Virus infections as risk factors in the development of bronchopulmonary dysplasia (BPD)

Dmitrieva, Anna (2024): Virus infections as risk factors in the development of bronchopulmonary dysplasia (BPD). Dissertation, LMU München: Medizinische Fakultät

Abstract

Bronchopulmonary dysplasia (BPD) is a multifactorial chronic lung disease primarily affecting premature infants, often resulting from the complex interplay of preterm birth, mechanical ventilation, and oxygen therapy. The complicated relationship between inflammation, oxidative stress, and impaired lung growth contributes to the development of this challenging condition. The immune system of prematurely born children, often referred to as preterm or premature infants, is underdeveloped compared to those born at full term. Premature birth and the associated underdeveloped respiratory system render affected infants more susceptible to various infections. Viral infections in infants with BPD often manifest with heightened severity, posing a substantial challenge in clinical management. Virus infections represent a significant global health concern, affecting millions of individuals annually and posing a substantial burden on healthcare systems. Gammaherpesviruses, a subgroup of the Herpesviridae family, encompass notable pathogens such as Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV). These viruses present significant health concerns due to their association with various cancers and their intricate evasion strategies against the host immune system. Both EBV and KSHV can cause severe respiratory complications in individuals with compromised immune systems. A key challenge in studying human herpesviruses is the absence of a dependable small animal model for investigating fundamental aspects of viral pathogenesis. Murine gammaherpesvirus 68 (MHV-68) serves as a naturally occurring virus genetically related to human gammaherpesviruses, including EBV and KSHV. My study addressed the impact of MHV-68 infection on the development of BPD in one of the major lung cell types – fibroblasts: CCL-206 and neonatal primary mouse lung fibroblasts (in vitro part). This investigation presents novel outcomes resulting from early postnatal exposure to clinically significant hyperoxia concentrations (FiO2 = 0.4, 24 hours) with the following MHV-68 infection. A significant finding in this study was the observed impact of O2 treatment (FiO2 = 0.4), leading to a noteworthy decrease in Caspase 3/7 activity, necrosis, and proliferation in primary fibroblasts. Importantly, this effect occurred without any discernible changes in cell morphology. The study suggests that hyperoxic conditions potentially trigger adaptive mechanisms in primary fibroblasts within the initial 24 hours post-exposure, moderating apoptosis and necrosis without altering cell morphology. Conversely, MHV-68 infection resulted in a substantial increase in necrosis and a decrease in apoptosis, proliferation, and cell migration capabilities. The infected cells exhibited reduced Pdgfrα gene expression, elevated Vegf gene expression, and irreversible morphological changes, indicative of potential cell-cycle arrest. Virus replication curve was significantly lower in cells exposed to hyperoxia, this finding demonstrated decreased proliferation of exposed cells. Notably, CCL-206 cells, being immortalized, displayed increased Caspase 3/7 activity, potentially attributed to their artificial ability for continuous proliferation. I conducted an investigation utilizing TGFβ stimulation on CCL-206 cells and primary fibroblasts to assess its potential influence on MHV-68 infection, juxtaposing its effects with those resulting from hyperoxia exposure. TGFβ treatment elicited distinct impacts on cellular responses and MHV-68 infection. Specifically, within the initial 24-hour post-virus infection period, TGFβ treatment exhibited no alterations in necrosis or apoptosis in fibroblasts, and it did not induce changes in cellular proliferation and migration. Owing to the disparate signaling pathways engaged, TGFβ cannot serve as a suitable comparative control for in vitro hyperoxia studies. Exploring BPD, we aimed to develop a clinically relevant animal model for studying lifelong consequences. The study employed a double-hit model involving hyperoxia exposure (FiO2 = 0.4) and MHV-68 infection in neonatal mice, revealing significant changes in Radial Alveolar Count (RAC) and septal wall thickness of the adult mice, indicating altered lung morphology after mice were treated in the early days of life, emphasizing the mutual influence nature of hyperoxia and viral infection injuries in adult alveoli. MHV-68 titer in lungs was significantly increased in mice prior exposed to hyperoxia, indicating the enhanced immune response in lung cells due to the preliminary hyperoxia exposure. The study's exploration of sex-related differences uncovered notable variations in lytic MHV-68 titer, RAC, and alveolar wall thickness between male and female mice, adding an additional layer of complexity to the interplay of infection, hyperoxia, and BPD.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: bronchopulmonary dysplasia, neonatal disease, hyperoxia, virus infection, herpesvirus
• Themengebiete: 600 Technik, Medizin, angewandte Wissenschaften ; 600 Technik, Medizin, angewandte Wissenschaften > 610 Medizin und Gesundheit
• Fakultäten: Medizinische Fakultät
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 27. Mai 2024
• 1. Bericht­erstatter:in: Adler, Heiko