Akt2 deficiency as a therapeutic strategy protects against acute lung injury

PEP-sNASP Peptide Alleviates LPS-Induced Acute Lung Injury Through the TLR4/TRAF6 Axis

Acute lung injury (ALI) is a severe inflammatory lung disease associated with macrophages. Somatic nuclear autoantigenic sperm protein (sNASP) is a negative regulator of Toll-like receptor (TLR) signaling that targets tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6) in macrophages, which is required to maintain homeostasis of the innate immune response. In the present study, we generated a cell permeable PEP-sNASP peptide using the sNASP protein N-terminal domain, and examined its potential therapeutic effect in a mouse model of ALI induced by the intranasal administration of lipopolysaccharide (LPS) and elucidated the underlying molecular mechanisms in RAW 264.7 cells. In vivo, PEP-sNASP peptide treatment markedly ameliorated pathological injury, reduced the wet/dry (W/D) weight ratio of the lungs and the production of proinflammatory cytokines (interleukin (IL)-1β, IL-6, and TNF-α). In vitro, we demonstrated that when the PEP-sNASP peptide was transduced into RAW 264.7 cells, it bound to TRAF6, which markedly decreased LPS-induced proinflammatory cytokines by inhibiting TRAF6 autoubiquitination, nuclear factor (NF)-κB activation, reactive oxygen species (ROS) and cellular nitric oxide (NO) levels. Furthermore, the PEP-sNASP peptide also inhibited NLR family pyrin domain containing 3 (NLRP3) inflammasome activation. Our results therefore suggest that the PEP-sNASP may provide a potential protein therapy against oxidative stress and pulmonary inflammation via selective TRAF6 signaling.

miR‑625‑5p suppresses inflammatory responses by targeting AKT2 in human bronchial epithelial cells

Asthma is a common chronic inflammatory airway disease; however, whether microRNAs (miRs) could be used in the treatment of asthma remains unclear. The aim of the present study was to investigate the role of miR‑625‑5p in the inflammatory response of human bronchial epithelial cells (HBECs). Inflammation in the HBEC line, 16HBEC, was induced using different concentrations of lipopolysaccharide (LPS), which demonstrated that 1 µg/ml LPS was an appropriate concentration for further experiments. The association between protein kinase B2 (AKT2) and miR‑625‑5p was verified using a luciferase reporter assay. LPS was added to 16HBECs following the administration of miR‑625‑5p mimics or miR‑625‑5p inhibitors, and cells with silenced or overexpressed AKT2 levels. miR‑625‑5p was expressed at a high level in LPS‑activated 16HBECs. Overexpression of miR‑625‑5p inhibited interleukin (IL)‑6 and tumor necrosis factor (TNF)‑α secretion in 16HBECs. Inhibition of miR‑625‑5p enhanced LPS‑induced IL‑6 and TNF‑α secretion. miR‑625‑5p negatively regulated the expression of AKT2 in 16HBECs. A dual‑luciferase reporter assay system confirmed that miR‑625‑5p directly targeted the 3'untranslated region of AKT2. Transfection with a small interfering RNA against AKT2 inhibited inhibitor of κB phosphorylation. In brief, miR‑625‑5p may protect LPS‑induced HBECs by targeting AKT2 and inhibiting the nuclear factor‑κB signaling pathway. Therefore, miR‑625‑5p may function as an inhibitor of asthma airway inflammation in HBECs by targeting AKT2.

Isoalantolactone suppresses LPS-induced inflammation by inhibiting TRAF6 ubiquitination and alleviates acute lung injury

Isoalantolactone (IAL) is a sesquiterpene lactone extracted from roots of Inula helenium L and has shown anti-inflammatory effects. In this study we investigated the therapeutic effects of IAL on acute lung injury (ALI) and elucidated the mechanisms underlying its anti-inflammation potential in vitro and in vivo. Treatment with lipopolysaccharide (LPS, 100 ng/mL) drastically stimulated production of inflammatory mediators such as NO, TNF-α, IL-1β, and IL-6 in mouse bone marrow-derived macrophages (BMDMs), which was dose-dependently suppressed by pretreatment with IAL (2.5, 5, 10, 20 μM). We further revealed that IAL suppressed LPS-induced NF-κB, ERK, and Akt activation. Moreover, the downregulation of non-degradable K63-linked polyubiquitination of TRAF6, an upstream transcription factor of NF-κB, contributed to the anti-inflammatory effects of IAL. ALI was induced in mice by intratracheal injection of LPS (5 mg/kg). Administration of IAL (20 mg/kg, i.p.) significantly suppressed pulmonary pathological changes, neutrophil infiltration, pulmonary permeability, and pro-inflammatory cytokine expression. Our results demonstrate that IAL is a potential therapeutic reagent against inflammation and ALI.

Functional Evidence of Pulmonary Extracellular Vesicles in Infectious and Noninfectious Lung Inflammation

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a highly complex process that can be triggered by both noninfectious (sterile) and infectious stimuli. Inflammatory lung responses are one of the key features in the pathogenesis of this devastating syndrome. How ALI/ARDS-associated inflammation develops remains incompletely understood, particularly after exposure to sterile stimuli. Emerging evidence suggests that extracellular vesicles (EVs) regulate intercellular communication and inflammatory responses in various diseases. In this study, we characterized the generation and function of pulmonary EVs in the setting of ALI/ARDS, induced by sterile stimuli (oxidative stress or acid aspiration) and infection (LPS/Gram-negative bacteria) in mice. EVs detected in bronchoalveolar lavage fluid (BALF) were markedly increased after exposure of animals to both types of stimuli. After sterile stimuli, alveolar type-І epithelial cells were the main source of the BALF EVs. In contrast, infectious stimuli-induced BALF EVs were mainly derived from alveolar macrophages (AMs). Functionally, BALF EVs generated in both the noninfectious and infectious ALI models promoted the recruitment of macrophages in in vivo mouse models. Furthermore, BALF EVs differentially regulated AM production of cytokines and inflammatory mediators, as well as TLR expression in AMs in vivo. Regardless of their origin, BALF EVs contributed significantly to the development of lung inflammation in both the sterile and infectious ALI. Collectively, our results provide novel insights into the mechanisms by which EVs regulate the development of lung inflammation in response to diverse stimuli, potentially providing novel therapeutic and diagnostic targets for ALI/ARDS.

Lung Epithelial Cell-Derived Microvesicles Regulate Macrophage Migration via MicroRNA-17/221-Induced Integrin β1 Recycling

Robust lung inflammation is one of the prominent features in the pathogenesis of acute lung injury (ALI). Macrophage migration and recruitment are often seen at the early stage of lung inflammatory responses to noxious stimuli. Using an acid inhalation-induced lung injury model, we explored the mechanisms by which acid exposure initiates macrophage recruitment and migration during development of ALI. The lung epithelium comprises a large surface area and functions as a first-line defense against noxious insults. We found that acid exposure induced a remarkable microvesicle (MV) release from lung epithelium as detected in bronchoalveolar lavage fluid. Significantly elevated RNA, rather than protein, was found in these epithelium-derived MVs after acid and included several highly elevated microRNAs, including microRNA (miR)-17 and miR-221. Acid-induced epithelial MV release promoted macrophage migration in vitro and recruitment into the lung in vivo and required, in part, MV shuttling of miR-17 and/or miR-221. Mechanistically, acid-induced epithelial MV miR-17/221 promoted β₁ integrin recycling and presentation back onto the surface of macrophages, in part via a Rab11-mediated pathway. Integrin β₁ is known to play an essential role in regulating macrophage migration. Taken together, acid-induced ALI results in epithelial MV shuttling of miR-17/221 that in turn modulates macrophage β₁ integrin recycling, promoting macrophage recruitment and ultimately contributing to lung inflammation.