Kidney Week

Abstract: SA-PO104

Dysregulation of the Ubiquitin Ligase Component Kelch-Like 3 Causes Na-Cl Cotransporter Activation and Salt Retention in Type 2 Diabetes Mellitus

Session Information

• Diabetic Kidney Disease: Basic - III
  October 27, 2018 | Location: Exhibit Hall, San Diego Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Diabetic Kidney Disease

• 601 Diabetic Kidney Disease: Basic

Authors

• Ishizawa, Kenichi, Teikyo University School of Medicine , Tokyo, Japan

Kenichi Ishizawa,

• Wang, Qin, Teikyo University School of Medicine , Tokyo, Japan

Qin Wang,

• Li, Jinping, Teikyo University School of Medicine , Tokyo, Japan

Jinping Li,

• Nemoto, Yoshikazu, Teikyo University School of Medicine , Tokyo, Japan

Yoshikazu Nemoto,

• Morimoto, Chikayuki, Teikyo University School of Medicine , Tokyo, Japan

Chikayuki Morimoto,

• Fujita, Toshiro, The University of Tokyo, Tokyo, Japan

Toshiro Fujita,

• Uchida, Shunya, Teikyo University School of Medicine , Tokyo, Japan

Shunya Uchida,

• Shibata, Shigeru, Teikyo University School of Medicine , Tokyo, Japan

Shigeru Shibata,

Background

Salt-sensitive hypertension is frequently associated with type 2 DM. However, the pathogenesis remains unclear. Kelch-like 3 (KLHL3) is a component of an E3 ubiquitin ligase complex that targets With-No-Lysine kinases for degradation, thereby regulating downstream Na-Cl cotransporter (NCC). Mutations and inactivation of KLHL3 increase NCC activity, resulting in hypertension and hyperkalemia. Previously, we have reported that angiotensin II (Shibata et al. PNAS 2014) and K⁺ depletion (Ishizawa et al. BBRC 2016) inactivate KLHL3 by protein kinase C (PKC)-mediated phosphorylation at S433 in the Kelch-domain. In this study, we examined the possible involvement of KLHL3 in the diabetic kidney, using a model of type 2 diabetes.

Methods

KLHL3 phosphorylated at S433 (KLHL3^S433-P), total KLHL3, and NCC levels were evaluated in the kidney of db/db mice by Western blotting. In some experiments, db/db mice received a PKC inhibitor bisindolylmaleimide I (BIMI), SGLT2 inhibitor ipragliflozin, and a thiazolidinedione pioglitazone.

Results

KLHL3^S433-P, NCC and active PKC levels were all increased in the kidney of db/db mice. Administration of BIM to db/db mice significantly reduced KLHL3^S433-P and NCC levels (P < 0.05). Consistently, urinary Na⁺ levels were increased in db/db mice receiving BIM (76 ± 8.7 μEq/6h in db/db mice receiving BIM vs. 48 ± 4.5 μEq/6h in db/db mice receiving vehicle; P < 0.05). To evaluate the effects of SGLT2 inhibition on this pathway, db/db mice received ipragliflozin or pioglitazone (as a control). Of note, KLHL3 phosphorylation and NCC induction were reduced by ipragliflozin but not by pioglitazone, although blood glucose levels were similarly reduced by the two hypoglycemic agents. PKC activity was reduced by ipragliflozin but not by pioglitazone, explaining the distinct effects of the two hypoglycemic agents on KLHL3 and NCC.

Conclusion

These data demonstrate the involvement of KLHL3 in the increased salt reabsorption in obese diabetes mellitus, and provide insights into the mechanisms for the protective effect of SGLT2 inhibitors.

Funding

• Government Support - Non-U.S.