Four-and-a-half LIM-domain protein (FHL2) affects diet induced (hepatic) steatosis and and lipid droplet formation

The four-and-a-half LIM-domain protein 2 (FHL2) is expressed in almost all tissues, including the liver, and exerts tissue- and cell context- specific functions. It acts as transcriptional cofactor and has already been shown to interact with > 50 proteins, amongst them signaling cascade proteins as well as proteins involved in the regulation of proliferation and apoptosis. Some studies revealed a role of FHL2 in liver disease and hepatocellular carcinoma, but its impact on (hepatic) lipid metabolism or non-alcoholic fatty liver disease (NAFLD) has not yet been studied.

The aim of this study was to investigate the role of FHL2 in NAFLD.

Methods and Results:

Starting 8 weeks after birth, male FHL2 wildtype (wt) and knockout (FHL2-/-) mice (littermates) were fed with a Western-type diet (WTD) containing 38% fat, 30% sucrose and 0.2% cholesterol for 19 weeks. Controls were fed with standard chow. Basal body weight did not differ between genotypes. However, WTD-induced weight gain was decreased in FHL2-/- compared to wt mice, although food-consumption and fatty-acid (FA) concentration in faeces did not differ, indicative for similar FA-uptake. Glucose tolerance was not impaired in WTD-fed FHL2-/- mice in contrast to their wt counterparts, which exhibited starting insulin resistance. Adipose tissue mass was massively increased in WTD-fed FHL2-/- mice and revealed significantly increased expression of fat-specific protein 27 (FSP27), annexin A6 (Anxa6) and genes of the perilipin family, which are all modulating lipid droplet formation and maturation as well as their lipolysis. Also in the liver, triglycerides (TG) levels were significantly decreased in FHL2-/- mice compared to wt mice, while cholesterol and bile acids (BA) levels did not differ between genotypes. Despite reduced steatosis, WTD-induced pro-inflammatory gene expression was lower in FHL2-/- mice compared to wt mice. Also in vitro, primary hepatocytes (mpH) isolated from FHL2-/- mice had lower basal TG levels compared to wt mpH. Similarly, siRNA-mediated FHL2 suppression in the human hepatoma cell line HepG2 caused reduced cellular TG levels. Interestingly, in vitro as in vivo lipid droplets appeared significantly smaller in FHL2 depleted hepatocytes, and fitting to this, revealed decreased perilipin 2 (Plin2) expression.

Conclusion:

FHL2 quantitatively and qualitatively affects (diet) induced (hepatic) steatosis. Analysis of the underlying mechanisms may lead to the identification of new prognostic markers or therapeutic targets for the development and progression of NAFLD.