Up-regulated expression of the phosphodiesterase nucleotide pyrophosphatase family member PC-1 is a marker and pathogenic factor for knee meniscal cartilage matrix calcification.
OBJECTIVE
Elevated cartilage inorganic pyrophosphate (PPi) production and PPi-generating nucleoside triphosphate pyrophosphohydrolase (NTPPPH) activity are strongly linked with aging-related cartilage calcification in meniscal and articular cartilages. We hypothesized that there were divergent relationships of 3 NTPPPH isozymes with cartilage matrix calcification and sought to identify them.


METHODS
We studied knee medial meniscal expression in situ of 3 NTPPPH isozymes of the phosphodiesterase nucleotide pyrophosphatase (PDNP) family: plasma cell membrane glycoprotein 1 (PC-1, or PDNP1), autotaxin (ATX, or PDNP2), and B10/PDNP3. We also used complementary DNA transfection to assess differential functions in matrix calcification of each NTPPPH isozyme in vitro in meniscal cells.


RESULTS
We observed diffuse cell-associated ATX and B10/PDNP3 expression in central (chondrocytic) and, to a lesser degree, peripheral (fibroblastic) regions of normal, degenerative uncalcified, and degenerative calcified menisci. In contrast, PC-1 expression was only robust at sites of apoptotic cells and calcification in central regions of degenerative menisci. Only PC-1 was abundant at the perimeter of meniscal cells and in association with meniscal cell-derived matrix vesicles (MVs). Because each PDNP-family isozyme was expressed by cells near calcifications, we transfected the isozymes in nonadherent knee meniscal cells cultured with ascorbic acid, beta-glycerophosphate, and dexamethasone supplementation to stimulate them to calcify the matrix. PC-1, but not ATX or B10/PDNP3, consistently promoted increased MV NTPPPH, MV-associated PPi, and extracellular PPi. PC-1 also increased matrix calcification (with hydroxyapatite crystals) by meniscal cells. ATX uniquely induced alkaline phosphatase activity, but promoted only moderately increased matrix calcification.


CONCLUSIONS
We identified divergent effects of 3 PDNP-family NTPPPH isozymes on meniscal cell matrix calcification. Increased expression of PC-1 is both a marker and a potential pathogenic factor for knee meniscal cartilage matrix calcification.
Johnson
K
K
VA Medical Center, San Diego, California 92161, USA.
Hashimoto
S
S
Lotz
M
M
Pritzker
K
K
Goding
J
J
Terkeltaub
R
R
D000375:Aging / Q000473:pathology; D015415:Biomarkers; D002114:Calcinosis / Q000378:metabolism / Q000473:pathology; D002358:Cartilage, Articular / Q000166:cytology / Q000201:enzymology / Q000473:pathology; D002478:Cells, Cultured; D002805:Chondrocalcinosis / Q000378:metabolism* / Q000473:pathology*; D005109:Extracellular Matrix / Q000201:enzymology / Q000473:pathology; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D005956:Glucose-6-Phosphate Isomerase / Q000378:metabolism; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D007719:Knee Joint / Q000473:pathology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D009097:Multienzyme Complexes; D020370:Osteoarthritis, Knee / Q000378:metabolism* / Q000473:pathology*; D010710:Phosphates / Q000378:metabolism; D043264:Phosphodiesterase I; D010727:Phosphoric Diester Hydrolases; D011755:Pyrophosphatases / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D000099189:Lysophospholipase D
D015415:Biomarkers; D016326:Extracellular Matrix Proteins; D005956:Glucose-6-Phosphate Isomerase; D006023:Glycoproteins; D007527:Isoenzymes; D008562:Membrane Glycoproteins; D009097:Multienzyme Complexes; D010710:Phosphates; D043264:Phosphodiesterase I; D010727:Phosphoric Diester Hydrolases; D011755:Pyrophosphatases; D000099189:Lysophospholipase D; C524442:Enpp3 protein, rat; C065962:ectonucleotide pyrophosphatase phosphodiesterase 1; C114607:CILP protein, human; C021895:nucleoside triphosphate pyrophosphatase