Pulmonary Epithelial TLR4 Activation Leads to Lung Injury in Neonatal Necrotizing Enterocolitis

Abstract

We seek to define the mechanisms leading to the development of lung disease in the setting of neonatal necrotizing enterocolitis (NEC), a life-threatening gastrointestinal disease of premature infants characterized by the sudden onset of intestinal necrosis. NEC development in mice requires activation of the lipopolysaccharide receptor toll-like receptor-4 (TLR4) on the intestinal epithelium, through its effects on modulating epithelial injury and repair. Although NEC-associated lung injury is more severe than the lung injury that occurs in premature infants without NEC, the mechanisms leading to its development remain unknown. We now show that the TLR4 expression in the lung gradually increases during postnatal development, and that mice and humans with NEC-associated lung inflammation express higher levels of pulmonary TLR4 than age-matched controls. NEC in wild-type newborn mice resulted in significant pulmonary injury that was prevented by deletion of TLR4 from the pulmonary epithelium, indicating a role for pulmonary TLR4 in lung injury development. Mechanistically, intestinal epithelial TLR4 activation induced high mobility group box-1 (HMGB1) release from the intestine which activated pulmonary epithelial TLR4, leading to the induction of the neutrophil recruiting C-X-C motif chemokine-5 (CXCL5) and the influx of pro-inflammatory neutrophils to the lung. Strikingly, the aerosolized administration of a novel carbohydrate TLR4 inhibitor prevented CXCL5 upregulation and blocked NEC-induced lung injury in mice. These findings illustrate the critical role of pulmonary TLR4 in the development of NEC-associated lung injury, and suggest that inhibition of this innate immune receptor in the neonatal lung may prevent this devastating complication of NEC.

A Novel Role for Necroptosis in the Pathogenesis of Necrotizing Enterocolitis

“…Although intestinal damage is the most significant contributor to illness in patients with NEC, these children also experience damage to peripheral organs, including the lungs and brain. 30,65,66 Remote organ injury in neonates with NEC occurs in part through the release of TLR4 ligands from the damaged gut, including high mobility group box 1 (HMGB1), which is released from dying intestine into the circulation, where it causes injury to both the lung and brain, through pathways that are incompletely understood. 30,67 It is noteworthy that HMGB1 also has been shown to form a complex with bacterial lipids during inflammation, which can trigger RIPK3-dependent immune responses, 68 suggesting the possibility that HMGB1 release also may induce necroptosis in these other organs.…”

Treg-Cell Control of a CXCL5-IL-17 Inflammatory Axis Promotes Hair-Follicle-Stem-Cell Differentiation During Skin-Barrier Repair

“…To determine if regulation of CXCL5 expression is a major mechanism by which Treg cells facilitate epidermal regeneration, we neutralized CXCL5 function in Treg-cell-depleted mice using an anti-CXCL5 monoclonal antibody (a-CXCL5 mAb) (Jia et al, 2016;Rousselle et al, 2013). Treg-cell-depleted mice were administered either an a-CXCL5 mAb or isotype control antibody during the recovery phase after epidermal injury.…”

Cognitive impairments induced by necrotizing enterocolitis can be prevented by inhibiting microglial activation in mouse brain

“…To further understand the pathways leading to NEC-induced microglial activation and impaired myelination, we next focused on the intestinal-derived TLR4 ligand HMGB1 (32,34), which is released from the injured intestine during mouse and human NEC (35). NEC was induced in wild-type mice and in mice lacking HMGB1 within the intestinal epithelium (HMGB1 IEC ), which we have previously generated and which displayed significantly lower amounts of HMGB1 in the circulation compared to wild-type controls when exposed to the experimental NEC (35). After NEC induction, HMGB1 IEC mice showed significantly (P < 0.0001) reduced microglial activation ( Fig.…”