Elucidating Mechanism of Ammonia Toxicity Using Cortical Organoids (P5-7.001)

Abstract

<h3>Objective:</h3> This study seeks to understand the cell type-specific changes that occur from acute ammonia exposure in the brain. We used cortical organoids derived from human inducible pluripotent stem cells because they reproduce aspects of spatial organization and cellular diversity seen <i>in vivo</i>. Importantly, cortical organoids contain neurons and astrocytes that are structurally juxtaposed, an intercellular interaction that is likely critical in acute ammonia toxicity. <h3>Background:</h3> Hyperammonemia is a common clinical outcome from a variety of pathologies including acute liver failure. At high levels, ammonia can produce cerebral edema and in severe cases result in brain herniation and death. Edema is thought to result from astrocyte swelling, but the precise mechanism of ammonia toxicity remains unknown. A better understanding of the cellular pathways involved will lead to targeted therapies and improved clinical outcomes. <h3>Design/Methods:</h3> Cortical organoids were exposed to supraphysiological levels of ammonia for 24 hours. Following exposure, organoids were dissociated and immunopanned to purify astrocytes and neurons. Gene expression changes between ammonia and unexposed samples were identified in a cell-specific manner. Gene ontology analysis was conducted to detect cellular pathways that are perturbed due to ammonia exposure. <h3>Results:</h3> Organoids exposed to high ammonia retained their structural integrity. Molecularly, we observed changes common to both neurons and astrocytes as well as cell-type specific signatures. Both astrocytes and neurons demonstrated upregulation of genes involved in cholesterol biosynthesis and lipid metabolism though a greater number of genes were upregulated in astrocytes, suggesting a possible link between these pathways in the setting of hyperammonemia. <h3>Conclusions:</h3> These results demonstrate a cell type-specific response following acute ammonia exposure and suggest cholesterol synthesis and lipid metabolism may play a role in ammonia toxicity. In future work, we will study cell type-specific functional consequences and proteomic changes to better understand how astrocytes and neurons responds to high ammonia environments. <b>Disclosure:</b> Dr. Barton has nothing to disclose. Ms. King has nothing to disclose. Mr. Sing has nothing to disclose. The institution of Dr. Sampson has received research support from NIH NIEHS K00. The institution of Dr. Sampson has received research support from Burroughs Wellcome Fund PDEP. The institution of an immediate family member of Dr. Sampson has received research support from Parkinsons Foundation. The institution of an immediate family member of Dr. Sampson has received research support from Parkinsons Foundation Stanley Fahn. The institution of an immediate family member of Dr. Sampson has received research support from ASAP Collab Network. The institution of an immediate family member of Dr. Sampson has received research support from NIEHS. An immediate family member of Dr. Sampson has received intellectual property interests from a discovery or technology relating to health care. Dr. Sloan has nothing to disclose.