Cyclophilin A as a Novel Mediator in Ventilator‐Induced Lung Injury

Abstract

RationaleCyclophilin A (CypA) is a ubiquitously distributed cytoplasmic protein. While focus has previously been on its intracellular roles, extracellular CypA and its receptor CD147 have emerged as a novel signalling axis in various inflammatory diseases. We explore the role of the CypA:CD147 axis in ventilator‐induced lung injury (VILI) and hypothesise that CypA is secreted into the alveolar space following epithelial insult where it promotes inflammation during acute lung injury (ALI).MethodsC57BL/6 mice received low‐stretch (LS; tidal volume: 8 mL/kg) or high‐stretch (HS: 40 mL/kg) ventilation for up to three hours (n=6–8/group). For inhibition experiments, mice received a 50 μL intratracheal dose of either a non‐permeable extracellular‐specific CypA inhibitor, MM‐284 (0.67 mM), or vehicle control, DMSO (10%), immediately prior to HS ventilation. Bronchoalveolar lavage fluid (BALF) CypA and soluble receptor for advanced glycation endproducts (sRAGE) were assessed by ELISA; cell activation status (surface ICAM‐1 expression) and intracellular CypA (iCypA) by flow cytometry; and matrix metalloproteinase‐2 (MMP‐2) by gelatin zymography.ResultsDuring VILI, there is a significant early upregulation of BALF CypA at two hours (LS: 663±268 vs HS: 2,586±1,054 pg/mL; p<0.05), preceding signs of physiological deterioration, with further increase at three hours. In contrast, plasma CypA levels showed no significant changes across three hours regardless of ventilation strategy and were consistently below BALF levels. iCypA decreased in EpCAM‐/T1α+ and EpCAM+/T1α‐epithelial cells but not alveolar macrophages. MM‐284 mediated inhibition of extracellular CypA led to protection from the development of VILI (vehicle: 50% vs MM‐284: 100% survival; p<0.05), attenuated lung wet:dry weight ratio (7.0±1.2 vs 5.0±0.2; p<0.001), BALF protein (3.7±1.4 vs 1.3±0.2 mg/mL; p<0.001), BALF sRAGE (40.3±11.2 vs 8.3±3.8 ng/mL; p<0.0001), and deteriorations in elastance and oxygenation (interaction p<0.01). Surprisingly, CypA inhibition appeared to have no impact on leukocyte recruitment into lung tissue but was associated with a reduction in stretch‐induced activation of alveolar macrophages (135.6±18.4 vs 21.8±45.4 ICAM‐1 MFI; p<0.001) and both EpCAM‐/T1α+ (129.1±28.7 vs 91.9±6.1 ICAM‐1 MFI; p<0.05) and EpCAM+/T1α‐(99.8±12.1 vs 76.5±15.2 ICAM‐1 MFI; p<0.05) epithelial cells. Further, CypA inhibition also led to a decrease in active MMP‐2 in BALF (0.9±0.5 vs 0.4±0.2 relative band intensity; p<0.05).ConclusionsWe have demonstrated the involvement of a novel mediator, CypA, in VILI. The early upregulation in BALF and corresponding decrease of iCypA in epithelial cells suggest that CypA is produced locally following epithelial injury. Inhibition of extracellular CypA promoted an impressive attenuation of VILI, particularly parameters related to alveolar‐capillary barrier integrity (e.g. BALF sRAGE, oedema formation, oxygenation, and MMP activity). Together, our findings support the CypA:CD147 axis as a novel mediator of epithelial cell dysfunction during the pathogenesis of VILI.Support or Funding InformationBritish Journal of Anaesthesia/Royal College of Anaesthetists