Cathepsin B

Cathepsin B (CTSB) is a thiol protease of 339 amino acids that participates in intracellular protein degradation and turnover. It also cleaves the extracellular matrix protein MEPE and has been implicated in tumor invasion and metastasis (UniProt: P07858). The protein is expressed widely across tissues and has been associated with keratolytic winter erythema, an autosomal dominant skin disorder characterized by recurrent palmoplantar erythema and seasonal variation in lesion severity.

In the context of Alzheimer's Disease, Cathepsin B is elevated in post-mortem AD brain tissue compared to age-matched controls. Proteomic analysis using TMT labeling across four subcellular fractions (P2, P3, S2, S3) detected upregulation with a mean log2 fold-change of 0.55 (Chaparral AD proteomics). This increase aligns with the known role of cathepsin B in protein homeostasis and degradation pathways, suggesting potential involvement in the proteolytic stress characteristic of AD pathology.