Abstract
Background
Dysregulated inflammation leads to morbidity and mortality in neonates. Neutrophil-mediated inflammation can cause inflammatory tissue damage. The mammalian target of rapamycin (mTOR) pathway governs IL-6Rα protein expression in human neutrophils. Shed IL-6Rα then participates in trans-signaling of IL-6/IL-6Rα to cells not otherwise sensitive to IL-6. Signaling to endothelial cells triggers efferocytosis where macrophages limit persistent inflammation by phagocytizing neutrophils. We hypothesized that preterm neonatal PMNs fail to synthesize IL-6Rα due to alterations in mTOR signaling.
Methods
We studied IL-6Rα expression, PAF receptor expression, and mTOR signaling in plasma and PAF-stimulated PMNs isolated from newborn infants and healthy adults using ELISA, real-time RT-PCR, western blotting, flow cytometry, and immunocytochemistry with phospho-specific antibodies.
Results
Compared to healthy adults, plasma from neonates contains significantly less soluble IL-6Rα. IL-6Rα mRNA expression in PAF-stimulated PMNs does not differ between neonates and adults, but IL-6Rα protein expression is decreased in preterm neonatal PMNs. Rapamycin, an mTOR inhibitor, blocks IL-6Rα protein expression. mTOR signaling following PAF stimulation is decreased in preterm neonatal PMNs.
Conclusions
Preterm neonatal PMNs exhibit decreased mTOR pathway signaling leading to decreased IL-6Rα synthesis. Decreased synthesis of IL-6Rα by neonatal PMNs may result in decreased IL-6/IL-6Rα trans-signaling with prolonged inflammatory response and increased morbidity.
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Acknowledgements
The authors gratefully acknowledge Diana Lim’s expertise and assistance with figure preparation and graphic design. This work was supported in part by the US NIH (K08HD049699 to C.C.Y. (NICHD); 5R37HL044525 to G.A.Z. (NHLBI)) and by the University of Utah Department of Pediatrics, Division of Neonatology.
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C.C.Y. and G.A.Z. conceived of the project and designed the experiments. C.C.Y. performed the patient phenotyping and recruited study participants. R.A.C., M.J.C., B.K.M., and C.C.Y. conducted experiments. R.A.C. and C.C.Y. wrote the manuscript.
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Campbell, R.A., Cody, M.J., Manne, B.K. et al. Interleukin 6 receptor alpha expression in PMNs isolated from prematurely born neonates: decreased expression is associated with differential mTOR signaling. Pediatr Res 86, 55–62 (2019). https://doi.org/10.1038/s41390-019-0388-6
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DOI: https://doi.org/10.1038/s41390-019-0388-6
