Year: 2012
Type: dissertation
Abstract: The formation of a functional and integrated vascular network is a basic process in the growth and maintenance of tissues and can be established by two forms of blood vessel growth in adults: angiogenesis and arteriogenesis. In this study, the ligands of the chemokine receptor CXCR4 and its role in angiogenesis (represented by the experimental myocardial infarction) and arteriogenesis (represented by the murine hind limb ischemia model) was investigated. The first approach identified the CXCL12 / CXCR4 axis in protection and regeneration after myocardial infarction associated with complex remodeling and inflammatory changes. Experimental MI was induced by ligation of the left descending coronary artery in CXCR4+/- and wild-type mice. After four weeks, infarct size was reduced in CXCR4+/- compared to wild-type mice. This was accompanied by altered inflammatory cell recruitment, namely diminished neutrophil content, delayed monocyte infiltration and predominance of Gr1low over classical Gr1high monocytes. Basal coronary flow and its recovery after MI were significantly impaired in CXCR4+/- mice. This was paralleled by reduced angiogenesis, myocardial vessel density and endothelial cell count. Despite defective angiogenesis, CXCR4+/- hearts showed no difference in CXCL12, VEGF or apoptosis-related gene expression. Lipofuscin-like accumulation in CXCR4+/- hearts and high levels of phosphatidylserine, which protect cardiomyocytes from hypoxic stress in vitro were detected. These data showed the crucial role of CXCR4 in endogenous remodeling processes after MI, contributing to inflammatory/progenitor cell recruitment and neovascularization, whereas its deficiency limits infarct size and causes adaptation to hypoxic stress. This should be carefully taken into account, when devising therapeutic strategies involving CXCL12 / CXCR4 axis. Chapter 2 provides new insights into the behavior of EPCs in response to angiogenic factors: MIF, VEGF, CXCL12 and CXCL1. Spleen derived EPCs exhibit endothelial-like properties, namely acLDL uptake, binding of lectin, and expression of mononuclear- and endothelial specific markers, as well as CXCR2 and CXCR4. rmMIF, rmVEGF, rmCXCL12 and rmCXCL1 enhanced the chemotactic capacity of EPCs, whereas only rmMIF and rmCXCL1 stimulation increased the number of transmigrated EPCs through an additional endothelial monolayer. Culturing EPCs on Matrigel showed that EPCs alone are not able to form tube-like structures, but integrate into capillary-line tubules in co-culture with endothelial cells with a high responsiveness to all test factors. Therefore, considering combined treatment of cell-based therapy including EPCs and angiogenic factors might provide new therapeutic approaches to regenerate injured tissues. The third part of this work intended to analyze the role of MIF in arteriogenesis in a murine hind limb ischemia model. The pro-inflammatory cytokine with chemokine-like functions plays a critical role in inflammatory diseases associated with attracting immune cells to sites of inflammation. In mice with femoral artery ligation, paw perfusion was diminished after rmMIF stimulation, whereas blocking MIF enhanced paw perfusion and therefore collateral formation. Accordingly, exogenous MIF reduced the number of tissue macrophages and CXCR2 positive cells in the ischemic skeletal muscle whereas blocking endogenous MIF resulted in an increase of macrophages. Monocytes likely stimulate arteriogenesis by stimulating migration and proliferation of endothelial cells and smooth muscle cells. Within this context M1 macrophages are considered pro-inflammatory whereas M2 macrophages are pro-angiogenic. Neither the polarization to M1 nor M2 macrophages was observed after rmMIF stimulation indicating that MIF does not affect the phenotype of tissue resident macrophages. However, blocking endogenous MIF affects the circulating blood monocytes including Ly6Clow and Ly6Chigh. I hypothesize that blocking MIF increases the recruitment of monocytes and specific subsets such as Ly6Clow monocytes from the bone marrow and the migration into the vessel wall. The divergent effect of MIF blockade on atherogenesis and arteriogenesis offers opportunities for selective therapeutic intervention in peripheral artery disease.
Source: RWTH Publications (RWTH Aachen)
Authors: Nancy Tuchscheerer, Jürgen Bernhagen
Language: English
Subfield: Oncology
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2588805970