Stress Granules and the Biology of TDP-43

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The major objectives of this ViCTER program are to test novel mechanisms of gene-environment interactions. We will test whether environmental toxicants linked to amyotrophic lateral sclerosis (ALS) act in part through genes linked to ALS, including the newly discovered gene, C9ORF72, as well as the gene PON2, which biotransforms environmental toxicants. We will also test whether toxicants might contribute to ALS by acting through the aryl hydrocarbon (AhR) receptor, which is known to mediate toxicant action in other diseases, such as cancers. Hexanucleotide expansions in C9ORF72 account for 30% of cases of familial ALS. Inclusion of samples from ALS patients through our co-investigator, Dr. Rademakers, allows us to generate iPSCs from subjects with these mutations. The AhR is a ligand- activated transcription factor that mediates many of the effects of environmental toxicants in hematopoiesis, lymphocyte development, adipogenesis and cancer. We hypothesize that AhR ligands and other environmental chemicals, many of which are neurotoxic might also increase the risk of ALS by stimulating transcription of genes linked to ALS. The experiments in this consortium could identify novel mechanisms through which environmental toxicants might contribute to ALS. In addition, the availability of novel, non-toxic AhR antagonists, which were generated by Dr. Sherr's team, offers the exciting prospect of potentially inhibiting the expression of genes linked to ALS, a strategy that might reduce or delay the pathophysiology of ALS. Aim 1 will determine the role of AhR and PON2 genetic variants in ALS using the Mayo ALS cohort; Dr. Rademakers will perform in-depth genetic analyses of AhR in ~750 ALS patients and matched controls ascertained at Mayo Clinic to determine whether there are common genetic risk variants and/or rare modifier variants or disease causing variants in AhR. In Aim 2, Dr. Murphy will generate iPSC lines from subjects identified by Dr. Rademakers who have ALS and express mutated C9ORF72 and PON2. In Aim 3, Dr. Wolozin will determine whether genes linked to ALS (e.g., TARDBP, C9ORF72 or PON2) increase the vulnerability and/or pathology in response to ALS-linked environmental toxicants in MN iPSCs. Toxicants linked to ALS will be utilized, including ¿- methyl amino alanine, neurotoxic organophosphates and environmental AhR ligands. In Aim 4, Dr. Sherr will determine whether AhR ligands increase the expression of ALS-linked genes and proteins, and modify the resulting phenotypes. He will use AhR-specific shRNA, novel inhibitors, qPCR and AhR-reporter-transduced iPSCs to characterize AhR expression and activity in MN iPSCs. Thus, in this consortium, we will determine if AhR contributes to ALS through regulation of ALS-associated genes, and whether such activation modifies the pathophysiology of genes or proteins linked to ALS.