Sin3A Controls FoxP3+Treg Production, Stability and Function

Abstract Purpose: Foxp3 T-regulatory (Treg) cells are key to immune homeostasis but the function of paired amphipathic helix protein, Sin3a, is unknown. Methods: We studied the effects of Sin3a deletion in Treg cells. Results: Sin3a−/− FoxP3Cre mice died from severe autoimmunity by 2–3 weeks of birth. Mice had enlarged lymph nodes, severe inflammation in lungs, skin, livers and kidneys and autoantibodies to islet cells, striated muscles, keratin, endomysium and gastric parietal cells. Percentages of FoxP3+ Tregs in LNs and spleens were lower (p values ranging from >0.01 to >0.0001) than controls and FoxP3 mRNA expression (>20-fold) and FoxP3 protein per Treg (>3-fold) were also significantly reduced in Sin3a−/− mice. Reduction of FoxP3+ Tregs in the periphery of Sin3a−/− FoxP3cre mice was largely due to the loss of FoxP3, determined by an increase of peripheral ex-Tregs as compared to WT (p<0.001 in sLN and spleens) within Sin3a−/− FoxP3Cre tdTomatoROSA26 lineage tracing mice. Increased mRNA expression of pro-apoptotic genes, decreased mRNA expression of anti-apoptotic genes, and increased presence of Annexin V on the cell surface indicate that apoptosis also contributed to peripheral Treg reduction. Sin3a−/− Tregs produced increased amounts of granzyme B, IFN-γ and IL-2 (12–45% of cells) and had impaired suppressive function (p<0.01). Sin3a was also essential for peripheral iTreg conversion since CD4+CD25− cells from Sin3a−/− FoxP3Cre mice lacked ability to convert to FoxP3+ iTregs ex vivo. Conclusions: The nuclear co-regulator, Sin3a, helps maintain the unique homeostatic properties of Treg cells. Therapeutic modulation of Treg functions may be possible by pharmacologic targeting of components within the Sin3a complex.