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Kidney Week

Abstract: SA-PO225

Ephrin-B1 Bound to Nephrin at the Slit Diaphragm Controls Podocyte Function through the JNK Pathway Independently with Nephrin Phosphorylation

Session Information

  • Glomerular: Cell Biology
    November 04, 2017 | Location: Hall H, Morial Convention Center
    Abstract Time: 10:00 AM - 10:00 AM

Category: Glomerular

  • 1003 Glomerular: Cell Biology

Authors

  • Fukusumi, Yoshiyasu, Dept. Cell Biology, Kidney Research Center, Niigata University, Niigata, Japan
  • Zhang, Ying, Dept. Cell Biology, Kidney Research Center, Niigata University, Niigata, Japan
  • Kawachi, Hiroshi, Dept. Cell Biology, Kidney Research Center, Niigata University, Niigata, Japan
Background

We have reported ephrin-B1 is a novel component of the slit diaphragm (SD), and interacts with nephrin via their extracellular domains in cis form. We also reported that the podocyte-specific ephrin-B1 conditional knockout (CKO) mice showed proteinuria and disarrangement of the SD molecules. However, the precise function of the ephrin-B1 and nephrin at the SD is not well elucidated yet.

Methods

The mechanisms of the phosphorylations of ephrin-B1 and nephrin, and their downstreams were analyzed with HEK293 cell system, the rat nephrotic model and the ephrin-B1 CKO mice. The role of the nephrin-binding ephrin-B1 in regulating cell function was analyzed.

Results

Analyses with the HEK cells showed that not only nephrin but also the nephrin-binding ephrin-B1 was phosphorylated by the anti-nephrin antibody stimulation, and that the phosphorylation was Src kinase dependent. By contrast, the nephrin bound to ephrin-B1 was not phosphorylated by the stimulation to ephrin-B1. The ephrin-B1 co-transfected with the truncated nephrin lacking phosphorylation sites was phosphorylated more evidently, indicating the nephrin phosphorylation lowered the phosphorylation of the nephrin-binding ephrin-B1. Although the phosphorylation of nephrin was enhanced by the co-expression with ephrin-B1, the co-expression of the ephrin-B1 lacking tyrosine residues did not enhance, indicating the phosphorylation of ephrin-B1 is necessary for the enhancement of nephrin phosphorylation. Ephrin-B1 phosphorylation was also detected in glomeruli of the nephrotic model caused by anti-nephrin antibody. The phosphorylated ephrin-B1 phosphorylated JNK evidently. By contrast, nephrin signaling did not phosphorylate JNK. JNK phosphorylation was not detected in glomeruli of the ephrin-B1 CKO mice. The wound-healing assay with the HEK cells showed that the phosphorylation of ephrin-B1 promoted the cell motility, while nephrin did not promote it.

Conclusion

The phosphorylations of nephrin and the nephrin-binding ephrin-B1 were causally regulated, and the phosphorylation of the ephrin-B1 transferred the signals to downstream via another route of the nephrin signaling. Ephrin-B1 controls podocyte function through JNK pathway. The ephrin-B1 resided together with nephrin at the SD plays an essential role in maintaining the podocyte function.

Funding

  • Government Support - Non-U.S.