Leptin Receptor+ Stromal Cells Create a Perisinusoidal Niche for Thrombopoiesis in the Bone Marrow By Synthesizing Cxcl14

Leptin Receptor expressing (LepR⁺) mesenchymal stromal cells are a critical source of multiple growth factors in the bone marrow that promote the maintenance of hematopoietic stem cells and early hematopoietic progenitors as well as the regeneration of hematopoietic and vascular cells. Here, we show that LepR+ cells promote thrombopoiesis in the bone marrow by synthesizing the chemokine Cxcl14. We systematically examined the Cxcl14 expression pattern by single cell RNA sequencing and using Cxcl14^dsRed knock-in mice. We found that Cxcl14 was mainly expressed in the bone marrow by perisinusoidal LepR+ cells. HSC frequency and function were not significantly affected when Cxcl14 was conditionally deleted from LepR⁺ cells; however, blood platelet counts decreased in Lepr-cre; Cxcl14 ^fl/fl mice. Megakaryocytes from Lepr-cre; Cxcl14^fl/fl bone marrow exhibited defective cytoplasmic maturation and proplatelet release based on deep imaging of the bone marrow. Lipidomic analysis showed Cxcl14 deletion reduced polyunsaturated fatty acids (PUFA) in triglycerides in megakaryocytes. RNA sequencing and western blot analysis showed that genes related to exogenous lipid uptake were downregulated in CD42⁺ megakaryocytes from Lepr-cre; Cxcl14^fl/fl mice. In vivo, the lower platelet counts in Lepr-cre; Cxcl14^fl/fl mice were rescued through a high PUFA diet. Our results suggest that Cxcl14 signaling can enhance lipid uptake through lipid transporters to promote megakaryocyte maturation. Moreover, recombinant mouse Cxcl14 protein increased the formation of colonies by megakaryocyte progenitors (CFU-Mk) in culture and accelerated the formation of proplatelets. LepR⁺ cells thus create a perisinusoidal niche for thrombopoiesis by synthesizing Cxcl14.