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 (MLE12) cells consistently exhibited a significant induction of Rcn3 accompanied with NFκB 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 with decreases in NFκB activation and NLRP3 levels but not in GRP78 and cleaved caspase-3 levels. The studies conducted in MLE12 cells consistently showed that Rcn3 knockdown blunted the activations of NFκB 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 NFκB/NLRP3/inflammasome axis and shed additional light on the mechanism of ARDS/ALI.

中文翻译：

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肺泡上皮中的网状局部蛋白3缺乏通过NFκB信号减弱LPS诱导的ALI

急性呼吸窘迫综合征（ARDS）的特征是继发于肺泡炎性反应过度的急性肺损伤（ALI）。Reticulocalbin 3（Rcn3）是分泌途径中的内质网（ER）管腔蛋白。我们先前曾报道Rcn3在肺发育和肺损伤修复过程中在II型肺泡上皮细胞（AECIIs）中不可或缺的作用。在本研究中，我们进一步观察到LPS诱导ALI期间肺泡上皮中Rcn3的明显诱导。体外肺泡上皮细胞（MLE12）始终表现出对Rcn3的显着诱导，并伴随LPS暴露而激活NFκB。我们通过使用强力霉素给药后在肺泡上皮细胞中选择性删除Rcn3的小鼠，检查了Rcn3在肺泡炎症反应中的作用。Rcn3缺乏明显减轻了由气管内LPS滴注引起的ALI和肺泡炎症，但没有使由腹膜内LPS注射引起的ALI和肺泡发炎（继发性损伤）；减轻的ALI伴随着NFκB激活和NLRP3水平的降低，但没有GRP78和裂解的caspase-3水平的降低。在MLE12细胞中进行的研究一致表明，LPS暴露后，Rcn3敲低减弱了NFκB信号和依赖NLRP3的炎性小体的激活。这些发现共同表明，Rcn3在通过NFκB/ NLRP3 /炎性体轴调节肺泡对肺部感染的炎症反应中具有新作用，并进一步阐明了ARDS / ALI的机制。