An Inducible Zebrafish Model of Thrombocytopenia Enables In Vivo Drug Screening and Reveals FGF Signaling as a Key Regulator of Platelet Regeneration.

BACKGROUND: Thrombocytopenia is a serious hematological disorder characterized by low platelet counts, with platelet recovery rate as a key prognostic factor. Current models have limitations such as acute toxicity, non-specific cell ablation, and poor capacity for dynamic observation of recovery. OBJECTIVES: This study aimed to establish a thrombocyte-specific ablation zebrafish model to study thrombocyte regeneration and screen for pro-recovery compounds. METHODS: We generated Tg(cd41:eGFP-NTR) zebrafish for inducible thrombocyte ablation using ronidazole (RNZ). The model was characterized via imaging, phenotypic assays, and transcriptomics. A targeted library of 132 compounds was screened, and hits were validated in Chemotherapy-Induced Thrombocytopenia (CIT) and Congenital Amegakaryocytic Thrombocytopenia (CAMT) zebrafish model and human Meg-01 cells. RESULTS: RNZ treatment caused rapid and specific depletion of thrombocytes through cell-autonomous apoptosis and macrophage-mediated clearance. This loss led to bleeding symptoms and reduced thrombus formation, resembling key features of thrombocytopenia. Transcriptomic analysis and functional studies showed that Fibroblast Growth Factor (FGF) signaling plays a critical role in thrombocyte recovery. Screening of the compound library identified three novel candidates that significantly accelerated recovery. Notably, tasisulam effectively rescued both CIT and CAMT phenotypes by driving thrombocyte recovery via the ERK signaling pathway. In addition, both tasisulam and 4-methylcatechol promoted thrombopoiesis in human Meg-01 cells, indicating conservation across species. CONCLUSION: This zebrafish model provides exceptional spatiotemporal resolution for investigating the pathogenesis and in vivo recovery dynamics of thrombocytopenia. It serves as a versatile platform for identifying therapeutic agents with cross-species efficacy and for uncovering key mechanisms regulating thrombocyte regeneration, revealing FGF signaling as a central regulator of thrombocyte recovery.