The role of Gremlin-1 in metabolic dysfunction-associated steatotic liver disease

Horn, Paul ORCID: 0000-0002-8755-7703 (2024). The role of Gremlin-1 in metabolic dysfunction-associated steatotic liver disease. University of Birmingham. Ph.D.

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Abstract

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD) is an increasing global health problem that is tightly linked to the rising prevalence of obesity and the metabolic syndrome. Hepatocellular lipid accumulation and lipotoxic injury prompt a chronic inflammatory response (metabolic dysfunction-associated steatohepatitis, MASH) that culminates with the activation of hepatic stellate cells (HSCs) and subsequent hepatic fibrogenesis. Liver fibrosis is the most prominent determinant of prognosis in patients with MASH but currently there are no treatments available that target hepatic fibrogenesis directly.
Gremlin-1 has been implicated in liver fibrosis in MASH via inhibition of bone morphogenetic protein (BMP) signalling and has thereby been identified as a potential therapeutic target. Using rat in vivo and human in vitro and ex vivo model systems of MASH fibrosis, we show that while Gremlin-1 was upregulated in human and rat MASH fibrosis, restricted to a small subpopulation of myofibroblasts, neutralisation of Gremlin- 1 activity with monoclonal therapeutic antibodies does not reduce liver inflammation or liver fibrosis. Lentiviral overexpression of Gremlin-1 in the hepatic stellate cell line LX-2 and primary HSCs led to changes in BMP-related gene expression, which did not translate into increased fibrogenesis. Furthermore, Gremlin-1 bound to heparin with high affinity, which appeared to prevent Gremlin-1 from entering the systemic circulation, prohibiting Gremlin-1-mediated organ crosstalk. Gremlin-1 also had no effect on hepatic endothelial cell activation and showed no significant expression changes in monocyte-derived macrophages.
Through an integrated analysis of bulk RNA sequencing data sets of human liver fibrosis and in vitro-activated hepatic stellate cells, we identified the activin and myostatin antagonist follistatin-like 3 (FSTL3) as strongly associated with hepatic fibrogenic responses. FSTL3 was upregulated in the HSC cell line LX-2 in response to transforming growth factor beta (TGFβ)1 and activin A, and in the hepatocyte cell line HepG2 in response to activin A. Inhibition of FSTL3 by siRNA-mediated knockdown altered fibrogenic gene expression in LX-2 cells and increased lipolytic gene expression in HepG2 cells, which translated into reduced hepatocellular lipid accumulation.
Overall, these findings suggest a redundant role for Gremlin-1 in the pathogenesis of liver fibrosis, which is unamenable to therapeutic targeting. The activin and myostatin inhibitor FSTL3 however seems to be involved in hepatic stellate cell activation and hepatocellular steatosis and warrants further investigation as a therapeutic target in liver fibrosis and MASH in particular.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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