Reduced SRSF1 Expression Correlates with LCK Exon Skipping and Impaired Treg Induction in Immune Thrombocytopenia.

Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by antibody-mediated platelet destruction and impaired regulatory T-cell (Treg) function, yet its molecular basis remains poorly defined. Here, we show that CD4+ naive T cells from patients with ITP exhibit diminished T-cell receptor (TCR) signaling and impaired in vitro Treg induction relative to healthy controls. RNA-sequencing revealed widespread alternative splicing dysregulation, most notably exon 8 skipping in LCK, a kinase central to TCR signaling and Treg differentiation. Using an LCK minigene combined with RNA pull-down mass spectrometry and RNA immunoprecipitation assays, we identified the splicing factor SRSF1 as a direct upstream regulator of LCK exon 8 skipping. Notably, SRSF1 expression was reduced in CD4+ naive T cells from ITP patients, and its overexpression restored in vitro Treg induction capacity. Antisense oligonucleotide (ASO)-mediated blockade of SRSF1 binding to LCK enhanced exon 8 skipping and attenuated TCR activation in Jurkat cells. Although murine Lck lacks the human-specific recursive splicing sites required for exon 8 exclusion, adoptive transfer of CD4+ naive T cells expressing the exon 8-skipped murine Lck into CD61-knockout mice significantly reduced Treg proportions and platelet counts in an active ITP model. Mechanistically, Jurkat cells engineered to express only the exon 8-skipped LCK variant showed markedly reduced binding to ZAP70 and CD3ζ, which may partly account for the attenuated TCR signaling and downstream FOXP3 induction. Together, these findings define a novel SRSF1-LCK splicing axis that may regulate Treg development in ITP.