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Differential Neuropathology, Genetics, and Transcriptomics in two kindred cases with Alzheimer’s Disease and Lewy Body Dementia

ABSTRACT: Alzheimer’s disease (AD) and Lewy body dementia (LBD) are two different forms of dementia but their pathology may involve the same cortical areas with overlapping cognitive manifestation. Dementia cases within the same family share a common genetic background. Nonetheless, the clinical phenotype may be different due to the different underlying molecular processes that come-up apart from genetics, causing diverse neurodegeneration. Through neuropathological, genetic and transcriptomic comparison of four different brain areas (substantia nigra, hippocampus, parietal lobe and basal ganglia), we defined commonalities and differences in the pathological processes of dementia in two kindred cases, a mother and a son, who developed a classical AD and an aggressive form of AD/LBD respectively. Genetic analysis did not reveal any pathogenic variants in the principal AD/LBD-causative genes. RNA sequencing highlighted high transcriptional dysregulation within the substantia nigra in LBD pathology, while AD underwent lower degree of transcriptional dysregulation, with the parietal lobe being the most involved brain area. Conversely, hippocampus (the most degenerated area) and basal ganglia (lacking specific lesions) expressed the lowest level of dysregulation. Our data suggest that there is a link between the transcriptional dysregulation and the amount of tissue damage accumulated across time, assessed through neuropathology. Moreover, we highlight that the molecular bases of AD and LBD follow very different pathways, which underlie their neuropathological signatures. Indeed, the transcriptome profiling through RNA sequencing may be an important tool in flanking the neuropathological analysis for a deeper understanding of AD and LBD pathogenesis.

ORGANISM(S): Homo sapiens

PROVIDER: GSE193438 | GEO | 2022/08/03

REPOSITORIES: GEO

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Project description:Aging is often characterized by a progressive loss of cognitive abilities due to the onset of different forms of dementia. Among these, Alzheimer’s Disease (AD) and dementia with Lewy bodies (LBD) are the most widespread ones. However, little is known about the common aspects between these conditions and how these aspects can be linked to aging itself. With this work, we aim to identify a molecular fil rouge that could link aging and different dementias in order to possibly highlight strategic targets for novel therapeutical approaches. A whole transcriptome analysis and a Gene Set Enrichment Analysis (GSEA) have been carried out on brain samples from hippocampus (HI), temporal and parietal cortex (TC, PC), cingulate cortex (CG), and substantia nigra (SN) from the Abbiategrasso Brain Bank (ABB) of subjects with a neuropathological diagnosis of AD and LBD (6 per pathology) and 3 age-matched controls with no dementia (CTRLs). Clinical and neuropsychological profile were obtained through serial evaluations, made at the baseline and in the following years. According to the ABB protocol, the neuropathological diagnosis was based on a complete histological characterization, including all the main proteinopathies and vascular scoring. Transcriptomic results showed some major differences in the number of differentially expressed genes (DEGs) between the two pathologies and in particular that AD brains gene expression is more affected compared to LBD’s one (DEGsAD=3156; DEGsLBD=278). Furthermore, the GSEA showed that in AD it is possible to cluster the analysed regions by biological processes (HI and TC: DEGs primarily related to synaptic transmission; PC, CG and SN: DEGs primarily related to proper protein folding and inflammation) while in LBD there is only a strong and peculiar involvement of SN (DEGs primarily related to proper protein folding and inflammation) and PC (DEGs primarily related to myelination and glial system activation). AD and LBD are different forms of dementia characterized by a definite time and severity-related pattern. Therefore, it is possible to draw a molecular map of pathology spreading in the brain that could unveil unexplored roads and possible shortcuts leading to a better understanding of AD and LBD pathogenesis. This could help to discover novel biological targets in order to develop effective and well-timed therapeutical approaches.

Project description:Background Semantic dementia (SD) is a subtype of frontotemporal dementia (FTD) characterized by language deficits due to severe temporal lobe degeneration. The consistent neuropathological diagnosis is FTD-TDP subtype C, with characteristic round TDP-43 protein inclusions in the dentate gyrus. Despite this striking clinicopathological concordance, the pathogenic mechanisms are largely unexplained forestalling the development of targeted therapeutics. Methods We carried out laser capture microdissection of the dentate gyrus of 15 SD patients and 17 non-demented controls, and assessed relative protein abundance changes by label-free quantitative mass spectrometry. To identify SD specific proteins, we compared our results to eight other FTD and Alzheimer’s disease (AD) proteomic datasets of cortical brain tissue, parallel with functional enrichment analyses and protein-protein interactions (PPI). Results Of the total 5,354 quantified proteins, 151 showed differential abundance (FDR<1%) in SD patients. Seventy-two proteins were previously found altered with the same directional change in at least one FTD/AD proteomic study, while 79 proteins were considered as showing potentially SD specific dysregulation. Functional enrichment indicated an overrepresentation of pathways related to the immune response, metabolic processes, and cell-junction assembly. PPI analysis highlighted a cluster of interacting proteins associated with adherens junction and cadherin binding– the cadherin-catenin complex. Multiple proteins in this complex showed strong and apparent specific upregulation in SD, including β-catenin (CTNNB1), γ-catenin (JUP), and N-cadherin (CDH2). Conclusions We discovered an increase of cell adhesion proteins in SD specifically constituting the cadherin-catenin complex at the synaptic membrane, essential for synaptic signaling. Although further validation is warranted, we anticipate that these findings will help unravel the disease processes underlying SD.

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Differential Neuropathology, Genetics, and Transcriptomics in two kindred cases with Alzheimer’s Disease and Lewy Body Dementia

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