Bone Marrow-Derived Mesenchymal Stem Cells (BM-MSCs) and Small Intestinal Submucosa (SIS) Hydrogel Composite Can Meliorate TNBS-Induced Experimental Colitis Through Regulating Inhibiting Macrophage Polarization Toward the M1 Phenotype

Abstract

An imbalance of macrophage polarization exerts influence over inflammatory bowel disease (IBD) pathogenesis. To investigate how macrophage polarization influences IBD, we engineered a composite system consisting of small intestinal submucosa (SIS) hydrogel combined with bone marrow-derived mesenchymal stem cells (BM-MSCs). The therapeutic potential of this construct was assessed by examining its regulatory effects on macrophage polarization both in a 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis mouse model and in RAW264.7 macrophages in vitro. Clone formation assay was executed to identify the influence of MSC-SIS-conditioned medium on the proliferation of RAW264.7. CD206 and CD86 were measured by flow cytometric. Quantitative real-time PCR (qRT-PCR) was conducted to evaluate cytokine gene expression. Experimental colitis was induced in mice using TNBS. Disease severity was assessed by calculating the clinical disease activity index (CDAI). Colonic tissues were subjected to histological and morphometric analyses, and serum levels of inflammatory cytokines were quantified using enzyme-linked immunosorbent assay (ELISA). Data indicated that the BM-MSCs and SIS hydrogel composite significantly promoted Raw264.7 proliferation. Compared with the lipopolysaccharide (LPS) + MSCs group, treatment with the combined MSCs and SIS hydrogel construct demonstrated a more pronounced inhibitory effect on M1 phenotype the autophagy of LPS-induced RAW264.7 in vitro; what is more, BM-MSCs and SIS hydrogel greatly inhibited cytokine mRNA levels in LPS-stimulated Raw264.7 cells compared with treatment with MSCs solely. In addition, the results implied that the mice in TNBS + MSC + SIS group had alleviated colitis compared with the TNBS + MSCs group, and the interleukin (IL)-1β and tumor necrosis factor-α (TNF-α) levels in the serum also decreased. In conclusion, these results indicate a better wound healing effect of SIS hydrogel on BM-MSCs through promoting cell regeneration and inhibiting macrophage polarization towards the M1 phenotype in a TNBS-induced experimental mouse model.

Keywords: bone marrow mesenchymal stem cells (BM-MSCs); experimental colitis; macrophage polarization; small intestinal submucosa (SIS).