Selective activation of FGFR4 by an FGF19 variant does not improve glucose metabolism in ob/ob mice

Abstract

FGF19 is a hormone that regulates bile acid and glucose homeostasis. Progress has been made in identifying cofactors for receptor activation. However, several functions of FGF19 have not yet been fully defined, including the actions of FGF19 on target tissues, its FGF receptor specificity, and the contributions of other cofactors, such as heparin. Here, we explore the requirements for FGF19-FGFR/co-receptor interactions and signaling in detail. We show that ␤Klotho was essential for FGF19 interaction with FGFRs 1c, 2c, and 3c, but FGF19 was able to interact directly with FGFR4 in the absence of ␤Klotho in a heparin-dependent manner. Further, FGF19 activated FGFR4 signaling in the presence or absence of ␤Klotho, but activation of FGFRs 1c, 2c, or 3c was completely ␤Klotho dependent. We then generated an FGF19 molecule, FGF19dCTD, which has a deletion of the C-terminal region responsible for ␤Klotho interaction. We determined that ␤Klotho-dependent FGFR1c, 2c, and 3c interactions and activation were abolished, and ␤Klotho-independent FGFR4 activation was preserved; therefore, FGF19dCTD is an FGFR4-specific activator. This unique FGF19 molecule specifically activated FGFR4-dependent signaling in liver and suppressed CYP7A1 expression in vivo, but was unable to activate signaling in adipose where FGFR4 expression is very low. Interestingly, unlike FGF19, treatment of ob/ob mice with FGF19dCTD failed to improve glucose levels and insulin sensitivity. These results suggest that FGF19-regulated liver bile acid metabolism could be independent of its glucose-lowering effect, and direct FGFR activation in adipose tissue may play an important role in the regulation of glucose homeostasis.T he FGF19 subfamily of fibroblast growth factors (FGFs), consisting of FGF19, FGF21, and FGF23, has been implicated in the regulation of many metabolic processes (1-4). One of the properties of this subfamily is atypical heparin binding (5). FGFs generally have a positively charged heparin-binding region that helps create high-affinity interactions with cell surface FGF receptors (FGFRs) (6). Compared with other FGFs, the crystal structures of FGF19 and FGF23 revealed a disrupted heparinbinding motif, which could weaken interactions with heparin or heparan sulfate (5, 7). Consistent with this, direct measurement of affinity for immobilized heparin showed that FGF21 did not interact with heparin and that FGF19 and FGF23 bound to heparin weakly compared with the affinity of immobilized heparin for the other FGFs (6). Consequently, members of this subfamily may not be retained by heparin-containing tissues or the extracellular matrix, thus making it possible for them to function as endocrine hormones.Another distinctive feature of this subfamily is the requirement for the co-receptors ␣Klotho or ␤Klotho in FGFR signaling complexes (8-11). With reduced affinity toward heparin, FGF19, 21, and 23 may use ␣Klotho or ␤Klotho proteins to stabilize their interactions with FGFRs to activate downstream signaling pathways. This requirement for either...

Sulfated Glycosaminoglycans Are Required for Specific and Sensitive Fibroblast Growth Factor (FGF) 19 Signaling via FGF Receptor 4 and betaKlotho

“…1 summarizes the effects of hFGF19 at nanomolar concentrations. Our findings are consistent with those of earlier studies, which examined the activity of hFGF19 at concentrations ranging from 10 to 100 nM (15,26,27). However, hFGF19 concentrations in the human circulation are reportedly in the subnanomolar range, most likely around 30 pM, which is 3-4 orders of magnitude lower than the concentrations tested previously (28 -30).…”

The effects of metformin on fibroblast growth factor 19, 21 and fibroblast growth factor receptor 1 in high-fat diet and streptozotocin induced diabetic rats

“…By binding to FGFR4, FGF19 inhibits CYP7A1, the rate limiting enzyme of bile acid biosynthesis, thus inhibiting bile acid synthesis. In addition, previous study showed that selective activation of FGFR4 failed to improve glucose metabolism in ob/ob mice [11]. Thus,…”

Dual actions of fibroblast growth factor 19 on lipid metabolism

“…protocol, and treated with various FGF molecules as previously described ( 15 ). Cells were collected 15 min after treatment, snap frozen in liquid nitrogen, and resuspended in lysis buffer, and the total and phosphorylated ERK were measured using an MSD whole cell lysate Phospho-ERK1/2 kit (Meso Scale Discovery) according to the manufacturer's instructions.…”