Article

Oxysterols Regulate Differentiation of Mesenchymal Stem Cells: Pro-Bone and Anti-Fat

Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California, USA.
Journal of Bone and Mineral Research (Impact Factor: 6.83). 06/2004; 19(5):830-40. DOI: 10.1359/JBMR.040115
Source: PubMed

ABSTRACT

Pluripotent mesenchymal stem cells can undergo lineage-specific differentiation in adult organisms. However, understanding of the factors and mechanisms that drive this differentiation is limited. We show the novel ability of specific oxysterols to regulate lineage-specific differentiation of mesenchymal stem cells into osteogenic cells while inhibiting their adipogenic differentiation. Such effects may have important implications for intervention with osteoporosis.
Oxysterols are products of cholesterol oxidation and are formed in vivo by a variety of cells including osteoblasts. Novel pro-osteogenic and anti-adipogenic effects of specific oxysterols on pluripotent mesenchymal cells are demonstrated in this report. Aging and osteoporosis are associated with a decrease in the number and activity of osteoblastic cells and a parallel increase in the number of adipocytic cells.
The M2-10B4 pluripotent marrow stromal cell line, as well as several other mesenchymal cell lines and primary marrow stromal cells, was used to assess the effects of oxysterols. All results were analyzed for statistical significance using ANOVA.
Pro-osteogenic and anti-adipogenic effects of specific oxysterols were assessed by the increase in early and late markers of osteogenic differentiation, including alkaline phosphatase activity, osteocalcin mRNA expression and mineralization, and the decrease in markers of adipogenic differentiation including lipoprotein lipase and adipocyte P2 mRNA expression and adipocyte formation. Complete osteogenic differentiation of M2 cells into cells expressing early and late markers of differentiation was achieved only when using combinations of specific oxysterols, whereas inhibition of adipogenesis could be achieved with individual oxysterols. Oxysterol effects were in part mediated by extracellular signal-regulated kinase and enzymes in the arachidonic acid metabolic pathway, i.e., cyclo-oxygenase and phospholipase A(2). Furthermore, we show that these specific oxysterols act in synergy with bone morphogenetic protein 2 in inducing osteogenic differentiation. These findings suggest that oxysterols may play an important role in the differentiation of mesenchymal stem cells and may have significant, previously unrecognized, importance in stem cell biology and potential therapeutic interventions.

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    • "In addition to Hh signaling, 20S, 22R, or 22S oxysterol at 10 µM concentration inhibits adipogenic differentiation of MSCs through extracellular signal-regulated kinases (ERK)[130]. 20S, 22R or 22S induced phosphorylated ERK and anti-adipogenic effects of these oxysterols are reversed by a specific ERK signaling inhibitor, PD98059[130]. Furthermore, MSCs treated with Oxysterol 34 or 49 had reduced expression of adipogenic transcripts such as PPARγ2, LPL and aP2, and adipocyte formation induced by PPARγ2 activator, troglitazone, but enhanced expression of osteogenic differentiation markers such as Runx2, Osterix (OSX), ALP, bone sialoprotein (BSP) and OCN in a dose dependent manner with an EC50 of approximately 0.8 µM for Oxysterol 34 and 0.9 µM for Oxysterol 49[131]. Recently, it was discovered that adipocytes contribute to the de novo synthesis of certain oxysterols. "
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    • "Oxysterols have potent effects on cell death processes, including apoptosis induction [15] [16]; reactive oxygen species (ROS) are reportedly involved in this effect [15]. In fact, oxysterols have been shown to exhibit cytotoxicity in a number of cell lines, including smooth muscle cells, fibroblasts, and vascular endothelial cells [17]. Mesenchymal stem cells (MSCs) are multipotent cells characterized by self-renewal and cellular differentiation abilities [18]. "
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    • "Caveolin-1 regulation of differentiation probably occurs within caveolae through interactions with receptors and downstream signaling molecules for differentiation stimuli. In accordance with this idea, MSC osteogenic differentiation can be promoted by the cholesterol biosynthesis inhibitor simvastatin [77-79], and by oxysterols, which suppress caveolin-1 expression and cause caveolin-1 translocation out of caveolae [80,81]. Also, bone marrow MSCs isolated from mouse models of osteoporosis or high bone mineral density have decreased and increased responsiveness to BMP2, respectively, due to dysregulated localization of the BMP receptor 1a with caveolin-1 isoforms, and dysregulated caveolae trafficking in response to BMP2 [82,83]. "
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