APOBEC3G mRNA expression in exposed seronegative and early stage HIV infected individuals decreases with removal of exposure and with disease progression

Abstract

Background: APOBEC3G is an antiretroviral factor that acts by inducing G to A mutations. In this study, we examined the expression of APOBEC3G in uninfected HIV-1 exposed individuals at the time of their partner's diagnosis and one year later. We then compared this expression with that of infected individuals at different disease stages. APOBEC3G mRNA was measured in PBMCs from three groups: healthy controls with no known risk factor to HIV infection (n = 26), exposed uninfected individuals who had unprotected sex with their HIV+ partners for at least 3 months (n = 37), and HIV infected patients at various disease stages (n = 45), including 8 patients with low HIV viral loads < 10,000 copies/mL (LVL) for at least 3 years. Additionally, we obtained sequences from the env, gag, pol, nef, vif and the LTR of the patients' virus.

Results: Exposed uninfected individuals expressed higher APOBEC3G than healthy controls (3.86 vs. 1.69 relative expression units), and their expression significantly decreased after a year from the HIV diagnosis and subsequent treatment of their partners. Infected individuals showed a positive correlation (Rho = 0.57, p = 0.00006) of APOBEC3G expression with CD4+ T cell count, and a negative correlation with HIV viremia (Rho = -0.54, p = 0.00004). The percentage of G to A mutations had a positive correlation (Rho = 0.43, p = 0.0226) with APOBEC3G expression, and it was higher in LVL individuals than in the other patients (IQR 8.27 to 9.64 vs. 7.06 to 8.1, p = 0.0084). Out of 8 LVLs, 3 had hypermutations, and 4 had premature stop codons only in viral vif.

Conclusion: The results suggest that exposure to HIV may trigger APOBEC3G expression in PBMCs, in the absence of infection. Additionally, cessation of exposure or advanced disease is associated with decreased APOBEC3G expression.

Figure 1

hA3G mRNA expression in ES, HC and HIV infected patients at different stages of disease. Results for log hAG3 mRNA expression in healthy control subjects, exposed seronegative individuals, HIV+ patients that have consistently low viral loads (LVL) < 10,000 copies/μL for at least 3 years, and typical progressors. Typical progressors are shown as a regression over CD4+ cell/μL, with Spearman's Rho and significance marked. Horizontal lines show the median, sloped solid line is the linear regression, and the flanking dashed lines show the 95% confidence interval for the mean. Horizontal lines with arrows show the significant differences between groups (Mann-Whitney's U test).

Figure 2

Relationship between log hA3G mRNA expression with log viral load. The sloped solid line is the linear regression, and the flanking dashed lines show the 95% confidence interval for the mean (Rho = -0.5418, p = 0.00004). Solid dots represent subjects with persistent < 10,000 copies/mL for more than 3 years, and the open dots are typical progressors.

Figure 3

hA3G mRNA expression in ES after one year ofexposure. Left panel. hA3G mRNA expression in exposed seronegative subjects at time of diagnosis of their partners, and after one year of follow up. There was a significant decrease (p = 0.0022, Wilcoxon sign test). The inset box plot is healthy control expression level, for reference purposes only. Right panel. Viral load in the partners of the ES subjects after a year of treatment. The overall reduction was also significant (Wicoxon's sign test p = 0.018).

Figure 4

Analysis of complete vif sequences derived from 20 different HIV+ individuals. Graphical representation of the G to A changes compared with HIV HXB2 reference. The nucleotide context GG, GA, GC or GT represents two contiguous bases, with G to A mutations occurring in the first base. hA3G mRNA levels are shown on the left column and significant hA3G-type hypermutations on the right column. The three significantly hypermutataded sequences are from patients having < 10,000 viral copies/mL for over three years.