ABSTRACT
Functional signaling between neural stem/progenitor cells (NSPCs) and brain endothelial cells (ECs) is essential to the coordination of organized responses during initial embryonic development and also during tissue repair, which occurs following brain injury. In this study, we investigated the molecular mechanisms underlying this functional signaling, using primary mouse brain ECs and NSPCs from embryonic mouse brain. EC/NSPC co-culture experiments have revealed that neural progenitors secrete factors supporting angiogenesis, which induce noticeable changes in endothelial morphology. We demonstrate that NSPCs influence the expression of mTOR and TGF-ß signaling pathway components implicated in the regulation of angiogenesis. Endothelial morphogenesis, an essential component of vascular development, is a complex process involving gene activation and the upregulation of specific cell signaling pathways. Recently identified small molecules, called microRNAs (miRNAs), regulate the expression of genes and proteins in many tissues, including brain and vasculature. We found that NSPCs induced considerable changes in the expression of at least 24 miRNAs and 13 genes in ECs. Three NSPC-regulated EC miRNAs were identified as the potential primary mediators of this NSPC/EC interaction. We found that the specific inhibition, or overexpression, of miRNAs miR-155, miR-100, and miR-let-7i subsequently altered the expression of major components of the mTOR, TGF-ß and IGF-1R signaling pathways in ECs. Overexpression of these miRNAs in ECs suppressed, while inhibition activated, the in vitro formation of capillary-like structures, a process representative of EC morphogenesis. In addition, we demonstrate that inhibition of FGF, VEGF, and TGF-ß receptor signaling abolished NSPC-promoted changes in the endothelial miRNA profiles. Our findings demonstrate that NSPCs induce changes in the miRNA expression of ECs, which are capable of activating angiogenesis by modulating distinct cell signaling pathways.
ABSTRACT
Bone marrow thymocytes in part mediate the bone-preserving effects of estrogen by decreasing their production of osteoclast growth factors such as interleukin-1 and -6 and tumor necrosis factor alpha in the presence of physiological amounts of estradiol. Although several in vitro studies implicate the T-lymphocyte as a candidate mediator of estrogen signaling in the skeleton, whether these cells or any lymphocytes ordinarily express one or both nuclear estrogen receptors was previously unresolved. The purpose of our investigation was therefore to ascertain, by using real-time PCR, immmunoblotting, and cytometric techniques, if any of the nuclear estrogen receptors could be detected in normal peripheral blood mononuclear cells (PBMNC) collected from healthy volunteers. The results of immunoblotting experiments revealed that both estrogen receptor alpha (ESR1) and beta (ESR2) proteins are expressed in nuclei, but not in the cytoplasm of PBMNC harvested from all of the 15 healthy male and female volunteers (aged 23-50 years) we tested. PBMNCs contained mRNA coding for the two major full-length isoforms of ESR2 and the expression of ESR2 protein was localized within a lymphocyte subpopulation by cytometric analysis. Our data provide further evidence that lymphocytes and monocytes are responsive to estrogen and underscore its importance in modulating the immune response, as well as the vascular and skeletal health of men and women.
