Matrix metalloproteinase-9 mediates post-hypoxic vascular pruning of cerebral blood vessels by degrading laminin and claudin-5

Blood-brain barrier biomarkers

The blood-brain barrier (BBB) is a dynamic interface that regulates the exchange of molecules and cells between the brain parenchyma and the peripheral blood. The BBB is mainly composed of endothelial cells, astrocytes and pericytes. The integrity of this structure is essential for maintaining brain and spinal cord homeostasis and protection from injury or disease. However, in various neurological disorders, such as traumatic brain injury, Alzheimer's disease, and multiple sclerosis, the BBB can become compromised thus allowing passage of molecules and cells in and out of the central nervous system parenchyma. These agents, however, can serve as biomarkers of BBB permeability and neuronal damage, and provide valuable information for diagnosis, prognosis and treatment. Herein, we provide an overview of the BBB and changes due to aging, and summarize current knowledge on biomarkers of BBB disruption and neurodegeneration, including permeability, cellular, molecular and imaging biomarkers. We also discuss the challenges and opportunities for developing a biomarker toolkit that can reliably assess the BBB in physiologic and pathophysiologic states.

β1 integrins play a critical role maintaining vascular integrity in the hypoxic spinal cord, particularly in white matter

Interactions between extracellular matrix (ECM) proteins and β1 integrins play an essential role maintaining vascular integrity in the brain, particularly under vascular remodeling conditions. As blood vessels in the spinal cord are reported to have distinct properties from those in the brain, here we examined the impact of β1 integrin inhibition on spinal cord vascular integrity, both under normoxic conditions, when blood vessels are stable, and during exposure to chronic mild hypoxia (CMH), when extensive vascular remodeling occurs. We found that a function-blocking β1 integrin antibody triggered a small degree of vascular disruption in the spinal cord under normoxic conditions, but under hypoxic conditions, it greatly enhanced (20-fold) vascular disruption, preferentially in spinal cord white matter (WM). This resulted in elevated microglial activation as well as marked loss of myelin integrity and reduced density of oligodendroglial cells. To understand why vascular breakdown is localized to WM, we compared expression levels of major BBB components of WM and grey matter (GM) blood vessels, but this revealed no obvious differences. Interestingly however, hypoxyprobe staining demonstrated that the most severe levels of spinal cord hypoxia induced by CMH occurred in the WM. Analysis of brain tissue revealed a similar preferential vulnerability of WM tracts to show vascular disruption under these conditions. Taken together, these findings demonstrate an essential role for β1 integrins in maintaining vascular integrity in the spinal cord, and unexpectedly, reveal a novel and fundamental difference between WM and GM blood vessels in their dependence on β1 integrin function during hypoxic exposure. Our data support the concept that the preferential WM vulnerability described may be less a result of intrinsic differences in vascular barrier properties between WM and GM, and more a consequence of differences in vascular density and architecture.

Drug Discovery Research for Traumatic Brain Injury Focused on Functional Molecules in Astrocytes

Traumatic brain injury (TBI) is severe damage to the head caused by traffic accidents, falls, and sports. Because TBI-induced disruption of the blood-brain barrier (BBB) causes brain edema and neuroinflammation, which are major causes of death or serious disabilities, protection and recovery of BBB function may be beneficial therapeutic strategies for TBI. Astrocytes are key components of BBB integrity, and astrocyte-derived bioactive factors promote and suppress BBB disruption in TBI. Therefore, the regulation of astrocyte function is essential for BBB protection. In the injured cerebrum of TBI model mice, we found that the endothelin ETB receptor, histamine H2 receptor, and transient receptor potential vanilloid 4 (TRPV4) were predominantly expressed in reactive astrocytes. We also showed that repeated administration of an ETB receptor antagonist, H2 receptor agonist, and TRPV4 antagonist alleviated BBB disruption and brain edema in a TBI mouse model. Furthermore, these drugs decreased the expression levels of astrocyte-derived factors promoting BBB disruption and increased the expression levels of astrocyte-derived protective factors in the injured cerebrum after TBI. These results suggest that the ETB receptor, H2 receptor, and TRPV4 are molecules that regulate astrocyte function, and might be attractive candidates for the development of therapeutic drugs for TBI.

Cellular and molecular mechanisms in vascular repair after traumatic brain injury: a narrative review

Traumatic brain injury (TBI) disrupts normal brain function and is associated with high morbidity and fatality rates. TBI is characterized as mild, moderate or severe depending on its severity. The damage may be transient and limited to the dura matter, with only subtle changes in cerebral parenchyma, or life-threatening with obvious focal contusions, hematomas and edema. Blood vessels are often injured in TBI. Even in mild TBI, dysfunctional cerebral vascular repair may result in prolonged symptoms and poor outcomes. Various distinct types of cells participate in vascular repair after TBI. A better understanding of the cellular response and function in vascular repair can facilitate the development of new therapeutic strategies. In this review, we analyzed the mechanism of cerebrovascular impairment and the repercussions following various forms of TBI. We then discussed the role of distinct cell types in the repair of meningeal and parenchyma vasculature following TBI, including endothelial cells, endothelial progenitor cells, pericytes, glial cells (astrocytes and microglia), neurons, myeloid cells (macrophages and monocytes) and meningeal lymphatic endothelial cells. Finally, possible treatment techniques targeting these unique cell types for vascular repair after TBI are discussed.

Spinal Cord Blood Vessels in Aged Mice Show Greater Levels of Hypoxia-Induced Vascular Disruption and Microglial Activation

In response to chronic mild hypoxia (CMH, 8% O2), spinal cord blood vessels launch a robust angiogenic response that is associated with transient disruption of the blood-spinal cord barrier (BSCB) which, in turn, triggers a microglial vasculo-protective response. Because hypoxia occurs in many age-related conditions, the goal of this study was to define how aging influences these responses by comparing events in young (8-10 weeks) and aged (20 months) mice. This revealed that aged mice had much greater (3-4-fold) levels of hypoxic-induced BSCB disruption than young mice and that, while the early stage of the angiogenic response in aged mice was no different to young mice, the maturation of newly formed vessels was significantly delayed. Interestingly, microglia in the spinal cords of aged mice were much more activated than young mice, even under normoxic conditions, and this was further enhanced by CMH, though, surprisingly, this resulted in reduced microglial clustering around leaky blood vessels and diminished vasculo-protection. Vascular disruption was associated with loss of myelin in spinal cord white matter (WM) in both young and aged mice. Furthermore, it was notable that the spinal cord of aged mice contained a lower density of Olig2+ oligodendroglial cells even under normoxic conditions and that CMH significantly reduced the density of Olig2+ cells in spinal cord WM of the aged, but not the young, mice. These results demonstrate that spinal cord blood vessels of aged mice are much more vulnerable to the damaging effects of hypoxia than young mice, in part due to the reduced vasculo-protection conferred by chronically activated microglial cells. These observations may have implications for the pathogenesis and/or treatment of spinal cord diseases such as amyotrophic lateral sclerosis (ALS) and suggest that an improvement in microglial function could offer therapeutic potential for treating these age-related conditions.

β1 integrin is essential for blood-brain barrier integrity under stable and vascular remodelling conditions; effects differ with age

BACKGROUND

Maintaining a tight blood-brain barrier (BBB) is an important prerequisite for the preservation of neurological health, though current evidence suggests it declines with age. While extracellular matrix-integrin interactions play critical roles in regulating the balance between vascular stability and remodeling, it remains to be established whether manipulation of integrin function weakens or strengthens vascular integrity. Indeed, recent reports have generated conflicting outcomes in this regard.

METHODS

Here, in young (8-10 weeks) and aged (20 months) mice, we examined the impact of intraperitoneal injection of a function-blocking β1 integrin antibody, both under normoxic conditions, when the BBB is stable, and during chronic mild hypoxic (CMH; 8% O₂) conditions, when a vigorous vascular remodeling response is ongoing. Brain tissue was examined by immunofluorescence (IF) for markers of vascular remodeling and BBB disruption, and microglial activation and proliferation. Data were analyzed using one-way analysis of variance (ANOVA) followed by Tukey's multiple comparison post-hoc test.

RESULTS

In both young and aged mice, β1 integrin block greatly amplified hypoxia-induced vascular disruption, though it was much less under normoxic conditions. Interestingly, under both normoxic and hypoxic conditions, β1 integrin antibody-induced BBB disruption was greater in young mice. Enhanced BBB breakdown was associated with increased levels of the leaky BBB marker MECA-32 and with greater loss of endothelial tight junction proteins and the adherens protein VE-cadherin. Surprisingly, β1 integrin blockade did not reduce hypoxia-induced endothelial proliferation, nor did it prevent the hypoxia-associated increase in vascularity. Commensurate with the increased vascular disruption, β1 integrin blockade enhanced microglial activation both in young and aged brain, though the impact was much greater in young brain. In vitro studies revealed that β1 integrin blockade also reduced the integrity of a brain endothelial monolayer and triggered disruptions in tight junction proteins.

CONCLUSIONS

These data demonstrate that β1 integrin plays an essential role in maintaining BBB integrity, both under stable normoxic conditions and during hypoxia-induced vascular remodeling. As β1 integrin blockade had a greater disruptive effect in young brain, effectively shifting the BBB phenotype of young brain towards that of the aged, we speculate that enhancing β1 integrin function at the aged BBB may hold therapeutic potential by reverting the deteriorating BBB phenotype back towards that of the young.

Hypoxia-induced vascular remodeling responses in the brain are much more robust than other organs

Exposure to chronic mild hypoxia (CMH; 8-10% O2) promotes a robust vascular remodeling response in the brain resulting in 50% increased vessel density over a period of two weeks. It is currently unknown whether blood vessels in other organs show similar responses. To address this question, mice were exposed to CMH for 4 days and various markers of vascular remodeling were examined in the brain along with heart, skeletal muscle, kidney, and liver. In contrast to brain, where CMH strongly promoted endothelial proliferation, none of the peripheral organs showed this response and in heart and liver, CMH notably reduced endothelial proliferation. While the MECA-32 endothelial activation marker was strongly induced by CMH in brain, in peripheral organs it was constitutively expressed either on a sub-population of vessels (heart and skeletal muscle) or on all vessels (kidney and liver), and notably, CMH did not affect expression. Endothelial expression of the tight junction proteins claudin-5 and ZO-1 were markedly increased on cerebral vessels, but in the peripheral organs examined, CMH either had no effect or reduced ZO-1 expression (liver). Finally, while CMH had no impact on the number of Mac-1 positive macrophages in the brain, heart, or skeletal muscle, this number was markedly decreased in the kidney but increased in the liver. Our findings show that the vascular remodeling responses to CMH are organ-specific, with the brain showing a strong angiogenic response and enhanced tight junction protein expression, but heart, skeletal muscle, kidney, and liver failing to show these responses.

TGF-β signaling pathway: Therapeutic targeting and potential for anti-cancer immunity

Transforming growth factor-β (TGFβ) is a pleiotropic secretory cytokine exhibiting both cancer-inhibitory and promoting properties. It transmits its signals via Suppressor of Mother against Decapentaplegic (SMAD) and non-SMAD pathways and regulates cell proliferation, differentiation, invasion, migration, and apoptosis. In non-cancer and early-stage cancer cells, TGFβ signaling suppresses cancer progression via inducing apoptosis, cell cycle arrest, or anti-proliferation, and promoting cell differentiation. On the other hand, TGFβ may also act as an oncogene in advanced stages of tumors, wherein it develops immune-suppressive tumor microenvironments and induces the proliferation of cancer cells, invasion, angiogenesis, tumorigenesis, and metastasis. Higher TGFβ expression leads to the instigation and development of cancer. Therefore, suppressing TGFβ signals may present a potential treatment option for inhibiting tumorigenesis and metastasis. Different inhibitory molecules, including ligand traps, anti-sense oligo-nucleotides, small molecule receptor-kinase inhibitors, small molecule inhibitors, and vaccines, have been developed and clinically trialed for blocking the TGFβ signaling pathway. These molecules are not pro-oncogenic response-specific but block all signaling effects induced by TGFβ. Nonetheless, targeting the activation of TGFβ signaling with maximized specificity and minimized toxicity can enhance the efficacy of therapeutic approaches against this signaling pathway. The molecules that are used to target TGFβ are non-cytotoxic to cancer cells but designed to curtail the over-activation of invasion and metastasis driving TGFβ signaling in stromal and cancer cells. Here, we discussed the critical role of TGFβ in tumorigenesis, and metastasis, as well as the outcome and the promising achievement of TGFβ inhibitory molecules in the treatment of cancer.

Dermal Telocytes: A Different Viewpoint of Skin Repairing and Regeneration

Fifteen years after their discovery, telocytes (TCs) are yet perceived as a new stromal cell type. Their presence was initially documented peri-digestively, and gradually throughout the interstitia of many (non-)cavitary mammalian, human, and avian organs, including skin. Each time, TCs proved to be involved in diverse spatial relations with elements of interstitial (ultra)structure (blood vessels, nerves, immune cells, etc.). To date, transmission electron microscopy (TEM) remained the single main microscopic technique able to correctly and certainly attest TCs by their well-acknowledged (ultra)structure. In skin, dermal TCs reiterate almost all (ultra)structural features ascribed to TCs in other locations, with apparent direct implications in skin physiology and/or pathology. TCs' uneven distribution within skin, mainly located in stem cell niches, suggests involvement in either skin homeostasis or dermatological pathologies. On the other hand, different skin diseases involve different patterns of disruption of TCs' structure and ultrastructure. TCs' cellular cooperation with other interstitial elements, their immunological profile, and their changes during remission of diseases suggest their role(s) in tissue regeneration/repair processes. Thus, expanding the knowledge on dermal TCs could offer new insights into the natural skin capacity of self-repairing. Moreover, it would become attractive to consider that augmenting dermal TCs' presence/density could become an attractive therapeutic alternative for treating various skin defects.

Exaggerated hypoxic vascular breakdown in aged brain due to reduced microglial vasculo-protection

In a recent study of young mice, we showed that chronic mild hypoxia (CMH, 8% O2 ) triggers transient blood-brain barrier (BBB) disruption, and that microglia play an important vasculo-protective function in maintaining BBB integrity. As hypoxia is a common component of many age-related diseases, here we extended these studies to aged mice and found that hypoxia-induced vascular leak was greatly amplified (5-fold to 10-fold) in aged mice, being particularly high in the olfactory bulb and midbrain. While aged mice showed no obvious difference in the early stages of hypoxic angiogenic remodeling, the compensatory increase in vascularity and vessel maturation was significantly delayed. Compared with young brain, microglia in the normoxic aged brain were markedly activated, and this was further increased under hypoxic conditions, but paradoxically, this correlated with reduced vasculo-protection. Microglial depletion studies showed that microglial still play an important vasculo-protective role in aged brain, but interestingly, partial attenuation of microglial activation with minocycline resulted in fewer vascular leaks and reduced loss of endothelial tight junction proteins. Taken together, these findings suggest that increased BBB disruption in hypoxic aged mice can be explained both by a delayed vascular remodeling response and reduced microglial vasculo-protection. Importantly, they show that overly activated microglia in the aged brain are less effective at maintaining vascular integrity, though this can be improved by reducing microglial activation with minocycline, suggesting therapeutic potential for enhancing BBB integrity in the hypoxia-predisposed elderly population.

Laminin as a Biomarker of Blood-Brain Barrier Disruption under Neuroinflammation: A Systematic Review

Laminin, a non-collagenous glycoprotein present in the brain extracellular matrix, helps to maintain blood–brain barrier (BBB) integrity and regulation. Neuroinflammation can compromise laminin structure and function, increasing BBB permeability. The aim of this paper is to determine if neuroinflammation-induced laminin functional changes may serve as a potential biomarker of alterations in the BBB. The 38 publications included evaluated neuroinflammation, BBB disruption, and laminin, and were assessed for quality and risk of bias (protocol registered in PROSPERO; CRD42020212547). We found that laminin may be a good indicator of BBB overall structural integrity, although changes in expression are dependent on the pathologic or experimental model used. In ischemic stroke, permanent vascular damage correlates with increased laminin expression (β and γ subunits), while transient damage correlates with reduced laminin expression (α subunits). Laminin was reduced in traumatic brain injury and cerebral hemorrhage studies but increased in multiple sclerosis and status epilepticus studies. Despite these observations, there is limited knowledge about the role played by different subunits or isoforms (such as 411 or 511) of laminin in maintaining structural architecture of the BBB under neuroinflammation. Further studies may clarify this aspect and the possibility of using laminin as a biomarker in different pathologies, which have alterations in BBB function in common.

Changes of FSTL1 and MMP-9 levels in patients with acute cerebral infarction and its relationship with hemorrhagic transformation

BACKGROUND

hemorrhagic transformation is a serious complication of acute ischemic stroke, which may lead to poor prognosis and delayed use of anticoagulant therapy.

METHODS

125 patients with cerebral infarction from December 2019 to December 2020 in the Second Affiliated Hospital of Zhejiang University were selected. All patients did not receive intravascular therapy, intravenous thrombolysis and other reperfusion treatment; and the relevant laboratory data were collected within 24 h after admission. At the same time, 15 healthy subjects were selected as the research objects for prospective analysis. Hemorrhagic transformation (HT) was defined as a condition in which computed tomography (CT) did not indicate bleeding at admission, but follow-up magnetic resonance imaging (MRI) or CT showed hemorrhage. The patients were divided into HT group (n = 50) and non-HT group (n = 75) according to whether there was HT after admission. The concentrations of FSTL1 and MMP-9 in peripheral blood of the two groups were detected.

RESULTS

The concentrations of FSTL1 and MMP-9 in acute cerebral infarction (ACI) group were significantly higher than those in control group. However the HT group had a higher concentration of FSTL1 and MMP-9 than the non-HT group. The serum FSTL1 and MMP-9 were independent risk factors for hemorrhagic transformation. The area under the ROC curve of FSTL1 and MMP-9 in diagnosis of HT was 0.809 and 0.856 respectively, and their combined value was 0.923.

CONCLUSION

The high levels of FSTL1 and MMP-9 had strong correlation with HT in ACI patients.

A functional polymorphism at the miR‑491‑5p binding site in the 3'‑untranslated region of the MMP‑9 gene increases the risk of developing ventilator‑associated pneumonia

Matrix metalloproteinase (MMP)‑9 is associated with the severity of ventilator‑associated pneumonia (VAP), while an rs1056629 SNP located in the 3'‑untranslated region (UTR) of MMP‑9 affects the microRNA (miRNA/miR)‑491‑mediated regulation of MMP‑9 expression. In the present study, the effect of rs1056629 on the development of VAP in patients with chronic obstructive pulmonary disease (COPD) was investigated. Patients with COPD were enrolled in the study and their genotypes of rs1056629 (CC, CA or AA) were determined. ELISA was used to analyze the levels of TNF‑α and IL‑6 in the monocytes of patients with COPD carrying differential genotypes of rs1056629. Reverse transcription‑quantitative PCR was carried out to evaluate the expression of miR‑491 and MMP‑9 mRNA in the different groups of patients with COPD. Luciferase assay was used to confirm the inhibitory role of miR‑491 in MMP‑9 expression. Western blot analysis was carried out to assess the expression of MMP‑9 protein in A549 and H1299 cells transfected with miR‑491 mimics. The risk and severity of VAP were significantly elevated in patients with COPD carrying the CC and AC genotypes of rs1056629. Although there was no difference in the expression of miR‑491 in patients carrying different genotypes of rs1056629, the expression levels of TNF‑α, IL‑6 and MMP‑9 were increased in patients with COPD carrying the CC and AC genotypes of rs1056629. The results of luciferase assay revealed that miR‑491 inhibited the expression of MMP‑9 through direct binding to the 3'UTR of MMP‑9. Transfection of miR‑491 mimics into A549 and H1299 cells markedly suppressed the expression of MMP‑9 in a concentration‑dependent manner. On the whole, the findings of the present study confirm that the CC and AC genotypes of rs1056629 increase the risk of developing VAP in patients with COPD by increasing the expression of MMP‑9.

Vascular and immunopathological role of Asymmetric Dimethylarginine (ADMA) in Experimental Autoimmune Encephalomyelitis

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide synthase (NOS) inhibitor/uncoupler inducing vascular pathology. Vascular pathology is an important factor for the development and progression of CNS pathology of MS, yet the role of ADMA in MS remains elusive. Patients with multiple sclerosis (MS) are reported to have elevated blood levels of ADMA, and mice with experimental autoimmune encephalomyelitis (EAE, an animal model of MS) generated by auto-immunization of myelin oligodendrocyte glycoprotein (MOG) and blood-brain barrier (BBB) disruption by pertussis toxin also had increased blood ADMA levels in parallel with induction of clinical disease. To explore the role of ADMA in EAE pathogenesis, EAE mice were treated with a daily dose of ADMA. It is of special interest that ADMA treatment enhanced the BBB disruption in EAE mice and exacerbated the clinical and CNS disease of EAE. ADMA treatment also induced the BBB disruption and EAE disease in MOG-immunized mice even without pertussis toxin treatment, suggesting the role of ADMA in BBB dysfunction in EAE. T-cell polarization studies also documented that ADMA treatment promotes T_H 1- and T_H 17-mediated immune responses but without affecting Treg-mediated immune response in EAE mice as well as in in vitro T-cell culture. Taken together, these data, for the first time, document the vascular and immunopathogenic roles of ADMA in EAE, thus pointing to the potential of ADMA-mediated mechanism as a new target of potential therapy for MS.

Telocytes are major constituents of the angiogenic apparatus

The current study investigated role of telocytes (TCs) in angiogenesis during embryonic development of quail using immunohistochemistry (IHC), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The angiogenic apparatus consisted of TCs, endothelial cells, and macrophages. TCs were identified morphologically by their telopodes and podoms using TEM and SEM and immunohistochemically using CD34, and vascular endothelial growth factor (VEGF). TCs also expressed CD68. TCs formed a three-dimensional network and established direct contact with blood vessels, sprouting endothelial cells, and active macrophages, while exerting their effect through paracrine signaling. VEGF was also expressed by endothelial cells and macrophages. Matrix metalloproteinase–9 (MMP-9) was expressed by TCs, endothelial cells, and macrophages. In conclusion, the expression of VEGF by TCs, endothelial cells, and macrophages is required for the proliferation and migration of endothelial cells and vascular growth. The expression of MMP-9 by TCs, endothelial cells, and macrophages is essential for the degradation of extracellular matrix (ECM) components during neoangiogenesis. Macrophages may facilitate phagocytosis and elimination of the degraded ECM components.

Notoginsenoside R1 activates the Ang2/Tie2 pathway to promote angiogenesis

BACKGROUND

Therapeutic angiogenesis is a novel strategy for the treatment of ischemic diseases that involves promotion of angiogenesis in ischemic tissues via the use of proangiogenic agents. However, effective proangiogenic drugs that activate the Ang2/Tie2 signaling pathway remain scarce.

PURPOSE

We aimed to investigate the proangiogenic activity of notoginsenoside R1 (NR1) isolated from total saponins of Panax notoginseng with regard to activation of the Ang2/Tie2 signaling pathway.

METHODS

We examined the proangiogenic effects of NR1 by assessing the effects of NR1 on the proliferation, migration, invasion and tube formation of human umbilical vein endothelial cells (HUVECs). The aortic ring assay and vascular endothelial growth factor receptor inhibitor (VRI)-induced vascular regression in the zebrafish model were used to confirm the proangiogenic effects of NR1 ex vivo and in vivo. Furthermore, the molecular mechanism was investigated by Western blot analysis.

RESULTS

We found that NR1 promoted the proliferation, mobility and tube formation of HUVECs in vitro. NR1 also increased the number of sprouting vessels in rat aortic rings and rescued VRI-induced vascular regression in zebrafish. NR1-induced angiogenesis was dependent on Tie2 receptor activation mediated by increased autocrine Ang2 in HUVECs, and inhibition of the Ang2/Tie2 pathway abrogated the proangiogenic effects of NR1.

CONCLUSIONS

Our results suggest that NR1 promotes angiogenesis by activating the Ang2/Tie2 signaling pathway. Thus, NR1-induced activation of the Ang2/Tie2 pathway is an effective proangiogenic approach. NR1 may be useful agent for the treatment of ischemic diseases.

Mild hypoxia triggers transient blood-brain barrier disruption: a fundamental protective role for microglia

We recently demonstrated that when mice are exposed to chronic mild hypoxia (CMH, 8% O2), blood vessels in the spinal cord show transient vascular leak that is associated with clustering and activation of microglia around disrupted vessels. Importantly, microglial depletion profoundly increased hypoxia-induced vascular leak, implying that microglia play a critical role maintaining vascular integrity in the hypoxic spinal cord. The goal of the current study was to examine if microglia play a similar vasculo-protective function in the brain. Employing extravascular fibrinogen leak as an index of blood-brain barrier (BBB) disruption, we found that CMH provoked transient vascular leak in cerebral blood vessels that was associated with activation and aggregation of Mac-1-positive microglia around leaky vessels. Interestingly, CMH-induced vascular leak showed regional selectivity, being much more prevalent in the brainstem and olfactory bulb than the cerebral cortex and cerebellum. Pharmacological depletion of microglia with the colony stimulating factor-1 receptor inhibitor PLX5622, had no effect under normoxic conditions, but markedly increased hypoxia-induced cerebrovascular leak in all regions examined. As in the spinal cord, this was associated with endothelial induction of MECA-32, a marker of leaky CNS endothelium, and greater loss of endothelial tight junction proteins. Brain regions displaying the highest levels of hypoxic-induced vascular leak also showed the greatest levels of angiogenic remodeling, suggesting that transient BBB disruption may be an unwanted side-effect of hypoxic-induced angiogenic remodeling. As hypoxia is common to a multitude of human diseases including obstructive sleep apnea, lung disease, and age-related pulmonary, cardiac and cerebrovascular dysfunction, our findings have important translational implications. First, they point to a potential pathogenic role of chronic hypoxia in triggering BBB disruption and subsequent neurological dysfunction, and second, they demonstrate an important protective role for microglia in maintaining vascular integrity in the hypoxic brain.

Chemically defined human vascular laminins for biologically relevant culture of hiPSC-derived brain microvascular endothelial cells

BACKGROUND

In recent years, differentiation of human induced pluripotent stem cells (hiPSCs) into brain-specific microvascular endothelial cells (iBMECs) has frequently been used to model the blood-brain barrier (BBB). However, there are limitations in the use of iBMECs for in vitro studies, such as transendothelial electrical resistance (TEER) instability, weak junctional expression of VE-cadherin, and lack of proper fluid shear stress response. In vivo, the basement membrane (BM) composition of the BBB evolves throughout development, and laminins become the dominant component of the mature vascular BM. However, laminin isoforms of the endothelial BM have not been used for culture of differentiated iBMECs. The main goal of this study is to investigate the effect of different laminin isoforms of the endothelial BM on iBMEC functionality and to determine whether better recapitulation of the physiological BM in vitro can address the aforementioned limitations of iBMECs.

METHODS

Using a previously reported method, hiPSCs were differentiated into iBMECs. The influence of main laminins of the endothelial BM, LN 411 and LN 511, on iBMEC functionality was studied and compared to a collagen IV and fibronectin mixture (CN IV-FN). Quantitative RT-PCR, immunocytochemistry, and TEER measurement were utilized to assess gene and protein expression and barrier properties of iBMECs on different extracellular matrices. Single-channel microfluidic devices were used to study the effect of shear stress on iBMECs.

RESULTS

LN 511, but not LN 411, improved iBMEC barrier properties and resulted in more sustained TEER stability. Immunocytochemistry showed improved junctional protein expression compared to iBMECs cultured on CN IV-FN. iBMECs cultured on LN 511 showed a reduction of stress fibers, indicating resting endothelial phenotype, whereas gene expression analysis revealed upregulation of multiple genes involved in endothelial activation in iBMECs on CN IV-FN. Finally, culturing iBMECs on LN 511 enhanced physiological responses to shear stress, including morphological changes and enhanced junctional protein association.

CONCLUSION

LN 511 improves the functionality and long-term barrier stability of iBMECs. Our findings suggest that incorporation of physiologically relevant LN 511 in iBMEC culture would be beneficial for disease modeling applications and BBB-on-a-chip platforms that accommodate fluid flow.

Heavy Metal-Induced Cerebral Small Vessel Disease: Insights into Molecular Mechanisms and Possible Reversal Strategies

Heavy metals are considered a continuous threat to humanity, as they cannot be eradicated. Prolonged exposure to heavy metals/metalloids in humans has been associated with several health risks, including neurodegeneration, vascular dysfunction, metabolic disorders, cancer, etc. Small blood vessels are highly vulnerable to heavy metals as they are directly exposed to the blood circulatory system, which has comparatively higher concentration of heavy metals than other organs. Cerebral small vessel disease (CSVD) is an umbrella term used to describe various pathological processes that affect the cerebral small blood vessels and is accepted as a primary contributor in associated disorders, such as dementia, cognitive disabilities, mood disorder, and ischemic, as well as a hemorrhagic stroke. In this review, we discuss the possible implication of heavy metals/metalloid exposure in CSVD and its associated disorders based on in-vitro, preclinical, and clinical evidences. We briefly discuss the CSVD, prevalence, epidemiology, and risk factors for development such as genetic, traditional, and environmental factors. Toxic effects of specific heavy metal/metalloid intoxication (As, Cd, Pb, Hg, and Cu) in the small vessel associated endothelium and vascular dysfunction too have been reviewed. An attempt has been made to highlight the possible molecular mechanism involved in the pathophysiology, such as oxidative stress, inflammatory pathway, matrix metalloproteinases (MMPs) expression, and amyloid angiopathy in the CSVD and related disorders. Finally, we discussed the role of cellular antioxidant defense enzymes to neutralize the toxic effect, and also highlighted the potential reversal strategies to combat heavy metal-induced vascular changes. In conclusion, heavy metals in small vessels are strongly associated with the development as well as the progression of CSVD. Chelation therapy may be an effective strategy to reduce the toxic metal load and the associated complications.

Hypercapnia Exacerbates the Blood-Brain Barrier Disruption Via Promoting HIF-1a Nuclear Translocation in the Astrocytes of the Hippocampus: Implication in Further Cognitive Impairment in Hypoxemic Adult Rats

Hypercapnia in combination with hypoxemia is usually present in severe respiratory disease in the intensive care unit (ICU) and can lead to more severe cognitive dysfunction. Increasing evidence has indicated that the compromised blood–brain barrier (BBB) in the hippocampus in hypoxemia conditions can result in cognitive dysfunction. However, the role and underlying mechanism of hypercapnia in the BBB disruption remains poorly known. A rat model of hypercapnia was first established in this study by intubation and mechanical ventilation with a small-animal ventilator. After this, the cognitive function of the experimental rats was assessed by the Morris water maze test. The BBB permeability was evaluated by the Evans Blue (EB) test and brain water content (BWC). Western blot analysis was carried out to detect the protein expressions of total and nuclear hypoxia-inducible factor-1α (HIF-1α), matrixmetalloproteinase-9 (MMP-9) and Aquaporins-4 (AQP-4) in the hippocampus tissue. Double immunofluorescence further verified the protein expression of different biomarkers was localized in the astrocytes of the hippocampus. Hypercapnia alone did not disrupt the BBB, but it could further enhance the BBB permeability in hypoxemia. Concomitantly, up-regulation of nuclear HIF-1α, AQP-4, MMP-9 protein expression along with increased degradation of the occludin and claudin-5 proteins was found in the hypercapnia rat model, while the total HIF-1α remained unchanged. Interestingly, these changes were independent of the acidosis induced by hypercapnia. Of note, after premedication of 2-Methoxyestradiol (2ME2, an inhibitor of HIF-1α nuclear translocation), the disrupted BBB could be restored resulting in improvement of the cognitive impairment. Meanwhile, accumulation of nuclear HIF-1α, protein expression of AQP-4 and MMP-9 and protein degradation of the occludin and claudin-5 were decreased. Thus, our study demonstrated that hypercapnia can further disrupt the BBB through promoting HIF-1α nuclear translocation and up-regulation of AQP-4 and MMP-9 in hypoxemia. It is therefore suggested that the cascade of hypercapnia-induced nuclear HIF-1α protein translocation in hypoxia-activated astrocytes may be a potential target for ameliorating cognitive impairment.

The correlation between hypoxia-inducible factor-1α, matrix metalloproteinase-9 and functional recovery following chronic spinal cord compression

The molecular mechanisms underlying cervical spondylotic myelopathy (CSM) are poorly understood. To assess the correlation between HIF-1α, MMP-9 and functional recovery following chronic cervical spinal cord compression (CSCI). Rats in the sham group underwent C5 semi-laminectomy, while a water-absorbable polyurethane polymer was implanted into the C6 epidural space in the chronic CSCI group. Basso, Beattie and Bresnahan score and somatosensory evoked potentials were used to evaluate neurological function. Hematoxylin and eosin staining was performed to assess pathological changes in the spinal cord, while immunohistochemical analysis was used to examine HIF-1α and MMP-9 expression on days 7, 28, 42 and 70 post-surgery. Normal rats were only used for HE staining. The BBB score was significantly reduced on day 28 following CSCI, while SEPs exhibited decreased amplitude and increased latency. In chronic CSCI group, the BBB score and SEPs significantly improved on day 70 compared with day 28. HE staining revealed different level of spinal cord edema after chronic CSCI. Compared with the sham group, immunohistochemical analyses revealed that HIF-1α- and MMP-9-positive cells were increased on day 7 and peaked on day 28. HIF-1α and MMP-9 expression were demonstrated to be significantly positively correlated, whereas HIF-1α expression and BBB score were significantly negatively correlated, as well MMP-9 expression and BBB score. HIF-1α and MMP-9 expression are increased following chronic spinal cord compression and are positively correlated with one another. Decreased expression of HIF-1α and MMP-9 may contribute to functional recovery following CSCI. This expression pattern of HIF-1α and MMP-9 may give a new perspective on the molecular mechanisms of CSM.

Ginsenoside F1 promotes angiogenesis by activating the IGF-1/IGF1R pathway

Ischemic stroke is one of the most lethal and highly disabling diseases that seriously affects the human health and quality of life. A therapeutic angiogenic strategy has been proposed to alleviate ischemia-induced injury by promoting angiogenesis and improving cerebrovascular function in the ischemic regions. The insulin-like growth factor 1 (IGF-1)/insulin-like growth factor 1 receptor (IGF1R) axis is crucial for cerebral angiogenesis and neurogenesis. However, effective drugs that prevent cerebral ischemic injury by inducing cerebral angiogenesis via activation of the IGF1R pathway are lacking. Here, we screened a pro-angiogenic agent ginsenoside F1 (GF1), a ginseng saponin isolated from a traditional Chinese medicine that was widely used in ischemic stroke treatment. It promoted the proliferation, mobility and tube formation of human umbilical vein endothelial cells and human brain microvascular endothelial cells, as well as pericytes recruitment to the endothelial tubes. GF1 stimulated vessel sprouting in the rat arterial ring and facilitated neovascularization in chicken embryo chorioallantoic membrane (CAM). In the in vivo experiments, GF1 rescued the axitinib-induced vascular defect in zebrafish. It also increased the microvessel density (MVD) and improved focal cerebral blood perfusion in the rat middle cerebral artery occlusion (MCAO) model. Mechanism studies revealed that GF1-induced angiogenesis depended on IGF1R activation mediated by the autocrine IGF-1 loop in endothelial cells. Based on our findings, GF1-induced activation of the IGF-1/IGF1R pathway to promote angiogenesis is an effective approach to alleviate cerebral ischemia, and GF1 is a potential agent that improves cerebrovascular function and promotes recovery from ischemic stroke.

Molecular mechanisms of IL-33-mediated stromal interactions in cancer metastasis

Molecular mechanisms underlying the cancer stroma in metastasis need further exploration. Here, we discovered that cancer-associated fibroblasts (CAFs) produced high levels of IL-33 that acted on tumor-associated macrophages (TAMs), causing them to undergo the M1 to M2 transition. Genomic profiling of metastasis-related genes in the IL-33-stimulated TAMs showed a >200-fold increase of MMP9. Signaling analysis demonstrated the IL-33-ST2-NF-κB-MMP9-laminin pathway that governed tumor stroma-mediated metastasis. In mouse and human fibroblast-rich pancreatic cancers, genetic deletion of IL-33, ST2, or MMP9 markedly blocked metastasis. Pharmacological inhibition of NF-κB and MMP9 also blocked cancer metastasis. Deletion of IL-33, ST2, or MMP9 restored laminin, a key basement membrane component associated with tumor microvessels. Together, our data provide mechanistic insights on the IL-33-NF-κB-MMP9-laminin axis that mediates the CAF-TAM-committed cancer metastasis. Thus, targeting the CAF-TAM-vessel axis provides an outstanding therapeutic opportunity for cancer treatment.

Delayed Administration of BQ788, an ETB Antagonist, after Experimental Traumatic Brain Injury Promotes Recovery of Blood-Brain Barrier Function and a Reduction of Cerebral Edema in Mice

Traumatic brain injury (TBI) is induced by immediate physical disruption of brain tissue, and causes death and disability. Studies on experimental TBI animal models show that disruption of the blood-brain barrier (BBB) underlies brain edema and neuroinflammation during the delayed phase of TBI. In neurological disorders, endothelin-1 (ET-1) is involved in BBB dysfunction and brain edema. In this study, the effect of ET antagonists on BBB dysfunction and brain edema were examined in a mouse focal TBI model using lateral fluid percussion injury (FPI). ET-1 and ET_B receptors were increased at 2-7 days after FPI, which was accompanied by extravasation of Evans blue (EB) and brain edema. Repeated intracerebroventricular administration of BQ788 (15 nmol/day), an ET_B antagonist, from 2 days after FPI promoted recovery of EB extravasation and brain edema, while FR 139317, an ET_A antagonist, had no effect. Delayed intravenous administration of BQ788 also promoted recovery from FPI-induced EB extravasation and brain edema. While FPI caused decreases in claudin-5, occludin, and zonula occludens-1 proteins, BQ788 reversed FPI-induced reductions of them. Immunohistochemical observation of the cerebrum after FPI showed that ET_B receptors are predominantly expressed in glial fibrillary acidic protein (GFAP)-positive astrocytes. BQ788 reduced FPI-induced increases in GFAP-positive astrocytes. GFAP-positive astrocytes produced vascular endothelial growth factor-A (VEGF-A) and matrix metalloproteinase-9 (MMP9). FPI-induced increases in VEGF-A and MMP-9 production were reversed by BQ788. These results suggest that ET_B receptor antagonism during the delayed phase of focal TBI promotes recovery of BBB function and reduction of brain edema.

Neurovascular Alterations in Alzheimer's Disease: Transporter Expression Profiles and CNS Drug Access

Despite a century of steady and incremental progress toward understanding the underlying biochemical mechanisms, Alzheimer's disease (AD) remains a complicated and enigmatic disease, and greater insight will be necessary before substantive clinical success is realised. Over the last decade in particular, a large body of work has highlighted the cerebral microvasculature as an anatomical region with an increasingly apparent role in the pathogenesis of AD. The causative interplay and temporal cascade that manifest between the brain vasculature and the wider disease progression of AD are not yet fully understood, and further inquiry is required to properly characterise these relationships. The purpose of this review is to highlight the recent advancements in research implicating neurovascular factors in AD, at both the molecular and anatomical levels. We begin with a brief introduction of the biochemical and genetic aspects of AD, before reviewing the essential concepts of the blood-brain barrier (BBB) and the neurovascular unit (NVU). In detail, we then examine the evidence demonstrating involvement of BBB dysfunction in AD pathogenesis, highlighting the importance of neurovascular components in AD. Lastly, we include within this review research that focuses on how altered properties of the BBB in AD impact upon CNS exposure of therapeutic agents and the potential clinical impact that this may have on people with this disease.

Tongxinluo Reverses the Hypoxia-suppressed Claudin-9 in Cardiac Microvascular Endothelial Cells

Background:

Claudin-5, claudin-9, and claudin-11 are expressed in endothelial cells to constitute tight junctions, and their deficiency may lead to hyperpermeability, which is the initiating process and pathological basis of cardiovascular disease. Although tongxinluo (TXL) has satisfactory antianginal effects, whether and how it modulates claudin-5, claudin-9, and claudin-11 in hypoxia-stimulated human cardiac microvascular endothelial cells (HCMECs) have not been reported.

Methods:

In this study, HCMECs were stimulated with CoCl₂ to mimic hypoxia and treated with TXL. First, the messenger RNA (mRNA) expression of claudin-5, claudin-9, and claudin-11 was confirmed. Then, the protein content and distribution of claudin-9, as well as cell morphological changes were evaluated after TXL treatment. Furthermore, the distribution and content histone H3K9 acetylation (H3K9ac) in the claudin-9 gene promoter, which guarantees transcriptional activation, were examined to explore the underlying mechanism, by which TXL up-regulates claudin-9 in hypoxia-stimulated HCMECs.

Results:

We found that hypoxia-suppressed claudin-9 gene expression in HCMECs (F = 7.244; P = 0.011) and the hypoxia-suppressed claudin-9 could be reversed by TXL (F = 61.911; P = 0.000), which was verified by its protein content changes (F = 29.142; P = 0.000). Moreover, high-dose TXL promoted the cytomembrane localization of claudin-9 in hypoxia-stimulated HCMECs, with attenuation of cell injury. Furthermore, high-dose TXL elevated the hypoxia-inhibited H3K9ac in the claudin-9 gene promoter (F = 37.766; P = 0.000), activating claudin-9 transcription.

Conclusions:

The results manifested that TXL reversed the hypoxia-suppressed claudin-9 by elevating H3K9ac in its gene promoter, playing protective roles in HCMECs.

Propofol protects against blood-spinal cord barrier disruption induced by ischemia/reperfusion injury

Propofol has been shown to exert neuroprotective effects on the injured spinal cord. However, the effect of propofol on the blood-spinal cord barrier (BSCB) after ischemia/reperfusion injury (IRI) is poorly understood. Therefore, we investigated whether propofol could maintain the integrity of the BSCB. Spinal cord IRI (SCIRI) was induced in rabbits by infrarenal aortic occlusion for 30 minutes. Propofol, 30 mg/kg, was intravenously infused 10 minutes before aortic clamping as well as at the onset of reperfusion. Then, 48 hours later, we performed histological and mRNA/protein analyses of the spinal cord. Propofol decreased histological damage to the spinal cord, attenuated the reduction in BSCB permeability, downregulated the mRNA and protein expression levels of matrix metalloprotease-9 (MMP-9) and nuclear factor-κB (NF-κB), and upregulated the protein expression levels of occludin and claudin-5. Our findings suggest that propofol helps maintain BSCB integrity after SCIRI by reducing MMP-9 expression, by inhibiting the NF-κB signaling pathway, and by maintaining expression of tight junction proteins.

Extracellular Matrix, a Hard Player in Angiogenesis

The extracellular matrix (ECM) is a complex network of proteins, glycoproteins, proteoglycans, and polysaccharides. Through multiple interactions with each other and the cell surface receptors, not only the ECM determines the physical and mechanical properties of the tissues, but also profoundly influences cell behavior and many physiological and pathological processes. One of the functions that have been extensively explored is its impingement on angiogenesis. The strong impact of the ECM in this context is both direct and indirect by virtue of its ability to interact and/or store several growth factors and cytokines. The aim of this review is to provide some examples of the complex molecular mechanisms that are elicited by these molecules in promoting or weakening the angiogenic processes. The scenario is intricate, since matrix remodeling often generates fragments displaying opposite effects compared to those exerted by the whole molecules. Thus, the balance will tilt towards angiogenesis or angiostasis depending on the relative expression of pro- or anti-angiogenetic molecules/fragments composing the matrix of a given tissue. One of the vital aspects of this field of research is that, for its endogenous nature, the ECM can be viewed as a reservoir to draw from for the development of new more efficacious therapies to treat angiogenesis-dependent pathologies.

Deficiency in matrix metalloproteinase-2 results in long-term vascular instability and regression in the injured mouse spinal cord

Angiogenesis plays a critical role in wound healing after spinal cord injury. Therefore, understanding the events that regulate angiogenesis has considerable relevance from a therapeutic standpoint. We evaluated the contribution of matrix metalloproteinase (MMP)-2 to angiogenesis and vascular stability in spinal cord injured MMP-2 knockout and wildtype (WT) littermates. While MMP-2 deficiency resulted in reduced endothelial cell division within the lesioned epicenter, there were no genotypic differences in vascularity (vascular density, vascular area, and endothelial cell number) over the first two weeks post-injury. However, by 21days post-injury MMP-2 deficiency resulted in a sharp decline in vascularity, indicative of vascular regression. Complementary in vitro studies of brain capillary endothelial cells confirmed MMP-2 dependent proliferation and tube formation. As deficiency in MMP-2 led to prolonged MMP-9 expression in the injured spinal cord, we examined both short-term and long-term exposure to MMP-9 in vitro. While MMP-9 supported endothelial tube formation and proliferation, prolonged exposure resulted in loss of tubes, findings consistent with vascular regression. Vascular instability is frequently associated with pericyte dissociation and precedes vascular regression. Quantification of PDGFrβ+ pericyte coverage of mature vessels within the glial scar (the reactive gliosis zone), a known source of MMP-9, revealed reduced coverage in MMP-2 deficient animals. These findings suggest that acting in the absence of MMP-2, MMP-9 transiently supports angiogenesis during the early phase of wound healing while its prolonged expression leads to vascular instability and regression. These findings should be considered while developing therapeutic interventions that block MMPs.