Death ligand-mediated apoptosis in HIV infection

Basic science and pathogenesis of ageing with HIV: potential mechanisms and biomarkers

: The increased prevalence of age-related comorbidities and mortality is worrisome in ageing HIV-infected patients. Here, we aim to analyse the different ageing mechanisms with regard to HIV infection. Ageing results from the time-dependent accumulation of random cellular damage. Epigenetic modifications and mitochondrial DNA haplogroups modulate ageing. In antiretroviral treatment-controlled patients, epigenetic clock appears to be advanced, and some haplogroups are associated with HIV infection severity. Telomere shortening is enhanced in HIV-infected patients because of HIV and some nucleoside analogue reverse transcriptase inhibitors. Mitochondria-related oxidative stress and mitochondrial DNA mutations are increased during ageing and also by some nucleoside analogue reverse transcriptase inhibitors. Overall, increased inflammation or 'inflammageing' is a major driver of ageing and could result from cell senescence with secreted proinflammatory mediators, altered gut microbiota, and coinfections. In HIV-infected patients, the level of inflammation and innate immunity activation is enhanced and related to most comorbidities and to mortality. This status could result, in addition to age, from the virus itself or viral protein released from reservoirs, from HIV-enhanced gut permeability and dysbiosis, from antiretroviral treatment, from frequent cytomegalovirus and hepatitis C virus coinfections, and also from personal and environmental factors, as central fat accumulation or smoking. Adaptive immune activation and immunosenescence are associated with comorbidities and mortality in the general population but are less predictive in HIV-infected patients. Biomarkers to evaluate ageing in HIV-infected patients are required. Numerous systemic or cellular inflammatory, immune activation, oxidative stress, or senescence markers can be tested in serum or peripheral blood mononuclear cells. The novel European Study to Establish Biomarkers of Human Ageing MARK-AGE algorithm, evaluating the biological age, is currently assessed in HIV-infected patients and reveals an advanced biological age. Some enhanced inflammatory or innate immune activation markers are interesting but still not validated for the patient's follow-up. To be able to assess patients' biological age is an important objective to improve their healthspan.

T-Cell Signaling in HIV-1 Infection

HIV exploits the T-cell signaling network to gain access to downstream cellular components, which serves as effective tools to break the cellular barriers. Multiple host factors and their interaction with viral proteins contribute to the complexity of HIV-1 pathogenesis and disease progression. HIV-1 proteins gp120, Nef, Tat and Vpr alter the T-cell signaling pathways by activating multiple transcription factors including NF-ĸB, Sp1 and AP-1. HIV-1 evades the immune system by developing a multi-pronged strategy. Additionally, HIV-1 encoded proteins influence the apoptosis in the host cell favoring or blocking T-cell apoptosis. Thus, T-cell signaling hijacked by viral proteins accounts for both viral persistence and immune suppression during HIV-1 infection. Here, we summarize past and present studies on HIV-1 T-cell signaling with special focus on the possible role of T cells in facilitating viral infection and pathogenesis

CD4+ T cell depletion in human immunodeficiency virus (HIV) infection: role of apoptosis

Human immunodeficiency virus (HIV) infection is principally a mucosal disease and the gastrointestinal (GI) tract is the major site of HIV replication. Loss of CD4+ T cells and systemic immune hyperactivation are the hallmarks of HIV infection. The end of acute infection is associated with the emergence of specific CD4+ and CD8+ T cell responses and the establishment of a chronic phase of infection. Abnormal levels of immune activation and inflammation persist despite a low steady state level of viremia. Although the causes of persistent immune hyperactivation remain incompletely characterized, physiological alterations of gastrointestinal tract probably play a major role. Failure to restore Th17 cells in gut-associated lymphoid tissues (GALT) might impair the recovery of the gut mucosal barrier. This review discusses recent advances on understanding the contribution of CD4+ T cell depletion to HIV pathogenesis.

The death-promoting molecule tumour necrosis factor-related apoptosis inducing ligand (TRAIL) is not required for the development of peripheral lymphopenia or granuloma necrosis during infection with virulent Mycobacterium avium

Disseminated infection with virulent Mycobacterium avium in C57Bl/6 (B6) mice leads to severe lymphocyte depletion in secondary lymphoid organs. In this study, we found an up-regulation of caspase-8 activity in spleen cell extracts from M. avium 25291-infected B6 mice compared to non-infected mice. The activation of this extrinsic apoptotic pathway correlated with an increase in inter-nucleosomal DNA fragmentation in CD4(+) spleen cells, as analysed by the terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay. These data suggest the involvement of death receptors in the induction of lymphocyte loss in the spleen, but previous work has excluded a role for tumour necrosis factor (TNF) receptors and Fas/CD95 in M. avium-induced lymphopenia. TNF-related apoptosis-inducing ligand (TRAIL) is expressed by different cell types of the immune system and induces apoptosis and killing of tumour cells while sparing normal cells. Here we used TRAIL(-/-) mice to determine if the absence of TRAIL prevented M. avium-induced immune pathology. We found that TRAIL-deficient mice still developed splenic lymphopenia during disseminated infection or granuloma necrosis during low-dose infections while exhibiting slightly increased susceptibility to M. avium 25291 when compared to B6 mice. However, in vivo proliferation of less virulent strains of M. avium was not influenced by TRAIL deficiency despite a decrease in interferon-γ production in infected B6.TRAIL(-/-) mice compared to B6 mice. Our results show that TRAIL does not play a significant role in either M. avium-induced pathology or protective immunity.

Apoptosis: a clinically useful measure of antiretroviral drug toxicity?

Antiretroviral therapy (ART) has improved life expectancy with HIV infection, but long-term toxicities associated with these medications are now a major global disease burden. There is a clear need to develop useful methods for monitoring patients on antiretroviral drugs for early signs of toxicity. Assays with predictive utility -- allowing therapy to be changed before serious end organ damage occurs -- would be ideal. Attempts to develop biochemical methods of monitoring ART toxicity have concentrated on the mitochondrial toxicity of nucleoside analogue reverse transcriptase inhibitors and have not generally lead to assays with widespread clinical applications. For example, plasma lactate and peripheral blood measurements of mitochondrial DNA associate with exposure to potentially toxic nucleoside analogue reverse transcriptase inhibitors but have not reliably predicted clinical toxicity. Better assays are needed, including markers of toxicity from additional drug classes. Apoptosis may be a potential marker of ART toxicity. Increased apoptosis has been demonstrated both in vitro and in vivo in association with various antiretroviral drug classes and a range of clinical toxicities. However, quantifying apoptosis on biopsy specimens of tissue (such as adipose tissue) is impractical for patient monitoring. Novel assays have been described that can quantify apoptosis using minute tissue samples and initial results from clinical samples suggest peripheral blood may have utility in predicting ART toxicities. The limitations and potential of such techniques for monitoring patients for drug side effects will be discussed.

Role of the Fas/FasL pathway in HIV or SIV disease

Human immunodeficiency virus disease involves progressive destruction of host immunity leading to opportunistic infections and increased rates for malignancies. Both depletion in immune cell numbers as well as defects in their effector functions are responsible for this immunodeficiency The broad impact of HIV reflects a similarly broad pattern of cell depletion including subsets that do not express viral receptors or support viral replication. Indirect cell killing, the destruction of uninfected cells, is due partly to activation of the Fas/FasL system for cell death. This death-signaling pathway is induced during HIV disease and contributes significantly to viral pathogenesis and disease.

Effects of HCV co-infection on apoptosis of CD4+ T-cells in HIV-positive patients

Apoptosis importantly contributes to loss of CD4+ T-cells in HIV infection, and modification of their apoptosis may explain why HIV/HCV (hepatitis C virus)-co-infected patients are more likely to die from liver-related causes, although the effects of HCV on HIV infection remain unclear. In the present study, we studied in a cross-sectional and serial analysis spontaneous ex vivo CD4+ T-cell apoptosis in HIV/HCV-co-infected and HIV-mono-infected patients before and after HAART (highly active antiretroviral therapy). Apoptosis of peripheral blood CD4+ T-cells was measured by both a PARP [poly(ADP-ribose) polymerase] and TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling) assay to detect cells with irreversible apoptosis. Although hepatitis C alone did not increase CD4+ T-cell apoptosis, HCV co-infection disproportionately increased elevated rates of apoptosis in CD4+ T-cells from untreated HIV-positive patients. Increased CD4+ T-cell apoptosis was closely correlated with HIV, but not HCV, viral loads. Under HAART, increased rates of CD4+ T-cell apoptosis rapidly decreased both in HIV-mono-infected and HIV/HCV-co-infected patients, without any significant difference in apoptosis rates between the two patient groups after 4 weeks of therapy. Nevertheless residual CD4+ T-cell apoptosis did not reach the normal levels seen in healthy controls and remained higher in HIV patients receiving protease inhibitors than in patients with other antiretroviral regimens. The results of the present study suggest that HCV co-infection sensitizes CD4+ T-cells towards apoptosis in untreated HIV-positive patients. However, this effect is rapidly lost under effective antiretroviral therapy.

Effect of antiretroviral therapy on apoptosis markers and morphology in peripheral lymph nodes of HIV-infected individuals

BACKGROUND

CD4+ T cell depletion and destruction and the involution of the lymphoid tissue are hallmarks of HIV infection. Although the underlying mechanisms are still unclear, apoptosis appears to play a central role. The objective of this study was to investigate the effect of antiretroviral therapy on the lymph node tissue, particularly with respect to morphology and apoptosis.

PATIENTS AND METHODS

Between 1997 and 1999, two inguinal lymph nodes were excised from 31 previously untreated individuals who were in an early stage of HIV infection, the first one prior to treatment and the second after 16 to 20 months of treatment. Paraffin sections were investigated for lymph node architecture, distribution of cellular and viral markers, apoptosis, and expression of apoptotic key molecules which indirectly reflect apoptotic processes.

RESULTS

After 16-20 months of antiretroviral therapy, a significant decrease in highly activated HIV-driven immune response was observed in the lymph node tissue as a marked reduction in follicular hyperplasia, a normalization of the follicular dendritic cell network, a significant increase in the number of CD4+ T cells, and a significant decrease in the number of CD8+ T cells. The expression of several proapoptotic (Fas, TRAIL, and active caspase 3) and antiapoptotic (Bcl-2 and IL-7Ralpha) molecules that were reconstituted in the tissues during therapy resembled their expression in lymph nodes of HIV-negative individuals. Limitations of the study are (a) the lack of untreated patients in the late stages, (b) for ethical reasons, the lack of a control group with untreated patients, and (c) for methodological reasons, the restriction of sequential measurements of apotpotic markers to one-third of the patients.

CONCLUSION

Antiretroviral therapy initiated in the early stages in HIV infection may halt the irreversible destruction of the lymph node tissue and may partially normalize apoptotic processes.

Inhibition of apoptosis prevents West Nile virus induced cell death

Background

West Nile virus (WNV) infection can cause severe meningitis and encephalitis in humans. Apoptosis was recently shown to contribute to the pathogenesis of WNV encephalitis. Here, we used WNV-infected glioma cells to study WNV-replication and WNV-induced apoptosis in human brain-derived cells.

Results

T98G cells are highly permissive for lytic WNV-infection as demonstrated by the production of infectious virus titre and the development of a characteristic cytopathic effect. WNV replication decreased cell viability and induced apoptosis as indicated by the activation of the effector caspase-3, the initiator caspases-8 and -9, poly(ADP-ribose)polymerase (PARP) cleavage and the release of cytochrome c from the mitochondria. Truncation of BID indicated cross-talk between the extrinsic and intrinsic apoptotic pathways. Inhibition of the caspases-8 or -9 inhibited PARP cleavage, demonstrating that both caspases are involved in WNV-induced apoptosis. Pan-caspase inhibition prevented WNV-induced apoptosis without affecting virus replication.

Conclusion

We found that WNV infection induces cell death in the brain-derived tumour cell line T98G by apoptosis under involvement of constituents of the extrinsic as well as the intrinsic apoptotic pathways. Our results illuminate the molecular mechanism of WNV-induced neural cell death.

Human and simian immunodeficiency virus-mediated upregulation of the apoptotic factor TRAIL occurs in antigen-presenting cells from AIDS-susceptible but not from AIDS-resistant species

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infections lead to AIDS in humans and rhesus macaques (RM), while they are asymptomatic in species naturally infected with SIV, such as chimpanzees, sooty mangabeys (SM), and African green monkeys (AGM). Differential CD4(+) T-cell apoptosis may be responsible for these species-specific differences in susceptibility to disease. To identify factors that influence the different apoptotic responses of these species, we analyzed virus-infected human and nonhuman primate peripheral blood mononuclear cells (PBMC). We found that the apoptotic factor TRAIL was present at higher levels in human and RM PBMC cultures and was mediating, at least in part, CD4(+) T-cell apoptosis in these cultures. The species-specific increase in TRAIL and death receptor expression observed with cultures also occurred in vivo in SIV-infected RM but not in SIV-infected SM. In human and RM myeloid immature dendritic cells and macrophages, the virus-induced expression of TRAIL and other interferon-inducible genes, which did not occur in the same cells from chimpanzee, SM, and AGM, was Tat dependent. Our results link the differential induction of TRAIL in human and nonhuman primate cells to species-specific differences in disease susceptibility.

Apoptotic cell signaling in lymphocytes from HIV+ patients during successful therapy

The impact of antiretroviral therapy (ART) on immune-reconstitution and its relationship with the complex scenario of multiple cell signaling associated with apoptosis in HIV infection has not yet been fully elucidated. Here we report the results of the analysis of the expression of 13 genes involved in the apoptotic pathway, simultaneously detected by RNA-protection assay in peripheral blood mononuclear cells (PBMCs) of 12 HIV-1-infected responder patients before and during successful ART. In particular, we calculated the correlations among apoptosis and viral load (VL) levels versus the quantitative expression of genes associated with death receptors or to Bcl-2 pathways. Nonparametric bivariate Spearman's analysis of significant correlations showed that apoptosis was directly correlated with mRNA levels for caspase-8, FasL, and TRAIL. Conversely, apoptosis levels were inversely correlated with mRNA levels for Bcl-xl, Bcl-2, and Mcl-1, respectively. In addition, while VL was directly correlated with the expression of caspase 8, it was inversely correlated with mRNA levels for Bcl-2 and Mcl-1. These results, although worthy of further investigation, show that variations of apoptosis levels in PBMCs of HIV-1+ patients during ART are strictly related to the modulation of a complex network of signaling involving both death and survival of lymphocytes.

Apoptosis-associated gene expression in HIV-infected patients in response to successful antiretroviral therapy

The simultaneous expression of 19 apoptosis-related genes was analyzed by RNA-protection assay in peripheral blood mononuclear cells of HIV-infected patients before and during successful antiretroviral therapy (ART). After 12 months of therapy, the expression of the pro-apoptotic genes FAS, FAS-L, FAF-1, FADD, CASPASE-8, DR3, TRAIL, TNFR-1, TRADD, and BAX was significantly downregulated with respect to time 0, while that of BCL-2, BCL-XL, and MCL-1 was significantly upregulated. The data suggest that inhibition of cell death in HIV-positive patients under successful therapy is the result of a complex network of multifactor signaling, correlated with both death and survival of lymphocytes.

HIV-1 gp120/V3-derived epitopes promote activation-induced cell death to superantigen-stimulated CD4+/CD45RO+ T cells

The third hypervirable (V3) domain of the HIV-1 envelope glycoprotein gp120 has been implicated in HIV pathogenesis via co-receptor usage of chemokine receptors CCR5 and CXCR4. As the protagonist cell populations in the asymptomatic phase of HIV-1 infection are infected macrophages and effector/memory (CD45RO+) CD4+ T cells that express CCR5, we established an in vitro model using human primary monocyte-derived macrophages and lymphocytes to investigate the role of V3 in affecting antigen presentation. We used staphylococcal enterotoxin A (SEA) as a superantigen at a low concentration of 1ng/ml, to activate naïve CD4+ T cells. Exposure of cells to SEA and lipoV3-liposomes increased the percentage of CD4+/CD45RO+/CCR5+ T cell population as compared to cells treated with SEA and plain liposomes. A consequent decrease of the percentage of CD4+/CD45RO+/CXCR4+ subset was observed. The V3-mediated activation was competitively inhibited by soluble V3-derived peptides with higher cationic charge. V3 enhanced also apoptosis as demonstrated by flow cytometry and intracellular calcium ion assays. These results reinforce the postulation that V3 alters the antigen presentation function itself, independent of specific antigens, thus leading to an enhanced activation-induced cell death (AICD) of responding T cells.

Trapping and apoptosis of novel subsets of memory T lymphocytes expressing CCR6 in the spleen of HIV-infected patients

CCR6, a homeostatic chemokine receptor, is shown here to characterize subsets of both central and effector memory T cells that secrete high levels of IL-2 and TNF-alpha in response to polyclonal and antigen-specific stimulation. CCR6(+) T lymphocytes disappeared dramatically from the peripheral blood of HIV-infected patients as HIV disease progressed. The capacity of CD4(+)CCR6(+) to secrete multiple cytokines remained intact among HIV-infected long-term nonprogressors but was partially lost from subjects with standard disease progression. CCR6(+) T lymphocytes, regardless of their CCR7 expression, accumulated in the spleen of HIV-infected patients, where they died by apoptosis. Assessment of CCR6 expression allowed us to describe novel memory T-cell subpopulations capable of high cytokine production and provided evidence of a pathologic CCR6-dependent pathway of memory T-cell homing that may participate in the loss of memory response against infections.

The human immunodeficiency virus type 1 tat protein enhances Cryptosporidium parvum-induced apoptosis in cholangiocytes via a Fas ligand-dependent mechanism

While Cryptosporidium parvum infection of the intestine has been reported in both immunocompetent and immunocompromised individuals, biliary infection is seen primarily in adult AIDS patients and is associated with development of AIDS cholangiopathy. However, the mechanisms of pathogen-induced AIDS cholangiopathy remain unclear. Since we previously demonstrated that the Fas/Fas ligand (FasL) system is involved in paracrine-mediated C. parvum cytopathicity in cholangiocytes, we also tested the potential synergistic effects of human immunodeficiency virus type 1 (HIV-1) transactivator of transcription (Tat)-mediated FasL regulation on C. parvum-induced apoptosis in cholangiocytes by semiquantitative reverse transcription-PCR, immunoblotting, immunofluorescence analysis, and immunogold electron microscopy. H69 cells do not express CXCR4 and CCR5, which are receptors required for direct HIV-1 viral infection. However, recombinant biologically active HIV-1-associated Tat protein increased FasL expression in the cytoplasm of cholangiocytes without a significant increase in apoptosis. We found that C. parvum-induced apoptosis was associated with translocation of intracellular FasL to the cell membrane surface and release of full-length FasL from infected H69 cells. Tat significantly (P < 0.05) increased C. parvum-induced apoptosis in bystander cells in a dose-dependent manner. Moreover, Tat enhanced both C. parvum-induced FasL membrane translocation and release of full-length FasL. In addition, the FasL neutralizing antibody NOK-1 and the caspase-8 inhibitor Z-IETD-fmk both blocked C. parvum-induced apoptosis in cholangiocytes. The data demonstrated that HIV-1 Tat enhances C. parvum-induced cholangiocyte apoptosis via a paracrine-mediated, FasL-dependent mechanism. Our results suggest that concurrent active HIV replication, with associated production of Tat protein, and C. parvum infection synergistically increase cholangiocyte apoptosis and thus jointly contribute to AIDS-related cholangiopathies.

Effect of subchronic exposure to acrylamide induced on the expression of bcl-2, bax and caspase-3 in the rat nervous system

Occupational exposure and experimental intoxication with acrylamide (ACR) produce a neuropathy characterized by nerve degeneration. We hypothesize that ACR differentially affects the expression of bcl-2, bax and caspase-3 in the central nervous system (CNS) and the peripheral nervous system (PNS) tissue. Male adult Wistar rats were given ACR (20, 40 mg/kg i.p. 3 days/week) for 8 weeks. Samples of the cerebral cortex, cerebellum, spinal cord and sciatic nerves were collected and examined for bcl-2, bax and caspase-3 expression using Western blotting. Subchronic exposure to ACR reduced cortical bcl-2 expression in the low dose, increased it in the high dose; the change of bcl-2 expression in the spinal cord and cerebellum followed the same pattern as that described in the cerebral cortex; there was no significant change in the expression of bax in the cerebral cortex and the spinal cord, however, in the cerebellum the change of bax expression and bcl-2 expression is just the reverse. Thus, the bcl-2/bax ratio of the CNS tissue was affected by exposure to ACR, it decreased in the low dose group and increased in the high group. Compared to control, densitometric analysis showed that in the sciatic nerves the expression of bcl-2 and bax expression was markedly increased following ACR administration. The expression of inactive isoforms (32 kDa) of caspase-3 was not altered in the cortices of ACR-treated rats, but increased in their spinal cords and sciatic nerves. Thus, subchronic exposure to ACR affected the expression of death-related proteins in the CNS and PNS tissue, which indicate there is the early molecular regulatory mechanism of apoptosis in the neuropathy induced by ACR.