Hypoxia differentially regulates arterial and venous smooth muscle cell proliferation via PDGFR-β and VEGFR-2 expression

Novel hypoxia-induced HIF-1αactivation in asthma pathogenesis

BACKGROUND

Asthma's complexity, marked by airway inflammation and remodeling, is influenced by hypoxic conditions. This study focuses on the role of Hypoxia-Inducible Factor-1 Alpha (HIF-1α) and P53 ubiquitination in asthma exacerbation.

METHODS

High-throughput sequencing and bioinformatics were used to identify genes associated with asthma progression, with an emphasis on GO and KEGG pathway analyses. An asthma mouse model was developed, and airway smooth muscle cells (ASMCs) were isolated to create an in vitro hypoxia model. Cell viability, proliferation, migration, and apoptosis were assessed, along with ELISA and Hematoxylin and Eosin (H&E) staining.

RESULTS

A notable increase in HIF-1α was observed in both in vivo and in vitro asthma models. HIF-1α upregulation enhanced ASMCs' viability, proliferation, and migration, while reducing apoptosis, primarily via the promotion of P53 ubiquitination through MDM2. In vivo studies showed increased inflammatory cell infiltration and airway structural changes, which were mitigated by the inhibitor IDF-11,774.

CONCLUSION

The study highlights the critical role of the HIF-1α-MDM2-P53 axis in asthma, suggesting its potential as a target for therapeutic interventions. The findings indicate that modulating this pathway could offer new avenues for treating the complex respiratory disorder of asthma.

Current state of signaling pathways associated with the pathogenesis of idiopathic pulmonary fibrosis

Idiopathic Pulmonary Fibrosis (IPF) represents a chronic and progressive pulmonary disorder distinguished by a notable mortality rate. Despite the elusive nature of the pathogenic mechanisms, several signaling pathways have been elucidated for their pivotal roles in the progression of this ailment. This manuscript aims to comprehensively review the existing literature on the signaling pathways linked to the pathogenesis of IPF, both within national and international contexts. The objective is to enhance the comprehension of the pathogenic mechanisms underlying IPF and offer a scholarly foundation for the advancement of more efficacious therapeutic strategies, thereby fostering research and clinical practices within this domain.

Hypoxia-inducible factor-1: Regulatory mechanisms and drug therapy in myocardial infarction

Myocardial infarction (MI), an acute cardiovascular disease characterized by coronary artery blockage, inadequate blood supply, and subsequent ischemic necrosis of the myocardium, is one of the leading causes of death. The cellular, physiological, and pathological responses following MI are complex, involving multiple intertwined pathological mechanisms. Hypoxia-inducible factor-1 (HIF-1), a crucial regulator of hypoxia, plays a significant role in of the development of MI by modulating the behavior of various cells such as cardiomyocytes, endothelial cells, macrophages, and fibroblasts under hypoxic conditions. HIF-1 regulates various post-MI adaptive reactions to acute ischemia and hypoxia through various mechanisms. These mechanisms include angiogenesis, energy metabolism, oxidative stress, inflammatory response, and ventricular remodeling. With its crucial role in MI, HIF-1 is expected to significantly influence the treatment of MI. However, the drugs available for the treatment of MI targeting HIF-1 are currently limited, and most contain natural compounds. The development of precision-targeted drugs modulating HIF-1 has therapeutic potential for advancing MI treatment research and development. This study aimed to summarize the regulatory role of HIF-1 in the pathological responses of various cells following MI, the diverse mechanisms of action of HIF-1 in MI, and the potential drugs targeting HIF-1 for treating MI, thus providing the theoretical foundations for potential clinical therapeutic targets.

Nucleolin Regulates Pulmonary Artery Smooth Muscle Cell Proliferation under Hypoxia by Modulating miRNA Expression

Hypoxia induces the abnormal proliferation of vascular smooth muscle cells (VSMCs), resulting in the pathogenesis of various vascular diseases. RNA-binding proteins (RBPs) are involved in a wide range of biological processes, including cell proliferation and responses to hypoxia. In this study, we observed that the RBP nucleolin (NCL) was downregulated by histone deacetylation in response to hypoxia. We evaluated its regulatory effects on miRNA expression under hypoxic conditions in pulmonary artery smooth muscle cells (PASMCs). miRNAs associated with NCL were assessed using RNA immunoprecipitation in PASMCs and small RNA sequencing. The expression of a set of miRNAs was increased by NCL but reduced by hypoxia-induced downregulation of NCL. The downregulation of miR-24-3p and miR-409-3p promoted PASMC proliferation under hypoxic conditions. These results clearly demonstrate the significance of NCL-miRNA interactions in the regulation of hypoxia-induced PASMC proliferation and provide insight into the therapeutic value of RBPs for vascular diseases.

DCBLD2 regulates vascular hyperplasia by modulating the platelet derived growth factor receptor-β endocytosis through Caveolin-1 in vascular smooth muscle cells

DCBLD2 is a neuropilin-like transmembrane protein that is up-regulated during arterial remodeling in humans, rats, and mice. Activation of PDGFR-β via PDGF triggers receptor phosphorylation and endocytosis. Subsequent activation of downstream signals leads to the stimulation of phenotypic conversion of VSMCs and arterial wall proliferation, which are common pathological changes in vascular remodeling diseases such as atherosclerosis, hypertension, and restenosis after angioplasty. In this study, we hypothesized that DCBLD2 regulates neointimal hyperplasia through the regulation of PDGFR-β endocytosis of vascular smooth muscle cells (VSMCs) through Caveolin-1 (Cav-1). Compared with wild-type (WT) mice or control littermate mice, the germline or VSMC conditional deletion of the Dcbld2 gene resulted in a significant increase in the thickness of the tunica media in the carotid artery ligation. To elucidate the underlying molecular mechanisms, VSMCs were isolated from the aorta of WT or Dcbld2-/- mice and were stimulated with PDGF. Western blotting assays demonstrated that Dcbld2 deletion increased the PDGF signaling pathway. Biotin labeling test and membrane-cytosol separation test showed that after DCBLD2 was knocked down or knocked out, the level of PDGFR-β on the cell membrane was significantly reduced, while the amount of PDGFR-β in the cytoplasm increased. Co-immunoprecipitation experiments showed that after DCBLD2 gene knock-out, the binding of PDGFR-β and Cav-1 in the cytoplasm significantly increased. Double immunofluorescence staining showed that PDGFR-β accumulated Cav-1/lysosomes earlier than for control cells, which indicated that DCBLD2 gene knock-down or deletion accelerated the endocytosis of PDGF-induced PDGFR-β in VSMCs. In order to confirm that DCBLD2 affects the relationship between Cav-1 and PDGFR-β, proteins extracted from VSMCs cultured in vitro were derived from WT and Dcbld2-/- mice, whereas co-immunoprecipitation suggested that the combination of DCBLD2 and Cav-1 reduced the bond between Cav-1 and PDGFR-β, and DCBLD2 knock-out was able to enhance the interaction between Cav-1 and PDGFR-β. Therefore, the current results suggest that DCBLD2 may inhibit the caveolae-dependent endocytosis of PDGFR-β by anchoring the receptor on the cell membrane. Based on its ability to regulate the activity of PDGFR-β, DCBLD2 may be a novel therapeutic target for the treatment of cardiovascular diseases.

CircRNA-miRNA interactions in atherogenesis

Atherosclerosis is the major cause of coronary artery disease (CAD) which includes unstable angina, myocardial infarction, and heart failure. The onset of atherogenesis, a process of atherosclerotic lesion formation in the intima of arteries, is driven by lipid accumulation, a vicious cycle of reactive oxygen species (ROS)-induced oxidative stress and inflammatory reactions leading to endothelial cell (EC) dysfunction, vascular smooth muscle cell (VSMC) activation, and foam cell formation which further fuel plaque formation and destabilization. In recent years, there is a surge in the number of publications reporting the involvement of circular RNAs (circRNAs) in the pathogenesis of cardiovascular diseases, cancers, and metabolic syndromes. These studies have advanced our understanding on the biological functions of circRNAs. One of the most common mechanism of action of circRNAs reported is the sponging of microRNAs (miRNAs) by binding to the miRNAs response element (MRE), thereby indirectly increases the transcription of their target messenger RNAs (mRNAs). Individual networks of circRNA-miRNA-mRNA associated with atherogenesis have been extensively reported, however, there is a need to connect these findings for a complete overview. This review aims to provide an update on atherogenesis-related circRNAs and analyze the circRNA-miRNA-mRNA interactions in atherogenesis. The atherogenic mechanisms and clinical relevance of each atherogenesis-related circRNA were systematically discussed for better understanding of the knowledge gap in this area.

Mechanoregulation of Vascular Endothelial Growth Factor Receptor 2 in Angiogenesis

The endothelial cells that compose the vascular system in the body display a wide range of mechanotransductive behaviors and responses to biomechanical stimuli, which act in concert to control overall blood vessel structure and function. Such mechanosensitive activities allow blood vessels to constrict, dilate, grow, or remodel as needed during development as well as normal physiological functions, and the same processes can be dysregulated in various disease states. Mechanotransduction represents cellular responses to mechanical forces, translating such factors into chemical or electrical signals which alter the activation of various cell signaling pathways. Understanding how biomechanical forces drive vascular growth in healthy and diseased tissues could create new therapeutic strategies that would either enhance or halt these processes to assist with treatments of different diseases. In the cardiovascular system, new blood vessel formation from preexisting vasculature, in a process known as angiogenesis, is driven by vascular endothelial growth factor (VEGF) binding to VEGF receptor 2 (VEGFR-2) which promotes blood vessel development. However, physical forces such as shear stress, matrix stiffness, and interstitial flow are also major drivers and effectors of angiogenesis, and new research suggests that mechanical forces may regulate VEGFR-2 phosphorylation. In fact, VEGFR-2 activation has been linked to known mechanobiological agents including ERK/MAPK, c-Src, Rho/ROCK, and YAP/TAZ. In vascular disease states, endothelial cells can be subjected to altered mechanical stimuli which affect the pathways that control angiogenesis. Both normalizing and arresting angiogenesis associated with tumor growth have been strategies for anti-cancer treatments. In the field of regenerative medicine, harnessing biomechanical regulation of angiogenesis could enhance vascularization strategies for treating a variety of cardiovascular diseases, including ischemia or permit development of novel tissue engineering scaffolds. This review will focus on the impact of VEGFR-2 mechanosignaling in endothelial cells (ECs) and its interaction with other mechanotransductive pathways, as well as presenting a discussion on the relationship between VEGFR-2 activation and biomechanical forces in the extracellular matrix (ECM) that can help treat diseases with dysfunctional vascular growth.

Circular RNA circLIFR regulates the proliferation, migration, invasion and apoptosis of human vascular smooth muscle cells via the miR-1299/KDR axis

Dysfunction of vascular smooth muscle cells (VSMCs) plays a critical role in the development of intracranial aneurysm (IA). Here, we explored the detailed role and mechanism of circular RNA (circRNA) LIF receptor subunit alpha (circLIFR, circ_0072309) in human umbilical artery smooth muscle cells (HUASMCs). CircLIFR, microRNA (miR)-1299 and kinase insert domain receptor (KDR) expression levels were evaluated by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot assays. Cell proliferation was assessed by Cell Counting Kit-8 (CCK-8) and 5-Ethynyl-2'-Deoxyuridine (EdU) assays. Cell migration was gauged by wound-healing and transwell assays. Cell invasion and apoptosis were detected by transwell assay and flow cytometry, respectively. Direct relationship between miR-1299 and circLIFR or KDR was verified by dual-luciferase reporter and RNA immunoprecipitation (RIP) assays. CircLIFR and KDR were down-regulated and miR-1299 was up-regulated in the artery wall tissues and ASMCs of IA patients. Enforced expression of circLIFR enhanced HUASMC proliferation, migration, invasion, and impeded apoptosis. Mechanistically, circLIFR directly targeted miR-1299, and miR-1299 was a downstream mediator of circLIFR in regulating the proliferation, migration, invasion and apoptosis of HUASMCs. KDR was identified as a direct and functional target of miR-1299 in HUASMCs. Furthermore, circLIFR was a post-transcriptional regulator of KDR expression through miR-1299. Our findings suggest that circLIFR, an underexpressed circRNA in IA, can regulate the proliferation, migration, invasion and apoptosis of HUASMCs depending on the miR-1299/KDR axis.

Prevascularized Micro-/Nano-Sized Spheroid/Bead Aggregates for Vascular Tissue Engineering

Efficient strategies to promote microvascularization in vascular tissue engineering, a central priority in regenerative medicine, are still scarce; nano- and micro-sized aggregates and spheres or beads harboring primitive microvascular beds are promising methods in vascular tissue engineering. Capillaries are the smallest type and in numerous blood vessels, which are distributed densely in cardiovascular system. To mimic this microvascular network, specific cell components and proangiogenic factors are required. Herein, advanced biofabrication methods in microvascular engineering, including extrusion-based and droplet-based bioprinting, Kenzan, and biogripper approaches, are deliberated with emphasis on the newest works in prevascular nano- and micro-sized aggregates and microspheres/microbeads.

Circular RNA circ-ARFIP2 regulates proliferation, migration and invasion in human vascular smooth muscle cells via miR-338-3p-dependent modulation of KDR

Dysfunction of vascular smooth muscle cells (VSMCs) plays a critical role in the pathogenesis of intracranial aneurysm (IA). Circular RNAs (circRNAs) have been implicated in the pathogenesis of IA by reducing microRNA (miRNA) activity. In this paper, we investigated the precise roles of circRNA ADP ribosylation factor interacting protein 2 (circ-ARFIP2, circ_0021001) in VSMC dysfunction. The levels of circ-ARFIP2, miR-338-3p and kinase insert domain receptor (KDR) were detected by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot. Ribonuclease (RNase) R and subcellular fractionation assays were used to assess the stability and localization of circ-ARFIP2, respectively. Cell viability was detected by Cell Counting Kit-8 (CCK-8) assay, and cell invasion was measured by transwell assay. Cell proliferation was gauged by 5-Ethynyl-2'-Deoxyuridine (EdU) assay. Cell migration was evaluated by transwell and wound-healing assays. Targeted correlations among circ-ARFIP2, miR-338-3p and KDR were validated by dual-luciferase reporter and RNA immunoprecipitation (RIP) assays. Circ-ARFIP2 and KDR were underexpressed and miR-338-3p was overexpressed in the arterial wall tissues of IA patients. Overexpression of circ-ARFIP2 in human umbilical artery smooth muscle cells (HUASMCs) showed a significant promotion in cell proliferation, migration and invasion. Mechanistically, circ-ARFIP2 targeted miR-338-3p, and circ-ARFIP2 regulated cell behaviors by miR-338-3p. KDR was a direct and functional target of miR-338-3p. Moreover, KDR was a downstream effector of circ-ARFIP2 function. Circ-ARFIP2 regulated KDR expression by targeting miR-338-3p. Our present findings demonstrated that the increased level of circ-ARFIP2 enhanced HUASMC proliferation, migration and invasion at least in part by the miR-338-3p/KDR axis.

Effect of pore size and spacing on neovascularization of a biodegradble shape memory polymer perivascular wrap

Neointimal hyperplasia (NH) is a main source of failures in arteriovenous fistulas and vascular grafts. Several studies have demonstrated the promise of perivascular wraps to reduce NH via promotion of adventitial neovascularization and providing mechanical support. Limited clinical success thus far may be due to inappropriate material selection (e.g., nondegradable, too stiff) and geometric design (e.g., pore size and spacing, diameter). The influence of pore size and spacing on implant neovascularization is investigated here for a new biodegradable, thermoresponsive shape memory polymer (SMP) perivascular wrap. Following an initial pilot, 21 mice were each implanted with six scaffolds: four candidate SMP macroporous designs (a-d), a nonporous SMP control (e), and microporous GORETEX (f). Mice were sacrificed after 4 (N = 5), 14 (N = 8), and 28 (N = 8) days. There was a statistically significant increase in neovascularization score between all macroporous groups compared to nonporous SMP (p < .023) and microporous GORETEX (p < .007) controls at Day 28. Wider-spaced, smaller-sized pore designs (223 μm-spaced, 640 μm-diameter Design c) induced the most robust angiogenic response, with greater microvessel number (p < .0114) and area (p < .0055) than nonporous SMPs and GORETEX at Day 28. This design also produced significantly greater microvessel density than nonporous SMPs (p = 0.0028) and a smaller-spaced, larger-sized pore (155 μm-spaced, 1,180 μm-sized Design b) design (p = .0013). Strong neovascularization is expected to reduce NH, motivating further investigation of this SMP wrap with controlled pore spacing and size in more advanced arteriovenous models.

Biomaterials for Bioprinting Microvasculature

Microvasculature functions at the tissue and cell level, regulating local mass exchange of oxygen and nutrient-rich blood. While there has been considerable success in the biofabrication of large- and small-vessel replacements, functional microvasculature has been particularly challenging to engineer due to its size and complexity. Recently, three-dimensional bioprinting has expanded the possibilities of fabricating sophisticated microvascular systems by enabling precise spatiotemporal placement of cells and biomaterials based on computer-aided design. However, there are still significant challenges facing the development of printable biomaterials that promote robust formation and controlled 3D organization of microvascular networks. This review provides a thorough examination and critical evaluation of contemporary biomaterials and their specific roles in bioprinting microvasculature. We first provide an overview of bioprinting methods and techniques that enable the fabrication of microvessels. We then offer an in-depth critical analysis on the use of hydrogel bioinks for printing microvascularized constructs within the framework of current bioprinting modalities. We end with a review of recent applications of bioprinted microvasculature for disease modeling, drug testing, and tissue engineering, and conclude with an outlook on the challenges facing the evolution of biomaterials design for bioprinting microvasculature with physiological complexity.

Decreased expression of circ_0020397 in intracranial aneurysms may be contributing to decreased vascular smooth muscle cell proliferation via increased expression of miR-138 and subsequent decreased KDR expression

Dysfunction of vascular smooth muscle cells (VSMCs) mediates intracranial aneurysm (IA). KDR is reported to alleviate IA progression via promoting VSMC proliferation, while the upstream regulators are still unclear. Arterial wall tissues at the aneurysm site from 12 patients were obtained. The real-time PCR result indicated that circRNA_0020397 was down-regulated, but miR-138 was up-regulated in artery wall tissues and cells of IA. Overexpressed circRNA_0020397 promoted proliferation of human umbilical artery SMCs. MiR-138 negatively regulated KDR via binding with 3'UTR of KDR mRNA. The expression of circRNA_0020397 was negatively correlated with miR-138. In conclusion, our findings demonstrated that decreased expression of circRNA_0020397 in IA may contribute to the decreased VSMC proliferation via increasing miR-138 expression and subsequently decreasing KDR expression.

Role of smooth muscle cells in coronary artery bypass grafting failure

Atherosclerosis is the underlying pathology of many cardiovascular diseases. The formation and rupture of atherosclerotic plaques in the coronary arteries results in angina and myocardial infarction. Venous coronary artery bypass grafts are designed to reduce the consequences of atherosclerosis in the coronary arteries by diverting blood flow around the atherosclerotic plaques. However, vein grafts suffer a high failure rate due to intimal thickening that occurs as a result of vascular cell injury and activation and can act as 'a soil' for subsequent atherosclerotic plaque formation. A clinically-proven method for the reduction of vein graft intimal thickening and subsequent major adverse clinical events is currently not available. Consequently, a greater understanding of the underlying mechanisms of intimal thickening may be beneficial for the design of future therapies for vein graft failure. Vein grafting induces inflammation and endothelial cell damage and dysfunction, that promotes vascular smooth muscle cell (VSMC) migration, and proliferation. Injury to the wall of the vein as a result of grafting leads to the production of chemoattractants, remodelling of the extracellular matrix and cell-cell contacts; which all contribute to the induction of VSMC migration and proliferation. This review focuses on the role of altered behaviour of VSMCs in the vein graft and some of the factors which critically lead to intimal thickening that pre-disposes the vein graft to further atherosclerosis and re-occurrence of symptoms in the patient.

Evaluation of Venous Stenosis Angioplasty in a Murine Arteriovenous Fistula Model

PURPOSE

To develop a clinically relevant model of percutaneous transluminal angioplasty (PTA) of venous stenosis in mice with arteriovenous fistula (AVF); to test the hypothesis that there is increased wall shear stress (WSS) after PTA; and to histologically characterize the vessels.

MATERIALS AND METHODS

Thirteen C57BL/6J male mice, 6-8 weeks old, underwent partial nephrectomy to create chronic kidney disease. Twenty-eight days later, an AVF was created from the right external jugular vein to the left carotid artery. Fourteen days later, an angioplasty or sham procedure was performed, and the mice were sacrificed 14 days later for histologic evaluation to identify the cells contributing to the vascular remodeling (α-SMA, FSP-1, CD31, and CD68), proliferation (Ki-67), cell death (TUNEL), and hypoxia staining (HIF-1α). Histomorphometric analysis was performed to assess lumen area, neointima+media area, and cellular density. Ultrasound was performed weekly after creation of the AVF.

RESULTS

Venous stenosis occurred 14 days after the creation of an AVF. PTA-treated vessels had significantly higher WSS; average peak systolic velocity, with increased lumen vessel area; and decreased neointima + media area compared to sham controls. There was a significant decrease in the staining of smooth muscle cells, fibroblasts, macrophages, HIF-1α, proliferation, and apoptosis and an increase in CD31-(+) cells.

CONCLUSIONS

A clinically relevant model of PTA of venous stenosis in mice was created. PTA-treated vessels had increased lumen vessel area and WSS. The alterations in tissue markers of vascular remodeling, tissue hypoxia, proliferation, and cell death may be implications for future design of drug and device development.

Beyond endothelial cells: Vascular endothelial growth factors in heart, vascular anomalies and placenta

Vascular endothelial growth factors regulate vascular and lymphatic growth. Dysregulation of VEGF signaling is connected to many pathological states, including hemangiomas, arteriovenous malformations and placental abnormalities. In heart, VEGF gene transfer induces myocardial angiogenesis. Besides vascular and lymphatic endothelial cells, VEGFs affect multiple other cell types. Understanding VEGF biology and its paracrine signaling properties will offer new targets for novel treatments of several diseases.

Screening of candidate G-quadruplex ligands for the human c-KIT promotorial region and their effects in multiple in-vitro models

Stabilization of G-quadruplex (G4) structures in promoters is a novel promising strategy to regulate gene expression at transcriptional and translational levels. c-KIT proto-oncogene encodes for a tyrosine kinase receptor. It is involved in several physiological processes, but it is also dysregulated in many diseases, including cancer. Two G-rich sequences able to fold into G4, have been identified in c-KIT proximal promoter, thus representing suitable targets for anticancer intervention. Herein, we screened an “in house” library of compounds for the recognition of these G4 elements and we identified three promising ligands. Their G4-binding properties were analyzed and related to their antiproliferative, transcriptional and post-transcriptional effects in MCF7 and HGC27 cell lines. Besides c-KIT, the transcriptional analysis covered a panel of oncogenes known to possess G4 in their promoters.

From these studies, an anthraquinone derivative (AQ1) was found to efficiently downregulate c-KIT mRNA and protein in both cell lines. The targeted activity of AQ1 was confirmed using c-KIT–dependent cell lines that present either c-KIT mutations or promoter engineered (i.e., α155, HMC1.2 and ROSA cells).

Present results indicate AQ1 as a promising compound for the target therapy of c-KIT-dependent tumors, worth of further and in depth molecular investigations.

PDGF-mediated PI3K/AKT/β-catenin signaling regulates gap junctions in corpus cavernosum smooth muscle cells

Erectile dysfunction (ED) is the most common sexual disorder that men report to healthcare providers. Gap junctions (GJs) are thought to be responsible for synchronous shrinkage of corpus cavernosum smooth muscle cells (CCSMCs), and play thus an important role in the maintenance of an erection. Hypoxia has been suggested as a pathological mechanism underlying ED. Here we demonstrate that hypoxia increased the expression of platelet-derived growth factor (PDGF) and the main GJ component connexin (Cx)43 in CCSMCs. Inhibiting PDGF receptor (PDGFR) activity decreased Cx43 expression. Treatment with different concentrations of PDGF increased the levels of phosphorylated protein kinase B (AKT), β-catenin, and Cx43, whereas inhibition of PDGFR or activation of phosphatidylinositol 3 kinase (PI3K)/AKT signaling altered β-catenin and Cx43 expression. Meanwhile, silencing β-catenin resulted in the downregulation of Cx43. These results demonstrate that PDGF secretion by CCSMCs and vascular endothelial cells is enhanced under hypoxic conditions, leading to increased Cx43 expression through PI3K/AKT/β-catenin signaling and ultimately affecting GJ function in ED. Thus, targeting this pathway is a potential therapeutic strategy for the treatment of ED.

RNAi therapy to the wall of arteries and veins: anatomical, physiologic, and pharmacological considerations

Background

Cardiovascular disease remains a major health care challenge. The knowledge about the underlying mechanisms of the respective vascular disease etiologies has greatly expanded over the last decades. This includes the contribution of microRNAs, endogenous non-coding RNA molecules, known to vastly influence gene expression. In addition, short interference RNA has been established as a mechanism to temporarily affect gene expression. This review discusses challenges relating to the design of a RNA interference therapy strategy for the modulation of vascular disease. Despite advances in medical and surgical therapies, atherosclerosis (ATH), aortic aneurysms (AA) are still associated with high morbidity and mortality. In addition, intimal hyperplasia (IH) remains a leading cause of late vein and prosthetic bypass graft failure. Pathomechanisms of all three entities include activation of endothelial cells (EC) and dedifferentiation of vascular smooth muscle cells (VSMC). RNA interference represents a promising technology that may be utilized to silence genes contributing to ATH, AA or IH. Successful RNAi delivery to the vessel wall faces multiple obstacles. These include the challenge of cell specific, targeted delivery of RNAi, anatomical barriers such as basal membrane, elastic laminae in arterial walls, multiple layers of VSMC, as well as adventitial tissues. Another major decision point is the route of delivery and potential methods of transfection. A plethora of transfection reagents and adjuncts have been described with varying efficacies and side effects. Timing and duration of RNAi therapy as well as target gene choice are further relevant aspects that need to be addressed in a temporo-spatial fashion.

Conclusions

While multiple preclinical studies reported encouraging results of RNAi delivery to the vascular wall, it remains to be seen if a single target can be sufficient to the achieve clinically desirable changes in the injured vascular wall in humans. It might be necessary to achieve simultaneous and/or sequential silencing of multiple, synergistically acting target genes. Some advances in cell specific RNAi delivery have been made, but a reliable vascular cell specific transfection strategy is still missing. Also, off-target effects of RNAi and unwanted effects of transfection agents on gene expression are challenges to be addressed. Close collaborative efforts between clinicians, geneticists, biologists, and chemical and medical engineers will be needed to provide tailored therapeutics for the various types of vascular diseases.

Hyperbaric oxygen inhibits venous neointimal hyperplasia following arteriovenous fistulization

Hypoxia following arteriovenous fistulization results in venous neointimal hyperplasia (VNH), potentially causing early arteriovenous fistula (AVF) dysfunction. In this study, we used hyperbaric oxygen (HBO) in a rabbit model of AVF to determine whether it could ameliorate early AVF failure. Chronic renal failure was induced by adenine in 96 adult rabbits randomly divided into 3 groups (n=32 in each group). The sham + HBO group underwent sham operation and received HBO. The AVF alone group underwent fistulization, but did not receive HBO. The AVF + HBO group underwent fistulization and received HBO. Each group was further divided into 4 subgroups of 8 rabbits each that were euthanized at 1, 7, 14 or 28 days post-operatively. At each time point, blood flow changes in the AVF venous segment were detected using a high-frequency duplex ultrasonography system. Immunohistochemical staining for proliferating cell nuclear antigen (PCNA), and hematoxylin and eosin staining were performed to evaluate VNH. Western blot analysis was performed to confirm the expression of hypoxia-inducible factor (HIF)-1α. At 14 and 28 days following HBO treatment, blood flow in the AVF + HBO group was greater than that at day 0. The AVF + HBO group had a smaller ratio of intima to media area, a lower HIF-1α protein expression, and a smaller percentage of PCNA-positive cells in the proximal vein than did the AVF alone group. Our results thus suggest that continuous HBO treatment following AVF significantly inhibits VNH and promotes blood flow. Therefore, early AVF failure may be prevented by the use of HBO therapy.

Histone deacetylase inhibitors promote eNOS expression in vascular smooth muscle cells and suppress hypoxia-induced cell growth

Hypoxia stimulates excessive growth of vascular smooth muscle cells (VSMCs) contributing to vascular remodelling. Recent studies have shown that histone deacetylase inhibitors (HDIs) suppress VSMC proliferation and activate eNOS expression. However, the effects of HDI on hypoxia-induced VSMC growth and the role of activated eNOS in VSMCs are unclear. Using an EdU incorporation assay and flow cytometry analysis, we found that the HDIs, butyrate (Bur) and suberoylanilide hydroxamic acid (SAHA) significantly suppressed the proliferation of hypoxic VSMC lines and induced apoptosis. Remarkable induction of cleaved caspase 3, p21 expression and reduction of PCNA expression were also observed. Increased eNOS expression and enhanced NO secretion by hypoxic VSMC lines were detected using Bur or SAHA treatment. Knockdown of eNOS by siRNA transfection or exposure of hypoxic VSMCs to NO scavengers weakened the effects of Bur and SAHA on the growth of hypoxic VSMCs. In animal experiments, administration of Bur to Wistar rats exposed to hypobaric hypoxia for 28 days ameliorated the thickness and collagen deposition in pulmonary artery walls. Although the mean pulmonary arterial pressure (mPAP) was not obviously decreased with Bur in hypoxic rats, right ventricle hypertrophy index (RVHI) was decreased and the oxygen partial pressure of arterial blood was elevated. Furthermore, cell viability was decreased and eNOS and cleaved caspase 3 were induced in HDI-treated rat pulmonary arterial SMCs. These findings imply that HDIs prevent hypoxia-induced VSMC growth, in correlation with activated eNOS expression and activity in hypoxic VSMCs.

Biomaterial-Based Approaches to Address Vein Graft and Hemodialysis Access Failures

Veins used as grafts in heart bypass or as access points in hemodialysis exhibit high failure rates, thereby causing significant morbidity and mortality for patients. Interventional or revisional surgeries required to correct these failures have been met with limited success and exorbitant costs, particularly for the US Centers for Medicare & Medicaid Services. Vein stenosis or occlusion leading to failure is primarily the result of neointimal hyperplasia. Systemic therapies have achieved little long-term success, indicating the need for more localized, sustained, biomaterial-based solutions. Numerous studies have demonstrated the ability of external stents to reduce neointimal hyperplasia. However, successful results from animal models have failed to translate to the clinic thus far, and no external stent is currently approved for use in the US to prevent vein graft or hemodialysis access failures. This review discusses current progress in the field, design considerations, and future perspectives for biomaterial-based external stents. More comparative studies iteratively modulating biomaterial and biomaterial-drug approaches are critical in addressing mechanistic knowledge gaps associated with external stent application to the arteriovenous environment. Addressing these gaps will ultimately lead to more viable solutions that prevent vein graft and hemodialysis access failures.

Age-dependent expression of VEGFR2 in deep brain arteries in small vessel disease, CADASIL, and healthy brains

Vascular myocytes are central to brain aging. Small vessel disease (SVD; arteriolosclerosis) is a widespread cause of lacunar stroke and vascular dementia and is characterized by fibrosis and depletion of vascular myocytes in small penetrating arteries. Vascular endothelial growth factor (VEGF) is associated with brain aging, and Immunolabeling for vascular endothelial growth factor receptor 2 (VEGFR2) is a potent determinant of cell fate. Here, we tested whether VEGFR2 in vascular myocytes is associated with older age and SVD in human brain. Immunolabeling for VEGFR2 in deep gray matter was assessed in older people with or without moderate-severe SVD or in younger people without brain pathology or with a monogenic form of SVD (Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy). All cases were without Alzheimer's disease pathology. Myocyte VEGFR2 was associated with increasing age (p = 0.0026) but not with SVD pathology or with sclerotic index or blood vessel density. We conclude that VEGFR2 is consistently expressed in small artery myocytes of older people and may mediate effects of VEGF on brain vascular aging.

Transforming growth factor-beta 1 produced by vascular smooth muscle cells predicts fibrosis in the gastrocnemius of patients with peripheral artery disease

Background

Lower leg ischemia, myopathy, and limb dysfunction are distinguishing features of peripheral artery disease (PAD). The myopathy of PAD is characterized by myofiber degeneration in association with extracellular matrix expansion, and increased expression of transforming growth factor-beta 1 (TGF-β1; a pro-fibrotic cytokine). In this study, we evaluated cellular expression of TGF-β1 in gastrocnemius of control (CTRL) and PAD patients and its relationship to deposited collagen, fibroblast accumulation and limb hemodynamics.

Methods

Gastrocnemius biopsies were collected from PAD patients with claudication (PAD-II; N = 25) and tissue loss (PAD-IV; N = 20) and from CTRL patients (N = 20). TGF-β1 in slide-mounted specimens was labeled with fluorescent antibodies and analyzed by quantitative wide-field, fluorescence microscopy. We evaluated co-localization of TGF-β1 with vascular smooth muscle cells (SMC) (high molecular weight caldesmon), fibroblasts (TE-7 antigen), macrophages (CD163), T cells (CD3) and endothelial cells (CD31). Collagen was stained with Masson Trichrome and collagen density was determined by quantitative bright-field microscopy with multi-spectral imaging.

Results

Collagen density increased from CTRL to PAD-II to PAD-IV specimens (all differences p < 0.05) and was prominent around microvessels. TGF-β1 expression increased with advancing disease (all differences p < 0.05), correlated with collagen density across all specimens (r = 0.864; p < 0.001), associated with fibroblast accumulation, and was observed exclusively in SMC. TGF-β1 expression inversely correlated with ankle-brachial index across PAD patients (r = −0.698; p < 0.001).

Conclusions

Our findings support a progressive fibrosis in the gastrocnemius of PAD patients that is caused by elevated TGF-β1 production in the SMC of microvessels in response to tissue hypoxia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0790-3) contains supplementary material, which is available to authorized users.

Prevention of Venous Neointimal Hyperplasia by a Multitarget Receptor Tyrosine Kinase Inhibitor

BACKGROUND/AIMS

Venous neointimal hyperplasia (NH) is the predominant cause of stenosis in hemodialysis arteriovenous grafts (AVG), but there is currently no clinically used therapy to prevent NH.

METHODS

A porcine AVG model was used to identify potential pharmacological targets to prevent NH. Sunitinib, a broad-spectrum tyrosine kinase inhibitor, was examined as a potential anti-NH drug utilizing in vitro and ex vivo models.

RESULTS

In an in vivo porcine model, PDGF, VEGF and their receptors PDGFR-α and VEGFR-2 were upregulated at the venous anastomosis within 2 weeks after AVG placement, with NH development by 4 weeks. Sunitinib inhibited PDGF-stimulated proliferation, migration, phosphorylation of MAPK and PI3K/Akt proteins and changes in the expression of cell-cycle regulatory proteins in vascular smooth-muscle cells as well as VEGF-stimulated endothelial cell proliferation in vitro. In an ex vivo model, significant NH was observed in porcine vein segments perfused for 12 days under pathological shear stress. Sunitinib (100 nM) inhibited NH formation, with the intima-to-lumen area ratio decreasing from 0.45 ± 0.25 to 0.04 ± 0.02 (p < 0.05) with treatment.

CONCLUSION

These findings demonstrate sunitinib to be a potential NH-preventive drug as well as the utility of an ex vivo model to investigate pharmacotherapies under pathophysiological flow conditions.

Hypoxia Differentially Regulates Arterial and Venous Smooth Muscle Cell Migration

OBJECTIVE

Intimal hyperplasia (IH) is a clinical concern leading to failure of up to 50% of vein grafts and 10% of arterial grafts after 10 years with no known current treatment. Recent studies have shown that hypoxia differentially regulates proliferation of vein derived smooth muscle cells (V-SMC) compared to artery derived smooth muscle cells (A-SMC). The objective of this study is to evaluate the effect of hypoxia on cellular migration and the mechanisms underlying the differential effects of hypoxia on A-SMC and V-SMC migration.

METHODS AND RESULTS

Hypoxic treatment (3-5% O2) of Smooth Muscle Cells (SMC) resulted in differential migration in scratch wound and electric cell substrate impedance sensing (ECIS) assays. Hypoxia led to greater migration compared to normoxia with venous derived wound closure (V-SMC 30.8% Normoxia to 67% Hypoxia) greater than arterial wound closure (A-SMC 6.2% Normoxia to 24.7% Hypoxia). Paracrine factors secreted by hypoxic endothelial cells induced more migration in SMC compared to factors secreted by normoxic endothelial cells. Migration of V-SMC was greater than A-SMC in the presence of paracrine factors. Neutralizing antibody to Vascular Endothelial Growth Factor Receptor -1 (VEGFR-1) completely inhibited V-SMC migration while there was only partial inhibition of A-SMC migration. A-SMC migration was completely inhibited by Platelet Derived Growth Factor BB (PDGF-BB) neutralizing antibody. p38 Mitogen Activated Protein kinase (p38 MAPK) inhibitor pre-incubation completely inhibited migration induced by paracrine factors in both A-SMC and V-SMC.

CONCLUSION

Our study determines that SMC migration under hypoxia occurs via both an autocrine and paracrine mechanism and is dependent on Vascular Endothelial Growth Factor-A (VEGF-A) in V-SMC and PDGF-BB in A-SMC. Migration of both A-SMC and V-SMC is inhibited by p38 MAPK inhibitor. These studies suggest that pharmacotherapeutic strategies directed at modulating p38 MAPK activity can be exploited to prevent IH in vascular grafts.

IGF-1 signaling in neonatal hypoxia-induced pulmonary hypertension: Role of epigenetic regulation

Pulmonary hypertension is a fatal disease characterized by a progressive increase in pulmonary artery pressure accompanied by pulmonary vascular remodeling and increased vasomotor tone. Although some biological pathways have been identified in neonatal hypoxia-induced pulmonary hypertension (PH), little is known regarding the role of growth factors in the pathogenesis of PH in neonates. In this study, using a model of hypoxia-induced PH in neonatal mice, we demonstrate that the growth factor insulin-like growth factor-1 (IGF-1), a potent activator of the AKT signaling pathway, is involved in neonatal PH. After exposure to hypoxia, IGF-1 signaling is activated in pulmonary endothelial and smooth muscle cells in vitro, and the IGF-1 downstream signal pAKT(S473) is upregulated in lungs of neonatal mice. We found that IGF-1 regulates ET-1 expression in pulmonary endothelial cells and that IGF-1 expression is regulated by histone deacetylases (HDACs). In addition, there is a differential cytosine methylation site in the IGF-1 promoter region in response to neonatal hypoxia. Moreover, inhibition of HDACs with apicidin decreases neonatal hypoxia-induced global DNA methylation levels in lungs and specific cytosine methylation levels around the pulmonary IGF-1 promoter region. Finally, HDAC inhibition with apicidin reduces chronic hypoxia-induced activation of IGF-1/pAKT signaling in lungs and attenuates right ventricular hypertrophy and pulmonary vascular remodeling. Taken together, we conclude that IGF-1, which is epigenetically regulated, is involved in the pathogenesis of pulmonary hypertension in neonatal mice. This study implicates a novel HDAC/IGF-1 epigenetic pathway in the regulation of hypoxia-induced PH and warrants further study of the role of IGF-1 in neonatal pulmonary hypertensive disease.

Endothelial uncoupling protein 2 regulates mitophagy and pulmonary hypertension during intermittent hypoxia

OBJECTIVES

Pulmonary hypertension (PH) is a process of lung vascular remodeling, which can lead to right heart dysfunction and significant morbidity. The underlying mechanisms leading to PH are not well understood, and therapies are limited. Using intermittent hypoxia (IH) as a model of oxidant-induced PH, we identified an important role for endothelial cell mitophagy via mitochondrial uncoupling protein 2 (Ucp2) in the development of IH-induced PH.

APPROACH AND RESULTS

Ucp2 endothelial knockout (VE-KO) and Ucp2 Flox (Flox) mice were subjected to 5 weeks of IH. Ucp2 VE-KO mice exhibited higher right ventricular systolic pressure and worse right heart hypertrophy, as measured by increased right ventricle weight/left ventricle plus septal weight (RV/LV+S) ratio, at baseline and after IH. These changes were accompanied by increased mitophagy. Primary mouse lung endothelial cells transfected with Ucp2 siRNA and subjected to cyclic exposures to CoCl2 (chemical hypoxia) showed increased mitophagy, as measured by PTEN-induced putative kinase 1 and LC3BII/I ratios, decreased mitochondrial biogenesis, and increased apoptosis. Similar results were obtained in primary lung endothelial cells isolated from VE-KO mice. Moreover, silencing PTEN-induced putative kinase 1 in the endothelium of Ucp2 knockout mice, using endothelial-targeted lentiviral silencing RNA in vivo, prevented IH-induced PH. Human pulmonary artery endothelial cells from people with PH demonstrated changes similar to Ucp2-silenced mouse lung endothelial cells.

CONCLUSIONS

The loss of endothelial Ucp2 leads to excessive PTEN-induced putative kinase 1-induced mitophagy, inadequate mitochondrial biosynthesis, and increased apoptosis in endothelium. An endothelial Ucp2-PTEN-induced putative kinase 1 axis may be effective therapeutic targets in PH.

VEGF receptors mediate hypoxic remodeling of adult ovine carotid arteries

Recent studies suggest that VEGF contributes to hypoxic remodeling of arterial smooth muscle, although hypoxia produces only transient increases in VEGF that return to normoxic levels despite sustained changes in arterial structure and function. To explore how VEGF might contribute to long-term hypoxic vascular remodeling, this study explores the hypothesis that chronic hypoxia produces sustained increases in smooth muscle VEGF receptor density that mediate long-term vascular effects of hypoxia. Carotid arteries from adult sheep maintained at sea level or altitude (3,820 m) for 110 days were harvested and denuded of endothelium. VEGF levels were similar in chronically hypoxic and normoxic arteries, as determined by immunoblotting. In contrast, VEGF receptor levels were significantly increased by 107% (VEGF-R1) and 156% (VEGF-R2) in hypoxic compared with normoxic arteries. In arteries that were organ cultured 24 h with 3 nM VEGF, VEGF replicated effects of hypoxia on abundances of smooth muscle α actin (SMαA), myosin light chain kinase (MLCK), and MLC20 and the effects of hypoxia on colocalization of MLC20 with SMαA, as measured via confocal microscopy. VEGF did not replicate the effects of chronic hypoxia on colocalization of MLCK with SMαA or MLCK with MLC20, suggesting that VEGF's role in hypoxic remodeling is highly protein specific, particularly for contractile protein organization. VEGF effects in organ culture were inhibited by VEGF receptor blockers vatalinib (240 nM) and dasatinib (6.3 nM). These findings support the hypothesis that long-term upregulation of VEGF receptors help mediate sustained effects of hypoxia on the abundance and colocalization of contractile proteins in arterial smooth muscle.

Lack of bcr and abr promotes hypoxia-induced pulmonary hypertension in mice

BACKGROUND

Bcr and Abr are GTPase activating proteins that specifically downregulate activity of the small GTPase Rac in restricted cell types in vivo. Rac1 is expressed in smooth muscle cells, a critical cell type involved in the pathogenesis of pulmonary hypertension. The molecular mechanisms that underlie hypoxia-associated pulmonary hypertension are not well-defined.

METHODOLOGY/PRINCIPAL FINDINGS

Bcr and abr null mutant mice were compared to wild type controls for the development of pulmonary hypertension after exposure to hypoxia. Also, pulmonary arterial smooth muscle cells from those mice were cultured in hypoxia and examined for proliferation, p38 activation and IL-6 production. Mice lacking Bcr or Abr exposed to hypoxia developed increased right ventricular pressure, hypertrophy and pulmonary vascular remodeling. Perivascular leukocyte infiltration in the lungs was increased, and under hypoxia bcr-/- and abr-/- macrophages generated more reactive oxygen species. Consistent with a contribution of inflammation and oxidative stress in pulmonary hypertension-associated vascular damage, Bcr and Abr-deficient animals showed elevated endothelial leakage after hypoxia exposure. Hypoxia-treated pulmonary arterial smooth muscle cells from Bcr- or Abr-deficient mice also proliferated faster than those of wild type mice. Moreover, activated Rac1, phosphorylated p38 and interleukin 6 were increased in these cells in the absence of Bcr or Abr. Inhibition of Rac1 activation with Z62954982, a novel Rac inhibitor, decreased proliferation, p38 phosphorylation and IL-6 levels in pulmonary arterial smooth muscle cells exposed to hypoxia.

CONCLUSIONS

Bcr and Abr play a critical role in down-regulating hypoxia-induced pulmonary hypertension by deactivating Rac1 and, through this, reducing both oxidative stress generated by leukocytes as well as p38 phosphorylation, IL-6 production and proliferation of pulmonary arterial smooth muscle cells.

Pulmonary artery smooth muscle cell proliferation and migration in fetal lambs acclimatized to high-altitude long-term hypoxia: role of histone acetylation

High-altitude long-term hypoxia (LTH) is known to induce pulmonary arterial smooth muscle cell (PASMC) proliferation in the fetus, leading to pulmonary arterial remodeling and pulmonary hypertension of the newborn. The mechanisms underlying these conditions remain enigmatic however. We hypothesized that epigenetic alterations in fetal PASMC induced by high-altitude LTH may play an important role in modulating their proliferation during pulmonary arterial remodeling. To test this hypothesis, we have analyzed epigenetic alterations in the pulmonary vasculature of fetal lambs exposed to high-altitude LTH [pregnant ewes were kept at 3,801 m altitude from ~40 to 145 days gestation] or to sea level atmosphere. Intrapulmonary arteries were isolated, and fetal PASMC were cultured from both control and LTH fetuses. Compared with controls, in LTH fetus pulmonary arteries measurements of histone acetylation and global DNA methylation demonstrated reduced levels of global histone 4 acetylation and DNA methylation, accompanied by the loss of the cyclin-dependent kinase inhibitor p21. Treatment of LTH fetal PASMCs with histone deacetylase (HDAC) inhibitor trichostatin A decreased their proliferation rate, in part because of altered expression of p21 at both RNA and protein level. In PASMC of LTH fetuses, HDAC inhibition also decreased PDGF-induced cell migration and ERK1/2 activation and modulated global DNA methylation. On the basis of these observations, we propose that epigenetic alterations (reduced histone acetylation and DNA methylation) caused by chronic hypoxia leads to fetal PASMC proliferation and vessel remodeling associated with vascular proliferative disease and that this process is regulated by p21.