Xiang Xiao

Effects of Endothelial Progenitor Cell-Derived Microvesicles on Hypoxia/Reoxygenation-Induced Endothelial Dysfunction and Apoptosis

Oxidative stress-induced endothelial dysfunction plays a key role in ischemia/reperfusion injury. Recent evidence indicates that endothelial progenitor cell-derived microvesicles (EPC-MVs) can promote angiogenesis of endothelial cells (ECs). Here, we investigated the potential effects of EPC-MVs on hypoxia/reoxygenation (H/R) injury in human brain microvascular ECs (hb-ECs). MVs were prepared from EPCs cultured in a serum deprivation (SD) medium (starving stress, sEPC-MVs) or SD medium containing tumor necrosis factor-α (TNFα) (apoptotic stress, aEPC-MVs). H/R injury model of hb-ECs was produced by 6u2009hr hypoxia (1% O2) and 24u2009hr reoxygenation. The H/R hb-ECs were co-cultured with EPC-MVs. Results showed that (1) H/R hb-ECs were dysfunctional and coupled with increased apoptosis and ROS overproduction; (2) under two different conditions, EPCs displayed remarkable difference in caspase 3 and miR126 expression, which were carried by the corresponsive EPC-MVs; (3) functionally, sEPC-MVs had beneficial effects on H/R hb-ECs, whereas aEPC-MVs had detrimental effects; (4) the diverse effects of sEPC-MVs and aEPC-MVs were associated with the changes in miR126 and eNOS expression and were abolished by PI3K inhibitor. In conclusion, sEPCs-MVs and aEPC-MVs are functionally different on hb-EC apoptosis and dysfunction via their carried RNAs associated with ROS production and PI3K/eNOS/NO pathway.

Angiotensin-Converting Enzyme 2 Priming Enhances the Function of Endothelial Progenitor Cells and Their Therapeutic Efficacy

Angiotensin-converting enzyme 2 (ACE2) is a lately discovered enzyme catalyzing Angiotensin II into Angiotensin 1-7. Angiotensin II has been reported to impair endothelial progenitor cell (EPC) function and is detrimental to stroke. Here, we studied the role of ACE2 in regulating EPC function in vitro and in vivo. EPCs were cultured from human renin and angiotensinogen transgenic (R+A+) mice and their controls (R−A−). In in vitro experiments, EPCs were transduced with lentivirus-ACE2 or lentivirus-green fluorescence protein. The effects of ACE2 overexpression on EPC function and endothelial NO synthase (eNOS)/nicotinamide adenine dinucleotide phosphate oxidase (Nox) expression were determined. ACE2, eNOS, and Nox inhibitors were used for pathway validation. In in vivo studies, the therapeutic efficacy of EPCs overexpressing ACE2 was determined at day 7 after ischemic stroke induced by middle cerebral artery occlusion. We found that (1) lentivirus-ACE2 transduction resulted in a 4-fold increase of ACE2 expression in EPCs. This was accompanied with an increase in eNOS expression and NO production, and a decrease in Nox2 and -4 expression and reactive oxygen species production. (2) ACE2 overexpression improved the abilities of EPC migration and tube formation, which were impaired in R+A+ mice. These effects were inhibited by ACE2 or eNOS inhibitor and further enhanced by Nox inhibitor. (3) Transfusion of lentivirus-ACE2–primed EPCs reduced cerebral infarct volume and neurological deficits, and increased cerebral microvascular density and angiogenesis. Our data demonstrate that ACE2 improves EPC function, via regulating eNOS and Nox pathways, and enhances the efficacy of EPC-based therapy for ischemic stroke.

Transfusion of CXCR4-Primed Endothelial Progenitor Cells Reduces Cerebral Ischemic Damage and Promotes Repair in db/db Diabetic Mice

This study investigated the role of stromal cell-derived factor-1α (SDF-1α)/CXC chemokine receptor 4 (CXCR4) axis in brain and endothelial progenitor cells (EPCs), and explored the efficacy of CXCR4 primed EPCs in treating ischemic stroke in diabetes. The db/db diabetic and db/+ mice were used in this study. Levels of plasma SDF-1α and circulating CD34+CXCR4+ cells were measured. Brain SDF-1α and CXCR4 expression were quantified at basal and after middle cerebral artery occlusion (MCAO). In in vitro study, EPCs were transfected with adenovirus carrying null (Ad-null) or CXCR4 (Ad-CXCR4) followed with high glucose (HG) treatment for 4 days. For pathway block experiments, cells were pre-incubated with PI3K inhibitor or nitric oxide synthase (NOS) inhibitor for two hours. The CXCR4 expression, function and apoptosis of EPCs were determined. The p-Akt/Akt and p-eNOS/eNOS expression in EPCs were also measured. In in vivo study, EPCs transfected with Ad-null or Ad-CXCR4 were infused into mice via tail vein. On day 2 and 7, the cerebral blood flow, neurologic deficit score, infarct volume, cerebral microvascular density, angiogenesis and neurogenesis were determined. We found: 1) The levels of plasma SDF-1α and circulating CD34+CXCR4+ cells were decreased in db/db mice; 2) The basal level of SDF-1α and MCAO-induced up-regulation of SDF-1α/CXCR4 axis were reduced in the brain of db/db mice; 3) Ad-CXCR4 transfection increased CXCR4 expression in EPCs and enhanced EPC colonic forming capacity; 4) Ad-CXCR4 transfection prevented EPCs from HG-induced dysfunction (migration and tube formation) and apoptosis via activation of PI3K/Akt/eNOS signal pathway; 4) Ad-CXCR4 transfection enhanced the efficacy of EPC infusion in attenuating infarct volume and promoting angiogenesis and neurogenesis. Our data suggest that Ad-CXCR4 primed EPCs have better therapeutic effects for ischemia stroke in diabetes than unmodified EPCs do.

Angiotensin-(1-7) counteracts angiotensin II-induced dysfunction in cerebral endothelial cells via modulating Nox2/ROS and PI3K/NO pathways.

Angiotensin (Ang) II, the main effector of the renin-angiotensin system, has been implicated in the pathogenesis of vascular diseases. Ang-(1-7) binds to the G protein-coupled Mas receptor (MasR) and can exert vasoprotective effects. We investigated the effects and underlying mechanisms of Ang-(1-7) on Ang II-induced dysfunction and oxidative stress in human brain microvascular endothelial cells (HbmECs). The pro-apoptotic activity, reactive oxygen species (ROS) and nitric oxide (NO) productions in HbmECs were measured. The protein expressions of nicotinamide adenine dinucleotide phosphate oxidase 2 (Nox2), serine/threonine kinase (Akt), endothelial nitric oxide synthase (eNOS) and their phosphorylated forms (p-Akt and p-eNOS) were examined by western blot. MasR antagonist and phosphatidylinositol-3-kinase (PI3K) inhibitor were used for receptor/pathway verification. We found that Ang-(1-7) suppressed Ang II-induced pro-apoptotic activity, ROS over-production and NO reduction in HbmECs, which were abolished by MasR antagonist. In addition, Ang-(1-7) down-regulated the expression of Nox2, and up-regulated the ratios of p-Akt/Akt and its downstream p-eNOS/eNOS in HbmECs. Exposure to PI3K inhibitor partially abrogated Ang-(1-7)-mediated protective effects in HbmECs. Our data suggests that Ang-(1-7)/MasR axis protects HbmECs from Ang II-induced dysfunction and oxidative stress via inhibition of Nox2/ROS and activation of PI3K/NO pathways.

EPC-Derived Microvesicles Protect Cardiomyocytes from Ang II-Induced Hypertrophy and Apoptosis

Cell-released microvesicles (MVs) represent a novel way of cell-to-cell communication. Previous evidence indicates that endothelial progenitor cells (EPCs)-derived MVs can modulate endothelial cell survival and proliferation. In this study, we evaluated whether EPC-MVs protect cardiomyocytes (CMs) against angiotensin II (Ang II)-induced hypertrophy and apoptosis. The H9c2 CMs were exposed to Ang II in the presence or absence of EPC-MVs. Cell viability, apoptosis, surface area and β-myosin heavy chain (β-MHC) expression were analyzed. Meanwhile, reactive oxygen species (ROS), serine/threonine kinase (Akt), endothelial nitric oxide synthase (eNOS), and their phosphorylated proteins (p-Akt, p-eNOS) were measured. Phosphatidylinositol-3-kinase (PI3K) and NOS inhibitors were used for pathway verification. The role of MV-carried RNAs in mediating these effects was also explored. Results showed 1) EPC-MVs were able to protect CMs against Ang II-induced changes in cell viability, apoptosis, surface area, β-MHC expression and ROS over-production; 2) The effects were accompanied with the up-regulation of Akt/p-Akt and its downstream eNOS/p-eNOS, and were abolished by PI3K inhibition or partially blocked by NOS inhibition; 3) Depletion of RNAs from EPC-MVs partially or totally eliminated the effects of EPC-MVs. Our data indicate that EPC-MVs protect CMs from hypertrophy and apoptosis through activating the PI3K/Akt/eNOS pathway via the RNAs carried by EPC-MVs.

The Role of Circulating Platelets Microparticles and Platelet Parameters in Acute Ischemic Stroke Patients

BACKGROUNDnPlatelet activation and aggregation are critical in the pathogenesis of acute ischemic stroke (AIS). Circulating platelet microparticles (PMPs) and platelet parameters are biologic markers of platelet function in AIS patients; however, their associations with stroke subtypes and infarct volume remain unknown.nnnMETHODSnWe recruited 112 AIS patients including large-artery atherosclerosis (LAA) and small-artery occlusion [SAO] subtypes and 35 controls in this study. Blood samples were collected at admission and after antiplatelet therapy. The levels of circulating PMPs and platelet parameters (mean platelet volume [MPV], platelet count, plateletocrit, and platelet distribution width) were determined by flow cytometry and hematology analysis, respectively. Infarct volume was examined at admission by magnetic resonance imaging.nnnRESULTSn(1) The levels of circulating PMPs and MPV were significantly elevated in AIS patients compared with healthy controls; (2) the level of circulating PMPs, but not platelet parameters, was decreased after antiplatelet therapy in AIS patients; (3) the infarct volume in LAA subtype was larger than that in SAO subtype. Notably, circulating PMP level was positively correlated with the infarct volume in LAA subtype. No association with infarct volume in either AIS subtype was observed for platelet parameters; and (4) according to the regression analysis, circulating PMP was an independent risk factor for the infarct volume in pooled AIS patients after adjustments of other impact factors (hypertension and diabetes).nnnCONCLUSIONSnOur results suggest that circulating PMP level is associated with cerebral injury of AIS, which offers a novel evaluation parameter for AIS patients.

Neuronal over-expression of ACE2 protects brain from ischemia-induced damage.

Angiotensin (Ang) II exaggerates cerebral injury in ischemic damage. Angiotensin-converting enzyme type 2 (ACE2) converts Ang II into Ang (1-7) and thus, may protect against the effects of Ang II. We hypothesized that neuronal ACE2 over-expression decreases ischemic stroke in mice with Ang II overproduction. Human renin and angiotensinogen double transgenic (RA) mice and RA mice with neuronal over-expression of ACE2 (SARA) were used for the study. The mean arterial pressure (MAP) was calculated from telemetry-recorded blood pressure (BP). SARA mice were infused peripherally with Norepinephrine to clamp the BP, or intracerebroventricularly-infused with a Mas receptor antagonist (A-779). Middle cerebral artery occlusion (MCAO) surgery was performed to induce permanent focal ischemic stroke. Cerebral blood flow (CBF) and neurological function were determined. Two days after surgery, brain samples were collected for various analyses. Results showed: 1) When compared to chronically hypertensive RA mice, SARA mice had lower basal MAP, less MCAO-induced infarct volume, and increased CBF, neurological function and cerebral microvascular density in the peri-infarct area; 2) These changes in SARA mice were not altered after MAP clamping, but partially reversed by brain infusion of A-779; 3) Ang (1-7)/Ang II ratio, angiogenic factors, endothelial nitric oxide synthase (eNOS) expression and nitric oxide production were increased, whereas, NADPH oxidase subunits and reactive oxygen species were decreased in the brain of SARA mice. ACE2 protects brain from ischemic injury via the regulation of NADPH oxidase/eNOS pathways by changing Ang (1-7)/Ang II ratio, independently of MAP changes.

Endothelial progenitor cells and neural progenitor cells synergistically protect cerebral endothelial cells from Hypoxia/reoxygenation-induced injury via activating the PI3K/Akt pathway

BackgroundProtection of cerebral endothelial cells (ECs) from hypoxia/reoxygenation (H/R)-induced injury is an important strategy for treating ischemic stroke. In this study, we investigated whether co-culture with endothelial progenitor cells (EPCs) and neural progenitor cells (NPCs) synergistically protects cerebral ECs against H/R injury and the underlying mechanism.ResultsEPCs and NPCs were respectively generated from inducible pluripotent stem cells. Human brain ECs were used to produce an in vitro H/R-injury model. Data showed: 1) Co-culture with EPCs and NPCs synergistically inhibited H/R-induced reactive oxygen species (ROS) over-production, apoptosis, and improved the angiogenic and barrier functions (tube formation and permeability) in H/R-injured ECs. 2) Co-culture with NPCs up-regulated the expression of vascular endothelial growth factor receptor 2 (VEGFR2). 3) Co-culture with EPCs and NPCs complementarily increased vascular endothelial growth factor (VEGF) and brain-derived neurotrophic factor (BDNF) levels in conditioned medium, and synergistically up-regulated the expression of p-Akt/Akt and p-Flk1/VEGFR2 in H/R-injured ECs. 4) Those effects could be decreased or abolished by inhibition of both VEGFR2 and tyrosine kinase B (TrkB) or phosphatidylinositol-3-kinase (PI3K).ConclusionsOur data demonstrate that EPCs and NPCs synergistically protect cerebral ECs from H/R-injury, via activating the PI3K/Akt pathway which mainly depends on VEGF and BDNF paracrine.

Angiotensin-(1–7) counteracts the effects of Ang II on vascular smooth muscle cells, vascular remodeling and hemorrhagic stroke: Role of the NFкB inflammatory pathway

Angiotensin (Ang)-(1-7) is a potential vasoprotective peptide. In the present study, we investigated its counteractive effects to Ang II on vascular smooth muscle cells (VSMCs) and intracerebral hemorrhagic stroke (ICH) through inflammatory mechanism. In in vitro experiments, human brain VSMCs (HBVSMCs) were treated with vehicle, Ang II, Ang II+Ang-(1-7), Ang II+A-779 or Ang II+Ang-(1-7)+A-779 (Mas receptor antagonist). HBVSMC proliferation, migration and apoptosis were determined by methyl thiazolyltetrazolium, wound healing assay and flow cytometry, respectively. In in vivo experiments, C57BL/6 mice were divided into vehicle, Ang II, Ang II+Ang-(1-7), Ang II+A-779 or Ang II+Ang-(1-7)+A-779 groups before they were subjected to collagenase-induced ICH or sham surgery. Hemorrhage volume and middle cerebral artery (MCA) remodeling were determined by histological analyses. Levels of NFκB, inhibitor of κBα (IκBα), tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein 1 (MCP-1) and interleukin (IL-8) were measured by western blot or ELISA. We found that 1) Ang II increased HBVSMC migration, proliferation and apoptosis, and increased the blood pressure (BP), neurological deficit score, MCA remodeling and hemorrhage volume in ICH mice. 2) Ang-(1-7) counteracted these effects of Ang II, which was independent of BP, with the down-regulation of NFκB, up-regulation of IκBα, and decreased levels of TNF-α, MCP-1 and IL-8. 3) The beneficial effects of Ang-(1-7) could be abolished by A-779. In conclusion, Ang-(1-7) counteracts the effects of Ang II on ICH via modulating NFκB inflammation pathway in HBVSMCs and cerebral microvessels.

Analyses of Endothelial Cells and Endothelial Progenitor Cells Released Microvesicles by Using Microbead and Q-Dot Based Nanoparticle Tracking Analysis

Accurate analysis of specific microvesicles (MVs) from biofluids is critical and challenging. Here we described novel methods to purify and detect MVs shed from endothelial cells (ECs) and endothelial progenitor cells (EPCs) by combining microbeads with fluorescence quantum dots (Q-dots) coupled nanoparticle tracking analysis (NTA). In the in vitro screening systems, we demonstrated that 1) anti-CD105 (EC marker) and anti-CD34 (EPC marker) conjugated-microbeads had the highest sensitivity and specificity for isolating respective MVs, which were confirmed with negative controls, CD41 and CD235a; 2) anti-CD144 (EC marker) and anti-KDR (EPC marker) conjugated-Q-dots exhibited the best sensitivity and specificity for their respective MV NTA detection, which were confirmed with positive control, anti-Annexin V (MV universal marker). The methods were further validated by their ability to efficiently recover the known amount of EC-MVs and EPC-MVs from particle-depleted plasma, and to detect the dynamical changes of plasma MVs in ischemic stroke patients, as compared with traditional flow cytometry. These novel methods provide ideal approaches for functional analysis and biomarker discovery of ECs- and EPCs- derived MVs.