Targeting Card9 as a Therapeutic Strategy in Acute Lung Injury

Background Acute lung injury (ALI) is a severe inflammatory condition with high mortality and limited treatment options. The balance between proinflammatory M1 and anti‐inflammatory M2 macrophage phenotypes is considered a critical determinant of disease progression and resolution in ALI. Caspase recruitment domain protein 9 (Card9), a key adapter protein in innate immunity, represents a potential therapeutic target for modulating the dysregulated immune response characteristic of ALI. Objective This study aimed to evaluate whether the therapeutic modulation of Card9 can attenuate the severity of LPS‐induced ALI by influencing macrophage polarization and key inflammatory signaling pathways, thereby informing potential clinical intervention strategies. Methods An LPS‐induced ALI model was established in Sprague–Dawley rats. Interventions included sodium aescinate (SA) and siRNA‐mediated Card9 knockdown. Lung injury was assessed histopathologically. Serum levels of cytokines (TNF‐ α , IL‐1 β , IL‐6, TGF‐ β , Arg1, and VEGFA) and myeloperoxidase (MPO) activity were measured by ELISA. Expression levels of Card9, PI3K, p65 NF‐ κ B, and JAK2 were analyzed. Macrophage subsets (CD86 + M1 and CD206 + M2) were quantified by flow cytometry. Results LPS challenge induced severe lung injury, elevated both pro‐ and anti‐inflammatory cytokines, and upregulated Card9 expression. Key inflammatory pathways (NF‐ κ B, JAK, and PI3K) were activated, accompanied by an increase in both M1 and M2 macrophage populations. Both SA and siRNA‐Card9 treatments effectively attenuated lung inflammation, reduced cytokine release, suppressed the activation of Card9 and its downstream pathways, and decreased the polarization of both M1 and M2 macrophages. Conclusion Card9 promotes inflammatory responses and modulates macrophage polarization in ALI. Therapeutic inhibition of Card9 significantly mitigates lung injury and favorably influences macrophage phenotype distribution, underscoring its potential as a viable clinical target for the treatment of ALI.