HuR ablation destabilizes Foxp3 mRNA and impairs regulatory T cell function, contributing to an autoimmune phenotype

Ulus Atasoy^1*Fatima Fattahi¹Jason S Ellis¹Laura Vallance¹Kristin Bahleda¹Julia Holden¹Sarah Socha¹Fahimeh Fattahi²Francisco Gomez-Rivera¹

• ¹University of Michigan, Ann Arbor, United States
• ²Department of Nursing, Arak University of Medical Sciences, Arak, Markazi, Iran

The RNA-binding protein HuR (Elavl1), a key post-transcriptional regulator, plays a critical role in T cell activation and function by stabilizing target mRNAs. To investigate the role of HuR in function of regulatory T cell (Treg), we generated the Foxp3 YFP/Cre HuR fl/fl mouse model, in which homozygous females and hemizygous males for Foxp3 developed a scurfy-like phenotype displaying autoimmune features. This included failure to thrive, splenomegaly, hair loss, tail stippling, and widespread multi-organ immune cell infiltration. Our molecular analysis showed a direct interaction between HuR and Foxp3 mRNA and the role of HuR in mediating mRNA stability. To our knowledge, this is the first study demonstrating HuR directly binds and stabilizes Foxp3 mRNA in Tregs, using a novel Treg-specific HuR-deficient mouse model, with implications for autoimmune regulation. Foxp3 mRNA stability and expression were significantly reduced in Tregs from these HuR KO mice, despite having higher frequency of YFP⁺ Tregs. RNA sequencing of YFP + Tregs from HuR KO mice revealed significant dysregulation of several pathways, including T helper differentiation pathway, in which Foxp3 played a central role. Protein-Protein Interaction (PPI) analysis showed a direct link between Foxp3 and Rorc (encoding RORγt), connecting Foxp3 to the T cell differentiation pathway via IL-23R. Our qPCR analysis supported these findings. A Treg functional assay demonstrated a reduction in the suppressive capacity of HuR-deficient Tregs. These findings together suggest that ablation of HuR in Tregs disrupts Foxp3 expression and Treg function, likely through dysregulation of T cell differentiation pathways involving RORC. This potentially contributes to a disrupted Treg-Th17 axis and autoimmune dysfunction. These data suggest a critical role for HuR-mediated post-transcriptional regulation in maintaining Foxp3 expression and immune homeostasis, although compensatory mechanisms such as increased IL-10 expression may also contribute.