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The intestinal epithelium forms a selective barrier maintained by tight junctions (TJs) and separating the luminal environment from the submucosal tissues. N-acylhomoserine lactone (AHL) quorum-sensing molecules produced by gram-negative bacteria in the gut can influence homeostasis of the host intestinal epithelium. In the present study, we evaluated the regulatory mechanisms affecting the impact of two representative long- and short-chain AHLs, N-3-(oxododecanoyl)- homoserine lactone (C12-HSL) and N-butyryl homoserine lactone (C4-HSL), on barrier function of human intestinal epithelial Caco-2 cells. Treatment with C12-HSL, but not with C4-HSL, perturbed Caco-2 barrier function; the effect was associated with decreased levels of the TJ proteins occludin and tricellulin and their delocalization from the TJs. C12-HSL also induced matrix metalloprotease (MMP)-2 and MMP-3 activation via lipid raft- and proteaseactivated receptor (PAR)-dependent signaling. Pretreatment with lipid raft disruptors, PAR antagonists, or MMP inhibitors restored the C12-HSL-induced loss of the TJ proteins and increased permeability of Caco-2 cell monolayers. These results indicate that PAR/lipid raft-dependent MMP-2 and -3 activation followed by degradation of occludin and tricellulin are involved in C12-HSL-induced alterations of epithelial paracellular barrier functions. [ABSTRACT FROM AUTHOR]

In recent years, we face an increase in the aging of the HIV-1-infected population, which is not only due to effective antiretroviral therapy but also to new infections among older people. Even with the use of the antiretroviral therapy, HIV-associated neurocognitive disorders represent an increasing problem as the HIV-1-infected population ages. Increased amyloid beta (Aβ) deposition is characteristic of HIV-1-infected brains, and it has been hypothesized that brain vascular dysfunction contributes to this phenomenon, with a critical role suggested for the blood-brain barrier in brain Aβ homeostasis. This review will describe the mechanisms by which the blood-brain barrier may contribute to brain Aβ accumulation, and our findings in the context of HIV-1 infection will be discussed. © 2012 IUBMB Life, 65(1):43-49, 2013 [ABSTRACT FROM AUTHOR]

Activation of matrix metalloproteinase-9 (MMP-9) is involved in HIV-1-induced disruption of the blood-brain barrier (BBB). In the present study, we hypothesize that peroxisome proliferator-activated receptor (PPAR)-α or PPARγ can protect against HIV-1-induced MMP-9 overexpression in brain endothelial cells (hCMEC cell line) by attenuating cellular oxidative stress and down-regulation of caveolae-associated redox signaling. Exposure to HIV-1-infected monocytes induced phosphorylation of ERK1/2 and Akt in hCMEC by 2.5- and 3.6-fold, respectively; however, these effects were attenuated by overexpression of PPARα or PPARγ and by silencing of caveolin-1 (cav-1). Coculture of hCMEC with HIV-1-infected monocytes significantly induced MMP-9 promoter and enzyme activity by 3- to 3.5-fold. Promoter mutation studies indicated that SP-1 (g1940t_g1941t) is an essential transcription factor involved in induction of MMP-9 promoter by HIV-1. In addition, HIV-1-stimulated activity of MMP-9 promoter was inhibited by mutation of AP-1 site 2 (c1918t_a1919g) and both (but not individual) NF-κB binding sites (g1389c and g1664c). PPAR overexpression, ERK1/2 or Akt inhibition, and silencing of cav-1 all effectively protected against HIV-1-induced MMP-9 promoter activity, indicating a close relationship among HIV-1-induced cerebrovascular toxicity, redox-regulated mechanisms, and functional caveolae. Such a link was further confirmed in MMP-9-deficient mice exposed to PPARα or PPARγ agonist and injected with die HIV-1-specific protein Tat into cerebral vasculature. Overall, our results indicate that ERK1/2, Akt, and cav-1 are involved in the regulatory mechanisms of PPAR-mediated protection against HIV-1-induced MMP-9 expression in brain endothelial cells. [ABSTRACT FROM AUTHOR]

Telomerase, via its catalytic component telomerase reverse transcriptase (TERT), extends telomeres of eukaryotic chromosomes. The importance of this reaction is related to the fact that teiomere shortening is a rate-limiting mechanism for human life span that induces cell senescence and contributes to the development of age-related pathologies. The aim of the present study was to evaluate whether the modulation of telomerase activity can influence human immunodeficiency virus type I (HIV-l)-mediated dysfunction of human brain endothelial cells (hCMEC/D3 cells) and transendothelial migration of HIV- 1-infected cells. Telomerase activ- ity was modulated in hCMEC/D3 cells via small interfering RNA-targeting human TERT (hTERT) or by using a specific pharmacological inhibitor of telomerase, TAG-6. The inhibition of hTERT resulted in the upregulation of HI V-i-induced overexpression of intercellular adhesion molecule-1 via the nuclear factor-KB-regulated mechanism and induced the transendothelial migration of HIV-l-infected mono- cytic U937 cells. In addition, the blocking of hTERT activity poten- tiated a HIV-induced downregulation of the expression of tight junction proteins. These results were confirmed in TERT-deficient mice injected with HIV-l-specific protein Tat into the cerebral vas- culature. Further studies revealed that the upregulation of matrix metalloproteinase-9 is the underlying mechanisms of disruption of tight junction proteins in hCMEC/D3 cells with inhibited TERT and exposed to HIV-1. These results indicate that the senescence of brain endothelial cells may predispose to the HIV-induced upregulation of inflammatory mediators and the disruption of the barrier function at the level of the brain endothelium. [ABSTRACT FROM AUTHOR]

The blood-brain barrier (BBB) plays an important role in HIV trafficking into the brain and the development of the central nervous system complications in HIV infection. Tight junctions are the main structural and functional elements that regulate the BBB integrity. Exposure of human brain microvascular endothelial cells (hCMEC/D3 cell line) to HIV-infected monocytes resulted in decreased expression of tight junction proteins, such as junctional adhesion molecule-A (JAM)-A, occludin, and zonula occludens (ZO)-1. Control experiments involved exposure to uninfected monocytes. Alterations of tight junction protein expression were associated with increased endothelial permeability and elevated tyransendothelial migration of HIV-infected monocytes across an in vitro model of the BBB. Notably, overexpression of the peroxisome proliferator-activated receptor (PPAR)α or PPARγ attenuated HIV-mediated dysregulation of tight junction proteins. With the use of exogenous PPARγ agonists and silencing of PPARα or PPARγ these protective effects were connected to down-regulation of matrix metalloproteinase (MMP) and proteasome activities. Indeed, the HIV-induced decrease in the expression of JAM-A and occludin was restored by inhibition of MMP activity. Moreover, both MMP and proteasome inhibitors attenuated HIV-mediated altered expression of ZO-1. The present data indicate that down-regulation of MMP and proteasome activities constitutes a novel mechanism of PPAR-induced protections against HIV-induced disruption of brain endothelial cells. [ABSTRACT FROM AUTHOR]

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors which down-regulate inflammatory signaling pathways. Therefore, we hypothesized that alterations of PPAR functions can contribute to human immunodeficiency virus-1 (HIV-1)-induced dysfunction of brain endothelial cells. Indeed, treatment with HIV-1 transactivator of transcription (Tat) protein decreased PPAR transactivation in brain endothelial cells. We next stably over-expressed PPARα and PPARγ in a newly developed cell line of human brain endothelial cells (hCMEC/D3 cells). Tat-induced up-regulation of inflammatory mediators, such as interleukin (IL)-1β, tumor necrosis factor-α, CCL2, and E-selectin were markedly attenuated in hCMEC/D3 over-expressing PPARα or PPARγ. These results were confirmed in CCL2 and E-selectin promoter activity studies. Similar protective effects were observed in hCMEC/D3 after activation of PPARγ by exogenous PPAR agonists (dPGJ2 and rosiglitazone). PPAR over-expression also prevented Tat-induced binding activity and transactivation of nuclear factor-κB. Importantly, increased PPAR activity attenuated induction of IL-1β, tumor necrosis factor-α, CCL2, and E-selectin in hCMEC/D3 cells co-cultured with HIV-1-infected Jurkat cells. The protective effects of PPAR over-expression were reversed by the antagonists of PPARα (MK886) or PPARγ (GW9662). The present data suggest that targeting PPAR signaling may provide a novel therapeutic approach to attenuate HIV-1-induced local inflammatory responses in brain endothelial cells. [ABSTRACT FROM AUTHOR]

Brain endothelial extracellular vesicles carrying amyloid beta (EV-Aβ) can be transferred to neural progenitor cells (NPCs) leading to NPC dysfunction. However, the events involved in this EV-mediated Aβ pathology are unclear. EV-proteomics studies identified Serpine-1 (plasminogen activator inhibitor 1, PAI-1) as a major connecting "hub" on several protein-protein interaction maps. Serpine-1 was described as a key player in Aβ pathology and was linked to HIV-1 infection as well. Therefore, the aim of this work was to address the hypothesis that Serpine-1 can be transferred via EVs from brain endothelial cells to NPCs and contribute to NPC dysfunction. HBMEC concentrated and released Serpine-1 via EVs, the effect that was potentiated by HIV-1 and Aβ. EVs loaded with Serpine-1 were readily taken up by NPCs, and HIV-1 enhanced this event. Interestingly, a highly specific Serpine-1 inhibitor PAI039 increased EV-Aβ transfer to NPCs in the presence of HIV-1. PAI039 also partially blocked mitochondrial network morphology and mitochondrial function alterations in the recipient NPCs, which developed mainly after HIV + Aβ-EV transfer. PAI039 partly attenuated HIV-EV-mediated decreased synaptic protein levels in NPCs, while increased synaptic protein levels in NPC projections. These findings contribute to a better understanding of the complex mechanisms underlying EV-Serpine-1 related Aβ pathology in the context of HIV infection. They are relevant to HIV-1 associated neurocognitive disorders (HAND) in an effort to elucidate the mechanisms of neuropathology in HIV infection.

Aim: Elevated brain deposits of amyloid beta (Aβ 40 ) contribute to neuropathology and cognitive dysfunction in Alzheimer's disease (AD). However, the role of the blood-brain barrier (BBB) as an interface for the transfer of Aβ 40 from the periphery into the brain is not well characterized. In addition, a substantial population of neural progenitor cells (NPCs) resides in close proximity to brain capillaries that form the BBB. The aim of this study is to understand the impact of brain endothelium-derived extracellular vesicles (EV) containing Aβ 40 on metabolic functions and differentiation of NPCs., Methods: Endothelial EVs were derived from an in vitro model of the brain endothelium treated with 100 nM Aβ 40 or PBS. We then analyzed the impact of these EVs on mitochondrial morphology and bioenergetic disruption of NPCs. In addition, NPCs were differentiated and neurite development upon exposure to EVs was assessed using the IncuCyte Zoom live cell imaging system., Results: We demonstrate that physiological concentrations of Aβ 40 can be transferred to accumulate in NPCs via endothelial EVs. This transfer results in mitochondrial dysfunction, disrupting crista morphology, metabolic rates, fusion and fission dynamics of NPCs, as well as their neurite development., Conclusion: Intercellular transfer of Aβ 40 is carried out by brain endothelium-derived EVs, which can affect NPC differentiation and induce mitochondrial dysfunction, leading to aberrant neurogenesis. This has pathological implications because NPCs growing into neurons are incorporated into cerebral structures involved in learning and memory, two common phenotypes affected in AD and related dementias., Competing Interests: Conflicts of interest All authors declared that there are no conflicts of interest.

HIV-1 crosses the blood-brain barrier (BBB) early in the course of systemic infection and resides in brain macrophages and microglia. The integrity of the brain endothelium is regulated by intercellular tight junctions, which also play a critical role in HIV-1-entry into the brain. Disruption of tight junctions, including changes in claudin-5 expression, is common in HIV-1-infected patients. Recent evidence indicates that both exposure to HIV-1 and HIV-1 specific proteins, such as Tat protein, can contribute to alterations of expression and distribution of claudin-5 in brain endothelial cells and brain microvessels.

Telomerase, via its catalytic component telomerase reverse transcriptase (TERT), extends telomeres of eukaryotic chromosomes. The importance of this reaction is related to the fact that telomere shortening is a rate-limiting mechanism for human life span that induces cell senescence and contributes to the development of age-related pathologies. The aim of the present study was to evaluate whether the modulation of telomerase activity can influence human immunodeficiency virus type 1 (HIV-1)-mediated dysfunction of human brain endothelial cells (hCMEC/D3 cells) and transendothelial migration of HIV-1-infected cells. Telomerase activity was modulated in hCMEC/D3 cells via small interfering RNA-targeting human TERT (hTERT) or by using a specific pharmacological inhibitor of telomerase, TAG-6. The inhibition of hTERT resulted in the upregulation of HIV-1-induced overexpression of intercellular adhesion molecule-1 via the nuclear factor-kappaB-regulated mechanism and induced the transendothelial migration of HIV-1-infected monocytic U937 cells. In addition, the blocking of hTERT activity potentiated a HIV-induced downregulation of the expression of tight junction proteins. These results were confirmed in TERT-deficient mice injected with HIV-1-specific protein Tat into the cerebral vasculature. Further studies revealed that the upregulation of matrix metalloproteinase-9 is the underlying mechanisms of disruption of tight junction proteins in hCMEC/D3 cells with inhibited TERT and exposed to HIV-1. These results indicate that the senescence of brain endothelial cells may predispose to the HIV-induced upregulation of inflammatory mediators and the disruption of the barrier function at the level of the brain endothelium.