Extracellular vesicles regulate gap junction-mediated intercellular communication and HIV-1 infection of human neural progenitor cells.

Human immunodeficiency virus-1 (HIV-1) has been shown to cross the blood-brain barrier and cause HIV-associated neurocognitive disorders (HAND) through a process that may involve direct or indirect interactions with the central nervous system (CNS) cells and alterations of amyloid ß (Aß) homeostasis. The present study focused on the mechanisms of HIV-1 infecting human neural progenitor cells (hNPCs) and affecting NPC intercellular communications with human brain endothelial cells (HBMEC). Despite the lack of the CD4 receptor, hNPCs were effectively infected by HIV-1 via a mechanism involving the chemokine receptors, CXCR4 and CCR5. HIV-1 infection increased expression of connexin-43 (Cx43), phosphorylated Cx43 (pCx43), and pannexin 2 (Panx2) protein levels in hNPCs, suggesting alterations in gap-junction (GJ) and pannexin channel communication. Indeed, a functional GJ assay indicated an increase in communication between HIV-infected hNPCs and non-infected HBMEC. We next analyzed the impact of HBMEC-derived extracellular vesicles (EVs) and EVs carrying Aß (EV-Aß) on the expression of Cx43, pCx43, and Panx2 in HIV-1 infected and non-infected hNPCs. Exposure to EV-Aß resulted in significant reduction of Cx43 and pCx43 protein expression in non-infected hNPCs when compared to EV controls. Interestingly, EV-Aß treatment significantly increased levels of Cx43, pCx43, and Panx2 in HIV-1-infected hNPCs when compared to non-infected controls. These results were confirmed in a GJ functional assay and an ATP release assay, which is an indicator of connexin hemichannel and/or pannexin channel functions. Overall, the current study demonstrates the importance of hNPCs in HIV-1 infection and indicates that intercellular communications between infected hNPCs and HBMEC can be effectively modulated by EVs carrying Aß as their cargo.

Adenovirus targets transcriptional and posttranslational mechanisms to limit gap junction function.

Adenoviruses are responsible for a spectrum of pathogenesis including viral myocarditis. The gap junction protein connexin43 (Cx43, gene name GJA1) facilitates rapid propagation of action potentials necessary for each heartbeat. Gap junctions also propagate innate and adaptive antiviral immune responses, but how viruses may target these structures is not understood. Given this immunological role of Cx43, we hypothesized that gap junctions would be targeted during adenovirus type 5 (Ad5) infection. We find reduced Cx43 protein levels due to decreased GJA1 mRNA transcripts dependent upon ß-catenin transcriptional activity during Ad5 infection, with early viral protein E4orf1 sufficient to induce ß-catenin phosphorylation. Loss of gap junction function occurs prior to reduced Cx43 protein levels with Ad5 infection rapidly inducing Cx43 phosphorylation events consistent with altered gap junction conductance. Direct Cx43 interaction with ZO-1 plays a critical role in gap junction regulation. We find loss of Cx43/ZO-1 complexing during Ad5 infection by co-immunoprecipitation and complementary studies in human induced pluripotent stem cell derived-cardiomyocytes reveal Cx43 gap junction remodeling by reduced ZO-1 complexing. These findings reveal specific targeting of gap junction function by Ad5 leading to loss of intercellular communication which would contribute to dangerous pathological states including arrhythmias in infected hearts.

Masters of manipulation: Viral modulation of the immunological synapse.

In order to thrive, viruses have evolved to manipulate host cell machinery for their own benefit. One major obstacle faced by pathogens is the immunological synapse. To enable efficient replication and latency in immune cells, viruses have developed a range of strategies to manipulate cellular processes involved in immunological synapse formation to evade immune detection and control T-cell activation. In vitro, viruses such as human immunodeficiency virus 1 and human T-lymphotropic virus type 1 utilise structures known as virological synapses to aid transmission of viral particles from cell to cell in a process termed trans-infection. The formation of the virological synapse provides a gateway for virus to be transferred between cells avoiding the extracellular space, preventing antibody neutralisation or recognition by complement. This review looks at how viruses are able to subvert intracellular signalling to modulate immune function to their advantage and explores the role synapse formation has in viral persistence and cell-to-cell transmission.

Tunneling nanotubes (TNT) mediate long-range gap junctional communication: Implications for HIV cell to cell spread.

Cell-to-cell communication is essen for the development of multicellular systems and is coordinated by soluble factors, exosomes, gap junction (GJ) channels, and the recently described tunneling nanotubes (TNTs). We and others have demonstrated that TNT-like structures are mostly present during pathogenic conditions, including HIV infection. However, the nature, function, and communication properties of TNTs are still poorly understood. In this manuscript, we demonstrate that TNTs induced by HIV infection have functional GJs at the ends of their membrane extensions and that TNTs mediate long-range GJ communication during HIV infection. Blocking or reducing GJ communication during HIV infection resulted in aberrant TNT cell-to-cell contact, compromising HIV spread and replication. Thus, TNTs and associated GJs are required for the efficient cell-to-cell communication and viral spread. Our data indicate that targeting TNTs/GJs may provide new therapeutic opportunities for the treatment of HIV.

Role of gap junctions and hemichannels in parasitic infections.

In vertebrates, connexins (Cxs) and pannexins (Panxs) are proteins that form gap junction channels and/or hemichannels located at cell-cell interfaces and cell surface, respectively. Similar channel types are formed by innexins in invertebrate cells. These channels serve as pathways for cellular communication that coordinate diverse physiologic processes. However, it is known that many acquired and inherited diseases deregulate Cx and/or Panx channels, condition that frequently worsens the pathological state of vertebrates. Recent evidences suggest that Cx and/or Panx hemichannels play a relevant role in bacterial and viral infections. Nonetheless, little is known about the role of Cx- and Panx-based channels in parasitic infections of vertebrates. In this review, available data on changes in Cx and gap junction channel changes induced by parasitic infections are summarized. Additionally, we describe recent findings that suggest possible roles of hemichannels in parasitic infections. Finally, the possibility of new therapeutic designs based on hemichannel blokers is presented.

Human immunodeficiency virus infection of human astrocytes disrupts blood-brain barrier integrity by a gap junction-dependent mechanism.

HIV infection of the CNS is an early event after primary infection, resulting in neurological complications in a significant number of individuals despite antiretroviral therapy (ART). The main cells infected with HIV within the CNS are macrophages/microglia and a small fraction of astrocytes. The role of these few infected astrocytes in the pathogenesis of neuroAIDS has not been examined extensively. Here, we demonstrate that few HIV-infected astrocytes (4.7 ± 2.8% in vitro and 8.2 ± 3.9% in vivo) compromise blood-brain barrier (BBB) integrity. This BBB disruption is due to endothelial apoptosis, misguided astrocyte end feet, and dysregulation of lipoxygenase/cyclooxygenase, BK(Ca) channels, and ATP receptor activation within astrocytes. All of these alterations in BBB integrity induced by a few HIV-infected astrocytes were gap junction dependent, as blocking these channels protected the BBB from HIV-infected astrocyte-mediated compromise. We also demonstrated apoptosis in vivo of BBB cells in contact with infected astrocytes using brain tissue sections from simian immunodeficiency virus-infected macaques as a model of neuroAIDS, suggesting an important role for these few infected astrocytes in the CNS damage seen with HIV infection. Our findings describe a novel mechanism of bystander BBB toxicity mediated by low numbers of HIV-infected astrocytes and amplified by gap junctions. This mechanism of toxicity contributes to understanding how CNS damage is spread even in the current ART era and how minimal or controlled HIV infection still results in cognitive impairment in a large population of infected individuals.

Layer specific changes of astroglial gap junctions in the rat cerebellar cortex by persistent Borna Disease Virus infection.

Neonatal Borna Disease Virus (BDV) infection of the Lewis rat brain, leads to Purkinje cell degeneration, in association with astroglial activation. Since astroglial gap junctions (GJ) are known to influence neuronal degeneration, we investigated BDV dependent changes in astroglial GJ connexins (Cx) Cx43, and Cx30 in the Lewis rat cerebellum, 4, and 8 weeks after neonatal infection. On the mRNA level, RT-PCR demonstrated a BDV dependent increase in cerebellar Cx43, and a decrease in Cx30, 8, but not 4 weeks p.i. On the protein level, Western blot analysis revealed no overall upregulation of Cx43, but an increase of its phosphorylated forms, 8 weeks p.i. Cx30 protein was downregulated. Immunohistochemistry revealed a BDV dependent reduction of Cx43 in the granular layer (GL), 4 weeks p.i. 8 weeks p.i., Cx43 immunoreactivity recovered in the GL, and was induced in the molecular layer (ML). Cx30 revealed a BDV dependent decrease in the GL, both 4, and 8 weeks p.i. Changes in astroglial Cxs correlated not with expression of the astrogliotic marker GFAP, which was upregulated in radial glia. With regard to functional coupling, primary cerebellar astroglial cultures, revealed a BDV dependent increase of Cx43, and Cx30 immunoreactivity and in spreading of the GJ permeant dye Lucifer Yellow. These results demonstrate a massive, BDV dependent reorganization of astroglial Cx expression, and of functional GJ coupling in the cerebellar cortex, which might be of importance for the BDV dependent neurodegeneration in this brain region.

Gap junctions mediate human immunodeficiency virus-bystander killing in astrocytes.

Human immunodeficiency virus (HIV) entry into the CNS is an early event after infection, resulting in neurological dysfunction in a significant number of individuals. As people with acquired immunodeficiency syndrome (AIDS) live longer, the prevalence of cognitive impairment is increasing, despite antiretroviral therapy. The mechanisms that mediate CNS dysfunction are still not completely understood, and include inflammation, viral presence, and/or replication. In this report, we characterize a novel role of gap junctions in transmitting and thereby amplifying toxic signals originating from HIV-infected astrocytes that trigger cell death in uninfected astrocytes. HIV-infected astrocytes were resistant to apoptosis; however, uninfected astrocytes forming gap junctions with infected astrocytes were apoptotic. Gap junction blockers abolished apoptosis in uninfected astrocytes, supporting the role of these channels in amplifying cell death. Our findings describe a novel mechanism of toxicity within the brain, triggered by low numbers of HIV-infected astrocytes and amplified by gap junctions, contributing to the pathogenesis of NeuroAIDS.

Coxsackievirus and adenovirus receptor, a tight junction membrane protein, is expressed in glomerular podocytes in the kidney.

In nephrosis, filtration slits of podocytes are greatly narrowed, and slit diaphragms are displaced by junctions with close contact. Freeze-fracture studies have shown that the newly formed junctions consist of tight junctions and gap junctions. Several tight-junction proteins are known as integral membrane components, including occludin and claudins; but none of them have been found in podocytes. Coxsackievirus and adenovirus receptor (CAR) has recently been identified as a virus receptor that is a 46-kDa integral membrane protein with two Ig-like domains in the extracellular region. In polarized epithelial cells, CAR is expressed at the tight junction, where it associates with ZO-1 and plays a role in the barrier to the movement of macromolecules and ions. In the present study, we investigated the expression and localization of CAR in rat kidneys treated with puromycin aminonucleoside (PAN) and in rat kidneys perfused for 15 minutes with protamine sulfate (PS). Both the experimental models have been used to induce tight junctions in podocytes. Ribonuclease protection assay and Western blot analysis revealed a distinct increase of CAR transcript and protein in glomeruli during PAN nephrosis but no increase in glomeruli by PS perfusion. Immunohistochemistry revealed a significant increase in CAR staining intensity along the glomerular capillary wall in PAN nephrosis and after PS perfusion. Immunoelectron microscopy demonstrated in both the models that the immunogold particles for CAR along the capillary wall were found predominantly at close cell-cell contact sites of podocytes but were rarely found at slit diaphragms. In cultured podocytes, CAR was localized at cell-cell contact sites. CAR distribution was identical to that of ZO-1 and different from that of a gap junction protein, connexin43. These findings indicate that CAR is an integral membrane component of tight junction in podocytes and that CAR expression in podocytes is regulated at the transcriptional level and in the redistribution of protein.

Binding of bovine papillomavirus type 4 E8 to ductin (16K proteolipid), down-regulation of gap junction intercellular communication and full cell transformation are independent events.

The E8 open reading frame of bovine papillomavirus type 4 encodes a small hydrophobic polypeptide that contributes to primary cell transformation by conferring to cells the ability to form foci and to grow in low serum and in suspension. Wild-type E8 binds in vitro to ductin, a component of gap junctions, and this binding is accompanied by a loss of gap junction intercellular communication in transformed bovine fibroblasts. However, through the analysis of a panel of E8 mutants, we show here that binding of E8 to ductin is not sufficient for down-regulation of gap junction communication and that there is no absolute correlation between down-regulation of gap junction communication and the transformed phenotype.