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Abstract: PO0609

Rac1 Promotes Kidney Collecting Duct Integrity by Limiting Actomyosin Activity

Session Information

Category: Development, Stem Cells, and Regenerative Medicine

  • 500 Development, Stem Cells, and Regenerative Medicine

Authors

  • Bock, Fabian, Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Elias, Bertha C., Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Dong, Xinyu, Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Viquez, Olga, Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Fogo, Agnes B., Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Pozzi, Ambra, Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Zent, Roy, Vanderbilt University Medical Center, Nashville, Tennessee, United States
Background

A polarized collecting duct (CD) is critical for an intact kidney. The branched kidney collecting system is formed from the ureteric bud (UB). This requires a dynamic actin cytoskeleton and balanced actomyosin activity allowing normal tissue polarization, morphology and function. The small Rho GTPase, Rac1, is a key molecular switch that controls actin polymerization and branching. We investigated the role of Rac1 in kidney collecting system morphogenesis by selectively deleting it in mice at the initiation of UB development.

Methods

We crossed Rac1flox/flox (f/f) with Hoxb7-cre deleting Rac1 in the ureteric bud starting at E10.5 and followed kidney development throughout adulthood. We also analyzed the role of Rac1 in regulating signaling, migration, spreading, tubulogenesis and polarity by utilizing primary inner medullary collecting duct Rac1 null cells.

Results

The kidneys of Hoxb7:Rac1f/f exhibited only a mild branching morphogenesis defect as Rac1 is expressed after most UB branching is complete. However, with aging the CD developed a disruption of epithelial integrity, resulting in fibrosis, and a urine concentration defect. Despite intact integrin signaling, Rac1-null CD cells had profound spreading, adhesion and polarity abnormalities that were independent of the major downstream Rac1 effector, Pak1. Instead, Rac1 null cells demonstrated defective WAVE2-Arp2/3 dependent actin cytoskeletal branching which resulted in excessive actomyosin activity and severe abnormalities in epithelial cell shape. The functional and morphological defects caused by Rac1 deficiency were reversed by direct myosin II inhibition using low dose blebbistatin.

Conclusion

Unexpectedly, Rac1 does not play a major role in early branching morphogenesis of the renal collecting system, however it is required for adult CD integrity. Mechanistically, Rac1 controls Arp2/3-dependent cytoskeletal branching which limits actomyosin hyperactivity allowing normal epithelial polarization, function and morphology.

Funding

  • NIDDK Support