Mechanisms of HIV-associated lymphocyte apoptosis

Exploring the dynamics of SARS-CoV-2 and HIV Co-infection: Mutation risks, therapeutic efficacy, and future variant prevention

High mutation rates in SARS-CoV-2, particularly among immunocompromised patients living with HIV, continue to complicate the current COVID-19 pandemic. The threshold for severe COVID-19 and a greater risk of mortality have increased in many immunocompromised individuals due to a weakened immune system. Low CD4+ T-cell counts in people living with both HIV and COVID-19 lead to prolonged disease duration and, therefore, an increased likelihood of viral infection with SARS-CoV-2 mutations in such individuals. These mutations could decrease the efficiency of ongoing vaccines and cause new outbreaks. Recently, the rise of new mutations in this patient population has created increasing concern; however, few data are currently available on the direct association of HIV infection with SARS-CoV-2 mutations. This review highlights the implications of SARS-CoV-2 and HIV co-infection, highlighting the need for extra caution and monitoring of the immune-compromised population during a pandemic. Access to HIV care and COVID-19 treatments, careful surveillance, and adapted health strategies are key to reducing risks and protecting these populations. Further research is required to elucidate the dynamics of mutations and develop intervention methods to manage COVID-19 among immunocompromised patients.

SAMHD1 enhances HIV-1-induced apoptosis in monocytic cells via the mitochondrial pathway

Sterile alpha motif (SAM) and histidine-aspartate (HD) domain-containing protein 1 (SAMHD1) inhibits HIV-1 replication in non-dividing cells by reducing the intracellular dNTP pool. SAMHD1 enhances spontaneous apoptosis in cells, but its effects on HIV-1-induced apoptosis and the underlying mechanisms remain unknown. Here we uncover a new mechanism by which SAMHD1 enhances HIV-1-induced apoptosis in monocytic cells through the mitochondrial pathway. We found that endogenous SAMHD1 enhances apoptosis levels induced by HIV-1 infection in dividing THP-1 cells. Mechanistically, SAMHD1 expression decreases the mitochondrial membrane potential and promotes cytochrome c release induced by HIV-1 infection in THP-1 cells, thereby enhancing mitochondrial apoptotic pathway. SAMHD1-enhanced apoptosis is associated with increased expression of the pro-apoptotic protein BCL-2-interacting killer (BIK) in cells. We further demonstrated that BIK contributes to SAMHD1-enhanced apoptosis during HIV-1 infection. Overall, our results reveal an unappreciated regulatory mechanism of SAMHD1 in enhancing HIV-1-induced apoptosis via the mitochondrial pathway in monocytic cells.

Programmed cell death: molecular mechanisms, biological functions, diseases, and therapeutic targets

Programmed cell death represents a precisely regulated and active cellular demise, governed by a complex network of specific genes and proteins. The identification of multiple forms of programmed cell death has significantly advanced the understanding of its intricate mechanisms, as demonstrated in recent studies. A thorough grasp of these processes is essential across various biological disciplines and in the study of diseases. Nonetheless, despite notable progress, the exploration of the relationship between programmed cell death and disease, as well as its clinical application, are still in a nascent stage. Therefore, further exploration of programmed cell death and the development of corresponding therapeutic methods and strategies holds substantial potential. Our review provides a detailed examination of the primary mechanisms behind apoptosis, autophagy, necroptosis, pyroptosis, and ferroptosis. Following this, the discussion delves into biological functions and diseases associated dysregulated programmed cell death. Finally, we highlight existing and potential therapeutic targets and strategies focused on cancers and neurodegenerative diseases. This review aims to summarize the latest insights on programmed cell death from mechanisms to diseases and provides a more reliable approach for clinical transformation.

The HIV-1 vpr R77Q Mutant Induces Apoptosis, G2 Cell Cycle Arrest, and Lower Production of Pro-Inflammatory Cytokines in Human CD4+ T Cells

Acquired immunodeficiency syndrome (AIDS) occurs when HIV depletes CD4+ helper T cells. Some patients develop AIDS slowly or not at all, and are termed long-term non-progressors (LTNP), and while mutations in the HIV-1 Viral Protein R (vpr) gene such as R77Q are associated with LTNP, mechanisms for this correlation are unclear. This study examines the induction of apoptosis, cell cycle arrest, and pro-inflammatory cytokine release in the HUT78 T cell line following infection with replication-competent wild-type strain NL4-3, the R77Q mutant, or a vpr Null mutant. Our results show a significant enhancement of apoptosis and G2 cell cycle arrest in HUT78 cells infected with R77Q, but not with WT NL4-3 or the vpr Null strain. Conversely, HUT78 cells infected with the WT virus show higher levels of necrosis. We also detected lower TNF and IL-6 release after infection with R77Q vs. WT. The apoptotic phenotype was also seen in the CEM cell line and in primary CD4+ T cells. Protein expression of the R77Q vpr variant was low compared to WT vpr, but expression levels alone cannot explain these phenotypes because the Null virus did not show apoptosis or G2 arrest. These results suggest that R77Q triggers a non-inflammatory apoptotic pathway that attenuates inflammation, possibly contributing to LTNP.

Transcriptionally Active Defective HIV-1 Proviruses and Their Association With Immunological Nonresponse to Antiretroviral Therapy

A subset of antiretroviral therapy-treated persons with human immunodeficiency virus (HIV), referred to as immunological nonresponders (INRs), fails to normalize CD4+ T-cell numbers. In a case-control study involving 26 INRs (CD4 < 250 cells/µL) and 25 immunological responders (IRs; CD4 ≥ 250 cells/µL), we evaluated the potential contribution of transcriptionally competent defective HIV-1 proviruses to poor CD4+ T-cell recovery. Compared to the responders, the INRs had higher levels of cell-associated HIV RNA (P = .034) and higher percentages of HLA-DR+ CD4+ T cells (P < .001). While not encoding replication-competent viruses, the RNA transcripts frequently encoded HIV-1 Gag-p17 and Nef proteins. These transcripts and/or resulting proteins may activate pathway(s) leading to the immunological nonresponse phenotype.

A macrophage-cell model of HIV latency reveals the unusual importance of the bromodomain axis

BACKGROUND

Although macrophages are now recognized as an essential part of the HIV latent reservoir, whether and how viral latency is established and reactivated in these cell types is poorly understood. To understand the fundamental mechanisms of viral latency in macrophages, there is an urgent need to develop latency models amenable to genetic manipulations and screening for appropriate latency-reversing agents (LRAs). Given that differentiated THP-1 cells resemble monocyte-derived macrophages in HIV replication mechanisms, we set out to establish a macrophage cell model for HIV latency using THP-1 cells.

METHODS

We created single-cell clones of THP-1 cells infected with a single copy of the dual-labeled HIVGKO in which a codon switched eGFP (csGFP) is under the control of the HIV-1 5' LTR promoter, and a monomeric Kusabira orange 2 (mKO2) under the control of cellular elongation factor one alpha promoter (EF1α). Latently infected cells are csGFP-, mKO2+, while cells with actively replicating HIV (or reactivated virus) are csGFP+,mKO2+. After sorting for latently infected cells, each of the THP-1 clones with unique integration sites for HIV was differentiated into macrophage-like cells with phorbol 12-myristate 13-acetate (PMA) and treated with established LRAs to stimulate HIV reactivation. Monocyte-derived macrophages (MDMs) harboring single copies of HIVGKO were used to confirm our findings.

RESULTS

We obtained clones of THP-1 cells with latently infected HIV with unique integration sites. When the differentiated THP-1 or primary MDMs cells were treated with various LRAs, the bromodomain inhibitors JQ1 and I-BET151 were the most potent compounds. Knockdown of BRD4, the target of JQ1, resulted in increased reactivation, thus confirming the pharmacological effect. The DYRK1A inhibitor Harmine and lipopolysaccharide (LPS) also showed significant reactivation across all three MDM donors. Remarkably, LRAs like PMA/ionomycin, bryostatin-1, and histone deacetylase inhibitors known to potently reactivate latent HIV in CD4 + T cells showed little activity in macrophages.

CONCLUSIONS

Our results indicate that this model could be used to screen for appropriate LRAs for macrophages and show that HIV latency and reactivation mechanisms in macrophages may be distinct from those of CD4 + T cells.

Functional Analysis of the Cathepsin D Gene Response to SGIV Infection in the Orange-Spotted Grouper, Epinephelus coioides

(1) Background: Lysosomal aspartic protease Cathepsin D (CD) is a key regulator and signaling molecule in various biological processes including activation and degradation of intracellular proteins, the antigen process and programmed cell death. However, the function of fish CD in virus infection remains largely unknown. (2) Methods: The functions of the CD gene response to SGIV infection was determined with light microscopy, reverse transcription quantitative PCR, Western blot and flow cytometry. (3) Results: In this study, Ec-Cathepsin D (Ec-CD) was cloned and identified from the orange-spotted grouper, Epinephelus coioides. The open reading frame (ORF) of Ec-CD consisted of 1191 nucleotides encoding a 396 amino acid protein with a predicted molecular mass of 43.17 kDa. Ec-CD possessed typical CD structural features including an N-terminal signal peptide, a propeptide region and a mature domain including two glycosylation sites and two active sites, which were conserved in other CD sequences. Ec-CD was predominantly expressed in the spleen and kidneys of healthy groupers. A subcellular localization assay indicated that Ec-CD was mainly distributed in the cytoplasm. Ec-CD expression was suppressed by SGIV stimulation and Ec-CD-overexpressing inhibited SGIV replication, SGIV-induced apoptosis, caspase 3/8/9 activity and the activation of reporter gene p53 and activating protein-1 (AP-1) in vitro. Simultaneously, Ec-CD overexpression obviously restrained the activated mitogen-activated protein kinase (MAPK) pathways, including extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK). In addition, Ec-CD overexpression negatively regulated the transcription level of pro-inflammatory cytokines and activation of the NF-κB promotor. (4) Conclusions: Our findings revealed that the Ec-CD possibly served a function during SGIV infection.

Impaired CD4+ T cell differentiation in HIV-1 infected patients receiving early anti-retroviral therapy

Differentiation of CD4+ T naïve (T_N) into central memory (T_CM) cells involves extensive molecular processes. We compared the transcriptomes of CD4+ T_N and T_CM cells from HIV-1 infected patients receiving early anti-retroviral therapy (ART; EA; n = 13) and controls (n = 15). Comparison of protein coding genes between T_CM and T_N revealed 533 and 82 differentially expressed genes (DEGs) in controls and EA, respectively. A high degree of transcriptional complexity was detected during transition of CD4+ T_N to T_CM cells in controls involving 70 TFs, 20 master regulators of T cell differentiation (TBX21, GATA3, RARA, FOXP3, RORC); in EA only 7 TFs were modulated with expression of several master regulators remaining unchanged during differentiation. Analysis of interactions between modulated TFs and target genes revealed important regulatory interactions missing in EA group. We conclude that T cell differentiation in EA patients is impaired due to reduced modulation of genes involved in transition from CD4+ T_N to T_CM cells.

Cardiovascular risks associated with protease inhibitors for the treatment of HIV

Introduction: Cumulative use of some first-generation protease inhibitors has been associated with higher rates of dyslipidemia and increased risk of cardiovascular disease. The protease inhibitors most commonly in use are atazanavir and darunavir, which have fewer detrimental lipid effects and greater tolerability. This paper aims to review the evidence of a potential association of these contemporary protease inhibitors with the risk of ischemic CVD and atherosclerotic markers.Areas covered: We searched for publications of randomized trials and observational studies on PubMed from 1 January 2000 onwards, using search terms including: protease inhibitors; darunavir; atazanavir; cardiovascular disease; cardiovascular events; dyslipidemia; mortality; carotid intima media thickness; arterial elasticity; arterial stiffness and drug discontinuation. Ongoing studies registered on clinicaltrials.gov as well as conference abstracts from major HIV conferences from 2015-2020 were also searched.Expert opinion: Atazanavir and darunavir are no longer part of first-line HIV treatment, but continue to be recommended as alternative first line, second- and third-line regimens, as part of two drug regimens, and darunavir is used as salvage therapy. Although these drugs will likely remain in use globally for several years to come, baseline CVD risk should be considered when considering their use, especially as the population with HIV ages.

Discovery of novel furo[2,3-d]pyrimidin-2-one-1,3,4-oxadiazole hybrid derivatives as dual antiviral and anticancer agents that induce apoptosis

A new series of furo[2,3-d]pyrimidine-1,3,4-oxadiazole hybrid derivatives were synthesized via an environmentally friendly, multistep synthetic tool and a one-pot Songoashira-heterocyclization protocol using, for the first time, nanostructured palladium pyrophosphate (Na₂ PdP₂ O₇ ) as a heterogeneous catalyst. Compounds 9a-c exhibited broad-spectrum activity with low micromolar EC₅₀ values toward wild and mutant varicella-zoster virus (VZV) strains. Compound 9b was up to threefold more potent than the reference drug acyclovir against thymidine kinase-deficient VZV strains. Importantly, derivative 9b was not cytostatic at the maximum tested concentration (CC₅₀  > 100 µM) and had an acceptable selectivity index value of up to 7.8. Moreover, all synthesized 1,3,4-oxadiazole hybrids were evaluated for their cytotoxic activity in four human cancer cell lines: fibrosarcoma (HT-1080), breast (MCF-7 and MDA-MB-231), and lung carcinoma (A549). Data showed that compound 8f exhibits moderate cytotoxicity, with IC₅₀ values ranging from 13.89 to 19.43 µM. Besides, compound 8f induced apoptosis through caspase 3/7 activation, cell death independently of the mitochondrial pathway, and cell cycle arrest in the S phase for HT1080 cells and the G1/M phase for A549 cells. Finally, the molecular docking study confirmed that the anticancer activity of the synthesized compounds is mediated by the activation of caspase 3.

In vitro Anti-HIV-1 Activity of the Recombinant HIV-1 TAT Protein Along With Tenofovir Drug

BACKGROUND

HIV-1 TAT protein is essential for the regulation of viral genome transcription. The first exon of TAT protein has a fundamental role in the stimulation of the extrinsic and intrinsic apoptosis pathways, but its anti-HIV activity is not clear yet.

METHODS

In the current study, we firstly cloned the first exon of the TAT coding sequence in the pET-24a expression vector and then protein expression was done in the Rosetta expression host. Next, the expressed TAT protein was purified by Ni-NTA column under native conditions. After that, the protein yield was determined by Bradford kit and NanoDrop spectrophotometry. Finally, the cytotoxicity effect and anti-Scr-HIV-1 activity of the recombinant TAT protein alone and along with Tenofovir drug were assessed by MTT and ELISA, respectively.

RESULTS

The recombinant TAT protein was successfully generated in E. coli, as confirmed by 13.5% SDS-PAGE and western blotting. The protein yield was ~150-200 μg/ml. In addition, the recombinant TAT protein at a certain dose with low toxicity could suppress Scr-HIV replication in the infected HeLa cells (~30%) that was comparable with a low toxic dose of Tenofovir drug (~40%). It was interesting that the recombinant TAT protein could enhance anti-HIV potency of Tenofovir drug up to 66%.

CONCLUSION

Generally, a combination of TAT protein and Tenofovir drug could significantly inhibit HIV-1 replication. It will be required to determine their mechanism of action in the next studies.

Apoptosis of Hepatocytes: Relevance for HIV-Infected Patients under Treatment

Due to medical advances over the past few decades, human immunodeficiency virus (HIV) infection, once a devastatingly mortal pandemic, has become a manageable chronic condition. However, available antiretroviral treatments (cART) cannot fully restore immune health and, consequently, a number of inflammation-associated and/or immunodeficiency complications have manifested themselves in treated HIV-infected patients. Among these chronic, non-AIDS (acquired immune deficiency syndrome)-related conditions, liver disease is one of the deadliest, proving to be fatal for 15–17% of these individuals. Aside from the presence of liver-related comorbidities, including metabolic disturbances and co-infections, HIV itself and the adverse effects of cART are the main factors that contribute to hepatic cell injury, inflammation, and fibrosis. Among the molecular mechanisms that are activated in the liver during HIV infection, apoptotic cell death of hepatocytes stands out as a key pathogenic player. In this review, we will discuss the evidence and potential mechanisms involved in the apoptosis of hepatocytes induced by HIV, HIV-encoded proteins, or cART. Some antiretroviral drugs, especially the older generation, can induce apoptosis of hepatic cells, which occurs through a variety of mechanisms, such as mitochondrial dysfunction, increased production of reactive oxygen species (ROS), and induction of endoplasmic reticulum (ER) stress and unfolded protein response (UPR), all of which ultimately lead to caspase activation and cell death.

Epigenetic Mechanisms Underlying HIV-Infection Induced Susceptibility of CD4+ T Cells to Enhanced Activation-Induced FasL Expression and Cell Death

BACKGROUND

Chronic immune activation and CD4 T cell depletion are significant pathogenic features of HIV infection. Expression of Fas ligand (FasL), a key mediator of activation-induced cell death in T cells, is elevated in people living with HIV-1 infection (PLWH). However, the epigenetic mechanisms underlying the enhanced induction of FasL expression in CD4 T lymphocytes in PLWH are not completely elucidated. Hence, the current work examined the effect of HIV infection on FasL promoter-associated histone modifications and transcriptional regulation in CD4 T lymphocytes in PLWH.

METHOD

Flow cytometric analysis was performed to examine the Fas-FasL expression on total CD4 T cells and naïve/memory CD4 T cell subsets. Epigenetic FasL promoter histone modifications were investigated by chromatin immunoprecipitation-quantitative real-time polymerase chain reaction analysis using freshly isolated total CD4 T lymphocytes from HIV-1 infected and noninfected individuals.

RESULTS

All naïve/memory CD4 T cell subsets from PLWH showed markedly greater frequency of FasL expression. Notably, examination of functional outcome of FasL/Fas co-expression demonstrated the preferential susceptibility of Tcm and Tem subsets to activation-induced apoptosis. Importantly, these CD4 T cells collectively demonstrated a distinct FasL promoter histone profile involving a coordinated cross-talk between histone H3 modifications leading to enhanced FasL gene expression. Specifically, levels of transcriptionally permissive histone H3K4-trimethylation (H3K4Me3) and histone H3K9-acetylation (H3K9Ac) were increased, with a concomitant decrease in the repressive H3K9-trimethylation (H3K9Me3).

CONCLUSION

The present work demonstrates that epigenetic mechanisms involving promoter-histone modifications regulate transcriptional competence and FasL expression in CD4 T cells from PLWH and render them susceptible to activation-induced cell death.

HIV-1 and SIV Infection Are Associated with Early Loss of Lung Interstitial CD4+ T Cells and Dissemination of Pulmonary Tuberculosis

Lung interstitial CD4+ T cells are critical for protection against pulmonary infections, but the fate of this population during HIV-1 infection is not well described. We studied CD4+ T cells in the setting of HIV-1 infection in human lung tissue, humanized mice, and a Mycobacterium tuberculosis (Mtb)/simian immunodeficiency virus (SIV) nonhuman primate co-infection model. Infection with a CCR5-tropic strain of HIV-1 or SIV results in severe and rapid loss of lung interstitial CD4+ T cells but not blood or lung alveolar CD4+ T cells. This is accompanied by high HIV-1 production in these cells in vitro and in vivo. Importantly, during early SIV infection, loss of lung interstitial CD4+ T cells is associated with increased dissemination of pulmonary Mtb infection. We show that lung interstitial CD4+ T cells serve as an efficient target for HIV-1 and SIV infection that leads to their early depletion and an increased risk of disseminated tuberculosis.

Corleis et al. show that lung parenchymal CD4+ T cells are permissive to HIV-1-dependent cell death. CD4+ T cell loss is highly significant in the interstitium but not the alveolar space, and loss of interstitial CD4+ T cells is associated with extrapulmonary dissemination of M. tuberculosis.

Transcriptional profiling indicates cAMP-driven reversal of HIV latency in monocytes occurs via transcription factor SP-1

Latent HIV reservoir is a major barrier to absolute HIV cure. Studies on latency reversal agents (LRA) have by far focused mainly on CD4+ T-lymphocytes, while myeloid reservoirs remain under-represented despite their persistence and key contribution to HIV pathogenesis. cAMP has been shown to increase HIV-1 transcription in latently-infected monocytes/macrophages. In this communication, we explored the potential of commercially available pharmacological drugs and phosphodiesterase inhibitors to reactivate HIV in latently-infected monocytic cell-line, U1. We showed that increased levels of intracellular cAMP reverse HIV latency in vitro, which is specific to cells of the myeloid lineage. High throughput RNA-seq analysis revealed that cAMP modulates transcriptional profile of latently HIV-infected cells and provides favourable cellular environment for HIV to produce viral proteins. This reactivation of latent HIV was inhibited by Mithramycin A, a selective Sp1 inhibitor, indicating that the reversal of HIV latency in monocytes is driven by transcription factor Sp1.

IL6 and FAS/FASL gene polymorphisms may be associated with disease progression in HIV-1-positive ethnically mixed patients

The progression of AIDS depends on the complex host and virus interactions. The most important disease progression hallmarks are immune activation and apoptosis. In this study, we address the prevalence of polymorphisms related to proinflammatory and apoptotic genes, such as IFNG (+874T/A), TNF (308G/A), IL6 (-174G/C), IL8 (-251A/T), FAS (-670A/G), and FASL (-124A/G) in 160 ethnically mixed HIV-1-infected patients from multicentre cohorts with different clinical outcomes (13 elite controllers [EC], 66 slow long-term non-progressors [LTNPs], and 81 progressors [P]). The genotyping was accomplished by TaqMan-qPCR. Among all the polymorphisms analyzed in the cytokines, the IL6 -174G/C polymorphism showed a higher frequency of GG genotype in the LTNP and LTNP+EC groups as compared to the P group. Moreover, there was a significantly higher frequency of the G allele in the LTNP and LTNP+EC groups as compared to the P group. On the other hand, the levels of CD4⁺ T lymphocytes were higher among individuals showing the AA and AG genotypes for the FASL -124A/G polymorphism as compared to the GG genotype. Furthermore, the AG and AA genotypes were more frequent, as compared to the GG genotype, in individuals showing a lower viral load. In contrast, for the FAS -670A/G polymorphism, a significantly higher viral load was observed in individuals with the AG genotype as compared to the GG genotype. In conclusion, we found three genetic allelic variants of the IL6 -174G/C, FASL -124A/G, and FAS -670A/G polymorphisms that were related to disease progression and immunological and virological markers in cohorts of HIV-1-positive ethnically mixed patients.

The roles of apoptosis, autophagy and unfolded protein response in arbovirus, influenza virus, and HIV infections

Virus infection induces different cellular responses in infected cells. These include cellular stress responses like autophagy and unfolded protein response (UPR). Both autophagy and UPR are connected to programed cell death I (apoptosis) in chronic stress conditions to regulate cellular homeostasis via Bcl2 family proteins, CHOP and Beclin-1. In this review article we first briefly discuss arboviruses, influenza virus, and HIV and then describe the concepts of apoptosis, autophagy, and UPR. Finally, we focus upon how apoptosis, autophagy, and UPR are involved in the regulation of cellular responses to arboviruses, influenza virus and HIV infections. Abbreviation: AIDS: Acquired Immunodeficiency Syndrome; ATF6: Activating Transcription Factor 6; ATG6: Autophagy-specific Gene 6; BAG3: BCL Associated Athanogene 3; Bak: BCL-2-Anatagonist/Killer1; Bax; BCL-2: Associated X protein; Bcl-2: B cell Lymphoma 2x; BiP: Chaperon immunoglobulin heavy chain binding Protein; CARD: Caspase Recruitment Domain; cART: combination Antiretroviral Therapy; CCR5: C-C Chemokine Receptor type 5; CD4: Cluster of Differentiation 4; CHOP: C/EBP homologous protein; CXCR4: C-X-C Chemokine Receptor Type 4; Cyto c: Cytochrome C; DCs: Dendritic Cells; EDEM1: ER-degradation enhancing-a-mannosidase-like protein 1; ENV: Envelope; ER: Endoplasmic Reticulum; FasR: Fas Receptor;G2: Gap 2; G2/M: Gap2/Mitosis; GFAP: Glial Fibrillary Acidic Protein; GP120: Glycoprotein120; GP41: Glycoprotein41; HAND: HIV Associated Neurodegenerative Disease; HEK: Human Embryonic Kidney; HeLa: Human Cervical Epithelial Carcinoma; HIV: Human Immunodeficiency Virus; IPS-1: IFN-β promoter stimulator 1; IRE-1: Inositol Requiring Enzyme 1; IRGM: Immunity Related GTPase Family M protein; LAMP2A: Lysosome Associated Membrane Protein 2A; LC3: Microtubule Associated Light Chain 3; MDA5: Melanoma Differentiation Associated gene 5; MEF: Mouse Embryonic Fibroblast; MMP: Mitochondrial Membrane Permeabilization; Nef: Negative Regulatory Factor; OASIS: Old Astrocyte Specifically Induced Substrate; PAMP: Pathogen-Associated Molecular Pattern; PERK: Pancreatic Endoplasmic Reticulum Kinase; PRR: Pattern Recognition Receptor; Puma: P53 Upregulated Modulator of Apoptosis; RIG-I: Retinoic acid-Inducible Gene-I; Tat: Transactivator Protein of HIV; TLR: Toll-like receptor; ULK1: Unc51 Like Autophagy Activating Kinase 1; UPR: Unfolded Protein Response; Vpr: Viral Protein Regulatory; XBP1: X-Box Binding Protein 1.

In-Vitro Subtype-Specific Modulation of HIV-1 Trans-Activator of Transcription (Tat) on RNAi Silencing Suppressor Activity and Cell Death

Human immunodeficiency virus (HIV) is a global health concern affecting millions of individuals with a wide variety of currently circulating subtypes affecting various regions of the globe. HIV relies on multiple regulatory proteins to modify the host cell to promote replication in infected T cells, and these regulatory proteins can have subtle phenotypic differences between subtypes. One of these proteins, HIV-1 Trans-Activator of Transcription (Tat), is capable of RNA interference (RNAi) Silencing Suppressor (RSS) activity and induction of cell death in T cells. However, the subtype-specific RSS activity and induction of cell death have not been explored. We investigated the ability of Tat subtypes and variants to induce RSS activity and cell death. TatB, from HIV-1 subtype B, was found to be a potent RSS activator by 40% whereas TatC, from HIV-1 subtype C, showed 15% RSS activity while subtype TatC variants exhibited varying levels. A high level of cell death (50–53%) was induced by subtype TatB when compared to subtype TatC (25–28%) and varying levels were observed with subtype TatC variants. These differential activities could be due to variations in the functional domains of Tat. These observations further our understanding of subtype-specific augmentation of Tat in HIV-1 replication and pathogenesis.

Contemporary protease inhibitors and cardiovascular risk

PURPOSE OF REVIEW

To review the evidence linking use of HIV protease inhibitors with excess risk of cardiovascular disease (CVD) in HIV+ populations.

RECENT FINDINGS

For the two contemporary most frequently used protease inhibitors, darunavir and atazanavir [both pharmacologically boosted with ritonavir (/r)], darunavir/r has been shown to be associated with increased CVD risk. The effect is cumulative with longer exposure increasing risk and an effect size comparable to what has been observed for previously developed protease inhibitors. Biological mechanisms may be overlapping and include perturbed lipid metabolism and accumulation of cholesterol derivatives within macrophages. Conversely, atazanavir/r has not been shown to be associated with CVD, possibly because of its ability to increase cardioprotective bilirubin levels.

SUMMARY

Evidence linking protease inhibitors to CVD is based on observational studies only, whereas plausible biological explanations are well established and derived from randomized trials and controlled experiments. Given the possible association with clinical disease, a conservative approach to apply the data in daily practise is proposed which is focused on individualization of care based on underlying risk of CVD.

CD45RO regulates the HIV-1 gp120-mediated apoptosis of T cells by activating Lck

CD45 has been reported to regulate the HIV-1 gp120-induced apoptosis of Jurkat cells. Here, we demonstrate that the extracellular domain of CD45 plays an important role in this function. We observed that CD45RO-transfected cells, but not cells transfected with other CD45 isoforms, underwent significant apoptosis induced by gp120. However, a CD45RA-transfected cell line treated with an O-glycan inhibitor was able to undergo apoptosis. The role of the extracellular domain of CD45 was further confirmed using CD45 isoform-transfected cell lines by analyzing the phosphorylation of Lck, which is a direct substrate of CD45 tyrosine phosphatase, and by using an Lck inhibitor. These results suggest that CD45RO modulates HIV-1 gp120-induced apoptosis by regulating the activity of Lck.

HIV-1 infection renders brain vascular pericytes susceptible to the extracellular glutamate

Reduced pericytes' coverage of endothelium in the brain is one of the structural changes leading to breach of the blood-brain barrier during HIV infection. We previously showed in central memory T (T_CM) cells that HIV latency increases cellular susceptibility to DNA damage. In this study, we investigated susceptibility of primary brain pericytes infected with HIV-1 to DNA damage in response to glutamate and TNF-α, both known to induce neuronal death during chronic inflammatory conditions. To infect pericytes, we used a single-cycle HIV-1 pseudotyped with VSV-G envelope glycoprotein and maintained the cultures until latency was established. Our data indicate that pericytes silence HIV-1 expression at similar rate compared to primary T_CM cells. TNF-α and IL-1β caused partial reactivation of the virus suggesting that progression of disease and neuroinflammation might facilitate virus reactivation from latency. Significant increases in the level of γH2AX, which reflect DNA damage, were observed in infected cultures exposed to TNF-α and glutamate at day 2 post-infection. Glutamate, an excitatory neurologic stimuli, also caused increases in the γH2AX level in latently infected pericytes, whereas PARP and DNA-PK inhibitors caused reductions in cell population suggesting that HIV-1 latency affects repairs of single- and double-strand DNA breaks. For comparison, we also analyzed latently infected astrocytes and determined that DNA damage response in astrocytes is less affected by HIV-1. In conclusion, our results indicate that productive infection and HIV-1 latency in pericytes interfere with DNA damage response, rendering them vulnerable to the agents that are characteristic of chronic neuroinflammatory disease conditions.

Gallid Herpesvirus 1 Initiates Apoptosis in Uninfected Cells through Paracrine Repression of p53

Apoptosis is a common innate defense mechanism of host cells against viral infection and is therefore suppressed by many viruses, including herpes simplex virus (HSV), via various strategies. A recent in vivo study reported the apoptosis of remote uninfected cells during Gallid herpesvirus 1 (GaHV-1) infection, yet little is known about this previously unknown aspect of herpesvirus-host interactions. The aim of the present study was to investigate the apoptosis of uninfected host cells during GaHV-1 infection. The present study used in vitro and in ovo models, which avoided potential interference by host antiviral immunity, and demonstrated that this GaHV-1-host interaction is independent of host immune responses and important for both the pathological effect of viral infection and early viral dissemination from the primary infection site to distant tissues. Further, we revealed that GaHV-1 infection triggers this process in a paracrine-regulated manner. Using genome-wide transcriptome analyses in combination with a set of functional studies, we found that this paracrine-regulated effect requires the repression of p53 activity in uninfected cells. In contrast, the activation of p53 not only prevented the apoptosis of remote uninfected cells and subsequent pathological damage induced by GaHV-1 infection but also delayed viral dissemination significantly. Moreover, p53 activation repressed viral replication both in vitro and in ovo, suggesting that dual cell-intrinsic mechanisms underlie the suppression of GaHV-1 infection by p53 activation. This study uncovers the mechanism underlying the herpesvirus-triggered apoptosis of remote host cells and extends our understanding of both herpesvirus-host interactions and the roles of p53 in viral infection.IMPORTANCE It is well accepted that herpesviruses suppress the apoptosis of host cells via various strategies to ensure sustained viral replication during infection. However, a recent in vivo study reported the apoptosis of remote uninfected cells during GaHV-1 infection. The mechanism and the biological meaning of this unexpected herpesvirus-host interaction are unclear. This study uncovers the mechanisms of herpesvirus-triggered apoptosis in uninfected cells and may also contribute to a mechanistic illustration of paracrine-regulated apoptosis induced by other viruses in uninfected host cells.

Characterization of Cellular Immune Responses in Thai Individuals With and Without HIV-Associated Neurocognitive Disorders

HIV-associated neurocognitive disorder (HAND) remains a challenge despite antiretroviral therapy (ART), and has been linked to monocyte/macrophage (M/M) migration to the brain. Due to the potential impact of T cell effector mechanisms in eliminating activated/HIV-infected M/M, T cell activation may play a role in the development of HAND. We sought to investigate the relationship between cognition and both CD8⁺ T cell activation (HLA-DR⁺/CD38⁺) and HIV-specific CD8⁺ T cell responses at the time of HIV diagnosis and 12 months postinitiation of ART. CD8⁺ T cell activation was increased in HAND compared to cognitive normal (NL) individuals and correlated directly with plasma viral load and inversely with the cognitive status. In addition, Gag-specific cytolytic activity (CD107a/b⁺) was decreased in HAND compared with NL individuals and correlated with their neurological testing, suggesting a potential role of cytotoxic CD8⁺ T cells in the mechanism of HAND development.

Viral control in chronic HIV-1 subtype C infection is associated with enrichment of p24 IgG1 with Fc effector activity

OBJECTIVE

Postinfection HIV viral control and immune correlates analysis of the RV144 vaccine trial indicate a potentially critical role for Fc receptor-mediated antibody functions. However, the influence of functional antibodies in clade C infection is largely unknown.

DESIGN

Plasma samples from 361 chronic subtype C-infected, antiretroviral therapy-naive participants were tested for their HIV-specific isotype and subclass distributions, along with their Fc receptor-mediated functional potential.

METHOD

Total IgG, IgG subclasses and IgA binding to p24 clade B/C and gp120 consensus C proteins were assayed by multiplex. Antibody-dependent uptake of antigen-coated beads and Fc receptor-mediated natural killer cell degranulation were evaluated as surrogates for antibody-dependent cellular phagocytosis (ADCP) and antibody-dependent cellular cytotoxicity (ADCC), respectively.

RESULTS

p24 IgG1 was the only subclass associated with viral control (P = 0.01), with higher p24-specific ADCP and ADCC responses detected in individuals with high p24 IgG1. Although p24 IgG1 levels were enriched in patients with elevated Gag-specific T-cell responses, these levels remained an independent predictor of low-viral loads (P = 0.04) and high CD4+ cell counts (P = 0.004) after adjusting for Gag-specific T-cell responses and for protective HLA class I alleles.

CONCLUSION

p24 IgG1 levels independently predict viral control in HIV-1 clade C infection. Whether these responses contribute to direct antiviral control via the recruited killing of infected cells via the innate immune system or simply mark a qualitatively superior immune response to HIV, is uncertain, but highlights the role of p24-specific antibodies in control of clade C HIV-1 infection.

Increasing procaspase 8 expression using repurposed drugs to induce HIV infected cell death in ex vivo patient cells

HIV persists because a reservoir of latently infected CD4 T cells do not express viral proteins and are indistinguishable from uninfected cells. One approach to HIV cure suggests that reactivating HIV will activate cytotoxic pathways; yet when tested in vivo, reactivating cells do not die sufficiently to reduce cell-associated HIV DNA levels. We recently showed that following reactivation from latency, HIV infected cells generate the HIV specific cytotoxic protein Casp8p41 which is produced by HIV protease cleaving procaspase 8. However, cell death is prevented, possibly due to low procaspase 8 expression. Here, we tested whether increasing procaspase 8 levels in CD4 T cells will produce more Casp8p41 following HIV reactivation, causing more reactivated cells to die. Screening 1277 FDA approved drugs identified 168 that increased procaspase 8 expression by at least 1.7-fold. Of these 30 were tested for anti-HIV effects in an acute HIV_IIIb infection model, and 9 drugs at physiologic relevant levels significantly reduced cell-associated HIV DNA. Primary CD4 T cells from ART suppressed HIV patients were treated with one of these 9 drugs and reactivated with αCD3/αCD28. Four drugs significantly increased Casp8p41 levels following HIV reactivation, and decreased total cell associated HIV DNA levels (flurbiprofen: p = 0.014; doxycycline: p = 0.044; indomethacin: p = 0.025; bezafibrate: P = 0.018) without effecting the viability of uninfected cells. Thus procaspase 8 levels can be increased pharmacologically and, in the context of HIV reactivation, increase Casp8p41 causing death of reactivating cells and decreased HIV DNA levels. Future studies will be required to define the clinical utility of this or similar approaches.

The cellular autophagy/apoptosis checkpoint during inflammation

Cell death is a major determinant of inflammatory disease severity. Whether cells live or die during inflammation largely depends on the relative success of the pro-survival process of autophagy versus the pro-death process of apoptosis. These processes interact and influence each other during inflammation and there is a checkpoint at which cells irrevocably commit to either one pathway or another. This review will discuss the concept of the autophagy/apoptosis checkpoint and its importance during inflammation, the mechanisms of inflammation leading up to the checkpoint, and how the checkpoint is regulated. Understanding these concepts is important since manipulation of the autophagy/apoptosis checkpoint represents a novel opportunity for treatment of inflammatory diseases caused by too much or too little cell death.

Virologic and immunologic aspects of HIV-hepatitis C virus coinfection

HIV/hepatitis C virus (HCV) coinfection is estimated to affect 2 million individuals globally. The acceleration of HCV-associated complications, particularly hepatic fibrosis, because of HIV coinfection has been well established, whereas the impact of HCV on HIV progression remains unclear. In this review, we summarize the current evidence on the impact of coinfection on the transmission and clinical progression of each infection. We focus on the virological and immunological alterations that contribute to HIV and HCV pathogenesis in coinfection and also review the disease-modifying effects of antiretroviral therapy as they pertain to HCV.

Hepatic fibrosis and immune phenotype vary by HCV viremia in HCV/HIV co-infected subjects: A Women's interagency HIV study

HCV and HIV independently lead to immune dysregulation. The mechanisms leading to advanced liver disease progression in HCV/HIV coinfected subjects remain unclear.In this cross-sectional study, we assessed the association of HCV viremia, liver fibrosis, and immune response patterns in well-characterized HIV phenotypes: Elite controllers (Elites), HIV controlled (ARTc), and HIV uncontrolled (ARTuc) matched by age and race. Groups were stratified by HCV RNA status. Regulatory T-cell frequencies, T-cell activation (HLADR+CD38+), apoptosis (Caspase-3+), and intracellular cytokines (interferon-γ, IL-2, IL-17) were assessed using multiparametric flow-cytometry. Liver fibrosis was scored by AST to platelet ratio index (APRI).We found liver fibrosis (APRI) was 50% lower in Elites and ARTc compared to ARTuc. Higher liver fibrosis was associated with significantly low CD4+ T cell counts (P < 0.001, coefficient r = -0.463). Immune activation varied by HIV phenotype but was not modified by HCV viremia. HCV viremia was associated with elevated CD8 T-cell Caspase-3 in Elites, ARTuc, and HIV- except ARTc. CD8 T-cell Caspase-3 levels were significantly higher in HCV RNA+ Elites (P = 0.04) and ARTuc (P = 0.001) and HIV- groups (P = 0.02) than ARTc. Importantly, ARTuc HCV RNA+ had significantly higher CD4 T-cell interleukin-17 levels than ARTuc HCV RNA- (P = 0.005).HIV control was associated with lower liver fibrosis in HCV/HIV co-infected women. HCV viremia is associated with an inflammatory CD4 TH-17 phenotype in absence of HIV control and higher frequency of pro-apoptosis CD8 T-cells critical to avert progression of HIV and HCV disease that is attenuated in ART controllers. Elite controllers with HCV viremia are more prone to CD8 T-cell apoptosis than ART controllers, which could have negative consequences over time, highlighting the importance of ART control in HCV/HIV coinfected individuals.

Impact of T cell activation, HIV replication and hepatitis C virus infection on neutrophil CD64 expression

BACKGROUND

Overexpression of the Fc receptor CD64 on neutrophils is associated with innate immune response and bacterial infections. During HIV infection a large set of immune disorders including T-lymphocyte over-activation, microbial translocation, impairment of neutrophil functions, and immunodeficiency may interplay with neutrophil CD64 expression.

METHODS

Associations of neutrophil CD64 expression with CD8⁺ T cell activation, CD4⁺ T cells number, HIV, and HCV replications were investigated in HIV infected patients using a standardized method.

RESULTS

Higher neutrophil CD64 expression was observed in HIV infected subjects compared to healthy controls (0.91 vs. 0.75, P < 0.001). Among 115 HIV infected patients, nine (8.8%) had a CD64 expression over the clinical threshold as calculated against bead standard (i.e., 1.5). HIV viremic patients were more likely to have an index above 1.5 (OR: 6.68, P values: 0.01). A trend for correlation between CD64 expression and CD8 T cell activation was observed (P values: 0.08). Blood CD4⁺ T lymphocyte depletion and HCV replication did not affect neutrophil CD64 expression.

CONCLUSIONS

HIV infection and HIV replication are associated with up-regulation of neutrophil CD64. CD64 overexpression above the clinical threshold was observed in a minor proportion of HIV infected individuals treated by antiretroviral therapy and may be a marker of neutrophil activation related to non-AIDS-linked comorbidities. © 2016 International Clinical Cytometry Society.

A NMF based approach for integrating multiple data sources to predict HIV-1-human PPIs

BACKGROUND

Predicting novel interactions between HIV-1 and human proteins contributes most promising area in HIV research. Prediction is generally guided by some classification and inference based methods using single biological source of information.

RESULTS

In this article we have proposed a novel framework to predict protein-protein interactions (PPIs) between HIV-1 and human proteins by integrating multiple biological sources of information through non negative matrix factorization (NMF). For this purpose, the multiple data sets are converted to biological networks, which are then utilized to predict modules. These modules are subsequently combined into meta-modules by using NMF based clustering method. The integrated meta-modules are used to predict novel interactions between HIV-1 and human proteins. We have analyzed the significant GO terms and KEGG pathways in which the human proteins of the meta-modules participate. Moreover, the topological properties of human proteins involved in the meta modules are investigated. We have also performed statistical significance test to evaluate the predictions.

CONCLUSIONS

Here, we propose a novel approach based on integration of different biological data sources, for predicting PPIs between HIV-1 and human proteins. Here, the integration is achieved through non negative matrix factorization (NMF) technique. Most of the predicted interactions are found to be well supported by the existing literature in PUBMED. Moreover, human proteins in the predicted set emerge as 'hubs' and 'bottlenecks' in the analysis. Low p-value in the significance test also suggests that the predictions are statistically significant.

Lipopolysaccharide Increases Immune Activation and Alters T Cell Homeostasis in SHIVB'WHU Chronically Infected Chinese Rhesus Macaque

Immune activation plays a significant role in the disease progression of HIV. Microbial products, especially bacterial lipopolysaccharide (LPS), contribute to immune activation. Increasing evidence indicates that T lymphocyte homeostasis disruptions are associated with immune activation. However, the mechanism by which LPS affects disruption of immune response is still not fully understood. Chronically SHIV_B'WHU-infected Chinese rhesus macaques received 50 μg/kg body weight LPS in this study. LPS administration affected the virus/host equilibrium by elevating the levels of viral replication and activating T lymphocytes. LPS induced upregulation of CD8⁺ naïve T cells and downregulated the number of CD4⁺ and CD8⁺ T effector memory cells. The downregulated effector memory cells are associated with a lower frequency of monofunctional and polyfunctional cells, and an upregulated programmed cell death-1 (PD-1) expression on CD4⁺ and CD8⁺ T cells was observed in monkeys after LPS stimulation. Our data provide new insights into the function of LPS in the immune activation in SHIV/HIV infection.

FAS -670 A/G polymorphism may be associated with the depletion of CD4(+) T lymphocytes in HIV-1 infection

In this study, the polymorphisms in the FAS and FASL genes was investigated in a sample of 198 HIV-1-seropositive individuals and 191 seronegative controls to evaluate a possible association between polymorphisms and the infection. The identification of the A and G alleles of the FAS -670 polymorphism was accomplished through polymerase chain reaction assays followed by digestion with the restriction enzyme MvaI. The identification of the A and G alleles of the FAS -124 polymorphism and the T and delT alleles of the FAS -169 polymorphism were performed using the amplification-created restriction site method followed by restriction fragment length polymorphism reactions. The comparative analysis of allelic and genotypic frequencies between the groups did not reveal any significant differences. However, the quantitative analysis of CD4(+) T lymphocytes suggests that the G allele of the FAS -670 A/G polymorphism can be a protective factor against the depletion of these cells in the course of an HIV-1 infection. Polymorphisms in the FAS and FASL genes were not associated with the number of CD8(+) T lymphocytes or the plasma viral load. Our findings suggest that the FAS -670 polymorphism may be associated with apoptosis of CD4(+) T lymphocytes after infection by HIV-1.

CD4+ T cells in HIV infection show increased levels of expression of a receptor for vasoactive intestinal peptide, VPAC2

Immune activation is a strong predictor of disease outcome in HIV infection and promotes the loss of CD4+ T cells. The neuropeptide, vasoactive intestinal peptide (VIP), has immune-modulating properties with specific receptors identified on lymphocytes; VPAC1 and VPAC2. Studies have shown that VIP limits immune activation and apoptosis in T cells by decreasing the expression of the apoptosis signaling molecule Fas ligand (FasL). VIP receptor surface expression has not been investigated by flow cytometry in the context of HIV infection and may represent a novel target for immune-modulating therapy. Eighty-seven untreated HIV-infected individuals with CD4 counts >200 and 57 uninfected controls were recruited from a primary health clinic in Cape Town, South Africa. Flow cytometry was used to determine levels of expression of VPAC1 and VPAC2, as well as FasL on CD4+ T cells, and these results were correlated with the immune activation phenotype %CD38+CD8+ T cells. VPAC2 expression was significantly increased in the HIV group (mean %VPAC2+CD4+ cells 19.25 vs. control 12.56; p ≤ 0.0001), but no difference in VPAC1 expression was observed. VPAC2 correlated positively with FasL (r = 0.310; p = 0.001), and there was a significant inverse correlation between FasL and the CD4 count (r = -0.211; p = 0.013) and a direct correlation with %CD38+CD8+ T cells (r = 0.39; p ≤ 0.0001). Thus, higher levels of immune activation correlated with higher levels of the death-signaling FasL and lower CD4 counts. VPAC2 may provide a novel target for the selective limitation of CD4+ T-cell death in HIV infection.

Short communication: Nitazoxanide inhibits HIV viral replication in monocyte-derived macrophages

We document the anti-HIV activity of nitazoxanide (NTZ), the first member of the thiazolide class of antiinfective drugs, originally effective against enteritis caused by Cryptosporidium parvum and Giardia lamblia. NTZ has been administered extensively worldwide, with no severe toxicities associated with its use. Here, we show for the first time that NTZ decreases HIV-1 replication in monocyte-derived macrophages (MDM) if present before or during HIV-1 infection. This NTZ effect is associated with downregulation of HIV-1 receptors CD4 and CCR5, and increasing gene expression of host cell anti-HIV resistance factors APOBEC3A/3G and tetherin. As NTZ is already in clinical use for other conditions, this newly described anti-HIV activity in MDM may facilitate innovative intensification strategies against HIV-1 when combined with current antiretroviral drug regimens.

Shift in monocyte apoptosis with increasing viral load and change in apoptosis-related ISG/Bcl2 family gene expression in chronically HIV-1-infected subjects

Although monocytes and macrophages are targets of HIV-1-mediated immunopathology, the impact of high viremia on activation-induced monocyte apoptosis relative to monocyte and macrophage activation changes remains undetermined. In this study, we determined constitutive and oxidative stress-induced monocyte apoptosis in uninfected and HIV(+) individuals across a spectrum of viral loads (n = 35; range, 2,243 to 1,355,998 HIV-1 RNA copies/ml) and CD4 counts (range, 26 to 801 cells/mm(3)). Both constitutive apoptosis and oxidative stress-induced apoptosis were positively associated with viral load and negatively associated with CD4, with an elevation in apoptosis occurring in patients with more than 40,000 (4.6 log) copies/ml. As expected, expression of Rb1 and interferon-stimulated genes (ISGs), plasma soluble CD163 (sCD163) concentration, and the proportion of CD14(++) CD16(+) intermediate monocytes were elevated in viremic patients compared to those in uninfected controls. Although CD14(++) CD16(+) frequencies, sCD14, sCD163, and most ISG expression were not directly associated with a change in apoptosis, sCD14 and ISG expression showed an association with increasing viral load. Multivariable analysis of clinical values and monocyte gene expression identified changes in IFI27, IFITM2, Rb1, and Bcl2 expression as determinants of constitutive apoptosis (P = 3.77 × 10(-5); adjusted R(2) = 0.5983), while changes in viral load, IFITM2, Rb1, and Bax expression were determinants of oxidative stress-induced apoptosis (P = 5.59 × 10(-5); adjusted R(2) = 0.5996). Our data demonstrate differential activation states in monocytes between levels of viremia in association with differences in apoptosis that may contribute to greater monocyte turnover with high viremia.

IMPORTANCE

This study characterized differential monocyte activation, apoptosis, and apoptosis-related gene expression in low- versus high-level viremic HIV-1 patients, suggesting a shift in apoptosis regulation that may be associated with disease state. Using single and multivariable analysis of monocyte activation parameters and gene expression, we supported the hypothesis that monocyte apoptosis in HIV disease is a reflection of viremia and activation state with contributions from gene expression changes within the ISG and Bcl2 gene families. Understanding monocyte apoptosis response may inform HIV immunopathogenesis, retention of infected macrophages, and monocyte turnover in low- or high-viral-load states.

Late-emerging strains of HIV induce T-cell homeostasis failure by promoting bystander cell death and immune exhaustion in naïve CD4 and all CD8 T-cells

The mechanisms involved in the decline of CD4 and CD8 T-cells that lead to HIV-induced immune dysregulation are not clearly understood. We hypothesize that late-emerging strains of HIV, such as CXCR4-tropic (X4) virions, induce T-cell homeostasis failure by promoting significantly more bystander cell death, and immune exhaustion in naïve CD4 and all CD8 T-cells, when compared to strain of HIV, such as CCR5-tropic (R5) virions, found early during the course of infection. In the reported study, inactivated X4 virions induced greater bystander cell death in sort-purified naïve CD4 T-cells compared to R5 virions, which was significant (p=0.013), and in memory CD8 T-cells, though the latter was not significant. A clearer understanding of the mechanisms involved in HIV-induced depletion of T-cell numbers and function could lead to therapies that prevent T-cell death and restore immune function. These therapies could improve current anti-retroviral and cure-related treatments by boosting the immune system's own ability to combat the virus.

Necroptosis takes place in human immunodeficiency virus type-1 (HIV-1)-infected CD4+ T lymphocytes

Human immunodeficiency virus type 1 (HIV-1) infection is characterized by progressive depletion of CD4+ T lymphocytes and dysfunction of the immune system. The numbers of CD4+ T lymphocytes in the human body are maintained constantly by homeostatic mechanisms that failed during HIV-1 infection, resulting in progressive loss of CD4+ T cells mainly via apoptosis. Recently, a non-apoptotic form of necrotic programmed cell death, named necroptosis, has been investigated in many biological and pathological processes. We then determine whether HIV-1-infected cells also undergo necroptosis. In this report, we demonstrate that HIV-1 not only induces apoptosis, but also mediates necroptosis in the infected primary CD4+ T lymphocytes and CD4+ T-cell lines. Necroptosis-dependent cytopathic effects are significantly increased in HIV-1-infected Jurkat cells that is lack of Fas-associated protein-containing death domain (FADD), indicating that necroptosis occurs as an alternative cell death mechanism in the absence of apoptosis. Unlike apoptosis, necroptosis mainly occurs in HIV-infected cells and spares bystander damage. Treatment with necrostatin-1(Nec-1), a RIP1 inhibitor that specifically blocks the necroptosis pathway, potently restrains HIV-1-induced cytopathic effect and interestingly, inhibits the formation of HIV-induced syncytia in CD4+ T-cell lines. This suggests that syncytia formation is mediated, at least partially, by necroptosis-related processes. Furthermore, we also found that the HIV-1 infection-augmented tumor necrosis factor-alpha (TNF-α) plays a key role in inducing necroptosis and HIV-1 Envelope and Tat proteins function as its co-factors. Taken together,necroptosis can function as an alternative cell death pathway in lieu of apoptosis during HIV-1 infection, thereby also contributing to HIV-1-induced cytopathic effects. Our results reveal that in addition to apoptosis, necroptosis also plays an important role in HIV-1-induced pathogenesis.

Role of inflammation in HIV-1 disease progression and prognosis

Inflammation and immune activation have been thrust to center stage in the understanding of HIV-1 disease pathogenesis and progression. Early work demonstrated that heightened levels of immune activation correlated with the extent of CD4 + T cell death in lymphoid tissue; however, this concept was not incorporated into the general view of disease pathogenesis. Since these early studies, the extension of life for patients on combination antiretroviral therapies (cART) has heralded a new era of non-AIDS-related diseases and incomplete restoration of immune function. The common link appears to be ongoing inflammation and immune activation. Thus, despite good control of viral loads, persons living with HIV (PLWH) remain at increased risk of inflammatory-associated complications such as cardiovascular disease and certain cancers. HIV-specific mechanisms as well as non-specific generalized responses to infection contribute to ongoing activation of the immune system. An early loss of gastrointestinal (GI) tract mucosal integrity, the pro-inflammatory cytokine milieu, co-infections and marked destruction of lymph node architecture are all factors contributing to the ongoing activation of the immune system as well as impaired immune recovery. It is becoming increasingly evident that the CD4 count and viral load do not provide a complete picture of the underlying state of the immune system. Heightened levels of inflammatory markers have been shown to predict increased mortality and other adverse events. Therefore, it will be important to incorporate these markers into management algorithms as soon as possible. This is particularly relevant in resource-poor countries where difficulties in cART roll-out and access are still encountered and, therefore, a mechanism for prioritizing individuals for therapy would be of value. This review will focus on the closely inter-related concepts of immune activation and inflammation. Both are broad concepts involving the interaction of various key players in the immune system. Importantly, immune activation promotes inflammation and thrombosis and similarly, inflammation and thrombosis induce immune activation. These concepts are thus intricately linked. Studies highlighting the potentially harmful effects of ongoing inflammation/immune activation are reviewed and the contributions of the GI tract "damage" and other co-infections such as CMV are explored. The complications resulting from persistent immune activation include enhanced CD4 + T cell death, lymphoid tissue destruction, and various pathologies related to chronic inflammation. Ultimately, we envision that the long-term management of the disease will incorporate both the identification and the amelioration of the potentially harmful effects of ongoing immune activation and inflammation.

The majority of CD4+ T-cell depletion during acute simian-human immunodeficiency virus SHIV89.6P infection occurs in uninfected cells

Untreated human immunodeficiency virus (HIV) infection is characterized by depletion of CD4(+) T cells, ultimately leading to the impairment of host immune defenses and death. HIV-infected CD4(+) T cells die from direct virus-induced apoptosis and CD8 T-cell-mediated elimination, but a broader and more profound depletion occurs in uninfected CD4(+) T cells via multiple indirect effects of infection. We fit mathematical models to data from experiments that tested an HIV eradication strategy in which five macaques with a proportion of CD4(+) T cells resistant to simian-human immunodeficiency virus (SHIV) entry were challenged with SHIV89.6P, a highly pathogenic dual-tropic chimeric SIV-HIV viral strain that results in rapid loss of both SHIV-susceptible and SHIV-resistant CD4(+) T cells. Our results suggest that uninfected (bystander) cell death accounts for the majority of CD4(+) T-lymphocyte loss, with at least 60% and 99% of CD4(+) T cell death occurring in uninfected cells during acute and established infection, respectively. Mechanisms to limit the profound indirect killing effects associated with HIV infection may be associated with immune preservation and improved long-term survival.

IMPORTANCE

HIV infection induces a massive depletion of CD4(+) T cells, leading to profound immunodeficiency, opportunistic infections, and eventually death. While HIV induces apoptosis (programmed cell death) by directly entering and replicating in CD4(+) T cells, uninfected CD4(+) T cells also undergo apoptosis due to ongoing toxic inflammation in the region of infection. In this paper, we use mathematical models in conjunction with data from simian-human immunodeficiency virus SHIV89.6P infection in macaques (a model of HIV infection in humans) to estimate the percentage of cell death that occurs in uninfected cells during the initial period of infection. We reveal that the vast majority of cell death occurs in these cells, which are not infected. The "bystander effects" that lead to enormous reductions in the number of uninfected CD4(+) T cells may be a target for future interventions that aim to limit the extent of damage caused by HIV.

Apoptosis in virus infection dynamics models

In this paper, on the basis of the simplified two-dimensional virus infection dynamics model, we propose two extended models that aim at incorporating the influence of activation-induced apoptosis which directly affects the population of uninfected cells. The theoretical analysis shows that increasing apoptosis plays a positive role in control of virus infection. However, after being included the third population of cytotoxic T lymphocytes immune response in HIV-infected patients, it shows that depending on intensity of the apoptosis of healthy cells, the apoptosis can either promote or comfort the long-term evolution of HIV infection. Further, the discrete-time delay of apoptosis is incorporated into the pervious model. Stability switching occurs as the time delay in apoptosis increases. Numerical simulations are performed to illustrate the theoretical results and display the different impacts of a delay in apoptosis.

HIV and interferon regulatory factor 1: a story of manipulation and control

Members of the interferon regulatory factor (IRF) family control the expression of numerous proteins, many of which are central to regulating host immune responses. IRF1 is one of the central mediators of the innate and adaptive immune responses required for antigen processing and presentation, Th1/Th2 differentiation, and natural killer (NK) cell and macrophage function. Many viruses have evolved mechanisms to target the IRF1 pathway in order to promote viral pathogenesis. During early HIV infection, IRF1 acts as a double-edged sword, critical for driving viral replication as well as eliciting antiviral responses. In this review, we describe the strategies that HIV-1 has evolved to modulate IRF1 in order to enhance viral replication and to disarm the host immune system. IRF1 has been shown to be an important factor in natural protection against HIV in highly exposed seronegative (HESN) individuals and is crucial in regulating the initial stages of HIV replication and HIV disease progression, as well as the establishment of latency. An understanding of how the protective effects of IRF1 responses are controlled in HESN individuals, naturally resistant to HIV infection, may provide important clues on how to regain control of HIV and tip the balance of immunity in favor of the host, or provide new opportunities to eliminate HIV in its host altogether.

Immune activation and HIV persistence: considerations for novel therapeutic interventions

PURPOSE OF REVIEW

One of the potential barriers to current HIV cure strategies is the persistence of elevated levels of immune activation despite otherwise effective antiretroviral therapy (ART). The purpose of this review is to examine the relationship between immune activation and HIV persistence, and to review the novel therapeutic interventions that are currently being pursued to target immune activation in treated HIV disease.

RECENT FINDINGS

Multiple groups have consistently observed that elevated levels of inflammation, immune activation, and immune dysfunction persist in ART-treated individuals, despite the successful suppression of plasma viremia. Increased immune activation may lead to viral persistence through multiple mechanisms. Several novel interventions aimed at decreasing persistent immune activation are being pursued and include studies aimed at decreasing low-level viral replication, approaches aimed at decreasing microbial translocation, interventions to treat co-infections, and therapies that directly target immune activation.

SUMMARY

There appears to be a clear and consistent relationship between immune activation and viral persistence in treated HIV disease. Whether this relationship is causal or mediated through other mechanisms is still unknown. Small-scale, pathogenesis-oriented interventional studies are necessary to further evaluate this relationship and the effect of potential interventions.

Long-term suppression of HIV-1C virus production in human peripheral blood mononuclear cells by LTR heterochromatization with a short double-stranded RNA

OBJECTIVES

A region in the conserved 5' long terminal repeat (LTR) promoter of the integrated HIV-1C provirus was identified for effective targeting by a short double-stranded RNA (dsRNA) to cause heterochromatization leading to a long-lasting decrease in viral transcription, replication and subsequent productive infection in human host cells.

METHODS

Small interfering RNAs (siRNAs) were transfected into siHa cells containing integrated LTR-luciferase reporter constructs and screened for efficiency of inducing transcriptional gene silencing (TGS). TGS was assessed by a dual luciferase assay and real-time PCR. Chromatin modification at the targeted region was also studied. The efficacy of potent siRNA was then checked for effectiveness in TZM-bl cells and human peripheral blood mononuclear cells (PBMCs) infected with HIV-1C virus. Viral Gag-p24 antigen levels were determined by ELISA.

RESULTS

One HIV-1C LTR-specific siRNA significantly decreased luciferase activity and its mRNA expression with no such effect on HIV-1B LTR. This siRNA-mediated TGS was induced by histone methylation, which leads to heterochromatization of the targeted LTR region. The same siRNA also substantially suppressed viral replication in TZM-bl cells and human PBMCs infected with various HIV-1C clinical isolates for ≥3 weeks after a single transfection, even of a strain that had a mismatch in the target region.

CONCLUSIONS

We have identified a potent dsRNA that causes long-term suppression of HIV-1C virus production in vitro and ex vivo by heritable epigenetic modification at the targeted C-LTR region. This dsRNA has promising therapeutic potential in HIV-1C infection, the clade responsible for more than half of AIDS cases worldwide.

HIV-1 Vpu - an ion channel in search of a job

Vpu is a small membrane protein encoded by HIV-1 and some SIV isolates. The protein is best known for its ability to degrade CD4 and to enhance the release of progeny virions from infected cells. However, Vpu also promotes host-cell apoptosis by deregulating the NFκB signaling pathway and it assembles into cation-conducting membrane pores. This review summarizes our current understanding of these various functions of Vpu with particular emphasis on recent progress in the Vpu field. This article is part of a Special Issue entitled: Viral Membrane Proteins - Channels for Cellular Networking.

Assessing main death pathways in T lymphocytes from HIV infected individuals

Increased lymphocyte death is a hallmark of human immunodeficiency virus (HIV) infection. Although virological factors have been linked to this phenomenon, increased cell death rates are still observed in treated individuals in which viral replication is halted. To understand the nature of this remaining altered cell death, we have developed a simple and fast assay to assess major cell death pathways in lymphocytes isolated from HIV-infected individuals. The combination of three factors: (i) antibody staining to identify CD3(+) CD4(+) and CD3(+) CD8(+) cells, (ii) assessment of mitochondrial and plasma membrane function using DiOC6(3) or JC-1 probes and vital dyes, and (iii) caspase inhibition, allowed for the quantification of caspase-independent and -dependent cell death in CD4 and CD8 T cells. The latter mechanism was divided in intrinsic and extrinsic apoptotic pathways according to the sensitivity of the dissipation of mitochondrial membrane potential to Z-VAD-fmk or Q-VD-oPH treatment. Our data show similar results for both caspase inhibitors in treated infected individuals, whereas Q-VD-oPH showed a more potent inhibition in viremic individuals, yielding lower levels of intrinsic apoptosis. Comparison of DiOC6(3) and JC-1 probes yielded similar results in CD4 T cells, allowing for a clear definition of death mechanism in these cells. However, in CD8 T-cells, JC-1 showed heterogeneous staining and detected significantly lower levels of cell death with a higher contribution of intrinsic apoptosis. In conclusion, we provide a simple method to assess CD4 T-cell death mechanisms in HIV-infected individuals. The reasons and consequences of mitochondrial heterogeneity in CD8 T-cells require further evaluation.

Genetic characterization of natural variants of Vpu from HIV-1 infected individuals from Northern India and their impact on virus release and cell death

BACKGROUND

Genetic studies reveal that vpu is one of the most variable regions in HIV-1 genome. Functional studies have been carried out mostly with Vpu derived from laboratory adapted subtype B pNL 4-3 virus. The rationale of this study was to characterize genetic variations that are present in the vpu gene from HIV-1 infected individuals from North-India (Punjab/Haryana) and determine their functional relevance.

METHODS

Functionally intact vpu gene variants were PCR amplified from genomic DNA of HIV-1 infected individuals. These variants were then subjected to genetic analysis and unique representative variants were cloned under CMV promoter containing expression vector as well as into pNL 4-3 HIV-1 virus for intracellular expression studies. These variants were characterized with respect to their ability to promote virus release as well as cell death.

RESULTS

Based on phylogenetic analysis and extensive polymorphisms with respect to consensus Vpu B and C, we were able to arbitrarily assign variants into two major groups (B and C). The group B variants always showed significantly higher virus release activity and exhibited moderate levels of cell death. On the other hand, group C variants displayed lower virus release activity but greater cell death potential. Interestingly, Vpu variants with a natural S61A mutation showed greater intracellular stability. These variants also exhibited significant reduction in their intracellular ubiquitination and caused greater virus release. Another group C variant that possessed a non-functional β-TrcP binding motif due to two critical serine residues (S52 and S56) being substituted with isoleucine residues, showed reduced virus release activity but modest cytotoxic activity.

CONCLUSIONS

The natural variations exhibited by our Vpu variants involve extensive polymorphism characterized by substitution and deletions that contribute toward positive selection. We identified two major groups and an extremely rare β-TrcP binding motif mutant that show widely varying biological activities with potential implications for conferring subtype-specific pathogenesis.