Recently we demonstrated that bone marrow derived mesenchymal stem cells (BM-MSC) have high potential as an autologous cell source for vascular tissue engineering. Since cardiovascular disease affects the mostly the elderly, it is important to assess the effects of donor aging on vascular cells or adult stem cells and their suitability for cellular therapies. Previous work showed that autologous smooth muscle cells from older donors produced vascular grafts with inferior mechanical properties that prevented implantation. In addition, in a recent study, we characterized rigorously the effect of organismal aging on the properties of BM-MSC. Our results showed that the proliferation potential and interestingly also the contractile function of BM-MSC declined with donor age.
Recent studies suggested that overexpression of embryonic pluripotency transcription factors may improve the function of adult stem cells. Indeed, our microarray analysis showed that overexpression of one of these factors, Nanog in adult (a)BM-MSC resulted in similar gene expression profile to Nanog+ neonatal (n)BM-MSC. Moreover, forced overexpression of Nanog in adult BM-MSC markedly upregulated genes involved in cell cycle, DNA replication, and DNA damage repair. Therefore, we proposed that overexpression of Nanog may be used to increase proliferation and enhance the differentiation potential of aBM-MSC. To this end, we used lentiviral vectors to overexpress Nanog in neonatal (nBM-MSC) and adult BM-MSC (aBM-MSC) and examined the effects on the properties of stem cells and tissue engineered vascular constructs (TEVs). Our results showed that Nanog overexpression significantly enhanced proliferation and clonogenic capacity of BM-MSC. In addition, TEVs constructed from Nanog expressing BM-MSC demonstrated significantly higher level of vascular contractility compared to that of control BM-TEV. Remarkably, enhanced vascular reactivity of aBM-TEV by Nanog was comparable to that of Nanog+ nBM-TEV. Using siRNA approaches we also demonstrated that Nanog expression increased fibrin gel compaction of BM-MSC through c-Jun amino-terminal kinase (JNK) and independent of TGF-β1.
Overall, expression of Nanog enhanced both the proliferation potential and vascular contractility of aBM-MSC to a similar level as those of nBM-MSC. Our results suggest that Nanog may be used to overcome aging effects of aBM-MSC and may also help us to determine other potential molecular targets that reverse the effects of donor aging on adult stem cells. Ultimately, these efforts may enhance the potential of bone marrow mesenchymal stem cells for treatment of cardiovascular disease as well as other cellular therapies which are more prevalent in the elderly.