Invited Speaker Abstract 2018 Hunter Cell Biology Meeting

MesP1-Derived PDGFRA+ Stromal Cells Regulate Hemogenic Endothelial Fate in the Aorta-Gonad Mesonephros (#15)

Vashe Chandrakanthan 1 2 , young Chan Kang 1 , Kathy Knezevic 1 , Prunella Rorimpandey 3 , Qiao Qiao 1 , Rema A Oliver 4 , Ashwin Unnikrishnan 1 , Yizhou Huang 1 , William Walsh 4 , Brendan Lee 5 , Chris Brownlee 5 , Carl Power 5 , Dominik Beck 1 , Samir Taoudi 6 , John E Pimanda 1 2 7
  1. Adult Cancer Program, Lowy Cancer Research Centre, The University of New South Wales, Randwick, NSW, Australia
  2. School of Medical Sciences, The University of New South Wales, Sydney, NSW, Australia
  3. School of Medical Sciences, The University of New South Wales, Randwick, NSW, Australia
  4. Surgical & Orthopaedic Research Laboratories, The University of New South Wales, Sydney, NSW, Australia
  5. Biomedical Image Facility, Mark Wainwright Analytical Centre, Lowy Cancer Research Centre, The University of New South Wales, Randwick, NSW, Australia
  6. Divisions of Molecular Medicine, Walter and Eliza Hall Institute, Parkville, Victoria, Australia
  7. Department of Hematology, The Prince of Wales Clinical School, University of New South Wales, Sydney, NSW, Australia

During embryonic development, the first hematopoietic stem cells (HSCs) emerge from the ventral surface of the dorsal aorta, via a process of endothelial to hematopoietic transition (EHT) at embryonic day (E) 10.5. The aorta-gonad mesonephros (AGM) region contains resident mesenchymal stem cell-like cells (MSC-LCs), but their identity and role in HSC generation are still obscure. To clarify the spatio-temporal distribution, functional hierarchy and developmental origins of cells in the AGM stroma, we used a library of compound transgenic mice, and isolated a population of PDGFRA+/Nestin-GFP (N-GFP)-/PDGFRB-/CD31- cells with MSC-LC activity in the E10.5 and E11.5 AGM. Freshly harvested MSC-LCs were adept at forming blood vessels with CD31+ luminal endothelium enveloped by PDGFRB+ pericytes, when transplanted subcutaneously into mice. Conditional ablation of PDGFRA+ or Nestin+ cells led to either complete or partial loss of MSC-LCs respectively, with severe loss of endothelial and pericyte-like cells, and concomitant loss of blood formation in the AGM. Lineage tracing studies using tamoxifen induction in PDGFRACreERT2/R26eYFP embryos showed that stromal, sub-endothelial, endothelial and long-term repopulating hematopoietic stem cells (LT-HSCs) cells in the E11.5 AGM were progeny of Mesp1+ PDGFRA cells. Mesoderm (Mesp1+) derived PDGFRA+ cells dominated the sub-endothelial and deeper ventral stroma in the AGM at E10.5 and E11.5 but were replaced by neural crest (Wnt1+) derived PDGFRA+ cells at E13.5. Re-aggregation of E11.5 Mesp1 derived MSC-LCs with E13.5 aortic or adult endothelial cells, which normally lack hemogenic capacity resulted in the generation of endothelial cell derived LT-HSCs, which was suppressed by dose-dependent inhibition of PDGF-AA/PDGFRA signalling. RNA-sequencing analysis of non-hemogenic E13.5 endothelial cells showed up-regulation of EHT, WNT, BMP and Notch signaling pathway genes when re-aggregated with E11.5 Mesp1 derived MSC-LCs. Taken together, we report that MSC-LC populations in the AGM are temporally dynamic, and that MesP1-derived MSC-LCs regulate hemogenic potential of the endothelium and that this cooperativity is dependent on PDGF-AA/PDGFRa signalling.