Seoyeon Bok 1, Alisha R. Yallowitz 1, Jun Sun 1, Jason McCormick 2, Michelle Cung 1, Lingling Hu 3, Sarfaraz Lalani 1, Zan Li 1, Branden R. Sosa 1, Tomas Baumgartner 2, Paul Byrne2,Tuo Zhang 4, Kyle W. Morse 3, Fatma F. Mohamed 5, Chunxi Ge 5, Renny T. Franceschi 5, Randy T. Cowling 6, Barry H. Greenberg 6, David J. Pisapia 1, Thomas A. Imahiyerobo 7, Shenela Lakhani 8, M. Elizabeth Ross 8, Caitlin E. Hoffman 9, Shawon Debnath 1,* & Matthew B. Greenblatt 1,10 ,*
1Department of Pathology and Laboratory Medicine, Weill Cornell Medicine, New York, NY, USA.
2Flow Cytometry Core Facility, Weill Cornell Medicine, New York, NY, USA.
3Department of Orthopedic Surgery, Hospital for Special Surgery, New York, NY, USA.
4Genomics Resources Core Facility, Weill Cornell Medicine, New York, NY, USA.
5Department of Periodontics, Prevention and Geriatrics, School of Dentistry, University of Michigan, Ann Arbor, MI, USA.
6Division of Cardiovascular Medicine, Department of Medicine, University of California, San Diego, CA, USA.
7Division of Plastic Surgery, Department of Surgery, New York-Presbyterian Hospital and Columbia University Medical Center, New York, NY, USA.
8Center for Neurogenetics, Feil Family Brain and Mind Research Institute, Weill Cornell Medicine, New York, NY, USA.
9Department of Neurological Surgery, Weill Cornell Medicine and New York-Presbyterian Hospital, New York, NY, USA.
10Research Division, Hospital for Special Surgery, New York, NY, USA.
*Corresponding author: correspondence to Shawon Debnath or Matthew B. Greenblatt
Craniosynostosis is a group of disorders of premature calvarial suture fusion. The identity of the calvarial stem cells (CSCs) that produce fusion-driving osteoblasts in craniosynostosis remains poorly understood. Here we show that both physiologic calvarial mineralization and pathologic calvarial fusion in craniosynostosis reflect the interaction of two separate stem cell lineages; a previously identified cathepsin K (CTSK) lineage CSC (CTSK+ CSC) and a separate discoidin domain-containing receptor 2 (DDR2) lineage stem cell (DDR2+ CSC) that we identified in this study. Deletion of Twist1, a gene associated with craniosynostosis in humans, solely in CTSK+ CSCs is sufficient to drive craniosynostosis in mice, but the sites that are destined to fuse exhibit an unexpected depletion of CTSK+ CSCs and a corresponding expansion of DDR2+ CSCs, with DDR2+ CSC expansion being a direct maladaptive response to CTSK+ CSC depletion. DDR2+ CSCs display full stemness features, and our results establish the presence of two distinct stem cell lineages in the sutures, with both populations contributing to physiologic calvarial mineralization. DDR2+ CSCs mediate a distinct form of endochondral ossification without the typical haematopoietic marrow formation. Implantation of DDR2+ CSCs into suture sites is sufficient to induce fusion, and this phenotype was prevented by co-transplantation of CTSK+ CSCs. Finally, the human counterparts of DDR2+ CSCs and CTSK+ CSCs display conserved functional properties in xenograft assays. The interaction between these two stem cell populations provides a new biologic interface for the modulation of calvarial mineralization and suture patency.