Alveolar epithelial cells are known as progenitor cells for the restoration from the damage in the lung. Calcitonin gene-related peptide (CGRP) has been reported to play an important role in the proliferation of various types of epithelial and endothelial cells. We investigated the effects of CGRP on the proliferation of alveolar epithelial cells in vitro and in vivo.

A549 cells were cultured in Dulbecco Modified Eagle Medium with 5% fatal bovin serum for 24 hours, then CGRP was added in vitro. The proliferation of DNA synthesis was measured using 5-bromo-2-deoxyuridine, an analog of thymidine, by enzyme-linked immunosorbent assay.

As one intracellular response to CGRP, we examined activation of p44/42- extracellular signal-regulated kinase (ERK) pathway by adding CGRP, using western blotting method.

Recombinant adenovirus encoding nuclear-targeted-human β-CGRP (rhCGRP) was administered into Male Wister rat (n = 5, 10 weeks old) lungs by intratracheal instillation in vivo. 7 days after the administration of CGRP, rat lungs were harvested and histological findings and immunohistochemical staining of proliferating cell nuclear antigen (PCNA) were evaluated to examine cell proliferation.

In vitro study, CGRP increased the proliferation of A549 cells in a dose and time dependent manner. CGRP8-37 (inhibitor of CGRP receptor) decreased CGRP induced proliferation of DNA synthesis. Phosphorylation of ERK pathway was observed within 15 minutes and peaked in one hour. U0126 (inhibitor of ERK pathway) decreased CGRP induced proliferation of DNA synthesis.In vivo study, histological examination of the lung indicated proliferation of alveolar epithelial cells in the rhCGRP-treated group and the nuclei of alveolar epithelial cells were positive for PCNA immunostaining.

In this study, we conclude that CGRP stimulates proliferation of human alveolar epithelial cells in vivo and in vitro.