miR155, triplicated in Down syndrome, regulates the development of neural stem cells and GABAergic interneurons in Alzheimer's disease mouse and human iPSC models.

INTRODUCTION: Dysfunctional microRNAs and GABAergic interneurons are features of Alzheimer's disease (AD). The role of neuronal microRNA155 (miR155), elevated in both AD and Down syndrome (DS), remains unknown. METHODS: We utilized in silico analyses of published databases, MIR155-deleted and -overexpressing human induced pluripotent stem cell (hiPSC)-derived cells, cortical organoids, and amyloid beta precursor protein (APP)/PS1-miR155 knockout mouse. RESULTS: MIR155HG (miR155 host gene) colocalizes with APP in a neuron-specific, topologically associated domain (TAD) in chromosome 21. In human neural stem cells (NSCs), neurons, and cortical organoids, MIR155 deletion enhanced NSC proliferation and GABAergic interneuron generation. MIR155 overexpression inhibited NSC marker expression and GABAergic interneuron generation. In APP/PS1 mice, miR155 deletion induced the expansion of hippocampal NSCs and increased hippocampal GABAergic interneurons. DISCUSSION: Our findings, alongside the extensive studies of the role of microglial miR155 in neuroinflammation, reveal previously unrecognized miR155 roles in hippocampal NSC dynamics and GABAergic interneuron development, highlighting miR155 as a therapeutic target.