Abstract
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.
Highlights
The incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) are secreted from the gastrointestinal tract following a meal and augment
The GLP-1 receptor (GLP-1R) and GIP receptor (GIPR) have distinct expression across various tissues [4], both receptors were originally identified in b-cells, where they mediate the principle action of incretins, insulin secretion
To test whether incretin receptors were heterogeneously expressed in b-cells, transcriptomes from publicly available human [12, 13, 18,19,20,21] and mouse [22] scRNAseq datasets were analyzed to determine the expression patterns of GLP1R/Glp1r and GIPR/Gipr
Summary
The incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) are secreted from the gastrointestinal tract following a meal and augment. The work starts with analysis of human and mouse single-cell RNASeq data to document the expression of the incretin receptor genes in islets cells. These data suggested significant heterogeneity in incretin receptor expression, which we expanded upon with studies measuring Glp1r RNA expression and GLP-1R protein presence on individual islet a-, b-, and d-cells.
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