Blockade of glucagon receptor induces a-cell hypersecretion by hyperaminoacidemia in mice
Blockade of the glucagon receptor (GCGR) has been shown to improve glycemic control. However, this therapeutic approach also brings side effects, such as a-cell hyperplasia and hyperglucagonemia, and the mechanisms underlying these side effects remain elusive. Here, we conduct single-cell transcriptomic sequencing of islets from male GCGR knockout (GCGR-KO) mice. Our analysis confirms the elevated expression of Gcg in GCGR-KO mice, along with enhanced glucagon secretion at single-cell level. Notably, Vgf (nerve growth factor inducible) is specifically upregulated in a cells of GCGR-KO mice. Inhibition of VGF impairs the formation of glucagon immature secretory granules and compromises glucagon maturation, lead to reduced a-cell hypersecretion of glucagon. We further demonstrate that activation of both mTOR-STAT3 and ERK-CREB pathways, induced by elevated circulation amino acids, is responsible for upregulation of Vgf and Gcg expression following glucagon receptor blockade. Thus, our findings elucidate a previously unappreciated molecular mechanism underlying hyperglucagonemia in GCGR blockade. Overall design: The pancreatic islets were isolated from 8-12-week-old male C57BL/6J mice.  To prepare the single-cell suspension, the purified islets were digested with 0.25% trypsin-EDTA and filtered through a 40 µm cell strainer. Cell viability was evaluated by trypan blue staining, followed by microscopy to ensure that cell viability was greater than 90%, and over 90% of cells were singlets.