Glomerular mesangial cell migration: Response to platelet secretory products

Glomerular mesangial cells migrate in response to platelet-derived growth factor (PDGF), but to date these cells have not been examined for migratory behavior in response to other platelet secretory products. Because migration might provide an additional mode of cell redistribution and local mesangial hypercellularity in certain forms of glomerular disease, we examined, in vitro, the potential of isolated rat mesangial cells to migrate toward gradients of platelet releasate and selected platelet secretory proteins. Chemotaxis assays were performed in two compartment blind well chambers, each compartment separated by a porous membrane. Releasate of activated platelets was added in incremental concentrations (25, 50, and 100 μg/ml) to lower compartments, and mesangial cells were placed in upper compartments. The chambers were then incubated at 37°C for 4 hours. Mesangial cell migration through the membranes was quantitated by scanning electron microscopy. Mesangial cells migrated toward platelet releasate in a linear dose-response, achieving cell numbers of approximately 40 times those of controls. Examination of specific platelet alpha granule secretory proteins disclosed a potent mesangial cell migratory response to platelet-released fibronectin (Fn), but not to transforming growth factor-alpha (TGF-α), -beta (TGF-β), epidermal growth factor (EGF), or platelet factor 4 (PF4). Secretory levels of platelet Fn (1 to 25 μg/ml) induced a maximum migratory response of approximately 60-fold over controls. Mesangial cell migration in response to both platelet Fn and platelet releasate was abrogated by blocking the integrin receptor for Fn with RGDS tetrapeptide. Thus, platelet Fn appears to be a prominent component of platelet releasate responsible for mesangial cell migration.