Broekhuizen, R. | bioRxiv Science

bioRxiv2023

Structural development of the human fetal kidney: new stages and cellular dynamics in nephrogenesis

Research on the ultrastructural development of the kidney is limited, and research on rodent kidneys prevails. Yet, large differences between rodent and human nephrogenesis exist and therefore translation between species is not desirable. At the same time, there is an increasing demand for human research, in addition to assessing the potential of novel therapies such as renal organoids. We therefore generated an interactive atlas of large transmission electron microscopy tile scans of first trimester human kidneys, specifically Carnegie stage 20 until post-conceptional week 12. Analysis identified key ultrastructural features of proximal and distal progenitor cells such as cell shape, microvilli and luminal budding in the renal vesicle. Regarding glomerular development, we identified a new W-shaped body stage and three distinct sub-stages of the well-known capillary loop stage. Chromatin organization, nuclear shape and location were used to describe tubule cell identity and maturity, indicating a specific order of tubular maturation. The greatest congruence with adult tissue was seen in proximal tubules and the least in distal tubules. Finally, cytoplasmic glycogen depositions in collecting duct cells, which are absent in adult tissue, were found to be an early feature distinguishing distal tubules from collecting ducts as well as differentiating cortical from medullary collecting ducts. The findings of this research provide new fundamental insights for researchers who aim to understand and recreate kidney development.

developmental biology↗

bioRxiv2020

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

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.

pharmacology and toxicology↗