Liquid chromatography/mass spectrometry based detection and semi-quantitative analysis of INSL5 in human and murine tissues.

RATIONALE: Insulin-like peptide 5 (INSL5) is a hormone produced by enteroendocrine L-cells in the colon that has recently been implicated in the control of metabolic homeostasis. However, research into its physiology has been hindered by the reported unreliability of commercially available immunoassays and additional detection assays would benefit this emerging field. METHODS: Peptides from purified murine L-cells and homogenates from both human and mouse colonic tissues were extracted by precipitating larger proteins with acetonitrile. Untargeted liquid chromatography/tandem mass spectrometry (LC/MS/MS) analyses, followed by database searching, were used to detect and identify various INSL5 gene derived peptides and characterise their precise sequence. A similar approach was developed to quantify INSL5 levels in primary intestinal culture supernatants after purification and concentration by solid-phase extraction. RESULTS: Mass spectral analysis of purified enteroendocrine cells and tissue homogenates identified the exact sequence of A and B chains of INSL5 endogenously expressed in L-cells. Differences in the endogenously processed peptide and the Swissprot database entry were observed for murine INSL5, whereas the human sequence matched previous predictions from heterologous expression experiments. INSL5 was detected in the supernatant of human and mouse primary colonic cultures and concentrations increased after treatment with a known L-cell stimulus. CONCLUSIONS: The first LC/MS/MS-based method capable of the detection and semi-quantitative analysis of endogenous INSL5 using MS-based techniques has been demonstrated. The methodology will enable the identification of stimulants for INSL5 secretion from murine and human primary colonic epithelial cultures.

SCFAs strongly stimulate PYY production in human enteroendocrine cells.

Peptide-YY (PYY) and Glucagon-Like Peptide-1 (GLP-1) play important roles in the regulation of food intake and insulin secretion, and are of translational interest in the field of obesity and diabetes. PYY production is highest in enteroendocrine cells located in the distal intestine, mirroring the sites where high concentrations of short chain fatty acids (SCFAs) are produced by gut microbiota. We show here that propionate and butyrate strongly increased expression of PYY but not GCG in human cell line and intestinal primary culture models. The effect was predominantly attributable to the histone deacetylase inhibitory activity of SCFA and minor, but significant contributions of FFA2 (GPR43). Consistent with the SCFA-dependent elevation of PYY gene expression, we also observed increased basal and stimulated PYY hormone secretion. Interestingly, the transcriptional stimulation of PYY was specific to human-derived cell models and not reproduced in murine primary cultures. This is likely due to substantial differences in PYY gene structure between mouse and human. In summary, this study revealed a strong regulation of PYY production by SCFA that was evident in humans but not mice, and suggests that high fibre diets elevate plasma concentrations of the anorexigenic hormone PYY, both by targeting gene expression and hormone secretion.