Endothelial cells signaling and patterning under hypoxia: a mechanistic integrative computational model including the Notch-Dll4 pathway

Introduction: Several signaling pathways are activated during hypoxia to promote angiogenesis, leading to endothelial cell patterning, interaction, and downstream signaling. Understanding the mechanistic signaling differences between endothelial cells under normoxia and hypoxia and their response to different stimuli can guide therapies to modulate angiogenesis. We present a novel mechanistic model of interacting endothelial cells, including the main pathways involved in angiogenesis. Methods: We calibrate and fit the model parameters based on well-established modeling techniques that include structural and practical parameter identifiability, uncertainty quantification, and global sensitivity. Results: Our results indicate that the main pathways involved in patterning tip and stalk endothelial cells under hypoxia differ, and the time under hypoxia interferes with how different stimuli affect patterning. Additionally, our simulations indicate that Notch signaling might regulate vascular permeability and establish different Nitric Oxide release patterns for tip/stalk cells. Following simulations with various stimuli, our model suggests that factors such as time under hypoxia and oxygen availability must be considered for EC pattern control. Discussion: This project provides insights into the signaling and patterning of endothelial cells under various oxygen levels and stimulation by VEGFA and is our first integrative approach toward achieving EC control as a method for improving angiogenesis. Overall, our model provides a computational framework that can be built on to test angiogenesis-related therapies by modulation of different pathways, such as the Notch pathway.

Trafficking dynamics of VEGFR1, VEGFR2, and NRP1 in human endothelial cells

The vascular endothelial growth factor (VEGF) family of cytokines are key drivers of blood vessel growth and remodeling. These ligands act via multiple VEGF receptors (VEGFR) and co-receptors such as Neuropilin (NRP) expressed on endothelial cells. These membrane-associated receptors are not solely expressed on the cell surface, they move between the surface and intracellular locations, where they can function differently. The location of the receptor alters its ability to 'see' (access and bind to) its ligands, which regulates receptor activation; location also alters receptor exposure to subcellularly localized phosphatases, which regulates its deactivation. Thus, receptors in different subcellular locations initiate different signaling, both in terms of quantity and quality. Similarly, the local levels of co-expression of other receptors alters competition for ligands. Subcellular localization is controlled by intracellular trafficking processes, which thus control VEGFR activity; therefore, to understand VEGFR activity, we must understand receptor trafficking. Here, for the first time, we simultaneously quantify the trafficking of VEGFR1, VEGFR2, and NRP1 on the same cells-specifically human umbilical vein endothelial cells (HUVECs). We build a computational model describing the expression, interaction, and trafficking of these receptors, and use it to simulate cell culture experiments. We use new quantitative experimental data to parameterize the model, which then provides mechanistic insight into the trafficking and localization of this receptor network. We show that VEGFR2 and NRP1 trafficking is not the same on HUVECs as on non-human ECs; and we show that VEGFR1 trafficking is not the same as VEGFR2 trafficking, but rather is faster in both internalization and recycling. As a consequence, the VEGF receptors are not evenly distributed between the cell surface and intracellular locations, with a very low percentage of VEGFR1 being on the cell surface, and high levels of NRP1 on the cell surface. Our findings have implications both for the sensing of extracellular ligands and for the composition of signaling complexes at the cell surface versus inside the cell.

Experiment-based computational model predicts that IL-6 classic and trans-signaling exhibit similar potency in inducing downstream signaling in endothelial cells

Inflammatory cytokine mediated responses are important in the development of many diseases that are associated with angiogenesis. Targeting angiogenesis as a prominent strategy has shown limited effects in many contexts such as cardiovascular diseases and cancer. One potential reason for the unsuccessful outcome is the mutual dependent role between inflammation and angiogenesis. Inflammation-based therapies primarily target inflammatory cytokines such as interleukin-6 (IL-6) in T cells, macrophages, cancer cells, and muscle cells, and there is a limited understanding of how these cytokines act on endothelial cells. Thus, we focus on one of the major inflammatory cytokines, IL-6, mediated intracellular signaling in endothelial cells by developing a detailed computational model. Our model quantitatively characterized the effects of IL-6 classic and trans-signaling in activating the signal transducer and activator of transcription 3 (STAT3), phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt), and mitogen-activated protein kinase (MAPK) signaling to phosphorylate STAT3, extracellular regulated kinase (ERK) and Akt, respectively. We applied the trained and validated experiment-based computational model to characterize the dynamics of phosphorylated STAT3 (pSTAT3), Akt (pAkt), and ERK (pERK) in response to IL-6 classic and/or trans-signaling. The model predicts that IL-6 classic and trans-signaling induced responses are IL-6 and soluble IL-6 receptor (sIL-6R) dose-dependent. Also, IL-6 classic and trans-signaling showed similar potency in inducing downstream signaling; however, trans-signaling induces stronger downstream responses and plays a dominant role in the overall effects from IL-6 due to the in vitro experimental setting of abundant sIL-6R. In addition, both IL-6 and sIL-6R levels regulate signaling strength. Moreover, our model identifies the influential species and kinetic parameters that specifically modulate the downstream inflammatory and/or angiogenic signals, pSTAT3, pAkt, and pERK responses. Overall, the model predicts the effects of IL-6 classic and/or trans-signaling stimulation quantitatively and provides a framework for analyzing and integrating experimental data. More broadly, this model can be utilized to identify potential targets that influence IL-6 mediated signaling in endothelial cells and to study their effects quantitatively in modulating STAT3, Akt, and ERK activation.

Inhibiting Anti-angiogenic VEGF165b Activates a Novel miR-17-20a-Calcipressin-3 Pathway that Revascularizes Ischemic Muscle in Peripheral Artery Disease

Background

VEGF165a increases the expression of microRNA-17-92 cluster, promoting developmental, retinal, and tumor angiogenesis. We have previously shown that VEGF165b, an alternatively spliced VEGF-A isoform, inhibits the VEGFR-STAT3 pathway in ischemic endothelial cells (ECs) to decrease their angiogenic capacity. In ischemic macrophages (Møs), VEGF165b inhibits VEGFR1 to induce S100A8/A9 expression, which drives M1-like polarization. Our current study aims to determine whether VEGF165b inhibition promotes perfusion recovery by regulating the miR-17-92 cluster in preclinical PAD.

Methods

Hind limb ischemia (HLI) induced by femoral artery ligation and resection was used as a preclinical PAD model. Hypoxia serum starvation (HSS) was used as an in vitro PAD model. VEGF165b was inhibited/neutralized by an isoform-specific VEGF165b antibody.

Results

Systematic analysis of miR-17-92 cluster members (miR-17-18a-19a-19b-20a-92) in experimental-PAD models showed that VEGF165b-inhibition induces miRNA-17-20a (within miR-17-92 cluster) in HSS-ECs and HSS-bone marrow derived macrophages (BMDMs) vs. respective normal and/or isotype matched IgG controls to enhance perfusion-recovery. Consistent with the bioinformatics analysis that revealed RCAN3 as a common target of miR-17 and miR-20a, Argonaute-2 pull-down assays showed decreased miR-17-20a expression and higher RCAN3 expression in the RISC complex of HSS-ECs and HSS-BMDMs vs. the respective controls. Inhibiting miR-17-20a induced RCAN3 levels to decrease ischemic angiogenesis and promoted M1-like polarization to impair perfusion recovery. Finally, using STAT3 inhibitors, S100A8/A9 silencers and VEGFR1-deficient ECs and Møs, we show that VEGF165b inhibition activates the miR-17-20a-RCAN3 pathway independent of VEGFR1-STAT3 or VEGFR1-S100A8/A9 in ischemic ECs and ischemic Møs, respectively.

Conclusion

Our data revealed a hereunto unrecognized therapeutic 'miR-17-20a-RCAN3' pathway in the ischemic vasculature that is VEGFR1-STAT3/S100A8/A9 independent and is activated only upon VEGF165b inhibition in PAD.

Direct endothelial ENaC activation mitigates vasculopathy induced by SARS-CoV2 spike protein

Introduction

Although both COVID-19 and non-COVID-19 ARDS can be accompanied by significantly increased levels of circulating cytokines, the former significantly differs from the latter by its higher vasculopathy, characterized by increased oxidative stress and coagulopathy in lung capillaries. This points towards the existence of SARS-CoV2-specific factors and mechanisms that can sensitize the endothelium towards becoming dysfunctional. Although the virus is rarely detected within endothelial cells or in the circulation, the S1 subunit of its spike protein, which contains the receptor binding domain (RBD) for human ACE2 (hACE2), can be detected in plasma from COVID-19 patients and its levels correlate with disease severity. It remains obscure how the SARS-CoV2 RBD exerts its deleterious actions in lung endothelium and whether there are mechanisms to mitigate this.

Methods

In this study, we use a combination of in vitro studies in RBD-treated human lung microvascular endothelial cells (HL-MVEC), including electrophysiology, barrier function, oxidative stress and human ACE2 (hACE2) surface protein expression measurements with in vivo studies in transgenic mice globally expressing human ACE2 and injected with RBD.

Results

We show that SARS-CoV2 RBD impairs endothelial ENaC activity, reduces surface hACE2 expression and increases reactive oxygen species (ROS) and tissue factor (TF) generation in monolayers of HL-MVEC, as such promoting barrier dysfunction and coagulopathy. The TNF-derived TIP peptide (a.k.a. solnatide, AP301) -which directly activates ENaC upon binding to its a subunit- can override RBD-induced impairment of ENaC function and hACE2 expression, mitigates ROS and TF generation and restores barrier function in HL-MVEC monolayers. In correlation with the increased mortality observed in COVID-19 patients co-infected with S. pneumoniae, compared to subjects solely infected with SARS-CoV2, we observe that prior intraperitoneal RBD treatment in transgenic mice globally expressing hACE2 significantly increases fibrin deposition and capillary leak upon intratracheal instillation of S. pneumoniae and that this is mitigated by TIP peptide treatment.

Endothelial cells signaling and patterning under hypoxia: a mechanistic integrative computational model including the Notch-Dll4 pathway

Several signaling pathways are activated during hypoxia to promote angiogenesis, leading to endothelial cell patterning, interaction, and downstream signaling. Understanding the mechanistic signaling differences between normoxia and hypoxia can guide therapies to modulate angiogenesis. We present a novel mechanistic model of interacting endothelial cells, including the main pathways involved in angiogenesis. We calibrate and fit the model parameters based on well-established modeling techniques. Our results indicate that the main pathways involved in the patterning of tip and stalk endothelial cells under hypoxia differ, and the time under hypoxia affects how a reaction affects patterning. Interestingly, the interaction of receptors with Neuropilin1 is also relevant for cell patterning. Our simulations under different oxygen concentrations indicate time- and oxygen-availability-dependent responses for the two cells. Following simulations with various stimuli, our model suggests that factors such as period under hypoxia and oxygen availability must be considered for pattern control. This project provides insights into the signaling and patterning of endothelial cells under hypoxia, contributing to studies in the field.

Peripheral arterial disease: A small and large vessel problem

Peripheral arterial disease (PAD) is one clinical manifestation of systemic atherosclerosis and is very common. Despite its prevalence, PAD remains underdiagnosed, undertreated, and understudied. The most common symptom in patients with PAD is intermittent claudication (IC), or pain in the lower extremities with walking or exertion, which is relieved after a short period of rest. Many patients with confirmed PAD are asymptomatic or have symptoms other than IC. Regardless of symptoms, patients with PAD have poor cardiovascular outcomes. PAD has largely been viewed a disease of large vessel atherosclerosis but what is becoming clear is that arterial plaques and occlusions are only one piece of the puzzle. Recent work has shown that abnormalities in the microvasculature contribute to the outcome of patients with PAD. From the perspective of the leg, limitation in blood flow is not the only problem as patients have a myriad of other problems, including muscle fibrosis, neuropathic changes, changes in the cellular respiration machinery and dysfunction of the small vessels that perfuse skeletal muscle and the supporting structures. Supervised exercise training remains one of the most effective tool to treat patients with PAD, however, the mechanisms behind its effectiveness are still being elucidated and use of structured exercise programs is not widespread. Medical therapy to treat systemic atherosclerosis is underutilized in patients with PAD. Invasive therapies are used only when patients with PAD have reached an advanced stage. While invasive strategies are effective in some patients with PAD, these strategies are costly, carry risk, and many patients are not amenable to invasive therapy. Appreciating the complex pathophysiology of PAD will hopefully spur new research and development of effective therapies for PAD.

Pentose Pathway Activation Is Superior to Increased Glycolysis for Therapeutic Angiogenesis in Peripheral Arterial Disease

Background In endothelial cells (ECs), glycolysis, regulated by PFKFB3 (6-phosphofructo-2-kinase/fructose-2,6-biphosphatase, isoform-3), is the major metabolic pathway for ATP generation. In preclinical peripheral artery disease models, VEGF₁₆₅a (vascular endothelial growth factor₁₆₅a) and microRNA-93 both promote angiogenesis. Methods and Results Mice following hind-limb ischemia (HLI) and ECs with, and without, hypoxia and serum starvation were examined with, and without, microRNA-93 and VEGF₁₆₅a. Post-HLI perfusion recovery was monitored. EC metabolism was studied using seahorse assay, and the expression and activity of major metabolism genes were assessed. Reactive oxygen species levels and EC permeability were evaluated. C57Bl/6J mice generated a robust angiogenic response to HLI, with ECs from ischemic versus nonischemic muscle demonstrating no increase in glycolysis. Balb/CJ mice generated a poor angiogenic response post-HLI; ischemic versus nonischemic ECs demonstrated significant increase in glycolysis. MicroRNA-93-treated Balb/CJ mice post-HLI showed better perfusion recovery, with ischemic versus nonischemic ECs showing no increase in glycolysis. VEGF₁₆₅a-treated Balb/CJ mice post-HLI showed no improvement in perfusion recovery with ischemic versus nonischemic ECs showing significant increase in glycolysis. ECs under hypoxia and serum starvation upregulated PFKFB3. In ECs under hypoxia and serum starvation, VEGF₁₆₅a versus control significantly upregulated PFKFB3 and glycolysis, whereas miR-93 versus control demonstrated no increase in PFKFB3 or glycolysis. MicroRNA-93 versus VEGF₁₆₅a upregulated glucose-6-phosphate dehydrogenase expression and activity, activating the pentose phosphate pathway. MicroRNA-93 versus control increased reduced nicotinamide adenine dinucleotide phosphate and virtually eliminated the increase in reactive oxygen species. In ECs under hypoxia and serum starvation, VEGF₁₆₅a significantly increased and miR-93 decreased EC permeability. Conclusions In peripheral artery disease, activation of the pentose phosphate pathway to promote angiogenesis may offer potential therapeutic advantages.

Perivascular adipose tissue promotes vascular dysfunction in murine lupus

Introduction

Patients with systemic lupus erythematosus (SLE) are at elevated risk for Q10 cardiovascular disease (CVD) due to accelerated atherosclerosis. Compared to heathy control subjects, lupus patients have higher volumes and densities of thoracic aortic perivascular adipose tissue (PVAT), which independently associates with vascular calcification, a marker of subclinical atherosclerosis. However, the biological and functional role of PVAT in SLE has not been directly investigated.

Methods

Using mouse models of lupus, we studied the phenotype and function of PVAT, and the mechanisms linking PVAT and vascular dysfunction in lupus disease.

Results and discussion

Lupus mice were hypermetabolic and exhibited partial lipodystrophy, with sparing of thoracic aortic PVAT. Using wire myography, we found that mice with active lupus exhibited impaired endothelium-dependent relaxation of thoracic aorta, which was further exacerbated in the presence of thoracic aortic PVAT. Interestingly, PVAT from lupus mice exhibited phenotypic switching, as evidenced by “whitening” and hypertrophy of perivascular adipocytes along with immune cell infiltration, in association with adventitial hyperplasia. In addition, expression of UCP1, a brown/beige adipose marker, was dramatically decreased, while CD45-positive leukocyte infiltration was increased, in PVAT from lupus mice. Furthermore, PVAT from lupus mice exhibited a marked decrease in adipogenic gene expression, concomitant with increased pro-inflammatory adipocytokine and leukocyte marker expression. Taken together, these results suggest that dysfunctional, inflamed PVAT may contribute to vascular disease in lupus.

Experiment-based Computational Model Predicts that IL-6 Trans-Signaling Plays a Dominant Role in IL-6 mediated signaling in Endothelial Cells

Inflammatory cytokine mediated responses are important in the development of many diseases that are associated with angiogenesis. Targeting angiogenesis as a prominent strategy has shown limited effects in many contexts such as peripheral arterial disease (PAD) and cancer. One potential reason for the unsuccessful outcome is the mutual dependent role between inflammation and angiogenesis. Inflammation-based therapies primarily target inflammatory cytokines such as interleukin-6 (IL-6) in T cells, macrophages, cancer cells, muscle cells, and there is a limited understanding of how these cytokines act on endothelial cells. Thus, we focus on one of the major inflammatory cytokines, IL-6, mediated intracellular signaling in endothelial cells by developing a detailed computational model. Our model quantitatively characterized the effects of IL-6 classic and trans-signaling in activating the signal transducer and activator of transcription 3 (STAT3), phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt), and mitogen-activated protein kinase (MAPK) signaling to phosphorylate STAT3, extracellular regulated kinase (ERK) and Akt, respectively. We applied the trained and validated experiment-based computational model to characterize the dynamics of phosphorylated STAT3 (pSTAT3), Akt (pAkt), and extracellular regulated kinase (pERK) in response to IL-6 classic and/or trans-signaling. The model predicts that IL-6 classic and trans-signaling induced responses are IL-6 and soluble IL-6 receptor (sIL-6R) dose-dependent. Also, IL-6 trans-signaling induces stronger downstream signaling and plays a dominant role in the overall effects from IL-6. In addition, both IL-6 and sIL-6R levels regulate signaling strength. Moreover, our model identifies the influential species and kinetic parameters that specifically modulate the pSTAT3, pAkt, and pERK responses, which represent potential targets for inflammatory cytokine mediated signaling and angiogenesis-based therapies. Overall, the model predicts the effects of IL-6 classic and/or trans-signaling stimulation quantitatively and provides a framework for analyzing and integrating experimental data. More broadly, this model can be utilized to identify targets that influence inflammatory cytokine mediated signaling in endothelial cells and to study the effects of angiogenesis- and inflammation-based therapies.

Machine Learning Approach to Predict In-Hospital Mortality in Patients Admitted for Peripheral Artery Disease in the United States

Background Peripheral artery disease (PAD) affects >10 million people in the United States. PAD is associated with poor outcomes, including premature death. Machine learning (ML) has been increasingly used on big data to predict clinical outcomes. This study aims to develop ML models to predict in-hospital mortality in patients hospitalized for PAD based on a national database. Methods and Results Inpatient hospitalization data were obtained from the 2016 to 2019 National Inpatient Sample. A total of 150 921 inpatients were identified with a primary diagnosis of PAD and PAD-related procedures using codes of the International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) and International Classification of Diseases, Tenth Revision, Procedure Coding System (ICD-10-PCS). Four ML models, including logistic regression, random forest, light gradient boosting, and extreme gradient boosting models, were trained to predict the risk of in-hospital death based on a selection of variables, including patient characteristics, comorbidities, procedures, and hospital-related factors. In-hospital mortality occurred in 1.8% of patients. The performance of the 4 models was comparable, with the area under the receiver operating characteristic curve ranging from 0.83 to 0.85, sensitivity of 77% to 82%, and specificity of 72% to 75%. These results suggest adequate predictability for clinical decision-making. In all 4 models, the total number of diagnoses and procedures, age, endovascular revascularization procedure, congestive heart failure, diabetes, and diabetes with complications were critical predictors of in-hospital mortality. Conclusions This study demonstrates the feasibility of ML in predicting in-hospital mortality in patients with a primary PAD diagnosis. Findings highlight the potential of ML models in identifying high-risk patients for poor outcomes and guiding personalized intervention.

Contrast-Enhanced Ultrasound Reveals Partial Perfusion Recovery After Hindlimb Ischemia as Opposed to Full Recovery by Laser Doppler Perfusion Imaging

Mouse models are critical in developing new therapeutic approaches to treat peripheral arterial disease (PAD). Despite decades of research and numerous clinical trials, the efficacy of available therapies is limited. This may suggest shortcomings in our current animal models and/or methods of assessment. We evaluated perfusion measurement methods in a mouse model of PAD by comparing laser Doppler perfusion imaging (LDPI, the most common technique), contrast-enhanced ultrasound (CEUS, an emerging technique) and fluorescent microspheres (conventional standard). Mice undergoing a femoral artery ligation were assessed by LDPI and CEUS at baseline and 1, 4, 7, 14, 28, 60, 90 and 150 d post-surgery to evaluate perfusion recovery in the ischemic hindlimb. Fourteen days after surgery, additional mice were measured with fluorescent microspheres, LDPI, and CEUS. LDPI and CEUS resulted in broadly similar trends of perfusion recovery until 7 d post-surgery. However, by day 14, LDPI indicated full recovery of perfusion, whereas CEUS indicated ∼50% recovery, which failed to improve even after 5 mo. In agreement with the CEUS results, fluorescent microspheres at day 14 post-surgery confirmed that perfusion recovery was incomplete. Histopathology and photoacoustic microscopy provided further evidence of sustained vascular abnormalities.

Loss of Id3 (Inhibitor of Differentiation 3) Increases the Number of IgM-Producing B-1b Cells in Ischemic Skeletal Muscle Impairing Blood Flow Recovery During Hindlimb Ischemia

OBJECTIVE

Neovascularization can maintain and even improve tissue perfusion in the setting of limb ischemia during peripheral artery disease. The molecular and cellular mechanisms mediating this process are incompletely understood. We investigate the potential role(s) for Id3 (inhibitor of differentiation 3) in regulating blood flow in a murine model of hindlimb ischemia (HLI). Approach and Results: HLI was modeled through femoral artery ligation and resection and blood flow recovery was quantified by laser Doppler perfusion imaging. Mice with global Id3 deletion had significantly impaired perfusion recovery at 14 and 21 days of HLI. Endothelial- or myeloid cell-specific deletion of Id3 revealed no effect on perfusion recovery while B-cell-specific knockout of Id3 (Id3BKO) revealed a significant attenuation of perfusion recovery. Flow cytometry revealed no differences in ischemia-induced T cells or myeloid cell numbers at 7 days of HLI, yet there was a significant increase in B-1b cells in Id3BKO. Consistent with these findings, ELISA (enzyme-linked immunoassay) demonstrated increases in skeletal muscle and plasma IgM. In vitro experiments demonstrated reduced proliferation and increased cell death when endothelial cells were treated with conditioned media from IgM-producing B-1b cells and tibialis anterior muscles in Id3BKO mice showed reduced density of total CD31+ and αSMA+CD31+ vessels.

CONCLUSIONS

This study is the first to demonstrate a role for B-cell-specific Id3 in maintaining blood flow recovery during HLI. Results suggest a role for Id3 in promoting blood flow during HLI and limiting IgM-expressing B-1b cell expansion. These findings present new mechanisms to investigate in peripheral artery disease pathogenesis.

Dynamic Multiscale Regulation of Perfusion Recovery in Experimental Peripheral Arterial Disease: A Mechanistic Computational Model

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A first-of-a-kind systems biology computational model is presented that describes multiscale regulation of perfusion recovery in experimental peripheral arterial disease.

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Multilevel model calibration and validation enable high-resolution model simulations for experimental peripheral arterial disease (mouse HLI).

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An integrative model-based mechanistic characterization of the intracellular, cellular, and tissue-level features critical for the dynamic reconstitution of perfusion following different patterns of occlusion-induced ischemia in HLI is described.

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Using a model-based virtual HLI mouse population, pharmacologic inhibition of cell necrosis is predicted as a strategy with high therapeutic potential to improve perfusion recovery; in real HLI mice, the positive impact of this new strategy is then experimentally studied and confirmed.

In peripheral arterial disease (PAD), the degree of endogenous capacity to modulate revascularization of limb muscle is central to the management of leg ischemia. To characterize the multiscale and multicellular nature of revascularization in PAD, we have developed the first computational systems biology model that mechanistically incorporates intracellular, cellular, and tissue-level features critical for the dynamic reconstitution of perfusion after occlusion-induced ischemia. The computational model was specifically formulated for a preclinical animal model of PAD (mouse hindlimb ischemia [HLI]), and it has gone through multilevel model calibration and validation against a comprehensive set of experimental data so that it accurately captures the complex cellular signaling, cell–cell communication, and function during post-HLI perfusion recovery. As an example, our model simulations generated a highly detailed description of the time-dependent spectrum-like macrophage phenotypes in HLI, and through model sensitivity analysis we identified key cellular processes with potential therapeutic significance in the pathophysiology of PAD. Furthermore, we computationally evaluated the in vivo effects of different targeted interventions on post-HLI tissue perfusion recovery in a model-based, data-driven, virtual mouse population and experimentally confirmed the therapeutic effect of a novel model-predicted intervention in real HLI mice. This novel multiscale model opens up a new avenue to use integrative systems biology modeling to facilitate translational research in PAD.

A systems biology model of junctional localization and downstream signaling of the Ang-Tie signaling pathway

The Ang–Tie signaling pathway is an important vascular signaling pathway regulating vascular growth and stability. Dysregulation in the pathway is associated with vascular dysfunction and numerous diseases that involve abnormal vascular permeability and endothelial cell inflammation. The understanding of the molecular mechanisms of the Ang–Tie pathway has been limited due to the complex reaction network formed by the ligands, receptors, and molecular regulatory mechanisms. In this study, we developed a mechanistic computational model of the Ang–Tie signaling pathway validated against experimental data. The model captures and reproduces the experimentally observed junctional localization and downstream signaling of the Ang–Tie signaling axis, as well as the time-dependent role of receptor Tie1. The model predicts that Tie1 modulates Tie2’s response to the context-dependent agonist Ang2 by junctional interactions. Furthermore, modulation of Tie1’s junctional localization, inhibition of Tie2 extracellular domain cleavage, and inhibition of VE-PTP are identified as potential molecular strategies for potentiating Ang2’s agonistic activity and rescuing Tie2 signaling in inflammatory endothelial cells.

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.

Peripheral vascular disease: preclinical models and emerging therapeutic targeting of the vascular endothelial growth factor ligand-receptor system

Introduction: Vascular endothelial growth factor (VEGF)-A is a sought therapeutic target for PAD treatment because of its potent role in angiogenesis. However, no therapeutic benefit was achieved in VEGF-A clinical trials, suggesting that our understanding of VEGF-A biology and ischemic angiogenic processes needs development. Alternate splicing in VEGF-A produces pro- and anti-angiogenic VEGF-A isoforms; the only difference being a 6-amino acid switch in the C-terminus of the final 8th exon of the gene. This finding has changed our understanding of VEGF-A biology and may explain the lack of benefit in VEGF-A clinical trials. It presents new therapeutic opportunities for peripheral arterial disease (PAD) treatment.Areas covered: Literature search was conducted to include: 1) predicted mechanism by which the anti-angiogenic VEGF-A isoform would inhibit angiogenesis, 2) unexpected mechanism of action, and 3) how this mechanism revealed novel signaling pathways that may enhance future therapeutics in PAD.Expert opinion: Inhibiting a specific anti-angiogenic VEGF-A isoform in ischemic muscle promotes perfusion recovery in preclinical PAD. Additional efforts focused on the production of these isoforms, and the pathways altered by modulating different VEGF receptor-ligand interactions, and how this new data may allow bedside progress offers new approaches to PAD are discussed.I.

Racial differences in the limb skeletal muscle transcriptional programs of patients with critical limb ischemia

Critical limb ischemia (CLI) is the most severe manifestation of peripheral artery disease (PAD) and is characterized by high rates of morbidity and mortality. As with most severe cardiovascular disease manifestations, Black individuals disproportionately present with CLI. Accordingly, there remains a clear need to better understand the reasons for this discrepancy and to facilitate personalized therapeutic options specific for this population. Gastrocnemius muscle was obtained from White and Black healthy adult volunteers and patients with CLI for whole transcriptome shotgun sequencing (WTSS) and enrichment analysis was performed to identify alterations in specific Reactome pathways. When compared to their race-matched healthy controls, both White and Black patients with CLI demonstrated similar reductions in nuclear and mitochondrial encoded genes and mitochondrial oxygen consumption across multiple substrates, indicating a common bioenergetic paradigm associated with amputation outcomes regardless of race. Direct comparisons between tissues of White and Black patients with CLI revealed hemostasis, extracellular matrix organization, platelet regulation, and vascular wall interactions to be uniquely altered in limb muscles of Black individuals. Among traditional vascular growth factor signaling targets, WTSS revealed only Tie1 to be significantly altered from White levels in Black limb muscle tissues. Quantitative reverse transcription polymerase chain reaction validation of select identified targets verified WTSS directional changes and supports reductions in MMP9 and increases in NUDT4P1 and GRIK2 as unique to limb muscles of Black patients with CLI. This represents a critical first step in better understanding the transcriptional program similarities and differences between Black and White patients in the setting of amputations related to CLI and provides a promising start for therapeutic development in this population.

Skeletal muscle capillary density is related to anaerobic threshold and claudication in peripheral artery disease

Peripheral artery disease (PAD) is characterized by impaired blood flow to the lower extremities, causing claudication and exercise intolerance. Exercise intolerance may result from reduced skeletal muscle capillary density and impaired muscle oxygen delivery. This cross-sectional study tested the hypothesis that capillary density is related to claudication times and anaerobic threshold (AT) in patients with PAD. A total of 37 patients with PAD and 29 control subjects performed cardiopulmonary exercise testing on a treadmill for AT and gastrocnemius muscle biopsies. Skeletal muscle capillary density was measured using immunofluorescence staining. PAD had decreased capillary density (278 ± 87 vs 331 ± 86 endothelial cells/mm², p = 0.05), peak VO₂ (15.7 ± 3.9 vs 24.3 ± 5.2 mL/kg/min, p ⩽ 0.001), and VO₂ at AT (11.5 ± 2.6 vs 16.1 ± 2.8 mL/kg/min, p ⩽ 0.001) compared to control subjects. In patients with PAD, but not control subjects, capillary density was related to VO₂ at AT (r = 0.343; p = 0.038), time to AT (r = 0.381; p = 0.020), and time after AT to test termination (r = 0.610; p ⩽ 0.001). Capillary density was also related to time to claudication (r = 0.332; p = 0.038) and time after claudication to test termination (r = 0.584; p ⩽ 0.001). In conclusion, relationships between capillary density, AT, and claudication symptoms indicate that, in PAD, exercise limitations are likely partially dependent on limited skeletal muscle capillary density and oxidative metabolism.

A mechanistic integrative computational model of macrophage polarization: Implications in human pathophysiology

Macrophages respond to signals in the microenvironment by changing their functional phenotypes, a process known as polarization. Depending on the context, they acquire different patterns of transcriptional activation, cytokine expression and cellular metabolism which collectively constitute a continuous spectrum of phenotypes, of which the two extremes are denoted as classical (M1) and alternative (M2) activation. To quantitatively decode the underlying principles governing macrophage phenotypic polarization and thereby harness its therapeutic potential in human diseases, a systems-level approach is needed given the multitude of signaling pathways and intracellular regulation involved. Here we develop the first mechanism-based, multi-pathway computational model that describes the integrated signal transduction and macrophage programming under M1 (IFN-γ), M2 (IL-4) and cell stress (hypoxia) stimulation. Our model was calibrated extensively against experimental data, and we mechanistically elucidated several signature feedbacks behind the M1-M2 antagonism and investigated the dynamical shaping of macrophage phenotypes within the M1-M2 spectrum. Model sensitivity analysis also revealed key molecular nodes and interactions as targets with potential therapeutic values for the pathophysiology of peripheral arterial disease and cancer. Through simulations that dynamically capture the signal integration and phenotypic marker expression in the differential macrophage polarization responses, our model provides an important computational basis toward a more quantitative and network-centric understanding of the complex physiology and versatile functions of macrophages in human diseases.

Angiopoietin-Tie Signaling Pathway in Endothelial Cells: A Computational Model

The angiopoietin-Tie signaling pathway is an important vascular signaling pathway involved in angiogenesis, vascular stability, and quiescence. Dysregulation in the pathway is linked to the impairments in vascular function associated with many diseases, including cancer, ocular diseases, systemic inflammation, and cardiovascular diseases. The present study uses a computational signaling pathway model validated against experimental data to quantitatively study various mechanistic aspects of the angiopoietin-Tie signaling pathway, including receptor activation, trafficking, turnover, and molecular mechanisms of its regulation. The model provides mechanistic insights into the controversial role of Ang2 and its regulators vascular endothelial protein tyrosine phosphatase (VE-PTP) and Tie1 and predicts synergistic effects of inhibition of VE-PTP, Tie1, and Tie2 cleavage on enhancing the vascular protective actions of Tie2.

Antiangiogenic VEGF165b Regulates Macrophage Polarization via S100A8/S100A9 in Peripheral Artery Disease

BACKGROUND

Atherosclerotic occlusions decrease blood flow to the lower limbs, causing ischemia and tissue loss in patients with peripheral artery disease (PAD). No effective medical therapies are currently available to induce angiogenesis and promote perfusion recovery in patients with severe PAD. Clinical trials aimed at inducing vascular endothelial growth factor (VEGF)-A levels, a potent proangiogenic growth factor to induce angiogenesis, and perfusion recovery were not successful. Alternate splicing in the exon-8 of VEGF-A results in the formation of VEGFxxxa (VEGF₁₆₅a) and VEGFxxxb (VEGF₁₆₅b) isoforms with existing literature focusing on VEGF₁₆₅b's role in inhibiting vascular endothelial growth factor receptor 2-dependent angiogenesis. However, we have recently shown that VEGF₁₆₅b blocks VEGF-A-induced endothelial vascular endothelial growth factor receptor 1 (VEGFR1) activation in ischemic muscle to impair perfusion recovery. Because macrophage-secreted VEGF₁₆₅b has been shown to decrease angiogenesis in peripheral artery disease, and macrophages were well known to play important roles in regulating ischemic muscle vascular remodeling, we examined the role of VEGF₁₆₅b in regulating macrophage function in PAD.

METHODS

Femoral artery ligation and resection were used as an in vivo preclinical PAD model, and hypoxia serum starvation was used as an in vitro model for PAD. Experiments including laser-Doppler perfusion imaging, adoptive cell transfer to ischemic muscle, immunoblot analysis, ELISAs, immunostainings, flow cytometry, quantitative polymerase chain reaction analysis, and RNA sequencing were performed to determine a role of VEGF₁₆₅b in regulating macrophage phenotype and function in PAD.

RESULTS

First, we found increased VEGF₁₆₅b expression with increased M1-like macrophages in PAD versus non-PAD (controls) muscle biopsies. Next, using in vitro hypoxia serum starvation, in vivo pre clinical PAD models, and adoptive transfer of VEGF₁₆₅b-expressing bone marrow-derived macrophages or VEGFR1^+/- bone marrow-derived macrophages (M1-like phenotype), we demonstrate that VEGF₁₆₅b inhibits VEGFR1 activation to induce an M1-like phenotype that impairs ischemic muscle neovascularization. Subsequently, we found S100A8/S100A9 as VEGFR1 downstream regulators of macrophage polarization by RNA-Seq analysis of hypoxia serum starvation-VEGFR1^+/+ versus hypoxia serum starvation-VEGFR1^+/- bone marrow-derived macrophages.

CONCLUSIONS

In our current study, we demonstrate that increased VEGF₁₆₅b expression in macrophages induces an antiangiogenic M1-like phenotype that directly impairs angiogenesis. VEGFR1 inhibition by VEGF₁₆₅b results in S100A8/S100A9-mediated calcium influx to induce an M1-like phenotype that impairs ischemic muscle revascularization and perfusion recovery.

Noninvasive In Vivo Quantification of Adeno-Associated Virus Serotype 9-Mediated Expression of the Sodium/Iodide Symporter Under Hindlimb Ischemia and Neuraminidase Desialylation in Skeletal Muscle Using Single-Photon Emission Computed Tomography/Computed Tomography

BACKGROUND

We propose micro single-photon emission computed tomography/computed tomography imaging of the hNIS (human sodium/iodide symporter) to noninvasively quantify adeno-associated virus 9 (AAV9)-mediated gene expression in a murine model of peripheral artery disease.

METHODS

AAV9-hNIS (2×10¹¹ viral genome particles) was injected into nonischemic or ischemic gastrocnemius muscles of C57Bl/6J mice following unilateral hindlimb ischemia ± the α-sialidase NA (neuraminidase). Control nonischemic limbs were injected with phosphate buffered saline or remained noninjected. Twelve mice underwent micro single-photon emission computed tomography/computed tomography imaging after serial injection of pertechnetate (^99mTcO₄^-), a NIS substrate, up to 28 days after AAV9-hNIS injection. Twenty four animals were euthanized at selected times over 1 month for ex vivo validation. Forty-two animals were imaged with ^99mTcO₄^- ± the selective NIS inhibitor perchlorate on day 10, to ascertain specificity of radiotracer uptake. Tissue was harvested for ex vivo validation. A modified version of the U-Net deep learning algorithm was used for image quantification.

RESULTS

As quantitated by standardized uptake value, there was a gradual temporal increase in ^99mTcO₄^- uptake in muscles treated with AAV9-hNIS. Hindlimb ischemia, NA, and hindlimb ischemia plus NA increased the magnitude of ^99mTcO₄^- uptake by 4- to 5-fold compared with nonischemic muscle treated with only AAV9-hNIS. Perchlorate treatment significantly reduced ^99mTcO₄^- uptake in AAV9-hNIS-treated muscles, demonstrating uptake specificity. The imaging results correlated well with ex vivo well counting (r²=0.9375; P<0.0001) and immunoblot analysis of NIS protein (r²=0.65; P<0.0001).

CONCLUSIONS

Micro single-photon emission computed tomography/computed tomography imaging of hNIS-mediated ^99mTcO₄^- uptake allows for accurate in vivo quantification of AAV9-driven gene expression, which increases under ischemic conditions or neuraminidase desialylation in skeletal muscle.

Limb Perfusion During Exercise Assessed by Contrast Ultrasound Varies According to Symptom Severity in Patients with Peripheral Artery Disease

BACKGROUND

In patients with peripheral artery disease (PAD), the severity of symptoms correlates poorly with ankle-brachial index (ABI). The aim of this study was to test the hypothesis that limb perfusion assessed using contrast-enhanced ultrasound (CEU) during contractile exercise varies according to functional class in patients with PAD, particularly those with ABIs in the 0.4 to 0.6 range whose symptoms vary widely.

METHODS

Bilateral quantitative CEU perfusion imaging of the calf was performed in normal control subjects (n = 10) and patients with PAD who had at least one limb with a moderately reduced ABI (0.4-0.6; n = 17). Imaging was performed at rest and immediately after 30 sec of modest periodic (0.3-Hz) plantar flexion (10 W).

RESULTS

In patients with PAD, Rutherford symptom classification for each limb varied widely, including in limbs with ABIs of 0.4 to 0.6 (n = 6 with mild or no symptoms, n = 14 with moderate to severe symptoms). CEU perfusion imaging parameters at rest were similar between control subjects and patients with PAD irrespective of ABI. In normal control subjects, limb flow increased on average by > 20-fold after only 30 sec of moderate exercise. In patients with PAD, muscle exercise perfusion for all limbs was reduced compared with control subjects and decreased according to the severity of ABI reduction, primarily from reduced microvascular flux rate. Even limbs with ABIs > 0.9 in patients with PAD had lower exercise perfusion than in control subjects (P = .03). In subjects with PAD, exercise perfusion was lower in those with moderate to severe versus mild symptoms when analyzed for all limbs (median, 30 IU/sec [interquartile range (IQR), 21-52 IU/sec] vs 84 IU/sec [IQR, 36-177 IU/sec]; P = .01) and limbs with ABIs of 0.4 to 0.6 (median, 26 IU/sec [IQR, 14-41 IU/sec] vs 54 IU/sec [IQR, 31-105 IU/sec]; P = .05).

CONCLUSIONS

In patients with PAD, CEU exercise perfusion imaging detects differences in limb muscle perfusion that are likely to be responsible for differences in symptom severity and can detect the flow abnormalities from microvascular dysfunction even in limbs with normal ABIs.

Perivascular cell-specific knockout of the stem cell pluripotency gene Oct4 inhibits angiogenesis

The stem cell pluripotency factor Oct4 serves a critical protective role during atherosclerotic plaque development by promoting smooth muscle cell (SMC) investment. Here, we show using Myh11-CreERT2 lineage-tracing with inducible SMC and pericyte (SMC-P) knockout of Oct4 that Oct4 regulates perivascular cell migration and recruitment during angiogenesis. Knockout of Oct4 in perivascular cells significantly impairs perivascular cell migration, increases perivascular cell death, delays endothelial cell migration, and promotes vascular leakage following corneal angiogenic stimulus. Knockout of Oct4 in perivascular cells also impairs perfusion recovery and decreases angiogenesis following hindlimb ischemia. Transcriptomic analyses demonstrate that expression of the migratory gene Slit3 is reduced following loss of Oct4 in cultured SMCs, and in Oct4-deficient perivascular cells in ischemic hindlimb muscle. Together, these results provide evidence that Oct4 plays an essential role within perivascular cells in injury- and hypoxia-induced angiogenesis.

Validation of heart failure quality of life tool and usage to predict all-cause mortality in acute heart failure in Uganda: the Mbarara heart failure registry (MAHFER)

BACKGROUND

The health-related quality of life (HRQoL) is an important treatment goal that could serve as low-cost prognostication tool in resource poor settings. We sought to validate the Kansas City Cardiomyopathy Questionnaire (KCCQ) and evaluate its use as a predictor of 3 months all-cause mortality among heart failure participants in rural Uganda.

METHODS

The Mbarara Heart Failure Registry Cohort study observes heart failure patients during hospital stay and in the community in rural Uganda. Participants completed health failure evaluations and HRQoL questionnaires at enrollment, 1 and 3 months of follow-up. We used Cronbach's alpha coefficients to define internal consistency, intraclass correlation coefficients as a reliability coefficient, and Cox proportional hazard models to predict the risk of 3 months all-cause mortality.

RESULTS

Among the 195 participants who completed HRQoL questionnaires, the mean age was 52 (standard deviation (SD) 21.4) years, 68% were women and 29% reported history of hypertension. The KCCQ had excellent internal consistency (87% Cronbach alpha) but poor reliability. Independent predictors of all-cause mortality within 3 months included: worse overall KCCQ score (Adjusted Hazard ratio (AHR) 2.9, 95% confidence interval (CI) 1.1, 8.1), highest asset ownership (AHR 3.6, 95% CI 1.2, 10.8), alcoholic drinks per sitting (AHR per 1 drink 1.4, 95% CI 1.0, 1.9), New York Heart Association (NYHA) functional class IV heart failure (AHR 2.6, 95% CI 1.3, 5.4), estimated glomerular filtration rate (eGFR) 30 to 59 ml/min/1.73 m2 (AHR 3.4, 95% CI 1.1, 10.8), and eGFR less than 15 ml/min/1.73 m2 (AHR 2.7, 95% CI 1.0, 7.1), each 1 pg/mL increase in Brain Natriuretic Peptide (BNP) (AHR, 1.0, 95% CI 1.0, 1.0), and each 1 ng/mL increase in Creatine-Kinase MB isomer (CKMB) (AHR 1.0, 95% CI 1.0, 1.1).

CONCLUSION

The KCCQ showed excellent internal consistency. Worse overall KCCQ score, highest asset ownership, increasing alcoholic drink per sitting, NYHA class IV, decreased estimated glomerular filtration rate, BNP, and CKMB predicted all-cause mortality at 3 months. The KCCQ could be an additional low-cost tool to aid in the prognostication of acute heart failure patients.

Extensive skeletal muscle cell mitochondriopathy distinguishes critical limb ischemia patients from claudicants

The most severe manifestation of peripheral arterial disease (PAD) is critical limb ischemia (CLI). CLI patients suffer high rates of amputation and mortality; accordingly, there remains a clear need both to better understand CLI and to develop more effective treatments. Gastrocnemius muscle was obtained from 32 older (51-84 years) non-PAD controls, 27 claudicating PAD patients (ankle-brachial index [ABI] 0.65 ± 0.21 SD), and 19 CLI patients (ABI 0.35 ± 0.30 SD) for whole transcriptome sequencing and comprehensive mitochondrial phenotyping. Comparable permeabilized myofiber mitochondrial function was paralleled by both similar mitochondrial content and related mRNA expression profiles in non-PAD control and claudicating patient tissues. Tissues from CLI patients, despite being histologically intact and harboring equivalent mitochondrial content, presented a unique bioenergetic signature. This signature was defined by deficits in permeabilized myofiber mitochondrial function and a unique pattern of both nuclear and mitochondrial encoded gene suppression. Moreover, isolated muscle progenitor cells retained both mitochondrial functional deficits and gene suppression observed in the tissue. These findings indicate that muscle tissues from claudicating patients and non-PAD controls were similar in both their bioenergetics profile and mitochondrial phenotypes. In contrast, CLI patient limb skeletal muscles harbor a unique skeletal muscle mitochondriopathy that represents a potentially novel therapeutic site for intervention.

Neuraminidase-mediated desialylation augments AAV9-mediated gene expression in skeletal muscle

BACKGROUND

Following systemic delivery, AAV9-mediated gene expression is significantly increased in ischemic versus non-ischemic muscle, suggesting that AAV9 is an attractive vector for treating peripheral arterial disease. Potential mechanisms underlying ischemia-augmented expression include: (i) increased vascular permeability and (ii) "unmasking" of endogenous AAV9 receptors. In the present study, we aimed to reconstitute the ischemic induction of AAV9 in vivo, using local injection of histamine (to increase vascular permeability) and neuraminidase (to desialylate cell surface glycans).

METHODS

Bioassays were performed to optimize the effects of histamine and neuraminidase after intramuscular injection. Histamine and/or neuraminidase were then injected intramuscularly shortly before intravenous injection of an AAV9 vector expressing luciferase. Luciferase expression was serially assessed with bioluminescence imaging. At the end of the study, tissues were harvested for assays of luciferase activity and AAV9 genome copy number aiming to assess AAV-mediated gene expression and transduction, respectively.

RESULTS

Intramuscular injection of either neuraminidase or neuraminidase plus histamine significantly increased both transduction and gene expression, whereas histamine alone had little effect. Pre-injection with neuraminidase increased AAV9-mediated gene delivery by four- to nine-fold and luciferase activity by 60-100-fold. Luciferase activity in neuraminidase-injected muscle was > 100-fold higher than in any off-target tissue (including heart, liver and brain).

CONCLUSIONS

The ischemic induction of AAV9-mediated gene expression in muscle can largely be reconstituted by pre-injecting neuraminidase intranmuscularly. This strategy may prove useful in future human gene therapy protocols as a quick and efficient means to selectively target systemically injected AAV9 to localized regions of muscle, thus decreasing the potential for adverse effects in off-target tissues.

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

Arteriogenesis, the growth of endogenous collateral arteries bypassing arterial occlusion(s), is a fundamental shear stress-induced adaptation with implications for treating peripheral arterial disease (PAD). Nonetheless, endothelial mechano-signaling during arteriogenesis is incompletely understood. Here we tested the hypothesis that a mechanosensitive microRNA, miR-199a-5p, regulates perfusion recovery and collateral arteriogenesis following femoral arterial ligation (FAL) via control of monocyte recruitment and pro-arteriogenic gene expression. We have previously shown that collateral artery segments exhibit distinctly amplified arteriogenesis if they are exposed to reversed flow following FAL in the mouse. We performed a genome-wide analysis of endothelial cells exposed to a biomimetic reversed flow waveform. From this analysis, we identified mechanosensitive miR-199a-5p as a novel candidate regulator of collateral arteriogenesis. In vitro, miR-199a-5p inhibited pro-arteriogenic gene expression (IKKβ, Cav1) and monocyte adhesion to endothelium. In vivo, following FAL in mice, miR-199a-5p overexpression impaired foot perfusion and arteriogenesis. In contrast, a single intramuscular anti-miR-199a-5p injection elicited a robust therapeutic response, including complete foot perfusion recovery, markedly augmented arteriogenesis (>3.4-fold increase in segment conductance), and improved gastrocnemius tissue composition. Finally, we found plasma miR-199a-5p to be elevated in human PAD patients with intermittent claudication compared to a risk factor control population. Through our transformative analysis of endothelial mechano-signaling in response to a biomimetic amplified arteriogenesis flow waveform, we have identified miR-199a-5p as both a potent regulator of arteriogenesis and a putative target for treating PAD.

Computer Simulation of TSP1 Inhibition of VEGF-Akt-eNOS: An Angiogenesis Triple Threat

The matricellular protein thrombospondin-1 (TSP1) is a potent inhibitor of angiogenesis. Specifically, TSP1 has been experimentally shown to inhibit signaling downstream of vascular endothelial growth factor (VEGF). The molecular mechanism of this inhibition is not entirely clear. We developed a detailed computational model of VEGF signaling to Akt-endothelial nitric oxide synthase (eNOS) to investigate the quantitative molecular mechanism of TSP1 inhibition. The model demonstrated that TSP1 acceleration of VEGFR2 degradation is sufficient to explain the inhibition of VEGFR2 and eNOS phosphorylation. However, Akt inhibition requires TSP1-induced phosphatase recruitment to VEGFR2. The model was then utilized to test various strategies for the rescue of VEGF signaling to Akt and eNOS. Inhibiting TSP1 was predicted to be not as effective as CD47 depletion in rescuing signaling to Akt. The model further predicts that combination strategy involving depletion of CD47 and inhibition of TSP1 binding to CD47 is necessary for effective recovery of signaling to eNOS. In all, computational modeling offers insight to molecular mechanisms involving TSP1 interaction with VEGF signaling and provides strategies for rescuing angiogenesis by targeting TSP1-CD47 axis.

Abstract 342: Helix-loop-helix Transcription Factor Id3 Promotes Ischemia-induced Angiogenesis

The development of new blood vessels is important during the progression of many diseases including cancer, obesity, and ischemia. While inhibiting blood vessel growth can prevent excess adiposity and tumor growth, it can also exacerbate symptoms of ischemia. Using flow cytometry to quantify total endothelial cells (ECs) in the gastrocnemius of mice who have undergone femoral artery resection (FAR), the number of ECs per gram of muscle increases approximately four-fold relative to uninjured gastrocnemius from the same mouse (442% increase, ± 208%) in a model of hindlimb ischemia. The helix-loop-helix (HLH) transcription factor Inhibitor of differentiation (ID3) promotes angiogenesis and whole tissue blood perfusion in models of cancer and obesity, but the potential role for ID3 in promoting ischemia-induced angiogenesis remains uninvestigated. Id3 mRNA levels in injured gastrocnemius are increased three days post-FAR relative to uninjured gastrocnemius (p < 0.05, n = 6). Furthermore, ID3 global knockout (KO) mice have attenuated perfusion recovery compared to wild type littermate controls at 14 days post-FAR (p < 0.05). Gastrocnemius muscles isolated from ID3 global KO mice 7 days post-FAR express higher levels of the cell cycle inhibitor p21 Cip1 mRNA than WT mice (p = 0.10, n = 3). Finally, flow cytometry analysis of cell subsets in a novel Id3 promoter-GFP reporter mouse line revealed that Id3 promoter activation is greater in CD31 + ECs than many other cell types (n = 10), suggesting ECs may be an important cell type in which ID3 is promoting pro-angiogenic effects. Together, these data support the hypothesis that ID3 promotes ischemia-induced angiogenesis by promoting EC proliferation and inhibiting cell cycle inhibitor p21 Cip1 . To investigate the role of ID3 in ECs during angiogenesis, an EC-specific, tamoxifen-inducible Id3 KO mouse (Id3 fl/fl Cdh5-Cre/ERT2) has been generated.

Abstract 008: Perivascular Cell-specific Knockout of the Stem Cell Pluripotency Gene Oct4 Inhibits Angiogenesis in Part by Attenuating Perivascular and Endothelial Cell Migration

Objective: Angiogenesis requires coordinated migration of endothelial cells (EC) and perivascular cells, including smooth muscle cells and pericytes (SMC-P). Perivascular cell-specific mechanisms by which SMC-P migrate and invest EC remain largely unknown. Herein, we used Myh11-CreER T2 SMC-P lineage tracing, combined with SMC-P specific knockout of the stem cell pluripotency gene Oct4, to test the hypothesis that SMC-P derived Oct4 regulates perivascular cell migration and recruitment necessary for angiogenesis.

Methods and Results: Myh11-CreER T2 ROSA floxed STOP eYFP Oct4 WT/WT and Myh11-CreER T2 ROSA floxed STOP eYFP Oct4 FL/FL littermate mice were injected with tamoxifen from 6-8 weeks of age to permanently label Myh11-expressing cells with eYFP, without or with Oct4 KO, respectively. Mice were subjected to either corneal alkali burn or hindlimb ischemia (HLI), monitored by live confocal imaging and laser doppler perfusion respectively, and sacrificed for tissue analysis. SMC-P Oct4 KO resulted in markedly impaired eYFP+ (SMC-P derived) migration and increased vascular leak following corneal alkali burn. EC neovascular area and migration distance were also significantly decreased in SMC-P specific Oct4 KO mice. Following HLI, SMC-P Oct4 KO mice had impaired perfusion recovery and decreased capillary density. Slit3 was expressed in eYFP+ cells of the microvasculature in both cornea and muscle and was downregulated following Oct4 KO. RNA-seq and qRT-PCR analysis of cultured SMC revealed dysregulation of Slit3 as well as additional members of the Slit-Robo pathway of guidance genes, including downregulation of the receptors Robo1 and Robo2 and upregulation of Slit2 following loss of Oct4.

Conclusions: Taken together, we demonstrate that SMC-P derived Oct4 is essential for angiogenesis in both corneal alkali burn and HLI models. These effects are at least partially due to Oct4-dependent regulation of the Slit-Robo pathway in SMC-P, with Oct4 KO resulting in dysregulated migration of both EC and SMC-P. To our knowledge, this is the first direct evidence that loss of a single gene exclusively in SMC-P impacts angiogenesis following injury.

MicroRNA-146a Regulates Perfusion Recovery in Response to Arterial Occlusion via Arteriogenesis

The growth of endogenous collateral arteries that bypass arterial occlusion(s), or arteriogenesis, is a fundamental shear stress-induced adaptation with implications for treating peripheral arterial disease. MicroRNAs (miRs) are key regulators of gene expression in response to injury and have strong therapeutic potential. In a previous study, we identified miR-146a as a candidate regulator of vascular remodeling. Here, we tested whether miR-146a regulates in vitro angiogenic endothelial cell (EC) behaviors, as well as perfusion recovery, arteriogenesis, and angiogenesis in response to femoral arterial ligation (FAL) in vivo. We found miR-146a inhibition impaired EC tube formation and migration in vitro. Following FAL, Balb/c mice were treated with a single, intramuscular injection of anti-miR-146a or scramble locked nucleic acid (LNA) oligonucleotides directly into the non-ischemic gracilis muscles. Serial laser Doppler imaging demonstrated that anti-miR-146a treated mice exhibited significantly greater perfusion recovery (a 16% increase) compared mice treated with scramble LNA. Moreover, anti-miR-146a treated mice exhibited a 22% increase in collateral artery diameter compared to controls, while there was no significant effect on in vivo angiogenesis or muscle regeneration. Despite exerting no beneficial effects on angiogenesis, the inhibition of mechanosensitive miR-146a enhances perfusion recovery after FAL via enhanced arteriogenesis.

Muscle-derived extracellular superoxide dismutase inhibits endothelial activation and protects against multiple organ dysfunction syndrome in mice

Multiple organ dysfunction syndrome (MODS) is a detrimental clinical complication in critically ill patients with high mortality. Emerging evidence suggests that oxidative stress and endothelial activation (induced expression of adhesion molecules) of vital organ vasculatures are key, early steps in the pathogenesis. We aimed to ascertain the role and mechanism(s) of enhanced extracellular superoxide dismutase (EcSOD) expression in skeletal muscle in protection against MODS induced by endotoxemia. We showed that EcSOD overexpressed in skeletal muscle-specific transgenic mice (TG) redistributes to other peripheral organs through the circulation and enriches at the endothelium of the vasculatures. TG mice are resistant to endotoxemia (induced by lipopolysaccharide [LPS] injection) in developing MODS with significantly reduced mortality and organ damages compared with the wild type littermates (WT). Heterogenic parabiosis between TG and WT mice conferred a significant protection to WT mice, whereas mice with R213G knock-in mutation, a human single nucleotide polymorphism leading to reduced binding EcSOD in peripheral organs, exacerbated the organ damages. Mechanistically, EcSOD inhibits vascular cell adhesion molecule 1 expression and inflammatory leukocyte adhesion to the vascular wall of vital organs, blocking an early step of the pathology in organ damage under endotoxemia. Therefore, enhanced expression of EcSOD in skeletal muscle profoundly protects against MODS by inhibiting endothelial activation and inflammatory cell adhesion, which could be a promising therapy for MODS.

Systems Pharmacology of VEGF165b in Peripheral Artery Disease

We built a whole‐body computational model to study the role of the poorly understood vascular endothelial growth factor (VEGF)_165b splice isoform in peripheral artery disease (PAD). This model was built and validated using published and new experimental data from cells, mice, and humans, and explicitly accounts for known properties of VEGF_165b: lack of extracellular matrix (ECM)‐binding and weak phosphorylation of vascular endothelial growth factor receptor‐2 (VEGFR2) in vitro. The resulting model captures all known information about VEGF_165b distribution and signaling in human PAD, and provides novel, nonintuitive insight into VEGF_165b mechanism of action in vivo. Although VEGF_165a and VEGF_165b compete for VEGFR2 in vitro, simulations show that these isoforms do not compete for VEGFR2 at much lower physiological concentrations. Instead, reduced VEGF_165a may drive impaired VEGFR2 signaling. The model predicts that VEGF_165b does compete for binding to VEGFR1, supporting a VEGFR1‐mediated response to anti‐VEGF_165b. The model predicts a key role for VEGF_165b in PAD, but in a different way than previously hypothesized.

Therapeutic Angiogenesis for Peripheral Artery Disease: Lessons Learned in Translational Science

Peripheral arterial disease (PAD) is a major health care problem. There have been limited advances in medical therapies, and a huge burden of symptomatic patients with intermittent claudication and critical limb ischemia who have limited treatment options. Angiogenesis is the growth and proliferation of blood vessels from existing vasculature. For approximately 2 decades, "therapeutic angiogenesis" has been studied as an investigational approach to treat patients with symptomatic PAD. Despite literally hundreds of positive preclinical studies, results from human clinical studies thus far have been disappointing. Here we present an overview of where the field of therapeutic angiogenesis stands today and examine lessons learned from previously conducted clinical trials. The objective is not to second-guess past efforts but to place the lessons in perspective to allow for trial success in the future to improve agent development, trial design, and ultimately, clinical outcomes for new therapeutics for PAD.

BAG3 (Bcl-2-Associated Athanogene-3) Coding Variant in Mice Determines Susceptibility to Ischemic Limb Muscle Myopathy by Directing Autophagy

BACKGROUND

Critical limb ischemia is a manifestation of peripheral artery disease that carries significant mortality and morbidity risk in humans, although its genetic determinants remain largely unknown. We previously discovered 2 overlapping quantitative trait loci in mice, Lsq-1 and Civq-1, that affected limb muscle survival and stroke volume after femoral artery or middle cerebral artery ligation, respectively. Here, we report that a Bag3 variant (Ile81Met) segregates with tissue protection from hind-limb ischemia.

METHODS

We treated mice with either adeno-associated viruses encoding a control (green fluorescent protein) or 2 BAG3 (Bcl-2-associated athanogene-3) variants, namely Met81 or Ile81, and subjected the mice to hind-limb ischemia.

RESULTS

We found that the BAG3 Ile81Met variant in the C57BL/6 (BL6) mouse background segregates with protection from tissue necrosis in a shorter congenic fragment of Lsq-1 (C.B6-Lsq1-3). BALB/c mice treated with adeno-associated virus encoding the BL6 BAG3 variant (Ile81; n=25) displayed reduced limb-tissue necrosis and increased limb tissue perfusion compared with Met81- (n=25) or green fluorescent protein- (n=29) expressing animals. BAG3Ile81, but not BAG3Met81, improved ischemic muscle myopathy and muscle precursor cell differentiation and improved muscle regeneration in a separate, toxin-induced model of injury. Systemic injection of adeno-associated virus-BAG3Ile81 (n=9), but not BAG3Met81 (n=10) or green fluorescent protein (n=5), improved ischemic limb blood flow and limb muscle histology and restored muscle function (force production). Compared with BAG3Met81, BAG3Ile81 displayed improved binding to the small heat shock protein (HspB8) in ischemic skeletal muscle cells and enhanced ischemic muscle autophagic flux.

CONCLUSIONS

Taken together, our data demonstrate that genetic variation in BAG3 plays an important role in the prevention of ischemic tissue necrosis. These results highlight a pathway that preserves tissue survival and muscle function in the setting of ischemia.

A MicroRNA93-Interferon Regulatory Factor-9-Immunoresponsive Gene-1-Itaconic Acid Pathway Modulates M2-Like Macrophage Polarization to Revascularize Ischemic Muscle

BACKGROUND

Currently, no therapies exist for treating and improving outcomes in patients with severe peripheral artery disease (PAD). MicroRNA93 (miR93) has been shown to favorably modulate angiogenesis and to reduce tissue loss in genetic PAD models. However, the cell-specific function, downstream mechanisms, or signaling involved in miR93-mediated ischemic muscle neovascularization is not clear. Macrophages were best known to modulate arteriogenic response in PAD, and the extent of arteriogenic response induced by macrophages is dependent on greater M2 to M1 activation/polarization state. In the present study, we identified a novel mechanism by which miR93 regulates macrophage polarization to promote angiogenesis and arteriogenesis to revascularize ischemic muscle in experimental PAD.

METHODS

In vitro (macrophages, endothelial cells, skeletal muscle cells under normal and hypoxia serum starvation conditions) and in vivo experiments in preclinical PAD models (unilateral femoral artery ligation and resection) were conducted to examine the role of miR93-interferon regulatory factor-9-immunoresponsive gene-1 (IRG1)-itaconic acid pathway in macrophage polarization, angiogenesis, arteriogenesis, and perfusion recovery.

RESULTS

In vivo, compared with wild-type controls, miR106b-93-25 cluster-deficient mice (miR106b-93-25^-/-) showed decreased angiogenesis and arteriogenesis correlating with increased M1-like macrophages after experimental PAD. Intramuscular delivery of miR93 in miR106b-93-25^-/- PAD mice increased angiogenesis, arteriogenesis, and the extent of perfusion, which correlated with more M2-like macrophages in the proximal and distal hind-limb muscles. In vitro, miR93 promotes and sustains M2-like polarization even under M1-like polarizing conditions (hypoxia serum starvation). Delivery of bone marrow-derived macrophages from miR106b-93-25^-/- to wild-type ischemic muscle decreased angiogenesis, arteriogenesis, and perfusion, whereas transfer of wild-type macrophages to miR106b-93-25^-/- had the opposite effect. Systematic analysis of top differentially upregulated genes from RNA sequencing between miR106b-93-25^-/- and wild-type ischemic muscle showed that miR93 regulates IRG1 function to modulate itaconic acid production and macrophage polarization. The 3' untranslated region luciferase assays performed to determine whether IRG1 is a direct target of miR93 revealed that IRG1 is not an miR93 target but that interferon regulatory factor-9, which can regulate IRG1 expression, is an miR93 target. In vitro, increased expression of interferon regulatory factor-9 and IRG1 and itaconic acid treatment significantly decreased endothelial angiogenic potential.

CONCLUSIONS

miR93 inhibits interferon regulatory factor-9 to decrease IRG1-itaconic acid production to induce M2-like polarization in ischemic muscle to enhance angiogenesis, arteriogenesis, and perfusion recovery in experimental PAD.