Microbiome Composition Regulates Cathepsin Expression in Vaginal Fluid Across BV Diagnoses and Community State Types

Bacterial vaginosis (BV) is associated with disruption of the vaginal microbiome and extracellular matrix (ECM) remodeling, yet the contribution of host proteases to this process remains unclear. This study investigated whether expression and activity of cathepsins K, L, S, and V differ by BV diagnosis and community state type (CST). We hypothesized that BV and BV associated CSTs would exhibit increased expression and activity of collagen and elastin-degrading cathepsins.

Vaginal fluid samples were collected and classified by BV diagnosis and CST. Cathepsin expression was evaluated by Western blotting to distinguish inactive and active enzyme forms. Proteolytic activity was assessed using multiplex cathepsin zymography. Statistical analyses compared cathepsin expression and activity across diagnoses and CSTs. Principal component analysis and linear regression were performed to assess associations between cathepsin activity, microbial diversity, and CST.

Procathepsin K expression was significantly increased in BV-positive and CST IV samples, while total cathepsin L expression was significantly elevated in samples with Nugent-intermediate scores. Cathepsins S and V showed variation in inactive and active forms in Nugent-intermediate and CST III samples. In contrast, total cathepsin activity, including cathepsins K and V, did not significantly differ across BV diagnoses or CSTs. Overall, cathepsin activity varied between individuals rather than by clinical classification.

Cathepsin expression and maturation state differ by microbiome composition, suggesting that the vaginal microbiome may regulate post-translational processing of cathepsins. As a result, cathepsin activity appears to be regulated at the individual level rather than strictly by BV diagnosis or CST. These findings link vaginal microbiome composition to ECM remodeling and potential adverse reproductive outcomes.