Tatsuya Yoshizawa

Hypoxia can occur in pancreatic β‐cells in type 2 diabetes. Although hypoxia exerts deleterious effects on β‐cell function, the associated mechanisms are largely unknown. Here, we show that the transcriptional repressor basic helix–loop–helix family member e40 (BHLHE40) is highly induced in hypoxic mouse and human β‐cells and suppresses insulin secretion. Conversely, BHLHE40 deficiency in hypoxic MIN6 cells or β‐cells of ob/ob mice reverses defects in insulin secretion. Mechanistically, BHLHE40 represses the expression of Mafa , encoding the transcription factor musculoaponeurotic fibrosarcoma oncogene family A (MAFA), by attenuating the binding of pancreas/duodenum homeobox protein 1 (PDX1) to its enhancer region. Impaired insulin secretion in hypoxic β‐cells was recovered by MAFA re‐expression. Collectively, our work identifies BHLHE40 as a key hypoxia‐induced transcriptional repressor in β‐cells that inhibit insulin secretion by suppressing MAFA expression.