title: The cystatin M/E-cathepsin L balance is essential for tissue homeostasis in epidermis, hair follicles, and cornea.
abstract: Cystatin M/E (CST6) is a nonredundant, epithelium-specific protease inhibitor with a presumed role in epidermal differentiation and tumor suppression. We have previously reported that cystatin M/E deficiency in Cst6(-/-) mice causes neonatal lethality because of excessive transepidermal water loss. Biochemical evidence suggests that cystatin M/E controls the activity of legumain, cathepsin L, cathepsin V, and transglutaminase-3. Using a genetic approach we sought to define the role of cystatin M/E in epithelial biology by identification of its target proteases and their downstream functions. Ablation of cathepsin L in a Cst6(-/-) background (Cst6(-/-)Ctsl(-/-) double-knockout mice) restored viability and resulted in normalization of stratum corneum morphology. Ablation of legumain or transglutaminase-3 in Cst6(-/-) mice, however, did not rescue the lethal phenotype. Intriguingly, both Cst6(-/-)Ctsl(-/-) and Cst6(-/-)Ctsl(+/-) mice were viable, but the absence of cystatin M/E caused scarring alopecia in adult animals. In the cornea of Cst6(-/-)Ctsl(+/-) mice, we observed keratitis, hyperplasia, and transition to a cornified epithelium. Evidence is provided that activation of cathepsin D and transglutaminase-1 are downstream events, dependent of cathepsin L activity. We conclude that a tightly regulated balance between cathepsin L and cystatin M/E is essential for tissue integrity in epidermis, hair follicles, and corneal epithelium.
authors.affiliation: Department of Dermatology, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands. p.zeeuwen@ncmls.ru.nl
authors.forename: Patrick L J M
authors.initials: PL
authors.lastname: Zeeuwen
authors.forename: Ivonne M J J
authors.initials: IM
authors.lastname: van Vlijmen-Willems
authors.forename: Tsing
authors.initials: T
authors.lastname: Cheng
authors.forename: Diana
authors.initials: D
authors.lastname: Rodijk-Olthuis
authors.forename: Kiyotaka
authors.initials: K
authors.lastname: Hitomi
authors.forename: Ikuko
authors.initials: I
authors.lastname: Hara-Nishimura
authors.forename: Susan
authors.initials: S
authors.lastname: John
authors.forename: Neil
authors.initials: N
authors.lastname: Smyth
authors.forename: Thomas
authors.initials: T
authors.lastname: Reinheckel
authors.forename: Wiljan J A J
authors.initials: WJ
authors.lastname: Hendriks
authors.forename: Joost
authors.initials: J
authors.lastname: Schalkwijk
mesh_terms: D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D056668:Cathepsin L / Q000235:genetics / Q000378:metabolism*; D003315:Cornea / Q000378:metabolism*; D055332:Cystatin M / Q000235:genetics / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000235:genetics; D017931:DNA Primers; D004817:Epidermis / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006197:Hair / Q000378:metabolism*; D006706:Homeostasis; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016133:Polymerase Chain Reaction; D000099240:Asparaginyl Endopeptidase
chemical_list: D056668:Cathepsin L; D055332:Cystatin M; D003546:Cysteine Endopeptidases; D017931:DNA Primers; D000099240:Asparaginyl Endopeptidase; C494025:Cst6 protein, mouse; C534278:Ctsl protein, mouse