Disruption of MAGI2-RapGEF2-Rap1 signaling contributes to podocyte dysfunction in congenital nephrotic syndrome caused by mutations in MAGI2.

Abstract

The essential role of membrane associated guanylate kinase 2 (MAGI2) in podocytes is indicated by the phenotypes of severe glomerulosclerosis of both MAGI2 knockout mice and in patients with congenital nephrotic syndrome (CNS) caused by mutations in MAGI2. Here, we show that MAGI2 forms a complex with the Rap1 guanine nucleotide exchange factor, RapGEF2, and that this complex is lost when expressing MAGI2 CNS variants. Co-expression of RapGEF2 with wild-type MAGI2, but not MAGI2 CNS variants, enhanced activation of the small GTPase Rap1, a central signaling node in podocytes. In mice, podocyte-specific RapGEF2 deletion resulted in spontaneous glomerulosclerosis, with qualitative glomerular features comparable to MAGI2 knockout mice. Knockdown of RapGEF2 or MAGI2 in human podocytes caused similar reductions in levels of Rap1 activation and Rap1-mediated downstream signaling. Furthermore, human podocytes expressing MAGI2 CNS variants show severe abnormalities of cellular morphology and dramatic loss of actin cytoskeletal organization, features completely rescued by pharmacological activation of Rap1 via a non-MAGI2 dependent upstream pathway. Finally, immunostaining of kidney sections from patients with congenital nephrotic syndrome and MAGI2 mutations showed reduced podocyte Rap1-mediated signaling. Thus, MAGI2-RapGEF2-Rap1 signaling is essential for normal podocyte function. Hence, disruption of this pathway is an important cause of the renal phenotype induced by MAGI2 CNS mutations.

• Authors: Bingbing Zhu, Aili Cao, Jianhua Li, James Young, Jenny Wong, Shazia Ashraf, Agnieszka Bierzynska, Madhav C Menon, Steven Hou, Charles Sawyers, Kirk N Campbell, Moin A Saleem, John C He, Friedhelm Hildebrandt, Vivette D D'Agati, Wen Peng, Lewis Kaufman
• Journal: Kidney international (Kidney Int) Vol. 96 Issue 3 Pg. 642-655 (09 2019) ISSN: 1523-1755 [Electronic] United States
• PMID: 31171376 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2019 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.

Chemical References

• 8-(4-chloro-phenylthio)-2'-O-methyladenosine-3'-5'-cyclic monophosphate
• Adaptor Proteins, Signal Transducing
• CNrasGEF protein, mouse
• Guanine Nucleotide Exchange Factors
• Nerve Tissue Proteins
• RAPGEF2 protein, human
• Shelterin Complex
• TERF2IP protein, human
• Telomere-Binding Proteins
• Cyclic AMP
• Guanylate Kinases
• MAGI2 protein, human
• Magi2 protein, mouse
• Rap1 protein, mouse
• rap1 GTP-Binding Proteins

Topics

• Adaptor Proteins, Signal Transducing (genetics, metabolism)
• Animals
• Cell Line
• Cyclic AMP (analogs & derivatives, pharmacology)
• Guanine Nucleotide Exchange Factors (genetics, metabolism)
• Guanylate Kinases (genetics, metabolism)
• Humans
• Mice
• Mice, Knockout
• Mutation
• Nephrotic Syndrome (genetics, pathology)
• Nerve Tissue Proteins (metabolism)
• Podocytes (pathology)
• Shelterin Complex
• Signal Transduction (drug effects, genetics)
• Telomere-Binding Proteins (agonists, metabolism)
• rap1 GTP-Binding Proteins (metabolism)