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

Local cytokine concentrations and oxygen pressure are related to maturation of the collateral circulation in humans

OBJECTIVES

Our aim was to determine cytokine and oxygen gradients over the collateral circulation in humans.

BACKGROUND

The molecular background of the maturation of the collateral circulation in response to coronary narrowing is poorly understood in humans, partly because of difficulties in obtaining local samples from the human collateral circulation.

METHODS

Coronary collateral blood was sampled in 60 patients with nontotal (n = 25) or total coronary occlusions (n = 35) using a special wide-lumen catheter. Coronary collateral flow index (CFI) was assessed by intracoronary pressure measurements. Oxygenation and lactate content was measured as well as 30 cytokines potentially involved in collateral artery growth, using a custom-made multiplex assay.

RESULTS

No rise in lactate or change in pH was found in collateral blood. Oxygen gradient between coronary and collateral arterial blood correlated inversely with CFI (r = -0.61, p < 0.001). Locally increased plasma levels were found for basic fibroblast growth factor, eotaxin, macrophage migration inflammatory factor, monocyte chemoattractant protein-1, and transforming growth factor-beta, while stem cell factor and stem cell growth factor-beta were significantly decreased. The highest cytokine gradients were found in patients with the least developed collateral circulation. The majority of cytokines correlated more strongly with the pO(2) gradient across the collateral bed than with CFI.

CONCLUSIONS

Intravascular ischemia during brief balloon coronary occlusion is absent in human coronary collateral arteries. The oxygen gradient found over the collateral circulation is increased in patients with a less matured collateral circulation and relates to local levels of several known pro-arteriogenic cytokines. In case of a more developed collateral circulation, relatively low levels of cytokines are present, suggesting that growth factor therapy might be beneficial at this stage.

Chloride intracellular channel-4 is a determinant of native collateral formation in skeletal muscle and brain

The capacity of the collateral circulation to lessen injury in occlusive vascular disease depends on the density and caliber of native (preexisting) collaterals, as well as their ability to outwardly remodel in ischemia. Native collateral conductance varies widely among healthy individuals, yet little is known about what specifies collateral formation. Chloride intracellular channel (CLIC)4 protein is required for endothelial cell hollowing, a process necessary for vessel formation during embryogenesis and ischemia. Whether CLIC4 has other physiological roles in vascular biology is uncertain. We studied collateral formation and remodeling in mice deficient in CLIC1 and CLIC4. Vascular responses to femoral artery ligation were similar in Clic1(-/-) and wild-type mice. In contrast, immediately after ligation perfusion dropped more in Clic4(-/-) than wild-type mice, suggesting fewer preexisting collaterals, a finding confirmed by angiography, greater ischemia, and worse recovery of perfusion; however, collateral remodeling was unaffected. Likewise, native cerebral collateral density in Clic4(-/-) (but not Clic1(-/-)) mice was reduced, resulting in severe infarctions. This was associated with impaired perinatal formation and stabilization of nascent collaterals. Clic4 hemizygous mice had intermediate deficits in the above parameters, suggesting a gene-dose effect. Ischemia augmented CLIC1 and CLIC4 expression similarly in wild-type mice. However, CLIC1 increased 3-fold more in Clic4(-/-) mice, suggesting compensation. Despite greater ischemia in Clic4(-/-) mice, hypoxia-inducible factor-1alpha, vascular endothelial growth factor (VEGF) and angiopoietin-2 increased less compared to wild-type, suggesting CLIC4 exerts influences upstream of hypoxia-inducible factor-1alpha-VEGF signaling. Hence, CLIC4 represents the second gene that, along with VEGF shown by us previously, specifies native collateral formation.

Endothelial glycocalyx dimensions are reduced in growing collateral arteries and modulate leucocyte adhesion in arteriogenesis

During collateral artery growth, monocytes adhere to the endothelium and secrete cytokines from the perivascular space promoting arteriogenesis. Recently, the endothelial glycocalyx has been shown to modulate leucocyte infiltration in atherogenic regions. The role of this endothelial surface coating in arteriogenesis, however, has not been investigated so far. We now report that local plasma levels of hyaluronic acid are specifically increased in collateral arterial blood of coronary artery disease patients and hypothesized that components of the endothelial glycocalyx are shed during arteriogenesis, resulting in decreased glycocalyx dimensions and an increased leucocyte extravasation. In a rabbit model of femoral artery ligation, electron microscopy revealed a decrease in glycocalyx dimensions in collateral arteries compared with quiescent anastomoses (67.5 ± 47.2 nm versus 101.0 ± 11.3 nm; P < 0.001). This decrease was correlated with a higher number of perivascular macrophages around collateral arteries. The additional glycocalyx perturbation by local hyaluronidase infusion almost completely removed the endothelial surface layer and temporarily stimulated leucocyte accumulation in the perivascular space. However, complete perturbation of the glycocalyx by hyaluronidase infusion resulted in a significant attenuation of collateral artery growth assessed by microsphere-based perfusion measurements (ml/min/100 mmHg: hyaluronidase: 27.5 ± 3.5; Controls: 47.1 ± 3.83; P < 0.001) and a lower percentage of actively proliferating vascular smooth muscle cells. A decreased expression of the shear-stress regulated pro-arteriogenic genes eNOS and TGF-β1 suggests an impaired mechanotransduction as the underlying mechanisms. For the first time, we describe the role of the endothelial glycocalyx in collateral artery growth. Although complete abrogation led to attenuated arteriogenesis, shedding of glycocalyx components is observed during collateral artery growth.

Release of proinflammatory mediators and expression of proinflammatory adhesion molecules by endothelial progenitor cells

Cell therapy with endothelial progenitor cells (EPCs) is an emerging therapeutic option to promote angiogenesis or endothelial repair. Although the release of angiogenic paracrine factors is known to contribute to their therapeutic effect, little is known about their release of proinflammatory factors and expression of proinflammatory adhesion molecules. "Early" EPCs and "late" EPCs were isolated from human peripheral blood and their release of chemokines and thromboinflammatory mediators as well as their expression of the proinflammatory adhesion molecules was assessed at baseline and with stimulation. The effect of simvastatin on monocyte chemoattractant protein-1 (MCP-1) secretion by late EPCs from patients with vascular disease was also evaluated. All groups of EPCs released chemokines and thromboinflammatory mediators. Early EPCs primarily released thromboinflammatory mediators such as tissue factor (0.5 +/- 0.1 ng/million cells, P < 0.05), whereas adult late EPCs primarily released chemokines such as MCP-1 (287 +/- 98 ng/million cells, P < 0.05). Stimulation with tumor necrosis factor (TNF)-alpha augmented the expression of proinflammatory adhesion molecules and paracrine factors by all EPC subtypes. The release of MCP-1 by late EPCs was markedly reduced by simvastatin treatment of the cells. All EPC subtypes expressed proinflammatory paracrine factors and adhesion molecules involved in atherosclerosis. Future clinical studies should therefore not only assess the efficacy of EPCs but also monitor inflammatory activation following EPC transplantation in patients. Pharmacological modulation of EPCs before and after transplantation may represent a novel approach to improve their safety.

Suppression of inflammatory signaling in monocytes from patients with coronary artery disease

Monocytes and T-cells play an important role in the development of atherosclerotic coronary artery disease (CAD). Transcriptome analysis of circulating mononuclear cells from carefully matched atherosclerotic and control patients will potentially provide insights into the pathophysiology of atherosclerosis and supply biomarkers for diagnostic purposes. From patients undergoing coronary angiography because of anginal symptoms, we carefully matched 18 patients with severe triple-vessel CAD to 13 control patients without angiographic signs of CAD. All patients were on statin and aspirin treatment. Elevated soluble-ICAM levels demonstrated increased vascular inflammation in atherosclerotic patients. RNA from circulating CD4+ T-cells, CD14+ monocytes, lipopolysaccharide-stimulated monocytes, and macrophages was subjected to genome-wide expression analysis. In CD14+ monocytes, few inflammatory genes were overexpressed in control patients, while atherosclerotic patients showed overexpression of a group of Krüppel-associated box - containing transcription factors involved in negative regulation of gene expression. These differences disappeared upon LPS-stimulation or differentiation towards macrophages. No consistent changes in T cell transcriptomes were detected. Large inter-individual variability prevented the use of single differentially expressed genes as biomarkers, while monocyte gene expression signature predicted patient status with an accuracy of 84%. In this comprehensive analysis of circulating cell transcriptomes in atherosclerotic CAD, cautious patient matching revealed only small differences in transcriptional activity in different mononuclear cell types. Only an indication of a negative feedback to inflammatory gene expression was detected in atherosclerotic patients. Transcriptome differences of circulating cells possibly play less of a role than hitherto thought in the individual patient's susceptibility to atherosclerotic CAD, when appropriately matched for clinical symptoms and medication taken.