DAAM2 Variants Cause Nephrotic Syndrome via Actin Dysregulation

Am J Hum Genet. 2020 Dec 3;107(6):1113-1128. doi: 10.1016/j.ajhg.2020.11.008.

Ronen Schneider ¹, Konstantin Deutsch ¹, Gregory J Hoeprich ², Jonathan Marquez ³, Tobias Hermle ⁴, Daniela A Braun ¹, Steve Seltzsam ¹, Thomas M Kitzler ¹, Youying Mao ¹, Florian Buerger ¹, Amar J Majmundar ¹, Ana C Onuchic-Whitford ⁵, Caroline M Kolvenbach ¹, Luca Schierbaum ¹, Sophia Schneider ¹, Abdul A Halawi ¹, Makiko Nakayama ¹, Nina Mann ¹, Dervla M Connaughton ¹, Verena Klämbt ¹, Matias Wagner ⁶, Korbinian M Riedhammer ⁷, Lutz Renders ⁸, Yoshichika Katsura ⁹, Dean Thumkeo ⁹, Neveen A Soliman ¹⁰, Shrikant Mane ¹¹, Richard P Lifton ¹², Shirlee Shril ¹, Mustafa K Khokha ³, Julia Hoefele ¹³, Bruce L Goode ², Friedhelm Hildebrandt ¹⁴

Affiliations

1 Department of Pediatrics, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.
2 Department of Biology, Brandeis University, Waltham, MA 02454, USA.
3 Pediatric Genomics Discovery Program, Department of Pediatrics and Genetics, Yale University School of Medicine, New Haven, CT 06520, USA.
4 Renal Division, Department of Medicine, Faculty of Medicine and Medical Center, University of Freiburg, Freiburg 79106, Germany.
5 Department of Pediatrics, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA; Renal Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
6 Institute of Human Genetics, Klinikum rechts der Isar, School of Medicine, Technical University of Munich, Munich 81675, Germany; Institute of Neurogenomics, Helmholtz Zentrum München, Neuherberg 85764, Germany.
7 Institute of Human Genetics, Klinikum rechts der Isar, School of Medicine, Technical University of Munich, Munich 81675, Germany; Department of Nephrology, Klinikum rechts der Isar, School of Medicine, Technical University of Munich, Munich 81675, Germany.
8 Department of Nephrology, Klinikum rechts der Isar, School of Medicine, Technical University of Munich, Munich 81675, Germany.
9 Department of Drug Discovery Medicine, Medical Innovation Center, Kyoto University Graduate School of Medicine, Kyoto 606-8507, Japan.
10 Department of Pediatrics, Center of Pediatric Nephrology & Transplantation, Kasr Al Ainy School of Medicine, Cairo University, Cairo 11562, Egypt; Egyptian Group for Orphan Renal Diseases (EGORD), Cairo, Egypt.
11 Department of Genetics, Yale University School of Medicine, New Haven, CT 06520, USA.
12 Laboratory of Human Genetics and Genomics, the Rockefeller University, New York, NY 10065-6399, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815-6789, USA.
13 Institute of Human Genetics, Klinikum rechts der Isar, School of Medicine, Technical University of Munich, Munich 81675, Germany.
14 Department of Pediatrics, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA. Electronic address: [email protected].

PMID: 33232676 DOI: 10.1016/j.ajhg.2020.11.008

Abstract

The discovery of >60 monogenic causes of nephrotic syndrome (NS) has revealed a central role for the actin regulators RhoA/Rac1/Cdc42 and their effectors, including the formin INF2. By whole-exome sequencing (WES), we here discovered bi-allelic variants in the formin DAAM2 in four unrelated families with steroid-resistant NS. We show that DAAM2 localizes to the cytoplasm in podocytes and in kidney sections. Further, the variants impair DAAM2-dependent actin remodeling processes: wild-type DAAM2 cDNA, but not cDNA representing missense variants found in individuals with NS, rescued reduced podocyte migration rate (PMR) and restored reduced filopodia formation in shRNA-induced DAAM2-knockdown podocytes. Filopodia restoration was also induced by the formin-activating molecule IMM-01. DAAM2 also co-localizes and co-immunoprecipitates with INF2, which is intriguing since variants in both formins cause NS. Using in vitro bulk and TIRF microscopy assays, we find that DAAM2 variants alter actin assembly activities of the formin. In a Xenopus daam2-CRISPR knockout model, we demonstrate actin dysregulation in vivo and glomerular maldevelopment that is rescued by WT-DAAM2 mRNA. We conclude that DAAM2 variants are a likely cause of monogenic human SRNS due to actin dysregulation in podocytes. Further, we provide evidence that DAAM2-associated SRNS may be amenable to treatment using actin regulating compounds.

Keywords

DAAM2; actin cytoskeleton; formins; monogenic kidney diseases; podocytopathy; steroid-resistant nephrotic syndrome.

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