Primary ciliary dyskinesia (PCD) is an autosomal recessive disease caused by mutations that disrupt ciliary function and result in defective mucociliary clearance (MCC). Mucociliary clearance is a critical innate defense mechanism, and impaired MCC contributes to the pathogenesis of several airway diseases, including PCD, asthma, cystic fibrosis (CF), and chronic obstructive pulmonary disease (COPD). PCD is genetically heterogeneous, and sequencing of candidate genes, homozygosity mapping, and more recently, whole-exome sequencing, have now identified mutations in over a dozen genes that cause PCD. These genetic studies are not only rapidly advancing the diagnosis of PCD, but are expanding the definition of PCD, and patients with previously undiagnosed respiratory disease may actually have variant forms of PCD. We have identified mutations in 7 new genes that cause PCD. While some of these genes have been identified in patients with a typical PCD phenotype and encode proteins that are known components of the ciliary axoneme, others have been identified in patients with an atypical PCD phenotype, and the mutated proteins are completely uncharacterized. Our hypothesis is that the different clinical phenotypes observed in PCD are due to mutations in genes that perform different roles in the proper assembly, activity, or regulation of cilia. Therefore, the goal of this proposal is to investigate the function of thre novel PCD causing genes, sperm associated antigen 1 (SPAG1), radial spoke head homolog 1 (RSPH1), and growth arrest-specific protein 2-like 2 (GAS2L2), each of which is associated with a different clinical phenotype. To more completely understand the role of genetic variation on mucociliary clearance and its role in disease, it is essential to understand the functions of these genes. We will investigate the function of these genes using different model systems and a variety of techniques. First, we will study the expression and localization of the normal proteins in well- differentiated cultures of human airway epithelial (HAE) cells, using quantitative RT-PCR and immunostaining. We will then use shRNA technology to knock down expression of the novel genes and a new method to culture samples of nasal epithelial cells directly from PCD patients. Cilia will be examined by electron microscopy for structural defects, and measurements of ciliary beat frequency, waveform, mucociliary transport, and nitric oxide production will be performed to determine the role of the missing protein. Proteins that interact with SPAG1, RSPH1, and GAS2L2 will be identified using biochemical crosslinking techniques, immunoprecipitation, and mass spectrometry. Finally, mice that have a deletion in the Rsph1 gene will be studied to determine what effects the absence of this gene has on mucociliary clearance and disease pathogenesis in vivo. These studies will lead to an increased understanding of the role of these proteins in cilia structure and function, mucociliary clearance, and respiratory health, and may lead to the developments of new therapeutic treatments for a variety of respiratory diseases, including PCD, asthma, CF, and COPD.
This research is focused on understanding the molecular function of three newly identified genes that cause the disease primary ciliary dyskinesia (PCD) when mutated. This is a rare disease that is caused by defects in the structure or function of the cilia that move mucus and inhaled foreign material, including bacteria and viruses, out of the airways. By understanding how the proteins encoded by these genes function and how they are altered in disease, we may be able to improve the treatments available for PCD and other airway diseases.
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