CDDO-imidazolide ameliorates sepsis-induced ARDS by enhancing mitophagy via the Nrf2 pathway to prohibit alveolar macrophage pyroptosis and HMGB1 release

Abstract

Accumulating evidence suggests that NLRP3-mediated alveolar macrophage (AM) pyroptosis and subsequent high mobility group box protein 1 (HMGB1) secretion play significant roles in the pathogenesis of acute respiratory distress syndrome (ARDS). Nrf2 has been shown to be individually involved in regulating pyroptosis. In this study, we investigate the ability of CDDO-imidazolide, a potent Nrf2 activator, to regulate AM pyroptosis and HMGB1 secretion in sepsis-associated ARDS, along with its underlying mechanism. The in vitro alveolar macrophage (AM) pyroptosis model, established by stimulating J774A.1 cells with LPS and ATP, was treated with CDDO-imidazolide or utilized Nrf2-knockout cells. The mice are intraperitoneally administered with CDDO-imidazolide before the in vivo sepsis-associated ARDS model is constructed via caecal ligation perforation and the Nrf2 inhibitor, ML385. In vitro studies reveal that the use of 3-MA to prohibit PINK1/Parkin-dependent mitophagy aggravates NLRP3-mediated pyroptosis and HMGB1 release in J774A.1 cells via LPS and ATP exposure. CDDO-imidazolide also significantly prevents NLRP3-mediated pyroptosis and HMGB1 release to increase PINK1/Parkin-dependent mitophagy, but these effects are not detected in Nrf2-knockout macrophages. Most importantly, CDDO-imidazolide significantly alleviates NLRP3 inflammasome protein expression in the lung tissues of septic mice and HMGB1 protein levels in the serum and bronchoalveolar lavage fluid (BALF), which can be reversed by ML385. Taken together, our results demonstrate that CDDO-imidazolide prominently protects the lungs by promoting Nrf2 activation and enhancing PINK1/Parkin mitophagy to inhibit AM pyroptosis and HMGB1 release. These findings provide novel insights for therapeutic strategies for sepsis-associated ARDS.

1. Introduction

Sepsis is a complex, multistep pathological process characterized by an excessive inflammatory response of host cells to both Gram-positive and Gram-negative bacteria [1]. The lungs are among the most vulnerable organs during sepsis, with over half of septic patients developing acute respiratory distress syndrome (ARDS) [2]. Accumulating evidence indicates that sepsis can induce programmed cell death in alveolar macrophages (AMs), particularly pyroptosis, which contributes to the progression of ARDS [3]. Therefore, inhibiting or reducing AM pyroptosis may serve as a potential therapeutic strategy to alleviate sepsis-induced ARDS.

Our previous series of investigations revealed that AM pyroptosis and its inflammatory mediator, high mobility group box 1 (HMGB1), induced by cardiopulmonary bypass and sepsis led to the translocation of HMGB1 from the nucleus to the cytoplasm and ultimately to the extracellular fluid, thereby initiating and amplifying the inflammatory response and causing pulmonary damage [4,5]. Thus, suppressing AM pyroptosis and HMGB1 secretion could serve as a therapeutic approach to mitigate ARDS in sepsis.

Recently, with respect to the pathogenesis of sepsis, the activation of the Nod-Like Receptor Family Pyrin Domain Containing 3 (NLRP3) inflammasome to induce pyroptosis in AMs has been identified as a causative factor [6]. Briefly, NLRP3 recruits the effector proinflammatory cysteinyl aspartate-specific proteinase-1 (caspase-1) via its adaptor, apoptosis-associated speck-like protein containing a CARD (ASC) complex, followed by the activation of caspase-1 [7]. The Gasdermin D (GSDMD) is cleaved by activated caspase-1 into the N-terminal domain of GSDMD (GSDMD-N), which ultimately leads to cell pyroptosis and the secretion of inflammatory cytokines, including IL-1β [8]. Several recent studies have demonstrated that NLRP3 inflammasome activation leads to the release of proinflammatory cytokines such as IL-1β and HMGB1, which play crucial roles in the pathogenesis of ARDS by promoting inflammation and lung tissue damage. Previous studies showed that in a murine model of ARDS, genetic deletion or pharmacological inhibition of NLRP3 significantly attenuated lung injury and improved survival rates, highlighting the importance of NLRP3 as a potential therapeutic target [9,10]. Other studies reported that NLRP3 activation was associated with increased M1 macrophage polarization and pyroptosis and alveolar-capillary barrier disruption in patients with ARDS, further supporting its role in the disease process [11–13].