Type 1 diabetes mellitus is autoimmune T cells mediated destruction of β-cells. Mesenchymal stem cells (MSCs) are considered a promising treatment for T1DM due to the strong immunosuppressive and regenerative capacity. However, the comprehensive mechanism is still unclear. Our previous study indicated that the transforming growth factor beta-induced gene (TGFBI) is highly expressed in human umbilical cord derived mesenchymal stem cells (hUC-MSCs), which is also implicated in T1DM. Thus, our study aimed to investigate TGFBI mediated immunomodulatory properties of hUC-MSCs in the treatment of T1DM. In this study, a stably knockdown TGFBI lentiviral vector was successfully constructed and transfected into hUC-MSCs to obtain sh-TGFBI-MSCs. MSCs transduced with the control lentivirus were also referred as negative control (sh-NC-MSCs). To evaluate the role of TGFBI in the treatment effects of hUC-MSCs in T1DM mice, sh-TGFBI-MSCs and sh-NC-MSCs were intravenously administered to STZ-induced T1DM mice. We found that silencing TGFBI significantly abrogated the therapeutic effects of hUC-MSCs on T1DM model. Histologic analysis performed via H&E and insulin immunohistochemical staining revealed that sh-NC-MSCs infusion suppressed insulitis and preserved insulin-producing cells in the islets. However, sh-TGFBI-MSCs transplantation cannot effectively protect the destructive islet tissue and insulin-producing cells. Flow cytometry results showed that silencing TGFBI significantly weakened the ability of hUC-MSCs to inhibit the secretion of pro-inflammatory cytokines IFN-γ and IL-17A in the spleen of T1DM model mice. Additionally, according to immunofluorescence analysis we found that downregulating TGFBI markedly mitigated the suppressive effects of hUC-MSCs on suppressing the infiltration of T cells labeled with green fluorescent CD3 antibody in the pancreas in STZ-induced T1DM model. In vitro we constructed a co-culture system to culture MSCs and CD3+T cells sorted by CD3 MicroBeads. Consistent with in vivo, we further proved that TGFBI derived from hUC-MSCs could repress the activated T cells proliferation. Mechanistically, TGFBI secreted by hUC-MSCs could be able to repress activated T cells proliferation by interfering with the T cells expression of G1/S checkpoint CyclinD2 and arrests T cells in G0G1 phase. In conclusion, we have demonstrated that TGFBI secreted by hUC-MSCs can suppress the proliferation of activated T cells and the precise mechanism of this phenomenon remains to be determined, our analysis suggests CyclinD2 downregulation and T cell cycle arrest may be involved. Our study provides new sight into immunoregulatory mechanism of the hUC-MSCs mediated by TGFBI，which might be therapeutic target for the treatment of T1DM.
15 Sep 2022 - 17 Sep 2022