Microvascular degeneration in hereditary cystatin C amyloid angiopathy of the brain

The Amyloid-Tau-Neuroinflammation Axis in the Context of Cerebral Amyloid Angiopathy

Cerebral amyloid angiopathy (CAA) is typified by the cerebrovascular deposition of amyloid. Currently, there is no clear understanding of the mechanisms underlying the contribution of CAA to neurodegeneration. Despite the fact that CAA is highly associated with the accumulation of Aβ, other types of amyloids have been shown to associate with the vasculature. Interestingly, in many cases, vascular amyloidosis has been associated with an active immune response and perivascular deposition of hyperphosphorylated tau. Despite the fact that in Alzheimer’s disease (AD) a major focus of research has been the understanding of the connection between parenchymal amyloid plaques, tau aggregates in the form of neurofibrillary tangles (NFTs), and immune activation, the contribution of tau and neuroinflammation to neurodegeneration associated with CAA remains understudied. In this review, we discussed the existing evidence regarding the amyloid diversity in CAA and its relation to tau pathology and immune response, as well as the possible contribution of molecular and cellular mechanisms, previously associated with parenchymal amyloid in AD and AD-related dementias, to the pathogenesis of CAA. The detailed understanding of the “amyloid-tau-neuroinflammation” axis in the context of CAA could open the opportunity to develop therapeutic interventions for dementias associated with CAA that are currently being proposed for AD and AD-related dementias.

Preparation and Culturing of Human Primary Vascular Cells

Cerebral amyloid angiopathy (CAA) results from amyloid accumulation within arteries of the cerebral cortex and leptomeninges. This condition is age-related, especially prevalent in Alzheimer's disease (AD), and the main feature of certain hereditary disorders (i.e., HCHWA-I). The vascular smooth muscle cells (VSMCs) appear to play a vital role in the development of CAA, which makes them well suited as an experimental model to study the disease and screen for possible remedies. We describe two different methods for isolating and culturing human VSMCs: First, using the human umbilical cord as an easy source of robust cells, and secondly, using brain tissue that provides the proper cerebral VSMCs, but is more problematic to work with. The umbilical cord also provides human umbilical vascular endothelial cells (HUVEC), useful primary cells for vascular research. Finally, the maintenance, preservation, and characterization of the isolated vascular cells are described.

Cystatin C, a potential marker for cerebral microvascular compliance, is associated with white-matter hyperintensities progression

Cerebral white matter hyperintensities (WMHs) are central MRI markers of the brain aging process, but the mechanisms for its progression remain unclear. In this study, we aimed to determine whether the baseline serum cystatin C level represented one mechanism underlying WMH progression, and whether it was associated with the long-term progression of cerebral WMH volume in MRI. 166 consecutive individuals who were ≥50 years of age and who underwent initial/follow-up MRI evaluations within an interval of 34–45 months were included. Serum cystatin C level, glomerular-filtration rate (GFR), and other laboratory parameters were measured at their initial evaluation and at the end of follow-up. Cerebrovascular risk factors, medications, and blood-pressure parameters were also reviewed. WMH progression rate was measured by subtracting WMH volume at baseline from that at the follow-up using volumetric analysis, divided by the MRI intervals. At baseline, WMH volume was 9.61±13.17 mL, mean GFR was 77.3±22.8 mL/min, and mean cystatin C level was 0.92±0.52 mg/L. After 37.9±3.4 months, the change in WMH volume was 3.64±6.85 mL, the progression rate of WMH volume was 1.18±2.28 mL/year, the mean ΔGFR was 2.4±7.9 mL/min, and the mean Δcystatin C was 0.03±0.34 mg/L. The progression rate of WMH volume was linearly associated with cystatin C level (B coefficient = 0.856; 95% confidence interval [CI] 0.174−1.538; P = 0.014), along with the baseline WMH volume (B = 0.039; 95% CI 0.019−0.059; P<0.001), after adjusting for the conventional vascular risk factors, laboratory parameters, medication profiles, and GFR. Especially, patients with a baseline level of cystatin C ≥1.00 mg/L exhibited a much higher progression rate of WMH as compared with those with a baseline level of cystatin C <1.00 mg/L (1.60±1.91 mL/year vs. 0.82±1.63 mL/year, P = 0.010). We concluded that serum cystatin C level is independently associated with the long-term progression rate of the cerebral WMH volume. Therefore, serum cystatin C level might predict the progression of cerebral WMH.

Pathological changes in basement membranes and dermal connective tissue of skin from patients with hereditary cystatin C amyloid angiopathy

Hereditary cystatin C amyloid angiopathy (HCCAA) is a genetic disease caused by a mutation in the cystatin C gene. Cystatin C is abundant in cerebrospinal fluid and the most prominent pathology in HCCAA is cerebral amyloid angiopathy due to mutant cystatin C amyloid deposition with associated cerebral hemorrhages, typically in young adult carriers. Analyses of post-mortem brain samples shows that pathological changes are limited to arteries and regions adjacent to arteries. The severity of pathological changes at post-mortem has precluded the elucidation of the evolution of histological changes. Mutant cystatin C deposition in carriers is systemic and has, for example, been described in the skin, suggesting similar pathological mechanisms both in the brain and outside of the central nervous system. The aim of this study was to use skin biopsies from asymptomatic and symptomatic carriers to study intermediate events in HCCAA pathogenesis. We found that cystatin C deposition in minimally affected samples was limited to the basement membrane (BM) between the dermis and epidermis. When the deposits were more advanced, they extended to other BM regions in the skin. Our results showed that the immunoreactivity of the BM protein COLIV was increased to a similar extent in all carrier biopsies and cystatin C deposits were in close association with COLIV. The density of fibroblasts in the upper dermis of carrier skin was increased, whereas the distribution of other cell types examined did not differ compared with control biopsies. COLIV and cystatin C immunoreactivity in carrier biopsies was closely associated with the fibroblasts. The results of this study, in conjunction with our previous results regarding pathological BM changes in leptomeningeal arteries of patients, suggest that BM changes are early and important events in HCCAA pathogenesis that could facilitate cystatin C deposition and aggregation.

Deposition of collagen IV and aggrecan in leptomeningeal arteries of hereditary brain haemorrhage with amyloidosis

Hereditary Cystatin C Amyloid Angiopathy (HCCAA) is a rare genetic disease in Icelandic families caused by a mutation in the cystatin C gene, CST3. HCCAA is classified as a cerebral amyloid angiopathy and mutant cystatin C forms amyloid deposits in cerebral arteries resulting in fatal haemorrhagic strokes in young adults. The aetiology of HCCAA pathology is not clear and there is, at present, no animal model of the disease. The aim of this study was to increase understanding of the cerebral vascular pathology of HCCAA patients with an emphasis on structural changes within the arterial wall of affected leptomeningeal arteries. Examination of post-mortem samples revealed extensive changes in the walls of affected arteries characterised by deposition of extracellular matrix constituents, notably collagen IV and the proteoglycan aggrecan. Other structural abnormalities were thickening of the laminin distribution, intimal thickening concomitant with a frayed elastic layer, and variable reduction in the integrity of endothelia. Our results show that excess deposition of extracellular matrix proteins in cerebral arteries of HCCAA is a prominent feature of the disease and may play an important role in its pathogenesis.

Preparation of cultured human vascular cells

Cerebral amyloid angiopathy (CAA) results from amyloid accumulation within arteries of the cerebral cortex and leptomeninges. This condition is age-related, especially prevalent in Alzheimer's disease (AD), and the main feature of certain hereditary disorders (i.e., HCHWA-I). The vascular smooth muscle cells (VSMCs) appear to play a vital role in the development of CAA, which makes them well suited as an experimental model to study the disease and screen for possible remedies. We describe two different methods for isolating and culturing human VSMCs. First, using the human umbilical cord as an easy source of robust cells, and secondly, using brain tissue that provides the proper cerebral VSMCs, but is more problematic to work with. The umbilical cord also provides human umbilical vascular endothelial cells (HUVECs), useful primary cells for vascular research. Finally, the maintenance, preservation, and characterization of the isolated vascular cells are described.

Contribution of cystatin C gene polymorphisms to cerebral white matter lesions

BACKGROUND

Vascular remodeling plays an important role in the development of arteriosclerosis and any of the resulting white matter lesions in the brain. An imbalance between cysteine proteases and the cysteine protease inhibitor cystatin C (CST3) may exacerbate vascular remodeling through degradation of extracellular matrix proteins. Therefore, we evaluated the association between functional polymorphisms in the CST3 gene and the development of cerebral white matter lesions.

METHODS

In a total of 2,676 participants, 3 CST3 genepolymorphisms were genotyped in 92 cases with severe deep white matter hyperintensity (DWMH), and 184 subjects were randomly selected age- and sex-matched controls without any signs of DWMH. The genetic effects of these polymorphisms on DWMH and plasma CST3 levels were examined. CST3 expression vectors were transfected into an astrocytoma cell line and the expression level of CST3 mRNA was analyzed by quantitative RT-PCR. Intracellular and secreted levels of CST3 in the cell culture were quantified by Western blot and ELISA, respectively.

RESULTS

A significant association was found between one CST3 gene haplotype and DWMH (p = 0.002). This haplotype was also associated with lower plasma CST3 levels (p = 0.01). An in vitro transfection study revealed that the +148A allele, which is included in the risk haplotype, significantly reduced the secretion and increased the intracellular accumulation of CST3; however, it had no effect on the mRNA expression.

CONCLUSIONS

Our study shows that polymorphisms in the CST3 gene are significantly associated with the likelihood of DWMH. Substitution of A for G at +148 of the CST3 gene decreased the extracellular availability of CST3 in vitro, which might result in the activation of protease activity.

Serum cystatin C and the risk of Alzheimer disease in elderly men

BACKGROUND

Multiple lines of research suggest that increased cystatin C activity in the brain protects against the development of Alzheimer disease (AD).

METHODS

Serum cystatin C levels were analyzed at two examinations of the Uppsala Longitudinal Study of Adult Men, a longitudinal, community-based study of elderly men (age 70 years, n = 1,153 and age 77 years, n = 761, a subset of the age 70 examination). Cox regressions were used to examine associations between serum cystatin C and incident AD. AD cases were identified by cognitive screening and comprehensive medical chart review in all subjects.

RESULTS

On follow-up (median 11.3 years), 82 subjects developed AD. At age 70 years, lower cystatin C was associated with higher risk of AD independently of age, APOE4 genotype, glomerular filtration rate, diabetes, hypertension, stroke, cholesterol, body mass index, smoking, education level, and plasma amyloid-beta protein 40 and 42 levels (hazard ratio [HR] for lowest [<1.12 micromol/L] vs highest [>1.30 micromol/L] tertile = 2.67, 95% CI 1.22-5.83, p < 0.02). The results were similar at age 77 years (43 participants developed AD during follow-up). Furthermore, a 0.1-mumol/L decrease of cystatin C between ages 70 and 77 years was associated with a 29% higher risk of incident AD (HR 1.29, 95% CI 1.03-1.63, p < 0.03).

CONCLUSIONS

Low levels of serum cystatin C precede clinically manifest Alzheimer disease (AD) in elderly men free of dementia at baseline and may be a marker of future risk of AD. These findings strengthen the evidence for a role for cystatin C in the development of clinical AD.

Solubilized cystatin C amyloid is cytotoxic to cultured human cerebrovascular smooth muscle cells

Cerebral amyloid angiopathy (CAA) is characterized by the accumulation of amyloid within arteries of the cerebral cortex and leptomeninges. This condition is age related, especially prevalent in Alzheimer's disease (AD) and the main feature of certain hereditary disorders. The vascular smooth muscle cells (VSMC) appear to play a vital role in the development of CAA and have been found to produce the amyloid beta precursor protein (AbetaPP) and process it to Abeta the major component of most CAA amyloid. Moreover, synthesized Abeta has proven to be toxic to cerebral VSMC in culture possibly explaining the disintegration and disappearance of the muscle cells from affected cerebral blood vessels seen in CAA. An aggressive and extremely rare form of CAA, known as Hereditary Cerebral Hemorrhage With Amyloidosis-Icelandic Type (HCHWA-I), exhibits this withdrawal of VSMC as amyloid accumulates in the vessel wall. However, the amyloid in HCHWA-I is made from a variant of cystatin C (L68Q) instead of the more common Abeta. To evaluate possible cytotoxicity in this condition solubilized cystatin C amyloid extracted from HCHWA-I leptomeninges was applied to cerebral smooth muscle cells in culture and was found to kill the cells.

Hereditary cystatin C amyloid angiopathy: genetic, clinical, and pathological aspects

Hereditary cystatin C amyloid angiopathy (HCCAA) is a rare, fatal amyloid disease in young people in Iceland caused by a mutation in cystatin C, which is an inhibitor of several cysteine proteinases, such as cathepsins S, B, and K. The same mutation in cystatin C, L68Q, has been found in all patients examined so far pointing to a common founder. Most of the families can be traced to a region in the northwest of Iceland, around Breidafjordur bay. Mutated cystatin C forms amyloid, predominantly in brain arteries and arterioles, but also to a lesser degree in tissues outside the central nervous system such as skin, lymph nodes, testis, spleen, submandibular salivary glands, and adrenal cortex. The amyloid deposition in the vessel walls causes thickening of the walls leading to occlusion or rupture and resulting in brain hemorrhage. Although the amyloid can be detected outside the brain, the clinical manifestation is restricted to the brain, and usually consists of repeated hemorrhages leading to paralysis. Sometimes the initial signs of hemorrhage are dementia and personality changes.

Truncated cystatin C in cerebrospiral fluid: Technical artefact or biological process?

Cystatin C, a low molecular weight cysteine proteinase inhibitor present in human body fluids at physiological concentrations, is more expressed in cerebrospinal fluid (CSF) than in plasma. Mass spectrometric characterization showed that after 3 months of storage of human CSF at -20 degrees C, cystatin C was cleaved in the peptide bond between R8 and L9 and lost its eight N-termini amino acids, whereas this cleavage did not occur when stored at -80 degrees C. This truncation occurred in all CSF samples studied irrespective of the underlying neurological status, indicating a storage-related artefact rather than a physiological or pathological processing of the protein. These results stress the importance of optimal preanalytical storage conditions of any sample prior to proteomics studies.

Causative and susceptibility genes for Alzheimer's disease: a review

Alzheimer's disease (AD) is the most common type of dementia in the elderly population. Three genes have been identified as responsible for the rare early-onset familial form of the disease: the amyloid precursor protein (APP) gene, the presenilin 1 (PSEN1) gene and the presenilin 2 (PSEN2) gene. Mutations in these genes, however, account for less than 5% of the total number of AD cases. The remaining 95% of AD patients are mostly sporadic late-onset cases, with a complex aetiology due to interactions between environmental conditions and genetic features of the individual. In this paper, we review the most important genes supposed to be involved in the pathogenesis of AD, known as susceptibility genes, in an attempt to provide a comprehensive picture of what is known about the genetic mechanisms underlying the onset and progression of AD. Hypotheses about the role of each gene in the pathogenic pathway are discussed, taking into account the functions and molecular features, if known, of the coded protein. A major susceptibility gene, the apolipoprotein E (APOE) gene, found to be associated with sporadic late-onset AD cases and the only one, whose role in AD has been confirmed in numerous studies, will be included in a specific chapter. As the results reported by association studies are conflicting, we conclude that a better understanding of the complex aetiology that underlies AD may be achieved likely through a multidisciplinary approach that combines clinical and neurophysiological characterization of AD subtypes and in vivo functional brain imaging studies with molecular investigations of genetic components.

Hypoxia and reoxygenation of brain microvascular smooth muscle cells in vitro: cellular responses and expression of cerebral amyloid angiopathy-associated proteins

Hypoxia is known to cause complex cascades of physiological, biochemical, and morphological changes in the brain. Cerebral microvascular smooth muscle cell (MV-SMC) damage may occur following hypoxic conditions and lead to SMC dysfunction. However, little is known about the exact cellular and molecular responses of these cells to hypoxia. To partly address these questions, MV-SMC were isolated from human brain, cultured and placed in conditions of ambient hypoxia (H) and hypoxia followed by reoxygenation (H/R). Cell morphology, proliferation, and the expression of amyloid precursor protein (APP) and cystatin C peptide were investigated and compared (after induction of hypoxia) between cerebral MV- and human aortic SMC. Our results show that MV-SMC proliferation was inhibited after 48 h of hypoxia and H/R, whereas aortic SMC proliferation was stimulated after 48 h of hypoxia and H/R. Hypoxia and H/R induced an increase of intracellular APP and cystatin C expression in both types of SMC, though the effect of H and H/R on APP upregulation was quantitatively more robust in MV-SMC than aortic SMC. Patterns of hypoxia-induced APP upregulation in SMC differed significantly from those found in cultured neuronal cells (PC12, NT2). These results suggest that hypoxia and H/R-induced APP and cystatin C upregulation appear to occur independently of the inhibition of cerebral MV-SMC proliferation. Overexpression of APP and cystatin C in response to hypoxia may thus represent an initiating event in the pathogenesis of amyloid angiopathy, or mediate progression of this microvascular lesion.

Alzheimer's disease and the cystatin C gene polymorphism: an association study

Cystatin C is an amyloidogenic protein that colocalizes with beta-amyloid (Abeta) within arteriolar walls in Alzheimer disease (AD) brains. Recently, a coding polymorphism in the cystatin C gene (CST3) has been claimed to confer risk for the development of late-onset AD. In the present work we have tested the frequencies of CST3-A and CST3-G alleles and used chi-square and logistic regression analyses to assess the association among the CST3 polymorphism, apolipoprotein E4 (APOE4), and AD in a series of 159 AD patients and 155 controls. The CST3-A allele was seen to be an accumulation risk factor for early-onset AD. Furthermore, a synergistic association among the CST3-A allele, APOE4 and AD was found in AD patients whose ages were between 60 and 74 years.

Codeposition of cystatin C with amyloid-beta protein in the brain of Alzheimer disease patients

Immunohistochemical analysis of brains of patients with Alzheimer disease (AD) revealed that the cysteine proteinase inhibitor cystatin C colocalizes with amyloid beta-protein (Abeta) in parenchymal and vascular amyloid deposits. No evidence of cerebral hemorrhage was observed in any of the brains studied. Immunoelectron microscopy demonstrated dual staining of amyloid fibrils with anti-Abeta and anti-cystatin C antibodies. Cystatin C immunoreactivity was also observed in amyloid deposits in the brain of transgenic mice overexpressing human beta amyloid precursor protein. Massive deposition of the variant cystatin C in the cerebral vessels of patients with the Icelandic form of hereditary cerebral hemorrhage with amyloidosis is thought to be responsible for the pathological processes leading to stroke. Anti-cystatin C antibodies strongly labeled pyramidal neurons within cortical layers most prone to amyloid deposition in the brains of AD patients. Immunohistochemistry with antibodies against the carboxyl-terminus of Abeta(x-42) showed intracellular immunoreactivity in the same neuronal subpopulation. It remains to be established whether the association of cystatin C to Abeta plays a primary role in amyloidogenesis of AD or is a late event in which the protein is bound to the previously formed Abeta amyloid fibrils.

A polymorphism in the cystatin C gene is a novel risk factor for late-onset Alzheimer's disease

OBJECTIVE

To investigate whether or not a coding polymorphism in the cystatin C gene (CST3) contributes risk for AD.

DESIGN

A case-control genetic association study of a Caucasian dataset of 309 clinic- and community-based cases and 134 community-based controls.

RESULTS

The authors find a signficant interaction between the GG genotype of CST3 and age/age of onset on risk for AD, such that in the over-80 age group the GG genotype contributes two-fold increased risk for the disease. The authors also see a trend toward interaction between APOE epsilon4-carrying genotype and age/age of onset in this dataset, but in the case of APOE the risk decreases with age. Analysis of only the community-based cases versus controls reveals a significant three-way interaction between APOE, CST3 and age/age of onset.

CONCLUSION

The reduced or absent risk for AD conferred by APOE in older populations has been well reported in the literature, prompting the suggestion that additional genetic risk factors confer risk for later-onset AD. In the author's dataset the opposite effects of APOE and CST3 genotype on risk for AD with increasing age suggest that CST3 is one of the risk factors for later-onset AD. Although the functional significance of this coding polymorphism has not yet been reported, several hypotheses can be proposed as to how variation in an amyloidogenic cysteine protease inhibitor may have pathologic consequences for AD.

Gelsolin-related spinal and cerebral amyloid angiopathy

Gelsolin-related amyloidosis (familial amyloidosis, Finnish type) is a rare disorder, reported worldwide in kindreds carrying a G654A or G654T gelsolin gene mutation. Facial palsy, mild peripheral neuropathy, and corneal lattice dystrophy are characteristic, but atrophic bulbar palsy, ataxia of gait, and minor cognitive impairment may occur. In histological and immunohistochemical studies of the central nervous system in 4 patients with a G654A gelsolin mutation, we found widespread spinal, cerebral, and meningeal amyloid angiopathy, with deposition of gelsolin-related amyloid (AGel). Marked extravascular deposits occurred in the dura, spinal nerve roots, and sensory ganglia. The amyloid deposits were also variably immunoreactive for apolipoprotein E (ApoE), alpha1-antichymotrypsin (alpha1-ACT), and cystatin C (Cys C). Cerebral perivascular fibrinogen immunoreactivity was occasionally noted. The patients showed posterior column degeneration and diffuse loss of myelin in the centrum semiovale with perivascular accentuation. Postmortem magnetic resonance imaging, performed on 1 patient, showed white matter lesions, colocalizing with the histological abnormalities. Our study shows that deposition of AGel in the spinal and cerebral blood vessel walls, meninges, as well as spinal nerve roots and sensory ganglia is an essential feature of this form of systemic amyloidosis and may contribute to the central nervous system symptoms.