Orthodontic tensile strain induces angiogenesis via type IV collagen degradation by matrix metalloproteinase‐12

Background and Objective During orthodontic tooth movement (OTM), periodontal ligament (PDL) is remodeled dynamically, which requires sufficient blood supply for the regeneration of PDL. However, little is known about the remodeling of blood vessels during OTM. In this study, we hypothesized that the orthodontic tensile strain upregulates matrix metalloproteinase‐12 (MMP‐12) expression in the tension zone and induces angiogenesis via degradation of type IV collagen (Col‐IV) in vascular endothelial basement membrane during the early stage of OTM. Material and Methods Temporal and spatial MMP‐12 expression in the tension zone of PDL, during the early stage of OTM, were examined by immunohistochemistry in rats. Continuous tensile strain was applied to cultured human immortalized PDL cell lines (HPL cells) and MMP‐12 expression was examined in vitro. Colocalization of MMP‐12 and Col‐IV in vivo were examined by immunohistochemistry. To investigate whether MMP‐12 produced by HPL cells could degrade Col‐IV, recombinant Col‐IV was incubated in the culture supernatants of HPL cells. Intact Col‐IV in vitro was also examined by western blot analysis. Finally, the changes in blood vessels in the PDL were examined by micro‐computed tomography analysis with perfused contrast agents and by conventional histological analysis. Results Orthodontic tensile strain induced MMP‐12 expression in PDL cells in vivo and in vitro. Immunohistochemistry revealed that MMP‐12‐positive cells were observed adjacent to the Col‐IV‐positive tubular area in the tension zone of PDL. MMP‐12 in culture supernatant of HPL cells degraded recombinant Col‐IV, and specific MMP‐12 inhibitor blocked the Col‐IV degradation. Micro‐computed tomography analysis and conventional histological analysis demonstrated that the areas of blood vessels were increased in the tension zone of the PDL after OTM. Conclusion We discovered that the orthodontic tensile strain upregulates MMP‐12 expression in the tension zone of PDL and induces angiogenesis via degradation of Col‐IV in the vascular endothelial basement membrane.