Calcitonin gene-related peptide inhibits interleukin-1 beta -induced interleukin-8 secretion in human type II alveolar epithelial cells

Aim: Our previous data have shown that type II alveolar epithelial (AEII) cells express neuropeptide calcitonin gene-related peptide (CGRP), and that pro-inflammatory factor interleukin1- beta (IL-1 beta ) induces CGRP secretion in the A549 human AEII cell line. In the present study, we investigated the effect of endogenous and exogenous CGRP on IL-1 beta -induced chemokine interleukin-8 (IL-8) secretion. Methods: We used enzyme-linked immunosorbent assay (ELISA) and RT-PCRto detect IL-8 protein and mRNA levels, respectively. siRNA and the stably trans-fected cell line were used to knock down and overexpress the CGRP gene, respectively, and chemiluminescence assay was used to detect reactive oxygen species (ROS) formation. Results: CGRP-1 receptor antagonist hCGRP sub(8-37) (0.1-1 nmol-L super(-1)) greatly amplified IL-1 beta -induced IL-8 production. The inhibition of CGRP expression by siRNA significantly increased IL-8 secretion upon IL-1 beta stimulation. However, cell clones stably transfected with CGRP showed significantly inhibited mRNAandproteinlevelsofIL-8 inducedbyIL-1 beta . Conclusion: These data imply that AEII cell-derived CGRP suppress IL-1 beta -induced IL-8 secretion in an autocrine-paracrine mode. Further investigation showed that CGRP attenuated IL-1 beta -aroused ROS formation, which is an early indication of pro-inflammatory factor signaling.