Anomalies in Nef expression within the central nervous system of HIV-1 positive individuals/AIDS patients with or without AIDS dementia complex

HIV Nef Expression Down-modulated GFAP Expression and Altered Glutamate Uptake and Release and Proliferation in Astrocytes

HIV infection of astrocytes leads to restricted gene expression and replication but abundant expression of HIV early genes Tat, Nef and Rev. A great deal of neuroHIV research has so far been focused on Tat protein, its effects on astrocytes, and its roles in neuroHIV. In the current study, we aimed to determine effects of Nef expression on astrocytes and their function. Using transfection or infection of VSVG-pseudotyped HIV viruses, we showed that Nef expression down-modulated glial fibrillary acidic protein (GFAP) expression. We then showed that Nef expression also led to decreased GFAP mRNA expression. The transcriptional regulation was further confirmed using a GFAP promoter-driven reporter gene assay. We performed transcription factor profiling array to compare the expression of transcription factors between Nef-intact and Nef-deficient HIV-infected cells and identified eight transcription factors with expression changes of 1.5-fold or higher: three up-regulated by Nef (Stat1, Stat5, and TFIID), and five down-regulated by Nef (AR, GAS/ISRE, HIF, Sp1, and p53). We then demonstrated that removal of the Sp1 binding sites from the GFAP promoter resulted in a much lower level of the promoter activity and reversal of Nef effects on the GFAP promoter, confirming important roles of Sp1 in the GFAP promoter activity and for Nef-induced GFAP expression. Lastly, we showed that Nef expression led to increased glutamate uptake and decreased glutamate release by astrocytes and increased astrocyte proliferation. Taken together, these results indicate that Nef leads to down-modulation of GFAP expression and alteration of glutamate metabolism in astrocytes, and astrocyte proliferation and could be an important contributor to neuroHIV.

Insights Into the Role of Mortalin in Alzheimer’s Disease, Parkinson’s Disease, and HIV-1-Associated Neurocognitive Disorders

Mortalin is a chaperone protein that regulates physiological functions of cells. Its multifactorial role allows cells to survive pathological conditions. Pharmacological, chemical, and siRNA-mediated downregulation of mortalin increases oxidative stress, mitochondrial dysfunction leading to unregulated inflammation. In addition to its well-characterized function in controlling oxidative stress, mitochondrial health, and maintaining physiological balance, recent evidence from human brain autopsies and cell culture–based studies suggests a critical role of mortalin in attenuating the damage seen in several neurodegenerative diseases. Overexpression of mortalin provides an important line of defense against accumulated proteins, inflammation, and neuronal loss, a key characteristic feature observed in neurodegeneration. Neurodegenerative diseases are a group of progressive disorders, sharing pathological features in Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and HIV-associated neurocognitive disorder. Aggregation of insoluble amyloid beta-proteins and neurofibrillary tangles in Alzheimer’s disease are among the leading cause of neuropathology in the brain. Parkinson’s disease is characterized by the degeneration of dopamine neurons in substantia nigra pars compacta. A substantial synaptic loss leading to cognitive decline is the hallmark of HIV-associated neurocognitive disorder (HAND). Brain autopsies and cell culture studies showed reduced expression of mortalin in Alzheimer’s, Parkinson’s, and HAND cases and deciphered the important role of mortalin in brain cells. Here, we discuss mortalin and its regulation and describe how neurotoxic conditions alter the expression of mortalin and modulate its functions. In addition, we also review the neuroprotective role of mortalin under neuropathological conditions. This knowledge showcases the importance of mortalin in diverse brain functions and offers new opportunities for the development of therapeutic targets that can modulate the expression of mortalin using chemical compounds.

CD4 and MHC-I downregulation are conserved in primary HIV-1 Nef alleles from brain and lymphoid tissues, but Pak2 activation is highly variable

HIV-1 compartmentalization in the CNS has been demonstrated for gag, pol, and env genes. However, little is known about tissue compartmentalization of nef genes and their functional characteristics in brain. We have cloned 97 nef genes and characterized 10 Nef proteins from autopsy brain and lymphoid tissues from 2 patients with AIDS and HIV-1-associated dementia. Distinct compartmentalization of brain versus lymphoid nef genes was demonstrated within each patient. CD4 and MHC-I downregulation were conserved in all tissue-derived Nefs. However, MHC-I downregulation by brain-derived Nefs was weaker than downregulation by lymphoid-derived Nefs. The motifs KEEE- or EKEE- at the PACS-1 binding site represented brain-specific signature patterns in these 2 patients and contributed to the reduced MHC-I downregulation activity of brain-derived Nefs from these patients. Pak2 association was highly variable in Nefs from both patients. Three of 10 tissue-derived Nefs coimmunoprecipitated activated Pak2, with strong association demonstrated for only 2 Nefs. The ability of Nef to associate with activated Pak2 did not correlate with brain or lymphoid tissue origin. Nef genes from viruses isolated from brain by coculture with PBMC were not closely related to sequences amplified directly from brain tissue, suggesting that viral selection or adaptation occurred during coculture. This study of tissue-derived HIV-1 Nefs demonstrates that CD4 and MHC-I downregulation are highly conserved Nef functions, while Pak2 association is variable in late stage AIDS patients.

Cysteine 138 mutation in HIV-1 Nef from patients with delayed disease progression

Background: The nef gene from HIV-1 has been shown to be an important pathogenic factor when considering development of AIDS. Detection of nef variants with an effect on immune modulation is important to understand HIV-1 pathogenesis and has possible impact on treatment strategies. Methods: The nef gene of HIV-1 isolates from patients in a long-term non-progressor (LTNP) cohort and a slow-progressor (SP) cohort (n = 11) was analysed and compared with isolates from a control patient group of progressors (n = 18). Most of the patients with delayed disease progression had extensive medical records, providing an insight into the LTNP disease profile and allowing for the stratification of patients based on their CD4 cell decline. Results: In sequences from nine patients, most of the functional domains of HIV-1 Nef appeared intact, and no major deletions were observed to possibly account for an effect on the delayed disease status. However, the results demonstrate a high incidence of a single amino acid polymorphism (cysteine 138) in HIV-1 Nef. The allelic frequency of cysteine 138 between the delayed disease progression group and the progressor group was found to be statistically significant (P = 0.0139). The phylogeny of isolates was investigated and the variants harbouring the cysteine 138 mutation clustered independently. Conclusion: The present study describes a viral genetic polymorphism related to AIDS disease progression. The polymorphism (cysteine 138) has previously been reported to confer decreased viral replication (Premkumar DR, et al. AIDS Res Hum Retroviruses 1996; 12(4): 337–45). A sequence database search for comparative mutations revealed a high frequency of cysteine 138 in patients with reported SP AIDS.

Adaptive changes after human immunodeficiency virus type 1 transmission

Primary HIV-1 infection (PHI) is associated with a period of viremia, the resolution of which generally coincides with the development of both humoral and cellular immune responses. In this study replication-competent quasispecies were derived from virus isolated from an individual before and after seroconversion. Virus was also isolated from the presumed donor. Phenotypic and genotypic analysis of biological clones identified transmission of an R5/M-tropic phenotype. However, the ability of clones derived from the recipient to replicate in primary macrophages and PBMCs was restricted after transmission. This apparent selection process was supported by analysis of molecular clones derived from the isolated virus. Analysis of the ratio of synonymous and nonsynonymous substitutions predicted the existence of selective pressure soon after transmission, coincident with the development of HIV-1-specific antibodies. An Env trans-complementation assay demonstrated that the infectivity of a clone derived from the recipient after seroconversion was enhanced in the presence of a selected neutralizing antibody, indicating that the developing humoral immune response may have at least in part contributed to the selective pressure identified.

Genetic and functional diversity of human immunodeficiency virus type 1 subtype B Nef primary isolates

We have characterized the functional integrity of seven primary Nef isolates: five from a long-term nonprogressing human immunodeficiency virus (HIV)-infected individual and one each from two patients with AIDS. One of the seven Nefs was defective for CD4 downregulation, two others were defective for PAK-2 activation, and one Nef was defective for PAK-2 activation and major histocompatibility complex (MHC) class I downregulation. Five of the Nefs were tested and found to be functional for the enhancement of virus particle infectivity. The structural basis for each of the functional defects has been analyzed by constructing a consensus nef, followed by mutational analysis of the variant amino acid residues. Mutations A29V and F193I were deleterious to CD4 downregulation and PAK-2 activation, respectively, while S189R rendered Nef defective for both MHC class I downregulation and PAK-2 activation. A search of the literature identified HIVs from five patients with Nefs predominantly mutated at F193 and from one patient with Nefs predominantly mutated at A29. A29 is highly conserved in all HIV subtypes except for subtype E. F193 is conserved in subtype B (and possibly in the closely related subtype D), but none of the other HIV group M subtypes. Our results suggest that functional distinctions may exist between HIV subtypes.

Recombinant nef HIV-IIIB protein is toxic to human neurons in culture

The expression of HIV-1 negative factor (nef) has been positively correlated with HIV disease progression [Z. Hanna, D.G. Kay, N. Rebai, A. Guimond, S. Jothy, P. Jocicoeur, Nef harbors a makor determinant of pathogenicity for an AIDS-like disease induced by HIV-1 in transgenic mice. Cell 95 (1998) 163-175]. Nef expression has been detected in HIV infected human brains with neuronal damage [A. Ranki, M. Nyberg, V. Ovod, M. Haltia, I. Elovaara, R. Raininko, H. Haapsalo, K. Krohn, Abundant expression of HIV Nef and Rev proteins in brain astrocytes in associated with dementia, AIDS 9(9) (1995) 1001-1008; Y. Saito, L.R. Sharer, M.G. Epstein, J. Michaels, M. Mintz, M. Londer, K. Golding, B.M. Blumberg, Overexpression of nef as a marker for restricted HIV-1 infection of astrocytes in postmorten paediatric central tissues, Neurology 14 (1994) 474-480]. It is postulated that nef may contribute to the neuronal damage observed in the brain of those with late HIV disease. To test this, the potential toxicity of recombinant nef (from HIV-1 IIIB) was compared to the neurotoxin human tumour necrosis alpha (TNFalpha) on human brain cells in culture. SK-N-SH neuroblastoma, primary human neurons and glial cells were exposed to recombinant nef or TNFalpha protein for 3 days or twice over 6 days. Cell viability was assessed by Trypan Blue, lactate dehydrogenase (LDH) release and MTT assays. Nuclear fragmentation was detected using the Hoechst Blue nuclear dye assay. Both nef and TNFalpha (100 ng/ml) caused a significant 30% reduction of SK-N-SH cell numbers after 3 days exposure (P=0. 001). At this time, exposure to nef caused evident fragmented nuclei in these cultures. Human neuronal cultures had a 32 and 33% decrease in cell number after 6 days exposure to either nef or TNFalpha, respectively (P<0.001). Furthermore, as previously shown [J. He, C.M. DeCastro, G.R. Vandenbark, J. Busciglio, D. Gabuzda, Astrocyte apoptosis induced by HIV-1 transactivation of the c-kit protoonocogene, Proc. Natl. Acad. Sci. 94 (1997) 3954-3959], a 3-day exposure to nef significantly reduced human glial cell number by 25% (P=0.001). Recombinant nef and TNFalpha compromise human neurons in culture. Thus, like other virotoxins, it is shown for the first time that nef may also contribute to neuronal damage that has been reported in dementia in late HIV disease.

Rapid full-length genomic sequencing of two cytopathically heterogeneous Australian primary HIV-1 isolates

Two Australian HIV-1 isolates, derived from patient blood (HIV(MBC200)) and cerebrospinal fluid (HIV(MBC925)), were characterized after in vitro culture in peripheral blood mononuclear cells (PBMC). Although virus replication was similar, as measured by cell-free reverse transcriptase activity, only one of the two isolates (HIV-1(MCB200)) consistently induced cell syncytia and depleted the PBMC population of CD4+ cells by cell killing. A novel technique, devised for rapidly obtaining high-quality viral sequence data and the full-length genomic sequence of these two isolates, is presented. Analysis of the predicted sequence of the viral Env proteins provides correlates of the observed phenotypes. Phylogenetic analysis derived using near full-length sequence of these and other HIV-1 subtype B genomic sequences (including two other Australian isolates) shows a star-shaped phylogeny with each member having a similar genetic diversity. These data expand the database of genomic sequence available from well-characterized primary clinical isolates of HIV-1 using a novel rapid technique.

SIV/HIV Nef recombinant virus (SHIVnef) produces simian AIDS in rhesus macaques

The simian immunodeficiency virus (SIV) nef gene is an important determinant of viral load and acquired immunodeficiency syndrome (AIDS) in macaques. A role(s) for the HIV-1 nef gene in infection and pathogenesis was investigated by constructing recombinant viruses in which the nef gene of the pathogenic molecular clone SIVmac239 nef was replaced with either HIV-1sf2nef or HIV-1sf33nef. These chimeras, designated SHIV-2nef and SHIV-33nef, expressed HIV-1 Nef protein and replicated efficiently in cultures of rhesus macaque lymphoid cells. In two SHIV-2nef-infected juvenile rhesus macaques and in one of two SHIV-33nef-infected juvenile macaques, virus loads remained at low levels in both peripheral blood and lymph nodes in acute and chronic phases of infection (for >83 weeks). In striking contrast, the second SHIV-33nef-infected macaque showed high virus loads during the chronic stage of infection (after 24 weeks). CD4+ T-cell numbers declined dramatically in this latter animal, which developed simian AIDS (SAIDS) at 47-53 weeks after inoculation; virus was recovered at necropsy at 53 weeks and designated SHIV-33Anef. Sequence analysis of the HIV-1sf33 nef gene in SHIV-33Anef revealed four consistent amino acid changes acquired during passage in vivo. Interestingly, one of these consensus mutations generated a tyr-x-x-leu (Y-X-X-L) motif in the HIV-1sf33 Nef protein. This motif is characteristic of certain endocytic targeting sequences and also resembles a src-homology region-2 (SH-2) motif found in many cellular signaling proteins. Four additional macaques infected with SHIV-33Anef contained high virus loads, and three of these animals progressed to fatal SAIDS. Several of the consensus amino acid changes in Nef, including Y-X-X-L motif, were retained in these recipient animals exhibiting high virus load and disease. In summary, these findings indicate that the SHIV-33Anef chimera is pathogenic in rhesus macaques and that this approach, i.e., construction of chimeric viruses, will be important for analyzing the function(s) of HIV-1 nef genes in immunodeficiency in vivo, testing antiviral therapies aimed at inhibiting AIDS, and investigating adaptation of this HIV-1 accessory gene to the macaque host.