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Improving Vascular Repair and Regeneration through Modulating Methylation in MSCs?

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Review of “Knockdown of DNMT1 and DNMT3a Promotes the Angiogenesis of Human Mesenchymal Stem Cells Leading to Arterial Specific Differentiation” from Stem Cells by Stuart P. Atkinson

Adult vascular repair and regeneration using endothelial cell (EC) differentiated from patient-derived human mesenchymal stem cells (hMSCs) [1] has a bright future. However, some of the basic mechanisms at play, such as the contribution of DNA methylation, are not well understood. DNA methylation can regulate EC differentiation of embryonic stem cells (ESCs) [2], but we need more studies to discover if similar mechanisms are at play in hMSCs.

A new publication from Tong-Cun Zhang and Nan Wang (Tianjin University of Science and Technology, China) sought to find this out by studying DNA methylation dynamics in hMSCs undergoing EC-specific differentiation. Their new Stem Cells study demonstrates that inhibiting the Dnmt1 and Dnmt3a DNA methyltransferases in hMSCs, and thereby reducing DNA methylation levels, may be an interesting means to boost EC-differentiation and enhance their in vivo function in adult vascular repair and regeneration [3].

Initial analysis of DNA methylation status demonstrated high DNA methylation levels at the promoter regions of EC specification and arterial marker genes in hMSCs. However, upon EC-specific differentiation, many of these genes lost promoter specific methylation at the same time as Dnmt1 and Dnmt3a expression levels decreased. 

To confirm any link between DNA methylation and arterial endothelial differentiation, the study employed an inhibitor of DNMT (5-aza-dc) and RNAi-mediated stable knockdown MSCs to study if the forced inhibition of DNA methylation affected endothelial differentiation. The results seemed to pan out - a loss in DNMT activity increased the expression of endothelial marker genes, enhanced endothelial differentiation, and heightened angiogenic capability. This all conferred a greater ability of hMSC-derived ECs and form blood vessels in an in vivo Matrigel plug assay in immunocompromised mice (See Figure) and so confirmed the utility of DNMT modulation in vascular repair and regeneration.

The authors also looked at the mechanism behind DNMTs downregulation during normal EC differentiation, concentrating on miRNAs. A combination of bioinformatic and expression analyses soon identified that miR30a and miR152 may target Dnmt3a and Dnmt1 respectively, while specific in vitro knockdown of these miRNAs inhibited arterial/endothelial marker gene expression.

Collectively, these data suggest that modulation of DNA methylation is key to hMSC endothelial differentiation and arterial cell determination, and highlights a role for miRNAs in this process. Looking forward, the application of this knowledge could enhance differentiation protocols in order to produce sufficient endothelial cells from hMSCs to be relevant for cell therapy and tissue engineering purposes. 

References

  1. Ball SG, Shuttleworth CA, and Kielty CM Platelet-derived growth factor receptors regulate mesenchymal stem cell fate: implications for neovascularization. Expert Opin Biol Ther 2010;10:57-71.
  2. Banerjee S and Bacanamwo M DNA methyltransferase inhibition induces mouse embryonic stem cell differentiation into endothelial cells. Exp Cell Res 2010;316:172-180.
  3. Zhang R, Wang N, Zhang LN, et al. Knockdown of DNMT1 and DNMT3a Promotes the Angiogenesis of Human Mesenchymal Stem Cells Leading to Arterial Specific Differentiation. Stem Cells 2016;34:1273-1283.