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Title: Mechanisms of kidney vascularisation and the roles of macrophages in renal organogenesis
Author: Munro, David
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2019
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The major function of the adult kidney is to filter blood. This task requires a complex vasculature that must be accurately assembled during development. To better understand renal endothelial development, I imaged the vascular tree of embryonic kidneys in 3D. From this, I detailed the origins of the first renal blood vessels and demonstrated that endothelia patterned in cycles alongside the splitting of the cap mesenchyme (nephron progenitor population) and branching of the ureteric bud. Notably, endothelia avoided the cap mesenchyme throughout development. Based on their gene expression patterns, I identified the anti-angiogenic molecule, semaphorin-3f, and its receptor, neuropilin-2, as signalling candidates that may control this endothelial patterning; however, these proteins were not required for endothelial avoidance from the cap mesenchyme. I demonstrated how renal vascularisation occurs in synchrony with the two major processes involved in renal organogenesis: branching morphogenesis and nephrogenesis. Moreover, I showed that angiogenesis predominates in kidney vascularisation and that the role of vasculogenesis is minimal (at most). I next investigated whether macrophages may facilitate renal vascularisation. Kidney macrophage origins have been defined, but their functions during development remain largely unknown. Macrophages arrived in the caudal part of the mouse embryo between E9.5-E10.5, as nephron precursors began collecting at the caudal end of the Wolffian duct. From this stage onwards, macrophages largely avoided populations of nephron progenitors. Instead, most mature macrophages interacted with the vasculature in the renal interstitium. Perivascular macrophages wrapped around, but were not carried within, blood vessels. As well as interacting with the vasculature, these macrophages engulfed erythrocytes and apoptotic endothelia during development. I also identified many galectin-3+ (Mac2+) cells within the kidney, which co-expressed the macrophage/monocyte-restricted marker, Csf1r, and were often carried within the vasculature. Mac2+ cells were present in the kidney from E11.5 onwards, dramatically increasing in number later in development. Single cell RNA-sequencing and subsequent gene over-representation testing indicated that mature F4/80hiCD206hi macrophages, but not Mac2hi cells, were enriched for mRNA transcripts linked to vascular development. Accordingly, kidney macrophage-depletion resulted in abnormal renal vascularisation, characterised by fewer endothelial anastomoses. These results suggest that macrophage-endothelial-communication is important for kidney organogenesis.
Supervisor: Davies, Jamie ; Hohenstein, Peter Sponsor: Medical Research Council (MRC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: microscopy ; kidney blood vessel formation ; cap mesenchyme ; macrophages ; kidney development