E2F1 induces neuroglial cell death by activation of the calpain pathway in an in vitro model of HIV Encephalitis

• Published in: Journal of neurovirology 2006-05, Vol.12, p.35-36
• Main Authors: Jordan-Sciutto, K L, Wang, Ying, Chodroff, R A, Strachan, G D, White, M G, Lindl, KA, Kolson, D L
• Format: Article
• Language: English
• Subjects: Adenovirus; Human immunodeficiency virus 1
• ISSN: 1355-0284

HIV Encephalitis (HIVE), the pathological substrate of HIV Associated Dementia (HAD) is characterized by microgliosis, astrogliosis, neuronal loss and dendritic damage. Neuronal damage in HIVE has been linked to soluble factors released by HIV infected macrophage/microglia that infiltrate the central nervous system (CNS), not direct neuronal infection. However, the exact mechanism of neuronal death in HIVE remains unknown. Interestingly, the proapoptotic cell cycle protein, E2F1, exhibits increased immunoreactivity and altered subcellular distribution in several neurodegenerative diseases including Alzheimer's Disease, Parkinson's Disease, Amyotrophic Lateral Sclerosis and HIVE. However, in these diseases E2F1 localized predominantly to the cytoplasm, a localization distinct from its well-defined nuclear role as a transcription factor during apoptosis and cell cycle progression. Based on these observations we hypothesized that cytoplasmic E2F1 might also contribute to neuronal death in HIVE. We used an in vitro model of HIVE in which we treated primary rat neuroglial cultures with supernatants from human monocyte-derived-macrophages infected with a neurovirulent strain of HIV-1 (HIV M/M). Using a concentration of HIV M/M that produced 50% neuronal loss by 20 hours, we observed increased E2F1 expression, accompanied by increased calpain activation by western blotting. To determine if increased expression of cytoplasmic E2F1 increased calpain activity, we utilized adenovirus vectors to express a cytoplasm-localized E2F1 deletion mutant (E2F1 (ISO-437)). As predicted, we observed increased calpain activity and cell loss. Furthermore, we observed an increase in E2F1/14-3-3 complex formation in our HIV M/M exposed cultures; such complex formation has been associated with increased E2F1 protein stability. Based on our in vitro observations, we propose that increased E2F1 stability mediated by 14-3-3 binding and cytoplasmic complex formation may contribute to calpain activation and subsequent neuronal death in HIVE.