In utero LPS exposure impairs preterm diaphragm contractility

Preterm birth is associated with inflammation of the fetal membranes (chorioamnionitis). We aimed to establish how chorioamnionitis affects contractile function and phenotype of the preterm diaphragm. Pregnant ewes received intra-amniotic injections of saline or 10 mg lipopolysaccharide (LPS) 2d or 7d prior to delivery at 121d gestation (term = 150d). Diaphragm strips were dissected for assessment of contractile function after terminal anesthesia. The inflammatory cytokine response, myosin heavy chain (MHC) fibre, proteolytic pathways and intracellular molecular signalling were analyzed using qPCR, ELISA, immunofluorescence staining, biochemical assays and Western blot. Diaphragm peak twitch force and maximal tetanic force were approximately 30 lower than control in 2d and 7d LPS groups. Activation of the NF-kappaB pathway, an inflammatory response and increased proteasome activity, were observed in the 2d LPS group relative to control or 7d LPS group. No inflammatory response was evident after a 7d LPS exposure. 7d LPS exposure markedly decreased p70S6K phosphorylation but there was no effect on other signalling pathways. MHC IIa fibre proportion was lower than control in the 7d LPS group. MHC I fibre proportions were not different between groups. Results demonstrate that intrauterine LPS impairs preterm diaphragmatic contractility after 2d and 7d exposure. Diaphragm dysfunction resulting from 2d LPS exposure was associated with transient activation of pro-inflammatory signalling with subsequent increased atrophic gene expression and enhanced proteasome activity. Persistent impaired contractility for 7d LPS exposure was associated with down-regulation of a key component of the protein synthetic signalling pathway and reduction in MHC IIa fibre proportions.