Calcitonin gene-related peptide promotes epithelial reparative and anticolitic functions of IL-4 educated human macrophages

Abstract

Interleukin-4 activated human macrophages [M(IL4)s] promote epithelial wound healing and exert an anticolitic effect in a murine model. Blood monocyte-derived M(IL4)s from healthy donors and individuals with Crohn's disease had increased mRNA expression of the calcitonin gene-related peptide (CGRP) receptor chain, receptor activity modifying protein-1 (RAMP1), raising the issue of neural modulation of the M(IL4)s reparative function. Thus, human M(IL4)s were treated with CGRP and the cells' phagocytotic, epithelial wound repair and anticolitic functions were assessed. Initial studies confirmed upregulation of expression of the CGRP receptor, which was localized to the cell surface and was functional as determined by CGRP-evoked increases in cAMP. M(IL4,CGRP)s had increased mannose receptor (CD206) and FcγRIIa (CD32a) mRNA expression, a subtle, but significant, increase in phagocytosis and decreased chemokine production following the exposure to Escherichia coli. When delivered systemically (10⁶ cells IP) to oxazolone-treated rag1^-/- mice, M(IL4,CGRP) had an anticolitic effect superior to M(IL4)s from the same blood donor. Conditioned medium (CM) from M(IL4,CGRP) had increased amounts of transforming growth factor (TGF)-β and increased wound-healing capacity compared with matched M(IL4)-CM in the human CaCo₂ epithelial cell line in-vitro wounding assay. Moreover, M(IL4,CGRP)s displayed increased cyclooxygenase (COX)-1 and prostaglandin D₂ (PGD₂), and CM from M(IL4,CGRP)s treated with indomethacin or SC-560 to inhibit COX-1 activity failed to promote repair of wounded CaCo₂ cell monolayers. These data confirm the human M(IL4)s' anticolitic effect that was enhanced by CGRP and may be partially dependent on macrophage COX-1/PGD₂ activity. Thus, input from neurone-derived molecules is a local modifier capable of boosting the anticolitic effect of autologous M(IL4) transfer.NEW & NOTEWORTHY A novel pathway is identified whereby interleukin-4-educated human macrophages [M(IL4)s] exposed to calcitonin gene-related peptide (CGRP) reduce oxazolone-induced colitis and promote epithelial wound healing in vitro through COX1-dependent signaling. Support is provided for the concept of macrophage transfer to treat enteric inflammation where neuroimmune interaction, in this case CGRP neuropeptide, produced under inflammatory conditions will reinforce the anticolitic and wound repair capacity of M(IL4) autologous-based therapy for IBD treatment.

Keywords: CGRP; IBD; M(IL4); immunotherapy; neuroimmune interaction; wound healing.