Linked deficiencies in extracellular PP(i) and osteopontin mediate pathologic calcification associated with defective PC-1 and ANK expression.
Osteopontin and PP(i) both suppress hydroxyapatite deposition. Extracellular PP(i) deficiency causes spontaneous hypercalcification, yet unchallenged osteopontin knockout mice have only subtle mineralization abnormalities. We report that extracellular PP(i) deficiency promotes osteopontin deficiency and correction of osteopontin deficiency prevents hypercalcification, suggesting synergistic inhibition of hydroxyapatite deposition. Nucleotide pyrophosphatase phosphodiesterase (NPP) isozymes including PC-1 (NPP1) function partly to generate PP(i), a physiologic calcification inhibitor. PP(i) transport is modulated by the membrane channel protein ANK. Spontaneous articular cartilage calcification, increased vertebral cortical bone formation, and peripheral joint and intervertebral ossific ankylosis are associated with both PC-1 deficiency and expression of truncated ANK in ank/ank mice. To assess how PC-1, ANK, and PP(i) regulate both calcification and cell differentiation, we studied cultured PC-1 -/- and ank/ank mouse calvarial osteoblasts. PC-1 -/- osteoblasts demonstrated approximately 50% depressed NPP activity and markedly lowered extracellular PP(i) associated with hypercalcification. These abnormalities were rescued by transfection of PC-1 but not of the NPP isozyme B10/NPP3. PC-1 -/- and ank/ank cultured osteoblasts demonstrated not only comparable extracellular PP(i) depression and hypercalcification but also marked reduction in expression of osteopontin (OPN), another direct calcification inhibitor. Soluble PC-1 (which corrected extracellular PP(i) and OPN), and OPN itself (> or = 15 pg/ml), corrected hypercalcification by PC-1 -/- and ank/ank osteoblasts. Thus, linked regulatory effects on extracellular PP(i) and OPN expression mediate the ability of PC-1 and ANK to regulate calcification.
Johnson
Kristen
K
Veterans Affairs Medical Center, University of California-San Diego, La Jolla, California 92161, USA.
Goding
James
J
Van Etten
Deborah
D
Sali
Adnan
A
Hu
Shou-Ih
SI
Farley
David
D
Krug
Hollis
H
Hessle
Lovisa
L
Millán
José Luis
JL
Terkeltaub
Robert
R
D000469:Alkaline Phosphatase / Q000032:analysis; D000818:Animals; D001483:Base Sequence; D001842:Bone and Bones / Q000166:cytology; D002113:Calcification, Physiologic; D002114:Calcinosis; D017931:DNA Primers; D018076:DNA, Complementary; D011756:Diphosphates / Q000378:metabolism*; D045604:Extracellular Fluid / Q000502:physiology; D008565:Membrane Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D010006:Osteoblasts / Q000502:physiology; D053495:Osteopontin; D028061:Phosphate Transport Proteins; D010727:Phosphoric Diester Hydrolases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D011755:Pyrophosphatases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012795:Sialoglycoproteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*
D017931:DNA Primers; D018076:DNA, Complementary; D011756:Diphosphates; D008565:Membrane Proteins; D028061:Phosphate Transport Proteins; D011994:Recombinant Proteins; D012795:Sialoglycoproteins; C506896:Spp1 protein, mouse; C410982:ank protein, mouse; D053495:Osteopontin; D000469:Alkaline Phosphatase; D010727:Phosphoric Diester Hydrolases; C065962:ectonucleotide pyrophosphatase phosphodiesterase 1; D011755:Pyrophosphatases