Platelet Microparticles Enhance the Vasoregenerative Potential of Angiogenic Early Outgrowth Cells After Vascular Injury

Abstract

Background-Angiogenic early outgrowth cells (EOCs) have been reported to contribute to endothelial regeneration and to limit neointima formation after vascular injury. Vascular pathologies comprise platelet activation and concomitant generation of platelet microparticles (PMPs). We hypothesized that PMPs may interact with EOCs in the context of vascular injury and modulate their regenerative potential. Methods and Results-Using flow cytometry, confocal microscopy, and scanning electron microscopy, we demonstrated the binding of thrombin/collagen-induced PMPs to EOCs with subsequent membrane assimilation and incorporation. This interaction promoted phenotypic alterations of EOCs with increased expression of endothelial cell markers and transfer of the chemokine receptor CXCR4 to EOCs with enhanced responsiveness to its ligand CXCL12/SDF-1␣. In addition, PMPs augmented the adhesion of EOCs to extracellular matrix components and to the injured vessel wall and accelerated cytoskeletal reorganization and migration of EOCs. PMPs induced changes in the EOC secretome toward a more proangiogenic profile and amplified the EOC-mediated induction of proliferation, migration, and capillary tube formation by mature endothelial cells. Compared with untreated EOCs, the injection of PMP-treated EOCs resulted in accelerated reendothelialization after arterial denudation injury in athymic nude mice, whereas the EOC-mediated reduction of neointima formation remained unchanged. Conclusions-Our data provide evidence that PMPs can boost the potential of EOCs to restore endothelial integrity after vascular injury. Major mechanisms involve the enhancement of EOC recruitment, migration, differentiation, and release of proangiogenic factors. (Circulation. 2010;122:495-506.)Key Words: endothelium Ⅲ inflammation Ⅲ restenosis Ⅲ platelets R estenosis resulting from neointimal hyperplasia, negative remodeling, and elastic recoil is considered the Achilles heel of interventional cardiology. 1 In addition to the control of inflammatory reactions and smooth muscle cell (SMC) expansion, reendothelialization after vascular damage is a crucial mechanism limiting neointima formation. 2 Endothelial regeneration at sites of primary or iatrogenic vascular injury has been thought to rely mainly on the migration and proliferation of resident endothelial cells from the adjacent intact vasculature. However, recent studies revised this concept by demonstrating that angiogenic early outgrowth cells (EOCs), which exhibit phenotypic features of myeloid and endothelial cells and are known as endothelial progenitor cells, are recruited to sites of injury and accelerate reendothelialization. 3 Notably, infusion of EOCs attenuates neointimal hyperplasia after arterial injury. 4 -6 Furthermore, EOCs may contribute to neovascularization in both ischemic hind limbs and acute myocardial infarction models. 7 Clinical studies demonstrating a negative correlation of the number and functional capacity of circulating CD34 ϩ vascular endothelial growth factor receptor-2 (V...

Phagocytosis of platelets enhances endothelial cell survival under serum deprivation

“…It was reported that platelets and platelet microparticles could support the integrity of the endothelium. [25][26][27] In this study, when platelets were added to cultured HUVECs, endothelium viability was enhanced and cell apoptosis was highly suppressed. Our data support the promotion of cell survival via platelet internalization.…”

Microparticles in Angiogenesis

“…MPs obtained from in vitro activated platelets increase the ability of 7-day cultured angiogenic early outgrowth cells (which exhibit phenotypic features of myeloid and endothelial cells and are known as EPCs) isolated from peripheral blood to regenerate vascular injury. 51 These effects include changes in the phenotype of these cells such as increased expression of the endothelial markers (CD31 and vascular endothelial-cadherin) and CXCR4, indicating their maturation toward endothelial cells. Furthermore, platelet MPs enhance Akt activation in response to CXCL12 on angiogenic early outgrowth cells, suggesting a sensitization of CXCR4 pathway by platelet MPs.…”

“…50 Also, treatment with platelet MPs increases EPC homing at the sites of vascular injury and proliferation of mature endothelial cells through a mechanism implicating VEGF, EGF, hepatocyte growth factor, interleukin-␤, tumor necrosis factor-␣, and CXCR4 secretion. 51 This leads to favor vascular repair and neovascularization. (Illustration credit: Cosmocyte/Ben Smith).…”

Immune system and regulation of regeneration

“…Опосредованное микро-частицами тромбоцитов фосфорилирование Akt наблюдается также в ýндотелиальных клетках. Показана повышенная регенерация ýндотелиоци-тов после инъекции обработанных микрочасти-цами ранних генераций ýндотелиоцитов (ýндоте-лиальных предшественников) в сонную артерию мыши при повреждении [72]. Кроме того, акти-вированные тромбоциты выделяют медиаторы с антиапоптотическим действием, такие как HGF, SDF-1, серотонин, аденозиндифосфат и сфинго-зин-1-фосфат, несущие сигналы к выживанию ýндотелиоцитам и MSCs в местах повреждения сосудов.…”