Potentiation of IL-4 signaling by retinoic acid in intestinal epithelial cells and macrophages - mechanisms and targets

Authors: Chen, Celine; Smith, Allen; Cheung, Lumei; Pham, Quynhchi; Urban, Joseph; Dawson, Harry

Submitted to: Frontiers in Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2020
Publication Date: 5/5/2020
Citation: Chen, C.T., Smith, A.D., Cheung, L., Pham, Q., Urban Jr, J.F., Dawson, H.D. 2020. Potentiation of IL-4 signaling by retinoic acid in intestinal epithelial cells and macrophages - mechanisms and targets. Frontiers in Immunology. 10.3389. https://doi.org/10.3389/fimmu.2020.00605.
DOI: https://doi.org/10.3389/fimmu.2020.00605

Interpretive Summary: Diet is thought to play an important role in the control of inflammation. Previously we demonstrated that the most bioactive vitamin A metabolite, all-trans retinoic acid (ATRA) potentiated the mRNA expression of several IL-4 induced chemokines (chemokine (C-C motif) ligand 11 ((CCL11), CCL17, CCL22 and CCL26) associated with alternative activation (M2a) of porcine macrophages in vitro. Alternative activations of macrophages are necessary to maintain immune homeostasis and limit inflammation. In the current series of studies, we extended these findings to porcine epithelial cells and human macrophages. We demonstrate that ATRA increases the mRNA of the interleukin 4 receptor and in 2 porcine epithelial cell lines. Signaling through the receptor was also enhanced. In human THP-1 cells, ATRA synergistically increased IL-4 –induced CCL2, CCL13, CCL26 RNA and protein levels. The mRNA, protein and enzyme activity for Transglutaminase 2, a universal marker of M2 macrophage differentiation, were synergistically induced in THP-1 cells pretreated with ATRA and then treated with IL-4. Thus, in human macrophages and in porcine macrophages, ATRA increased signaling in response to IL-4. Given the prevalence of allergic and parasitic diseases worldwide and the close similarities in the porcine and human immune responses, these findings have important implications for the nutritional regulation of allergic inflammation at mucosal surfaces.

Technical Abstract: We previously demonstrated that IL4, IL13, CLCA1 and CCL26 mRNA were significantly upregulated in the lungs of animals given a low dose of all trans-retinoic acid (ATRA) and infected with Ascaris. We also demonstrated that in vitro administered ATRA induces a state of partial alternative activation in porcine macrophages (Mfs) and amplifies certain aspects of M2a activation induced by IL-4. Given these results, we wanted to test the effect of ATRA on IL-4 responses in two porcine intestinal epithelial cell lines, IPEC1 and IPEC-J2. We observed that ATRA increased mRNA for the IL-4 receptor alpha chain. ATRA increased IL-4 induced phosphorylation of signal transducer and activator of transcription 6 (STAT6) and mRNA expression of the chloride channel, calcium activated, family member 1 (CLCA1), important for mucus formation, and chemokine (C-C motif) ligand 26 (CCL26), a potent eosinophil chemoattractant. We next wanted to extend these findings to human THP-1 cells. Herein, we extend these findings to human Mfs. In human THP-1 cells, ATRA synergistically increased IL-4–induced CCL2, CCL13 and CCL26 mRNA and protein levels. Transglutaminase 2 mRNA, protein and enzyme activity were synergistically induced in THP-1 cells pretreated with ATRA and then treated with IL-4. Thus, in porcine epithelial cells and porcine and human macrophages, ATRA increased signaling in response to IL-4. Given the prevalence of allergic and parasitic diseases worldwide and the close similarities in the porcine and human immune responses, these findings have important implications for the nutritional regulation of allergic inflammation at mucosal surfaces.