• Stimulus-response coupling in mouse and human islet β-cells
• Role of G-protein-coupled receptors in islet function
• Novel insulin secretagogues

Stimulus-response coupling in mouse and human islets
My research interests are directed towards defining signal transduction pathways involved in the regulated secretion of islet hormones, and mechanisms through which β-cell mass is regulated. Techniques used by members of my group include isolation of islets of Langerhans from experimental animals; cell culture; measurement of apoptosis by caspase assays; measurement of ATP and NAD(P)H generation; detection of islet cell proliferation in vitro and in vivo by BrdU incorporation into DNA; transient and stable transfection of cells for gene overexpression and knock down; isolation and analysis of RNA and DNA; quantitative and single cell RT-PCR; differential gene expression; calcium microfluorimetry; dynamic hormone secretion in perifusion; measurement of hormone and cyclic nucleotide levels by immunoassay; immunocyto/histochemistry; Western blotting of PAGE-fractionated proteins; measurement of serine/threonine and tyrosine kinase activities in situ and in vitro; intra-peritoneal glucose and insulin tolerance tests. Much of the published research on intracellular pathways involved in the regulation of insulin secretion is performed on rodent islets or β-cell lines. While there is an overlap in many instances between regulatory mechanisms in rodents and humans, there are some important differences. The only way to define which β-cell signalling systems identified in animal models also function in humans is to carry out the experiments using human islets. Through a long-term collaboration with Professor Stephanie Amiel and Dr. Guo Cai Huang at King’s College Hospital, we are using isolated human islets to determine the signal transduction cascades operative in human β-cells that regulate the exocytotic release of insulin, glucagon and somatostatin.

Role of G-protein-coupled receptors in islet function

A number of islet G-protein-coupled receptors (GPCRs) are under investigation by pharmaceutical companies as potential targets for diabetes therapies. We have identified that human islets express mRNAs encoding 293 GPCRs, the majority of which have unknown function in islets, so there is considerable scope for discovery of druggable GPCR candidates. We have been investigating the roles played by a range of GPCR families in regulating islet hormone secretion, enhancing β-cell proliferation and protecting β-cells against apoptosis. Recent focus has been on islet receptors activated by cannabinoids (CB1, CB2 and GPR55), the hypothalamic peptide kisspeptin (GPR54), the chemokine CCL5 (GPR75) and the adhesion receptor, GPR56. In addition, through a collaborative project with Dr. Gavin Bewick we have discovered a novel role for islet PYY receptors in the maintenance of β-cell mass.

Novel insulin secretagogues                                              
Numerous plants have been used in traditional medicines for the treatment of diabetes and several naturally occurring peptides may activate stimulatory receptors in β-cells. We are examining the therapeutic potential of plant-derived extracts and novel peptides by measuring their effects on dynamic insulin secretion from MIN6 β-cells and isolated mouse and human islets in vitro. We are also studying the intracellular signalling events activated by these novel insulin secretagogues in β-cells and assessing their effects on improving glucose tolerance in mice in vivo.