In-silico analysis of claudin-5 reveals novel putative sites for post-translational modifications: Insights into potential molecular determinants of blood-brain barrier breach during HIV-1 infiltration

Association of Plasma Claudin-5 with Age and Alzheimer Disease

The blood-brain barrier (BBB) plays pivotal roles in synaptic and neuronal functioning by sealing the space between adjacent microvascular endothelial cells. BBB breakdown is present in patients with mild cognitive impairment (MCI) or Alzheimer disease (AD). Claudin-5 (CLDN-5) is a tetra-spanning protein essential for sealing the intercellular space between adjacent endothelial cells in the BBB. In this study, we developed a blood-based assay for CLDN-5 and investigated its diagnostic utility using 100 cognitively normal (control) subjects, 100 patients with MCI, and 100 patients with AD. Plasma CLDN-5 levels were increased in patients with AD (3.08 ng/mL) compared with controls (2.77 ng/mL). Plasma levels of phosphorylated tau (pTau181), a biomarker of pathological tau, were elevated in patients with MCI or AD (2.86 and 4.20 pg/mL, respectively) compared with control subjects (1.81 pg/mL). In patients with MCI or AD, plasma levels of CLDN-5-but not pTau181-decreased with age, suggesting some age-dependent BBB changes in MCI and AD. These findings suggest that plasma CLDN-5 may a potential biochemical marker for the diagnosis of AD.

Molecular neuroimaging of inflammation in HIV

People with HIV now have near-normal life expectancies due to the success of effective combination antiretroviral therapy (cART). Following cART initiation, immune recovery occurs, and opportunistic diseases become rare. Despite this, high rates of non-infectious comorbidities persist in treated people with HIV, hypothesized to be related to persistent immuno-activation. One such comorbidity is cognitive impairment, which may partly be driven by ongoing neuro-inflammation in otherwise effectively treated people with HIV. In order to develop therapeutic interventions to address neuro-inflammation in effectively treated people with HIV, a deeper understanding of the pathogenic mechanisms driving persistent neuro-inflammatory responses and the ability to better characterize and measure neuro-inflammation in the central nervous system is required. This review highlights recent advances in molecular neuroimaging techniques which have the potential to assess neuro-inflammatory responses within the central nervous system in HIV disease. Proton magnetic resonance spectroscopy (1H-MRS) has been utilized to assess neuro-inflammatory responses since early in the HIV pandemic and shows promise in recent studies assessing different antiretroviral regimens. 1H-MRS is widely available in both resource-rich and some resource-constrained settings and is relatively inexpensive. Brain positron emission tomography (PET) imaging using Translocator Protein (TSPO) radioligands is a rapidly evolving field; newer TSPO-radioligands have lower signal-to-noise ratio and have the potential to localize neuro-inflammation within the brain in people with HIV. As HIV therapeutics evolve, people with HIV continue to age and develop age-related comorbidities including cognitive disorders. The use of novel neuroimaging modalities in the field is likely to advance in order to rapidly assess novel therapeutic interventions and may play a role in future clinical assessments.

Effect of human immunodeficiency virus on the brain: A review

Thirty million people are infected with human immunodeficiency virus (HIV) worldwide, and HIV-associated neurocognitive disorder (HAND) is one of the most common comorbidities of HIV. However, the effect of HIV on the brain has not been fully investigated. This article aimed to review the changes to the brain due to HIV in terms of atrophy, diffusion changes, and hyperintensities. Studies have observed significant atrophy in subcortical gray matter, as well as in cortical white and gray matter. Moreover, the ventricles enlarge, and the sulci widen. Although HIV causes changes to the white and gray matter of the brain, few diffusion tensor imaging studies have investigated the changes to gray matter integrity. White and gray matter hyperintensities have frequently been observed in HIV-positive individuals, with the subcortical gray matter (caudate nucleus and putamen) and periventricular white matter frequently affected. In conclusion, subcortical gray matter is the first brain region to be affected and is affected most severely. Additionally, this review highlights the gaps in the literature, since the effect of HIV on the brain is not fully known. Future studies should continue to investigate the effect of HIV on the brain in different stages of the disease, and alternate therapies should be developed since highly active antiretroviral therapy is currently ineffective at treating HAND.

HIV-1 persistence in the central nervous system: viral and host determinants during antiretroviral therapy

Despite remarkable therapeutic advances in the past two decades, the elimination of human immunodeficiency virus type 1 (HIV-1) from latent reservoirs constitutes a major barrier to eradication and preventing neurological disease associated with HIV/AIDS. Invasion of the central nervous system (CNS) by HIV-1 occurs early in infection, leading to viral infection and productive persistence in brain macrophage-like cells (BMCs) including resident microglia and infiltrating macrophages. HIV-1 persistence in the brain and chronic neuroinflammation occur despite effective treatment with antiretroviral therapy (ART). This review examines the evidence from clinical studies, in vivo and in vitro models for HIV-1 CNS persistence, as well as therapeutic considerations in targeting latent CNS reservoirs.

IL-17A and IL-17F repair HIV-1 gp140 damaged Caco-2 cell barriers by upregulating tight junction genes

It is widely accepted that impairment of the intestinal epithelial barrier from HIV/AIDS contributes significantly to microbial translocation and systemic immune activation. Such factors present potential targets for novel treatments aimed toward a functional cure. However, the extracellular mechanisms of intestinal barrier repair are poorly understood. In the current study, we investigated the abilities of IL-17A and IL-17F to repair the damaged barrier caused by HIV-1 gp140 using Caco-2 monolayers. It was found that HIV-1 gp140 downregulated the expression of tight junction-associated genes and disrupted the barrier integrity of Caco-2 monolayers. However, IL-17A and IL-17F treatment reversed the HIV-1 gp140-induced barrier dysfunction by upregulating the expression of tight junction-associated genes, the combination of which resulted in a stronger induction of barrier repair. Furthermore, the effects of IL-17A and IL-17F were reduced by downregulation of Act1 with siRNA and inhibition of NF-κB and MAPK pathways with BAY11-7082 and U0126, respectively. These data indicated that the NF-κB and MAPK pathways are involved in the repair of barrier integrity mediated by IL-17A and IL-17F, and IL-17 pathways are potential targets for gut barrier restoration therapies during HIV/AIDS.

Petri Net-Based Model of Helicobacter pylori Mediated Disruption of Tight Junction Proteins in Stomach Lining during Gastric Carcinoma

Tight junctions help prevent the passage of digestive enzymes and microorganisms through the space between adjacent epithelial cells lining. However, Helicobacter pylori encoded virulence factors negatively regulate these tight junctions and contribute to dysfunction of gastric mucosa. Here, we have predicted the regulation of important tight junction proteins, such as Zonula occludens-1, Claudin-2 and Connexin32 in the presence of pathogenic proteins. Molecular events such as post translational modifications and crosstalk between phosphorylation, O-glycosylation, palmitoylation and methylation are explored which may compromise the integrity of these tight junction proteins. Furthermore, the signaling pathways disrupted by dysregulated kinases, proteins and post-translational modifications are reviewed to design an abstracted computational model showing the situation-dependent dynamic behaviors of these biological processes and entities. A qualitative hybrid Petri Net model is therefore constructed showing the altered host pathways in the presence of virulence factor cytotoxin-associated gene A, leading to the disruption of tight junction proteins. The model is qualitative logic-based, which does not depend on any kinetic parameter and quantitative data and depends on knowledge derived from experiments. The designed model provides insights into the tight junction disruption and disease progression. Model is then verified by the available experimental data, nevertheless formal in vitro experimentation is a promising way to ensure its validation. The major findings propose that H. pylori activated kinases are responsible to trigger specific post translational modifications within tight junction proteins, at specific sites. These modifications may favor alterations in gastric barrier and provide a route to bacterial invasion into host cells.

Treating HIV Infection in the Central Nervous System

Combination antiretroviral treatment is associated with clear benefits in HIV-positive subjects, and is also effective in the central nervous system (CNS), meaning HIV-associated dementia is now an uncommon event. Nevertheless, a significant number of patients show symptoms of neurocognitive impairment which may negatively affect their quality of life. Although several risk factors for HIV-associated neurocognitive disorders have been identified, there is no clear recommendation for their prevention and management. In this review, the penetration of drugs into the cerebrospinal fluid/CNS is discussed as well as the viral and clinical consequences associated with higher/lower compartmental exposure. We also review the potential interventions according to the currently identified underlying mechanisms, including persistent CNS immune activation, legacy effects, low-level viral replication and escape, co-morbidities, and antiretroviral-associated direct and indirect 'neurotoxicity'. Adjunctive therapies and interventions (including neuro-rehabilitation) are then briefly discussed. The treatment of HIV infection in the CNS is a complex area of therapeutics requiring multidisciplinary interventions and further study.

Antiretroviral Treatment with Efavirenz Disrupts the Blood-Brain Barrier Integrity and Increases Stroke Severity

The introduction of antiretroviral drugs (ARVd) changed the prognosis of HIV infection from a deadly disease to a chronic disease. However, even with undetectable viral loads, patients still develop a wide range of pathologies, including cerebrovascular complications and stroke. It is hypothesized that toxic side effects of ARVd may contribute to these effects. To address this notion, we evaluated the impact of several non-nucleoside reverse transcriptase inhibitors (NNRTI; Efavirenz, Etravirine, Rilpivirine and Nevirapine) on the integrity of the blood-brain barrier, and their impact on severity of stroke. Among studied drugs, Efavirenz, but not other NNRTIs, altered claudin-5 expression, increased endothelial permeability, and disrupted the blood-brain barrier integrity. Importantly, Efavirenz exposure increased the severity of stroke in a model of middle cerebral artery occlusion in mice. Taken together, these results indicate that selected ARVd can exacerbate HIV-associated cerebrovascular pathology. Therefore, careful consideration should be taken when choosing an anti-retroviral therapy regimen.

Claudins in viral infection: from entry to spread

Tight junctions are critically important for many physiological functions, including the maintenance of cell polarity, regulation of paracellular permeability, and involvement in signal transduction pathways to regulate integral cellular processes. Furthermore, tight junctions enable epithelial cells to form physical barriers, which act as an innate immune mechanism that can impede viral infection. Viruses, in turn, have evolved mechanisms to exploit tight junction proteins to gain access to cells or spread through tissues in an infected host. Claudin family proteins are integral components of tight junctions and are thought to play crucial roles in regulating their permeability. Claudins have been implicated in the infection process of several medically important human pathogens, including hepatitis C virus, dengue virus, West Nile virus, and human immunodeficiency virus, among others. In this review, we summarize the role of claudins in viral infections and discuss their potential as novel antiviral targets. A better understanding of claudins during viral infection may provide insight into physiological roles of claudins and uncover novel therapeutic antiviral strategies.

Junctional proteins of the blood-brain barrier: New insights into function and dysfunction

The blood-brain barrier (BBB) is a highly complex and dynamic barrier. It is formed by an interdependent network of brain capillary endothelial cells, endowed with barrier properties, and perivascular cells (astrocytes and pericytes) responsible for inducing and maintaining those properties. One of the primary properties of the BBB is a strict regulation of paracellular permeability due to the presence of junctional complexes (tight, adherens and gap junctions) between the endothelial cells. Alterations in junction assembly and function significantly affect BBB properties, particularly barrier permeability. However, such alterations are also involved in remodeling the brain endothelial cell surface and regulating brain endothelial cell phenotype. This review summarizes the characteristics of brain endothelial tight, adherens and gap junctions and highlights structural and functional alterations in junctional proteins that may contribute to BBB dysfunction.

Systems Proteomics View of the Endogenous Human Claudin Protein Family

Claudins are the major transmembrane protein components of tight junctions in human endothelia and epithelia. Tissue-specific expression of claudin members suggests that this protein family is not only essential for sustaining the role of tight junctions in cell permeability control but also vital in organizing cell contact signaling by protein-protein interactions. How this protein family is collectively processed and regulated is key to understanding the role of junctional proteins in preserving cell identity and tissue integrity. The focus of this review is to first provide a brief overview of the functional context, on the basis of the extensive body of claudin biology research that has been thoroughly reviewed, for endogenous human claudin members and then ascertain existing and future proteomics techniques that may be applicable to systematically characterizing the chemical forms and interacting protein partners of this protein family in human. The ability to elucidate claudin-based signaling networks may provide new insight into cell development and differentiation programs that are crucial to tissue stability and manipulation.

Compartmentalized intrathecal immunoglobulin synthesis during HIV infection - a model of chronic CNS inflammation?

HIV infects the central nervous system (CNS) during primary infection and persists in resident macrophages. CNS infection initiates a strong local immune response that fails to control the virus but is responsible for by-stander lesions involved in neurocognitive disorders. Although highly active anti-retroviral therapy now offers an almost complete control of CNS viral proliferation, low-grade CNS inflammation persists. This review focuses on HIV-induced intrathecal immunoglobulin (Ig) synthesis. Intrathecal Ig synthesis early occurs in more than three-quarters of patients in response to viral infection of the CNS and persists throughout the course of the disease. Viral antigens are targeted but this specific response accounts for <5% of the whole intrathecal synthesis. Although the nature and mechanisms leading to non-specific synthesis are unknown, this prominent proportion is comparable to that observed in various CNS viral infections. Cerebrospinal fluid-floating antibody-secreting cells account for a minority of the whole synthesis, which mainly takes place in perivascular inflammatory infiltrates of the CNS parenchyma. B-cell traffic and lineage across the blood-brain-barrier have not yet been described. We review common technical pitfalls and update the pending questions in the field. Moreover, since HIV infection is associated with an intrathecal chronic oligoclonal (and mostly non-specific) Ig synthesis and associates with low-grade axonal lesions, this could be an interesting model of the chronic intrathecal synthesis occurring during multiple sclerosis.

Neuropathogenesis of HIV: from initial neuroinvasion to HIV-associated neurocognitive disorder (HAND)

Early in the HIV epidemic, the central nervous system (CNS) was recognized as a target of infection and injury in the advanced stages of disease. Though the most severe forms of HIV-associated neurocognitive disorder (HAND) related to severe immunosuppression are rare in the current era of widespread combination antiretroviral therapy (cART), evidence now supports pathological involvement of the CNS throughout the course of infection. Recent work suggests that the stage for HIV neuropathogenesis may be set with initial viral entry into the CNS, followed by initiation of pathogenetic processes including neuroinflammation and neurotoxicity, and establishment of local, compartmentalized HIV replication that may reflect a tissue reservoir for HIV. Key questions still exist as to when HIV establishes local infection in the CNS, which CNS cells are the primary targets of HIV, and what mechanistic processes underlie the injury to neurons that produce clinical symptoms of HAND. Advances in these areas will provide opportunities for improved treatment of patients with established HAND, prevention of neurological disease in those with early stage infection, and understanding of HIV tissue reservoirs that will aid efforts at HIV eradication.