Role of thrombomodulin expression on hematopoietic stem cells

• Published in: Journal of thrombosis and haemostasis 2020-01, Vol.18 (1), p.123-135
• Main Authors: Basu, Sreemanti, Liang, Hai Po Helena, Hernandez, Irene, Zogg, Mark, Fields, British, May, Jennifer, Ogoti, Yamini, Wyseure, Tine, Mosnier, Laurent O., Burns, Robert T., Carlson, Karen, Weiler, Hartmut
• Format: Article
• Language: English
• Subjects: Activated protein C; Animals; Bone marrow; Cell activation; Cytology; Endothelium; Flow cytometry; Hematopoiesis; Hematopoietic Stem Cells; hemostasis; Lymphocytes B; Mice; Mice, Inbred C57BL; Peripheral blood; Proteins; Receptor, PAR-1 - genetics; Ribonucleic acid; RNA; Signal Transduction; Stem cell transplantation; Stem cells; Supplements; Thrombin; Thrombomodulin; Thrombomodulin - genetics; thrombosis; Transcription
• ISSN: 1538-7933; 1538-7836; 1538-7836
• DOI: 10.1111/jth.14663

Background Activation of protease‐activated receptor 1 (PAR1) by either thrombin or activated protein C (aPC) differentially regulate the quiescence and bone marrow (BM) retention of hematopoietic stem cells (HSC). Murine HSC co‐express THBD, PAR1, and endothelial protein C receptor (EPCR), suggesting that HSC sustain quiescence in a quasi‐cell autonomous manner due to the binding of thrombin present in the microenvironment to THBD, activation of EPCR‐bound protein C by the thrombin‐THBD‐complex, and subsequent activation of PAR1 by the aPC‐EPCR complex. Objective To determine the role of THBD expression on HSC for sustaining stem cell quiescence and BM retention under homeostatic conditions. Methods Hematopoietic stem cell function was analyzed in mice with constitutive or temporally controlled complete THBD‐deficiency by flow cytometry, functional assays, and single cell RNA profiling. Results THBD was expressed in mouse, but not human, HSC, progenitors, and immature B cells. Expression in vascular endothelium was conserved in humans' BM. Mice with constitutive THBD deficiency had a normal peripheral blood profile, altered BM morphology, reduced numbers of progenitors and immature B cells, pronounced extramedullary hematopoiesis, increased HSC frequency, and marginally altered transcriptionally defined HSC stemness. Transplantation experiments indicated near normal engraftment and repopulating ability of THBD‐deficient HSC. Transgenic aPC supplementation normalized BM histopathology and HSC abundance, and partially restored transcriptional stemness, but had no effect on B cell progenitors and extramedullary hematopoiesis. Temporally controlled THBD gene ablation in adult mice did not cause the above abnormalities. Conclusion THBD expression on HSPC has minor effects on homeostatic hematopoiesis in mice, and is not conserved in humans.