Effect of sleeve gastrectomy on the expression of meteorin-like (METRNL) and Irisin (FNDC5) in muscle and brown adipose tissue and its impact on uncoupling proteins in diet-induced obesity rats.

BACKGROUND

Bariatric surgery is well established as a treatment for obesity and associated complications. This procedure improves metabolic homeostasis through changes in energy expenditure. We hypothesized that sleeve gastrectomy (SG) improves metabolic homeostasis by modulating energy expenditure and enhancing thermogenesis through increasing the expression level of meteorin-like protein (METRNL) and fibronectin type III domain-containing protein 5 (FNDC5/Irisin) through uncoupling proteins 1/2/3 (UCP1, UCP2, and UCP3).

OBJECTIVES

To study the effect of SG on the levels of proteins involved in thermogenesis process.

SETTING

Laboratory rats at Kuwait University.

METHODS

Male Sprague-Dawley rats, aged 4 to 5 weeks, were divided into 2 groups, control (n = 11) and diet-induced obesity (DIO) (n = 22). The control group was fed regular rat chow ad libitum, whereas the DIO group was fed cafeteria diet "high-fat/carbohydrate diet" ad libitum. At 21 weeks, rats in the DIO group that weighed 20% more than the control group animals underwent surgery. These rats were randomly subdivided into Sham and SG operation groups. Gene expression was evaluated, and enzyme-linked immunosorbent assays were employed to assess the changes in gene and protein levels in tissue and circulation.

RESULTS

The protein expression data revealed an increase in METRNL levels in the muscles and white adipose tissue of SG animals. METRNL level in circulation in SG animals was reduced compared with control and Sham rats. The level of Irisin increased in the muscle of SG animals compared with the control and Sham group animals; however, a decrease in Irisin level was observed in the white adipose tissue and brown adipose tissue of SG animals compared with controls. Gene expression analysis revealed decreased METRNL levels in muscle tissues in the SG group compared with the control group animals. Increased expression of FNDC5 (Irisin), UCP2, and UCP3 in the muscle tissue of SG animals was also observed. Furthermore, the levels of UCP1, UCP2, UCP3, and METRNL in the brown adipose tissue of SG animals were upregulated. No significant alteration in the gene expression of Irisin was observed in brown adipose tissue.

CONCLUSIONS

Sleeve gastrectomy induces weight loss through complex mechanisms that may include browning of fat.