Elevated 5-HTR7 deteriorates dysregulated megakaryocytopoiesis in immune thrombocytopenic purpura via up-regulating the PKA/Orai1/ERK1/2 pathway

Dysregulated megakaryocytopoiesis contributes to reduced platelet counts in immune thrombocytopenic purpura (ITP), yet the mechanism remains elusive. Although 5-hydroxytryptamine receptor 7 (5-HTR7) has been implicated in megakaryocyte biology, its pathogenic involvement in ITP is undefined. This study investigated the impact of 5-HTR7 on megakaryocyte maturation in ITP using flow cytometry, immunofluorescence, and single-cell RNA sequencing. Analyses revealed elevated 5-HTR7 expression on megakaryocytes from ITP patients compared to healthy controls. Pharmacological inhibition of 5-HTR7 using SB269970A not only rescued megakaryocyte maturation defects in vitro but also restored circulating platelet levels in a mouse model of active ITP. Single-cell RNA sequencing coupled with western blot validation identified ERK1/2 phosphorylation in SB269970A-treated megakaryocytes. Mechanistically, 5-HTR7 impaired megakaryocyte maturation through the PKA/Orai1/ERK axis by suppressing store-operated calcium entry, as confirmed via confocal microscopy. In conclusion, elevated expression of 5-HTR7 impairs maturation of megakaryocytes, causing lower platelet counts in ITP and offering a potential therapeutic target for ITP management.