Cysteine cathepsins are potent collagenases and elastases that regulate tissue maintenance and contribute to tissue degeneration. Extracellular matrix (ECM) remodeling by cathepsins is linked to a number of diseases such as cancer, osteoporosis and tendinopathy. Our lab has shown that cathepsin K (catK) and cathepsin L (catL) contribute to the tendon degradation (made mostly of collagen). However, it is still unknown how these cathepsins work together to cleave collagen. We analyzed the impact catK deficiency has on collagen cleavage by catL. We hypothesized that without catK, collagen cannot be primed for cleavage by catL. To test our hypothesis, we used a catK knockout (catK-/-) mouse model, confirming the gene deficiency with polymerase chain reaction. We homogenized Achilles tendons from catK-/- and wild type (WT) controls, then incubated the tendon ECM with catL. Finally, we compared the fragments released by catL with SDS-PAGE. Our results showed a significant decrease in the released collagen fragments from the catK-/- ECM compared to the WT ECM, confirming our hypothesis. This suggests that exposure to catK is necessary for catL-mediated collagen cleavage. This work is significant because we can better understand the proteolytic network, specifically how catK and catL work together to degrade collagen.
