Abstract: SA-OR006

The Interaction between MAGI2 and RapGEF2 Sustains Podocyte Rap1GTPase Signaling and Is Critical for Glomerular Filter Function

Session Information

  • A View on the Glomerulus
    November 04, 2017 | Location: Room 294, Morial Convention Center
    Abstract Time: 05:30 PM - 05:42 PM

Category: Glomerular

  • 1003 Glomerular: Cell Biology

Authors

  • Zhu, Bingbing, Icahn School of Medicine at Mount Sinai, New York, United States
  • Hildebrandt, Friedhelm, Boston Childrens Hospital, Harvard Medical School, Boston, Massachusetts, United States
  • D'Agati, Vivette D., Columbia University College of Physicians and Surgeons, New York, New York, United States
  • Peng, Wen, Putuo Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai, China
  • Kaufman, Lewis, Icahn School of Medicine at Mount Sinai, New York, New York, United States
  • Li, Jianhua, Icahn School of Medicine at Mount Sinai, New York, New York, United States
  • Wong, Jenny, Icahn School of Medicine at Mount Sinai, New York, New York, United States
  • Campbell, Kirk N., Icahn School of Medicine at Mount Sinai, New York, New York, United States
  • Ashraf, Shazia, Boston Childrens Hospital, Harvard Medical School, Boston, Massachusetts, United States
  • Bierzynska, Agnieszka, University of Bristol, Bristol, United Kingdom
  • Saleem, Moin, University of Bristol, Bristol, United Kingdom
  • Sawyers, Charles, MSKCC, New York, New York, United States
  • He, John C., Icahn School of Medicine at Mount Sinai, New York, New York, United States
Background

The essential role of MAGI2 in proper podocyte function is reflected by the severe FSGS phenotypes of both MAGI2 knockout mice and of humans with congenital nephrotic syndrome (CNS) caused by mutations in MAGI2.

Results

In the current work, we perform co-immunoprecipitation experiments that show MAGI2 directly binds the Rap1 guanine nucleotide exchange factor, RapGEF2, and that this interaction is lost when expressing MAGI2 variants that cause CNS. In cultured cells, co-expression of RapGEF2 with wild-type MAGI2, but not MAGI2 variants known to cause CNS, dramatically enhanced activation of the small GTPase Rap1, a pathway we previously demonstrated to be essential for normal podocyte function. Furthermore, in mice, podocyte specific deletion of RapGEF2 resulted in spontaneous proteinuria with FSGS, substantiating the critical importance of RapGEF2 to sustain normal podocyte function. Although the FSGS phenotype of MAGI2 knockout mice is considerably more severe than that of RapGEF2, both models show comparable qualitative glomerular features including mesangial expansion, focal segmental and global sclerosis, podocyte loss, and glomerular epithelial cell proliferation, suggesting mechanistic similarities. Indeed, knockdown of either RapGEF2 or MAGI2 in cultured podocytes caused nearly identical reductions in levels of Rap1GTPase activation, dramatic reductions in many Rap1 downstream signaling targets, and similarly high rates of podocyte apoptosis. Finally, immunostaining of kidney sections from CNS patients with MAGI2 mutations also suggested reduced glomerular Rap1GTPase mediated signaling.

Conclusion

We conclude that Rap1 activation induced by the complex of MAGI2 and RapGEF2 is indispensable for normal podocyte homeostasis.

Funding

  • NIDDK Support