Expression of protease-activated receptor 1 and 2 and anti-tubulogenic activity of protease-activated receptor 1 in human endothelial colony-forming cells

Complement MASP-1 Modifies Endothelial Wound Healing

Endothelial wound-healing processes are fundamental for the maintenance and restoration of the circulatory system and are greatly affected by the factors present in the blood. We have previously shown that the complement protein mannan-binding lectin-associated serine protease-1 (MASP-1) induces the proinflammatory activation of endothelial cells and is able to cooperate with other proinflammatory activators. Our aim was to investigate the combined effect of mechanical wounding and MASP-1 on endothelial cells. Transcriptomic analysis showed that MASP-1 alters the expression of wound-healing-related and angiogenesis-related genes. Both wounding and MASP-1 induced Ca2+ mobilization when applied individually. However, MASP-1-induced Ca2+ mobilization was inhibited when the treatment was preceded by wounding. Mechanical wounding promoted CREB phosphorylation, and the presence of MASP-1 enhanced this effect. Wounding induced ICAM-1 and VCAM-1 expression on endothelial cells, and MASP-1 pretreatment further increased VCAM-1 levels. MASP-1 played a role in the subsequent stages of angiogenesis, facilitating the breakdown of the endothelial capillary network on Matrigel®. Our findings extend our general understanding of endothelial wound healing and highlight the importance of complement MASP-1 activation in wound-healing processes.

Thrombin receptor PAR1 silencing in endothelial colony-forming cells modifies stemness and vasculogenic properties

BACKGROUND

The involvement of thrombin receptor PAR1 in blood vessel development has been largely demonstrated in knockout mice; however, its implication in adult mouse angiogenesis seems very moderate.

OBJECTIVES

We aimed to explore the potential relationships between PAR1, stemness, and angiogenic properties of human endothelial colony-forming cells (ECFCs).

METHODS AND RESULTS

PAR1 activation on ECFCs using the selective PAR1-activating peptide induced a significant decrease in CD133 expression (RTQ-PCR analysis). In line, silencing of PAR1 gene expression with siRNA increased CD133 mRNA as well as intracellular CD133 protein expression. To confirm the link between CD133 and PAR1, we explored the association between PAR1 and CD133 levels in fast and slow fibroblasts prone to reprogramming. An imbalance between PAR1 and CD133 levels was evidenced, with a decreased expression of PAR1 in fast reprogramming fibroblasts expressing a high CD133 level. Regarding in vitro ECFC angiogenic properties, PAR1 silencing with specific siRNA induced cell proliferation evidenced by the overexpression of Ki67. However, it did not impact migration properties nor ECFC adhesion on smooth muscle cells or human arterial endothelial cells. In a mouse model of hind-limb ischemia, PAR1 silencing in ECFCs significantly increased postischemic revascularization compared to siCtrl-ECFCs along with a significant increase in cutaneous blood flows (P < .0001), microvessel density (P = .02), myofiber regeneration (P < .0001), and human endothelial cell incorporation in muscle (P < .0001).

CONCLUSION

In conclusion, our work describes for the first time a link between PAR1, stemness, and vasculogenesis in human ECFCs.

Effects of the factor Xa inhibitor rivaroxaban on the differentiation of endothelial progenitor cells

BACKGROUND

We evaluated the efficacy of the factor Xa inhibitor rivaroxaban on the differentiation ability of vascular endothelial progenitor cells (EPCs), which play roles in vascular injury repair and atherogenesis. Antithrombotic treatment in patients with atrial fibrillation undergoing percutaneous coronary intervention (PCI) is challenging, and current guidelines recommend oral anticoagulant monotherapy 1 year or more after PCI. However, biological evidence of the pharmacological effects of anticoagulants is insufficient.

METHODS

EPC colony-forming assays were performed using peripheral blood-derived CD34-positive cells from healthy volunteers. Adhesion and tube formation of cultured EPCs were assessed in human umbilical cord-derived CD34-positive cells. Endothelial cell surface markers were assessed using flow cytometry, and Akt and endothelial nitric oxide synthase (eNOS) phosphorylation were examined using western blot analysis of EPCs. Adhesion, tube formation and endothelial cell surface marker expression was observed in EPCs transfected with small interfering RNA (siRNA) against protease-activated receptor (PAR)-2. Finally, EPC behaviors were assessed in patients with atrial fibrillation undergoing PCI in whom warfarin was changed to rivaroxaban.

RESULTS

Rivaroxaban increased the number of large EPC colonies and increased the bioactivities of EPCs, including adhesion and tube formation. Rivaroxaban also increased vascular endothelial growth factor receptor (VEGFR)-1, VEGFR-2, Tie-2, and E-selectin expression as well as Akt and eNOS phosphorylation. PAR-2 knockdown increased the bioactivities of EPCs and endothelial cell surface marker expression. Patients in whom the number of large colonies increased after switching to rivaroxaban showed better vascular repair.

CONCLUSIONS

Rivaroxaban increased the differentiation ability of EPCs, leading to potential advantages in the treatment of coronary artery disease.

Thrombin impairs the angiogenic activity of extravillous trophoblast cells via monocyte chemotactic protein-1 (MCP-1): A possible link with preeclampsia

Cytokines' secretion from the decidua and trophoblast cells has been known to regulate trophoblast cell functions, such as Extravillous trophoblasts (EVTs) cell migration and invasion and remodeling of spiral arteries. Defective angiogenesis and spiral arteries transformation are mainly caused by proinflammatory cytokines and excessive thrombin generation during preeclampsia. Monocyte chemotactic protein-1 (MCP-1), a crucial cytokine, has a role in maintaining normal pregnancy. In this study, we explored whether thrombin regulates the secretion of MCP-1 in HTR-8/SVneo cells; if yes, what is its function? We used HTR-8/SVneo cells, developed from first trimester villous explants of early pregnancy, as the model of EVTs. MCP-1 gene silencing was performed using gene-specific siRNA. qPCR and ELISA were performed to estimate the expression and secretion of MCP-1. Here, we found that thrombin enhanced the secretion of MCP-1 in HTR-8/SVneo cells. Proteinase-activated receptor-1 (PAR-1) was found as the primary receptor, regulating MCP-1 secretion in these cells. Furthermore, MCP-1 secretion is modulated via protein kinase C (PKC) α, β, and Rho/Rho-kinase-dependent pathways. Thrombin negatively regulates HTR-8/SVneo cells' ability to mimic tube formation in an MCP-1 dependent manner. In conclusion, we propose that thrombin-controlled MCP-1 secretion may play an essential role in normal placental development and successful pregnancy maintenance. Improper thrombin production and MCP-1 secretion during pregnancy might cause inadequate vascular formation and transformation of spiral arteries, which may contribute to pregnancy disorders, such as preeclampsia.

Novel positive allosteric modulator of protease-activated receptor 1 promotes skin wound healing in hairless mice

BACKGROUND AND PURPOSE

Protease-activated receptor 1 (PAR1) is a GPCR expressed in several skin cell types, including keratinocyte and dermal fibroblast. PAR1 activation plays a crucial role in the process of skin wound healing such as thrombosis, inflammation, proliferation and tissue repair. In the present study, we identified a novel positive allosteric modulator of PAR1, GB83, and investigated its effect on skin wound healing.

EXPERIMENTAL APPROACH

The enhancement of PAR1 activity by GB83 was measured using Fluo-4 calcium assay. In silico docking analysis of GB83 in PAR1 was performed using dock ligands method (CDOCKER) with CHARMm force field. Effects of GB83 on cell viability and gene expression were observed using MTS assay and quantitative real-time PCRs, respectively. SKH-1 hairless mice were used to investigate the wound healing effect of GB83.

KEY RESULTS

We demonstrated that GB83 did not activate PAR1 by itself but strongly enhanced PAR1 activation by thrombin and PAR1-activating peptide (AP). In silico docking analysis revealed that GB83 can bind to the PAR1 binding site of vorapaxar. GB83 significantly promoted PAR1-mediated cell viability and migration. In addition, the enhancement of PAR1 activity by GB83 strongly increased gene expression of TGF-β, fibronectin and type I collagen in vitro and promoted skin wound healing in vivo.

CONCLUSION AND IMPLICATIONS

Our results revealed that GB83 is the first positive allosteric modulator of PAR1 and it can be a useful pharmacological tool for studying PAR1 and a potential therapeutic agent for skin wound healing.

Therapeutic Potential of Endothelial Colony-Forming Cells in Ischemic Disease: Strategies to Improve their Regenerative Efficacy

Cardiovascular disease (CVD) comprises a range of major clinical cardiac and circulatory diseases, which produce immense health and economic burdens worldwide. Currently, vascular regenerative surgery represents the most employed therapeutic option to treat ischemic disorders, even though not all the patients are amenable to surgical revascularization. Therefore, more efficient therapeutic approaches are urgently required to promote neovascularization. Therapeutic angiogenesis represents an emerging strategy that aims at reconstructing the damaged vascular network by stimulating local angiogenesis and/or promoting de novo blood vessel formation according to a process known as vasculogenesis. In turn, circulating endothelial colony-forming cells (ECFCs) represent truly endothelial precursors, which display high clonogenic potential and have the documented ability to originate de novo blood vessels in vivo. Therefore, ECFCs are regarded as the most promising cellular candidate to promote therapeutic angiogenesis in patients suffering from CVD. The current briefly summarizes the available information about the origin and characterization of ECFCs and then widely illustrates the preclinical studies that assessed their regenerative efficacy in a variety of ischemic disorders, including acute myocardial infarction, peripheral artery disease, ischemic brain disease, and retinopathy. Then, we describe the most common pharmacological, genetic, and epigenetic strategies employed to enhance the vasoreparative potential of autologous ECFCs by manipulating crucial pro-angiogenic signaling pathways, e.g., extracellular-signal regulated kinase/Akt, phosphoinositide 3-kinase, and Ca²⁺ signaling. We conclude by discussing the possibility of targeting circulating ECFCs to rescue their dysfunctional phenotype and promote neovascularization in the presence of CVD.

Factor Xa and thrombin induce endothelial progenitor cell activation. The effect of direct oral anticoagulants

Factor Xa (FXa) and thrombin exert non-hemostatic cellular actions primarily mediated through protease-activated receptors (PARs). We investigated the effect of FXa and thrombin on human late-outgrowth endothelial cells (OECs), a type of endothelial progenitor cells (EPCs), and on human umbilical vein endothelial cells (HUVECs). The effect of direct oral anticoagulants (DOACs), rivaroxaban and dabigatran, was also studied. The membrane expression of intercellular adhesion molecule-1 (ICAM-1) and the secretion of monocyte chemoattractant protein-1 (MCP-1) were used as cell activation markers. FXa and thrombin increase the ICAM-1 expression and the MCP-1 secretion on both cells, being higher on OECs. Vorapaxar, a specific PAR-1 antagonist, completely inhibits FXa-induced activation of both cells and thrombin-induced HUVEC activation, but only partially thrombin-induced OEC activation. Furthermore, thrombin-receptor activating peptide; TRAP-6, only partially activates OECs. OECs do not membrane-express PAR-4, therefore it may not be involved on thrombin-induced OEC activation. Rivaroxaban and dabigatran inhibit OEC and HUVEC activation by FXa and thrombin, respectively. Rivaroxaban enhances thrombin-induced OEC and HUVEC activation, which is completely inhibited by vorapaxar. The inhibition of OEC and HUVEC activation by vorapaxar and DOACs may represent a new pleiotropic effect of these drugs. The pathophysiological and clinical significance of our findings need to be established.

Protease-activated receptors (PARs): mechanisms of action and potential therapeutic modulators in PAR-driven inflammatory diseases

Inflammatory diseases have become increasingly prevalent with industrialization. To address this, numerous anti-inflammatory agents and molecular targets have been considered in clinical trials. Among molecular targets, protease-activated receptors (PARs) are abundantly recognized for their roles in the development of chronic inflammatory diseases. In particular, several inflammatory effects are directly mediated by the sensing of proteolytic activity by PARs.

PARs belong to the seven transmembrane domain G protein-coupled receptor family, but are unique in their lack of physiologically soluble ligands. In contrast with classical receptors, PARs are activated by N-terminal proteolytic cleavage. Upon removal of specific N-terminal peptides, the resulting N-termini serve as tethered activation ligands that interact with the extracellular loop 2 domain and initiate receptor signaling. In the classical pathway, activated receptors mediate signaling by recruiting G proteins. However, activation of PARs alternatively lead to the transactivation of and signaling through receptors such as co-localized PARs, ion channels, and toll-like receptors.

In this review we consider PARs and their modulators as potential therapeutic agents, and summarize the current understanding of PAR functions from clinical and in vitro studies of PAR-related inflammation.

The role of endothelial colony forming cells in kidney cancer's pathogenesis, and in resistance to anti-VEGFR agents and mTOR inhibitors: A speculative review

Renal cell carcinoma (RCC) is highly dependent on angiogenesis, due to the overactivation of the VHL/HIF/VEGF/VEGFRs axis; this justifies the marked sensitivity of this neoplasm to antiangiogenic agents which, however, ultimately fail to control tumor growth. RCC also frequently shows alterations in the mTOR signaling pathway, and mTOR inhibitors have shown a similar pattern of initial activity/late failure as pure antiangiogenic agents. Understanding mechanisms of resistance to these agents would be key to improve the outcome of our patients. Circulating endothelial cells are a family of mainly bone marrow-derived progenitors, which have been postulated to be responsible of the reactivation of angiogenesis in different tumors. In this review, we shall discuss the complex nature and function of these cells, the evidence pro and contra their contribution to tumor vascularization, especially as far as RCC is concerned, and their possible role in determining resistance to presently available treatments.

Dysregulation of VEGF-induced proangiogenic Ca2+ oscillations in primary myelofibrosis-derived endothelial colony-forming cells

Endothelial progenitor cells could be implicated in the aberrant neoangiogenesis that occurs in bone marrow and spleen in patients with primary myelofibrosis (PMF). However, antivascular endothelial growth factor (VEGF) monotherapy had only a modest and transient effect in these individuals. Recently it was found that VEGF-induced proangiogenic intracellular Ca(2+) oscillations could be impaired in endothelial progenitor cells of subjects with malignancies. Therefore, we employed Ca(2+) imaging, wavelet analysis, and functional assays to assess whether and how VEGF-induced Ca(2+) oscillations are altered in PMF-derived endothelial progenitor cells. We focused on endothelial colony-forming cells (ECFCs), which are the only endothelial progenitor cell subtype capable of forming neovessels both in vivo and in vitro. VEGF triggers repetitive Ca(2+) spikes in both normal ECFCs (N-ECFCs) and ECFCs obtained from PMF patients (PMF-ECFCs). However, the spiking response to VEGF is significantly weaker in PMF-ECFCs. VEGF-elicited Ca(2+) oscillations are patterned by the interaction between inositol-1,4,5-trisphosphate-dependent Ca(2+) mobilization and store-operated Ca(2+) entry. However, in most PMF-ECFCs, Ca(2+) oscillations are triggered by a store-independent Ca(2+) entry pathway. We found that diacylglycerol gates transient receptor potential canonical 1 channel to trigger VEGF-dependent Ca(2+) spikes by recruiting the phospholipase C/inositol-1,4,5-trisphosphate signaling pathway, reflected as a decrease in endoplasmic reticulum Ca(2+) content. Finally, we found that, apart from being less robust and dysregulated as compared with N-ECFCs, VEGF-induced Ca(2+) oscillations modestly stimulate PMF-ECFC growth and in vitro angiogenesis. These results may explain the modest effect of anti-VEGF therapies in PMF.

Thrombin receptor PAR-1 activation on endothelial progenitor cells enhances chemotaxis-associated genes expression and leukocyte recruitment by a COX-2-dependent mechanism

BACKGROUND

Endothelial colony forming cells (ECFC) represent a subpopulation of endothelial progenitor cells involved in endothelial repair. The activation of procoagulant mechanisms associated with the vascular wall's inflammatory responses to injury plays a crucial role in the induction and progression of atherosclerosis. However, little is known about ECFC proinflammatory potential.

AIMS

To explore the role of the thrombin receptor PAR-1 proinflammatory effects on ECFC chemotaxis/recruitment capacity.

METHODS AND RESULTS

The expression of 30 genes known to be associated with inflammation and chemotaxis was quantified in ECFC by real-time qPCR. PAR-1 activation with the SFLLRN peptide (PAR-1-ap) resulted in a significant increase in nine chemotaxis-associated genes expression, including CCL2 and CCL3 whose receptors are present on ECFC. Furthermore, COX-2 expression was found to be dramatically up-regulated consequently to PAR-1 activation. COX-2 silencing with the specific COX-2-siRNA also triggered down-regulation of the nine target genes. Conditioned media (c.m.) from control-siRNA- and COX-2-siRNA-transfected ECFC, stimulated or not with PAR-1-ap, were produced and tested on ECFC capacity to recruit leukocytes in vitro as well in the muscle of ischemic hindlimb in a preclinical model. The capacity of the c.m. from ECFC stimulated with PAR-1-ap to recruit leukocytes was abrogated when COX-2 gene expression was silenced in vitro (in terms of U937 cells migration and adhesion to endothelial cells) as well as in vivo. Finally, the postnatal vasculogenic stem cell derived from infantile hemangioma tumor (HemSC) incubated with PAR-1-ap increased leukocyte recruitment in Matrigel(®) implant.

CONCLUSIONS

PAR-1 activation in ECFC increases chemotactic gene expression and leukocyte recruitment at ischemic sites through a COX-2-dependent mechanism.