The short chain fatty acid propionate stimulates GLP-1 and PYY secretion via free fatty acid receptor 2 in rodents

Abstract

Background and objectives: The gut hormones peptide YY (PYY) and glucagon-like peptide 1 (GLP-1) acutely suppress appetite. The short chain fatty acid (SCFA) receptor, free fatty acid receptor 2 (FFA2) is present on colonic enteroendocrine L cells, and a role has been suggested for SCFAs in appetite regulation. Here, we characterise the in vitro and in vivo effects of colonic propionate on PYY and GLP-1 release in rodents, and investigate the role of FFA2 in mediating these effects using FFA2 knockout mice.

Methods: We used Wistar rats, C57BL6 mice and free fatty acid receptor 2 knockout (FFA(-/-)) mice on a C57BL6 background to explore the impact of the SCFA propionate on PYY and GLP-1 release. Isolated colonic crypt cultures were used to assess the effects of propionate on gut hormone release in vitro. We subsequently developed an in vivo technique to assess gut hormone release into the portal vein following colonic infusion of propionate.

Results: Propionate stimulated the secretion of both PYY and GLP-1 from wild-type primary murine colonic crypt cultures. This effect was significantly attenuated in cultures from FFA2(-/-) mice. Intra-colonic infusion of propionate elevated PYY and GLP-1 levels in jugular vein plasma in rats and in portal vein plasma in both rats and mice. However, propionate did not significantly stimulate gut hormone release in FFA2(-/-) mice.

Conclusions: Intra-colonic administration of propionate stimulates the concurrent release of both GLP-1 and PYY in rats and mice. These data demonstrate that FFA2 deficiency impairs SCFA-induced gut hormone secretion both in vitro and in vivo.

Figures

Figure 1

The effect of propionate on GLP-1 and PYY secretion from primary murine L cells. Mixed primary colonic cultures were incubated with propionate (1–50 mmol l−1) (a, c). At a concentration of 50 mmol l−1, NaCl had no effect on gut hormone release (b, d). GLP-1 and PYY secretion in each well was expressed as a percentage of total GLP-1 or PYY contained within the well and normalised to the basal secretion measured in parallel within the same experiment. Data represent means±s.e.m. (n=6–24 wells). Significance is shown relative to basal secretion (0 mmol l−1) (a, c) or to the iso-osmotic NaCl control (b, d) using one-way ANOVA (a, F=11.73, P<0.0001; b, F=7.931, P=0.0022; c, F=24.75, P<0.0001; d, F=25.99, P<0.0001) with a Bonferroni post hoc test (*P<0.05, **P<0.01, ***P<0.001).

Figure 2

Intra-colonic administration of propionate increases jugular and portal vein plasma gut hormone concentrations in male Wistar rats. Blood samples were collected over a 60-min period, via a jugular vein cannula (a, c), and at t=15 min from the portal vein (b, d), following an intra-colonic injection (2.5 ml) of 180 mmol l−1 propionate or saline (matched for pH and sodium content) in isoflurane-anaesthetised rats. Data represent means±s.e.m. (n=10–14 per group). Significance was determined using two-way ANOVA (a, c) or unpaired t-test (b, d) (*P<0.05).

Figure 3

Propionate-induced PYY and GLP-1 secretion is attenuated in FFA2−/− primary murine L cells. Primary colonic cultures from FFA2 knockout (−/−) or WT (+/+) littermates were incubated with or without propionate (50 mmol l−1). PYY (a) and GLP-1 (b) secretion in each well was expressed as a percentage of total PYY or GLP-1 contained within the well and normalised to the basal secretion (0 mmol l−1) measured in parallel within the same experiment. Data represent means±s.e.m. (n=22–38 wells). Significance is shown relative to basal secretion using one-way ANOVA (a, F=19.31, P<0.0001; b, F=8.816, P<0.0001) with a Bonferroni post hoc test (**P<0.01; ***P<0.001).

Figure 4

Intra-colonic administration of propionate increases portal vein plasma PYY and GLP-1 levels in vivo in mice via an FFA2-dependent mechanism. Blood samples were collected from the portal vein 5 min after an intra-colonic injection (300 μl) of propionate (180 mmol l−1) or saline (matched for pH and sodium content) in isoflurane-anaesthetised FFA2 knockout (−/−) mice or WT littermates (+/+). Data represent means±s.e.m. (n=5–7 per group). Significance was determined using one-way ANOVA (a, F=2.457, P=0.094; b, F=2.660, P=0.076) with a Bonferroni post hoc test (*P<0.05).