CD45 -mediated inhibition of HIV-1 Nef signaling in human microglia: Mechanisms and implications for AIDS dementia

Abstract

Microglia are involved in the regulation of inflammatory and anti-microbial responses during central nervous system infection. IFNbeta is an anti-viral cytokine induced by activated glial cells and inflammatory cells in HIV encephalitis. Because of the anti-inflammatory properties of IFNbeta, it is also used to treat multiple sclerosis. Despite the importance of IFNbeta signaling in CNS cells, little information is available, particularly in microglia. I investigated IFNbeta-induced signaling in primary human microglia and found that IFNbeta activates several signaling pathways. IFNbeta induced a nuclear factor-kappaB (NF-kappaB): DNA complex and adenovirus-mediated transduction of IkappaBalpha super repressor inhibited beta-chemokine production induced by IFNbeta. IFNbeta also activated ERK MAPK, which contributed to AP-1 activation and serine phosphorylation of Stat1 transcription factor. Because astrocytes are also significant producers of cytokines and chemokines, I then asked whether IFNbeta could trigger similar pathways in astrocytes. Using RANTES as the readout, I showed that in astrocytes IFNbeta alone did not activate NF-kappaB or MAPK, but it synergized with IL-1 to activate MAPK (p38) and the IFN-stimulated response element, as well as CCAAT enhancer binding protein (C/EBPbeta). Together, these studies revealed novel pathways of glial activation by IFNbeta that lead to chemokine induction. The proinflammatory activity of IFNbeta was surprising and demonstrates the complexity of the cytokine signaling that needs to be considered when interpreting the activity of IFNbeta in patients.;Microglia express CD45, a transmembrane protein tyrosine phosphatase critical in immune cell activation, but its role in the regulation of viral gene expression is unknown. In the second part of my thesis, I describe a novel role of CD45 in the inhibition of HIV-1 production in primary human microglia. Treatment of primary human microglia with an antibody to CD45RO induced tyrosine phosphatase activity and inhibited HIV-1 production, specifically HIV-1 long terminal repeat (LTR) activity by dephosphorylating HIV-1 negative factor (Nef)-induced phosphorylation of hematopoietic cell kinase (Hck). In kinase-inactive Hck expressing cells, HIV-1 LTR activity was not induced, possibly due to decreased activation NF-kappaB and C/EBP. Our results establish an anti-HIV-1 activity of microglial CD45 that targets Nef-Hck signaling and may help us to propose better therapies for HIV-1 encephalitis.