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A Uromodulin Mutation Drives Autoimmunity and Kidney Mononuclear Phagocyte Endoplasmic Reticulum Stress.

ABSTRACT: We identified a family with a UMOD gene mutation (C106F) resulting in glomerular inflammation and complement deposition. To determine if the observed phenotype is due to immune system activation by mutant uromodulin, a mouse strain with a homologous cysteine to phenylalanine mutation (C105F) in the UMOD gene was generated using CRISPR-Cas9 gene editing and the effect of this mutation on mononuclear phagocytic cells was examined. Mutant mice developed high levels of intracellular and secreted aggregated uromodulin, resulting in anti-uromodulin antibodies and circulating uromodulin containing immune complexes with glomerular deposition and kidney fibrosis with aging. F4/80⁺ and CD11c⁺ kidney cells phagocytize uromodulin. Differential gene expression analysis by RNA sequencing of F4/80⁺ phagocytic cells revealed activation of the activating transcription factor 5 (ATF5)-mediated stress response pathway in mutant mice. Phagocytosis of mutant uromodulin by cultured dendritic cells resulted in activation of the endoplasmic reticulum stress response pathway and markers of cell inactivation, an effect not seen with wild-type protein. Mutant mice demonstrate a twofold increase in T-regulatory cells, consistent with induction of immune tolerance, resulting in decreased inflammatory response and improved tissue repair following ischemia-reperfusion injury. The C105F mutation results in autoantibodies against aggregated misfolded protein with immune complex formation and kidney fibrosis. Aggregated uromodulin may induce dendritic cell tolerance following phagocytosis through an unfolded protein/endoplasmic reticulum stress response pathway, resulting in decreased inflammation following tissue injury.

SUBMITTER: Plotkin M

PROVIDER: S-EPMC7722528 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Background: Uromodulin (Tamm-Horsfall) protein is secreted by the thick ascending limb into urine and crosses the basolateral membrane into the kidney interstitium and blood. Uromodulin may engage the kidney’s innate immune system with pro and anti-inflammatory effects described. Mutations in the UMOD gene are a cause of autosomal dominant tubulointerstitial kidney disease (ADTKD) due to protein misfolding and endoplasmic reticulum stress. We identified a family with a UMOD mutation (C106F) that leads to glomerular and interstitial inflammation atypical for ADTKD. Methods: To determine if the observed phenotype is due to mutant uromodulin induced changes in the innate or adaptive immune system, we developed a transgenic (tg) mouse with a homologous 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 mutant mice demonstrated aggregate formation not seen in wt mice. Tg/+ mice displayed increased F4/80+ mononuclear phagocyte (MP) and podocyte inflammasome activity at baseline. 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. Differential gene expression analysis by RNA sequencing of kidney MP revealed activation of the ATF4 mediated stress response pathway and genes associated with the development of tissue fibrosis. Conclusions: The C106F mutation results in glomerular and interstitial inflammatory kidney disease due to interaction of aggregated misfolded protein with mononuclear phagocytic cells resulting in ER stress response. The resulting alteration in the immune system leads to improved kidney repair following acute injury but fibrosis and chronic renal failure with aging.

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A Uromodulin Mutation Drives Autoimmunity and Kidney Mononuclear Phagocyte Endoplasmic Reticulum Stress.

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