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Acute respiratory distress syndrome (ARDS) is characterized by acute lung injury (ALI) secondary to an excessive alveolar inflammatory response. Reticulocalbin 3 (Rcn3) is an endoplasmic reticulum (ER) lumen protein in the secretory pathway. We previously reported the indispensable role of Rcn3 in type II alveolar epithelial cells (AECIIs) during lung development and the lung injury repair process. In the present study, we further observed a marked induction of Rcn3 in the alveolar epithelium during LPS-induced ALI. In vitro alveolar epithelial (MLE-12) cells consistently exhibited a significant induction of Rcn3 accompanied with NF-κB activation in response to LPS exposure. We examined the role of Rcn3 in the alveolar inflammatory response by using mice with a selective deletion of Rcn3 in alveolar epithelial cells upon doxycycline administration. The Rcn3 deficiency significantly blunted the ALI and alveolar inflammation induced by intratracheal LPS instillation but not that induced by an intraperitoneal LPS injection (secondary insult); the alleviated ALI was accompanied by decreases in NF-κB activation and NLRP3 levels but not in GRP78 and cleaved caspase-3 levels. The studies conducted in MLE-12 cells consistently showed that Rcn3 knockdown blunted the activations of NF-κB signaling and NLRP3-dependent inflammasome upon LPS exposure. Collectively, these findings suggest a novel role for Rcn3 in regulating the alveolar inflammatory response to pulmonary infection via the NF-κB/NLRP3/inflammasome axis and shed additional light on the mechanism of ARDS/ALI.

Objectives: Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is one type of respiratory failure characterized by rapid onset of widespread inflammation in the lungs. Curcumin has been reported to be an anti-inflammatory factor through enhancing the function of regulatory T cells (Tregs). This study aimed to explore the effect of curcumin on the differentiation of Tregs and the role of curcumin in ALI/ARDS., Methods: A cecal ligation and puncture (CLP)-induced acute lung injury mouse model was used to explore the effect of curcumin in ALI/ARDS. The severity of lung injury was evaluated. Immunohistochemistry of IL-17A and MPO in lung tissue was examined. Treg-related cytokine levels in serum and bronchoalveolar lavage fluid (BALF) were tested. The expression of nuclear factor-kappa B (NF-κB) in lung tissue was detected. Macrophages in lung tissue were detected by immunofluorescence. Splenic CD4+CD25+FOXP3+ Tregs were quantified, and the differentiation of Tregs from naïve CD4 + T cell and STAT5 was evaluated. The expression of IL-10 during naïve CD4 + T cell differentiation in vitro was tested., Results: Curcumin alleviated lung injury in the induced CLP mouse model and suppressed inflammation. IL-17A, MPO-producing neutrophils, and NF-κB p65 expression in lungs of CLP mice decreased significantly after pretreatment with curcumin. We found curcumin could regulate M1/M2 macrophage levels in lungs of CLP mice. This may have been through regulating the differentiation of Tregs and the production of Treg-derived IL-10. Treg-derived IL-10 is the main factor that could affect macrophage polarization. We found curcumin could increase Treg proportions in vivo and up-regulate IL-10 expression in serum and BALF of CLP mice. In our in vitro experiments, we found curcumin could promote Treg differentiation and increase the production of IL-10., Conclusions: Curcumin can reduce the degree of severity of ALI and uncontrolled inflammation through promoting the differentiation of naïve CD4 + T cells to CD4+ CD25+ FOXP3+ Tregs. Curcumin promotes the conversion of macrophages from M1 to M2. The differentiation of Tregs induced by curcumin may be one source of IL-10 immune modulation., Competing Interests: Declaration of Competing Interest None., (Copyright © 2020 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

Abstract: Isoforskolin was isolated from Coleus forskohlii native to Yunnan in China. We hypothesize that isoforskolin pretreatment attenuates acute lung injury induced by lipopolysaccharide (endotoxin). Three acute lung injury models were used: situ perfused rat lung, rat and mouse models of endotoxic shock. Additionally, lipopolysaccharide stimulated proinflammatory cytokine production was evaluated in human mononuclear leukocyte. In situ perfused rat lungs, pre-perfusion with isoforskolin (100, and 200μM) and dexamethasone (65μM, positive control) inhibited lipopolysaccharide (10 mg/L) induced increases in lung neutrophil adhesion rate, myeloperoxidase activity, lung weight Wet/Dry ratio, permeability-surface area product value, and tumor necrosis factor (TNF)-α levels. In rats, pretreatments with isoforskolin (5, 10, and 20 mg/kg, i.p.) and dexamethasone (5mg/kg, i.p.) markedly reduced lipopolysaccharide (6mg/kg i.v.) induced increases of karyocyte, neutrophil counts and protein content in bronchoalveolar lavage fluid, and plasma myeloperoxidase activity. Lung histopathology showed that morphologic changes induced by lipopolysaccharide were less pronounced in the isoforskolin and dexamethasone pretreated rats. In mice, 5 mg/kg isoforskolin and dexamethasone caused 100% and 80% survival, respectively, after administration of lipopolysaccharide (62.5mg/kg, i.v., 40% survival if untreated). In human mononuclear leukocyte, isoforskolin (50, 100, and 200μM) and dexamethasone (10μM) pre-incubation lowered lipopolysaccharide (2μg/mL) induced secretion of the cytokine TNF-α, and interleukins (IL)-1β, IL-6, and IL-8. In conclusion, pretreatment with isoforskolin attenuates lipopolysaccharide-induced acute lung injury in several models, and it is involved in down-regulation of inflammatory responses and proinflammatory cytokines TNF-α, IL-1β, IL-6, and IL-8. [Copyright &y& Elsevier]