Human Umbilical Cord Mesenchymal Stem Cells Alleviate Inflammatory Bowel Disease Through Inhibiting ERK Phosphorylation In Neutrophils

Background: Inflammatory bowel disease(IBD)reflects the inflammatory circumstances of the colon and small intestine.The principal types of this disease are Crohn disease(CD)and ulcerative colitis(UC).IBD is a complicated disease that originates as a result of interactions of different factors such as environmental and genetic,leading to immunological responses and inflammation in the intestine.In IBD,the immune system is in an overactive state.Mesenchymal stem cells(MSCs),multipotent stromal cells that can be isolated from many tissues,including bone marrow and adipose tissue,have been studied extensively for the treatment of IBD due to their immunomodulatory capability.Neutrophils(also known as neutrocytes)are the significantly abundant type of white blood cell(60% to 70%)in large mammals.They feature an essential part of innate immunity.Neutrophils are enrolled in the site of injury within minutes following trauma and are the hallmark of acute inflammation.However,functional neutrophils are essential for maintaining intestinal balance in the process of MSCs alleviating IBD.Methods: In this study,we established a dextran sulfate sodium(DSS)-induced C57BL/6 mouse IBD model.We evaluated the effects of human umbilical cord MSCs on repairing IBD by observing mouse body weight,fecal traits,colon/spleen gross view,tissue hematoxylin and eosin(HE)/immunohistochemical staining,and inflammatory factors.We used magnetic beads to sort out infiltrating neutrophils in intestinal tissues and identified their phenotypes.At the same time,the neutrophil inflammatory environment was simulated in vitro to study the signaling pathways of MSCs regulating neutrophil phenotype.Results: Human umbilical cord MSCs(hUCMSCs)effectively alleviated DSS-induced weight loss,colon shortening,and intestinal mucosal injury,and reduced clinical disease activity index(DAI).The number of neutrophils that infiltrated the intestines of mice treated with h UCMSCs was decreased and polarized toward the N2 phenotype;at the same time,ERK phosphorylation was inhibited.In vitro experiments showed that addition of the ERK phosphorylation inhibitor,PD98059 down-regulated the expression of N1 neutrophils,while up-regulating that of N2 neutrophils.The colon tissues from patients with IBD were infiltrated with neutrophils.Further,relative to healthy controls,the markers of N1 neutrophils(ICAM-1,FAS,and CCL3)were highly expressed in colon tissues from patients with IBD,whereas the markers of N2 neutrophils(VEGF,CCL2,and CXCR4)were almost undetectable.Conclusion: During the alleviation of IBD,h UCMSCs polarize neutrophils toward the“N2” phenotype by inhibiting activation of ERK signaling.