TNF-stimulated gene-6 (TSG-6) is a key regulator in switching stemness and biological properties of mesenchymal stem cells.

Mesenchymal stem cells (MSCs) are largely studied for their promising therapeutic properties. TSG-6, a potent tissue-protective and anti-inflammatory factor, has been demonstrated to be responsible for a significant part of wound healing-promoting properties mediated by MSCs. Nevertheless, current knowledge approximately the biological function of TSG-6 in MSCs is limited. Here, we demonstrated that TSG-6 is a crucial factor that influences many functional properties of MSCs. The transcriptomic sequencing analysis of WT and TSG-6-/- -MSCs shows that the loss of TSG-6 leads to the perturbation of several transcription factors, cytokines and other pathways involved in MSCs biological processes. TSG-6-/- -MSCs appeared morphologically different with dissimilar cytoskeleton organization, significant reduced size of extracellular vesicles, decreased cell proliferative rate and loss of differentiation abilities compared to the WT cells. These cellular impacts may be likely due to TSG-6 commitments in driving changes in the extracellular matrix (ECM) environment. The supplementation of ECM with exogenous TSG-6, in fact, rescued cell proliferation and changes in morphology. Importantly, TSG-6 deficient MSCs displayed an increased capacity to release IL-6 conferring pro-inflammatory and pro-tumorigenic properties to MSCs. Overall, our data provide strong evidences that TSG-6 is crucial for the maintenance of stemness and biological properties of murine MSCs. SIGNIFICANCE STATEMENT: MSCs are a heterogeneous population of pluripotent stem cells that are difficult to study due to the lack of specific markers. Isolation, culture and in vitro manipulation may influence the expansion of a selective clone exhibiting specific functions. Hence, heterogeneity and lack of predictive biomarkers of their efficacy widely impact the translational use of MSCs. TSG-6, acting as an autocrine factor regulating morphology and several MSC cellular processes, is crucial for the maintenance of stemness and biological properties. Its loss drives to the abrogation of immunomodulatory properties and, also of the stemness capacities conferring to MSCs a pro-tumorigenic phenotype. These observations warrant further investigations with human MSCs and pave the way for using TSG-6 as useful predictive marker for monitoring the effects of MSC-based therapy. © AlphaMed Press 2019.