Loss of Fas apoptosis inhibitory molecule leads to spontaneous obesity and hepatosteatosis

Abstract

Altered hepatic lipogenesis is associated with metabolic diseases such as obesity and hepatosteatosis. Insulin resistance and compensatory hyperinsulinaemia are key drivers of these metabolic imbalances. Fas apoptosis inhibitory molecule (FAIM), a ubiquitously expressed antiapoptotic protein, functions as a mediator of Akt signalling. Since Akt acts at a nodal point in insulin signalling, we hypothesize that FAIM may be involved in energy metabolism. In the current study, C57BL/6 wild-type (WT) and FAIM-knockout (FAIM-KO) male mice were fed with normal chow diet and body weight changes were monitored. Energy expenditure, substrate utilization and physical activities were analysed using a metabolic cage. Liver, pancreas and adipose tissue were subjected to histological examination. Serum glucose and insulin levels and lipid profiles were determined by biochemical assays. Changes in components of the insulin signalling pathway in FAIM-KO mice were examined by immunoblots. We found that FAIM-KO mice developed spontaneous non-hyperphagic obesity accompanied by hepatosteatosis, adipocyte hypertrophy, dyslipidaemia, hyperglycaemia and hyperinsulinaemia. In FAIM-KO liver, lipogenesis was elevated as indicated by increased fatty acid synthesis and SREBP-1 and SREBP-2 activation. Notably, protein expression of insulin receptor beta was markedly reduced in insulin target organs of FAIM-KO mice. Akt phosphorylation was also lower in FAIM-KO liver and adipose tissue as compared with WT controls. In addition, phosphorylation of insulin receptor substrate-1 and Akt2 in response to insulin treatment in isolated FAIM-KO hepatocytes was also markedly attenuated. Altogether, our data indicate that FAIM is a novel regulator of insulin signalling and plays an essential role in energy homoeostasis. These findings may shed light on the pathogenesis of obesity and hepatosteatosis.

Fas apoptosis inhibitory molecules: more than death‐receptor antagonists in the nervous system

“…Regarding the absence of FAIM‐S and FAIM‐L in nervous system, mice did not show any obvious neuronal phenotype, although it was not specifically analyzed (Huo et al . ).…”

“…A recently published study by the same group reported that FAIM-KO mice developed spontaneous non-hyperphagic obesity, an increased fatty acid synthesis in liver, and reduced insulin receptor beta, suggesting the involvement of FAIM-S in energy homeostasis and insulin signaling. Regarding the absence of FAIM-S and FAIM-L in nervous system, mice did not show any obvious neuronal phenotype, although it was not specifically analyzed (Huo et al 2016).…”

FAIM Is a Non-redundant Defender of Cellular Viability in the Face of Heat and Oxidative Stress and Interferes With Accumulation of Stress-Induced Protein Aggregates

“…These mice were normal with respect to development, survival, and phenotype. They were not obese and thus differed from the FAIM KO mice constructed by Huo et al (2009Huo et al ( , 2016. We examined skin-derived fibroblasts which have been shown to be susceptible to menadione- (Shalini et al, 2012) and arsenite- (Harada et al, 2008;Kim et al, 2015) induced oxidative stress.…”

Inclusion of endophenotypes in a standard GWAS facilitate a detailed mechanistic understanding of genetic elements that control blood lipid levels

“…The two genes are not obvious candidate genes for phytosterol levels but they are involved in lipid metabolism. FAIM deficiency enhances SREBP signaling and promotes lipogenesis in liver 34 . FOXL2 represses expression of Star, a protein that controls cholesterol transport from the outer to the inner mitochondrial membranes 35 , 36 .…”