FNDC4 reduces hepatocyte inflammatory cell death via AMPKα in metabolic dysfunction-associated steatotic liver disease

Highlights•Hepatic FNDC4 expression is decreased in patients with MASLD.•FNDC4 gene silencing promotes hepatocyte apoptosis.•FNDC4 treatment prevents TNF-α-induced hepatocyte inflammatory cell death via AMPKα.•FNDC4 reduces hepatocyte mitochondrial damage improving mitochondrial biogenesis, dynamics and OXPHOS protein expression.SummaryBackgroundThe molecular mediators responsible for the progression of metabolic dysfunction-associated steatotic liver disease (MASLD) to steatohepatitis (MASH) have not yet been completely disentangled. We sought to analyze whether FNDC4, an hepatokine and adipokine with anti-inflammatory properties, is involved in TNF-α-induced inflammatory cell death in patients with MASLD.MethodsPlasma FNDC4 (n = 168) and hepatic FNDC4 and inflammatory cell death (n = 65) were measured in samples from patients with severe obesity with available liver biopsy-proven MASLD diagnosis. The effect of FNDC4 on TNF-α-induced pyroptosis, apoptosis and necroptosis (PANoptosis) and mitochondrial dysfunction was studied in vitro using human HepG2 hepatocytes.ResultsCompared with individuals with normal liver, patients with type 2 diabetes and MASLD exhibited decreased hepatic FNDC4 mRNA and protein levels, which were related to liver inflammation. An overexpression of TNF-α, its receptor TNF-R1 and factors involved in inflammatory cell death was also found in the liver of these patients. FNDC4-knockdown in HepG2 hepatocytes increased apoptotic cell death, while FNDC4 treatment blunted NLRP3 inflammasome-induced pyroptosis, apoptosis and necroptosis in TNF-α-stimulated hepatocytes. Moreover, FNDC4 improved TNF-α-induced hepatocyte mitochondrial dysfunction by enhancing mitochondrial DNA (mtDNA) copy number and OXPHOS complex subunits I, II, III and V protein expression. Mechanistically, AMP-activated protein kinase α (AMPKα) was required for the FNDC4-mediated inhibition of cell death and increase in mtDNA content.ConclusionsFNDC4 acts as a hepatocyte survival factor favouring mitochondrial homeostasis and decreasing inflammatory cell death via AMPKα. Collectively, our study identifies FNDC4 as an attractive target to prevent hepatocellular damage in patients with MASLD.Graphical abstract