Bone marrow cells contribute to neointimal formation after stent implantation in swine

M2 macrophage-derived exosomes promote the c-KIT phenotype of vascular smooth muscle cells during vascular tissue repair after intravascular stent implantation

Rationale: For intravascular stent implantation to be successful, the processes of vascular tissue repair and therapy are considered to be critical. However, the mechanisms underlying the eventual fate of vascular smooth muscle cells (VSMCs) during vascular tissue repair remains elusive. In this study, we hypothesized that M2 macrophage-derived exosomes to mediate cell-to-cell crosstalk and induce dedifferentiation phenotypes in VSMCs. Methods: In vivo, 316L bare metal stents (BMS) were implanted from the left iliac artery into the abdominal aorta of 12-week-old male Sprague-Dawley (SD) rats for 7 and 28 days. Hematoxylin and eosin (HE) were used to stain the neointimal lesions. En-face immunofluorescence staining of smooth muscle 22 alpha (SM22α) and CD68 showed the rat aorta smooth muscle cells (RASMCs) and macrophages. Immunohistochemical staining of total galactose-specific lectin 3 (MAC-2) and total chitinase 3-like 3 (YM-1) showed the total macrophages and M2 macrophages. In vitro, exosomes derived from IL-4+IL-13-treated macrophages (M2Es) were isolated by ultracentrifugation and characterized based on their specific morphology. Ki-67 staining was conducted to assess the effects of the M2Es on the proliferation of RASMCs. An atomic force microscope (AFM) was used to detect the stiffness of the VSMCs. GW4869 was used to inhibit exosome release. RNA-seq was performed to determine the mRNA profiles of the RASMCs and M2Es-treated RASMCs. Quantitative real-time PCR (qRT-PCR) analysis was conducted to detect the expression levels of the mRNAs. Western blotting was used to detect the candidate protein expression levels. T-5224 was used to inhibit the DNA binding activity of AP-1 in RASMCs. Results: M2Es promote c-KIT expression and softening of nearby VSMCs, hence accelerating the vascular tissue repair process. VSMCs co-cultured in vitro with M2 macrophages presented an increased capacity for de-differentiation and softening, which was exosome dependent. In addition, the isolated M2Es helped to promote VSMC dedifferentiation and softening. Furthermore, the M2Es enhanced vascular tissue repair potency by upregulation of VSMCs c-KIT expression via activation of the c-Jun/activator protein 1 (AP-1) signaling pathway. Conclusions: The findings of this study emphasize the prominent role of M2Es during VSMC dedifferentiation and vascular tissue repair via activation of the c-Jun/AP-1 signaling pathway, which has a profound impact on the therapeutic strategies of coronary stenting techniques.

Conditional expression of the type 2 angiotensin II receptor in mesenchymal stem cells inhibits neointimal formation after arterial injury

Percutaneous coronary interventions (PCIs) are an effective treatment for obstructive coronary artery diseases. However, the procedure's success is limited by remodeling and formation of neointima. In the present study, we engineered rat mesenchymal stem cells (MSCs) to express type 2 angiotensin II receptor (AT2R) using a tetracycline-regulated system that can strictly regulate AT2R expression. We tested the ability of the modified MSCs to reduce neointima formation following arterial injury. We subjected rats to balloon injury, and reverse transcriptase polymerase chain reaction (RT-PCR) indicated no significant AT2R expression in normal rat arteries. Low expression of AT2R was observed at 28 days after balloon-induced injury. Interestingly, MSCs alone were unable to reduce neointimal hyperplasia after balloon-induced injury; after transplantation of modified MSCs, doxycycline treatment significantly upregulated neointimal AT2R expression and inhibited osteopontin mRNA expression, as well as neointimal formation. Taken together, these results suggest that transplantation of MSCs conditionally expressing AT2R could effectively suppress neointimal hyperplasia following balloon-induced injury. Therefore, MSCs with a doxycycline-controlled gene induction system may be useful for the management of arterial injury after PCI.

Phenotype and differentiation of bone marrow-derived smooth muscle progenitor cells

1. Smooth muscle progenitor cells (SPC) are undifferentiated vascular smooth muscle cells implicated in many hyperplastic diseases of the blood vessels. However, few in vitro studies have investigated the characteristics of SPC. 2. In the present study, we constructed a recombinant plasmid with the enhanced green fluorescent protein (GFP) gene and a rat SM22α promoter, which was exclusively promoted in a smooth muscle cell lineage. Constructs were then transferred into adherent mononuclear cells derived from rat bone marrow. After 3 days, GFP-positive cells, which should be SPC, were isolated by flow cytometry. 3. Flow cytometric analysis and dual immunofluorescent staining showed that the GFP-positive cells expressed both α-smooth muscle actin (a specific marker for smooth muscle) and the chemokine receptor CXCR4 (abundant on precursor cells), but not calmodulin or CD31. After stimulation of SPC with 50 ng/mL platelet-derived growth factor-BB, CXCR4 levels decreased and calmodulin protein content increased, as determined by western blot analysis. 4. On the basis of these results, we conclude that SPC have dual characteristics of both precursor and smooth muscle cells, and might well differentiate into smooth muscle-like cells under certain conditions.

Polymorphonuclear blood leukocytes and restenosis after intracoronary implantation of drug-eluting stents

Peripheral blood contents of osteonectin-positive progenitor cells and polymorphonuclear granulocytes were examined by flow cytometry in 38 patients after myocardial revascularisation with drug-eluting stents. Repeat coronary angiography performed 6-12 months after stent implantation revealed in-stent restenosis in 15 patients and its absence in 23 patients. The plasma levels of osteonectin-positive progenitor cells, neutrophils, and basophils did not differ in patients with and without restenosis. Eosinophil blood levels in patients with and without restenosis were 262+/-68 and 124+/-67 cells/microL (mean+/-SD, p<0.001), respectively. Only one of 19 patients (5%) with eosinophil content lower than the distribution median for the entire group developed restenosis, whereas in the group with eosinophil contents higher than the median (n=19) restenosis occurred in 14 patients (74%, p<0.001). Our findings suggest that the frequency of restenoses after stenting is related to high peripheral blood eosinophil content.

Regulation of arterial remodeling and angiogenesis by urokinase-type plasminogen activatorThis article is one of a selection of papers from the NATO Advanced Research Workshop on Translational Knowledge for Heart Health (published in part 2 of a 2-part Special Issue)

A wide variety of disorders are associated with an imbalance in the plasminogen activator system, including inflammatory diseases, atherosclerosis, intimal hyperplasia, the response mechanism to vascular injury, and restenosis. Urokinase-type plasminogen activator (uPA) is a multifunctional protein that in addition to its fibrinolytic and matrix degradation capabilities also affects growth factor bioavailability, cytokine modulation, receptor shedding, cell migration and proliferation, phenotypic modulation, protein expression, and cascade activation of proteases, inhibitors, receptors, and modulators. uPA is the crucial protein for neointimal growth and vascular remodeling. Moreover, it was recently shown to be implicated in the stimulation of angiogenesis, which makes it a promising multipurpose therapeutic target. This review is focused on the mechanisms by which uPA can regulate arterial remodeling, angiogenesis, and cell migration and proliferation after arterial injury and the means by which it modulates gene expression in vascular cells. The role of domain specificity of urokinase in these processes is also discussed.