Targeting miRNA-mediated immune activation in humanized mice

Islet autoimmunity, the presymptomatic phase of type 1 diabetes (T1D), is characterized by aberrations in immune activation versus T-cell tolerance. However, the molecular underpinnings remain poorly understood. MiRNAs regulate multiple targets and thereby can alter complex cellular states. During recent onset of islet autoimmunity, increased miRNA92a and miRNA181a expression in CD4+T cells contribute to aberrant immune activation and impaired regulatory T cell (Treg) induction. Mechanistically, we showed that miRNA92a increases T follicular helper (TFH) cell differentiation, while miRNA181a enhances the sensitivity of CD4+T cells to antigenic stimulation involving increased NFAT5 signaling. Both miRNAs inhibit negative regulators of T cell activation and impair Treg induction in vitro. Blocking these miRNAs or NFAT5 in NOD mice reduces immune activation paralleled by local increases in Treg frequencies. Here, using humanized mice (murine MHC-deficient, HLA-DQ8-transgenic, NOD-Scid-IL2Rg-KO) reconstituted with human hematopoietic cells, we investigated the role of these miRNAs and downstream signaling pathways in immune activation vs. Treg induction. Inhibiting miRNA92a reduced immune activation as highlighted by significantly decreased pancreas-infiltrating insulin-specific CD4+T cells accompanied by decreased insulin-specific TFH precursors (insulin-specific CD4+CXCR5+PD1highT cells [% of insulin-specific CD4+]: control antagomir: 18.8±5.3% vs. miRNA92a antagomir: 3.6±3.6%; p<0.05). Moreover, NFAT5 blockade significantly increased Treg frequencies in the peripheral blood (CD25highFxop3highTregs: vehicle: 9.9±1.2% vs. NFAT5 inhibitor: 14.8±1.0%; p<0.05), as well as in the spleen of humanized mice. These initial findings highlight positive effects of miRNA92a or NFAT5 inhibition on reducing immune activation in the setting of a human immune system in vivo. Further studies will test the implication of these molecules as targetable signaling intermediates to interfere with aberrant immune activation during ongoing islet autoimmunity