Abstract 2094
Pulmonary: General Lung Biology Poster Symposium, Sunday, 5/2
CGRP is a neuropeptide localized to sensory nerves and neuroendocrine cells (NEC) within the airways where it functions as both a neurotransmitter and a modulator of bronchomotor tone. Recent studies indicate that the number and volume of CGRP-containing NEC are increased during oxygen exposure, a stimulus which induces airway smooth muscle hyperplasia. Because CGRP has been shown to have mitogenic properties in tracheal epithelial cells, we hypothesized that CGRP would also stimulate proliferation of human bronchial smooth muscle cells (BSMC). Methods. BSMC were growth arrested in modified MCDB 131 + 0.5% serum for 48 hr prior to addition of recombinant human αCGRP(10-710-12M). Cells were incubated in room air + 5%CO2 for 36-48 hrs. In separate cultures, the CGRP receptor antagonist, (8-37)CGRP was added 30 min prior to CGRP. DNA synthesis was assessed every 12 hrs by [3H]thymidine incorporation. Cell counts were performed at 0,24, and 48 hrs in cells exposed to 10-7 and 10-12M CGRP. The cAMP response was tested by RIA following 10 min incubations with CGRP (10-7-10-12M) in the presence of isobutyl-methylxanthine. Trends were analyzed using ANOVA with Bonferroni multiple comparison testing. Results. We found that CGRP increased thymidine incorporation inversely to concentration (p<0.0001) with detectable differences occurring at both 12 and 24 hrs. At 24 hrs, 10-12M CGRP produced a 31% increase in DNA synthesis while 10-7M CGRP produced a 22% reduction (p<0.05). Pre-incubation with (8-37)CGRP abolished these changes in DNA synthesis. At 48 hrs, cell counts were greater in plates treated with 10-12M CGRP than in those treated with 10-7M (10-7M: 3.4×104 vs. 10-12M: 4.4×104 cells, p<0.05). CGRP stimulated cAMP production in a concentration-dependent fashion (p<0.0001), with 10-7M increasing levels 1.7-fold over baseline. Conclusions. We conclude that CGRP alters proliferation of BSMC in a concentration-dependent manner and that the effector region of the peptide is distinct from amino acids (8-37). Furthermore, the mitogenic action is unlikely to be cAMP mediated, as higher cAMP levels correlated with growth inhibition. Thus it appears that CGRP released from NEC is not only capable of altering airway smooth muscle tone, but airway smooth muscle cell proliferation as well.
