Neonatal Respiratory Infections Lead to Brainstem Neuroinflammation

Introduction

Respiratory infections are one of the most common diseases and causes of morbidity among newborns. During the acute phase, infections are known to cause widespread peripheral inflammation. However, the effect of this inflammation on the critical neural centers that control breathing has not been fully explored. This study utilized a well-detailed model to investigate the acute response of the medulla oblongata, which contains vital respiratory regions, to neonatal respiratory infections.

Source of the Paper

This paper was authored by Kateleen E Hedley, Henry M Gomez, Eda Kecelioglu, Olivia R Carroll, Phillip Jobling, Jay C Horvat, and Melissa A Tadros, among others. The authors are affiliated with the School of Biomedical Sciences & Pharmacy and the Hunter Medical Research Institute at the University of Newcastle, Australia. The paper was published in the Journal of Neuroinflammation in 2024.

Detailed Research Process

Research Models and Sample Processing

1. Neonatal Mouse Model Processing: A neonatal mouse model was used to study the impact of respiratory infections on the medulla oblongata. Within 24 hours of birth, BALB/c mice were intranasally injected with Chlamydia muridarum (CMU) or treated with a placebo (SPG). Tissue samples were collected on day 15 post-birth (P15), when peripheral inflammation peaks.

2. Sample Classification: Four groups were formed: Female SPG group (FSPG), Female CMU group (FCMU), Male SPG group (MSPG), and Male CMU group (MCMU). Each group had 7-8 samples, with a total of 55 mice participating in the experiment from 13 litters.

3. Tissue Processing and RNA Extraction: RNA was extracted from the lungs and medulla oblongata, followed by RT-qPCR analysis to confirm the expression of infection and inflammation markers. RNA extraction from the medulla oblongata was carried out using the RNeasy® Mini Kit (QIAGEN), while RNA extraction from lung tissue followed standard protocols.

Analytical Techniques and Experiments

1. RT-qPCR: RT-qPCR was conducted to compare inflammation marker expression among various groups. Key genes examined included: CXCL9, CXCL10, IL-13, KCNN4, BDNF, TGFβ, PTGS2, STAT6, and others. All qPCR primers were rigorously designed and validated, ensuring experimental reliability.

2. Immunofluorescence Labeling: IBA1 and GFAP were used to label glial cells in the medulla oblongata, aiming to observe changes in microglia and astrocytes. Images were captured using an Olympus BX50 microscope and DP72 camera, and fluorescence intensity and percentage area were quantified using ImageJ software.

Research Results

Peripheral Response

1. Weight Changes: Infected CMU mice showed significantly lower weight gain rates from day 6 to day 15 of the experiment, consistent with the health deterioration caused by infection.

2. Lung Inflammation Markers: On day 15, lung tissue measurements revealed significant 16S expression, indicating successful infection in all infected groups. Further analysis showed significant upregulation of CXCL9, NLRP3, TNFα, and IL-1β in the lungs of infected mice, indicating notable peripheral inflammatory responses with no gender differences.

Inflammation Response in the Medulla Oblongata

1. Inflammatory Response in Female Mice:

   • CXCL9 and CXCL10: Significantly upregulated in the FCMU group; these cytokines help in the migration and activation of immune cells, limiting infection spread.
   • BDNF and IL-13: Significantly upregulated in the female infected group, with BDNF mainly involved in brain development and neuroprotection, and IL-13 having anti-inflammatory properties.
   • KCNN4: Significantly upregulated, believed to play a negative role in neuroinflammatory responses, though its specific impact requires further study.

2. Inflammatory Response in Male Mice:

   • PTGS2 and STAT6: Significantly downregulated in the MCMU group, indicating a more suppressed inflammatory response in male mice, potentially leading to poorer long-term health outcomes.

Microglia and Astrocyte Reactions

1. NTS and DMX Changes:
   • Microglia: Differences in quantity and morphology of microglia were significant between female and male mice. Females showed a reduction in cell count and MFI in the DMX, exhibiting a stronger anti-inflammatory response; whereas males showed an increase in cell count and MFI in the DMX, indicating a stronger inflammatory response.
   • Astrocytes: Area percentage increased in the NTS but showed no significant changes in the DMX.

Conclusion

This study is the first to systematically explore the acute impact of neonatal respiratory infections on the medulla oblongata’s respiratory centers, finding that sex significantly influences the neuroinflammatory response. Female mice demonstrated a stronger neuroprotective inflammatory response, while male mice had a more suppressed inflammatory response. These findings emphasize that respiratory infections during critical developmental periods may have long-term effects on the neural centers, potentially leading to permanent respiratory system dysfunction. This study provides essential evidence for future clinical interventions, particularly sex-specific treatment strategies for neonatal respiratory infections.

Significance of the Study

This research significantly enhances our understanding of how neonatal respiratory infections impact the central nervous system, especially the sex-specific reactions of the medulla oblongata’s respiratory centers. The results not only help explain long-term health issues related to neonatal pneumonia but also provide scientific evidence for developing new treatment strategies, which could have profound implications in clinical practice.