Fibroblast Growth Factor Activity Research Articles

Three feedback loops precisely regulating serum phosphate concentration

Parathyroid hormone (PTH) and vitamin D were considered the major factors regulating phosphate homeostasis. Now, with the identification of fibroblast growth factor 23 (FGF23), a phosphaturic molecule inhibiting calcitriol and PTH, they need to be integrated into three feedback loops involving parathyroid, bone, and kidney. PTH and calcitriol are required for the appropriate synthesis of FGF23 by bone cells. PTH also regulates klotho expression in the kidney and thereby the phosphaturic action of FGF23.

A high‐content screening assay in transgenic zebrafish identifies two novel activators of fgf signaling

Zebrafish have become an invaluable vertebrate animal model to interrogate small molecule libraries for modulators of complex biological pathways and phenotypes. We have recently described the implementation of a quantitative, high-content imaging assay in multi-well plates to analyze the effects of small molecules on Fibroblast Growth Factor (FGF) signaling in vivo. Here we have evaluated the capability of the assay to identify compounds that hyperactivate FGF signaling from a test cassette of agents with known biological activities. Using a transgenic zebrafish reporter line for FGF activity, we screened 1040 compounds from an annotated library of known bioactive agents, including FDA-approved drugs. The assay identified two molecules, 8-hydroxyquinoline sulfate and pyrithione zinc, that enhanced FGF signaling in specific areas of the brain. Subsequent studies revealed that both compounds specifically expanded FGF target gene expression. Furthermore, treatment of early stage embryos with either compound resulted in dorsalized phenotypes characteristic of hyperactivation of FGF signaling in early development. Documented activities for both agents included activation of extracellular signal-related kinase (ERK), consistent with FGF hyperactivation. To conclude, we demonstrate the power of automated quantitative high-content imaging to identify small molecule modulators of FGF.

Comparative effect of FGF2, synthetic peptides 1-28 N-POMC and ACTH on proliferation in rat adrenal cell primary cultures

There is evidence that pro-opiomelanocortin (POMC)-derived peptides other than adrenocorticotropic hormone (ACTH) have a role in adrenal cell proliferation. We compared the activity of synthetic rat N-terminal POMC fragment 1-28 with disulfide bridges (N-POMC(w)) and without disulfide bridges (N-POMC(w/o)), with the activity of fibroblast growth factor (FGF2), a widely studied adrenal growth factor, and ACTH, in well-characterized pure cultures of both isolated adrenal Glomerulosa (G) and Fasciculata/Reticularis (F/R) cells. Three days of FGF2-treatment had a proliferative effect similar to serum, and synthetic peptide N-POMC(w) induced proliferation more efficiently than N-POMC(w/o). Moreover, both induced proliferation via the ERK1/2 pathway. In contrast, sustained ACTH treatment decreased proliferation and viability through apoptosis induction, but not necrosis, and independently of PKA and PKC pathways. Further elucidation of 1-28 POMC signal transduction is of interest, and primary cultures of adrenal cells were found to be useful for examining the trophic activity of this peptide.

Endothelial mesenchymal transformation mediated by IL-1β-induced FGF-2 in corneal endothelial cells

This review describes the molecular mechanism of endothelial mesenchymal transformation (EMT) mediated by fibroblast growth factor-2 (FGF-2) in corneal endothelial cells (CECs). Corneal fibrosis is not frequently observed in corneal endothelium/Descemet’s membrane complex; but when this pathologic tissue is produced, it causes a loss of vision by physically blocking light transmittance. Herein, we will address the cellular activities of FGF-2 and its signaling pathways during the EMT process. Furthermore, we will discuss the role of inflammation on FGF-2-mediated EMT. Interleukin-1β (IL-1β) greatly upregulates FGF-2 production in CECs, thus leading to FGF-2-mediated EMT; the whole spectrum of the injury-mediated inflammation (IL-1β pathway) and the subsequent EMT process (FGF-2 pathway) will be briefly discussed. Intervention in the two pathways will provide the means to block EMT before inflammation causes an irreversible change, such as the production of retrocorneal fibrous membrane observed in human eyes.

Fibroblast growth factor 23 as a phosphotropic hormone and beyond

Fibroblast growth factor 23 (FGF23) is produced by bone and reduces serum phosphate by inhibiting proximal tubular phosphate reabsorption and intestinal phosphate absorption. Excess actions of FGF23 cause several kinds of hypophosphatemic rickets/osteomalacia while deficient actions of FGF23 result in hyperphosphatemic tumoral calcinosis. In addition, FGF23 has been shown to prevent the development of hyperphosphatemia during the progression of chronic kidney disease-mineral and bone disorder. Epidemiological studies have indicated that high FGF23 levels are associated with unfavorable events including higher mortality, cardiovascular events, progression of CKD and fracture; however, these associations are not observed unequivocally and it is not evident why they are present. While FGF23 has been shown to be a hormone that regulates phosphate metabolism, it remains to be established whether FGF23 has roles other than regulating mineral homeostasis.

Purification and Refolding of Overexpressed Human Basic Fibroblast Growth Factor inEscherichia coli

This work describes the integration of expanded bed adsorption (EBA) and adsorptive protein refolding operations used to recover purified and biologically active human basic fibroblast growth factor from inclusion bodies expressed in E. coli. Insoluble overexpressed human basic fibroblast growth factor has been purified on CM Hyper Z matrix by expanded bed adsorption after isolation and solubilization in 8 M urea. The adsorption was made in expanded bed without clarification steps such as centrifugation. Column refolding was done by elimination of urea and elution with NaCl. The human basic fibroblast growth factor was obtained as a highly purified soluble monomer form with similar behavior in circular dichroism and fluorescence spectroscopy as native protein. A total of 92.52% of the available human basic fibroblast growth factor was recovered as biologically active and purified protein using the mentioned purification and refolding process. This resulted in the first procedure describing high-throughput purification and refolding of human basic fibroblast growth factor in one step and is likely to have the greatest benefit for proteins that tend to aggregate when refolded by dilution.

FGF and retinoic acid activity gradients control the timing of neural crest cell emigration in the trunk

Coordination between functionally related adjacent tissues is essential during development. For example, formation of trunk neural crest cells (NCCs) is highly influenced by the adjacent mesoderm, but the molecular mechanism involved is not well understood. As part of this mechanism, fibroblast growth factor (FGF) and retinoic acid (RA) mesodermal gradients control the onset of neurogenesis in the extending neural tube. In this paper, using gain- and loss-of-function experiments, we show that caudal FGF signaling prevents premature specification of NCCs and, consequently, premature epithelial-mesenchymal transition (EMT) to allow cell emigration. In contrast, rostrally generated RA promotes EMT of NCCs at somitic levels. Furthermore, we show that FGF and RA signaling control EMT in part through the modulation of elements of the bone morphogenetic protein and Wnt signaling pathways. These data establish a clear role for opposition of FGF and RA signaling in control of the timing of NCC EMT and emigration and, consequently, coordination of the development of the central and peripheral nervous system during vertebrate trunk elongation.

Induction of Smooth Muscle Cell Migration During Arteriogenesis Is Mediated by Rap2

Collateral artery growth or arteriogenesis is the primary means of the circulatory system to maintain blood flow in the face of major arterial occlusions. Arteriogenesis depends on activation of fibroblast growth factor (FGF) receptors, but relatively little is known about downstream mediators of FGF signaling. We screened for signaling components that are activated in response to administration of FGF-2 to cultured vascular smooth muscle cells (VSMCs) and detected a significant increase of Rap2 but not of other Ras family members, which corresponded to a strong upregulation of Rap2 and C-Raf in growing collaterals from rabbits with femoral artery occlusion. Small interfering RNAs directed against Rap2 did not affect FGF-2 induced proliferation of VSMC but strongly inhibited their migration. Inhibition of FGF receptor-1 (FGFR1) signaling by infusion of a sulfonic acid polymer or infection with a dominant-negative FGFR1 adenovirus inhibited Rap2 upregulation and collateral vessel growth. Similarly, expression of dominant-negative Rap2 blocked arteriogenesis, whereas constitutive active Rap2 enhanced collateral vessel growth. Rap2 is part of the arteriogenic program and acts downstream of the FGFR1 to stimulate VSMC migration. Specific modulation of Rap2 might be an attractive target to manipulate VSMC migration, which plays a role in numerous pathological processes.

Fibroblast Growth Factor 23 (FGF23) and Alpha-Klotho Stimulate Osteoblastic MC3T3.E1 Cell Proliferation and Inhibit Mineralization

Elevated serum levels of the phosphate-regulating hormone fibroblast growth factor 23 (FGF23) are found in patients with phosphate wasting diseases and chronic kidney disease-mineral and bone disorder (CKD-MBD). These diseases are associated with rickets and renal osteodystrophy, respectively. FGF23 is secreted from osteoblastic cells and signals through FGFRs, membrane coreceptor alpha-Klotho (Klotho), and, possibly, a circulating form of Klotho. Despite the absence of detectable Klotho on osteoblastic cells, studies have suggested that forced FGF23 expression in osteoblasts inhibited mineralization. Thus, we examined the effects of exogenously applied FGF23 on osteoblastic MC3T3.E1 cell proliferation and differentiation, with and without soluble Klotho. MC3T3.E1 cells were cultured in osteoblast differentiation medium, supplemented with FGF23 (0.1–1,000 ng/mL), Klotho (50 ng/mL), the combination FGF23 + Klotho, and FGF2 (100 ng/mL) as a control. Neither FGF23 nor Klotho exposure affected proliferation of day 4 growth phase cells or mineralization of day 14 cultures. In contrast, FGF23 + Klotho resulted in inhibition of mineralization and osteoblast activity markers at day 14, and a slight, reproducible induction of proliferation. Inhibition of FGFR1, but not FGFR2 or FGFR3, completely restored FGF23 + Klotho-induced inhibition of alkaline phosphatase (ALP) activity at day 7. ALP activity was partially restored by the MAPK inhibitor U0126 but not inhibitors p38 and P13K. Thus, soluble Klotho enables FGF23 signaling in MC3T3.E1 cells, likely through FGFR 1(IIIc). Elevated FGF23 actions, in part, appear to parallel FGF2 with lower potency. In addition to affecting bone via indirect phosphate wasting pathways, supraphysiological FGF23 and soluble Klotho may directly impact bone in diseases with elevated FGF23 levels.

Senataxin modulates neurite growth through fibroblast growth factor 8 signalling

Senataxin is encoded by the SETX gene and is mainly involved in two different neurodegenerative diseases, the dominant juvenile form of amyotrophic lateral sclerosis type 4 and a recessive form of ataxia with oculomotor apraxia type 2. Based on protein homology, senataxin is predicted to be a putative DNA/RNA helicase, while senataxin interactors from patients' lymphoblast cell lines suggest a possible involvement of the protein in different aspects of RNA metabolism. Except for an increased sensitivity to oxidative DNA damaging agents shown by some ataxia with neuropathy patients' cell lines, no data are available about possible functional consequences of dominant SETX mutations and no studies address the function of senataxin in neurons. To start elucidating the physiological role of senataxin in neurons and how disease-causing mutations in this protein lead to neurodegeneration, we analysed the effect of senataxin on neuronal differentiation in primary hippocampal neurons and retinoic acid-treated P19 cells by modulating the expression levels of wild-type senataxin and three different dominant mutant forms of the protein. Wild-type senataxin overexpression was required and sufficient to trigger neuritogenesis and protect cells from apoptosis during differentiation. These actions were reversed by silencing of senataxin. In contrast, overexpression of the dominant mutant forms did not affect the regular differentiation process in primary hippocampal neurons. Analysis of the cellular pathways leading to neuritogenesis and cytoprotection revealed a role of senataxin in modulating the expression levels and signalling activity of fibroblast growth factor 8. Silencing of senataxin reduced, while overexpression enhanced, fibroblast growth factor 8 expression levels and the phosphorylation of related target kinases and effector proteins. The effects of senataxin overexpression were prevented when fibroblast growth factor 8 signalling was inhibited, while exogenous fibroblast growth factor 8 reversed the effects of senataxin silencing. Overall, these results reveal a key role of senataxin in neuronal differentiation through the fibroblast growth factor 8 signalling and provide initial molecular bases to explain the neurodegeneration associated with loss-of-function mutations in senataxin found in recessive ataxia. The lack of effect on neuritogenesis observed with the overexpression of the dominant mutant forms of senataxin apparently excludes a dominant negative effect of these mutants while favouring haploinsufficiency as the pathogenic mechanism implicated in the amyotrophic lateral sclerosis 4-related degenerative condition. Alternatively, a different protein function, other than the one involved in neuritogenesis, may be implicated in these dominant degenerative processes.

Regulation of serum 1,25(OH)2 vitamin D3 levels by fibroblast growth factor 23 is mediated by FGF receptors 3 and 4.

Fibroblast growth factor 23 (FGF23) is a phosphaturic hormone implicated in the pathogenesis of several hypophosphatemic disorders. FGF23 causes hypophosphatemia by decreasing the expression of sodium phosphate cotransporters (NaPi-2a and NaPi-2c) and decreasing serum 1,25(OH)(2)Vitamin D(3) levels. We previously showed that FGFR1 is the predominant receptor for the hypophosphatemic actions of FGF23 by decreasing renal NaPi-2a and 2c expression while the receptors regulating 1,25(OH)(2)Vitamin D(3) levels remained elusive. To determine the FGFRs regulating 1,25(OH)(2)Vitamin D(3) levels, we studied FGFR3(-/-)FGFR4(-/-) mice as these mice have shortened life span and are growth retarded similar to FGF23(-/-) and Klotho(-/-) mice. Baseline serum 1,25(OH)(2)Vitamin D(3) levels were elevated in the FGFR3(-/-)FGFR4(-/-) mice compared with wild-type mice (102.2 ± 14.8 vs. 266.0 ± 34.0 pmol/l; P = 0.001) as were the serum levels of FGF23. Administration of recombinant FGF23 had no effect on serum 1,25(OH)(2)Vitamin D(3) in the FGFR3(-/-)FGFR4(-/-) mice (173.4 ± 32.7 vs. 219.7 ± 56.5 pmol/l; vehicle vs. FGF23) while it reduced serum 1,25(OH)(2)Vitamin D(3) levels in wild-type mice. Administration of FGF23 to FGFR3(-/-)FGFR4(-/-) mice resulted in a decrease in serum parathyroid hormone (PTH) levels and an increase in serum phosphorus levels mediated by increased renal phosphate reabsorption. These data indicate that FGFR3 and 4 are the receptors that regulate serum 1,25(OH)(2)Vitamin D(3) levels in response to FGF23. In addition, when 1,25(OH)(2)Vitamin D(3) levels are not affected by FGF23, as in FGFR3(-/-)FGFR4(-/-) mice, a reduction in PTH can override the effects of FGF23 on renal phosphate transport.

FLRT3 as a key player on chick limb development

Limb outgrowth is maintained by a specialized group of cells, the apical ectodermal ridge (AER), a thickening of the limb epithelium at its distal tip. It has been shown that fibroblast growth factor (FGF) activity and activation of the Erk pathway are crucial for AER function. Recently, FLRT3, a transmembrane protein able to interact with FGF receptors, has been implicated in the activation of ERK by FGFs. In this study, we show that flrt3 expression is restricted to the AER, co-localizing its expression with fgf8 and pERK activity. Loss-of-function studies have shown that silencing of flrt3 affects the integrity of the AER and, subsequently, its proper function during limb bud outgrowth. Our data also indicate that flrt3 expression is not regulated by FGF activity in the AER, whereas ectopic WNT3A is able to induce flrt3 expression. Overall, our findings show that flrt3 is a key player during chicken limb development, being necessary but not sufficient for proper AER formation and maintenance under the control of BMP and WNT signalling.

Impact of activating fibroblast growth factor receptor 3 mutation in endochondral ossification

Impact of activating fibroblast growth factor receptor 3 mutation in endochondral ossification

Elevated hepatic fatty acid oxidation, high plasma fibroblast growth factor 21, and fasting bile acids in nonalcoholic steatohepatitis

Data from studies in patients with nonalcoholic steatohepatitis (NASH) suggest an increased hepatic fatty acid oxidation. We have previously shown higher fasting plasma bile acid concentrations in patients with NASH. In-vivo and in-vitro studies suggest that bile acids by binding to peroxisome proliferator-activated receptor α activate fibroblast growth factor 21 (FGF21) and increase hepatic fatty acid oxidation. Plasma bile acid levels were quantified in healthy controls (n=38) and patients with biopsy-proven NASH (n=36). Plasma concentration of fatty acids, β-hydroxybutyrate, insulin, glucose, leptin, alanine aminotransferase, FGF21, and 8-hydroxydeoxyguanosine, a measure of oxidative stress, were measured in 16 healthy controls and 10 patients with NASH in the fasted state and in response to 3 h of infusion of intralipid. In a subgroup of these patients (n=6 each), plasma ceramide subspecies were quantified. Fasting plasma bile acids, FGF21, and leptin concentrations were significantly higher in patients with NASH. In response to intralipid infusion there was an increase in plasma β-hydroxybutyrate and free fatty acid levels in both controls and NASH; however, the ratio of β-hydroxybutyrate/free fatty acid was higher in NASH (P=0.02). Plasma FGF21 concentration increased in response to intralipid in patients with NASH only (P<0.01). Plasma leptin, insulin, glucose, and alanine transferase concentrations did not change in either group after infusion of intralipid. Increase in total ceramides in response to intralipid was greater in NASH. Elevated bile acids and FGF21 may be responsible for the higher hepatic fatty acid oxidation in NASH.

Fibroblast growth factor-2 regulation of sprouty and NR4A genes in bovine ovarian granulosa cells

Fibroblast growth factors (FGFs) alter ovarian function, at least in part by inhibiting steroid hormone secretion and affecting survival of granulosa cells. The mechanism of action of FGFs in ovarian follicle cells is largely unknown; in the present study we identified the major pathways used by FGF2 in non-luteinizing granulosa cells cultured under serum-free conditions. FGF2 increased abundance of mRNA encoding SPRY1, 2, and 4, but not SPRY3. Common pathways employed by FGF2 in the regulation of SPRY1, 2, and 4, as demonstrated by immunoblot and inhibitor studies, included ERK1/2 and Akt signaling. In contrast, PKC activation was necessary for FGF2-stimulated expression of SPRY1 and 4, but not for SPRY2. Intracellular calcium flux is critical and sufficient for SPRY2 expression, but not for SPRY1 and 4. We also identified the orphan nuclear receptor NR4A1 as a potential early response gene in FGF2 signaling, whose expression, like that of SPRY2, is critically dependent on calcium signaling. Together, these data identify FGF2-target genes in follicular granulosa cells, and demonstrate alternative pathway use for the differential control of SPRY genes.

Abstract 1100: Correlation of basic fibroblast growth factor and cyclooxygenase-2 activity in non-small lung cancer cells

Abstract Basic fibroblast growth factor (FGF-2) is a potent wide-spectrum mitogen and the dysregulation of its expression is associated with cell proliferation and immortalization in a wide variety of tumors. Its oncogenic nature may depend, in part, on its ability to prevent apoptosis. Its antisense gene, NUDT6, encodes a novel Nudix motif protein of unknown function, and overexpression of NUDT6 is known to suppress FGF-dependent cell proliferation (Baguma-Nibasheka et al, Mol Cell Endocrinol 267:127-136, 2007). Cyclooxygenase-2 (COX-2) is a key enzyme in prostaglandin synthesis whose up-regulation has been implicated in the promotion of lung cancer. COX-2 inhibition suppresses growth and induces apoptosis in human non-small cell lung cancer (NSCLC) cells. In this study, we evaluated the hypothesis that the antitumor activity of COX-2 inhibitors in lung cancer may involve modulation of FGF-2, which is overexpressed in NSCLC. Results: FGF, NUDT6 and COX-2 are co-expressed in NSCLC cells, and FGF-2 and COX-2, but not NUDT6 messenger RNA levels, as well as cell proliferation, are decreased by serum deprivation. Selective inhibition of COX-2 suppresses FGF-2 but not NUDT6 expression, and FGF-2 knockdown negates the effect of COX-2 inhibition on cell proliferation. These findings indicate that the antitumor effects of COX-2 inhibition in NSCLC may be mediated via suppression of FGF-2. Supported by the Frostburg State University of Biology Department. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1100. doi:10.1158/1538-7445.AM2011-1100

Fibroblast growth factor 23 regulates renal 1,25-dihydroxyvitamin D and phosphate metabolism via the MAP kinase signaling pathway in Hyp mice

In X-linked hypophosphatemia (XLH) and in its murine homologue, the Hyp mouse, increased circulating concentrations of fibroblast growth factor 23 (FGF-23) are critical to the pathogenesis of disordered metabolism of phosphate (P(i)) and 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. In this study, we hypothesized that in Hyp mice, FGF-23-mediated suppression of renal 1,25(OH)(2)D production and P(i) reabsorption depends on activation of mitogen-activated protein kinase (MAPK) signaling. Wild-type and Hyp mice were administered either vehicle or the MEK inhibitor PD0325901 (12.5 mg/kg) orally daily for 4 days. At baseline, the renal abundance of early growth response 1 (egr1) mRNA was approximately 2-fold greater in Hyp mice than in wild-type mice. Treatment with PD0325901 greatly suppressed egr1 mRNA abundance in both wild-type and Hyp mice. In Hyp mice, PD0325901 induced an 8-fold increase in renal 1α-hydroxylase mRNA expression and a 4-fold increase in serum 1,25(OH)(2)D concentrations compared with vehicle-treated Hyp mice. Serum P(i) levels in Hyp mice increased significantly after treatment with PD0325901, and the increase was associated with increased renal Npt2a mRNA abundance and brush-border membrane Npt2a protein expression. These findings provide evidence that in Hyp mice, MAPK signaling is constitutively activated in the kidney and support the hypothesis that the FGF-23-mediated suppression of renal 1,25(OH)(2)D production and P(i) reabsorption depends on activation of MAPK signaling via MEK/ERK1/2. These findings demonstrate the physiologic importance of MAPK signaling in the actions of FGF-23 in regulating renal 1,25(OH)(2)D and P(i) metabolism.

EphrinB1 interacts with the transcriptional co-repressor Groucho/xTLE4

Ephrin signaling is involved in various morphogenetic events, such as axon guidance, hindbrain segmentation, and angiogenesis. We conducted a yeast two-hybrid screen using the intracellular domain (ICD) of EphrinB1 to gain biochemical insightinto the function of the EphrinB1 ICD. We identified the transcriptional co-repressor xTLE1/Groucho as an EphrinB1 interacting protein. Whole-mount in situ hybridization of Xenopus embryos confirmed the co-localization of EphrinB1 and a Xenopus counterpart to TLE1, xTLE4, during various stages of development. The EphrinB1/xTLE4 interaction was confirmed by co-immunoprecipitation experiments. Further characterization of the interaction revealed that the carboxy-terminal PDZ binding motif of EphrinB1 and the SP domain of xTLE4 are required for binding. Additionally, phosphorylation of EphrinB1 by a constitutively activated fibroblast growth factor receptor resulted in loss of the interaction, suggesting that the interaction is modulated by tyrosine phosphorylation of the EphrinB1 ICD.

Osteo‐renal regulation of systemic phosphate metabolism

Impaired kidney function and subsequent skeletal responses play a critical role in disrupting phosphate balance in chronic kidney disease (CKD) patients with mineral and bone disorder (CKD-MBD). In patients with CKD-MBD, the inability of the kidney to maintain normal mineral ion balance affects bone remodeling to induce skeletal fracture and extraskeletal vascular calcification. In physiological conditions, bone-derived fibroblast growth factor 23 (FGF23) acts on the kidney to reduce serum phosphate and 1,25-dihydroxyvitamin D levels. In humans, increased bioactivity of FGF23 leads to increased urinary phosphate excretion, which induces hypophosphatemic diseases (e.g., rickets/osteomalacia). However, reduced FGF23 activity is associated with hyperphosphatemic diseases (e.g., tumoral calcinosis). In patients with CKD, high serum levels of FGF23 fail to reduce serum phosphate levels and lead to numerous complications, including vascular calcification, one of the important determinants of mortality of CKD-MBD patients. Of particular significance, molecular, biochemical and morphological changes in patients with CKD-MBD are mostly due to osteo-renal dysregulation of mineral ion metabolism. Furthermore, hyperphosphatemia can partly contribute to the development of secondary hyperparathyroidism in patients with CKD-MBD. Relatively new pharmacological agents including sevelamer hydrochloride, calcitriol analogs and cinacalcet hydrochloride are used either alone, or in combination, to minimize hyperphosphatemia and hyperparathyroidism associated complications to improve morbidity and mortality of CKD-MBD patients. This article will briefly summarize how osteo-renal miscommunication can induce phosphate toxicity, resulting in extensive tissue injuries.

Activation of FGFR(IIIc) isoforms promotes activin-induced mesendoderm development in mouse embryonic stem cells and reduces Sox17 coexpression in EpCAM+ cells

Activin induces the formation of definitive endoderm from mouse ES cells dependent on active fibroblast growth factor (Fgf) signaling. Here we report that Fgf4 is dispensable for activin A-induced differentiation of mouse ES cells into endoderm. We find that Fgf4−/− cells readily differentiate into definitive endoderm without exogenous administration of Fgf4. Additionally, we investigate the spatio-temporal dynamics of Fgf receptor (FGFR) isoform distribution in activin A-treated ES cell cultures and find that FGFR(III)c isoforms are expressed in DE as well as non-DE populations, whereas FGFR2(III)b and FGFR4 are found specifically enriched in the DE fraction. Ligands that preferentially activate the FGFR(III)c isoforms induce mesendoderm markers T and Gsc, but reduce expression of the DE marker Sox17 in activin-induced EpCAM+ cells. In contrast, ligands specifically activating FGFR(III)b isoforms have no effect on either population. Activation of FGFR(III)c isoforms results in a strong mitogenic effect on activin A-induced ES cell progeny early in the differentiation period whereas activation of FGFR(III)b isoforms has only a moderate mitogenic effect confined to the late differentiation period. We conclude that FGFR(III)c-isoform activation selectively drives the differentiation of mES cells toward mesendoderm and that Fgf4 is dispensable for the differentiation into definitive endoderm.