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Abstract: PO0672

FRMD3/Protein 4.1O Increases Hippo Signaling in a Glucose-Dependent Manner

Session Information

Category: Diabetic Kidney Disease

  • 601 Diabetic Kidney Disease: Basic

Authors

  • Koenigshausen, Eva, Heinrich-Heine-Universitat Dusseldorf, Dusseldorf, Nordrhein-Westfalen, Germany
  • Matten, Larissa, Heinrich-Heine-Universitat Dusseldorf, Dusseldorf, Nordrhein-Westfalen, Germany
  • Rieckmann, Sonja, Heinrich-Heine-Universitat Dusseldorf, Dusseldorf, Nordrhein-Westfalen, Germany
  • Vienken, Theresia, Heinrich-Heine-Universitat Dusseldorf, Dusseldorf, Nordrhein-Westfalen, Germany
  • Wiech, Thorsten, Institute of Pathology, University Hospital Hamburg-Eppendorf, Hamburg, Germany
  • Rump, Lars C., Heinrich-Heine-Universitat Dusseldorf, Dusseldorf, Nordrhein-Westfalen, Germany
  • Sellin, Lorenz, Heinrich-Heine-Universitat Dusseldorf, Dusseldorf, Nordrhein-Westfalen, Germany
Background

FRMD3 is as a candidate gene for diabetic nephropathy and encodes for protein 4.1O. Different splice variants 207, 204, 201 are expressed in the kidney cortex. Previous data show that protein 4.1O links nephrin to the actin cytoskeleton.
In diabetic kidney disease Hippo signaling is increased. Phosphorylated Yes-associated kinase (YAP) and its paralogue TAZ are sequestered into the cytoplasm and degraded (Hippo signaling on). Unphosphorylated YAP/TAZ translocates into the nucleus and activates target genes via different transcription factors (Hippo signaling off).

Methods

Human kidney biopsy samples from healthy and diabetic patients were stained for protein 4.1O with immunohistochemistry. HEK293T cells were stimulated with low (5mmol/l) or high (25 mmol/l) glucose and an osmotic control (mannitol). RNA was isolated and PCR performed. HEK293T cells expressed protein 4.1O 207, 201, 204 or the control vector. Cells were stimulated with low, high glucose or mannitol. After cell lysis, westernblot was performed for phospho-YAP 397 and actin. Co-immunopreciptiation was performed under high, low and osmotic control conditions.

Results

Protein 4.1O expression is detected in healthy human glomeruli. In diabetic patients with CKD stage 3b to 5 and gross proteinuria protein 4.1O expression is increased in podocytes. High glucose leads to enhanced transcription of FRMD3. Under high glucose condition, protein 4.1O 207 and 201 significantly increase YAP phosphorylation. However, protein 4.1O 204 (lacking a c-terminal domain) does not increase YAP phosphorylation under high glucose condition. Functionally, protein 4.1O 207 and nephrin interaction is increased under high glucose conditions.

Conclusion

Expression of protein 4.1O is increased in human diabetic kidney disease and under high glucose conditions. Hippo Signaling is activated under high glucose conditions if protein 4.1O 207 and 201, but not 204, is expressed. The lacking cytoplasmic domain in protein 4.1O 201 may play the essential role in controlling Hippo signaling under high glucose conditions. Identifying the underlying pathomechanism for glucose-dependent regulation of the Hippo pathway by different splice variants of protein 4.1O will help to understand its molecular function in diabetic nephropathy.