Abstract 81: Pharmacological Inhibition of Calpain Attenuates Adipose Tissue Apoptosis, Macrophage Accumulation and Inflammation in Diet-induced Obese Mice

Abstract

Background and Objective Obesity is associated with low-grade chronic inflammation and apoptosis that contributes to development of insulin resistance and other metabolic complications. Adipose tissue macrophages have been proposed as a link between obesity and insulin resistance. However, the mechanisms underlying these processes are not defined. Calpains are calcium-dependent neutral cysteine proteases that are essential for multiple cellular functions, such as cytoskeletal remodeling and apoptotic cell death. Recent studies have demonstrated that activated calpain promotes adipocyte differentiation in vitro, and enhances macrophage recruitment during nephropathy. However, the functional role of calpain activation in adipose tissue macrophage accumulation and obesity remains to be elucidated. The purpose of this study was to define whether pharmacological inhibition of calpain influences diet-induced obesity and adipose tissue macrophage accumulation in mice. Methods and Results Male C57BL/6 mice (8 weeks old; n=10 per group) were fed either low (10% kcal) or high (60% kcal) fat diet for 12 weeks. Calpeptin, a calpain inhibitor (2.5 mg/kg/day) or vehicle (DMSO) was administered daily by osmotic mini-pumps for 12 weeks. Calpeptin administration did not influence high fat diet induced body weight and fat mass gain throughout the study. Calpain inhibition had no effect on glucose and insulin tolerance in obese mice. However, calpain inhibition highly reduced adipocyte apoptosis, adipose tissue collagen and macrophage accumulation as evident by TUNEL, Picro Sirius and CD68 immunostaining. Real-time PCR analysis showed that calpain inhibition significantly suppressed inflammatory cytokines (TNFα, IL-6, MCP-1, F4/80) expression in adipose tissue (P<0.05 vs vehicle). In addition, Oil Red O staining revealed that calpain inhibition also suppressed accumulation of hepatic fat. Conclusion Pharmacological inhibition of calpain attenuated macrophage accumulation, adipocyte apoptosis, fibrosis and inflammation in diet-induced obese mice without influencing body weight gain and insulin tolerance.