AUTHOR=Zou Nanyu , Liu Ran , Li Changjun 

TITLE=Cathepsin K+ Non-Osteoclast Cells in the Skeletal System: Function, Models, Identity, and Therapeutic Implications

JOURNAL=Frontiers in Cell and Developmental Biology

VOLUME=10

YEAR=2022

URL=https://www.frontiersin.org/journals/cell-and-developmental-biology/articles/10.3389/fcell.2022.818462

DOI=10.3389/fcell.2022.818462

ISSN=2296-634X

ABSTRACT=<p>Cathepsin K (Ctsk) is a cysteine protease of the papain superfamily initially identified in differentiated osteoclasts; it plays a critical role in degrading the bone matrix. However, subsequent <italic>in vivo</italic> and <italic>in vitro</italic> studies based on animal models elucidate novel subpopulations of Ctsk-expressing cells, which display markers and properties of mesenchymal stem/progenitor cells. This review introduces the function, identity, and role of Ctsk<sup>+</sup> cells and their therapeutic implications in related preclinical osseous disorder models. It also summarizes the available <italic>in vivo</italic> models for studying Ctsk<sup>+</sup> cells and their progeny. Further investigations of detailed properties and mechanisms of Ctsk<sup>+</sup> cells in transgenic models are required to guide potential therapeutic targets in multiple diseases in the future.</p>