Loss of MMP-2 disrupts skeletal and craniofacial development and results in decreased bone mineralization, joint erosion and defects in osteoblast and osteoclast growth

Abstract

The 'vanishing bone' or inherited osteolysis/arthritis syndromes represent a heterogeneous group of skeletal disorders characterized by mineralization defects of affected bones and joints. Differing in anatomical distribution, severity and associated syndromic features, gene identification in each 'vanishing bone' disorder should provide unique insights into genetic/molecular pathways contributing to the overall control of skeletal growth and development. We previously described and then demonstrated that the novel autosomal recessive osteolysis/arthritis syndrome, multicentric osteolysis with arthritis (MOA) (MIM #605156), was caused by inactivating mutations in the MMP2 gene [Al Aqeel, A., Al Sewairi, W., Edress, B., Gorlin, R.J., Desnick, R.J. and Martignetti, J.A. (2000) Inherited multicentric osteolysis with arthritis: A variant resembling Torg syndrome in a Saudi family. Am. J. Med. Genet., 93, 11-18.]. These in vivo results were counterintuitive and unexpected since previous in vitro studies suggested that MMP-2 overexpression and increased activity, not deficiency, would result in the bone and joint features of MOA. The apparent lack of a murine model [Itoh, T., Ikeda, T., Gomi, H., Nakao, S., Suzuki, T. and Itohara, S. (1997) Unaltered secretion of beta-amyloid precursor protein in gelatinase A (matrix metalloproteinase 2)-deficient mice. J. Biol. Chem., 272, 22389-22392.] has hindered studies on disease pathogenesis and, more fundamentally, in addressing the paradox of how functional loss of a single proteolytic enzyme results in an apparent increase in bone loss. Here, we report that Mmp2-/- mice display attenuated features of human MOA including progressive loss of bone mineral density, articular cartilage destruction and abnormal long bone and craniofacial development. Moreover, these changes are associated with markedly and developmentally restricted decreases in osteoblast and osteoclast numbers in vivo. Mmp2-/- mice have approximately 50% fewer osteoblasts and osteoclasts than control littermates at 4 days of life but these differences have nearly resolved by 4 weeks of age. In addition, despite normal cell numbers in vivo at 8 weeks of life, Mmp2-/- bone marrow cells are unable to effectively support osteoblast and osteoclast growth and differentiation in culture. Targeted inhibition of MMP-2 using siRNA in human SaOS2 and murine MC3T3 osteoblast cell lines resulted in decreased cell proliferation rates. Taken together, our findings suggest that MMP-2 plays a direct role in early skeletal development and bone cell growth and proliferation. Thus, Mmp2-/- mice provide a valuable biological resource for studying the pathophysiological mechanisms underlying the human disease and defining the in vivo physiological role of MMP-2.

Differential effects between the loss of MMP-2 and MMP-9 on structural and tissue-level properties of bone

“…Regardless of the exact mechanism, this study confirms previous reports that germ-line deletion of MMP-2 and separately MMP-9 causes reduced BMD (11,35) and reduced bone length, (6) respectively; and it further extends these changes to differential effects on the biomechanical, architectural, and compositional properties of bone. Of course, these effects could arise from the absence of these MMPs in chondrocytes during endochondral bone formation, but the persistence of the phenotype at 16 weeks of age, when bone remodeling and modeling are active, suggests that these MMPs are important to the organization of bone matrix with sufficient quality.…”

“…(6,34) MMP-2, on the other hand, is expressed primarily by osteoblasts and plays a yet to be fully understood role in canaliculi formation. (11,35) Specifically, Mmp2 À/À bones display a . Fig.…”

“…disrupted canalicular network but with little osteocyte death, (11,35) and this phenomenon may impede the accumulation of mineral within the matrix. Thus this could explain the observed decrease in mineralization at the tissue level in Mmp2…”

Biomimetic Extracellular Matrix-Incorporated Scaffold Induces Osteogenic Gene Expression in Human Marrow Stromal Cells

“…Loss of MMP2 has been attributed to decreased mineralization and defects in the growth of osteoblasts and osteoclasts. 47 MMP2 has also been implicated as a negative regulator of chondrogeneis.…”

Targeting a Single Function of the Multifunctional Matrix Metalloprotease MT1-MMP

“…The collagen degrading properties of MT1-MMP include both a direct collagenolytic activity and the ability to activate proMMP-2, the proform of the secreted gelatinase MMP-2 (4,(7)(8)(9), but the relative importance of these activities remains elusive. Mutations in the human MMP-2 gene give rise to severe bone disorders (10) and although ablation of the gene in mice was initially reported only to result in minor growth impairments (11), detailed analyses have revealed that MMP-2-deficient mice share many of the characteristics of the human disease in an attenuated form (12,13). In mice expressing a mutated collagen, modified in the classical collagenase cleavage site, concomitant MMP-2 deficiency was shown to severely impact skeletal development (14).…”