Mechanisms linking cerebrovascular dysfunction and tauopathy: Adding a layer of epiregulatory complexity

APOE- ε4-induced Fibronectin at the blood-brain barrier is a conserved pathological mediator of disrupted astrocyte-endothelia interaction in Alzheimer's disease

Blood-brain barrier (BBB) dysfunction is a key feature of Alzheimer's disease (AD), particularly in individuals carrying the APOE-ε4 allele. This dysfunction worsens neuroinflammation and hinders the removal of toxic proteins, such as amyloid-beta (Aβ42), from the brain. In post-mortem brain tissues and in animal models, we previously reported that fibronectin accumulates at the BBB predominantly in APOE-ε4 carriers. Furthermore, we found a loss-of-function variant in the fibronectin 1 ( FN1 ) gene significantly reduces aggregated fibronectin levels and decreases AD risk among APOE-ε4 carriers. Yet, the molecular mechanisms downstream of fibronectin at the BBB remain unclear. The extracellular matrix (ECM) plays a crucial role in maintaining BBB homeostasis and orchestrating the interactions between BBB cell types, including endothelia and astrocytes. Understanding the mechanisms affecting the ECM and BBB cell types will be critical for developing effective therapies against AD, especially among APOE-ε4 carriers. Here, we demonstrate that APOE-ε4 , Aβ42, and inflammation drive the induction of FN1 expression in several models including zebrafish, mice, iPSC-derived human 3D astrocyte and 3D cerebrovascular cell cultures, and in human brains. Fibronectin accumulation disrupts astroglial-endothelial interactions and the signalling cascade between vascular endothelial growth factor (VEGF), heparin-binding epidermal growth factor (HBEGF) and Insulin-like growth factor 1 (IGF1). This accumulation of fibronectin in APOE-ε4- associated AD potentiates BBB dysfunction, which strongly implicates reducing fibronectin deposition as a potential therapeutic target for AD.

Graphical abstract

Accessibility text

This image illustrates the effects of different APOE isoforms (ApoE-ε3 and ApoE-ε4) on blood-brain barrier (BBB) integrity, focusing on the molecular interactions between astrocytes and endothelial cells. This figure emphasizes the detrimental effects of ApoE-ε4 on BBB integrity via fibronectin accumulation and altered signaling pathways. The top section provides a schematic overview of the blood-brain barrier, highlighting astrocytes, endothelial cells, and their interface. The left panel represents the ApoE-ε3 condition: Normal fibronectin (FN1) levels support healthy interactions between astrocytes and endothelial cells. Growth factors, including VEGFA, HBEGF, and IGF1, maintain BBB integrity through their respective receptors (VEGFR and EGFR). Green arrows indicate activation of these signaling pathways. The right panel depicts the ApoE-ε4 condition: Elevated fibronectin (FN1) disrupts astrocyte-endothelium interactions. FN1 binds integrins and activates focal adhesion kinase (FAK), inhibiting VEGFA, which is required for endothelial HBEGF that in turn activates IGF1 signaling. Red symbols indicate inhibition of HBEGF, VEGFA, and IGF1 pathways, leading to BBB dysfunction.

Highlights

APOE-ε4 drives fibronectin deposition in Alzheimer's, disrupting astrocyte-endothelia interactions. APOE-ε4 and fibronectin co-localize, forming aggregates at blood-brain barrier (BBB). Fibronectin alters the signaling between VEGF, IGF1, and HBEGF impairing BBB function. Reducing fibronectin restores BBB integrity and offsets APOE-ε4 pathology.

NCBP2-AS2 is a mitochondrial microprotein, regulates energy metabolism and neurogenesis, and is downregulated in Alzheimer's disease

Microproteins, short functional peptides encoded by small genes, are emerging as critical regulators of cellular processes, yet their roles in mitochondrial function and neurodegeneration remain underexplored. In this study, we identify NCBP2-AS2 as an evolutionarily conserved mitochondrial microprotein with significant roles in energy metabolism and neurogenesis. Using a combination of cellular and molecular approaches, including CRISPR/Cas9 knockout models, stoichiometric co- immunoprecipitation, and advanced imaging techniques, we demonstrate that NCBP2-AS2 localizes to the inner mitochondrial space and interacts with translocase of the inner membrane (TIM) chaperones. These interactions suggest a role in ATPase subunit transport, supported by the observed reductions in ATPase subunit levels and impaired glucose metabolism in NCBP2-AS2-deficient cells. In zebrafish, NCBP2-AS2 knockout led to increased astroglial proliferation, microglial abundance, and enhanced neurogenesis, particularly under amyloid pathology. Notably, we show that NCBP2-AS2 expression is consistently downregulated in human Alzheimer's disease brains and zebrafish amyloidosis models, suggesting a conserved role in neurodegenerative pathology. These findings reveal a novel link between mitochondrial protein transport, energy metabolism, and neural regeneration, positioning NCBP2-AS2 as a potential therapeutic target for mitigating mitochondrial dysfunction and promoting neurogenesis in neurodegenerative diseases such as Alzheimer's disease.

New evidence of vascular defects in neurodegenerative diseases revealed by single cell RNA sequencing

Neurodegenerative diseases (NDs) involve the progressive loss of neuronal structure or function in the brain and spinal cord. Despite their diverse etiologies, NDs manifest similar pathologies. Emerging research identifies vascular defects as a previously neglected hallmark of NDs. The development and popularization of single-cell RNA sequencing (scRNA-seq) technologies have significantly advanced our understanding of brain vascular cell types and their molecular characteristics, including gene expression changes at the single-cell level in NDs. These unprecedented insights deepen our understanding of the pathogenic mechanisms underlying NDs. However, the occurrence and role of vascular defects in disease progression remain largely unexplored. In this paper, we systematically summarize recent advances in the structure and organization of the central nervous system vasculature in mice, healthy individuals, and patients with NDs, focussing primarily on disease-specific alterations in vascular cell types or subtypes. Combining scRNA-seq with pathology evidence, we propose that vascular defects, characterized by disruptions in cell types and structural integrity, may serve as common early features of NDs. Finally, we discuss several pathways through which vascular defects in NDs lead to neuronal degeneration. A deeper understanding of the causes and contributions of vascular defects to NDs aids in elucidating the pathogenic mechanisms and developing meaningful therapeutic interventions.

ABCA7-dependent induction of neuropeptide Y is required for synaptic resilience in Alzheimer's disease through BDNF/NGFR signaling

Genetic variants in ABCA7, an Alzheimer's disease (AD)-associated gene, elevate AD risk, yet its functional relevance to the etiology is unclear. We generated a CRISPR-Cas9-mediated abca7 knockout zebrafish to explore ABCA7's role in AD. Single-cell transcriptomics in heterozygous abca7+/- knockout combined with Aβ42 toxicity revealed that ABCA7 is crucial for neuropeptide Y (NPY), brain-derived neurotrophic factor (BDNF), and nerve growth factor receptor (NGFR) expressions, which are crucial for synaptic integrity, astroglial proliferation, and microglial prevalence. Impaired NPY induction decreased BDNF and synaptic density, which are rescuable with ectopic NPY. In induced pluripotent stem cell-derived human neurons exposed to Aβ42, ABCA7-/- suppresses NPY. Clinical data showed reduced NPY in AD correlated with elevated Braak stages, genetic variants in NPY associated with AD, and epigenetic changes in NPY, NGFR, and BDNF promoters linked to ABCA7 variants. Therefore, ABCA7-dependent NPY signaling via BDNF-NGFR maintains synaptic integrity, implicating its impairment in increased AD risk through reduced brain resilience.

Multi-target drugs for Alzheimer's disease

Alzheimer's disease (AD), a leading cause of dementia, increasingly challenges our healthcare systems and society. Traditional therapies aimed at single targets have fallen short owing to the complex, multifactorial nature of AD that necessitates simultaneous targeting of various disease mechanisms for clinical success. Therefore, targeting multiple pathologies at the same time could provide a synergistic therapeutic effect. The identification of new disease targets beyond the classical hallmarks of AD offers a fertile ground for the design of new multi-target drugs (MTDs), and building on existing compounds have the potential to yield in successful disease modifying therapies. This review discusses the evolving landscape of MTDs, focusing on their potential as AD therapeutics. Analysis of past and current trials of compounds with multi-target activity underscores the capacity of MTDs to offer synergistic therapeutic effects, and the flourishing genetic understanding of AD will inform and inspire the development of MTD-based AD therapies.

From Alzheimer's disease to vascular dementia: Different roads leading to cognitive decline

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.