HIV-1 Transactivator Protein Induces ZO-1 and Neprilysin Dysfunction in Brain Endothelial Cells via the Ras Signaling Pathway

HIV-Associated Neurocognitive Disorder: A Look into Cellular and Molecular Pathology

Despite combined antiretroviral therapy (cART) limiting HIV replication to undetectable levels in the blood, people living with HIV continue to experience HIV-associated neurocognitive disorder (HAND). HAND is associated with neurocognitive impairment, including motor impairment, and memory loss. HIV has been detected in the brain within 8 days of estimated exposure and the mechanisms for this early entry are being actively studied. Once having entered into the central nervous system (CNS), HIV degrades the blood-brain barrier through the production of its gp120 and Tat proteins. These proteins are directly toxic to endothelial cells and neurons, and propagate inflammatory cytokines by the activation of immune cells and dysregulation of tight junction proteins. The BBB breakdown is associated with the progression of neurocognitive disease. One of the main hurdles for treatment for HAND is the latent pool of cells, which are insensitive to cART and prolong inflammation by harboring the provirus in long-lived cells that can reactivate, causing damage. Multiple strategies are being studied to combat the latent pool and HAND; however, clinically, these approaches have been insufficient and require further revisions. The goal of this paper is to aggregate the known mechanisms and challenges associated with HAND.

Disruption of blood-brain barrier: effects of HIV Tat on brain microvascular endothelial cells and tight junction proteins

Although the widespread use of antiretroviral therapy (ART) has prolonged the life span of people living with HIV (PLWH), the incidence of HIV-associated neurocognitive disorders (HAND) in PLWH is also gradually increasing, seriously affecting the quality of life for PLWH. However, the pathogenesis of HAND has not been elucidated, which leaves HAND without effective treatment. HIV protein transactivator of transcription (Tat), as an important regulatory protein, is crucial in the pathogenesis of HAND, and its mechanism of HAND has received widespread attention. The blood-brain barrier (BBB) and its cellular component brain microvascular endothelial cells (BMVECs) play a necessary role in protecting the central nervous system (CNS), and their damage associated with Tat is a potential therapeutic target of HAND. In this review, we will study the Tat-mediated damage mechanism of the BBB and present multiple lines of evidence related to BMVEC damage caused by Tat.

Toll-like receptor 4 and CD11b expressed on microglia coordinate eradication of Candida albicans cerebral mycosis

The fungal pathogen Candida albicans is linked to chronic brain diseases such as Alzheimer's disease (AD), but the molecular basis of brain anti-Candida immunity remains unknown. We show that C. albicans enters the mouse brain from the blood and induces two neuroimmune sensing mechanisms involving secreted aspartic proteinases (Saps) and candidalysin. Saps disrupt tight junction proteins of the blood-brain barrier (BBB) to permit fungal brain invasion. Saps also hydrolyze amyloid precursor protein (APP) into amyloid β (Aβ)-like peptides that bind to Toll-like receptor 4 (TLR4) and promote fungal killing in vitro while candidalysin engages the integrin CD11b (Mac-1) on microglia. Recognition of Aβ-like peptides and candidalysin promotes fungal clearance from the brain, and disruption of candidalysin recognition through CD11b markedly prolongs C. albicans cerebral mycosis. Thus, C. albicans is cleared from the brain through innate immune mechanisms involving Saps, Aβ, candidalysin, and CD11b.

CTRP7 Is a Biomarker Related to Insulin Resistance and Oxidative Stress: Cross-Sectional and Intervention Studies In Vivo and In Vitro

Objective

CTRP7 is a cytokine that is known to be associated with obesity. However, its relationship with insulin resistance (IR) and metabolic diseases remains unknown. The aim of this study is to investigate the relationship between CTRP7 and IR under in vivo and in vitro conditions.

Methods

CTRP7 expression in mice and hepatocytes was determined using RT-qPCR and western blotting. Circulating CTRP7 concentrations were measured with an ELISA kit. EHC, OGTT, lipid-infusion, physical activity, and cold-stimulation experiments were performed in humans and mice. SOD, GSH, and MDA were measured by commercial kits. ROS levels were detected using dichlorofluorescein diacetate.

Results

The expression levels of CTRP7 protein in the liver and fat of ob/ob and db/db mice were higher than that of WT mice. Individuals with IGT, T2DM, and obesity had higher circulating CTRP7 levels. CTRP7 levels were associated with HOMA-IR, obesity, and other metabolic parameters. During OGTT, serum CTRP7 levels gradually decreased, while CTRP7 levels significantly increased during EHC in response to hyperinsulinemia in healthy individuals without IR. In addition, lipid infusion-induced IR further increased serum CTRP7 levels in healthy adults. Physical activity increased serum CTRP7 levels in healthy individuals and CTRP7 protein expression in iWAT and skeletal muscle in mice. Under in vitro conditions, the expression of the CTRP7 protein was inhibited in a glucose concentration-dependent manner but was promoted by FFAs and insulin stimulation in hepatocytes. Furthermore, CTRP7 overexpression facilitated oxidative stress and suppressed the phosphorylation of insulin signaling molecules in hepatocytes.

Conclusions

Our evidence shows that CTRP7 could be a useful biomarker and potential treatment target in IR and metabolic disorders.

Mechanisms underlying protective effects of vitamin E against mycotoxin deoxynivalenol-induced oxidative stress and its related cytotoxicity in primary human brain endothelial cells

Fusarium mycotoxins are one of the largest families of mycotoxins. Among these mycotoxins, deoxynivalenol is the most widespread pollutant of grains. However, the mechanism underlying the effect of deoxynivalenol on cytotoxicity in human brain endothelial cells was still unclear. This study examined whether deoxynivalenol induced oxidative stress-associated cytotoxicity in primary human brain endothelial cells (HBEC-5i), and explored whether Vitamin E (VE), a selective antioxidant, had protective effects on deoxynivalenol-treated cells. Deoxynivalenol (10-50 μM) concentration-dependently induced cytotoxicity in HBEC-5i cells. Deoxynivalenol (IC50 = 20 μM) activated mitochondrial apoptotic pathway by modulating antioxidant protein expressions (Nrf2, HO-1 and NQO1). More significantly, pre-treatment with VE (20 μM) attenuated the deoxynivalenol-induced cytotoxicity in this cell model. Together, VE significantly alleviated the apoptotic effects of deoxynivalenol in HBEC-5i cells suggesting that it protected the cells against deoxynivalenol-induced oxidative damage. Our findings provided new insight that VE had the potential to ameliorate neurotoxicity of deoxynivalenol.

Methamphetamine and HIV-Tat Protein Synergistically Induce Oxidative Stress and Blood-Brain Barrier Damage via Transient Receptor Potential Melastatin 2 Channel

Synergistic impairment of the blood-brain barrier (BBB) induced by methamphetamine (METH) and HIV-Tat protein increases the risk of HIV-associated neurocognitive disorders (HAND) in HIV-positive METH abusers. Studies have shown that oxidative stress plays a vital role in METH- and HIV-Tat-induced damage to the BBB but have not clarified the mechanism. This study uses the human brain microvascular endothelial cell line hCMEC/D3 and tree shrews to investigate whether the transient receptor potential melastatin 2 (TRPM2) channel, a cellular effector of the oxidative stress, might regulate synergistic damage to the BBB caused by METH and HIV-Tat. We showed that METH and HIV-Tat damaged the BBB in vitro, producing abnormal cell morphology, increased apoptosis, reduced protein expression of the tight junctions (TJ) including Junctional adhesion molecule A (JAMA) and Occludin, and a junctional associated protein Zonula occludens 1 (ZO1), and increased the flux of sodium fluorescein (NaF) across the hCMEC/D3 cells monolayer. METH and HIV-Tat co-induced the oxidative stress response, reducing catalase (CAT), glutathione peroxidase (GSH-PX), and superoxide dismutase (SOD) activity, as well as increased reactive oxygen species (ROS) and malonaldehyde (MDA) level. Pretreatment with n-acetylcysteine amide (NACA) alleviated the oxidative stress response and BBB damage characterized by improving cell morphology, viability, apoptosis levels, TJ protein expression levels, and NaF flux. METH and HIV-Tat co-induced the activation and high protein expression of the TRPM2 channel, however, early intervention using 8-Bromoadenosine-5′-O-diphosphoribose (8-Br-ADPR), an inhibitor of TPRM2 channel, or TRPM2 gene knockdown attenuated the BBB damage. Oxidative stress inhibition reduced the activation and high protein expression of the TRPM2 channel in the in vitro model, which in turn reduced the oxidative stress response. Further, 8-Br-ADPR attenuated the effects of METH and HIV-Tat on the BBB in tree shrews—namely, down-regulated TJ protein expression and increased BBB permeability to Evans blue (EB) and NaF. In summary, the TRPM2 channel can regulate METH- and HIV-Tat-induced oxidative stress and BBB injury, giving the channel potential for developing drug interventions to reduce BBB injury and neuropsychiatric symptoms in HIV-infected METH abusers.

Rho-kinase inhibitor hydroxyfasudil protects against HIV-1 Tat-induced dysfunction of tight junction and neprilysin/Aβ transfer receptor expression in mouse brain microvessels

HIV-1 transactivator protein (Tat) induces tight junction (TJ) dysfunction and amyloid-beta (Aβ) clearance dysfunction, contributing to the development and progression of HIV-1-associated neurocognitive disorder (HAND). The Rho/ROCK signaling pathway has protective effects on neurodegenerative disease. However, the underlying mechanisms of whether Rho/ROCK protects against HIV-1 Tat-caused dysfunction of TJ and neprilysin (NEP)/Aβ transfer receptor expression have not been elucidated. C57BL/6 mice were administered sterile saline (i.p., 100 μL) or Rho-kinase inhibitor hydroxyfasudil (HF) (i.p., 10 mg/kg) or HIV-1 Tat (i.v., 100 μg/kg) or HF 30 min before being exposed to HIV-1 Tat once a day for seven consecutive days. Evans Blue (EB) leakage was detected via spectrophotometer and brain slides in mouse brains. The protein and mRNA levels of zonula occludens-1 (ZO-1), occludin, NEP, receptor for advanced glycation end products (RAGE), and low-density lipoprotein receptor-related protein 1 (LRP1) in mouse brain microvessels were, respectively, analyzed by Western blotting and quantitative real-time polymerase chain reaction (qRT-PCR) analyses. Exposure of the mice to HIV-1 Tat increased the amount of EB leakage, EB fluorescence intensity, blood–brain barrier (BBB) permeability, as well as the RAGE protein and mRNA levels, and decreased the protein and mRNA levels of ZO-1, occludin, NEP, and LRP1 in mouse brain microvessels. However, these effects were weakened by Rho-kinase inhibitor HF. Taken together, these results provide information that the Rho/ROCK signaling pathway is involved in HIV-1 Tat-induced dysfunction of TJ and NEP/Aβ transfer receptor expression in the C57BL/6 mouse brain. These findings shed some light on potentiality of inhibiting Rho/Rock signaling pathway in handling HAND.

Alzheimer's disease-like perturbations in HIV-mediated neuronal dysfunctions: understanding mechanisms and developing therapeutic strategies

Excessive exposure to toxic substances or chemicals in the environment and various pathogens, including viruses and bacteria, is associated with the onset of numerous brain abnormalities. Among them, pathogens, specifically viruses, elicit persistent inflammation that plays a major role in Alzheimer's disease (AD) as well as dementia. AD is the most common brain disorder that affects thought, speech, memory and ability to execute daily routines. It is also manifested by progressive synaptic impairment and neurodegeneration, which eventually leads to dementia following the accumulation of Aβ and hyperphosphorylated Tau. Numerous factors contribute to the pathogenesis of AD, including neuroinflammation associated with pathogens, and specifically viruses. The human immunodeficiency virus (HIV) is often linked with HIV-associated neurocognitive disorders (HAND) following permeation through the blood-brain barrier (BBB) and induction of persistent neuroinflammation. Further, HIV infections also exhibited the ability to modulate numerous AD-associated factors such as BBB regulators, members of stress-related pathways as well as the amyloid and Tau pathways that lead to the formation of amyloid plaques or neurofibrillary tangles accumulation. Studies regarding the role of HIV in HAND and AD are still in infancy, and potential link or mechanism between both is not yet established. Thus, in the present article, we attempt to discuss various molecular mechanisms that contribute to the basic understanding of the role of HIV-associated neuroinflammation in AD and HAND. Further, using numerous growth factors and drugs, we also present possible therapeutic strategies to curb the neuroinflammatory changes and its associated sequels.

Extracellular Vesicles: A Possible Link between HIV and Alzheimer's Disease-Like Pathology in HIV Subjects?

The longevity of people with HIV/AIDS has been prolonged with the use of antiretroviral therapy (ART). The age-related complications, especially cognitive deficits, rise as HIV patients live longer. Deposition of beta-amyloid (Aβ), a hallmark of Alzheimer's disease (AD), has been observed in subjects with HIV-associated neurocognitive disorders (HAND). Various mechanisms such as neuroinflammation induced by HIV proteins (e.g., Tat, gp120, Nef), excitotoxicity, oxidative stress, and the use of ART contribute to the deposition of Aβ, leading to dementia. However, progressive dementia in older subjects with HIV might be due to HAND, AD, or both. Recently, extracellular vesicles (EVs)/exosomes, have gained recognition for their importance in understanding the pathology of both HAND and AD. EVs can serve as a possible link between HIV and AD, due to their ability to package and transport the toxic proteins implicated in both AD and HIV (Aβ/tau and gp120/tat, respectively). Given that Aß is also elevated in neuron-derived exosomes isolated from the plasma of HIV patients, it is reasonable to suggest that neuron-to-neuron exosomal transport of Aβ and tau also contributes to AD-like pathology in HIV-infected subjects. Therefore, exploring exosomal contents is likely to help distinguish HAND from AD. However, future prospective clinical studies need to be conducted to compare the exosomal contents in the plasma of HIV subjects with and without HAND as well as those with and without AD. This would help to find new markers and develop new treatment strategies to treat AD in HIV-positive subjects. This review presents comprehensive literatures on the mechanisms contributing to Aβ deposition in HIV-infected cells, the role of EVs in the propagation of Aβ in AD, the possible role of EVs in HIV-induced AD-like pathology, and finally, possible therapeutic targets or molecules to treat HIV subjects with AD.

Role of Cav-1 in HIV-1 Tat-Induced Dysfunction of Tight Junctions and Aβ-Transferring Proteins

Objective

To evaluate the role of caveolin-1 (Cav-1) in HIV-1 Tat-induced dysfunction of tight junction and amyloid β-peptide- (Aβ-) transferring proteins.

Methods

A Cav-1 shRNA interference target sequence was cloned into the lentiviral vector pHBLV-U6-Scramble-ZsGreen-Puro and verified by double enzyme digestion and DNA sequencing. Human cerebral microvascular endothelium (HBEC-5i) cells were transduced with viral particles made in 293T cells by transfection with lentiviral packaging plasmids. HBEC-5i cells transduced with Cav-1 shRNA or Ctr shRNA were exposed to HIV-1 Tat for 24 h, and the protein and mRNA levels of the tight junction protein occludin, Aβ-transferring protein, receptor for advanced glycation end products (RAGE), low-density lipoprotein receptor-related protein- (LRP-) 1, and RhoA were evaluated with Western blot and real-time reverse transcription polymerase chain reaction (qRT-PCR) assays, respectively.

Results

After sequencing, an RNA interference recombinant lentivirus expressing a vector targeting Cav-1 was successfully established. The recombined lentiviral particles were made by using 293T cells to package the recombined lentiviral vector. A stable monoclonal cell line with strong GFP expression was acquired with a Cav-1 knockdown rate of 85.7%. The occludin protein and mRNA levels in the Ctr shRNA group were decreased with HIV-1 Tat exposure but were upregulated in the Cav-1 shRNA group. The HIV-1 Tat-induced alterations of RAGE and LRP-1 protein and mRNA levels in the Ctr shRNA group were attenuated in the Cav-1 shRNA group. The RhoA protein levels in the Ctr shRNA group were upregulated by HIV-1 Tat exposure but were downregulated in the Cav-1 shRNA group.

Conclusion

These results show that HIV-1 Tat-induced downregulation of occludin and LRP-1 and upregulation of RAGE and RhoA may result in the accumulation of Aβ in the brain. Silencing the Cav-1 gene with shRNA plays a key role in the protection against HIV-1 Tat-induced dysfunction of the blood-brain barrier and Aβ accumulation.

Neprilysin in the Cerebrospinal Fluid and Serum of Patients Infected With HIV1-Subtypes C and B

OBJECTIVE

Neprilysin (NEP) is the dominant Aβ peptide-degrading enzyme in the brain. HIV-1 subtype B transactivator of transcription protein is known to interfere with NEP function, but whether this is true of HIV-1C transactivator of transcription, which has a defective chemokine motif, is not known. This study aimed to analyze the impact of HIV subtype on NEP-mediated cleavage of Aβ by comparing cerebrospinal fluid (CSF) and serum levels of NEP between HIV+ (27 patients with HIV-1B and 26 with HIV-1C), healthy HIV- controls (n = 13), and patients with Alzheimer disease (n = 24).

METHODS

NEP and Aβ oligomers 38, 40, 42 levels were measured in CSF and serum by immunoassays. Ratios between NEP and Aβ-38, 40, 42, and total were calculated in CSF and serum. Comparisons between HIV(+) and HIV(-) were adjusted by linear regression for sex and age; HIV subtype comparisons were adjusted for nadir CD4 and plasma viral load suppression.

RESULTS

Levels of NEP and ratios in CSF were comparable for HIV-1C and B subtypes. The ratio of serum NEP/Aβ-40 was lower for HIV1-C than HIV1-B (P = 0.032). The CSF/serum index of NEP/Aβ-40, NEP/Aβ-42, and NEP/Aβ-total were lower for HIV1-B than HIV1-C (P = 0.008, 0.005, and 0.017, respectively), corroborating the findings for serum. CSF NEP was comparable for HIV+, HIV-, and AD.

CONCLUSION

There was impact of HIV subtype on NEP. The ratio of NEP/Aβ-40 on serum was lower on HIV1-C than HIV1-B. These results are consistent with the results of CSF Aβ-42 levels decreased in HIV1-C compared with HIV1-B, suggesting higher amyloid β deposit on HIV1-C than HIV1-B.

HIV and Alzheimer's disease: complex interactions of HIV-Tat with amyloid β peptide and Tau protein

In patients infected with the human immunodeficiency virus (HIV), the HIV-Tat protein may be continually produced despite adequate antiretroviral therapy. As the HIV-infected population is aging, it is becoming increasingly important to understand how HIV-Tat may interact with proteins such as amyloid β and Tau which accumulate in the aging brain and eventually result in Alzheimer's disease. In this review, we examine the in vivo data from HIV-infected patients and animal models and the in vitro experiments that show how protein complexes between HIV-Tat and amyloid β occur through novel protein-protein interactions and how HIV-Tat may influence the pathways for amyloid β production, degradation, phagocytosis, and transport. HIV-Tat may also induce Tau phosphorylation through a cascade of cellular processes that lead to the formation of neurofibrillary tangles, another hallmark of Alzheimer's disease. We also identify gaps in knowledge and future directions for research. Available evidence suggests that HIV-Tat may accelerate Alzheimer-like pathology in patients with HIV infection which cannot be impacted by current antiretroviral therapy.

Therapeutic Target and Cell-signal Communication of Chlorpromazine and Promethazine in Attenuating Blood-Brain Barrier Disruption after Ischemic Stroke

Ischemic stroke destroys blood–brain barrier (BBB) integrity. There are currently no effective treatments available in the clinical setting. Post-ischemia treatment with phenothiazine drugs [combined chlorpromazine and promethazine (C+P)] has been shown to be neuroprotective in stroke. The present study determined the effect of C+P in BBB integrity. Sprague-Dawley rats were divided into the following groups (n=8 each): (1) stroke, (2) stroke treated by C+P with temperature control, and (3) stroke treated by C+P without temperature control. Infarct volume and neurological deficits were measured to assess the neuroprotective effect of C+P. BBB permeability was determined by brain edema and Evans blue leakage. Expression of BBB integral molecules, including proteins of aquaporin-4 and -9 (AQP-4, AQP-9), matrix metalloproteinase-2 and -9 (MMP-2, MMP-9), zonula occludens-1 (ZO-1), claudin-1/5, occludin, and laminin were determined by Western blot. Stroke caused brain infarction and neurological deficits, as well as BBB damage, which were all attenuated by C+P through drug-induced hypothermia. When the reduced temperature was controlled to physiological levels, C+P still conferred neuroprotection, suggesting a therapeutic effect independent of hypothermia. Furthermore, C+P significantly attenuated the increase in AQP-4, AQP-9, MMP-2, and MMP-9 levels after stroke, and reversed the decrease in tight junction protein (ZO-1, claudin-1/5, occludin) and basal laminar protein (laminin) levels. This study clearly indicates a beneficial effect of C+P on BBB integrity after stroke, which may be independent of drug-induced hypothermia. These findings further prove the clinical target and cell-signal communication of C+P treatment, which may direct us closer toward the development of an efficacious neuroprotective therapy.

Assessment of HBEC-5i endothelial cell line cultivated in astrocyte conditioned medium as a human blood-brain barrier model for ABC drug transport studies

Endothelial cells are main components of the Blood-Brain Barrier (BBB) and form a tight monolayer that regulates the passage of molecules, with the ATP-Binding Cassette (ABC) transporters efflux pumps. We have developed a human in vitro model of HBEC-5i endothelial cells cultivated alone or with human astrocytes conditioned medium on insert. HBEC-5i cells showed a tight monolayer within 14 days, expressing ZO-1 and claudin 5, a low apparent permeability to small molecules, with a TEER stability during five days. The P-gp, BCRP, MRPs transporters were well expressed and functional. Accumulation and efflux ratio measurement with different ABC transporters substrates (Rhodamine 123, BCECF AM, Hoechst 33342) and inhibitors (verapamil, Ko143, probenecid and cyclosporin A) were conducted. At barrier level, the functionality of ABC transporters was three-fold enhanced in astrocyte conditioned medium. We validated our model by the transport of pharmacological substrates: caffeine, rivaroxaban, and methotrexate. The rivaroxaban and methotrexate were released with an efflux ratio >3 and were decreased by more than half with inhibitors. HBEC-5i model could be used as relevant tool in preclinical studies for assessing the permeability of therapeutic molecules to cross human BBB.

HIV Neuroinfection and Alzheimer's Disease: Similarities and Potential Links?

Environmental factors such as chemicals, stress and pathogens are now widely believed to play important roles in the onset of some brain diseases, as they are associated with neuronal impairment and acute or chronic inflammation. Alzheimer’s disease (AD) is characterized by progressive synaptic dysfunction and neurodegeneration that ultimately lead to dementia. Neuroinflammation also plays a prominent role in AD and possible links to viruses have been proposed. In particular, the human immunodeficiency virus (HIV) can pass the blood-brain barrier and cause neuronal dysfunction leading to cognitive dysfunctions called HIV-associated neurocognitive disorders (HAND). Similarities between HAND and HIV exist as numerous factors involved in AD such as members of the amyloid and Tau pathways, as well as stress-related pathways or blood brain barrier (BBB) regulators, seem to be modulated by HIV brain infection, leading to the accumulation of amyloid plaques or neurofibrillary tangles (NFT) in some patients. Here, we summarize findings regarding how HIV and some of its proteins such as Tat and gp120 modulate signaling and cellular pathways also impaired in AD, suggesting similarities and convergences of these two pathologies.