Angiopoietin-2 is vasoprotective in the acute phase of cerebral ischemia

Neuroprotective Effect of Angiopoietin2 Is Associated with Angiogenesis in Mouse Brain Following Ischemic Stroke

Angiogenic factors play an important role in protecting, repairing, and reconstructing vessels after ischemic stroke. In the brains of transient focal cerebral ischemic mice, we observed a reduction in infarct volume after the administration of Angiopoietin 2 (Angpt2), but whether this process is promoted by Angpt2-induced angiogenesis has not been fully elaborated. Therefore, this study explored the angiogenic activities, in reference to CD34 which is a marker of activated ECs and blood vessels, of cultured ECs in vitro and in ischemic damaged cerebral area in mice following Angpt2 administration. Our results demonstrate that Angpt2 administration (100 ng/mL) is neuroprotective by significantly increasing the CD34 expression in in vitro-cultured ECs, reducing the infarct volume and mitigating neuronal loss, as well as enhancing CD34⁺ vascular length and area. In conclusion, these results indicate that Angpt2 promotes repair and attenuates ischemic injury, and that the mechanism of this is closely associated with angiogenesis in the brain after stroke.

The Role of PKC and HIF-1 and the Effect of Traditional Chinese Medicinal Compounds on Cerebral Ischemia-Reperfusion Injury

Neuronal death occurs during cerebral ischemia. However, when hemoperfusion and oxygen supply are resumed to the ischemic focus of the brain tissue, the brain tissue damage is further aggravated, resulting in cerebral ischemia-reperfusion injury (CIRI) to the patients. Protein kinase C (PKC) plays an important role in CIRI. Through the IP3/DAG/Ca²⁺ signaling pathway, it promotes the influx of calcium ions in neurons and causes calcium overload, which aggravates the damage. At the same time, when brain cells are hypoxic, hypoxia-inducible factor-1 (HIF-1) is expressed, which regulates the expression of Bcl-2 and Bax through the PI3K/Akt signaling pathway and reduces nerve cell injury. It also fights hypoxic-ischemic injury by increasing the production of vascular endothelial growth factor (VEGF) to promote blood vessel formation. The PKC and HIF-1 signaling pathways are also linked to CIRI. HIF-1 activates the PKC and ERK pathways via the upregulation of VEGF, leading to increased Cx43 phosphorylation and dysfunction and aggravating CIRI. Existing studies have shown that certain traditional Chinese medicine (TCM) compounds regulate the PKC and HIF-1 signaling pathways and alleviate CIRI. These compounds downregulate the PKC and the activity of the PKC-related signaling pathways to alleviate CIRI. They can also promote the expression of HIF-1, increase the content of VEGF in ischemic tissues to promote the generation of blood vessels, and improve microcirculation. TCM compounds can inhibit the cascade of reactions underlying disease occurrence and development by targeting multiple components using different herbal formulations to improve the structural and material changes in the brain cells, which alleviate CIRI and protect the brain tissue. This study briefly describes the role of PKC and HIF-1, their relationship in CIRI, and the effect of TCM on them.

Biomarkers of Angiogenesis and Neuroplasticity as Promising Clinical Tools for Stroke Recovery Evaluation

Several key issues impact the clinical practice of stroke rehabilitation including a patient’s medical history, stroke experience, the potential for recovery, and the selection of the most effective type of therapy. Until clinicians have answers to these concerns, the treatment and rehabilitation are rather intuitive, with standard procedures carried out based on subjective estimations using clinical scales. Therefore, there is a need to find biomarkers that could predict brain recovery potential in stroke patients. This review aims to present the current state-of-the-art stroke recovery biomarkers that could be used in clinical practice. The revision of biochemical biomarkers has been developed based on stroke recovery processes: angiogenesis and neuroplasticity. This paper provides an overview of the biomarkers that are considered to be ready-to-use in clinical practice and others, considered as future tools. Furthermore, this review shows the utility of biomarkers in the development of the concept of personalized medicine. Enhancing brain neuroplasticity and rehabilitation facilitation are crucial concerns not only after stroke, but in all central nervous system diseases.

Role of the neurovascular unit in the process of cerebral ischemic injury

Cerebral ischemic injury exhibits both high morbidity and mortality worldwide. Traditional research of the pathogenesis of cerebral ischemic injury has focused on separate analyses of the involved cell types. In recent years, the neurovascular unit (NVU) mechanism of cerebral ischemic injury has been proposed in modern medicine. Hence, more effective strategies for the treatment of cerebral ischemic injury may be provided through comprehensive analysis of brain cells and the extracellular matrix. However, recent studies that have investigated the function of the NVU in cerebral ischemic injury have been insufficient. In addition, the metabolism and energy conversion of the NVU depend on interactions among multiple cell types, which make it difficult to identify the unique contribution of each cell type. Therefore, in the present review, we comprehensively summarize the regulatory effects and recovery mechanisms of four major cell types (i.e., astrocytes, microglia, brain-microvascular endothelial cells, and neurons) in the NVU under cerebral ischemic injury, as well as discuss the interactions among these cell types in the NVU. Furthermore, we discuss the common signaling pathways and signaling factors that mediate cerebral ischemic injury in the NVU, which may help to provide a theoretical basis for the comprehensive elucidation of cerebral ischemic injury.

Angiopoietin: A Novel Neuroprotective/Neurotrophic Agent

Angiopoietin (Ang) is an angiogenic factor, but its neuroprotective and neurotrophic effects have recently come to light. Ang exerts neuroprotective effects by inhibiting neuronal apoptosis, protecting the blood-brain/blood-spinal cord barrier, reducing inflammation and promoting neovascularization. In addition, Ang can also promote neural development and neurite outgrowth via activation of the PI3K/Akt signaling pathway and binding to the Tie2 receptor and/or integrin receptor. In addition, Ang and vascular endothelial growth factor (VEGF) are known to interact in blood vessels in the nervous system and the combination of Ang and VEGF can mitigate the negative effects of VEGF, such as inflammation and local edema. These data indicated that Ang is a novel neuroprotective/neurotrophic factor, which may become a new tool for the treatment of nerve injury.

Angioneurins - Key regulators of blood-brain barrier integrity during hypoxic and ischemic brain injury

The loss of blood-brain barrier (BBB) integrity leading to vasogenic edema and brain swelling is a common feature of hypoxic/ischemic brain diseases such as stroke, but is also central to the etiology of other CNS disorders. In the past decades, numerous proteins, belonging to the family of angioneurins, have gained increasing attention as potential therapeutic targets for ischemic stroke, but also other CNS diseases attributed to BBB dysfunction. Angioneurins encompass mediators that affect both neuronal and vascular function. Recently, increasing evidence has been accumulated that certain angioneurins critically determine disease progression and outcome in stroke among others through multifaceted effects on the compromised BBB. Here, we will give a concise overview about the family of angioneurins. We further describe the most important cellular and molecular components that contribute to structural integrity and low permeability of the BBB under steady-state conditions. We then discuss BBB alterations in ischemic stroke, and highlight underlying cellular and molecular mechanisms. For the most prominent angioneurin family members including vascular endothelial growth factors, angiopoietins, platelet-derived growth factors and erythropoietin, we will summarize current scientific literature from experimental studies in animal models, and if available from clinical trials, on the following points: (i) spatiotemporal expression of these factors in the healthy and hypoxic/ischemic CNS, (ii) impact of loss- or gain-of-function during cerebral hypoxia/ischemia for BBB integrity and beyond, and (iii) potential underlying molecular mechanisms. Moreover, we will highlight novel therapeutic strategies based on the activation of endogenous angioneurins that might improve BBB dysfuntion during ischemic stroke.

Angiopoietin-2 induces the neuronal differentiation of mouse embryonic NSCs via phosphatidylinositol 3 kinase-Akt pathway-mediated phosphorylation of mTOR

The fate of neural stem cells (NSCs) is decided by numerous growth factors. Among these factors, the well-known angiogenic factor angiopoietin-2 (Ang-2) has been revealed to participate in neurogenesis separate from its role in angiogenesis. However, the effect of Ang-2 on the fate determination of mouse embryonic NSCs and the underlying mechanism remain unclear. This result of this study indicated that treatment of mouse embryonic NSCs with 200 ng/ml Ang-2 significantly promoted neuronal differentiation without affecting glial differentiation, and mammalian target of rapamycin (mTOR) was phosphorylated in a phosphatidylinositol 3-kinase (PI3K)/Akt-dependent manner during this process. Rapamycin, a specific mTOR inhibitor, suppressed the increase in neuronal differentiation stimulated by Ang-2, and this suppression did not result from an effect of Ang-2 or rapamycin on the apoptosis of differentiated NSCs. Collectively, our research demonstrates that PI3K/Akt pathway-mediated mTOR phosphorylation plays an important role in the Ang-2-enhanced neuronal differentiation of mouse embryonic NSCs.

ADAMTS13 controls vascular remodeling by modifying VWF reactivity during stroke recovery

Angiogenic response is essential for ischemic brain repair. The von Willebrand factor (VWF)-cleaving protease disintegrin and metalloprotease with thrombospondin type I motif, member 13 (ADAMTS13) is required for endothelial tube formation in vitro, but there is currently no in vivo evidence supporting a function of ADAMTS13 in angiogenesis. Here we show that mice deficient in ADAMTS13 exhibited reduced neovascularization, brain capillary perfusion, pericyte and smooth muscle cell coverage on microvessels, expression of the tight junction and basement membrane proteins, and accelerated blood-brain barrier (BBB) breakdown and extravascular deposits of serum proteins in the peri-infarct cortex at 14 days after stroke. Deficiency of VWF or anti-VWF antibody treatment significantly increased microvessels, perfused capillary length, and reversed pericyte loss and BBB changes in Adamts13^-/- mice. Furthermore, we observed that ADAMTS13 deficiency decreased angiopoietin-2 and galectin-3 levels in the isolated brain microvessels, whereas VWF deficiency had the opposite effect. Correlating with this, overexpression of angiopoietin-2 by adenoviruses treatment or administration of recombinant galectin-3 normalized microvascular reductions, pericyte loss, and BBB breakdown in Adamts13^-/- mice. The vascular changes induced by angiopoietin-2 overexpression and recombinant galectin-3 treatment in Adamts13^-/- mice were abolished by the vascular endothelial growth factor receptor-2 antagonist SU1498. Importantly, treating wild-type mice with recombinant ADAMTS13 at 7 days after stroke markedly increased neovascularization and vascular repair and improved functional recovery at 14 days. Our results suggest that ADAMTS13 controls key steps of ischemic vascular remodeling and that recombinant ADAMTS13 is a putative therapeutic avenue for promoting stroke recovery.

Increased CSF biomarkers of angiogenesis in Parkinson disease

Objective:

To study biomarkers of angiogenesis in Parkinson disease (PD), and how these are associated with clinical characteristics, blood–brain barrier (BBB) permeability, and cerebrovascular disease.

Methods:

In this cross-sectional analysis, 38 elderly controls and 100 patients with PD (82 without dementia and 18 with dementia) were included from the prospective Swedish BioFinder study. CSF samples were analyzed for the angiogenesis biomarkers vascular endothelial growth factor (VEGF); its receptors, VEGFR-1 and VEGFR-2; placental growth factor (PlGF); angiopoietin 2 (Ang2); and interleukin-8. BBB permeability, white matter lesions (WMLs), and cerebral microbleeds (CMB) were assessed. CSF angiogenesis biomarkers were also measured in 2 validation cohorts: (1) 64 controls and 87 patients with PD with dementia; and (2) 35 controls and 93 patients with neuropathologically confirmed diagnosis of PD with and without dementia.

Results:

Patients with PD without dementia displayed higher CSF levels of VEGF, PlGF, and sVEGFR-2, and lower levels of Ang2, compared to controls. Similar alterations in VEGF, PlGF, and Ang2 levels were observed in patients with PD with dementia. Angiogenesis markers were associated with gait difficulties and orthostatic hypotension as well as with more pronounced BBB permeability, WMLs, and CMB. Moreover, higher levels of VEGF and PlGF levels were associated with increased CSF levels of neurofilament light (a marker of neurodegeneration) and monocyte chemotactic protein–1 (a marker of glial activation). The main results were validated in the 2 additional cohorts.

Conclusions:

CSF biomarkers of angiogenesis are increased in PD, and they are associated with gait difficulties, BBB dysfunction, WMLs, and CMB. Abnormal angiogenesis may be important in PD pathogenesis and contribute to dopa-resistant symptoms.

The angiopoietin/TIE receptor system: Focusing its role for ischemia-reperfusion injury

Ischemia and reperfusion (I/R) are of fatal consequence for the affected organs, as they provoke a profound inflammatory reaction. This thoroughly destroys cells and tissues, inducing functional failure or even complete loss of organ function. Since I/R is primarily a vascular problem, the interaction between the endothelium and the surrounding environment is of great significance. The angiopoietins (ANG) and the TIE receptors are key players for the vascular homeostasis. This review summarizes biochemical and cellular mechanisms leading to I/R injury. After a brief introduction to the ANG/TIE system, a comprehensive overview of its role for the development of I/R syndrome is given. Finally, current therapeutic approaches to mitigate the consequences of I/R by modulating ANG/TIE signaling are reviewed in detail.

Protein tyrosine phosphorylation in the ischemic brain

Cerebral ischemia, a pathological condition in which brain tissue experiences a shortage of cerebral blood flow, is associated with cerebrovascular disease, brain trauma, epilepsy, and cardiac arrest. A reduction in blood flow leaves the brain tissue unsupplied with oxygen and glucose, thus leading to cell death in the ischemic core as well as subsequent peripheral injury in the penumbra. Neurons in the penumbra, where reperfusion occurs, are functionally inactive but still viable. Many biochemical changes, which may lead to neuronal cell death, thereby induce dysfunction of the central nervous system. However, the mechanisms responsible for ischemic stroke-induced cell damage remain to be determined. Protein phosphorylation has been implicated in the regulation of diverse cellular responses in the brain. Initially, tyrosine phosphorylation was considered to be involved in the regulation of cell growth and development. In addition, a variety of synaptic and cellular functions mediated by tyrosine phosphorylation in the brain were found to be associated with relatively high levels of protein tyrosine kinase activity. However, the involvement of this protein tyrosine kinase activity in ischemic cell death is still not fully understood. This review summarizes recent advances dealing with the possible implications of protein tyrosine phosphorylation in the ischemic brain.