ER-associated degradation in cystinosis pathogenesis and the prospects of precision medicine
Varsha Venkatarangan, … , Si Houn Hahn, Ming Li
Varsha Venkatarangan, … , Si Houn Hahn, Ming Li
Published August 10, 2023
Citation Information: J Clin Invest. 2023;133(19):e169551. https://doi.org/10.1172/JCI169551.
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Research Article Cell biology Nephrology

ER-associated degradation in cystinosis pathogenesis and the prospects of precision medicine

Abstract

Cystinosis is a lysosomal storage disease that is characterized by the accumulation of dipeptide cystine within the lumen. It is caused by mutations in the cystine exporter, cystinosin. Most of the clinically reported mutations are due to the loss of transporter function. In this study, we identified a rapidly degrading disease variant, referred to as cystinosin(7Δ). We demonstrated that this mutant is retained in the ER and degraded via the ER-associated degradation (ERAD) pathway. Using genetic and chemical inhibition methods, we elucidated the roles of HRD1, p97, EDEMs, and the proteasome complex in cystinosin(7Δ) degradation pathway. Having understood the degradation mechanisms, we tested some chemical chaperones previously used for treating CFTR F508Δ and demonstrated that they could facilitate the folding and trafficking of cystinosin(7Δ). Strikingly, chemical chaperone treatment can reduce the lumenal cystine level by approximately 70%. We believe that our study conclusively establishes the connection between ERAD and cystinosis pathogenesis and demonstrates the possibility of using chemical chaperones to treat cystinosin(7Δ).

Authors

Varsha Venkatarangan, Weichao Zhang, Xi Yang, Jess Thoene, Si Houn Hahn, Ming Li

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Figure 5

Cystinosin(7Δ)-GFP is degraded by the ERAD pathway.

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Cystinosin(7Δ)-GFP is degraded by the ERAD pathway. (A) CHX chase assay ...
(A) CHX chase assay of cystinosin(7Δ)-GFP in cells pretreated with either vehicle or Kifunensine (1.5 μg/mL). Kifunensine was treated for 16 hours before addition of CHX. (B and C) Quantification of bands 1 and 3 in A. (D) Cystinosin(7Δ)-GFP has a stronger interaction with HRD1 than WT cystinosin-GFP. (E) Relative levels of HRD1 precipitated by either cystinosin(7Δ)-GFP (100%) or WT cystinosin-GFP (1.12%). (F) Knocking out HRD1 stabilizes band 1, but not band 3, of cystinosin(7Δ)-GFP. (G) Quantification of relative protein levels of bands 1 and 3 in E. (H) Knockdown stabilizes both bands 1and 3 of cystinosin(7Δ)-GFP. (I and J) Quantification of relative protein levels of bands 1and 3 in G. Error bars: SD. All quantifications and data analysis were performed based on 3 independent replicates.