Cathepsin K is a type of lysosomal cysteine protease which belongs to the papain-like cysteine peptidase family; other members include Cathepsin B, Cathepsin D and Cathepsin L etc. Physiologically, Cathepsin K functions in mediating cellular protein turnover, collagen degradation, and remodeling of the extracellular matrix, which plays an important role in pulmonary fibrosis [5,6,7,8]. Here, CTSK is linked to pulmonary fibrosis.