Acute lung injury (ALI) is a respiratory disease that widely exists in the world and can develop into severe respiratory failure, also known as acute respiratory distress syndrome (ARDS) [1]. Despite advances in both basic and clinical medical research on ALI, the mortality rate of severe patients remains high [2]. ALI progression is characterized by excessive inflammatory response, damage to alveolar structure and impairment of pulmonary function [3,4]. During the development ALI, macrophages could develop into two types: proinflammatory M1-type macrophages, or anti-inflammatory M2-type macrophages [5]. The severe inflammatory response is triggered by M1 macrophage polarization, which promotes the release of proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β) [6,7]. During the injury recovery process, M2 polarization of macrophages are typically induced by cytokines, such as interleukin-4 (IL-4), and interleukin-10 (IL-10) [8]. Consequently, it is urgent to strengthen the understanding of the pathogenesis of ALI and investigate novel therapeutic approaches.

ANAPC5 (Anaphase-promoting complex subunit 5), also named APC5, is an E3 ubiquitin ligase [9]. A previous report clarified that ANAPC5 regulates the ubiquitin of E2F transcription factor (E2F1), and knockdown of ANAPC5 enhances interleukin-17 (IL-17) signaling and upregulates IL-6 expression in mouse bone marrow cells, suggesting ANAPC5 exhibited anti-inflammatory effect [10]. In multiple datasets related to ALI and M1 macrophage, the expression of ANAPC5 was significantly downregulated in lipopolysaccharide (LPS)-treated mouse lung tissues [11,12] and the mouse macrophage RAW264.7 cells [13]. The expression of ANAPC5 in M1 macrophages was lower than that in M2 macrophages [14]. However, little is known about the function and mechanism of ANAPC5 in ALI.

Epidermal growth factor receptor (EGFR) is a transmembrane protein that is frequently dysregulated in various diseases [15]. EGFR inhibitor alleviates mechanical ventilation-induced alveolar and pulmonary vascular leakage and reduces neutrophil accumulation in bronchoalveolar lavage fluid (BALF) in mice [16]. The phosphorylation of EGFR has been reported to promote the M1 polarization in macrophages. The inhibition of EGFR expression or phosphorylation obstructs the inflammatory response and M1 polarization induced by LPS in RAW264.7 cells [17]. Depletion of EGFR suppresses M1 polarization of macrophage [18]. Besides, a previous study has confirmed the binding of ubiquitin ligases to EGFR leads to the degradation of EGFR [15]. Cluster of differentiation 24 (CD24) serves as an immune checkpoint negatively controlling the process of inflammatory response [19]. There is a literature reporting that absence of EGFR induces the upregulation of CD24 expression in a lung cancer cell, and CD24 is potential a therapeutical target of EGFR [20]. Therefore, this study aims to investigate whether ANAPC5 regulates macrophage polarization by regulating EGFR/CD24 axis to affect the development of ALI.

In this report, the function and mechanism of ANAPC5 in ALI was investigated through the in vitro and in vivo experiments. The intratracheal instillation of LPS has been regarded as a widely approach to establish the ALI mouse model. The examination of biochemical indicators and pathological analysis were used to explore the role of ANAPC5 in ALI. Additionally, M1 polarization of macrophages was also induced by LPS in RAW264.7 cells. After the gain-of-function experiments, we explored whether ANAPC5 regulated M1/M2 macrophage phenotypes through the EGFR/CD24 axis in RAW264.7 cells. Our results provided evidence that ANAPC5 as a therapeutic target alleviates ALI through regulating the EGFR/CD24 axis.