title: Increased cathepsin D release by Hyp mouse osteoblast cells.
abstract: The X-linked hypophosphatemia (XLH), the most common form of hereditary rickets, is caused by loss-of-function mutations of PHEX (phosphate-regulating gene with homology to endopeptidases on the X chromosome) leading to rachitic bone disease and hypophosphatemia. Available evidence today indicates that the bone defect in XLH is caused not only by hypophosphatemia and altered vitamin D metabolism but also by factor(s) locally released by osteoblast cells (ObCs). The identity of these ObC-derived pathogenic factors remains unclear. In our present study, we report our finding of a prominent protein in the culture media derived from ObC of the hypophosphatemic (Hyp) mice, a murine homolog of human XLH, which was identified as the murine procathepsin D (Cat D). By metabolic labeling studies, we further confirmed that Hyp mouse ObCs released greater amount of Cat D into culture media. This increased Cat D release by Hyp mouse ObCs was unlikely to be due to nonspecific cell damage or heterogeneous cell population and was found to be associated with an increased Cat D expression at the protein level, possibly due to a reduced Cat D degradation. However, we were not able to detect a direct effect of PHEX protein on Cat D cleavage. In support of the involvement of Cat D in mediating the inhibitory effect of Hyp mouse ObC-conditioned media on ObC calcification, we found that exposure to Cat D inhibited ObC (45)Ca incorporation and that inhibition of Cat D abolished the inhibitory effect of Hyp mouse-conditioned media on ObC calcification. In conclusion, results from our present study showed that Hyp mouse ObCs release a greater amount of Cat D, which may contribute to the inhibitory effect of Hyp mouse ObC-conditioned media on ObC mineralization.
authors.affiliation: Medical and Research Services, Greater Los Angeles Veterans Affairs Healthcare System at Sepulveda, CA, USA.
authors.forename: Naoko
authors.initials: N
authors.lastname: Matsumoto
authors.forename: Oak D
authors.initials: OD
authors.lastname: Jo
authors.forename: Remi N J
authors.initials: RN
authors.lastname: Shih
authors.forename: Elsa J
authors.initials: EJ
authors.lastname: Brochmann
authors.forename: Samuel S
authors.initials: SS
authors.lastname: Murray
authors.forename: Victor
authors.initials: V
authors.lastname: Hong
authors.forename: Jane
authors.initials: J
authors.lastname: Yanagawa
authors.forename: Norimoto
authors.initials: N
authors.lastname: Yanagawa
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002402:Cathepsin D / Q000378:metabolism*; D002460:Cell Line; D017674:Hypophosphatemia / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D053402:PHEX Phosphate Regulating Neutral Endopeptidase; D011506:Proteins / Q000494:pharmacology
chemical_list: D011506:Proteins; D002402:Cathepsin D; D053402:PHEX Phosphate Regulating Neutral Endopeptidase; C506231:PHEX protein, human; C506232:Phex protein, mouse; D002118:Calcium