Coexistence of transthyretin- and Aβ-type cerebral amyloid angiopathy in a patient with hereditary transthyretin V30M amyloidosis

Alzheimer's Disease With Cardiac Transthyretin Amyloidosis: A Clinicopathological Study of Autopsy Cases

The relationship between Alzheimer's disease and cardiac transthyretin amyloidosis (ATTR) has been reported epidemiologically. However, the details of its clinicopathological characteristics are unclear. To clarify the pathogenesis of Alzheimer's disease combined with cardiac ATTR, 50 autopsy cases of Alzheimer's disease with cardiac hypertrophy were examined. Transthyretin amyloid deposition was studied by immunostaining in cases where amyloid deposition was suspected in various organs by HE staining. ATTR in systemic organs was also examined. The pathological diagnosis of Alzheimer's disease was done based on the National Institute on Aging and Alzheimer's Association (NIA-AA) guidelines. Cerebral amyloid angiopathy (CAA) was rated on a 3-point scale according to the Vonsattel scale. The pathological diagnosis of cardiac ATTR was done using a 3-point scale based on previously published findings on amyloid amounts. Six out of 50 patients were found to have cardiac ATTR by immunostaining and protein mass analysis of myocardial tissue. The sex distribution of the six patients was two males (Cases 3 and 6) and four females (Cases 1, 2, 4, and 5), and their ages were 97, 89, 91, 104, 86, and 77 years in Cases 1-6, respectively. In Cases 1-6, the NIAA score/CAA assessment/ATTR stages were intermediate/severe/G3, intermediate/moderate/G3, high/severe/G3, high/severe/G2, high/severe/G2, and intermediate/moderate/G2, respectively. Cases 1-5 also had cerebral infarction. In all cases, Transthyretin amyloid deposition was seen mainly in the vessel walls of various organs throughout the body. In the heart, transthyretin amyloid deposition was observed in the myocardial vessel walls and between myocardial fibers. On autopsy, cardiogenic cerebral infarction or heart failure was considered to be the main cause of death in Cases 1-5. These results indicate that Alzheimer's disease could be regarded as a systemic disease rather than just a localized disease presenting with dementia.

Targeted sequencing of selected functional genes in patients with wild-type transthyretin amyloidosis

OBJECTIVE

Wild-type transthyretin (ATTRwt) amyloidosis is caused by the misfolding and deposition of the transthyretin protein (TTR) in the absence of mutations in the TTR gene. Studies regarding the variant form of ATTR amyloidosis (ATTRv) suggest that the presence of single-nucleotide polymorphisms (SNP) in genes other than the TTR, may influence the development of the disease. However, other genetic factors involved in the aetiopathogenesis of ATTRwt are currently unknown. This work investigates the presence of sequence variants in genes selected for their possible impact on ATTRwt amyloidosis. To do so, targeted sequencing of 84 protein-coding genes was performed in a cohort of 27 patients diagnosed with ATTRwt.

RESULTS

After applying quality and frequency filtering criteria, 72 rare or novel genetic variants were found. Subsequent classification according to the ACMG-AMP criteria resulted in 17 variants classified as of uncertain significance in 14 different genes. To our knowledge, this is the first report associating novel gene variants with ATTRwt amyloidosis. In conclusion, this study provides potential insights into the aetiopathogenesis of ATTRwt amyloidosis by linking novel coding-gene variants with the occurrence of the disease.

A case of transthyretin-related cerebral amyloid angiopathy. The other side of hereditary transthyretin amyloidosis

The target organs for familial transthyretin amyloidosis are typically the nerves, the heart or even the eyes due to the accumulation of amyloid deposits. Less frequently, these deposits can occur within the central nervous system and drive a specific phenotype of cerebral amyloid angiopathy. We report the case of a 72-year-old woman showing evidence of cerebral amyloid angiopathy, in a context of hereditary transthyretin amyloidosis (hATTR) due to p.(Ser77Tyr) mutation of the TTR gene. Her cognitive assessment on a two-year follow-up was remarkably steady. A very limited number of patients with hereditary transthyretin amyloidosis associated with a cerebral amyloid angiopathy have been reported. Few characteristics could distinguish them from classic cerebral amyloid angiopathy, and more data are needed to highlight specific features. Screening for peripheral neuropathy should be considered for patients referred to memory clinic for atypical cerebral amyloid angiopathy.

Epigenetic profiling of Italian patients identified methylation sites associated with hereditary transthyretin amyloidosis

Hereditary transthyretin (TTR) amyloidosis (hATTR) is a rare life-threatening disorder caused by amyloidogenic coding mutations located in TTR gene. To understand the high phenotypic variability observed among carriers of TTR disease-causing mutations, we conducted an epigenome-wide association study (EWAS) assessing more than 700,000 methylation sites and testing epigenetic difference of TTR coding mutation carriers vs. non-carriers. We observed a significant methylation change at cg09097335 site located in Beta-secretase 2 (BACE2) gene (standardized regression coefficient = -0.60, p = 6.26 × 10-8). This gene is involved in a protein interaction network enriched for biological processes and molecular pathways related to amyloid-beta metabolism (Gene Ontology: 0050435, q = 0.007), amyloid fiber formation (Reactome HSA-977225, q = 0.008), and Alzheimer's disease (KEGG hsa05010, q = 2.2 × 10-4). Additionally, TTR and BACE2 share APP (amyloid-beta precursor protein) as a validated protein interactor. Within TTR gene region, we observed that Val30Met disrupts a methylation site, cg13139646, causing a drastic hypomethylation in carriers of this amyloidogenic mutation (standardized regression coefficient = -2.18, p = 3.34 × 10-11). Cg13139646 showed co-methylation with cg19203115 (Pearson's r2 = 0.32), which showed significant epigenetic differences between symptomatic and asymptomatic carriers of amyloidogenic mutations (standardized regression coefficient = -0.56, p = 8.6 × 10-4). In conclusion, we provide novel insights related to the molecular mechanisms involved in the complex heterogeneity of hATTR, highlighting the role of epigenetic regulation in this rare disorder.

Amyloid cross-seeding raises new dimensions to understanding of amyloidogenesis mechanism

Hallmarks of most of the amyloid pathologies are surprisingly found to be heterocomponent entities such as inclusions and plaques which contain diverse essential proteins and metabolites. Experimental studies have already revealed the occurrence of coaggregation and cross-seeding during amyloid formation of several proteins and peptides, yielding multicomponent assemblies of amyloid nature. Further, research reports on the co-occurrence of more than one type of amyloid-linked pathologies in the same individual suggest the possible cross-talk among the disease related amyloidogenic protein species during their amyloid growth. In this review paper, we have tried to gain more insight into the process of coaggregation and cross-seeding during amyloid aggregation of proteins, particularly focusing on their relevance to the pathogenesis of the protein misfolding diseases. Revelation of amyloid cross-seeding and coaggregation seems to open new dimensions in our mechanistic understanding of amyloidogenesis and such knowledge may possibly inspire better designing of anti-amyloid therapeutics.

Hepatocyte-like cells reveal novel role of SerpinA1 in transthyretin amyloidosis

Transthyretin (TTR)-related familial amyloid polyneuropathy (ATTR) results from aggregation and extracellular disposition of misfolded TTR variants. Growing evidence suggests the importance of hepatic chaperones for modulation of pathogenesis. We took advantage of iPSC-derived hepatocyte-like cells (HLCs) derived from ATTR patients (ATTR-HLCs) to compare chaperone gene expression to healthy individuals (H-HLCs). From the set of genes analyzed, chaperones that are predominantly located extracellularly were differently expressed. Expression of the chaperones showed a high correlation with TTR in both ATTR-HLCs and H-HLCs. In contrast, after TTR knockdown, the correlation was mainly affected in ATTR-HLCs suggesting that variant TTR expression triggers abberant chaperone expression. Serpin peptidase inhibitor clade A member 1 (SERPINA1/alpha-1 antitrypsin) was the only extracellular chaperone that was markedly upregulated after TTR knockdown in ATTR-HLCs. Co-immunoprecipitation revealed that SerpinA1 physically interacts with TTR. In vitro assays indicated that SerpinA1 can interfere with TTR aggregation. Taken together, our results suggest that extracellular chaperones play a crucial role in ATTR pathogenesis, in particular SerpinA1, which may affect amyloid formation.