Role of Endothelial Nanog in Homeostasis of Adult Tissue Microenvironment

Elevated level of expression of transcription factor (TF) Nanog regulates pluripotency of stem cells. However, the biological significance of low-level expression of Nanog remains unknown. Thus, the goal of this study was to elucidate the role of Nanog in adult vascular endothelial cell (ECs). In view of that, I examined the physiological relevance of quantitative decrease in the expression of Nanog gene in relation to normal EC homeostasis. To examine this, I have used ROSAmT/mG::Nanogfl/+::Cdh5CreERT2 mice to quantitatively reduce the expression of Nanog after tamoxifen (TAM) administration. Here, we incorporated genetic lineage tracing method combined with high-resolution microscopy to visualize green-fluorescent-protein (GFP)-positive ECs in adult vasculature. Loss-of single EC-specific Nanog allele quantitatively reduced VEGFR2 and TERT proteins, and increased EC death. At mechanistic level, ECs stimulated with Wnt3a increased hTERT gene and protein expression; and microscopic analysis showed nuclear accumulation of Nanog and hTERT in response to Wnt3a. Wnt3a also induced Telomerase Activity (TA) in ECs. In a chromatin immunoprecipitation (ChIP) assay, NANOG directly bound to the hTERT promoter; and NANOG transcriptionally activated the hTERT-promoter luciferase reporter activity in ECs. Loss of Nanog in Wnt3a stimulated ECs, reduced hTERT protein level, and reduced luciferase reporter activity. Furthermore, forced expression of NANOG increased expression of hTERT, VEGFR2 and Cyclin-D1 proteins in ECs. Functionally, the loss of single EC-Nanog allele mediated cardiac hypertrophy like phenotype in mouse hearts. Moreover, the re-expression of hTERT into Nanog-depleted ECs partially restored EC survival, proliferation. Together, these series of data uncover a novel mechanism on role of Nanog in the regulation of EC homeostasis in their native tissue microenvironment.