MaryAnne Achieng

The kidney maintains fluid homeostasis by reabsorbing essential compounds and excreting waste. Proximal tubule cells, crucial for reabsorbing sugars, ions, and amino acids, are highly susceptible to injury, often leading to pathologies necessitating dialysis or transplants. Human pluripotent stem cell-derived kidney organoids offer a platform to model renal development, function, and disease, but proximal nephron differentiation and maturation in these structures is incomplete. Here, we drive proximal tubule development in pluripotent stem cell-derived kidney organoids by mimicking in vivo proximal differentiation. Transient PI3K inhibition during early nephrogenesis activates Notch signaling, shifting nephron axial differentiation towards epithelial and proximal precursor states that mature to proximal convoluted tubule cells broadly expressing physiology-imparting solute carriers including organic cation and organic anion family members. The "proximal-biased" organoids thus acquire function, and on exposure to nephrotoxic injury, display tubular collapse and DNA damage, and upregulate injury response markers HAVCR1/KIM1 and SOX9 while downregulating proximal transcription factor HNF4A. Here, we show that proximally biased human-derived kidney organoids provide a robust model to study nephron development, injury responses, and a platform for therapeutic discovery.

Abstract Current human pluripotent stem cell-derived kidney organoids contain nephron-like structures that lack organotypic patterning. It is thought that during human development, nephrons form their proximal-distal axial polarity in response to collecting duct-derived signals that are absent in kidney organoids. To delineate how nephron polarities establish, we profiled human kidney development by spatial transcriptomic approaches. Our analyses describe a new axial polarity in the nephron and demonstrate that the nephron proximal-distal polarity develops adjacent to a transcriptional boundary in the collecting duct where non-canonical WNT11 is downregulated and canonical WNT9B ligand is upregulated. The nephron region closest to this boundary in turn activates a series of canonical WNT target genes inferring positional nephron identities. To establish whether a canonical WNT source can improve organoid patterning to an in vivo -like state, we bioengineered self-organizing WNT-secreting synthetic organizers. Organizer-coupled kidney organoids respond to WNT ligands by forming expression gradients and developing distal cell identities. Tuning the WNT dose produced nephrons with continuous patterning along the proximal-distal axis. Strikingly, polarized iPSC-derived nephrons directed their distal tubules towards the WNT-source, indicating axial patterning and morphogenetic programs are tuned by WNTs from the synthetic organizers. Our data present a strategy to control organ patterning, build an artificial kidney, and highlights the power of synthetic organizer systems for advancing organoid models.