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.
