Maintenance of cathepsin D-dependent autophagy-lysosomal function protects against cardiac ischemia/reperfusion injury.

Cardiac ischemia/reperfusion(I/R) induced-cardiac vascular endothelial injury is an important pathological process that appears in the early stage of cardiac I/R injury. The autophagy-lysosomal pathway is essential for the maintenance of cellular homeostasis. However, in cardiac I/R injury, the role of the autophagy-lysosomal pathway is controversial. The present study aimed to use oxygen-glucose deprivation/oxygen-glucose resupply(OGD/OGR) in human coronary artery endothelial cells(HCAECs) with I/R injury to assess the role of the autophagy-lysosomal pathway in I/R-induced endothelial injury. The results revealed lysosomal dysfunction and impaired autophagic flux in endothelial cells exposed to OGD/OGR. Meanwhile, our data showed that the levels of cathepsin D(CTSD) decreased time-dependently. Knockdown of CTSD caused lysosomal dysfunction and impaired autophagic flux. Conversely, restoration of CTSD levels protected HCAECs against OGD/OGR induced-defects in autophagy-lysosomal function and cellular damage. Our findings indicated that I/R induced-impaired autophagic flux, rather than excessive autophagic initiation, mediates endothelial cells injury. The maintenance of autophagy-lysosomal function is critical to protect endothelial cells against I/R injury, and CTSD is a key regulator. Thus, strategies focused on restoring CTSD function are potentially novel treatments for cardiac reperfusion injury.

Ovariectomy Causes Degeneration of Perivascular Adipose Tissue.

Women are more resistant than men to the development of vascular diseases. However, menopause is a factor leading to deterioration of female vascular integrity, and it is reported that the risk of vascular diseases such as atherosclerosis and abdominal aortic aneurysm is increased in postmenopausal women. Although it is suggested that perivascular adipose tissue (PVAT) is deeply involved in the increased risk of vascular disease development, the effect of menopause on PVAT integrity is unknown. In this study, we aimed to elucidate the effect of menopause on PVAT in ovariectomized (OVX) rats. PVAT was divided into 4 regions based on characteristics. Hypertrophy and increased inflammation of adipocytes in the PVAT were observed in the OVX group, but the effects of OVX were different for each region. OVX induced matrix metalloproteinase (MMP) -9 which degrade extracellular matrix such as elastin and collagen fibers in PVAT. Degeneration of the arterial fibers of the thoracic and abdominal aorta were observed in the OVX group. These results indicate that OVX can cause dysfunction of PVAT which can cause degradation of arterial fibers. Appropriate management of PVAT may play an important role in the prevention and treatment of diseases originating from ovarian hypofunction.

Role of Vascular Smooth Muscle Cell Phenotype Switching in Arteriogenesis.

Arteriogenesis is one of the primary physiological means by which the circulatory collateral system restores blood flow after significant arterial occlusion in peripheral arterial disease patients. Vascular smooth muscle cells (VSMCs) are the predominant cell type in collateral arteries and respond to altered blood flow and inflammatory conditions after an arterial occlusion by switching their phenotype between quiescent contractile and proliferative synthetic states. Maintaining the contractile state of VSMC is required for collateral vascular function to regulate blood vessel tone and blood flow during arteriogenesis, whereas synthetic SMCs are crucial in the growth and remodeling of the collateral media layer to establish more stable conduit arteries. Timely VSMC phenotype switching requires a set of coordinated actions of molecular and cellular mediators to result in an expansive remodeling of collaterals that restores the blood flow effectively into downstream ischemic tissues. This review overviews the role of VSMC phenotypic switching in the physiological arteriogenesis process and how the VSMC phenotype is affected by the primary triggers of arteriogenesis such as blood flow hemodynamic forces and inflammation. Better understanding the role of VSMC phenotype switching during arteriogenesis can identify novel therapeutic strategies to enhance revascularization in peripheral arterial disease.

Estrogen Plays a Crucial Role in Rab9-Dependent Mitochondrial Autophagy, Delaying Arterial Senescence.

Background The risk of cardiovascular disease is known to increase after menopause. Mitochondria, which undergo quality control via mitochondrial autophagy, play a crucial role in the regulation of cellular senescence. The aim of this study was to investigate whether the effect of estrogen-mediated protection from senescence on arteries is attributed to the induction of mitochondrial autophagy. Methods and Results We used human umbilical vein cells, vascular smooth muscle cells, and 12-week-old female C57BL/6 mice. The administration of 17ß-estradiol (E2) to cells inhibited cellular senescence and mitochondrial dysfunction. Furthermore, E2 increased mitochondrial autophagy, maintaining mitochondrial function, and retarding cellular senescence. Of note, E2 did not modulate LC3 (light chain 3), and ATG7 (autophagy related 7) deficiency did not suppress mitochondrial autophagy in E2-treated cells. Conversely, E2 increased the colocalization of Rab9 with LAMP2 (lysosomal-associated membrane protein 2) signals. The E2-mediated effects on mitochondrial autophagy were abolished by the knockdown of either Ulk1 or Rab9. These results suggest that E2-mediated mitochondrial autophagy is associated with Rab9-dependent alternative autophagy. E2 upregulated SIRT1 (sirtuin 1) and activated LKB1 (liver kinase B1), AMPK (adenosine monophosphate-activated protein kinase), and Ulk1, indicating that the effect of E2 on the induction of Rab9-dependent alternative autophagy is mediated by the SIRT1/LKB1/AMPK/Ulk1 pathway. Compared with the sham-operated mice, ovariectomized mice showed reduced mitochondrial autophagy and accelerated mitochondrial dysfunction and arterial senescence; these detrimental alterations were successfully rescued by the administration of E2. Conclusions We showed that E2-induced mitochondrial autophagy plays a crucial role in the delay of vascular senescence. The Rab9-dependent alternative autophagy is behind E2-induced mitochondrial autophagy.

Phosphodiesterase 1C integrates store-operated calcium entry and cAMP signaling in leading-edge protrusions of migrating human arterial myocytes.

In addition to maintaining cellular ER Ca2+ stores, store-operated Ca2+ entry (SOCE) regulates several Ca2+-sensitive cellular enzymes, including certain adenylyl cyclases (ADCYs), enzymes that synthesize the secondary messenger cyclic AMP (cAMP). Ca2+, acting with calmodulin, can also increase the activity of PDE1-family phosphodiesterases (PDEs), which cleave the phosphodiester bond of cAMP. Surprisingly, SOCE-regulated cAMP signaling has not been studied in cells expressing both Ca2+-sensitive enzymes. Here, we report that depletion of ER Ca2+ activates PDE1C in human arterial smooth muscle cells (HASMCs). Inhibiting the activation of PDE1C reduced the magnitude of both SOCE and subsequent Ca2+/calmodulin-mediated activation of ADCY8 in these cells. Because inhibiting or silencing Ca2+-insensitive PDEs had no such effects, these data identify PDE1C-mediated hydrolysis of cAMP as a novel and important link between SOCE and its activation of ADCY8. Functionally, we showed that PDE1C regulated the formation of leading-edge protrusions in HASMCs, a critical early event in cell migration. Indeed, we found that PDE1C populated the tips of newly forming leading-edge protrusions in polarized HASMCs, and co-localized with ADCY8, the Ca2+ release activated Ca2+ channel subunit, Orai1, the cAMP-effector, protein kinase A, and an A-kinase anchoring protein, AKAP79. Because this polarization could allow PDE1C to control cAMP signaling in a hyper-localized manner, we suggest that PDE1C-selective therapeutic agents could offer increased spatial specificity in HASMCs over agents that regulate cAMP globally in cells. Similarly, such agents could also prove useful in regulating crosstalk between Ca2+/cAMP signaling in other cells in which dysregulated migration contributes to human pathology, including certain cancers.

Polarized Proteins in Endothelium and Their Contribution to Function.

Protein localization in endothelial cells is tightly regulated to create distinct signaling domains within their tight spatial restrictions including luminal membranes, abluminal membranes, and interendothelial junctions, as well as caveolae and calcium signaling domains. Protein localization in endothelial cells is also determined in part by the vascular bed, with differences between arteries and veins and between large and small arteries. Specific protein polarity and localization is essential for endothelial cells in responding to various extracellular stimuli. In this review, we examine protein localization in the endothelium of resistance arteries, with occasional references to other vessels for contrast, and how that polarization contributes to endothelial function and ultimately whole organism physiology. We highlight the protein localization on the luminal surface, discussing important physiological receptors and the glycocalyx. The protein polarization to the abluminal membrane is especially unique in small resistance arteries with the presence of the myoendothelial junction, a signaling microdomain that regulates vasodilation, feedback to smooth muscle cells, and ultimately total peripheral resistance. We also discuss the interendothelial junction, where tight junctions, adherens junctions, and gap junctions all convene and regulate endothelial function. Finally, we address planar cell polarity, or axial polarity, and how this is regulated by mechanosensory signals like blood flow.

Phosphodiesterase 4D7 selectively regulates cAMP-mediated control of human arterial endothelial cell transcriptomic responses to fluid shear stress.

Human arterial endothelial cells (HAECs) regulate their phenotype by integrating signals encoded in the frictional forces exerted by flowing blood, fluid shear stress (FSS). High laminar FSS promotes establishment of adaptive HAEC phenotype protective against atherosclerosis, whereas low or disturbed FSS cause HAECs to adopt atheroprone phenotypes. A vascular endothelial cadherin (VE cadherin)-based mechanosensory complex allows HAECs to regulate barrier function, cell morphology,/ and gene expression in response to FSS. Previously, we reported that this mechanosensor integrated exchange protein activated by cAMP (EPAC1) and a PDE4D gene derived cyclic nucleotide phosphodiesterase (PDE), but had not identified the PDE4D variant involved. Our hypothesis here was that only one of the two ∼100 kDa PDE4D variants expressed in HAECs coordinated these responses. Now, we show one unique PDE4D splice variant, PDE4D7, controls transcriptional responses of HAECs to FSS while another, PDE4D5, does not. Adaptive transcriptional responses of HAECs subjected to laminar FSS in vitro were blunted in cells in which PDE4D7 was silenced, but unaffected in cells with silenced PDE4D5. This work identifies a specific therapeutic target for the treatment or prevention of atherosclerosis and improves our understanding of the role of cAMP signaling in modulating mechanosensory signal transduction in the vascular endothelium.

Review of the Techniques Used for Investigating the Role Elastin and Collagen Play in Arterial Wall Mechanics.

The arterial wall is characterised by a complex microstructure that impacts the mechanical properties of the vascular tissue. The main components consist of collagen and elastin fibres, proteoglycans, Vascular Smooth Muscle Cells (VSMCs) and ground matrix. While VSMCs play a key role in the active mechanical response of arteries, collagen and elastin determine the passive mechanics. Several experimental methods have been designed to investigate the role of these structural proteins in determining the passive mechanics of the arterial wall. Microscopy imaging of load-free or fixed samples provides useful information on the structure-function coupling of the vascular tissue, and mechanical testing provides information on the mechanical role of collagen and elastin networks. However, when these techniques are used separately, they fail to provide a full picture of the arterial micromechanics. More recently, advances in imaging techniques have allowed combining both methods, thus dynamically imaging the sample while loaded in a pseudo-physiological way, and overcoming the limitation of using either of the two methods separately. The present review aims at describing the techniques currently available to researchers for the investigation of the arterial wall micromechanics. This review also aims to elucidate the current understanding of arterial mechanics and identify some research gaps.

Arterialization requires the timely suppression of cell growth.

The formation of arteries is thought to occur by the induction of a highly conserved arterial genetic programme in a subset of vessels that will later experience an increase in oxygenated blood flow1,2. The initial steps of arterial specification require both the VEGF and Notch signalling pathways3-5. Here, we combine inducible genetic mosaics and transcriptomics to modulate and define the function of these signalling pathways in cell proliferation, arteriovenous differentiation and mobilization. We show that endothelial cells with high levels of VEGF or Notch signalling are intrinsically biased to mobilize and form arteries; however, they are not genetically pre-determined, and can also form veins. Mechanistically, we found that increased levels of VEGF and Notch signalling in pre-arterial capillaries suppresses MYC-dependent metabolic and cell-cycle activities, and promotes the incorporation of endothelial cells into arteries. Mosaic lineage-tracing studies showed that endothelial cells that lack the Notch-RBPJ transcriptional activator complex rarely form arteries; however, these cells regained the ability to form arteries when the function of MYC was suppressed. Thus, the development of arteries does not require the direct induction of a Notch-dependent arterial differentiation programme, but instead depends on the timely suppression of endothelial cell-cycle progression and metabolism, a process that precedes arterial mobilization and complete differentiation.

Ontogeny of arterial macrophages defines their functions in homeostasis and inflammation.

Arterial macrophages have different developmental origins, but the association of macrophage ontogeny with their phenotypes and functions in adulthood is still unclear. Here, we combine macrophage fate-mapping analysis with single-cell RNA sequencing to establish their cellular identity during homeostasis, and in response to angiotensin-II (AngII)-induced arterial inflammation. Yolk sac erythro-myeloid progenitors (EMP) contribute substantially to adventitial macrophages and give rise to a defined cluster of resident immune cells with homeostatic functions that is stable in adult mice, but declines in numbers during ageing and is not replenished by bone marrow (BM)-derived macrophages. In response to AngII inflammation, increase in adventitial macrophages is driven by recruitment of BM monocytes, while EMP-derived macrophages proliferate locally and provide a distinct transcriptional response that is linked to tissue regeneration. Our findings thus contribute to the understanding of macrophage heterogeneity, and associate macrophage ontogeny with distinct functions in health and disease.

Scavenging Intracellular ROS Attenuates p-Cresyl Sulfate-Triggered Osteogenesis through MAPK Signaling Pathway and NF-κB Activation in Human Arterial Smooth Muscle Cells.

Osteogenesis in human arterial smooth muscle cell (HASMC) is a key feature of uremic vascular calcification (UVC). Concerning pro-oxidant properties of p-cresyl sulfate (PCS), the therapeutic effect of reactive oxygen species (ROS) scavenger on PCS triggered inflammatory signaling transduction in osteogenesis was investigated in this translational research. Based on severity level of chronic kidney disease (CKD), arterial specimens with immunohistochemistry stain were quantitatively analyzed for UVC, oxidative injury and osteogenesis along with PCS concentrations. To mimic human UVC, HASMC model was used to explore whether PCS-induced ROS could trigger mitogen-activated protein kinase (MAPK) pathways with nuclear factor-κB (NF-κB) translocation that drive context-specific gene/protein expression, including Runt-related transcription factor 2 (Runx2) and alkaline phosphatase (ALP). In parallel with PCS accumulation, CKD arteries corresponded with UVC severity, oxidative DNA damage (8-hydroxy-2'-deoxyguanosine), Runx2 and ALP. PCS directly phosphorylated extracellular signal-regulated kinase (ERK)/c-Jun N-terminal kinase (JNK)/P38 (pERK/pJNK/pP38) and modulated NF-κB translocation to promote expressions of Runx2 and ALP in HASMC. Notably, intracellular ROS scavenger attenuated pERK signaling cascade and downstream osteogenic differentiation. Collectively, our data demonstrate PCS induces osteogenesis through triggering intracellular ROS, pERK/pJNK/pP38 MAPK pathways and NF-κB translocation to drive Runx2 and ALP expressions, culminating in UVC. Beyond mineral dysregulation, osteocytic conversion in HASMC could be the stimulation of PCS. Thus PCS may act as a pro-osteogenic and pro-calcific toxin. From the perspective of translational medicine, PCS and intracellular ROS could serve as potential therapeutic targets for UVC in CKD patients.

Flexible endoscopic micro-optical coherence tomography for three-dimensional imaging of the arterial microstructure.

Micro-optical coherence tomography (µOCT) is a novel imaging approach enabling visualization of the microstructures of biological tissues at a cellular or sub-cellular level. However, it has been challenging to develop a miniaturized flexible endoscopic µOCT probe allowing helical luminal scanning. In this study, we built a flexible endoscopic µOCT probe with an outer diameter of 1.2 mm, which acquires three-dimensional images of the arterial microstructures via helical scanning with an axial and lateral resolutions of 1.83 µm and 3.38 µm in air, respectively. Furthermore, the depth of focus of the µOCT imaging probe was extended two-fold using a binary phase spatial filter. We demonstrated that the present endoscopic µOCT could image cellular level features of a rabbit artery with high-risk atheroma and a bioresorbable scaffold-implanted swine coronary artery. This highly-translatable endoscopic µOCT will be a useful tool for investigating coronary artery disease and stent biology.

TIM­3 inhibits PDGF­BB­induced atherogenic responses in human artery vascular smooth muscle cells.

Increasing evidence suggests that T­cell immunoglobulin and mucin domain 3 (TIM­3) displays anti­atherosclerotic effects, but its role in vascular smooth muscle cells (VSMCs) has not been reported. The present study aimed to investigate the function of TIM­3 and its roles in human artery VSMCs (HASMCs). A protein array was used to investigate the TIM­3 protein expression profile, which indicated that TIM­3 expression was increased in the serum of patients with lower extremity arteriosclerosis obliterans disease (LEAOD) compared with healthy individuals. Immunohistochemistry and western blotting of arterial tissue further revealed that TIM­3 expression was increased in LEAOD artery tissue compared with normal artery tissue. Additionally, platelet­derived growth factor­BB (PDGF­BB) displayed a positive correlation with TIM­3 expression in HASMCs. TIM­3 decreased the migration and proliferation of PDGF­BB­induced HASMCs, and anti­TIM­3 blocked the effects of TIM­3. The effect of TIM­3 on the proliferation and migration of HASMCs was further investigated using LV­TIM­3­transduced cells. The results revealed that TIM­3 also inhibited PDGF­BB­induced expression of the inflammatory factors interleukin­6 and tumor necrosis factor­α by suppressing NF­κB activation. In summary, the present study revealed that TIM­3 displayed a regulatory role during the PDGF­BB­induced inflammatory reaction in HASMCs, which indicated that TIM­3 may display anti­atherosclerotic effects.

Porcine arterial ECM hydrogel: Designing an in vitro angiogenesis model for long-term high-throughput research.

The field of angiogenesis research provides deep understanding regarding this important process, which plays fundamental roles in tissue development and different abnormalities. In vitro models offer the advantages of low-cost high-throughput research of angiogenesis while sparing animal lives, and enabling the use of human cells. Nevertheless, prevailing in vitro models lack stability and are limited to a few days' assays. This study, therefore, examines the hypothesis that closely mimicking the vascular microenvironment can more reliably support longer angiogenesis processes in vitro. To this end, porcine arterial extracellular matrix (paECM)- a key component of blood vessels-was isolated and processed into a thermally induced hydrogel and characterized in terms of composition, structure, and mechanical properties, thus confirming the preservation of important characteristics of arterial extracellular matrix. This unique hydrogel was further tailored into a three-dimensional model of angiogenesis using endothelial cells and supporting cells, in a configuration that allows high-throughput quantitative analysis of cell viability and proliferation, cell migration, and apoptosis, thus revealing the advantages of paECM over frequently used biomaterials. Markedly, when applied with well-known effectors of angiogenesis, the model measures reflected the expected response, hence validating its efficacy and establishing its potential as a promising tool for the research of angiogenesis.

Assessment of ICAM-1 N-glycoforms in mouse and human models of endothelial dysfunction.

Endothelial dysfunction is a critical event in vascular inflammation characterized, in part, by elevated surface expression of adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1). ICAM-1 is heavily N-glycosylated, and like other surface proteins, it is largely presumed that fully processed, complex N-glycoforms are dominant. However, our recent studies suggest that hypoglycosylated or high mannose (HM)-ICAM-1 N-glycoforms are also expressed on the cell surface during endothelial dysfunction, and have higher affinity for monocyte adhesion and regulate outside-in endothelial signaling by different mechanisms. Whether different ICAM-1 N-glycoforms are expressed in vivo during disease is unknown. In this study, using the proximity ligation assay, we assessed the relative formation of high mannose, hybrid and complex α-2,6-sialyated N-glycoforms of ICAM-1 in human and mouse models of atherosclerosis, as well as in arteriovenous fistulas (AVF) of patients on hemodialysis. Our data demonstrates that ICAM-1 harboring HM or hybrid epitopes as well as ICAM-1 bearing α-2,6-sialylated epitopes are present in human and mouse atherosclerotic lesions. Further, HM-ICAM-1 positively associated with increased macrophage burden in lesions as assessed by CD68 staining, whereas α-2,6-sialylated ICAM-1 did not. Finally, both HM and α-2,6-sialylated ICAM-1 N-glycoforms were present in hemodialysis patients who had AVF maturation failure compared to successful AVF maturation. Collectively, these data provide evidence that HM- ICAM-1 N-glycoforms are present in vivo, and at levels similar to complex α-2,6-sialylated ICAM-1 underscoring the need to better understand their roles in modulating vascular inflammation.

Vitrified Human Umbilical Arteries as Potential Grafts for Vascular Tissue Engineering.

BACKGROUND: The development of a biological based small diameter vascular graft (d < 6 mm), that can be properly stored over a long time period at - 196 °C, in order to directly be used to the patients, still remains a challenge. In this study the decellularized umbilical arteries (UAs) where vitrified, evaluated their composition and implanted to a porcine model, thus serving as vascular graft. METHODS: Human UAs were decellularized using 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) and sodium dodecyl sulfate (SDS) detergents. Then, vitrified with vitrification solution 55 (VS55) solution, remained for 6 months in liquid nitrogen and their extracellular matrix composition was compared to conventionally cryopreserved UAs. Additionally, total hydroxyproline, sulphated glycosaminoglycan and DNA content were quantified in all samples. Finally, the vitrified umbilical arteries implanted as common carotid artery interposition graft to a porcine animal model. RESULTS: Decellularized and vitrified UAs characterized by proper preservation of extracellular matrix proteins and tissue architecture, whereas conventionally cryopreserved samples exhibited a disorganized structure. Total hydroxyproline content was preserved, although sulphated glycosaminoglycan and DNA contents presented significantly alterations in all samples. Implanted UAs successfully recellularized and remodeled as indicated by the histological analysis. CONCLUSION: Decellularized and vitrified UAs retained their structure function properties and can be possible used as an alternative source for readily accessible small diameter vascular grafts.

Ritanserin blocks CaV1.2 channels in rat artery smooth muscles: electrophysiological, functional, and computational studies.

CaV1.2 channel blockers or 5-HT2 receptor antagonists constitute effective therapy for Raynaud's syndrome. A functional link between the inhibition of 5-HT2 receptors and CaV1.2 channel blockade in arterial smooth muscles has been hypothesized. Therefore, the effects of ritanserin, a nonselective 5-HT2 receptor antagonist, on vascular CaV1.2 channels were investigated through electrophysiological, functional, and computational studies. Ritanserin blocked CaV1.2 channel currents (ICa1.2) in a concentration-dependent manner (Kr = 3.61 µM); ICa1.2 inhibition was antagonized by Bay K 8644 and partially reverted upon washout. Conversely, the ritanserin analog ketanserin (100 µM) inhibited ICa1.2 by ~50%. Ritanserin concentration-dependently shifted the voltage dependence of the steady-state inactivation curve to more negative potentials (Ki = 1.58 µM) without affecting the slope of inactivation and the activation curve, and decreased ICa1.2 progressively during repetitive (1 Hz) step depolarizations (use-dependent block). The addition of ritanserin caused the contraction of single myocytes not yet dialyzed with the conventional method. Furthermore, in depolarized rings, ritanserin, and to a lesser extent, ketanserin, caused a concentration-dependent relaxation, which was antagonized by Bay K 8644. Ritanserin and ketanserin were docked at a region of the CaV1.2 α1C subunit nearby that of Bay K 8644; however, only ritanserin and Bay K 8644 formed a hydrogen bond with key residue Tyr-1489. In conclusion, ritanserin caused in vitro vasodilation, accomplished through the blockade of CaV1.2 channels, which was achieved preferentially in the inactivated and/or resting state of the channel. This novel activity encourages the development of ritanserin derivatives for their potential use in the treatment of Raynaud's syndrome.

Genomic Characterization of Endothelial Enhancers Reveals a Multifunctional Role for NR2F2 in Regulation of Arteriovenous Gene Expression.

RATIONALE: Significant progress has revealed transcriptional inputs that underlie regulation of artery and vein endothelial cell fates. However, little is known concerning genome-wide regulation of this process. Therefore, such studies are warranted to address this gap. OBJECTIVE: To identify and characterize artery- and vein-specific endothelial enhancers in the human genome, thereby gaining insights into mechanisms by which blood vessel identity is regulated. METHODS AND RESULTS: Using chromatin immunoprecipitation and deep sequencing for markers of active chromatin in human arterial and venous endothelial cells, we identified several thousand artery- and vein-specific regulatory elements. Computational analysis revealed that NR2F2 (nuclear receptor subfamily 2, group F, member 2) sites were overrepresented in vein-specific enhancers, suggesting a direct role in promoting vein identity. Subsequent integration of chromatin immunoprecipitation and deep sequencing data sets with RNA sequencing revealed that NR2F2 regulated 3 distinct aspects related to arteriovenous identity. First, consistent with previous genetic observations, NR2F2 directly activated enhancer elements flanking cell cycle genes to drive their expression. Second, NR2F2 was essential to directly activate vein-specific enhancers and their associated genes. Our genomic approach further revealed that NR2F2 acts with ERG (ETS-related gene) at many of these sites to drive vein-specific gene expression. Finally, NR2F2 directly repressed only a small number of artery enhancers in venous cells to prevent their activation, including a distal element upstream of the artery-specific transcription factor, HEY2 (hes related family bHLH transcription factor with YRPW motif 2). In arterial endothelial cells, this enhancer was normally bound by ERG, which was also required for arterial HEY2 expression. By contrast, in venous endothelial cells, NR2F2 was bound to this site, together with ERG, and prevented its activation. CONCLUSIONS: By leveraging a genome-wide approach, we revealed mechanistic insights into how NR2F2 functions in multiple roles to maintain venous identity. Importantly, characterization of its role at a crucial artery enhancer upstream of HEY2 established a novel mechanism by which artery-specific expression can be achieved.

Endovascular trophoblast and spiral artery remodeling.

Spiral artery remodeling, which is indispensable for successful pregnancy, is accomplished by endovascular trophoblasts that move upstream along the arterial wall, replace the endothelium, and disrupt the muscular lining. This review outlines the possible factors that could regulate endovascular trophoblast differentiation and invasion. First, high oxygen tension in the spiral artery could initiate endovascular trophoblast invasion. Second, activation of maternal decidual natural killer (dNK) cells could support perivascular invasion of interstitial trophoblasts and consequently could facilitate the endovascular trophoblast invasion. Third, maternal platelets trapped by the endovascular trophoblasts could enhance endovascular trophoblast invasion, which is in part mediated by chemokine CCL5 (C-C motif ligand 5) released from the activated platelets and chemokine receptor CCR1 (C-C chemokine receptor type 1) expressed specifically on the endovascular trophoblasts. The rat, in which trophoblast cells exhibit extensive interstitial and endovascular invasion, could be a suitable model animal for the study of human spiral artery remodeling. Apparently paradoxical results came from the rat study, i.e., exposure to hypoxia or depletion of dNK cells resulted in acceleration of the endovascular trophoblast invasion. This implies the presence of as-yet-undetermined regulator(s) whose effects on endovascular trophoblast invasion surpass the effects of surrounding oxygen tension or maternal dNK cells. In the future, clarification of the molecular differences between human interstitial and endovascular trophoblasts as well as establishment of the pregnant rat model exhibiting shallow endovascular trophoblast invasion and preeclamptic symptoms will contribute to elucidating the mechanism of spiral artery remodeling.

Decellularization of submillimeter-diameter vascular scaffolds using peracetic acid.

Various decellularization methods for allogenic and xenogenic bioscaffolds have been previously reported; however, decellularization methods for very thin (submillimeter-diameter) vascular tissues have not been discussed well. In this study, rat tail arteries (inner diameter, 0.6 mm) were decellularized with peracetic acid (PAA) and DNase I. PAA treatment is expected not only to disrupt cell membranes which improves the decellularization efficiency in the subsequent DNase treatment, but also to sterilize vascular scaffolds. We succeeded in adequate cell removal by immersing in 0.3% isotonic PAA solution and subsequent washing with DNase solution. For the DNase washing process, the perfusion method was superior in terms of cell removal to the static immersion method. Graft lumen was modified with a peptide composed of a collagen binding sequence and endothelial progenitor cell-binding sequence, (Pro-Hyp-Gly)7-Gly-Gly-Gly-Arg-Glu-Asp-Val, as previously reported. They were patent in rat allogeneic transplantation model for 2 weeks, but unexpectedly resulted in graft rupture or tear formation, thereafter, suggesting reduced mechanical strength of the decellularized scaffolds. Histology showed that the thickness of the extracellular matrix (ECM) was decreased by the perfusion of the DNase solution. The method of combination of PAA and DNase was not necessarily optimal for the decellularization of very thin vascular tissues. The decellularization method is a compromise between effective cell removal and maintenance of the ECM nature. Since the acceptability of ECM denaturation by the host tissue highly depends on individual cases, decellularization methods should be carefully selected according to the type of target tissue and its intended use.