Cathepsinek

Cathepsinek is the Polish term for cathepsins, a family of proteolytic enzymes that function primarily as lysosomal proteases in many animal cells. The cathepsin family includes cysteine proteases such as cathepsins B, L, S, K, C and F; as well as aspartic proteases such as cathepsins D and E; and a serine protease, cathepsin G, along with exopeptidase activities like those of cathepsin A. These enzymes are typically active in the acidic environment of lysosomes but can also be found in the extracellular space under certain physiological and pathological conditions.

In physiology, cathepsinek participate in intracellular protein turnover and autophagy, helping cells recycle proteins and maintain homeostasis. They also contribute to antigen processing, where proteolysis of proteins in antigen-presenting cells generates peptides for presentation by MHC class II molecules to the immune system. Beyond degradation, several cathepsins remodel the extracellular matrix and influence processes such as inflammation, wound healing, and bone remodeling; for example, cathepsin K is notable for its activity in bone and cartilage tissue.

Regulation of cathepsinek occurs at multiple levels, including gene expression, synthesis as inactive zymogens, and trafficking to lysosomes where the low pH supports enzymatic activity. Inhibitors, both endogenous and synthetic, help modulate their activity; E-64 is a commonly used experimental inhibitor of cysteine cathepsins. Clinically, cathepsinek have attracted attention as potential therapeutic targets in cancer, osteoporosis, neurodegenerative diseases, and inflammatory conditions, with cathepsin inhibitors studied in clinical trials; some, such as cathepsin K inhibitors, have faced development challenges and limited success. In research, cathepsinek serve as tools to study lysosomal function, protein turnover, and antigen processing.