Skeletal muscle integrin‐linked kinase contributes to adipose tissue fibrosis and adipogenesis in diet‐induced obese mice
Authors: Lark Dan , Williams Ian , Kang Li , Shakir Sumaira , Hughey Curtis , Zent Roy , Pozzi Ambra , Wasserman David 
Published: November 2023

Diet‐induced obesity (DIO) elicits a complex phenotype where insulin resistance (IR) is induced, at least in part, by tissue‐specific accumulation of lipids in metabolically active organs (e.g. skeletal muscle (SkM)). Recent efforts by a number of groups have demonstrated a causal role of extracellular matrix expansion and integrin receptor signaling in the etiology of insulin resistance, but their impact on lipid metabolism is poorly understood. We have recently demonstrated that mice lacking integrin‐linked kinase (ILK), an intracellular scaffolding protein involved in integrin signaling, specifically in SkM (mILK‐KO mice) prevents IR and fat accumulation in SkM independent of changes in body composition or energy expenditure in DIO mice. Here, we tested the hypothesis that excess lipid in DIO mILK‐KO mice preferentially accumulates in adipose tissue and liver.

Wild‐type (WT) and SkM ILK deficient (mILK‐KO) mice fed a chow or high fat (HF) diet for 16 (histology) or 27 (all other measurements) weeks were used for these studies. Mice were fasted for five hours prior to collection of plasma or tissue. Free fatty acids (FFAs), diacylglycerol (DAG), triacylglycerol (TAG) and phospholipid (PL) content was measured with gas chromatography (n=6–8/group). Adipocyte size was measured using H&E stained sections and fibrosis was assessed as percent area stained with Masson's Trichrome using unbiased ImageJ scripts (n=10–14/group). Plasma adiponectin was determined using a commercially available ELISA kit (ALPCO) (n=4–6/group). Total acetyl‐CoA carboxylase (ACC), perilipin, fatty acid synthase (FAS) and peroxisome proliferator activated receptor gamma (PPARγ) were measured via western blot (n=8/group).

Epididymal adipose fat pads were larger in DIO mILK‐KO mice than WT mice. Adipose tissue of DIO mILK‐KO mice contained more TG compared to WT mice with no differences in chow‐fed mice. No differences in TGs were observed in livers of mILK‐KO mice. Adipocyte size was greater in HF‐fed mILK‐KO mice compared to HF‐fed WT mice. Adipogenesis markers (ACC, Perilipin, FAS and PPARγ) are all decreased in adipose tissue of mILK‐KO mice compared to HF‐fed WT mice. Extracellular matrix accumulation was significantly reduced in adipose tissue of HF‐fed mILK‐KO mice compared to HF‐fed WT mice. Plasma adiponectin was elevated in HF‐fed mILK‐KO mice compared to WT mice.

Limited adipose tissue expansion is a major contributor to multiple aspects of the metabolic syndrome. In obesity, the capacity to store lipid is restricted by fibrosis that establishes a structural barrier to adipocyte expansion. Here, we demonstrate that loss of SkM ILK improves adipose tissue health by reducing fibrosis, increasing adipocyte size, decreasing expression of adipogenesis markers and enhancing TG storage. Collectively, these findings suggest that SkM ILK, through a currently undefined mechanism, is a novel contributor to adipose tissue fibrosis and may be a viable approach to treat the metabolic syndrome.

Support or Funding Information

This research was supported by NIH/NIDDK funding to DHW (DK 054902) and an American Heart Association postdoctoral fellowship to DSL (16POST29910001).