RNA sequencing unravels novel L cell constituents and mechanisms of GLP-1 secretion in human gastric bypass-operated intestine

Diabetologia. 2024 Feb;67(2):356-370. doi: 10.1007/s00125-023-06046-8. Epub 2023 Nov 30.

Abstract

Aims/hypothesis: Roux-en-Y gastric bypass surgery (RYGB) frequently results in remission of type 2 diabetes as well as exaggerated secretion of glucagon-like peptide-1 (GLP-1). Here, we assessed RYGB-induced transcriptomic alterations in the small intestine and investigated how they were related to the regulation of GLP-1 production and secretion in vitro and in vivo.

Methods: Human jejunal samples taken perisurgically and 1 year post RYGB (n=13) were analysed by RNA-seq. Guided by bioinformatics analysis we targeted four genes involved in cholesterol biosynthesis, which we confirmed to be expressed in human L cells, for potential involvement in GLP-1 regulation using siRNAs in GLUTag and STC-1 cells. Gene expression analyses, GLP-1 secretion measurements, intracellular calcium imaging and RNA-seq were performed in vitro. OGTTs were performed in C57BL/6j and iScd1-/- mice and immunohistochemistry and gene expression analyses were performed ex vivo.

Results: Gene Ontology (GO) analysis identified cholesterol biosynthesis as being most affected by RYGB. Silencing or chemical inhibition of stearoyl-CoA desaturase 1 (SCD1), a key enzyme in the synthesis of monounsaturated fatty acids, was found to reduce Gcg expression and secretion of GLP-1 by GLUTag and STC-1 cells. Scd1 knockdown also reduced intracellular Ca2+ signalling and membrane depolarisation. Furthermore, Scd1 mRNA expression was found to be regulated by NEFAs but not glucose. RNA-seq of SCD1 inhibitor-treated GLUTag cells identified altered expression of genes implicated in ATP generation and glycolysis. Finally, gene expression and immunohistochemical analysis of the jejunum of the intestine-specific Scd1 knockout mouse model, iScd1-/-, revealed a twofold higher L cell density and a twofold increase in Gcg mRNA expression.

Conclusions/interpretation: RYGB caused robust alterations in the jejunal transcriptome, with genes involved in cholesterol biosynthesis being most affected. Our data highlight SCD as an RYGB-regulated L cell constituent that regulates the production and secretion of GLP-1.

Keywords: GLP-1; Gastric bypass surgery; Glucagon-like peptide-1; Intestine; Obesity; RNA sequencing; Remission; SCD; Stearoyl-CoA desaturase; Type 2 diabetes.

MeSH terms

  • Animals
  • Blood Glucose / metabolism
  • Cholesterol
  • Diabetes Mellitus, Type 2* / metabolism
  • Gastric Bypass* / methods
  • Glucagon-Like Peptide 1 / metabolism
  • Humans
  • L Cells
  • Mice
  • Mice, Inbred C57BL
  • RNA
  • RNA, Messenger
  • Sequence Analysis, RNA

Substances

  • Glucagon-Like Peptide 1
  • RNA
  • Cholesterol
  • RNA, Messenger
  • Blood Glucose