Mesenchmal stem cells (MSCs) can be differentiated into either adipocytes or osteoblasts, and a reciprocal relationship exists between adipogenesis and osteogenesis. Multiple transcription factors and signaling pathways have been reported to regulate adipogenic or osteogenic differentiation, respectively, yet the molecular mechanism underlying the cell fate alteration between adipogenesis and osteogenesis still remains to be illustrated. MicroRNAs are important regulators in diverse biological processes by repressing protein expression of their targets. Here, miR-22 was found to regulate adipogenic and osteogenic differentiation of human adipose tissue-derived mesenchymal stem cells (hADMSCs) in opposite directions. Our data showed that miR-22 decreased during the process of adipogenic differentiation but increased during osteogenic differentiation. On one hand, overexpression of miR-22 in hADMSCs could inhibit lipid droplets accumulation and repress the expression of adipogenic transcription factors and adipogenic-specific genes. On the other hand, enhanced alkaline phosphatase activity and matrix mineralization, as well as increased expression of osteo-specific genes, indicated a positive role of miR-22 in regulating osteogenic differentiation. Target databases prediction and validation by Dual Luciferase Reporter Assay, western blot, and real-time polymerase chain reaction identified histone deacetylase 6 (HDAC6) as a direct downstream target of miR-22 in hADMSCs. Inhibition of endogenous HDAC6 by small-interfering RNAs suppressed adipogenesis and stimulated osteogenesis, consistent with the effect of miR-22 overexpression in hADMSCs. Together, our results suggested that miR-22 acted as a critical regulator of balance between adipogenic and osteogenic differentiation of hADMSCs by repressing its target HDAC6.

A better understanding of the molecular mechanisms underlying the differentiation of human adipose tissue-derived mesenchymal stem cells (hAD-MSCs) could provide new insights into the pathogenesis of a number of diseases, such as obesity and diabetes, and broaden the spectrum of potential hAD-MSCs-based cell therapy. In this study, we reported that a human microRNA, hsa-miR-138, could inhibit the adipogenic differentiation of hAD-MSCs. Our results showed that miR-138 was significantly down-regulated during adipogenic differentiation. Overexpression of miR-138 in hAD-MSCs could effectively reduce lipid droplets accumulation, inhibit expression of key adipogenic transcription factors cytidine-cytidine-adenosine-adenosine-thymidine (CCAAT) enhancer binding protein alpha and peroxisome proliferator-activated receptor gamma 2 as well as several other adipogenic marker genes, such as fatty acid binding protein 4 and lipoprotein lipase. Further studies showed that the expression of adenovirus early region 1-A-like inhibitor of differentiation 1 (EID-1), a nuclear receptor coregulator, was inversely correlated with that of miR-138 when hAD-MSCs were differentiated into adipocytes. Knockdown of EID-1 by RNA interference inhibited adipocyte differentiation of hAD-MSCs. In addition, luciferase reporter assays demonstrated that miR-138 directly targeted the 3' untranslated region of EID-1, implying that the negative role of miR-138 in the adipocyte differentiation of hAD-MSCs is at least partially mediated via repressing EID-1. Taken together, this study shows that miR-138 plays a negative role in adipogenic differentiation and sheds light on the role of miRNAs during differentiation of hAD-MSCs toward adipocytes.

The success of treatment for sclerodermatous chronic graft-versus-host disease (ScGVHD) remains disappointing. The immunomodulatory ability of bone marrow (BM)-derived mesenchymal stem cells (MSCs) shows promise in treating GVHD, especially given its previous success in treating patients with acute GVHD (aGVHD). The potential efficacy and safety issues for treating cGVHD, particularly ScGVHD, remain to be clarified, however. Here, we report 4 patients with ScGVHD who received MSCs expanded ex vivo from unrelated donors by intra-BM injection. After MSC infusion, the ratio of helper T lymphocyte (Th) 1 cells to Th2 cells was dramatically reversed, with an increase in Th1 and a decrease in Th2 achieving a new balance. Correspondingly, symptoms gradually improved in all 4 patients. During the course of MSC treatment, the patients' vital signs and laboratory results remained normal. At the time of this report, none of the 4 patients had experienced recurrence of leukemia. Although this study alone cannot guarantee the application of MSCs in ScGVHD, our findings strongly suggest that this treatment is therapeutically practicable, with no detectable side effects. This approach may provide new insight into the clinical treatment of ScGVHD, with the aim of greatly increasing the survival rate in patients with leukemia who undergo allogeneic BM transplantation (BMT).

The ERK-MAPK signaling pathway plays a pivotal role during mesenchymal stem cell (MSC) differentiation. Studies have demonstrated that ERK-MAPK promotes adipogenesis and osteogenesis through the phosphorylation of differentiation-associated transcription factors and that it is the only active signaling in all three lineages (adipogenic, chondrogenic, and osteogenic) during MSC differentiation. Recent studies pointed to the significant roles of microRNA-21 (miR-21) during several physiological and pathological processes, especially stem cell fate determination. The miR-21 expression pattern is also correlated with ERK-MAPK activity. Here, we found that miR-21 expression is elevated and associated with an increased differentiation potential in MSCs during adipogenesis and osteogenesis. The overexpression of miR-21 elevated the expression level of the differentiation-associated genes PPARγ and Cbfa-1 during MSC differentiation, whereas miR-21 knockdown reduced the expression level of both genes. The ERK-MAPK signaling pathway activity had an increasing tendency to respond to miR-21 upregulation and a decreasing tendency to respond to miR-21 down-regulation during the first 4 days of adipogenesis and osteogenesis. Our data indicate that miR-21 modulated ERK-MAPK signaling activity by repressing SPRY2 expression, a known regulator of the receptor tyrosine kinase (RTK) signaling pathway, to affect the duration and magnitude of ERK-MAPK activity. The ERK-MAPK signaling pathway was regulated by Sprouty2 (SPRY2) expression via a miR-21-mediated mechanism during MSC differentiation.