Developing a Humanized Mouse Model of Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is the most common chronic lung disease of infancy, and is associated with significant morbidity, mortality and cost. Its pathogenesis remains poorly understood and predictors of the disease remain to be identified. We are committed to elucidating the mechanisms that lead to BPD so that preventive strategies can be developed to decrease its incidence. Our work implicates the role of fetal monocytes in the etiology of BPD: Fetal monocytes are the precursors to alveolar macrophages, which have important immune functions in the developing neonatal lung. An ongoing barrier in BPD research is the limitation in studying normal and abnormal immune development in the lungs of human infants. In the proposed project, we seek to develop a humanized mouse model of hyperoxia-induced lung injury, in order to study the role of human fetal monocytes in the pathophysiology of BPD. Our hypothesis is that fetal monocytes isolated from the cord blood of premature infants who develop BPD will give rise to the BPD phenotype in a humanized mouse model of hyperoxia-induced lung injury. Through the bedside resources of the Prentice Birth Cohort established in 2008 by Dr. Mestan (K23 HL093302), in collaboration with our Northwestern colleagues who have unique expertise in humanized mice (Dr. Misharin) and murine models of BPD (Dr. Farrow), we are well-positioned to test this hypothesis. In the proposed project, we will instill cryopreserved human fetal monocytes, collected from Prentice NICU patients, into newborn mice with a human immune system. In these mice (available through Dr. Misharin in the Northwestern Division of Pulmonary/Critical Care Medicine), the human GM-CSF gene has been “knocked-in”, providing excellent engraftment and function of human alveolar macrophage xenografts. In Aim 1, we will reconstitute lungs of newborn pups with human alveolar macrophages within 24 hours after birth using cryopreserved human fetal monocytes (via intranasal instillation) from 5 BPD cases, and 5 gestational age-matched non-BPD controls. Immediately following monocyte instillation, mice will be exposed to chronic hyperoxia (75% oxygen for 14 days) versus room air. At day 14, the lungs will be harvested for histology and multi-parameter flow cytometry, using a specialized panel developed by Dr. Misharin and colleagues at Northwestern. We hypothesize that histologic changes and alveolar macrophage profiles will correlate with human BPD. In Aim 2, we will perform RNA-seq on the human alveolar macrophages isolated from Aim 1, and compare transcriptome profiles among BPD cases and non-BPD controls, +/- exposure to hyperoxia. We expect that differences in gene expression among alveolar macrophages derived from BPD fetal monocytes will correlate with histologic changes of BPD. The proposed work will use innovative approaches and recent technologic advances to gain novel insight into mechanisms by which fetal stress leads to lung developmental dysfunctions that predispose to the onset of BPD. These findings will advance our long-term goal of identifying early predictive markers of BPD and therapeutic targets to prevent it. Identification of fetal mechanisms that drive the development of BPD in premature infants would represent a major advance in this complex field.