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Determination of Bone Markers in Pycnodysostosis: Effects of Cathepsin K Deficiency on Bone Matrix Degradation
Author(s) -
Nishi Yoshikazu,
Atley Lynn,
Eyre David E.,
Edelson Jacob G.,
SupertiFurga Andrea,
Yasuda Toshiyuki,
Desnick Robert J.,
Gelb Bruce D.
Publication year - 1999
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1359/jbmr.1999.14.11.1902
Subject(s) - cathepsin k , n terminal telopeptide , bone resorption , osteoclast , bone remodeling , cathepsin , type i collagen , chemistry , endocrinology , medicine , microbiology and biotechnology , osteocalcin , biology , biochemistry , alkaline phosphatase , enzyme , in vitro
Pycnodysostosis (Pycno) is an autosomal recessive osteosclerotic skeletal dysplasia that is caused by the markedly deficient activity of cathepsin K. This lysosomal cysteine protease has substantial collagenase activity, is present at high levels in osteoclasts, and is secreted into the subosteoclastic space where bone matrix is degraded. In vitro studies revealed that mutant cathepsin K proteins causing Pycno did not degrade type I collagen, the protein that constitutes 95% of organic bone matrix. To determine the in vivo effects of cathepsin K mutations on bone metabolism in general and osteoclast‐mediated bone resorption specifically, several bone metabolism markers were assayed in serum and urine from seven Pycno patients. Two markers of bone synthesis, type I collagen carboxy‐terminal propeptide and osteocalcin, were normal in all Pycno patients. Tartrate‐resistent acid phosphatase, an osteoclast marker, was also normal in these patients. Two markers that detect type I collagen telopeptide cross‐links from the N and C termini, NTX and CTX, respectively, were low in Pycno. A third marker which detects a more proximal portion of the C terminus of type I collagen in serum, ICTP, was elevated in Pycno, a seemingly paradoxical result. The finding of decreased osteoclast‐mediated type I collagen degradation as well as the use of alternative collagen cleavage sites by other proteases, and the accumulation of larger C‐terminal fragments containing the ICTP epitope, established a unique biochemical phenotype for Pycno.