Although children born to HIV-infected (HIV+) women receiving antiretroviral therapy during pregnancy show virtually no adverse clinical effects at birth, the antiretroviral nucleoside analog drugs are known to damage nuclear and mitochondrial DNA. In this study, biomarkers of mitochondrial toxicity and genotoxicity have been examined in a well-characterized sample set consisting of infants born to HIV-uninfected (HIV-) mothers (n = 30), and HIV- infants (n = 20) born to HIV-infected (HIV+) mothers who received either no antiretroviral therapy (n = 10) or zidovudine (3'-azido-3'-deoxythymidine [AZT]) during pregnancy (n = 10). DNA from cord blood leukocytes and peripheral blood leukocytes taken at 1 and 2 years of age was examined for loss of mitochondrial DNA (mtDNA) and telomere integrity. Telomere length, a measure of nuclear DNA damage, was the same in all infants at birth and at age 1 year. The quantity of mtDNA was assessed relative to nuclear DNA using a polymerase chain reaction-based chemiluminescence detection (PCR-CID) method that determined mitochondrial D Loop gene copies relative to nuclear 18S RNA gene copies by comparison with a standard curve. MtDNA quantity was expressed as a ratio of gene copy numbers. In infants of uninfected mothers (AZT-/HIV-) at the three time points, the ratios were 442 to 515, whereas in infants of untreated AZT-/HIV+ mothers the ratios were 261 to 297, and in infants of AZT-treated (AZT+/HIV+) mothers the ratios were 146 to 203. At all three time points, differences between the AZT-/HIV- group and the two HIV+ groups were statistically significant (p <.05), and differences between the AZT-/HIV+ and AZT+/HIV+ groups were also statistically significant (p <.05), demonstrating that AZT exposure causes a persistent depletion of mtDNA. The study shows that children of HIV+ mothers are at risk for mitochondrial damage that is further increased in infants of mothers receiving AZT during pregnancy.

HIV invades the brain during acute infection. Yet, it is unknown whether long-lived infected brain cells release productive virus that can egress from the brain to re-seed peripheral organs. This understanding has significant implication for the brain as a reservoir for HIV and most importantly HIV interplay between the brain and peripheral organs. Given the sheer number of astrocytes in the human brain and their controversial role in HIV infection, we evaluated their infection in vivo and whether HIV infected astrocytes can support HIV egress to peripheral organs. We developed two novel models of chimeric human astrocyte/ human peripheral blood mononuclear cells: NOD/scid-IL-2Rgc null (NSG) mice (huAstro/ HuPBMCs) whereby we transplanted HIV (non-pseudotyped or VSVg-pseudotyped) infected or uninfected primary human fetal astrocytes (NHAs) or an astrocytoma cell line (U138MG) into the brain of neonate or adult NSG mice and reconstituted the animals with human peripheral blood mononuclear cells (PBMCs). We also transplanted uninfected astrocytes into the brain of NSG mice and reconstituted with infected PBMCs to mimic a biological infection course. As expected, the xenotransplanted astrocytes did not escape/ migrate out of the brain and the blood brain barrier (BBB) was intact in this model. We demonstrate that astrocytes support HIV infection in vivo and egress to peripheral organs, at least in part, through trafficking of infected CD4+ T cells out of the brain. Astrocyte-derived HIV egress persists, albeit at low levels, under combination antiretroviral therapy (cART). Egressed HIV evolved with a pattern and rate typical of acute peripheral infection. Lastly, analysis of human cortical or hippocampal brain regions of donors under cART revealed that astrocytes harbor between 0.4-5.2% integrated HIV gag DNA and 2-7% are HIV gag mRNA positive. These studies establish a paradigm shift in the dynamic interaction between the brain and peripheral organs which can inform eradication of HIV reservoirs.

The Wnt/␤-catenin pathway is involved in diverse cell functions governing development and disease. ␤-Catenin, a central mediator of this pathway, binds to members of the TCF/LEF family of transcription factors to modulate hundreds of genes. Active Wnt/␤-catenin/TCF-4 signaling plays a significant role in repression of HIV-1 replication in multiple cell targets, including astrocytes. To determine the mechanism by which active ␤-catenin/TCF-4 leads to inhibition of HIV replication, we knocked down ␤-catenin or TCF/LEF members in primary astrocytes and astrocytomas transiently transfected with an HIV long terminal repeat (LTR)-luciferase reporter that contained an integrated copy of the HIV LTR-luciferase construct. Knockdown of either ␤-catenin or TCF-4 induced LTR activity by 2-to 3-fold under both the episomal and integrated conditions. This knockdown also increased presence of serine 2-phosphorylated RNA polymerase II (Pol II) on the HIV LTR as well as enhanced its processivity. Knockdown of ␤-catenin/TCF-4 also impacted tethering of other transcription factors on the HIV promoter. Specifically, knockdown of TCF-4 enhanced binding of C/EBP␤, C/EBP␦, and NF-B to the HIV LTR, while ␤-catenin knockdown increased binding of C/EBP␤ and C/EBP␦ but had no effect on NF-B. Approximately 150 genes in astrocytes were impacted by ␤-catenin knockdown, including genes involved in inflammation/immunity, uptake/transport, vesicular transport/exocytosis, apoptosis/ cellular stress, and cytoskeleton/trafficking. These findings indicate that modulation of the ␤-catenin/TCF-4 axis impacts the basal level of HIV transcription in astrocytes, which may drive low level/persistent HIV in astrocytes that can contribute to ongoing neuroinflammation, and this axis also has profound effects on astrocyte biology.

Typically, IFN-γ is an antiviral cytokine that inhibits the replication of many viruses, including HIV. However, in the CNS, IFN-γ induces HIV-productive replication in astrocytes. Although astrocytes in vitro are refractory to HIV replication, recent in vivo evidence demonstrated that astrocytes are infected by HIV, and their degree of infection is correlated with proximity to activated macrophages/microglia. The ability of IFN-γ to induce HIV replication in astrocytes suggests that the environmental milieu is critical in regulating the permissiveness of astrocytes to HIV infection. We evaluated the mechanism by which IFN-γ relieves restricted HIV replication in astrocytes. We demonstrate that although astrocytes have robust endogenous β-catenin signaling, a pathway that is a potent inhibitor of HIV replication, IFN-γ diminished β-catenin signaling in astrocytes by 40%, as evaluated by both active β-catenin protein expression and β-catenin-mediated T cell factor/lymphoid enhancer reporter (TOPflash) activity. Further, IFN-γ–mediated inhibition of β-catenin signaling was dependent on its ability to induce an antagonist of the β-catenin signaling pathway, Dickkopf-related protein 1, in a STAT 3-dependent manner. Inhibition of STAT3 and Dickkopf-related protein 1 abrogated the ability of IFN-γ to enhance HIV replication in astrocytes. These data demonstrated that IFN-γ induces HIV replication in astrocytes by antagonizing the β-catenin pathway. To our knowledge, this is the first report to point to an intricate cross-talk between IFN-γ signaling and β-catenin signaling that may have biologic and virologic effects on HIV outcome in the CNS, as well as on broader processes where the two pathways interface.

SUMMARYAside from an intermediate stage in thymic T-cell development, the expression of CD4 and CD8 is generally thought to be mutually exclusive, associated with helper or cytotoxic T-cell functions, respectively. Stimulation of CD8 + T cells, however, induces the de novo expression of CD4. We demonstrate that while superantigen (staphylococcal enterotoxin B, SEB) and anti-CD3/CD28 costimulation of puri®ed CD8