164 College St
Toronto, ON M5S 3E2
Investigating the Signalling Dynamics and Functional Role of FGFR5 in Pancreatic Beta Cells
* This is an open PhD defence—all welcome. *
Dawn Kilkenny and Jonathan Rocheleau
Loss of glucose homeostasis due to reduced beta cell mass and function are characteristics of the metabolic disorder diabetes. Identifying protein targets that affect beta cell mass and function may lead to better therapeutic strategies to treat this disease.
One such family of protein target is the Fibroblast Growth Factor Receptors (FGFRs) of tyrosine kinases. FGFR1, the canonical receptor, influences insulin processing and glucose metabolism by triggering intracellular signalling events upon ligand stimulation. FGFR5, the newest member of this family, exhibits the capacity for extracellular FGF ligand binding yet presents a unique intracellular domain that lacks tyrosine kinase capacity to initiate signalling.
Although its structure predicts down-regulation of FGFR1-mediated signalling, FGFR5 signalling and its effects in beta cells were previously unknown.
We used a combination of traditional biochemical assays and quantitative live cell fluorescence microscopy to probe the expression, signalling and physiological consequences of FGFR5 in beta cells.
We developed a novel microfluidics-based protocol to improve adenoviral transduction of pancreatic islets to deliver genetic material to a majority of cells throughout the tissue and improve the study of protein function in primary ex vivo beta cells.
We created a library of fluorescent protein-tagged functional isoforms of FGFR5 and identified receptor localization to insulin secretory granules, association with SHP-1 phosphatase via the receptor’s unique intracellular region and ligand-independent activation of the MAPK pathway.
Furthermore, FGFR5 expression was found to increase total insulin content, cell adhesion, and improve beta cell survival during pro-inflammatory cytokine-induced stress but did not affect beta cell proliferation.
Using a combination of co-immunoprecipitation and advanced quantitative fluorescence microscopy, we found that FGFR5 exists as asymmetric trimers at the plasma membrane and forms hetero-complexes with FGFR1, suggesting regulation of canonical receptor signalling.
These findings represent advancement in our understanding of FGFR5 biology, specifically in the context of beta cell physiology.
The engineered protein constructs and microfluidic device platform provide tools for further characterization of the effects of FGFR5 on insulin processing and signalling dynamics to better understand how the receptor could be targeted to treat diabetes.