Hypertrophy dependent doubling of L-cells in Roux-en-Y gastric bypass operated rats

Abstract

Background and aims: Roux-en-Y gastric bypass (RYGB) leads to a rapid remission of type 2 diabetes mellitus (T2DM), but the underlying mode of action remains incompletely understood. L-cell derived gut hormones such as glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) are thought to play a central role in the anti-diabetic effects of RYGB; therefore, an improved understanding of intestinal endocrine L-cell adaptability is considered pivotal.

Methods: The full rostrocaudal extension of the gut was analyzed in rats after RYGB and in sham-operated controls ad libitum fed or food restricted to match the body weight of RYGB rats. Total number of L-cells, as well as regional numbers, densities and mucosa volumes were quantified using stereological methods. Preproglucagon and PYY mRNA transcripts were quantified by qPCR to reflect the total and relative hormone production capacity of the L-cells.

Results: RYGB surgery induced hypertrophy of the gut mucosa in the food exposed regions of the small intestine coupled with a doubling in the total number of L-cells. No changes in L-cell density were observed in any region regardless of surgery or food restriction. The total gene expression capacity of the entire gut revealed a near 200% increase in both PYY and preproglucagon mRNA levels in RYGB rats associated with both increased L-cell number as well as region-specific increased transcription per cell.

Conclusions: Collectively, these findings indicate that RYGB in rats is associated with gut hypertrophy, an increase in L-cell number, but not density, and increased PYY and preproglucagon gene expression. This could explain the enhanced gut hormone dynamics seen after RYGB.

Figure 1. RYGB surgery and sampling procedure.

The RYGB surgical procedures connecting the upper jejunum (alimentary channel, red) to the gastric pouch circumpassing the duodenum (biliopancreatic channel, green) (A–B). At termination each segment was sampled using stereological sampling principles into two sets of 7–9 transverse biopsies. One set was used for histology, one set for qPCR analyses (C).

Figure 2. Body weight change for gastric bypass (n = 5) and sham-operated rats ad libitum fed (n = 5) and sham-operated body weight matched (n = 5) (A).

Average daily food intake over 20 weeks for sham operated ad libitum fed rats and for gastric bypass rats (B).

Figure 3. Representative micrographs of gut morphology (A–C) and GLP-2 immunohistochemistry (D–F) in the alimentary channel of SHAM, RYGB and SHAM WM animals.

Figure 4. Stereological estimates of total and regional gut volume (A–B), L-cell number (C–D) and L-cell density (E–F).

All values are presented as mean ± SEM. One-way ANOVA with Tukey's Multiple Comparison post-hoc test, (* = p<0.05,** = p<0.01, *** = p<0.001 for significance).

Figure 5. Regional preproglucagon (A) and PYY (B) gene expression normalized to 18s and corrected for the varying epithelial volume (C–D).

Total preproglucagon (E) and PYY (F) gene expression. All values are arbitrary units presented as mean ± SEM. Statistical analysis: One-way ANOVA with Tukey's Multiple Comparison post-hoc test, SHAM vs. RYGB (*); VW vs. RYGB (?). (*? = p<0.05,**?? = p<0.01, for significance).