Cerebral hemodynamics in CADASIL before and after acetazolamide challenge assessed with MRI bolus tracking

Assessment of Small Vessel Function Using 7T MRI in Patients With Sporadic Cerebral Small Vessel Disease: The ZOOM@SVDs Study

BACKGROUND AND OBJECTIVES

Cerebral small vessel disease (cSVD) is a major cause of stroke and dementia, but little is known about disease mechanisms at the level of the small vessels. 7T-MRI allows assessing small vessel function in vivo in different vessel populations. We hypothesized that multiple aspects of small vessel function are altered in patients with cSVD and that these abnormalities relate to disease burden.

METHODS

Patients and controls participated in a prospective observational cohort study, the ZOOM@SVDs study. Small vessel function measures on 7T-MRI included perforating artery blood flow velocity and pulsatility index in the basal ganglia and centrum semiovale, vascular reactivity to visual stimulation in the occipital cortex, and reactivity to hypercapnia in the gray and white matter. Lesion load on 3T-MRI and cognitive function were used to assess disease burden.

RESULTS

Forty-six patients with sporadic cSVD (mean age ± SD 65 ± 9 years) and 22 matched controls (64 ± 7 years) participated in the ZOOM@SVDs study. Compared with controls, patients had increased pulsatility index (mean difference 0.09, p = 0.01) but similar blood flow velocity in basal ganglia perforating arteries and similar flow velocity and pulsatility index in centrum semiovale perforating arteries. The duration of the vascular response to brief visual stimulation in the occipital cortex was shorter in patients than in controls (mean difference -0.63 seconds, p = 0.02), whereas reactivity to hypercapnia was not significantly affected in the gray and total white matter. Among patients, reactivity to hypercapnia was lower in white matter hyperintensities compared with normal-appearing white matter (blood-oxygen-level dependent mean difference 0.35%, p = 0.001). Blood flow velocity and pulsatility index in basal ganglia perforating arteries and reactivity to brief visual stimulation correlated with disease burden.

DISCUSSION

We observed abnormalities in several aspects of small vessel function in patients with cSVD indicative of regionally increased arteriolar stiffness and decreased reactivity. Worse small vessel function also correlated with increased disease burden. These functional measures provide new mechanistic markers of sporadic cSVD.

Advances in Management of the Stroke Etiology One-Percenters

PURPOSE OF REVIEW

Uncommon causes of stroke merit specific attention; when clinicians have less common etiologies of stoke in mind, the diagnosis may come more easily. This is key, as optimal management will in many cases differs significantly from "standard" care.

RECENT FINDINGS

Randomized controlled trials (RCT) on the best medical therapy in the treatment of cervical artery dissection (CeAD) have demonstrated low rates of ischemia with both antiplatelet and vitamin K antagonism. RCT evidence supports the use of anticoagulation with vitamin K antagonism in "high-risk" patients with antiphospholipid antibody syndrome (APLAS), and there is new evidence supporting the utilization of direct oral anticoagulation in malignancy-associated thrombosis. Migraine with aura has been more conclusively linked not only with increased risk of ischemic and hemorrhagic stroke, but also with cardiovascular mortality. Recent literature has surprisingly not provided support the utilization of L-arginine in the treatment of patients with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS); however, there is evidence at this time that support use of enzyme replacement in patients with Fabry disease. Additional triggers for reversible cerebral vasoconstriction syndrome (RCVS) have been identified, such as capsaicin. Imaging of cerebral blood vessel walls utilizing contrast-enhanced MRA is an emerging modality that may ultimately prove to be very useful in the evaluation of patients with uncommon causes of stroke. A plethora of associations between cerebrovascular disease and COVID-19 have been described. Where pertinent, authors provide additional tips and guidance. Less commonly encountered conditions with updates in diagnosis, and management along with clinical tips are reviewed.

Roles of NG2 Glia in Cerebral Small Vessel Disease

Cerebral small vessel disease (CSVD) is one of the most prevalent pathologic processes affecting 5% of people over 50 years of age and contributing to 45% of dementia cases. Increasing evidence has demonstrated the pathological roles of chronic hypoperfusion, impaired cerebral vascular reactivity, and leakage of the blood-brain barrier in CSVD. However, the pathogenesis of CSVD remains elusive thus far, and no radical treatment has been developed. NG2 glia, also known as oligodendrocyte precursor cells, are the fourth type of glial cell in addition to astrocytes, microglia, and oligodendrocytes in the mammalian central nervous system. Many novel functions for NG2 glia in physiological and pathological states have recently been revealed. In this review, we discuss the role of NG2 glia in CSVD and the underlying mechanisms.

Cerebral Small Vessel Disease-Related Dementia: More Questions Than Answers

Cerebral small vessel disease (CSVD) has emerged as a common factor driving age-dependent diseases, including stroke and dementia. CSVD-related dementia will affect a growing fraction of the aging population, requiring improved recognition, understanding, and treatments. This review describes evolving criteria and imaging biomarkers for the diagnosis of CSVD-related dementia. We describe diagnostic challenges, particularly in the context of mixed pathologies and the absence of highly effective biomarkers for CSVD-related dementia. We review evidence regarding CSVD as a risk factor for developing neurodegenerative disease and potential mechanisms by which CSVD leads to progressive brain injury. Finally, we summarize recent studies on the effects of major classes of cardiovascular medicines relevant to CSVD-related cognitive impairment. Although many key questions remain, the increased attention to CSVD has resulted in a sharper vision for what will be needed to meet the upcoming challenges imposed by this disease.

Association between cerebrovasoreactivity and stroke in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy

Background

Impaired cerebrovasoreactivity is thought to play an important role in the pathophysiology of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). We aimed to clarify the association between cerebrovascular reactivity and stroke in patients with CADASIL.

Methods

We retrospectively recruited 14 patients with CADASIL, eight of whom had symptomatic stroke. They underwent quantitative single-photon emission computed tomography using an autoradiographic method at rest and after acetazolamide (ACZ) administration. Regional cerebral blood flow (rCBF) in the cerebral cortex, lenticular nucleus, thalamus, and cerebellum was measured. We compared the rCBF parameters between patients with and without stroke.

Results

The baseline characteristics and magnetic resonance imaging findings were similar between the two groups, except for a higher frequency of pyramidal tract sign (75% vs. 0%) and a larger number of old lacunes (15.4 ± 8.8 vs. 2.2 ± 1.8) in the patients with stroke. Of the rCBF parameters measured, significantly lower flow (mL/100 g/min) was observed in ACZ-rCBF in the thalamus (35.6 ± 9.4 vs. 51.1 ± 7.6, p = 0.01) and ΔrCBF in the thalamus (10.6 ± 3.7 vs. 21.0 ± 7.9, p = 0.02) in the patients with stroke.

Conclusion

Cerebrovasoreactivity in the thalamus was significantly associated with stroke in patients with CADASIL.

CADASIL Affects Multiple Aspects of Cerebral Small Vessel Function on 7T-MRI

OBJECTIVE

Cerebral small vessel diseases (cSVDs) are a major cause of stroke and dementia. We used cutting-edge 7T-MRI techniques in patients with Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL), to establish which aspects of cerebral small vessel function are affected by this monogenic form of cSVD.

METHODS

We recruited 23 CADASIL patients (age 51.1 ± 10.1 years, 52% women) and 13 age- and sex-matched controls (46.1 ± 12.6, 46% women). Small vessel function measures included: basal ganglia and centrum semiovale perforating artery blood flow velocity and pulsatility, vascular reactivity to a visual stimulus in the occipital cortex and reactivity to hypercapnia in the cortex, subcortical gray matter, white matter, and white matter hyperintensities.

RESULTS

Compared with controls, CADASIL patients showed lower blood flow velocity and higher pulsatility index within perforating arteries of the centrum semiovale (mean difference - 0.09 cm/s, p = 0.03 and 0.20, p = 0.009) and basal ganglia (mean difference - 0.98 cm/s, p = 0.003 and 0.17, p = 0.06). Small vessel reactivity to a short visual stimulus was decreased (blood-oxygen-level dependent [BOLD] mean difference -0.21%, p = 0.04) in patients, while reactivity to hypercapnia was preserved in the cortex, subcortical gray matter, and normal appearing white matter. Among patients, reactivity to hypercapnia was decreased in white matter hyperintensities compared to normal appearing white matter (BOLD mean difference -0.29%, p = 0.02).

INTERPRETATION

Multiple aspects of cerebral small vessel function on 7T-MRI were abnormal in CADASIL patients, indicative of increased arteriolar stiffness and regional abnormalities in reactivity, locally also in relation to white matter injury. These observations provide novel markers of cSVD for mechanistic and intervention studies. ANN NEUROL 2023;93:29-39.

White Matter Tract Injury by MRI in CADASIL Patients is Associated With Iron Accumulation

BACKGROUND

Widespread white matter (WM) injury is a hallmark feature of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). However, controversies about the mechanism of WM tract injury exist persistently. Excessive iron accumulation, frequently reported in CADASIL patients, might cause WM tract injury.

PURPOSE

To test the association between iron accumulation and WM tract injury in CADASIL patients.

STUDY TYPE

Retrospective.

POPULATION

A total of 35 CADASIL patients (age = 50.4 ± 6.4, 62.9% female) and 48 healthy controls (age = 55.7 ± 8.0, 68.8% female).

FIELD STRENGTH/SEQUENCE

Diffusion-weighted spin-echo echo-planar sequence; enhanced susceptibility-weighted angiography (ESWAN) gradient echo sequence on a 3 T scanner.

ASSESSMENT

The phase images acquired by ESWAN were used to calculate quantitative susceptibility mapping (QSM). Iron accumulation was evaluated in deep gray matters using QSM. WM tract injury was quantified by diffusion metrics based on WM major tracts skeleton. We compared iron deposition between groups and analyzed the correlation between WM tract injury and iron deposition in regions showing significant differences from healthy controls. Exploratory analysis was carried out to investigate whether WM tract injury mediated the relationship between iron deposition and cognitive impairment evaluated by Mini-Mental State Examination (MMSE).

STATISTICAL TESTS

General linear model (GLM), partial correlation, stepwise linear regression and mediation analysis were used. The threshold of statistical significance was set as p < 0.05.

RESULTS

Compared with healthy controls, CADASIL patients had significantly increased iron deposition in the caudate and putamen. Aberrant iron deposition in these two regions was significantly associated with decreased WM fractional anisotropy (FA) (caudate, r = -0.373； putamen, r = - 0.421), and increased radial diffusivity (RD) (caudate, r = 0.372; putamen, r = 0.386). Furthermore, WM tract injury mediated the relationship between iron deposition and cognitive impairment.

DATA CONCLUSION

Patients with CADASIL show increased iron deposition in the caudate and putamen that is correlated to WM tract injury, which may in turn mediate the association with cognitive impairment.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 2.

Vascular smooth muscle cell dysfunction in neurodegeneration

Vascular smooth muscle cells (VSMCs) are the key moderators of cerebrovascular dynamics in response to the brain's oxygen and nutrient demands. Crucially, VSMCs may provide a sensitive biomarker for neurodegenerative pathologies where vasculature is compromised. An increasing body of research suggests that VSMCs have remarkable plasticity and their pathophysiology may play a key role in the complex process of neurodegeneration. Furthermore, extrinsic risk factors, including environmental conditions and traumatic events can impact vascular function through changes in VSMC morphology. VSMC dysfunction can be characterised at the molecular level both preclinically, and clinically ex vivo. However the identification of VSMC dysfunction in living individuals is important to understand changes in vascular function at the onset and progression of neurological disorders such as dementia, Alzheimer's disease, and Parkinson's disease. A promising technique to identify changes in the state of cerebral smooth muscle is cerebrovascular reactivity (CVR) which reflects the intrinsic dynamic response of blood vessels in the brain to vasoactive stimuli in order to modulate regional cerebral blood flow (CBF). In this work, we review the role of VSMCs in the most common neurodegenerative disorders and identify physiological systems that may contribute to VSMC dysfunction. The evidence collected here identifies VSMC dysfunction as a strong candidate for novel therapeutics to combat the development and progression of neurodegeneration, and highlights the need for more research on the role of VSMCs and cerebrovascular dynamics in healthy and diseased states.

Cognition, mood and behavior in CADASIL

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CADASIL is responsible for cognitive, mood or behavior disturbances.

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Cognitive disturbances range from moderate cognitive slowing to impairment of executive functions and may progress to a global decrease of cognitive efficiency up to severe dementia.

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Mood disturbances are extremely variable in intensity, depression is the most frequent symptom.

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Behavioral changes may occur at all stage of the disease, but are often associated with the onset of cognitive alterations. Apathy is the most prominent behavior alteration.

CADASIL is the most common familial cerebral small vessel disease (cSVD). Stereotyped mutations of the NOTCH3 gene are responsible for this archetypal ischemic cSVD that can lead, at the very end stage, to severe dementia. Variable cognitive alterations, mood, or behavior disturbances are frequently observed during the course of the disease. In this review, these clinical manifestations, their occurrence, severity and duration are analyzed in relation to the disease progression. Also, the potential relationships with cerebral lesions and treatment options are discussed.

The pericyte: A critical cell in the pathogenesis of CADASIL

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CADASIL is the most common hereditary small vessel disease presenting with strokes and subcortical vascular dementia caused by mutations in the NOTCH3 gene.

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CADASIL is a vasculopathy primarily involving vascular smooth-muscle cells.

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Arteriolar and capillary pericyte damage or deficiency is a key feature in disease pathogenesis.

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Pericyte-mediated cerebral venous insufficiency may explain white matter lesions and increased perivascular spaces.

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Central role of the pericyte offers novel approaches to the treatment of CADASIL.

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a hereditary small vessel disease presenting with migraine, mood and cognitive disorders, focal neurological deficits, recurrent ischemic attacks, lacunar infarcts and brain white matter changes. As they age, CADASIL patients invariably develop cognitive impairment and subcortical dementia. CADASIL is caused by missense mutations in the NOTCH3 gene resulting in a profound cerebral vasculopathy affecting primarily arterial vascular smooth muscle cells, which target the microcirculation and perfusion. Based on a thorough review of morphological lesions in arteries, veins, and capillaries in CADASIL, we surmise that arteriolar and capillary pericyte damage or deficiency appears a key feature in the pathogenesis of the disease. This may affect critical pericyte-endothelial interactions causing stroke injury and vasomotor disturbances. Changes in microvascular permeability due to perhaps localized blood-brain barrier alterations and pericyte secretory dysfunction likely contribute to delayed neuronal as well as glial cell death. Moreover, pericyte-mediated cerebral venous insufficiency may explain white matter lesions and the dilatation of Virchow-Robin perivascular spaces typical of CADASIL. The postulated central role of the pericyte offers some novel approaches to the study and treatment of CADASIL and enable elucidation of other forms of cerebral small vessel diseases and subcortical vascular dementia.

Prostaglandin E2 Dilates Intracerebral Arterioles When Applied to Capillaries: Implications for Small Vessel Diseases

Prostaglandin E2 (PGE2) has been widely proposed to mediate neurovascular coupling by dilating brain parenchymal arterioles through activation of prostanoid EP4 receptors. However, our previous report that direct application of PGE2 induces an EP1-mediated constriction strongly argues against its direct action on arterioles during neurovascular coupling, the mechanisms sustaining functional hyperemia. Recent advances have highlighted the role of capillaries in sensing neuronal activity and propagating vasodilatory signals to the upstream penetrating parenchymal arteriole. Here, we examined the effect of capillary stimulation with PGE2 on upstream arteriolar diameter using an ex vivo capillary-parenchymal arteriole preparation and in vivo cerebral blood flow measurements with two-photon laser-scanning microscopy. We found that PGE2 caused upstream arteriolar dilation when applied onto capillaries with an EC50 of 70 nM. The response was inhibited by EP1 receptor antagonist and was greatly reduced, but not abolished, by blocking the strong inward-rectifier K+ channel. We further observed a blunted dilatory response to capillary stimulation with PGE2 in a genetic mouse model of cerebral small vessel disease with impaired functional hyperemia. This evidence casts previous findings in a different light, indicating that capillaries are the locus of PGE2 action to induce upstream arteriolar dilation in the control of brain blood flow, thereby providing a paradigm-shifting view that nonetheless remains coherent with the broad contours of a substantial body of existing literature.

Peripheral arteriopathy caused by Notch3 gain-of-function mutation involves ER and oxidative stress and blunting of NO/sGC/cGMP pathway

Notch3 mutations cause Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL), which predisposes to stroke and dementia. CADASIL is characterised by vascular dysfunction and granular osmiophilic material (GOM) accumulation in cerebral small vessels. Systemic vessels may also be impacted by Notch3 mutations. However vascular characteristics and pathophysiological processes remain elusive. We investigated mechanisms underlying the peripheral vasculopathy mediated by CADASIL-causing Notch3 gain-of-function mutation. We studied: (i) small arteries and vascular smooth muscle cells (VSMCs) from TgNotch3R169C mice (CADASIL model), (ii) VSMCs from peripheral arteries from CADASIL patients, and (iii) post-mortem brains from CADASIL individuals. TgNotch3R169C vessels exhibited GOM deposits, increased vasoreactivity and impaired vasorelaxation. Hypercontractile responses were normalised by fasudil (Rho kinase inhibitor) and 4-phenylbutyrate (4-PBA; endoplasmic-reticulum (ER) stress inhibitor). Ca2+ transients and Ca2+ channel expression were increased in CADASIL VSMCs, with increased expression of Rho guanine nucleotide-exchange factors (GEFs) and ER stress proteins. Vasorelaxation mechanisms were impaired in CADASIL, evidenced by decreased endothelial nitric oxide synthase (eNOS) phosphorylation and reduced cyclic guanosine 3',5'-monophosphate (cGMP) levels, with associated increased soluble guanylate cyclase (sGC) oxidation, decreased sGC activity and reduced levels of the vasodilator hydrogen peroxide (H2O2). In VSMCs from CADASIL patients, sGC oxidation was increased and cGMP levels decreased, effects normalised by fasudil and 4-PBA. Cerebral vessels in CADASIL patients exhibited significant oxidative damage. In conclusion, peripheral vascular dysfunction in CADASIL is associated with altered Ca2+ homoeostasis, oxidative stress and blunted eNOS/sGC/cGMP signaling, processes involving Rho kinase and ER stress. We identify novel pathways underlying the peripheral arteriopathy induced by Notch3 gain-of-function mutation, phenomena that may also be important in cerebral vessels.

Changes in the Morphology, Number, and Protein Levels of Plasma Exosomes in CADASIL Patients

BACKGROUND

Exosomes are nano-sized extracellular vesicles which are secreted by cells and usually found in body fluids. Previous research has shown that exosomal secretion and autophagy-lysosomal pathway synergistically participates in intracellular abnormal protein elimination. The main pathological manifestations of Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is abnormal accumulation of mutant NOTCH3, and CADASIL vascular smooth muscle cells have been found with autophagy-lysosomal dysfunction. However, whether plasma exosomes change in CADASIL patients is still unclear.

OBJECTIVE

We are aimed to investigate the differences of plasma exosomes between CADASIL patients and healthy controls.

METHODS

The subjects included 30 CADASIL patients and 30 healthy controls without NOTCH3 mutation. The severity of white matter lesions (WMLs) of CADASIL patients was quantified by Fazekas score. Transmission electron microscopy and nanoparticle tracking analysis were performed to characterize plasma exosomes. In addition, NOTCH3, Neurofilament light and Aβ42 levels in plasma exosomes were quantified by enzyme-linked immunosorbent assays.

RESULTS

We found that exosomes from CADASIL patients were lower in quantity. In addition, CADASIL plasma exosomes had significantly lower levels of NOTCH3 and significantly increased levels of NFL than those of matched healthy subjects. Interestingly, plasma exosome NOTCH3 levels of CADASIL patients significantly correlated with severity of WMLs.

CONCLUSION

The exosome NOTCH3 may be related to the pathological changes of CADASIL, which provides a basis for the pathogenesis research of CADASIL. In addition, plasma exosome NOTCH3 and NFL levels may act as biomarkers to monitor and predict disease progression and measure therapeutic effectiveness in the future clinical trials.

CADASIL from Bench to Bedside: Disease Models and Novel Therapeutic Approaches

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a monogenic disease caused by NOTCH3 mutations and characterized by typical clinical, neuroradiological, and pathological features. NOTCH3 belongs to a family of highly conserved transmembrane receptors rich of epidermal growth factor repeats, mostly expressed in vascular smooth muscle cells and pericytes, which perform essential developmental functions and are involved in tissues maintenance and renewal. To date, no therapeutic option for CADASIL is available except for few symptomatic treatments. Novel in vitro and in vivo models are continuously explored with the aim to investigate underlying pathogenic mechanisms and to test novel therapeutic approaches. In this scenario, knock-out, knock-in, and transgenic mice studies have generated a large amount of information on molecular and biological aspects of CADASIL, despite that they incompletely reproduce the human phenotype. Moreover, the field of in vitro models has been revolutionized in the last two decades by the introduction of induced pluripotent stem cells (iPSCs) technology. As a consequence, novel therapeutic approaches, including immunotherapy, growth factors administration, and antisense oligonucleotides, are currently under investigation. While waiting that further studies confirm the promising results obtained, the data reviewed suggest that our therapeutic approach to the disease could be transformed, generating new hope for the future.

Brain imaging factors associated with progression of subcortical hyperintensities in CADASIL over 2-year follow-up

BACKGROUND AND PURPOSE

Mutations in the NOTCH3 gene cause cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a cerebral small vessel disease manifesting with stroke, migraine and dementia in adults. The disease displays significant phenotypic variability that is incompletely explained. Early abnormalities in vascular function have been shown in animal models. We postulated that studying changes in vascular function may offer insights into disease progression.

METHODS

Twenty-two subjects with CADASIL [50% female, 50 (±11) years] from 19 pedigrees were included in a longitudinal multimodality study using brain magnetic resonance imaging (MRI), clinical measures, neuropsychology and measures of peripheral vascular function. MRI studies included measurement of structural brain changes, cerebral blood flow (CBF) and cerebrovascular reactivity by arterial spin labelling and a CO₂ respiratory challenge.

RESULTS

Over 2 years, new stroke or transient ischaemic attack (TIA) occurred in five (23%) subjects and new significant disability in one (5%). There were significant increases in number of lacunes, subcortical hyperintensity volume and microbleeds, and a decrease in brain volume. CBF declined by 3.2 (±4.5) ml/100 g/min over 2 years. CBF and carotid-femoral pulse wave velocity at baseline predicted change in subcortical hyperintensity volume at follow-up. Carotid intima-media thickness and age predicted brain atrophy. Baseline CBF was lower in subjects who showed a decline in attention and working memory.

CONCLUSIONS

Cerebral blood flow predicts radiological progression of hyperintensities and thus is a potential biomarker of disease progression in CADASIL. Over 2 years, there were changes in several relevant imaging biomarkers (CBF, brain volume, lacunes, microbleeds and hyperintensity volume). Future studies in CADASIL should consider assessment of CBF as prognostic factor.

Pathophysiological Mechanisms and Potential Therapeutic Targets in Cerebral Autosomal Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy (CADASIL)

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), is a hereditary small-vessels angiopathy caused by mutations in the NOTCH 3 gene, located on chromosome 19, usually affecting middle-ages adults, whose clinical manifestations include migraine with aura, recurrent strokes, mood disorders, and cognitive impairment leading to dementia and disability. In this review, we provide an overview of the current knowledge on the pathogenic mechanisms underlying the disease, focus on the corresponding therapeutic targets, and discuss the most promising treatment strategies currently under investigations. The hypothesis that CADASIL is an appropriate model to explore the pathogenesis of sporadic cerebral small vessel disease is also reviewed.

ER stress and Rho kinase activation underlie the vasculopathy of CADASIL

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) leads to premature stroke and vascular dementia. Mechanism-specific therapies for this aggressive cerebral small vessel disease are lacking. CADASIL is caused by NOTCH3 mutations that influence vascular smooth muscle cell (VSMC) function through unknown processes. We investigated molecular mechanisms underlying the vasculopathy in CADASIL focusing on endoplasmic reticulum (ER) stress and RhoA/Rho kinase (ROCK). Peripheral small arteries and VSMCs were isolated from gluteal biopsies of CADASIL patients and mesentery of TgNotch3R169C mice (CADASIL model). CADASIL vessels exhibited impaired vasorelaxation, blunted vasoconstriction, and hypertrophic remodeling. Expression of NOTCH3 and ER stress target genes was amplified and ER stress response, Rho kinase activity, superoxide production, and cytoskeleton-associated protein phosphorylation were increased in CADASIL, processes associated with Nox5 upregulation. Aberrant vascular responses and signaling in CADASIL were ameliorated by inhibitors of Notch3 (γ-secretase inhibitor), Nox5 (mellitin), ER stress (4-phenylbutyric acid), and ROCK (fasudil). Observations in human CADASIL were recapitulated in TgNotch3R169C mice. These findings indicate that vascular dysfunction in CADASIL involves ER stress/ROCK interplay driven by Notch3-induced Nox5 activation and that NOTCH3 mutation-associated vascular pathology, typical in cerebral vessels, also manifests peripherally. We define Notch3-Nox5/ER stress/ROCK signaling as a putative mechanism-specific target and suggest that peripheral artery responses may be an accessible biomarker in CADASIL.

Progression and Classification of Granular Osmiophilic Material (GOM) Deposits in Functionally Characterized Human NOTCH3 Transgenic Mice

CADASIL is a NOTCH3-associated cerebral small vessel disease. A pathological ultrastructural disease hallmark is the presence of NOTCH3-protein containing deposits called granular osmiophilic material (GOM), in small arteries. How these GOM deposits develop over time and what their role is in disease progression is largely unknown. Here, we studied the progression of GOM deposits in humanized transgenic NOTCH3^Arg182Cys mice, compared them to GOM deposits in patient material, and determined whether GOM deposits in mice are associated with a functional CADASIL phenotype. We found that GOM deposits are not static, but rather progress in ageing mice, both in terms of size and aspect. We devised a GOM classification system, reflecting size, morphology and electron density. Six-month-old mice showed mostly early stage GOM, whereas older mice and patient vessels showed predominantly advanced stage GOM, but also early stage GOM. Mutant mice did not develop the most severe GOM stage seen in patient material. This absence of end-stage GOM in mice was associated with an overall lack of histological vascular pathology, which may explain why the mice did not reveal functional deficits in cerebral blood flow, cognition and motor function. Taken together, our data indicate that GOM progress over time, and that new GOM deposits are continuously being formed. The GOM staging system we introduce here allows for uniform GOM deposit classification in future mouse and human studies, which may lead to more insight into a potential association between GOM stage and CADASIL disease severity, and the role of GOM in disease progression.

Stem cell factor and granulocyte colony-stimulating factor promote brain repair and improve cognitive function through VEGF-A in a mouse model of CADASIL

Cerebral autosomal dominant arteriopathy with subcortical infarct and leukoencephalopathy (CADASIL) is a cerebral small vascular disease caused by NOTCH3 gene mutation in vascular smooth muscle cells (VSMCs), leading to ischemic stroke and vascular dementia. To date, the pathogenesis of CADASIL remains poorly understood, and there is no treatment that can slow the progression of CADASIL. Using a transgenic mouse model of CADASIL (TgNotch3R90C), this study reveals novel findings for understanding CADASIL pathogenesis that decreased cerebral vascular endothelial growth factor (VEGF/VEGF-A) is linked to reduced cerebral blood vessel density. Reduced endothelial cell (EC) proliferation and angiogenesis are seen in TgNotch3R90C mouse brain-isolated ECs. Decreased dendrites, axons, and synapses in the somatosensory and motor cortex layer 2/3 and in the hippocampal CA1, and reduced neurogenesis in both the subventricular zone and subgranular zone occur in 15-month-old TgNotch3R90C mice. These reductions in neuron structures, synapses, and neurogenesis are significantly correlated to decreased cerebral vasculature in the corresponding areas. Impaired spatial learning and memory in TgNotch3R90C mice are significantly correlated with the reduced cerebral vasculature, neuron structures, and synapses. Repeated treatment of stem cell factor and granulocyte colony-stimulating factor (SCF+G-CSF) at 9 and 10 months of age improves cognitive function, increases cerebral VEGF/VEGF-A, restores cerebral vasculature, and enhances regeneration of neuronal structures, synaptogenesis and neurogenesis in TgNotch3R90C mice. Pretreatment with Avastin, an angiogenesis inhibitor by neutralizing VEGF-A, completely eliminates the SCF+G-CSF-enhanced cognitive function, vascular and neuronal structure regeneration, synaptogenesis and neurogenesis in TgNotch3R90C mice. SCF+G-CSF-enhanced EC proliferation and angiogenesis in TgNotch3R90C mouse brain-isolated ECs are also blocked by Avastin pretreatment. These data suggest that SCF+G-CSF treatment may repair Notch3R90C mutation-damaged brain through the VEGF-A-mediated angiogenesis. This study provides novel insight into the involvement of VEGF/VEGF-A in the pathogenesis of CADASIL and sheds light on the mechanism underlying the SCF+G-CSF-enhanced brain repair in CADASIL.

Aura and Stroke: relationship and what we have learnt from preclinical models

BACKGROUND

Population-based studies have highlighted a close relationship between migraine and stroke. Migraine, especially with aura, is a risk factor for both ischemic and hemorrhagic stroke. Interestingly, stroke risk is highest for migraineurs who are young and otherwise healthy.

MAIN BODY

Preclinical models have provided us with possible mechanisms to explain the increased vulnerability of migraineurs' brains towards ischemia and suggest a key role for enhanced cerebral excitability and increased incidence of microembolic events. Spreading depolarization (SD), a slowly propagating wave of neuronal depolarization, is the electrophysiologic event underlying migraine aura and a known headache trigger. Increased SD susceptibility has been demonstrated in migraine animal models, including transgenic mice carrying human mutations for the migraine-associated syndrome CADASIL and familial hemiplegic migraine (type 1 and 2). Upon experimentally induced SD, these mice develop aura-like neurological symptoms, akin to patients with the respective mutations. Migraine mutant mice also exhibit an increased frequency of ischemia-triggered SDs upon experimental stroke, associated with accelerated infarct growth and worse outcomes. The severe stroke phenotype can be explained by SD-related downstream events that exacerbate the metabolic mismatch, including pericyte contraction and neuroglial inflammation. Pharmacological suppression of the genetically enhanced SD susceptibility normalizes the stroke phenotype in familial hemiplegic migraine mutant mice. Recent epidemiologic and imaging studies suggest that these preclinical findings can be extrapolated to migraine patients. Migraine patients are at risk for particularly cardioembolic stroke. At the same time, studies suggest an increased incidence of coagulopathy, atrial fibrillation and patent foramen ovale among migraineurs, providing a possible path for microembolic induction of SD and, in rare instances, stroke in hyperexcitable brains. Indeed, recent imaging studies document an accelerated infarct progression with only little potentially salvageable brain tissue in acute stroke patients with a migraine history, suggesting an increased vulnerability towards cerebral ischemia.

CONCLUSION

Preclinical models suggest a key role for enhanced SD susceptibility and microembolization to explain both the occurrence of migraine attacks and the increased stroke risk in migraineurs. Therapeutic targeting of SD and microembolic events, or potential causes thereof, will be promising for treatment of aura and may also prevent ischemic infarction in vulnerable brains.

Modeling CADASIL vascular pathologies with patient-derived induced pluripotent stem cells

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a rare hereditary cerebrovascular disease caused by a NOTCH3 mutation. However, the underlying cellular and molecular mechanisms remain unidentified. Here, we generated non-integrative induced pluripotent stem cells (iPSCs) from fibroblasts of a CADASIL patient harboring a heterozygous NOTCH3 mutation (c.3226C>T, p.R1076C). Vascular smooth muscle cells (VSMCs) differentiated from CADASIL-specific iPSCs showed gene expression changes associated with disease phenotypes, including activation of the NOTCH and NF-κB signaling pathway, cytoskeleton disorganization, and excessive cell proliferation. In comparison, these abnormalities were not observed in vascular endothelial cells (VECs) derived from the patient's iPSCs. Importantly, the abnormal upregulation of NF-κB target genes in CADASIL VSMCs was diminished by a NOTCH pathway inhibitor, providing a potential therapeutic strategy for CADASIL. Overall, using this iPSC-based disease model, our study identified clues for studying the pathogenic mechanisms of CADASIL and developing treatment strategies for this disease.

Perivascular neurotransmitters: Regulation of cerebral blood flow and role in primary headaches

In order to understand the nature of the relationship between cerebral blood flow (CBF) and primary headaches, we have conducted a literature review with particular emphasis on the role of perivascular neurotransmitters. Primary headaches are in general considered complex polygenic disorders (genetic and environmental influence) with pathophysiological neurovascular alterations. Identified candidate headache genes are associated with neuro- and gliogenesis, vascular development and diseases, and regulation of vascular tone. These findings support a role for the vasculature in primary headache disorders. Moreover, neuronal hyperexcitability and other abnormalities have been observed in primary headaches and related to changes in hemodynamic factors. In particular, this relates to migraine aura and spreading depression. During headache attacks, ganglia such as trigeminal and sphenopalatine (located outside the blood-brain barrier) are variably activated and sensitized which gives rise to vasoactive neurotransmitter release. Sympathetic, parasympathetic and sensory nerves to the cerebral vasculature are activated. During migraine attacks, altered CBF has been observed in brain regions such as the somatosensory cortex, brainstem and thalamus. In regulation of CBF, the individual roles of neurotransmitters are partly known, but much needs to be unraveled with respect to headache disorders.

Functional Magnetic Resonance Imaging of Inhibitory Control Reveals Decreased Blood Oxygen Level Dependent Effect in Cerebral Autosomal Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy

Background and Purpose- Small-vessel damage in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is associated with impaired vascular constriction and dilation. We used a functional magnetic resonance imaging task with an event-related design of stimulus to explore the anticipated abnormally decreased blood oxygen level dependent effect in CADASIL. Methods- Twenty-one CADASIL patients and 16 healthy controls performed a Go/No-go task exploring reactive and proactive phases of inhibition control in a 3-T magnet. Results- Error number and reaction times were not different between patients and controls. Analysis of the reactive inhibition (No-go/baseline contrast) did not show clusters of lower or higher blood oxygen level dependent effect in patients or controls. Analysis of the proactive inhibition (alertness contrast) in CADASIL patients revealed a lower blood oxygen level dependent effect in the alerting network (anterior cingulate cortex and insula, thalamus), lower brain stem and left cerebellar hemisphere (crus I) that is involved in executive functions. Conclusions- In CADASIL patients, an event-related Go/No-go task reveals a lower blood oxygen level dependent effect in the alerting network and areas involved in executive functions possibly reflecting the altered hemodynamic response secondary to small-vessel changes. Our observation extends the role of MR in demonstrating one of the fundamental pathophysiological changes of CADASIL.

RVCL-S and CADASIL display distinct impaired vascular function

OBJECTIVE

We aimed to evaluate the role of endothelial-dependent and endothelial-independent vascular reactivity in retinal vasculopathy with cerebral leukoencephalopathy and systemic manifestations (RVCL-S) and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), both cerebral small vessel diseases are considered models for stroke, vascular dementia, and migraine.

METHODS

RVCL-S (n = 18) and CADASIL (n = 23) participants with TREX1 and NOTCH3 mutations, respectively, were compared with controls matched for age, body mass index, and sex (n = 26). Endothelial function was evaluated by flow-mediated vasodilatation, and endothelial-independent vascular reactivity (i.e., vascular smooth muscle cell function) was assessed by dermal blood flow response to capsaicin application.

RESULTS

Flow-mediated vasodilatation was decreased in participants with RVCL-S compared with controls (2.32% ± 3.83% vs 5.76% ± 3.07% change in diameter, p = 0.023) but normal in participants with CADASIL. Vascular smooth muscle cell function was reduced in participants with CADASIL compared with controls (maximal dermal blood flow increase at 40 minutes after capsaicin: 1.38 ± 0.88 vs 2.22 ± 1.20 arbitrary units, p = 0.010) but normal in participants with RVCL-S.

CONCLUSIONS

We identified endothelial dysfunction in RVCL-S and confirmed impaired vascular smooth muscle cell relaxation in CADASIL. Our findings may prove to be biomarkers for disease progression in both monogenic cerebral small vessel diseases and improve mechanistic insight in their pathophysiology. This may help in understanding common neurovascular disorders, including stroke, dementia, and migraine.

Vasoreactivity in CADASIL: Comparison to structural MRI and neuropsychology

Impaired cerebrovascular reactivity precedes histological and clinical evidence of CADASIL in animal models. We aimed to more fully characterise peripheral and cerebral vascular function and reactivity in a cohort of adult CADASIL patients, and explore the associations of these with conventional clinical, imaging and neuropsychological measures. A total of 22 adults with CADASIL gave informed consent to participate in an exploratory study of vascular function in CADASIL. Clinical assessment, comprehensive vascular assessment, MRI and neuropsychological testing were conducted. We measured cerebral vasoreactivity with transcranial Doppler and arterial spin labelling MRI with hypercapnia challenge. Number and volume of lacunes, subcortical hyperintensity volume, microbleeds and normalised brain volume were assessed on MRI. Analysis was exploratory and examined the associations between different markers. Cerebrovascular reactivity measured by ASL correlated with peripheral vasoreactivity measured by flow mediated dilatation. Subjects with ≥5 lacunes were older, with higher carotid intima-media thickness and had impaired cerebral and peripheral vasoreactivity. Subjects with depressive symptoms, disability or delayed processing speed also showed a trend to impaired vasoreactivity. Impaired vasoreactivity and vascular dysfunction may play a significant role in the pathophysiology of CADASIL, and vascular assessments may be useful biomarkers of severity in both longitudinal and clinical trials.

Effects of Cerebral Blood Flow and White Matter Integrity on Cognition in CADASIL Patients

Background: It remains unclear whether the degree of white matter tract damage or cerebral hypoperfusion can better predict global cognitive impairment in CADASIL. We sought to determine the independent effects of cerebral perfusion status and white matter integrity on the cognition. Methods: We reviewed prospectively collected clinical and imaging data from genetically-confirmed CADASIL patients who underwent both arterial spin labeling (ASL) perfusion MRI and diffusion tensor imaging (DTI). We analyzed the cerebral blood flow (CBF), mean diffusion (MD), and fractional anisotropy (FA) by dividing the brain tissue into white matter hyperintensity (WMH) and normal-appearing white matter (NAWM). Global cognitive function was evaluated by using Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA). Results: Of the included 29 CADASIL patients, the mean age was 48.4 ± 7.9 years, and 17 (58.6%) were women. MD was significantly correlated with CBF in both WMH (r = -0.407, P = 0.035) and NAWM (r = -0.437, P = 0.023) after adjusting for age and WMH volume. A MoCA score was obtained in 13 patients and was significantly correlated with CBF in both WMH (r = 0.742, P = 0.004) and NAWM (r = 0.659, P = 0.014). Both CBF in WMH (area under the curve, 0.767; 95% CI, 0.586-0.947, P = 0.015) and MD in WMH (area under the curve, 0.740; 95% CI, 0.557-0.924, P = 0.028) were good predictors for cognitive impairment (MMSE score < 27). However, multiple linear regression analysis revealed that global cognitive function was independently associated with CBF in WMH only (standardized β = 0.485, P = 0.015), after adjusting for age, gender, WMH volume, the presence of subcortical infarcts and DTI metrics. Conclusions: Our findings suggested that cerebral hypoperfusion was more strongly associated with global cognitive dysfunction than the severity of brain microstructural damage, supporting that CBF assessed by ASL could serve as a candidate imaging indicator for monitoring alterations of global cognitive function in CADASIL.

CADASIL mutant NOTCH3(R90C) decreases the viability of HS683 oligodendrocytes via apoptosis

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common hereditary cerebral small vessel disease caused by mutations in NOTCH3. Prevailing models suggest that demyelination occurs secondary to vascular pathology. However, in zebrafish, NOTCH3 is also expressed in mature oligodendrocytes. Thus, we hypothesized that in addition to vascular defects, mutant NOTCH3 may alter glial function in individuals with CADASIL. The aim of this study was to characterize the direct effects of a mutant NOTCH3 protein in HS683 oligodendrocytes. HS683 oligodendrocytes transfected with wild-type NOTCH3, mutant NOTCH3(R90C), and empty control vector were used to study the impact of the NOTCH3(R90C) mutant on its protein hydrolytic processing, cell viability, apoptosis, autophagy, oxidative stress, and the related upstream events using immunoblotting, immunofluorescence, RT-PCR, and flow cytometry. We determined that HS683 oligodendrocytes transfected with mutant NOTCH3(R90C), which is the hotspot mutation site-associated with CADASIL, exhibited aberrant NOTCH3 proteolytic processing. Compared to cells overexpressing wild-type NOTCH3, cells overexpressing NOTCH3(R90C) were less viable and had a higher rate of apoptosis. Immunoblotting revealed that cells transfected with NOTCH3(R90C) had higher levels of intrinsic mitochondrial apoptosis, extrinsic death receptor path-related apoptosis, and autophagy compared with cells transfected with wild-type NOTCH3. This study suggests that in patients with CADASIL, early defects in glia influenced by NOTCH3(R90C) may directly contribute to white matter pathology in addition to secondary vascular defects. This study provides a potential therapeutic target for the future treatment of CADASIL.

Pathogenesis of white matter changes in cerebral small vessel diseases: beyond vessel-intrinsic mechanisms

Cerebral small vessel diseases (SVDs) are a leading cause of age and hypertension-related stroke and dementia. The salient features of SVDs visible on conventional brain magnetic resonance images include white matter hyperintensities (WMHs) on T2-weighted images, small infarcts, macrohemorrhages, dilated perivascular spaces, microbleeds and brain atrophy. Among these, WMHs are the most common and often the earliest brain tissue changes. Moreover, over the past two decades, large population- and patient-based studies have established the clinical importance of WMHs, notably with respect to cognitive and motor disturbances. Here, we seek to provide a new and critical look at the pathogenesis of SVD-associated white matter (WM) changes. We first review our current knowledge of WM biology in the healthy brain, and then consider the main clinical and pathological features of WM changes in SVDs. The most widely held view is that SVD-associated WM lesions are caused by chronic hypoperfusion, impaired cerebrovascular reactivity (CVR) or blood–brain barrier (BBB) leakage. Here, we assess the arguments for and against each of these mechanisms based on population, patient and experimental model studies, and further discuss other potential mechanisms. Specifically, building on two recent seminal studies that have uncovered an anatomical and functional relationship between oligodendrocyte progenitor cells and blood vessels, we elaborate on how small vessel changes might compromise myelin remodelling and cause WM degeneration. Finally, we propose new directions for future studies on this hot research topic.

Stimulation of adult hippocampal neurogenesis by physical exercise and enriched environment is disturbed in a CADASIL mouse model

In the course of CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy), a dysregulated adult hippocampal neurogenesis has been suggested as a potential mechanism for early cognitive decline. Previous work has shown that mice overexpressing wild type Notch3 and mice overexpressing Notch3 with a CADASIL mutation display impaired cell proliferation and survival of newly born hippocampal neurons prior to vascular abnormalities. Here, we aimed to elucidate how the long-term survival of these newly generated neurons is regulated by Notch3. Knowing that adult neurogenesis can be robustly stimulated by physical exercise and environmental enrichment, we also investigated the influence of such stimuli as potential therapeutic instruments for a dysregulated hippocampal neurogenesis in the CADASIL mouse model. Therefore, young-adult female mice were housed in standard (STD), environmentally enriched (ENR) or running wheel cages (RUN) for either 28 days or 6 months. Mice overexpressing mutated Notch3 and developing CADASIL (TgN3^R169C), and mice overexpressing wild type Notch3 (TgN3^WT) were used. We found that neurogenic stimulation by RUN and ENR is apparently impaired in both transgenic lines. The finding suggests that a disturbed neurogenic process due to Notch3-dependent micromilieu changes might be one vascular-independent mechanism contributing to cognitive decline observed in CADASIL.

Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL) as a model of small vessel disease: update on clinical, diagnostic, and management aspects

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common and best known monogenic small vessel disease. Here, we review the clinical, neuroimaging, neuropathological, genetic, and therapeutic aspects based on the most relevant articles published between 1994 and 2016 and on the personal experience of the authors, all directly involved in CADASIL research and care. We conclude with some suggestions that may help in the clinical practice and management of these patients.

CADASIL accelerated by acute hypotension: Arterial and venous contribution to leukoaraiosis

OBJECTIVE

To underline the importance of blood pressure regulation in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) and to describe changes that occur in the veins in this condition, specifically venous collagenosis associated with leukoaraiosis.

METHODS

Case report with neuroimaging and pathologic data.

RESULTS

A 61-year-old man with genetically confirmed CADASIL was initially lucid following a motor vehicle accident but subsequently became hypotensive (60/40 mm Hg) due to an open femur fracture and required intubation. Multiple new white matter infarcts appeared on brain imaging. A second hypotensive episode days later was associated with new coin-sized infarcts in the bilateral corona radiata and cerebellar peduncles, and resulted in quadriplegia. No embolic source was found on cardiac or vascular imaging. He died 5 weeks post trauma. Autopsy revealed extensive subcortical and periventricular leukoencephalopathy and multiple cavitations involving deep subcortical gray and white matter. Small arteries had thickened walls, disruption of the muscularis, and intimal periodic acid-Schiff (PAS)-positive material. Both larger periventricular and small caliber veins had thickened walls that were PAS-negative and trichrome-positive, consistent with venous collagenosis. There was no pathologic evidence of global hypoxia or diffuse axonal injury.

CONCLUSIONS

The findings suggest rapid acceleration of CADASIL pathology from acute hypotension in the setting of impaired vasoreactivity. In addition, collagenosis of veins in the affected white matter regions suggests that the veins may play an important, though largely overlooked, role in maintaining white matter integrity.

Other cerebrovascular occlusive disease

In this chapter we review the optimal imaging modalities for subacute and chronic stroke. We discuss the utility of computed tomography (CT) and multimodal CT imaging. Further, we analyze the importance of specific magnetic resonance imaging sequences, such as diffusion-weighted imaging for acute ischemic stroke, T2/fluid-attenuated inversion recovery for subacute and chronic stroke, and susceptibility imaging for detection of intracranial hemorrhages. Different ischemic stroke mechanisms are reviewed, and how these imaging modalities may aid in the determination of such. Further, we analyze how topographic patterns in ischemic stroke may provide important clues to the diagnosis, in addition to the temporal evolution of the stroke. Lastly, specific cerebrovascular occlusive diseases are reviewed, with emphasis on the optimal imaging modalities and their findings in each condition.

Mechanistic insights into a TIMP3-sensitive pathway constitutively engaged in the regulation of cerebral hemodynamics

Cerebral small vessel disease (SVD) is a leading cause of stroke and dementia. CADASIL, an inherited SVD, alters cerebral artery function, compromising blood flow to the working brain. TIMP3 (tissue inhibitor of metalloproteinase 3) accumulation in the vascular extracellular matrix in CADASIL is a key contributor to cerebrovascular dysfunction. However, the linkage between elevated TIMP3 and compromised cerebral blood flow (CBF) remains unknown. Here, we show that TIMP3 acts through inhibition of the metalloprotease ADAM17 and HB-EGF to regulate cerebral arterial tone and blood flow responses. In a clinically relevant CADASIL mouse model, we show that exogenous ADAM17 or HB-EGF restores cerebral arterial tone and blood flow responses, and identify upregulated voltage-dependent potassium channel (K_V) number in cerebral arterial myocytes as a heretofore-unrecognized downstream effector of TIMP3-induced deficits. These results support the concept that the balance of TIMP3 and ADAM17 activity modulates CBF through regulation of myocyte K_V channel number.

DOI:http://dx.doi.org/10.7554/eLife.17536.001

There are currently no effective treatments or cures for small blood vessel diseases of the brain, which lead to strokes and subsequent decreases in mental abilities. Normally, smooth muscle cells that surround the vessels relax or contract to regulate blood flow and ensure the right amount of oxygen and nutrients reaches the different regions of the brain. In a syndrome called CADASIL, which is the most common form of inherited small vessel disease, a genetic mutation causes the smooth muscle cells to weaken over time.

The accumulation of several proteins – including one called TIMP3 – around the smooth muscle cells plays a key role in the smooth muscle cell weakening seen in CADASIL. Capone et al. have now studied mice that display the symptoms of CADASIL to investigate how TIMP3 decreases blood flow through blood vessels in the brain. This revealed that TIMP3 inactivates another protein called ADAM17. The latter protein is normally responsible for starting a signaling pathway that helps smooth muscle cells to regulate blood flow according to the needs of the brain cells. Artificially adding more ADAM17 to the brains of the CADASIL mice reduced their symptoms of small vessel disease.

Using smooth muscle cells freshly isolated from the brains of CADASIL mice, Capone et al. also demonstrated that abnormal TIMP3-ADAM17 signaling increases the number of voltage-dependent potassium channels in the membrane of the muscle cells. Having too many of these channels impairs the flow of blood through vessels in the brain.

Further experiments are needed to investigate whether correcting TIMP3-ADAM17 signaling could prevent strokes in people with inherited CADASIL. It also remains to be seen whether similar signaling mechanisms are at play in other small vessel diseases.

DOI:http://dx.doi.org/10.7554/eLife.17536.002

Diffuse Brain Hypoperfusion in Advanced Leukoencephalopathy with Calcifications and Cysts

Leukoencephalopathy with calcifications and cysts (LCC) is an uncommon condition of unknown etiology occurring in children and adults. Pathological findings include obliterative hyalinosis of the small vessels, myelin loss, intense gliosis, Rosenthal fiber formation, microcalcifications, and hemosiderin deposits. Herein we report a 55-year-old man with LCC documented 10 years ago, in whom we examined brain perfusion by pseudocontinuous arterial spin labeling technique. We demonstrated diffused hypoperfusion of the affected white matter (WM) and of the subcortical gray matter (GM) and cortical GM in the patient in comparison to a group of healthy control subjects, using both qualitative evaluation and region of interest analysis. WM and subcortical GM hypoperfusion reflects the known distribution of LCC microangiopathy. We speculate that cortical hypoperfusion may be related to cerebral atrophy or may reflect deafferentation secondary to severe leukoencephalopathy, and may possibly contribute to severe motor and cognitive impairment. Further studies addressing cerebral blood flow in LCC are necessary.

Respiratory challenge MRI: Practical aspects

Respiratory challenge MRI is the modification of arterial oxygen (PaO₂) and/or carbon dioxide (PaCO₂) concentration to induce a change in cerebral function or metabolism which is then measured by MRI. Alterations in arterial gas concentrations can lead to profound changes in cerebral haemodynamics which can be studied using a variety of MRI sequences. Whilst such experiments may provide a wealth of information, conducting them can be complex and challenging. In this paper we review the rationale for respiratory challenge MRI including the effects of oxygen and carbon dioxide on the cerebral circulation. We also discuss the planning, equipment, monitoring and techniques that have been used to undertake these experiments. We finally propose some recommendations in this evolving area for conducting these experiments to enhance data quality and comparison between techniques.

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Oxygen and carbon dioxide affect cerebral blood flow and metabolism.

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This can be imaged with various MRI sequences.

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The practicalities of these techniques are reviewed.

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Examples of how this has been used to understand disease mechanisms.

Consensus statement for diagnosis of subcortical small vessel disease

Vascular cognitive impairment (VCI) is the diagnostic term used to describe a heterogeneous group of sporadic and hereditary diseases of the large and small blood vessels. Subcortical small vessel disease (SVD) leads to lacunar infarcts and progressive damage to the white matter. Patients with progressive damage to the white matter, referred to as Binswanger's disease (BD), constitute a spectrum from pure vascular disease to a mixture with neurodegenerative changes. Binswanger's disease patients are a relatively homogeneous subgroup with hypoxic hypoperfusion, lacunar infarcts, and inflammation that act synergistically to disrupt the blood-brain barrier (BBB) and break down myelin. Identification of this subgroup can be facilitated by multimodal disease markers obtained from clinical, cerebrospinal fluid, neuropsychological, and imaging studies. This consensus statement identifies a potential set of biomarkers based on underlying pathologic changes that could facilitate diagnosis and aid patient selection for future collaborative treatment trials.

Superficial temporal artery-to-middle cerebral artery bypass surgery for middle cerebral artery stenosis in a patient with cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy

Cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy is a rare hereditary small vessel disease. Ischemic events are the main clinical manifestation of this condition. Here, we present a case in which superficial temporal artery-to-middle cerebral artery anastomosis was performed in a patient with cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy who developed cerebral infarctions caused by severe middle cerebral artery stenosis. Cerebral blood flow and cerebrovascular reactivity were effectively improved using double anastomoses. To our knowledge, surgical revascularization for patients with this condition has not yet been described in the literature. Superficial temporal artery-to-middle cerebral artery anastomosis is effective for patients with cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy who show marked regional cerebral hypoperfusion.

Development of Point of Care Testing Device for Neurovascular Coupling From Simultaneous Recording of EEG and NIRS During Anodal Transcranial Direct Current Stimulation

This paper presents a point of care testing device for neurovascular coupling (NVC) from simultaneous recording of electroencephalogram (EEG) and near infrared spectroscopy (NIRS) during anodal transcranial direct current stimulation (tDCS). Here, anodal tDCS modulated cortical neural activity leading to hemodynamic response can be used to identify the impaired cerebral microvessels functionality. The impairments in the cerebral microvessels functionality may lead to impairments in the cerebrovascular reactivity (CVR), where severely reduced CVR predicts the chances of transient ischemic attack and ipsilateral stroke. The neural and hemodynamic responses to anodal tDCS were studied through joint imaging with EEG and NIRS, where NIRS provided optical measurement of changes in tissue oxy-([Formula: see text] and deoxy-([Formula: see text]) hemoglobin concentration and EEG captured alterations in the underlying neuronal current generators. Then, a cross-correlation method for the assessment of NVC underlying the site of anodal tDCS is presented. The feasibility studies on healthy subjects and stroke survivors showed detectable changes in the EEG and the NIRS responses to a 0.526 A/[Formula: see text] of anodal tDCS. The NIRS system was bench tested on 15 healthy subjects that showed a statistically significant (p < 0.01) difference in the signal-to-noise ratio (SNR) between the ON- and OFF-states of anodal tDCS where the mean SNR of the NIRS device was found to be 42.33 ± 1.33 dB in the ON-state and 40.67 ± 1.23 dB in the OFF-state. Moreover, the clinical study conducted on 14 stroke survivors revealed that the lesioned hemisphere with impaired circulation showed significantly (p < 0.01) less change in [Formula: see text] than the nonlesioned side in response to anodal tDCS. The EEG study on healthy subjects showed a statistically significant (p < 0.05) decrease around individual alpha frequency in the alpha band (8-13 Hz) following anodal tDCS. Moreover, the joint EEG-NIRS imaging on 4 stroke survivors showed an immediate increase in the theta band (4-8 Hz) EEG activity after the start of anodal tDCS at the nonlesioned hemisphere. Furthermore, cross-correlation function revealed a significant (95% confidence interval) negative cross correlation only at the nonlesioned hemisphere during anodal tDCS, where the log-transformed mean-power of EEG within 0.5-11.25 Hz lagged [Formula: see text] response in one of the stroke survivors with white matter lesions. Therefore, it was concluded that the anodal tDCS can perturb the local neural and the vascular activity (via NVC) which can be used for assessing regional NVC functionality where confirmatory clinical studies are required.

Mouse model of CADASIL reveals novel insights into Notch3 function in adult hippocampal neurogenesis

Could impaired adult hippocampal neurogenesis be a relevant mechanism underlying CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy)? Memory symptoms in CADASIL, the most common hereditary form of vascular dementia, are usually thought to be primarily due to vascular degeneration and white matter lacunes. Since adult hippocampal neurogenesis, a process essential for the integration of new spatial memory occurs in a highly vascularized niche, we considered dysregulation of adult neurogenesis as a potential mechanism for the manifestation of dementia in CADASIL. Analysis in aged mice overexpressing Notch3 with a CADASIL mutation, revealed vascular deficits in arteries of the hippocampal fissure but not in the niche of the dentate gyrus. At 12 months of age, cell proliferation and survival of newborn neurons were reduced not only in CADASIL mice but also in transgenic controls overexpressing wild type Notch3. At 6 months, hippocampal neurogenesis was altered in CADASIL mice independent of overt vascular abnormalities in the fissure. Further, we identified Notch3 expression in hippocampal precursor cells and maturing neurons in vivo as well as in cultured hippocampal precursor cells. Overexpression and knockdown experiments showed that Notch3 signaling negatively regulated precursor cell proliferation. Notch3 overexpression also led to deficits in KCl-induced precursor cell activation. This suggests a cell-autonomous effect of Notch3 signaling in the regulation of precursor proliferation and activation and a loss-of-function effect in CADASIL. Consequently, besides vascular damage, aberrant precursor cell proliferation and differentiation due to Notch3 dysfunction might be an additional independent mechanism for the development of hippocampal dysfunction in CADASIL.

Genetics of ischaemic stroke in young adults

Background

Stroke may be a clinical expression of several inherited disorders in humans. Recognition of the underlined genetic disorders causing stroke is important for a correct diagnosis, for genetic counselling and, even if rarely, for a correct therapeutic management. Moreover, the genetics of complex diseases such the stroke, in which multiple genes interact with environmental risk factors to increase risk, has been revolutionized by the Genome-Wide Association Study (GWAS) approach.

Scope of review

Here we review the single-gene causes of ischemic stroke, bringing the reader from the candidate gene method toward the exciting new horizons of genetic technology.

Major conclusions

The aetiological diagnosis of ischemic stroke in young adults is more complex than in the elderly. The identification of a genetic cause is important to provide appropriate counseling and to start a correct therapy, when available. The advent of GWAS technology, such as for other complex pathological conditions, has contributed enormously to the understanding of many of these genetic bases. For success large, well phenotyped case cohorts are required, and international collaborations are essential.

General significance

This review focuses on the main causes of genetically-based ischemic stroke in young adults, often classified as indeterminate, investigating also the recent findings of the GWAS, in order to improve diagnostic and therapeutic management.

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The aetiological diagnosis of stroke in young adults needs a different and more complex diagnostic work up than in older adults.

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Stroke may be a clinical expression of several inherited disorders in humans.

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The most common genetic causes of stroke are CADASIL, Fabry and mitochondrial diseases.

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Recognition of the underlined genetic disorders causing stroke is important for the correct management of the patient.

Effects of sapropterin on endothelium-dependent vasodilation in patients with CADASIL: a randomized controlled trial

BACKGROUND AND PURPOSE

Cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a rare autosomal dominant disorder caused by NOTCH3 mutations, is characterized by vascular smooth muscle and endothelial cells abnormalities, altered vasoreactivity, and recurrent lacunar infarcts. Vasomotor function may represent a key factor for disease progression. Tetrahydrobiopterin, essential cofactor for nitric oxide synthesis in endothelial cells, ameliorates endothelial function. We assessed whether supplementation with sapropterin, a synthetic tetrahydrobiopterin analog, improves endothelium-dependent vasodilation in CADASIL patients.

METHODS

In a 24-month, multicenter randomized, double-blind, placebo-controlled trial, CADASIL patients aged 30 to 65 years were randomly assigned to receive placebo or sapropterin 200 to 400 mg BID. The primary end point was change in the reactive hyperemia index by peripheral arterial tonometry at 24 months. We also assessed the safety and tolerability of sapropterin. Analysis was done by intention-to-treat.

RESULTS

The intention-to-treat population included 61 patients. We found no significant difference between sapropterin (n=32) and placebo (n=29) in the primary end point (mean difference in reactive hyperemia index by peripheral arterial tonometry changes 0.19 [95% confidence interval, -0.18, 0.56]). Reactive hyperemia index by peripheral arterial tonometry increased after 24 months in 37% of patients on sapropterin and in 28% on placebo; however, after adjustment for age, sex, and clinical characteristics, improvement was not associated with treatment arm. The proportion of patients with adverse events was similar on sapropterin and on placebo (50% versus 48.3%); serious adverse events occurred in 6.3% versus 13.8%, respectively.

CONCLUSIONS

Sapropterin was safe and well-tolerated at the average dose of 5 mg/kg/day, but did not affect endothelium-dependent vasodilation in CADASIL patients.

CLINICAL TRIAL REGISTRATION URL

https://www.clinicaltrialsregister.eu. Unique identifier: 2007-004370-55.

CADASIL and CARASIL

CADASIL and CARASIL are hereditary small vessel diseases leading to vascular dementia. CADASIL commonly begins with migraine followed by minor strokes in mid-adulthood. Dominantly inherited CADASIL is caused by mutations (n > 230) in NOTCH3 gene, which encodes Notch3 receptor expressed in vascular smooth muscle cells (VSMC). Notch3 extracellular domain (N3ECD) accumulates in arterial walls followed by VSMC degeneration and subsequent fibrosis and stenosis of arterioles, predominantly in cerebral white matter, where characteristic ischemic MRI changes and lacunar infarcts emerge. The likely pathogenesis of CADASIL is toxic gain of function related to mutation-induced unpaired cysteine in N3ECD. Definite diagnosis is made by molecular genetics but is also possible by electron microscopic demonstration of pathognomonic granular osmiophilic material at VSMCs or by positive immunohistochemistry for N3ECD in dermal arteries. In rare, recessively inherited CARASIL the clinical picture and white matter changes are similar as in CADASIL, but cognitive decline begins earlier. In addition, gait disturbance, low back pain and alopecia are characteristic features. CARASIL is caused by mutations (presently n = 10) in high-temperature requirement. A serine peptidase 1 (HTRA1) gene, which result in reduced function of HTRA1 as repressor of transforming growth factor-β (TGF β) -signaling. Cerebral arteries show loss of VSMCs and marked hyalinosis, but not stenosis.

Novel pathological features and potential therapeutic approaches for CADASIL: insights obtained from a mouse model of CADASIL

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common condition of hereditary stroke and vascular dementia. CADASIL is caused by Notch3 mutation, leading to progressive degeneration of vascular smooth muscle cells (vSMCs) of the small arteries in the brain. However, the pathogenesis of CADASIL remains largely unknown, and treatment that can stop or delay the progression of CADASIL is not yet available. Using both wild type mice and transgenic mice carrying the human mutant Notch3 gene (CADASIL mice), we have recently characterized the pathological features of CADASIL and determined the therapeutic efficacy of two hematopoietic growth factors, stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF) in CADASIL. Our findings have revealed novel pathological changes in the endothelium of cerebral capillaries and in the neural stem cells (NSCs). We have also observed the impairment of cognitive function in CADASIL mice. Moreover, SCF+G-CSF treatment improves cognitive function, inhibits Notch3 mutation-induced vSMC degeneration, cerebral blood bed reduction, cerebral capillary damage, and NSC loss, and increases neurogenesis and angiogenesis. Here we compile an overview of our recently published studies, which provide new insights into understanding the pathogenesis of CADASIL and developing therapeutic strategies for this devastating neurological disease.