Nrf2 modulates immunosuppressive ability and cellular senescence of human umbilical cord mesenchymal stem cells.

In the application of human umbilical cord-derived mesenchymal stem cells (UC-MSCs) as clinical therapeutics, long term cells ex vivo expansion results in decline in their function. It has been widely concerned that cellular senescence is associated with UC-MSCs immunomodulatory ability. In this study, we evaluated the effects of consecutive passages on cellular senescence and the immunomodulatory abilities of UC-MSCs. Long term-cultured UC-MSCs showed decreased proliferation, senescence phenotypes and impaired immunosuppressive effects on PHA induced peripheral blood mononuclear cell (PBMC) proliferation. We found that Nrf2, a transcription factor that responds to oxidative stress, that showed decreased expression in long term-cultured UC-MSCs, and the further knock-down of Nrf2 in UC-MSCs induced premature senescence, decreased proliferation ability and immunosuppressive abilities. Furthermore, the protein expression of IDO-1 were decreased in response to the downregulation of Nrf2 in UC-MSCs, suggesting that Nrf2 regulates the immunosuppressive properties of UC-MSCs via Nrf2-mediated IDO-1 expression. In conclusion, our results demonstrate that Nrf2 plays a key role in the regulation of the immunosuppressive properties of UC-MSCs, and we suggest that these findings might provide a strategy to enhance the functionality of UC-MSCs for use in therapeutic applications.

miR-21 regulates immunosuppression mediated by myeloid-derived suppressor cells by impairing RUNX1-YAP interaction in lung cancer.

BACKGROUND: Myeloid-derived suppressor cells (MDSCs) are known suppressors of antitumor immunity and contribute to immunosuppressive microenvironment during tumor development including lung cancer. Accumulating evidence shows microRNAs (miRNAs) affect tumor-expanded MDSC accumulation and function in tumor microenvironment and favor solid tumor growth. Herein, we aim to characterize the role of miR-21 in regulating the accumulation and activity of MDSCs in lung cancer. METHODS: The proportions of MDSCs, T helper cells (Th), and cytotoxic T lymphocytes (CTL) were evaluated by flow cytometric analyses of peripheral blood and tumor tissues collected from Lewis lung-cancer-bearing mice. T cell proliferation assay was performed in CD4+ or CD8+ T cells cocultured with MDSCs. MDSC apoptosis was examined by flow cytometric analysis. The levels of IL-10, TGF-ß, and GM-CSF in mouse serum were determined by ELISA. miR-21 targeting RUNX1 and RUNX1 interaction with YAP were evaluated by RIP, dual-luciferase reporter gene, and ChIP assays. RESULTS: MiR-21 inhibition by its antagomir reduced the proportion of MDSCs, increased the proportion of Th and CTL in peripheral blood and tumor tissues of Lewis lung-cancer-bearing mice, protected Th and CTL from the suppression of MDSCs, increased apoptosis of MDSCs, but reduced IL-10, TGF-ß and GM-CSF levels in mouse serum. RUNX1 could transcriptionally inhibit the YAP expression, whereas miR-21 targeting RUNX1 led to elevated YAP expression levels. Mechanistic investigation showed that miR-21 maintained MDSC accumulation in tumor microenvironment and promoted immunosuppressive ability of MDSCs in Lewis lung-cancer-bearing mice by down-regulating RUNX1and up-regulating YAP. CONCLUSIONS: Taken together, the study provides evidence that targeting miR-21 in MDSCs may be developed as an immunotherapeutic approach to combat lung cancer development.

Long-term culture in vitro impairs the immunosuppressive activity of mesenchymal stem cells on T cells.

Improved knowledge of the immunological properties of mesenchymal stem cells (MSCs) creates a potential cell-mediated immunotherapeutic approach for arthritic diseases. The low frequency of MSCs necessitates their in vitro expansion prior to clinical use. As sequential passage has been used as the most popular strategy for expansion of MSCs, the effect of long-term culture on the immunological properties of MSCs is not clear. In this study, we observed that the morphology of MSCs showed the typical characteristics of the Hayflick model of cellular aging during sequential expansion. The growth kinetics of MSCs decreased while the number of MSCs staining positive for SA ß-gal (senescence marker) increased in long-term culture. Although long-term culture exerts less of an effect on the immunophenotype of MSCs, the immunosuppressive effects of MSCs on the allogeneic T-cell proliferation, activation-antigen expression (CD69 and CD25) and cytokine production (IFN-γ, TNF-α, IL-10) were significantly impaired following stimulation with phytohemagglutinin (PHA).