Insulin receptor signaling regulates renal collecting duct and intercalated cell antibacterial defenses
Matthew J. Murtha, … , Brian Becknell, John David Spencer
Matthew J. Murtha, … , Brian Becknell, John David Spencer
Published November 12, 2018
Citation Information: J Clin Invest. 2018;128(12):5634-5646. https://doi.org/10.1172/JCI98595.
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Research Article Immunology Nephrology

Insulin receptor signaling regulates renal collecting duct and intercalated cell antibacterial defenses

Abstract

People with diabetes mellitus have increased infection risk. With diabetes, urinary tract infection (UTI) is more common and has worse outcomes. Here, we investigate how diabetes and insulin resistance impact the kidney’s innate defenses and urine sterility. We report that type 2 diabetic mice have increased UTI risk. Moreover, insulin-resistant prediabetic mice have increased UTI susceptibility, independent of hyperglycemia or glucosuria. To identify how insulin resistance affects renal antimicrobial defenses, we genetically deleted the insulin receptor in the kidney’s collecting tubules and intercalated cells. Intercalated cells, located within collecting tubules, contribute to epithelial defenses by acidifying the urine and secreting antimicrobial peptides (AMPs) into the urinary stream. Collecting duct and intercalated cell–specific insulin receptor deletion did not impact urine acidification, suppressed downstream insulin-mediated targets and AMP expression, and increased UTI susceptibility. Specifically, insulin receptor–mediated signaling regulates AMPs, including lipocalin 2 and ribonuclease 4, via phosphatidylinositol-3-kinase signaling. These data suggest that insulin signaling plays a critical role in renal antibacterial defenses.

Authors

Matthew J. Murtha, Tad Eichler, Kristin Bender, Jackie Metheny, Birong Li, Andrew L. Schwaderer, Claudia Mosquera, Cindy James, Laura Schwartz, Brian Becknell, John David Spencer

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Figure 6

Insulin-mediated PI3K/AKT activation regulates AMP expression.

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Insulin-mediated PI3K/AKT activation regulates AMP expression. (A and B)...
(A and B) Lcn2 and RNase4 mRNA expression in mOMCD1, mIMCD3, and human renal epithelial cells treated with vehicle control (gray bars) or insulin (white bars) for 24 hours. AMP expression is derived from 3 independent experiments performed in triplicate (n = 3). Columns represent mean and SEM. Asterisks denote significant P values for the indicated pairwise comparisons (Student’s t test). (C) Representative Western blots probed for pAKT (ser473), RNase4, and GAPDH from human renal epithelial cells treated with insulin with or without wortmannin (wort). (D) ELISA quantitated Lcn2 concentrations in renal epithelial cell culture media following insulin with or without wortmannin treatment (n = 3). Columns represent mean and SEM. Asterisks indicate significant P values for the indicated pairwise comparison as determined by 1-way ANOVA with Tukey’s test. (E) Relative Lcn2 and Rnase4 mRNA expression in noninfected kidneys from wortmannin (striped bars) or vehicle-treated (white bars) C57BL/6J mice (n = 6 mice/treatment). (F) One hour before UPEC challenge, female C57BL/6J mice were treated with intraperitoneal wortmannin (squares) or vehicle control (circles). At 6 HPI, urine was collected, bladders were harvested, and UPEC colonies were enumerated. The horizontal line indicates the geometric mean. (E, F) Asterisks denote significant P values for the pairwise comparisons (Mann-Whitney U test). (G) Representative Western blots confirm wortmannin suppression of renal AKT (ser473) phosphorylation. Each lane shows kidney pAKT activity from a separate mouse. *P < 0.05, **P < 0.01, ***P < 0.001.