Shared and disparate genomic features of TDP-43 proteinopathies

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Project Summary/Abstract TAR DNA-binding ~43kDa (TDP-43) inclusions are the pathological hallmark of frontotemporal lobar degeneration with TDP-43 (FTLD-TDP) and amyotrophic lateral sclerosis (ALS). Despite shared pathological features, ALS and FTLD-TDP can present with heterogenous clinical features including cognitive/behavioral impairments (i.e., FTLD-TDP), motor neuron dysfunction (i.e., ALS), or both (i.e., ALS-FTD). Moreover, certain genetic mutations typically only result in ALS or FTLD-TDP, but other mutations can cause FLTD-TDP and/or ALS within the same family. Together, the shared and disparate pathological, clinical, and genetic features of FTLD-TDP, ALS, and ALS-FTD support the notion that they are part of a clinicopathologic spectrum. However, the vast majority of ALS and FTLD-TDP cases are considered sporadic and have no known causal mutation. The underlying molecular mechanisms that contribute to the observed clinical heterogeneity across sporadic TDP-43 proteinopathies are not well understood. Supporting evidence for a genetic component to sporadic cases, common genetic variants have been associated with disease risk for either ALS or FTLD-TDP. However, combined studies across TDP-43 proteinopathies are rare. Thus, the extent to which risk alleles are shared or disparate across these phenotypes is unclear. While there is mounting evidence of shared genetic factors that explain the biological mechanisms that drive susceptibility to both diseases, considerably less effort has focused on the disparate genetic features across TDP-43 proteinopathies. Identifying disparate variants may contribute to our understanding of disease-specific drivers. The first aim of this proposal is to identify both the shared and disparate genomic features that drive individual-level cognitive/behavioral and/or neuromuscular presentations of these syndromes. TDP-43 pathology and neurodegeneration are observed in characteristic neuroanatomical regions that correlate with the clinical presentations of ALS and FTLD-TDP, but it is unclear what contributes to this regional selective vulnerability. Previous work has demonstrated clear regional differences in gene expression within the same individuals. Gene expression quantitative trait loci analyses can identify genomic loci that explain variation in gene expression. However, these associations are highly tissue and cell type specific, which may obscure important differences. This is especially true within neurodegenerative disorders, as observed gene expression differences may reflect cell type composition differences rather than true transcriptional regulation. The second aim of this proposal is to investigate genetic contributions to regionally specific differential gene expression, including cell type specific expression, in ALS and FTLD-TDP. Overall, this proposal leverages genotype and transcriptomic approaches to understand molecular contributions of regional selective vulnerability in ALS and FTLD-TDP. In disentangling this heterogeneity, it may be possible to inform efforts to develop therapeutic targets that attenuate the course of these neurodegenerative diseases.