Defining cellular and molecular mechanisms of hereditary transthyretin amyloidosis
Giadone, Richard Michael
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Hereditary transthyretin amyloidosis (ATTR amyloidosis) is a multi-system protein folding disorder that results from >100 described mutations in the transthyretin (TTR) gene. In the disease, non-natively folded TTR, originally produced by the liver, travels throughout circulation and deposits extracellularly at downstream target organs. The multi-tissue etiology of the disease makes it difficult to study in vitro, while no mouse model accurately recapitulates disease pathology. Therefore, we utilized patient-specific induced pluripotent stem cells (iPSCs) to test the hypothesis that production of and exposure to destabilized TTRs results in distinct cellular and molecular changes. The liver’s contribution to the deposition of TTR at distal tissues is understudied. As a result, in Aim 1 we sought to assess the effects of destabilized TTR production on effector hepatic cells. To this end, we utilized gene editing to generate isogenic, patient iPSCs expressing either mutant or wild-type TTR. Combining this tool with single cell RNAseq, we identified hepatic proteostasis factors, including unfolded protein response (UPR) pathways, whose expression coincided with the production of destabilized TTR. Enhancing endoplasmic reticulum (ER) proteostasis within patient hepatic cells via exogenous activation of adaptive UPR signaling, we demonstrated preferential reduction in the secretion of pathogenic TTR. In turn, we demonstrated that production of disease-associated TTR correlates with expression of proteostasis factors capable of regulating TTR secretion and in turn downstream pathogenesis. ATTR amyloidosis patients exhibit extreme phenotypic variation (e.g. TTR fibril deposits at cardiac tissue and/or peripheral nerves). In Aim 2, we sought to define responses of target cell types to pathologically-diverse TTRs. To accomplish this, we profiled transcriptomic changes resulting from exposure to a variety of destabilized TTRs to determine 1) target cell response to TTR exposure and 2) how this response changes across diverse variants and cell types. In doing so, we found that TTR exposure elicits distinct variant- and cell type-specific transcriptional responses. Herein, we addressed our central hypothesis by profiling destabilized TTR production within hepatic cells and TTR exposure at target cell types. Collectively, these data may result in the discovery of unidentified and potentially druggable pathologically-associated pathways for ATTR amyloidosis and other systemic amyloid diseases.
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