3208 – PROLONGED THROMBOCYTOPENIA IN BONE MARROW TRANSPLANT PATIENTS IS CAUSED BY IMPAIRED SUPPORT OF PLATELET PRECURSOR CELLS BY ALTERED BONE MARROW NICHES

Abstract

Listen

Translate article

Prolonged thrombocytopenia affects one-third of patients who undergo a bone marrow transplant (BMT). It is a serious complication associated with significantly reduced survival. There is no alternative treatment aside from platelet transfusion to assist in platelet recovery post-BMT, which carries risks and complications. Platelet production occurs in the bone marrow in a multi-stage process, with each stage involving different niche cells. Little is known about the niches that regulate different types of platelet precursors, including megakaryocyte progenitors (MkPs), or how they respond to a BMT. Consistent with humans, mice have persistent reductions in platelets post-BMT. This was accompanied by reduced MkPs and megakaryocytes, but not hematopoietic stem cells. There were reduced perivascular niche cells and sinusoidal endothelial cells, and increased numbers of adipocytes post-BMT. Recent studies on human biopsies also show that patients with persistent thrombocytopenia have altered perivascular niche cells. To identify the niche cells that interact with the platelet precursors in situ, we used 7-colour Opal immunofluorescence. We used markers to phenotype megakaryocytes, MkPs and niche cells in mouse bone marrow sections and quantified their interactions using image analysis. The megakaryocytes and MkPs interacted closely with sinusoids and arterioles but negatively with trabecular bone. Post-BMT, MkPs were closer to the sinusoids and arterioles while the megakaryocytes are further away from arterioles. To identify novel proteins that regulate platelet production we are currently profiling bone marrow niche cells from mice post-BMT vs control using scRNA-seq. Collectively, our results show that endothelial and perivascular niche cells are important for platelet production and disruption in these niche cells may contribute to prolonged thrombocytopenia post-BMT. Prolonged thrombocytopenia affects one-third of patients who undergo a bone marrow transplant (BMT). It is a serious complication associated with significantly reduced survival. There is no alternative treatment aside from platelet transfusion to assist in platelet recovery post-BMT, which carries risks and complications. Platelet production occurs in the bone marrow in a multi-stage process, with each stage involving different niche cells. Little is known about the niches that regulate different types of platelet precursors, including megakaryocyte progenitors (MkPs), or how they respond to a BMT. Consistent with humans, mice have persistent reductions in platelets post-BMT. This was accompanied by reduced MkPs and megakaryocytes, but not hematopoietic stem cells. There were reduced perivascular niche cells and sinusoidal endothelial cells, and increased numbers of adipocytes post-BMT. Recent studies on human biopsies also show that patients with persistent thrombocytopenia have altered perivascular niche cells. To identify the niche cells that interact with the platelet precursors in situ, we used 7-colour Opal immunofluorescence. We used markers to phenotype megakaryocytes, MkPs and niche cells in mouse bone marrow sections and quantified their interactions using image analysis. The megakaryocytes and MkPs interacted closely with sinusoids and arterioles but negatively with trabecular bone. Post-BMT, MkPs were closer to the sinusoids and arterioles while the megakaryocytes are further away from arterioles. To identify novel proteins that regulate platelet production we are currently profiling bone marrow niche cells from mice post-BMT vs control using scRNA-seq. Collectively, our results show that endothelial and perivascular niche cells are important for platelet production and disruption in these niche cells may contribute to prolonged thrombocytopenia post-BMT.