Mesenchymal stem cells (MSCs) are a very important adult stem cell population with a multitude of potential applications in regenerative medicine. The thorough characterization of the bone marrow MSC (BM-MSC) population derived from the BALB/c species was essential, considering the significance of the murine model amongst animal models. In the present study, we examined the effect of gender, age, and in vitro culture on the basic properties (proliferation, differentiation, and immunosuppressive potential) of BM-MSCs. We found a decline in the progenitor frequencies from the BM of adult mice, lower MSC frequencies in all female donors, and an increase in the BM-MSC proliferation rate upon in vitro propagation. We also examined BM-MSCs for the expression of the 3 major embryonic stem cell transcription factors, Oct3/4, Sox-2, and Nanog, as well as 2 mRNA binding proteins, coding region determinant binding protein/insulin-like growth factor 2 mRNA binding protein 1 (Crd-bp/Imp1) and Deleted in azoospermia-like (Dazl), which are expressed in primitive stem cells, umbilical cord blood-hematopoietic stem cells and amniotic fluid stem cells, respectively. Further, it has been reported that these 2 genes are critical for embryonic development. In this study, therefore, we report, for the first time, the expression of Crd-bp/Imp1 and Dazl in BM-MSCs. Dazl, Oct3/4, and Sox2 were detected in relatively low levels in contrast to Crd-bp/Imp1, its major target c-Myc, as well as Nanog, which were expressed redundantly, irrespective of sex, donor age, or in vitro passaging. These findings could further support the extrinsic theory of aging of the MSC population and the potential implication of embryonic genes in adult stem cell physiology.

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Objectives Degeneration of articular cartilage is central to OA pathology; however, the molecular mechanisms leading to these irreversible changes are still poorly understood. Here, we investigated how changes in the chondrocyte translational apparatus may contribute to the pathology of OA. Methods Normal and OA human knee cartilage was used to analyze the activity of different components of the translational machinery. Chondrocytes isolated from lesional and non-lesional areas of OA cartilage were used to estimate relative rate of protein synthesis by metabolic labeling. Experimental OA was induced by transection of the anterior cruciate ligament in rats to investigate changes in the translational apparatus associated with OA. The role of IL-1β signaling was assessed in vitro using rat articular chondrocytes. Expression of mRNAs was analyzed by qPCR and protein levels by immunohistochemistry and Western blotting. Results We identified several novel traits of OA chondrocytes, including upregulation of the Serine/Threonine kinases AKT2 and AKT3 at the post-transcriptional level and increased rate of total protein synthesis, likely due to inactivation of 4E-BP1, a known repressor of cap-dependent translation. We found that 4E-BP1 inactivation is mTOR-dependent and crucial for upregulation of protein synthesis in general and in particular for MMP13 and ADAMTS5 expression. In addition, IL-1β treatment led to 4E-BP1 inactivation and upregulation of protein synthesis in articular chondrocytes. Conclusions Precise control of protein synthesis is vital for cartilage homeostasis and its dysregulation contributes to the molecular pathology of OA. Our study therefore identifies a novel set of potential therapeutic targets.

Regulatory T cells (Treg cells) inhibit effector T cells and maintain immune system homeostasis. Treg cell maturation in peripheral sites requires inhibition of protein kinase mTORC1 and TGF-beta-1 (TGF-beta). While Treg cell maturation requires protein synthesis, mTORC1 inhibition downregulates it, leaving unanswered how Treg cells achieve essential mRNA translation for development and immune suppression activity. Using human CD4+ T cells differentiated in culture and genome-wide transcription and translation profiling, here we report that TGF-beta transcriptionally reprograms naive T cells to express Treg cell differentiation and immune suppression mRNAs, while mTORC1 inhibition impairs translation of T cell mRNAs but not those induced by TGF-beta. Rather than canonical mTORC1/eIF4E/eIF4G translation, Treg cell mRNAs utilize the eIF4G homolog DAP5 and initiation factor eIF3d in a non-canonical translation mechanism that requires cap-dependent binding by eIF3d directed by Treg cell mRNA 5’ noncoding regions. Silencing DAP5 in isolated human naive CD4+ T cells impairs their differentiation into Treg cells. Treg cell differentiation is mediated by mTORC1 downregulation and TGF-beta transcriptional reprogramming that establishes a DAP5/eIF3d-selective mechanism of mRNA translation.

Mesenchymal stem cells (MSCs) are a population of cells harboring in many tissues with the ability to differentiate toward many different lineages. Unraveling the molecular profile of MSCs is of great importance due to the fact that these cells are very often used in preclinical and clinical studies. We have previously reported the expression of insulin-like growth factor 2 mRNA binding protein 1 (IGF2BP1) an oncofetal mRNA-binding protein-in different stem cell types such as bone marrow (BM)-MSC and umbilical cord blood (UCB)-hematopoietic stem cells. Here, we demonstrate that MSCs of adipose tissue, BM, and UC origin have a differential pattern of IGF2BP1 and ten-eleven-translocate 1/2 (TET1/2) expression that could correlate with their proliferation potential. Upon IGF2BP1 interference, a significant reduction of cell proliferation is observed, accompanied by reduced expression of c-MYC and GLI1 and increased p21. We also present, for the first time, evidence that IGF2BP1 is epigenetically regulated by TET1 and TET2 demethylases. Specifically, we show that TET1 directly binds to the promoter of IGF2BP1 gene and affects the hydroxymethylation status of its promoter. These results indicate that IGF2BP1 and TET1/2 contribute to the stemness of MSCs, at least regarding their proliferative potential.