Endothelial LRP1 transports amyloid-β(1-42) across the blood-brain barrier

Rebuilding insight into the pathophysiology of Alzheimer's disease through new blood-brain barrier models

The blood-brain barrier is a unique function of the microvasculature in the brain parenchyma that maintains homeostasis in the central nervous system. Blood-brain barrier breakdown is a common pathology in various neurological diseases, such as Alzheimer's disease, stroke, multiple sclerosis, and Parkinson's disease. Traditionally, it has been considered a consequence of neuroinflammation or neurodegeneration, but recent advanced imaging techniques and detailed studies in animal models show that blood-brain barrier breakdown occurs early in the disease process and may precede neuronal loss. Thus, the blood-brain barrier is attractive as a potential therapeutic target for neurological diseases that lack effective therapeutics. To elucidate the molecular mechanism underlying blood-brain barrier breakdown and translate them into therapeutic strategies for neurological diseases, there is a growing demand for experimental models of human origin that allow for functional assessments. Recently, several human induced pluripotent stem cell-derived blood-brain barrier models have been established and various in vitro blood-brain barrier models using microdevices have been proposed. Especially in the Alzheimer's disease field, the human evidence for blood-brain barrier dysfunction has been demonstrated and human induced pluripotent stem cell-derived blood-brain barrier models have suggested the putative molecular mechanisms of pathological blood-brain barrier. In this review, we summarize recent evidence of blood-brain barrier dysfunction in Alzheimer's disease from pathological analyses, imaging studies, animal models, and stem cell sources. Additionally, we discuss the potential future directions for blood-brain barrier research.

Associations of liver function with plasma biomarkers for Alzheimer's Disease

BACKGROUND

Blood-based biomarkers for Alzheimer's disease (AD) are promising to be used in clinical settings. The liver is an important degradation organ of the body. Whether liver function affects the levels of AD biomarkers needs to be studied.

OBJECTIVE

To investigate the associations between liver function and the plasma levels of AD biomarkers.

METHODS

We conducted an ADNI cohort-based cross-sectional study. Thirteen liver function markers commonly used in clinical settings were analyzed: total protein (TP), albumin (AL), globulin (GL), AL/GL ratio (A/G), total bilirubin (TB), direct bilirubin (DB), indirect bilirubin (IB), alanine aminotransferase (ALT), aspartate aminotransferase (AST), AST/ALT ratio, alkaline phosphatase (ALP), lactate dehydrogenase (LDH), and γ-glutamyltransferase (GGT). Liquid chromatography-tandem mass spectrometry was used to detect the plasma Aβ42 and Aβ40 concentrations. Single Molecule array technique was used to measure the plasma p-tau181 and NfL concentrations. We used linear regression models to analyze the associations between liver function markers and the levels of AD plasma biomarkers.

RESULTS

ALP was positively associated with the levels of plasma Aβ42 (β = 0.16, P = 0.018) and Aβ40 (β = 0.21, P = 0.004). LDH was positively associated with the levels of plasma p-tau181 (β = 0.09, P = 0.022). While NfL was correlated with multiple liver function markers, including AL, A/G, ALT, AST/ALT, and LDH.

CONCLUSION

Liver function was associated with the plasma levels of AD biomarkers. It needs to consider the potential influence of liver function on the reference ranges and the interpretation of results for AD biomarkers before clinical use.

Depression in Alzheimer's Disease: Epidemiology, Mechanisms, and Treatment

Depression and Alzheimer's disease (AD) are substantial public health concerns. In the past decades, a link between the 2 disease entities has received extensive acknowledgment, yet the complex nature of this relationship demands further clarification. Some evidence indicates that midlife depression may be an AD risk factor, while a chronic course of depression in late life may be a precursor to or symptom of dementia. Recently, multiple pathophysiological mechanisms have been proposed to underlie the bidirectional relationship between depression and AD, including genetic predisposition, immune dysregulation, accumulation of AD-related biomarkers (e.g., amyloid-β and tau), and alterations in brain structure. Accordingly, numerous therapeutic approaches, such as pharmacology treatments, psychotherapy, and lifestyle interventions, have been suggested as potential means of interfering with these pathways. However, the current literature on this topic remains fragmented and lacks a comprehensive review characterizing the association between depression and AD. In this review, we aim to address these gaps by providing an overview of the co-occurrence and temporal relationship between depression and AD, as well as exploring their underlying mechanisms. We also examine the current therapeutic regimens for depression and their implications for AD management and outline key challenges facing the field.

LRP1 in GABAergic neurons is a key link between obesity and memory function

OBJECTIVE

Low-density lipoprotein receptor-related protein-1 (LRP1) regulates energy homeostasis, blood-brain barrier integrity, and metabolic signaling in the brain. Deficiency of LRP1 in inhibitory gamma-aminobutyric acid (GABA)ergic neurons causes severe obesity in mice. However, the impact of LRP1 in inhibitory neurons on memory function and cognition in the context of obesity is poorly understood.

METHODS

Mice lacking LRP1 in GABAergic neurons (Vgat-Cre; LRP1loxP/loxP) underwent behavioral tests for locomotor activity and motor coordination, short/long-term and spatial memory, and fear learning/memory. This study evaluated the relationships between behavior and metabolic risk factors and followed the mice at 16 and 32 weeks of age.

RESULTS

Deletion of LRP1 in GABAergic neurons caused a significant impairment in memory function in 32-week-old mice. In the spatial Y-maze test, Vgat-Cre; LRP1loxP/loxP mice exhibited decreased travel distance and duration in the novel arm compared with controls (LRP1loxP/loxP mice). In addition, GABAergic neuron-specific LRP1-deficient mice showed a diminished capacity for performing learning and memory tasks during the water T-maze test. Moreover, reduced freezing time was observed in these mice during the contextual and cued fear conditioning tests. These effects were accompanied by increased neuronal necrosis and satellitosis in the hippocampus. Importantly, the distance and duration in the novel arm, as well as the performance of the reversal water T-maze test, negatively correlated with metabolic risk parameters, including body weight, serum leptin, insulin, and apolipoprotein J. However, in 16-week-old Vgat-Cre; LRP1loxP/loxP mice, there were no differences in the behavioral tests or correlations between metabolic parameters and cognition.

CONCLUSIONS

Our findings demonstrate that LRP1 from GABAergic neurons is important in regulating normal learning and memory. Metabolically, obesity caused by GABAergic LRP1 deletion negatively regulates memory and cognitive function in an age-dependent manner. Thus, LRP1 in GABAergic neurons may play a crucial role in maintaining normal excitatory/inhibitory balance, impacting memory function, and reinforcing the potential importance of LRP1 in neural system integrity.

The Intersection of cerebral cholesterol metabolism and Alzheimer's disease: Mechanisms and therapeutic prospects

Alzheimer's disease (AD) is a common neurodegenerative disease in the elderly, the exact pathogenesis of which remains incompletely understood, and effective preventive and therapeutic drugs are currently lacking. Cholesterol plays a vital role in cell membrane formation and neurotransmitter synthesis, and its abnormal metabolism is associated with the onset of AD. With the continuous advancement of imaging techniques and molecular biology methods, researchers can more accurately explore the relationship between cholesterol metabolism and AD. Elevated cholesterol levels may lead to vascular dysfunction, thereby affecting neuronal function. Additionally, abnormal cholesterol metabolism may affect the metabolism of β-amyloid protein, thereby promoting the onset of AD. Brain cholesterol levels are regulated by multiple factors. This review aims to deepen the understanding of the subtle relationship between cholesterol homeostasis and AD, and to introduce the latest advances in cholesterol-regulating AD treatment strategies, thereby inspiring readers to contemplate deeply on this complex relationship. Although there are still many unresolved important issues regarding the risk of brain cholesterol and AD, and some studies may have opposite conclusions, further research is needed to enrich our understanding. However, these findings are expected to deepen our understanding of the pathogenesis of AD and provide important insights for the future development of AD treatment strategies targeting brain cholesterol homeostasis.

Unraveling the Role of the Blood-Brain Barrier in the Pathophysiology of Depression: Recent Advances and Future Perspectives

Depression is a highly prevalent psychological disorder characterized by persistent dysphoria, psychomotor retardation, insomnia, anhedonia, suicidal ideation, and a remarkable decrease in overall well-being. Despite the prevalence of accessible antidepressant therapies, many individuals do not achieve substantial improvement. Understanding the multifactorial pathophysiology and the heterogeneous nature of the disorder could lead the way toward better outcomes. Recent findings have elucidated the substantial impact of compromised blood-brain barrier (BBB) integrity on the manifestation of depression. BBB functions as an indispensable defense mechanism, tightly overseeing the transport of molecules from the periphery to preserve the integrity of the brain parenchyma. The dysfunction of the BBB has been implicated in a multitude of neurological disorders, and its disruption and consequent brain alterations could potentially serve as important factors in the pathogenesis and progression of depression. In this review, we extensively examine the pathophysiological relevance of the BBB and delve into the specific modifications of its components that underlie the complexities of depression. A particular focus has been placed on examining the effects of peripheral inflammation on the BBB in depression and elucidating the intricate interactions between the gut, BBB, and brain. Furthermore, this review encompasses significant updates on the assessment of BBB integrity and permeability, providing a comprehensive overview of the topic. Finally, we outline the therapeutic relevance and strategies based on BBB in depression, including COVID-19-associated BBB disruption and neuropsychiatric implications. Understanding the comprehensive pathogenic cascade of depression is crucial for shaping the trajectory of future research endeavors.

Transcytosis-Driven Treatment of Neurodegenerative Disorders by mRNA-Expressed Antibody-Transferrin Conjugates

The recent setbacks in the withdrawal and approval delays of antibody treatments of neurodegenerative disorders (NDs), attributed to their poor entry across the blood-brain barrier (BBB), emphasize the need to bring novel approaches to enhance the entry across the BBB. One such approach is conjugating the antibodies that bind brain proteins responsible for NDs with the transferrin molecule. This glycoprotein transports iron into cells, connecting with the transferrin receptors (TfRs), piggybacking an antibody-transferrin complex that can subsequently release the antibody in the brain or stay connected while letting the antibody bind. This process increases the concentration of antibodies in the brain, enhancing therapeutic efficacy with targeted delivery and minimum systemic side effects. Currently, this approach is experimented with using drug-transferring conjugates assembled in vitro. Still, a more efficient and safer alternative is to express the conjugate using mRNA technology, as detailed in this paper. This approach will expedite safer discoveries that can be made available at a much lower cost than the recombinant process with in vitro conjugation. Most importantly, the recommendations made in this paper may save the antibodies against the NDs that seem to be failing despite their regulatory approvals.

Contribution of Direct Cerebral Vascular Transport in Brain Substance Clearance

The accumulation of harmful substances has long been recognized as a likely cause of many neurodegenerative diseases. The two classic brain clearance pathways are cerebrospinal fluid (CSF) and vascular circulation systems. Since the discovery of the glymphatic system, research on the CSF pathway has gained momentum, and impaired CSF clearance has been implicated in virtually all neurodegenerative animal models. However, the contribution of the direct participation of vascular transport across the blood-brain barrier in clearing substances is often ignored in glymphatic papers. Supportive evidence for the direct involvement of parenchymal vasculature in substance clearance is accumulated. First, multiple mechanisms have been proposed for the vascular drainage of exogenous and endogenous substances across the blood-brain barriers. Second, the "traditional" role of arachnoid villi and granulations as the main site for CSF draining into the vasculature system has been questioned. Third, MRI studies using different CSF tracers indicate that parenchymal vasculature directly participates in tracer efflux, consistent with immunohistochemical findings. Here we will review evidence in the literature that supports the direct participation of the parenchymal vascular system in substance clearance, in addition to the CSF clearance pathways.

Transient Receptor Potential Channels in the Healthy and Diseased Blood-Brain Barrier

The large family of transient receptor potential (TRP) channels are integral membrane proteins that function as environmental sensors and act as ion channels after activation by mechanical (touch), physical (heat, pain), and chemical stimuli (pungent compounds such as capsaicin). Most TRP channels are localized in the plasma membrane of cells but some of them are localized in membranes of organelles and function as intracellular Ca2+-ion channels. TRP channels are involved in neurological disorders but their precise role(s) and relevance in these disorders are not clear. Endothelial cells of the blood-brain barrier (BBB) express TRP channels such as TRP vanilloid 1-4 and are involved in thermal detection by regulating BBB permeability. In neurological disorders, TRP channels in the BBB are responsible for edema formation in the brain. Therefore, drug design to modulate locally activity of TRP channels in the BBB is a hot topic. Today, the application of TRP channel antagonists against neurological disorders is still limited.

Repetitive head trauma and apoE4 induce chronic cerebrovascular alterations that impair tau elimination from the brain

Repetitive mild traumatic brain injuries (r-mTBI) sustained in the military or contact sports have been associated with the accumulation of extracellular tau in the brain, which may contribute to the pathogenesis of neurodegenerative tauopathies. The expression of the apolipoprotein E4 (apoE4) isoform has been associated with higher levels of tau in the brain, and worse clinical outcomes after r-mTBI, though the influence of apoE genotype on extracellular tau dynamics in the brain is poorly understood. We recently demonstrated that extracellular tau can be eliminated across blood-brain barrier (BBB), which is progressively impaired following r-mTBI. The current studies investigated the influence of repetitive mild TBI (r-mTBI) and apoE genotype on the elimination of extracellular solutes from the brain. Following intracortical injection of biotin-labeled tau into humanized apoE-Tr mice, the levels of exogenous tau residing in the brain of apoE4 mice were elevated compared to other isoforms, indicating reduced tau elimination. Additionally, we found exposure to r-mTBI increased tau residence in apoE2 mice, similar to our observations in E2FAD animals. Each of these findings may be the result of diminished tau efflux via LRP1 at the BBB, as LRP1 inhibition significantly reduced tau uptake in endothelial cells and decreased tau transit across an in vitro model of the BBB (basolateral-to-apical). Notably, we showed that injury and apoE status, (particularly apoE4) resulted in chronic alterations in BBB integrity, pericyte coverage, and AQP4 polarization. These aberrations coincided with an atypical reactive astrocytic gene signature indicative of diminished CSF-ISF exchange. Our work found that CSF movement was reduced in the chronic phase following r-mTBI (>18 months post injury) across all apoE genotypes. In summary, we show that apoE genotype strongly influences cerebrovascular homeostasis, which can lead to age-dependent deficiencies in the elimination of toxic proteins from the brain, like tau, particularly in the aftermath of head trauma.

The role of ATP-binding cassette transporter G1 (ABCG1) in Alzheimer's disease: A review of the mechanisms

The maintenance of cholesterol homeostasis is essential for central nervous system function. Consequently, factors that affect cholesterol homeostasis are linked to neurological disorders and pathologies. Among them, ATP-binding cassette transporter G1 (ABCG1) plays a significant role in atherosclerosis. However, its role in Alzheimer's disease (AD) is unclear. There is inconsistent information regarding ABCG1's role in AD. It can increase or decrease amyloid β (Aβ) levels in animals' brains. Clinical studies show that ABCG1 is involved in AD patients' impairment of cholesterol efflux capacity (CEC) in the cerebrospinal fluid (CSF). Lower Aβ levels in the CSF are correlated with ABCG1-mediated CEC dysfunction. ABCG1 modulates α-, β-, and γ-secretase activities in the plasma membrane and may affect Aβ production in the mitochondria-associated endoplasmic reticulum (ER) membrane (MAM) cell compartment. Despite contradictory findings regarding ABCG1's role in AD, this review shows that ABCG1 has a role in Aβ generation via modulation of membrane secretases. It is, however, necessary to investigate the underlying mechanism(s). ABCG1 may also contribute to AD pathology through its role in apoptosis and oxidative stress. As a result, ABCG1 plays a role in AD and is a candidate for drug development.

Astrocyte-derived lactoferrin reduces β-amyloid burden by promoting the interaction between p38 kinase and PP2A phosphatase in male APP/PS1 transgenic mice

BACKGROUND AND PURPOSE

Overexpression of astrocytic lactoferrin (Lf) was observed in the brain of Alzheimer's disease (AD) patients, whereas the role of astrocytic Lf in AD progression remains unexplored. In this study, we aimed to evaluate the effects of astrocytic Lf on AD progression.

EXPERIMENTAL APPROACH

Male APP/PS1 mice with astrocytes overexpressing human Lf were developed to evaluate the effects of astrocytic Lf on AD progression. N2a-sw cells also were employed to further uncover the mechanism of astrocytic Lf on β-amyloid (Aβ) production.

KEY RESULTS

Astrocytic Lf overexpression increased protein phosphatase 2A (PP2A) activity and reduced amyloid precursor protein (APP) phosphorylation, Aβ burden and tau hyperphosphorylation in APP/PS1 mice. Mechanistically, astrocytic Lf overexpression promoted the uptake of astrocytic Lf into neurons in APP/PS1 mice, and conditional medium from astrocytes overexpressing Lf inhibited p-APP (Thr668) expression in N2a-sw cells. Furthermore, recombinant human Lf (hLf) significantly enhanced PP2A activity and inhibited p-APP expression, whereas inhibition of p38 or PP2A activities abrogated the hLf-induced p-APP down-regulation in N2a-sw cells. Additionally, hLf promoted the interaction of p38 and PP2A via p38 activation, thereby enhancing PP2A activity, and low-density lipoprotein receptor-related protein 1 (LRP1) knockdown significantly reversed the hLf-induced p38 activation and p-APP down-regulation.

CONCLUSIONS AND IMPLICATIONS

Our data suggested that astrocytic Lf promoted neuronal p38 activation, via targeting to LRP1, subsequently promoting p38 binding to PP2A to enhance PP2A enzyme activity, which finally inhibited Aβ production via APP dephosphorylation. In conclusion, promoting astrocytic Lf expression may be a potential strategy against AD.

LINKED ARTICLES

This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

Cathepsin B-Responsive Programmed Brain Targeted Delivery System for Chemo-Immunotherapy Combination Therapy of Glioblastoma

Tumor-associated macrophages (TAMs) are closely related to the progression of glioblastoma multiform (GBM) and its development of therapeutic resistance to conventional chemotherapy. TAM-targeted therapy combined with conventional chemotherapy has emerged as a promising strategy to combat GBM. However, the presence of the blood-brain barrier (BBB) severely limits the therapeutic efficacy. Meanwhile, the lack of ability to distinguish different targeted cells also poses a challenge for precise therapy. Herein, we propose a cathepsin B (CTSB)-responsive programmed brain-targeted delivery system (D&R-HM-MCA) for simultaneous TAM-targeted and GBM-targeted delivery. D&R-HM-MCA could cross the BBB via low density lipoprotein receptor-associated protein 1 (LRP1)-mediated transcytosis. Upon reaching the GBM site, the outer angiopep-2 modification could be detached from D&R-HM-MCA via cleavage of the CTSB-responsive peptide, which could circumvent abluminal LRP1-mediated efflux. The exposed p-aminophenyl-α-d-mannopyranoside (MAN) modification could further recognize glucose transporter-1 (GLUT1) on GBM and macrophage mannose receptor (MMR) on TAMs. D&R-HM-MCA could achieve chemotherapeutic killing of GBM and simultaneously induce TAM polarization from anti-inflammatory M2 phenotype to pro-inflammatory M1 phenotype, thus resensitizing the chemotherapeutic response and improving anti-GBM immune response. This CTSB-responsive brain-targeted delivery system not only can improve brain delivery efficiency, but also can enable the combination of chemo-immunotherapy against GBM. The effectiveness of this strategy may provide thinking for designing more functional brain-targeted delivery systems and more effective therapeutic regimens.

Coronal ApoE Protein Combines with LRP1 to Inactivate GSK3β That Mitigates Silica Nanoparticle-Induced Brain Lesion

Silica nanoparticles (SiO2 NPs) are widely used engineered materials that warrant their obvious environmental exposure risk. Our previous study has shown that different routes of SiO2 NP exposure on the glycogen synthase kinase 3 beta (GSK3β) activity were related to the serum proteins enriched on the surface of SiO2 NPs, which implied that a particular protein in the serum changed the inherent toxic behavior of SiO2 NPs and inhibited the activation of GSK3β by SiO2 NPs. Here, we identified that the SiO2 NP surface enriched a large amount of apolipoprotein E (ApoE), and the ApoE protein corona bound to the lipoprotein receptor-related protein 1 (LRP1) to inactivate GSK3β, thereby reducing the damage of SiO2 NPs to the brain. This work presented the first evidence that specific biocorona reduced the toxicity of SiO2 NPs at the molecular level, which helped to elucidate the role of specific corona components on nanotoxicity.

Are high copper levels related to Alzheimer's and Parkinson's diseases? A systematic review and meta-analysis of articles published between 2011 and 2022

Copper performs an important role in the brain, but in high levels it can be neurotoxic. Further, some authors have described that copper dyshomeostasis could be related with neurodegenerative diseases. Thus, this review was performed to observe whether high copper levels are related to Alzheimer's and Parkinson's diseases (AD and PD), using the literature published recently. Articles that measured copper levels in AD or PD patients was included, as well as they that measured copper levels in models used to mimic these diseases. Also, results about high copper levels effects and its relationship with AD and PD observed in laboratory animals are considered. In summary, 38 and 24 articles with AD and PD patients were included, respectively. Despite of the heterogeneity between the studies in humans, meta-analysis has demonstrated that there is an increase in free and total copper levels in the blood of AD patients compared to controls, and a decrease in copper levels in PD patients. A decrease in the metal content in postmortem brain tissue was observed in AD and PD. In manuscripts using animal models that mimic AD and PD, it was included seven and three articles, respectively. Two of them have reported an increase in copper concentrations in AD model, and one in PD model. Finally, studies with laboratory animals have concluded that high copper levels are related to oxidative stress, neuroinflammation, mitochondrial dysfunction, changes in neurotransmitter levels, cell death, and reduced both cognitive and locomotor activity, which are also described in AD or PD.

Blood-brain barrier transporters: An overview of function, dysfunction in Alzheimer's disease and strategies for treatment

The blood-brain-barrier (BBB) has a major function in maintaining brain homeostasis by regulating the entry of molecules from the blood to the brain. Key players in BBB function are BBB transporters which are highly expressed in brain endothelial cells (BECs) and critical in mediating the exchange of nutrients and waste products. BBB transporters can also influence drug delivery into the brain by inhibiting or facilitating the entry of brain targeting therapeutics for the treatment of brain disorders, such as Alzheimer's disease (AD). Recent studies have shown that AD is associated with a disrupted BBB and transporter dysfunction, although their roles in the development in AD are not fully understand. Modulation of BBB transporter activity may pose a novel approach to enhance the delivery of drugs to the brain for enhanced treatment of AD. In this review, we will give an overview of key functions of BBB transporters and known changes in AD. In addition, we will discuss current strategies for transporter modulation for enhanced drug delivery into the brain.

Extension domain of amyloid processor protein inhibits amyloidogenic cleavage and balances neural activity in a traumatic brain injury mouse model

BACKGROUND

Mechanisms underlying cognitive dysfunction following traumatic brain injury (TBI) partially due to abnormal amyloid processor protein (APP) cleavage and neural hyperactivity. Binding of the extension domain of APP (ExD17) to the GABAbR1 receptor results in reduced neural activity, which might play a role in the mechanisms of cognitive dysfunction caused by TBI.

METHODS

Stretch-induced injury was utilized to establish a cell injury model in HT22 cells. The TBI model was created by striking the exposed brain tissue with a free-falling weight. Topical or intraperitoneal administration of ExD17 was performed. Cell viability was assessed through a cell counting kit-8 assay, while intracellular Ca2+ was measured using Fluo-4. Western blotting was used to investigate the expression of APP amyloidogenic cleavage proteins, GABAbR1, phospholipase C (PLC), PLCB3, and synaptic proteins. ELISA was performed to analyze the levels of Aβ42. Seizures were assessed using electroencephalography (EEG). Behaviors were evaluated through the novel object recognition test, open field test, elevated plus maze test, and nest-building test.

RESULTS

ExD17 improved cell viability and reduced intracellular calcium in the cell injury model. The treatment also suppressed the increased expression of APP amyloidogenic cleavage proteins and Aβ42 in both cell injury and TBI models. ExD17 treatment reversed the abnormal expression of GABAbR1, GRIA2, p-PLCG1/PLCG1 ratio, and p-PLCB3/PLCB3 ratio. In addition, ExD17 treatment reduced neural activity, seizure events, and their duration in TBI. Intraperitoneal injection of ExD17 improved behavioral outcomes in the TBI mouse model.

CONCLUSIONS

ExD17 treatment results in a reduction of amyloidogenic APP cleavage and neuroexcitotoxicity, ultimately leading to an improvement in the behavioral deficits observed in TBI mice.

Elevated CSF angiopoietin-2 correlates with blood-brain barrier leakiness and markers of neuronal injury in early Alzheimer's disease

Breakdown of the neurovascular unit is associated with blood-brain barrier (BBB) leakiness contributing to cognitive decline and disease pathology in the early stages of Alzheimer's disease (AD). Vascular stability depends on angiopoietin-1 (ANGPT-1) signalling, antagonised by angiopoietin-2 (ANGPT-2) expressed upon endothelial injury. We examined the relationship between CSF ANGPT-2 and CSF markers of BBB leakiness and core AD biomarkers across three independent cohorts: (i) 31 AD patients and 33 healthy controls grouped according to their biomarker profile (i.e., AD cases t-tau > 400 pg/mL, p-tau > 60 pg/mL and Aβ42 < 550 pg/mL); (ii) 121 participants in the Wisconsin Registry for Alzheimer's Prevention or Wisconsin Alzheimer's Disease Research study (84 participants cognitively unimpaired (CU) enriched for a parental history of AD, 20 participants with mild cognitive impairment (MCI), and 17 with AD); (iii) a neurologically normal cohort aged 23-78 years with paired CSF and serum samples. CSF ANGPT-2, sPDGFRβ, albumin and fibrinogen levels were measured by sandwich ELISA. In cohort (i), CSF ANGPT-2 was elevated in AD and correlated with CSF t-tau and p-tau181 but not Aβ42. ANGPT-2 also correlated positively with CSF sPDGFRβ and fibrinogen - markers of pericyte injury and BBB leakiness. In cohort (ii), CSF ANGPT-2 was highest in MCI and correlated with CSF albumin in the CU and MCI cohorts but not in AD. CSF ANGPT-2 also correlated with CSF t-tau and p-tau and with markers of neuronal injury (neurogranin and α-synuclein) and neuroinflammation (GFAP and YKL-40). In cohort (iii), CSF ANGPT-2 correlated strongly with the CSF/serum albumin ratio. Serum ANGPT-2 showed non-significant positive associations with CSF ANGPT-2 and the CSF/serum albumin ratio. Together, these data indicate that CSF and possibly serum ANGPT-2 is associated with BBB leakiness in early AD and is closely related to tau pathology and neuronal injury. The utility of serum ANGPT-2 as a biomarker of BBB damage in AD requires further study.

Alzheimer's disease brain endothelial-like cells reveal differential drug transporter expression and modulation by potentially therapeutic focused ultrasound

The blood-brain barrier (BBB) has a key function in maintaining homeostasis in the brain, partly modulated by transporters, which are highly expressed in brain endothelial cells (BECs). Transporters mediate the uptake or efflux of compounds to and from the brain and they can also challenge the delivery of drugs for the treatment of Alzheimer's disease (AD). Currently there is a limited understanding of changes in BBB transporters in AD. To investigate this, we generated brain endothelial-like cells (iBECs) from induced pluripotent stem cells (iPSCs) with familial AD (FAD) Presenilin 1 (PSEN1) mutation and identified AD-specific differences in transporter expression compared to control (ctrl) iBECs. We first characterized the expression levels of 12 BBB transporters in AD-, Ctrl-, and isogenic (PSEN1 corrected) iBECs to identify any AD specific differences. We then exposed the cells to focused ultrasound (FUS) in the absence (FUSonly) or presence of microbubbles (MB) (FUS+MB), which is a novel therapeutic method that can be used to transiently open the BBB to increase drug delivery into the brain, however its effects on BBB transporter expression are largely unknown. Following FUSonly and FUS+MB, we investigated whether the expression or activity of key transporters could be modulated. Our findings demonstrate that PSEN1 mutant FAD (PSEN1AD) possess phenotypical differences compared to control iBECs in BBB transporter expression and function. Additionally, we show that FUSonly and FUS+MB can modulate BBB transporter expression and functional activity in iBECs, having potential implications on drug penetration and amyloid clearance. These findings highlight the differential responses of patient cells to FUS treatment, with patient-derived models likely providing an important tool for modelling therapeutic effects of FUS.

High-Fat Diets in Animal Models of Alzheimer's Disease: How Can Eating Too Much Fat Increase Alzheimer's Disease Risk?

High dietary intake of saturated fatty acids is a suspected risk factor for neurodegenerative diseases, including Alzheimer's disease (AD). To decipher the causal link behind these associations, high-fat diets (HFD) have been repeatedly investigated in animal models. Preclinical studies allow full control over dietary composition, avoiding ethical concerns in clinical trials. The goal of the present article is to provide a narrative review of reports on HFD in animal models of AD. Eligibility criteria included mouse models of AD fed a HFD defined as > 35% of fat/weight and western diets containing > 1% cholesterol or > 15% sugar. MEDLINE and Embase databases were searched from 1946 to August 2022, and 32 preclinical studies were included in the review. HFD-induced obesity and metabolic disturbances such as insulin resistance and glucose intolerance have been replicated in most studies, but with methodological variability. Most studies have found an aggravating effect of HFD on brain Aβ pathology, whereas tau pathology has been much less studied, and results are more equivocal. While most reports show HFD-induced impairment on cognitive behavior, confounding factors may blur their interpretation. In summary, despite conflicting results, exposing rodents to diets highly enriched in saturated fat induces not only metabolic defects, but also cognitive impairment often accompanied by aggravated neuropathological markers, most notably Aβ burden. Although there are important variations between methods, particularly the lack of diet characterization, these studies collectively suggest that excessive intake of saturated fat should be avoided in order to lower the incidence of AD.

Pericyte Control of Gene Expression in the Blood-Brain Barrier Endothelium: Implications for Alzheimer's Disease

Background

A strong body of evidence suggests that cerebrovascular pathologies augment the onset and progression of Alzheimer's disease (AD). One distinctive aspect of this cerebrovascular dysfunction is the degeneration of brain pericytes-often overlooked supporting cells of blood-brain barrier endothelium.

Objective

The current study investigates the influence of pericytes on gene and protein expressions in the blood-brain barrier endothelium, which is expected to facilitate the identification of pathophysiological pathways that are triggered by pericyte loss and lead to blood-brain barrier dysfunction in AD.

Methods

Bioinformatics analysis was conducted on the RNA-Seq expression counts matrix (GSE144474), which compared solo-cultured human blood-brain barrier endothelial cells against endothelial cells co-cultured with human brain pericytes in a non-contact model. We constructed a similar cell culture model to verify protein expression using western blots.

Results

The insulin resistance and ferroptosis pathways were found to be enriched. Western blots of the insulin receptor and heme oxygenase expressions were consistent with those observed in RNA-Seq data. Additionally, we observed more than 5-fold upregulation of several genes associated with neuroprotection, including insulin-like growth factor 2 and brain-derived neurotrophic factor.

Conclusions

Results suggest that pericyte influence on blood-brain barrier endothelial gene expression confers protection from insulin resistance, iron accumulation, oxidative stress, and amyloid deposition. Since these are conditions associated with AD pathophysiology, they imply mechanisms by which pericyte degeneration could contribute to disease progression.

Current Anti-Amyloid-β Therapy for Alzheimer's Disease Treatment: From Clinical Research to Nanomedicine

Recent successive approval of anti-amyloid-β (Aβ) monoclonal antibodies as disease-modifying therapies against Alzheimer's disease (AD) has raised great confidence in the development of anti-AD therapies; however, the current therapies still face the dilemma of significant adverse reactions and limited effects. In this review, we summarized the therapeutic characteristics of the approved anti-Aβ immunotherapies and dialectically analyzed the gains and losses from clinical trials. The review further proposed the reasonable selection of animal models in preclinical studies from the perspective of different animal models of Aβ deposition and deals in-depth with the recent advances of exploring preclinical nanomedical application in Aβ targeted therapy, aiming to provide a reliable systematic summary for the development of novel anti-Aβ therapies. Collectively, this review comprehensively dissects the pioneering work of Aβ-targeted therapies and proposed perspective insight into AD-modified therapies.

ANKS1A regulates LDL receptor-related protein 1 (LRP1)-mediated cerebrovascular clearance in brain endothelial cells

Brain endothelial LDL receptor-related protein 1 (LRP1) is involved in the clearance of Aβ peptides across the blood-brain barrier (BBB). Here we show that endothelial deficiency of ankyrin repeat and SAM domain containing 1 A (ANKS1A) reduces both the cell surface levels of LRP1 and the Aβ clearance across the BBB. Association of ANKS1A with the NPXY motifs of LRP1 facilitates the transport of LRP1 from the endoplasmic reticulum toward the cell surface. ANKS1A deficiency in an Alzheimer's disease mouse model results in exacerbated Aβ pathology followed by cognitive impairments. These deficits are reversible by gene therapy with brain endothelial-specific ANKS1A. In addition, human induced pluripotent stem cell-derived BBBs (iBBBs) were generated from endothelial cells lacking ANKS1A or carrying the rs6930932 variant. Those iBBBs exhibit both reduced cell surface LRP1 and impaired Aβ clearance. Thus, our findings demonstrate that ANKS1A regulates LRP1-mediated Aβ clearance across the BBB.

Mechanisms behind changes of neurodegeneration biomarkers in plasma induced by sleep deprivation

Acute sleep deprivation has been shown to affect cerebrospinal fluid and plasma concentrations of biomarkers associated with neurodegeneration, though the mechanistic underpinnings remain unknown. This study compared individuals who, for one night, were either subject to total sleep deprivation or free sleep, (i) examining plasma concentrations of neurodegeneration biomarkers the morning after sleep deprivation or free sleep and (ii) determining how overnight changes in biomarkers plasma concentrations correlate with indices of meningeal lymphatic and glymphatic clearance functions. Plasma concentrations of amyloid-β 40 and 42, phosphorylated tau peptide 181, glial fibrillary acid protein and neurofilament light were measured longitudinally in subjects who from Day 1 to Day 2 either underwent total sleep deprivation (n = 7) or were allowed free sleep (n = 21). The magnetic resonance imaging contrast agent gadobutrol was injected intrathecally, serving as a cerebrospinal fluid tracer. Population pharmacokinetic model parameters of gadobutrol cerebrospinal fluid-to-blood clearance were utilized as a proxy of meningeal lymphatic clearance capacity and intrathecal contrast-enhanced magnetic resonance imaging as a proxy of glymphatic function. After one night of acute sleep deprivation, the plasma concentrations of amyloid-β 40 and 42 were reduced, but not the ratio, and concentrations of the other biomarkers were unchanged. The overnight change in amyloid-β 40 and 42 plasma concentrations in the sleep group correlated significantly with indices of meningeal lymphatic clearance capacity, while this was not seen for the other neurodegeneration biomarkers. However, overnight change in plasma concentrations of amyloid-β 40 and 42 did not correlate with the glymphatic marker. On the other hand, the overnight change in plasma concentration of phosphorylated tau peptide 181 correlated significantly with the marker of glymphatic function in the sleep deprivation group but not in the sleep group. The present data add to the evidence of the role of sleep and sleep deprivation on plasma neurodegeneration concentrations; however, the various neurodegeneration biomarkers respond differently with different mechanisms behind sleep-induced alterations in amyloid-β and tau plasma concentrations. Clearance capacity of meningeal lymphatics seems more important for sleep-induced changes in amyloid-β 40 and 42 plasma concentrations, while glymphatic function seems most important for change in plasma concentration of phosphorylated tau peptide 181 during sleep deprivation. Altogether, the present data highlight diverse mechanisms behind sleep-induced effects on concentrations of plasma neurodegeneration biomarkers.

LRP1 and RAGE Genes Transporting Amyloid and Tau Protein in the Hippocampal CA3 Area in an Ischemic Model of Alzheimer's Disease with 2-Year Survival

Explaining changes at the gene level that occur during neurodegeneration in the CA3 area is crucial from the point of view of memory impairment and the development of post-ischemic dementia. An ischemic model of Alzheimer's disease was used to evaluate changes in the expression of genes related to amyloid transport in the CA3 region of the hippocampus after 10 min of brain ischemia with survival of 2, 7 and 30 days and 12, 18 and 24 months. The quantitative reverse transcriptase PCR assay revealed that the expression of the LRP1 and RAGE genes involved in amyloid transport was dysregulated from 2 days to 24 months post-ischemia in the CA3 area of the hippocampus. LRP1 gene expression 2 and 7 days after ischemia was below control values. However, its expression from day 30 to 24 months, survival after an ischemic episode was above control values. RAGE gene expression 2 days after ischemia was below control values, reaching a maximum increase 7 and 30 days post-ischemia. Then, after 12, 18 and 24 months, it was again below the control values. The data indicate that in the CA3 area of the hippocampus, an episode of brain ischemia causes the increased expression of the RAGE gene for 7-30 days during the acute phase and that of LRP1 from 1 to 24 months after ischemia during the chronic stage. In other words, in the early post-ischemic stage, the expression of the gene that transport amyloid to the brain increases (7-30 days). Conversely, in the late post-ischemic stage, amyloid scavenging/cleaning gene activity increases, reducing and/or preventing further neuronal damage or facilitating the healing of damaged sites. This is how the new phenomenon of pyramidal neuronal damage in the CA3 area after ischemia is defined. In summary, post-ischemic modification of the LRP1 and RAGE genes is useful in the study of the ischemic pathways and molecular factors involved in the development of Alzheimer's disease.

Bone Marrow-Derived GCA+ Immune Cells Drive Alzheimer's Disease Progression

Alzheimer's disease (AD) is an age-related degenerative disease of the central nervous system (CNS), whereas the role of bone marrow immune cells in the pathogenesis of AD remains unclear. Here, the study reveals that compared to matched healthy individuals, AD patients have higher circulating grancalcin (GCA) levels, which negatively correlate with cognitive function. Bone marrow-derived GCA+ immune cells, which secret abundant GCA and increase during aging, preferentially invaded the hippocampus and cortex of AD mouse model in a C-C Motif Chemokine Receptor 10 (CCR10)-dependent manner. Transplanting GCA+ immune cells or direct stereotaxic injection of recombinant GCA protein intensified amyloid plaque load and aggravated cognitive and memory impairments. In contrast, genetic ablation of GCA in the hematopoietic compartment improves cognitive and memory function. Mechanistically, GCA competitively binds to the low-density lipoprotein receptor-related protein 1 (LRP1) in microglia, thus inhibiting phagocytosis and clearance of Aβ and potentiating neuropathological changes. Importantly, GCA-neutralizing antibody treatment rejuvenated cognitive and memory function and constrained AD progression. Together, the study demonstrates a pathological role of GCA+ immune cells instigating cognitive and memory decline, suggesting that GCA+ immune cells can be a potential target for innovative therapeutic strategies in AD.

Local perfusion of capillaries reveals disrupted beta-amyloid homeostasis at the blood-brain barrier in Tg2576 murine Alzheimer's model

BACKGROUND

Parenchymal accumulation of beta-amyloid (Aβ) characterizes Alzheimer's disease (AD). Aβ homeostasis is maintained by two ATP-binding cassette (ABC) transporters (ABCC1 and ABCB1) mediating efflux, and the receptor for advanced glycation end products (RAGE) mediating influx across the blood-brain barrier (BBB). Altered transporter levels and disruption of tight junctions (TJ) were linked to AD. However, Aβ transport and the activity of ABCC1, ABCB1 and RAGE as well as the functionality of TJ in AD are unclear.

METHODS

ISMICAP, a BBB model involving microperfusion of capillaries, was used to assess BBB properties in acute cortical brain slices from Tg2576 mice compared to wild-type (WT) controls using two-photon microscopy. TJ integrity was tested by vascularly perfusing biocytin-tetramethylrhodamine (TMR) and quantifying its extravascular diffusion as well as the diffusion of FM1-43 from luminal to abluminal membranes of endothelial cells (ECs). To assess ABCC1 and ABCB1 activity, calcein-AM was perfused, which is converted to fluorescent calcein in ECs and gets actively extruded by both transporters. To probe which transporter is involved, probenecid or Elacridar were applied, individually or combined, to block ABCC1 and ABCB1, respectively. To assess RAGE activity, the binding of 5-FAM-tagged Aβ by ECs was quantified with or without applying FPS-ZM1, a RAGE antagonist.

RESULTS

In Tg2576 mouse brain, extravascular TMR was 1.8-fold that in WT mice, indicating increased paracellular leakage. FM1-43 staining of abluminal membranes in Tg2576 capillaries was 1.7-fold that in WT mice, indicating reduced TJ integrity in AD. While calcein was undetectable in WT mice, its accumulation was significant in Tg2576 mice, suggesting lower calcein extrusion in AD. Incubation with probenecid or Elacridar in WT mice resulted in a marked calcein accumulation, yet probenecid alone had no effect in Tg2576 mice, implying the absence of probenecid-sensitive ABC transporters. In WT mice, Aβ accumulated along the luminal membranes, which was undetectable after applying FPS-ZM1. In contrast, marginal Aβ fluorescence was observed in Tg2576 vessels, and FPS-ZM1 was without effect, suggesting reduced RAGE binding activity.

CONCLUSIONS

Disrupted TJ integrity, reduced ABCC1 functionality and decreased RAGE binding were identified as BBB alterations in Tg2576 mice, with the latter finding challenging the current concepts. Our results suggest to manage AD by including modulation of TJ proteins and Aβ-RAGE binding.

LRPAP1 is released from activated microglia and inhibits microglial phagocytosis and amyloid beta aggregation

Low-density lipoprotein receptor-related protein-associated protein 1 (LRPAP1), also known as receptor associated protein (RAP), is an endoplasmic reticulum (ER) chaperone and inhibitor of LDL receptor related protein 1 (LRP1) and related receptors. These receptors have dozens of physiological ligands and cell functions, but it is not known whether cells release LRPAP1 physiologically at levels that regulate these receptors and cell functions. We used mouse BV-2 and human CHME3 microglial cell lines, and found that microglia released nanomolar levels of LRPAP1 when inflammatory activated by lipopolysaccharide or when ER stressed by tunicamycin. LRPAP1 was found on the surface of live activated and non-activated microglia, and anti-LRPAP1 antibodies induced internalization. Addition of 10 nM LRPAP1 inhibited microglial phagocytosis of isolated synapses and cells, and the uptake of Aβ. LRPAP1 also inhibited Aβ aggregation in vitro. Thus, activated and stressed microglia release LRPAP1 levels that can inhibit phagocytosis, Aβ uptake and Aβ aggregation. We conclude that LRPAP1 release may regulate microglial functions and Aβ pathology, and more generally that extracellular LRPAP1 may be a physiological and pathological regulator of a wide range of cell functions.

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.

Amyloid-Beta Peptides 40 and 42 Employ Distinct Molecular Pathways for Cell Entry and Intracellular Transit at the Blood-Brain Barrier Endothelium

The blood-brain barrier (BBB) plays a critical role in maintaining the equilibrium between amyloid beta (Aβ) levels in blood and the brain by regulating Aβ transport. Our previous publications demonstrated that BBB trafficking of Aβ42 and Aβ40 is distinct and is disrupted under various pathophysiological conditions. However, the intracellular mechanisms that allow BBB endothelium to differentially handle Aβ40 and Aβ42 have not been clearly elucidated. In this study, we identified mechanisms of Aβ endocytosis in polarized human cerebral microvascular endothelial cell monolayers. Our studies demonstrated that Aβ peptides with fluorescent label (F-Aβ) were internalized by BBB endothelial cells via energy, dynamin, and actin-dependent endocytosis. Interestingly, endocytosis of F-Aβ40 but not F-Aβ42 was substantially reduced by clathrin inhibition, whereas F-Aβ42 but not F-Aβ40 endocytosis was reduced by half after inhibiting the caveolae-mediated pathway. Following endocytosis, both isoforms were sorted by the endo-lysosomal system. Although Aβ42 was shown to accumulate more in the lysosomes, which could lead to its higher degradation and/or aggregation at lower lysosomal pH, Aβ40 demonstrated robust accumulation in recycling endosomes, which may facilitate its exocytosis by the endothelial cells. These results provide a mechanistic insight into the selective ability of BBB endothelium to transport Aβ40 versus Aβ42. This knowledge contributes to the understanding of molecular pathways underlying Aβ accumulation in the BBB endothelium and associated BBB dysfunction. Moreover, it allows us to establish mechanistic rationale for altered Aβ40:Aβ42 ratios and anomalous amyloid deposition in the cerebral vasculature as well as brain parenchyma during Alzheimer's disease progression. SIGNIFICANCE STATEMENT: Differential interaction of Aβ40 and Aβ42 isoforms with the blood-brain barrier (BBB) endothelium may contribute to perturbation in Aβ42:Aβ40 ratio, which is associated with Alzheimer's disease (AD) progression and severity. The current study identified distinct molecular pathways by which Aβ40 and Aβ42 are trafficked at the BBB, which regulates equilibrium between blood and brain Aβ levels. These findings provide molecular insights into mechanisms that engender BBB dysfunction and promote Aβ accumulation in AD brain.

Ion Channels and Ionotropic Receptors in Astrocytes: Physiological Functions and Alterations in Alzheimer's Disease and Glioblastoma

The human brain is composed of nearly one hundred billion neurons and an equal number of glial cells, including macroglia, i.e., astrocytes and oligodendrocytes, and microglia, the resident immune cells of the brain. In the last few decades, compelling evidence has revealed that glial cells are far more active and complex than previously thought. In particular, astrocytes, the most abundant glial cell population, not only take part in brain development, metabolism, and defense against pathogens and insults, but they also affect sensory, motor, and cognitive functions by constantly modulating synaptic activity. Not surprisingly, astrocytes are actively involved in neurodegenerative diseases (NDs) and other neurological disorders like brain tumors, in which they rapidly become reactive and mediate neuroinflammation. Reactive astrocytes acquire or lose specific functions that differently modulate disease progression and symptoms, including cognitive impairments. Astrocytes express several types of ion channels, including K+, Na+, and Ca2+ channels, transient receptor potential channels (TRP), aquaporins, mechanoreceptors, and anion channels, whose properties and functions are only partially understood, particularly in small processes that contact synapses. In addition, astrocytes express ionotropic receptors for several neurotransmitters. Here, we provide an extensive and up-to-date review of the roles of ion channels and ionotropic receptors in astrocyte physiology and pathology. As examples of two different brain pathologies, we focus on Alzheimer's disease (AD), one of the most diffuse neurodegenerative disorders, and glioblastoma (GBM), the most common brain tumor. Understanding how ion channels and ionotropic receptors in astrocytes participate in NDs and tumors is necessary for developing new therapeutic tools for these increasingly common neurological conditions.

Lauric acid provides neuroprotection against oxidative stress in mouse model of hyperglycaemic stroke

During ischemic stroke, higher glucose level linked worse outcomes were reported even in patients without pre-existing diabetes. Evidence suggest that such worse stroke outcomes were mainly due to production of reactive, toxic glucose metabolites that expands oxidative damage inside the brain. As a consequence of high oxidative stress, microvasculature structures and tight junctions compromised their functionally, infarct volume expands and brain edema exacerbates. In a mouse model of ischemic stroke with induced acute hyperglycaemia, Lauric acid (LA) as a natural saturated fatty acid demonstrated neuroprotection by attenuating infarct volume and brain edema. In addition, in the ipsilateral hyperglycaemic brain, the LA significantly increased the expression of tight junction representative protein (occludin) as well as anti-oxidative markers; Manganese superoxide dismutase (Mn) SOD, Extracellular superoxide dismutase (Ec-SOD) and nuclear factor-erythroid factor 2-related factor 2 (Nrf2) in the ipsilateral region against hyperglycemic ischemic stroke. LA treated animals showed a significant reduction in the production of lipid peroxidation products (4-HNE) in the microvascular structures, maintained the blood brain barrier (BBB) integrity. LA linked neuroprotective outcomes were further confirmed by behavioral tests, where functional outcomes and motor coordination were improved significantly. Furthermore, LA treatment enhanced food intake, decreased mortality rate, and net body weight loss. Conclusively, LA modulated ischemic insult exacerbated by hyperglycemia and provided neuroprotection.

Alzheimer's Progenitor Amyloid-β Targets and Dissolves Microbial Amyloids and Impairs Biofilm Function

Alzheimer's disease (AD) is a leading form of dementia where the presence of extra-neuronal plaques of Amyloid-β (Aβ) is a pathological hallmark. However, Aβ peptide is also observed in the intestinal tissues of AD patients and animal models. In this study, it is reported that Aβ monomers can target and disintegrate microbial amyloids of FapC and CsgA formed by opportunistic gut pathogens, Pseudomonas aeruginosa and Escherichia coli, explaining a potential role of Aβ in the gut-brain axis. Employing a zebrafish-based transparent in vivo system and whole-mount live-imaging, Aβ is observed to diffuse into the vasculature and subsequently localize with FapC or CsgA fibrils that were injected into the tail muscles of the fish. FapC aggregates, produced after Aβ treatment (Faβ), present selective toxicity to SH-SY5Y neuronal cells while the intestinal Caco-2 cells are shown to phagocytose Faβ in a non-toxic cellular process. After remodeling by Aβ, microbial fibrils lose their native function of cell adhesion with intestinal Caco-2 cells and Aβ dissolves and detaches the microbial fibrils already attached to the cell membrane. Taken together, this study strongly indicates an anti-biofilm role for Aβ monomers that can help aid in the future development of selective anti-Alzheimer's and anti-infective medicine.

Proteomic alterations in the brain and blood-brain barrier during brain Aβ accumulation in an APP knock-in mouse model of Alzheimer's disease

BACKGROUND

Blood-brain barrier (BBB) dysfunction is supposed to be an early event in the development of Alzheimer's disease (AD). This study aimed to investigate the relationship between BBB alterations and AD progression in terms of amyloid-β peptide (Aβ) accumulation in the brains of humanized amyloid precursor protein knock-in (APP-KI) mice.

METHODS

Brain Aβ accumulation was examined using immunohistochemical analysis. Alterations in differentially expressed proteins were determined using sequential window acquisition of all theoretical fragment ion mass spectroscopy (SWATH-MS)-based quantitative proteomics, and Metascape, STRING, Gene Ontology, and KEGG were used for network analyses of altered biological pathways and processes. Statistical significance was determined using the unpaired two-tailed Student's t-test and Welch's t-test for two groups and one-way analysis of variance followed by Tukey's test for more than two groups. Correlations between two groups were determined using Pearson's correlation analysis.

RESULTS

Brain Aβ accumulation in APP-KI mice was detectable at 2 months, increased significantly at 5 months, and remained elevated at 12 months of age. The levels of differentially expressed proteins in isolated brain capillaries were higher in younger mice, whereas those in the brain were higher in older mice. Network analyses indicated changes in basement membrane-associated and ribosomal proteins in the brain capillaries. There were no significant changes in key proteins involved in drug or Aβ transport at the BBB. In contrast, solute carrier transporter levels in astrocytes, microglia, and neurons were altered in the brain of older mice. Moreover, the levels of the lipid transporters Apoe and Apoj were upregulated in both the brain and isolated brain capillaries after Aβ accumulation.

CONCLUSIONS

Our results suggest that changes in the brain occurred after advanced Aβ accumulation, whereas initial Aβ accumulation was sufficient to cause alterations in the BBB. These findings may help elucidate the role of BBB alterations in AD progression and predict the distribution of drugs across the BBB in the brain of patients with AD.

Calcium sensor Yellow Cameleon 3.6 as a tool to support the calcium hypothesis of Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) is a neurodegenerative disease with increasing relevance as dementia cases rise. The etiology of AD is widely debated. The Calcium Hypothesis of Alzheimer's disease and brain aging states that the dysfunction of calcium signaling is the final common pathway leading to neurodegeneration. When the Calcium Hypothesis was originally coined, the technology did not exist to test it, but with the advent of Yellow Cameleon 3.6 (YC3.6) we are able to test its validity.

METHODS

Here we review use of YC3.6 in studying Alzheimer's disease using mouse models and discuss whether these studies support or refute the Calcium Hypothesis.

RESULTS

YC3.6 studies showed that amyloidosis preceded dysfunction in neuronal calcium signaling and changes in synapse structure. This evidence supports the Calcium Hypothesis.

DISCUSSION

In vivo YC3.6 studies point to calcium signaling as a promising therapeutic target; however, additional work is necessary to translate these findings to humans.

PCSK9 and the nervous system: a no-brainer?

In the past 20 years, PCSK9 has been shown to play a pivotal role in LDL cholesterol metabolism and cardiovascular health by inducing the lysosomal degradation of the LDL receptor. PCSK9 was discovered by the cloning of genes up-regulated after apoptosis induced by serum deprivation in primary cerebellar neurons, but despite its initial identification in the brain, the precise role of PCSK9 in the nervous system remains to be clearly established. The present article is a comprehensive review of studies published or in print before July 2023 that have investigated the expression pattern of PCSK9, its effects on lipid metabolism as well as its putative roles specifically in the central and peripheral nervous systems, with a special focus on cerebrovascular and neurodegenerative diseases.

ApoE-modified liposomes encapsulating resveratrol and salidroside alleviate manifestations of Alzheimer's disease in APP/PS-1 mice

OBJECTIVE

Alzheimer's disease (AD) is a neurodegenerative disease that is associated with aging and is influenced by both genetic and environmental factors. Several studies and clinical trials have demonstrated that resveratrol (Res) and salidroside (Sal) are not only biologically safe but also influence AD biomarker trajectories. However, their clinical applications have been quite limited due to poor specificity, low solubility, and insufficient blood-brain barrier (BBB) penetration. Therefore, we developed a nano-drug delivery system in which Res and Sal were encapsulated in liposomes, which were surface-modified with ApoE (ApoE-Res/Sal-Lips) to compensate for these deficiencies.

METHOD

In this study, ApoE-Res/Sal-Lips were prepared using a standard thin-film hydration method for liposomes. Then, cellular uptake of the loaded liposomes was assessed in vitro using fluorescent staining assays. A BBB model was constructed to investigate the capacity of the liposomes to cross the BBB in vitro, and the ability of liposomes to target the brain was observed by in vivo imaging. In addition, the neuroprotective effects of the different liposome formulations in APP/PS-1 mice were evaluated by measuring the changes in levels of oxidative, anti-inflammatory, and anti-apoptotic factors in the mice brains.

RESULTS

In vitro, ApoE-Res/Sal-Lips increased the uptake of Res and Sal by bEnd.3 and N2a cells, enhanced BBB penetration, and improved transport efficiency. In vivo, the ApoE-Res/Sal-Lips were found to alleviate AD pathological symptoms, reduce learning and memory impairments, and improve brain function.

CONCLUSION

ApoE-Res/Sal-Lips provide a new method for the treatment of AD.

Vascular Ageing: Mechanisms, Risk Factors, and Treatment Strategies

Ageing constitutes the biggest risk factor for poor health and adversely affects the integrity and function of all the cells, tissues, and organs in the human body. Vascular ageing, characterised by vascular stiffness, endothelial dysfunction, increased oxidative stress, chronic low-grade inflammation, and early-stage atherosclerosis, may trigger or exacerbate the development of age-related vascular diseases, which each year contribute to more than 3.8 million deaths in Europe alone and necessitate a better understanding of the mechanisms involved. To this end, a large number of recent preclinical and clinical studies have focused on the exponential accumulation of senescent cells in the vascular system and paid particular attention to the specific roles of senescence-associated secretory phenotype, proteostasis dysfunction, age-mediated modulation of certain microRNA (miRNAs), and the contribution of other major vascular risk factors, notably diabetes, hypertension, or smoking, to vascular ageing in the elderly. The data generated paved the way for the development of various senotherapeutic interventions, ranging from the application of synthetic or natural senolytics and senomorphics to attempt to modify lifestyle, control diet, and restrict calorie intake. However, specific guidelines, considering the severity and characteristics of vascular ageing, need to be established before widespread use of these agents. This review briefly discusses the molecular and cellular mechanisms of vascular ageing and summarises the efficacy of widely studied senotherapeutics in the context of vascular ageing.

Acute sleep loss decreases CSF-to-blood clearance of Alzheimer's disease biomarkers

INTRODUCTION

Sleep deprivation increases cerebrospinal fluid (CSF) amyloid beta (Aβ) and tau levels; however, sleep's effect on Aβ and tau in plasma is unknown.

METHODS

In a cross-over design, CSF Aβ and tau concentrations were measured in five cognitively normal individuals who had blood and CSF collected every 2 hours for 36 hours during sleep-deprived and normal sleep control conditions.

RESULTS

Aβ40, Aβ42, unphosphorylated tau threonine181 (T181), unphosphorylated tau threonine-217 (T217), and phosphorylated T181 (pT181) concentrations increased ∼35% to 55% in CSF and decreased ∼5% to 15% in plasma during sleep deprivation. CSF/plasma ratios of all Alzheimer's disease (AD) biomarkers increased during sleep deprivation while the CSF/plasma albumin ratio, a measure of blood-CSF barrier permeability, decreased. CSF and plasma Aβ42/40, pT181/T181, and pT181/Aβ42 ratios were stable longitudinally in both groups.

DISCUSSION

These findings show that sleep loss alters some plasma AD biomarkers by lowering brain clearance mechanisms and needs to be taken into account when interpreting individual plasma AD biomarkers but not ratios.

Ferulic Acid Improves Synaptic Plasticity and Cognitive Impairments by Alleviating the PP2B/DARPP-32/PP1 Axis-Mediated STEP Increase and Aβ Burden in Alzheimer's Disease

The burden of Alzheimer's disease, the most prevalent neurodegenerative disease, is increasing exponentially due to the increase in the elderly population worldwide. Synaptic plasticity is the basis of learning and memory, but it is impaired in AD. Uncovering the disease's underlying molecular pathogenic mechanisms involving synaptic plasticity could lead to the identification of targets for better disease management. Using primary neurons treated with Aβ and APP/PS1 animal models, we evaluated the effect of the phenolic compound ferulic acid (FA) on synaptic dysregulations. Aβ led to synaptic plasticity and cognitive impairments by increasing STEP activity and decreasing the phosphorylation of the GluN2B subunit of NMDA receptors, as well as decreasing other synaptic proteins, including PSD-95 and synapsin1. Interestingly, FA attenuated the Aβ-upregulated intracellular calcium and thus resulted in a decrease in PP2B-induced activation of DARPP-32, inhibiting PP1. This cascade event maintained STEP in its inactive state, thereby preventing the loss of GluN2B phosphorylation. This was accompanied by an increase in PSD-95 and synapsin1, improved LTP, and a decreased Aβ load, together leading to improved behavioral and cognitive functions in APP/PS1 mice treated with FA. This study provides insight into the potential use of FA as a therapeutic strategy in AD.

Low-density lipoprotein receptor-related protein-1 (LRP1) in the glial lineage modulates neuronal excitability

The low-density lipoprotein related protein receptor 1 (LRP1), also known as CD91 or α-Macroglobulin-receptor, is a transmembrane receptor that interacts with more than 40 known ligands. It plays an important biological role as receptor of morphogens, extracellular matrix molecules, cytokines, proteases, protease inhibitors and pathogens. In the CNS, it has primarily been studied as a receptor and clearance agent of pathogenic factors such as Aβ-peptide and, lately, Tau protein that is relevant for tissue homeostasis and protection against neurodegenerative processes. Recently, it was found that LRP1 expresses the Lewis-X (Lex) carbohydrate motif and is expressed in the neural stem cell compartment. The removal of Lrp1 from the cortical radial glia compartment generates a strong phenotype with severe motor deficits, seizures and a reduced life span. The present review discusses approaches that have been taken to address the neurodevelopmental significance of LRP1 by creating novel, lineage-specific constitutive or conditional knockout mouse lines. Deficits in the stem cell compartment may be at the root of severe CNS pathologies.

LRP1 Deficiency Promotes Mitostasis in Response to Oxidative Stress: Implications for Mitochondrial Targeting after Traumatic Brain Injury

The brain undergoes oxidative stress and mitochondrial dysfunction following physiological insults such as Traumatic brain injury (TBI), ischemia-reperfusion, and stroke. Pharmacotherapeutics targeting mitochondria (mitoceuticals) against oxidative stress include antioxidants, mild uncouplers, and enhancers of mitochondrial biogenesis, which have been shown to improve pathophysiological outcomes after TBI. However, to date, there is no effective treatment for TBI. Studies have suggested that the deletion of LDL receptor-related protein 1 (LRP1) in adult neurons or glial cells could be beneficial and promote neuronal health. In this study, we used WT and LRP1 knockout (LKO) mouse embryonic fibroblast cells to examine mitochondrial outcomes following exogenous oxidative stress. Furthermore, we developed a novel technique to measure mitochondrial morphometric dynamics using transgenic mitochondrial reporter mice mtD2g (mitochondrial-specific Dendra2 green) in a TBI model. We found that oxidative stress increased the quantity of fragmented and spherical-shaped mitochondria in the injury core of the ipsilateral cortex following TBI, whereas rod-like elongated mitochondria were seen in the corresponding contralateral cortex. Critically, LRP1 deficiency significantly decreased mitochondrial fragmentation, preserving mitochondrial function and cell growth following exogenous oxidative stress. Collectively, our results show that targeting LRP1 to improve mitochondrial function is a potential pharmacotherapeutic strategy against oxidative damage in TBI and other neurodegenerative diseases.

Sleep deprivation modulates APOE and LDL receptor-related protein 1 through thyroid hormone T4 and impairs Aβ clearance in hippocampus of rats

Alzheimer's disease is the most common form of dementia. One of its pathological hallmarks is Aβ accumulation, which is influenced by APOE genotype and expression, as well as by sleep homeostasis. However, conflicting mechanisms for APOE roles in Aβ clearance have been reported, and the relationship between APOE and sleep also remains unclear. In this study, we aimed to investigate how hormonal alteration caused by sleep deprivation affects APOE and its receptors in rats, and to evaluate the role of different cell types in Aβ clearance. Paradoxical sleep deprivation for 96 h increased Aβ level in hippocampus with concomitant reduction of APOE and LRP1 at the time point within the resting period. Sleep deprivation also significantly reduced T4 levels in both active and resting times. To evaluate the effect of T4 variation, C6 glial cells and primary brain endothelial cells were treated with T4. High T4 level (300 ng/mL) increased APOE, but reduced LRP1 and LDL-R in C6 cells, while in primary endothelial cells, LDL-R levels were increased. Treatment of C6 cells with exogenous APOE reduced LRP1 and Aβ uptake. These results suggest that T4 modulates LRP1 and LDL-R in both cell types, but in the opposite manner, thus, sleep deprivation might modify the ratio of the receptors in blood-brain barrier and glial cells by altering T4 levels. Considering that LRP1 and LDL-R are important for Aβ clearance, sleep deprivation might also affect the degree of participation of glia in Aβ clearance, and consequently, turnover of Aβ in the brain.

High affinity of β-amyloid proteins to cerebral capillaries: implications in chronic lead exposure-induced neurotoxicity in rats

Lead (Pb) is a known environmental risk factor in the etiology of Alzheimer's disease (AD). The existing reports suggest that Pb exposure increases beta-amyloid (Aβ) levels in brain tissues and cerebrospinal fluid (CSF) and facilitates the formation of amyloid plaques, which is a pathological hallmark for AD. Pb exposure has long been associated with cerebral vasculature injury. Yet it remained unclear if Pb exposure caused excessive Ab buildup in cerebral vasculature, which may damage the blood-brain barrier and cause abnormal Ab accumulation. This study was designed to investigate the impact of chronic Pb exposure on Aβ accumulation in cerebral capillary and the expression of low-density lipoprotein receptor protein-1 (LRP1), a critical Aβ transporter, in brain capillary and parenchyma. Sprague-Dawley rats received daily oral gavage at doses of 0, 14 (low-dose), and 27 (high-dose) mg Pb/kg as Pb acetate, 5 d/wk, for 4 or 8 wks. At the end of Pb exposure, a solution containing Aβ40 was infused into the brain via the cannulated internal carotid artery. Data by ELISA showed a strikingly high affinity of Ab to cerebral vasculature, which was approximately 7-14 times higher than that to the parenchymal fractions collected from control brains. Pb exposure further aggravated the Aβ accumulation in cerebral vasculature in a dose-dependent manner. Western blot analyses revealed that Pb exposure decreased LRP1 expression in cortical capillaries and hippocampal parenchyma. Immunohistochemistry (IHC) studies further revealed a disrupted distribution of LRP1 alongside hippocampal vasculature accompanied with a decreased expression in hippocampal neurons by Pb exposure. Taken together, the current study demonstrated that the cerebral vasculature naturally possessed a high affinity to Aβ present in circulating blood. Pb exposure significantly increased Aβ accumulation in cerebral vasculature; such an increased Aβ accumulation was due partly to the diminished expression of LRP1 in response to Pb in tested brain regions. Perceivably, Pb-facilitated Ab aggravation in cerebral vasculature may contribute to Pb-associated amyloid alterations.

Elevated CSF angiopoietin-2 correlates with blood-brain barrier leakiness and markers of neuronal injury in early Alzheimer's disease

Breakdown of the neurovascular unit in early Alzheimer's disease (AD) leads to leakiness of the blood-brain barrier (BBB), contributing to cognitive decline and disease pathology. Vascular stability depends on angiopoietin-1 (ANGPT1) signalling, antagonised by angiopoietin-2 (ANGPT2) upon endothelial injury. We have examined the relationship between CSF ANGPT2 and CSF markers of BBB leakiness and disease pathology, across three independent cohorts: (i) 31 AD patients and 33 healthy controls grouped according to their biomarker profile (i.e., AD cases t-tau > 400 pg/mL, p-tau > 60 pg/mL and Aβ42 < 550 pg/mL); (ii) 121 participants in the Wisconsin Registry for Alzheimer's Prevention or Wisconsin Alzheimer's Disease Research study (84 participants cognitively unimpaired (CU) enriched for a parental history of AD, 19 participants with mild cognitive impairment (MCI), and 21 with AD); (iii) a neurologically normal cohort aged 23-78 years with paired CSF and serum samples. CSF ANGPT2 level was measured by sandwich ELISA. In cohort (i), CSF ANGPT2 was elevated in AD, correlating with CSF t-tau and p-tau181 but not Aβ42. ANGPT2 also correlated positively with CSF sPDGFRβ and fibrinogen - markers of pericyte injury and BBB leakiness. In cohort (ii), CSF ANGPT2 was highest in MCI. CSF ANGT2 correlated with CSF albumin in the CU and MCI cohorts but not in AD. ANGPT2 also correlated with t-tau and p-tau and with markers of neuronal injury (neurogranin and α-synuclein) and neuroinflammation (GFAP and YKL-40). In cohort (iii), CSF ANGPT2 correlated strongly with the CSF:serum albumin ratio. Increased CSF ANGPT2 and the CSF:serum albumin ratio showed non-significant associations with elevated serum ANGPT2 in this small cohort. Together, these data indicate that CSF ANGPT2 is associated with BBB leakiness in early AD and is closely related to tau pathology and neuronal injury. The utility of serum ANGPT2 as a biomarker of BBB damage in AD requires further study.

Endocrine Regulation of Microvascular Receptor-Mediated Transcytosis and Its Therapeutic Opportunities: Insights by PCSK9-Mediated Regulation

Currently, many neurological disorders lack effective treatment options due to biological barriers that effectively separate the central nervous system (CNS) from the periphery. CNS homeostasis is maintained by a highly selective exchange of molecules, with tightly controlled ligand-specific transport systems at the blood-brain barrier (BBB) playing a key role. Exploiting or modifying these endogenous transport systems could provide a valuable tool for targeting insufficient drug delivery into the CNS or pathological changes in the microvasculature. However, little is known about how BBB transcytosis is continuously regulated to respond to temporal or chronic changes in the environment. The aim of this mini-review is to draw attention to the sensitivity of the BBB to circulating molecules derived from peripheral tissues, which may indicate a fundamental endocrine-operating regulatory system of receptor-mediated transcytosis at the BBB. We present our thoughts in the context of the recent observation that low-density lipoprotein receptor-related protein 1 (LRP1)-mediated clearance of brain amyloid-β (Aβ) across the BBB is negatively regulated by peripheral proprotein convertase subtilisin/kexin type 9 (PCSK9). We hope that our conclusions will inspire future investigations of the BBB as dynamic communication interface between the CNS and periphery, whose peripheral regulatory mechanisms could be easily exploited for therapeutic purposes.

Molecular Heterogeneity of the Brain Endothelium

The blood-brain barrier (BBB) is part of a neurovascular structure located in the brain's micro vessels, that is essential to maintain brain homeostasis, but prevents the brain uptake of most drugs. Because of its importance in neuro-pharmacotherapy, the BBB has been the subject of extensive research since its discovery over 100 years ago. Major advances in understanding the structure and function of the barrier have been made. Drugs are re-designed to cross the BBB. However, despite these efforts, overcoming the BBB efficiently to treat brain diseases safely remains challenging. The majority of BBB research studies focus on the BBB as a homogenous structure throughout the different brain regions. However, this simplification may lead to an inadequate understanding of the BBB function with significant therapeutic consequences. From this perspective, we analyzed the gene and protein expression profiles of the BBB in the micro vessels from the brains of mice that were isolated from two different brain regions, namely the cortex and the hippocampus. The expression profile of the inter-endothelial junctional protein (claudin-5), three ABC transporters (P-glycoprotein, Bcrp and Mrp-1), and three BBB receptors (lrp-1, TRF and GLUT-1) were analyzed. Our gene and protein analysis showed that the brain endothelium in the hippocampus exhibits different expression profiles compared to the brain cortex. Specifically, brain endothelial cells (BECs) of the hippocampus express higher gene levels of abcb1, abcg2, lrp1, and slc2a1 compared to the BECs of the cortex regions with a trend of increase for claudin-5, while BECs of the cortex express higher gene levels of abcc1 and trf compared to the hippocampus. At the protein levels, the P-gp expression was found to be significantly higher in the hippocampus compared to the cortex, while TRF was found to be up-regulated in the cortex. These data suggest that the structure and function of the BBB are not homogeneous, and imply that drugs are not delivered similarly among the different brain regions. Appreciation of the BBB heterogeneity by future research programs is thus critical for efficient drug delivery and the treatment of brain diseases.

Dissecting the neurovascular unit in physiology and Alzheimer's disease: Functions, imaging tools and genetic mouse models

The neurovascular unit (NVU) plays an essential role in regulating neurovascular coupling, which refers to the communication between neurons, glia, and vascular cells to control the supply of oxygen and nutrients in response to neural activity. Cellular elements of the NVU coordinate to establish an anatomical barrier to separate the central nervous system from the milieu of the periphery system, restricting the free movement of substances from the blood to the brain parenchyma and maintaining central nervous system homeostasis. In Alzheimer's disease, amyloid-β deposition impairs the normal functions of NVU cellular elements, thus accelerating the disease progression. Here, we aim to describe the current knowledge of the NVU cellular elements, including endothelial cells, pericytes, astrocytes, and microglia, in regulating the blood-brain barrier integrity and functions in physiology as well as alterations encountered in Alzheimer's disease. Furthermore, the NVU functions as a whole, therefore specific labeling and targeting NVU components in vivo enable us to understand the mechanism mediating cellular communication. We review approaches including commonly used fluorescent dyes, genetic mouse models, and adeno-associated virus vectors for imaging and targeting NVU cellular elements in vivo.

Heparan sulfate proteoglycan in Alzheimer's disease: aberrant expression and functions in molecular pathways related to amyloid-β metabolism

Alzheimer's disease (AD) is the most common form of dementia. Currently, there is no effective treatment for AD, as its etiology remains poorly understood. Mounting evidence suggests that the accumulation and aggregation of amyloid-β peptides (Aβ), which constitute amyloid plaques in the brain, is critical for initiating and accelerating AD pathogenesis. Considerable efforts have been dedicated to shedding light on the molecular basis and fundamental origins of the impaired Aβ metabolism in AD. Heparan sulfate (HS), a linear polysaccharide of the glycosaminoglycan family, co-deposits with Aβ in plaques in the AD brain, directly binds and accelerates Aβ aggregation, and mediates Aβ internalization and cytotoxicity. Mouse model studies demonstrate that HS regulates Aβ clearance and neuroinflammation in vivo. Previous reviews have extensively explored these discoveries. Here, this review focuses on the recent advancements in understanding abnormal HS expression in the AD brain, the structural aspects of HS-Aβ interaction, and the molecules involved in modulating Aβ metabolism through HS interaction. Furthermore, this review presents a perspective on the potential effects of abnormal HS expression on Aβ metabolism and AD pathogenesis. In addition, the review highlights the importance of conducting further research to differentiate the spatiotemporal components of HS structure and function in the brain and AD pathogenesis.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) in the central nervous system

The gene encoding proprotein convertase subtilisin/kexin type 9 (PCSK9) and its protein product have been widely studied for their role in cholesterol and lipid metabolism. PCSK9 increases the rate of metabolic degradation of low-density lipoprotein receptors, preventing the diffusion of low-density lipoprotein (LDL) from plasma into cells and contributes to high lipoprotein-bound cholesterol levels in the plasma. While most research has focused on the regulation and disease relevance of PCSK9 to the cardiovascular system and lipid metabolism, there is a growing body of evidence that PCSK9 plays a crucial role in pathogenic processes in other organ systems, including the central nervous system. PCSK9's impact on the brain is not yet fully understood, though several recent studies have sought to illuminate its impact on various neurodegenerative and psychiatric disorders, as well as its connection with ischemic stroke. Cerebral PCSK9 expression is low but is highly upregulated during disease states. Among others, PCSK9 is known to play a role in neurogenesis, neural cell differentiation, central LDL receptor metabolism, neural cell apoptosis, neuroinflammation, Alzheimer's Disease, Alcohol Use Disorder, and stroke. The PCSK9 gene contains several polymorphisms, including both gain-of-function and loss-of-function mutations which profoundly impact normal PCSK9 signaling and cholesterol metabolism. Gain-of-function mutations lead to persistent hypercholesterolemia and poor health outcomes, while loss-of-function mutations generally lead to hypocholesterolemia and may serve as a protective factor against diseases of the liver, cardiovascular system, and central nervous system. Recent genomic studies have sought to identify the end-organ effects of such mutations and continue to identify evidence of a much broader role for PCSK9 in extrahepatic organ systems. Despite this, there remain large gaps in our understanding of PCSK9, its regulation, and its effects on disease risk outside the liver. This review, which incorporates data from a wide range of scientific disciplines and experimental paradigms, is intended to describe PCSK9's role in the central nervous system as it relates to cerebral disease and neuropsychiatric disorders, and to examine the clinical potential of PCSK9 inhibitors and genetic variation in the PCSK9 gene on disease outcomes, including neurological and neuropsychiatric disease.