The L cell transcriptome is unaffected by vertical sleeve gastrectomy but highly dependent upon position within the gastrointestinal tract

Abstract

Altered GLP-1 secretion from L cells has been implicated in the development of type 2 diabetes mellitus and its resolution following bariatric surgery. However, changes in L cell gene expression, which may form the basis for altered functionality after high fat diet (HFD) or bariatric surgery, have either not been investigated or have given conflicting results. We developed a gcg-DTR-eGFP reporter mouse to isolate ileal and colonic L cells from HFD fed insulin resistant mice and mice showing improved glucose tolerance following vertical sleeve gastrectomy (VSG). Transcriptomic sequencing and identification of genes differentially expressed in response to HFD or VSG revealed small changes with HFD, primarily in immune related genes, but no regulation following VSG. In contrast, large differences were observed between ileal and colonic L cells due to the differential expression of genes involved in nutrient transport and metabolism, reflecting to some extent the differences in the surrounding epithelium. We showed that, in line with the gene expression data, colonic and ileal L cells exhibit differing GLP-1 responses to nutrients (glucose and the gly-sar dipeptide) and hormones (vasopressin). Thus, we hypothesise that colonic and ileal L cells have different physiological roles, with ileal L cells contributing more to postprandial glucose homeostasis by responding to dietary nutrients and colonic cells responding more to non-dietary stimulants.