MAFB is essential for the maintenance of adult human α-cell identity and glucagon secretion

<jats:p>Dysregulated hormone secretion and erosion of endocrine cell identity are features of type 1 and type 2 diabetes, but the transcriptional programs maintaining adult human islet identity and function remain poorly defined. The large MAF transcription factor MAFB is expressed in human α- and β-cells, marks their most functionally mature subpopulations, and is downregulated in diabetes, but its role in adult human islets has not been tested directly. Using shRNA-mediated MAFB knockdown (KD) in whole and CD26+ α-cell-enriched human pseudoislets, we found that whole pseudoislet MAFB KD impaired glucagon synthesis and secretion while only modestly reducing insulin content and cAMP-potentiated insulin release. Single-cell profiling detected no β-cell transcriptional response beyond MAFB KD itself, consistent with buffering by the related β-cell-enriched MAFA transcription factor. In contrast, α-cell-restricted MAFB KD unmasked a cell-autonomous requirement for MAFB in stimulus-secretion coupling. MAFB deficiency also destabilized α-cell identity, downregulating canonical α-cell and neuroendocrine secretory genes while ectopically inducing mesenchymal and extracellular matrix remodeling programs. In addition, MAFB-dependent downregulation of electron transport chain genes was confined to a large α-cell subcluster, manifesting as impaired islet-wide mitochondrial respiration within the broader α-cell population. Together, these findings identify MAFB as an essential adult human α-cell maintenance factor that links diabetes-associated downregulation to impaired glucagon secretion, α-cell identity erosion, and mitochondrial dysfunction.</jats:p>