Abnormal Fetuin-A levels in obese horses are associated with activated TLR4/NF-ƙB/MAPK axis and depleted FBXW7 E3 ubiquitin ligase.

Abstract

Fetuin-A (FetA) is a multifactorial glycoprotein primarily synthesized by the liver with additional expression in adipose tissue, the abundance of which is tightly regulated by the FBXW7 E3 ubiquitin ligase. Recently, FetA has been implicated in the pathogenesis of insulin resistance and associated metabolic failures in humans through its potent and selective inhibition of insulin receptor tyrosine kinase activity, however, no studies have yet directly investigated its role in the development and progression of equine obesity. In this investigation, FetA levels were measured in serum, liver, and adipose tissue derived from healthy and obese horses using quantitative PCR, ELISA and Western blotting to assess gene expression and protein levels. Immunohistochemistry was used to detect FBXW7 and FetA in liver tissue, while immunoblotting assessed insulin receptor (INSR) phosphorylation and FetA protein levels in liver and adipose tissues following FBXW7 supplementation. Obesity-affected tissues exhibited significantly elevated FetA expression at both protein and mRNA levels compared with healthy samples. Moreover, increased FetA was accompanied by activation of the TLR4/NF-ƙB axis and its downstream MAPK targets including JNK1 and p38, as well as elevated circulating pro-inflammatory cytokines IL-1β and TNF-α. Interestingly, liver FBXW7 levels inversely correlated with high FetA concentrations, and were significantly downregulated under obesity condition. The treatment of liver and adipose tissue biopsies with exogenous FBXW7 protein markedly reduced total FetA expression, which subsequently restored insulin signalling through increased INSR phosphorylation. Overall, horses affected by obesity exhibit abnormally high FetA levels and dysregulated TLR4/NF-ƙB/MAPK pathway, accompanied by suppressed FBXW7 expression, which may represent a potential therapeutic target for restoring insulin sensitivity in metabolically compromised horses.