Fibroblast Growth Factor Receptor-1 Signaling in Pancreatic Islet β-Cells Is Modulated by the Extracellular Matrix

Abstract

Maintenance of pancreatic beta-cell mass depends on extracellular stimuli that promote survival and proliferation. In the islet, these stimuli come from the beta-cell microenvironment and include extracellular matrix deposited by associated vascular endothelial cells. Fibroblast growth factor receptor-1 (FGFR1) has recently been implicated as a signaling pathway that is important for normal beta-cell function. We would like to understand how extracellular matrix and FGFR1 signaling interact to promote beta-cell survival and proliferation. To examine beta-cell-specific receptor responses, we created lentiviral vectors with rat insulin promoter-driven expression of Venus fluorescent protein-tagged full-length (R1betav) and kinase-deficient (KDR1betav) FGFR1. Significant FGF-1-dependent activation of ERK1/2 was observed in betaTC3 cells, dispersed beta-cells, and beta-cells in intact islets. This response was enhanced by R1betav expression and reduced by KDR1betav expression. Plating-dispersed beta-cells on collagen type IV resulted in enhanced expression of endogenous FGFR1 that was associated with sustained activation of ERK1/2. Conversely, plating cells on laminin reduced expression of FGFR1, and this reduction was associated with transient activation of ERK1/2. Addition of neutralizing antibodies to inhibit beta-cell attachment to laminin via alpha(6)-integrin increased high-affinity FGF-1-binding at the plasma membrane and resulted in sustained ERK1/2 activity similar to cells plated on collagen type IV. These data show that the FGF-stimulated beta-cell response is negatively affected by alpha(6)-integrin binding to laminin and suggest regulation associated with vascular endothelial cell remodeling.

Fibroblast Growth Factor Receptor Like-1 (FGFRL1) Interacts with SHP-1 Phosphatase at Insulin Secretory Granules and Induces Beta-cell ERK1/2 Protein Activation

“…The islets of these mice contained a diminished number of beta-cells with reduced glucose sensitivity and impaired insulin processing, demonstrating the importance of FGF signaling in maintenance of beta-cell physiology and glucose homeostasis. We previously confirmed FGFR1 activity in adult murine pancreatic beta-cells, and we further showed changes in islet glucose-stimulated metabolism and insulin secretion in the presence of the FGFR1-ligand FGF21 (2,22). Overall, these data suggest that FGFR1-induced signaling regulates beta-cell biology via classical intracellular signaling responses and may be associated with the onset and progression of metabolic disorders such as diabetes.…”

“…Pancreatic islets were isolated from 8-to 12-week-old C57BL6 male mice by collagenase digestion (Roche Applied Science) (22). Islets were equilibrated in full RPMI 1640 medium supplemented with 11 mM glucose, 10% FBS, and 5 units/ml penicillin/streptomycin prior to mRNA harvest or dispersion to single cells using Accutase (Sigma) for fixation and immunostaining as described previously (2).…”

“…Immunoprecipitation-␤TC3 cells were harvested as described previously (2). Cell lysates (500 g/sample) were pre-cleared with protein A/G PLUS-agarose bead slurry (20 l/sample; Santa Cruz Biotechnology) by incubating on a rotating platform (30 min, 4°C).…”

“…Fibroblast growth factors (FGFs) compose a large family of 23 polypeptides that exhibit diverse yet redundant roles in biological processes such as cellular proliferation, differentiation, and metabolism (1)(2)(3)(4)(5). Activation of intracellular signaling cascades is classically mediated by ligand interaction with high affinity cell surface tyrosine kinase receptors FGFR1-4 that are structurally similar and exhibit a high degree of sequence homology at the amino acid level (6,7).…”

Endothelial cell signalling supports pancreatic beta cell function in the rat

“…Indeed, the high islet vascular density and the vascular phenotype, with a great number of fenestrations, is induced and maintained by secretion of vascular endothelial growth factor from the beta cells [9][10][11]. Recently, we and others have shown that endothelial cells signal back and contribute to maintenance [12], and during certain conditions even expansion, of the adult beta cell mass [6,[13][14][15]. In the present study, we tested the hypothesis that islet endothelial cell products may directly influence beta cell function.…”