P: 78 Mechanism of Alzheimer Type II Astrocyte Development: Implication for the Defective Neuronal Integrity and Neurobehavioral Deficits Associated With Chronic Hepatic Encephalopathy

Abstract

BACKGROUND: Chronic hepatic encephalopathy (CHE) is a major neurological condition that occurs following chronic liver failure (CLF) following drug-induced hepatotoxicity, viral hepatitis, or exposure to various hepatotoxins. CHE is characterized by mental confusion, behavioral changes, and motor disturbances. The molecular basis for CHE remains elusive. The presence of Alzheimer type II astrocytes (AT2A) is the only histopathological findings observed in CHE. However, little is currently known regarding its development, and its involvement in the pathogenesis of CHE. METHODS: Astrocytic glia maturation factor and other inflammatory factors were measured by western blots, immunohistochemistry, and by ELISA. AT2A was analyzed by histopathology. RESULTS: We identified increased levels of astrocytc glia maturation factor (GMF), a factor strongly implicated in neuroinflammation and in the overexpression of various inflammatory factors (IL-1β, TNF-α, IL-6, chemokine (C-X-C motif) ligand 1 (CXCL1), matrix metalloproteinase-3 (MMP-3), prostaglandin E2 (PGE2) and cyclooxygenase 2 (COX2), as well as reduced levels of α-tubulin and glial fibrillary acidic protein, along with increased levels of aggregated nuclear protein lamin a/c in the thioacetamide-induced rat model of CHE. Further, we identified reduced levels of neuronal proteins, PSD95, synaptophysin, and NMDA-nr1. Moreover, synaptic density and dendritic complexity are reduced post-CLF. Since elevated blood/brain ammonia levels have been strongly implicated in the pathogenesis of CHE, while exposure of cultured astrocytes to ammonia was shown to develop AT2A, we utilized this in vitro system to delineate mechanisms by which ammonia contributes to the development of AT2A. We found increased levels of GMF, aggregated nuclear protein lamin a/c, and inflammatory factors (IL-1β, TNF-α, IL-6, CXCL1, MMP-3, PGE2 and COX2), as well as reduced levels and oxidized forms of α-tubulin in astrocytes post-ammonia treatment, which was similar to that found in vivo. Further, exposure of cultured neurons to conditioned media (CM) from ammonia-treated astrocytes (AT2A), but not ammonia per se, resulted in reduced levels of neuronal PSD95, synaptophysin and NMDA-nr1, as well as reduced synaptic density and dendritic complexity. Noteworthy, pharmacological inhibition of GMF, or silencing GMF by CRISPR reversed the defective neuronal integrity post-exposure of neurons to CM from ammonia-treated astrocytes in vitro. CONCLUSIONS: These findings strongly suggest that increased levels of GMF post-CLF may negatively impact neuronal integrity that may ultimately contribute to the neurobehavioral/cognitive and motor deficits observed in CHE. We anticipate that our studies aimed at a better understanding of the molecular mechanisms involved in the development of AT2A, and its impact on neuronal integrity in CHE, will greatly facilitate the identification of agents capable of ameliorating this debilitating condition.