The generation of induced pluripotent stem (iPS) cells is an important tool for regenerative medicine. However, the main restriction is the risk of tumor development. In this study we found that during the early stages of somatic cell reprogramming toward a pluripotent state, specific gene expression patterns are altered. Therefore, we developed a method to generate partial-iPS (PiPS) cells by transferring four reprogramming factors (OCT4, SOX2, KLF4, and c-MYC) to human fibroblasts for 4 d. PiPS cells did not form tumors in vivo and clearly displayed the potential to differentiate into endothelial cells (ECs) in response to defined media and culture conditions. To clarify the mechanism of PiPS cell differentiation into ECs, SET translocation (myeloid leukemia-associated) (SET) similar protein (SETSIP) was indentified to be induced during somatic cell reprogramming. Importantly, when PiPS cells were treated with VEGF, SETSIP was translocated to the cell nucleus, directly bound to the VE-cadherin promoter, increasing vascular endothelialcadherin (VE-cadherin) expression levels and EC differentiation. Functionally, PiPS-ECs improved neovascularization and blood flow recovery in a hindlimb ischemic model. Furthermore, PiPS-ECs displayed good attachment, stabilization, patency, and typical vascular structure when seeded on decellularized vessel scaffolds. These findings indicate that reprogramming of fibroblasts into ECs via SETSIP and VEGF has a potential clinical application.shear stress | stem cell therapy | vascular tissue engineering

Reendothelialization involves endothelial progenitor cell (EPC) homing, proliferation, and differentiation, which may be influenced by fluid shear stress and local flow pattern. This study aims to elucidate the role of laminar flow on embryonic stem (ES) cell differentiation and the underlying mechanism. We demonstrated that laminar flow enhanced ES cell–derived progenitor cell proliferation and differentiation into endothelial cells (ECs). Laminar flow stabilized and activated histone deacetylase 3 (HDAC3) through the Flk-1–PI3K–Akt pathway, which in turn deacetylated p53, leading to p21 activation. A similar signal pathway was detected in vascular endothelial growth factor–induced EC differentiation. HDAC3 and p21 were detected in blood vessels during embryogenesis. Local transfer of ES cell–derived EPC incorporated into injured femoral artery and reduced neointima formation in a mouse model. These data suggest that shear stress is a key regulator for stem cell differentiation into EC, especially in EPC differentiation, which can be used for vascular repair, and that the Flk-1–PI3K–Akt–HDAC3–p53–p21 pathway is crucial in such a process.

X-box binding protein 1 (XBP1) is a key signal transducer in endoplasmic reticulum stress response, and its potential role in the atherosclerosis development is unknown. This study aims to explore the impact of XBP1 on maintaining endothelial integrity related to atherosclerosis and to delineate the underlying mechanism. We found that XBP1 was highly expressed at branch points and areas of atherosclerotic lesions in the arteries of ApoE ؊/؊ mice, which was related to the severity of lesion development. In vitro study using human umbilical vein endothelial cells (HUVECs) indicated that disturbed flow increased the activation of XBP1 expression and splicing. Overexpression of spliced XBP1 induced apoptosis of HUVECs and endothelial loss from blood vessels during ex vivo cultures because of caspase activation and down-regulation of VE-cadherin resulting from transcriptional suppression and matrix metalloproteinase-mediated degradation. Reconstitution of VEcadherin by Ad-VEcad significantly increased Ad-XBP1s-infected HUVEC survival. Importantly, Ad-XBP1s gene transfer to the vessel wall of ApoE ؊/؊ mice resulted in development of atherosclerotic lesions after aorta isografting. These results indicate that XBP1 plays an important role in maintaining endothelial integrity and atherosclerosis development, which provides a potential therapeutic target to intervene in atherosclerosis.caspase ͉ endothelial integrity ͉ Ve-cadherin ͉ vessel graft ͉ mouse model A therosclerosis is a leading cause of death worldwide (1, 2).Accumulating evidence suggests that atherosclerosis is a multifactorial disease that can be initiated by risk factors (3-6). An important feature of atherosclerosis is its geographic distribution along the artery wall, i.e., occurring more frequently at curved or branching points in the vasculature, indicating that the flow pattern exerts an important role in the development of atherosclerotic lesions (7,8).Endothelial cells (ECs) are key cellular components of blood vessels, functioning as selectively permeable barriers between blood and tissues. It is believed that risk factors induce EC apoptosis, leading to the denudation or dysfunction of the intact endothelial monolayer, which causes lipid accumulation, monocyte adhesion, and inflammatory reactions that initiate atherosclerotic lesion (5, 9-12). Although information on risk factorinduced atherosclerosis has been accumulating, the underlying mechanism remains unclear.The X-box binding protein 1 (XBP1) was originally identified as a bZIP protein capable of binding to the cis-acting X box present in the promoter regions of human major histocompatibility complex class II genes (13) and is known to be essential for liver growth and B lymphocyte differentiation (14,15). In mammalian cells, XBP1 is a key signal transducer in the endoplasmic reticulum (ER) stress response. It has also been reported that there is a link between XBP1 and human disease (16,17). Although ER stress is reported to be involved in atherosclerosis (18)(19)(20)(21)(22), the role of XB...

Background-Histone deacetylase 3 (HDAC3) is known to play a crucial role in the differentiation of endothelial progenitors. The role of HDAC3 in mature endothelial cells, however, is not well understood. Here, we investigated the function of HDAC3 in preserving endothelial integrity in areas of disturbed blood flow, ie, bifurcation areas prone to atherosclerosis development. Methods and Results-En face staining of aortas from apolipoprotein E-knockout mice revealed increased expression of HDAC3, specifically in these branching areas in vivo, whereas rapid upregulation of HDAC3 protein was observed in endothelial cells exposed to disturbed flow in vitro. Interestingly, phosphorylation of HDAC3 at serine/threonine was observed in these cells, suggesting that disturbed flow leads to posttranscriptional modification and stabilization of the HDAC3 protein. Coimmunoprecipitation experiments showed that HDAC3 and Akt form a complex. Using a series of constructs harboring deletions, we found residues 136 to 206 of HDAC3 to be crucial in this interaction. Enforced expression of HDAC3 resulted in increased phosphorylation of Akt and upregulation of its kinase activity. In line with these findings, knockdown of HDAC3 with lentiviral vectors (shHDAC3) led to a dramatic decrease in cell survival accompanied by apoptosis in endothelial cells. In aortic isografts of apolipoprotein E-knockout mice treated with shHDAC3, a robust atherosclerotic lesion was formed. Surprisingly, 3 of the 8 mice that received shHDAC3-infected grafts died within 2 days after the operation. Miller staining of the isografts revealed disruption of the basement membrane and rupture of the vessel. Conclusions-Our findings demonstrated that HDAC3 serves as an essential prosurvival molecule with a critical role in maintaining the endothelial integrity via Akt activation and that severe atherosclerosis and vessel rupture in isografted vessels of apolipoprotein E-knockout mice occur when HDAC3 is knocked down. (Circulation. 2010;121:132-142.)

Background— Vascular endothelial cell growth factor plays a pivotal role in angiogenesis via regulating endothelial cell proliferation. The X-box binding protein 1 (XBP1) is believed to be a signal transducer in the endoplasmic reticulum stress response. It is unknown whether there is crosstalk between vascular endothelial cell growth factor signaling and XBP1 pathway. Methods and Results— We found that vascular endothelial cell growth factor induced the kinase insert domain receptor internalization and interaction through C-terminal domain with the unspliced XBP1 and the inositol requiring enzyme 1 α in the endoplasmic reticulum, leading to inositol requiring enzyme 1 α phosphorylation and XBP1 mRNA splicing, which was abolished by siRNA-mediated knockdown of kinase insert domain receptor. Spliced XBP1 regulated endothelial cell proliferation in a PI3K/Akt/GSK3β/β-catenin/E2F2–dependent manner and modulated the cell size increase in a PI3K/Akt/GSK3β/β-catenin/E2F2–independent manner. Knockdown of XBP1 or inositol requiring enzyme 1 α decreased endothelial cell proliferation via suppression of Akt/GSK3β phosphorylation, β-catenin nuclear translocation, and E2F2 expression. Endothelial cell–specific knockout of XBP1 ( XBP1ecko ) in mice retarded the retinal vasculogenesis in the first 2 postnatal weeks and impaired the angiogenesis triggered by ischemia. Reconstitution of XBP1 by Ad-XBP1s gene transfer significantly improved angiogenesis in ischemic tissue in XBP1ecko mice. Transplantation of bone marrow from wild-type o XBP1ecko mice could also slightly improve the foot blood reperfusion in ischemic XBP1ecko mice. Conclusions— These results suggest that XBP1 can function via growth factor signaling pathways to regulate endothelial proliferation and angiogenesis.

Cardiovascular disease (CVD) is a major cause of death in smokers, particularly in those with chronic obstructive pulmonary disease (COPD). Circulating endothelial progenitor cells (EPC) are required for endothelial homeostasis, and their dysfunction contributes to CVD. To investigate EPC dysfunction in smokers, we isolated and expanded blood outgrowth endothelial cells (BOEC) from peripheral blood samples from healthy nonsmokers, healthy smokers, and COPD patients. BOEC from smokers and COPD patients showed increased DNA double-strand breaks and senescence compared to nonsmokers. Senescence negatively correlated with the expression and activity of sirtuin-1 (SIRT1), a protein deacetylase that protects against DNA damage and cellular senescence. Inhibition of DNA damage response by silencing of ataxia telangiectasia mutated (ATM) kinase resulted in upregulation of SIRT1 expression and decreased senescence. Treatment of BOEC from COPD patients with the SIRT1 activator resveratrol or an ATM inhibitor (KU-55933) also rescued the senescent phenotype. Using an in vivo mouse model of angiogenesis, we demonstrated that senescent BOEC from COPD patients are dysfunctional, displaying impaired angiogenic ability and increased apoptosis compared to cells from healthy nonsmokers. Therefore, this study identifies epigenetic regulation of DNA damage and senescence as pathogenetic mechanisms linked to endothelial progenitors' dysfunction in smokers and COPD patients. These defects may contribute to vascular disease and cardiovascular events in smokers and could therefore constitute therapeutic targets for intervention.

Conclusions:We developed a protocol to generate SMCs from PiPS cells through a dickkopf 3 signaling pathway, useful for generating tissue-engineered vessels. These findings provide a new insight into the mechanisms of SMC differentiation with vast therapeutic potential.

Background-Embryonic stem cells possess the ability to differentiate into endothelium. The ability to produce large volumes of endothelium from embryonic stem cells could provide a potential therapeutic modality for vascular injury.We describe an approach that selects endothelial cells using magnetic beads that may be used therapeutically to treat arterial injury. Methods and Results-Large numbers of endothelial cells (ECs) with high purity were produced using Sca-1 ϩ cells isolated with magnetic beads from predifferentiated embryonic stem cells (ESCs) cultured in ␣-MEM containing 10 ng/mL VEGF 165 for a minimum of 21 days (esEC). The transcription regulator histone deacetylase (HDAC3) was essential for VEGF-induced EC differentiation. Immunofluorescence or fluorescence-activated cell sorter (FACS) analysis revealed that esECs expressed a full range of EC lineage-specific markers including CD31, CD106, CD144, Flk-1, Flt-1, and von Willebrand factor (vWF). FACS analysis confirmed that 99% of esECs were CD31-positive and 75% vWF-positive. Furthermore, almost all cells were positive for DiI-acLDL uptake. When matrigel containing esECs was subcutaneously implanted into mice, various vessel-like structures were observed indicating their endothelial cell like phenotype. In keeping with this, when esECs infected with adenovirus-LacZ were injected into denuded femoral arteries of mice, they were found to form a neo-endothelium that covered the injured areas (86%Ϯ13.6%), which resulted in a 73% decrease in neointimal area 2 weeks after injury. B alloon angioplasty and stenting is routinely used in clinical practice to treat patients with flow-limiting atherosclerosis. However, stenting is limited by restenosis, a homeostatic response to vascular injury, which leads to the recurrence of symptoms. Balloon inflation at high pressures and the foreign metallic stent struts lead to loss of the endothelium with subsequent smooth muscle cell (SMC) proliferation and matrix deposition leading to luminal narrowing after the procedure. It has been shown that accelerated re-endothelialization by mature endothelial cells (ECs) effectively inhibits SMC migration, proliferation, and neointima formation, and therefore, prevents the development of the early stages of restenosis after vascular injury. 1 In recent years, increasing evidence indicates a repairing capacity of endothelial progenitor cells (EPCs), 2,3 providing a novel cell therapeutic option for various vascular diseases. Conclusions-We conclude thatEmbryonic stem cells (ESCs) are a promising source of pluripotent stem cells. They have the capacity for unlimited growth and self-renewal and the ability to differentiate into all types of mature tissue cells. In the past several years, accumulating evidence indicates that ES cells can differentiate into ECs in vitro or in vivo. 4 -8 Methods to produce large number of ECs with high purity from ES cells in vitro are lacking, and little is known about the mechanism of EC differentiation and the therapeutic potential of ESC-derived ...