Impact of phosphatidylinositol metabolism for ciliary biology and renal function

• Applicant: Dr. Markus Schüler
• Subject Area: Nephrology
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 401343905

Chronic kidney disease is a common disease and its prevalence is increasing worldwide. Independently of its etiology the progression of impaired kidney function is based on fibrotic remodeling processes. However, the underlying molecular factors and mechanisms are poorly understood. Monogenic, mendelian disorders with renal involvement offer the unique potential to identify these unknown factors and to provide further understanding of the molecular mechanisms involved in this pathogenesis. Primary cilia are hairlike cellular microtubule based organelles that exist on the surface of almost every quiescent cell of the human body and owe substantial importance for diverse essential cellular functions. Mutations in genes that encode for ciliary proteins lead to a broad complex of disorders, which have collectively been termed “ciliopathies”. The phenotypic spectrum is characterized by early renal interstitial fibrosis and tubular basement membrane disintegration. The term nephronophthisis-related ciliopathies (NPHP-RC) summarizes a group of rare autosomal-recessive kidney diseases which account for the majority of genetically caused end-stage renal disease during the first three decades of life. By whole exome sequencing of one affected individual with NPHP-RC we identified a homozygous truncating mutation in PIK3C2A leading to ciliary dysfunction. The enzyme belongs to the family of phosphatidylinositol - 3-kinases, which serve crucial roles in cell physiology, such as endo- and exocytosis. PIK3C2A was detected in close proximity to the ciliary base and its substrate localizes within the ciliary axoneme. However, its ciliary function remains unknown. This project plans to investigate the cellular und ciliary function of PIK3C2A and its lipid products as well as the importance for the pathophysiology of CKD and ciliopathies. Therefore, we established primary human cell cultures of the homozygous, the heterozygous and wildtype allele carrier as well as of affected individuals with NPHP-RC of different molecular causes. This resource enables us to examine the role of the kinase for periciliary transport processes and ciliary signaling. The renal and extra-renal function of the enzyme and its products will be investigated in vivo by using a hypomorphic Pik3c2a mouse model. In order to examine the general renal und ciliary function of the phosphoinositide pathway the project will be complemented by a further mouse model (Inpp5e). This project will extend the understanding of ciliary biology and renal remodeling processes which may have relevance to kidney dieases in general.

• DFG Programme: Research Grants