Background: FGFR1c and KLB form an ill-defined FGF21 signaling complex. Results: FGFR1c competes with galectin for binding to KLB. KLB and FGFR1c interact in a 1:1 heterocomplex, and subsequent addition of FGF21 induces FGFR1c dimers. Conclusion: KLB and FGFR1c activity and dynamics suggest that the galectin lattice modulates FGF21 signaling. Significance: The galectin lattice is a novel target to potentiate therapeutic effects of FGF21.
Fibroblast growth factor-21 (FGF21) has therapeutic potential for metabolic syndrome due to positive effects on fatty acid metabolism in liver and white adipose tissue. FGF21 also improves pancreatic islet survival in excess palmitate; however, much less is known about FGF21-induced metabolism in this tissue. We first confirmed FGF21-dependent activity in islets by identifying expression of the cognate coreceptor Klothoβ, and by measuring a ligand-stimulated decrease in acetyl-CoA carboxylase expression. To further reveal the effect of FGF21 on metabolism, we employed a unique combination of two-photon and confocal autofluorescence imaging of the NAD(P)H and mitochondrial NADH responses while holding living islets stationary in a microfluidic device. These responses were further correlated to mitochondrial membrane potential and insulin secretion. Glucose-stimulated responses were relatively unchanged by FGF21. In contrast, responses to glucose in the presence of palmitate were significantly reduced compared to controls showing diminished NAD(P)H, mitochondrial NADH, mitochondrial membrane potential, and insulin secretion. Consistent with the glucose-stimulated responses being smaller due to continued fatty acid oxidation, mitochondrial membrane potential was increased in FGF21-treated islets by using the fatty acid transport inhibitor etomoxir. Citrate-stimulated NADPH responses were also significantly larger in FGF21-treated islets suggesting preference for citrate cycling rather than acetyl-CoA carboxylase-dependent fatty acid synthesis. Overall, these data show a reduction in palmitate-induced potentiation of glucose-stimulated metabolism and insulin secretion in FGF21-treated islets, and establish the use of autofluorescence imaging and microfluidic devices to investigate cell metabolism in a limited amount of living tissue.
dimerization of the receptor-ligand complex and then oligomerization. Past research, through predominantly biochemical methods, have concluded that EphA2 signaling depends on the degrees of multimerization of the proteins and the topology of the ligand presentation. However, clustering mechanisms of EphA2 proteins are not well understood because these signaling molecules function in the cell membrane, which is an environment that is difficult to characterize and manipulate. Our hypothesis is that the multi-scale organization of EphA2 in the cell membrane regulates its biochemical function. To mimic the cell-cell junction, we use a supported lipid bilayer -cell membrane hybrid system. Breast cancer cells presenting EphA2 are cultured on a fluid lipid bilayer consisting of ligand fusion proteins, which can stably interact with a subset of capturing lipids within the bilayer. This interaction allows us to control the protein density, precisely image it, and maintain molecular mobility so ligand-induced receptor clustering can occur. Receptor cluster size is varied by changing the cluster size and degrees of oligomerization of its ligand. On the nanometer length scale, antibodies are used to cross link monomeric forms of ligand fusion proteins and thereby vary the degrees of oligomerization. On the micrometer scale, patterned chromium substrates are used to segregate ligands into corrals of variable cluster sizes. Our results suggest that the spatial organization of receptor plays a role in orchestrating the cascade of signaling switches.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.