Gut hormones in the regulation of metabolism
Hormones from the gastrointestinal tract play key roles in the control of appetite and insulin release. Drugs based around one of these hormones, glucagon-like peptide-1 (GLP-1), have recently proved to be highly successful for treating type 2 diabetes. This has led to the current focus on developing strategies to enhance the release of endogenous GLP-1 and other gut peptides, in the hope that this may identify novel treatments for diabetes and obesity and mimic the beneficial physiological effects of gastric bypass surgery. Understanding the mechanisms that underlie secretion from gut endocrine cells is central to this approach, and forms the focus of our research.
In collaboration with the group of Dr Frank Reimann, we employ a variety of optical and electrophysiological recording techniques to monitor stimulus detection and vesicle release from primary and immortalized GLP-1-secreting L cells. As the identification of living gut endocrine cells was a previous major impediment to this field of research, we have generated transgenic mouse models in which GLP-1-expressing cells, or other target cells of interest, are labelled by cell-specific fluorescent markers. These are amenable to purification by flow cytometry and identification in primary culture for single cell recordings. The combination of single cell recordings with transcriptional analysis of FACS-purified cell populations has generated new models for nutrient sensing by L cells. Detection of nutrients in the gut lumen appears to involve electrogenic ion-coupled transporters located on the apical L cell membrane, generating small electrical signals that are subsequently amplified by voltage-gated Ca2+ entry and other signalling pathways such as cAMP elevation and stored Ca2+ release. Comparisons between different enteroendocrine cell types suggest that the pathways identified in L cells are likely to reflect more general stimulus detection mechanisms employed by a wider population of gut endocrine cells.
Parker, H. E., Wallis, K., le Roux, C. W., Wong, K. Y., Reimann, F. and Gribble, F. M. Molecular mechanisms underlying bile acid stimulated glucagon-like peptide-1 secretion. Br. J. Pharmacol. 165, 414–423 (2012).
Tolhurst, G., Zheng, Y., Parker, H. E., Habib, A. M,, Reimann, F. and Gribble, F. M. Glutamine triggers and potentiates glucagon-like peptide-1 secretion by raising cytosolic Ca2+ and cAMP. Endocrinol 152, 405–413 (2011).
Greenfield, F. R., Farooqi, I. S., Keogh, J., Henning, E., Habib, A. M., Blackwood, A., Reimann, F., Holst, J. J. and Gribble, F. M. Oral glutamine increases circulating GLP-1, glucagon and insulin levels in lean, obese and type 2 diabetic subjects. Am. J. Clin. Nutr. 89, 106–113 (2009).
Reimann, F., Ward, P.S. and Gribble, F.M. Signalling mechanisms underlying the release of Glucagon-Like Peptide-1. Diabetes 55, S78–S85 (2006).
Cox, J. J., Reimann, F., Nicholas, A. K., Thornton, G., Roberts, E., Springell, K., Karbani, G., Jafri, H., Mannan, J., Raashid, J., Al-Gazali, L., Hamamy, H., Valente, E.M., Gorman, S., Williams, R., McHale, D.P., Wood, J.N., Gribble, F.M. & Woods, C.G. An SCN9A channelopathy causes congenital inability to experience pain. Nature 444, 894–898 (2006).
O'Malley, D., Reimann, F., Simpson, A. K. & Gribble, F. M. Sodium-coupled glucose cotransporters contribute to hypothalamic glucose sensing. Diabetes 55, 3381–3386 (2006).
Gameiro, A., Reimann, F., Habib, A. M., O‘Malley, D., Williams, L., Simpson, A. K. and Gribble, F. M. The neurotransmitters glycine and GABA stimulate glucagon-like peptide-1 release from the GLUTag cell line. J. Physiol. 569, 761–772 (2005).
Reimann, F., Maziarz, M., Flock, G., Habib, A. M., Drucker, D. J. and Gribble, F. M. Characterization and functional role of voltage gated cation conductances in the glucagon-like peptide-1 secreting GLUTag cell line. J. Physiol. 563, 161–175 (2005).
Reimann, F., Williams, L., Silva Xavier, G. da, Rutter, G. A. and Gribble, F. M. Glutamine potently stimulates Glucagon-Like Peptide-1 secretion from GLUTag cells. Diabetologia 47, 1592–1601 (2004).
Gribble, F. M., Williams, L., Simpson, A. K. and Reimann, F. A novel glucose-sensing mechanism contributing to Glucagon-Like Peptide-1 secretion from the GLUTag cell line. Diabetes 52, 1147–1154 (2003).