Fengmin Li1, Jian Yang2,3, Van Anthony M Villar2,4, Laureano D Asico2,4, Xiaobo Ma4, Ines Armando2,4, Hironobu Sanada5, Minoru Yoneda5, Robin A Felder6, Pedro A Jose2,4,7, Xiaoyan Wang8,9. 1. Department of Physiology and Biophysics, Georgetown University Medical Center, Washington, DC, USA. 2. Division of Nephrology, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA. 3. Department of Nutrition, The Third Affiliated Hospital of Chongqing Medical University, Chongqing, People's Republic of China. 4. Division of Renal Diseases and Hypertension, Department of Medicine, The George Washington University, Walter G. Ross Hall, Suite 740-C, 2300 I Street, N.W., Washington, DC, 20037, USA. 5. Division of Health Science Research, Fukushima Welfare Federation of Agricultural Cooperatives, Fukushima, Japan. 6. Department of Pathology, The University of Virginia, Charlottesville, VA, USA. 7. Department of Pharmacology and Physiology, The George Washington University, Washington, DC, USA. 8. Division of Nephrology, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA. xywang@gwu.edu. 9. Division of Renal Diseases and Hypertension, Department of Medicine, The George Washington University, Walter G. Ross Hall, Suite 740-C, 2300 I Street, N.W., Washington, DC, 20037, USA. xywang@gwu.edu.
Abstract
AIMS/HYPOTHESIS: We hypothesised that renal sorting nexin 5 (SNX5) regulates the insulin-degrading enzyme (IDE) and, thus, circulating insulin levels. We therefore studied the dynamic interaction between SNX5 and IDE in human renal proximal tubule cells (hRPTCs), as well as in rat and mouse kidneys. METHODS: The regulation of IDE by SNX5 expressed in the kidney was studied in vitro and in vivo. Snx5 or mock siRNA was added to immortalised hRPTCs (passage <20) in culture or selectively infused, via osmotic mini-pump, into the remnant kidney of uninephrectomised mice and rats. RESULTS: SNX5 co-localised with IDE at the plasma membrane and perinuclear area of hRPTCs and in the brush border membrane of proximal tubules of human, rat, and mouse kidneys. Insulin increased the co-localisation and co-immunoprecipitation of SNX5 and IDE in hRPTCs. Silencing SNX5 in hRPTCs decreased IDE expression and activity. Renal-selective silencing of Snx5 (SNX5 protein: 100 ± 25 vs 29 ± 10, p < 0.05 [% of control]) in C57Bl/6J mice decreased IDE protein (100 ± 13 vs 57 ± 6, p < 0.05 [% of control]) and urinary insulin excretion, impaired the responses to insulin and glucose, and increased blood insulin and glucose levels. Spontaneously hypertensive rats (SHRs) had increased blood insulin and glucose levels and decreased renal SNX5 (100 ± 27 vs 29 ± 6, p < 0.05 [% of control]) and IDE (100 ± 5 vs 75 ± 4, p < 0.05 [% of control]) proteins, compared with normotensive Wistar-Kyoto (WKY) rats. Kidney Snx5-depleted WKY rats also had increased blood insulin and glucose levels. The expression of SNX5 and IDE was decreased in RPTCs from SHRs and hypertensive humans compared with cells from normotensive volunteers, indicating a common cause for hyperinsulinaemia and hypertension. CONCLUSIONS/ INTERPRETATION: Renal SNX5 positively regulates IDE expression and function. This study is the first to demonstrate the novel and crucial role of renal SNX5 in insulin and glucose metabolism.
AIMS/HYPOTHESIS: We hypothesised that renal sorting nexin 5 (SNX5) regulates the insulin-degrading enzyme (IDE) and, thus, circulating insulin levels. We therefore studied the dynamic interaction between SNX5 and IDE in human renal proximal tubule cells (hRPTCs), as well as in rat and mouse kidneys. METHODS: The regulation of IDE by SNX5 expressed in the kidney was studied in vitro and in vivo. Snx5 or mock siRNA was added to immortalised hRPTCs (passage <20) in culture or selectively infused, via osmotic mini-pump, into the remnant kidney of uninephrectomised mice and rats. RESULTS:SNX5 co-localised with IDE at the plasma membrane and perinuclear area of hRPTCs and in the brush border membrane of proximal tubules of human, rat, and mouse kidneys. Insulin increased the co-localisation and co-immunoprecipitation of SNX5 and IDE in hRPTCs. Silencing SNX5 in hRPTCs decreased IDE expression and activity. Renal-selective silencing of Snx5 (SNX5 protein: 100 ± 25 vs 29 ± 10, p < 0.05 [% of control]) in C57Bl/6J mice decreased IDE protein (100 ± 13 vs 57 ± 6, p < 0.05 [% of control]) and urinary insulin excretion, impaired the responses to insulin and glucose, and increased blood insulin and glucose levels. Spontaneously hypertensiverats (SHRs) had increased blood insulin and glucose levels and decreased renal SNX5 (100 ± 27 vs 29 ± 6, p < 0.05 [% of control]) and IDE (100 ± 5 vs 75 ± 4, p < 0.05 [% of control]) proteins, compared with normotensive Wistar-Kyoto (WKY) rats. Kidney Snx5-depleted WKY rats also had increased blood insulin and glucose levels. The expression of SNX5 and IDE was decreased in RPTCs from SHRs and hypertensivehumans compared with cells from normotensive volunteers, indicating a common cause for hyperinsulinaemia and hypertension. CONCLUSIONS/ INTERPRETATION: Renal SNX5 positively regulates IDE expression and function. This study is the first to demonstrate the novel and crucial role of renal SNX5 in insulin and glucose metabolism.
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