Clusterin/Apolipoprotein J immunoreactivity is associated with white matter damage in cerebral small vessel diseases.

AIM: Brain clusterin is known to be associated with the amyloid-ß deposits in Alzheimer's disease (AD). We assessed the distribution of clusterin immunoreactivity in cerebrovascular disorders, particularly focusing on white matter changes in small vessel diseases. METHODS: Post-mortem brain tissues from the frontal or temporal lobes of a total of 70 subjects with various disorders including cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), cerebral amyloid angiopathy (CAA) and AD were examined using immunohistochemistry and immunofluorescence. We further used immunogold electron microscopy to study clusterin immunoreactivity in extracellular deposits in CADASIL. RESULTS: Immunostaining with clusterin antibodies revealed strong localization in arterioles and capillaries, besides cortical neurones. We found that clusterin immunostaining was significantly increased in the frontal white matter of CADASIL and pontine autosomal dominant microangiopathy and leukoencephalopathy subjects. In addition, clusterin immunostaining correlated with white matter pathology severity scores. Immunostaining in axons ranged from fine punctate deposits in single axons to larger confluent areas with numerous swollen axon bulbs, similar to that observed with known axon damage markers such as non-phosphorylated neurofilament H and the amyloid precursor protein. Immunofluorescence and immunogold electron microscopy experiments showed that whereas clusterin immunoreactivity was closely associated with vascular amyloid-ß in CAA, it was lacking within the granular osmiophilic material immunolabelled by NOTCH3 extracelluar domain aggregates found in CADASIL. CONCLUSIONS: Our results suggest a wider role for clusterin associated with white matter damage in addition to its ability to chaperone proteins for clearance via the perivascular drainage pathways in several disease states.

Pyramidal neurons of the prefrontal cortex in post-stroke, vascular and other ageing-related dementias.

Dementia associated with cerebrovascular disease is common. It has been reported that ∼30% of elderly patients who survive stroke develop delayed dementia (post-stroke dementia), with most cases being diagnosed as vascular dementia. The pathological substrates associated with post-stroke or vascular dementia are poorly understood, particularly those associated with executive dysfunction. Three separate yet interconnecting circuits control executive function within the frontal lobe involving the dorsolateral prefrontal cortex, anterior cingulate cortex and the orbitofrontal cortex. We used stereological methods, along with immunohistological and related cell morphometric analysis, to examine densities and volumes of pyramidal neurons of the dorsolateral prefrontal cortex, anterior cingulate cortex and orbitofrontal cortex in the frontal lobe from a total of 90 elderly subjects (age range 71-98 years). Post-mortem brain tissues from post-stroke dementia and post-stroke patients with no dementia were derived from our prospective Cognitive Function After Stroke study. We also examined, in parallel, samples from ageing controls and similar age subjects pathologically diagnosed with Alzheimer's disease, mixed Alzheimer's disease and vascular dementia, and vascular dementia. We found pyramidal cell volumes in layers III and V in the dorsolateral prefrontal cortex of post-stroke and vascular dementia and, of mixed and Alzheimer's disease subjects to be reduced by 30-40% compared to post-stroke patients with no dementia and controls. There were no significant changes in neuronal volumes in either the anterior cingulate or orbitofrontal cortices. Remarkably, pyramidal neurons within the orbitofrontal cortex were also found to be smaller in size when compared to those in the other two neocortical regions. To relate the cell changes to cognitive function, we noted significant correlations between neuronal volumes and total CAMCOG, orientation and memory scores and clinical dementia ratings. Total estimated neuronal densities were not significantly changed between patients with post-stroke dementia and post-stroke patients with no dementia groups or ageing controls in any of the three frontal regions. In further morphometric analysis of the dorsolateral prefrontal cortex, we showed that neither diffuse cerebral atrophy nor neocortical thickness explained the selective neuronal volume effects. We also noted that neurofilament protein SMI31 immunoreactivity was increased in post-stroke and vascular dementia compared with post-stroke patients with no dementia and correlated with decreased neuronal volumes in subjects with post-stroke dementia and vascular dementia. Our findings suggest selective regional pyramidal cell atrophy in the dorsolateral prefrontal cortex-rather than neuronal density changes per se-are associated with dementia and executive dysfunction in post-stroke dementia and vascular dementia. The changes in dorsolateral prefrontal cortex pyramidal cells were not associated with neurofibrillary pathology suggesting there is a vascular basis for the observed highly selective neuronal atrophy.

Quantitative vascular pathology and phenotyping familial and sporadic cerebral small vessel diseases.

We quantified vascular changes in the frontal lobe and basal ganglia of four inherited small vessel diseases (SVDs) including cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), pontine autosomal dominant microangiopathy and leukoencephalopathy (PADMAL), hereditary multi-infarct dementia of Swedish type (Swedish hMID), and hereditary endotheliopathy with retinopathy, nephropathy, and stroke (HERNS). Vascular pathology was most severe in CADASIL, and varied with marginally greater severity in the basal ganglia compared to the frontal lobe. The overall sclerotic index values in frontal lobe were in the order CADASIL ≥ HERNS > PADMAL > Swedish hMID > sporadic SVD, and in basal ganglia CADASIL > HERNS > Swedish hMID > PADMAL> sporadic SVD. The subcortical white matter was almost always more affected than any gray matter. We observed glucose transporter-1 (GLUT-1) protein immunoreactivities were most affected in the white matter indicating capillary degeneration whereas collagen IV (COL4) immunostaining was increased in PADMAL cases in all regions and tissue types. Overall, GLUT-1 : COL4 ratios were higher in the basal ganglia indicating modifications in capillary density compared to the frontal lobe. Our study shows that the extent of microvascular degeneration varies in these genetic disorders exhibiting common end-stage pathologies but is the most aggressive in CADASIL.

Quantification of myelin loss in frontal lobe white matter in vascular dementia, Alzheimer's disease, and dementia with Lewy bodies.

The aim of this study was to characterize myelin loss as one of the features of white matter abnormalities across three common dementing disorders. We evaluated post-mortem brain tissue from frontal and temporal lobes from 20 vascular dementia (VaD), 19 Alzheimer's disease (AD) and 31 dementia with Lewy bodies (DLB) cases and 12 comparable age controls. Images of sections stained with conventional luxol fast blue were analysed to estimate myelin attenuation by optical density. Serial adjacent sections were then immunostained for degraded myelin basic protein (dMBP) and the mean percentage area containing dMBP (%dMBP) was determined as an indicator of myelin degeneration. We further assessed the relationship between dMBP and glutathione S-transferase (a marker of mature oligodendrocytes) immunoreactivities. Pathological diagnosis significantly affected the frontal but not temporal lobe myelin attenuation: myelin density was most reduced in VaD compared to AD and DLB, which still significantly exhibited lower myelin density compared to ageing controls. Consistent with this, the degree of myelin loss was correlated with greater %dMBP, with the highest %dMBP in VaD compared to the other groups. The %dMBP was inversely correlated with the mean size of oligodendrocytes in VaD, whereas it was positively correlated with their density in AD. A two-tier regression model analysis confirmed that the type of disorder (VaD or AD) determines the relationship between %dMBP and the size or density of oligodendrocytes across the cases. Our findings, attested by the use of three markers, suggest that myelin loss may evolve in parallel with shrunken oligodendrocytes in VaD but their increased density in AD, highlighting partially different mechanisms are associated with myelin degeneration, which could originate from hypoxic-ischaemic damage to oligodendrocytes in VaD whereas secondary to axonal degeneration in AD.

Neuropathological correlates of temporal pole white matter hyperintensities in CADASIL.

BACKGROUND AND PURPOSE: White matter (WM) hyperintensities on MRI or leukoaraiosis is characteristic of stroke syndromes. Increased MRI signals in the anterior temporal pole are suggested to be diagnostic for cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), with 90% sensitivity and 100% specificity. The structural correlates of these specific WM hyperintensities seen on T2-weighted and FLAIR sequences in the temporal pole of CADASIL are unclear. We assessed pathological changes in postmortem tissue from the temporal pole to reveal the cause of CADASIL-specific WM hyperintensities. METHODS: A combination of tinctorial and immunostaining approaches and in vitro imaging methods were used to quantify the extent of perivascular space (PVS), arteriosclerosis determined as the sclerotic index, WM myelination as the myelin index, and damage within the WM as accumulated degraded myelin basic protein in samples of the anterior temporal pole from 9 CADASIL and 8 sporadic subcortical ischemic vascular dementia cases, and 5 similarly aged (young) and 5 older controls. Luxol fast blue-stained serial sections from a CADASIL case were also used to reconstruct the temporal pole, which was then compared to the MR images. RESULTS: Luxol fast blue sections used to reconstruct the temporal pole revealed an abundance of enlarged PVS in the WM that topographically appeared as indistinct opaque regions. The mean and total areas of the PVS per WM area (%PVS) were significantly greater in CADASIL compared to the controls. The myelin index was severely reduced in CADASIL in relation to the subcortical ischemic vascular dementia and control sample that was consistent with increased immunoreactivity of degraded myelin basic protein, indicating myelin degeneration. Cerebral microvessels associated with the PVS exhibited a 4.5-fold greater number of basophilic (hyalinized) vessels and a 57% increase in the sclerotic index values in CADASIL subjects compared to young controls. A significant correlation between the quantity of hyalinized vessels and sclerotic index values was also apparent (P<0.05). CONCLUSIONS: Our findings suggest that MRI hyperintensities in the temporal pole of CADASIL patients are explained by enlarged PVS and degeneration of myelin accompanied by lack of drainage of the interstitial fluid rather than lacunar infarcts. Consistent with the lack of MR hypersignals in the temporal pole of older subcortical ischemic vascular dementia subjects, our observations imply greater progression of pathological changes in CADASIL patients.

Differential deposition of amyloid beta peptides in cerebral amyloid angiopathy associated with Alzheimer's disease and vascular dementia.

Cerebral amyloid angiopathy (CAA) caused by deposition of amyloid beta (Abeta) peptides in the cerebrovasculature, involves degeneration of normal vascular components and increases the risk of infarction and cerebral hemorrhage. Accumulating evidence suggests that sporadic CAA is also a significant contributor to cognitive decline and dementia in the elderly. However, the mechanisms by which CAA arises are poorly understood. While neuronal sources of Abeta peptides are sufficient to cause CAA in transgenic mice overexpressing the amyloid precursor protein, there is reason to believe that in aging man, vascular disease modulates the disease process. To better understand CAA mechanisms in dementia, we assessed the frontal cortex of 62 consecutive cases of Alzheimer's disease (AD), vascular dementia (VaD), and mixed dementia (MD) using immunohistochemistry with antibodies to Abeta, smooth muscle actin and the carboxyl-terminal peptides to detect Abeta(40) and Abeta(42). While vascular Abeta deposition was invariably associated with smooth muscle degeneration as indicated by absence of smooth muscle cell actin reactivity, VaD/MD cases exhibited markedly more vascular Abeta(42) deposits and smooth muscle actin loss compared to AD cases with similar degrees of CAA and Abeta(40) deposition. This suggests that distinct mechanisms are responsible for the differential deposition of Abeta in CAA associated with AD and that associated with ischemic/cerebrovascular disease. It is plausible that experimental studies on the effects of cerebrovascular disease on Abeta production and elimination will yield important clues on the pathogenesis of CAA.