Enhanced metanephric specification to functional proximal tubule enables toxicity screening and infectious disease modelling in kidney organoids.

While pluripotent stem cell-derived kidney organoids are now being used to model renal disease, the proximal nephron remains immature with limited evidence for key functional solute channels. This may reflect early mispatterning of the nephrogenic mesenchyme and/or insufficient maturation. Here we show that enhanced specification to metanephric nephron progenitors results in elongated and radially aligned proximalised nephrons with distinct S1 - S3 proximal tubule cell types. Such PT-enhanced organoids possess improved albumin and organic cation uptake, appropriate KIM-1 upregulation in response to cisplatin, and improved expression of SARS-CoV-2 entry factors resulting in increased viral replication. The striking proximo-distal orientation of nephrons resulted from localized WNT antagonism originating from the organoid stromal core. PT-enhanced organoids represent an improved model to study inherited and acquired proximal tubular disease as well as drug and viral responses.

The Kidney Contains Ontogenetically Distinct Dendritic Cell and Macrophage Subtypes throughout Development That Differ in Their Inflammatory Properties.

BACKGROUND: Mononuclear phagocytes (MPs), including macrophages, monocytes, and dendritic cells (DCs), are phagocytic cells with important roles in immunity. The developmental origin of kidney DCs has been highly debated because of the large phenotypic overlap between macrophages and DCs in this tissue. METHODS: We used fate mapping, RNA sequencing, flow cytometry, confocal microscopy, and histo-cytometry to assess the origin and phenotypic and functional properties of renal DCs in healthy kidney and of DCs after cisplatin and ischemia reperfusion-induced kidney injury. RESULTS: Adult kidney contains at least four subsets of MPs with prominent Clec9a-expression history indicating a DC origin. We demonstrate that these populations are phenotypically, functionally, and transcriptionally distinct from each other. We also show these kidney MPs exhibit unique age-dependent developmental heterogeneity. Kidneys from newborn mice contain a prominent population of embryonic-derived MHCIInegF4/80hiCD11blow macrophages that express T cell Ig and mucin domain containing 4 (TIM-4) and MER receptor tyrosine kinase (MERTK). These macrophages are replaced within a few weeks after birth by phenotypically similar cells that express MHCII but lack TIM-4 and MERTK. MHCII+F4/80hi cells exhibit prominent Clec9a-expression history in adulthood but not early life, indicating additional age-dependent developmental heterogeneity. In AKI, MHCIInegF4/80hi cells reappear in adult kidneys as a result of MHCII downregulation by resident MHCII+F4/80hi cells, possibly in response to prostaglandin E2 (PGE2). RNA sequencing further suggests MHCII+F4/80hi cells help coordinate the recruitment of inflammatory cells during renal injury. CONCLUSIONS: Distinct developmental programs contribute to renal DC and macrophage populations throughout life, which could have important implications for therapies targeting these cells.