Postischemic angiogenic factor expression in stroke-prone rats

Endothelin receptor antagonists alleviate blood-brain barrier disruption and cerebral edema in a mouse model of traumatic brain injury: A comparison between bosentan and ambrisentan

Traumatic brain injury (TBI) is induced by the immediate physical disruption of brain tissue. TBI causes disruption of the blood-brain barrier (BBB) and brain edema. In the cerebrospinal fluid (CSF) of TBI patients, endothelin-1 (ET-1) is increased, suggesting that ET-1 aggravates TBI-induced brain damage. In this study, the effect of bosentan (ET_A/ET_B antagonist) and ambrisentan (ET_A antagonist) on BBB dysfunction and brain edema were examined in a mouse model of TBI using lateral fluid percussion injury (FPI). FPI to the mouse cerebrum increased the expression levels of ET-1 and ET_B receptors. Administration of bosentan (3 or 15 mg/kg/day) and ambrisentan (0.1 or 0.5 mg/kg/day) at 6 and 24 h after FPI ameliorated BBB disruption and cerebral brain edema. Delayed administration of bosentan from 2 days after FPI also reduced BBB disruption and brain edema, while ambrisentan had no significant effects. FPI-induced expression levels of ET-1 and ET_B receptors were reduced by bosentan, but not by ambrisentan. In cultured mouse astrocytes and brain microvessel endothelial cells, ET-1 (100 nM) increased prepro--ET-1 mRNA, which was inhibited by bosentan, but not by ambrisentan. FPI-induced alterations of the expression levels of matrix metalloproteinase-9, vascular endothelial growth factor-A, and angiopoietin-1 in the mouse cerebrum were reduced by delayed administration of bosentan, while ambrisentan had no significant effects. These results suggest that ET antagonists are effective in improving BBB disruption and cerebral edema in TBI patients and that an ET_A/ET_B non-selective type of antagonists is more effective.

Angiopoietin-1/Tie-2 signal after focal traumatic brain injury is potentiated by BQ788, an ETB receptor antagonist, in the mouse cerebrum: Involvement in recovery of blood-brain barrier function

Angiopoietin-1, an angiogenic factor, stabilizes brain microvessels through Tie-2 receptor tyrosine kinase. In traumatic brain injury, blood-brain barrier (BBB) disruption is an aggravating factor that induces brain edema and neuroinflammation. We previously showed that BQ788, an endothelin ET_B receptor antagonist, promoted recovery of BBB function after lateral fluid percussion injury (FPI) in mice. To clarify the mechanisms underlying BBB recovery mediated by BQ788, we examined the involvements of the angiopoietin-1/Tie-2 signal. When angiopoietin-1 production and Tie-2 phosphorylation were assayed by quantitative reverse transcription polymerase chain reaction and western blotting, increased angiopoietin-1 production and Tie-2 phosphorylation were observed in 7-10 days after FPI in the mouse cerebrum, whereas no significant effects were obtained at 5 days. When BQ788 (15 nmol/day, i.c.v.) were administered in 2-5 days after FPI, increased angiopoietin-1 production and Tie-2 phosphorylation were observed. Immunohistochemical observations showed that brain microvessels and astrocytes contained angiopoietin-1 after FPI, and brain microvessels also contained phosphorylated Tie-2. Treatment with endothelin-1 (100 nM) decreased angiopoietin-1 production in cultured astrocytes and the effect was inhibited by BQ788 (1 μM). Five days after FPI, increased extravasation of Evans blue dye accompanied by reduction in claudin-5, occludin, and zonula occludens-1 proteins were observed in mouse cerebrum while these effects of FPI were reduced by BQ788 and exogenous angiopoietin-1 (1 μg/day, i.c.v.). The effects of BQ788 were inhibited by co-administration of a Tie-2 kinase inhibitor (40 nmol/day, i.c.v.). These results suggest that BQ788 administration after traumatic brain injury promotes recovery of BBB function through activation of the angiopoietin-1/Tie-2 signal.

A Mesenchymal stem cell line (B10) increases angiogenesis in a rat MCAO model

A human mesenchymal stem cell line (B10) transplantation has been shown to improve ischemia-induced neurological deficits in animal stroke models. To understand the underlying mechanism, we have investigated the effects of B10 transplantation on cerebral angiogenesis in a rat middle cerebral artery occlusion (MCAO) model. B10 cells were transplanted intravenously 24 h after MCAO. Immunofluorescence staining results showed that compared to PBS-groups, vWF positive vessel and endoglin positive new vessels were increased in B10-transplanted MCAO groups in the lesion areas. The mRNA of angiogenesis factors including placental growth factor and hypoxia inducible factor (HIF)-1α were increased 3 days after MCAO in the core and IBZ areas of B10-transplanted group. Angiopoetin1 mRNA was increased only in the IBZ. Western blotting results showed that HIF-1α and vascular endothelial growth factor (VEGF) proteins were increased in B10-transplanted group. Both HIF-1α and VEGF were expressed in macrophage/microglia in the core area. In the IBZ, however, HIF-1α was expressed both in astrocytes and macrophage/microglia, while VEGF was expressed only in macrophage/microglia. Moreover, TGFβ protein levels were found to be increased in B10-transplanted group in the core and IBZ regions. Cell culture experiments using a human microglia cell line (HMO6) and B10 showed that IL-1β induced VEGF mRNA expression in both cell types. IL-1β was found to be highly expressed in B10 cells, and its co-culture with HMO6 further increased that in B10. Co-culture increased VEGF mRNA in both B10 and HMO6. In the rat brains, IL-1β was expressed in macrophage/microglia and transplanted-B10 cells in the core. IL-1β positive cell number was increased slightly, but significantly in B10-transplanted rats. To explore further, IL-1β expression was silenced in B10 cells by transfecting mRNA specific siRNA, and then transplanted in MCAO rats. Immunostaining result showed that endoglin positive area was decreased in IL-1β-silenced B10 transplanted groups compared to nonsilenced-B10 transplanted groups. Interestingly, vessel-like structure appeared as early as 3 days after MCAO in IL-1β-silenced B10-transplanted group. Thus our results demonstrated that B10 cells increased angiogenesis in MCAO rat model, through the regulation of HIF-1α and VEGF expression, where IL-1β might play a role.

Neuroprotection by progesterone after transient cerebral ischemia in stroke-prone spontaneously hypertensive rats

We investigated the neuroprotective effects of progesterone (P4) treatment in stroke-prone spontaneously hypertensive rats (SHRSPs) given 60-min transient middle cerebral artery occlusion (tMCAO). The treatment groups were: (1) Wistar-Kyoto (normotensive sham), (2) SHRSP (hypertensive sham), (3) tMCAO SHRSPs (SHRSP+tMCAO), and (4) SHRSP+tMCAO+P4. P4 (8mg/kg) was administered 1h after occlusion and then daily for 14days. We measured cerebral infarction volume, blood pressure and body weight. Behavioral outcomes were analyzed at post-stroke days 3, 9, and 14. To assess morphological protection we measured activation of microglia and astrocytes, oxidative stress, apoptosis, expression of vascular endothelial growth factor (VEGF), an angiogenic marker, and IL-1β, a marker of inflammation, on day 14 post-stroke. There was no effect of P4 on body weight or systolic blood pressure compared to the SHRSP+tMCAO group. However, grip strength and sensory neglect measures in the P4 group were improved compared to SHRSP+tMCAO. In addition, significantly larger infarct volumes were seen in the SHRSP+tMCAO group compared to SHRSP+tMCAO+P4. Increased markers of the injury cascade such as macrophages, activated astrocytes, superoxide anion and apoptotic cells observed in the SHRSP+tMCAO group were significantly decreased by P4. We conclude that, despite hypertensive comorbidity, P4 improves functional outcomes and attenuates stroke infarct in hypertensive rats by reducing superoxide anion expression and by decreasing inflammation and neuronal apoptosis.

Angiopoietin-2 promoter haplotypes confer an increased risk of stroke in a Chinese Han population

Angiopoietin-2 is an important mediator of angiogenesis, and we hypothesized that genetic variants of ANGPT2 (the gene encoding angiopoietin-2) would result in abnormal angiogenesis and contribute to stroke susceptibility. To test our hypothesis, we investigated the association of variants in the promoter of ANGPT2 with stroke in a multi-centre case-control study. We found that the C allele of rs3739390 conferred a 1.42-fold risk of lacunar infarction {adjusted OR (odds ratio), 1.42 [95% CI (confidence interval), 1.08–1.87]; P=0.012} and a 2.10-fold higher transcriptional activity than did the corresponding G allele rs3739390G. The haplotype G-G-T conferred a 1.54-fold risk of atherothrombotic stroke and a 1.64-fold risk for haemorrhagic stroke, whereas the haplotype G-C-C conferred approx. a 2.0-fold risk of each subtype of stroke. In conclusion, our results indicate that haplotypes in the promoter of ANGPT2 confer a high risk of stroke in a Chinese population.

Estradiol regulates angiopoietin-1 mRNA expression through estrogen receptor-alpha in a rodent experimental stroke model

BACKGROUND AND PURPOSE

Female, compared with male, animals are protected from cerebral ischemic injury. Physiological concentrations of 17beta-estradiol (E2) reduce damage in experimental stroke. E2 augments angiogenesis in reproductive organs and noncerebral vascular beds. We hypothesized that E2 protects brain in stroke through modulation of angiogenesis. We quantified molecular markers of angiogenesis and capillary density before and after unilateral middle cerebral artery occlusion (MCAO).

METHODS

Female animals were ovariectomized, treated with 25 microg E2 or placebo implants, and subjected to 2-hour MCAO and 22 hours of reperfusion. Brain angiopoietin-1 (Ang-1), Ang-2, Tie-1, Tie-2, vascular endothelial growth factor (VEGF), VEGF R1, and VEGF R2 mRNA levels were determined by RNAse protection assays, and CD31-positive vessels were counted.

RESULTS

E2, but not ischemia, upregulated cerebral Ang-1 mRNA by 49%. Capillary density was higher in the brains of E2-treated animals. In estrogen receptor-alpha knockout (ERKO) mice, E2-mediated induction of Ang-1 mRNA was absent relative to wild-type littermates.

CONCLUSIONS

These results suggest that E2 increases Ang-1 and enhances capillary density in brain under basal conditions, priming the MCA territory for survival after experimental focal ischemia.

Plasma angiopoietin-1, angiopoietin-2, angiopoietin receptor tie-2, and vascular endothelial growth factor levels in acute coronary syndromes

BACKGROUND

Angiopoietin (Ang) -1 and -2, their receptor Tie-2, and vascular endothelial growth factor (VEGF) regulate angiogenesis and may be important in myocardial collateral development. Elevated levels of growth factors and their receptors are reported in myocardial infarction (MI), but changes after an acute coronary event are unknown.

METHODS AND RESULTS

Plasma Ang-1, Ang-2, Tie-2, and VEGF levels were measured on admission (baseline) and at 48 hours (acute stage) in 126 patients with acute coronary syndrome (82 MI, 44 unstable angina pectoris). Baseline levels were compared with those of 40 patients with stable angina and 40 healthy controls. Measurements were repeated in 38 MI patients at 6 and 18 weeks (chronic stage). Baseline Ang-2 and Tie-2 levels were highest in MI patients (P<0.001). Patients with MI and unstable angina pectoris had higher VEGF levels compared with stable angina patients and healthy control subjects (P<0.001). In patients with acute MI, serial changes in all indexes from baseline to 18 weeks were observed (all P<0.001). Ang-1 levels were unchanged from baseline to 6 weeks but were elevated at 18 weeks. Ang-2 changes followed a biphasic pattern, being higher at baseline and 6 weeks but lower at 48 hours and 18 weeks. Tie-2 levels increased from baseline and remained elevated in the chronic phase. VEGF peaked at 6 weeks and then decreased toward baseline at 18 weeks.

CONCLUSIONS

Plasma Ang-2, Tie-2, and VEGF levels but not Ang-1 levels were increased in patients with acute coronary syndrome. Serial changes in the plasma levels and interrelationships among Ang-1, Ang-2, Tie-2, and VEGF levels from the acute to the chronic stages in MI may reflect the progressive stages of angiogenesis activity in the ischemic-necrotic myocardium in vivo.

Angiopoietin-1-induced PI3-kinase activation prevents neuronal apoptosis

Although angiopoietin-1 (Ang-1) is recognized as an endothelial growth factor, its presence in brain following an ischemic event suggests a role in the evolution of neuronal damage. Using primary neuronal cultures, we showed that neurons express Ang-1 and possess the functional angiopoietin-receptor Tie-2, which is phosphorylated in the presence of Ang-1. We further investigated in vitro whether Ang-1 could protect neurons against either excitotoxic necrosis or apoptosis induced by serum deprivation (SD). A neuroprotective effect for Ang-1 was detected exclusively in the apoptotic paradigm. Treatment of cells with the phosphatidyl-inositol 3-kinase (PI3-K) inhibitor, LY294002, inhibited Ang-1-induced phosphorylation of Akt, restored the cleavage of the effector caspase-3, and reduced the protective effect of Ang-1 against SD-induced toxicity. These findings suggest that Ang-1 has a neuroprotective effect against apoptotic stress and that this effect is dependent on the PI3-K/Akt pathway and inhibition of caspase-3 cleavage. This study provides evidence that Ang-1 is not just angiogenic but also neuroprotective. The understanding of neuroprotective mechanisms induced by Ang-1 may promote strategies based on the pleiotropic effects of angiogenic factors. Such approaches could be useful for the treatment of brain diseases in which both neuronal death and angiogenesis are involved.