Oral Presentation 29th Australian and New Zealand Bone and Mineral Society Annual Scientific Meeting 2019

Single cell transcriptional mapping defines the cellular landscape of the bone microenvironment (#51)

Ryan C. Chai 1 , Matthew A. Summers 1 2 , Alexander P. Corr 1 2 , Weng Hua Khoo 1 , Sunny Z. Wu 1 , Alex Swarbrick 1 2 , John A. Eisman 1 2 3 , Graham R. Williams 4 , Duncan Bassett 4 , Paul A. Baldock 1 2 , Peter I. Croucher 1 2
  1. Bone Biology, Garvan Institute of Medical Research, Sydney, NSW, Australia
  2. School of Clinical Medicine, Faculty of Medicine, University of New South Wales, Sydney, NSW, Australia
  3. School of Medicine Sydney, University of Notre Dame Australia, Sydney, NSW, Australia
  4. Molecular Endocrinology Laboratory, Department of Medicine, Imperial College London, London, UK

The bone marrow is a highly complex microenvironment with distinct compartments. These include the endosteal diaphysis, endosteal metaphysis and the marrow. Many distinct cell types interact closely to form niches in these compartments with key roles in haematopoiesis and bone homeostasis. The cell types and molecular factors that comprise these different niches remain poorly understood. We hypothesised that single cell mapping would define the cellular landscape of the endosteum and this would differ from those in the marrow space.

 To address this we developed a method to isolate cells lining the endosteum of the diaphysis and metaphysis and cells of the marrow compartment from the femur of C57BL/6J mice. 133,942 cells from the three compartments of 25 mice were isolated and subjected to single cell RNA sequencing using the 10x Chromium platform.

 Unsupervised clustering analysis revealed 33 distinct cell types, representing multiple clusters of myeloid, lymphoid and non-haematopoietic cells, each with distinct transcriptional profiles (Figure. 1). These clusters showed distinct patterns of distribution between the three compartments with the non-haematopoietic and monocyte clusters enriched in the endosteal surface of the diaphysis and metaphysis. High resolution mapping and trajectory analysis of the non-haematopoietic osteogenic cell cluster revealed 6 sub-types, consisting of mesenchymal stromal cells, fibroblasts, osteoprogenitors, preosteoblasts, mature osteoblasts and osteocytes. The monocyte lineage consists of progenitor cells, early monocytes, 4 distinct macrophage clusters and osteoclasts including populations specific to the endosteum, with unique gene signatures compared to their marrow-derived counterparts.

 In conclusion, this study provides the most comprehensive census of the cell types present in the bone microenvironment to date, identifying heterogeneity, distinct transcriptional profiles and spatial distribution. Our data offered new insights into the landscape of the bone microenvironment and potential factors that might regulate skeletal health.

 

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