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Kidney Week

Abstract: TH-PO807

A Uromodulin Mutation Resulting in Innate Immune System Activation

Session Information

Category: Genetic Diseases of the Kidneys

  • 1002 Genetic Diseases of the Kidneys: Non-Cystic

Authors

  • Plotkin, Matthew D., University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States
  • Stone, Annjanette, Central Arkansas Veterans Healthcare System, Little Rock, Arkansas, United States
Background

Uromodulin (Tamm-Horsfall) is secreted by the thick ascending limb into urine but also crosses basolateral membranes into the interstitium and blood. Uromodulin may function as part of kidney’s innate immune system with pro and anti-inflammatory effects. Mutations in the UMOD gene are a cause of autosomal dominant tubulointerstitial kidney disease (ADTKD) due to tubular injury and endoplasmic reticulum (ER) stress. We identified a family with a novel UMOD mutation (C106F). Biopsies from affected members showed glomerular and interstitial inflammation atypical for ADTKD.

Methods

To determine if this mutation causes the observed phenotype through changes in membrane targeting and activation of the innate immune system, we examined a kidney epithelial cell line with stable transfection of mutant protein and developed a transgenic (tg) mouse with an orthologous cysteine to phenylalanine mutation (C105F) in the UMOD gene using CRISPR-Cas9 gene editing.

Results

LLC-PK1 cells expressing wt and mutant protein had increased basolateral secretion of protein compared with cells expressing wt or mutant protein alone. EM examination of mutant medium showed protein aggregates in contrast to filaments in wt medium. Immunoprecipitation of plasma uromodulin from tg/tg mice demonstrated dimer formation not seen in tg/+ or wt mice. Tg/+ and tg/tg mice displayed increased inflammasome activity at baseline with increased NLRP3 receptor, phospho NF-kB p65 and cleaved caspase 11 levels but no expression of ER stress markers. NLRP3 expression was located in macrophages and podocytes. Tg/+ mice developed glomerular and interstitial matrix deposition, myofibroblast proliferation and increased creatinine with aging. Following ischemia-reperfusion injury, tg/+ mice had no increase in inflammasome activation over baseline in contrast to wt littermates and displayed improved tubular repair and renal function at 7 days.

Conclusion

In summary, the C106F mutation results in glomerular and interstitial inflammatory kidney disease. A mouse model demonstrates that mutant protein enters the interstitium and blood and activates the innate immune system resulting in fibrosis with aging but improved repair following acute injury.

Funding

  • Veterans Affairs Support