Investigation of PAC1 receptors in healthy and pathological human corneas
Introduction: PACAP is a widespread neuropeptide with diverse physiological functions. It exerts general cytoprotective effects, thus playing a role in regeneration processes. This effect has been proven in vitro and in animal experiments in vivo, for both endogenous and exogenous PACAP. PACAP occurs in the ocular tissues and it also has protective effects in the cornea: it stimulates corneal regeneration, stimulates tear secretion and in gene deficient animals increased keratinization and corneal blurring can be observed. However, no human data are known. Our aim was to investigate the PAC1 receptor, in human corneal samples and to examine its changes in corneal diseases. Methods: Human corneas removed during surgical procedures were processed for routine histological investigaton and PAC1 receptor immunohistochemistry, PCR and Western blot. The PAC1 receptor-expressing keratocytes in the corneal stroma were counted in standard areas and were compared using t-test. Results: We showed that PAC1 receptor is expressed in the basal layers of the corneal epithelium and in the endothelium in all cases. In normal corneas no or minimal staining was observed in the stroma, while in re-grafts and other inflammatory conditions, significant increases in the number of PAC1 receptor expressing stromal keratocytes were observed. Molecular biological methods confirmed the presence of the peptide and its specific receptor. Conclusion: Our results show that PAC1 receptor is expressed in the corneal epithelium and endothelium, while the receptor expression increases in inflammatory conditions in the stromal keratocytes. This suggests that the PACAP/PAC1 receptor pathway plays a significant role in regeneration processes.