Akt/Nox2/NF-κB signaling pathway is involved in Tat-induced HIV-1 long terminal repeat (LTR) transactivation

Human immunodeficiency virus (HIV) regulatory protein Tat has pro-oxidant property, which might contribute to Tat-induced long terminal repeat region (LTR) transactivation. However, the intracellular mechanisms whereby Tat triggers ROS production, and the relationship between Tat-induced ROS production and LTR transactivation, are still subject to debate. The present study was undertaken to evaluate the specific effects of Tat on nicotinamide adenine denucleotide phosphate (NADPH) oxidase in MAGI cells, and to determine the specific role of NADPH oxidase in Tat-induced LTR transactivation. Application of Tat to MAGI cells caused increases in ROS formation that were prevented by both pharmacologic NADPH oxidase inhibitors and by siRNA Nox2, but not by other inhibitors of pro-oxidant enzymes or siRNA Nox4. Furthermore, inhibition of NADPH oxidase by both pharmacologic NADPH oxidase inhibitors and by siRNA Nox2 attenuated Tat-induced p65 phosphorylation and IKK phosphorylation. Phosphatidylinositol 3-kinase/Akt signaling pathway was involved in Tat-induced NADPH oxidase stimulation. Finally, NADPH oxidase inhibitors or Nox2 siRNA, but not control siRNA, inhibited Tat-induced LTR transactivation. Tat-induced HIV-1 LTR transactivation was inhibited in wortmannin or LY294002 treated cells compared to control cells. Together, these data describe a specific and biologically significant signaling component of the MAGI cells response to Tat, and suggest the PI3K/Akt signaling pathway might originate in part with Tat-induced activation of NADPH oxidase and LTR transactivation.     

MiR-217 is involved in Tat-induced HIV-1 long terminal repeat (LTR) transactivation by down-regulation of SIRT1

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression and may contribute to the development and progression of many infective diseases including human immunodeficiency virus 1 (HIV-1) infection. The Tat protein is fundamental to viral gene expression. In this study, our goal was to investigate the regulation of a specific miRNA (known as miR-217) in multinuclear activation of galactosidase indicator (MAGI) cells and explore the mechanisms by which miR-217 influenced Tat-induced HIV-1 transactivation through down-regulation of SIRT1 expression. We showed that miR-217 was up-regulated when Tat was expressed in multinuclear activation of galactosidase indicator cells. Forced expression of "miR-217 mimics" increased Tat-induced LTR transactivation. In addition, miR-217 significantly inhibited SIRT1 protein expression by acting on the 3'-UTR of the SIRT1 mRNA. In turn, the decrease in SIRT1 protein abundance provoked by miR-217 affected two important types of downstream signaling molecules that were regulated by Tat. Lower expression of SIRT1 caused by miR-217 enhanced Tat-induced phosphorylation of IKK and p65-NFkB and also exacerbated the loss of AMPK phosphorylation triggered by Tat. Our results uncover previously unknown links between Tat and a specific host cell miRNA that targets SIRT1. We also demonstrate that this regulatory mechanism impinges on p65-NFkB and AMPK signaling: two important host cell pathways that influence HIV-1 pathogenesis. Our results also suggest that strategies to augment SIRT1 protein expression by down-regulation of miR-217 may have therapeutic benefits to prevent HIV-1 replication.     

HIV-1 Tat increases BAG3 via NF-κB signaling to induce autophagy during HIV-associated neurocognitive disorder

The human immunodeficiency virus-1 (HIV-1) regulatory protein Tat plays an important role during HIV-1-associated neurocognitive disorders (HAND) by inducing neuronal autophagy. In this study, we used immunohistochemistry, immunofluorescence, western blot, qRT-PCR, and RNA interference to elucidate the involvement of Bcl-2-associated athanogene 3 (BAG3) in the pathogenesis of HIV-1 Tat-induced autophagy during HAND. We found that BAG3 expression is elevated in astrocytes in frontal cortex of macaques infected with simian immunodeficiency virus-human immunodeficiency chimeric virus (SHIV). In addition, in human primary glioblastoma cells (U87), HIV-1 Tat upregulated BAG3 in an NF-κB-dependent manner to induce autophagy. Importantly, suppression of BAG3 or inhibition of NF-κB activity reversed the HIV-1 Tat-induced autophagy. These results indicate that HIV-1 Tat induces autophagy by upregulating BAG3 via NF-κB signaling, which suggests BAG3 and NF-κB could potentially serve as novel targets for HAND therapies.     

(-)-Epigallocatechin gallate amplifies interleukin-1-stimulated interleukin-6 synthesis in osteoblast-like MC3T3-E1 cells

We previously reported that interleukin-1 (IL-1), a potent bone resorptive cytokine, stimulates the synthesis of interleukin-6 (IL-6) via activation of p44/p42 mitogen-activated protein (MAP) kinase and p38 MAP kinase in osteoblast-like MC3T3-E1 cells, and that AMP-activated protein kinase (AMPK) negatively regulates the IL-1-induced IL-6 synthesis through the inhibitor of κB (IκB)/nuclear factor-κB (NF-κB) pathway. On the other hand, it is recognized that catechin possesses a beneficial property for bone metabolism. Among them, (-)-epigallocatechin gallate (EGCG) is an abundant and major bioactive component. In the present study, we investigated the effect of EGCG on the IL-1 stimulated IL-6 synthesis in osteoblast-like MC3T3-E1 cells. EGCG significantly enhanced the IL-1-stimulated IL-6 synthesis in a dose-dependent manner in the range between 50 and 100 μM. EGCG increased the mRNA levels of IL-6 stimulated by IL-1. IL-1-induced phosphorylation of IκB and NF-κB were suppressed by EGCG. On the other hand, EGCG failed to affect the IL-1-induced phosphorylation of p44/p42 MAP kinase, p38 MAP kinase and AMPK. These results strongly suggest that EGCG enhances IL-1-stimulated IL-6 synthesis through inhibiting the AMPK-IκB/NF-κB pathway at the point between AMPK and IκB/NF-κB in osteoblasts.     

Docosahexaenoic acid inhibition of inflammation is partially via cross-talk between Nrf2/heme oxygenase 1 and IKK/NF-κB pathways

We examined the underlying mechanisms involved in n-3 docosahexaenoic acid (DHA) inhibition of inflammation in EA.hy926 cells. The present results demonstrated that pretreatment with DHA (50 and 100 μM) inhibited tumor necrosis factor-alpha (TNF-α)-induced intercellular adhesion molecule 1 (ICAM-1) protein, mRNA expression and promoter activity. In addition, TNF-α-stimulated inhibitory kappa B (IκB) kinase (IKK) phosphorylation, IκB phosphorylation and degradation, p65 nuclear translocation, and nuclear factor-κB (NF-κB) and DNA binding activity were attenuated by pretreatment with DHA. DHA triggered early-stage and transient reactive oxygen species (ROS) generation and significantly increased the protein expression of heme oxygenase 1 (HO-1), induced nuclear factor erythroid 2-related factor 2 (Nrf2) translocation to the nucleus and up-regulated antioxidant response element (ARE)-luciferase reporter activity. Moreover, DHA inhibited Nrf2 ubiquitination and proteasome activity. DHA activated Akt, p38 and ERK1/2 phosphorylation, and specific inhibitors of respective pathways attenuated DHA-induced Nrf2 nuclear translocation and HO-1 expression. Transfection with HO-1 siRNA knocked down HO-1 expression and partially reversed the DHA-mediated inhibition of TNF-α-induced p65 nuclear translocation and ICAM-1 expression. Importantly, we show for the first time that HO-1 plays a down-regulatory role in NF-κB nuclear translocation, and inhibition of Nrf2 ubiquitination and proteasome activity are involved in increased cellular Nrf2 level by DHA. In this study, we show that HO-1 plays a down-regulatory role in NF-κB nuclear translocation and that the protective effect of DHA against inflammation is partially via up-regulation of Nrf2-mediated HO-1 expression and inhibition of IKK/NF-κB signaling pathway.     

Polysaccharides from Dicliptera chinensis ameliorate liver disturbance by regulating TLR-4/NF-κB and AMPK/Nrf2 signalling pathways

The purpose of this study was to alleviate liver disturbance by applying polysaccharides from Dicliptera chinensis (DCP) to act on the adenosine monophosphate–activated protein kinase/ nuclear factor erythroid 2-related factor 2 (AMPK/ Nrf2) oxidative stress pathway and the Toll-like receptor 4 (TLR-4)/ nuclear factor kappa-B (NF-κB) inflammatory pathway and to establish an in vivo liver disturbance model using male C57BL/6J and TLR-4 knockout (^−/−) mice. For this, we evaluated the expression levels of SREBP-1 and Nrf2 after silencing the expression of AMPK using siRNA technology. Our results show that with regard to the TLR-4/ NF-κB inflammatory pathway, DCP inhibits TLR-4, up-regulates the expression of peroxisome proliferator-activated receptor-γ (PPAR-γ), reduces the expression of phospho(p)-NF-κB and leads to the reduction of downstream inflammatory factors, such as tumour necrosis factor-α (TNF-α), interleukin (IL)-6 and IL-1β, thereby inhibiting the inflammatory response. Regarding the AMPK/ Nrf2 oxidative stress pathway, DCP up-regulates the expression of p-AMPK and Nrf2, in addition to regulating glucose and lipid metabolism, oxidative stress and ameliorating liver disturbance symptoms. In summary, our study shows that DCP alleviates liver disturbances by inhibiting mechanisms used during liver inflammation and oxidative stress depression, which provides a new strategy for the clinical treatment of liver disturbance.     

Epigallocatechin-3-gallate prevents lupus nephritis development in mice via enhancing the Nrf2 antioxidant pathway and inhibiting NLRP3 inflammasome activation

Patients with lupus nephritis show an impaired oxidative status and increased levels of interleukin (IL)-1β and IL-18, which are closely linked to inflammation and correlated with disease activity. Although epigallocatechin-3-gallate (EGCG), the major bioactive polyphenol present in green tea with antioxidant and free radical scavenging activities, has been reported to have anti-inflammatory effects by inhibiting nuclear factor-kappa B (NF-κB)-mediated inflammatory responses in vivo, its effectiveness for the treatment of lupus nephritis is still unknown. In the present study, 12-week-old New Zealand black/white (NZB/W) F1 lupus-prone mice were treated daily with EGCG by gavage until sacrificed at 34 weeks old for clinical, pathological, and mechanistic evaluation. We found that the administration (1) prevented proteinuria, renal function impairment, and severe renal lesions; (2) increased renal nuclear factor E2-related factor 2 (Nrf2) and glutathione peroxidase activity; (3) reduced renal oxidative stress, NF-κB activation, and NLRP3 mRNA/protein expression and protein levels of mature caspase-1, IL-1β, and IL-18; and (4) enhanced splenic regulatory T (Treg) cell activity. Our data clearly demonstrate that EGCG has prophylactic effects on lupus nephritis in these mice that are highly associated with its effects of enhancing the Nrf2 antioxidant signaling pathway, decreasing renal NLRP3 inflammasome activation, and increasing systemic Treg cell activity.     

Anti-neuroinflammatory Effect of Emodin in LPS-Stimulated Microglia: Involvement of AMPK/Nrf2 Activation

AMPK/Nrf2 signaling regulates multiple antioxidative factors and exerts neuroprotective effects. Emodin is one of the main bioactive components extracted from Polygonum multiflorum, a plant possessing important activities for human health and for treating a variety of diseases. This study examined whether emodin can activate AMPK/Nrf2 signaling and induce the expression of genes targeted by this pathway. In addition, the anti-neuroinflammatory properties of emodin in lipopolysaccharide (LPS)-stimulated microglia were examined. In microglia, the emodin treatment increased the levels of LKB1, CaMKII, and AMPK phosphorylation. Emodin increased the translocation and transactivity of Nrf2 and enhanced the levels of HO-1 and NQO1. In addition, the emodin-mediated expression of HO-1 and NQO1 was attenuated completely by an AMPK inhibitor (compound C). Moreover, emodin decreased dramatically the LPS-induced production of NO and PGE₂ as well as the protein expression and promoter activity of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). In addition, emodin effectively inhibited the production of pro-inflammatory cytokines, TNF-α and IL-6, and reduced the level of IκBα phosphorylation, leading to the suppression of the nuclear translocation, phosphorylation, and transactivity of NF-κB. Emodin also suppressed the LPS-stimulated activation of STATs, JNK, and p38 MAPK. The anti-inflammatory effects of emodin were reversed by transfection with Nrf-2 and HO-1 siRNA and by a co-treatment with an AMPK inhibitor. These results suggest that emodin isolated from P. multiflorum can be used as a natural anti-neuroinflammatory agent that exerts its effects by inducing HO-1 and NQO1 via AMPK/Nrf2 signaling in microglia.     

Blocking of tripartite motif 8 protects against lipopolysaccharide (LPS)-induced acute lung injury by regulating AMPKα activity

Acute lung injury (ALI) and its more serious form, respiratory distress syndrome (ARDS), are considered as an acute and severe inflammatory process existing in lungs, and still remain high mortality rates. Tripartite motif 8 (TRIM8) contains an N-terminal RING finger, which is followed by two B-boxes and a coiled-coil domain, belonging to the TRIM/RBCC family and playing significant role in meditating inflammation, oxidative stress and apoptosis. In the study, we investigated the role of TRIM8 in ALI induced by lipopolysaccharide (LPS) and the underlying molecular mechanisms. The in vitro results indicated that LPS time-dependently enhanced TRIM8 expression in lung epithelial cells. Suppressing TRIM8 markedly ameliorated LPS-elicited inflammatory response, as evidenced by the down-regulated mRNA levels of interleukin-1β (IL-1β), IL-6 and tumor necrosis factor-α (TNF-α) in cells mainly through inactivating nuclear factor-kappa B (NF-κB) signaling pathway; however, over-expressing TRIM8 markedly promoted inflammation in LPS-challenged cells. In addition, LPS-induced oxidative stress was accelerated by TRIM8 over-expression, while being alleviated by TRIM8 knockdown by regulating Nrf2 signaling. Importantly, TRIM8 could negatively meditate AMP-activated protein kinase-α (AMPKα) activation to modulate LPS-triggered inflammatory response and ROS generation in vitro. Additionally, our in vivo findings suggested that TRIM8 knockdown effectively attenuated LPS-induced lung injury nu decrease of lung wet/dry (W/T) ratio, protein concentrations, neutrophil infiltration, myeloperoxidase (MPO) activity, reactive oxygen species (ROS) production and superoxide dismutase (SOD) depletion. Meanwhile, the loss of TRIM8 markedly lessened IL-1β, IL-6 and TNF-α expression in lung tissues of LPS-challenged mice, and reduced NF-κB phosphorylation. Furthermore, TRIM8 knockdown evidently improved nuclear factor-erythroid 2 related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) expressions in lung of LPS-treated mice. The anti-inflammation and anti-oxidant role of TRIM8-silence might be associated with AMPKα phosphorylation. Together, our study firstly provided a support that TRIM8 knockdown effectively protected LPS-induced ALI against inflammation and oxidative stress largely dependent on the promotion of AMPKα pathway.