title: Phosphatase actions at the site of appositional mineralization in bisphosphonate-affected bones of the rat.
abstract: Tissue-nonspecific alkaline phosphatase (TNSALP) and Ca-ATPase are known to play roles in bone mineralization, but how these enzymes contribute to appositional mineralization has been illusive. Here we examined the active sites of these enzymes in appositional mineralization using the bones of young rats being administered with 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) for 5 days. The doses of HEBP totally abolished mineralization of newly formed bone matrix except in matrix vesicles (MVs), and hence allowed precise localization of MVs and phosphatase reactions within non-mineralized extracellular matrix. Intense TNSALP and ATPase reactions were confirmed along the limited portions of osteoblast membranes where intimate cell-cell contacts were maintained. Diffuse reactions of these enzymes were throughout the osteoid implicating efflux of TNSALP and ATPase molecules into extracellular matrix from the osteoblast membranes. Phosphatase reactions associated with MVs varied both in intensity and location among the individual vesicles; newly formed MVs were almost free of reactions but appeared to gain those activities later in the osteoid. These data suggest that TNSALP and ATPase are released from the osteoblast membrane and later integrated into MVs within the osteoid. The osteoblasts may thus regulate appositional mineralization of bone from a distance at least in part by providing phosphatases via MVs.
authors.affiliation: Section of Biostructural Science, Department of Hard Tissue Engineering, Division of Bio-Matrix, Tokyo Medical and Dental University Graduate School, Tokyo, Japan.
authors.forename: Yi
authors.initials: Y
authors.lastname: Li
authors.forename: Hiroto
authors.initials: H
authors.lastname: Nakayama
authors.forename: Takuya
authors.initials: T
authors.lastname: Notani
authors.forename: Masud
authors.initials: M
authors.lastname: Ahmad
authors.forename: Makoto J
authors.initials: MJ
authors.lastname: Tabata
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Takano
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D050071:Bone Density Conservation Agents / Q000494:pharmacology*; D001857:Bone Matrix / Q000201:enzymology / Q000648:ultrastructure; D002113:Calcification, Physiologic / Q000187:drug effects / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000378:metabolism* / Q000648:ultrastructure; D002450:Cell Communication / Q000187:drug effects; D002462:Cell Membrane / Q000201:enzymology / Q000648:ultrastructure; D022162:Cytoplasmic Vesicles / Q000201:enzymology / Q000648:ultrastructure; D012968:Etidronic Acid / Q000494:pharmacology*; D005109:Extracellular Matrix / Q000201:enzymology / Q000648:ultrastructure; D005260:Female; D006056:Golgi Apparatus / Q000201:enzymology / Q000648:ultrastructure; D006651:Histocytochemistry; D008247:Lysosomes / Q000201:enzymology / Q000648:ultrastructure; D010006:Osteoblasts / Q000201:enzymology / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar
chemical_list: D050071:Bone Density Conservation Agents; D000469:Alkaline Phosphatase; D000252:Calcium-Transporting ATPases; D012968:Etidronic Acid