CXCL12/SDF‐1 Stimulates Megakaryocyte β‐1,4‐Galactosyltransferase 1 Activity to Enhance Platelet Production in Vivo

Abstract

Platelet recovery following bone marrow (BM) transplant and chemotherapy is crucial to prevent bleeding complications. The chemokine SDF‐1 promotes megakaryocyte (MK) migration towards BM sinusoids increasing platelet production. Here we show that SDF‐1 upregulates expression of the glycan structure Type‐2‐Lactosaminoglycan (LacNAc), synthesized by β4Galactosyltransferase1 (β4galt1). We hypothesized that SDF‐1 increases LacNAc synthesis promoting platelet production. Supporting this hypothesis, β4galt1–/– mice had severe macrothrombocytopenia (80% reduction) with increased BMMK numbers (35%), which localized poorly with BM sinusoids (50%), compared to WT MKs (72%). β4galt1–/– hematopoietic stem cells (HSCs) transplanted into lethally irradiated WT mice restored BMMKs, which failed to migrate to sinusoids and produce circulating platelets. We next treated WT and β4galt1–/– mice with the myeloablative chemotherapeutic agent 5‐Fluorouracil (5‐FU), which decreased platelet counts by 50% in both phenotypes. SDF‐1 injections increased platelet counts by 70% in 5‐FU treated WT mice but not in β4galt1–/– mice. Importantly, WT but not β4galt1–/– platelets had increased LacNAc expression after SDF‐1 injections.β4galt1–/– BMMKs had increased β1 integrin expression. Expression of laminin, β1 integrin ligand, was upregulated in β4galt1–/– MKs and sinusoids. Our results suggest that SDF‐1 upregulates β4GalT1‐dependentLacNAc expression promoting MK interaction with BM sinusoids, likely regulating β1 integrin expression and interaction with components of the extracellular matrix, specifically laminin.