Endothelial Progenitor Cells Modulate the Phenotype of Smooth Muscle Cells and Increase Their Neointimal Accumulation Following Vascular Injury

Abstract

Background Smooth muscle cells (SMCs) are the main driver of neointima formation and restenosis following vascular injury. In animal models, endothelial progenitor cells (EPCs) accelerate endothelial regeneration and reduce neointima formation after arterial injury; however, EPC-capture stents do not reduce target vessel failure compared with conventional stents. Here we examined the influence of EPCs on features of SMCs pivotal for their impact on injury-induced neointima formation including proliferation, migration, and phenotype switch. Methods and Results EPCs, their conditioned medium, and EPC-derived microparticles induced proliferation of SMCs while limiting their apoptosis. In transwell membrane experiments and scratch assays, EPCs stimulated migration of SMCs and accelerated their recovery from scratch-induced injury. Treatment of SMCs with an EPC-derived conditioned medium or microparticles triggered transformation of SMCs toward a synthetic phenotype. However, co-cultivation of EPCs and SMCs enabling direct cell–cell contacts preserved their original phenotype and protected from the transformative effect of SMC cholesterol loading. Adhesion of EPCs to SMCs was stimulated by SMC injury and reduced by blocking CXCR2 and CCR5. Interaction of EPCs with SMCs modulated their secretory products and synergistically increased the release of selected chemokines. Following carotid wire injury in athymic mice, injection of EPCs resulted not only in reduced neointima formation but also in altered cellular composition of the neointima with augmented accumulation of SMCs. Conclusion EPCs stimulate proliferation and migration of SMCs and increase their neointimal accumulation following vascular injury. Furthermore, EPCs context-dependently modify the SMC phenotype with protection from the transformative effect of cholesterol when a direct cell–cell contact is established.

Pathogenesis and Clinical Significance of In-Stent Restenosis in Patients with Diabetes

“…Local and systemic inflammation plays a key role in the activation of the proliferative process, which consists of the proliferation, migration, and differentiation of vascular smooth muscle cells (VSMCs) as well as the migration of matrix metalloproteinases (MMPs), DNA replication, and extracellular matrix synthesis [25]. Endothelial progenitor cells were shown to take part in the stimulation of the proliferation and migration of VSMCs, which leads to an increase in their neointimal accumulation following vascular wall injury [27]. All these processes result in neointimal hyperplasia [28].…”

Engagement of the CXCL12–CXCR4 Axis in the Interaction of Endothelial Progenitor Cell and Smooth Muscle Cell to Promote Phenotype Control and Guard Vascular Homeostasis

“…Of note, inflammatory activation of cells with recombinant low-dose TNFα strongly amplified expression and secretion of CXCL12 in SMCs and EPCs. As we have previously observed that EPC-derived microvesicles (MVs, also known as microparticles or extracellular vesicles) alone may modulate key functions of SMCs and as MVs harbor and transfer bioactive substances including chemokines and microRNAs [ 20 , 21 , 22 ], we also evaluated the presence of CXCL12 in MVs. Indeed, a notable amount of CXCL12 could be identified in MVs derived from EPCs (EPC-MV) and SMCs (SMC-MV), indicating that a relevant portion of released CXLC12 is transferred to MVs ( Figure 1 C).…”

“…In a recent study, we have shown that heterocellular interaction of EPCs and SMCs results in the alteration of the secretion profile with a selective positive synergy of co-cultivation for certain factors [ 20 ]. Following co-incubation of EPCs and SMCs, we measured not only significantly higher CXCL12 protein levels compared to the respective supernatants of EPC and SMC monocultures but also over-additive absolute values of CXCL12 (803 ± 61 pg/μL) when related to the combined supernatant derived from both monocultures (305 ± 31 pg/μL), indicating a positive synergy of co-cultivation for the release of CXCL12 ( Figure 1 E).…”

“…Proliferation and migration of SMCs are crucial processes contributing to atherogenesis and the early stage of neointima formation and EPCs have been shown to modify these capacities of SMCs [ 6 , 20 ]. Proliferation- and cell cycle analysis using BrdU-/7-AAD staining now revealed that inhibition of CXCR4 using blocking Abs or the small-molecule CXCR4 inhibitor AMD3100 (not shown) as well as blockade of CXCL12 using Abs did not relevantly reduce the stimulatory effects of EPCs, CM-EPC and EPC-MV with no significant changes in cell cycle progression and number of cells in S1-phase ( Figure 2 A,B).…”

“…We have recently shown that EPCs may modulate the phenotype of SMCs, stimulate their proliferation and migration and finally increase their neointimal accumulation following vascular injury [ 20 ]. Considering that both cell types not only release CXCL12 and express CXCR4 but also implement sender and receiver functions for the CXCL12–CXCR4 signaling cascade with its double-edged role in injury-induced restenosis and atherosclerosis, we now sought to analyze the role of the CXCL12–CXCR4 axis in various modes of EPC–SMC interaction including migration, proliferation and phenotype control.…”