IFN-gamma orchestrates mesenchymal stem cell plasticity through the signal transducer and activator of transcription 1 and 3 and mammalian target of rapamycin pathways

Background: Mesenchymal stem cells (MSCs) display a therapeutic plasticity because of their ability to modulate immunity, foster tissue repair, and differentiate into mesodermal cells. IFN-? has been described to differently affect human mesenchymal stem cell (hMSC) and mouse mesenchymal stem cell (mMSC) immunomodulation and differentiation, depending on the inflammatory milieu. Objective: We aimed at dissecting the relevant intracellular pathways through which IFN-? affects MSC plasticity and the consequence of their manipulation on MSC functions. Methods: Modification of relevant IFN-?-dependent pathways in mMSCs was carried out . in vitro through gene silencing or chemical inhibition of key components. Functional outcomes were assessed by means of Western blotting, real-time PCR, differentiation, and proliferation assays on MSCs. The effect on T cells was addressed by T-cell proliferation assays; the effect of mammalian target of rapamycin (mTOR) manipulation in MSCs was studied . in vivo in a mouse model of delayed-type hypersensitivity assay. To address whether similar mechanisms are involved also in hMSCs on IFN-? stimulation, the effect of chemical inhibition on the same intracellular pathways was assessed by means of Western blotting, and the final outcome on immunomodulatory properties was evaluated based on real-time PCR and T-cell proliferation. Results: We revealed that in mMSCs IFN-?-induced immunoregulation is mediated by early phosphorylation of signal transducer and activator of transcription (STAT) 1 and STAT3, which is significantly enhanced by an extracellular signal-regulated kinase 1/2-dependent mTOR inhibition, thereby promoting pSTAT1 nuclear translocation. Accordingly, after intracellular mTOR inhibition, MSCs augmented their ability to inhibit T-cell proliferation and control delayed-type hypersensitivity . in vivo. Similarly, on mTOR blockade, hMSCs also enhanced their immunoregulatory features. A sustained exposure to IFN-? led to inhibition of STAT3 activity, which in mMSCs resulted in an impaired proliferation and differentiation. Conclusion: These results provide new insights about MSC intracellular pathways affected by IFN-?, demonstrating that pharmacologic or genetic manipulation of MSCs can enhance their immunomodulatory functions, which could be translated into novel therapeutic approaches.