Inhibition of IRE1α by KIRA8 restores spingosine-1-phosphate lyase activity and improves insulin sensitivity in muscle cells

Aims: Sphingosine-1-phosphate lyase (S1PL), a key enzyme in sphingolipid degradation, has been implicated in Insulin resistance and type 2 diabetes. This study aimed to determine whether inhibition of IRE1α phosphorylation by KIRA8 during ER stress could restore S1PL activity, improve Insulin signaling in C2C12 myotubes, and alleviate high-fat diet (HFD)-induced Insulin resistance in mice.

Materials and methods: C2C12 myotubes were treated with palmitate (PA) or tunicamycin to induce ER stress. Effects of KIRA8 on pAkt, pIRE1α, glucose uptake, and S1PL activity were assessed. S1PL expression was modulated via Sgpl1 overexpression. Male C57BL/6N mice were fed a normal chow diet (NCD) or HFD for 10 weeks; KIRA8 was administered intraperitoneally to HFD-fed mice. Body weight, glucose and Insulin tolerance, and histological changes in adipose tissue and liver were evaluated. pIRE1α, S1PL expression, and activity were measured in soleus muscle.

Results: PA and tunicamycin reduced Akt phosphorylation and glucose uptake, increased pIRE1α, and inhibited S1PL activity all of which were reversed by KIRA8-mediated inhibition of pIRE1α in C2C12 myotubes. Sgpl1 overexpression enhanced S1PL activity and rescued Insulin signaling. S1PL metabolites, phosphoethanolamine and hexadecenal, improved pAkt in PA-treated cells. In vivo, KIRA8 reduced body weight, adipose mass and liver size, and improved glucose metabolism. It also restored S1PL expression and activity and reduced pIRE1α in muscle.

Conclusions: IRE1α activation inhibits S1PL and impairs Insulin signaling. KIRA8 restores S1PL function and Insulin sensitivity during ER stress, identifying the IRE1α-S1PL axis as a potential therapeutic target for type 2 diabetes.

C2C12 myotubes; High-fat diet; IRE1α; Insulin signaling; KIRA8; S1PL.