Combined effects of hyperglycemic conditions and HIV-1 Nef: a potential model for induced HIV neuropathogenesis

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

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

HIV in the cART era and the mitochondrial: immune interface in the CNS

HIV-associated neurocognitive disorders (HAND) persist in the era of effective combined antiretroviral therapy (cART). A large body of literature suggests that mitochondrial dysfunction is a prospective etiology of HAND in the cART era. While viral load is often suppressed and the immune system remains intact in HIV+ patients on cART, evidence suggests that the central nervous system (CNS) acts as a reservoir for virus and low-level expression of viral proteins, which interact with mitochondria. In particular, the HIV proteins glycoprotein 120, transactivator of transcription, viral protein R, and negative factor have each been linked to mitochondrial dysfunction in the brain. Moreover, cART drugs have also been shown to have detrimental effects on mitochondrial function. Here, we review the evidence generated from human studies, animal models, and in vitro models that support a role for HIV proteins and/or cART drugs in altered production of adenosine triphosphate, mitochondrial dynamics, mitophagy, calcium signaling and apoptosis, oxidative stress, mitochondrial biogenesis, and immunometabolism in the CNS. When insightful, evidence of HIV or cART-induced mitochondrial dysfunction in the peripheral nervous system or other cell types is discussed. Lastly, therapeutic approaches to targeting mitochondrial dysfunction have been summarized with the aim of guiding new investigations and providing hope that mitochondrial-based drugs may provide relief for those suffering with HAND.

Immunomodulatory Role of Complement Proteins in the Neuropathology Associated with Opiate Abuse and HIV-1 Co-Morbidity

The complement system which is a critical mediator of innate immunity plays diverse roles in the neuropathogenesis of HIV-1 infection such as clearing HIV-1 and promoting productive HIV-1 replication. In the development of HIV-1 associated neurological disorders (HAND), there may be an imbalance between complement activation and regulation, which may contribute to the neuronal damage as a consequence of HIV-1 infection. It is well recognized that opiate abuse exacerbates HIV-1 neuropathology, however, little is known about the role of complement proteins in opiate induced neuromodulation, specifically in the presence of co-morbidity such as HIV-1 infection. Complement levels are significantly increased in the HIV-1-infected brain, thus HIV-induced complement synthesis may represent an important mechanism for the pathogenesis of AIDS in the brain, but remains underexplored. Anti-HIV-1 antibodies are able to initiate complement activation in HIV-1 infected CNS cells such as microglia and astrocytes during the course of disease progression; however, this complement activation fails to clear and eradicate HIV-1 from infected cells. In addition, the antiretroviral agents used for HIV therapy cause dysregulation of lipid metabolism, endothelial, and adipocyte cell function, and activation of pro-inflammatory cytokines. We speculate that both HIV-1 and opiates trigger a cytokine-mediated pro-inflammatory stimulus that modulates the complement cascade to exacerbate the virus-induced neurological damage. We examined the expression levels of C1q, SC5b-9, C5L2, C5aR, C3aR, and C9 key members of the complement cascade both in vivo in post mortem brain frontal cortex tissue from patients with HAND who used/did not use heroin, and in vitro using human microglial cultures treated with HIV tat and/or heroin. We observed significant expression of C1q and SC5b-9 by immunofluorescence staining in both the brain cortical and hippocampal region in HAND patients who abused heroin. Additionally, we observed increased gene expression of C5aR, C3aR, and C9 in the brain tissue of both HIV-1 infected patients with HAND who abused and did not abuse heroin, as compared to HIV negative controls. Our results show a significant increase in the expression of complement proteins C9, C5L2, C5aR, and C3aR in HIV transfected microglia and an additional increase in the levels of these complement proteins in heroin-treated HIV transfected microglia. This study highlights the a) potential roles of complement proteins in the pathogenesis of HIV-1-related neurodegenerative disorders; b) the combined effect of an opiate, like heroin, and HIV viral protein like HIV tat on complement proteins in normal human microglial cells and HIV transfected microglial cells. In the context of HAND, targeting selective steps in the complement cascade could help ameliorating the HIV burden in the CNS, thus investigations of complement-related therapeutic approaches for the treatment of HAND are warranted.

An Overview of Human Immunodeficiency Virus Type 1-Associated Common Neurological Complications: Does Aging Pose a Challenge?

With increasing survival of patients infected with human immunodeficiency virus type 1 (HIV-1), the manifestation of heterogeneous neurological complications is also increasing alarmingly in these patients. Currently, more than 30% of about 40 million HIV-1 infected people worldwide develop central nervous system (CNS)-associated dysfunction, including dementia, sensory, and motor neuropathy. Furthermore, the highly effective antiretroviral therapy has been shown to increase the prevalence of mild cognitive functions while reducing other HIV-1-associated neurological complications. On the contrary, the presence of neurological disorder frequently affects the outcome of conventional HIV-1 therapy. Although, both the children and adults suffer from the post-HIV treatment-associated cognitive impairment, adults, especially depending on the age of disease onset, are more prone to CNS dysfunction. Thus, addressing neurological complications in an HIV-1-infected patient is a delicate balance of several factors and requires characterization of the molecular signature of associated CNS disorders involving intricate cross-talk with HIV-1-derived neurotoxins and other cellular factors. In this review, we summarize some of the current data supporting both the direct and indirect mechanisms, including neuro-inflammation and genome instability in association with aging, leading to CNS dysfunction after HIV-1 infection, and discuss the potential strategies addressing the treatment or prevention of HIV-1-mediated neurotoxicity.

eEF2 and Ras-GAP SH3 domain-binding protein (G3BP1) modulate stress granule assembly during HIV-1 infection

Stress granules (SG) are translationally silent sites of RNA triage induced by environmental stresses including viral infection. Here we show that HIV-1 Gag blocks SG assembly irrespective of eIF2α phosphorylation and even when SG assembly is forced by overexpression of Ras-GAP SH3 domain-binding protein (G3BP1) or TIAR. The overexposed loops in the amino-terminal capsid domain of Gag and host eukaryotic elongation factor 2 (eEF2) are found to be critical for the SG blockade via interaction. Moreover, cyclophilin A (CypA) stabilizes the Gag-eEF2 association. eEF2 depletion not only lifts the SG blockade but also results in impaired virus production and infectivity. Gag also disassembles preformed SGs by recruiting G3BP1, thereby displacing eEF2, revealing another unsuspected virus-host interaction involved in the HIV-1-imposed SG blockade. Understanding how HIV-1 counters anti-viral stress responses will lay the groundwork for new therapeutic strategies to bolster host cell immune defences against HIV-1 and other pathogens.

Roles of HIV-1 capsid in viral replication and immune evasion

The primary roles of the human immunodeficiency virus type 1 (HIV-1) capsid (CA) protein are to encapsidate and protect the viral RNA genome. It is becoming increasing apparent that HIV-1 CA is a multifunctional protein that acts early during infection to coordinate uncoating, reverse transcription, nuclear import of the pre-integration complex and integration of double stranded viral DNA into the host genome. Additionally, numerous recent studies indicate that CA is playing a crucial function in HIV-1 immune evasion. Here we summarize the current knowledge on HIV-1 CA and its interactions with the host cell to promote infection. The fact that CA engages in a number of different protein-protein interactions with the host makes it an interesting target for the development of new potent antiviral agents.

HIV-1 Nef is transferred from expressing T cells to hepatocytic cells through conduits and enhances HCV replication

HIV-1 infection enhances HCV replication and as a consequence accelerates HCV-mediated hepatocellular carcinoma (HCC). However, the precise molecular mechanism by which this takes place is currently unknown. Our data showed that infectious HIV-1 failed to replicate in human hepatocytic cell lines. No discernible virus replication was observed, even when the cell lines transfected with HIV-1 proviral DNA were co-cultured with Jurkat T cells, indicating that the problem of liver deterioration in the co-infected patient is not due to the replication of HIV-1 in the hepatocytes of the HCV infected host. Instead, HIV-1 Nef protein was transferred from nef-expressing T cells to hepatocytic cells through conduits, wherein up to 16% (average 10%) of the cells harbored the transferred Nef, when the hepatocytic cells were co-cultured with nef-expressing Jurkat cells for 24 h. Further, Nef altered the size and numbers of lipid droplets (LD), and consistently up-regulated HCV replication by 1.5∼2.5 fold in the target subgenomic replicon cells, which is remarkable in relation to the initially indolent viral replication. Nef also dramatically augmented reactive oxygen species (ROS) production and enhanced ethanol-mediated up-regulation of HCV replication so as to accelerate HCC. Taken together, these data indicate that HIV-1 Nef is a critical element in accelerating progression of liver pathogenesis via enhancing HCV replication and coordinating modulation of key intra- and extra-cellular molecules for liver decay.

The role of miR-146a in dorsal root ganglia neurons of experimental diabetic peripheral neuropathy

Sensory neurons mediate diabetic peripheral neuropathy. Using a mouse model of diabetic peripheral neuropathy (BKS.Cg-m+/+Lepr(db)/J (db/db) mice) and cultured dorsal root ganglion (DRG) neurons, the present study showed that hyperglycemia downregulated miR-146a expression and elevated interleukin-1 receptor-activated kinase (IRAK1) and tumor necrosis factor receptor-associated factor 6 (TRAF6) levels in DRG neurons. In vitro, elevation of miR-146a by miR-146a mimics in DRG neurons increased neuronal survival under high-glucose conditions. Downregulation and elevation of miR-146a in DRG neurons, respectively, were inversely related to IRAK1 and TRAF6 levels. Treatment of diabetic peripheral neuropathy with sildenafil, a phosphodiesterase type 5 inhibitor, augmented miR-146a expression and decreased levels of IRAK1 and TRAF6 in the DRG neurons. In vitro, blockage of miR-146a in DRG neurons abolished the effect of sildenafil on DRG neuron protection and downregulation of IRAK1 and TRAF6 proteins under hyperglycemia. Our data provide the first evidence showing that miR-146a plays an important role in mediating DRG neuron apoptosis under hyperglycemic conditions.

HIV-1 Nef in macrophage-mediated disease pathogenesis

Combined anti-retroviral therapy (cART) has significantly reduced the number of AIDS-associated illnesses and changed the course of HIV-1 disease in developed countries. Despite the ability of cART to maintain high CD4+ T-cell counts, a number of macrophage-mediated diseases can still occur in HIV-infected subjects. These diseases include lymphoma, metabolic diseases, and HIV-associated neurological disorders. Within macrophages, the HIV-1 regulatory protein "Nef" can modulate surface receptors, interact with signaling pathways, and promote specific environments that contribute to each of these pathologies. Moreover, genetic variation in Nef may also guide the macrophage response. Herein, we review findings relating to the Nef-macrophage interaction and how this relationship contributes to disease pathogenesis.

HIV-1 Nef breaches placental barrier in rat model

The vertical transmission of HIV-1 from the mother to fetus is known, but the molecular mechanism regulating this transmission is not fully characterized. The fetus is highly protected by the placenta, which does not permit microbial pathogens to cross the placental barrier. In the present study, a rat model was established to observe the effect of HIV-1 protein Nef on placental barrier. Evans blue dye was used to assay permeability of placental barrier and fourteen day pregnant Sprague Dawley rats were injected intravenously with 2% Evans blue dye along with various concentrations of recombinant Nef. After an hour, animals were sacrificed and dye migration was observed through the assimilation of peripheral blood into fetus. Interestingly, traces of recombinant Nef protein were detected in the embryo as well as amniotic fluid and amniotic membrane along with placenta and uterus. Our study indicates that recombinant HIV-1-Nef protein breaches the placental barrier and allows the migration of Evans blue dye to the growing fetus. Further the concentration of Nef protein in blood is directly proportional to the intensity of dye migration and to the amount of Nef protein detected in uterus, placenta, amniotic membrane, amniotic fluid and embryo. Based on this study, it can be concluded that the HIV-1 Nef protein has a direct effect on breaching of the placental barrier in the model we have established in this study. Our observations will be helpful to understand the molecular mechanisms related to this breach of placental barrier by Nef in humans and may be helpful to identify specific Nef inhibitors.

Oxygen matters: tissue culture oxygen levels affect mitochondrial function and structure as well as responses to HIV viroproteins

Mitochondrial dysfunction is implicated in a majority of neurodegenerative disorders and much study of neurodegenerative disease is done on cultured neurons. In traditional tissue culture, the oxygen level that cells experience is dramatically higher (21%) than in vivo conditions (1-11%). These differences can alter experimental results, especially, pertaining to mitochondria and oxidative metabolism. Our results show that primary neurons cultured at physiological oxygen levels found in the brain showed higher polarization, lower rates of ROS production, larger mitochondrial networks, greater cytoplasmic fractions of mitochondria and larger mitochondrial perimeters than those cultured at higher oxygen levels. Although neurons cultured in either physiological oxygen or atmospheric oxygen exhibit significant increases in mitochondrial reactive oxygen species (ROS) production when treated with the human immunodeficiency virus (HIV) virotoxin trans-activator of transcription, mitochondria of neurons cultured at physiological oxygen underwent depolarization with dramatically increased cell death, whereas those cultured at atmospheric oxygen became hyperpolarized with no increase in cell death. Studies with a second HIV virotoxin, negative regulation factor (Nef), revealed that Nef treatment also increased mitochondrial ROS production for both the oxygen conditions, but resulted in mitochondrial depolarization and increased death only in neurons cultured in physiological oxygen. These results indicate a role for oxidative metabolism in a mechanism of neurotoxicity during HIV infection and demonstrate the importance of choosing the correct, physiological, culture oxygen in mitochondrial studies performed in neurons.

Phosphodiesterase-5 is a therapeutic target for peripheral neuropathy in diabetic mice

Peripheral neuropathy is a common and major complication of diabetes, the underlying mechanisms of which are not fully understood. Using a mouse model of type II diabetes, the present study investigated the role of phosphodiesterase-5 (PDE5) in peripheral neuropathy. BKS.Cg-m+/+Leprdb/J (db/db) mice were treated with sildenafil, a specific inhibitor of PDE5, at doses of 2 and 10 mg/kg or saline. Levels of PDE5 and morphometric parameters in sciatic nerve tissue as well as the motor and sensory function were measured in these mice. In diabetic mice, PDE5 expression in sciatic nerve tissue was significantly upregulated, whereas the myelin sheath thickness, myelin basic protein (MBP), and subcutaneous nerve fibers were significantly reduced. Treatment with sildenafil significantly improved neurological function, assayed by motor and sensory conducting velocities and thermal and mechanical noxious stimuli, concomitantly with increases in myelin sheath thickness, MBP levels, and subcutaneous nerve fibers. In vitro, hyperglycemia upregulated PDE5 in Schwann cells and reduced Schwann cell proliferation, migration, and expression of brain-derived neurotrophic factor (BDNF). Blockage of PDE5 with sildenafil increased cyclic guanosine monophosphate (cGMP) and completely abolished the effect of hyperglycemia on Schwann cells. Sildenafil upregulated cGMP-dependent protein kinase G I (PKGI), whereas inhibition of PKGI with a PKG inhibitor, KT5823, suppressed the inhibitory effect of sildenafil on Schwann cells. These data indicate that hyperglycemia substantially upregulates PDE5 expression and that the cGMP/PKG signaling pathway activated by sildenafil mediates the beneficial effects of sildenafil on diabetic peripheral neuropathy.

Insulin and growth hormone-releasing peptide-6 (GHRP-6) have differential beneficial effects on cell turnover in the pituitary, hypothalamus and cerebellum of streptozotocin (STZ)-induced diabetic rats

Poorly controlled type1 diabetes is associated with hormonal imbalances and increased cell death in different tissues, including the pituitary, hypothalamus and cerebellum. In the pituitary, lactotrophs are the cell population with the greatest increase in cell death, whereas in the hypothalamus and cerebellum astrocytes are most highly affected. Insulin treatment can delay, but does not prevent, diabetic complications. As ghrelin and growth hormone (GH) secretagogues are reported to prevent apoptosis in different tissues, and to modulate glucose homeostasis, a combined hormonal treatment may be beneficial. Hence, we analyzed the effect of insulin and GH-releasing peptide 6 (GHRP-6) on diabetes-induced apoptosis in the pituitary, hypothalamus and cerebellum of diabetic rats. Adult male Wistar rats were made diabetic by streptozotocin injection (65 mg/kg ip) and divided into four groups from diabetes onset: those receiving a daily sc injection of saline (1 ml/kg/day), GHRP-6 (150 μg/kg/day), insulin (1-8U/day) or insulin plus GHRP-6 for 8 weeks. Control non-diabetic rats received saline (1 ml/kg/day). Diabetes increased cell death in the pituitary, hypothalamus and cerebellum (P<0.05). In the pituitary, insulin treatment prevented diabetes-induced apoptosis (P<0.01), as well as the decline in prolactin and GH mRNA levels (P<0.05). In the hypothalamus, neither insulin nor GHRP-6 decreased diabetes-induced cell death. However, the combined treatment of insulin+GHRP-6 prevented the diabetes induced-decrease in glial fibrillary acidic protein (GFAP) levels (P<0.05). In the cerebellum, although insulin treatment increased GFAP levels (P<0.01), only the combined treatment of insulin+ GHRP-6 decreased diabetes-induced apoptosis (P<0.05). In conclusion, insulin and GHRP-6 exert tissue specific effects in STZ-diabetic rats and act synergistically on some processes. Indeed, insulin treatment does not seem to be effective on preventing some of the diabetes-induced alterations in the central nervous system.

HIV-1 Nef increases astrocyte sensitivity towards exogenous hydrogen peroxide

Background

HIV-1 infected individuals are under chronic exposure to reactive oxygen species (ROS) considered to be instrumental in the progression of AIDS and the development of HIV-1 associated dementia (HAD). Astrocytes support neuronal function and protect them against cytotoxic substances including ROS. The protein HIV-1 Nef, a progression factor in AIDS pathology is abundantly expressed in astrocytes in patients with HAD, and thus may influence its functions.

Results

Endogenous expressed HIV-1 Nef leads to increased sensitivity of human astrocytes towards exogenous hydrogen peroxide but not towards TNF-alpha. Cell death of nef-expressing astrocytes exposed to 10 μM hydrogen peroxide for 30 min occurred within 4 h.

Conclusion

HIV-1 Nef may contribute to neuronal dysfunction and the development of HAD by causing death of astrocytes through decreasing their tolerance for hydrogen peroxide.

Paradoxical contractile properties in the knee extensors of HIV-infected men treated with antiretroviral therapy

We assessed contractile properties in the knee extensors of 18 men with the human immunodeficiency virus (HIV+) being treated with antiretroviral therapy (ART), and 9 healthy controls matched for age and body mass index. We found significant, divergent differences between groups with regard to force relaxation. Half-times of twitch relaxation were shorter (62.6 ± 5.4 ms vs. 48.9 ± 3.0 ms; p = 0.045) and maximum rates of torque relaxation were slower (0.47% ± 0.04%(s-)1 vs. 1.32% ± 0.10%(s-)1; p < 0.001) in HIV+ individuals. These preliminary findings suggest potential intramuscular impairments in HIV+ individuals on ART, perhaps because of interactions between calcium handling and mitochondrial dysfunction.