Longxuan Li

In the hypoxic central nervous system, endothelial cell proliferation is followed by astrocyte activation, proliferation, and increased expression of the α6β4 integrin and dystroglycan

Cerebral hypoxia induces a profound angiogenic response in the central nervous system (CNS). Using a mouse model of chronic cerebral hypoxia, we previously demonstrated that angiogenic vessels in the hypoxic CNS show marked upregulation of the extracellular matrix (ECM) protein fibronectin, along with increased expression of its major receptor, α5β1 integrin on brain endothelial cells (BEC). As cerebral hypoxia also leads to glial activation, the aim of the current study was to define the temporal relationship between BEC responses and glial cell activation in this model of cerebral hypoxia. This revealed that BEC fibronectin/α5β1 integrin expression and proliferation both reached maximal level after 4‐day hypoxia. Interestingly, up to 4‐day hypoxia, all dividing cells were BEC, but at later time‐points proliferating astrocytes were also observed. GFAP staining revealed that hypoxia induced marked astrocyte activation that reached maximal level between 7‐ and 14‐day hypoxia. As newly formed cerebral capillaries require ensheathment by astrocyte end‐feet to acquire mature brain endothelium characteristics, we next examined how expression of astrocyte end‐feet adhesion molecules is regulated by hypoxia. This showed that the astrocyte adhesion receptors α6β4 integrin and dystroglycan were both markedly upregulated, with a time‐course that closely resembled astrocyte activation. Taken together, this evidence shows that cerebral hypoxia promotes first an endothelial response, in which fibronectin promotes BEC proliferation. This is then followed by an astrocyte response, involving astrocyte activation, proliferation, and reorganization of astrocyte end‐feet, which correlates with increased expression of astrocyte end‐feet adhesion molecules.

Microglial activation state exerts a biphasic influence on brain endothelial cell proliferation by regulating the balance of TNF and TGF-β1

BackgroundStudies of cerebral ischemia and other neuroinflammatory states have demonstrated a strong association between new vessel formation and microglial recruitment and activation, raising the possibility that microglia may be involved in promoting angiogenesis. As endothelial cell proliferation is a fundamental early step in angiogenesis, the aim of this study was to test this hypothesis by examining the influence of microglial secreted factors on brain endothelial cell (BEC) proliferation using BrdU incorporation.MethodsPrimary cultures of mouse BEC, microglia and astrocytes were used in this study. Proliferation of BEC was examined by BrdU incorporation. ELISA was used to quantify TNF and TGF-β1 levels within cell culture supernatants.ResultsMicroglia regulated BEC proliferation in a biphasic manner; microglia conditioned medium (MG-CM) from resting microglia inhibited, while that from activated microglia promoted BEC proliferation. A screen of microglial cytokines revealed that BEC proliferation was inhibited by TGF-β1, but promoted by TNF. ELISA showed that TNF and TGF-β1 were both present in MG-CM, and that while TGF-β1 dominated in resting MG-CM, TNF levels were massively increased in activated MG-CM, shifting the balance in favor of TNF. Antibody-blocking studies revealed that the influence of MG-CM to inhibit or promote BEC proliferation was largely attributable to the cytokines TGF-β1 and TNF, respectively.ConclusionThis data suggests that microglial activation state might be an important determinant of cerebral angiogenesis; inhibiting BEC proliferation and neovascularization in the normal central nervous system (CNS), but stimulating the growth of new capillaries under neuroinflammatory conditions.

An angiogenic role for the α5β1 integrin in promoting endothelial cell proliferation during cerebral hypoxia.

Fibronectin is a critical regulator of vascular modelling, both in development and in the adult. In the hypoxic adult central nervous system (CNS), fibronectin is induced on angiogenic vessels, and endothelial cells show strong induction of the two fibronectin receptors α5β1 and αvβ3 integrins. In a previous study, we found that the αvβ3 integrin is dispensable for hypoxic-induced cerebral angiogenesis, but a role for the endothelial α5β1 integrin was suggested. To directly investigate the role of endothelial α5 integrin in cerebral angiogenesis, wild-type mice and mice lacking α5 integrin expression in endothelial cells (α5-EC-KO) were subject to hypoxia (8% O(2)) for 0, 2, 4, 7 or 14 days. Quantification of cerebral vessel density and endothelial-specific proteins claudin-5 and Glut-1 revealed that α5-EC-KO mice displayed an attenuated angiogenic response, which correlated with delayed endothelial proliferation. α5-EC-KO mice showed no defect in the ability to organize a cerebrovascular fibronectin matrix, and no compensatory increase in vascular αvβ3 integrin expression. Consistent with these findings, primary α5KO brain endothelial cells (BEC) in culture exhibited delayed growth and proliferation. Taken together, these studies demonstrate an important angiogenic role for the α5β1 integrin in promoting BEC proliferation in response to cerebral hypoxia.

Upregulation of Fibronectin and the α5β1 and αvβ3 Integrins on Blood Vessels within the Cerebral Ischemic Penumbra

Following focal cerebral ischemia, blood vessels in the ischemic border, or penumbra, launch an angiogenic response. In light of the critical role for fibronectin in angiogenesis, and the observation that fibronectin and its integrin receptors are strongly upregulated on angiogenic vessels in the hypoxic CNS, the aim of this study was to establish whether angiogenic vessels in the ischemic CNS also show this response. Focal cerebral ischemia was established in C57/Bl6 mice by middle cerebral artery occlusion (MCA:O), and brain tissue analyzed 7 days following re-perfusion, a time at which angiogenesis is ongoing. Within the ischemic core, immunofluorescent (IF) studies demonstrated vascular expression of MECA-32, a marker of leaky cerebral vessels, and vascular breakdown, defined by loss of staining for the endothelial marker, CD31, and the vascular adhesion molecules, laminin, dystroglycan and α6 integrin. Within the ischemic penumbra, dual-IF with CD31 and Ki67 revealed the presence of proliferating endothelial cells, indicating ongoing angiogenesis. Significantly, vessels in the ischemic penumbra showed strong upregulation of fibronectin and the fibronectin receptors, α5β1 and αvβ3 integrins. Taken together with our recent finding that the α5β1 integrin plays an important role in promoting cerebral angiogenesis in response to hypoxia, these results suggest that stimulation of the fibronectin-α5β1 integrin signaling pathway may provide a novel approach to amplifying the intrinsic angiogenic response to cerebral ischemia.

Absence of the αvβ3 integrin dictates the time-course of angiogenesis in the hypoxic central nervous system: accelerated endothelial proliferation correlates with compensatory increases in α5β1 integrin expression

Cerebral angiogenesis is an important adaptive response to hypoxia. As the αvβ3 integrin is induced on angiogenic vessels in the ischemic central nervous system (CNS), and the suggested angiogenic role for this integrin in other systems, it is important to determine whether the αvβ3 integrin is an important mediator of cerebral angiogenesis. αvβ3 integrin expression was examined in a model of cerebral hypoxia, in which mice were subject to hypoxia (8% O2) for 0, 4, 7, or 14 days. Immunofluorescence and western blot analysis revealed that in the hypoxic CNS, αvβ3 integrin was strongly induced on angiogenic brain endothelial cells (BEC), along with its ligand vitronectin. In the hypoxia model, β3 integrin-null mice showed no obvious defect in cerebral angiogenesis. However, early in the angiogenic process, BEC in these mice showed an increased mitotic index that correlated closely with increased α5 integrin expression. In vitro experiments confirmed α5 integrin upregulation on β3 integrin-null BEC, which also correlated with increased BEC proliferation on fibronectin. These studies confirm hypoxic induction of αvβ3 integrin on angiogenic vessels, but suggest distinct roles for the BEC integrins αvβ3 and α5β1 in cerebral angiogenesis, with αvβ3 having a nonessential role, and α5β1 promoting BEC proliferation.

The temporal expression patterns of fibronectin and its receptors-α5β1 and αvβ3 integrins on blood vessels after cerebral ischemia.

PURPOSE We previously demonstrated that 7 days post-ischemia, angiogenic vessels in the ischemic penumbra show strong upregulation of fibronectin (Fn) and its receptors, α5β1 and αvβ3 integrins. The aim of the current study was to precisely define the time-course of angiogenic responses and glial activation following experimental ischemia in the mouse. METHODS Male C57Bl/6 mice were subject to 90 minutes of ischemia by temporary occlusion of the middle cerebral artery followed by reperfusion. Vascular remodeling and glial activation were then examined in the brains of these mice after 0, 1, 2, 4, 7 and 14 days post-ischemia. RESULTS Immunofluorescent studies demonstrated that in the ischemic penumbra, blood vessel density increased up to day 14. In contrast, within the ischemic core, vessel density declined, reaching a low point at day 4, but then started to increase. In the penumbra, expression of Fn and the α5 and β3 integrins peaked at day 7, and this coincided exactly with maximal endothelial proliferation. CONCLUSIONS Our results suggest that upregulation of the Fn-α5β1/αVβ3 integrin axis on blood vessels stimulates BEC proliferation at an early stage of angiogenesis post-ischemia. This could form the basis of novel therapeutic strategies aimed at promoting angiogenesis following cerebral ischemia.

Vascular expression of angiopoietin1, α5β1 integrin and tight junction proteins is tightly regulated during vascular remodeling in the post-ischemic brain

The post-stroke angiogenic response is accompanied by changes of tight junctions (TJs) of the blood-brain barrier (BBB). However, the precise dynamic change of TJ proteins (TJPs) in the different stages of stroke-induced vascular remodeling and the molecules mediating these processes have yet to be fully defined. To investigate the temporal relationship between changes in TJPs, the pro-angiogenic factor α5β1 integrin and the anti-permeability factor Ang1 in cerebral vessels following cerebral ischemic stroke, male C57Bl/6 mice were subject to 90min of ischemia by temporary occlusion of the middle cerebral artery followed by reperfusion and their brains analyzed 0, 1, 2, 4, 7 and 14days post-ischemia. Immunofluorescent studies demonstrated that in the ischemic penumbra, TJPs claudin-5 and ZO-1 levels decreased during the early stages of vascular remodeling, but then increased in the later stages. In contrast, within the ischemic core, TJPs levels decreased over the 14-day time-course, plateaued at day 4, and remained at low levels up to day 14. In the penumbra, Ang1 expression was induced, peaking at the same time point as α5β1 expression. Consistent with these findings, oxygen glucose deprivation/reperfusion induced expression of α5β1 and Ang1 on brain endothelial cell (BEC) in a similar manner in vitro, which correlated closely with BEC proliferation and increased expression of TJPs. Our results demonstrate that in the post-ischemic penumbra, a tight temporal correlation exists between the angiogenic markers α5β1 and Ang1 and the TJPs, suggesting a potential role for Ang1 and α5β1 in promoting BBB integrity following ischemic stroke.

Motor neurone disease-associated neck pain misdiagnosed as cervical spondylosis: A case report and literature review

BACKGROUND Motor neurone disease (MND) is a chronic, progressive and currently incurable neurodegenerative disorder. Although pain as a symptom appears in many patients with MND, it is often misdiagnosed as other diseases when occurs before the onset of weakness. Patients are often assigned to non-neurological departments due to the atypical symptoms, which can lead to diagnostic delay and inappropriate treatment. OBJECTIVE To analyze the causes of misdiagnosis and improve the clinicians understanding of neck pain in patients with MND. METHODS We reviewed relevant literature and retrospectively reported a misdiagnosis case of MND-associated neck pain. RESULTS A case of MND presenting prominently as neck pain was suspected of suffering from cervical spondylosis and wrongly assigned to orthopedic clinic. When eventually being diagnosed as MND, his neck pain was found to be caused by intracranial hypertension (ICH) resulting from hypoxia via insidious respiratory failure through ventilator insufficiency. CONCLUSION Careful evaluation of the clinical progression of the symptoms, extensive EMG and nerve conduction study, as well as the establishment of better clinical approach to the diagnosis and higher public awareness allow a reduction of misdiagnosis.

Integrin α5β1-Ang1/Tie2 receptor cross-talk regulates brain endothelial cell responses following cerebral ischemia

We have previously demonstrated that in response to cerebral ischemia (CI), the growth factor angiopoietin-1 (Ang1) and α5β1 integrin are both induced in cerebral vessels, which likely provide positive signals driving the endogenous angiogenic response and vascular protection after CI. However, the precise relationship between endothelial Ang1 and α5β1 integrin after CI remains poorly understood. Here, we investigated the effects of the interaction between the Ang1/Tie2 system and α5β1 integrin on brain endothelial cells (BECs) under cerebral ischemic conditions in vivo and in vitro. Immunofluorescence analysis demonstrated that integrin α5β1 co-localized with Tie2/phosphorylated Tie2 on cerebral vessels in the penumbra. The in vitro study showed that oxygen–glucose deprivation/restoration (OGD/R) induced the expression of the Ang1 receptor Tie2 on BECs in a manner similar to that for integrin α5 and Ang1 in response to OGD/R, accompanied by increased activation of Tie2 and its downstream effectors focal adhesion kinase (FAK) and Akt. Knockdown of α5 integrin markedly suppressed OGD/R-induced Tie2 receptor activation in BECs, while in contrast, priming BECs with Ang1 promoted the expression of α5 integrin as well as the Tie2 downstream transcription factor Ets-1 in OGD-treated BECs. In line with this, Ets-1 knockdown significantly attenuated Ang1-mediated upregulation of α5 integrin. Functionally, Ang1 induced cell migration and tube formation of BECs after OGD, but this effect was inhibited by diminishment of the levels of α5 integrin in BECs. Taken together, our data indicate that the Ang1/Tie2 system cross-talks with integrin α5β1 in BECs after CI, which may contribute to the endogenous angiogenic vascular protective response following CI.Stroke: Interacting signals promote new blood vessel formationInteractions between two molecular signaling systems on the surface of brain blood vessel cells may regulate the response to cerebral ischemic (CI) strokes, in which the blood supply and hence oxygen to part of the brain is interrupted by blockages, such as blood clots. Researchers led by Longxuan Li at Gongli Hospital, the Second Military Medical University, Shanghai, and Richard Milner at the Scripps Research Institute, La Jolla, USA, used mice and cultured cells to study these interactions. The results suggest that the cell surface receptor proteins that mediate both signaling systems localize in the same area of blood cell membranes in response to a CI stroke. Molecular “cross-talk” between these systems may promote the formation of new blood vessels to repair the damage caused by a stroke. These insights could assist development of drugs to treat CI strokes.

Exosomes from MiR-30d-5p-ADSCs Reverse Acute Ischemic Stroke-Induced, Autophagy-Mediated Brain Injury by Promoting M2 Microglial/Macrophage Polarization

Background/Aims: Recent studies have indicated that exosomes secreted from adipose-derived stem cells (ADSCs) have important effects in the treatment of ischemic injury. However, the treatment mechanism is unclear. This study aimed to investigate whether ADSC-derived exosomes enriched with microRNA (miR)-30d-5p have a protective effect on acute ischemic stroke (AIS). Methods: In the current study, inflammatory factors and miR-30d-5p expression were assessed in 70 subjects with AIS and 35 healthy controls. Exosomes were characterized by transmission electron microscopy and further examined using nanoparticle tracking analyses. A rat model of AIS and an in vitro model of oxygen- and glucose-deprived (OGD) primary microglia were established to study the protective mechanism of exosomes from miR-30d-5p-overexpressing ADSCs in ischemia-induced nerve injury. Results: The results showed that following AIS, the expression of inflammatory cytokines increased, while the anti-inflammatory cytokines IL-4, IL-10, and miR-30d-5p decreased both in patients and in animal models. Moreover, in vitro studies demonstrated that suppression of autophagy significantly reduced the OGD-induced inflammatory response. In addition, exosome treatment was more effective in suppressing the inflammatory response by reversing OGD-induced and autophagy-mediated microglial polarization to M1. Furthermore, in vivo studies showed that exosomes derived from ADSCs significantly decreased the cerebral injury area of infarction by suppressing autophagy and promoting M2 microglia/macrophage polarization. Conclusions: Our results suggest that miR-30d-5p-enhanced ADSC-derived exosomes prevent cerebral injury by inhibiting autophagy-mediated microglial polarization to M1.