CCL3 aggravates intestinal tissue damage in NEC by promoting macrophage chemotaxis and M1 macrophage polarization.

Necrotizing enterocolitis (NEC) is a life-threatening inflammatory gastrointestinal disease in neonates, the mechanism of which is poorly elucidated. Intestinal mucosal barrier imbalance due to excessive inflammatory response is an important endogenous cause of NEC. Our study elucidates a novel mechanism of NEC development, in which CCL3 regulated the chemotaxis, polarization, and function of macrophages to promote NET progression. Our data show that CCL3 is highly expressed in the intestinal tissues of NEC patients and mice and induce macrophage infiltration. Transcriptome data from high-throughput sequencing showed that CCL3 strongly induced macrophages switch into a pro-inflammatory phenotype. Mechanistically, in vivo experiments confirmed that CCL3 induced M1 polarization of macrophages in NEC intestinal tissue, thereby aggravating inflammatory injury of intestinal tissue which can be reversed by anti-CCL3 treatment; in accordance, in vitro experiments showed that CCL3 could significantly enhance the expression of M1-related genes (e.g. iNOS, IRF5, CD86) in both peritoneal macrophages and bone marrow derived macrophages while inhibit the expression of M2-related genes (e.g. Arg-1, FIZZ1, YM1), which could also be reversed by anti-CCl3 treatment. Herein, our study has elucidated a novel mechanism of CCL3 involvement in the pathogenesis of NEC, in which the upregulated CCL3 expression exacerbated inflammatory intestinal damage via regulating macrophage chemotaxis and M1 phenotype polarization, suggesting that blocking CCL3 may be a potential strategy for effective intervention of NEC.