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 2

IR deletion in renal collecting ducts and ICs.

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IR deletion in renal collecting ducts and ICs. (A) The Insr lox allele b...
(A) The Insr lox allele before (IRflox) and after Cre-mediated exon 4 deletion (IRKO). The arrows labeled P2 and P3 indicate the PCR primer position. (B) Schematic of the breeding strategy used to delete the IR in renal collecting ducts and ICs using KSP-Cre and V-ATPase-Cre transgenic mice, respectively. (C) PCR shows a single 488-bp product indicative of the IR lox allele in kidneys and bladders of IRflox mice. In IRKO mouse kidneys, PCR generated the 488-bp product and a smaller 388-bp product. The 388-bp product confirms organ-specific Insr exon 4 deletion and the 488-bp product is attributed to other renal cell types in which Cre-recombination did not occur. Gapdh served as a loading control. Each lane identifies results from a separate mouse. (D) Relative Insr transcript expression in total kidney homogenate, dissected medulla, and FACS-isolated ICs from IRKO mice (white bars) compared with IRflox control mice (gray bars). Asterisks denote significance among genotypes (n = 5–6 mice/genotype; unpaired t test). *P < 0.05, **P < 0.01. (E) Representative Western blots probed for β-IR and GAPDH in dissected renal medulla and FACS-isolated ICs from IRflox and IRKO mice. (F) Western blots probed for pAKT (ser473) and GAPDH in dissected renal medulla from insulin-treated IRflox and IRKO mice. Each lane depicts kidney AKT phosphorylation from separate mice.