Kidney Week

Abstract: FR-OR114

Keap1/Nrf2 Signaling Reveals Homeostatic Function in Renal and Cardiovascular Physiology

Session Information

• Stress Signaling and Fibrosis
  November 03, 2017 | Location: Room 277, Morial Convention Center
  Abstract Time: 06:18 PM - 06:30 PM

Category: Cell Biology

• 201 Cell Signaling, Oxidative Stress

Authors

• Jobbagy, Soma, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States

Soma Jobbagy

• Vitturi, Dario A, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States

Dario A Vitturi,

• Salvatore, Sonia Rosana, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States

Sonia Rosana Salvatore,

• Hahn, Scott, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States

Scott Hahn,

• Straub, Adam, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States

Adam Straub,

• Subramanya, Arohan R., University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States

Arohan R. Subramanya,

• Freeman, Bruce, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States

Bruce Freeman,

• Schopfer, Francisco J, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States

Francisco J Schopfer,

Background

Keap1/Nrf2 signaling is well-established as a master regulator of cellular responses to oxidative stress; however, recent findings suggest that this pathway additionally performs key functions in renal solute and water homeostasis. Herein we study the functional consequences of constitutive graded Nrf2 activation on renal salt and water handling and integrate renal and cardiovascular endpoints.

Methods

Wild-type, Keap1 hypomorphic (Keap1^f/f), and Nrf2^-/- mice were studied under control conditions or in response to dietary sodium maneuvers, and renal and plasma biomarkers were assayed by IF, PCR, immunoblot, and HPLC-MS/MS. Cardiovascular function was assessed by radiotelemetry and wire myography.

Results

Keap1^f/f mice exhibited 5-fold upregulation of Nrf2 target gene NQO1 in the kidney and were polyuric. Consistent with a urine concentrating defect and volume depletion, hematocrits were higher in the Keap1^f/f cohort (45.5% vs 37.2% WT). The latter was not attributable to upregulation of renal EPO expression or increased RBC antioxidant enzyme production, and resolved after salt loading. 2-fold down-regulated expression of total NKCC2 and NCC by western blot implicated a distal nephron defect. Compensatory activation of WNK signaling was consistent with 2-fold elevation in plasma renin activity and led to 3-fold increase in phospho-to-total NCC ratio in Keap1^f/f mice after sodium depletion. Finally, 2-fold reduction in renal cycolooxygenase-1 and -2 in Keap1^f/f mice suggests crosstalk between Nrf2 and prostaglandin signaling, and resulted in reduction in vasodilatory PGI₂. Blood pressure was unchanged between WT and Keap1^f/f mice, however heart rate was significantly depressed in the Keap1^f/f cohort. Wire myography revealed impaired vasodilation of resistance arteries in response to ACh.

Conclusion

Mice with genetic Keap1 hypomorphism were studied as a pharmacomimetic model of chemical Nrf2 inducers to delineate physiologic effects of this pathway. Keap1^f/f mice display distal nephron defect with reduced urine concentrating function and volume depletion. Compensatory activation of RAS- and WNK-signaling likely serves to mitigate solute and water loss in this model. Differences in prostanoid biosynthesis suggest a mechanism underlying renal and vascular effects of constitutive Nrf2 activity.

Funding

• NIDDK Support