Phosphorylation of pRb is differentially regulated in neurons in HIV-Associated Dementia

• Published in: Journal of neurovirology 2007-01, Vol.13, p.61-61
• Main Authors: Akay, C, Wang, Y, Chodroff, R A, Kolson, D L, Jordan-Sciutto, K L
• Format: Article
• Language: English
• Subjects: Human immunodeficiency virus 1
• ISSN: 1355-0284

HIV Associated Dementia (HAD) is characterized by microgliosis, astrogliosis, neuronal loss and dendritic damage. While the mechanisms of neuronal death in HAD remain only partially defined, neuronal damage has been linked to soluble factors released by HIV infected, and non-infected, activated macrophages/microglia in the brain. The inflammatory infiltrate secretes both neurotoxic and neuroprotective factors. Phosphorylation of pRb has been shown to be required in in vitro models of neuronal apoptosis including trophic factor withdrawal, beta-amyloid treatment and oxidative stress. To define the differential effects of neurotoxic and neuroprotective factors on pRb phosphorylation in HAD, we used an in vitro model where we treated primary rat neuroglial cultures with supematants from human monocyte-derived-macrophages infected with a neurovirulent strain of HIV-1 (HIV-M/M). We assessed pRb phosphorylation on characterized sites and the interaction of these phospho-pRb isoforms with cell cycle proteins. Using dilutions of HIV-M/M that produced 25% neuronal loss by 4 hours or 50% neuronal loss by 20 hours, we observed an early increase in p-pRbSer249/Thr252, and p-pRbSer795 by western blotting (WB), and a late increase in p-pRbSer780 by HIV-M/M by both WB and immunofluorescence (IF), similar to results obtained in cultures treated with Rantes. BDNF led to a delayed increase in these p-pRb epitopes. We observed similar increases by WB and IFA in the mid-frontal cortices of autopsied brain tissue of HIV(+) individuals. We did not observe an increase in p-pRbSer608 or p-pRbThr821 levels with either HIV-M/M, BDNF or Rantes by WB in vivo. Interestingly, p-pRbSer807/811, which was observed in the cytoplasm of untreated neurons by IF, was detected in the nuclei of neurons in HIV M/M treated cultures, while its protein levels were not increased, as assessed by WB. p-pRbSer807/811 is a known epitope for cdk5. By co-immunoprecipitation, we observed a loss of interaction of p-pRbSer807/811 with cdk5 when cultures were exposed to HIV-M/M, whereas it was not disrupted in response to BDNF, Rantes or NGF treatment. Thus, we hypothesize that phosphorylation of pRb is differentially regulated in neurons in response to neurotrophic factors and the binding between p-pRbSer807/811 and cdk5 might be a determining factor in neuronal viability.