Cathepsin B Levels Correlate with the Severity of Canine Myositis.

Cathepsins are protease enzymes vital for normal physiological functions, such as digestion, coagulation, hormone secretion, bone resorption, apoptosis, autophagy, and both innate and adaptive immunity. Their altered expression and/or activity is associated with various pathological conditions, including inflammatory processes. In this study, we investigated the expression levels of cathepsins in muscle specimens collected from dogs affected by inflammatory myopathy (IM) of variable severity established through histopathological analysis. Samples collected from dogs affected by IM at mild, moderate, and severe stages and from healthy (control) dogs were analyzed for the expression profile of 35 proteases using a proteome profiler array. Among the other proteases, cathepsin B was upregulated to an extent depending on disease progression. By exploring the molecular mechanisms underlying the impact of cathepsin B on the disease, we found that the upregulation of cathepsin B in diseased tissues correlates with increased TGFβ-1 expression levels and elevated phosphorylation levels of the TGFβ-1 signaling mediator SMAD2/3. These results suggest that cathepsin B might be involved in the onset and progression of fibrosis commonly occurring in IM diseased dogs. Overall, our findings reveal that modulating cathepsin B activity may hold therapeutic potential for IM.