title: Immunolocalization of matrix metalloproteinase-13 on bone surface under osteoclasts in rat tibia.
abstract: Matrix metalloproteinase (MMP)-13 (an interstitial collagenase also called collagenase 3) is involved in degradation of extracellular matrix in various tissues. Using immunohistochemistry and Western blotting, we investigated localization of MMP-13 in rat tibia, to clarify the role of MMP-13 in bone resorption. MMP-13 reactivity was mainly seen on bone surfaces under osteoclasts, and in some osteocytes and their lacunae near osteoclasts. However, immunoreactivity was not seen in chondrocytes or osteoclasts. MMP-13 was also localized on cement lines in the epiphysis. In the growth plate erosion zone, perivascular cells showed MMP-13 reactivity. Immunoelectron microscopy revealed that MMP-13 was localized on the bone surfaces, under the ruffled borders and some clear zones of osteoclasts. Gold-labeled MMP-13 was closely associated with collagen fibrils. Gold labeling was also detected in Golgi apparatus of osteocytes adjacent to osteoclasts and bone lining cells. Western blotting showed that MMP-13 was mainly associated with mineralized bone matrix. These findings suggest that MMP-13 synthesized and secreted by osteoblast-lineage cells is localized under the ruffled borders of osteoclasts. MMP-13 may play an important role in degradation of type I collagen in bone matrix, acting in concert with cathepsin K and MMP-9 produced by osteoclasts. MMP-13 in perivascular cells may be involved in removal of cartilage matrix proteins such as type II collagen and aggrecan.
authors.affiliation: Department of Oral Morphology, Okayama University Graduate School of Medicine and Dentistry, Okayama, Japan. nakam@md.okayama-u.ac.jp
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Nakamura
authors.forename: Ginga
authors.initials: G
authors.lastname: Sato
authors.forename: Azumi
authors.initials: A
authors.lastname: Hirata
authors.forename: Toshio
authors.initials: T
authors.lastname: Yamamoto
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001857:Bone Matrix / Q000378:metabolism / Q000648:ultrastructure; D017364:Collagenases / Q000378:metabolism*; D007150:Immunohistochemistry; D053509:Matrix Metalloproteinase 13; D008854:Microscopy, Electron; D010010:Osteoclasts / Q000166:cytology* / Q000201:enzymology* / Q000648:ultrastructure; D010011:Osteocytes / Q000166:cytology / Q000201:enzymology / Q000648:ultrastructure; D051381:Rats; D013977:Tibia / Q000166:cytology / Q000201:enzymology* / Q000648:ultrastructure
chemical_list: D017364:Collagenases; D053509:Matrix Metalloproteinase 13; C507083:Mmp13 protein, rat