Myeloid p38α signaling promotes intestinal IGF‐1 production and inflammation‐associated tumorigenesis

Abstract The protein kinase p38α plays a key role in cell homeostasis, and p38α signaling in intestinal epithelial cells protects against colitis‐induced tumorigenesis. However, little is known on the contribution of p38α signaling in intestinal stromal cells. Here, we show that myeloid cell‐specific downregulation of p38α protects mice against inflammation‐associated colon tumorigenesis. The reduced tumorigenesis correlates with impaired detection in the colon of crucial chemokines for immune cell recruitment. We identify insulin‐like growth factor‐1 (IGF‐1) as a novel mediator of the p38α pathway in macrophages. Moreover, using genetic and pharmacological approaches, we confirm the implication of IGF‐1 produced by myeloid cells in colon inflammation and tumorigenesis. We also show a correlation between IGF‐1 pathway activation and the infiltration of myeloid cells with active p38α in colon samples from patients with ulcerative colitis or colon cancer. Altogether, our results uncover an important role for myeloid IGF‐1 downstream of p38α in colitis‐associated tumorigenesis and suggest the interest in evaluating IGF‐1 therapies for inflammation‐associated intestinal diseases, taking into consideration IGF‐1 signaling and immune cell infiltration in patient biopsies.

Data information: Statistical analysis was performed by using Mann-Whitney test for the comparison of two groups or ANOVA using Bonferroni post hoc correction for multiple groups. Data are expressed as the average AE SD.
▸ Figure EV2. Mice with p38a-deficient myeloid cells show reduced DSS-induced colitis and decreased leukocyte recruitment during intestinal inflammation.
A Representative images of H&E-stained colon sections from animals either untreated or treated with DSS for 6 days and analyzed at the indicated days. Scale bars, 100 lm. B-D Representative colon sections stained for CD45 (B), MPO (C), and CD3 (D) from untreated mice or mice treated with DSS for 6 days and analyzed at day 7 (n ≥ 5).
Quantifications are shown in the histogram. Scale bars, 100 lm.

in myeloid cells reduces susceptibility to intestinal inflammation.
A Relative IGF-1 mRNA levels in peritoneal macrophages (n ≥ 8). B, C Body weight (B) and disease activity index (C) were recorded daily during DSS-induced colitis (n ≥ 31). This is a pool from three experiments, which are shown Representative images of H&E-stained sections from mice either untreated or treated with DSS for 6 days and analyzed at the indicated days. Scale bars, 100 lm E, F Representative colon sections stained for phospho-STAT3 (E) or phospho-IGF1R (F) from mice treated with DSS for 6 days and analyzed at the indicated days.
Data information: Statistical analysis was performed by using Mann-Whitney test for the comparison of two groups or ANOVA using Bonferroni post hoc correction for multiple groups. Data are expressed as the average AE SD. A Percentage of Ly6C hi and CCR2 + in bone marrow cells that were alive and CD45 + CD11b + from untreated WT and p38a-D MC mice (n = 11). B Percentage of Ly6C hi and CCR2 + in bone marrow cells that were alive and CD45 + CD11b + from untreated WT and IGF-1-D MC mice (n ≥ 5). C A mouse chemokine antibody array was interrogated using pools of whole colon extracts derived from non-stimulated mice either WT or p38a-D MC (n = 5/genotype).

EV4
Quantifications are shown in the lower panel. Arbitrary units (a.u.) are referred to the expression level of each chemokine in WT mice, which was given the value of 1. D Percentage of CD45 + CD11b + cells in the live cell population from colons of untreated WT and p38a-D MC mice (n = 8). E The indicated cell populations were sorted from the bone marrow of mice, and genomic DNA was analyzed by qPCR for the levels of floxed exon 2 versus exon 12 (as a control) of the Mapk14 gene encoding p38a (n ≥ 5). F Representative bone marrow sections stained for phospho-IGF1R from untreated mice. Scale bars, 100 lm. G Bone marrow sections from untreated mice (n ≥ 9) were stained for phospho-IGF1R. The histograms show the quantification of all cells that were stained for phospho-IGF1R + (left panel) or only cells that show moderate (2 + ) and high (3 + ) intensities (right panel).
Data information: Statistical analysis was performed by using Mann-Whitney test for the comparison of two groups or ANOVA using Bonferroni post hoc correction for multiple groups. Data are expressed as the average AE SD. Commensal microbiota lead to a situation of tightly controlled inflammation, which involves constant recruitment of monocytes from hematopoietic stem cells (HSCs) in the bone marrow to the intestine. Intestinal macrophages rely on p38a to control the expression of IGF-1 and chemokines that are important for this process. Under pathological conditions that increase intestinal inflammation, immune cell recruitment is boosted and a vicious cycle may start that leads to the development of chronic inflammation and eventually, in certain cases, to the formation of tumors. IGF-1 produced by myeloid cells may also facilitate tumorigenesis by acting directly on tumor cells.