Secretion Of Fibroblast Growth Factor Research Articles

Th2 Cytokines Increase the Expression of Fibroblast Growth Factor 21 in the Liver.

Interleukin-4 (IL-4) and IL-13 are the major T helper 2 (Th2) cytokines, and they are involved in the regulation of metabolism in the adipose tissue. The liver contains diverse innate and adaptive immune cells, but it remains to be determined whether Th2 cytokines modulate energy metabolism in the liver. Here, using gene expression data from the Gene Expression Omnibus (GEO) and the BXD mouse reference population, we determined that the Th2 cytokines IL-4 and IL-13 increase the secretion of fibroblast growth factor 21 (FGF21) in the liver. In vitro experiments confirmed that FGF21 was highly expressed in response to IL-4 and IL-13, and this response was abolished by the Janus kinase (JAK)-signal transducer and activator of transcription 6 (STAT6) blockade. Moreover, FGF21 expression in response to Th2 cytokines was augmented by selective peroxisome proliferator-activated receptor α (PPARα) inhibition. In vivo administration of IL-4 increased FGF21 protein levels in the liver in a STAT6-dependent manner, but FGF21 secretion in response to IL-4 was not observed in the epididymal white adipose tissue (eWAT) despite the activation of STAT6. Intraperitoneal administration of IL-33, an activator of type 2 immune responses, significantly increased the level of FGF21 in the serum and liver after 24 h, but repeated administration of IL-33 attenuated this effect. Taken together, these data demonstrate that the IL-4/IL-13–STAT6 axis regulates metabolic homeostasis through the induction of FGF21 in the liver.

The bone is the major source of high circulating intact fibroblast growth factor-23 in acute murine polymicrobial sepsis induced by cecum ligation puncture.

Fibroblast growth factor-23 (FGF23), a bone-produced hormone, plays a critical role in mineral homeostasis. Human diseases associated with excessive intact circulating FGF23 (iFGF23) result in hypophosphatemia and low vitamin D hormone in patients with normal kidney function. In addition, there is accumulating evidence linking FGF23 with inflammation. Based on these studies and the frequent observation of hypophosphatemia among septic patients, we sought to elucidate further the relationship between FGF23 and mineral homeostasis in a clinically relevant murine polymicrobial sepsis model. Medium-severity sepsis was induced by cecum ligation puncture (CLP) in adult CD-1 mice of both sexes. Healthy CD-1 mice (without CLP) were used as controls. Forty-eight hours post-CLP, spontaneous urine was collected, and serum, organs and bones were sampled at necropsy. Serum iFGF23 increased ~20-fold in CLP compared to control mice. FGF23 protein concentration was increased in the bones, but not in spleen or liver of CLP mice. Despite the ~20-fold iFGF23 increase, we did not observe any significant changes in mineral homeostasis or parathyroid hormone levels in the blood of CLP animals. Urinary excretion of phosphate, calcium, and sodium remained unchanged in male CLP mice, whereas female CLP mice exhibited lower urinary calcium excretion, relative to healthy controls. In line with renal FGF23 resistance, expression of phosphate-, calcium- and sodium-transporting proteins did not show consistent changes in the kidneys of male and female CLP mice. Renal expression of the co-receptor αKlotho was downregulated in female, but not in male CLP mice. In conclusion, our data demonstrate that the dramatic, sex-independent rise in serum iFGF23 post-CLP was mainly caused by an upregulation of FGF23 secretion in the bone. Surprisingly, the upsurge in circulating iFGF23 did not alter humoral mineral homeostasis in the acutely septic mice. Hence, the biological function of elevated FGF23 in sepsis remains unclear and warrants further studies.

Fix That PHEX Loss

Phosphorous has a critical role in multiple biological functions in the body, such as skeletal mineralization, and an imbalance of this can lead to several musculoskeletal disorders. An important regulator of renal phosphate excretion is fibroblast growth factor 23 (FGF23) which is produced by osteocytes and osteoblasts themselves thus providing a mechanism for the skeletal system to influence its own mineralization needs. PHEX is a gene that regulates FGF23 secretion therefore a loss-of-function mutation in this gene would result in elevated circulating FGF23 and phosphate depletion. This mutation has been identified as a cause for X-linked hypophosphatemia (XLH). Treatment of XLH has been limited and mainly involved phosphorous replacement in combination with 1,25(OH) vitamin D. Antiresorptive osteoporosis treatment can exacerbate the skeletal mineralization process. Here we present a patient with multiple fractures who was on denosumab treatment for presumed osteoporosis before being found to have PHEX mutation. The patient is a 64 year-old female with past medical history of bilateral hip replacement and recurrent femur fractures who was seen in clinic in 2014 due to recurrent fractures and diagnosis of osteoporosis since early 2000s. She had only tried alendronate up until that point. Due to the recurrent fractures she was switched to denosumab therapy while workup was underway for secondary causes. She was found to have low phosphorous levels and elevated FGF23 therefore genetic counseling was pursued and was recommended to check for PHEX mutation. The testing came back positive for loss-of-function mutation in PHEX, and by that point she had received 3 doses of denosumab therapy. She suffered another femoral fracture which was determined to be an atypical fracture, and therefore denosumab treatment was stopped and she was continued on phosphorous replacement as well as 1,25(OH) vitamin D replacement. Most recently her phosphorous levels have been controlled with therapy, and there is current discussion underway to try burosumab, an antibody to FGF23. During evaluation for osteoporosis, it is important to consider phosphorous roles in skeletal mineralization. If recurrent fractures are seen in a patient with low phosphorous levels, especially while they are on conventional antiresorptive osteoporosis medications, genetic testing for PHEX mutations should be considered as well as safely stopping antiresorptive medications.

Aldosterone Is Positively Associated With Circulating FGF23 Levels in Chronic Kidney Disease Across Four Species, and May Drive FGF23 Secretion Directly.

BackgroundChronic kidney disease (CKD) is accompanied by increases in circulating fibroblast growth factor 23 (FGF23) and aldosterone levels. Here, we tested the hypothesis that aldosterone may be one of the driving forces behind increased FGF23 secretion in CKD.MethodsUsing data from a prospective study in humans, a retrospective study in dogs and cats, and an experimental study in 5/6-nephrectomized mice, we analyzed the relationship between circulating FGF23 and serum aldosterone levels in CKD across four species. To assess the effects of acute inhibition of aldosterone signaling on circulating FGF23, we acutely treated mice with established CKD with the mineralocorticoid receptor blocker canrenone (50 mg/kg iv/sc), and measured intact FGF23 before and 24 h as well as 72 h after start of administration of the drug.ResultsWe found a tight positive association between circulating intact FGF23 and serum aldosterone in human, canine, and feline CKD patients, as well as in experimental murine CKD (humans: rS = 0.57, p = 0.0368; dogs: rS = 0.66, p = 0.0019; cats: rS = 0.75, p = 0.0003; mice: rS = 0.49, p = 0.0004). Injection of canrenone in mice with established CKD did not lead to changes in FGF23 levels within 24 h, but reduced FGF23 in all mice at 72 h.ConclusionAldosterone may drive enhanced FGF23 secretion in CKD, possibly explaining the tight positive association between circulating intact FGF23 and aldosterone in human, canine, and feline CKD patients as well as in experimental CKD models.

Fibroblast Growth Factor 23 in Children with Chronic Kidney Disease

Background: Decreased of glomerular filtration rate in chronic kidney disease (CKD) changes the calciumand phosphate balance. High phosphate levels in children with CKD stimulate secretion of FibroblastGrowth Factor 23 (FGF23). High FGF23 levels have harmful that potentially increase the morbidity andmortality of children with CKD.Objective: To analyze the level of FGF23 in children with CKD.Methods: A cross sectional study was performed in Pediatric Nephrology Ward and Outpatient Clinic ofDr. Soetomo General Hospital Surabaya, during December 2019-March 2020 for children with CKD stage1-5, aged 3 months to 18 years old. Children on phosphate-binder, vitamin D therapy, or severely ill wereexcluded. Blood level of FGF23 was measured using ELISA with statistic analysis with SPSS 20.Results: A total of 52 CKD stage 1-5 children were involved, mean age was 11.44 years old, and 50% wereboys. There were 51% children have FGF23 level more than 30 pg/ml. The lowest mean of FGF23 levelswas found in the CKD grade 1 (8.94 ± 8.77 pg/mL) and the highest mean at CKD grade 5 (113.30 ± 78.73pg/mL).Conclusion: The FGF23 level increasing accordance with increasing in the grade of CKD

UVB-Induced ciRS-7 Activates Melanogenesis by Paracrine Effects.

Antisense to the cerebellar degeneration-related protein 1 transcript (CDR1as or ciRS-7) is an important member of the circular RNA family and is involved in the regulation of numerous biological functions. Keratinocytes and fibroblasts (FBs) affect melanogenesis through paracrine effects. However, whether ciRS-7 is involved in melanogenesis by regulating paracrine effects remains unclear. This study demonstrates for the first time that ciRS-7 is highly expressed in keratinocytes, FBs, and melanocytes (MCs). Ultraviolet B (UVB) irradiation promotes ciRS-7 expression in keratinocytes and FBs. Following inhibition of ciRS-7 expression in keratinocytes and FBs, the culture supernatant from these cells inhibited melanogenesis of MCs. Further analyses revealed that the expression and secretion of fibroblast growth factor 2 (FGF2) and phosphorylation of STAT3 and AKT in keratinocytes and FBs were significantly downregulated following inhibition of ciRS-7 expression, whereas the level of miR-7 was increased. Overexpression of miR-7 in keratinocytes and FBs significantly inhibited the expression of FGF2. In conclusion, our findings demonstrate that UVB-induced ciRS-7 triggers melanogenesis in MCs through regulation of the miR-7/STAT3 and AKT/FGF2 paracrine axis in both keratinocytes and FBs. ciRS-7 may serve as a regulator in the development of pigmented skin diseases.

Diagnostic performance of 68Ga-DOTATOC PET/CT in tumor-induced osteomalacia.

Tumor-induced osteomalacia (TIO) is caused by typically small tumors that secrete fibroblast growth factor 23 (FGF23). As tumor resection is the only effective treatment for TIO, it is important to detect the culprit tumor. We aimed to assess the utility of 68Gallium-DOTA-D-Phe(1)-Tyr(3)-octreotide (68Ga-DOTATOC) PET/CT in TIO and the correlation between biochemical parameters and the PET/CT results. Thirty-five patients with clinically suspected TIO who had undergone 68Ga-DOTATOC PET/CT were retrospectively analyzed. 68Ga-DOTATOC PET/CT results were compared with biochemical parameters and the final diagnosis, including histopathology. 68Ga-DOTATOC PET/CT detected focal uptake consistent with TIO in 21/35 patients, one of which was considered false positive. In 16 patients, the cause of osteomalacia was confirmed histologically as phosphaturic mesenchymal tumor (n = 15) or fibrous dysplasia (n = 1). The other four patients were judged clinically as true positive by subsequent MRI and the clinical course. Overall, the detection rate of 68Ga-DOTATOC PET/CT was 57% (20/35). Median tumor maximum standardized uptake value (SUVmax) was 6.9 (range 1.5-37.7). There was no significant difference in serum intact FGF23 level between DOTATOC-positive and DOTATOC-negative cases, and no significant correlation was observed between intact FGF23 level and tumor SUVmax. 68Ga-DOTATOC PET/CT was clinically useful in detecting culprit tumors and subsequent patient management in TIO.

Complement-mediated release of fibroblast growth factor 2 from human RPE cells

PurposeComplement activation is associated with choroidal neovascularization (CNV) in age-related macular degeneration (AMD). Fibroblast growth factor 2 (FGF2) and membrane attack complex (MAC) are present in eyes of patients with CNV. Herein, we investigated the effect of complement activation on FGF2 release in human retinal pigment epithelial (RPE) cells. MethodsCultured human RPE cells were primed with an anti-RPE antibody and then treated with C1q-depleted human serum in the presence or absence of Tec kinases inhibitor (LFM-A13). 38 cytokines/chemokines levels were measured by Luminex technology. Secretion of FGF2 and interleukin (IL)-6 was assessed by ELISA. Tec protein was measured by Western blot. mRNA expression of FGF2, chemokine (C-X-C motif) ligand 1 (CXCL-1), and family members of Tec kinases was evaluated by qPCR. Cell viability and MAC deposition were determined by WST-1 assay and flow cytometry, respectively. ResultsComplement activation caused increased FGF2 and IL-6 release. FGF2 was released when C6-depleted human serum was reconstituted with C6. Anti-C5 antibody significantly attenuated complement-mediated FGF2 release, but not IL-6. FGF2 mRNA levels were not affected, while CXCL-1 mRNA levels were increased by complement activation. FGF2-containing extracellular vesicles were detected in response to complement challenge. Tec mRNA and protein were expressed in RPE cells. In the presence of LFM-A13, secretion of FGF2, but not IL-6, and MAC deposition were significantly decreased and cell viability was significantly increased in complement-treated cells when compared to controls. ConclusionsComplement plays an important role to release FGF2 from RPE cells. Tec kinase is involved in MAC formation and complement-mediated FGF2 release. This information suggests a role for complement activation to mediate neovascularization in conditions such as AMD, and may elucidate potential therapeutic targets.

Caloric Intake in Renal Patients: Repercussions on Mineral Metabolism.

The aim of this paper is to review current knowledge about how calorie intake influences mineral metabolism focussing on four aspects of major interest for the renal patient: (a) phosphate (P) handling, (b) fibroblast growth factor 23 (FGF23) and calcitriol synthesis and secretion, (c) metabolic bone disease, and (d) vascular calcification (VC). Caloric intake has been shown to modulate P balance in experimental models: high caloric intake promotes P retention, while caloric restriction decreases plasma P concentrations. Synthesis and secretion of the phosphaturic hormone FGF23 is directly influenced by energy intake; a direct correlation between caloric intake and FGF23 plasma concentrations has been shown in animals and humans. Moreover, in vitro, energy availability has been demonstrated to regulate FGF23 synthesis through mechanisms in which the molecular target of rapamycin (mTOR) signalling pathway is involved. Plasma calcitriol concentrations are inversely proportional to caloric intake due to modulation by FGF23 of the enzymes implicated in vitamin D metabolism. The effect of caloric intake on bone is controversial. High caloric intake has been reported to increase bone mass, but the associated changes in adipokines and cytokines may as well be deleterious for bone. Low caloric intake tends to reduce bone mass but also may provide indirect (through modulation of inflammation and insulin regulation) beneficial effects on bone. Finally, while VC has been shown to be exacerbated by diets with high caloric content, the opposite has not been demonstrated with low calorie intake. In conclusion, although prospective studies in humans are needed, when planning caloric intake for a renal patient, it is important to take into consideration the associated changes in mineral metabolism.

FGF21 Induced by the ASK1-p38 Pathway Promotes Mechanical Cell Competition by Attracting Cells

Cell competition is a social cellular phenomenon in which unfit cells are selectively eliminated to maintain tissue homeostasis.1-3 Recent studies have revealed that mechanical forces induce competitive cell-cell interactions in Drosophila.4-6 This mechanical cell competition has also been reported to play an important role in mammalian cells, using Madin-Darby canine kidney (MDCK) cells depleted of a polarity regulator Scribble in a tetracycline-inducible manner (scribKD cells).7scribKD cells are hypersensitive to crowding due to the lower homeostatic density than wild-type (WT) cells,7,8 and in the context of cell competition, scribKD cells are compacted and eliminated by WT cells.7-10 Although p38 and p53 are involved in this process,7,10 the molecular mechanism by which WT cells recognize and mechanically eliminate scribKD cells remains unclear. Here, we report that scribKD cells secrete fibroblast growth factor 21 (FGF21) to drive cell competition. Knockdown of FGF21 in scribKD cells or loss of FGFR1 in WT cells suppresses cell competition, suggesting that WT cells recognize scribKD cells through FGF21. FGF21-containing culture medium of scribKD cells activates cell motility. Moreover, FGF21 promotes the compression and elimination of scribKD cells by attracting surrounding WT cells. We also demonstrate that activation of the apoptosis signal-regulating kinase 1 (ASK1)-p38 pathway in scribKD cells induces FGF21 to drive cell competition. Our findings reveal a mechanism whereby WT cells mechanically eliminate scribKD cells and propose a new function for FGF21 in cell-cell communication.

The HIF-PHI BAY 85-3934 (Molidustat) Improves Anemia and Is Associated With Reduced Levels of Circulating FGF23 in a CKD Mouse Model.

Fibroblast growth factor-23 (FGF23) is a critical factor in chronic kidney disease (CKD), with elevated levels causing alterations in mineral metabolism and increased odds for mortality. Patients with CKD develop anemia as the kidneys progressively lose the ability to produce erythropoietin (EPO). Anemia is a potent driver of FGF23 secretion; therefore, a hypoxia-inducible factor prolyl hydroxylase inhibitor (HIF-PHI) currently in clinical trials to elevate endogenous EPO to resolve anemia was tested for effects on iron utilization and FGF23-related parameters in a CKD mouse model. Mice were fed either a casein control diet or an adenine-containing diet to induce CKD. The CKD mice had markedly elevated iFGF23 and blood urea nitrogen (BUN), hyperphosphatemia, and anemia. Cohorts of mice were then treated with a patient-equivalent dose of BAY 85-3934 (BAY; Molidustat), which elevated EPO and completely resolved aberrant complete blood counts (CBCs) in the CKD mice. iFGF23 was elevated in vehicle-treated CKD mice (120-fold), whereas circulating iFGF23 was significantly attenuated (>60%) in the BAY-treated CKD mice. The BAY-treated mice with CKD also had reduced BUN, but there was no effect on renal vitamin D metabolic enzyme expression. Consistent with increased EPO, bone marrow Erfe, Transferrin receptor (Tfrc), and EpoR mRNAs were increased in BAY-treated CKD mice, and in vitro hypoxic marrow cultures increased FGF23 with direct EPO treatment. Liver Bmp-6 and hepcidin expression were downregulated in all BAY-treated groups. Femur trabecular parameters and cortical porosity were not worsened with BAY administration. In vitro, differentiated osteocyte-like cells exposed to an iron chelator to simulate iron depletion/hypoxia increased FGF23; repletion with holo-transferrin completely suppressed FGF23 and normalized Tfrc1. Collectively, these results support that resolving anemia using a HIF-PHI during CKD was associated with lower BUN and reduced FGF23, potentially through direct restoration of iron utilization, thus providing modifiable outcomes beyond improving anemia for this patient population. © 2021 American Society for Bone and Mineral Research (ASBMR).

Small hepatitis B virus surface antigen promotes malignant progression of hepatocellular carcinoma via endoplasmic reticulum stress-induced FGF19/JAK2/STAT3 signaling.

Chronic hepatitis B virus (HBV) infection is one of the major global health problems. Although the small protein of hepatitis B virus surface antigen (HBsAg), SHBs, is the most abundant HBV viral protein, its pathogenic role and molecular mechanism in malignant progression of HBV-related hepatocellular carcinoma (HCC) remain largely unknown. Here we reported that SHBs expression induced epithelial-mesenchymal transition (EMT) process in HCC cells and significantly increased their migratory and invasive ability as well as metastatic potential. Mechanistically, SHBs expression in HCC cells induced endoplasmic reticulum (ER) stress that activated the activating transcription factor 4 (ATF4) to increase the expression and secretion of fibroblast growth factor 19 (FGF19). The autocrine released FGF19 in turn activated JAK2/STAT3 signaling for induction of EMT process in HCC. Notably, SHBs was positively correlated with the expression of mesenchymal markers, the phosphorylation status of JAK2 and STAT3 as well as FGF19 levels in human HCC samples. HCC patients with SHBs positive had a more advanced clinical stage and worse prognosis. These results suggest an important role of SHBs in the metastasis and progression of HCC and may highlight a potential target for preventive and therapeutic intervention of HBV-related HCC and its malignant progression.

FGF2 and IL-1β - explorers of unconventional secretory pathways at a glance.

Fibroblast growth factor 2 (FGF2) and interleukin 1β (IL-1β) were among the earliest examples of a subclass of proteins with extracellular functions that were found to lack N-terminal secretory signal peptides and were shown to be secreted in an ER- and Golgi-independent manner. Many years later, a number of alternative secretory pathways have been discovered, processes collectively termed unconventional protein secretion (UPS). In the course of these studies, unconventional secretion of FGF2 and IL-1β were found to be based upon distinct pathways, mechanisms and molecular machineries. Following a concise introduction into various pathways mediating unconventional secretion and transcellular spreading of proteins, this Cell Science at a Glance poster article aims at a focused analysis of recent key discoveries providing unprecedented detail about the molecular mechanisms and machineries driving FGF2 and IL-1β secretion. These findings are also highly relevant for other unconventionally secreted cargoes that, like FGF2 and IL1β, exert fundamental biological functions in biomedically relevant processes, such as tumor-induced angiogenesis and inflammation.

Functional Assay to Correlate Protein Oligomerization States with Membrane Pore Formation.

In-membrane oligomerization is decisive for the function (or dysfunction) of many proteins. Techniques were developed to characterize membrane-inserted oligomers and the hereby obtained oligomerization states were intuitively related to the function of these proteins. However, in many cases, it is unclear whether the obtained oligomerization states are functionally relevant or are merely the consequence of nonspecific aggregation. Using fibroblast growth factor 2 (FGF2) as a model system, we addressed this methodological challenge. FGF2 oligomerizes in a PI(4,5)P2-dependent manner at the inner plasma membrane leaflet. This process results in membrane insertion and the formation of a lipidic membrane pore, the key intermediate in unconventional secretion of FGF2. To tackle the problem of discriminating functional oligomers from irrelevant aggregates, we present a statistical single molecule and single vesicle assay determining the brightness of individually diffusing in-membrane oligomers and correlating their oligomerization state with membrane pore formation. Importantly, time-dependent membrane pore formation was analyzed with an ensemble of single vesicles providing detailed statistics. Our findings demonstrate that quantifying oligomeric states alone does not allow for a deep understanding of the structure-function relationship of membrane-inserted oligomers.

On the participation of eosinophils in tissue recovery after a local cold injury

The article studies the correlation of the content of peripheral blood and red bone marrow eosinophils with the level of secretion of fibroblast growth factor (FGF-21), insulin-like factor (IGF-1) and vasculoendothelial growth factor (VEGF-C) in blood serum during the formation of dermal collagen after local cold damage. Animals of the experimental group after the onset of narcotic sleep on the depilated skin of the back were simulated contact frostbite of the 3rd degree. On the 3rd, 7th, 14th and 21st day of the experiment, the concentrations of growth factors, % dermal collagen content, and also the content of eosinophils in peripheral blood and red bone marrow were determined in the blood serum. The research results showed that the development of eosinopenia after a local cold injury occurs due to the sequestration of eosinophils in the affected area. The presence of reactive changes after a local cold injury not only in peripheral blood, but also in the red bone marrow may indicate the participation of eosinophils in tissue repair processes after a local cold injury.

P0904EFFECT OF EMPAGLIFLOZIN ON SERUM MARKERS OF OSTEOCYTE AND OSTEOBLAST FUNCTION AND ALBUMINURIA IN DIABETIC AND NON-DIABETIC PATIENTS WITH CHRONIC KIDNEY DISEASE

Abstract Background and Aims Sodium-glucose co-transporter 2 (SGLT2) inhibitors are new class of oral antidiabetic drugs that show potent cardio- and nephroprotective actions. Despite having a favorable safety profile the treatment with SGLT2 inhibitors has been associated with several side-effects including increased risk of fractures. Although the pathomechanism of this complication has not been elucidated these drugs may inhibit tubular reabsorption of phosphate which may stimulate a secretion of fibroblast growth factor 23 (FGF23). The study was designed to assess the effect of SGLT2 inhibitor on markers of calcium-phosphate metabolism, bone turnover and early glomerular injury in diabetic and non-diabetic patients with stage 3 chronic kidney disease (CKD). Method 41 patients with chronic kidney disease including 23 without diabetes (13 M, 11F, age 52.9±0.7 years, estimated glomerular filtration rate (eGFR) 38.6±10.8 ml/min/1.73 m2) and 18 with type 2 diabetes (12 M, 6F, age 58.8±1.4 years, eGFR 38.8±7.7 ml/min/1.73 m2) were recruited. Main inclusion criteria were CKD stage 3 and urine albumin secretion >100 mg/g creatinine. All subjects received oral empagliflozin 10 mg once daily for 7 days. Serum calcium, phosphorus, parathormone (PTH), calcitriol, bone alkaline phosphatase (BAP), FGF23 and urine calcium, phosphate and albumin were measured at baseline and after 7 days of empagliflozin treatment. Results Plasma calcitriol, serum and urine calcium, phosphorus and BAP did not change significantly during the administration of empagliflozin. Urine phosphate/creatinine ratio was similar in both subgroups at baseline and did not change during empagliflozin administration. Plasma PTH was higher in non-diabetics than in diabetics both at baseline and after empagliflozin. The increase of PTH after empagliflozin tended to be higher in diabetic patients (p=0.07). There was only a trend towards an increase of serum FGF23 in both non-diabetic and diabetic subgroup (by 4.2±0.2 vs. 9.3±1.1 pg/mL, ns). BAP was significantly higher at baseline in diabetic patients but did not significantly change after empagliflozin in the subgroups. Albumin/creatinine ratio decrease after empagliflozin administration was significant only in non-diabetic patients (-62±17 vs. -2±8 mg/g in diabetic patients, p=0.03 for difference). Conclusion Our study showed no effect of short-time administration of empagliflozin on calcium-phosphate and bone metabolism markers in patients with both diabetic and non-diabetic CKD. Empagliflozin decreased albuminuria significantly only in non-diabetic CKD that may suggest a potentially greater nephroprotective effect of this SGLT2 inhibitor in non-diabetic than in diabetic nephropathy.

The effect of an oral sodium phosphate load on parathyroid hormone and fibroblast growth factor 23 secretion in normo- and hypercalciuric stone-forming patients.

Abnormalities of parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) secretion may cause calcium-phosphate (Ca-P) metabolism disorders in nephrolithiasis. Post-phosphate-load alterations in serum Ca, P and PTH, phosphaturia and calciuria enable monitoring hormonal regulation of Ca-P homeostasis. Our study aimed to determine differences in: 1.selected Ca-P metabolism parameters between healthy and kidney-stone-forming individuals, 2.PTH and FGF23 secretion induced by sodium-phosphate-load(NaP-load) in patients with/without hypercalciuria, 3.secretion of Ca-P related hormones in patients with low and normal/high serum concentrations of 25-hydroxyvitamin D3 (25OHD3). Sodium phosphates NaH2PO4/Na2HPO4-100mmol were administered orally for five days in 19 hypercalciuric [urinary Ca(U-Ca) 6.5±1.7mmol/d]-HSF, 35 normocalciuric (2.5±1mmol/d)-NSF stone-forming patients and 19 controls (U-Ca 2.5±1.4mmol/d)-CG. On days 1 and 5 PTH-,FGF23-,Ca-,P were determined before and after NaP-load. The areas under PTH, FGF23 curves (AUC) were calculated. U-Ca, urinary phosphate (U-P) and sodium (U-Na) were also determined. Following NaP-load, patients and controls exhibited expected alterations in Ca-P homeostasis. Despite changes in phosphate and PTH, no differences in FGF23 concentrations were observed. Patients differed from controls in having higher AUCPTH, calciuria and natriuresis, taking longer for PTH and P to normalize and lack of correlation between AUCPTH and phosphaturia. Post-NaP-load hypocalciuric effect of PTH secretion in NSF was less pronounced than in CG. In the HSFs, the hypocalciuric effect was more pronounced than in NSFs, but insufficient to correct hypercalciuria. In all stone-formers with low 25OHD3 concentrations, the AUCFGF23 was significantly increased on first (1215±605vs766±315 p=0.0457) and fifth days (1211±641vs777±299 p=0.041) of NaP-load, compared to normal/high 25OHD3-patients. Hypercalciuric patients with low 25OHD3 concentrations had greater AUCPTH5 than those with normal/high 25OHD3 (1005±401vs835±220 p=0.0341). Compared to controls, kidney-stone-forming patients exhibited enhanced PTH secretion after NaP-load. The HSFs showed a more pronounced hypocalciuric effect than NSFs, but insufficient to correct hypercalciuria. In hypercalciuric stone-formers with low 25OHD3, FGF23 engagement in hyperphosphatemia reduction increased.

Glucagon Regulates Energy Balance via FGF21 Signaling in the Brain

Glucagon is an essential regulator of glucose and lipid metabolism that also promotes weight loss. Thus, novel therapeutics that stimulate glucagon‐receptor (GCGR) signaling are promising targets for treatment of obesity and diabetes; however, the mechanism(s) underlying these effects are yet to be fully elucidated. We previously identified that hepatic glucagon signaling increases the secretion of Fibroblast Growth Factor 21 (FGF21), a fasting hormone that regulates energy balance. We have recently observed that mice deficient for liver Fgf21 are partially resistant to the anti‐obesity effects of GCGR agonism, implicating hepatic FGF21 as an essential component of glucagon’s weight‐loss effects. FGF21 signals through the canonical FGF‐receptors coupled with an obligate co‐receptor (bKlotho, Klb). Expression of KLB, and therefore FGF21 signaling, is limited to adipose tissue, liver, and brain, specifically within the suprachiasmatic nucleus (SCN) of the hypothalamus and the hindbrain. The hypothalamus is a critical regulator of energy balance; thus, we hypothesized that the anti‐obesity action of the glucagon‐FGF21 system signals through a central mechanism. To test this hypothesis, we generated mice with neuronal Klb deficiency (Klbflox x Synapsin1Cre: KlbΔCNS). KlbΔCNS mice are less susceptible to diet‐induced obesity than control mice (p<0.01), with no differences in food intake or energy expenditure. Following chronic GCGR activation via the selective GCGR agonist IUB288, KlbΔCNS mice exhibit a partial reduction in body weight (11%) in comparison to control mice (18%) (p<0.001), suggesting that FGF21 mediates glucagon’s anti‐obesity properties through central action. Similar to the congenital knockout, wildtype mice treated with a selective KLB antagonist via intracerebroventricular administration also exhibited partial reductions in body weight following chronic IUB288 treatment. Consistent with GCGR‐stimulated, neuronal FGF21 signaling, we found that neuronal activation, measured via cFos expression, was increased in the SCN following IUB288 injection. To further interrogate SCN‐specific FGF21 signaling, we generated mice with SCN‐specific Klb deficiency (KlbΔSCN) via targeted adenoviral Cre recombinase induction. KlbΔSCN mice display an increase in food intake, body, and fat mass compared to control mice. Changes in food intake were associated with an increase in both light‐ and dark‐phase feeding for KlbΔSCN mice compared to controls (p<0.001). Future studies will aim to continue to interrogate SCN‐specific FGF21 signaling via the pharmaceutical antagonist and the KlbΔCNS model. Taken together, these data suggest that 1) KLB/FGF21 signaling of the SCN is critical for normal energy balance and 2) glucagon mediates part of its anti‐obesity properties through FGF21‐KLB signaling in the CNS. In sum, these findings provide insight for future treatments against obesity and the metabolic syndrome.Support or Funding InformationThe project described was supported by the NIH grant 1R01DK112934.

The Na,K-ATPase acts upstream of phosphoinositide PI(4,5)P2 facilitating unconventional secretion of Fibroblast Growth Factor 2

FGF2 is a tumor cell survival factor that is exported from cells by an ER/Golgi-independent secretory pathway. This unconventional mechanism of protein secretion is based on direct translocation of FGF2 across the plasma membrane. The Na,K-ATPase has previously been shown to play a role in this process, however, the underlying mechanism has remained elusive. Here, we define structural elements that are critical for a direct physical interaction between FGF2 and the α1 subunit of the Na,K-ATPase. In intact cells, corresponding FGF2 mutant forms were impaired regarding both recruitment at the inner plasma membrane leaflet and secretion. Ouabain, a drug that inhibits both the Na,K-ATPase and FGF2 secretion, was found to impair the interaction of FGF2 with the Na,K-ATPase in cells. Our findings reveal the Na,K-ATPase as the initial recruitment factor for FGF2 at the inner plasma membrane leaflet being required for efficient membrane translocation of FGF2 to cell surfaces.

Nature’s remedy to phosphate woes: calciprotein particles regulate systemic mineral metabolism

Calciprotein particles, colloidal complexes of calcium phosphate and plasma protein fetuin-A, have emerged as mediators of multiple biological effects attributed to phosphate. A new study postulates that circulating calciprotein particles, not phosphate, regulate the production of the major bone-derived phosphatonin, fibroblast growth factor-23. The signaling events coupling calciprotein particles sensing in bone to fibroblast growth factor-23 secretion remain to be established.