Effect of exogenous surfactant on phosphatidylinositol 3-kinase-Akt pathway and peroxisome proliferator activated receptor-γ during endotoxin induced acute respiratory distress syndrome

Up-regulation of miR-146b-3p protects septic mice with acute respiratory distress syndrome by inhibiting PI3K/AKT signaling pathway

This study aimed to explore the role of miR-146b-3p in acute respiratory distress syndrome in septic mice. Ten mice were randomly selected as normal group (n = 10, without any treatment) and 60 septic mice with acute respiratory distress syndrome were divided into model group (n = 10, without any treatment), negative control (NC) mimic group (n = 10, injected with NC mimic), miR-146b-3p mimic group (n = 10, injected with miR-146b-3p mimic), si-NC group (n = 10, injected with PI3Kγ siRNA NC), si-PI3Kγ group (n = 10, injected with PI3Kγ silencing plasmid), and miR-146b-3p mimic + oe-PI3Kγ group (n = 10, injected with miR-146b-3p mimic + PI3Kγ overexpression plasmid). We found that miR-146b-3p negatively regulated PI3Kγ. Compared with normal group, model mice had decreased expression of miR-146b-3p, increased expressions of PI3Kγ, p-AKT, ASC, NLRP3 and Caspase-1 proteins, higher W/D ratio, and more serum IL-1β and IL-18 content (all P < 0.05). All indicators in miR-146b-3p mimic group and si-PI3Kγ group were significantly improved as compared to model group (all P < 0.05). Over-expression of PI3Kγ could weaken the treatment effect of miR-146b-3p mimic in model mice. Therefore, up-regulation of miR-146b-3p can inhibit PI3K/AKT signaling pathway to improve acute respiratory distress syndrome in septic mice.

PPARγ signaling and emerging opportunities for improved therapeutics

Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated nuclear receptor that regulates glucose and lipid metabolism, endothelial function and inflammation. Rosiglitazone (RGZ) and other thiazolidinedione (TZD) synthetic ligands of PPARγ are insulin sensitizers that have been used for the treatment of type 2 diabetes. However, undesirable side effects including weight gain, fluid retention, bone loss, congestive heart failure, and a possible increased risk of myocardial infarction and bladder cancer, have limited the use of TZDs. Therefore, there is a need to better understand PPARγ signaling and to develop safer and more effective PPARγ-directed therapeutics. In addition to PPARγ itself, many PPARγ ligands including TZDs bind to and activate G protein-coupled receptor 40 (GPR40), also known as free fatty acid receptor 1. GPR40 signaling activates stress kinase pathways that ultimately regulate downstream PPARγ responses. Recent studies in human endothelial cells have demonstrated that RGZ activation of GPR40 is essential to the optimal propagation of PPARγ genomic signaling. RGZ/GPR40/p38 MAPK signaling induces and activates PPARγ co-activator-1α, and recruits E1A binding protein p300 to the promoters of target genes, markedly enhancing PPARγ-dependent transcription. Therefore in endothelium, GPR40 and PPARγ function as an integrated signaling pathway. However, GPR40 can also activate ERK1/2, a proinflammatory kinase that directly phosphorylates and inactivates PPARγ. Thus the role of GPR40 in PPARγ signaling may have important implications for drug development. Ligands that strongly activate PPARγ, but do not bind to or activate GPR40 may be safer than currently approved PPARγ agonists. Alternatively, biased GPR40 agonists might be sought that activate both p38 MAPK and PPARγ, but not ERK1/2, avoiding its harmful effects on PPARγ signaling, insulin resistance and inflammation. Such next generation drugs might be useful in treating not only type 2 diabetes, but also diverse chronic and acute forms of vascular inflammation such as atherosclerosis and septic shock.

Immunomodulatory properties of surfactant preparations

Surfactant replacement significantly decreased acute pulmonary morbidity and mortality among preterm neonates with respiratory distress syndrome. Besides improving lung function and oxygenation, surfactant is also a key modulator of pulmonary innate and acquired immunity regulating lung inflammatory processes. In this review, we describe the immunomodulatory features of surfactant preparations. Various surfactant preparations decrease the proinflammatory cytokine and chemokine release, the oxidative burst activity, and the nitric oxide production in lung inflammatory cells such as alveolar neutrophils, monocytes and macrophages; they also affect lymphocyte proliferative response and immunoglobulin production, as well as natural killer and lymphokine-activated killer cell activity. In addition, surfactant preparations are involved in airway remodeling, as they decrease lung fibroblast proliferation capacity and the release of mediators involved in remodeling. Moreover, they increase cell transepithelial resistance and VEGF synthesis in lung epithelial cells. A number of different signaling pathways and molecules are involved in these processes. Because the inhibition of local immune response may decrease lung injury, surfactant therapeutic efficacy may be related not only to its biophysical characteristics but, at least in part, to its anti-inflammatory features and its effects on remodeling processes. However, further studies are required to identify which surfactant preparation ensures the highest anti-inflammatory activity, thereby potentially decreasing the inflammatory process underlying respiratory distress syndrome. In perspective, detailed characterization of these anti-inflammatory effects could help to improve the next generation of surfactant preparations.

Influenza A induced cellular signal transduction pathways

Influenza A is a negative sense single stranded RNA virus that belongs to the Orthomyxoviridae Family. This enveloped virus contains 8 segments of viral RNA which encodes 11 viral proteins. Influenza A infects humans and is the causative agent of the flu. Annually it infects approximately 5% to 15% of the population world wide and results in an estimated 250,000 to 500,000 deaths a year. The nature of influenza A replication results in a high mutation rate which results in the need for seasonal vaccinations. In addition the zoonotic nature of the influenza virus allows for recombination of viral segments from different strains creating new variants that have not been encountered before. This type of mutation is the method by which pandemic strains of the flu arises. Infection with influenza results in a respiratory illness that for most individuals is self limiting. However in susceptible populations which include individuals with pre-existing pulmonary or cardiac conditions, the very young and the elderly fatal complications may arise. The most serious of these is the development of viral pneumonia which may be accompanied by secondary bacterial infections. Progression of pneumonia leads to the development of acute respiratory distress syndrome (ARDS), acute lung injury (ALI) and potentially respiratory failure. This progression is a combined effect of the host immune system response to influenza infection and the viral infection itself. This review will focus on molecular aspects of viral replication in alveolar cells and their response to infection. The response of select innate immune cells and their contribution to viral clearance and lung epithelial damage will also be discussed. Molecular aspects of antiviral response in the cells in particular the protein kinase RNA dependent response, and the oligoadenylate synthetase RNAse L system in relation to influenza infection.