Disruption of glucagon receptor increase a-cell glucagon expression and secretion beyond hyperplasia in zebrafish

Glucagon receptor (GCGR) is a potential target for diabetes therapy. Several emerging GCGR antagonism-based therapies are under pre-clinical and clinical development. However, the GCGR antagonism as well as GCGR deficient animal accompanied with a-cell hyperplasia and hyperglucagonemia, which may limit the application of GCGR antagonism. To better understand the physiological changes in the a cells during the GCGR disruption, we performed the single cell sequencing of a cells isolated from control and gcgr-/- zebrafish. We found that a cells in gcgr-/- zebrafish dramatically increased glucagon (both gcga and gcgb) expression, we also found that several transcriptional factors that regulate glucagon expression were also increased. Based on the sequencing data, we further experimentally confirmed that gcgr-/- up-regulated glucagon mRNA level by in situ hybridization, and the gcgr-/- increased glucagon promoter activity indicated by reporter line Tg(gcga: GFP). Moreover, our results also revealed that a cells increased glucagon granule population and glucagon level in gcgr-/- zebrafish. These data suggested that hyperglucagonemia in the organism of GCGR antagonism not only contributed by the a-cell hyperplasia but also contributed by the increased glucagon expression and secretion from a cells. Our study provided more comprehensive understanding of physiological changes of a-cell during the GCGR disruption. Overall design: The 7 dfp (days post fertilization) zebrafish larvae a cells were subjected to single cell RNA-sequencing. We obtained 576 cells sequencing data (384 gcgr-/- and 192 control), After quality control and excluded the potential contaminated ß cells and d cells, 285 high-quality cells were obtained for subsequent analysis (197 gcgr-/- and 88 control).