The normal adult mammalian lung has a robust capacity to regenerate following injury, and evidence for alveolar regeneration was recently demonstrated in adult man. In contrast, mounting evidence suggests COPD/emphysema represents a failure of regeneration. COPD represents an enormous worldwide clinical and social burden, with currently no cure besides lung transplantation.
An appealing therapeutic option is induction of endogenous lung regeneration using retinoic acid (RA), demonstrated to stimulate alveolar regeneration in animal models of emphysema. However, clinical trials investigating retinoids for chronic lung diseases have been disappointing. Thus, there is a profound stimulus to understand how the regeneration-inducing effects of RA in animal models translate to man.
The molecular regulation of RA signalling in emphysema has not been investigated hitherto, and the role of RA in repair of specific human alveolar cell types, alveolar type 2 cells and lung microvascular endothelial cells, is unknown. Work in this thesis was conducted to address these questions. We demonstrated that CYP26A1, which breaks down RA, is enriched on an mRNA and protein level in emphysematous lung tissue. We also demonstrated using in vitro cell culture assays that RA is unlikely to directly regulate alveolar epithelial wound healing. In contrast, RA stimulated lung microvascular endothelial angiogenesis, likely via retinoic acid receptor alpha, and was associated with induction of angiogenic genes.
Further work presented herein involved development of an ex vivo model of lung regeneration using precision cut lung slices (PCLS) derived from adult human distal lung tissue. We demonstrated that human PCLS retain architecture and viability through slicing, that 10% serum supplementation is inappropriate for long-term PCLS culture, and that human PCLS remain viable for at least 4 days in culture, suggesting they are amenable to development of an injury/repair model within this time frame.