Abstract
Matrix metalloproteinases (MMPs) are a family of zinc proteolytic enzymes important in embryonic development and pathological processes. Cardiac neural crest (CNC) cells are derived from the dorsal portion of neural tube through an epithehal-to - mesenchymal cell transition and then migrate along the basement membrane of ectoderm, enter the pharyngeal arches, and subsequently participate in the septation of the heart during embryonic development. My studies showed that one of the MMPs, MMP-2 (gelatinase A, or 72 kDa type IV collagenase), was deposited in CNC migration pathway and was expressed by CNC cells after they entered the pharyngeal arches. Furthermore, the distribution pattern of MMP-2 was disrupted by migrating CNC cells. This suggested that MMP enzymatic activity might play an important role in CNC migration. To test this hypothesis, a synthetic MMP inhibitor KB8301 was injected into the cell-free space adjacent to the premigratory CNC cells. The distance that CNC migrated in the injected side was significantly decreased compared with that in the noninjected side and in the vehicle treated embryos. Enzyme activity assays showed that the activity of MMPs decreased about 30% after KB8301 injection. This demonstrated that enzymatic activity of MMPs is an important mediator for CNC migration. The natural inhibitors of MMPs, TIMPs, were also studied. TIMP-2, which not only has the inhibitory activity against MMPs, but also participates in the activation of proMMP-2, was expressed exclusively in a subpopulation of CNC cells during their early migration. Local delivery of exogenous TIMP-2 significantly decreased CNC migratory distance as well as MMP activity in vivo. The pattern of TIMP-3 expression suggests that this inhibitor is not likely to have a role in early NC migration but could be involved in pharyngeal arch and cardiac. Overall, my studies support the hypothesis that MMP activity is an important mediator of CNC cell migration.