Inhibition of estrogen receptor alpha stabilizes regulatory T cell function in autoimmune hepatitis

Regulatory T cell (Treg) dysfunction is a hallmark of autoimmune hepatitis (AIH), a serious hepatopathy often progressing to end-stage liver disease despite immunosuppression. Treg impairment in AIH has been linked to defective signaling through the aryl hydrocarbon receptor (AhR), a modulator of adaptive immunity. Herein, we investigated whether increased estrogen receptor alpha (ERα), an AhR non-canonical binding partner, impacts Treg immunity and contributes to the sex bias observed in AIH.

Tregs were isolated from the peripheral blood of pre-menopausal, post-menopausal and male patients with AIH, as well as controls. Their function, stability, transcriptome and response to AhR were assessed in the absence or presence of methylpiperidinopyrazole (MPP), an ERα-selective antagonist. Therapeutic effects of MPP were tested in a model of Concanavalin-A-induced liver injury in humanized mice.

ERα was upregulated in Tregs from pre-menopausal females with AIH (1.1 ± 0.3) compared with healthy pre-menopausal females (0.4 ± 0.1; p = 0.038), and in pre-menopausal compared with post-menopausal females with AIH (0.3 ± 0.1; p = 0.04). In pre-menopausal females with AIH, MPP enhanced Treg suppressive capacity (2.5-fold increase; p = 0.001), restored response to AhR activation (2-fold increase; p = 0.03), and reduced functional plasticity, evidenced by decreased IL-17A and RORC expression under pro-inflammatory conditions. MPP also ameliorated Concanavalin-A-induced hepatitis in NOD/scid/gamma mice reconstituted with human CD4+ ERα+ cells, as shown by reduced ALT levels (101 ± 24 vs. 25 ± 8; p = 0.024), diminished hepatic inflammation on histology, and increased intrahepatic CD4+FOXP3+ and CD4+CD39+ T-cell frequencies. Bioinformatic and inhibition analyses identified hypoxia-inducible factor-1α as a key inducer of ERα in AIH Tregs.

ERα upregulation drives Treg dysfunction in pre-menopausal females with AIH and likely contributes to the sex bias in the disease. ERα blockade stabilizes Tregs and limits inflammation in vivo, representing a promising therapeutic strategy to enhance and sustain immune tolerance in AIH.

Regulatory T cell (Treg) dysfunction plays a key role in the breakdown of immune tolerance in autoimmune hepatitis (AIH), a severe hepatopathy that often progresses to end-stage liver disease despite immunosuppression. Here we report that upregulation of estrogen receptor-alpha (ERα) alters Treg function and stability in pre-menopausal females with AIH, and that blockade of ERα using a specific antagonist stabilizes Tregs and curbs inflammation in humanized mice with liver injury. These findings implicate aberrant ERα signaling in the sex bias of AIH and support ERα inhibition as a potential therapeutic strategy to re-establish immune tolerance.