Lung developmental defects caused by type I collagen mutations in mouse models of osteogenesis imperfecta - Patients with skeletal dysplasias, including osteogenesis imperfecta (OI), often suffer from congenital respiratory problems that have limited therapeutic opportunities, and increased perinatal and early childhood mortality. OI is caused by dominant mutations in COL1A1 and COL1A2 genes or by loss of function of genes involved in COL1 processing (e.g., CRTAP, encoding an essential protein for collagen post-translational modification and folding). The current concept is that the respiratory abnormalities in OI are secondary to the skeletal defects, such as thoracic wall deformities and deviations of the spine curvature (kyphoscoliosis), which do not allow proper expansion and inflation of the lungs leading to restrictive disease. We demonstrated that COL1 production is dysregulated in lung fibroblasts from a mouse model of OI lacking the Crtap gene (CrtapKO). These mice also exhibit defective lung alveolar formation, loss of alveolar epithelial cells, and several changes in genes expression, including decreased myofibroblast markers, as quantified by spatially resolved transcriptomics. In addition, CrtapKO mice and two others mouse models of OI with COL1 mutations (Col1a2G610C/+ and oim/oim) exhibit altered respiratory mechanics at 3 months of age. Based on this evidence and because COL1 is expressed in most tissues including the lung, our central hypothesis is that the respiratory defects in patients with OI and other skeletal dysplasias are due to intrinsic lung dysfunction that, in the future, could be treated and/or corrected independently from the skeletal fragility. The specific goals are 1) dissect the contribution of intrinsic lung defects versus extrinsic skeletal defects to impaired lung functions in OI; and 2) unravel cellular and molecular mechanisms triggered by COL1 defects leading to abnormal lung development and impaired respiratory function. To test our hypothesis, we assembled a team with complementary expertise that is uniquely positioned to accomplish our goals. The specific aims are: to determine the respiratory phenotype of a novel knock-in mouse model expressing a classical Col1a1 OI glycine substitution mutation in the lung but not in the skeleton (Col1a1Flox/+;Tbx4-Cre) and compare it to that of mice expressing this mutation globally (aim 1). To identify the cause of impaired alveolar morphogenesis and key pathways contributing to changes in alveolar mesenchymal-epithelial cell interactions in CrtapKO cell cultures and organoids (aim 2). To identify causes of impaired alveolar morphogenesis and abnormal patterning and function of lung cells in CrtapKO mice in vivo by analyzing the entire transcriptome in 5-7 µm lung sections with 100 µm or better lateral resolution during the critical stage of alveolar formation (aim 3). Together, aims 1-3 will provide mechanistic insights and establish the relationship between the collagen matrix and cellular dysfunction causing lung-intrinsic defects in OI leading to a better understanding of the role of the matrix in the last stage of lung development. Ultimately, this work will provide new insights into more common diseases of collagen dysregulation in the lung such as fibrosis and bronchopulmonary dysplasia.
