Inhibition of autophagy and chemokine induction by sphingosine 1-phosphate receptor 1 through NF-κB signaling in human pulmonary endothelial cells infected with influenza A viruses

Sphingosine 1-phosphate signaling during infection and immunity

Sphingolipids are essential components of all eukaryotic membranes. The bioactive sphingolipid molecule, Sphingosine 1-Phosphate (S1P), regulates various important biological functions. This review aims to provide a comprehensive overview of the role of S1P signaling pathway in various immune cell functions under different pathophysiological conditions including bacterial and viral infections, autoimmune disorders, inflammation, and cancer. We covered the aspects of S1P pathways in NOD/TLR pathways, bacterial and viral infections, autoimmune disorders, and tumor immunology. This implies that targeting S1P signaling can be used as a strategy to block these pathologies. Our current understanding of targeting various components of S1P signaling for therapeutic purposes and the present status of S1P pathway inhibitors or modulators in disease conditions where the host immune system plays a pivotal role is the primary focus of this review.

Ozanimod differentially preserves human cerebrovascular endothelial barrier proteins and attenuates matrix metalloproteinase-9 activity following in vitro acute ischemic injury

Endothelial integrity is critical in mitigating a vicious cascade of secondary injuries following acute ischemic stroke (AIS). Matrix metalloproteinase-9 (MMP-9), a contributor to endothelial integrity loss, is elevated during stroke and is associated with worsened stroke outcome. We investigated the FDA-approved selective sphingosine-1-phosphate receptor 1 (S1PR1) ligand, ozanimod, on the regulation/activity of MMP-9 as well as endothelial barrier components [platelet endothelial cell adhesion molecule 1 (PECAM-1), claudin-5, and zonula occludens 1 (ZO-1)] in human brain microvascular endothelial cells (HBMECs) following hypoxia plus glucose deprivation (HGD). We previously reported that S1PR1 activation improves HBMEC integrity; however, mechanisms underlying S1PR1 involvement in endothelial cell barrier integrity have not been clearly elucidated. We hypothesized that ozanimod would attenuate an HGD-induced increase in MMP-9 activity that would concomitantly attenuate the loss of integral barrier components. Male HBMECs were treated with ozanimod or vehicle and exposed to 3 h of normoxia (21% O2) or HGD (1% O2). Immunoblotting, zymography, qRT-PCR, and immunocytochemical labeling techniques assessed processes related to MMP-9 and barrier markers. We observed that HGD acutely increased MMP-9 activity and reduced claudin-5 and PECAM-1 levels, and ozanimod attenuated these responses. In situ analysis, via PROSPER, suggested that attenuation of MMP-9 activity may be a primary factor in maintaining these integral barrier proteins. We also observed that HGD increased intracellular mechanisms associated with augmented MMP-9 activation; however, ozanimod had no effect on these select factors. Thus, we conclude that ozanimod has the potential to attenuate HGD-mediated decreases in HBMEC integrity in part by decreasing MMP-9 activity as well as preserving barrier properties.NEW & NOTEWORTHY We have identified a potential novel mechanism by which ozanimod, a selective sphingosine-1-phosphate receptor 1 (S1PR1) agonist, attenuates hypoxia plus glucose deprivation (HGD)-induced matrix metalloproteinase-9 (MMP-9) activity and disruptions in integral human brain endothelial cell barrier proteins. Our results suggest that ischemic-like injury elicits increased MMP-9 activity and alterations of barrier integrity proteins in human brain microvascular endothelial cells (HBMECs) and that ozanimod via S1PR1 attenuates these HGD-induced responses, adding to its therapeutic potential in cerebrovascular protection during the acute phase of ischemic stroke.

The battle for autophagy between host and influenza A virus

Influenza A virus (IAV) is an infectious pathogen, threatening the population and public safety with its epidemics. Therefore, it is essential to better understand influenza virus biology to develop efficient strategies against its pathogenicity. Autophagy is an important cellular process to maintain cellular homeostasis by cleaning up the hazardous substrates in lysosome. Accumulating research has also suggested that autophagy is a critical mechanism in host defense responses against IAV infection by degrading viral particles and activating innate or acquired immunity to induce viral clearance. However, IAV has conversely hijacked autophagy to strengthen virus infection by blocking autophagy maturation and further interfering host antiviral signalling to promote viral replication. Therefore, how the battle for autophagy between host and IAV is carried out need to be known. In this review, we describe the role of autophagy in host defence and IAV survival, and summarize the role of influenza proteins in subverting the autophagic process as well as then concentrate on how host utilize antiviral function of autophagy to prevent IAV infection.

Antiviral Activity of a Cyclic Pro-Pro-β3-HoPhe-Phe Tetrapeptide against HSV-1 and HAdV-5

The core of Cyclolinopeptide A (CLA, cyclo(LIILVPPFF)), responsible for its high immunosuppressive activity, contains a Pro-Pro-Phe-Phe sequence. A newly synthesized cyclic tetrapeptide, cyclo(Pro-Pro-β3-HoPhe-Phe) (denoted as 4B8M) bearing the active sequence of CLA, was recently shown to exhibit a wide array of anti-inflammatory properties in mouse models. In this investigation, we demonstrate that the peptide significantly inhibits the replication of human adenovirus C serotype 5 (HAdV-5) and Herpes simplex virus type-1 (HSV-1) in epithelial lung cell line A-549, applying Cidofovir and Acyclovir as reference drugs. Based on a previously established mechanism of its action, we propose that the peptide may inhibit virus replication by the induction of PGE2 acting via EP2/EP4 receptors in epithelial cells. In summary, we reveal a new, antiviral property of this anti-inflammatory peptide.

MRSA-induced endothelial permeability and acute lung injury are attenuated by FTY720 S-phosphonate

Disruption of the lung endothelial barrier is a hallmark of acute respiratory distress syndrome (ARDS), for which no effective pharmacologic treatments exist. Prior work has demonstrated that FTY720 S-phosphonate (Tys), an analog of sphingosine-1-phosphate (S1P) and FTY720, exhibits potent endothelial cell (EC) barrier protective properties. In this study, we investigated the in vitro and in vivo efficacy of Tys against methicillin-resistant Staphylococcus aureus (MRSA), a frequent bacterial cause of ARDS. Tys-protected human lung EC from barrier disruption induced by heat-killed MRSA (HK-MRSA) or staphylococcal α-toxin and attenuated MRSA-induced cytoskeletal changes associated with barrier disruption, including actin stress fiber formation and loss of peripheral VE-cadherin and cortactin. Tys-inhibited Rho and myosin light chain (MLC) activation after MRSA and blocked MRSA-induced NF-κB activation and release of the proinflammatory cytokines, IL-6 and IL-8. In vivo, intratracheal administration of live MRSA in mice caused significant vascular leakage and leukocyte infiltration into the alveolar space. Pre- or posttreatment with Tys attenuated MRSA-induced lung permeability and levels of alveolar neutrophils. Posttreatment with Tys significantly reduced levels of bronchoalveolar lavage (BAL) VCAM-1 and plasma IL-6 and KC induced by MRSA. Dynamic intravital imaging of mouse lungs demonstrated Tys attenuation of HK-MRSA-induced interstitial edema and neutrophil infiltration into lung tissue. Tys did not directly inhibit MRSA growth or viability in vitro. In conclusion, Tys inhibits lung EC barrier disruption and proinflammatory signaling induced by MRSA in vitro and attenuates acute lung injury induced by MRSA in vivo. These results support the potential utility of Tys as a novel ARDS therapeutic strategy.

The Crossroads between Host Copper Metabolism and Influenza Infection

Three main approaches are used to combat severe viral respiratory infections. The first is preemptive vaccination that blocks infection. Weakened or dead viral particles, as well as genetic constructs carrying viral proteins or information about them, are used as an antigen. However, the viral genome is very evolutionary labile and changes continuously. Second, chemical agents are used during infection and inhibit the function of a number of viral proteins. However, these drugs lose their effectiveness because the virus can rapidly acquire resistance to them. The third is the search for points in the host metabolism the effect on which would suppress the replication of the virus but would not have a significant effect on the metabolism of the host. Here, we consider the possibility of using the copper metabolic system as a target to reduce the severity of influenza infection. This is facilitated by the fact that, in mammals, copper status can be rapidly reduced by silver nanoparticles and restored after their cancellation.

Down-regulation of miR-155 inhibits inflammatory response in human pulmonary microvascular endothelial cells infected with influenza A virus by targeting sphingosine-1-phosphate receptor 1

Background:

Endothelial cells play a key role in the cytokine storm caused by influenza A virus. MicroRNA-155 (miR-155) is an important regulator in inflammation. Its role in the inflammatory response to influenza A infection, however, has yet to be elucidated. In this study, we explored the role as well as the underlying mechanism of miR-155 in the cytokine production in influenza A-infected endothelial cells.

Methods:

Human pulmonary microvascular endothelial cells (HPMECs) were infected with the influenza A virus strain H1N1. The efficiency of H1N1 infection was confirmed by immunofluorescence. The expression levels of proinflammatory cytokines and miR-155 were determined using real-time polymerase chain reaction. A dual-luciferase reporter assay characterized the interaction between miR-155 and sphingosine-1-phosphate receptor 1 (S1PR1). Changes in the target protein levels were determined using Western blot analysis.

Results:

MiR-155 was elevated in response to the H1N1 infection in HPMECs (24 h post-infection vs. 0 h post-infection, 3.875 ± 0.062 vs. 1.043 ± 0.013, P = 0.001). Over-expression of miR-155 enhanced inflammatory cytokine production (miR-155 mimic vs. negative control, all P < 0.05 in regard of cytokine levels) and activation of nuclear factor kappa B in infected HPMECs (miR-155 mimic vs. negative control, P = 0.004), and down-regulation of miR-155 had the opposite effect. In addition, S1PR1 was a direct target of miR-155 in the HPMECs. Inhibition of miR-155 enhanced the expression of the S1PR1 protein. Down-regulation of S1PR1 decreased the inhibitory effect of the miR-155 blockade on H1N1-induced cytokine production and nuclear factor kappa B activation in HPMECs.

Conclusion:

MiR-155 maybe modulate influenza A-induced inflammatory response by targeting S1PR1.

MicroRNA-4485 ameliorates severe influenza pneumonia via inhibition of the STAT3/PI3K/AKT signaling pathway

The present study aimed to explore the potential roles and mechanism of microRNA-4485 (miR-4485) in severe influenza pneumonia. miR-4485 expression was detected in patients with severe H1N1 pneumonia using quantitative PCR. Furthermore, the effects of aberrantly expressed miR-4485 on H1N1-infected A549 cells were investigated using Cell Counting Kit-8, terminal deoxynucleotidyl transferase dUTP nick end labeling, western blotting and (ELISA) assays. Furthermore, the regulatory relationships between miR-4485 and the STAT3-mediated PI3K/AKT/mTOR signaling pathway were explored using a luciferase reporter and rescue assay. MiR-4485 expression was downregulated following H1N1 infection and in patients with H1N1 pneumonia. In addition, miR-4485 alleviated H1N1-induced A549 cell injury by promoting cell viability and the production of cytokines, as well as reducing apoptosis in A549 cells. Furthermore, STAT3 was revealed to be a target gene of miR-4485. Additionally, STAT3 silencing reversed the protective effects of miR-4485 knockdown on H1N1-induced cell injury via inhibition of the PI3K/AKT/mTOR signaling pathway. In conclusion, miR-4485 inhibited H1N1-induced severe pneumonia in A549 cells by targeting STAT3 via the PI3K/AKT/mTOR signaling pathway.

Redox control in the pathophysiology of influenza virus infection

Triggered in response to external and internal ligands in cells and animals, redox homeostasis is transmitted via signal molecules involved in defense redox mechanisms through networks of cell proliferation, differentiation, intracellular detoxification, bacterial infection, and immune reactions. Cellular oxidation is not necessarily harmful per se, but its effects depend on the balance between the peroxidation and antioxidation cascades, which can vary according to the stimulus and serve to maintain oxygen homeostasis. The reactive oxygen species (ROS) that are generated during influenza virus (IV) infection have critical effects on both the virus and host cells. In this review, we outline the link between viral infection and redox control using IV infection as an example. We discuss the current state of knowledge on the molecular relationship between cellular oxidation mediated by ROS accumulation and the diversity of IV infection. We also summarize the potential anti-IV agents available currently that act by targeting redox biology/pathophysiology.

Autophagy is involved in the acute lung injury induced by H9N2 influenza virus

Influenza A virus usually leads to economic loss to breeding farms and pose a serious threat to human health. Virus infecting tissues directly and influenza virus-induced excessive production of inflammatory factors play the key role in pathogenesis of the disease, but the mechanism is not well clarified. Here, the role of autophagy was investigated in H9N2 influenza virus-triggered inflammation. The results showed that autophagy was induced by H9N2 virus in A549 cells and in mice. Inhibiting autophagy by an autophagy inhibitor (3-methyladenine, 3-MA) or knockdown of Atg5(autophagy-related gene) by Atg5 siRNA significantly suppressed H9N2 virus replication, H9N2 virus-triggered inflammatory cytokines and chemokines, including IL-1β, TNF-α, IL-8, and CCL5 in vitro and in vivo, and suppressed H9N2 virus-triggered acute lung injury as indicated as accumulative mortality of mice, inflammatory cellular infiltrate and interstitial edema, thickening of the alveolar walls in mice lung tissues, increased inflammatory cytokines and chemokines, increased W/D ratio in mice. Moreover, autophagy mediated inflammatory responses through Akt-mTOR, NF-κB and MAPKs signaling pathways. Our data showed that autophagy was essential in H9N2 influenza virus-triggered inflammatory responses, and autophagy could be target to treat influenza virus-caused lung inflammation.