Page 60 - 2018_09-Mondo

A. McCabe et al.
HSC from myeloablative injury.12,13 Therefore, CD41hi HSCs may represent more committed progenitors that augment HSC-protective niches during SAA. It is current- ly unclear if Mk preservation is necessary for or predictive of HSC rescue. However, our finding that HSC loss pre- cedes Mk loss would argue in favor of a decline in megakaryopoiesis as a result of reduced CD41hi HSCs.
We identify a unique population of PDPN-expressing Mfs that restrict the HSC compartment and contribute to thrombocytopenia during SAA. PDPN regulates con- tractility and migration of lymphatic endothelial cells, FRCs, and tumor cells.48 Thus PDPN signaling in Mfs may influence hematopoiesis in a similar manner by reg- ulating BM stiffness or migration within BM niches. Because increased or decreased matrix stiffness impairs proplatelet extension by Mks in vitro, it is possible that SAA-induced stromal stiffness restricts thrombopoiesis.45 PDPN expression is low and confined mainly to stromal cells in the BM at steady state and even upon radiation injury. PDPN is specifically increased on Mfs in the BM during SAA, and anti-PDPN antibody specifically reduced CD11blo/- Mfs, but not CD11b+ Mfs, during SAA. Our data demonstrate a direct correlation between CD11blo/- Mfs and SAA pathogenesis. Future studies to test the impact of PDPN expression on Mf migration and survival during SAA are warranted.
not impact SAA-induced RANTES was somewhat surpris- ing. However, our data and a previous report demonstrate that clone 8.1.1 does not interfere with CLEC-2 binding.34 Thus, PDPN blockade with clone 8.1.1 during SAA likely does not interfere with CLEC-2-driven RANTES produc- tion. Clone 8.1.1 may interfere with CLEC-2 binding,50 though very high concentrations of antibody were need- ed, and it is unlikely that this can be achieved in vivo. Our observations demonstrate protection independently of CLEC-2; however, future studies are necessary to test the involvement of the CLEC-2-PDPN axis and define the pre- cise action of PDPN in the BM during SAA.
Podoplanin-expressing Mfs are increased in SAA, con- sistent with previous reports that PDPN is expressed on inflammatory Mfs in response to IFNγ during infection.49 PDPN is a CLEC-2 ligand that triggers downstream signal- ing in CLEC2-expressing cells. However CLEC-2/PDPN ligation also elicits bidirectional signaling, eliciting RANTES production from PDPN-expressing cells.33,34 We noted increased RANTES in SAA, relative to radiation controls. Thus, our observation that PDPN blockade did
Acknowledgments
We would like to acknowledge Kathleen Curran and Candace Ross at the New York State Department of Health Wadsworth Center (Albany, NY) for running CBCs on blood samples. We would like to thank Dr. Livingston Van De Water for helpful dis- cussion.
Funding
This work was supported by R01 GM105949 to KCM, an Aplastic Anemia and MDS International Foundation grant to KCM, and BM160071 (DOD-BMFRP-IDA) to KCM.
References
1. Chen J. Animal models for acquired bone marrow failure syndromes. Clin Med Res. 2005;3(2):102-108.
2. ScheinbergP,ChenJ.Aplasticanemia:what have we learned from animal models and from the clinic. Semin Hematol. 2013; 50(2):156-164.
3. Young NS, Maciejewski J. The pathophysi- ology of acquired aplastic anemia. N Engl J Med. 1997;336(19):1365-1372.
4. RoderickJE,Gonzalez-PerezG,KuksinCA, et al. Therapeutic targeting of NOTCH sig- naling ameliorates immune-mediated bone marrow failure of aplastic anemia. J Exp Med. 2013;210(7):1311-1329.
5. Bloom ML, Wolk AG, Simon-Stoos KL, Bard JS, Chen J, Young NS. A mouse model of lymphocyte infusion-induced bone mar- row failure. Exp Hematol. 2004; 32(12):1163-1172.
6. Lu J, Basu A, Melenhorst JJ, Young NS, Brown KE. Analysis of T-cell repertoire in hepatitis-associated aplastic anemia. Blood. 2004;103(12):4588-4593.
7. SolomouEE,KeyvanfarK,YoungNS.T-bet, a Th1 transcription factor, is up-regulated in T cells from patients with aplastic anemia. Blood. 2006;107(10):3983-3991.
8. Zoumbos NC, Ferris WO, Hsu SM, et al.
Analysis of lymphocyte subsets in patients with aplastic anaemia. Br J Haematol. 1984;58(1):95-105.
Chemokine-mediated interaction of hematopoietic progenitors with the bone marrow vascular niche is required for thrombopoiesis. Nat Med. 2004;10(1):64-
15. Haas S, Hansson J, Klimmeck D, et al. Inflammation-Induced Emergency Megakaryopoiesis Driven by Hematopoietic Stem Cell-like Megakaryocyte Progenitors. Cell Stem Cell. 2015;17(4):422-434.
16. Gekas C, Graf T. CD41 expression marks myeloid-biased adult hematopoietic stem cells and increases with age. Blood. 2013;121(22):4463-4472.
17. Chang MK, Raggatt LJ, Alexander KA, et al. Osteal tissue macrophages are intercalated throughout human and mouse bone lining tissues and regulate osteoblast function in vitro and in vivo. J Immunol. 2008;181(2): 1232-1244.
18. Chow A, Lucas D, Hidalgo A, et al. Bone marrow CD169+ macrophages promote the retention of hematopoietic stem and progenitor cells in the mesenchymal stem cell niche. J Exp Med. 2011;208(2):261-271.
19. Winkler IG, Sims NA, Pettit AR, et al. Bone marrow macrophages maintain hematopoi- etic stem cell (HSC) niches and their deple- tion mobilizes HSCs. Blood. 2010;116(23): 4815-4828.
Interferon-γ impacts SAA disease progression, yet neu- tralization of IFNγ is not currently a treatment option dur- ing this disease. Our finding that IFNγ maintains Mfs pro- vides the rationale for targeting Mfs during BM failure. We reveal that Mfs errantly express PDPN during SAA and antagonizing PDPN signaling rescues HSCs and enhances platelet output, thus revealing a novel circuit in the microenvironment during BM failure. Understanding the mechanisms whereby PDPN expression in Mfs regu- lates HSC function and platelet production may reveal novel treatment options for SAA.
9. Chen J, Lipovsky K, Ellison FM, Calado RT,
Young NS. Bystander destruction of 71.
hematopoietic progenitor and stem cells in a mouse model of infusion-induced bone marrow failure. Blood. 2004;104(6):1671- 1678.
10. Zoumbos NC, Gascon P, Djeu JY, Young NS. Interferon is a mediator of hematopoi- etic suppression in aplastic anemia in vitro and possibly in vivo. Proc Natl Acad Sci USA. 1985;82(1):188-192.
11. Townsley DM, Desmond R, Dunbar CE, Young NS. Pathophysiology and manage- ment of thrombocytopenia in bone marrow failure: possible clinical applications of TPO receptor agonists in aplastic anemia and myelodysplastic syndromes. Int J Hematol. 2013;98(1):48-55.
12. Zhao M, Perry JM, Marshall H, et al. Megakaryocytes maintain homeostatic qui- escence and promote post-injury regenera- tion of hematopoietic stem cells. Nat Med. 2014;20(11):1321-1326.
13. Bruns I, Lucas D, Pinho S, et al. Megakaryocytes regulate hematopoietic stem cell quiescence through CXCL4 secre- tion. Nat Med. 2014;20(11):1315-1320.
14. Avecilla ST, Hattori K, Heissig B, et al.
1460
haematologica | 2018; 103(9)