Interferon-β Signaling Is Enhanced in Patients With Insufficient Coronary Collateral Artery Development and Inhibits Arteriogenesis in Mice

Trafficking and effect of released DNA on cGAS-STING signaling pathway and cardiovascular disease

Evidence from clinical research and animal studies indicates that inflammation is an important factor in the occurrence and development of cardiovascular disease (CVD). Emerging evidence shows that nucleic acids serve as crucial pathogen-associated molecular patterns (PAMPs) or non-infectious damage-associated molecular patterns (DAMPs), are released and then recognized by pattern recognition receptors (PRRs), which activates immunological signaling pathways for host defense. Mechanistically, the released nucleic acids activate cyclic GMP-AMP synthase (cGAS) and its downstream receptor stimulator of interferon genes (STING) to promote type I interferons (IFNs) production, which play an important regulatory function during the initiation of an innate immune response to various diseases, including CVD. This pathway represents an essential defense regulatory mechanism in an organism's innate immune system. In this review, we outline the overall profile of cGAS-STING signaling, summarize the latest findings on nucleic acid release and trafficking, and discuss their potential role in CVD. This review also sheds light on potential directions for future investigations on CVD.

ApoA-I Nanotherapy Rescues Postischemic Vascular Maladaptation by Modulating Endothelial Cell and Macrophage Phenotypes in Type 2 Diabetic Mice

BACKGROUND

Diabetes is a major risk factor for peripheral arterial disease. Clinical and preclinical studies suggest an impaired collateral remodeling and angiogenesis in response to atherosclerotic arterial occlusion in diabetic conditions, although the underlying mechanisms are poorly understood.

OBJECTIVE

To clarify the cellular and molecular mechanisms underlying impaired postischemic adaptive vascular responses and to evaluate rHDL (reconstituted HDL)-ApoA-I nanotherapy to rescue the defect in type 2 diabetic mouse model of hindlimb ischemia.

METHODS AND RESULTS

Hindlimb ischemia was induced by unilateral femoral artery ligation. Collateral and capillary parameters together with blood flow recovery were analyzed from normoxic adductor and ischemic gastrocnemius muscles, respectively, at day 3 and 7 post-ligation. In response to femoral artery ligation, collateral lumen area was significantly reduced in normoxic adductor muscles. Distally, ischemic gastrocnemius muscles displayed impaired perfusion recovery and angiogenesis paralleled with persistent inflammation. Muscle-specific mRNA sequencing revealed differential expression of genes critical for smooth muscle proliferation and sprouting angiogenesis in normoxic adductor and ischemic gastrocnemius, respectively, at day 7 post-ligation. Genes typical for macrophage (Mϕ) subsets were differentially expressed across both muscle types. Cell-specific gene expression, flow cytometry, and immunohistochemistry revealed persistent IFN-I response gene upregulation in arterial endothelial cells, ECs and Mϕs from T2DM mice associated with impaired collateral remodeling, angiogenesis and perfusion recovery. Furthermore, rHDL nanotherapy rescued impaired collateral remodeling and angiogenesis through dampening EC and Mϕ inflammation in T2DM mice.

CONCLUSIONS

Our results suggest that an impaired collateral remodeling and sprouting angiogenesis in T2DM mice is associated with persistent IFN-I response in ECs and Mϕs. Dampening persistent inflammation and skewing ECs and Mϕ phenotype toward less inflammatory ones using rHDL nanotherapy may serve as a potential therapeutic target for T2DM peripheral arterial disease.

SerpinG1: A Novel Biomarker Associated With Poor Coronary Collateral in Patients With Stable Coronary Disease and Chronic Total Occlusion

Background This study aimed to explore predictive biomarkers of coronary collateralization in patients with chronic total occlusion. Methods and Results By using a microarray expression profiling program downloaded from the Gene Expression Omnibus database, weighted gene coexpression network analysis was constructed to analyze the relationship between potential modules and coronary collateralization and screen out the hub genes. Then, the hub gene was identified and validated in an independent cohort of patients (including 299 patients with good arteriogenic responders and 223 patients with poor arteriogenic responders). Weighted gene coexpression network analysis showed that SERPING1 in the light-cyan module was the only gene that was highly correlated with both the gene module and the clinical traits. Serum levels of serpinG1 were significantly higher in patients with bad arteriogenic responders than in patients with good arteriogenic responders (472.53±197.16 versus 314.80±208.92 μg/mL; P<0.001) and were negatively associated with the Rentrop score (Spearman r=-0.50; P<0.001). Receiver operating characteristic curve analysis indicated that the area under the curve was 0.77 (95% CI, 0.72-0.81; P<0.001) for serum serpinG1 in prediction of bad arteriogenic responders. After adjusting for traditional cardiovascular risk factors, serum serpinG1 levels (per SD) remained an independent risk factor for bad arteriogenic responders (odds ratio, 2.20 [95% CI, 1.76-2.74]; P<0.001). Conclusions Our findings illustrate that SERPING1 screened by weighted gene coexpression network analysis was associated with poor collateralization in patients with chronic total occlusion.

p38 MAPK priming boosts VSMC proliferation and arteriogenesis by promoting PGC1α-dependent mitochondrial dynamics

Vascular smooth muscle cell (VSMC) proliferation is essential for arteriogenesis to restore blood flow after artery occlusion, but the mechanisms underlying this response remain unclear. Based on our previous findings showing increased VSMC proliferation in the neonatal aorta of mice lacking the protease MT4-MMP, we aimed at discovering new players in this process. We demonstrate that MT4-MMP absence boosted VSMC proliferation in vitro in response to PDGF-BB in a cell-autonomous manner through enhanced p38 MAPK activity. Increased phospho-p38 in basal MT4-MMP-null VSMCs augmented the rate of mitochondrial degradation by promoting mitochondrial morphological changes through the co-activator PGC1α as demonstrated in PGC1α^−/− VSMCs. We tested the in vivo implications of this pathway in a novel conditional mouse line for selective MT4-MMP deletion in VSMCs and in mice pre-treated with the p38 MAPK activator anisomycin. Priming of p38 MAPK activity in vivo by the absence of the protease MT4-MMP or by anisomycin treatment led to enhanced arteriogenesis and improved flow recovery after femoral artery occlusion. These findings may open new therapeutic opportunities for peripheral vascular diseases.

Leptomeningeal anastomoses: Mechanisms of pial collateral remodeling in ischemic stroke

Arterial collateralization, as determined by leptomeningeal anastomoses or pial collateral vessels, is a well‐established vital player in cerebral blood flow restoration and neurological recovery from ischemic stroke. A secondary network of cerebral collateral circulation apart from the Circle of Willis, exist as remnants of arteriole development that connect the distal arteries in the pia mater. Recent interest lies in understanding the cellular and molecular adaptations that control the growth and remodeling, or arteriogenesis, of these pre‐existing collateral vessels. New findings from both animal models and human studies of ischemic stroke suggest a multi‐factorial and complex, temporospatial interplay of endothelium, immune and vessel‐associated cell interactions may work in concert to facilitate or thwart arteriogenesis. These valuable reports may provide critical insight into potential predictors of the pial collateral response in patients with large vessel occlusion and may aid in therapeutics to enhance collateral function and improve recovery from stroke.

This article is categorized under:

Neurological Diseases > Molecular and Cellular Physiology

The cGAS-STING signaling in cardiovascular and metabolic diseases: Future novel target option for pharmacotherapy

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling exert essential regulatory function in microbial-and onco-immunology through the induction of cytokines, primarily type I interferons. Recently, the aberrant and deranged signaling of the cGAS-STING axis is closely implicated in multiple sterile inflammatory diseases, including heart failure, myocardial infarction, cardiac hypertrophy, nonalcoholic fatty liver diseases, aortic aneurysm and dissection, obesity, etc. This is because of the massive loads of damage-associated molecular patterns (mitochondrial DNA, DNA in extracellular vesicles) liberated from recurrent injury to metabolic cellular organelles and tissues, which are sensed by the pathway. Also, the cGAS-STING pathway crosstalk with essential intracellular homeostasis processes like apoptosis, autophagy, and regulate cellular metabolism. Targeting derailed STING signaling has become necessary for chronic inflammatory diseases. Meanwhile, excessive type I interferons signaling impact on cardiovascular and metabolic health remain entirely elusive. In this review, we summarize the intimate connection between the cGAS-STING pathway and cardiovascular and metabolic disorders. We also discuss some potential small molecule inhibitors for the pathway. This review provides insight to stimulate interest in and support future research into understanding this signaling axis in cardiovascular and metabolic tissues and diseases.

The association of interferon-alpha with development of collateral circulation after artery occlusion

Background

Previous studies have demonstrated that interferon (IFN) signaling is enhanced in patients with poor collateral circulation (CC). However, the role and mechanisms of IFN‐alpha in the development of CC remain unknown.

Methods

We studied the serum levels of IFN‐alpha and coronary CC in a case–control study using logistics regression, including 114 coronary chronic total occlusion (CTO) patients with good coronary CC and 94 CTO patients with poor coronary CC. Restricted cubic splines was used to flexibly model the association of the levels of IFN‐alpha with the incidence of good CC perfusion restoration after systemic treatment with IFN‐alpha was assessed in a mice hind‐limb ischemia model.

Results

Compared with the first IFN‐alpha tertile, the risk of poor CC was higher in the third IFN‐alpha tertile (OR: 4.79, 95% CI: 2.22–10.4, p < .001). A cubic spline‐smoothing curve showed that the risk of poor CC increased with increasing levels of serum IFN‐alpha. IFN‐alpha inhibited the development of CC in a hindlimb ischemia model. Arterioles of CC in the IFN‐alpha group were smaller in diameter than in the control group.

Conclusion

Patients with CTO and with poor CC have higher serum levels of IFN‐alpha than CTO patients with good CC. IFN‐alpha might impair the development of CC after artery occlusion.

TREML4 Promotes Inflammatory Programs in Human and Murine Macrophages and Alters Atherosclerosis Lesion Composition in the Apolipoprotein E Deficient Mouse

The Triggering Receptor Expressed on Myeloid cells-like 4 (TREML4) is a member of the TREM receptor family, known modulators of inflammatory responses. We have previously found that TREML4 expression positively correlates with human coronary arterial calcification (CAC). However, the role of TREML4 in the pathogenesis of cardiovascular disease remains incompletely defined. Since macrophages play a key role in inflammatory conditions, we investigated if activated macrophages selectively expressed TREML4 and found that carriage of either one of the eQTL SNP's previously associated with increased TREML4 expression conferred higher expression in human inflammatory macrophages (M1) compared to alternatively activated macrophages (M2). Furthermore, we found that TREML4 expression in human M1 dysregulated several inflammatory pathways related to leukocyte activation, apoptosis and extracellular matrix degradation. Similarly, murine M1 expressed substantial levels of Treml4, as did oxLDL treated macrophages. Transcriptome analysis confirmed that murine Treml4 controls the expression of genes related to inflammation and lipid regulation pathways, suggesting a possible role in atherosclerosis. Analysis of Apoe-/-/Treml4-/- mice showed reduced plaque burden and lesion complexity as indicated by decreased stage scores, macrophage content and collagen deposition. Finally, transcriptome analysis of oxLDL-loaded murine macrophages showed that Treml4 represses a specific set of genes related to carbohydrate, ion and amino acid membrane transport. Metabolomic analysis confirmed that Treml4 deficiency may promote a beneficial relationship between iron homeostasis and glucose metabolism. Together, our results suggest that Treml4 plays a role in the development of cardiovascular disease, as indicated by Treml4-dependent dysregulation of macrophage inflammatory pathways, macrophage metabolism and promotion of vulnerability features in advanced lesions.

An Emerging Role for isomiRs and the microRNA Epitranscriptome in Neovascularization

Therapeutic neovascularization can facilitate blood flow recovery in patients with ischemic cardiovascular disease, the leading cause of death worldwide. Neovascularization encompasses both angiogenesis, the sprouting of new capillaries from existing vessels, and arteriogenesis, the maturation of preexisting collateral arterioles into fully functional arteries. Both angiogenesis and arteriogenesis are highly multifactorial processes that require a multifactorial regulator to be stimulated simultaneously. MicroRNAs can regulate both angiogenesis and arteriogenesis due to their ability to modulate expression of many genes simultaneously. Recent studies have revealed that many microRNAs have variants with altered terminal sequences, known as isomiRs. Additionally, endogenous microRNAs have been identified that carry biochemically modified nucleotides, revealing a dynamic microRNA epitranscriptome. Both types of microRNA alterations were shown to be dynamically regulated in response to ischemia and are able to influence neovascularization by affecting the microRNA’s biogenesis, or even its silencing activity. Therefore, these novel regulatory layers influence microRNA functioning and could provide new opportunities to stimulate neovascularization. In this review we will highlight the formation and function of isomiRs and various forms of microRNA modifications, and discuss recent findings that demonstrate that both isomiRs and microRNA modifications directly affect neovascularization and vascular remodeling.

Stimulation of Collateral Vessel Growth by Inhibition of Galectin 2 in Mice Using a Single-Domain Llama-Derived Antibody

Background

In the presence of arterial stenosis, collateral artery growth (arteriogenesis) can alleviate ischemia and preserve tissue function. In patients with poorly developed collateral arteries, Gal‐2 (galectin 2) expression is increased. In vivo administration of Gal‐2 inhibits arteriogenesis. Blocking of Gal‐2 potentially stimulates arteriogenesis. This study aims to investigate the effect of Gal‐2 inhibition on arteriogenesis and macrophage polarization using specific single‐domain antibodies.

Methods and Results

Llamas were immunized with Gal‐2 to develop anti–Gal‐2 antibodies. Binding of Gal‐2 to monocytes and binding inhibition of antibodies were quantified. To test arteriogenesis in vivo, Western diet‐fed LDLR.(low‐density lipoprotein receptor)–null Leiden mice underwent femoral artery ligation and received treatment with llama antibodies 2H8 or 2C10 or with vehicle. Perfusion restoration was measured with laser Doppler imaging. In the hind limb, arterioles and macrophage subtypes were characterized by histology, together with aortic atherosclerosis. Llama‐derived antibodies 2H8 and 2C10 strongly inhibited the binding of Gal‐2 to monocytes (93% and 99%, respectively). Treatment with these antibodies significantly increased perfusion restoration at 14 days (relative to sham, vehicle: 41.3±2.7%; 2H8: 53.1±3.4%, P=0.016; 2C10: 52.0±3.8%, P=0.049). In mice treated with 2H8 or 2C10, the mean arteriolar diameter was larger compared with control (vehicle: 17.25±4.97 μm; 2H8: 17.71±5.01 μm; 2C10: 17.84±4.98 μm; P<0.001). Perivascular macrophages showed a higher fraction of the M2 phenotype in both antibody‐treated animals (vehicle: 0.49±0.24; 2H8: 0.73±0.15, P=0.007; 2C10: 0.75±0.18, P=0.006). In vitro antibody treatment decreased the expression of M1‐associated cytokines compared with control (P<0.05 for each). Atherosclerotic lesion size was comparable between groups (overall P=0.59).

Conclusions

Inhibition of Gal‐2 induces a proarteriogenic M2 phenotype in macrophages, improves collateral artery growth, and increases perfusion restoration in a murine hind limb model.

A Pro-Inflammatory Biomarker-Profile Predicts Amputation-Free Survival in Patients with Severe Limb Ischemia

Patients with Severe Limb Ischemia (SLI) have a high risk of amputation and mortality. Here, we investigated a panel of serum biomarkers with the aim of identifying biomarkers for major events and mechanisms that contribute to disease progression in established SLI. A panel of biomarkers including GROα, HGF, SCF, SCGFβ, SDF1α, TRAIL, IL-6, IL-8, FGFβ, GCSF, GMCSF, IP10, MCP1, PDGFbb, RANTES, TNFα, VEGF, sICAM, sVCAM, TM, and E-selectin was measured in serum samples from a subset (n = 108) of the JUVENTAS cohort. The primary outcome was major events, defined as major amputation or death. The inflammatory biomarkers IL-6, IL-8, GROα and IP-10 were significantly elevated in patients who reached a major endpoint. Results were validated in a secondary cohort (n = 146). Cox regression showed that adjusted hazard ratios were 1.40 (95% CI: 1.15-1.70, p = 0.0007) and 1.48 (95% CI 1.16-1.87, p = 0.001) for IL-6 and IP-10 in a fully adjusted model containing both biomarkers. A prediction model using IL-6 and IP-10 showed predictive accuracy with an AUC of ~ 78% in both discovery and validation cohorts, which is higher than previously published models. We conclude that inflammatory biomarkers predict major events in patients with SLI and allow the creation of biomarker-based risk-prediction models.

Decrease in Secondary Neck Vessels in Multiple Sclerosis: A 5-year Longitudinal Magnetic Resonance Angiography Study

BACKGROUND

Studies have previously shown greater arterial and venous extracranial vascular changes in persons with multiple sclerosis (PwMS) when compared to healthy controls (HCs).

OBJECTIVES

To determine the change in the number and size of secondary neck vessels in PwMS and HCs over a 5-year follow-up period.

METHODS

Both at baseline and follow-up, 83 PwMS and 25 HCs underwent magnetic resonance angiography (MRA) imaging and analysis. The number and cross-sectional area (CSA) of all secondary neck vessels (excluding the common/internal carotid, vertebral artery, and internal jugular vein) measured at levels from C2-T1 were determined by semi-automated edge detection/ contouring software. The longitudinal change in the number and CSA of the secondary neck vessels from the PwMS and HCs were analyzed by non-parametric Wilcoxon repeated measure. Benjamini-Hochberg procedure adjusted for false discovery rate (FDR).

RESULTS

For over 5 years, PwMS demonstrated a consistent longitudinal decrease in both the number of secondary neck vessels (Z-change between -3.3 and -5.4, q=0.001) and their CSA (Zchange between -2.9 and -5.2, q=0.004). On the contrary, the HCs did not demonstrate a significant longitudinal change in secondary neck vessels over the follow-up period. Due to the longitudinal decrease, the PwMS showed a lower number of secondary neck vessels when compared to HCs measured at follow-up (p<0.029, except for C4 with trending p=0.071). The PwMS changes were also corroborated within each MS phenotype.

CONCLUSION

PwMS demonstrate a significant mid-term decrease in the number and the size of the secondary neck vessels. The clinical relevance of these findings and the effect on intracranial blood flow are currently unknown.

IRF3 and IRF7 mediate neovascularization via inflammatory cytokines

OBJECTIVE

To elucidate the role of interferon regulatory factor (IRF)3 and IRF7 in neovascularization.

METHODS

Unilateral hind limb ischaemia was induced in Irf3-/- , Irf7-/- and C57BL/6 mice by ligation of the left common femoral artery. Post-ischaemic blood flow recovery in the paw was measured with laser Doppler perfusion imaging. Soleus, adductor and gastrocnemius muscles were harvested to investigate angiogenesis and arteriogenesis and inflammation.

RESULTS

Post-ischaemic blood flow recovery was decreased in Irf3-/- and Irf7-/- mice compared to C57BL/6 mice at all time points up to and including sacrifice, 28 days after surgery (t28). This was supported by a decrease in angiogenesis and arteriogenesis in soleus and adductor muscles of Irf3-/- and Irf7-/- mice at t28. Furthermore, the number of macrophages around arterioles in adductor muscles was decreased in Irf3-/- and Irf7-/- mice at t28. In addition, mRNA expression levels of pro-inflammatory cytokines (tnfα, il6, ccl2) and growth factor receptor (vegfr2), were decreased in gastrocnemius muscles of Irf3-/- and Irf7-/- mice compared to C57BL/6 mice.

CONCLUSION

Deficiency of IRF3 and IRF7 results in impaired post-ischaemic blood flow recovery caused by attenuated angiogenesis and arteriogenesis linked to a lack of inflammatory components in ischaemic tissue. Therefore, IRF3 and IRF7 are essential regulators of neovascularization.

Elevated monocyte-specific type I interferon signalling correlates positively with cardiac healing in myocardial infarct patients but interferon alpha application deteriorates myocardial healing in rats

Monocytes are involved in adverse left ventricular (LV) remodelling following myocardial infarction (MI). To provide therapeutic opportunities we aimed to identify gene transcripts in monocytes that relate to post-MI healing and evaluated intervention with the observed gene activity in a rat MI model. In 51 MI patients treated by primary percutaneous coronary intervention (PCI), the change in LV end-diastolic volume index (EDVi) from baseline to 4-month follow-up was assessed using cardiovascular magnetic resonance imaging (CMR). Circulating monocytes were collected at day 5 (Arterioscler Thromb Vasc Biol 35:1066-1070, 2015; Cell Stem Cell 16:477-487, 2015; Curr Med Chem 13:1877-1893, 2006) after primary PCI for transcriptome analysis. Transcriptional profiling and pathway analysis revealed that patients with a decreased LV EDVi showed an induction of type I interferon (IFN) signalling (type I IFN pathway: P value < 0.001; false discovery rate < 0.001). We subsequently administered 15,000 Units of IFN-α subcutaneously in a rat MI model for three consecutive days following MI. Cardiac function was measured using echocardiography and infarct size/cardiac inflammation using (immuno)-histochemical analysis. We found that IFN-α application deteriorated ventricular dilatation and increased infarct size at day 28 post-MI. Moreover, IFN-α changed the peripheral monocyte subset distribution towards the pro-inflammatory monocyte subset whereas in the myocardium, the presence of the alternative macrophage subset was increased at day 3 post-MI. Our findings suggest that induction of type I IFN signalling in human monocytes coincides with adverse LV remodelling. In rats, however, IFN-α administration deteriorated post-MI healing. These findings underscore important but also contradictory roles for the type I IFN response during cardiac healing following MI.

TLDc proteins: new players in the oxidative stress response and neurological disease

Oxidative stress (OS) arises from an imbalance in the cellular redox state, which can lead to intracellular damage and ultimately cell death. OS occurs as a result of normal ageing, but it is also implicated as a common etiological factor in neurological disease; thus identifying novel proteins that modulate the OS response may facilitate the design of new therapeutic approaches applicable to many disorders. In this review, we describe the recent progress that has been made using a range of genetic approaches to understand a family of proteins that share the highly conserved TLDc domain. We highlight their shared ability to prevent OS-related cell death and their unique functional characteristics, as well as discussing their potential application as new neuroprotective factors. Furthermore, with an increasing number of pathogenic mutations leading to epilepsy and hearing loss being discovered in the TLDc protein TBC1D24, understanding the function of this family has important implications for a range of inherited neurological diseases.

Monocytic microRNA profile associated with coronary collateral artery function in chronic total occlusion patients

An expansive collateral artery network is correlated with improved survival in case of adverse cardiac episodes. We aimed to identify cellular microRNAs (miRNA; miR) important for collateral artery growth. Chronic total occlusion (CTO) patients (n = 26) were dichotomized using pressure-derived collateral flow index (CFI_p) measurements; high collateral capacity (CFI_p > 0.39; n = 14) and low collateral (CFI_p < 0.39; n = 12) capacity. MiRNA profiling via next generation sequencing from various monocyte phenotypes (freshly isolated monocytes, monocytes cultured without stimulant, or stimulation with lipopolysaccharide, interleukin 4, transforming growth factor beta-1, or interferon gamma) revealed significantly different miRNA expression patterns between high versus low collateral capacity patients. Validation by real-time polymerase chain reaction demonstrated significantly decreased expression of miR339-5p in all stimulated monocyte phenotypes of low collateral capacity patients. MiR339-5p showed significant correlation with CFI_p values in stimulated monocytes. Ingenuity pathway analysis of predicted gene targets of miR339-5p and differential gene expression data from high versus low CFI_p patients (n = 20), revealed significant association with STAT3 pathway, and also suggested a possible regulatory role for this signaling pathway. These results identify a novel association between miR339-5p and coronary collateral function. Future work examining modulation of miR339-5p and downstream effects on the STAT3 pathway and subsequent collateral vessel growth are warranted.

IFN-β affects the angiogenic potential of circulating angiogenic cells by activating calpain 1

Circulating angiogenic cells (CACs) are monocyte-derived cells with endothelial characteristics, which contribute to both angiogenesis and arteriogenesis in a paracrine way. Interferon-β (IFN-β) is known to inhibit these divergent processes in animals and patients. We hypothesized that IFN-β might act by affecting the differentiation and function of CACs. CACs were cultured from peripheral blood mononuclear cells and phenotypically characterized by surface expression of monocytic and endothelial markers. IFN-β significantly reduced the number of CACs by 18–64%. Apoptosis was not induced by IFN-β, neither in mononuclear cells during differentiation, nor after maturation to CACs. Rather, IFN-β impaired adhesion to, and spreading on, fibronectin, which was dependent on α5β1 (VLA-5)-integrin. IFN-β affected the function of VLA-5 in mature CACs, leading to rounding and detachment of cells, by induction of calpain 1 activity. Cell rounding and detachment was completely reversed by inhibition of calpain 1 activity in mature CACs. During in vitro capillary formation, CAC addition and calpain 1 inhibition enhanced sprouting of endothelial cells to a comparable extent, but were not sufficient to rescue tube formation in the presence of IFN-β. We show that the IFN-β-induced reduction of the numbers of in vitro differentiated CACs is based on activation of calpain 1, resulting in an attenuated adhesion to extracellular matrix proteins via VLA-5. In vivo, this could lead to inhibition of vessel formation due to reduction of the locally recruited CAC numbers and their paracrine angiogenic factors.

Neovascularization of the atherosclerotic plaque: interplay between atherosclerotic lesion, adventitia-derived microvessels and perivascular fat

PURPOSE OF REVIEW

Neovascularization is a prominent feature in advanced human atherosclerotic plaques. This review surveys recent evidence for and remaining uncertainties regarding a role of neovascularization in atherosclerotic plaque progression. Specific emphasis is given to hypoxia, angiogenesis inhibition, and perivascular adipose tissue (PVAT).

RECENT FINDINGS

Immunohistochemical and imaging studies showed a strong association between hypoxia, inflammation and neovascularization, and the progression of the atherosclerotic plaque both in humans and mice. Whereas in humans, a profound invasion of microvessels from the adventitia into the plaque occurs, neovascularization in mice is found mainly (peri)adventitially. Influencing neovascularization in mice affected plaque progression, possibly by improving vessel perfusion, but supportive clinical data are not available. Whereas plaque neovascularization contributes to monocyte/macrophage accumulation in the plaque, lymphangiogenesis may facilitate egress of cells and waste products. A specific role for PVAT and its secreted factors is anticipated and wait further clinical evaluation.

SUMMARY

Hypoxia, inflammation, and plaque neovascularization are associated with plaque progression as underpinned by recent imaging data in humans. Recent studies provide new insights into modulation of adventitia-associated angiogenesis, PVAT, and plaque development in mice, but there is still a need for detailed information on modulating human plaque vascularization in patients.

Circulating MicroRNAs Characterizing Patients with Insufficient Coronary Collateral Artery Function

BACKGROUND

Coronary collateral arteries function as natural bypasses in the event of coronary obstruction. The degree of collateral network development significantly impacts the outcome of patients after an acute myocardial infarction (AMI). MicroRNAs (miRNAs, miRs) have arisen as biomarkers to identify heterogeneous patients, as well as new therapeutic targets in cardiovascular disease. We sought to identify miRNAs that are differentially expressed in chronic total occlusion (CTO) patients with well or poorly developed collateral arteries.

METHODS AND RESULTS

Forty-one CTO patients undergoing coronary angiography and invasive assessment of their coronary collateralization were dichotomized based on their collateral flow index (CFI). After miRNA profiling was conducted on aortic plasma, four miRNAs were selected for validation by real-time quantitative reverse transcription polymerase chain reaction in patients with low (CFI<0.39) and high (CFI>0.39) collateral artery capacity. We confirmed significantly elevated levels of miR423-5p (p<0.05), miR10b (p<0.05), miR30d (p<0.05) and miR126 (p<0.001) in patients with insufficient collateral network development. We further demonstrated that each of these miRNAs could serve as circulating biomarkers to discriminate patients with low collateral capacity (p<0.01 for each miRNA). We also determined significantly greater expression of miR30d (p<0.05) and miR126 (p<0.001) in CTO patients relative to healthy controls.

CONCLUSION

The present study identifies differentially expressed miRNAs in patients with high versus low coronary collateral capacity. We have shown that these miRNAs can function as circulating biomarkers to discriminate between patients with insufficient or sufficient collateralization. This is the first study to identify miRNAs linked to coronary collateral vessel function in humans.

Exercise promotes collateral artery growth mediated by monocytic nitric oxide

OBJECTIVE

Collateral artery growth (arteriogenesis) is an important adaptive response to hampered arterial perfusion. It is unknown whether preventive physical exercise before limb ischemia can improve arteriogenesis and modulate mononuclear cell function. This study aimed at investigating the effects of endurance exercise before arterial occlusion on MNC function and collateral artery growth.

APPROACH AND RESULTS

After 3 weeks of voluntary treadmill exercise, ligation of the right femoral artery was performed in mice. Hindlimb perfusion immediately after surgery did not differ from sedentary mice. However, previous exercise improved perfusion restoration ≤7 days after femoral artery ligation, also when exercise was stopped at ligation. This was accompanied by an accumulation of peri-collateral macrophages and increased expression of endothelial nitric oxide synthase and inducible nitric oxide synthase (iNOS) in hindlimb collateral and in MNC of blood and spleen. Systemic monocyte and macrophage depletion by liposomal clodronate but not splenectomy attenuated exercise-induced perfusion restoration, collateral artery growth, peri-collateral macrophage accumulation, and upregulation of iNOS. iNOS-deficient mice did not show exercise-induced perfusion restoration. Transplantation of bone marrow-derived MNC from iNOS-deficient mice into wild-type animals inhibited exercise-induced collateral artery growth. In contrast to sedentary controls, thrice weekly aerobic exercise training for 6 months in humans increased peripheral blood MNC iNOS expression.

CONCLUSIONS

Circulating mononuclear cell-derived inducible nitric oxide is an important mediator of exercise-induced collateral artery growth.

Genetic association study of coronary collateral circulation in patients with coronary artery disease using 22 single nucleotide polymorphisms corresponding to 10 genes involved in postischemic neovascularization

BACKGROUND

Collateral growth in patients with coronary artery disease (CAD) is highly heterogeneous. Although multiple factors are thought to play a role in collateral development, the contribution of genetic factors to coronary collateral circulation (CCC) is largely unknown. The goal of this study was to assess whether functional single nucleotide polymorphisms (SNPs) in genes involved in vascular growth are associated with CCC.

METHODS

677 consecutive CAD patients were enrolled in the study and their CCC was assessed by the Rentrop method. 22 SNPs corresponding to 10 genes involved in postischemic neovascularization were genotyped and multivariate logistic regression models were adjusted using clinically relevant variables to estimate odds ratios and used to examine associations of allelic variants, genotypes and haplotypes with CCC.

RESULTS

Statistical analysis showed that the HIF1A rs11549465 and rs2057482; VEGFA rs2010963, rs1570360, rs699947, rs3025039 and rs833061; KDR rs1870377, rs2305948 and rs2071559; CCL2 rs1024611, rs1024610, rs2857657 and rs2857654; NOS3 rs1799983; ICAM1 rs5498 and rs3093030; TGFB1 rs1800469; CD53 rs6679497; POSTN rs3829365 and rs1028728; and LGALS2 rs7291467 polymorphisms, as well as their haplotype combinations, were not associated with CCC (p < 0.05).

CONCLUSIONS

We could not validate in our cohort the association of the NOS3 rs1799983, HIF1A rs11549465, VEGFA rs2010963 and rs699947, and LGALS2 rs7291467 variants with CCC reported by other authors. A validated SNP-based genome-wide association study is required to identify polymorphisms influencing CCC.

The future of collateral artery research

In the event of obstructive coronary artery disease, collateral arteries have been deemed an alternative blood source to preserve myocardial tissue perfusion and function. Monocytes play an important role in modulating this process, by local secretion of growth factors and extracellular matrix degrading enzymes. Extensive efforts have focused on developing compounds for augmenting the growth of collateral vessels (arteriogenesis). Nonetheless, clinical trials investigating the therapeutic potential of these compounds resulted in disappointing outcomes. Previous studies focused on developing compounds that stimulated collateral vessel growth by enhancing monocyte survival and activity. The limited success of these compounds in clinical studies, led to a paradigm shift in arteriogenesis research. Recent studies have shown genetic heterogeneity between CAD patients with sufficient and insufficient collateral vessels. The genetic predispositions in patients with poorly developed collateral vessels include overexpression of arteriogenesis inhibiting signaling pathways. New directions of arteriogenesis research focus on attempting to block such inhibitory pathways to ultimately promote arteriogenesis. Methods to detect collateral vessel growth are also critical in realizing the therapeutic potential of newly developed compounds. Traditional invasive measurements of intracoronary derived collateral flow index remain the gold standard in quantifying functional capacity of collateral vessels. However, advancements made in hybrid diagnostic imaging modalities will also prove to be advantageous in detecting the effects of pro-arteriogenic compounds.

Determinants of human coronary collaterals

The human coronary collateral circulation is prognostically relevant. The understanding of collateral formation and its determinants may guide future therapeutic strategies aiming at promoting collateral growth and functionality, and hence reducing the global burden of coronary artery disease (CAD).

Differential Effects of IFN-β on the Survival and Growth of Human Vascular Smooth Muscle and Endothelial Cells

It has been documented that interferon (IFN)-β is effective against the genesis of atherosclerosis or hyperplastic arterial disease in animal model. The main mechanism of the efficacy was antiproliferative action on the growth of vascular smooth muscle cells (SMC). To understand more about the mechanisms that are responsible for the efficacy, we examined minutely the effects of IFN-β on the apoptosis and growth of vascular SMC and endothelial cells (EC). IFN-β enhanced SMC apoptosis in serum starved medium. Conversely, EC apoptosis induced by serum and growth factor deprivation was inhibited by IFN-β. The induction of SMC apoptosis and anti-apoptotic effect on EC linked to the expression of pro-apoptotic bax mRNA and caspase-3 activities. Anti-apoptotic bcl-2 mRNA was also up-regulated in EC. IFN-β inhibited SMC growth in a dose dependent manner. However, the growth of EC was rather enhanced by a low dose of IFNs. The antiproliferative effect on SMC associated with the activation of p21 and increase of G0/G1 arrested cells. The growth stimulation on EC was considered to link with increase of S and G2/M phase cells. SMC produced IFN-β in response to various stimulants. However, IFN-β was not induced in EC. These suggested that endogenous IFN-β from SMC may act on EC and affect to EC functions. In this study, it was clarified that IFN-β enhances SMC apoptosis and inhibits the EC apoptosis, and stimulates the EC growth. These effects were considered to contribute to a cure against hyperplastic arterial diseases as the mechanisms in the efficacy of IFN-β.

The dual PPARα/γ agonist aleglitazar increases the number and function of endothelial progenitor cells: implications for vascular function and atherogenesis

BACKGROUND AND PURPOSE

Aleglitazar is a dual PPARα/γ agonist but little is known about its effects on vascular function and atherogenesis. Hence, we characterized its effects on circulating angiogenic cells (CAC), neoangiogenesis, endothelial function, arteriogenesis and atherosclerosis in mice.

EXPERIMENTAL APPROACH

C57Bl/6 wild-type (WT, normal chow), endothelial NOS (eNOS)(-/-) (normal chow) and ApoE(-/-) (Western-type diet) mice were treated with aleglitazar (10 mg·kg(-1) ·day(-1) , i.p.) or vehicle.

KEY RESULTS

Aleglitazar enhanced expression of PPARα and PPARγ target genes, normalized glucose tolerance and potently reduced hepatic fat in ApoE(-/-) mice. In WT mice, but not in eNOS(-/-) , aleglitazar up-regulated Sca-1/VEGFR2-positive CAC in the blood and bone marrow and up-regulated diLDL/lectin-positive CAC. Aleglitazar augmented CAC migration and enhanced neoangiogenesis. In ApoE(-/-) mice, aleglitazar up-regulated CAC number and function, reduced markers of vascular inflammation and potently improved perfusion restoration after hindlimb ischaemia and aortic endothelium-dependent vasodilatation. This was associated with markedly reduced formation of atherosclerotic plaques. In human cultured CAC from healthy donors and patients with coronary artery disease with or without diabetes mellitus, aleglitazar increased migration and colony-forming units in a concentration-dependent manner. Furthermore, oxidative stress-induced CAC apoptosis and expression of p53 were reduced, while telomerase activity and expression of phospho-eNOS and phospho-Akt were elevated. Comparative agonist and inhibitor experiments revealed that aleglitazar's effects on CAC migration and colony-forming units were mediated by both PPARα and PPARγ signalling and required Akt.

CONCLUSIONS AND IMPLICATIONS

Aleglitazar augments the number, function and survival of CAC, which correlates with improved vascular function, enhanced arteriogenesis and prevention of atherosclerosis in mice.

Integrative DNA, RNA, and protein evidence connects TREML4 to coronary artery calcification

Coronary artery calcification (CAC) is a heritable and definitive morphologic marker of atherosclerosis that strongly predicts risk for future cardiovascular events. To search for genes involved in CAC, we used an integrative transcriptomic, genomic, and protein expression strategy by using next-generation DNA sequencing in the discovery phase with follow-up studies using traditional molecular biology and histopathology techniques. RNA sequencing of peripheral blood from a discovery set of CAC cases and controls was used to identify dysregulated genes, which were validated by ClinSeq and Framingham Heart Study data. Only a single gene, TREML4, was upregulated in CAC cases in both studies. Further examination showed that rs2803496 was a TREML4 cis-eQTL and that the minor allele at this locus conferred up to a 6.5-fold increased relative risk of CAC. We characterized human TREML4 and demonstrated by immunohistochemical techniques that it is localized in macrophages surrounding the necrotic core of coronary plaques complicated by calcification (but not in arteries with less advanced disease). Finally, we determined by von Kossa staining that TREML4 colocalizes with areas of microcalcification within coronary plaques. Overall, we present integrative RNA, DNA, and protein evidence implicating TREML4 in coronary artery calcification. Our findings connect multimodal genomics data with a commonly used clinical marker of cardiovascular disease.

The collateral circulation of the heart

The coronary arteries have been regarded as end arteries for decades. However, there are functionally relevant anastomotic vessels, known as collateral arteries, which interconnect epicardial coronary arteries. These vessels provide an alternative source of blood supply to the myocardium in cases of occlusive coronary artery disease. The relevance of these collateral arteries is a matter of ongoing debate, but increasing evidence indicates a relevant protective role in patients with coronary artery disease. The collateral circulation can be assessed by different methods; the gold standard involves intracoronary pressure measurements. While the first clinical trials to therapeutically induce growth of collateral arteries have been unavailing, recent pilot studies using external counterpulsation or growth factors such as granulocyte colony stimulating factor (G-CSF) have shown promising results.

Mechanistic, technical, and clinical perspectives in therapeutic stimulation of coronary collateral development by angiogenic growth factors

Stimulation of collateral vessel development in the heart by angiogenic growth factor therapy has been tested in animals and humans for almost two decades. Discordance between the outcome of preclinical studies and clinical trials pointed to the difficulties of translation from animal models to patients. Lessons learned in this process identified specific mechanistic, technical, and clinical hurdles, which need to be overcome. This review summarizes current understanding of the mechanisms leading to the establishment of a functional coronary collateral network and the biological processes growth factor therapies should stimulate even under conditions of impaired natural adaptive vascular response. Vector delivery methods are recommended to maximize angiogenic gene therapy efficiency and reduce side effects. Optimization of clinical trial design should include the choice of clinical end points which provide mechanistic proof-of-concept and also reflect clinical benefits (e.g., surrogates to assess increased collateral flow reserve, such as myocardial perfusion imaging). Guidelines are proposed to select patients who may respond to the therapy with high(er) probability. Both short and longer term strategies are outlined which may help to make therapeutic angiogenesis (TA) work in the future.

Exercise training and peripheral arterial disease

Peripheral arterial disease (PAD) is a common vascular disease that reduces blood flow capacity to the legs of patients. PAD leads to exercise intolerance that can progress in severity to greatly limit mobility, and in advanced cases leads to frank ischemia with pain at rest. It is estimated that 12 to 15 million people in the United States are diagnosed with PAD, with a much larger population that is undiagnosed. The presence of PAD predicts a 50% to 1500% increase in morbidity and mortality, depending on severity. Treatment of patients with PAD is limited to modification of cardiovascular disease risk factors, pharmacological intervention, surgery, and exercise therapy. Extended exercise programs that involve walking approximately five times per week, at a significant intensity that requires frequent rest periods, are most significant. Preclinical studies and virtually all clinical trials demonstrate the benefits of exercise therapy, including improved walking tolerance, modified inflammatory/hemostatic markers, enhanced vasoresponsiveness, adaptations within the limb (angiogenesis, arteriogenesis, and mitochondrial synthesis) that enhance oxygen delivery and metabolic responses, potentially delayed progression of the disease, enhanced quality of life indices, and extended longevity. A synthesis is provided as to how these adaptations can develop in the context of our current state of knowledge and events known to be orchestrated by exercise. The benefits are so compelling that exercise prescription should be an essential option presented to patients with PAD in the absence of contraindications. Obviously, selecting for a lifestyle pattern that includes enhanced physical activity prior to the advance of PAD limitations is the most desirable and beneficial.

Characterization of the differential response of endothelial cells exposed to normal and elevated laminar shear stress

Most acute coronary events occur in the upstream region of stenotic atherosclerotic plaques that experience laminar shear stress (LSS) elevated above normal physiological levels. Many studies have described the atheroprotective effect on endothelial behavior of normal physiological LSS (approximately 15 dynes/cm²) compared to static or oscillatory shear stress (OSS), but it is unknown whether the levels of elevated shear stress imposed by a stenotic plaque would preserve, enhance or reverse this effect. Therefore we used transcriptomics and related functional analyses to compare human endothelial cells exposed to laminar shear stress of 15 (LSS15-normal) or 75 dynes/cm² (LSS75-elevated). LSS75 upregulated expression of 145 and downregulated expression of 158 genes more than twofold relative to LSS15. Modulation of the metallothioneins (MT1-G, -M, -X) and NADPH oxidase subunits (NOX2, NOX4, NOX5, and p67phox) accompanied suppression of reactive oxygen species production at LSS75. Shear induced changes in dual specificity phosphatases (DUSPs 1, 5, 8, and 16 increasing and DUSPs 6 and 23 decreasing) were observed as well as reduced ERK1/2 but increased p38 MAP kinase phosphorylation. Amongst vasoactive substances, endothelin-1 expression decreased whereas vasoactive intestinal peptide (VIP) and prostacyclin expression increased, despite which intracellular cAMP levels were reduced. Promoter analysis by rVISTA identified a significant over representation of ATF and Nrf2 transcription factor binding sites in genes upregulated by LSS75 compared to LSS15. In summary, LSS75 induced a specific change in behavior, modifying gene expression, reducing ROS levels, altering MAP kinase signaling and reducing cAMP levels, opening multiple avenues for future study. J. Cell. Physiol. 226: 2841–2848, 2011. © 2011 Wiley-Liss, Inc.

Vascular growth in health and disease

Vascular growth forms the first functional organ system during development, and continues into adult life, wherein it is often associated with disease states. Genetically determined vasculogenesis produces a primary vascular plexus during ontogenesis. Angiogenesis, occurring, e.g., in response to metabolic stress within hypoxic tissues, enhances tissue capillarization. Arteriogenesis denotes the adaptive outgrowth of pre-existent collateral arteries to bypass arterial stenoses in response to hemodynamic changes. It has been debated whether vasculogenesis occurs in the adult, and whether or not circulating progenitor cells structurally contribute to vessel regeneration. Secondly, the major determinants of vascular growth – genetic predisposition, metabolic factors (hypoxia), and hemodynamics – cannot be assigned in a mutually exclusive fashion to vasculogenesis, angiogenesis, and arteriogenesis, respectively; rather, mechanisms overlap. Lastly, all three mechanisms of vessel growth seem to contribute to physiological embryogenesis as well as adult adaptive vascularization as occurs in tumors or to circumvent arterial stenosis. Thus, much conceptual and terminological confusion has been created, while therapies targeting neovascularization have yielded promising results in the lab, but failed randomized studies when taken to the bedside. Therefore, this review article aims at providing an exact definition of the mechanisms of vascular growth and their contribution to embryonic development as well as adult adaptive revascularization. We have been looking for potential reasons for why clinical trials have failed, how vitally the application of appropriate methods of measuring and assessment influences study outcomes, and how relevant, e.g., results gained in models of vascular occlusive disease may be for antineoplastic strategies, advocating a reverse bedside-to-bench approach, which may hopefully yield successful approaches to therapeutically targeting vascular growth.

Transcriptome analysis in endothelial progenitor cell biology

The use of endothelial progenitor cells (EPCs) is a promising new treatment option for cardiovascular diseases. Many of the underlying mechanisms that result in an improvement of endothelial function in vivo remain poorly elucidated to this date, however. We summarize the current positions and potential applications of gene-expression profiling in the field of EPC biology. Based on our own and published gene-expression data, we demonstrate that gene-expression profiling can efficiently be used to characterize different EPC types. Furthermore, we highlight the potential of gene-expression profiling for the analysis of changes that EPCs undergo during culture and examine changes in gene transcription in diseased patients. Transcriptome profiling is a powerful tool for the characterization and functional analysis of EPCs in health and disease.

A unifying hypothesis for scleroderma: identifying a target cell for scleroderma

We propose that a recent change in the conception of the role of type 1 interferon and the identification of adventitial stem cells suggests a unifying hypothesis for scleroderma. This hypothesis begins with vasospasm. Vasospasm is fully reversible unless, as proposed here, the resulting ischemia leads to apoptosis and activation of type 1 interferon. The interferon, we propose, initiates immune amplification, including characteristic scleroderma-specific antibodies. We propose that the interferon also acts on adventitial stem cells, producing myofibroblasts, rarefaction, and intimal hyperplasia--three morphologic changes that characterize this disease. Regulator of G-protein signaling 5 (RGS5), a regulator of vasoactive G-protein-coupled receptors, is a cell type-specific marker of pericytes and scleroderma myofibroblasts. RGS5 may provide a key link between initial hyperplasia and fibrosis in this disease.

Poor coronary collateral vessel development in patients with mild to moderate renal insufficiency

BACKGROUND

The development of coronary collaterals is crucial to survival through acute ischemia. Mild to moderate loss of renal function has been suggested to play a role in this event, but evidential data are scarce. The aim of this study was to investigate the relationship between mild to moderate renal insufficiency and coronary collateral development in patients with chronic total coronary artery occlusion.

METHODS AND RESULTS

A total of 83 patients with mild to moderate loss of renal function (30 mL/min/1.73 m(2) ≤ eGFR < 90 mL/min/1.73 m(2)) with chronic total coronary artery occlusion were included in our study. The collateral circulation was graded according to Rentrop classification and the function of collateral circulation was graded according to Werner collateral connection (CC) grades. Compared to patients with good collateral circulation (Rentrop = 2,3), eGFR was found to be lower in those patients with poor coronary collateral circulation (Rentrop = 0,1) (63.30 ± 10.51 vs. 54.13 ± 10.56, P = 0.02). eGFR was also found to be lower in poorly functioning coronary collateral circulation (CC = 0,1) than in efficiently functioning coronary collateral circulation (CC = 2) (55.22 ± 9.98 vs. 66.28 ± 9.16, P = 0.03). Multiple logistic regression analysis showed that low eGFR was independently associated with poor coronary collateral circulation (Rentrop = 0,1, 95% CI, 0.09-1.09, P = 0.044) and poor function of coronary collateral circulation (CC = 0,1, 95% CI, 0.02-0.17, P = 0.02).

CONCLUSIONS

Lower eGFR is associated with poorer coronary collateral vessel development in patients experiencing mild to moderate renal insufficiency. Moreover, eGFR represents an independent factor affecting coronary collateral vessel development.

Blocking interferon {beta} stimulates vascular smooth muscle cell proliferation and arteriogenesis

Increased interferon (IFN)-β signaling in patients with insufficient coronary collateralization and an inhibitory effect of IFNβ on collateral artery growth in mice have been reported. The mechanisms of IFNβ-induced inhibition of arteriogenesis are unknown. In stimulated monocytes from patients with chronic total coronary artery occlusion and decreased arteriogenic response, whole genome expression analysis showed increased expression of IFNβ-regulated genes. Immunohistochemically, the IFNβ receptor was localized in the vascular media of murine collateral arteries. Treatment of vascular smooth muscle cells (VSMC) with IFNβ resulted in an attenuated proliferation, cell-cycle arrest, and increased expression of cyclin-dependent kinase inhibitor-1A (p21). The growth inhibitory effect of IFNβ was attenuated by inhibition of p21 by RNA interference. IFNβ-treated THP1 monocytes showed enhanced apoptosis. Subsequently, we tested if collateral artery growth can be stimulated by inhibition of IFNβ-signaling. RNA interference of the IFNβ receptor-1 (IFNAR1) increased VSMC proliferation, cell cycle progression, and reduced p21 gene expression. IFNβ signaling and FAS and TRAIL expression were attenuated in monocytes from IFNAR1(-/-) mice, indicating reduced monocyte apoptosis. Hindlimb perfusion restoration 1 week after femoral artery ligation was improved in IFNAR1(-/-) mice compared with wild-type mice as assessed by infusion of fluorescent microspheres. These results demonstrate that IFNβ inhibits collateral artery growth and VSMC proliferation through p21-dependent cell cycle arrest and induction of monocyte apoptosis. Inhibition of IFNβ stimulates VSMC proliferation and collateral artery growth.

The human coronary collateral circulation

BACKGROUND

Coronary collaterals are an alternative source of blood supply to myocardium jeopardized by ischaemia. Well-developed coronary collateral arteries in patients with coronary artery disease (CAD) mitigate myocardial infarcts and improve survival.

METHODS AND RESULTS

Collateral arteries preventing myocardial ischaemia during brief vascular occlusion are present in 1/3 of patients with CAD. Among individuals without relevant coronary stenoses, there are preformed collateral arteries preventing myocardial ischaemia in 20-25%. Collateral flow sufficient to prevent myocardial ischaemia during coronary occlusion amounts to double dagger25% of the normal flow through the open vessel. Myocardial infarct size, the most important prognostic determinant after such an event, is the product of coronary artery occlusion time, area at risk for infarction and the inverse of collateral supply. Coronary collateral flow can be assessed only during vascular occlusion of the collateral-receiving artery. The gold standard for coronary collateral assessment is the measurement of intracoronary occlusive pressure- or velocity-derived collateral flow index expressing collateral as a fraction of flow during vessel patency. Approximately one of five patients with CAD cannot be revascularized by percutaneous coronary intervention or coronary artery bypass grafting. Therapeutic promotion of collateral growth is a valuable treatment strategy in those patients.

CONCLUSIONS

Promotion of collateral growth should aim at inducing the development of large conductive collateral arteries (i.e. arteriogenesis) and not so much the sprouting of capillary like vessels (i.e. angiogenesis). Large conductive collateral arteries appear to be effectively promoted via the activation of monocytes/macrophages by means of granulocyte-colony stimulating factor or of augmenting coronary flow velocity.

Cardiovascular risk factors and collateral artery formation

Arterial lumen narrowing and vascular occlusion is the actual cause of morbidity and mortality in atherosclerotic disease. Collateral artery formation (arteriogenesis) refers to an active remodelling of non-functional vascular anastomoses to functional collateral arteries, capable to bypass the site of obstruction and preserve the tissue that is jeopardized by ischaemia. Hemodynamic forces such as shear stress and wall stress play a pivotal role in collateral artery formation, accompanied by the expression of various cytokines and invasion of circulating leucocytes. Arteriogenesis hence represents an important compensatory mechanism for atherosclerotic vessel occlusion. As arteriogenesis mostly occurs when lumen narrowing by atherosclerotic plaques takes place, presence of cardiovascular risk factors (e.g. hypertension, hypercholesterolaemia and diabetes) is highly likely. Risk factors for atherosclerotic disease affect collateral artery growth directly and indirectly by altering hemodynamic forces or influencing cellular function and proliferation. Adequate collateralization varies significantly among atherosclerotic patients, some profit from the presence of extensive collateral networks, whereas others do not. Cardiovascular risk factors could increase the risk of adverse cardiovascular events in certain patients because of the reduced protection through an alternative vascular network. Likewise, drugs primarily thought to control cardiovascular risk factors might contribute or counteract collateral artery growth. This review summarizes current knowledge on the influence of cardiovascular risk factors and the effects of cardiovascular medication on the development of collateral vessels in experimental and clinical studies.