MCPIP1 Regulates Atf3-Ap1s2 Pathway to Limit Mucosal Inflammation

Inflammatory bowel disease (IBD) is a chronic non-specific inflammatory disease that occurs in the gastrointestinal tract and is characterized by recurrent episodes. Its causes and mechanisms remain unclear and may be related to abnormalities in both innate and acquired immune responses within the mucosal tissue, damage to the intestinal mucosal barrier, genetic susceptibility, imbalance of gut microbiota, and external environmental factors. In the inflammatory intestinal mucosa, a large number of activated immune cells infiltrate, and clinical attention is increasingly focused on targeted biological immunotherapy for the abnormal activation of various immune cells and pro-inflammatory cytokines within the IBD inflammatory intestinal mucosa. However, the immune response mechanisms of monocyte-macrophages in the development of IBD are still unclear. Therefore, in-depth research on the functions and immune regulatory mechanisms of monocyte-macrophages in the occurrence of IBD has become a hot topic in the global IBD research field.
Recently, Professor Liu Zhanju’s team from Tongji University published a research paper titled MCPIP1 restrains mucosal inflammation by orchestrating the intestinal monocyte to macrophage maturation via an ATF3-AP1S2 axis in the journal Gut.This paper focuses on how the MCPIP1 molecule regulates the Atf3-Ap1s2 signaling pathway to control the maturation of monocyte-macrophages in the intestinal mucosal innate layer, thereby limiting intestinal mucosal inflammation.
MCPIP1 Regulates Atf3-Ap1s2 Pathway to Limit Mucosal Inflammation
Macrophages primarily originate from the yolk sac, fetal liver, and hematopoietic stem cells. Under physiological conditions, monocytes in peripheral blood express high levels of CCR2 and are chemotactically recruited into tissues or lymph nodes by MCP-1 (CCL2), undergoing a traditional differentiation process (i.e., stages P1, P2, P3, P4) to mature into macrophages and colonize the intestines, thereby regulating intestinal mucosal immune homeostasis. Among these, macrophages that mature mainly in stages P3 and P4 exert anti-inflammatory and bactericidal effects. When intestinal inflammation occurs, the differentiation of monocytes into macrophages is hindered, remaining in the immature stages P1/P2 and producing a large number of pro-inflammatory cytokines (such as IL-1β, IL-6, TNF-α) and chemokines (such as CCL2, CCL3, CCL4) that participate in the inflammatory amplification response. The study also found that mature macrophages exhibit high plasticity and heterogeneity, polarizing towards pro-inflammatory (M1 type) or anti-inflammatory (M2 type) directions under different induction conditions, thus performing different biological functions. Therefore, studying the maturation process of monocytes into macrophages within tissues and the polarization states of mature macrophages, as well as exploring potential promoting or hindering factors, is of great significance for the research on immune regulation and mechanisms in IBD.
First, the authors found that MCPIP1 myeloid cell-specific knockout (Mcpip1∆Mye) mice developed spontaneous inflammation in multiple organs, primarily manifested in the gastrointestinal system as damage to the integrity of the intestinal epithelial barrier, massive infiltration of immune cells in the intestinal mucosa, and increased migratory capacity of myeloid cells to the intestinal mucosa. These mice originated from the laboratory of Professor Pappachan E Kolattukudy and Professor Niu Jianzhi at the Burnett Biomedical Sciences Institute, University of Central Florida. By constructing a mouse model of acute colitis using DSS/TNBS, the authors found that the Mcpip1∆Mye mice exhibited more severe colitis, characterized by destruction of the intestinal mucosal epithelial structure, increased infiltration of myeloid cells, especially monocyte-macrophages, and a blockage in the maturation process of monocytes migrating from peripheral blood to macrophages (increased proportion of P1 cells and decreased proportion of P3/P4 cells), along with elevated pro-inflammatory cytokines.
To further clarify the subpopulations of CD11b+ myeloid cells in the intestinal mucosal innate layer, the authors isolated CD11b+ cells from the intestinal mucosal innate layer of DSS-model Mcpip1∆Mye mice and their control group, and through single-cell sequencing analysis, found that monocyte-macrophages could be further divided into five groups. Based on the characteristics of each cell group, it was discovered that in the intestinal mucosa of Mcpip1∆Mye mice, two groups belonged to the P1 cell group, two groups belonged to the P2 cell group, and one group belonged to the P3/P4 cell group, which showed a decreased proportion. Additionally, the authors also found through single-cell sequencing that the Ccr2+Il-1β+Tlr2+Cx3cr1Cd163Mrc1Ly6c+ cell group exhibited clear pro-inflammatory characteristics, which may be an important reason for the exacerbation of inflammation in Mcpip1∆Mye mice.
Subsequently, the authors compared RNA sequencing and single-cell sequencing data, along with RIP-seq data analysis, and found that the specific knockout of MCPIP1 in macrophages could lead to increased expression levels of molecules such as Atf3 and Ap1s2. Luciferase assays, CUT&TAG assays, and Western blot assays indicated that the Atf3 protein could promote the expression level of Ap1s2 by binding to the promoter region of the Ap1s2 molecule, and this signaling pathway was inhibited by MCPIP1. By inhibiting the expression of Atf3 and Ap1s2 in BMDMs in vitro, the authors found that the polarization of macrophages towards M2 increased and their migratory capacity decreased; by inhibiting the expression of Ap1s2 in vivo, it was found that the colitis in Mcpip1∆Mye mice was relatively alleviated, as evidenced by a decrease in myeloid cell infiltration and an improvement in the previously hindered maturation state of monocytes into macrophages (decreased proportion of P1 cells and increased proportion of P3/P4 cells).
Furthermore, the authors collected peripheral blood CD14+ cells and intestinal mucosa from IBD patients and healthy contributors, and through PCR detection and immunofluorescence staining experiments, found that the expression level of MCPIP1 was increased in patients, which may indicate that this molecule is in an adaptive increase state within the patients and has a negative feedback regulation on itself. In vitro, when CD14+ cells were cultured into macrophages and the expression of Atf3 and Ap1s2 was inhibited, it was similarly found that the polarization of macrophages towards M2 increased, suggesting that inhibiting the Atf3-Ap1s2 signaling pathway plays a role in suppressing the progression of inflammation and promoting immune homeostasis regulation.
In conclusion, this work emphasizes the important role of macrophages in intestinal mucosal immunity and innovatively proposes that MCPIP1 can exert an anti-inflammatory effect by downregulating the Atf3-Ap1s2 signaling pathway. This study reveals the potential of Ap1s2 as a molecular target and provides new ideas for the clinical diagnosis and treatment of IBD.
MCPIP1 Regulates Atf3-Ap1s2 Pathway to Limit Mucosal Inflammation
Professor Liu Zhanju from Tongji University and Shanghai Tenth People’s Hospital is the corresponding author of this paper. Dr. Lü Huiying, Dr. Zhang Cui, and Dr. Wu Wei from Tongji University School of Medicine and Shanghai Tenth People’s Hospital are the co-first authors of this paper. This work also received strong support from Professor Zhu Ruixin of Tongji University and Professors Pappachan E Kolattukudy and Niu Jianzhi of the Burnett Biomedical Sciences Institute, University of Central Florida.

Original Link:

https://doi:10.1136/gutjnl-2022-327183

Editor: Eleven

References

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