Exposure of Endothelium to Biomimetic Flow Waveforms Yields Identification of miR-199a-5p as a Potent Regulator of Arteriogenesis

Extracellular vesicles from 3D cultured dermal papilla cells improve wound healing via Krüppel-like factor 4/vascular endothelial growth factor A -driven angiogenesis

Background

Non-healing wounds are an intractable problem of major clinical relevance. Evidence has shown that dermal papilla cells (DPCs) may regulate the wound-healing process by secreting extracellular vesicles (EVs). However, low isolation efficiency and restricted cell viability hinder the applications of DPC-EVs in wound healing. In this study, we aimed to develop novel 3D-DPC spheroids (tdDPCs) based on self-feeder 3D culture and to evaluate the roles of tdDPC-EVs in stimulating angiogenesis and skin wound healing.

Methods

To address the current limitations of DPC-EVs, we previously developed a self-feeder 3D culture method to construct tdDPCs. DPCs and tdDPCs were identified using immunofluorescence staining and flow cytometry. Subsequently, we extracted EVs from the cells and compared the effects of DPC-EVs and tdDPC-EVs on human umbilical vein endothelial cells (HUVECs) in vitro using immunofluorescence staining, a scratch-wound assay and a Transwell assay. We simultaneously established a murine model of full-thickness skin injury and evaluated the effects of DPC-EVs and tdDPC-EVs on wound-healing efficiency in vivo using laser Doppler, as well as hematoxylin and eosin, Masson, CD31 and α-SMA staining. To elucidate the underlying mechanism, we conducted RNA sequencing (RNA-seq) of tdDPC-EV- and phosphate-buffered saline-treated HUVECs. To validate the RNA-seq data, we constructed knockdown and overexpression vectors of Krüppel-like factor 4 (KLF4). Western blotting, a scratch-wound assay, a Transwell assay and a tubule-formation test were performed to detect the protein expression, cell migration and lumen-formation ability of KLF4 and vascular endothelial growth factor A (VEGFA) in HUVECs incubated with tdDPC-EVs after KLF4 knockdown or overexpression. Dual-luciferase reporter gene assays were conducted to verify the activation effect of KLF4 on VEGFA.

Results

We successfully cultured tdDPCs and extracted EVs from DPCs and tdDPCs. The tdDPC-EVs significantly promoted the proliferation, lumen formation and migration of HUVECs. Unlike DPC-EVs, tdDPC-EVs exhibited significant advantages in terms of promoting angiogenesis, accelerating wound healing and enhancing wound-healing efficiency both in vitro and in vivo. Bioinformatics analysis and further functional experiments verified that the tdDPC-EV-regulated KLF4/VEGFA axis is pivotal in accelerating wound healing.

Conclusions

3D cultivation can be utilized as an innovative optimization strategy to effectively develop DPC-derived EVs for the treatment of skin wounds. tdDPC-EVs significantly enhance wound healing via KLF4/VEGFA-driven angiogenesis.

Atherosclerosis-associated endothelial dysfunction is promoted by miR-199a-5p/SIRT1 axis regulated by circHIF1ɑ

BACKGROUND AND AIMS

Atherosclerosis (AS) is a chronic inflammatory disease that damages the arterial wall as a result of hyperlipidemia and causes endothelial cell dysfunction, which increases the risk of atherothrombotic events. Multiple pathological conditions have shown ectopic miR-199a-5p levels to cause endothelial injury, but its role in the AS competitive endogenous RNA (CeRNA) network is still unknown.

METHODS AND RESULTS

The high-fat diet (HFD) apoE-/- mouse model was constructed in vivo, and ECs were cultured under ox-LDL treatment to induce EC injury in vitro. Immunohistochemistry and immunofluorescence staining were used to assess the effect of miR-199a-5p on the macrophage, SMC, collagen content, and endothelial coverage in the artery wall of mouse model. miR-199a-5p level was validated to be overexpression in the aorta tissue of HFD apoE-/- mice and in the ox-LDL-treated ECs, and even in the plasma EVs of the patients with cerebral AS. Silencing of miR-199a-5p significantly attenuated atherosclerotic progress in HFD apoE-/- mice, and the gain/loss-of-function assay indicated that miR-199a-5p overexpression aggravated ox-LDL-induced disabilities of endothelial proliferation, motility, and neovascularization based on cell counting kit-8 assay, transwell assay and matrigel assay. Mechanistically, miR-199a-5p prevented EC activation by activating the FOXO signaling pathway by targeting SIRT1. Additionally, circular RNA (circRNA) circHIF1ɑ was identified as having a low expression in the ox-LDL-treated EC and mediated SIRT1 expression via sponging miR-199a-5p to rescue ox-LDL-induced EC injury.

CONCLUSIONS

Our study demonstrated the vital role of miR-199a-5p/SIRT1 axis regulated by circHIF1ɑ in AS pathogenesis and provided novel effective targets for AS treatment.

Optimized workflow to modify microRNA expression in primary human intravascular cells

BACKGROUND

A comprehensive dissection of the role of microRNAs (miRNAs) in gene regulation and subsequent cell functions requires a specific and efficient knockdown or overexpression of the miRNA of interest; these are achieved by transfecting the cell of interest with a miRNA inhibitor or a miRNA mimic, respectively. Inhibitors and mimics of miRNAs with a unique chemistry and/or structural modifications are available commercially and require different transfection conditions. Here, we aimed to investigate how various conditions affect the transfection efficacy of two miRNAs with high and low endogenous expression, miR-15a-5p and miR-20b-5p respectively, in human primary cells.

RESULTS

MiRNA inhibitors and mimics from two commonly used commercial vendors were employed, i.e., mirVana (Thermo Fisher Scientific) and locked nucleic acid (LNA) miRNA (Qiagen). We systematically examined and optimized the transfection conditions of such miRNA inhibitors and mimics to primary endothelial cells and monocytes using either a lipid-based carrier (lipofectamine) for delivery or an unassisted uptake. Transfection of LNA inhibitors with either phosphodiester (PE)- or phosphorothioate (PS)-modified nucleotide bonds, delivered using a lipid-based carrier, efficiently downregulated the expression levels of miR-15a-5p already 24 h following transfection. MirVana miR-15a-5p inhibitor displayed a less efficient inhibitory effect, which was not improved 48 h following a single transfection or two consecutive transfections. Interestingly, LNA-PS miR-15a-5p inhibitor efficiently reduced the levels of miR-15a-5p when delivered without a lipid-based carrier in both ECs and monocytes. When using a carrier, mirVana and LNA miR-15a-5p and miR-20b-5p mimics showed similar efficiency 48 h following transfection to ECs and monocytes. None of the miRNA mimics effectively induced overexpression of the respective miRNA when given to primary cells without a carrier.

CONCLUSION

LNA miRNA inhibitors efficiently downregulated the cellular expression of miRNA, such as miR-15a-5p. Furthermore, our findings suggest that LNA-PS miRNA inhibitors can be delivered in the absence of a lipid-based carrier, whereas miRNA mimics need the aid of a lipid-based carrier to achieve sufficient cellular uptake.

Differential Expression of Peripheral Circulating MicroRNA-146a Between Patients with Atherosclerotic Vulnerable Plaque and Stable Plaque

Atherosclerotic plaque rupture and subsequent cardiovascular complications threaten the population's health worldwide. The polymorphism of miR-146a rs2910164 was significantly associated with the risk of vulnerable plaques. However, it remains unclear whether the circulating miR-146a is differentially expressed in stable and vulnerable plaques and thus, serves as a potential biomarker.This study aims to analyze the differential expression of circulating miR-146a between patients with stable and vulnerable plaques to explore the potential molecular mechanisms.Public databases were searched from their inception up to November 2022. A study reporting the specific circulating miR-146a levels between patients with stable and vulnerable plaques was included. The study quality was assessed using the modified genetic 8-stars Newcastle-Ottawa scale. The differential expression levels of miR-146a were evaluated using the standardized mean difference (SMD).Eight studies with 978 patients were included and analyzed. The results showed that miR-146a expression levels were significantly higher in the vulnerable plaque population than in the stable plaque population (SMD: 1.91; 95% confidence interval: 1.35, 2.47; P < 0.01). A similar statistical significance was found in subgroup analyses regarding sample source, disease type, and vulnerable plaque characteristics. Sensitivity analysis suggested the robustness of the results. Analysis of downstream genes suggested that miR-146a-targeted regulation of ACTN4, SARM1, and ULK2 may affect intraplaque hemorrhage.Patients with vulnerable plaque have higher circulating miR-146a levels than those with stable plaque. However, based on the limitations of this study, high-quality studies are still needed to confirm the results.

Sex-specific effects of daily tadalafil on diabetic heart kinetics in RECOGITO, a randomized, double-blind, placebo-controlled trial

Cyclic GMP-phosphodiesterase type 5 (PDE5) inhibition has been shown to counteract maladaptive cardiac changes triggered by diabetes in some but not all studies. We performed a single-center, 20-week, double-blind, randomized, placebo-controlled trial (NCT01803828) to assess sex differences in cardiac remodeling after PDE5 inhibition in patients with diabetic cardiomyopathy. A total of 122 men and women (45 to 80 years) with long-duration (>3 years) and well-controlled type 2 diabetes mellitus (T2DM; HbA1c < 86 mmol/mol) were selected according to echocardiographic signs of cardiac remodeling. Patients were randomly assigned (1:1) to placebo or oral tadalafil (20 mg, once daily). The primary outcome was to evaluate sex differences in cardiac torsion change. Secondary outcomes were changes in cardiovascular, metabolic, immune, and renal function. At 20 weeks, the treatment-by-sex interaction documented an improvement in cardiac torsion (-3.40°, -5.96; -0.84, P = 0.011) and fiber shortening (-1.19%, -2.24; -0.14, P = 0.027) in men but not women. The primary outcome could not be explained by differences in cGMP concentrations or tadalafil pharmacodynamics. In both sexes, tadalafil improved hsa-miR-199-5p expression, biomarkers of cardiovascular remodeling, albuminuria, renal artery resistive index, and circulating Klotho concentrations. Immune cell profiling revealed an improvement in low-grade chronic inflammation: Classic CD14⁺⁺CD16^- monocytes reduced, and Tie2⁺ monocytes increased. Nine patients (14.5%) had minor adverse reactions after tadalafil administration. Continuous PDE5 inhibition could offer a strategy to target cardiorenal complications of T2DM, with sex- and tissue-specific responses. Further studies are needed to confirm Klotho and hsa-miR-199-5p as markers for T2DM complications.

Key regulatory miRNAs in lipid homeostasis: implications for cardiometabolic diseases and development of novel therapeutics

Dysregulation of lipid metabolism is associated with cardiovascular/metabolic diseases, including atherosclerosis, liver diseases and type 2 diabetes mellitus (T2DM). Several miRNAs have been reported as regulators of different stages of lipid homeostasis, including cholesterol/fatty acid biosynthesis, degradation, transport, storage, and low-density (LDL) and high-density lipoprotein (HDL) formation. Indeed, various miRNAs are emerging as attractive therapeutic candidates for metabolic/cardiovascular disease (CVD). Here, we summarize the roles of miR-19b, miR-20a, miR-21, miR-27, miR-29, miR-34a, miR-144, miR-148a, and miR-199a in post-transcriptional regulation of genes involved in lipid metabolism and their therapeutic potential. We also discuss experimental strategies for further development of these miRNAs as novel cardiometabolic therapeutics. Teaser: miRNAs have emerged as crucial regulators of lipid homeostasis. Here, we highlight key miRNAs that regulate lipid metabolism and their therapeutic potential in cardiometabolic disease states.

Up-regulation of caveolin 1 mediated by chitosan activates Wnt/ β-catenin pathway in chronic refractory wound diabetic rat model

Diabetes mellitus (DM) can be implicated in the perturbations of vascular integrity and the dysfunction of angiogenesis. Chitosan has the advantage of promoting the vascular endothelial cell proliferation. However, the molecular mechanism of action in the promotion of wound healing by chitosan derivatives is still debated. In the current study, DM with chronic wound (CW) model rats were prepared and treated with chitosan. Vascular endothelial cells isolated from granulation tissues were conducted by RNA sequencing. Two thousand three hundred and sixteen genes were up-regulated, while 1,864 genes were down-regulated after chitosan treatment compared to CW group. Here, we observed that caveolin 1 (CAV1) was highly expressed induced by chitosan. Furthermore, we observed that CAV1 knockdown could compromise the activation of Wnt pathway by reduction of β-catenin in rat aortic endothelial cells (RAOECs) and brain endothelium four cells (RBE4s). Moreover, we determined a direct interaction between CAV1 and β-catenin by IP assay. The C-terminus of CAV1 and β-catenin (24 to 586 amino acids) contributed to the interaction of these two proteins. Finally, the protein docking analysis indicated that the fragments of β-catenin (253–261 ‘FYAITTLHN’ and 292–303 ‘KFLAITTDCLQI’) might have affected the structure by CAV1 and facilitated the resistance to degradation. Taken together, our study demonstrates that chitosan can up-regulate CAV1 expression, and CAV1 can interact with β-catenin for promotion of canonical Wnt signaling pathway activity. Our results deepens the molecular mechanism of the Wnt pathway in vascular endothelial cells and is beneficial to developing new targets to assist in enhancing the pharmacological effect of chitosan on wound healing and angiogenesis against DM.

Mechanosensitive miR-100 coordinates TGFβ and Wnt signaling in osteocytes during fluid shear stress

Organism scale mechanical forces elicit cellular scale changes through coordinated regulation of multiple signaling pathways. The mechanisms by which cells integrate signaling to generate a unified biological response remains a major question in mechanobiology. For example, the mechanosensitive response of bone and other tissues requires coordinated signaling by the transforming growth factor beta (TGFβ) and Wnt pathways through mechanisms that are not well‐defined. Here we report a new microRNA‐dependent mechanism that mediates mechanosensitive crosstalk between TGFβ and Wnt signaling in osteocytes exposed to fluid shear stress (FSS). From 60 mechanosensitive microRNA (miRs) identified by small‐RNAseq, miR100 expression is suppressed by in vivo hindlimb loading in the murine tibia and by cellular scale FSS in OCY454 cells. Though FSS activates both TGFβ and Wnt signaling in osteocytes, only TGFβ represses miR‐100 expression. miR‐100, in turn, antagonizes Wnt signaling by targeting and inhibiting expression of Frizzled receptors (FZD5/FZD8). Accordingly, miR‐100 inhibition blunts FSS‐ and TGFβ‐inducible Wnt signaling. Therefore, our results identify FSS‐responsive miRNAs in osteocytes, including one that integrates the mechanosensitive function of two essential signaling pathways in the osteoanabolic response of bone to mechanical load.

New Directions in Therapeutic Angiogenesis and Arteriogenesis in Peripheral Arterial Disease

The prevalence of peripheral arterial disease (PAD) in the United States exceeds 10 million people, and PAD is a significant cause of morbidity and mortality across the globe. PAD is typically caused by atherosclerotic obstructions in the large arteries to the leg(s). The most common clinical consequences of PAD include pain on walking (claudication), impaired functional capacity, pain at rest, and loss of tissue integrity in the distal limbs that may lead to lower extremity amputation. Patients with PAD also have higher than expected rates of myocardial infarction, stroke, and cardiovascular death. Despite advances in surgical and endovascular procedures, revascularization procedures may be suboptimal in relieving symptoms, and some patients with PAD cannot be treated because of comorbid conditions. In some cases, relieving obstructive disease in the large conduit arteries does not assure complete limb salvage because of severe microvascular disease. Despite several decades of investigational efforts, medical therapies to improve perfusion to the distal limb are of limited benefit. Whereas recent studies of anticoagulant (eg, rivaroxaban) and intensive lipid lowering (such as PCSK9 [proprotein convertase subtilisin/kexin type 9] inhibitors) have reduced major cardiovascular and limb events in PAD populations, chronic ischemia of the limb remains largely resistant to medical therapy. Experimental approaches to improve limb outcomes have included the administration of angiogenic cytokines (either as recombinant protein or as gene therapy) as well as cell therapy. Although early angiogenesis and cell therapy studies were promising, these studies lacked sufficient control groups and larger randomized clinical trials have yet to achieve significant benefit. This review will focus on what has been learned to advance medical revascularization for PAD and how that information might lead to novel approaches for therapeutic angiogenesis and arteriogenesis for PAD.

An Insight into the microRNAs Associated with Arteriovenous and Cavernous Malformations of the Brain

Background: Brain arteriovenous malformations (BAVMs) and cerebral cavernous malformations (CCMs) are rare developmental anomalies of the intracranial vasculature, with an irregular tendency to rupture, and as of yet incompletely deciphered pathophysiology. Because of their variety in location, morphology, and size, as well as unpredictable natural history, they represent a management challenge. MicroRNAs (miRNAs) are strands of non-coding RNA of around 20 nucleotides that are able to modulate the expression of target genes by binding completely or partially to their respective complementary sequences. Recent breakthroughs have been made on elucidating their contribution to BAVM and CCM occurrence, growth, and evolution; however, there are still countless gaps in our understanding of the mechanisms involved. Methods: We have searched the Medline (PubMed; PubMed Central) database for pertinent articles on miRNAs and their putative implications in BAVMs and CCMs. To this purpose, we employed various permutations of the terms and idioms: ‘arteriovenous malformation’, ‘AVM’, and ‘BAVM’, or ‘cavernous malformation’, ‘cavernoma’, and ‘cavernous angioma’ on the one hand; and ‘microRNA’, ‘miRNA’, and ‘miR’ on the other. Using cross-reference search; we then investigated additional articles concerning the individual miRNAs identified in other cerebral diseases. Results: Seven miRNAs were discovered to play a role in BAVMs, three of which were downregulated (miR-18a, miR-137, and miR-195*) and four upregulated (miR-7-5p, miR-199a-5p, miR-200b-3p, and let-7b-3p). Similarly, eight miRNAs were identified in CCM in humans and experimental animal models, two being upregulated (miR-27a and mmu-miR-3472a), and six downregulated (miR-125a, miR-361-5p, miR-370-3p, miR-181a-2-3p, miR-95-3p, and let-7b-3p). Conclusions: The following literature review endeavored to address the recent discoveries related to the various implications of miRNAs in the formation and growth of BAVMs and CCMs. Additionally, by presenting other cerebral pathologies correlated with these miRNAs, it aimed to emphasize the potential directions of upcoming research and biological therapies.

MicroRNA-665 Regulates Cell Proliferation and Apoptosis of Vascular Smooth Muscle Cells by Targeting TGFBR1

Coronary artery disease (CAD) is one of the heavy health burdens worldwide. Aberrant proliferation of vascular smooth muscle cells (VSMCs) contributes to the occurrence and development of CAD. This study aimed at exploring differentially expressed microRNAs (miRNAs) and their regulatory mechanisms in the development of CAD.The miRNA expression profile of GSE28858 was obtained from the Gene Expression Omnibus database. Differentially expressed miRNAs (DEmiRNAs) between CAD and healthy control samples were analyzed using limma package in R. Target genes of DEmiRNAs were predicted, and a miRNA-target gene network was constructed. The relationship between miR-665 and transforming growth factor beta receptor 1 (TGFBR1) was selected for further analysis. The interaction between miR-665 and TGFBR1 was confirmed by dual luciferase reporter assay. Effects of miR-665 on cell viability and apoptosis of VSMCs were evaluated by cell counting kit-8 (CCK-8) assay and flow cytometry, respectively. Besides, western blot assays for BCL2L11 and caspase 3 were also conducted.A total of 38 upregulated miRNAs and 28 downregulated miRNAs were identified. The expression level of miR-665 was significantly downregulated in patients with CAD. TGFBR1 was proved to be a target gene of miR-665. Besides, ectopic expression of miR-665 obviously inhibited VSMC growth and promoted VSMC apoptosis. TGFBR1 overexpression in VSMCs transfected with miR-665 mimic could restore the effect of miR-665 on the proliferation and apoptosis of VSMCs.MiR-665 might participate in the proliferation and apoptosis of VSMCs by targeting TGFBR1.

MicroRNA-9 rescues hyperglycemia-induced endothelial cell dysfunction and promotes arteriogenesis through downregulating Notch1 signaling

Hyperglycemia-induced endothelial dysfunction plays a major role in the pathogenesis of diabetic vascular complications. MicroRNAs are potential therapeutic agents to improve hyperglycemia-induced endothelial dysfunction. This study examined the relationship of miR-9 with Notch1 signaling in hyperglycemia-induced endothelial dysfunction. Human umbilical vein endothelial cells (HUVECs) were exposed to 30 mM glucose concentration. Cell viability including proliferation, adhesion, migration and tube formation was significantly impaired. Quantitative real time polymerase chain reaction (qRT-PCR) or Western blot demonstrated that miR-9 expression remarkably decreased and expression of Notch1 and its effectors (Hes1, Hey1, Hey2) were upregulated. Transfection with miR-9 improved cell function, inhibited mRNA and protein expression of Notch1 and its effectors. Although basal expression of the arterial endothelium biomarker Ephrin B2 was almost undetectable in HUVECs, double-label immunofluorescence revealed that transfection with miR-9 upregulated Ephrin B2 expression. By contrast, such protective effects of miR-9 overexpression were eliminated due to use of miR-9 inhibitor. Dual luciferase assay further confirmed a significant inverse correlation between miR-9 and Notch1. In addition, Notch1 overactiviation was mimicked in HUVECs by transfecting with Notch1 intracellular domain (NICD1). MiR-9 significantly inhibited NICD1 mRNA expression and alleviated hyperglycemia-induced injury of the NICD1-overexpressing cells. Taken together, our data support upregulating miR-9 expression as a potential therapeutic strategy to antagonize hyperglycemia-induced injury by inhibiting Notch1 signaling.

Studying endothelial cell shedding and orientation using adaptive perfusion-culture in a microfluidic vascular chip

Most tissue-engineered blood vessels are endothelialized by static cultures in vitro. However, it has not been clear whether endothelial cell-shedding and local damage may occur in an endothelial layer formed by static cultures under the effect of blood flow shear postimplantation. In this study, we report a bionic and cost-effective vascular chip platform, and proved that a static culture of endothelialized tissue-engineered blood vessels had the problem of a large number of endothelial cells falling off under the condition imitating the human arterial blood flow, and we addressed this challenge by regulating the flow field in a vascular chip. Electrospun membranes made of highly oriented or randomly distributed poly(ε-caprolactone) fibers were used as the vascular scaffolds, on which endothelial cells proliferated well and eventually formed dense intima layers. We noted that the monolayers gradually adapted to the artery-like microenvironment through the regulation of chip flow field, which also revealed improved cellular orientations. In conclusion, we have proposed a vascular chip with adaptive flow patterns to gradually accommodate the statically cultured vascular endothelia to the shear environment of arterial flow field and enhanced the orientation of the endothelial cells. This strategy may find numerous potential applications such as screening of vascular engineering biomaterials and maturation parameters, studying of vascular biology and pathology, and construction of vessel-on-a-chip models for drug analysis, among others.

Deciphering the vascular labyrinth: role of microRNAs and candidate gene SNPs in brain AVM development - literature review

Background: Brain arteriovenous malformations (AVMs) are a relatively infrequent vascular pathology of unknown etiology that, despite their rarity, cause the highest number of hemorrhagic strokes under the age of 30 years. They pose a challenge to all forms of treatment due to their variable morphology, location, size, and, last but not least, evolving nature. MicroRNAs (miRNAs) are non-coding RNA strands that may suppress the expression of target genes by binding completely or partially to their complementary sequences. Single nucleotide polymorphisms (SNPs), as the name implies, are variations in a single nucleotide in the DNA, usually found in the non-coding segments. Although the majority of SNPs are harmless, some located in the proximity of candidate genes may result in altered expression or function of these genes and cause diseases or affect how different pathologies react to treatment. The roles miRNAs and certain SNPs play in the development and growth of AVMs are currently uncertain, yet progress in deciphering the minutiae of this pathology is already visible. Methods and Results: We performed an electronic Medline (PubMed, PubMed Central) and Google Academic exploration using permutations of the terms: "arteriovenous malformations," "single nucleotide polymorphisms," "microRNA," "non-coding RNA," and "genetic mutations." The findings were then divided into two categories, namely the miRNAs and the candidate gene SNPs associated with AVMs respectively. 6 miRNAs and 12 candidate gene SNPs were identified and discussed. Conclusions: The following literature review focuses on the discoveries made in ascertaining the different implications of miRNAs and candidate gene SNPs in the formation and evolution of brain AVMs, as well as highlighting the possible directions of future research and biological treatment. Abbreviations: ACVRL1/ALK1: activin receptor-like kinase 1; Akt: protein kinase B; ANGPTL4: angiopoietin-like 4; ANRIL: antisense noncoding RNA in the INK4 locus; AVM: arteriovenous malformation; AVM-BEC: arteriovenous malformation brain endothelial cell; BRCA1: breast cancer type 1 susceptibility protein; CCS: case-control study; CDKN2A/B: cyclin-dependent kinase inhibitor 2A/B; CLTC: clathrin heavy chain; DNA: deoxyribonucleic acid; ERK: extracellular signal-regulated kinase; GPR124: probable G-protein coupled receptor 124; GWAS: genome-wide association study; HHT: hereditary hemorrhagic telangiectasia; HIF1A: hypoxia-inducible factor 1A; IA: intracranial aneurysm; ICH: intracranial hemorrhage; Id-1: inhibitor of DNA-binding protein A; IL-17: interleukin 17; MAP4K3: mitogen-activated protein kinase kinase kinase kinase 3; miRNA: microRNA; MMP: matrix metalloproteinase; NFkB: nuclear factor kappa-light-chain of activated B cells; NOTCH: neurogenic locus notch homolog; p38MAPK: p38 mitogen-activated protein kinase; PI3K: phosphoinositide 3-kinase; RBBP8: retinoblastoma-binding protein 8; RNA: ribonucleic acid; SNAI1: Snail Family Transcriptional Repressor 1; SNP: single nucleotide polymorphism; SOX-17: SRY-related HMG-box; TGF-β: transformation growth factor β; TGFR: transformation growth factor receptor; TIMP-4, tissue inhibitor of metalloproteinase 4; TSP-1: thrombospondin-1; UTR: untranslated region; VEGF: Vascular Endothelial Growth Factor; VSMC: vascular smooth muscle cell; Wnt1: Wnt family member 1.

Epigenetic regulators of the revascularization response to chronic arterial occlusion

Peripheral arterial disease (PAD) is the leading cause of lower limb amputation and estimated to affect over 202 million people worldwide. PAD is caused by atherosclerotic lesions that occlude large arteries in the lower limbs, leading to insufficient blood perfusion of distal tissues. Given the severity of this clinical problem, there has been long-standing interest in both understanding how chronic arterial occlusions affect muscle tissue and vasculature and identifying therapeutic approaches capable of restoring tissue composition and vascular function to a healthy state. To date, the most widely utilized animal model for performing such studies has been the ischaemic mouse hindlimb. Despite not being a model of PAD per se, the ischaemic hindlimb model does recapitulate several key aspects of PAD. Further, it has served as a valuable platform upon which we have built much of our understanding of how chronic arterial occlusions affect muscle tissue composition, muscle regeneration and angiogenesis, and collateral arteriogenesis. Recently, there has been a global surge in research aimed at understanding how gene expression is regulated by epigenetic factors (i.e. non-coding RNAs, histone post-translational modifications, and DNA methylation). Thus, perhaps not unexpectedly, many recent studies have identified essential roles for epigenetic factors in regulating key responses to chronic arterial occlusion(s). In this review, we summarize the mechanisms of action of these epigenetic regulators and highlight several recent studies investigating the role of said regulators in the context of hindlimb ischaemia. In addition, we focus on how these recent advances in our understanding of the role of epigenetics in regulating responses to chronic arterial occlusion(s) can inform future therapeutic applications to promote revascularization and perfusion recovery in the setting of PAD.

Noncoding RNAs in Critical Limb Ischemia

Peripheral artery disease, caused by chronic arterial occlusion of the lower extremities, affects over 200 million people worldwide. Peripheral artery disease can progress into critical limb ischemia (CLI), its more severe manifestation, which is associated with higher risk of limb amputation and cardiovascular death. Aiming to improve tissue perfusion, therapeutic angiogenesis held promise to improve ischemic limbs using delivery of growth factors but has not successfully translated into benefits for patients. Moreover, accumulating studies suggest that impaired downstream signaling of these growth factors (or angiogenic resistance) may significantly contribute to CLI, particularly under harsh environments, such as diabetes mellitus. Noncoding RNAs are essential regulators of gene expression that control a range of pathophysiologies relevant to CLI, including angiogenesis/arteriogenesis, hypoxia, inflammation, stem/progenitor cells, and diabetes mellitus. In this review, we summarize the role of noncoding RNAs, including microRNAs and long noncoding RNAs, as functional mediators or biomarkers in the pathophysiology of CLI. A better understanding of these ncRNAs in CLI may provide opportunities for new targets in the prevention, diagnosis, and therapeutic management of this disabling disease state.

Applications of Ultrasound to Stimulate Therapeutic Revascularization

Many pathological conditions are characterized or caused by the presence of an insufficient or aberrant local vasculature. Thus, therapeutic approaches aimed at modulating the caliber and/or density of the vasculature by controlling angiogenesis and arteriogenesis have been under development for many years. As our understanding of the underlying cellular and molecular mechanisms of these vascular growth processes continues to grow, so too do the available targets for therapeutic intervention. Nonetheless, the tools needed to implement such therapies have often had inherent weaknesses (i.e., invasiveness, expense, poor targeting, and control) that preclude successful outcomes. Approximately 20 years ago, the potential for using ultrasound as a new tool for therapeutically manipulating angiogenesis and arteriogenesis began to emerge. Indeed, the ability of ultrasound, especially when used in combination with contrast agent microbubbles, to mechanically manipulate the microvasculature has opened several doors for exploration. In turn, multiple studies on the influence of ultrasound-mediated bioeffects on vascular growth and the use of ultrasound for the targeted stimulation of blood vessel growth via drug and gene delivery have been performed and published over the years. In this review article, we first discuss the basic principles of therapeutic ultrasound for stimulating angiogenesis and arteriogenesis. We then follow this with a comprehensive cataloging of studies that have used ultrasound for stimulating revascularization to date. Finally, we offer a brief perspective on the future of such approaches, in the context of both further research development and possible clinical translation.