Mechanical Ventilation Exacerbates Poly (I:C) Induced Acute Lung Injury: Central Role for Caspase-11 and Gut-Lung Axis

Abstract

Background: The mechanisms by which moderate tidal volume ventilation (MTV) may exacerbate preexisting lung injury remain unclear. We hypothesized that in two hit model (polyinosinic-polycytidylic acid (Poly(I:C)), a synthetic analog of dsRNA and MTV), systemic endotoxemia via gut-lung axis would lead to non-canonical (i.e. caspase-11 dependent) and canonical (caspase-1 dependent) inflammasome activation and programmed necrotic cell death (pyroptosis) contributing to acute lung injury (ALI) in intact mice.Methods: Anesthetized mice were administered Poly(I:C) intratracheally and then 6 h later, they were mechanically ventilated for 4 h with otherwise non-injurious MTV (10ml/kg). Changes in intestinal and alveolar capillary permeability were measured. Further documentation of ALI was assessed by evans blue albumin permeability, protein and IL-1 family concentration in bronchoalveolar lavage fluid (BALF) or plasma, and histopathology in cohorts of wildtype, whole body genetically ablated caspase-11 (caspase-11-/-), caspase-1/caspase-11 double knockout (caspase-1/11-/-), gasdermin D (GSDMD-/-), and NLRP3-/- mice. Results: Non-injurious MTV exacerbated mild Poly(I:C) lung injury including disruption of alveolar-capillary barrier and increased levels of IL-6, HMGB1, IL-1β in BALF and IL-18 in plasma. Combined (Poly(I:C)-MTV) injury was associated with increase in gastrointestinal permeability and endotoxin in plasma and BALF. Poly(I:C)-MTV injury was sensitive to caspase-11 deletion with no further contribution of caspase-1 except for maturation and release of IL-18 (that itself was sensitive to deletion of NLRP3). Combined injury led to large increases in pro-caspase-11 and its cleaved product as well as cleaved product of caspase-1. Genetic ablation of GSDMD attenuated alveolar-capillary disruption and maturation and release of cytokines in combined injury model.Conclusions: The previously noted TLR-4 independent exacerbation of mild Poly(I:C)-induced ALI by otherwise non-injurious MTV is associated with an increase in gut permeability resulting in systemic endotoxemia. The gut-lung axis resulted in activation of pulmonary non-canonical (cytosolic mediated caspase-11 activation) and canonical (caspase-1) inflammasome (NLRP3) mediated ALI in this two hit model resulting in GSDMD sensitive alveolar capillary barrier disruption, pyroptosis (in alveolar macrophages) and cytokine maturation and release (IL-1β; IL-18). Pharmacologic strategies at disrupting communication between gut and lung, inhibition of inflammasomes or effector molecule (GSDMD) in pyroptosis may be useful in ALI.