STEM CELLS 2006;24: 2744 -2752

Background/Aim: Although transplantation of MSC derived from bone marrow or adipose tissues has been shown in proangiogenic action in hindlimb ischemia model of nude mice, little information is available regarding comparison of the angiogenic potency between human adipose stromal cells (hADSC) and bone marrow stromal cells (hBMSC). We compared their therapeutic potential by transplantation of equal numbers of hADSC or hBMSC in a nude mice model of hindlimb ischemia.

Tumor necrosis factor-alpha (TNF-alpha) is a skeletal catabolic agent that stimulates osteoclastogenesis and inhibits osteoblast function. Although TNF-alpha inhibits the mineralization of osteoblasts, the effect of TNF-alpha on mesenchymal stem cells (MSC) is not clear. In this study, we determined the effect of TNF-alpha on osteogenic differentiation of stromal cells derived from human adipose tissue (hADSC) and the role of NF-kappaB activation on TNF-alpha activity. TNF-alpha treatment dose-dependently increased osteogenic differentiation over the first 3 days of treatment. TNF-alpha activated ERK and increased NF-kappaB promoter activity. PDTC, an NF-kappaB inhibitor, blocked the osteogenic differentiation induced by TNF-alpha and TLR-ligands, but U102, an ERK inhibitor, did not. Overexpression of miR-146a induced the inhibition of IRAK1 expression and inhibited basal and TNF-alpha- and TLR ligand-induced osteogenic differentiation. TNF-alpha and TLR ligands increased the expression of transcriptional coactivator with PDZ-binding motif (TAZ), which was inhibited by the addition of PDTC. A ChIP assay showed that p65 was bound to the TAZ promoter. TNF-alpha also increased osteogenic differentiation of human gastroepiploic artery smooth muscle cells. Our data indicate that TNF-alpha enhances osteogenic differentiation of hADSC via the activation of NF-kappaB and a subsequent increase of TAZ expression.

Valproic acid (VPA) has been used as an anticonvulsant agent for the treatment of epilepsy, as well as a mood stabilizer for the treatment of bipolar disorder, for several decades. The mechanism of action for these effects remains to be elucidated and is most likely multifactorial. Recently, VPA has been reported to inhibit histone deacetylase (HDAC) and HDAC has been reported to play roles in differentiation of mammalian cells. In this study, the effects of HDAC inhibitors on differentiation and proliferation of human adipose tissue-derived stromal cells (hADSC) and bone marrow stromal cells (hBMSC) were determined. VPA increased osteogenic differentiation in a dose dependent manner. The pretreatment of VPA before induction of differentiation also showed stimulatory effects on osteogenic differentiation of hMSC. Trichostatin A (TSA), another HDAC inhibitor, also increased osteogenic differentiation, whereas valpromide (VPM), a structural analog of VPA which does not possess HDAC inhibitory effects, did not show any effect on osteogenic differentiation on hADSC. RT-PCR and Real-time PCR analysis revealed that VPA treatment increased osterix, osteopontin, BMP-2, and Runx2 expression. The addition of noggin inhibited VPA-induced potentiation of osteogenic differentiation. VPA inhibited proliferation of hADSC and hBMSC. Our results suggest that VPA enhance osteogenic differentiation, probably due to inhibition of HDAC, and could be useful for in vivo bone engineering using hMSC.

A better understanding of the molecular mechanisms that govern human adipose tissue-derived mesenchymal stem cells (hASCs) differentiation could provide new insights into a number of diseases including obesity. Our previous study demonstrated that microRNA-21 (miR-21) controls the adipogenic differentiation of hASCs. In this study, we determined the expression of miR-21 in white adipose tissues in a high-fat diet (HFD)-induced obesity mouse model to examine the relationship between miR-21 and obesity and the effect of miR-21 on hASCs proliferation. Our study showed biphasic changes of miR-21 expression and a correlation between miR-21 level and adipocyte number in the epididymal fat of HFD mice. Over-expression of miR-21 decreased cell proliferation, whereas inhibiting miR-21 with 2'-O-methyl-antisense RNA increased it. Over-expression of miR-21 decreased both protein and mRNA levels of STAT3, whereas inhibiting miR-21 with 2'-O-methyl-antisense RNA increased these levels. The activity of a luciferase construct containing the miR-21 target site from the STAT3 3'UTR was lower in LV-miR21-infected hASCs than in LV-miLacZ infected cells. RNA interference-mediated down-regulation of STAT3 decreased cell proliferation without affecting adipogenic differentiation. These findings provide the evidence of the correlation between miR-21 level and adipocyte number in the white adipose tissue of HFD-induced obese mice, which provides new insights into the mechanisms of obesity.