Dynamic Modification of Sphingomyelin in Lipid Microdomains Controls Development of Obesity, Fatty Liver, and Type 2 Diabetes

Abstract

Lipid microdomains or caveolae, small invaginations of plasma membrane, have emerged as important elements for lipid uptake and glucose homeostasis. Sphingomyelin (SM) is one of the major phospholipids of the lipid microdomains. In this study, we investigated the physiological function of sphingomyelin synthase 2 (SMS2) using SMS2 knock-out mice, and we found that SMS2 deficiency prevents high fat diet-induced obesity and insulin resistance. Interestingly, in the liver of SMS2 knock-out mice, large and mature lipid droplets were scarcely observed. Treatment with siRNA for SMS2 also decreased the large lipid droplets in HepG2 cells. Additionally, the siRNA of SMS2 decreased the accumulation of triglyceride in liver of leptin-deficient (ob/ob) mice, strongly suggesting that SMS2 is involved in lipid droplet formation. Furthermore, we found that SMS2 exists in lipid microdomains and partially associates with the fatty acid transporter CD36/FAT and with caveolin 1, a scaffolding protein of caveolae. Because CD36/FAT and caveolin 1 exist in lipid microdomains and are coordinately involved in lipid droplet formation, SMS2 is implicated in the modulation of the SM in lipid microdomains, resulting in the regulation of CD36/FAT and caveolae. Here, we established new cell lines, in which we can completely distinguish SMS2 activity from SMS1 activity, and we demonstrated that SMS2 could convert ceramide produced in the outer leaflet of the plasma membrane into SM. Our findings demonstrate the novel and dynamic regulation of lipid microdomains via conformational changes in lipids on the plasma membrane by SMS2, which is responsible for obesity and type 2 diabetes.

Ceramide kinase deficiency improves diet‐induced obesity and insulin resistance

“…CERK-/-and wild type (WT) mice were fed a high-fat diet from 4 to 15 weeks of age. In this obesity model, 14-20 weeks of diet are sufficient to cause obesity and insulin-resistance [7]. As expected, the body weights of the WT mice were significantly increased (Fig.…”

“…After first strand cDNA synthesis, real-time PCR was performed as described previously [7]. The transcript levels were normalized with hypoxanthine guanine phosphoribosyl transferase (HPRT …”

“…For diet-induced obesity (DIO), the CERK-/-mice and wild type mice (C57BL/6J) were fed a high fat diet (60% kcal from fat; 58Y1, TestDiet, Richmond, IN) from 4 to 15 weeks of age, and body weights were measured weekly. Glucose tolerance tests (GTT) were performed as described previously [7].…”

“…SDS-PAGE and Western blotting were performed according to standard methods described previously [7], using anti-CCR2 mouse IgG (Santa Cruz Biotechnology), anti-ERK (p42/44) MAP kinase rabbit IgG (Cell Signaling Technology), or anti-phosphorylated ERK (pERK) mouse IgG (Santa Cruz Biotechnology) as the primary antibody, and an anti-mouse IgG-HRP antibody (GE Healthcare), or anti-rabbit IgG-HRP antibody (GE Healthcare) as the secondary antibody. Bands were detected using a combination of an ECL plus kit (GE Healthcare) and X-ray film exposure.…”

Hepatic lipase deficiency produces glucose intolerance, inflammation and hepatic steatosis

“…In addition, NAFLD is commonly associated with MetS risk factors such as obesity, IR, hypertension and dyslipidemia. Albeit the precise mechanisms linking characteristics of the MetS and NAFLD are not completely known, a complex relationship exists between the two (Marchesini & Marzocchi 2007, Mitsutake et al 2011. In this sense, an excess of glucose and triglycerides, which are key components in the MetS, is produced by fatty liver (Anstee et al 2013, Yki-Jarvinen 2014.…”