Mutant uromodulin expression leads to altered homeostasis of the endoplasmic reticulum and activates the unfolded protein response

Abstract

Uromodulin is the most abundant urinary protein in physiological conditions. It is exclusively produced by renal epithelial cells lining the thick ascending limb of Henle’s loop (TAL) and it plays key roles in kidney function and disease. Mutations in UMOD, the gene encoding uromodulin, cause autosomal dominant tubulointerstitial kidney disease uromodulin-related (ADTKD-UMOD), characterised by hyperuricemia, gout and progressive loss of renal function. While the primary effect of UMOD mutations, retention in the endoplasmic reticulum (ER), is well established, its downstream effects are still largely unknown. To gain insight into ADTKD-UMOD pathogenesis, we performed transcriptional profiling and biochemical characterisation of cellular models (immortalised mouse TAL cells) of robust expression of wild type or mutant GFP-tagged uromodulin. In this model mutant uromodulin accumulation in the ER does not impact on cell viability and proliferation. Transcriptional profiling identified 109 genes that are differentially expressed in mutant cells relative to wild type ones. Up-regulated genes include several ER resident chaperones and protein disulphide isomerases. Consistently, pathway enrichment analysis indicates that mutant uromodulin expression affects ER function and protein homeostasis. Interestingly, mutant uromodulin expression induces the Unfolded Protein Response (UPR), and specifically the IRE1 branch, as shown by an increased splicing of XBP1. Consistent with UPR induction, we show increased interaction of mutant uromodulin with ER chaperones Bip, calnexin and PDI. Using metabolic labelling, we also demonstrate that while autophagy plays no role, mutant protein is partially degraded by the proteasome through ER-associated degradation. Our work demonstrates that ER stress could play a central role in ADTKD-UMOD pathogenesis. This sets the bases for future work to develop novel therapeutic strategies through modulation of ER homeostasis and associated protein degradation pathways.

Autosomal Dominant Tubulointerstitial Kidney Disease with Adult Onset due to a Novel Renin Mutation Mapping in the Mature Protein

“…In view of the results emerging from ADTKD literature, it is interesting to note that ER homeostasis could actually be a common denominator not only for ADTKD- REN but more generally for all forms part of this heterogeneous disease. First, in the case of UMOD , the ADTKD gene for which mutations have been studied the most at the molecular level, ER stress and induction of pro-inflammatory cytokines have been identified as important factors in the disease pathogenesis 20–25 . Second, ADTKD- MUC1 is likely due to altered protein homeostasis as intracellular accumulation of aberrant, frameshifted protein MUC1-fs is necessary to trigger kidney disease 1 .…”

Biallelic Expression of Mucin-1 in Autosomal Dominant Tubulointerstitial Kidney Disease: Implications for Nongenetic Disease Recognition

“…This circumstance is very similar to the situation in ADTKD-UMOD, where mutant protein accumulates in the endoplasmic reticulum and leads to an unfolded protein response in humans and recent mouse models. [28][29][30][31] A clear distinction between the two diseases is becoming more evident. In UMOD-associated disease, many different pathogenic mutations have been described, 32 whereas all MUC1 mutations found to date effectively lead to the same aberrant protein.…”

ERp29 counteracts the suppression of malignancy mediated by endoplasmic reticulum stress and promotes the metastasis of colorectal cancer

“…ERS is one of the known hemostatic imbalances of bioactivity occurring in an attempt to maintain the functions of the cells (38,39). Numerous environmental changes including modifying the canonical protein synthesis machinery may induce cell ERS (40,41). Molecular chaperone proteins function as a protective measure in ERS, and ERp29, a pivotal component, has been associated with cancer of the breast, gallbladder and pancreas (42–44).…”