Mutations in the ATP-binding cassette transporter ABCA3 are associated with fatal surfactant deficiency and Respiratory Distress Syndrome (RDS) in neonates, and interstitial lung disease in older children and adults. Located in the limiting membrane of lamellar bodies, ABCA3 is critical for lamellar body genesis and the transport of phospholipid in alveolar type 2 epithelial cells. ABCA3 mutations form part of a growing number of diseases termed "conformational disorders" in which the mutant protein is misfolded, retained in the endoplasmic reticulum (ER) and degraded by ubiquitinproteosome degradation. When this quality control system is overwhelmed, mutant protein accumulates in the ER and triggers the activation/expression of stress and other proteins (ER Stress). Certain ABCA3 trafficking mutants can be rescued in vitro by protein chaperones that promote appropriate folding and improved trafficking. We have recently demonstrated that although ABCA3 mice have decreased phospholipid synthesis, they survive to adulthood, and ABCA3-/- mice fail to form lamellar bodies, the expression of mature SP-B is disrupted, their lungs fail to inflate and they die soon after birth. Using transgenic reconstitution of homozygous null mice with wild type or ABCA3 with mutations associated with human disease, we intend to develop mouse models of the human disease, determine their response to lung injury and test potential therapeutics for limiting adverse effects. We hypothesize that expression of human mutations of ABCA3 in mice will provide a model of human disease, and that heterozygous and mutant ABCA3 mice will be more susceptible to bleomycin- and hyperoxia-induced lung injury. Further, we hypothesize that ABCA3 mutations are associated with increases in hyaluronan (HA) and its receptors that promote macrophage accumulation, and which can be ameliorated using anti-HA or -receptor strategies.
Specific Aim 1 will determine the response of wild type and ABCA3, as well as mice with conditional expression of wild type or ABCA3 mutations, to bleomycin- and hyperoxia-induced lung injury.
Specific Aim 2 will examine alveolar type II cells isolated from ABCA3-/- mice reconstituted with WT or ABCA3 mutations to determine lamellar body morphology, the presence of ER stress response, and will test chemical chaperones and anti-HA/receptor approaches for their effects on the ER stress response.
Specific Aim 3 will determine the effects of chaperones and anti-HA/receptor approaches on the response to bleomycin- or hyperoxia-induced lung injury in mice reconstituted with WT or ABCA3 mutations.
Mutations in the gene for the ABCA3 transporter cause a variety of lung diseases that result in either death in the immediate newborn period or chronic lung disease in children and into adulthood. We want to develop mouse models of the human mutations in this gene so as to study their susceptibility to lung injury, the mechanisms of disease, and to test potential therapies. Since they have been implicated in inflammation after lung injury, we are also interested in studying the role of the extracellular matrix molecule hyaluronan (HA) and its receptors in the disease processes associated with ABCA3 mutations. We believe that the data from these studies will have implications for the pathogenesis of genetic lung diseases as well as provide vital information in the development of potential therapies. Further, the findings emanating from these studies will be relevant to other severe conditions of the lung (e.g. cystic fibrosis) and liver (e.g. alpha-1-antitrypsin deficiency) that have similar mechanisms of disease.
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