RFX6 maintains gene expression and function of adult human islet a cells

ABSTRACT

Mutations in the gene encoding the transcription factor RFX6 are associated with human diabetes mellitus. Within pancreatic islets, RFX6 expression is most abundant in islet a cells, and a cell RFX6 expression is altered in diabetes. However, the roles of RFX6 in regulating gene expression, glucagon output and other crucial human adult a cell functions are not yet understood. We developed a method for selective genetic targeting of human a cells and assessed RFX6-dependent a cell function. RFX6 suppression with RNA interference led to impaired a cell exocytosis and dysregulated glucagon secretion in vitro and in vivo. By contrast, these phenotypes were not observed with RFX6 suppression across all islet cells. Transcriptomics in a cells revealed RFX6-dependent expression of genes governing nutrient sensing, hormone processing, and secretion, with some of these exclusively expressed in human a cells. Mapping of RFX6 DNA-binding sites in primary human islet cells identified a subset of direct RFX6 target genes. Together, these data unveil RFX6-dependent genetic targets and mechanisms crucial for regulating adult human a cell function.

ARTICLE HIGHLIGHTS

· RFX6 is expressed in all islet endocrine cell types and is dysregulated in multiple forms of diabetes, but its function has not yet been delineated in a cells.

· We used specific targeting of shRNA-mediated suppression of RFX6 in primary human a cells to unveil glucagon secretion phenotypes.

· RFX6 is required in adult human a cells to maintain gene regulation and hallmark functions, including regulated glucagon secretion.

· RNA-sequencing and CUT&RUN studies reveal distinct RFX6 genetic targets in adult human a and b cells.