Candesartan prevents arteriopathy progression in cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy model

Monogenic causes of cerebral small vessel disease- models for vascular cognitive impairment and dementia?

PURPOSE OF REVIEW

Recent advancements in molecular biomarkers and therapeutic options for Alzheimer's disease have brought into focus the need for greater progress in the second most common cause of dementia, vascular cognitive impairment and dementia (VCID). We examine how the study of monogenic causes of VCID has contributed to the understanding of its pathophysiology and potential biomarker and treatment research.

RECENT FINDINGS

It is widely accepted that conditions which disrupt the cerebral small vessels contribute to vascular pathologies including stroke and cerebral microbleeds, ultimately leading to vascular cognitive impairment and dementia. Among these conditions are a range of monogenic small vessel diseases (SVDs) such as CADASIL, CARASIL, Fabry disease and COL4A-related disorders.

SUMMARY

This review indicates the importance of furthering research into monogenic SVDs in order to gain insight into the pathomechanisms of VCID more broadly. Monogenic conditions are easier to model than sporadic VCID and can serve as a guide for identifying biomarkers for diagnosis, monitoring and intervention outcomes.

Role of ARMS2/HTRA1 risk alleles in the pathogenesis of neovascular age-related macular degeneration

Age-related macular degeneration (AMD) is one of the leading causes of severe irreversible blindness worldwide in the elderly population. AMD is a multifactorial disease mainly caused by advanced age, environmental factors, and genetic variations. Genome-wide association studies (GWAS) have strongly supported the link between ARMS2/HTRA1 locus on chromosome 10q26 and AMD development, encompassing multiple variants, rs10490924 (c.205G > T, p.A69S in ARMS2), insertion/deletion (del443/ins54 in ARMS2), and rs11200638 (in HTRA1 promoter region). In this comprehensive review, we provide an overview of the role played by ARMS2/HTRA1 risk alleles in neovascular AMD pathogenesis, covering GWAS, in vitro studies, and animal models, shedding light on their underlying molecular genetic mechanisms. Further extensive research is also imperative, including confirmation of these findings, identifying novel treatment targets, and advancing primary and secondary prevention strategies for AMD.

Rational correction of pathogenic conformational defects in HTRA1

Loss-of-function mutations in the homotrimeric serine protease HTRA1 cause cerebral vasculopathy. Here, we establish independent approaches to achieve the functional correction of trimer assembly defects. Focusing on the prototypical R274Q mutation, we identify an HTRA1 variant that promotes trimer formation thus restoring enzymatic activity in vitro. Genetic experiments in Htra1R274Q mice further demonstrate that expression of this protein-based corrector in trans is sufficient to stabilize HtrA1-R274Q and restore the proteomic signature of the brain vasculature. An alternative approach employs supramolecular chemical ligands that shift the monomer-trimer equilibrium towards proteolytically active trimers. Moreover, we identify a peptidic ligand that activates HTRA1 monomers. Our findings open perspectives for tailored protein repair strategies.

Genetically proxied HTRA1 protease activity and circulating levels independently predict risk of ischemic stroke and coronary artery disease

Genetic variants in HTRA1 are associated with stroke risk. However, the mechanisms mediating this remain largely unknown, as does the full spectrum of phenotypes associated with genetic variation in HTRA1. Here we show that rare HTRA1 variants are linked to ischemic stroke in the UK Biobank and BioBank Japan. Integrating data from biochemical experiments, we next show that variants causing loss of protease function associated with ischemic stroke, coronary artery disease and skeletal traits in the UK Biobank and MyCode cohorts. Moreover, a common variant modulating circulating HTRA1 mRNA and protein levels enhances the risk of ischemic stroke and coronary artery disease while lowering the risk of migraine and macular dystrophy in genome-wide association study, UK Biobank, MyCode and BioBank Japan data. We found no interaction between proxied HTRA1 activity and levels. Our findings demonstrate the role of HTRA1 for cardiovascular diseases and identify two mechanisms as potential targets for therapeutic interventions.

Pathophysiology of cerebral small vessel disease: a journey through recent discoveries

Cerebral small vessel disease (cSVD) encompasses a heterogeneous group of age-related small vessel pathologies that affect multiple regions. Disease manifestations range from lesions incidentally detected on neuroimaging (white matter hyperintensities, small deep infarcts, microbleeds, or enlarged perivascular spaces) to severe disability and cognitive impairment. cSVD accounts for approximately 25% of ischemic strokes and the vast majority of spontaneous intracerebral hemorrhage and is also the most important vascular contributor to dementia. Despite its high prevalence and potentially long therapeutic window, there are still no mechanism-based treatments. Here, we provide an overview of the recent advances in this field. We summarize recent data highlighting the remarkable continuum between monogenic and multifactorial cSVDs involving NOTCH3, HTRA1, and COL4A1/A2 genes. Taking a vessel-centric view, we discuss possible cause-and-effect relationships between risk factors, structural and functional vessel changes, and disease manifestations, underscoring some major knowledge gaps. Although endothelial dysfunction is rightly considered a central feature of cSVD, the contributions of smooth muscle cells, pericytes, and other perivascular cells warrant continued investigation.

Modeling of age-related neurological disease: utility of zebrafish

Many age-related neurological diseases still lack effective treatments, making their understanding a critical and urgent issue in the globally aging society. To overcome this challenge, an animal model that accurately mimics these diseases is essential. To date, many mouse models have been developed to induce age-related neurological diseases through genetic manipulation or drug administration. These models help in understanding disease mechanisms and finding potential therapeutic targets. However, some age-related neurological diseases cannot be fully replicated in human pathology due to the different aspects between humans and mice. Although zebrafish has recently come into focus as a promising model for studying aging, there are few genetic zebrafish models of the age-related neurological disease. This review compares the aging phenotypes of humans, mice, and zebrafish, and provides an overview of age-related neurological diseases that can be mimicked in mouse models and those that cannot. We presented the possibility that reproducing human cerebral small vessel diseases during aging might be difficult in mice, and zebrafish has potential to be another animal model of such diseases due to their similarity of aging phenotype to humans.

Progress in the Study of the Role and Mechanism of HTRA1 in Diseases Related to Vascular Abnormalities

High temperature requirement A1 (HTRA1) is a member of the serine protease family, comprising four structural domains: IGFBP domain, Kazal domain, protease domain and PDZ domain. HTRA1 encodes a serine protease, a secreted protein that is widely expressed in the vasculature. HTRA1 regulates a wide range of physiological processes through its proteolytic activity, and is also involved in a variety of vascular abnormalities-related diseases. This article reviews the role of HTRA1 in the development of vascular abnormalities-related hereditary cerebral small vessel disease (CSVD), age-related macular degeneration (AMD), tumors and other diseases. Through relevant research advances to understand the role of HTRA1 in regulating signaling pathways or refolding, translocation, degradation of extracellular matrix (ECM) proteins, thus directly or indirectly regulating angiogenesis, vascular remodeling, and playing an important role in vascular homeostasis, further understanding the mechanism of HTRA1's role in vascular abnormality-related diseases is important for HTRA1 to be used as a therapeutic target in related diseases.

Neuroprotective effects of oral metformin before stroke on cerebral small-vessel disease

BACKGROUND

Metformin (MET) treatment prior to stroke might have neuroprotective effects other than hypoglycemic effects. This study evaluated whether MET treatment prior to stroke is associated with neurological severity and functional outcome in patients with stroke who were not indicated for endovascular treatment and whether the effects of MET differ for each ischemic stroke subtype.

METHODS

We investigated 160 type 2 diabetes mellitus patients with ischemic stroke without endovascular treatment who were taking some oral antidiabetic agents prior to stroke in two tertiary hospitals. Lower neurological severity was defined as a National Institutes of Health Stroke Scale score of 3 or lower on admission, and favorable functional outcome was defined as a modified Rankin Scale score = 0-2 at discharge. We analyzed the effects of MET on the neurological severity and functional outcome in each ischemic stroke subtype on logistic regression analysis with adjustments for multiple confounding factors.

RESULTS

MET treatment prior to stroke was associated with lower stroke severity and favorable functional outcome. In the stroke subtypes, MET use affected both neurological severity (P = 0.037) and functional outcome (P = 0.041) in only patients with small-vessel disease (SVD).

CONCLUSIONS

MET may be useful to improve the outcome of patients with SVD.

Genetically proxied HTRA1 protease activity and circulating levels independently predict risk of ischemic stroke and coronary artery disease

HTRA1 has emerged as a major risk gene for stroke and cerebral small vessel disease with both rare and common variants contributing to disease risk. However, the precise mechanisms mediating this risk remain largely unknown as does the full spectrum of phenotypes associated with genetic variation in HTRA1 in the general population. Using a family-history informed approach, we first show that rare variants in HTRA1 are linked to ischemic stroke in 425,338 European individuals from the UK Biobank with replication in 143,149 individuals from the Biobank Japan. Integrating data from biochemical experiments on 76 mutations occurring in the UK Biobank, we next show that rare variants causing loss of protease function in vitro associate with ischemic stroke, coronary artery disease, and skeletal traits. In addition, a common causal variant (rs2672592) modulating circulating HTRA1 mRNA and protein levels enhances the risk of ischemic stroke, small vessel stroke, and coronary artery disease while lowering the risk of migraine and age-related macular dystrophy in GWAS and UK Biobank data from > 2,000,000 individuals. There was no evidence of an interaction between genetically proxied HTRA1 activity and levels. Our findings demonstrate a central role of HTRA1 for human disease including stroke and coronary artery disease and identify two independent mechanisms that might qualify as targets for future therapeutic interventions.

A brief overview of a mouse model of cerebral hypoperfusion by bilateral carotid artery stenosis

Vascular cognitive impairment (VCI) refers to all forms of cognitive disorder related to cerebrovascular diseases, including vascular mild cognitive impairment, post-stroke dementia, multi-infarct dementia, subcortical ischemic vascular dementia (SIVD), and mixed dementia. Among the causes of VCI, more attention has been paid to SIVD because the causative cerebral small vessel pathologies are frequently observed in elderly people and because the gradual progression of cognitive decline often mimics Alzheimer's disease. In most cases, small vessel diseases are accompanied by cerebral hypoperfusion. In mice, prolonged cerebral hypoperfusion is induced by bilateral carotid artery stenosis (BCAS) with surgically implanted metal micro-coils. This cerebral hypoperfusion BCAS model was proposed as a SIVD mouse model in 2004, and the spreading use of this mouse SIVD model has provided novel data regarding cognitive dysfunction and histological/genetic changes by cerebral hypoperfusion. Oxidative stress, microvascular injury, excitotoxicity, blood-brain barrier dysfunction, and secondary inflammation may be the main mechanisms of brain damage due to prolonged cerebral hypoperfusion, and some potential therapeutic targets for SIVD have been proposed by using transgenic mice or clinically used drugs in BCAS studies. This review article overviews findings from the studies that used this hypoperfused-SIVD mouse model, which were published between 2004 and 2021.

Proteomic Analysis Reveals Potential Exosomal Biomarkers in Patients With Sporadic Alzheimer Disease

BACKGROUND

Despite substantial progress made in the past decades, the pathogenesis of sporadic Alzheimer disease (sAD) and related biological markers of the disease are still controversially discussed. Cerebrospinal fluid and functional brain imaging markers have been established to support the clinical diagnosis of sAD. Yet, due to the invasiveness of such diagnostics, less burdensome markers have been increasingly investigated in the past years. Among such markers, extracellular vesicles may yield promise in (early) diagnostics and treatment monitoring in sAD.

MATERIALS AND METHODS

In this pilot study, we collected the blood plasma of 18 patients with sAD and compared the proteome of extracted extracellular vesicles with the proteome of 11 age-matched healthy controls. The resulting proteomes were characterized by Gene Ontology terms and between-group statistics.

RESULTS

Ten distinct proteins were found to significantly differ between sAD patients and controls (P<0.05, False Discovery Rate, corrected). These proteins included distinct immunoglobulins, fibronectin, and apolipoproteins.

CONCLUSIONS

These findings lend further support for exosomal changes in neurodegenerative disorders, and particularly in sAD. Further proteomic research could decisively advance our knowledge of sAD pathophysiology as much as it could foster the development of clinically meaningful biomarkers.

Role of cytokines and reactive oxygen species in brain aging

Aging is a complex process that produces profound effects on the brain. Although a number of external factors can promote the initiation and progression of brain aging, peripheral and central changes in the immune cells with time, also play an important role. Immunosenescence, which is an age-associated decline in immune function and Inflammaging, a low-grade inflammatory state in the aging brain contribute to an elevation in cytokine and reactive oxygen species production. In this review, we focus on the pro-inflammatory state that is established in the brain as a consequence of these two phenomena and the resulting detrimental changes in brain structure, function and repair that lead to a decline in central and neuroendocrine function.

Pathophysiology and probable etiology of cerebral small vessel disease in vascular dementia and Alzheimer's disease

Vascular cognitive impairment and dementia (VCID) is commonly caused by vascular injuries in cerebral large and small vessels and is a key driver of age-related cognitive decline. Severe VCID includes post-stroke dementia, subcortical ischemic vascular dementia, multi-infarct dementia, and mixed dementia. While VCID is acknowledged as the second most common form of dementia after Alzheimer's disease (AD) accounting for 20% of dementia cases, VCID and AD frequently coexist. In VCID, cerebral small vessel disease (cSVD) often affects arterioles, capillaries, and venules, where arteriolosclerosis and cerebral amyloid angiopathy (CAA) are major pathologies. White matter hyperintensities, recent small subcortical infarcts, lacunes of presumed vascular origin, enlarged perivascular space, microbleeds, and brain atrophy are neuroimaging hallmarks of cSVD. The current primary approach to cSVD treatment is to control vascular risk factors such as hypertension, dyslipidemia, diabetes, and smoking. However, causal therapeutic strategies have not been established partly due to the heterogeneous pathogenesis of cSVD. In this review, we summarize the pathophysiology of cSVD and discuss the probable etiological pathways by focusing on hypoperfusion/hypoxia, blood-brain barriers (BBB) dysregulation, brain fluid drainage disturbances, and vascular inflammation to define potential diagnostic and therapeutic targets for cSVD.

The emerging role of the HTRA1 protease in brain microvascular disease

Pathologies of the brain microvasculature, often referred to as cerebral small-vessel disease, are important contributors to vascular dementia, the second most common form of dementia in aging societies. In addition to their role in acute ischemic and hemorrhagic stroke, they have emerged as major cause of age-related cognitive decline in asymptomatic individuals. A central histological finding in these pathologies is the disruption of the vessel architecture including thickening of the vessel wall, narrowing of the vessel lumen and massive expansion of the mural extracellular matrix. The underlying molecular mechanisms are largely unknown, but from the investigation of several disease forms with defined etiology, high temperature requirement protein A1 (HTRA1), a secreted serine protease degrading primarily matrisomal substrates, has emerged as critical factor and potential therapeutic target. A genetically induced loss of HTRA1 function in humans is associated with cerebral autosomal-recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL), a rare, hereditary form of brain microvascular disease. Recently, proteomic studies on cerebral amyloid angiopathy (CAA), a common cause of age-related dementia, and cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), the most prevalent monogenic small-vessel disease, have provided evidence for an impairment of HTRA1 activity through sequestration into pathological protein deposits, suggesting an alternative mechanism of HTRA1 inactivation and expanding the range of diseases with HTRA1 involvement. Further investigations of the mechanisms of HTRA1 regulation in the brain microvasculature might spawn novel strategies for the treatment of small-vessel pathologies.

Heterozygous Pathogenic and Likely Pathogenic Symptomatic HTRA1 Variant Carriers in Cerebral Small Vessel Disease

High temperature requirement serine peptidase A1 (HTRA1) related cerebral small vessel disease (CSVD) includes both symptomatic heterozygous HTRA1 variant carrier and cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) patients. Presently, most reported symptomatic heterozygous HTRA1 variant carrier cases are sporadic family reports with a lack of specific characteristics. Additionally, the molecular mechanism of heterozygous HTRA1 gene variants is unclear. We conducted this review to collect symptomatic carriers of heterozygous HTRA1 gene variants reported as of 2022, analyzed all pathogenicity according to American College of Medical Genetics and Genomics (ACMG) variant classification, and summarized the cases with pathogenic and likely pathogenic HTRA1 variants gender characteristics, age of onset, geographical distribution, initial symptoms, clinical manifestations, imaging signs, HTRA1 gene variant information and to speculate its underlying pathogenic mechanisms. In this review, we summarized the following characteristics of pathogenic and likely pathogenic symptomatic HTRA1 variant carriers: to date, the majority of reported symptomatic HTRA1 carriers are in European and Asian countries, particularly in China which was found to have the highest number of reported cases. The age of first onset is mostly concentrated in the fourth and fifth decades. The heterozygous HTRA1 gene variants were mostly missense variants. The two variant sites, 166-182 aa and 274-302 aa, were the most concentrated. Clinicians need to pay attention to de novo data and functional data, which may affect the pathogenicity analysis. The decrease in HtrA1 protease activity is currently the most important explanation for the genetic pathogenesis.

The Transcriptional Landscapes and Key Genes in Brain Arteriovenous Malformation Progression in a Venous Hypertension Rat Model Revealed by RNA Sequencing

Background

Brain arteriovenous malformations (bAVM) are abnormal vascular lesions characterized by direct connections between arteries and veins without an intervening capillary bed. The primary goal for brain AVM treatment is to prevent rupture and hemorrhage; however, the underlying molecular mechanisms are still unknown.

Methods

We constructed venous hypertension (VH) rat model with end-to-end anastomosis of the proximal left common carotid artery and the left distal external jugular vein. Thirty-eight adult rats were randomly assigned to four groups: the 0-week (n=5), the 1-week VH group (n=12), the 3-week VH group (n=9), and the 6-week VH group (n=12). We measured the hemodynamics and diameter of the arterialized veins. An RNA sequencing of arterialized veins was conducted, followed by comprehensive bioinformatics analysis to identify key genes and biological pathways involved in VH progression. The candidate genes from RNA-Seq were validated by RT-qPCR and immunostaining in human tissues.

Results

We observed high-flow and low resistance characteristics in VH models. A total of 317 upregulated and 258 downregulated common genes were consistently differentially expressed during VH progression. Thirteen co-expression modules were obtained by WGCNA analysis, and 4 key modules were identified. Thirteen genes: Adamts8, Adamtsl3, Spon2, Adamtsl2, Chad, Itga7, Comp, Itga8, Bmp6, Fst, Smad6, Smad7, Grem1, and Nog with differential expressions were identified using the density of maximum neighborhood component (DMNC) algorithm in Cytohubba. The expression of five potential genes (Adamts8, Adamtsl3, Spon2, Adamtsl2, Itga8) were increased in RT-qPCR, while in human bAVM tissue, the protein levels of Adamtsl2 and Itga8 were significant elevated and Spon2 and Adamtsl3 were decreased.

Conclusion

The identified gene networks of Adamtsl3, Spon2, Adamtsl2, and Itga8 provided key genes for further intervention.

Proteomic profiling in cerebral amyloid angiopathy reveals an overlap with CADASIL highlighting accumulation of HTRA1 and its substrates

Cerebral amyloid angiopathy (CAA) is an age-related condition and a major cause of intracerebral hemorrhage and cognitive decline that shows close links with Alzheimer's disease (AD). CAA is characterized by the aggregation of amyloid-β (Aβ) peptides and formation of Aβ deposits in the brain vasculature resulting in a disruption of the angioarchitecture. Capillaries are a critical site of Aβ pathology in CAA type 1 and become dysfunctional during disease progression. Here, applying an advanced protocol for the isolation of parenchymal microvessels from post-mortem brain tissue combined with liquid chromatography tandem mass spectrometry (LC-MS/MS), we determined the proteomes of CAA type 1 cases (n = 12) including a patient with hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D), and of AD cases without microvascular amyloid pathology (n = 13) in comparison to neurologically healthy controls (n = 12). ELISA measurements revealed microvascular Aβ1-40 levels to be exclusively enriched in CAA samples (mean: > 3000-fold compared to controls). The proteomic profile of CAA type 1 was characterized by massive enrichment of multiple predominantly secreted proteins and showed significant overlap with the recently reported brain microvascular proteome of patients with cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a hereditary cerebral small vessel disease (SVD) characterized by the aggregation of the Notch3 extracellular domain. We found this overlap to be largely attributable to the accumulation of high-temperature requirement protein A1 (HTRA1), a serine protease with an established role in the brain vasculature, and several of its substrates. Notably, this signature was not present in AD cases. We further show that HTRA1 co-localizes with Aβ deposits in brain capillaries from CAA type 1 patients indicating a pathologic recruitment process. Together, these findings suggest a central role of HTRA1-dependent protein homeostasis in the CAA microvasculature and a molecular connection between multiple types of brain microvascular disease.