Sex-differences in LPS-induced neonatal lung injury.

Being of the male sex has been identified as a risk factor for multiple morbidities associated with preterm birth, including bronchopulmonary dysplasia (BPD). Exposure to inflammatory stress is a well-recognized risk factor for developing BPD. Whether there is a sex difference in pulmonary innate immune TLR4 signaling, lung injury and subsequent abnormal lung development is unknown. Neonatal (P0) male and female mice (ICR) were exposed to systemic LPS (5 mg/kg, IP) and innate immune signaling, and the transcriptional response were assessed (1 and 5 hours), along with lung development (P7). Male and female mice demonstrated a similar degree of impaired lung development with decreased radial alveolar counts, increased surface area, increased airspace area and increased mean linear intercept. We found no differences between male and female mice in the baseline pulmonary expression of key components of TLR4-NFκB signaling, or in the LPS-induced pulmonary expression of key mediators of neonatal lung injury. Finally, we found no difference in the kinetics of LPS-induced pulmonary NFκB activation between male and female mice. Together, these data support the conclusion that the innate immune response to early postnatal LPS exposure and resulting pulmonary sequelae is similar in male and female mice.

The hepatic innate immune response is lobe-specific in a murine model endotoxemia.

The liver plays a central role in the innate immune response to endotoxemia. While previous studies have demonstrated lobe-specific transcriptional responses to various insults, whether this is true in response to endotoxemia is unknown. We sought to assess whether there were significant intra- and inter-lobe differences in the murine hepatic innate immune transcriptional response to endotoxemia. Adult male ICR mice were exposed to i.p. LPS (5 mg/kg, 30 min, 60 min, 5 h) and primary ( Tnf, Cxcl1, Nfkbia, Tnfiap3) and secondary ( Il6, Nos2) innate immune response gene expression was assessed in the left medial, right medial, left lateral, and right lateral lobes, and the papillary and caudate processes. The expression of all innate immune response genes increased following i.p. LPS challenge. When tested at the early time points (30 and 60 min), the left medial lobe and caudate process consistently demonstrated the highest induction of gene expression. Most inter-lobe differences were attenuated at later time points (5 h). To improve reproducibility of the study of endotoxemia induced by i.p. LPS challenge, inclusion of appropriate methodological details regarding collection of hepatic tissue should be included when reporting scientific results in published manuscripts.

Immunotolerant p50/NFκB Signaling and Attenuated Hepatic IFNß Expression Increases Neonatal Sensitivity to Endotoxemia.

Sepsis is a major cause of neonatal morbidity and mortality. The current paradigm suggests that neonatal susceptibility to infection is explained by an innate immune response that is functionally immature. Recent studies in adults have questioned a therapeutic role for IFNß in sepsis; however, the role of IFNß in mediating neonatal sensitivity to sepsis is unknown. We evaluated the transcriptional regulation and expression of IFNß in early neonatal (P0) and adult murine models of endotoxemia (IP LPS, 5 mg/kg). We found that hepatic, pulmonary, and serum IFNß expression was significantly attenuated in endotoxemic neonates when compared to similarly exposed adults. Furthermore, endotoxemia induced hepatic p65/NFκB and IRF3 activation exclusively in adults. In contrast, endotoxemia induced immunotolerant p50/NFκB signaling in neonatal mice without evidence of IRF3 activation. Consistent with impaired IFNß expression and attenuated circulating serum levels, neonatal pulmonary STAT1 signaling and target gene expression was significantly lower than adult levels. Using multiple in vivo approaches, the source of hepatic IFNß expression in endotoxemic adult mice was determined to be the hepatic macrophage, and experiments in RAW 264.7 cells confirmed that LPS-induced IFNß expression was NFκB dependent. Finally, treating neonatal mice with IFNß 2 h after endotoxemia stimulated pulmonary STAT1 signaling and STAT1 dependent gene expression. Furthermore, IFNß treatment of endotoxemic neonatal animals resulted in significantly improved survival following exposure to lethal endotoxemia. In conclusion, endotoxemia induced IFNß expression is attenuated in the early neonatal period, secondary to impaired NFκB-p65/IRF3 signaling. Pre-treatment with IFNß decreases neonatal sensitivity to endotoxemia. These results support further study of the role of impaired IFNß expression and neonatal sensitivity to sepsis.