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APOBEC3G expression is restricted to neurons in the brains of pigtailed macaques
M Sarah Hill1, Ellyn R Mulcahy, Melissa L Gomez
1Department of Anatomy and Cell Biology, 5007 Wahl Hall West, University of Kansas Medical Center, Kansas City, Kansas 66160, USA.
Abstract:
The Vif protein of human immunodeficiency virus-1 (HIV-1) has been shown to interact with members of the APOBEC family of cytidine deaminases, particularly APOBEC3G/F. In this study, we isolated RNA from 12 regions of the brain from two pigtailed macaques that were exsanguinated and perfused with saline. Our results indicate that APOBEC3G was detected in all regions of the brain analyzed. Immunoblot analysis using lysates prepared from these same regions of the brain and a monoclonal antibody to APOBEC3G confirmed the RT-PCR findings. To determine which cell types express APOBEC3G, immunohistochemical studies were performed using this monoclonal antibody on whole brain sections. Our results clearly show that the pyramidal neurons within the gray matter of cerebral and cerebellar cortices express APOBEC3G. However, APOBEC3G expression in the pyramidal neurons appeared to be nuclear or associated with nuclei. In contrast to our findings in the cerebral cortex, immunohistochemical analysis of the spleen and kidney tissues revealed that APOBEC3G expression in the cells of these tissues was predominantly cytoplasmic. We further investigated the expression of APOBEC3G in astrocytes. Immunohistochemical staining of serial sections was performed using antibodies to glial fibrillary acidic protein (GFAP) and APOBEC3G. As expected, the cortical and cerebellar white matter showed extensive immunostaining of astrocytes with the antibody against GFAP but a lack of reactivity to the antibody to APOBEC3G. Additionally, Immunoblot analysis of lysates prepared from primary human fetal astrocytes revealed a lack of APOBEC3G expression. Taken together, these results indicate that APOBEC3G expression is restricted to neurons in the brain and that astrocytes and microglia probably do not express this protein or express it at levels undetectable by immunohistochemistry. These finding have implications for the brain as a potential reservoir for Vif-defective viruses.
Insights
APOBEC3G, a key protein interacting with HIV-1 Vif, is found in macaque brain neurons but not in astrocytes or microglia. This suggests the brain may harbor Vif-defective viruses.
Area of Science:
- Neuroscience
- Virology
- Immunology
Background:
- The Vif protein of human immunodeficiency virus-1 (HIV-1) interacts with APOBEC cytidine deaminases, including APOBEC3G/F.
- APOBEC3G is implicated in innate antiviral defense mechanisms.
Purpose of the Study:
- To investigate the expression and cellular localization of APOBEC3G in the brain.
- To determine if astrocytes and microglia express APOBEC3G.
- To assess the implications of APOBEC3G expression in the brain for HIV-1 reservoirs.
Main Methods:
- RNA isolation from 12 macaque brain regions.
- Reverse transcription-polymerase chain reaction (RT-PCR) for APOBEC3G detection.
- Immunoblot analysis using a monoclonal antibody against APOBEC3G.
- Immunohistochemical studies on brain sections, spleen, and kidney.
- Immunohistochemical staining for glial fibrillary acidic protein (GFAP) to identify astrocytes.
- Immunoblot analysis of primary human fetal astrocytes.
Main Results:
- APOBEC3G was detected in all analyzed brain regions of pigtailed macaques.
- Immunohistochemistry confirmed APOBEC3G expression in pyramidal neurons within the cerebral and cerebellar cortices, with nuclear localization.
- APOBEC3G was predominantly cytoplasmic in spleen and kidney cells.
- Astrocytes in white matter and primary human fetal astrocytes showed no detectable APOBEC3G expression.
Conclusions:
- APOBEC3G expression in the brain is primarily restricted to neurons.
- Astrocytes and microglia likely do not express APOBEC3G at detectable levels.
- The brain's neuronal APOBEC3G expression has implications for the potential of the brain to act as a reservoir for Vif-defective HIV-1 strains.
