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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 LPS receptor 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. In this study, we now show that 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 do 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 release from the intestine, which activated pulmonary epithelial TLR4, leading to the induction of the neutrophil recruiting CXCL5 and the influx of proinflammatory 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 they suggest that inhibition of this innate immune receptor in the neonatal lung may prevent this devastating complication of NEC.

The type 17 cytokine receptors are thought to play critical roles in mucosal immunity. We have shown that intestinal epithelial expression of IL–17 receptor control the development of microbiota in the terminal ileum and conditional deletion of these receptors results in overgrowth of segmented filamentous bacteria. To study the roles of these receptors in response to an attaching and effacing pathogen we challenged intestinal specific Il17ra mice and Il17rc mice with Citrobacter rodentium (C. rodentium). Conditional deletion of Il17ra and l17rc Iresulted in increased bacterial growth in the colon as well as enhanced dissemination to the liver suggesting that intestinal epithelial IL–17 receptors expression is required for control of this infection. This was supported by unbiased RNAseq analysis of the colon that showed diminished expression of Pigr, Tnfsf13 and Nox1 in the absence of Il17ra. IgA has crucial role in mucosal immunity to protect from pathogenic bacteria. PIGR binds dimeric IgA and translocation into lumen, while TNFSF13 activates induce differentiation to plasma cells following–crass switch. C. rodentium specific IgA in stool and C. rodentium specific IgA producing cells in lamina propria were reduced in Il17ra mice. These results suggested IL-17 receptor signaling regulates transcytosis of C. rodentium specific IgA as well as secretion of bacteria specific IgA. On the other hands Nox1 can produce apical hydrogen peroxide. Nox1 null mice were more sensitive for C. rodentium infection. Furthermore Nox1 was expressed by IL–17A stimulation in colonic organoid. Taken together, IL–17 receptor signaling control to produce C. rodentium specific IgA through PIGR and TNFSF13 as well as hydrogen peroxide through NOX1.

The mechanisms that lead to the development of remote lung injury after trauma remain unknown, although a central role for the gut in the induction of lung injury has been postulated. We hypothesized that the development of remote lung injury after trauma/hemorrhagic shock requires activation of TLR4 in the intestinal epithelium, and we sought to determine the mechanisms involved. We show that trauma/hemorrhagic shock caused lung injury in wild-type mice, but not in mice that lack TLR4 in the intestinal epithelium, confirming the importance of intestinal TLR4 activation in the process. Activation of intestinal TLR4 after trauma led to increased endoplasmic reticulum (ER) stress, enterocyte apoptosis, and the release of circulating HMGB1, whereas inhibition of ER stress attenuated apoptosis, reduced circulating HMGB1, and decreased lung injury severity. Neutralization of circulating HMGB1 led to reduced severity of lung injury after trauma, and mice that lack HMGB1 in the intestinal epithelium were protected from the development of lung injury, confirming the importance of the intestine as the source of HMGB1, whose release of HMGB1 induced a rapid protein kinase C ζ–mediated internalization of surface tight junctions in the pulmonary epithelium. Strikingly, the use of a novel small-molecule TLR4 inhibitor reduced intestinal ER stress, decreased circulating HMGB1, and preserved lung architecture after trauma. Thus, intestinal epithelial TLR4 activation leads to HMGB1 release from the gut and the development of lung injury, whereas strategies that block upstream TLR4 signaling may offer pulmonary protective strategies after trauma.

Neonates are particularly susceptible to infection by colonizing microbes, and mammals protect their offspring via antibodies secreted into breast milk. Necrotizing Enterocolitis(NEC) is a disease of preterm infants characterized by intestinal epithelial damage and inflammation associated with the microbiota. The incidence of NEC is significantly lower in infants fed with maternal milk, though the mechanisms underlying this protective benefit are not clear. Here, we show that maternal Immunoglobulin A (IgA) is an important factor in protection against NEC. Analysis of IgA-binding within fecal samples from preterm infants indicated that breast milk was the predominant source of IgA in the first month of life and that a relative decrease in the fraction of bacteria bound by IgA is associated with the development of NEC. Sequencing of IgA-bound and unbound bacteria revealed that NEC was associated with increasing domination of the IgA unbound microbiota by Enterobacteriaceae, prior to disease onset. Further, we confirmed that IgA is critical in preventing NEC in a murine model, where we demonstrate that pups reared by IgA deficient mothers are susceptible to disease despite exposure to maternal milk. This study illustrates the importance of maternal IgA in shaping the host-microbiota relationship of preterm neonates and provides evidence that IgA is a critical factor in maternal milk necessary for the prevention of NEC.

Necrotizing enterocolitis (NEC) is the leading cause of gastrointestinal-related mortality in premature infants, and it develops under conditions of exaggerated TLR4 signaling in the newborn intestinal epithelium. Because NEC does not develop spontaneously, despite the presence of seemingly tonic stimulation of intestinal TLR4, we hypothesized that mechanisms must exist to constrain TLR4 signaling that become diminished during NEC pathogenesis and focused on the intracellular stress response protein and chaperone heat shock protein-70 (Hsp70). We demonstrate that the induction of intracellular Hsp70 in enterocytes dramatically reduced TLR4 signaling, as assessed by LPS-induced NF-κB translocation, cytokine expression, and apoptosis. These findings were confirmed in vivo, using mice that either globally lacked Hsp70 or overexpressed Hsp70 within the intestinal epithelium. TLR4 activation itself significantly increased Hsp70 expression in enterocytes, which provided a mechanism of autoinhibition of TLR4 signaling in enterocytes. In seeking to define the mechanisms involved, intracellular Hsp70-mediated inhibition of TLR4 signaling required both its substrate-binding EEVD domain and association with the cochaperone CHIP, resulting in ubiquitination and proteasomal degradation of TLR4. The expression of Hsp70 in the intestinal epithelium was significantly decreased in murine and human NEC compared with healthy controls, suggesting that loss of Hsp70 protection from TLR4 could lead to NEC. In support of this, intestinal Hsp70 overexpression in mice and pharmacologic upregulation of Hsp70 reversed TLR4-induced cytokines and enterocyte apoptosis, as well as prevented and treated experimental NEC. Thus, a novel TLR4 regulatory pathway exists within the newborn gut involving Hsp70 that may be pharmacologically activated to limit NEC severity.

The gastrointestinal tract harbors a complex immune system to contend with both normal flora and invasive pathogens. Recently, interleukin (IL)-22 signaling has proven to play a critical role in maintaining the gut barrier, promoting epithelial healing and controlling inflammation from attaching and effacing pathogens. Specifically, IL-22 produced by Th17 cells and group 3 innate lymphoid cells (ILCs) is critical for host resistance to the attaching and effacing gut pathogen Citrobacter rodentium. However, the importance of intestinal epithelial IL-22Ra1 signaling in regulating secretory cell development and protecting against infectious colitis remains unknown. We hypothesize that intestinal IL-22 signaling plays an important role in mucosal host defense against infectious colitis by regulating the intestinal cell types that maintain the gut barrier. To test this hypothesis, we generated mice that selectively lack the receptor for IL-22, IL-22RA1, and discovered these mice have a striking phenotype of intestinal cell differentiation. We demonstrate that abrogation of intestinal IL-22 signaling led to a decreased number of goblet and paneth cells and decreased expression of the antimicrobial peptide Reg3g. Further, the IL-22RA1 intestinal specific knock-out mice were more susceptible to C. rodentium colitis than WT mice as demonstrated by increased weight loss that correlated with increased spleen bacterial burden, decreased epithelial cell proliferation and disrupted mucosal architecture. These findings offer insights into the protective role that IL-22 plays on mediating intestinal mucosal host defense and how critical IL-22 signaling is to intestinal cell differentiation and attenuating infectious colitis.

IL-22 is an IL-10-related cytokine and produced by Th17 and other immune cells that signals via IL-22Ra1 and IL-10R2. IL-22RA is widely expressed on non-immune tissues. IL-22 binding to IL-22 receptor complex leads to STAT3 activation. IL-22 has shown to have hepatoprotective effects through STAT3 in liver injury model. However it is unclear if IL-22 can directly regulate antimicrobial programs in the liver. Using intra-abdominal infection with Klebsiella pneumoniae (KP) where recombinant IL-22 (rIL-22) was administered 2 hours after infection, we found that rIL-22 reduced bacterial burdens in liver. This was associated with reduced liver necrosis and reduced serum ALT levels. rIL-22 required hepatic IL-22Ra1 as rIL-22 therapy was ineffective in liver specific IL-22Ra1 KO mice in terms of controlling bacterial burden or liver injury. rIL-22 also required hepatic STAT3 as rIL-22 therapy was also ineffective in liver specific STAT3 KO mice. Administration of anti-gp-130 conferred a mark increase in KP growth in the liver but this could be rescued by rIL-22, demonstrating that the effect of rIL-22 is independent of gp130. Serum from rIL-22 treated mice showed potent bacteriostatic activity against KP and this activity was dependent on lipocalin-2 (Lcn2). However, in vivo, the antimicrobial activity was independent of Lcn2 as rIL-22 was still therapeutic in Lcn2-/- mice. We are currently investigating the mechanisms underlying the lcn-2 independent activity of rIL-22.

Necrotizing enterocolitis (NEC) is the leading cause of death from gastrointestinal disease in premature infants and the specific molecular mechanisms responsible for NEC development remain unclear. NEC is characterized by intestinal epithelial barrier disruption and impaired mucosal healing. Recent evidence suggests a critical role for IL-22 in the regulation of intestinal epithelial barrier integrity and gut inflammation in inflammatory bowel disease. Thus, we hypothesized that IL-22 signaling plays an important role in NEC pathogenesis. To test this, we subjected wild type and IL-22Ra1 intestinal specific knock out mice (villin-cre X IL22ra1fl/fl) to an experimental model of NEC using gavage formula feeds and intermittent hypoxia. NEC severity was assessed by intestinal mucosal cytokines and a NEC severity score assigned by a blinded pathologist. We discovered the IL-22Ra1 intestinal specific knock out mice demonstrated earlier NEC-related mortality than WT mice. Further, histology on the IL-22Ra1 intestinal specific knock out mice demonstrated disruption in the intestinal mucosal architecture and upregulation of pro-inflammatory cytokines. Taken together, these data suggest that IL-22 signaling may play an important role in attenuating the immune response in NEC pathogenesis. These findings raise the possibility for novel therapeutic approaches in the management of this devastating disease by exploring the efficacy of IL-22 treatment for NEC and the mechanisms involved.