FGF23-regulated production of Fetuin-A (AHSG) in osteocytes

Sexually dimorphic effects of prenatal alcohol exposure on the murine skeleton

BACKGROUND

Prenatal alcohol exposure (PAE) can result in lifelong disabilities known as foetal alcohol spectrum disorder (FASD) and is associated with childhood growth deficiencies and increased bone fracture risk. However, the effects of PAE on the adult skeleton remain unclear and any potential sexual dimorphism is undetermined. Therefore, we utilised a murine model to examine sex differences with PAE on in vitro bone formation, and in the juvenile and adult skeleton.

METHODS

Pregnant C57BL/6J female mice received 5% ethanol in their drinking water during gestation. Primary calvarial osteoblasts were isolated from neonatal offspring and mineralised bone nodule formation and gene expression assessed. Skeletal phenotyping of 4- and 12-week-old male and female offspring was conducted by micro-computed tomography (µCT), 3-point bending, growth plate analyses, and histology.

RESULTS

Osteoblasts from male and female PAE mice displayed reduced bone formation, compared to control (≤ 30%). Vegfa, Vegfb, Bmp6, Tgfbr1, Flt1 and Ahsg were downregulated in PAE male osteoblasts only, whilst Ahsg was upregulated in PAE females. In 12-week-old mice, µCT analysis revealed a sex and exposure interaction across several trabecular bone parameters. PAE was detrimental to the trabecular compartment in male mice compared to control, yet PAE females were unaffected. Both male and female mice had significant reductions in cortical parameters with PAE. Whilst male mice were negatively affected along the tibial length, females were only distally affected. Posterior cortical porosity was increased in PAE females only. Mechanical testing revealed PAE males had significantly reduced bone stiffness compared to controls; maximum load and yield were reduced in both sexes. PAE had no effect on total body weight or tibial bone length in either sex. However, total growth plate width in male PAE mice compared to control was reduced, whilst female PAE mice were unaffected. 4-week-old mice did not display the altered skeletal phenotype with PAE observed in 12-week-old animals.

CONCLUSIONS

Evidence herein suggests, for the first time, that PAE exerts divergent sex effects on the skeleton, possibly influenced by underlying sex-specific transcriptional mechanisms of osteoblasts. Establishing these sex differences will support future policies and clinical management of FASD.

Targeted silencing of GNAS in a human model of osteoprogenitor cells results in the deregulation of the osteogenic differentiation program

Introduction

The dysregulation of cell fate toward osteoprecursor cells associated with most GNAS-based disorders may lead to episodic de novo extraskeletal or ectopic bone formation in subcutaneous tissues. The bony lesion distribution suggests the involvement of abnormal differentiation of mesenchymal stem cells (MSCs) and/or more committed precursor cells. Data from transgenic mice support the concept that GNAS is a crucial factor in regulating lineage switching between osteoblasts (OBs) and adipocyte fates. The mosaic nature of heterotopic bone lesions suggests that GNAS genetic defects provide a sensitized background for ectopic osteodifferentiation, but the underlying molecular mechanism remains largely unknown.

Methods

The effect of GNAS silencing in the presence and/or absence of osteoblastic stimuli was evaluated in the human L88/5 MSC line during osteodifferentiation. A comparison of the data obtained with data coming from a bony lesion from a GNAS-mutated patient was also provided.

Results

Our study adds some dowels to the current fragmented notions about the role of GNAS during osteoblastic differentiation, such as the premature transition of immature OBs into osteocytes and the characterization of the differences in the deposed bone matrix.

Conclusion

We demonstrated that our cell model partially replicates the in vivo behavior results, resulting in an applicable human model to elucidate the pathophysiology of ectopic bone formation in GNAS-based disorders.

Novel insights into osteocyte and inter-organ/tissue crosstalk

Osteocyte, a cell type living within the mineralized bone matrix and connected to each other by means of numerous dendrites, appears to play a major role in body homeostasis. Benefiting from the maturation of osteocyte extraction and culture technique, many cross-sectional studies have been conducted as a subject of intense research in recent years, illustrating the osteocyte-organ/tissue communication not only mechanically but also biochemically. The present review comprehensively evaluates the new research work on the possible crosstalk between osteocyte and closely situated or remote vital organs/tissues. We aim to bring together recent key advances and discuss the mutual effect of osteocyte and brain, kidney, vascular calcification, muscle, liver, adipose tissue, and tumor metastasis and elucidate the therapeutic potential of osteocyte.

MCP1 Inverts the Correlation between FGF23 and Omega 6/3 Ratio: Is It Also True in Renal Transplantation?

During chronic kidney disease (CKD) progression, an increase in fibroblast growth factor (FGF23) is present. In stage 5, a positive correlation between FGF23 and omega-6 (n-6) polyunsaturated fatty acids (PUFAs) emerges. Hypothesizing that the rising positive correlation between monocyte chemoattractant protein 1 (MCP1) and n-6 in stage 4 could be the cause, we previously explored FGF23 and MCP1's roles in dyslipidemia and cardiovascular risk in CKD. In the present paper, we retraced the study evaluating 40 kidney transplant patients (KTx), a cohort where several factors might modify the previous relationships found. An ELISA and gas chromatography assessed the MCP1, FGF23, and PUFA levels. Despite the FGF23 increase (p < 0.0001), low MCP1 levels were found. A decrease in the n-6/n-3 ratio (p = 0.042 CKD stage 4 vs. 5) lowered by the increase in both n-3 αlinolenic (p = 0.012) and docosapentaenoic acid (p = 0.049) was observed. A negative correlation between FGF23 and the n-6/n-3 ratio in CKD stage 4 (r2 -0.3 p = 0.043) and none with MCP1 appeared. According to our findings, different mechanisms in the relationship between FGF23, PUFAs, and MCP1 in CKD and KTx patients might be present, which is possibly related to the immunosuppressive status of the last. Future research will further clarify our hypothesis.

Fetuin-A, fibroblast growth factor 23 and inflammation in critically ill patients with sepsis

Fetuin-A is a glycoprotein with multifaceted roles, produced mainly in the liver. FGF23 has been reported to control Fetuin-A production in hepatocytes and in the bone. Furthermore, several studies have showed that higher circulating FGF23 levels stimulate inflammatory cytokines in the liver. However, the mechanistic insights linking bilirubin-Fetuin-A, FGF23 and inflammation in patients with sepsis is poorly understood. Therefore, further experimental research is required to link Fetuin, FGF23 and inflammation in the animal models of sepsis to gain further mechanistic insight.

The Saga of Endocrine FGFs

Fibroblast growth factors (FGFs) are cell-signaling proteins with diverse functions in cell development, repair, and metabolism. The human FGF family consists of 22 structurally related members, which can be classified into three separate groups based on their action of mechanisms, namely: intracrine, paracrine/autocrine, and endocrine FGF subfamilies. FGF19, FGF21, and FGF23 belong to the hormone-like/endocrine FGF subfamily. These endocrine FGFs are mainly associated with the regulation of cell metabolic activities such as homeostasis of lipids, glucose, energy, bile acids, and minerals (phosphate/active vitamin D). Endocrine FGFs function through a unique protein family called klotho. Two members of this family, α-klotho, or β-klotho, act as main cofactors which can scaffold to tether FGF19/21/23 to their receptor(s) (FGFRs) to form an active complex. There are ongoing studies pertaining to the structure and mechanism of these individual ternary complexes. These studies aim to provide potential insights into the physiological and pathophysiological roles and therapeutic strategies for metabolic diseases. Herein, we provide a comprehensive review of the history, structure–function relationship(s), downstream signaling, physiological roles, and future perspectives on endocrine FGFs.

In Vitro Investigation on Degradable Mg-Based Biomaterial under the Impact of the Serum Glycoprotein Fetuin

Biomedical applications of magnesium (Mg) and its alloys are generally dependent on their degradation behavior in vivo. Despite its attractive properties, which make Mg suitable for orthopedic applications, the in vivo material-tissue (bone, blood, and lymph tissues) interaction is not yet fully understood. To investigate the influence of major serum proteins on the degradation, this study focused on fetuin, which is one of the major non-collagenous plasma proteins and which is essential for biomineralization. This study used a physiological setup to investigate the influence of fetuin on the degradation behavior of pure Mg in the presence of calcium (Ca). Extruded pure Mg samples were immersed under cell culture conditions in Hank’s balanced salt solution (HBSS) under defined Ca regimes. The results showed a significant decrease in the degradation rate (DR) when both fetuin and Ca were present in an immersion medium as compared to media where they were not simultaneously present. A possible reason for this behavior was the forming of a dense, protein-degradation products protection barrier at the material surface. Furthermore, the limitation of freely available Ca might be a reason for a decreased degradation. The cultivation of primary osteoblasts (pOB) was possible at the fetuin-coated Mg-surface without additional serum supplementation.

Identification of Differential Expression Cytokines in Hemolysis, Elevated Liver Enzymes, and Low Platelet Syndrome by Proteome Microarray Analysis and Further Verification

To screen the differential expression cytokines (DECs) in hemolysis, elevated liver enzymes, and low platelet (HELLP) syndrome, establish its differential cytokines spectra, and provide the clues for its diagnosis and pathogenic mechanism researches. Sera from four HELLP syndrome patients and four healthy controls were detected by proteome microarray. Then the analysis of Gene Ontology (GO) enrichment, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, and protein–protein interaction (PPI) network were performed and possible hub proteins were selected out, further verified by Enzyme Linked Immunosorbent Assay (ELISA) in sera from 21 HELLP syndrome patients and 21 healthy controls. Thirty DECs were defined according to P-value and fold change between HELLP group and control group. GO enrichment analysis showed that DECs were mainly involved in the regulation of inflammatory response and have relationship to growth factor binding, transmembrane receptor protein kinase, and cytokine receptor activity. Seven possible hub proteins were defined by PPI analysis, including IGFBP-3/Follistatin-like 1/FLRG/Fetuin A and MMP-13/Thrombospondin-5/Aggrecan. ELISA showed higher serum levels of Fetuin A/IGFBP-3/FLGR/MMP-13/Thrombospondin-5 in HELLP group than those in controls, while the levels of Follistatin-like 1 and Aggrecan were lower in HELLP patients (all P < 0.05 or <0.01).The serological DECs spectra of HELLP syndrome was established and seven possible hub proteins that may be more closely related to the disease have been verified, providing new clues for its pathogenesis, diagnosis, and clinical treatment.

FGF23 and Fetuin-A Interaction and Mesenchymal Osteogenic Transformation

Recently, we found a strict bone association between Fibroblast growth factor 23 (FGF23) and Fetuin-A, both involved in cardiovascular and mineral bone disorders. In this study, an uninvestigated bone marrow positivity for both was found. Though the role of exogenous FGF23 on mesenchymal cells (MSCs) was reported, no information is as yet available on the possible production of this hormone by MSCs. To further analyze these uninvestigated aspects, we studied human primary cells and mouse and human cell lines by means of immunostaining, qRT-PCR, enzyme linked immunosorbent assays, chromatin immunoprecipitation, transfection, and a streamlined approach for the FGF23⁻Fetuin-A interaction called Duolink proximity ligation assay. Mesenchymal cells produce but do not secrete FGF23 and its expression increases during osteo-differentiation. Fibroblast growth factor 23 is also involved in the regulation of Fetuin-A by binding directly to the Fetuin-A promoter and then activating its transcription. Both FGF23 overexpression and addition induced an upregulation of Fetuin-A in the absence of osteo-inducer factors. Fibroblast growth factor 23 and Fetuin-A promoter were increased by osteo-inducer factors with this effect being abolished after FGF23 silencing. In conclusion, both FGF23 and Fetuin-A are present and strictly linked to each other in MSCs with FGF23 driving Fetuin-A production. This mechanism suggests a role for these two proteins in the osteoblast differentiation.

Clinical implications of fetuin-A

Fetuin-A, also termed alpha2-Heremans-Schmid glycoprotein, is a 46kDa hepatocyte derived protein (hepatokine) and serves multifaceted functions.

Pathophysiology and treatment of cardiovascular disease in pediatric chronic kidney disease

Life expectancy in patients with all stages of chronic kidney disease (CKD) falls far short of that in the general population. Cardiovascular disease is the leading cause of mortality in pediatric patients with CKD. In contrast to the intimal atherosclerotic lesions that characterize cardiovascular disease in the general population, vascular endothelial dysfunction, medial arterial calcification, and cardiac dysfunction contribute to cardiovascular pathological conditions in CKD. The pathogenesis of these lesions, the origins of which can be identified in the absence of traditional cardiovascular risk factors, is incompletely understood. CKD-mediated vascular calcification in CKD is characterized by a transition of vascular smooth muscle cells to an osteoblast-like phenotype and altered bone and mineral metabolism are strongly linked to progressive cardiovascular disease in this population. Renal osteodystrophy therapies, including phosphate binders, vitamin D analogs, and calcimimetics, have an impact on the progression of cardiovascular disease. However, cardiovascular disease has its origins before the development of secondary hyperparathyroidism, and optimal therapeutic regimens that minimize cardiac dysfunction, vascular calcification, and early mortality remain to be defined.

Fetuin-A deficiency is associated with infantile cortical hyperostosis (Caffey disease)

BACKGROUND

Infantile cortical hyperostosis (ICH)/Caffey disease is an inflammatory collagenopathy of infancy, manifested by subperiosteal bone hyperplasia. Genetically, ICH was linked with heterozygosity for an R836C mutation in the COL1A1 gene. Although an autosomal-recessive trait is also suspected, it has not been proven thus far.

METHODS

A case of an infant male born to consanguineous parents is reported, presenting with classical findings, course, and clinical outcome of ICH. Whole-exome sequencing (WES) was performed in order to identify a possible underlying genetic defect.

RESULTS

WES analysis revealed a novel homozygous nonsense mutation in lysine 2 of fetuin-A, encoded by the ALPHA-2-HS-GLYCOPROTEIN (AHSG) gene (c.A4T; p.K2X). Fetuin-A is an important regulator of bone remodeling and an inhibitor of ectopic mineralization. By enzyme-linked immunosorbent assay (ELISA), we show a complete deficiency of this protein in the patient's serum, compared to controls.

CONCLUSION

A novel homozygous nonsense mutation in AHSG gene has been found in ICH patient with a typical phenotype, resulting in fetuin-A deficiency. This finding postulates an autosomal-recessive mode of inheritance in ICH, which, unlike the autosomal-dominant inheritance associated with COL1A1, is associated with AHSG and fetuin-A deficiency.

Fetuin-A levels are increased in the adipose tissue of diabetic obese humans but not in circulation

Background

The hepatokine fetuin-A is linked to obesity and type 2 diabetes, but its presence and expression in adipose tissue remain unclear. In this study, we aimed to assess the circulating levels of fetuin-A and its expression in subcutaneous adipose tissue (SAT) from diabetic and non-diabetic obese subjects and their modulation by exercise.

Methods

SAT and blood were obtained from adults obese (diabetic, n=118 and non-diabetic, n=166) before and after a 3-month exercise program (diabetic, n=40 and non-diabetic, n=36, respectively). Plasma fetuin-A was assayed using ELISA. The presence and expression of fetuin-A in SAT, peripheral blood mononuclear cells (PBMCs) and cell lines (3T3-L1, THP-1, HepG2, RAW 264.7) were analysed using confocal microscopy, immunoblotting and qRT-PCR.

Results

Plasma fetuin-A level did not significantly differ between diabetic and non-diabetic obese subjects. However, when the non-diabetic group was divided into metabolically healthy and unhealthy phenotypes, significantly higher fetuin-A level was observed in the unhealthy sub-group. Circulating fetuin-A was mainly associated with glycaemic markers. In SAT, fetuin-A protein level was significantly higher in the diabetic obese subjects but its mRNA was not detected. Similarly, fetuin-A protein was detected in PBMCs, but its mRNA was not. In line with this, the use of various cell lines and culture media indicated that the presence of fetuin-A in SAT and PBMCs was due to its uptake from circulation rather than its endogenous expression. Finally, physical exercise decreased fetuin-A levels in both plasma and SAT in both groups.

Conclusions

Fetuin-A levels increased in association with diabetes in SAT but not in circulation in the obese subjects. Moreover, physical exercise decreased fetuin-A level. Fetuin-A potentially acts as a hepatokine taken up by other tissues, such as adipose tissue.

Electronic supplementary material

The online version of this article (10.1186/s12944-018-0919-x) contains supplementary material, which is available to authorized users.

FGF23 and Fetuin-A Interaction in the Liver and in the Circulation

Recently it has been demonstrated that Fetuin-A, an anti-inflammatory protein synthesized by the liver, is produced also in bone by an FGF23-regulated pathway. FGF23 has been also demonstrated to induce inflammatory cytokine production in the liver. This study aimed to explore if FGF23 plays a role in the Fetuin-A production in the liver cells too and the possible relationships with FGF23 pro-inflammatory effects.

FGF23 and Fetuin-A were studied in liver, kidney and in plasma with immunochemistry, immunoprecipitation, western blot, chromatin immunoprecipitation, duolink, ELISA, qrtPCR methodology.

FGF23 is produced, but not secreted by the liver cells. In hepatocytes and circulation, FGF23 was present only strictly linked to Fetuin-A, while Fetuin-A was found also in unbounded form. No link was observed in the kidney. FGF23 up to 600 pg/ml stimulates, while, at higher concentrations, reduces Fetuin-A expression. Notably, overall the range of concentrations, FGF23 stimulates Fetuin-A promoter, TNFα and IL6 expression. In the nucleus, FGF23 seems to act as a direct transcription factor of Fetuin-A promoter.

These results suggest that FGF23 played a direct regulatory role in Fetuin-A expression in liver cells with a biphasic effect: Fetuin-A progressively increases when FGF23 increases up to 400-600 pg/mL, and declines at higher FGF23 concentrations. These results lead us to hypothesize: a) a possible epigenetic post-transcriptional regulation; b) a possible counter-regulatory effect of FGF23 induced inflammatory cytokines (TNFα/ NF-κB mechanism). This study could add an additional key for the interpretation of the possible mechanisms linking FGF23, Fetuin-A and inflammation in CKD patients and suggests a role for FGF23 as transcription factor.

Bone Quality Assessment as Measured by Trabecular Bone Score in Patients With End-Stage Renal Disease on Dialysis

Patients with end-stage renal disease (ESRD) on maintenance hemodialysis (HD) exhibit osteoporosis and increased fracture risk. Dual-energy X-ray absorptiometry scan measurements and calculation of fracture risk assessment toll score underestimate fracture risk in these patients and do not estimate bone quality. Trabecular bone score (TBS) has been recently proposed as an indirect measure of bone microarchitecture. In this study, we investigated alterations of bone quality in patients with ESRD on HD, using TBS. Fifty patients with ESRD on HD, with a mean age 62 years, and 52 healthy individuals matched for age, body mass index, and gender, were enrolled. All participants had a bone mineral density (BMD) measurement by dual-energy X-ray absorptiometry scan at the lumbar spine, femoral neck, total hip, and 1/3 radius. TBS was evaluated using TBS iNsight. Serum fetuin-A and plasma fibroblast growth factor-23 (FGF-23) (C-terminal) were also measured. Patients on dialysis had significantly lower BMD values at all skeletal sites measured. Plasma FGF-23 levels significantly increased and serum fetuin-Α significantly decreased in patients on dialysis compared with controls. TBS was significantly reduced in patients on dialysis compared with controls (1.11 ± 0.16 vs 1.30 ± 0.13, p < 0.001, respectively) independently of age; BMD; duration of dialysis; and serum levels of alkaline phosphatase, 25-OH-vitamin D, parathyroid hormone, fetuin-A, or plasma FGF-23. Patients on HD who were diagnosed with an osteoporotic vertebral fracture had numerically lower TBS values, albeit without reaching statistical significance, compared with patients on dialysis without a fracture (1.044 ± 0.151 vs 1.124 ± 0.173, respectively, p = 0.079). Bone microarchitecture, as assessed by TBS, is significantly altered in ESRD on patients on HD independently of BMD values and metabolic changes that reflect chronic kidney disease-mineral and bone disorder.

Newly Developed Rat Model of Chronic Kidney Disease-Mineral Bone Disorder

Aim: Chronic kidney disease–mineral bone disorder (CKD–MBD) is associated with all-cause and cardiovascular morbidity and mortality in patients with CKD. Thus, elucidating its pathophysiological mechanisms is essential for improving the prognosis. We evaluated characteristics of CKD–MBD in a newly developed CKD rat model.

Methods: We used male Sprague–Dawley (SD) rats and spontaneously diabetic Torii (SDT) rats, which are used as models for nonobese type 2 diabetes. CKD was induced by 5/6 nephrectomy (Nx). At 10 weeks, the rats were classified into six groups and administered with a vehicle or a low- or high-dose paricalcitol thrice a week. At 20 weeks, the rats were sacrificed; blood and urinary biochemical analyses and histological analysis of the aorta were performed.

Results: At 20 weeks, hemoglobin A1c (HbA1c) levels, blood pressure, and renal function were not significantly different among the six groups. Serum calcium and phosphate levels tended to be higher in SDT-Nx rats than in SD-Nx rats. The urinary excretion of calcium and phosphate was significantly greater in SDT-Nx rats than in SD-Nx rats. After administering paricalcitol, serum parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) levels were significantly higher in SDT-Nx rats than in SD-Nx rats. The degree of aortic calcification was significantly more severe and the aortic calcium content was significantly greater in SDT-Nx rats than in SD-Nx rats.

Conclusions: We suggest that our new CKD rat model using SDT rats represents a useful CKD–MBD model, and this model was greatly influenced by paricalcitol administration. Further studies are needed to clarify the detailed mechanisms underlying this model.

Proteomic profiling of archaeological human bone

Ancient protein analysis provides clues to human life and diseases from ancient times. Here, we performed shotgun proteomics of human archeological bones for the first time, using rib bones from the Hitotsubashi site (AD 1657-1683) in Tokyo, called Edo in ancient times. The output data obtained were analysed using Gene Ontology and label-free quantification. We detected leucocyte-derived proteins, possibly originating from the bone marrow of the rib. Particularly prevalent and relatively high expression of eosinophil peroxidase suggests the influence of infectious diseases. This scenario is plausible, considering the overcrowding and unhygienic living conditions of the Edo city described in the historical literature. We also observed age-dependent differences in proteome profiles, particularly for proteins involved in developmental processes. Among them, alpha-2-HS-glycoprotein demonstrated a strong negative correlation with age. These results suggest that analysis of ancient proteins could provide a useful indicator of stress, disease, starvation, obesity and other kinds of physiological and pathological information.

Osteocytic signalling pathways as therapeutic targets for bone fragility

Osteocytes are differentiated osteoblasts that become surrounded by matrix during the process of bone formation. Acquisition of the osteocyte phenotype is achieved by profound changes in gene expression that facilitate adaptation to the changing cellular environment and constitute the molecular signature of osteocytes. During osteocytogenesis, the expression of genes that are characteristic of the osteoblast are altered and the expression of genes and/or proteins that impart dendritic cellular morphology, regulate matrix mineralization and control the function of cells at the bone surface are ordely modulated. The discovery of mutations in human osteocytic genes has contributed, in a large part, to our understanding of the role of osteocytes in bone homeostasis. Osteocytes are targets of the mechanical force imposed on the skeleton and have a critical role in integrating mechanosensory pathways with the action of hormones, which thereby leads to the orchestrated response of bone to environmental cues. Current, therapeutic approaches harness this accumulating knowledge by targeting osteocytic signalling pathways and messengers to improve skeletal health.