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The lysosomal V-ATPase B1 subunit in proximal tubule is linked to nephropathic cystinosis

Jamalpoor, A.; van Eerde, A.; Lilien, M. R.; van Gelder, C. A.; Zaal, E. A.; Valentijn, F. A.; Broekhuizen, R.; zielhuis, E.; Egido, J. E.; Altelaar, M.; Berkers, C. R.; Masereeuw, R.; Janssen, M. J.

2020-07-25 pharmacology and toxicology
10.1101/2020.07.24.219808 bioRxiv
Show abstract

Variants in ATP6V1B1, the gene encoding the B1 subunit of the vacuolar H+-ATPase lead to distal renal tubular acidosis and hearing loss of variable degree. Apart from metabolic acidosis, a 23-month-old girl with pathogenic ATP6V1B1 variants presented with increased granulocyte cystine levels, and symptoms of renal Fanconi syndrome, indicating an unknown link to proximal tubulopathy and cystinosis, a disorder of the proximal tubule caused by variants in the CTNS gene. Here, we demonstrated that ATP6V1B1 is expressed in proximal tubules of human kidney tissue, though to a lesser extent than in distal tubules. Further, we used CRISPR/Cas9 technology to selectively knockout ATP6V1B1 or CTNS in human renal proximal tubule cells and performed a full metabolomic and proteomic analysis to compare their phenotype to isogenic control cells. In line with the clinical data, the loss of ATP6V1B1 disrupted the chemiosmotic coupling between the lysosomal V ATPase B1 subunit and cystinosin and resulted in intralysosomal accumulation of cystine and autophagy activation in renal proximal tubule cells. In conclusion, we identified ATP6V1B1 as a central player in renal proximal tubule cells, regulating lysosomal cystine transport and autophagy, and its absence can lead to proximal tubule dysfunction.

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