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

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 - and {beta}-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+ -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 {beta}-cell transcriptional response beyond MAFB KD itself, consistent with buffering by the related {beta}-cell-enriched MAFA transcription factor. In contrast, -cell-restricted MAFB KD unmasked a cell-autonomous requirement for MAFB in stimulus-secretion coupling. MAFB deficiency also destabilized -cell identity, downregulating canonical -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 -cell subcluster, manifesting as impaired islet-wide mitochondrial respiration within the broader -cell population. Together, these findings identify MAFB as an essential adult human -cell maintenance factor that links diabetes-associated downregulation to impaired glucagon secretion, -cell identity erosion, and mitochondrial dysfunction.