Adult progenitor cells in vascular remodeling during atherosclerosis

The mobilization and recruitment of bone marrow-derived, circulating or tissue resident progenitor cells giving rise to smooth muscle-like cells have been implicated in neointima hyperplasia after arterial injury and in accelerated forms of arterial lesion formation, e.g., transplant arteriopathy or graft vasculopathy. By contrast, convincing evidence has emerged that the vascular homing of endothelial progenitor cells (EPCs) contributes to endothelial recovery, thus limiting neointima formation after arterial injury. In the chronic context of primary atherosclerosis, plaque progression and destabilization, a more complex picture has become apparent. In patients with coronary artery disease, the number and function of EPCs have been linked with an improved endothelial function or regeneration, but have been inversely correlated with cardiovascular risk. In animal models, however, the injection of bone marrow cells or EPCs, or the application of stem-cell mobilizing factors, have been associated with an exacerbation of atherosclerosis and unstable plaque phenotypes, whereas the contribution of bone marrow-derived smooth muscle progenitors to primary atherosclerosis appears to be rather confined. Here, we discuss crucial biochemical cues, namely chemokines, adhesion molecules, growth factors and pharmacological means that guide and control the context-specific mobilization, recruitment and fate of vascular progenitor cells in arterial remodeling during atherosclerosis.     

Inhibition of inflammatory endothelial responses by a pathway involving caspase activation and p65 cleavage

Suppression of NF kappa B activation has been involved in the elimination of survival programs during endothelial cell (EC) apoptosis. We used alpha-tocopheryl succinate (alpha-TOS) to trigger apoptosome formation and the subsequent activation of executioner caspases. The level of bcl-2 was reduced by alpha-TOS, and its downregulation potentiated and its overexpression suppressed pro-apoptotic effects of alpha-TOS, indicating a mitochondrial role in alpha-TOS-induced apoptosis in EC. alpha-TOS treatment was associated with induction of TUNEL-positive apoptosis in EC with a high but not with a low proliferation index. The use of the pan-caspase inhibitor z-VAD.fmk suggested the involvement of caspases in cleavage of p65, and in inhibition of nuclear translocation of p65 and NF kappa B-dependent transactivation of a gene construct encoding the green fluorescence protein elicited by TNF alpha in contact-arrested EC. The suppression by alpha-TOS of inflammatory EC responses induced by TNF alpha such as VCAM-1 mRNA and surface protein expression and shear-resistant arrest of monocytic cells were also reversed by z-VAD.fmk. NF kappa B-dependent transactivation was preserved in alpha-TOS-treated EC stably transfected with a caspase-noncleavable p65 mutant but not with its truncated form, thus establishing a direct link between alpha-TOS-induced effects and p65 cleavage. Our data infer a pathway by which caspase activation in EC inhibits NF kappa B-dependent inflammatory activation and monocyte recruitment, and provide evidence for a relationship between pro-apoptotic and anti-inflammatory pathways.     

MIF is a noncognate ligand of CXC chemokine receptors in inflammatory and atherogenic cell recruitment

The cytokine macrophage migration inhibitory factor (MIF) plays a critical role in inflammatory diseases and atherogenesis. We identify the chemokine receptors CXCR2 and CXCR4 as functional receptors for MIF. MIF triggered G(alphai)- and integrin-dependent arrest and chemotaxis of monocytes and T cells, rapid integrin activation and calcium influx through CXCR2 or CXCR4. MIF competed with cognate ligands for CXCR4 and CXCR2 binding, and directly bound to CXCR2. CXCR2 and CD74 formed a receptor complex, and monocyte arrest elicited by MIF in inflamed or atherosclerotic arteries involved both CXCR2 and CD74. In vivo, Mif deficiency impaired monocyte adhesion to the arterial wall in atherosclerosis-prone mice, and MIF-induced leukocyte recruitment required Il8rb (which encodes Cxcr2). Blockade of Mif but not of canonical ligands of Cxcr2 or Cxcr4 in mice with advanced atherosclerosis led to plaque regression and reduced monocyte and T-cell content in plaques. By activating both CXCR2 and CXCR4, MIF displays chemokine-like functions and acts as a major regulator of inflammatory cell recruitment and atherogenesis. Targeting MIF in individuals with manifest atherosclerosis can potentially be used to treat this condition.     

Controlled intramyocardial release of engineered chemokines by biodegradable hydrogels as a treatment approach of myocardial infarction

Myocardial infarction (MI) induces a complex inflammatory immune response, followed by the remodelling of the heart muscle and scar formation. The rapid regeneration of the blood vessel network system by the attraction of hematopoietic stem cells is beneficial for heart function. Despite the important role of chemokines in these processes, their use in clinical practice has so far been limited by their limited availability over a long time‐span in vivo. Here, a method is presented to increase physiological availability of chemokines at the site of injury over a defined time‐span and simultaneously control their release using biodegradable hydrogels. Two different biodegradable hydrogels were implemented, a fast degradable hydrogel (FDH) for delivering Met‐CCL5 over 24 hrs and a slow degradable hydrogel (SDH) for a gradual release of protease‐resistant CXCL12 (S4V) over 4 weeks. We demonstrate that the time‐controlled release using Met‐CCL5‐FDH and CXCL12 (S4V)‐SDH suppressed initial neutrophil infiltration, promoted neovascularization and reduced apoptosis in the infarcted myocardium. Thus, we were able to significantly preserve the cardiac function after MI. This study demonstrates that time‐controlled, biopolymer‐mediated delivery of chemokines represents a novel and feasible strategy to support the endogenous reparatory mechanisms after MI and may compliment cell‐based therapies.     

Establishment of a New Murine Elastase-Induced Aneurysm Model Combined with Transplantation

Introduction

The aim of our study was to develop a reproducible murine model of elastase-induced aneurysm formation combined with aortic transplantation.

Methods

Adult male mice (n = 6–9 per group) underwent infrarenal, orthotopic transplantation of the aorta treated with elastase or left untreated. Subsequently, both groups of mice were monitored by ultrasound until 7 weeks after grafting.

Results

Mice receiving an elastase-pretreated aorta developed aneurysms and exhibited a significantly increased diastolic vessel diameter compared to control grafted mice at 7 week after surgery (1.11±0.10 mm vs. 0.75±0.03 mm; p≤0,001). Histopathological examination revealed disruption of medial elastin, an increase in collagen content and smooth muscle cells, and neointima formation in aneurysm grafts.

Conclusions

We developed a reproducible murine model of elastase-induced aneurysm combined with aortic transplantation. This model may be suitable to investigate aneurysm-specific inflammatory processes and for use in gene-targeted animals.