Discordance between GLP-1R gene and protein expression in mouse pancreatic islet cells

• Published in: The Journal of biological chemistry Vol. 295; no. 33; pp. 11529 - 11541
• Main Authors: Gray, Sarah M., Xin, Yurong, Ross, Elizabeth C., Chazotte, Bryanna M., Capozzi, Megan E., El, Kimberley, Svendsen, Berit, Ravn, Peter, Sloop, Kyle W., Tong, Jenny, Gromada, Jesper, Campbell, Jonathan E., D'Alessio, David A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 14.08.2020; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; cell sorting; Cells, Cultured; flow cytometry; G protein–coupled receptor (GPCR); Gene Expression; GLP-1R antibody; glucagon-like peptide 1 receptor (GLP-1R); Glucagon-Like Peptide-1 Receptor - analysis; Glucagon-Like Peptide-1 Receptor - genetics; glucose-dependent insulinotropic polypeptide receptor (GIPR); heterogeneity; Humans; incretin; Insulin-Secreting Cells - metabolism; islet; Metabolism; Mice; Mice, Inbred C57BL; Single-Cell Analysis; GLP-1R antibody; G protein–coupled receptor (GPCR); cell sorting; incretin; glucose-dependent insulinotropic polypeptide receptor (GIPR); flow cytometry; metabolism; islet; glucagon-like peptide 1 receptor (GLP-1R); heterogeneity
• ISSN: 0021-9258; 1083-351X; 1083-351X
• DOI: 10.1074/jbc.RA120.014368

The insulinotropic actions of glucagon-like peptide 1 receptor (GLP-1R) in β-cells have made it a useful target to manage type 2 diabetes. Metabolic stress reduces β-cell sensitivity to GLP-1, yet the underlying mechanisms are unknown. We hypothesized that Glp1r expression is heterogeneous among β-cells and that metabolic stress decreases the number of GLP-1R–positive β-cells. Here, analyses of publicly available single-cell RNA-Seq sequencing (scRNASeq) data from mouse and human β-cells indicated that significant populations of β-cells do not express the Glp1r gene, supporting heterogeneous GLP-1R expression. To check these results, we used complementary approaches employing FACS coupled with quantitative RT-PCR, a validated GLP-1R antibody, and flow cytometry to quantify GLP-1R promoter activity, gene expression, and protein expression in mouse α-, β-, and δ-cells. Experiments with Glp1r reporter mice and a validated GLP-1R antibody indicated that >90% of the β-cells are GLP-1R positive, contradicting the findings with the scRNASeq data. α-cells did not express Glp1r mRNA and δ-cells expressed Glp1r mRNA but not protein. We also examined the expression patterns of GLP-1R in mouse models of metabolic stress. Multiparous female mice had significantly decreased β-cell Glp1r expression, but no reduction in GLP-1R protein levels or GLP-1R–mediated insulin secretion. These findings suggest caution in interpreting the results of scRNASeq for low-abundance transcripts such as the incretin receptors and indicate that GLP-1R is widely expressed in β-cells, absent in α-cells, and expressed at the mRNA, but not protein, level in δ-cells.