The role of substance P in the pathogenesis of pterygia

PURPOSE. Pterygium is a prevalent ocular surface disorder thought to be triggered by chronic ultraviolet damage to the limbus. One of the enigmatic features of pterygium is its wing-like shape, and the mechanism(s) supporting its centripetal growth remain to be elucidated. Because the growth pattern of pterygia mirrors the radial arrangement of corneal nerves, the authors propose that neuropeptides may facilitate its directional growth. This hypothesis prompted an investigation of the role of the sensory neuropeptide substance P (SP) and its receptor (NK1 receptor) in directing cell migration in pterygia that may explain the characteristic growth pattern. METHODS. Immunohistochemical analysis for SP and the NK1 receptor was performed on five pterygium specimens with corresponding autologous conjunctiva and limbus. Migration of pterygium epithelium, fibroblasts, and vascular endothelial cells toward SP was assessed by using a modified Boyden chamber. RESULTS. SP and NK1 receptors were localized to infiltrating fibroblasts, mononuclear cells and the epithelia of pterygium, conjunctiva, and limbus, with elevated NK1 receptor staining observed in pterygia. SP at nanomolar concentrations induced cell migration in pterygium fibroblasts and vascular endothelium in a dose-dependent fashion, which was inhibited by an NK1 receptor antagonist. Pterygium epithelial cells were not migratory in these experiments. CONCLUSIONS. For the first time, this study showed the presence of NK1 receptor in pterygia and that SP is a potent chemoattractant for pterygium fibroblasts and vascular endothelial cells, implying that SP may contribute to the shape of pterygia through its profibrogenic and angiogenic action.