Current HIV Research - Volume 12, Issue 3, 2014

In the previous issue of Current HIV Research, we introduced a series of research and review articles (Part I) emphasizing the role of macrophages in the pathogenesis of AIDS and CNS diseases, as well as implications for therapeutic intervention. We present several additional articles, in Part II of this issue, further emphasizing the importance of host-virus interactions in disease and consideration for avenues of therapy and new investigation. An interesting mechanism of host dysregulation of gene expression is demonstrated here by Duan et al. where HIV-1 Tat protein impairs factalkine gene expression, leading to impaired microglial-neuronal interactions and concomitant activation of inflammation (i.e. the NFkB pathway) [3]. It is interesting to speculate that Tat, through fractalkine dysregulation, may alter the retention and migration properties of peripheral derived macrophages, and thereby contributes to the pathogenesis of HIV in CNS as well as the reservoir of infection. At the same time, down-modulation of the host-factor, heme oxygenase (HO-1), permits increased release of macrophage derived glutamate, which in turn can exert toxic effects on neurons. This mechanism, as well as pharmacological modulation of HO-1 and neurotoxicity, suggests that pharmacological HO-modulation may have therapeutic efficacy, as discussed in the paper by Ambegaokar [2], in HIV induced CNS disorders as well as in other diseases associated with neurotoxicity. The monocyte/macrophage system is of interest in the context of HIV replication as macrophages provide an important reservoir of HIV infection and contribute to immune dysregulation. Upon differentiation macrophages become highly susceptible to HIV infection, relative to monocytes. The paper by Alijawai et al. demonstrates how modulation of the Wnt/ßcatenin signaling pathway can serve as a restriction mechanism in monocytes, with down-modulation of ß-catenin upon differentiation [1]. The authors further pointed out that Wnt ligands could be involved in the suppression of post integration HIV replication events in macrophages exposed to soluble factors produced by monocytes. As such, pharmacological intervention with the Wnt/ß-catenin signaling pathway could be used to suppress HIV replication, or alternatively, to activate latent reservoirs of HIV infection. Peripheral derived monocytes/macrophages and/or activated microglia play prominent roles in the pathogenesis of HIV in CNS, as discussed throughout part I and II of this thematic issue. The alteration of the myeloid lineage in the setting of HIV infection and increased organ invasion is not limited to the CNS, at least in the setting of encephalitis. Here, our group demonstrates macrophage invasion into visceral tissues in patients with HIV encephalitis, with evidence of underlying renal disease. It is apparent that altered monocyte/macrophage homeostasis tissue invasion in HIV infection contribute to comorbid conditions in AIDS according to Fischer et al. [4]. As tissue invasion in patients with AIDS, but without encephalitis, also appears to be increased, altered macrophage trafficking may play an important role in immune dysfunction and comorbidities in patients with HIV infection and AIDS. It is likely that strategies directed to specific pathways dysregulated in HIV infection, or through utilization of strategies to normalize immune polarization, activation, and/or migration into tissues may be important, not only to address CNS associated manifestations of HIV infection, but also to treat comorbidities involving altered myeloid homeostasis and trafficking. In the coming years, studies in these directions should provide insights and novel therapeutic strategies, well beyond the context of HIV infection.

Cells of the monocyte/macrophage lineage are an important target for HIV-1 infection. They are often at anatomical sites linked to HIV-1 transmission and are an important vehicle for disseminating HIV-1 throughout the body, including the central nervous system. Monocytes do not support extensive productive HIV-1 replication, but they become more susceptible to HIV-1infection as they differentiate into macrophages. The mechanisms guiding susceptibility of HIV-1 replication in monocytes versus macrophages are not entirely clear. We determined whether endogenous activity of β-catenin signaling impacts differential susceptibility of monocytes and monocyte-derived macrophages (MDMs) to productive HIV-1 replication. We show that monocytes have an approximately 4-fold higher activity of β-catenin signaling than MDMs. Inducing β-catenin in MDMs suppressed HIV-1 replication by 5-fold while inhibiting endogenous β-catenin signaling in monocytes by transfecting with a dominant negative mutant for the downstream effector of β- catenin (TCF-4) promoted productive HIV-1 replication by 6-fold. These findings indicate that β-catenin/TCF-4 is an important pathway for restricted HIV-1 replication in monocytes and plays a significant role in potentiating HIV-1 replication as monocytes differentiate into macrophages. Targeting this pathway may provide a novel strategy to purge the latent reservoir from monocytes/macrophages, especially in sanctuary sites for HIV-1 such as the central nervous system.

Heme oxygenase-1 (HO-1) is a highly inducible and ubiquitous cellular enzyme that subserves cytoprotective responses to toxic insults, including inflammation and oxidative stress. In neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and multiple sclerosis, HO-1 expression is increased, presumably reflecting an endogenous neuroprotective response against ongoing cellular injury. In contrast, we have found that in human immunodeficiency virus (HIV) infection of the brain, which is also associated with inflammation, oxidative stress and neurodegeneration, HO-1 expression is decreased, likely reflecting a unique role for HO-1 deficiency in neurodegeneration pathways activated by HIV infection. We have also shown that HO-1 expression is significantly suppressed by HIV replication in cultured macrophages which represent the primary cellular reservoir for HIV in the brain. HO-1 deficiency is associated with release of neurotoxic levels of glutamate from both HIV-infected and immune-activated macrophages; this glutamate-mediated neurotoxicity is suppressed by pharmacological induction of HO-1 expression in the macrophages. Thus, HO-1 induction could be a therapeutic strategy for neuroprotection against HIV infection and other neuroinflammatory brain diseases. Here, we review various stimuli and signaling pathways regulating HO-1 expression in macrophages, which could promote neuronal survival through HO-1-modulation of endogenous antioxidant and immune modulatory pathways, thus limiting the oxidative stress that can promote HIV disease progression in the CNS. The use of pharmacological inducers of endogenous HO-1 expression as potential adjunctive neuroprotective therapeutics in HIV infection is also discussed.

Microglia are critical for the pathogenesis of HIV-associated dementia not only by acting as conduits of viral entry but also as reservoirs for productive and latent virus infection, and as producers of neurotoxins. Interaction between CX3CL1 (fractalkine) and FKN receptor (CX3CR1) is highly functional in the brain, and is known to regulate a complex network of paracrine and autocrine interactions between neurons and microglia. The aim of the present study was to determine which extent of HIV-1 Tat protein causes the alteration of CX3CR1 expression and to investigate the regulatory mechanism for CX3CR1 expression. Here we showed that exposure of primary microglia and BV2 cells to exogenous Tat protein resulted in down-regulation of CX3CR1 mRNA and protein expression, with a concomitant induction of proinflammatory responses. Next, we further showed that NF-κB activation by Tat treatment negatively regulated CX3CR1 expression. Since a YY1 binding site ~10kb upstream of CX3CR1 promoter was predicted in rats, mice and humans, the classical NF-κB-YY1 regulatory pathway was considered. Our findings indicated that Tat repressed CX3CR1 expression via NF-κB-YY1 regulatory pathway. To gain insight into the effect of Tat on CX3CL1-CX3CR1 communication, calcium mobilization, MAPK activation and microglial migration, respectively, were tested in microglial cells after successive treatment with Tat and CX3CL1. The results suggested that Tat disrupted the responses of microglia to CX3CL1. Taken together, these results demonstrate that HIV-1 Tat protein suppresses CX3CR1 expression in microglia via NF-κB-YY1 pathway and attenuates CX3CL1-induced functional response of microglia.

The invasion of circulating monocytes/macrophages (Mφ)s from the peripheral blood into the central nervous system (CNS) appears to play an important role in the pathogenesis of HIV dementia (HIV-D), the most severe form of HIV-associated neurocognitive disorders (HAND), often confirmed histologically as HIV encephalitis (HIVE). In order to determine if trafficking of monocytes/Mφs is exclusive to the CNS or if it also occurs in organs outside of the brain, we have focused our investigation on visceral tissues of patients with HIVE. Liver, lymph node, spleen, and kidney autopsy tissues from the same HIVE cases investigated in earlier studies were examined by immunohistochemistry for the presence of CD14, CD16, CD68, Ki-67, and HIV-1 p24 expression. Here, we report a statistically significant increase in accumulation of Mφs in kidney, spleen, and lymph node tissues in specimens from patients with HIVE. In liver, we did not observe a significant increase in parenchymal macrophage accumulation, although perivascular macrophage accumulation was consistently observed with nodular lesions in 4 of 5 HIVE cases. We also observed an absence of CD14 expression on splenic Mφs in HIVE cases, which may implicate the spleen as a potential source of increased plasma soluble CD14 in HIV infection. HIV-1 p24 expression was observed in liver, lymph node and spleen but not kidney. Interestingly, renal pathology suggestive of chronic tubulointerstitial nephritis (possibly due to chronic pyelonephritis), including tubulointerstitial scarring, chronic interstitial inflammation and focal global glomerulosclerosis, without evidence of HIV-associated nephropathy (HIVAN), was seen in four of eight HIVE cases. Focal segmental and global glomerulosclerosis with tubular dilatation and prominent interstitial inflammation, consistent with HIVAN, was observed in two of the eight cases. Abundant cells expressing monocyte/Mφ cell surface markers, CD14 and CD68, were also CD16+ and found surrounding dilated tubules and adjacent to areas of glomerulosclerosis. The finding of co-morbid HIVE and renal pathology characterized by prominent interstitial inflammation may suggest a common mechanism involving the invasion of activated monocytes/Mφs from circulation. Monocyte/Mφ invasion of visceral tissues may play an important role in the immune dysfunction as well as comorbidity in AIDS and may, therefore, provide a high value target for the design of therapeutic strategies.

Nef is one of the accessory proteins of the human immunodeficiency virus type 1 (HIV-1). Nef is translated from multiple-spliced mRNAs transcribed from the viral genome, whose mRNAs have a relatively long 5' untranslated region (5'UTR). Here, we identified a cis element in the 5'UTR of Nef mRNA essential for efficient Nef translation, which was named the Nef-translation essential region (NER). Mutants with a deleted NER in the 5'UTR of the HIV-1 NL4-3 strain showed an almost undetectable Nef expression owing to a low Nef translation efficiency. The NER of the NL4-3 strain was predicted to form putative stem loops. Although the 5'UTR showed significant but relatively low internal ribosome entry site (IRES) activity, the mechanism of 5’cap-dependent translation mainly contributed to the Nef translation from its Nef mRNA. Altogether, it was clarified that not only the 5' cap but also the NER in the 5'UTR is an essential cis element for efficient Nef translation, which is not a typical 5'-cap-dependent mechanism, and that there must be an as yet unknown mechanism using the NER for efficient Nef translation.

Immunologic and genetic factors are involved in HIV-1/AIDS pathogenesis. Defensins are key molecules in innate immunity that participate in the control and/or development of infection and disease. Using PCR-RFLPs, we determined the association between HIV-1/AIDS and human β-defensin 1 (DEFB1) 5’UTR -52 G/A (rs1799946), -44 C/G (rs1800972), and -20 G/A (rs11362) polymorphisms in three groups of women from the state of Sinaloa, located in the Northwest region of Mexico: i) healthy blood donors; ii) sex-workers; and iii) HIV-1 patients. The -52GG genotype was more frequent in blood donors than in patients (p= 0.023; Odds Ratio, OR= 0.49; 95% CI= 0.25–0.95), whereas the - 52GA genotype was significantly higher in patients (p= 0.013; OR= 2.03; 95% CI= 1.11−3.79, statistical power SP= 98.8%), as well as the frequencies of -20A allele (p= 0.017; OR= 1.60; 95% CI= 1.06−2.40), -20AA genotype (p= 0.047; OR = 2.02; 95% CI= 0.93−4.33) and the ACA haplotype with respect to healthy blood donors (p= 0.000012; OR= 5.82; 95% CI= 2.33–16.43, SP= 99.89%) and sex-workers (p= 0.019; OR= 2.18; 95% CI= 1.07–4.46). Conversely, the ACG haplotype was higher in healthy blood donors than in patients (p= 0.009; OR= 0.55; 95% CI= 0.34–0.89). In addition, the -44CC genotype was associated with a low plasma viral load (p= 0.015), whereas AGA, AGG and GGA haplotypes were more prevalent in individuals with high CD4 counts (p= 0.004, 0.046, and 0.029, respectively). These findings associate DEFB1 5’UTR polymorphisms with HIV-1/AIDS in Mexican women for the first time.

Antiretroviral (ARV) prophylaxis for prevention of mother to child transmission (MTCT) of HIV could affect hemoglobin (Hb) development of infants. A cross-sectional descriptive study was conducted in 24 HIV-infected and 21 HIV-uninfected pregnancies. ARV drugs were administered to HIV-infected pregnancies at 21 weeks of gestational age and at labor. Their infants received zidovudine (ZDV) until 4 weeks of age. Blood samples of ARV-exposed and - unexposed infants were collected at delivery, 1, 2 and 4 months of age. Molecular analyses for α-thalassemia-1 Southeast Asian (SEA) type deletion, β-thalassemia mutations and Hb E were performed for excluding the thalassemia carrier infants. Hemoglobinopathy and Hb A, Hb F and Hb A2 were analyzed by using capillary electrophoresis (CE) while hematological parameters were measured using an automated blood counter. At delivery, 1 and 2 months of age, ARVexposed infants had significantly lower levels of RBC counts than ARV-unexposed infants (3.56 vs 4.90, 2.66 vs 4.62 and 3.01 vs 4.05 x1012/L; P <0.001, <0.001 and 0.001, respectively). At delivery, there was a trend for low hemoglobin level in the group of ARV-exposed infants as compared to the group of ARV-unexposed infants (149 vs 154 g/L; P = 0.09) and the significantly different levels were observed among the two groups at 1 and 2 months of age (89 vs 136 and 87 vs 110 g/L; P < 0.001 and 0.001, respectively). The development of Hb A, Hb F and Hb A2 levels from delivery to 4 months of age among the two groups was not significantly different. Therefore, ARV treatments for prevention of MTCT of HIV decreased RBC counts and hemoglobin but did not alter the development of Hb A, Hb F and Hb A2 of non-thalassemia carrier infants.