Date of Award
Doctor of Philosophy (PhD)
HIV-associated neurocognitive disorders (HAND) are a spectrum of HIV-related conditions affecting the central nervous system that range from mild memory impairments to severe dementia. HAND results from the release of inflammatory factors and excitotoxins by HIV-infected macrophages in the brain. These factors alter the extracellular environment and provoke a neuronal response, ultimately causing dendritic damage, synaptic loss, and neuronal death. Our previous data indicate that components of the cell cycle regulatory machinery are elevated in neurons from post-mortem brain tissue of HAND patients. One of these upregulated proteins, the transcription factor E2F1, is known to activate gene targets required for G1-to-S phase progression as well as for apoptosis. Despite its increased neuronal expression, E2F1 target genes are unchanged by HIV-induced neuronal damage in vitro. Furthermore, E2F1 displays a predominantly cytoplasmic localization, a site inconsistent with its role as a transcription factor.
Utilizing an in vitro model of HIV-induced neurotoxicity, we assessed the role of E2F1 in HIV-mediated neuronal damage. To begin, we evaluated the contributions of two death pathways - calpain-mediated and caspase-mediated cell death - in cortical neurons treated with H2O2 and NMDA as they mature in culture. Although both calpain-activated and caspase-activated death were detected in cortical neurons at 1 week of age, only calpain-mediated neuronal death was observed at 3 weeks of age, suggesting that calpain is the dominant death pathway. We then tested the effect of E2F1 gene disruption on HIV-induced neuronal loss. Neuronal damage and death was significantly attenuated in neurons expressing mutant E2F1 protein compared to wildtype cultures. Furthermore, we identified E2F1 as a novel calpain substrate and showed that E2F1 cleavage by calpain produces an E2F1 fragment that stably accumulates in neurons during HIV-mediated neuronal damage, suggesting a neurotoxic role for this E2F1 isoform. Finally, preliminary studies to investigate a putative RNA-binding role for E2F1 in the neuronal cytosol are outlined. Together, these data implicate E2F1 in a calpain-mediated pathway of HIV-induced neurotoxicity. Future work to understand the role of E2F1 in neurons and the consequences of calpain cleavage of E2F1 could provide important insights into disease progression and therapeutic strategies.
Zyskind, Jacob, "A Role for Cell Cycle Protein E2F1 in HIV-Induced Neurotoxicity" (2015). Publicly Accessible Penn Dissertations. 1174.