Universität zu Köln

Odenthal, Johanna ORCID: 0000-0002-2979-8322 (2023). Loss of cytoskeletal and polarity regulation as key pathogenic principles in glomerular disease. PhD thesis, Universität zu Köln.

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Abstract

Injury to glomerular podocytes constitutes the predominant cause of glomerular diseases and therefore loss of kidney function. Podocytes are specialized epithelial cells within glomeruli indispensable for the filtration process. Their cell bodies extrude numerous large primary and smaller foot processes that completely enwrap glomerular capillaries. The only cell-cell contact established between adjacent foot processes of neighbouring cells is the slit diaphragm. In addition to contributing to the filtration barrier and preventing the loss of blood proteins into the urine, the slit diaphragm is a vital signaling platform that integrates external signals with the intracellular signaling machinery. The sophisticated architecture of podocytes and their foot processes requires a dynamic actin cytoskeleton and its tight regulation through pathways such as polarity signalling. Upon injury, podocytes start to retract their foot processes, leading to loss of the slit diaphragm and ultimately disruption of the filter apparatus. A common finding upon this so-called effacement are actin cytoskeleton rearrangements. Understanding pathways and key players of actin regulation in podocytes that could prevent the progression of foot process effacement is therefore desirable. This thesis investigated the loss of actin and polarity regulation as key principles of podocyte injury. A first focus was thereby put on utilizing the fruit fly Drosophila melanogaster and in particular nephrocytes as in vivo model for glomerular diseases and to establish solid and reproducible experimental read-outs. Expression of human transgenes in nephrocytes was then used to characterize a so far unknown patient mutation in alpha-Actinin 4, an actin-crosslinking protein. In addition to demonstrating that the mutation alters actin localization, the Drosophila model was utilized to assess the pathogenic potential of the mutant protein. In light of the fact that expression of the mutant variant resulted in severe morphological and functional phenotypes in nephrocytes, it was determined that the novel variant is indeed a pathogenic ACTN4 variant. By this, the power of Drosophila as in vivo tool to complement clinical and genetic diagnostics was emphasized. Lastly, a possible link between podocyte polarity signaling and actin regulation was further investigated by using both, murine and Drosophila models. Here, single and double knockout of Par3A and Par3B in murine podocytes revealed, that the proteins share redundant functions, as only double knockout of Par3A and -B led to a glomerular phenotype. Further analyses in Drosophila nephrocytes focussed on knockdown of the Drosophila Par3 homologue bazooka. Depletion of Bazooka in nephrocytes led to differential expression of various actin-binding and -regulating proteins, including increased activity of the small GTPase Rho1 (the Drosophila RhoA homologue). Interestingly, Rho1 activation could be reverted upon transgenic expression of murine Par3A but not Par3B, indicating that the two proteins also exhibit distinct but unknown functions. These findings strengthen the link between perturbed polarity signalling and dysregulated actin dynamics, making polarity proteins a strong target to possibly counteract the progression of podocyte disease.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Odenthal, Johanna johanna.odenthal@uk-koeln.de orcid.org/0000-0002-2979-8322 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-702559
Date:	June 2023
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Medicine > Innere Medizin > Klinik II für Innere Medizin - Nephrologie, Rheumatologie, Diabetologie und Allgemeine Innere Medizin
Subjects:	Life sciences Medical sciences Medicine
Uncontrolled Keywords:	Keywords Language Glomerular Disease English Nephrozyte English Polarity signaling English Actin regulation English Drosophila melanogaster UNSPECIFIED
Date of oral exam:	24 October 2022
Referee:	Name Academic Title Benzing, Thomas Prof. Dr. med. Roth, Siegfried Prof. Dr. rer. nat.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/70255