The novel role of macrophage migration inhibitory factor (MIF) in mediating adiposity and non-alcoholic fatty liver disease (NAFLD)

Abstract

Metabolic abnormalities characterized by obesity is linked with hepatic disease. This dissertation explored the role of cytokine, macrophage Migration Inhibitory Factor (MIF) in regulating obesity and non-alcoholic fatty liver disease (NAFLD). We have two key findings: (1) Adipose MIF regulates obesity through inhibiting hormone-sensitive lipase (HSL): Extracellular MIF downregulates HSL through binding with its cell membrane receptor, CD74 leading to activation of AMPK/JNK signaling pathway following high fat diet (HFD) feeding. Blocking this extracellular effect by either neutralizing MIF antibody or knocking down CD74 reversed the occurrence of obesity. Unexpectedly, mice with MIF global deletion also had reduced HSL activation and expression in adipose tissue. This finding led us to investigate the role of a potential distinct MIF regulatory pathway, in which intracellular MIF downregulates JNK activation by binding to the intracellular protein, Jab1/Csn5. Thus, our present data suggest that both intracellular and extracellular MIF have opposing effects to regulate HSL, but the extracellular actions predominate to downregulate HSL and exacerbate the development of obesity during HFD. (2) MIF upregulates stability of CD74 which contributes to the development of NAFLD: High MIF receptor, CD74 exacerbates the development of NAFLD. MIF has non-inflammatory effects in regulating CD74. Normally, caspase-4 promotes the degradation of CD74. Following endocytosis, MIF inhibited caspase-4 cleavage and activation. Thus, inhibition of intracellular MIF accumulation upregulated cleavage of caspase-4, leading to CD74 degradation. Our results suggest that MIF stabilizes CD74 through inhibition of caspase-4, which may be an important mechanism for regulating NAFLD in the absence of inflammation. Overall, our study elucidates the complex mechanisms by which MIF regulates obesity and NAFLD. These findings provide valuable insights into potential therapeutic avenues to address metabolic dysfunctions associated with obesity and NAFLD.