Role of integrin-linked kinase for functional capacity of endothelial progenitor cells in patients with stable coronary artery disease

Differentiation potential and functional properties of a CD34‑CD133+ subpopulation of endothelial progenitor cells

Endothelial progenitor cells (EPCs) promote angiogenesis and play an important role in myocardial and vascular repair after ischemia and infarction. EPCs consist of different subpopulations including CD34‑CD133+ EPCs, which are precursors of more mature CD34+CD133+ EPCs and functionally more active in terms of homing and endothelial regeneration. In the present study we analyzed the functional and differentiation abilities of CD34‑CD133+ EPCs. Isolation of EPC populations (CD34+CD133+, CD34‑CD133+) were performed by specific multi‑step magnetic depletion. After specific stimulation a significant higher adhesive and migrative capacity of CD34‑CD133+ cells could be detected compared to CD34+CD133+ cells (P<0.001, respectively). Next to this finding, not only significantly higher rates of proliferation (P<0.005) were detected among CD34‑CD133+ cells, but also a higher potential of cell‑differentiation capacity into other cell types. Next to a significant increase of CD34‑CD133+ EPCs differentiating into a fibroblast cell‑type (P<0.001), an enhancement into a hepatocytic cell‑type (P=0.033) and a neural cell‑type (P=0.016) could be measured in contrast to CD34+CD133+ cells. On the other hand, there was no significant difference in differentiation into a cardiomyocyte cell‑type between these EPC subpopulations (P=0.053). These results demonstrate that EPC subpopulations vary in their functional abilities and, to different degrees, have the capacity to transdifferentiate into unrelated cell‑types such as fibroblasts, hepatocytes, and neurocytes. This indicates that CD34‑CD133+ cells are more pluripotent compared to the CD34+CD133+ EPC subset, which may have important consequences for the therapy of vascular diseases.

Anti-PCSK9 antibodies inhibit pro-atherogenic mechanisms in APOE*3Leiden.CETP mice

LDL-cholesterol (LDL-C) is a causal pathogenic factor in atherosclerosis. Monoclonal anti-proprotein convertase subtilisin/kexin type 9 (PCSK9) neutralizing antibodies are novel potent LDL-lowering drugs which reduce cardiovascular events. To characterize their effect on atherogenesis, APOE*3Leiden.CETP mice were fed a high cholesterol/high fat diet (WTD) or normal chow (NC) for 18 weeks. Mice on WTD were injected with the human anti-PCSK9 antibody mAb1 (PL-45134, 10 mg*kg^-1 s.c.) or 0.9% saline every 10 days. PCSK9 inhibition decreased total cholesterol in serum of APOE*3Leiden.CETP mice and prevented the development of atherosclerosis. The plaque area in the aortic root was reduced by half and macrophage infiltration determined by Ly6c and Mac-3 staining was ameliorated. PCSK9 inhibition decreased markers of inflammation in mononuclear cells (Il-6, Tnfa mRNA), and in serum (CXCL-1,-10,-13; complement factor C5a) compared to control WTD fed animals. The number of circulating Sca-1/VEGF-R2 positive endothelial progenitor cells of the peripheral blood and spleen-derived diLDL/lectin double positive circulating angiogenic cells was increased. To conclude, the PCSK9-mediated anti-atherosclerotic effect involves the upregulation of pro-regeneratory endothelial progenitor cells, a reduction of inflammation and change of plaque composition.

The role of integrin α2 in cell and matrix therapy that improves perfusion, viability and function of infarcted myocardium

Injectable delivery matrices hold promise in enhancing engraftment and the overall efficacy of cardiac cell therapies; however, the mechanisms responsible remain largely unknown. Here we studied the interaction of a collagen matrix with circulating angiogenic cells (CACs) in a mouse myocardial infarction model. CACs + matrix treatment enhanced CAC engraftment, and improved myocardial perfusion, viability and function compared to cells or matrix alone. Integrin-linked kinase (ILK) was up-regulated in matrix-cultured CACs. Integrin α2β1 blocking prevented ILK up-regulation, significantly reduced the adhesion, proliferation, and paracrine properties of matrix-cultured CACs, and negated the benefits of CACs + matrix therapy in vivo. Furthermore, integrin α5 was essential for the angiogenic potential of CACs on matrix. These findings indicate that the synergistic therapeutic effect of CACs + matrix therapy in MI requires the matrix to enhance CAC function via α2β1 and α5 integrin signaling mechanisms, rather than simply delivering the cells.

Cord blood endothelial progenitor cells as therapeutic and imaging probes

Numerous studies demonstrated that neovascularization processes associated with severe tissue ischemia commonly found in conditions such as cardiovascular disorders and tumor growth occur via angiogenic and vasculogenic mechanisms. Over the past decade, it has been demonstrated that endothelial progenitor cells (EPCs) play a significant role in neo-angiogenic and neovasculogenic processes. Due to their ability to self-renew, circulate, home to the ischemic sites and differentiate into mature endothelial cells, EPCs derived from various sources hold enormous potential to be used as therapeutic agents in pro- or anti-angiogenic strategies for the treatment of ischemic and tumor conditions, respectively. However, the development of EPC-based therapies requires accompanying, noninvasive imaging protocol for in vivo tracking of transplanted cells. Hence, this review focuses on cord blood-derived EPCs and their role in neovascularization with emphasis on the potential use of EPCs as a therapeutic and imaging probe.

MRI tracking of FePro labeled fresh and cryopreserved long term in vitro expanded human cord blood AC133+ endothelial progenitor cells in rat glioma

BACKGROUND

Endothelial progenitors cells (EPCs) are important for the development of cell therapies for various diseases. However, the major obstacles in developing such therapies are low quantities of EPCs that can be generated from the patient and the lack of adequate non-invasive imaging approach for in vivo monitoring of transplanted cells. The objective of this project was to determine the ability of cord blood (CB) AC133+ EPCs to differentiate, in vitro and in vivo, toward mature endothelial cells (ECs) after long term in vitro expansion and cryopreservation and to use magnetic resonance imaging (MRI) to assess the in vivo migratory potential of ex vivo expanded and cryopreserved CB AC133+ EPCs in an orthotopic glioma rat model.

MATERIALS, METHODS AND RESULTS

The primary CB AC133+ EPC culture contained mainly EPCs and long term in vitro conditions facilitated the maintenance of these cells in a state of commitment toward endothelial lineage. At days 15-20 and 25-30 of the primary culture, the cells were labeled with FePro and cryopreserved for a few weeks. Cryopreserved cells were thawed and in vitro differentiated or i.v. administered to glioma bearing rats. Different groups of rats also received long-term cultured, magnetically labeled fresh EPCs and both groups of animals underwent MRI 7 days after i.v. administration of EPCs. Fluorescent microscopy showed that in vitro differentiation of EPCs was not affected by FePro labeling and cryopreservation. MRI analysis demonstrated that in vivo accumulation of previously cryopreserved transplanted cells resulted in significantly higher R2 and R2* values indicating a higher rate of migration and incorporation into tumor neovascularization of previously cryopreserved CB AC133+ EPCs to glioma sites, compared to non-cryopreserved cells.

CONCLUSION

Magnetically labeled CB EPCs can be in vitro expanded and cryopreserved for future use as MRI probes for monitoring the migration and incorporation to the sites of neovascularization.

Integrin-linked kinase regulates vasomotor function by preventing endothelial nitric oxide synthase uncoupling: role in atherosclerosis

RATIONALE

Atherosclerotic lesions develop in regions of disturbed flow, whereas laminar flow protects from atherogenesis; however, the mechanisms involved are not completely elucidated. Integrins are mechanosensors of shear stress in endothelial cells, and integrin-linked kinase (ILK) is important for blood vessel integrity and cardiovascular development.

OBJECTIVES

To explore the role of ILK in vascular function by studying conditionally ILK-deficient (cKO) mice and human atherosclerotic arteries.

RESULTS

ILK expression was detected in the endothelial cell layer of nonatherosclerotic vessels but was absent from the endothelium of atherosclerotic arteries. Live ultrasound imaging revealed that acetylcholine-mediated vasodilatation was impaired in cKO mice. These mice exhibited lowered agonist-induced nitric oxide synthase (NOS) activity and decreased cyclic guanosine monophosphate and nitrite production. ILK deletion caused endothelial NOS (eNOS) uncoupling, reflected in reduced tetrahydrobiopterin (BH4) levels, increased BH2 levels, decreased dihydrofolate reductase expression, and increased eNOS-dependent generation of superoxide accompanied by extensive vascular protein nitration. ILK reexpression prevented eNOS uncoupling in cKO cells, whereas superoxide formation was unaffected by ILK depletion in eNOS-KO cells, indicating eNOS as a primary source of superoxide anion. eNOS and ILK coimmunoprecipitated in aortic lysates from control animals, and eNOS-ILK-shock protein 90 interaction was detected in human normal mammary arteries but was absent from human atherosclerotic carotid arteries. eNOS-ILK interaction in endothelial cells was prevented by geldanamycin, suggesting heat shock protein 90 as a binding partner.

CONCLUSIONS

Our results identify ILK as a regulatory partner of eNOS in vivo that prevents eNOS uncoupling, and suggest ILK as a therapeutic target for prevention of endothelial dysfunction related to shear stress-induced vascular diseases.

Differential chemokine receptor expression regulates functional specialization of endothelial progenitor cell subpopulations

Postnatal vasculogenesis is mediated by endothelial progenitor cells (EPCs) which consist of subpopulations with different functional capacities. Our goal was to profile chemokine receptor expression on relevant subsets of EPCs and to characterize their role for effector functions. CD34(+)/CD133(+)/VEGFR2(+) EPCs were characterized by high expression of chemokine receptors CXCR4, CX3CR1, BLT1, and low level expression of CXCR2 and CCR2, while primordial CD34(-)/CD133(+)/VEGFR2(+) EPCs express these chemokine receptors at comparably low levels. Migration assays revealed that SDF-1, fractalkine, and LTB4 significantly increase migration of CD34(-)/CD133(+)/VEGFR2(+) EPCs, while SDF-1 was the only potent agonist of migration of CD34(+)/CD133(+)/VEGFR2(+) EPCs. SDF-1, fractalkine, and LTB4 trigger significant increase adhesion of CD34(+)/CD133(+)/VEGFR2(+) EPCs, while in CD34(-)/CD133(+)/VEGFR2(+) EPCs SDF-1 and fractalkine are equipotent agonists and LTB4 triggers a smaller though still significant increase in adhesion. Differential expression of specific chemokine receptors is an important regulator in terms of migration and adhesion of biologically relevant EPC-subpopulations, which may have implications for cell therapeutic strategies for treatment of ischemic vascular disease.

Integrin-linked kinase is a central mediator in angiotensin II type 1- and chemokine receptor CXCR4 signaling in myocardial hypertrophy

Inflammation and pro-hypertrophic signaling are important for development and progression of myocardial hypertrophy (LVH) and chronic heart failure (CHF). Here we investigated the relevance of integrin-linked kinase (ILK) for chemokine receptor CXCR4- and angiotensin II type 1-triggered signaling and its regulation and role in cardiac remodeling. Using ELISA, real-time-PCR, and Western blotting, the present study demonstrates that SDF-1 and its receptor CXCR4 are up-regulated in plasma and left ventricles, respectively, in mouse models of cardiac hypertrophy (transaortic constriction, transgenic cardiac-specific overexpression of rac1) and in human CHF in association with increased cardiac ILK-expression. In isolated cardiomyocytes, ILK is activated by CXCR4-ligation and necessary for SDF-1-triggered activation of rac1, NAD(P)H oxidase, and release of reactive oxygen species. Importantly, the pro-hypertrophic peptide angiotensin II induces ILK-activation dependent on rac1 in cardiomyocytes, where ILK is necessary for angiotensin II-mediated stimulation of hypertrophy genes and protein synthesis. We conclude that in both SDF-1- and angiotensin II-triggered signaling, ILK is a central mediator of rac1-induced oxidative stress and myocardial hypertrophy.

Human cord blood-derived AC133+ progenitor cells preserve endothelial progenitor characteristics after long term in vitro expansion

Background

Stem cells/progenitors are central to the development of cell therapy approaches for vascular ischemic diseases. The crucial step in rescuing tissues from ischemia is improvement of vascularization that can be achieved by promoting neovascularization. Endothelial progenitor cells (EPCs) are the best candidates for developing such an approach due to their ability to self-renew, circulate and differentiate into mature endothelial cells (ECs). Studies showed that intravenously administered progenitors isolated from bone marrow, peripheral or cord blood home to ischemic sites. However, the successful clinical application of such transplantation therapy is limited by low quantities of EPCs that can be generated from patients. Hence, the ability to amplify the numbers of autologous EPCs by long term in vitro expansion while preserving their angiogenic potential is critically important for developing EPC based therapies. Therefore, the objective of this study was to evaluate the capacity of cord blood (CB)-derived AC133+ cells to differentiate, in vitro, towards functional, mature endothelial cells (ECs) after long term in vitro expansion.

Methodology

We systematically characterized the properties of CB AC133+ cells over the 30 days of in vitro expansion. During 30 days of culturing, CB AC133+ cells exhibited significant growth potential that was manifested as 148-fold increase in cell numbers. Flow cytometry and immunocytochemistry demonstrated that CB AC133+ cells' expression of endothelial progenitor markers was not affected by long term in vitro culturing. After culturing under EC differentiation conditions, cells exhibited high expression of mature ECs markers, such as CD31, VEGFR-2 and von Willebrand factor, as well as the morphological changes indicative of differentiation towards mature ECs. In addition, throughout the 30 day culture cells preserved their functional capacity that was demonstrated by high uptake of DiI fluorescently conjugated-acetylated-low density lipoprotein (DiI-Ac-LDL), in vitro and in vivo migration towards chemotactic stimuli and in vitro tube formation.

Conclusions

These studies demonstrate that primary CB AC133+ culture contained mainly EPCs and that long term in vitro conditions facilitated the maintenance of these cells in the state of commitment towards endothelial lineage.