Background & aims: Decreased levels or function of nucleotide-binding oligomerization domain 2 (NOD2) are associated with Crohn's disease. NOD2 regulates intestinal inflammation, and also is expressed by human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs), to regulate their differentiation. We investigated whether NOD2 is required for the anti-inflammatory activities of MSCs in mice with colitis.
Methods: Colitis was induced in mice by administration of dextran sulfate sodium or trinitrobenzene sulfonic acid. Mice then were given intraperitoneal injections of NOD2-activated hUCB-MSCs; colon tissues and mesenteric lymph nodes were collected for histologic analyses. A bromodeoxyuridine assay was used to determine the ability of hUCB-MSCs to inhibit proliferation of human mononuclear cells in culture.
Results: Administration of hUCB-MSCs reduced the severity of colitis in mice. The anti-inflammatory effects of hUCB-MSCs were greatly increased by activation of NOD2 by its ligand, muramyl dipeptide (MDP). Administration of NOD2-activated hUCB-MSCs increased anti-inflammatory responses in colons of mice, such as production of interleukin (IL)-10 and infiltration by T regulatory cells, and reduced production of inflammatory cytokines. Proliferation of mononuclear cells was inhibited significantly by co-culture with hUCB-MSCs that had been stimulated with MDP. MDP induced prolonged production of prostaglandin (PG)E2 in hUCB-MSCs via the NOD2-RIP2 pathway, which suppressed proliferation of mononuclear cells derived from hUCB. PGE2 produced by hUCB-MSCs in response to MDP increased production of IL-10 and T regulatory cells. In mice, production of PGE2 by MSCs and subsequent production of IL-10 were required to reduce the severity of colitis.
Conclusions: Activation of NOD2 is required for the ability of hUCB-MSCs to reduce the severity of colitis in mice. NOD2 signaling increases the ability of these cells to suppress mononuclear cell proliferation by inducing production of PGE2.
Keywords: 5,6-carboxy fluorescein succinimidyl ester; CFSE; CM; COX-2; DSS; Foxp3; IBD; IDO-1; IFN; IL; Immune Regulation; LPS; MDP; MLN; MLR; MNC; MPO; Mouse Model; NF-κB; NO; NOD2; PBS; PG; RIP; Signal Transduction; T-helper cell; TLR; TNBS; TNF; Th; Toll-like receptor; Treg; UCM; culture media; cyclooxygenase-2; dextran sulfate sodium; forkhead box p3; hMNC; hUCB-MSCs; human mononuclear cell; human umbilical cord blood-derived mesenchymal stem cells; indoleamine-2,3-dioxygenase-1; interferon; interleukin; lipopolysaccharide; mesenteric lymph node; mixed lymphocyte reaction; mononuclear cell; muramyl dipeptide; myeloperoxidase; nitric oxide; nuclear factor-κB; nucleotide-binding oligomerization domain 2; phosphate-buffered saline; prostaglandin; receptor-interacting protein; regulatory T cell; siRNA; small interfering RNA; trinitrobenzene sulfonic acid; tumor necrosis factor; umbilical cord blood-derived mesenchymal stem cell conditioned medium.
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