The development of colony-stimulating factor-1 as a therapy to promote organ maturation

With much of our health beginning at development, proper growth is essential to give us the best start at life. This thesis has focused on the development of the kidneys and lungs. Both lung immaturity and impaired nephron formation contribute significantly to the high mortality rates associated with preterm birth and intrauterine growth restriction. Medical advancements have included oxygen supplementation and corticosteroids, however they cause damage to the developing lung and are associated with increased risk of long-term adverse health outcomes. In the kidney, increasing evidence supports the link between the in utero environment, nephron endowment and the risk of renal disorders. Understanding the mechanisms that govern normal organogenesis will facilitate the development of novel therapies aimed at enhancing organ maturation. Colony-stimulating factor-1 (CSF-1) is a haemopoietic growth factor and the primary regulator of macrophage differentiation, proliferation and survival. Traditionally CSF-1 is recognised for its functions in immune regulation, however a greater appreciation of macrophage heterogeneity indicates that CSF-1 signalling also contributes significantly to non-immune processes such as development and tissue regeneration. The essential role of CSF-1 in organogenesis is highlighted by the extensive developmental abnormalities associated with CSF-1 deficiency. In previous studies, the addition of CSF-1 to embryonic lung and kidney explants resulted in increased branching and nephron formation. Furthermore, results of a preliminary study also indicated that CSF-1 treatment enhances nephron endowment and alveolar formation in vivo. Recognising the potential clinical benefits, we have been diligent in securing the intellectual property for CSF-1 as a modality for enhanced organ maturation and growth (US Patent 8,153,584). As such, this thesis has formed the basis of the preclinical development program investigating the applicability of CSF-1 as a therapy for promoting kidney and lung development. This thesis has utilised the neonatal mouse as a developmental model. Mice are born at a stage where earlier aspects of organ development are still ongoing, thereby providing a technically accessible organogenic window to investigate enhancement with CSF-1. In the four subsequent studies, CSF-1 and the promotion of nephrogenesis and alveolar formation has been systematically addressed. Firstly, a thorough characterisation of CSF-1R location and trophic macrophages in postnatal development of the mouse was performed. CSF-1 was then administered to neonatal mice to investigate whether increasing CSF-1 would enhance development of the kidneys and lungs. In the third study, the alveologenic capabilities of CSF-1 were trialled in the clinically relevant neonatal hyperoxia model; which mimics the disruption of alveolar formation in preterm infants caused by oxygen supplementation. Clinical applicability was also the focus of the forth study which investigated assays to translate the in vitro promotion of nephrogenesis from an embryonic murine to human setting for potential use in fetal obstructive uropathy. The results of this thesis have strengthened understanding of macrophages in the developing kidney and lung, and taken significant steps in the development of a CSF-1 therapy for the promotion of organogenesis. In particular, a correlation between macrophages and key periods of development in both organs is demonstrated, and this study is the first to report the role of M2 macrophages in alveolar development. Administration of CSF-1 to neonates had a beneficial effect in increasing body weight and kidney growth, with results strengthening the link between CSF-1 and the IGF-1 growth axis as a mechanism of trophic action. We have also demonstrated promising safety data for CSF-1 use in clinically relevant settings of developmental inflammation, although efficacy was limited with regard to the rescue of alveolar perturbation. Furthermore, the establishment of an in utero fetal tissue collection method and organ culture assay has relevance for future testing of nephrogenic agents. Overall, this thesis provides the foundation for ongoing preclinical testing of CSF-1, and highlights the relevance of CSF-1 as a potential clinical intervention for promoting organ development in premature infants and ureteral-obstructed fetuses.