Human pluripotent stem cell-derived macrophages modify development of human kidney organoids
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Introduction
The human fetal kidney contains macrophages, innate immune cells postulated to enhance its development. Macrophages have also been implicated in the pathobiology of human kidney malformations and Wilms tumour. Human pluripotent stem cell (hPSC)-derived kidney organoids contain nephrons differentiated from intermediate mesoderm-like precursors. Endothelia are present between organoid tubules but fail to efficiently populate glomeruli. These organoids lack macrophages, as expected because in vivo kidney macrophages invade from yolk sac and liver.
Methods
We hypothesised that combining hPSC-derived macrophages with hPSC-derived kidney precursors modifies nephrogenesis. Macrophages harvested at early or later maturation stages were added to kidney precursors in numbers of 1%, 5% or 20% compared with constant numbers of nephrogenic cells.
Results
No macrophages, as assessed by CD68 immunostaining, were detected in organoids without added macrophages. In contrast, composite organoids contained macrophages located between tubules, mimicking native human fetal kidneys. Quantification of tissue macrophages at the end of 18-day organoid culture positively correlated with the numbers of macrophages added. Assessed by CD31/PECAM-1 and CD68 co-immunostaining, some macrophages were near vessels but added macrophages neither increased the proportion of vessels nor endothelial invasion of glomeruli. Early-stage macrophages significantly increased the percentage area occupied by glomeruli, as assessed by synaptopodin immunostaining. The highest macrophage numbers inhibited overall growth, assessed by organoid area, additionally generating dysmorphic tissue when later stage macrophages were added.
Conclusion
Depending on their maturation stage and quantity, macrophages have beneficial or harmful effects on organoids. This supports the proposition that macrophages play roles in normal and abnormal development of human kidneys.
