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The transcription factor E2F1 is known to regulate cell proliferation and has been thought to modulate tumorigenesis via this mechanism alone. Here we show that mice deficient in E2F1 exhibit enhanced angiogenesis. The proangiogenic phenotype in E2F1 deficiency is the result of overproduction of vascular endothelial growth factor (VEGF) and is prevented by VEGF blockade. Under hypoxic conditions, E2F1 down-regulates the expression of VEGF promoter activity by associating with p53 and specifically down- regulating expression of VEGF but not other hypoxia-inducible genes, suggesting a promoter structure context-dependent regulation mechanism. We found that the minimum VEGF promoter mediating transcriptional repression by E2F1 features an E2F1- binding site with four Sp-1 sites in close proximity. These data disclose an unexpected function of endogenous E2F1: regulation of angiogenic activity via p53-dependent transcriptional control of VEGF expression. [ABSTRACT FROM AUTHOR]

The cell surface receptor α4 integrin plays a critical role in the homing, engraftment, and maintenance of hematopoietic progenitor cells (HPCs) in the bone marrow (BM). Down-regulation or functional blockade of α4 integrin or its ligand vascular cell adhesion molecule-1 mobilizes long-term HPCs. We investigated the role of α4 integrin in the mobilization and homing of BM endothelial progenitor cells (EPCs). EPCs with endothelial colony-forming activity in the BM are exclusively α4 integrin-expressing cells. In vivo, a single dose of anti-α4 integrin antibody resulted in increased circulating EPC counts for 3 d. In hindlimb ischemia and myocardial infarction, systemically administered anti-α4 integrin antibody increased recruitment and incorporation of BM EPCs in newly formed vasculature and improved functional blood flow recovery and tissue preservation. Interestingly, BM EPCs that had been preblocked with anti-α4 integrin ex vivo or collected from α4 integrin-deficient mice incorporated as well as control cells into the neovasculature in ischemic sites, suggesting that α4 integrin may be dispensable or play a redundant role in EPC homing to ischemic tissue. These data indicate that functional disruption of α4 integrin may represent a potential angiogenic therapy for ischemic disease by increasing the available circulating supply of EPCs. [ABSTRACT FROM AUTHOR]

We have identified a subpopulation of stem cells within adult human BM, isolated at the single-cell level, that self-renew without loss of multipotency for more than 140 population doubtings and exhibit the capacity for differentiation into cells of all 3 germ layers. Based on surface marker expression, these clonally expanded human BM-derived multipotent stem cells (hBMSCs) do not appear to belong to any previously described BM-derived stem cell population. Intramyocardial transplantation of hBMSCs after myocardial infarction resulted in robust engraftment of transplanted cells, which exhibited colocalization with markers of cardiomyocyte (CMC), EC, and smooth muscle cell (SMC) identity, consistent with differentiation of hBMSCs into multiple lineages in vivo. Furthermore, upregulation of paracrine factors including angiogenic cytokines and antiapoptotic factors, and proliferation of host ECs and CMCs, were observed in the hBMSC-transplanted hearts. Coculture of hBMSCs with CMCs, ECs, or SMCs revealed that phenotypic changes ofhBMSCs result from both differentiation and fusion. Collectively, the favorable effect of hBMSC transplantation after myocardial infarction appears to be due to augmentation of proliferation and preservation of host myocardial tissues as well as differentiation of hBMSCs for tissue regeneration and repair. To our knowledge, this is the first demonstration that a specific population of multipotent human BM-derived stem cells can induce both therapeutic neovascularization and endogenous and exogenous cardiomyogenesis. [ABSTRACT FROM AUTHOR]

Endothelial cystathionine γ-lyase (CSEγ) contributes to cardiovascular homeostasis, mainly through production of H 2 S. However, the molecular mechanisms that control CSEγ gene expression in the endothelium during cardiovascular diseases are unclear. The aim of the current study is to determine the role of specific histone deacetylases (HDACs) in the regulation of endothelial CSEγ. Reduced CSEγ mRNA expression and protein abundance were observed in human aortic endothelial cells (HAEC) exposed to oxidized LDL (OxLDL) and in aortas from atherogenic apolipoprotein E knockout (ApoE -/- ) mice fed a high-fat diet compared with controls. Intact murine aortic rings exposed to OxLDL (50 μg/ml) for 24 h exhibited impaired endothelium-dependent vasorelaxation that was blocked by CSEγ overexpression or the H 2 S donor NaHS. CSEγ expression was upregulated by pan-HDAC inhibitors and by class II-specific HDAC inhibitors, but not by other class-specific inhibitors. The HDAC6 selective inhibitor tubacin and HDAC6-specific siRNA increased CSEγ expression and blocked OxLDL-mediated reductions in endothelial CSEγ expression and CSEγ promoter activity, indicating that HDAC6 is a specific regulator of CSEγ expression. Consistent with this finding, HDAC6 mRNA, protein expression, and activity were upregulated in OxLDL-exposed HAEC, but not in human aortic smooth muscle cells. HDAC6 protein levels in aortas from high-fat diet-fed ApoE -/- mice were comparable to those in controls, whereas HDAC6 activity was robustly upregulated. Together, our findings indicate that HDAC6 is upregulated by atherogenic stimuli via posttranslational modifications and is a critical regulator of CSEγ expression in vascular endothelium. Inhibition of HDAC6 activity may improve endothelial function and prevent or reverse the development of atherosclerosis. NEW & NOTEWORTHY Oxidative injury to endothelial cells by oxidized LDL reduced cystathionine γ-lyase (CSEγ) expression and H 2 S production, leading to endothelial dysfunction, which was prevented by histone deacetylase 6 (HDAC6) inhibition. Our data suggest HDAC6 as a novel therapeutic target to prevent the development of atherosclerosis., (Copyright © 2017 the American Physiological Society.)

Background: Estradiol (E2) modulates the kinetics of circulating endothelial progenitor cells (EPCs) and favorably affects neovascularization after ischemic injury. However, the roles of estrogen receptors alpha (ER alpha) and beta (ER beta) in EPC biology are largely unknown., Methods and Results: In response to E2, migration, tube formation, adhesion, and estrogen-responsive element-dependent gene transcription activities were severely impaired in EPCs obtained from ER alpha-knockout mice (ER alphaKO) and moderately impaired in ER betaKO EPCs. The number of ER alphaKO EPCs (42.4+/-1.5; P<0.001) and ER betaKO EPCs (55.4+/-1.8; P=0.03) incorporated into the ischemic border zone was reduced as compared with wild-type (WT) EPCs (72.5+/-1.3). In bone marrow transplantation (BMT) models, the number of mobilized endogenous EPCs in E2-treated mice was significantly reduced in ER alphaKO BMT (WT mice transplanted with ER alphaKO bone marrow) (2.03+/-0.18%; P=0.004 versus WT BMT) and ER betaKO BMT (2.62+/-0.07%; P=0.02 versus WT) compared with WT BMT (2.87+/-0.13%) (WT to WT BMT as control) mice. Capillary density at the border zone of ischemic myocardium also was significantly reduced in ER alphaKO BMT and ER betaKO BMT compared with WT mice (WT BMT, 1718+/-75/mm2; ER alphaKO BMT, 1107+/-48/mm2; ER betaKO BMT, 1567+/-50/mm2). ER alpha mRNA was expressed more abundantly on EPCs compared with ER beta. Moreover, vascular endothelial growth factor was significantly downregulated on ER alphaKO EPCs compared with WT EPCs both in vitro and in vivo., Conclusions: Both ER alpha and ER beta contribute to E2-mediated EPC activation and tissue incorporation and to preservation of cardiac function after myocardial infarction. ER alpha plays a more prominent role in this process. Moreover, ER alpha contributes to upregulation of vascular endothelial growth factor, revealing possible mechanisms of an effect of E2 on EPC biology. Finally, these data provide additional evidence of the importance of bone marrow-derived EPC phenotype in ischemic tissue repair.

The cell surface receptor alpha4 integrin plays a critical role in the homing, engraftment, and maintenance of hematopoietic progenitor cells (HPCs) in the bone marrow (BM). Down-regulation or functional blockade of alpha4 integrin or its ligand vascular cell adhesion molecule-1 mobilizes long-term HPCs. We investigated the role of alpha4 integrin in the mobilization and homing of BM endothelial progenitor cells (EPCs). EPCs with endothelial colony-forming activity in the BM are exclusively alpha4 integrin-expressing cells. In vivo, a single dose of anti-alpha4 integrin antibody resulted in increased circulating EPC counts for 3 d. In hindlimb ischemia and myocardial infarction, systemically administered anti-alpha4 integrin antibody increased recruitment and incorporation of BM EPCs in newly formed vasculature and improved functional blood flow recovery and tissue preservation. Interestingly, BM EPCs that had been preblocked with anti-alpha4 integrin ex vivo or collected from alpha4 integrin-deficient mice incorporated as well as control cells into the neovasculature in ischemic sites, suggesting that alpha4 integrin may be dispensable or play a redundant role in EPC homing to ischemic tissue. These data indicate that functional disruption of alpha4 integrin may represent a potential angiogenic therapy for ischemic disease by increasing the available circulating supply of EPCs.