Abstract

Background Obesity, which results from a caloric intake and energy expenditure imbalance, is highly prevalent worldwide. Cathepsin S (CTSS), which is a cysteine protease, is elevated in obesity and may regulate a variety of physiological processes. This study sought to investigate the functional role of CTSS in obesity. Methods Mice were administrated 60 mg/kg of RO5444101 in vivo and fed a high-fat diet (HFD) to induce obesity. The weights of the mice fed a normal-chow diet and a HFD were measured. The expression levels of total triglycerides (TG), total cholesterol (TC), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and monocyte chemoattractant protein-1 (MCP-1) were assessed using appropriate corresponding assay kits. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used to estimate the messenger ribonucleic acid (mRNA) expression of CTSS in the serum and the release of M1- and M2-type cytokines, and western blot was used to measure the phosphorylated-nuclear factor kappaB (NF-kappaB) p65 and NF-κB p65 proteins. The mRNA and protein expressions of sterol regulatory element-binding protein 1 (SREBP1), fatty acid synthase (FASN), leptin, and adiponectin were also evaluated by RT-qPCR and western blot. Further, hematoxylin and eosin (H&E), immunohistochemical, and red oil O staining were employed to detect the pathological changes of the epididymal white adipose tissue (eWAT), the macrophage infiltration in the eWAT, and lipid accumulation, respectively. Results We found that CTSS was elevated in the plasma, visceral adipose, and liver tissues of the obese mice. After the administration of 60 mg/kg of RO5444101, the weight of the obese mice decreased, insulin resistance was inhibited, and adipocyte formation was suppressed. The CTSS inhibitor also decreased the level of macrophage infiltration in the eWAT, MCP-1 expression, and the release of M1- and M2-type cytokines in the HFD-induced mice. The CTSS inhibitor appear