Current HIV Research (v.12, #3)
Editorial (Thematic Issue: The Monocyte/Macrophage in the Pathogenesis of AIDS: The Next Frontier for Therapeutic Intervention in the CNS and Beyond: Part II) (163-163).
In the previous issue of Current HIV Research, we introduced a series of research and review articles (Part I) emphasizing therole of macrophages in the pathogenesis of AIDS and CNS diseases, as well as implications for therapeutic intervention. Wepresent several additional articles, in Part II of this issue, further emphasizing the importance of host-virus interactions indisease and consideration for avenues of therapy and new investigation. An interesting mechanism of host dysregulation ofgene expression is demonstrated here by Duan et al. where HIV-1 Tat protein impairs factalkine gene expression, leading toimpaired microglial-neuronal interactions and concomitant activation of inflammation (i.e. the NFkB pathway) . It isinteresting to speculate that Tat, through fractalkine dysregulation, may alter the retention and migration properties ofperipheral derived macrophages, and thereby contributes to the pathogenesis of HIV in CNS as well as the reservoir ofinfection. At the same time, down-modulation of the host-factor, heme oxygenase (HO-1), permits increased release ofmacrophage derived glutamate, which in turn can exert toxic effects on neurons. This mechanism, as well as pharmacologicalmodulation of HO-1 and neurotoxicity, suggests that pharmacological HO-modulation may have therapeutic efficacy, asdiscussed in the paper by Ambegaokar , in HIV induced CNS disorders as well as in other diseases associated withneurotoxicity.The monocyte/macrophage system is of interest in the context of HIV replication as macrophages provide an importantreservoir of HIV infection and contribute to immune dysregulation. Upon differentiation macrophages become highlysusceptible to HIV infection, relative to monocytes. The paper by Alijawai et al. demonstrates how modulation of the Wnt/Βcateninsignaling pathway can serve as a restriction mechanism in monocytes, with down-modulation of Β-catenin upondifferentiation . The authors further pointed out that Wnt ligands could be involved in the suppression of post integrationHIV replication events in macrophages exposed to soluble factors produced by monocytes. As such, pharmacologicalintervention with the Wnt/Β-catenin signaling pathway could be used to suppress HIV replication, or alternatively, to activatelatent 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 infectionand increased organ invasion is not limited to the CNS, at least in the setting of encephalitis. Here, our group demonstratesmacrophage invasion into visceral tissues in patients with HIV encephalitis, with evidence of underlying renal disease. It isapparent that altered monocyte/macrophage homeostasis tissue invasion in HIV infection contribute to comorbid conditions inAIDS according to Fischer et al. . As tissue invasion in patients with AIDS, but without encephalitis, also appears to beincreased, altered macrophage trafficking may play an important role in immune dysfunction and comorbidities in patients withHIV infection and AIDS. It is likely that strategies directed to specific pathways dysregulated in HIV infection, or throughutilization of strategies to normalize immune polarization, activation, and/or migration into tissues may be important, not onlyto address CNS associated manifestations of HIV infection, but also to treat comorbidities involving altered myeloidhomeostasis and trafficking. In the coming years, studies in these directions should provide insights and novel therapeuticstrategies, well beyond the context of HIV infection.
β-Catenin/TCF-4 Signaling Regulates Susceptibility of Macrophages and Resistance of Monocytes to HIV-1 Productive Infection by Yosra Aljawai, Maureen H. Richards, Melanie S. Seaton, Srinivas D. Narasipura, Lena Al-Harthi (164-173).
Cells of the monocyte/macrophage lineage are an important target for HIV-1 infection. They are often atanatomical 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 becomemore susceptible to HIV-1infection as they differentiate into macrophages. The mechanisms guiding susceptibility ofHIV-1 replication in monocytes versus macrophages are not entirely clear. We determined whether endogenous activity ofβ-catenin signaling impacts differential susceptibility of monocytes and monocyte-derived macrophages (MDMs) toproductive HIV-1 replication. We show that monocytes have an approximately 4-fold higher activity of β-cateninsignaling than MDMs. Inducing β-catenin in MDMs suppressed HIV-1 replication by 5-fold while inhibiting endogenousβ-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 animportant pathway for restricted HIV-1 replication in monocytes and plays a significant role in potentiating HIV-1replication as monocytes differentiate into macrophages. Targeting this pathway may provide a novel strategy to purge thelatent reservoir from monocytes/macrophages, especially in sanctuary sites for HIV-1 such as the central nervous system.
Heme Oxygenase-1 Dysregulation in the Brain: Implications for HIVAssociated Neurocognitive Disorders by Surendra S. Ambegaokar, Dennis L. Kolson (174-188).
Heme oxygenase-1 (HO-1) is a highly inducible and ubiquitous cellular enzyme that subserves cytoprotectiveresponses to toxic insults, including inflammation and oxidative stress. In neurodegenerative diseases such as Alzheimer'sdisease, Parkinson's disease and multiple sclerosis, HO-1 expression is increased, presumably reflecting an endogenousneuroprotective response against ongoing cellular injury. In contrast, we have found that in human immunodeficiencyvirus (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 pathwaysactivated by HIV infection. We have also shown that HO-1 expression is significantly suppressed by HIV replication incultured macrophages which represent the primary cellular reservoir for HIV in the brain. HO-1 deficiency is associatedwith release of neurotoxic levels of glutamate from both HIV-infected and immune-activated macrophages; thisglutamate-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 otherneuroinflammatory brain diseases. Here, we review various stimuli and signaling pathways regulating HO-1 expression inmacrophages, which could promote neuronal survival through HO-1-modulation of endogenous antioxidant and immunemodulatory pathways, thus limiting the oxidative stress that can promote HIV disease progression in the CNS. The use ofpharmacological inducers of endogenous HO-1 expression as potential adjunctive neuroprotective therapeutics in HIVinfection is also discussed.
HIV-1 Tat Disrupts CX3CL1-CX3CR1 Axis in Microglia via the NF-?BYY1 Pathway by Ming Duan, Honghong Yao, Yu Cai, Ke Liao, Pankaj Seth, Shilpa Buch (189-200).
Microglia are critical for the pathogenesis of HIV-associated dementia not only by acting as conduits of viralentry but also as reservoirs for productive and latent virus infection, and as producers of neurotoxins. Interaction betweenCX3CL1 (fractalkine) and FKN receptor (CX3CR1) is highly functional in the brain, and is known to regulate a complexnetwork of paracrine and autocrine interactions between neurons and microglia. The aim of the present study was todetermine which extent of HIV-1 Tat protein causes the alteration of CX3CR1 expression and to investigate the regulatorymechanism for CX3CR1 expression. Here we showed that exposure of primary microglia and BV2 cells to exogenous Tatprotein resulted in down-regulation of CX3CR1 mRNA and protein expression, with a concomitant induction ofproinflammatory responses. Next, we further showed that NF-κB activation by Tat treatment negatively regulatedCX3CR1 expression. Since a YY1 binding site ~10kb upstream of CX3CR1 promoter was predicted in rats, mice andhumans, the classical NF-κB-YY1 regulatory pathway was considered. Our findings indicated that Tat repressed CX3CR1expression via NF-κB-YY1 regulatory pathway. To gain insight into the effect of Tat on CX3CL1-CX3CR1communication, calcium mobilization, MAPK activation and microglial migration, respectively, were tested in microglialcells after successive treatment with Tat and CX3CL1. The results suggested that Tat disrupted the responses of microgliato CX3CL1. Taken together, these results demonstrate that HIV-1 Tat protein suppresses CX3CR1 expression inmicroglia via NF-κB-YY1 pathway and attenuates CX3CL1-induced functional response of microglia.
Mononuclear Phagocyte Accumulation in Visceral Tissue in HIV Encephalitis: Evidence for Increased Monocyte/Macrophage Trafficking and Altered Differentiation by Tracy Fischer, Christina M. Wyatt, Vivette D. D'Agati, Sidney Croul, Laura McCourt, Susan Morgello, Jay Rappaport (201-212).
The invasion of circulating monocytes/macrophages (MΦ)s from the peripheral blood into the central nervoussystem (CNS) appears to play an important role in the pathogenesis of HIV dementia (HIV-D), the most severe form ofHIV-associated neurocognitive disorders (HAND), often confirmed histologically as HIV encephalitis (HIVE). In order todetermine if trafficking of monocytes/M?s is exclusive to the CNS or if it also occurs in organs outside of the brain, wehave focused our investigation on visceral tissues of patients with HIVE. Liver, lymph node, spleen, and kidney autopsytissues from the same HIVE cases investigated in earlier studies were examined by immunohistochemistry for thepresence of CD14, CD16, CD68, Ki-67, and HIV-1 p24 expression. Here, we report a statistically significant increase inaccumulation of M?s in kidney, spleen, and lymph node tissues in specimens from patients with HIVE. In liver, we didnot observe a significant increase in parenchymal macrophage accumulation, although perivascular macrophageaccumulation was consistently observed with nodular lesions in 4 of 5 HIVE cases. We also observed an absence of CD14expression on splenic MΦs in HIVE cases, which may implicate the spleen as a potential source of increased plasmasoluble 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, withoutevidence of HIV-associated nephropathy (HIVAN), was seen in four of eight HIVE cases. Focal segmental and globalglomerulosclerosis with tubular dilatation and prominent interstitial inflammation, consistent with HIVAN, was observedin two of the eight cases. Abundant cells expressing monocyte/MΦ cell surface markers, CD14 and CD68, were alsoCD16+ and found surrounding dilated tubules and adjacent to areas of glomerulosclerosis. The finding of co-morbid HIVEand renal pathology characterized by prominent interstitial inflammation may suggest a common mechanism involvingthe invasion of activated monocytes/MΦs from circulation. Monocyte/MΦ invasion of visceral tissues may play animportant role in the immune dysfunction as well as comorbidity in AIDS and may, therefore, provide a high value targetfor the design of therapeutic strategies.
Identification of Essential cis Element in 5'UTR of Nef mRNA for Nef Translation by Minami Yamamoto, Keisuke Harada, Shozo Shoji, Shogo Misumi, Nobutoki Takamune (213-219).
Nef is one of the accessory proteins of the human immunodeficiency virus type 1 (HIV-1). Nef is translatedfrom multiple-spliced mRNAs transcribed from the viral genome, whose mRNAs have a relatively long 5' untranslatedregion (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-1NL4-3 strain showed an almost undetectable Nef expression owing to a low Nef translation efficiency. The NER of theNL4-3 strain was predicted to form putative stem loops. Although the 5'UTR showed significant but relatively lowinternal ribosome entry site (IRES) activity, the mechanism of 5'cap-dependent translation mainly contributed to the Neftranslation from its Nef mRNA. Altogether, it was clarified that not only the 5' cap but also the NER in the 5'UTR is anessential cis element for efficient Nef translation, which is not a typical 5'-cap-dependent mechanism, and that there mustbe an as yet unknown mechanism using the NER for efficient Nef translation.
DEFB1 5'UTR Polymorphisms Modulate the Risk of HIV-1 Infection in Mexican Women by J.A. Estrada-Aguirre, I. Osuna-Ramírez, E. Prado Montes de Oca, L.A. Ochoa-Ramirez, M. Ramirez, L.G. Magallon-Zazueta, M.S. Gonzalez-Beltran, S.G. Cazarez-Salazar, H. Rangel-Villalobos, J.S. Velarde-Felix (220-226).
Immunologic and genetic factors are involved in HIV-1/AIDS pathogenesis. Defensins are key molecules ininnate immunity that participate in the control and/or development of infection and disease. Using PCR-RFLPs, wedetermined the association between HIV-1/AIDS and human ?-defensin 1 (DEFB1) 5'UTR -52 G/A (rs1799946), -44C/G (rs1800972), and -20 G/A (rs11362) polymorphisms in three groups of women from the state of Sinaloa, located inthe Northwest region of Mexico: i) healthy blood donors; ii) sex-workers; and iii) HIV-1 patients. The -52GG genotypewas 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 ACGhaplotype 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 weremore prevalent in individuals with high CD4 counts (p= 0.004, 0.046, and 0.029, respectively). These findings associateDEFB1 5'UTR polymorphisms with HIV-1/AIDS in Mexican women for the first time.
Preventive Antiretroviral Therapy in Non-Thalassemia Carrier Infants Exposed to Mother-to-Child Transmission of HIV Decreases Cord and After Delivery Red Blood Production without Altering the Development of Hemoglobin by Sakorn Pornprasert, Rotjanee Wongnoi, Peninnah Oberdorfer, Pannee Sirivatanapa (227-231).
Antiretroviral (ARV) prophylaxis for prevention of mother to child transmission (MTCT) of HIV could affecthemoglobin (Hb) development of infants. A cross-sectional descriptive study was conducted in 24 HIV-infected and 21HIV-uninfected pregnancies. ARV drugs were administered to HIV-infected pregnancies at 21 weeks of gestational ageand 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 ?-thalassemia-1 SoutheastAsian (SEA) type deletion, β-thalassemia mutations and Hb E were performed for excluding the thalassemia carrierinfants. Hemoglobinopathy and Hb A, Hb F and Hb A2 were analyzed by using capillary electrophoresis (CE) whilehematological parameters were measured using an automated blood counter. At delivery, 1 and 2 months of age, ARVexposedinfants had significantly lower levels of RBC counts than ARV-unexposed infants (3.56 vs 4.90, 2.66 vs 4.62 and3.01 vs 4.05 x1012/L; P <0.001, <0.001 and 0.001, respectively). At delivery, there was a trend for low hemoglobin levelin the group of ARV-exposed infants as compared to the group of ARV-unexposed infants (149 vs 154 g/L; P = 0.09) andthe significantly different levels were observed among the two groups at 1 and 2 months of age (89 vs 136 and 87 vs 110g/L; P < 0.001 and 0.001, respectively). The development of Hb A, Hb F and Hb A2 levels from delivery to 4 months ofage among the two groups was not significantly different. Therefore, ARV treatments for prevention of MTCT of HIVdecreased RBC counts and hemoglobin but did not alter the development of Hb A, Hb F and Hb A2 of non-thalassemiacarrier infants.