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  • Title: Association of collagenase and tissue inhibitor of metalloproteinases (TIMP) with hypertrophic cell enlargement in the growth plate.
    Author: Dean DD, Muniz OE, Howell DS.
    Journal: Matrix; 1989 Nov; 9(5):366-75. PubMed ID: 2559303.
    Abstract:
    In the transition from proliferating to hypertrophic cell zones in the growth plate, there is an increased in chondrocyte cell volume and a corresponding decrease in collagen content to allow for cell enlargement. To substantiate our hypothesis that collagenase is responsible for these changes, growth plates from rats treated with bisphosphonate (HEBP) were compared histologically and biochemically with growth plates from normal and vitamin D and phosphate deficient (-VDP) rats. HEBP-treated rats developed an expanded hypertrophic cell zone (HCZ) characterized by the presence of two distinct populations of hypertrophic cells. The proximal hypertrophic cells were only 2-fold enlarged compared to the proliferating cells, whereas 1/6 of the distal hypertrophic cells were enlarged almost 5-fold and appeared morphologically identical with hypertrophic cells from normal and -VDP rats. The HEBP growth plates were divided into cross-sectional thirds and analyzed for active and latent collagenase. The juxta-metaphyseal (lower 1/3) cartilage contained 100% of the fully enlarged hypertrophic cells and appeared identical to those found in normal and -VDP growth plates, along with 81% of the active and 77% of the total collagenase. Collagenase and tissue inhibitor of metalloproteinases (TIMP) were measured in extracts of similarly divided tissues. The presence of true collagenas was confirmed by using [3H]-telopeptide-free collagen. TIMP levels were inversely related to the presence of active collagenase and cellular hypertrophy. Substantial levels of latent collagenase were found in the extracellular fluid at sites of active collagenolysis, but not in the fluid phase surrounding the 2-fold enlarged hypertrophic cells. It is postulated that increased amounts of active collagenase and insufficient levels of TIMP may account for the reduced collagen content seen in the lower HCZ of both -VDP and HEBP rickets. Unlike active collagenase, which remains localized by binding to collagen, latent enzyme is probably restricted in its mobility throughout the extracellular space by diffusion, itself, or the interstices of the extracellular matrix.
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