Fibroblast Growth Factor 23 (FGF23) leads to endolysosomal routing of the renal phosphate co-transporters NaPi-IIa and NaPi-IIc in vivo

2021 ◽  
Author(s):  
Catharina J Küng ◽  
Betül Haykir ◽  
Udo Schnitzbauer ◽  
Daniela Egli-Spichtig ◽  
Nati Hernando ◽  
...  
Keyword(s):  
Growth Factor ◽  
Fibroblast Growth Factor ◽  
Time Course ◽  
Fibroblast Growth Factor 23 ◽  
Fibroblast Growth ◽  
Extracellular Signal ◽  
Early Endosomes ◽  
Lysosomal Proteases ◽  
Intracellular Pathway

The sodium-dependent phosphate co-transporters NaPi-IIa and NaPi-IIc located at the brush border membrane of renal proximal tubules are regulated by numerous factors, including fibroblast growth factor 23 (FGF23). FGF23 downregulates NaPi-IIa and NaPi-IIc abundance after activating a signaling pathway involving phosphorylation of the extracellular signal-regulated protein kinase (phospho-ERK1/2). FGF23 also downregulates the expression of renal 1-α-hydroxylase (Cyp27b1) and upregulates 24-hydroxylase (Cyp24a1), thus reducing plasma calcitriol levels. Here, we examined the time course of the FGF23-induced internalization of NaPi-IIa and NaPi-IIc and their intracellular pathway towards degradation in vivo. Mice were injected intraperitoneally with recombinant human FGF23 (rh-FGF23) in the absence (biochemical analysis) or presence (immunohistochemistry) of leupeptin, an inhibitor of lysosomal proteases. Phosphorylation of ERK1/2 was enhanced 60 minutes after rh-FGF23 administration, and increased phosphorylation was still detected 480 minutes post-injection. Co-localization of phospho-ERK1/2 with NaPi-IIa was seen at 60, 120 and partly at 480 minutes. The abundance of both co-transporters was reduced 240 minutes after rh-FGF23 administration, with a further reduction at 480 minutes. NaPi-IIa and NaPi-IIc were found to co-localize with clathrin and early endosomal antigen 1 (EEA1) as early as 120 minutes after rh-FGF23 injection. Both co-transporters partially co-localized with cathepsin B and Lamp1, markers of lysosomes, 120 minutes after rh-FGF23 injection. Thus, NaPi-IIa and NaPi-IIc are internalized within 2 hours upon rh-FGF23 injection. Both co-transporters share the pathway of clathrin-mediated endocytosis that leads first to early endosomes, finally resulting in trafficking towards the lysosome as early as 120 minutes after rh-FGF23 administration.

scholarly journals Direct and indirect effects of parathyroid hormone on circulating levels of fibroblast growth factor 23 in vivo

2011 ◽  
Vol 80 (5) ◽  
pp. 475-482 ◽  
Author(s):  
Ignacio López ◽  
M. Encarnación Rodríguez-Ortiz ◽  
Yolanda Almadén ◽  
Fátima Guerrero ◽  
A. Montes de Oca ◽  
...  
Keyword(s):  
Parathyroid Hormone ◽  
Growth Factor ◽  
Fibroblast Growth Factor ◽  
Indirect Effects ◽  
Fibroblast Growth Factor 23 ◽  
Fibroblast Growth ◽  
Direct And Indirect Effects ◽  
Circulating Levels

scholarly journals The emerging role of the fibroblast growth factor-23–klotho axis in renal regulation of phosphate homeostasis

2007 ◽  
Vol 194 (1) ◽  
pp. 1-10 ◽  
Author(s):  
Mohammed S Razzaque ◽  
Beate Lanske
Keyword(s):  
Growth Factor ◽  
Fibroblast Growth Factor ◽  
Fibroblast Growth Factor 23 ◽  
Ion Homeostasis ◽  
Experimental Studies ◽  
Receptor Activation ◽  
Fibroblast Growth ◽  
Phosphate Homeostasis ◽  
Downstream Signaling

Normal mineral ion homeostasis is tightly controlled by numerous endocrine factors that coordinately exert effects on intestine, kidney, and bone to maintain physiological balance. The importance of the fibroblast growth factor (FGF)-23–klotho axis in regulating mineral ion homeostasis has been proposed from recent research observations. Experimental studies suggest that 1) FGF23 is an important in vivo regulator of phosphate homeostasis, 2) FGF23 acts as a counter regulatory hormone to modulate the renal 1α-hydroxylase and sodium–phosphate cotransporter activities, 3) there is a trend of interrelationship between FGF23 and parathyroid hormone activities, 4) most of the FGF23 functions are conducted through the activation of FGF receptors, and 5) such receptor activation needs klotho, as a cofactor to generate downstream signaling events. These observations clearly suggest the emerging roles of the FGF23–klotho axis in maintaining mineral ion homeostasis. In this brief article, we will summarize how the FGF23–klotho axis might coordinately regulate normal mineral ion homeostasis, and how their abnormal regulation could severely disrupt such homeostasis to induce disease pathology.

Fibroblast Growth Factor 23 (FGF23) Induces Ventricular Arrhythmias and Prolongs QTc Interval in Mice in an FGF Receptor 4-Dependent Manner

2021 ◽  
Author(s):  
Jonah M. Graves ◽  
Julian A. Vallejo ◽  
Chelsea S. Hamill ◽  
Derek Wang ◽  
Rohan Ahuja ◽  
...  
Keyword(s):  
Growth Factor ◽  
Fibroblast Growth Factor ◽  
Ventricular Arrhythmias ◽  
Ex Vivo ◽  
Fibroblast Growth Factor 23 ◽  
Left Ventricular ◽  
Qtc Interval ◽  
Fibroblast Growth ◽  
Fgf Receptor

Fibroblast growth factor 23 (FGF23) is a phosphate regulating protein hormone released by osteocytes. FGF23 becomes markedly elevated in chronic kidney disease (CKD), for which the leading cause of death is cardiovascular disease, particularly sudden cardiac death. Previously, we found that FGF23 increases intracellular Ca2+ in cardiomyocytes and alters contractility in mouse ventricles ex vivo via FGF-receptor 4 (FGFR4). In the present study, we demonstrate that FGF23 induces cardiac arrhythmias and prolongs QTc interval in mice, and we tested whether these effects are mediated through FGFR4. In isolated Langendorff perfused hearts, FGF23 perfusion increased mechanical arrhythmias in the form of premature ventricular beats (PVBs), and induced runs of ventricular tachycardia in six of 11 animals, which were attenuated with pretreatment of an anti-FGFR4 blocking antibody. Ex vivo ECG analysis of isolated intact hearts showed increased ventricular arrhythmias and QTc prolongation after FGF23 infusion compared to vehicle. In vivo, injection of FGF23 into the jugular vein led to the emergence of premature ventricular contractions (PVCs) in 5 out of 11 experiments. FGF23 also produced a significant lengthening effect upon QTc interval in vivo. In vivo FGFR4 blockade ameliorated the arrhythmogenic and QTc prolonging effects of FGF23. Finally, FGF23 increased cardiomyocyte Ca2+ levels in intact left ventricular muscle which was inhibited by FGR4 blockade. We conclude that FGF23/FGFR4 signaling in the heart may contribute to ventricular arrhythmogenesis and repolarization disturbances commonly observed in patients with CKD via Ca2+ overload and may be an important therapeutic target to reduce cardiac mortality in CKD.

scholarly journals A Control Region Near the Fibroblast Growth Factor 23 Gene Mediates Response to Phosphate, 1,25(OH)2D3, and LPS In Vivo

Endocrinology ◽  
2019 ◽  
Vol 160 (12) ◽  
pp. 2877-2891 ◽  
Author(s):  
Seong Min Lee ◽  
Alex H Carlson ◽  
Melda Onal ◽  
Nancy A Benkusky ◽  
Mark B Meyer ◽  
...  
Keyword(s):  
Growth Factor ◽  
Fibroblast Growth Factor ◽  
Fibroblast Growth Factor 23 ◽  
Mouse Strains ◽  
Fibroblast Growth ◽  
Vitamin D Metabolism ◽  
Dihydroxyvitamin D3 ◽  
Acute Injection ◽  
Insight Into

Abstract Fibroblast growth factor 23 (FGF23) is a bone-derived hormone involved in the control of phosphate (P) homeostasis and vitamin D metabolism. Despite advances, however, molecular details of this gene’s regulation remain uncertain. In this report, we created mouse strains in which four epigenetically marked FGF23 regulatory regions were individually deleted from the mouse genome using CRISPR/Cas9 gene-editing technology, and the consequences of these mutations were then assessed on Fgf23 expression and regulation in vivo. An initial analysis confirmed that bone expression of Fgf23 and circulating intact FGF23 (iFGF23) were strongly influenced by both chronic dietary P treatment and acute injection of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. However, further analysis revealed that bone Fgf23 expression and iFGF23 could be rapidly upregulated by dietary P within 3 and 6 hours, respectively; this acute upregulation was lost in the FGF23-PKO mouse containing an Fgf23 proximal enhancer deletion but not in the additional enhancer-deleted mice. Of note, prolonged dietary P treatment over several days led to normalization of FGF23 levels in the FGF23-PKO mouse, suggesting added complexity associated with P regulation of FGF23. Treatment with 1,25(OH)2D3 also revealed a similar loss of Fgf23 induction and blood iFGF23 levels in this mouse. Finally, normal lipopolysaccharide (LPS) induction of Fgf23 expression was also compromised in the FGF23-PKO mouse, a result that, together with our previous report, indicates that the action of LPS on Fgf23 expression is mediated by both proximal and distal Fgf23 enhancers. These in vivo data provide key functional insight into the genomic enhancers through which Fgf23 expression is mediated.

scholarly journals Sclerostin directly stimulates osteocyte synthesis of fibroblast growth factor-23

2020 ◽  
Author(s):  
Nobuaki Ito ◽  
Matthew Prideaux ◽  
Asiri R. Wijenayaka ◽  
Dongqing Yang ◽  
Renee T. Ormsby ◽  
...  
Keyword(s):  
Growth Factor ◽  
Mrna Expression ◽  
Fibroblast Growth Factor ◽  
Cell Model ◽  
Ex Vivo ◽  
Fibroblast Growth Factor 23 ◽  
Mrna Levels ◽  
Fibroblast Growth ◽  
Pi Homeostasis

AbstractOsteocyte produced fibroblast growth factor 23 (FGF23) is the key regulator of serum phosphate (Pi) homeostasis. The interplay between parathyroid hormone (PTH), FGF23 and other proteins that regulate FGF23 production and serum Pi levels is complex and incompletely characterised. Evidence suggests that the protein product of the SOST gene, sclerostin (SCL), also a PTH target and also produced by osteocytes, plays a role in FGF23 expression, however the mechanism for this effect is unclear. Part of the problem of understanding the interplay of these mediators is the complex multi-organ system that achieves Pi homeostasis in vivo. In the current study, we sought to address this using a unique cell line model of the osteocyte, IDG-SW3, known to express FGF23 at both the mRNA and protein levels. In cultures of differentiated IDG-SW3 cells, both PTH1-34 and recombinant human (rh) SCL remarkably induced Fgf23 mRNA expression dose-dependently within 3 hours. Both rhPTH1-34 and rhSCL also strongly induced C-terminal FGF23 protein secretion. Secreted intact FGF23 levels remained unchanged, consistent with constitutive post-translational cleavage of FGF23 in this cell model. Both rhPTH1-34 and rhSCL treatments significantly suppressed mRNA levels of Phex, Dmp1 and Enpp1 mRNA, encoding putative negative regulators of FGF23 levels, and induced Galnt3 mRNA expression, encoding N-acetylgalactosaminyl-transferase 3 (GalNAc-T3), which protects FGF23 from furin-like proprotein convertase-mediated cleavage. The effect of both rhPTH1-34 and rhSCL was antagonised by pre-treatment with the NF-κβ signalling inhibitors, BAY11 and TPCK. RhSCL also stimulated FGF23 mRNA expression in ex vivo cultures of human bone. These findings provide evidence for the direct regulation of FGF23 expression by sclerostin. Locally expressed sclerostin via the induction of FGF23 in osteocytes thus has the potential to contribute to the regulation of Pi homeostasis.

scholarly journals Identification of novel small molecules that elevate Klotho expression

2011 ◽  
Vol 441 (1) ◽  
pp. 453-461 ◽  
Author(s):  
Gwendalyn D. King ◽  
CiDi Chen ◽  
Mickey M. Huang ◽  
Ella Zeldich ◽  
Patricia L. Brazee ◽  
...  
Keyword(s):  
Growth Factor ◽  
Fibroblast Growth Factor ◽  
Fibroblast Growth Factor 23 ◽  
Functional Change ◽  
In Vivo Studies ◽  
Luciferase Expression ◽  
Fibroblast Growth ◽  
Opossum Kidney

The absence of Klotho (KL) from mice causes the development of disorders associated with human aging and decreased longevity, whereas increased expression prolongs lifespan. With age, KL protein levels decrease, and keeping levels consistent may promote healthier aging and be disease-modifying. Using the KL promoter to drive expression of luciferase, we conducted a high-throughput screen to identify compounds that activate KL transcription. Hits were identified as compounds that elevated luciferase expression at least 30%. Following validation for dose-dependent activation and lack of cytotoxicity, hit compounds were evaluated further in vitro by incubation with opossum kidney and Z310 rat choroid plexus cells, which express KL endogenously. All compounds elevated KL protein compared with control. To determine whether increased protein resulted in an in vitro functional change, we assayed FGF23 (fibroblast growth factor 23) signalling. Compounds G–I augmented ERK (extracellular-signal-regulated kinase) phosphorylation in FGFR (fibroblast growth factor receptor)-transfected cells, whereas co-transfection with KL siRNA (small interfering RNA) blocked the effect. These compounds will be useful tools to allow insight into the mechanisms of KL regulation. Further optimization will provide pharmacological tools for in vivo studies of KL.

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