Gradual Suppression of Transcytosis Governs Functional Blood-Retinal Barrier Formation

Interaction of major facilitator superfamily domain containing 2A with the blood-brain barrier

The functional and structural integrity of the blood-brain barrier is crucial in maintaining homeostasis in the brain microenvironment; however, the molecular mechanisms underlying the formation and function of the blood-brain barrier remain poorly understood. The major facilitator superfamily domain containing 2A has been identified as a key regulator of blood-brain barrier function. It plays a critical role in promoting and maintaining the formation and functional stability of the blood-brain barrier, in addition to the transport of lipids, such as docosahexaenoic acid, across the blood-brain barrier. Furthermore, an increasing number of studies have suggested that major facilitator superfamily domain containing 2A is involved in the molecular mechanisms of blood-brain barrier dysfunction in a variety of neurological diseases; however, little is known regarding the mechanisms by which major facilitator superfamily domain containing 2A affects the blood-brain barrier. This paper provides a comprehensive and systematic review of the close relationship between major facilitator superfamily domain containing 2A proteins and the blood-brain barrier, including their basic structures and functions, cross-linking between major facilitator superfamily domain containing 2A and the blood-brain barrier, and the in-depth studies on lipid transport and the regulation of blood-brain barrier permeability. This comprehensive systematic review contributes to an in-depth understanding of the important role of major facilitator superfamily domain containing 2A proteins in maintaining the structure and function of the blood-brain barrier and the research progress to date. This will not only help to elucidate the pathogenesis of neurological diseases, improve the accuracy of laboratory diagnosis, and optimize clinical treatment strategies, but it may also play an important role in prognostic monitoring. In addition, the effects of major facilitator superfamily domain containing 2A on blood-brain barrier leakage in various diseases and the research progress on cross-blood-brain barrier drug delivery are summarized. This review may contribute to the development of new approaches for the treatment of neurological diseases.

Huang-Lian-Jie-Du decoction inhibits CD4+ T cell infiltration into CNS in MCAO rats by regulating BBB

BACKGROUND

Stroke, especially ischemic stroke (IS), represents a major global health challenge due to its high incidence, disability, mortality, recurrence, and economic impact. The limited therapeutic window for thrombolysis underscores the need for new treatments. The blood-brain barrier (BBB), which protects the brain, becomes compromised following ischemia-reperfusion injury, allowing peripheral immune cell infiltration and subsequent neuroinflammation. Huang-Lian-Jie-Du Decoction (HLJDT), a traditional formula with significant neuroprotective effects demonstrated in preliminary studies and literature reviews, has not yet been fully explored for its potential to inhibit peripheral immune cell infiltration through BBB protection.

PURPOSE

This study aims to: (1) Evaluate the efficacy of HLJDT in treating MCAO. (2) Observe the regulatory effect of HLJDT on the infiltration of CD4+ T cells into the central nervous system. (3) Investigate the effect of HLJDT on the Wnt/β-Catenin Signaling Pathway.

METHODS

A focal MCAO reperfusion model will be used to evaluate HLJDT's effects on neurological function (Zea Longa and Garcia scores), infarction volume (TTC staining), and pathological changes (HE and NISSL staining). Immune-inflammatory responses will be assessed using ELISA for cytokines, flow cytometry for T lymphocyte distribution, and immunofluorescence staining for CD4+ T cell infiltration. The interaction of T cell antigens (LFA-1) and endothelial adhesion molecules (ICAM-1) will be studied with ELISA and immunofluorescence. BBB protection will be evaluated with Evans blue staining and transmission electron microscopy. Mechanisms of T cell infiltration will be examined using transmission electron microscopy and Western blotting (WB) for key proteins. Additionally, the impact of HLJDT on the Wnt/β-catenin pathway will be assessed with WB.

RESULTS

HLJDT significantly improves neurological scores, reduces infarction volume, and mitigates pathological damage. It balances CD4+ T cell responses by inhibiting pro-inflammatory cytokines and enhancing anti-inflammatory ones, reducing CD4+ T cell CNS infiltration. HLJDT inhibits LFA-1/ICAM-1 interactions. It can also inhibit CD4+ T cell infiltration by repairing paracellular and transcellular structures of the BBB, with the Wnt/β-catenin signaling pathway playing a key role in this process.

CONCLUSION

We have innovatively demonstrated for the first time that HLJDT can regulate the balance between peripheral and central immune inflammation. It inhibits LFA-1/ICAM-1-mediated cell adhesion and, by modulating the Wnt/β-catenin pathway, improves the paracellular and transcellular structures of the blood-brain barrier, thereby suppressing CD4+ T cell infiltration and providing multifaceted protective effects for MCAO rats.

Exploring Endothelial Cell Dysfunction's Impact on the Brain-Retina Microenvironment Connection: Molecular Mechanisms and Implications

The intricate linking between the health of blood vessels and the functioning of neurons has attracted growing attention in the context of disorders that affect the neurological environment. Endothelial cells, forming the blood-brain barrier and blood-retinal barrier, play a fundamental role in maintaining the integrity of the brain-retina microenvironment connection. This review explores the molecular foundations of endothelial cell dysfunction and its implications for the brain-retina interaction. A comprehensive analysis of the complex factors contributing to endothelial dysfunction is presented, including oxidative stress, inflammation, reduced nitric oxide signaling, and disrupted vascular autoregulation. The significance of endothelial dysfunction extends to neurovascular coupling, synaptic plasticity, and trophic support. To our knowledge, there is currently no existing literature review addressing endothelial microvascular dysfunction and its interplay with the brain-retina microenvironment. The review also explains bidirectional communication between the brain and retina, highlighting how compromised endothelial function can disrupt this vital crosstalk and inhibit normal physiological processes. As neurodegenerative diseases frequently exhibit vascular involvement, a deeper comprehension of the interaction between endothelial cells and neural tissue holds promise for innovative therapeutic strategies. By targeting endothelial dysfunction, we may enhance our ability to preserve the intricate dynamics of the brain-retina microenvironment connection and ameliorate the progression of neurological disorders.

The Blood-Brain Barrier: Composition, Properties, and Roles in Brain Health

Blood vessels are critical to deliver oxygen and nutrients to tissues and organs throughout the body. The blood vessels that vascularize the central nervous system (CNS) possess unique properties, termed the blood-brain barrier (BBB), which allow these vessels to tightly regulate the movement of ions, molecules, and cells between the blood and the brain. This precise control of CNS homeostasis allows for proper neuronal function and protects the neural tissue from toxins and pathogens, and alterations of this barrier are important components of the pathogenesis and progression of various neurological diseases. The physiological barrier is coordinated by a series of physical, transport, and metabolic properties possessed by the brain endothelial cells (ECs) that form the walls of the blood vessels. These properties are regulated by interactions between different vascular, perivascular, immune, and neural cells. Understanding how these cell populations interact to regulate barrier properties is essential for understanding how the brain functions in both health and disease contexts.

The role of transcytosis in the blood-retina barrier: from pathophysiological functions to drug delivery

The blood-retina barrier (BRB) serves as a critical interface that separates the retina from the circulatory system, playing an essential role in preserving the homeostasis of the microenvironment within the retina. Specialized tight junctions and limited vesicle trafficking restrict paracellular and transcellular transport, respectively, thereby maintaining BRB barrier properties. Additionally, transcytosis of macromolecules through retinal vascular endothelial cells constitutes a primary mechanism for transporting substances from the vascular compartment into the surrounding tissue. This review summarizes the fundamental aspects of transcytosis including its function in the healthy retina, the biochemical properties of transcytosis, and the methodologies used to study this process. Furthermore, we discuss the current understanding of transcytosis in the context of pathological BRB breakdown and present recent findings that highlight significant advances in drug delivery to the retina based on transcytosis.

LRG1 Alters Pericyte Phenotype and Compromises Vascular Maturation

Upregulation of leucine-rich alpha-2-glycoprotein-1 (LRG1) contributes to aberrant neovascularization in many different diseases. In contrast, LRG1 is not involved in developmental angiogenesis. Here, we investigated the vasculopathic properties of LRG1 by examining its effect on developing retinal blood vessels. By injecting recombinant protein or an expression vector into the mouse retina during vascular development, we showed that exogenous LRG1 reduces pericyte coverage and NG2 expression. It leads to diminished collagen IV sheathing, fewer adhesion and gap junctions, and reduced vessel calibre and vascular density. Moreover, in mouse retinae containing exogenous LRG1, the developing blood-retinal barrier remains more permeable with significantly higher numbers of transcytotic vesicles present in microvascular endothelial cells. These results reveal that exogeneous LRG1 is sufficient to interfere with the maturation of developing retinal vessels and drive vessel development towards a dysfunctional phenotype. These observations deliver further evidence that LRG1 is an angiopathic factor and highlight the therapeutic potential of blocking LRG1 in diseases characterized by pathogenic angiogenesis or vascular remodelling.

Transcytosis of LDL Across Arterial Endothelium: Mechanisms and Therapeutic Targets

Transport of LDL (low-density lipoprotein) from plasma to arterial intima is thought to be rate limiting in the development of atherosclerosis. Its variation likely determines where lesions develop within arteries and might account for some of the currently unexplained difference in disease susceptibility between individuals. It may also be critical in the development of lipid-rich, unstable plaques. Mechanisms have been controversial but recent evidence suggests that caveolar transcytosis across endothelial cells is the dominant pathway. Receptors involved are LDLR (LDL receptor), SR-B1 (scavenger receptor class B type 1), and ALK1 (activin receptor-like kinase 1). The role of LDLR is influenced by IL-1β (interleukin-1β); the role of SR-B1 by HDL (high-density lipoprotein), DOCK4 (dedicator of cytokinesis 4), GPER (G-protein-coupled estrogen receptor), and HMGB1 (high mobility group box 1); and the role of ALK1 by BMP (bone morphogenetic protein) 9. Additionally, BMP4 stimulates transcytosis and FSTL1 (follistatin-like 1 protein) inhibits it. Fundamental transcytotic mechanisms include caveola formation, undocking, trafficking, and docking; they are influenced by cholesterol-lowering agents, MYDGF (myeloid-derived growth factor), MFSD2a (major facilitator superfamily domain containing 2a) in the blood-brain barrier, and inhibitors of dynamin-2 and tubulin polymerization. The relative merits of different therapeutic approaches are discussed, with statins, colchicine, benzimidazoles, and metformin being existing drugs that might be repurposed and salidroside and glycyrrhizic acid being nutraceuticals worth investigating. Finally, we discuss evidence against the ferry-boat model of transcytosis, the contributions of receptor-mediated, fluid-phase, and active transcytosis, and where inhibition of transcytosis might be most beneficial.

In vivo and In vitro assessment of the retinal toxicity of polystyrene nanoplastics

Plastic pollution has emerged as a critical global environmental challenge, yet the effects of the ingested plastic particles on ocular health remain largely unexplored. In this study, we investigated the impact of orally ingested polystyrene nanoplastics (PS-NPs) on the mouse retina. The in vivo experimental results showed that PS-NPs could penetrate the mouse retina within 2 h after gavage. Their levels increased at 4 h and remained detectable up to 24 h post-gavage. Prolonged exposure (28 days) to PS-NPs might disrupt the tight junctions of the inner blood-retinal barrier (iBRB). Moreover, PS-NPs induced oxidative stress in the retina by downregulating the expression of Nrf2 and HO-1, and potentially promoted apoptosis via the upregulation of Cleaved caspase 3. Additionally, we used human retinal microvascular endothelial cells (HRMECs) to model the iBRB and employed a human retinal pigment epithelial cell line (ARPE-19) to assess the potential toxicity of PS-NPs on the human retina. Our results indicated that PS-NPs penetrated and disrupted the simulated iBRB, inducing oxidative stress and promoting apoptosis in ARPE-19 cells. This study provides critical insights into the potential risks of ingested PS-NPs to retinal health and offers novel perspectives on the broader implications of plastic pollution for humans.

Caveolae-Mediated Transcytosis and Its Role in Neurological Disorders

The blood-brain barrier (BBB) controls the flow of substances to maintain a homeostatic environment in the brain, which is highly regulated and crucial for the normal function of the central nervous system (CNS). Brain endothelial cells (bECs), which are directly exposed to blood, play the most important role in maintaining the integrity of the BBB. Unlike endothelial cells in other tissues, bECs have two unique features: specialized endothelial tight junctions and actively suppressed transcellular vesicle trafficking (transcytosis). These features help to maintain the relatively low permeability of the CNS barrier. In addition to the predominant role of tight junctions in the BBB, caveolae-mediated adsorptive transcytosis has attracted much interest in recent years. The active suppression of transcytosis is dynamically regulated during development and in response to diseases. Altered caveolae-mediated transcytosis of bECs has been reported in several neurological diseases, but the understanding of this process in bECs is limited. Here, we review the process of caveolae-mediated transcytosis based on previous studies and discuss its function in the breakdown of the BBB in neurological disorders.

Canonical Wnt Signaling Suppresses Brain Endothelial Cell Transcytosis to Maintain Blood-Brain Barrier Integrity

Canonical Wnt signaling is essential for blood-brain barrier (BBB) development and maintenance. However, the subcellular mechanisms underlying this critical regulation have remained elusive. In this study, we use a physiological paradigm examining an early phase of acutely attenuated canonical Wnt signaling in adult brain endothelial cells (ECs) to investigate how the pathway regulates BBB integrity. Following canonical Wnt signaling attenuation via EC-specific knockout of β-catenin, we find that there is increased transcytosis in brain ECs, including a striking diversity of morphologically distinct vesicles, indicating multiple pathways are involved. In addition, we find that although the molecular composition of tight junctions (TJs) is altered following canonical Wnt signaling attenuation, such that Claudin-5 and ZO-1 expression is downregulated, TJs remain impermeable to molecules as small as 1.9 kDa. These findings reveal previously underappreciated role of Wnt signaling in regulating brain EC transcytosis and help illuminate subcellular mechanisms of BBB maintenance in adulthood, which is crucial for improving delivery of therapeutics to the brain.

A Brain Endothelial Cell Caveolin-1/CXCL10 Axis Promotes T Cell Transcellular Migration Across the Blood-Brain Barrier

The mechanisms that govern whether T cells cross blood-brain barrier (BBB) endothelium by transcellular versus paracellular routes are unclear. Caveolin-1 is a membrane scaffolding and signaling protein associated with transcellular transmigration through the endothelial cytoplasm. Here, we report that the neuroinflammatory chemokine CXCL10 induced transcellular, caveolar transmigration of CXCR3+ CD4+ T cells. Specifically, data revealed that CXCL10-induced transcellular transmigration requires expression of Caveolin-1 and ICAM-1 in brain endothelial cells and of the CXCL10 receptor, CXCR3, and LFA-1 in T cells. Moreover, Caveolin-1 promoted CXCL10 aggregation into brain endothelial cytoplasmic stores, providing a mechanism for activation and recruitment of CXCR3+ T cells to migrate at cytoplasmic locations, distal to cell-cell junctions. Consistent with our in vitro data, genetic ablation of Caveolin-1 reduces infiltration of CXCR3+ CD4+ T cells into the CNS in experimental autoimmune encephalomyelitis. Our findings establish a novel mechanism by which brain endothelial cells utilize Caveolin-1 dependent CXCL10 intracellular stores to license T cells for transcellular migration across the blood-brain barrier.

Neurovascular unit impairment in iron deficiency anemia

Iron is one of the crucial elements for CNS development and function and its deficiency (ID) is the most common worldwide nutrient deficit in the world. Iron deficiency anemia (IDA) in pregnant women and infants is a worldwide health problem due to its high prevalence and its irreversible long-lasting effects on brain development. Even with iron supplementation, IDA during pregnancy and/or breastfeeding can result in irreversible cognitive, motor, and behavioral impairments. The neurovascular unit (NVU) plays an important role in iron transport within the CNS as well as in the blood brain-barrier (BBB) formation and maturation, vasculogenesis/angiogenesis, neurovascular coupling and metabolic waste clearance. In animal models of IDA, significant changes have been observed at the capillary level, including alterations in iron transport, vasculogenesis, astrocyte endfeet, and pericytes. Despite these findings, the role of the NVU in IDA remains poorly understood. This review summarizes the potential effects of ID/IDA on brain development, myelination and neuronal function and discusses the role of NVU cells in iron metabolism, BBB, vasculogenesis/angiogenesis, neurovascular coupling and metabolic waste clearance. Furthermore, it emphasizes the need to view the NVU as a whole and as a potential target for ID/IDA. However, it remains unclear to what extent NVU alterations contribute to neuronal dysfunction, myelination abnormalities, and synaptic disturbances described in IDA.

Xixin Decoction's novel mechanism for alleviating Alzheimer's disease cognitive dysfunction by modulating amyloid-β transport across the blood-brain barrier to reduce neuroinflammation

Purpose

Xixin Decoction (XXD) is a classical formula that has been used to effectively treat dementia for over 300 years. Modern clinical studies have demonstrated its significant therapeutic effects in treating Alzheimer's disease (AD) without notable adverse reactions. Nevertheless, the specific mechanisms underlying its efficacy remain to be elucidated. This investigation sought to elucidate XXD's impact on various aspects of AD pathology, including blood-brain barrier (BBB) impairment, neuroinflammatory processes, and amyloid-β (Aβ) deposition, as well as the molecular pathways involved in these effects.

Methods

In vitro experiments were conducted using hCMEC/D3 and HBVP cell coculture to establish an in vitro blood-brain barrier (BBB) model. BBB damage was induced in this model by 24-h exposure to 1 μg/mL lipopolysaccharide (LPS). After 24, 48, and 72 h of treatment with 10% XXD-medicated serum, the effects of XXD were assessed through Western blotting, RT-PCR, and immunofluorescence techniques. In vivo, SAMP8 mice were administered various doses of XXD via gavage for 8 weeks, including high-dose XXD group (H-XXD) at 5.07 g kg-1·d-1, medium-dose XXD group (M-XXD) at 2.535 g kg-1·d-1, and low-dose XXD group (L-XXD) at 1.2675 g kg-1·d-1. Cognitive function was subsequently evaluated using the Morris water maze test. BBB integrity was evaluated using Evans blue staining, and protein expression levels were analyzed via ELISA, Western blotting, and immunofluorescence.

Results

In vitro experiments revealed that XXD-containing serum, when cultured for 24, 48, and 72 h, could upregulate the expression of P-gp mRNA and protein, downregulate CB1 protein expression, and upregulate CB2 and Mfsd2a protein expression. In vivo studies demonstrated that XXD improved spatial learning and memory abilities in SAMP8 mice, reduced the amount of Evans blue extravasation in brain tissues, modulated the BBB-associated P-gp/ECS axis, RAGE/LRP1 receptor system, as well as MRP2 and Mfsd2a proteins, and decreased the accumulation of Aβ in the brains of SAMP8 mice. Additionally, XXD upregulated the expression of TREM2, downregulated IBA1, TLR1, TLR2, and CMPK2 expression, and reduced the levels of pro-inflammatory factors NLRP3, NF-κB p65, COX-2, TNF-α, and IL-1β in the hippocampal tissues.

Conclusion

XXD may exert its effects by regulating the P-gp/ECS axis, the RAGE/LRP1 receptor system, and the expression of MRP2 and Mfsd2a proteins, thereby modulating the transport function of the BBB to expedite the clearance of Aβ, reduce cerebral Aβ accumulation, and consequently inhibit the activation of microglia induced by Aβ aggregation. This process may suppress the activation of the CMPK2/NLRP3 and TLRs/NF-κB pathways, diminish the production of inflammatory cytokines and chemokines, alleviate neuroinflammation associated with microglia in the brain of AD, and ultimately improve AD pathology.

Induction of a Müller Glial Cell-Specific Protective Pathway Safeguards the Retina From Diabetes-Induced Damage

Diabetes can lead to cell type-specific responses in the retina, including vascular lesions, glial dysfunction, and neurodegeneration, all of which contribute to retinopathy. However, the molecular mechanisms underlying these cell type-specific responses, and the cell types that are sensitive to diabetes have not been fully elucidated. Using single-cell transcriptomics, we profiled the transcriptional changes induced by diabetes in different retinal cell types in rat models as the disease progressed. Rod photoreceptors, a subtype of amacrine interneurons, and Müller glial cells (MGs) exhibited rapid responses to diabetes at the transcript levels. Genes associated with ion regulation were upregulated in all three cell types, suggesting a common response to diabetes. Furthermore, focused studies revealed that although MG initially increased the expression of genes playing protective roles, they cannot sustain this beneficial effect. We explored one of the candidate protective genes, Zinc finger protein 36 homolog (Zfp36), and observed that depleting Zfp36 in rat MGs in vivo using adeno-associated virus-based tools exacerbated diabetes-induced phenotypes, including glial reactivation, neurodegeneration, and vascular defects. Overexpression of Zfp36 slowed the development of these phenotypes. This work unveiled retinal cell types that are sensitive to diabetes and demonstrated that MGs can mount protective responses through Zfp36.

ARTICLE HIGHLIGHTS

Interplay between Netrin-1 and Norrin controls arteriovenous zonation of blood-retina barrier integrity

The integrity of the blood-retina barrier (BRB) is crucial for phototransduction and vision, by tightly restricting transport of molecules between the blood and surrounding neuronal cells. Breakdown of the BRB leads to the development of retinal diseases. Here, we show that Netrin-1/Unc5b and Norrin/Lrp5 signaling establish a zonated endothelial cell gene expression program that controls BRB integrity. Using single-cell RNA sequencing (scRNA-seq) of postnatal BRB-competent mouse retina endothelial cells (ECs), we identify >100 BRB genes encoding Wnt signaling components, tight junction proteins, and ion and nutrient transporters. We find that BRB gene expression is zonated across arteries, capillaries, and veins and regulated by opposing gradients of the Netrin-1 receptor Unc5b and Lrp5-β-catenin signaling between retinal arterioles and venules. Mice deficient for Ntn1 or Unc5b display more BRB leakage at the arterial end of the vasculature, while Lrp5 loss of function causes predominantly venular BRB leakage. ScRNA-seq of Ntn1 and Unc5b mutant ECs reveals down-regulated β-catenin signaling and BRB gene expression that is rescued by Ctnnb1 overactivation, along with BRB integrity. Mechanistically, we demonstrate that Netrin-1 and Norrin additively enhance β-catenin transcriptional activity and Lrp5 phosphorylation via the Discs large homologue 1 (Dlg1) scaffolding protein, and endothelial Lrp5-Unc5b function converges in protection of capillary BRB integrity. These findings explain how arteriovenous zonation is established and maintained in the BRB and reveal that BRB gene expression is regulated at the level of endothelial subtypes.

Müller cells and retinal angiogenesis: critical regulators in health and disease

Müller cells are the most abundant glial cells in the mammalian retina. Their morphology and metabolism enable them to be in close contact and interact biochemically and physically with almost all retinal cell types, including neurons, pericytes, endothelial cells, and other glial cells, influencing their physiology by releasing bioactive molecules. Studies indicate that Müller glial cells are the primary source of angiogenic growth factor secretion in the neuroretina. Because of this, over the past decade, it has been postulated that Müller glial cells play a significant role in maintaining retinal vascular homeostasis, with potential implications in vasoproliferative retinopathies. This review aims to summarize the current understanding of the mechanisms by which Müller glial cells influence retinal angiogenesis in health and disease, with a particular emphasis on three of the retinopathies with the most significant impact on visual health worldwide: diabetic retinopathy, retinopathy of prematurity, and age-related macular degeneration.

Immune responses drive chorioretinitis and retinal pathology after neonatal CMV infection

Human cytomegalovirus (CMV) causes a common congenital infection leading to long-term neurological impairments including brain, cochlear, and ocular pathology. Infection of newborn mice with murine (M)CMV is an established model of neuropathology caused by congenital CMV infection, with recent work suggesting that brain pathology may be driven by immune responses. In the eye, however, CMV retinitis is thought to result from virus-driven necrosis in the absence of T cell responses. We found that MCMV infection of newborn mice recapitulates human eye disease after congenital CMV infection, including focal chorioretinitis, inflamed vasculature, and disrupted blood-retinal barriers. Moreover, infection drove extensive T cell infiltration of the retina and marked gliosis. Blocking immune responses generally, or via targeting the chemokine receptor CXCR3, did not exacerbate retinal disease but instead prevented pathology despite retinal MCMV infection. Thus, our data establish this model for studies of congenital retinal disease and show that the immune system drives pathology in the neonatal eye after MCMV infection.

Caveolin-1 and Aquaporin-4 as Mediators of Fibrinogen-Driven Cerebrovascular Pathology in Hereditary Cerebral Amyloid Angiopathy

Hereditary Cerebral Amyloid Angiopathy (HCAA) is a rare inherited form of CAA, characterized by increased vascular deposits of amyloid peptides. HCAA provides a unique opportunity to study the pathogenic mechanisms linked to CAA, as it is associated with severe cerebrovascular pathology. Some of HCAA-associated amyloid-β (Aβ) mutations significantly enhance the interaction between fibrinogen and Aβ, resulting in altered fibrin structure and co-deposition with Aβ in the perivascular space. However, the mechanisms underlying perivascular fibrinogen deposition and the associated cerebrovascular pathology in HCAA remain unclear. To investigate this, we analyzed TgSwDI transgenic mice carrying HCAA-associated mutations and observed a significant age-dependent increase in fibrin(ogen) extravasation and fibrin(ogen)-Aβ colocalization in the perivascular space. Moreover, Caveolin-1, a protein involved in non-specific transcytosis across the endothelium, significantly increased with age in TgSwDI mice and correlated with fibrin(ogen) extravasation. Additionally, we noted significant aquaporin-4 (AQP4) depolarization in the CAA-laden blood vessels of TgSwDI mice, which also correlated with fibrin(ogen) extravasation and fibrin(ogen)-Aβ colocalization. Given that AQP4 plays a crucial role in Aβ clearance via the glymphatic pathway, its depolarization may disrupt this critical clearance mechanism, thereby exacerbating CAA pathology. To further explore the relationship between fibrin(ogen) and these factors, we depleted fibrinogen in TgSwDI mice using siRNA against fibrinogen. This intervention resulted in decreased CAA, reduced caveolin-1 levels, attenuated microglial activation, restored polarized expression of AQP4, and improved spatial memory in fibrinogen-depleted TgSwDI mice. These findings suggest that targeting fibrinogen could be a promising strategy for mitigating CAA pathology and its associated cerebrovascular pathology.

Significance Statement

Our study reveals the mechanism by which fibrin(ogen)-Aβ colocalization could exacerbates CAA pathology. Our findings highlight that the age-dependent increase of endothelial caveolin-1 could facilitate fibrin(ogen) extravasation, which binds with Aβ in the perivascular space inducing microglial neuroinflammation and AQP4 depolarization, thus exacerbating CAA pathology. Furthermore, fibrinogen depletion could mitigate CAA severity, reduce microglial activation, restore AQP4 polarization and memory impairment. These results suggest that targeting fibrinogen and caveolin-1-mediated transcytosis may offer new strategies to address CAA-associated cerebrovascular pathology.

Endothelial Rho kinase controls blood vessel integrity and angiogenesis

Background

The Rho kinases 1 and 2 (ROCK1/2) are serine-threonine specific protein kinases that control actin cytoskeleton dynamics. They are expressed in all cells throughout the body, including cardiomyocytes, smooth muscle cells and endothelial cells, and intimately involved in cardiovascular health and disease. Pharmacological ROCK inhibition is beneficial in mouse models of hypertension, atherosclerosis, and neointimal thickening that display overactivated ROCK. However, the consequences of endothelial ROCK signaling deficiency in vivo remain unknown. To address this issue, we analyzed endothelial cell (EC) specific ROCK1 and 2 deletions.

Methods

We generated Cdh5-CreERT2 driven, tamoxifen inducible loss of function alleles of ROCK1 and ROCK2 and analyzed mouse survival and vascular defects through cellular, biochemical, and molecular biology approaches.

Results

We observed that postnatal or adult loss of endothelial ROCK1 and 2 was lethal within a week. Mice succumbed to multi-organ hemorrhage that occurred because of loss of vascular integrity. ECs displayed deficient cytoskeletal actin polymerization that prevented focal adhesion formation and disrupted junctional integrity. Retinal sprouting angiogenesis was also perturbed, as sprouting vessels exhibited lack of polymerized actin and defective lumen formation. In a three-dimensional endothelial sprouting assay, combined knockdown of ROCK1/2 or knockdown or ROCK2 but not ROCK1 led to reduced sprouting, lumenization and cell polarization defects caused by defective actin and altered VE-cadherin dynamics. The isoform specific role of endothelial ROCK2 correlated with ROCK2 substrate specificity for FAK and LIMK. By analyzing single and three allele mutants we show that one intact allele of ROCK2 is sufficient to maintain vascular integrity in vivo.

Conclusion

Endothelial ROCK1 and 2 maintain junctional integrity and ensure proper angiogenesis and lumen formation. The presence of one allele of ROCK2 is sufficient to maintain vascular growth and integrity. These data indicate the need of careful consideration for the use of ROCK inhibitors in disease settings.

The Involvement of Glial Cells in Blood-Brain Barrier Damage in Neuroimmune Diseases

The blood-brain barrier and glial cells, particularly astrocytes, interact with each other in neuroimmune diseases. In the inflammatory environment typical of these diseases, alterations in vascular endothelial cell surface molecules and weakened cell connections allow immune cells and autoantibodies to enter the central nervous system. Glial cells influence the adhesion of endothelial cells by changing their morphology and releasing various signaling molecules. Multiple sclerosis has been the most studied disease in relation to vascular endothelial and glial cell interactions, but these cells also significantly affect the onset and severity of other neuroimmune conditions, including demyelinating and inflammatory diseases. In this context, we present an overview of these interactions and highlight how they vary across different neuroimmune diseases.

IOP-induced blood-retinal barrier compromise contributes to RGC death in glaucoma

The integrity of the blood-retinal barrier (BRB) has been largely unexplored in glaucoma. We reveal that elevated intraocular pressure (IOP) partially compromises the BRB in two human-relevant inherited mouse models of glaucoma (DBA/2J and Lmx1bV265D). Experimentally increasing IOP in mouse eyes further confirms this. Notably, the compromise induces subtle leakage, happening without bleeding or detected endothelial cell junction disruption, and it precedes neurodegeneration. Leakage occurs from peripheral veins in the retinal ganglion cell layer with a concomitant loss of the transcytosis inhibitor MFSD2A. Importantly, stabilizing β-catenin in retinal endothelial cells prevents both vascular leakage and neurodegeneration in the DBA/2J model. The occurrence of leakage in all 3 high IOP models indicates that BRB compromise may be a common, yet overlooked, mechanism in glaucoma. These findings suggest that IOP-induced BRB compromise plays a critical role in glaucoma, offering a new therapeutic target.

Infiltration of immune cells to the brain and its relation to the pathogenesis of Alzheimer's and Parkinson's diseases

The neurovascular unit, composed of vascular endothelium, vascular smooth muscle, extracellular matrix components, pericytes, astrocytes, microglia, and neurons, allows the highly regulated exchange of molecules and the limited trafficking of cells to the brain through coordinated signaling activity. The passage of peripheral immune cells to the brain parenchyma is observed when there is clear damage to the barriers of this neurovascular unit, as occurs in traumatic brain injury. The possibility of leukocyte infiltration to the brain in neurodegenerative conditions has been proposed. In this review, we focus on describing the evidence for peripheral immune cell infiltration to the brain in the two most frequent neurodegenerative diseases: Alzheimer's and Parkinson's diseases. In particular, we address the mechanisms that promote the passage of these cells into the brain under such pathological conditions. We also discuss the relevance of the resulting cellular interactions, which provide evidence that the presence of peripheral immune cells in the brain is a key point in these neurodegenerative diseases.

Mfsd2a regulates the blood-labyrinth-barrier formation and function through tight junctions and transcytosis

The Blood-Labyrinth Barrier (BLB) is pivotal for the maintenance of lymphatic homeostasis within the inner ear, yet the intricacies of its development and function are inadequately understood. The present investigation delves into the contribution of the Mfsd2a molecule, integral to the structural and functional integrity of the Blood-Brain Barrier (BBB), to the ontogeny and sustenance of the BLB. Our empirical findings delineate that the maturation of the BLB in murine models is not realized until approximately two weeks post-birth, with preceding stages characterized by notable permeability. Transcriptomic analysis elucidates a marked augmentation in Mfsd2a expression within the lateral wall of the cochlea in specimens exhibiting an intact BLB. Moreover, both in vitro and in vivo assays substantiate that a diminution in Mfsd2a expression detrimentally impacts BLB permeability and structural integrity, principally via the attenuation of tight junction protein expression and the enhancement of endothelial cell transcytosis. These insights underscore the indispensable role of Mfsd2a in ensuring BLB integrity and propose it as a viable target for therapeutic interventions aimed at the amelioration of hearing loss.

The Impact of High-Dose Fish Oil Supplementation on Mfsd2a, Aqp4, and Amyloid-β Expression in Retinal Blood Vessels of 5xFAD Alzheimer's Mouse Model

In patients with Alzheimer's disease (AD) and in animal models, the increased accumulation of amyloid β (Aβ) in retinal blood vessels strongly correlates with brain amyloid deposits and cognitive decline. The accumulation of Aβ in blood vessels may result from impaired transcytosis and a dysfunctional ocular glymphatic system in AD. High-dose fish oil (FO) supplementation has been shown to significantly change the expression of major facilitator superfamily domain-containing protein 2a (Mfsd2a), a key regulator of transcytosis, and Aquaporin 4 (Aqp4), an essential component of the glymphatic system in the retinas of WT mice. We examined the expression of Mfsd2a and Aqp4 in the retinas of 4-month-old 5xFAD female mice supplemented with high-dose FO for three weeks. There was a significant increase in Mfsd2a expression in 5xFAD retinas supplemented with FO compared to control 5xFAD mice. Additionally, the increase in Aqp4 expression observed in 4-month-old 5xFAD retinas, indicative of an impaired glymphatic system, was significantly decreased. Simultaneously, Aβ accumulation in 5xFAD retinal blood vessels was reduced following FO supplementation. These findings suggest that high-dose FO supplementation could serve as an adjunct in developing new treatments aimed at improving the regulation of transcytosis or the function of the glymphatic system in the AD retina.

Acyl-CoA synthetase 6 controls rod photoreceptor function and survival by shaping the phospholipid composition of retinal membranes

The retina is light-sensitive neuronal tissue in the back of the eye. The phospholipid composition of the retina is unique and highly enriched in polyunsaturated fatty acids, including docosahexaenoic fatty acid (DHA). While it is generally accepted that a high DHA content is important for vision, surprisingly little is known about the mechanisms of DHA enrichment in the retina. Furthermore, the biological processes controlled by DHA in the eye remain poorly defined as well. Here, we combined genetic manipulations with lipidomic analysis in mice to demonstrate that acyl-CoA synthetase 6 (Acsl6) serves as a regulator of the unique composition of retinal membranes. Inactivation of Acsl6 reduced the levels of DHA-containing phospholipids, led to progressive loss of light-sensitive rod photoreceptor neurons, attenuated the light responses of these cells, and evoked distinct transcriptional response in the retina involving the Srebf1/2 (sterol regulatory element binding transcription factors 1/2) pathway. This study identifies one of the major enzymes responsible for DHA enrichment in the retinal membranes and introduces a model allowing an evaluation of rod functioning and pathology caused by impaired DHA incorporation/retention in the retina.

Inhibition of soluble epoxide hydrolase as a therapeutic approach for blood-brain barrier dysfunction

The blood-brain barrier (BBB) is a protective semi-permeable structure that regulates the exchange of biomolecules between the peripheral blood and the central nervous system (CNS). Due to its specialized tight junctions and low vesicle trafficking, the BBB strictly limits the paracellular passage and transcellular transport of molecules to maintain the physiological condition of brain tissues. BBB breakdown is associated with many CNS disorders. Soluble epoxide hydrolase (sEH) is a hydrolase enzyme that converts epoxy-fatty acids (EpFAs) to their corresponding diols and is involved in the onset and progression of multiple diseases. EpFAs play a protective role in the central nervous system via preventing neuroinflammation, making sEH a potential therapeutic target for CNS diseases. Recent studies showed that sEH inhibition prevented BBB impairment caused by stroke, hemorrhage, traumatic brain injury, hyperglycemia and sepsis via regulating the expression of tight junctions. In this review, the protective actions of sEH inhibition on BBB and potential mechanisms are summarized, and some important questions that remain to be resolved are also addressed.

Activation of Wnt signaling mitigates blood-brain barrier disruption by inhibiting vesicular transcytosis after traumatic brain injury in mice

Elevated transport of Caveolin-1 (CAV-1) vesicles within vascular endothelial cells constitutes a significant secondary pathogenic event contributing to the compromise of the blood-brain barrier (BBB) post-traumatic brain injury (TBI). While Wnt/β-catenin signaling is recognized for its critical involvement in angiogenesis and the maintenance of BBB integrity, its influence on vascular endothelial transcytosis in the aftermath of TBI is not well-defined. This study aims to elucidate the impact of Wnt/β-catenin signaling on cerebrovascular vesicular transcytosis following TBI. In this experiment, adult male wild-type (WT) C57BL/6 mice underwent various interventions. TBI was induced utilizing the controlled cortical impact technique. Post-TBI, mice were administered either an inhibitor or an agonist of Wnt signaling via intraperitoneal injection. Recombinant adeno-associated virus (rAAV) was administered intracerebroventricularly to modulate the expression of the CAV-1 inhibitory protein, Major facilitator superfamily domain-containing 2a (Mfsd2a). This research utilized Evans blue assay, Western blot analysis, immunofluorescence, transmission electron microscopy, and neurobehavioral assessments. Post-TBI observations revealed substantial increases in macromolecule (Evans blue and albumin) leakage, CAV-1 transport vesicle count, astrocyte end-feet edema, and augmented aquaporin-4 (AQP4) expression, culminating in BBB disruption. The findings indicate that Wnt signaling pathway inhibition escalates CAV-1 transport vesicle activity and aggravates BBB compromise. Conversely, activating this pathway could alleviate BBB damage by curtailing CAV-1 vesicle presence. Post-TBI, there is a diminution in Mfsd2a expression, which is directly influenced by the modulation of WNT signals. Employing a viral approach to regulate Mfsd2a, we established that its down-regulation undermines the protective benefits derived from reducing CAV-1 transport vesicles through WNT signal enhancement. Moreover, we verified that the WNT signaling agonist LiCl notably ameliorates neurological deficits following TBI in mice. Collectively, our data imply that Wnt/β-catenin signaling presents a potential therapeutic target for safeguarding against BBB damage and enhancing neurological function after TBI.

Glutamatergic neuronal activity regulates angiogenesis and blood-retinal barrier maturation via Norrin/β-catenin signaling

Interactions among neuronal, glial, and vascular components are crucial for retinal angiogenesis and blood-retinal barrier (BRB) maturation. Although synaptic dysfunction precedes vascular abnormalities in many retinal pathologies, how neuronal activity, specifically glutamatergic activity, regulates retinal angiogenesis and BRB maturation remains unclear. Using in vivo genetic studies in mice, single-cell RNA sequencing (scRNA-seq), and functional validation, we show that deep plexus angiogenesis and paracellular BRB maturation are delayed in Vglut1-/- retinas where neurons fail to release glutamate. By contrast, deep plexus angiogenesis and paracellular BRB maturation are accelerated in Gnat1-/- retinas, where constitutively depolarized rods release excessive glutamate. Norrin expression and endothelial Norrin/β-catenin signaling are downregulated in Vglut1-/- retinas and upregulated in Gnat1-/- retinas. Pharmacological activation of endothelial Norrin/β-catenin signaling in Vglut1-/- retinas rescues defects in deep plexus angiogenesis and paracellular BRB maturation. Our findings demonstrate that glutamatergic neuronal activity regulates retinal angiogenesis and BRB maturation by modulating endothelial Norrin/β-catenin signaling.

Interactions between nanoparticles and pathological changes of vascular in Alzheimer's disease

Emerging evidence suggests that vascular pathological changes play a pivotal role in the pathogenesis of Alzheimer's disease (AD). The dysfunction of the cerebral vasculature occurs in the early course of AD, characterized by alterations in vascular morphology, diminished cerebral blood flow (CBF), impairment of the neurovascular unit (NVU), vasculature inflammation, and cerebral amyloid angiopathy. Vascular dysfunction not only facilitates the influx of neurotoxic substances into the brain, triggering inflammation and immune responses but also hampers the efflux of toxic proteins such as Aβ from the brain, thereby contributing to neurodegenerative changes in AD. Furthermore, these vascular changes significantly impact drug delivery and distribution within the brain. Therefore, developing targeted delivery systems or therapeutic strategies based on vascular alterations may potentially represent a novel breakthrough in AD treatment. This review comprehensively examines various aspects of vascular alterations in AD and outlines the current interactions between nanoparticles and pathological changes of vascular.

Gastrointestinal and brain barriers: unlocking gates of communication across the microbiota-gut-brain axis

Crosstalk between gut and brain has long been appreciated in health and disease, and the gut microbiota is a key player in communication between these two distant organs. Yet, the mechanisms through which the microbiota influences development and function of the gut-brain axis remain largely unknown. Barriers present in the gut and brain are specialized cellular interfaces that maintain strict homeostasis of different compartments across this axis. These barriers include the gut epithelial barrier, the blood-brain barrier and the blood-cerebrospinal fluid barrier. Barriers are ideally positioned to receive and communicate gut microbial signals constituting a gateway for gut-microbiota-brain communication. In this Review, we focus on how modulation of these barriers by the gut microbiota can constitute an important channel of communication across the gut-brain axis. Moreover, barrier malfunction upon alterations in gut microbial composition could form the basis of various conditions, including often comorbid neurological and gastrointestinal disorders. Thus, we should focus on unravelling the molecular and cellular basis of this communication and move from simplistic framing as 'leaky gut'. A mechanistic understanding of gut microbiota modulation of barriers, especially during critical windows of development, could be key to understanding the aetiology of gastrointestinal and neurological disorders.

Mechanisms underlying the efficacy and limitation of dopa and tetrahydrobiopterin therapies for the deficiency of GTP cyclohydrolase 1 revealed in a novel mouse model

Dopa and tetrahydrobiopterin (BH4) supplementation are recommended therapies for the dopa-responsive dystonia caused by GTP cyclohydrolase 1 (GCH1, also known as GTPCH) deficits. However, the efficacy and mechanisms of these therapies have not been intensively studied yet. In this study, we tested the efficacy of dopa and BH4 therapies by using a novel GTPCH deficiency mouse model, Gch1KI/KI, which manifested infancy-onset motor deficits and growth retardation similar to the patients. First, dopa supplementation supported Gch1KI/KI mouse survival to adulthood, but residual motor deficits and dwarfism remained. Interestingly, RNAseq analysis indicated that while the genes participating in BH4 biosynthesis and regeneration were significantly increased in the liver, no significant changes were observed in the brain. Second, BH4 supplementation alone restored the growth of Gch1KI/KI pups only in early postnatal developmental stage. High doses of BH4 supplementation indeed restored the total brain BH4 levels, but brain dopamine deficiency remained. While total brain TH levels were relatively increased in the BH4 treated Gch1KI/KI mice, the TH in the striatum were still almost undetectable, suggesting differential BH4 requirements among brain regions. Last, the growth of Gch1KI/KI mice under combined therapy outperformed dopa or BH4 therapy alone. Notably, dopamine was abnormally high in more than half, but not all, of the treated Gch1KI/KI mice, suggesting the existence of variable synergetic effects of dopa and BH4 supplementation. Our results provide not only experimental evidence but also novel mechanistic insights into the efficacy and limitations of dopa and BH4 therapies for GTPCH deficiency.

Vascular development, remodeling and maturation

The development of the vascular system is crucial in supporting the growth and health of all other organs in the body, and vascular system dysfunction is the major cause of human morbidity and mortality. This chapter discusses three successive processes that govern vascular system development, starting with the differentiation of the primitive vascular system in early embryonic development, followed by its remodeling into a functional circulatory system composed of arteries and veins, and its final maturation and acquisition of an organ specific semi-permeable barrier that controls nutrient uptake into tissues and hence controls organ physiology. Along these steps, endothelial cells forming the inner lining of all blood vessels acquire extensive heterogeneity in terms of gene expression patterns and function, that we are only beginning to understand. These advances contribute to overall knowledge of vascular biology and are predicted to unlock the unprecedented therapeutic potential of the endothelium as an avenue for treatment of diseases associated with dysfunctional vasculature.

The supplementation of a high dose of fish oil during pregnancy and lactation led to an elevation in Mfsd2a expression without any changes in docosahexaenoic acid levels in the retina of healthy 2-month-old mouse offspring

Introduction

During fetal development, the proper development of neural and visual systems relies on the maternal supplementation of omega-3 fatty acids through placental transfer. Pregnant women are strongly advised to augment their diet with additional sources of omega-3, such as fish oil (FO). This supplementation has been linked to a reduced risk of preterm birth, pre-eclampsia, and perinatal depression. Recently, higher doses of omega-3 supplementation have been recommended for pregnant women. Considering that omega-3 fatty acids, particularly docosahexaenoic acid (DHA), play a crucial role in maintaining the delicate homeostasis required for the proper functioning of the retina and photoreceptors the effects of high-dose fish oil (FO) supplementation during pregnancy and lactation on the retina and retinal pigmented epithelium (RPE) in healthy offspring warrant better understanding.

Methods

The fatty acid content and the changes in the expression of the genes regulating cholesterol homeostasis and DHA transport in the retina and RPE were evaluated following the high-dose FO supplementation.

Results

Our study demonstrated that despite the high-dose FO treatment during pregnancy and lactation, the rigorous DHA homeostasis in the retina and RPE of the two-month-old offspring remained balanced. Another significant finding of this study is the increase in the expression levels of major facilitator superfamily domain-containing protein (Mfsd2a), a primary DHA transporter. Mfsd2a also serves as a major regulator of transcytosis during development, and a reduction in Mfsd2a levels poses a major risk for the development of leaky blood vessels.

Conclusion

Impairment of the blood-retinal barrier (BRB) is associated with the development of numerous ocular diseases, and a better understanding of how to manipulate transcytosis in the BRB during development can enhance drug delivery through the BRB or contribute to the repair of central nervous system (CNS) barriers.

Glutamatergic neuronal activity regulates angiogenesis and blood-retinal barrier maturation via Norrin/β-catenin signaling

Interactions among neuronal, glial and vascular components are crucial for retinal angiogenesis and blood-retinal barrier (BRB) maturation. Although synaptic dysfunction precedes vascular abnormalities in many retinal pathologies, how neuronal activity, specifically glutamatergic activity, regulates retinal angiogenesis and BRB maturation remains unclear. Using in vivo genetic studies in mice, single-cell RNA-sequencing and functional validation, we show that deep plexus angiogenesis and paracellular BRB maturation are delayed in Vglut1 -/- retinas where neurons fail to release glutamate. In contrast, deep plexus angiogenesis and paracellular BRB maturation are accelerated in Gnat1 -/- retinas where constitutively depolarized rods release excessive glutamate. Norrin expression and endothelial Norrin/β-catenin signaling are downregulated in Vglut1 -/- retinas, and upregulated in Gnat1 -/- retinas. Pharmacological activation of endothelial Norrin/β-catenin signaling in Vglut1 -/- retinas rescued defects in deep plexus angiogenesis and paracellular BRB maturation. Our findings demonstrate that glutamatergic neuronal activity regulates retinal angiogenesis and BRB maturation by modulating endothelial Norrin/β-catenin signaling.

Breaking Barriers in Neuro-Oncology: A Scoping Literature Review on Invasive and Non-Invasive Techniques for Blood-Brain Barrier Disruption

The blood-brain barrier (BBB) poses a significant challenge to drug delivery for brain tumors, with most chemotherapeutics having limited permeability into non-malignant brain tissue and only restricted access to primary and metastatic brain cancers. Consequently, due to the drug's inability to effectively penetrate the BBB, outcomes following brain chemotherapy continue to be suboptimal. Several methods to open the BBB and obtain higher drug concentrations in tumors have been proposed, with the selection of the optimal method depending on the size of the targeted tumor volume, the chosen therapeutic agent, and individual patient characteristics. Herein, we aim to comprehensively describe osmotic disruption with intra-arterial drug administration, intrathecal/intraventricular administration, laser interstitial thermal therapy, convection-enhanced delivery, and ultrasound methods, including high-intensity focused and low-intensity ultrasound as well as tumor-treating fields. We explain the scientific concept behind each method, preclinical/clinical research, advantages and disadvantages, indications, and potential avenues for improvement. Given that each method has its limitations, it is unlikely that the future of BBB disruption will rely on a single method but rather on a synergistic effect of a combined approach. Disruption of the BBB with osmotic infusion or high-intensity focused ultrasound, followed by the intra-arterial delivery of drugs, is a promising approach. Real-time monitoring of drug delivery will be necessary for optimal results.

Blood-brain Barrier and Neurovascular Unit Dysfunction in Parkinson's Disease: From Clinical Insights to Pathogenic Mechanisms and Novel Therapeutic Approaches

The blood-brain barrier (BBB) plays a crucial role in the central nervous system by tightly regulating the influx and efflux of biological substances between the brain parenchyma and peripheral circulation. Its restrictive nature acts as an obstacle to protect the brain from potentially noxious substances such as blood-borne toxins, immune cells, and pathogens. Thus, the maintenance of its structural and functional integrity is vital in the preservation of neuronal function and cellular homeostasis in the brain microenvironment. However, the barrier's foundation can become compromised during neurological or pathological conditions, which can result in dysregulated ionic homeostasis, impaired transport of nutrients, and accumulation of neurotoxins that eventually lead to irreversible neuronal loss. Initially, the BBB is thought to remain intact during neurodegenerative diseases, but accumulating evidence as of late has suggested the possible association of BBB dysfunction with Parkinson's disease (PD) pathology. The neurodegeneration occurring in PD is believed to stem from a myriad of pathogenic mechanisms, including tight junction alterations, abnormal angiogenesis, and dysfunctional BBB transporter mechanism, which ultimately causes altered BBB permeability. In this review, the major elements of the neurovascular unit (NVU) comprising the BBB are discussed, along with their role in the maintenance of barrier integrity and PD pathogenesis. We also elaborated on how the neuroendocrine system can influence the regulation of BBB function and PD pathogenesis. Several novel therapeutic approaches targeting the NVU components are explored to provide a fresh outlook on treatment options for PD.

The Recent Advances in the Function and Mechanism of Caveolin-1 in Retinal Neovascularization

Retinal neovascularization diseases have relatively high rates of evitable blindness. Abnormal retinal neovascularization is their main hallmark, which can damage the structure and function of the eye and lead to impaired vision. Caveolin-1 is a membrane protein that is expressed in many types of retinal cells and is involved in retinal neovascularization. This review presents a comprehensive analysis of global research on specific functions of caveolin-1 in retinal neovascularization. We believe that the mechanism of action of caveolin-1 might be related to the regulation of relevant signal pathways and looked ahead the application prospects of modulating caveolin- 1 in retinal neovascularization diseases.

Blood-Brain Barrier Breakdown in Alzheimer's Disease: Mechanisms and Targeted Strategies

The blood-brain barrier (BBB) is a unique and selective feature of the central nervous system's vasculature. BBB dysfunction has been observed as an early sign of Alzheimer's Disease (AD) before the onset of dementia or neurodegeneration. The intricate relationship between the BBB and the pathogenesis of AD, especially in the context of neurovascular coupling and the overlap of pathophysiology in neurodegenerative and cerebrovascular diseases, underscores the urgency to understand the BBB's role more deeply. Preserving or restoring the BBB function emerges as a potentially promising strategy for mitigating the progression and severity of AD. Molecular and genetic changes, such as the isoform ε4 of apolipoprotein E (ApoEε4), a significant genetic risk factor and a promoter of the BBB dysfunction, have been shown to mediate the BBB disruption. Additionally, receptors and transporters like the low-density lipoprotein receptor-related protein 1 (LRP1), P-glycoprotein (P-gp), and the receptor for advanced glycation end products (RAGEs) have been implicated in AD's pathogenesis. In this comprehensive review, we endeavor to shed light on the intricate pathogenic and therapeutic connections between AD and the BBB. We also delve into the latest developments and pioneering strategies targeting the BBB for therapeutic interventions, addressing its potential as a barrier and a carrier. By providing an integrative perspective, we anticipate paving the way for future research and treatments focused on exploiting the BBB's role in AD pathogenesis and therapy.

Caveolin-1 mediates neuroinflammation and cognitive impairment in SARS-CoV-2 infection

Leukocyte infiltration of the CNS can contribute to neuroinflammation and cognitive impairment. Brain endothelial cells regulate adhesion, activation, and diapedesis of T cells across the blood-brain barrier (BBB) in inflammatory diseases. The integral membrane protein Caveolin-1 (Cav-1) critically regulates BBB permeability, but its influence on T cell CNS infiltration in respiratory viral infections is unknown. In this study, we sought to determine the role of Cav-1 at the BBB in neuroinflammation in a COVID-19 mouse model. We used mice genetically deficient in Cav-1 to test the role of this protein in T cell infiltration and cognitive impairment. We found that SARS-CoV-2 infection upregulated brain endothelial Cav-1. Moreover, SARS-CoV-2 infection increased brain endothelial cell vascular cell adhesion molecule-1 (VCAM-1) and CD3+ T cell infiltration of the hippocampus, a region important for short term learning and memory. Concordantly, we observed learning and memory deficits. Importantly, genetic deficiency in Cav-1 attenuated brain endothelial VCAM-1 expression and T cell infiltration in the hippocampus of mice with SARS-CoV-2 infection. Moreover, Cav-1 KO mice were protected from the learning and memory deficits caused by SARS-CoV-2 infection. These results indicate the importance of BBB permeability in COVID-19 neuroinflammation and suggest potential therapeutic value of targeting Cav-1 to improve disease outcomes.

Assessment of Inner Blood-Retinal Barrier: Animal Models and Methods

Proper functioning of the neural retina relies on the unique retinal environment regulated by the blood-retinal barrier (BRB), which restricts the passage of solutes, fluids, and toxic substances. BRB impairment occurs in many retinal vascular diseases and the breakdown of BRB significantly contributes to disease pathology. Understanding the different molecular constituents and signaling pathways involved in BRB development and maintenance is therefore crucial in developing treatment modalities. This review summarizes the major molecular signaling pathways involved in inner BRB (iBRB) formation and maintenance, and representative animal models of eye diseases with retinal vascular leakage. Studies on Wnt/β-catenin signaling are highlighted, which is critical for retinal and brain vascular angiogenesis and barriergenesis. Moreover, multiple in vivo and in vitro methods for the detection and analysis of vascular leakage are described, along with their advantages and limitations. These pre-clinical animal models and methods for assessing iBRB provide valuable experimental tools in delineating the molecular mechanisms of retinal vascular diseases and evaluating therapeutic drugs.

The Venular Side of Cerebral Amyloid Angiopathy: Proof of Concept of a Neglected Issue

Small vessel diseases (SVD) is an umbrella term including several entities affecting small arteries, arterioles, capillaries, and venules in the brain. One of the most relevant and prevalent SVDs is cerebral amyloid angiopathy (CAA), whose pathological hallmark is the deposition of amyloid fragments in the walls of small cortical and leptomeningeal vessels. CAA frequently coexists with Alzheimer's Disease (AD), and both are associated with cerebrovascular events, cognitive impairment, and dementia. CAA and AD share pathophysiological, histopathological and neuroimaging issues. The venular involvement in both diseases has been neglected, although both animal models and human histopathological studies found a deposition of amyloid beta in cortical venules. This review aimed to summarize the available information about venular involvement in CAA, starting from the biological level with the putative pathomechanisms of cerebral damage, passing through the definition of the peculiar angioarchitecture of the human cortex with the functional organization and consequences of cortical arteriolar and venular occlusion, and ending to the hypothesized links between cortical venular involvement and the main neuroimaging markers of the disease.

The Expression of Major Facilitator Superfamily Domain-Containing Protein2a (Mfsd2a) and Aquaporin 4 Is Altered in the Retinas of a 5xFAD Mouse Model of Alzheimer's Disease

Cerebral amyloid angiopathy (CAA) is characterized by amyloid β (Aβ) accumulation in the blood vessels and is associated with cognitive impairment in Alzheimer's disease (AD). The increased accumulation of Aβ is also present in the retinal blood vessels and a significant correlation between retinal and brain amyloid deposition was demonstrated in living patients and animal AD models. The Aβ accumulation in the retinal blood vessels can be the result of impaired transcytosis and/or the dysfunctional ocular glymphatic system in AD and during aging. We analyzed the changes in the mRNA and protein expression of major facilitator superfamily domain-containing protein2a (Mfsd2a), the major regulator of transcytosis, and of Aquaporin4 (Aqp4), the key player implicated in the functioning of the glymphatic system, in the retinas of 4- and 12-month-old WT and 5xFAD female mice. A strong decrease in the Mfsd2a mRNA and protein expression was observed in the 4 M and 12 M 5xFAD and 12 M WT retinas. The increase in the expression of srebp1-c could be at least partially responsible for the Mfsd2a decrease in the 4 M 5xFAD retinas. The decrease in the pericyte (CD13+) coverage of retinal blood vessels in the 4 M and 12 M 5xFAD retinas and in the 12 M WT retinas suggests that pericyte loss could be associated with the Mfsd2a downregulation in these experimental groups. The observed increase in Aqp4 expression in 4 M and 12 M 5xFAD and 12 M WT retinas accompanied by the decreased perivascular Aqp4 expression is indicative of the impaired glymphatic system. The findings in this study reveal the impaired Mfsd2a and Aqp4 expression and Aqp4 perivascular mislocalization in retinal blood vessels during physiological (WT) and pathological (5xFAD) aging, indicating their importance as putative targets for the development of new treatments that can improve the regulation of transcytosis or the function of the glymphatic system.

A hypothermia mimetic molecule (zr17-2) reduces ganglion cell death, gliosis, and electroretinogram distortion in male rats subjected to perinatal asphyxia

Introduction: Perinatal asphyxia (PA) represents a major problem in perinatology and may cause visual losses, including blindness. We, and others, have shown that hypothermia prevents retinal symptoms associated to PA. In the present work, we evaluate whether a hypothermia mimetic small molecule, zr17-2, has similar effects in the context of PA. Methods: Four experimental groups were studied in male rats: Naturally born rats as controls (CTL), naturally born rats injected s.c. with 50 µL of 330 nmols/L zr17-2 (ZR), animals that were exposed to PA for 20 min at 37°C (PA), and rats that were exposed to PA and injected with zr17-2 (PA-ZR). Forty-five days after treatment, animals were subjected to electroretinography. In addition, morphological techniques (TUNEL, H&E, multiple immunofluorescence) were applied to the retinas. Results: A reduction in the amplitude of the a- and b-wave and oscillatory potentials (OP) of the electroretinogram (ERG) was detected in PA animals. Treatment with zr17-2 resulted in a significant amelioration of these parameters (p < 0.01). In PA animals, a large number of apoptotic cells was found in the GCL. This number was significantly reduced by treatment with the small molecule (p < 0.0001). In a similar way, the thickness of the inner retina and the intensity of GFAP immunoreactivity (gliosis) increased in PA retinas (p < 0.0001). These parameters were corrected by the administration of zr17-2 (p < 0.0001). Furthermore, injection of the small molecule in the absence of PA did not modify the ERG nor the morphological parameters studied, suggesting a lack of toxicity. Discussion: In conclusion, our results indicate that a single s.c. injection of zr17-2 in asphyctic neonates may provide a novel and efficacious method to prevent the visual sequelae of PA.

The secreted neuronal signal Spock1 promotes blood-brain barrier development

The blood-brain barrier (BBB) is a unique set of properties of the brain vasculature which severely restrict its permeability to proteins and small molecules. Classic chick-quail chimera studies have shown that these properties are not intrinsic to the brain vasculature but rather are induced by surrounding neural tissue. Here, we identify Spock1 as a candidate neuronal signal for regulating BBB permeability in zebrafish and mice. Mosaic genetic analysis shows that neuronally expressed Spock1 is cell non-autonomously required for a functional BBB. Leakage in spock1 mutants is associated with altered extracellular matrix (ECM), increased endothelial transcytosis, and altered pericyte-endothelial interactions. Furthermore, a single dose of recombinant SPOCK1 partially restores BBB function in spock1 mutants by quenching gelatinase activity and restoring vascular expression of BBB genes including mcamb. These analyses support a model in which neuronally secreted Spock1 initiates BBB properties by altering the ECM, thereby regulating pericyte-endothelial interactions and downstream vascular gene expression.

The neurovascular unit in healthy and injured spinal cord

The neurovascular unit (NVU) reflects the close temporal and spatial link between neurons and blood vessels. However, the understanding of the NVU in the spinal cord is far from clear and largely based on generalized knowledge obtained from the brain. Herein, we review the present knowledge of the NVU and highlight candidate approaches to investigate the NVU, particularly focusing on the spinal cord. Several unique features maintain the highly regulated microenvironment in the NVU. Autoregulation and neurovascular coupling ensure regional blood flow meets the metabolic demand according to the blood supply or local neural activation. The blood-central nervous system barrier partitions the circulating blood from neural parenchyma and facilitates the selective exchange of substances. Furthermore, we discuss spinal cord injury (SCI) as a common injury from the perspective of NVU dysfunction. Hopefully, this review will help expand the understanding of the NVU in the spinal cord and inspire new insights into SCI.

Hypertension depresses but exercise training restores both Mfsd2a expression and blood-brain barrier function within PVN capillaries

Hypertension augments while exercise training corrects the increased vesicle trafficking (transcytosis) across the blood-brain barrier (BBB) within preautonomic areas and the autonomic imbalance. There is no information on a possible mechanism(s) conditioning these effects. Knowing that Mfsd2a is the major transporter of docosahexaenoic acid (DHA) and that Mfsd2a knockout mice exhibited leaky BBB, we sought to identify its possible involvement in hypertension- and exercise-induced transcytosis across the BBB. Spontaneously hypertensive rats (SHR) and Wistar rats were submitted to treadmill training (T) or kept sedentary (S) for 4 wk. Resting hemodynamic/autonomic parameters were recorded in conscious chronically cannulated rats. BBB permeability within the hypothalamic paraventricular nucleus (PVN) was evaluated in anesthetized rats. Brains were harvested for Mfsd2a and caveolin-1 (an essential protein for vesicle formation) expression. SHR-S versus Wistar-S exhibited elevated arterial pressure (AP) and heart rate (HR), increased vasomotor sympathetic activity, reduced cardiac parasympathetic activity, greater pressure variability, reduced HR variability, and depressed baroreflex control. SHR-S also showed increased BBB permeability, reduced Mfsd2a, and increased caveolin-1 expression. SHR-T versus SHR-S exhibited increased Mfsd2a density, reduced caveolin-1 protein expression, and normalized PVN BBB permeability, which were accompanied by resting bradycardia, partial AP drop, reduced sympathetic and normalized cardiac parasympathetic activity, increased HR variability, and reduced pressure variability. No changes were observed in Wistar-T versus Wistar-S. Training is an efficient tool to rescue Mfsd2a expression, which by transporting DHA into the endothelial cell reduces caveolin-1 availability and vesicles' formation. Exercise-induced Mfsd2a normalization is an important mechanism to correct both BBB function and autonomic control in hypertensive subjects.

The Neurovasculome: Key Roles in Brain Health and Cognitive Impairment: A Scientific Statement From the American Heart Association/American Stroke Association

BACKGROUND

Preservation of brain health has emerged as a leading public health priority for the aging world population. Advances in neurovascular biology have revealed an intricate relationship among brain cells, meninges, and the hematic and lymphatic vasculature (the neurovasculome) that is highly relevant to the maintenance of cognitive function. In this scientific statement, a multidisciplinary team of experts examines these advances, assesses their relevance to brain health and disease, identifies knowledge gaps, and provides future directions.

METHODS

Authors with relevant expertise were selected in accordance with the American Heart Association conflict-of-interest management policy. They were assigned topics pertaining to their areas of expertise, reviewed the literature, and summarized the available data.

RESULTS

The neurovasculome, composed of extracranial, intracranial, and meningeal vessels, as well as lymphatics and associated cells, subserves critical homeostatic functions vital for brain health. These include delivering O2 and nutrients through blood flow and regulating immune trafficking, as well as clearing pathogenic proteins through perivascular spaces and dural lymphatics. Single-cell omics technologies have unveiled an unprecedented molecular heterogeneity in the cellular components of the neurovasculome and have identified novel reciprocal interactions with brain cells. The evidence suggests a previously unappreciated diversity of the pathogenic mechanisms by which disruption of the neurovasculome contributes to cognitive dysfunction in neurovascular and neurodegenerative diseases, providing new opportunities for the prevention, recognition, and treatment of these conditions.

CONCLUSIONS

These advances shed new light on the symbiotic relationship between the brain and its vessels and promise to provide new diagnostic and therapeutic approaches for brain disorders associated with cognitive dysfunction.

Mfsd2a attenuated hypoxic-ischemic brain damage via protection of the blood-brain barrier in mfat-1 transgenic mice

Previous studies have shown that mfat-1 transgenic mice have protective effects against some central nervous system (CNS) disorders, owing to the high docosahexaenoic acid (DHA) content enriched in their brains. However, whether this protective effect is connected to the blood-brain barrier (BBB) remains unclear. This study aims to investigate the mechanisms of the protective effect against hypoxic-ischemic brain damage (HIBD) of mfat-1 transgenic mice. mfat-1 mice not only demonstrated a significant amelioration of neurological dysfunction and neuronal damage but also partly maintained the physiological permeability of the BBB after HIBD. We initially showed this was associated with elevated major facilitator superfamily domain-containing 2a (Mfsd2a) expression on the BBB, resulting from more lysophosphatidylcholine (LPC)-DHA entering the brain. Wild-type (WT) mice showed a similar Mfsd2a expression trend after long-term feeding with an LPC-DHA-rich diet. Knockdown of Mfsd2a by siRNA intra-cerebroventricular (ICV) injection neutralized the protective effect against HIBD-induced BBB disruption in mfat-1 mice, further validating the protective function of Mfsd2a on BBB. HIBD-induced BBB high permeability was attenuated by Mfsd2a, primarily through a transcellular pathway to decrease caveolae-like vesicle-mediated transcytosis. Taken together, these findings not only reveal that mfat-1 transgenic mice have higher expression of Mfsd2a on the BBB, which partly sustains BBB permeability via vesicular transcytosis to alleviate the severity of HIBD, but also suggest that dietary intake of LPC-DHA may upregulate Mfsd2a expression as a novel therapeutic strategy for BBB dysfunction and survival in HIBD patients.

Characterization of the structure and control of the blood-nerve barrier identifies avenues for therapeutic delivery

The blood barriers of the nervous system protect neural environments but can hinder therapeutic accessibility. The blood-brain barrier (BBB) is well characterized, consisting of endothelial cells with specialized tight junctions and low levels of transcytosis, properties conferred by contacting pericytes and astrocytes. In contrast, the blood-nerve barrier (BNB) of the peripheral nervous system is poorly defined. Here, we characterize the structure of the mammalian BNB, identify the processes that confer barrier function, and demonstrate how the barrier can be opened in response to injury. The homeostatic BNB is leakier than the BBB, which we show is due to higher levels of transcytosis. However, the barrier is reinforced by macrophages that specifically engulf leaked materials, identifying a role for resident macrophages as an important component of the BNB. Finally, we demonstrate the exploitation of these processes to effectively deliver RNA-targeting therapeutics to peripheral nerves, indicating new treatment approaches for nervous system pathologies.

Netrin-1 binding to Unc5B regulates Blood-Retina Barrier integrity

Background

The blood brain barrier (BBB) preserves neuronal function in the central nervous system (CNS) by tightly controlling metabolite exchanges with the blood. In the eye, the retina is likewise protected by the blood-retina barrier (BRB) to maintain phototransduction. We showed that the secreted guidance cue Netrin-1 regulated BBB integrity, by binding to endothelial Unc5B and regulating canonical β-catenin dependent expression of BBB gene expression.

Objective

Here, we investigated if Netrin-1-binding to endothelial Unc5B also controlled BRB integrity, and if this process involved Norrin/β-catenin signaling, which is the major known driver of BRB development and maintenance.

Methods

We analyzed Tamoxifen-inducible loss- and gain- of-function alleles of Unc5B, Ntn1 and Ctnnb1 in conjunction with tracer injections and biochemical signaling studies.

Results

Inducible endothelial Unc5B deletion, and inducible global Ntn1 deletion in postnatal mice reduced phosphorylation of the Norrin receptor LRP5, leading to reduced β-catenin and LEF1 expression, conversion of retina endothelial cells from a barrier-competent Claudin-5+/PLVAP- state to a Claudin-5-/PLVAP+ leaky phenotype, and extravasation of injected low molecular weight tracers. Inducible Ctnnb1 gain of function rescued vascular leak in Unc5B mutants, and Ntn1 overexpression induced BRB tightening. Unc5B expression in pericytes contributed to BRB permeability, via regulation of endothelial Unc5B. Mechanistically, Netrin-1-Unc5B signaling promoted β-catenin dependent BRB signaling by enhancing phosphorylation of the Norrin receptor LRP5 via the Discs large homologue 1 (Dlg1) intracellular scaffolding protein.

Conclusions

The data identify Netrin1-Unc5B as novel regulators of BRB integrity, with implications for diseases associated with BRB disruption.