Rab43 mitigates the inflammatory response in acute lung injury via MyD88 ubiquitination.

The development of acute lung injury (ALI) can induce an immune imbalance, and inflammatory response syndrome can induce clinical acute respiratory distress syndrome (ARDS), which has a high mortality rate of 35–40% in intensive care units. At present, there is a lack of specific therapeutic measures, so it’s urgent to explore new effective therapeutic methods and drug targets. Our group previously found that Rab43 can inhibit immune response disorders and promote inflammation resolution by regulating phagocytosis of macrophages. In particular, Rab43 shows promising potential in preventing and treating ALI/ARDS. However, its precise role and signaling mechanisms in the pathologic success of ALI development have not been elucidated. Myeloid-specific Rab43 knockout (Rab43-KO) mice were generated and used to construct a mouse model of acute lung injury after airway administration by LPS. HE staining was used for observing pathological changes in the lungs of ALI mice. The levels of systemic and local inflammation in mice were analyzed by flow cytometry. Activation of the TLR4-MyD88 signaling pathway was analyzed by Western blot and flow cytometry. MyD88 ubiquitination was determined by co-immunoprecipitation (co-IP), and expression of ubiquitinase-related genes was measured by quantitative real-time PCR (qPCR). Herein, descending Rab43 has been found in alveolar macrophages (AMs) and bone marrow-derived macrophages (BMDMs) upon LPS stimulation. Furthermore, Rab43 deficiency exacerbated LPS-induced ALI, and plasma levels of proinflammatory cytokines (TNF-α, IL-6, IL-1β) were 1.7-, 2.3-, and 1.5-fold higher in Rab43-KO mice, whose mortality at 72 h post-lethal LPS increased by 40%. Mechanistically, Rab43 deficiency elevated MyD88 protein levels by 80% without affecting MyD88 mRNA, leading to overactivation of the MAPK-NF-κB pathway. Co-IP assays confirmed Rab43 regulated the interaction of MyD88 with ubiquitin protein, a 58% reduction of MyD88-ubiquitin level in Rab43-KO BMDMs, accompanied by downregulated 40–55% expression of ubiquitinase genes A20, SPOP, HOIL-1, and OTUD4. Taken together, these results demonstrate that Rab43 alleviated the inflammation response by controlling MyD88 ubiquitination and degradation. Rab43 acts as a novel negative regulator of LPS-induced inflammation in ALI mice and macrophages by promoting MyD88 ubiquitination and degradation. This study identifies Rab43 as a potential therapeutic target for ALI/ARDS, filling the gap in our understanding of Rab GTPase-mediated regulation of MyD88-dependent inflammatory signaling.