Shawn Barton1, Alexia King1, Anson Sing1, Maureen Sampson1, Steven Sloan1
1Department of Human Genetics, Emory University
Objective:
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 in vivo. Importantly, cortical organoids contain neurons and astrocytes that are structurally juxtaposed, an intercellular interaction that is likely critical in acute ammonia toxicity.
Background:
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.
Design/Methods:
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.
Results:
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.
Conclusions:
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.