Recent evidence infers a contribution of smooth muscle cell (SMC) progenitors and stromal cell-derived factor (SDF)-1α to neointima formation after arterial injury. Inhibition of plaque area and SMC content in apolipoprotein E-deficient mice repopulated with LacZ ⁺ or CXCR4 ^−/− BM or lentiviral transfer of an antagonist reveals a crucial involvement of local SDF-1α and its receptor CXCR4 in neointimal hyperplasia via recruitment of BM-derived SMC progenitors. After arterial injury, SDF-1α expression in medial SMCs is preceded by apoptosis and inhibited by blocking caspase-dependent apoptosis. SDF-1α binds to platelets at the site of injury, triggers CXCR4- and P-selectin-dependent arrest of progenitor cells on injured arteries or matrix-adherent platelets, preferentially mobilizes and recruits c-kit ⁻ /platelet–derived growth factor receptor (PDGFR)-β ⁺ /lineage ⁻ /sca-1 ⁺ progenitors for neointimal SMCs without being required for their differentiation. Hence, the SDF-1α/CXCR4 axis is pivotal for vascular remodeling by recruiting a subset of SMC progenitors in response to apoptosis and in concert with platelets, epitomizing its importance for tissue repair and identifying a prime target to limit lesion development.

Objective—Chemokines and their receptors are crucially involved in the development of atherosclerotic lesions by directing monocyte and T cell recruitment. The CC-chemokine receptors 1 (CCR1) and 5 (CCR5) expressed on these cells bind chemokines implicated in atherosclerosis, namely CCL5/RANTES. Although general blockade of CCL5 receptors reduces atherosclerosis, specific roles of CCR1 and CCR5 have not been unequivocally determined.Methods and Results—We provide two independent lines of investigation to dissect the effects of Ccr1 and Ccr5 deletion in apolipoprotein E–deficient (ApoE^−/−) mice in a collaboration between Aachen/Germany and Geneva/Switzerland. Different strains of ApoE^−/−Ccr5^−/−mice, ApoE^−/−Ccr1^−/−mice or respective littermates, were fed a high-fat diet for 10 to 12 weeks. Plaque areas were quantified in the aortic roots and thoracoabdominal aortas. Concordantly, both laboratories found that lesion formation was reduced in ApoE^−/−Ccr5^−/−mice. Plaque quality and immune cells were assessed by immunohistochemistry or mRNA analysis. Whereas lesional macrophage content, aortic CD4, and Th1-related Tim3 expression were reduced, smooth muscle cell (SMC) content and expression of interleukin-10 in plaques, lesional SMCs, and splenocytes were elevated. Protection against lesion formation by Ccr5 deficiency was sustained over 22 weeks of high-fat diet or over 26 weeks of chow diet. Conversely, plaque area, T cell, and interferon-γ content were increased in ApoE^−/−Ccr1^−/−mice.Conclusion—Genetic deletion of Ccr5 but not Ccr1 in ApoE^−/−mice protects from diet-induced atherosclerosis, associated with a more stable plaque phenotype, reduced mononuclear cell infiltration, Th1-type immune responses, and increased interleukin-10 expression. This corroborates CCR5 as a promising therapeutic target.

Background— HMG-CoA-reductase inhibitors have been shown to exhibit pronounced immunomodulatory effects independent of lipid lowering. We have recently demonstrated that pretreatment with simvastatin profoundly improves survival in a cecal ligation and perforation (CLP) model of sepsis. Here, we studied whether treatment with simvastatin after onset of sepsis-induced hemodynamic alterations is beneficial and whether prolonged survival can also be achieved with other statins. Methods and Results— Mice were rendered septic by CLP. At 6 hours after sepsis induction, when profound hemodynamic alterations were manifest, treatment with atorvastatin, fluvastatin, pravastatin, simvastatin, or placebo was initiated. Except for fluvastatin (27±2.3 hours), survival time was extended from 23±1.2 hours for placebo-treated mice to 37±3.6 hours for simvastatin-treated, to 40±4.2 hours for atorvastatin-treated, and to 39±3.9 hours for pravastatin-treated mice. This profound improvement is based on the preservation of cardiac function and hemodynamic status in statin-treated animals, both of which are severely impaired in untreated CLP mice. As underlying mechanisms, improved susceptibility to endothelial nitric oxide synthase stimulation and reduced endothelial adhesion of leukocytes could be demonstrated after statin treatment. Conclusions— Well established in the treatment of lipid disorders and coronary artery disease, statins harbor the additional and novel potential of effective sepsis treatment. This benefit extends to several but not all statins tested.

Background— HMG-CoA reductase inhibitors, such as simvastatin, have been shown to exhibit pronounced immunomodulatory effects independent of lipid lowering but to date have not been used to treat severe inflammatory disease such as sepsis. We thus approached the question of whether treatment with simvastatin might improve cardiovascular function and survival in sepsis. Methods and Results— Mice treated with simvastatin and rendered septic by cecal ligation and perforation (CLP) show a mean survival time close to 4 times the value found in untreated mice. This dramatic improvement is based on a complete preservation of cardiac function and hemodynamic status, which are severely impaired in untreated CLP mice [eg, 20 hours after CLP, cardiac output declined from 1.24±0.09 to 0.87±0.11 mL · min ⁻¹ · g ⁻¹ in untreated mice ( P <0.005; n=12), while remaining unaltered (1.21±0.08 mL · min ⁻¹ · g ⁻¹ at baseline and 1.15±0.1 mL · min ⁻¹ · g ⁻¹ 20 hours after CLP, P =NS, n=12) in CLP mice treated with simvastatin]. Untreated CLP mice remained refractory to β-stimulation, whereas the responsiveness to dobutamine was restored by treatment with simvastatin. Susceptibility of coronary flow to endothelial nitric oxide synthase (eNOS) stimulation by bradykinin was close to 3 times as pronounced in untreated CLP mice as in untreated sham-operated mice, indicating a high level of eNOS activation secondary to sepsis. In addition, treatment with simvastatin reversed inflammatory alterations in CLP mice, namely, increased monocyte adhesion to endothelium. Conclusions— Simvastatin, which is well established in the treatment of lipid disorders and coronary artery disease, might have the additional potential of being an effective agent in sepsis treatment.

Circulating endothelial progenitor cells (EPCs) may contribute to endothelial regeneration; however, the exact mechanisms of their arterial homing remain elusive. We examined the role of the angiogenic chemokine receptor CXCR2 in the homing of human EPCs. Isolated EPCs expressed CXCR2 together with kinase insert domain–containing receptor, CD31, vascular endothelial cadherin, and CXCR4. Adhesion assays under flow conditions showed that EPCs preferentially adhered to β ₂ -integrin ligands, that firm arrest on fibronectin or fibrinogen was enhanced by the CXCR2 ligands CXCL1 or CXCL7, and that blockade of CXCR2 significantly reduced EPC adhesion on platelet-coated endothelial matrix. This was corroborated by the involvement of CXCR2 in EPC recruitment to denuded areas of murine carotid arteries ex vivo and in vivo. Notably, blocking CXCR2 inhibited the incorporation of human EPCs expressing CXCR2 at sites of arterial injury in athymic nude mice. Immunoreactivity for the β-thromboglobulin isoform CXCL7 was observed in murine platelets and denuded smooth muscle cells (SMCs) early after wire injury, and transcripts for CXCL7 and CXCL1 were detected in isolated human arterial SMCs. Human KDR ⁺ CXCR2 ⁺ cells showed better in situ adhesion to injured murine carotid arteries than KDR ⁺ CXCR2 ⁻ cells, were predominantly CD14 ⁺ , and improved CXCR2-dependent endothelial recovery after injury in nude mice. In conclusion, our data clearly demonstrate the importance of CXCR2 for the homing of circulating EPCs to sites of arterial injury and for endothelial recovery in vivo.