ATP6V0C-HIF-1α reciprocal activation drives acute lung injury.

The vacuolar H+-ATPase (V-ATPase) is an enzymatic complex responsible for pumping H+ into the cytosol, thereby maintaining intracellular pH; however, its role in acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is unclear. In this study, the functional relevance of V-ATPase and hypoxia inducible factor (HIF) 1 were assessed using alveolar-specific ATP6V0C knockout mice (Atp6v0cAT2-KO) and HIF1A knockout mice (Hif1aAT2-KO), respectively. ATP6V0C expression levels were measured in serum and bronchoalveolar lavage fluid (BALF) of patients with ARDS. ATP6V0C expression was increased in lung tissues from ALI murine models and BALF from patients with severe ARDS. Genetic deficiency of ATP6V0C in alveoli attenuated the functional, histologic, and inflammatory hallmarks of lipopolysaccharide (LPS)-induced ALI but did not alter the host's susceptibility to bacterial pathogens. Mechanistically, transcriptomic analyses revealed that ATP6V0C-regulated genes are highly enriched in the HIF-1 signaling pathway. HIF-1α was upregulated synchronously with ATP6V0C in injured lungs, while co-immunoprecipitation confirmed their interaction. Following LPS instillation, the signs of ALI were further exacerbated in Hif1afl/fl mice pretreated with lung epithelial tropic adeno-associated virus carrying ATP6V0C, but not in Hif1aAT2-KO mice. HIF-1α, as a transcriptional factor, in turn, regulated ATP6V0C expression, forming a positive feedback loop. ATP6V0C levels were increased in BALF but not serum in patients with ARDS. ATP6V0C levels in BALF correlate with ARDS severity. In summary, our study identified an ATP6V0C-HIF-1α detrimental feedback loop that exacerbates epithelial apoptosis and inflammation, thereby driving the progression of ALI. Targeting the ATP6V0C-HIF-1α loop may hence present a promising therapeutic strategy against ALI/ARDS.