α/X-box protein 1 (IRE1α/XBP1) pathway of the unfolded protein response is impaired in pediatric cholestatic liver disease explants

Background/AimsCholestatic liver diseases (CLD) are the leading indication for pediatric liver transplantation. Increased intrahepatic bile acid concentrations cause endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) is activated to maintain homeostasis. UPR dysregulation, including the inositol-requiring enzyme 1/X-box protein 1 (IRE1/XBP1) pathway, is associated with several adult liver diseases. We evaluated hepatic UPR expression in pediatric patients with end-stage CLD and hypothesize that an inability to appropriately activate the hepatic IRE1/XBP1 pathway is associated with the pathogenesis of CLD. MethodsWe evaluated 34 human liver explants. Cohorts included: pediatric CLD (Alagille, ALGS, and progressive familial intrahepatic cholestasis, PFIC), pediatric non-cholestatic liver disease controls (autoimmune hepatitis, AIH), adult CLD, and normal controls. We performed RNA-seq, quantitative PCR, and western blotting to measure expression differences of the hepatic UPR and other signaling pathways. ResultsMetascape pathway analysis demonstrated that the KEGG protein processing in ER pathway was downregulated in pediatric CLD compared to normal controls. Pediatric CLD had decreased hepatic IRE1/XBP1 pathway gene expression and decreased protein expression of p-IRE1 compared to normal controls. These CLD changes were not disease-specific to ALGS or PFIC. IRE1/XBP1 pathway gene expression was decreased in pediatric CLD compared to AIH disease controls. ConclusionPediatric CLD explants have decreased gene and protein expression of the protective IRE1/XBP1 pathway and down-regulated KEGG protein processing in the ER pathways. IRE1/XBP1 pathway expression differences occur when compared to both normal and non-cholestatic disease controls. Attenuated expression of the IRE1/XBP1 pathway is associated with cholestatic diseases and could be targeted to treat pediatric CLD.

cell biology↗

bioRxiv2021

Liver-specific Deletion Of Small Heterodimer Partner Alters Enterohepatic Bile Acid Levels And Promotes Bile Acid-Mediated Proliferation In Male Mice.

Small heterodimer partner (Shp) regulates several metabolic processes, including bile acid levels, but lacks the conserved DNA binding domain. Phylogenetic analysis revealed conserved genetic evolution of Shp, Fxr, Cyp7a1 and Cyp27a1, underscoring the importance of these molecules in maintaining bile acid homeostasis. Shp, although primarily studied as a downstream target of Farnesoid X Receptor (Fxr), has a distinct hepatic role that is poorly understood. Here we report that liver-specific Shp knockout (LShpKO) mice have impaired negative feedback of Cyp7a1 and Cyp8b1 upon bile acid challenge and demonstrate that a single copy of the Shp gene is sufficient to maintain this response. LShpKO mice also exhibit elevated total bile acid pool with higher bile acid fraction in the intestine mimicking the 1% cholic acid (CA) fed control mice. Agonistic activation of Fxr (GW4064) in the LShpKO did not alter the elevated basal expression of Cyp8b1 but lowered Cyp7a1 expression. We found that deletion of Shp led to an enrichment of distinct motifs and pathways associated with circadian rhythm, amino and carboxylic acid metabolism, copper ion transport, and DNA synthesis. LShpKO livers displayed a higher basal proliferation that was exacerbated specifically with bile acid challenge but not with another liver mitogen, TCPOBOP (TC). Overall, our data indicate that hepatic SHP uniquely regulates certain proliferative and metabolic cues.

physiology↗