Clade C HIV-1 isolates circulating in Southern Africa exhibit a greater frequency of dicysteine motif-containing Tat variants than those in Southeast Asia and cause increased neurovirulence.

BACKGROUND: HIV-1 Clade C (Subtype C; HIV-1C) is responsible for greater than 50% of infections worldwide. Unlike clade B HIV-1 (Subtype B; HIV-1B), which is known to cause HIV associated dementia (HAD) in approximately 15% to 30% of the infected individuals, HIV-1C has been linked with lower prevalence of HAD (0 to 6%) in India and Ethiopia. However, recent studies report a higher prevalence of HAD in South Africa, Zambia and Botswana, where HIV-1C infections predominate. Therefore, we examined whether Southern African HIV-1C is genetically distinct and investigated its neurovirulence. HIV-1 Tat protein is a viral determinant of neurocognitive dysfunction. Therefore, we focused our study on the variations seen in tat gene and its contribution to HIV associated neuropathogenesis. RESULTS: A phylogenetic analysis of tat sequences of Southern African (South Africa and Zambia) HIV isolates with those from the geographically distant Southeast Asian (India and Bangladesh) isolates revealed that Southern African tat sequences are distinct from Southeast Asian isolates. The proportion of HIV - 1C variants with an intact dicysteine motif in Tat protein (C30C31) was significantly higher in the Southern African countries compared to Southeast Asia and broadly paralleled the high incidence of HAD in these countries. Neuropathogenic potential of a Southern African HIV-1C isolate (from Zambia; HIV-1C 1084i), a HIV-1C isolate (HIV-1 IndieC1) from Southeast Asia and a HIV-1B isolate (HIV-1 ADA) from the US were tested using in vitro assays to measure neurovirulence and a SCID mouse HIV encephalitis model to measure cognitive deficits. In vitro assays revealed that the Southern African isolate, HIV-1C 1084i exhibited increased monocyte chemotaxis and greater neurotoxicity compared to Southeast Asian HIV-1C. In neurocognitive tests, SCID mice injected with MDM infected with Southern African HIV-1C 1084i showed greater cognitive dysfunction similar to HIV-1B but much higher than those exposed to Southeast Asian HIV - 1C. CONCLUSIONS: We report here, for the first time, that HIV-1C from Southern African countries is genetically distinct from Southeast Asian HIV-1C and that it exhibits a high frequency of variants with dicysteine motif in a key neurotoxic HIV protein, Tat. Our results indicate that Tat dicysteine motif determines neurovirulence. If confirmed in population studies, it may be possible to predict neurocognitive outcomes of individuals infected with HIV-1C by genotyping Tat.

Comparative longitudinal studies of HERV-K and HIV-1 RNA titers in HIV-1-infected patients receiving successful versus unsuccessful highly active antiretroviral therapy.

The viral kinetics of HERV-K in HIV-1-infected patients receiving highly active antiretroviral therapy (HAART) is not unknown. HERV-K kinetic modeling may provide insight into factors altering the effectiveness of HAART in suppressing HIV-1 burden. We conducted a longitudinal study measuring the HERV-K RNA titers in four patients with successful HIV-1-suppressive HAART and in six patients undergoing HAART failure. HERV-K titers were usually undetectable in patients with successful HAART, and when detected, HERV-K titers remained below 5000 copies/ml. On the other hand, HERV-K RNA was consistently detected in patients who failed to respond to HAART before and after HIV-1 rebounds (p < 0.001). Elevated HERV-K RNA titers frequently preceded HIV-1 rebounds. These results suggest that HERV-K viral load may predict HIV-1 reactivation. HERV-K RNA testing might be clinically useful in predicting the onset of HIV-1 resistance due to suboptimal antiretroviral drug levels and/or poor adherence to treatment.

A new Real-Time-RT-PCR for quantitation of human endogenous retroviruses type K (HERV-K) RNA load in plasma samples: increased HERV-K RNA titers in HIV-1 patients with HAART non-suppressive regimens.

Viral components of the human endogenous retroviruses type K (HERV-K) have been largely detected in plasma from HIV-1 infected individuals. A Sybr Green Real-Time RT-PCR approach was optimized for detection and quantitation of HERV-K RNA titers in plasma samples using the iCycler technology. The method detected 1000 HERV-K RNA copies/mL of plasma sample. The Intra- and Inter-assay performance revealed a coefficient of variations that ranged from 0.2 to 2.46%, demonstrating accuracy and reproducibility. We quantified the HERV-K RNA load in 20 HIV-1 patients receiving highly active antiretroviral therapy (HAART). We found increased HERV-K RNA titers in patients with non-suppressive HAART (patients who may develop drug-resistance and/or received suboptimal therapeutic doses), compared to suppressive regimens (p < 0.001). HERV-K RNA was not detected in HCV-1 positive or seronegative controls. Sequencing of Real-Time RT-PCR products revealed particular HERV-K subtypes activated in the HIV-1 infection. The application of this assay could expand the understanding of the role of HERV-K in the HIV-1 infection and others pathological conditions.

A twin-cysteine motif in the V2 region of gp120 is associated with SIV envelope trimer stabilization.

The V1 and V2 variable regions of the primate immunodeficiency viruses contribute to the trimer association domain of the gp120 exterior envelope glycoprotein. A pair of V2 cysteine residues at 183 and 191 ("twin cysteines") is present in several simian immunodeficiency viruses, human immunodeficiency virus type 2 (HIV-2) and some SIV(cpz) lineages, but not in HIV-1. To examine the role of this potentially disulfide-bonded twin-cysteine motif, the cysteine residues in the SIVmac239 envelope glycoproteins were individually and pairwise substituted by alanine residues. All of the twin-cysteine mutants exhibited decreases in gp120 association with the Env trimer, membrane-fusing activity, and ability to support virus entry. Thus, the twin-cysteine motif plays a role in Env trimer stabilization in SIV and may do so in HIV-2 and some SIV(cpz) as well. This implies that HIV-1 lost the twin-cysteines, and may have relatively unstable Env trimers compared to SIV and HIV-2.