A20 plays a critical role in the immunoregulatory function of mesenchymal stem cells.

Mesenchymal stem cells (MSCs) possess an immunoregulatory capacity and are a therapeutic target for many inflammation-related diseases. However, the detailed mechanisms of MSC-mediated immunosuppression remain unclear. In this study, we provide new information to partly explain the molecular mechanisms of immunoregulation by MSCs. Specifically, we found that A20 expression was induced in MSCs by inflammatory cytokines. Knockdown of A20 in MSCs resulted in increased proliferation and reduced adipogenesis, and partly reversed the suppressive effect of MSCs on T cell proliferation in vitro and inhibited tumour growth in vivo. Mechanistic studies indicated that knockdown of A20 in MSCs inhibited activation of the p38 mitogen-activated protein kinase (MAPK) pathway, which potently promoted the production of tumour necrosis factor (TNF)-α and inhibited the production of interleukin (IL)-10. Collectively, these data reveal a crucial role of A20 in regulating the immunomodulatory activities of MSCs by controlling the expression of TNF-α and IL-10 in an inflammatory environment. These findings provide novel insights into the pathogenesis of various inflammatory-associated diseases, and are a new reference for the future development of treatments for such afflictions.

Deubiquitinase MYSM1 Is Essential for Normal Bone Formation and Mesenchymal Stem Cell Differentiation.

Deubiquitinase MYSM1 has been shown to play a critical role in hematopoietic cell differentiation and hematopoietic stem cell (HSC) maintenance. Mesenchymal stem cells (MSCs) are multipotent stromal cells within the bone marrow. MSCs are progenitors to osteoblasts, chondrocytes, adipocytes, and myocytes. Although, MSCs have been extensively studied, the roles of MYSM1 in these cells remain unclear. Here we describe the function of MYSM1 on MSC maintenance and differentiation. In this report, we found that Mysm1-/- mice had a lower bone mass both in long bone and calvaria compared with their control counterpart. Preosteoblasts from Mysm1-/- mice did not show changes in proliferation or osteogenesis when compared to WT mice. Conversely, Mysm1-/- MSCs showed enhanced autonomous differentiation and accelerated adipogenesis. Our results demonstrate that MYSM1 plays a critical role in MSC maintenance and differentiation. This study also underscores the biological significance of deubiquitinase activity in MSC function. Mysm1 may represent a potential therapeutic target for controlling MSC lineage differentiation, and possibly for the treatment of metabolic bone diseases such as osteoporosis.

Delta-Like-1 Changes the Immunomodulatory Property of OP9 Cells.

As stromal cells and recently confirmed mesenchymal stem cells, OP9 cells support hematopoiesis stem cell (HSC) differentiation into the B lymphocyte lineage, yet Delta-like-1 (DL1) overexpressing OP9 (OP9DL1) cells promote the development of early T lymphocytes from HSC. However, the immunomodulatory capacity of OP9 or OP9DL1 on mature B and T cell proliferation has not been elucidated. Here, we show that OP9 and OP9DL1 have similar proliferation capacities and immunophenotypes except DL1 expression. Compared with OP9, OP9DL1 displayed more osteogenesis and less adipogenesis when cultured in the respective induction media. Both OP9 and OP9DL1 inhibited mature B and T cell proliferation. Furthermore, OP9 showed stronger inhibition on B cell proliferation and OP9DL1 exhibited stronger inhibition on T cell proliferation. With stimulation, both OP9 and OP9DL1 showed increased nitrate oxide (NO) production. The NO levels of OP9 were higher than that of OP9DL1 when stimulated with TNFα/IFNγ or LPS/IL4. Taken together, our study reveals a previously unrecognized role of OP9 and OP9DL1 in mature B and T cell proliferation. DL1 overexpression alone changed the properties of OP9 cells in addition to their role in early B cell development.

Effect of aged bone marrow microenvironment on mesenchymal stem cell migration.

Mesenchymal stem cells (MSCs) are known to have many notable features, especially their multiple differentiation ability and immunoregulatory capacity. MSCs are important stem cells in the bone marrow (BM), and their characteristics are affected by the BM microenvironment. However, effects of the BM microenvironment on the properties of MSCs are not well understood. In this study, we found that BM from aged mice decreased MSC colony formation. Flow cytometry data showed that the proportion of B220(+) cells in BM from aged mice was significantly lower than that in BM from young mice, while the proportion of CD11b(+), CD3(+), Gr-1(+), or F4/80(+) cells are on the contrary. CD11b(+), B220(+), and Ter119(+) cells from aged mice were not the subsets that decreased MSC colony formation. We further demonstrated that both BM from aged mice and young mice exhibited similar effects on the proliferation of murine MSC cell line C3H10T1/2. However, when cocultured with BM from aged mice, C3H10T1/2 showed slower migration ability. In addition, we found that phosphorylation of JNK (c-Jun N-terminal kinases) in C3H10T1/2 cocultured with BM from aged mice was lower than that in C3H10T1/2 cocultured with BM from young mice. Collectively, our data revealed that BM from aged mice could decrease the migration of MSCs from their niche through regulating the JNK pathway.