Neuronal densities and vascular pathology in the hippocampal formation in CADASIL

Analysis of the pathogenicity and pathological characteristics of NOTCH3 gene-sparing cysteine mutations in vitro and in vivo models

Background

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is one of the most common inherited cerebral small vessel diseases caused by the NOTCH3 gene mutation. This mutation leads to the accumulation of NOTCH3 extracellular domain protein (NOTCH3ECD) into the cerebral arterioles, causing recurrent stroke, white matter lesions, and cognitive impairment. With the development of gene sequencing technology, cysteine-sparing mutations can also cause CADASIL disease, however, the pathogenicity and pathogenic mechanisms of cysteine-sparing mutations remain controversial.

Objective

To analyze the pathogenicity and pathological features of cysteine-sparing mutations in both in vitro and in vivo mouse models.

Methods

A cysteine-sparing mutant of NOTCH3ECD R75Q was constructed by lentiviral transfection in vitro, and the NOTCH3 R75Q knock-in mouse model was constructed by CRISPR/Cas-mediated genome engineering in vivo. A cycloheximide pulse-chase experiment was used to analyze the degradation of NOTCH3 extracellular domain proteins, and the deposition characteristics of NOTCH3ECD were quantitatively analyzed by immunohistochemical staining. The characteristics of the smooth muscle cells and granular osmiophilic materials were observed using electron microscopy.

Results

We elucidated that the NOTCH3 R75Q mutation is pathogenic. NOTCH3ECD R75Q was found to be resistant to protein degradation and more likely to cause abnormal aggregation of NOTCH3ECD, resulting in reduced cell activity in vitro. The NOTCH3 R75Q mouse model showed pathological characteristics of CADASIL, with age-dependent NOTCH3ECD, granular osmiophilic material, and degenerated smooth muscle cells detected in the brain.

Conclusion

To our knowledge, this is the first study to analyze the pathogenicity of NOTCH3 R75Q cysteine-sparing mutations in both in vitro and in vivo models. We demonstrate that NOTCH3ECD induced by NOTCH3 R75Q mutation has toxic effects on cells and reveal the deposition characteristics of NOTCH3ECD in the brain. This provides a feasible model and lays the foundation for further studies on the pathogenesis and therapeutic strategies of NOTCH3 cysteine-sparing mutations.

Selective vulnerability of hippocampal sub-regions in patients with subcortical vascular mild cognitive impairment

Early diagnosis of subcortical vascular mild cognitive impairment (svMCI) is clinically essential because it is the most reversible subtype of all cognitive impairments. Since structural alterations of hippocampal sub-regions have been well studied in neurodegenerative diseases with pathophysiological cognitive impairments, we were eager to determine whether there is a selective vulnerability of hippocampal sub-fields in patients with svMCI. Our study included 34 svMCI patients and 34 normal controls (NCs), with analysis of T1 images and Montreal Cognitive Assessment (MoCA) scores. Gray matter volume (GMV) of hippocampal sub-regions was quantified and compared between the groups, adjusting for age, sex, and education. Additionally, we explored correlations between altered GMV in hippocampal sub-fields and MoCA scores in svMCI patients. Patients with svMCI exhibited selectively reduced GMV in several left hippocampal sub-regions, such as the hippocampal tail, hippocampal fissure, CA1 head, ML-HP head, CA4 head, and CA3 head, as well as decreased GMV in the right hippocampal tail. Specifically, GMV in the left CA3 head was inversely correlated with MoCA scores in svMCI patients. Our findings indicate that the atrophy pattern of patients with svMCI was predominantly located in the left hippocampal sub-regions. The left CA3 might be a crucial area underlying the distinct pathophysiological mechanisms of cognitive impairments with subcortical vascular origins.

Neuropathology of microbleeds in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL)

Cerebral microbleeds (CMBs) detected on magnetic resonance imaging are common in patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). The neuropathologic correlates of CMBs are unclear. In this study, we characterized findings relevant to CMBs in autopsy brain tissue of 8 patients with genetically confirmed CADASIL and 10 controls within the age range of the CADASIL patients by assessing the distribution and extent of hemosiderin/iron deposits including perivascular hemosiderin leakage (PVH), capillary hemosiderin deposits, and parenchymal iron deposits (PID) in the frontal cortex and white matter, basal ganglia and cerebellum. We also characterized infarcts, vessel wall thickening, and severity of vascular smooth muscle cell degeneration. CADASIL subjects had a significant increase in hemosiderin/iron deposits compared with controls. This increase was principally seen with PID. Hemosiderin/iron deposits were seen in the majority of CADASIL subjects in all brain areas. PVH was most pronounced in the frontal white matter and basal ganglia around small to medium sized arterioles, with no predilection for the vicinity of vessels with severe vascular changes or infarcts. CADASIL subjects have increased brain hemosiderin/iron deposits but these do not occur in a periarteriolar distribution. Pathogenesis of these lesions remains uncertain.

Evidence of beta amyloid independent small vessel disease in familial Alzheimer's disease

We studied small vessel disease (SVD) pathology in Familial Alzheimer's disease (FAD) subjects carrying the presenilin 1 (PSEN1) p.Glu280Ala mutation in comparison to those with sporadic Alzheimer's disease (SAD) as a positive control for Alzheimer's pathology and Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL) bearing different NOTCH3 mutations, as positive controls for SVD pathology. Upon magnetic resonance imaging (MRI) in life, some FAD showed mild white matter hyperintensities and no further radiologic evidence of SVD. In post-mortem studies, total SVD pathology in cortical areas and basal ganglia was similar in PSEN1 FAD and CADASIL subjects, except for the feature of arteriosclerosis which was higher in CADASIL subjects than in PSEN1 FAD subjects. Further only a few SAD subjects showed a similar degree of SVD pathology as observed in CADASIL. Furthermore, we found significantly enlarged perivascular spaces in vessels devoid of cerebral amyloid angiopathy in FAD compared with SAD and CADASIL subjects. As expected, there was greater fibrinogen-positive perivascular reactivity in CADASIL but similar reactivity in PSEN1 FAD and SAD groups. Fibrinogen immunoreactivity correlated with onset age in the PSEN1 FAD cases, suggesting increased vascular permeability may contribute to cognitive decline. Additionally, we found reduced perivascular expression of PDGFRβ AQP4 in microvessels with enlarged PVS in PSEN1 FAD cases. We demonstrate that there is Aβ-independent SVD pathology in PSEN1 FAD, that was marginally lower than that in CADASIL subjects although not evident by MRI. These observations suggest presence of covert SVD even in PSEN1, contributing to disease progression. As is the case in SAD, these consequences may be preventable by early recognition and actively controlling vascular disease risk, even in familial forms of dementia.

Ionizing radiation, cerebrovascular disease, and consequent dementia: A review and proposed framework relevant to space radiation exposure

Space exploration requires the characterization and management or mitigation of a variety of human health risks. Exposure to space radiation is one of the main health concerns because it has the potential to increase the risk of cancer, cardiovascular disease, and both acute and late neurodegeneration. Space radiation-induced decrements to the vascular system may impact the risk for cerebrovascular disease and consequent dementia. These risks may be independent or synergistic with direct damage to central nervous system tissues. The purpose of this work is to review epidemiological and experimental data regarding the impact of low-to-moderate dose ionizing radiation on the central nervous system and the cerebrovascular system. A proposed framework outlines how space radiation-induced effects on the vasculature may increase risk for both cerebrovascular dysfunction and neural and cognitive adverse outcomes. The results of this work suggest that there are multiple processes by which ionizing radiation exposure may impact cerebrovascular function including increases in oxidative stress, neuroinflammation, endothelial cell dysfunction, arterial stiffening, atherosclerosis, and cerebral amyloid angiopathy. Cerebrovascular adverse outcomes may also promote neural and cognitive adverse outcomes. However, there are many gaps in both the human and preclinical evidence base regarding the long-term impact of ionizing radiation exposure on brain health due to heterogeneity in both exposures and outcomes. The unique composition of the space radiation environment makes the translation of the evidence base from terrestrial exposures to space exposures difficult. Additional investigation and understanding of the impact of low-to-moderate doses of ionizing radiation including high (H) atomic number (Z) and energy (E) (HZE) ions on the cerebrovascular system is needed. Furthermore, investigation of how decrements in vascular systems may contribute to development of neurodegenerative diseases in independent or synergistic pathways is important for protecting the long-term health of astronauts.

Comparison of clinical and neuroimaging features between NOTCH3 mutations and nongenetic spontaneous intracerebral haemorrhage

BACKGROUND

The NOTCH3 mutation is a common cause of hereditary cerebral small vessel disease (CSVD) and may be a cause of spontaneous intracerebral haemorrhage (ICH). We aimed to investigate the clinical/imaging features for identifying the NOTCH3 mutations related ICH.

METHODS

The study was based on a cohort of 749 CSVD patients in Taiwan who received next-generation sequencing of CSVD genes including NOTCH3. Patients with history of ICH (n=206) were included for analysis. The CSVD neuroimaging markers were compared between the patients with NOTCH3 and without known genetic mutations.

RESULTS

After excluding the patients with other causes of ICH (structural lesions, systemic/medication-related, or amyloid angiopathy) and those without neuroimaging, 45 NOTCH3 mutation patients and 109 nongenetic ICH patients were included. The NOTCH3 mutation patients were more likely to have thalamic haemorrhage, a family history of stroke, and more severe CSVD neuroimaging markers. A five-point NOTCH3-ICH score was constructed and consisted of: history of stroke in siblings, thalamic haemorrhage, any deep nuclei lacunae, any hippocampal cerebral microbleed (CMB), and a thalamic CMB >5 (one point for each). A score ≥2 had a sensitivity of 88.9% and a specificity of 64.2% in identifying the NOTCH3 mutation. The NOTCH3 mutation patients had a higher risk of recurrent stroke (9.1 vs. 4.5 per 100 person-years; log-rank p = 0.03) during follow-up.

CONCLUSION

The patients with NOTCH3 mutation-related ICH had a higher burden of CMB in the hippocampus/thalamus and a higher recurrent stroke risk. The NOTCH3-ICH score may assist identifying genetic causes of ICH.

Relationships Between Memory Impairments and Hippocampal Structure in Patients With Subcortical Ischemic Vascular Disease

Background and Purpose

Patients with subcortical ischemic vascular disease (SIVD) suffer from memory disorders that are thought to be associated with the hippocampus. We aimed to explore changes in hippocampal subfields and the relationship between different hippocampal subfield volumes and different types of memory dysfunction in SIVD patients.

Methods

A total of 77 SIVD patients with cognitive impairment (SIVD-CI, n = 39) or normal cognition (HC-SIVD, n = 38) and 41 matched healthy controls (HCs) were included in this study. Memory function was measured in all subjects, and structural magnetic resonance imaging (MRI) was performed. Then, the hippocampus was segmented and measured by FreeSurfer 6.0 software. One-way ANOVA was used to compare the volume of hippocampal subfields among the three groups while controlling for age, sex, education and intracranial volume (ICV). Then, post hoc tests were used to evaluate differences between each pair of groups. Finally, correlations between significantly different hippocampal subfield volumes and memory scores were tested in SIVD patients.

Results

Almost all hippocampal subfields were significantly different among the three groups except for the bilateral hippocampal fissure (p = 0.366, p = 0.086, respectively.) and left parasubiculum (p = 0.166). Furthermore, the SIVD-CI patients showed smaller volumes in the right subiculum (p < 0.001), CA1 (p = 0.002), presubiculum (p = 0.002) and molecular layer of the hippocampus (p = 0.017) than the HC-SIVD patients. In addition, right subiculum volumes were positively related to Rey’s Auditory Verbal Learning Test (RAVLT) word recognition (r = 0.230, p = 0.050), reverse digit span test (R-DST) (r = 0.326, p = 0.005) and Rey–Osterrieth Complex Figure Test (ROCF) immediate recall (r = 0.247, p = 0.035) scores, right CA1 volumes were positively correlated with RAVLT word recognition (r = 0.261, p = 0.026), and right presubiculum volumes showed positive relationships with R-DST (r = 0.254, p = 0.030) and ROCF immediate recall (r = 0.242, p = 0.039) scores.

Conclusion

SIVD might lead to general reductions in volume in multiple hippocampal subfields. However, SIVD-CI patients showed atrophy in specific subfields, which might be associated with memory deficits.