Copy number variation and expression of exportin-4 associates with severity of fibrosis in metabolic associated fatty liver disease

Abstract

Background Liver fibrosis risk is a heritable trait, the outcome of which is the net deposition of extracellular matrix by hepatic stellate cell-derived myofibroblasts. Whereas nucleotide sequence variations have been extensively studied in liver fibrosis, the role of copy number variations (CNV) in which genes exist in abnormal numbers of copies (mostly due to duplication or deletion) has had limited exploration. Methods The impact of the XPO4 CNV on histological liver damage was examined in a cohort comprised 646 Caucasian patients with biopsy-proven MAFLD and 170 healthy controls. XPO4 expression was modulated and function was examined in human and animal models. Findings Here we demonstrate in a cohort of 816 subjects, 646 with biopsy-proven metabolic associated liver disease (MAFLD) and 170 controls, that duplication in the exportin 4 (XPO4) CNV is associated with the severity of liver fibrosis. Functionally, this occurs via reduced expression of hepatic XPO4 that maintains sustained activation of SMAD3/SMAD4 and promotes TGF-β1-mediated HSC activation and fibrosis. This effect was mediated through termination of nuclear SMAD3 signalling. XPO4 demonstrated preferential binding to SMAD3 compared to other SMADs and led to reduced SMAD3-mediated responses as shown by attenuation of TGFβ1 induced SMAD transcriptional activity, reductions in the recruitment of SMAD3 to target gene promoters following TGF-β1, as well as attenuation of SMAD3 phosphorylation and disturbed SMAD3/SMAD4 complex formation. Interpretation We conclude that a CNV in XPO4 is a critical mediator of fibrosis severity and can be exploited as a therapeutic target for liver fibrosis. Funding ME and JG are supported by the Robert W. Storr Bequest to the Sydney Medical Foundation, University of Sydney; a National Health and Medical Research Council of Australia (NHMRC) Program Grant (APP1053206) and Project and ideas grants (APP2001692, APP1107178 and APP1108422). AB is supported by an Australian Government Research Training Program (RTP) scholarship. EB is supported by Horizon 2020 under grant 634413 for the project EPoS.

Detangling the interrelations between MAFLD, insulin resistance, and key hormones

“…A role for variants in the interferon lambda 3/4 (IFNλ3/4), fibronectin type III domain-containing protein 5 (FNDC5), and fibroblast growth factor 21 (FGF-21) has also been described [47][48][49][50][51]. In addition, an emerging role for other types of genetic variations such as copy number variations (CNV) has been observed [52].…”

Update on genetics and epigenetics in metabolic associated fatty liver disease

“…Functional experiments showed that XPO4 CNV reduced liver expression of XPO4, resulting in hepatic stellate cells (HSC) activation and fibrosis via SMAD3/4 signaling. 92 More studies should be carried out to further illustrate the role of CNV in MAFLD.…”

“…90 Recent study revealed that FGF21 rs838133 variant was associated with elevated serum FGF21 level and increased hepatic inflammation in subjects with MAFLD. 48 92 More studies should be carried out to further illustrate the role of CNV in MAFLD.…”

Update cognition of nonalcoholic fatty liver disease/metabolism‐associated fatty liver disease

“…This supports the concept that genetic variation may play a key role in lean NAFLD patients who may have GAFLD and do not meet the MAFLD criteria. Metwally et al examined the relationship between copy number variations (CNVs) in exportin 4 (XPO4) with liver damage in MAFLD in a large cohort of patients and provided yet another proof that genetic variants may play an important role in some patients with hepatic steatosis 7 . Only a few prior studies have examined the role of CNVs in the development or progression of NAFLD, and XPO4 CNVs have only been previously examined in an Asian population.…”