The role of outer dynein arm docking complex components in primary ciliary dyskinesia

• Applicant: Dr. Rim Hjeij, Ph.D.
• Subject Area: Pediatric and Adolescent Medicine
• Term: since 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 321122358

Primary ciliary dyskinesia (PCD) is an autosomal recessive disorder resulting from defective ciliary motility and characterized by upper and lower respiratory infections. Outer dynein arms (ODAs) are multiprotein complexes attached to the outer microtubule doublet A generating the motive force for ciliary and flagellar beating. The outer dynein arm docking complex (ODA-DC) provides the docking sites for the outer dynein arm so that an absence of ODA-DC results in a deficiency in the ODAs from the axonemes. In 2013, we identified ARMC4 as an ODA-DC associated protein undetectable in the axonemes of respiratory cells from patients with CCDC114 mutations. Following this, we identified additional ODA-DC components such as CCDC151, TTC25 and MNS1 and characterized their functional role in PCD. Recently, we identified a new candidate Ca2+-binding protein to be associated with ODA-DC in human (EFCAB1) and we are currently working on its characterization. Based on our data, ODA-DC appears to differ between the different species but also between the respiratory and nodal cilia as well as in sperm flagella. A deeper analysis of the different cell types is needed to elucidate the structure and the mechanism by which this complex function in human. Additional knowledge about the composition of the ODA-DC is of great importance to improve PCD diagnostic procedures and patient care. The objectives of this current proposal are therefore as follows: 1. Molecular and cellular characterization of the novel calcium-binding protein EFCAB1 involved in ODA docking and DAW1 involved in ODA type 2 assembly in human PCD individuals 2. Identification of additional gene defects resulting in PCD due to abnormal ODA-DC function 3. Validation of candidate proteins by expression analyses in control and mutant tissue 4. Investigation of the functional role in the model organism planaria 5. Protein interaction studies of ODA-DC related and ODA proteins 6. Characterization of the ODA-DC defects by proteomic analysis of primary human airway cultures 7. Characterization of the multiprotein ODA-DC complex using sucrose gradient fractionation. Following this strategy, we expect that we will 1) succeed to detect novel components associated with the ODA-DC and 2) succeed to characterize the composition of the ODA-DC in human cilia and cell type specific differences in more detail. These data will improve our understanding of normal cilia biology and which will give additional insights into the pathogenesis of PCD, thus improving diagnosis and genetic counseling of affected individuals. In addition, we hope that we will be able to develop novel therapeutic strategies for PCD.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Heymut Omran