Immunohistochemical localization and mRNA expression of matrix Gla protein and fetuin-A in bone biopsies of hemodialysis patients

Evolution of Matrix Gla and Bone Gla Protein Genes in Jawed Vertebrates

Matrix Gla protein (Mgp) and bone Gla protein (Bgp) are vitamin-K dependent proteins that bind calcium in their γ-carboxylated versions in mammals. They are recognized as positive (Bgp) or negative (Mgp and Bgp) regulators of biomineralization in a number of tissues, including skeletal tissues of bony vertebrates. The Mgp/Bgp gene family is poorly known in cartilaginous fishes, which precludes the understanding of the evolution of the biomineralization toolkit at the emergence of jawed vertebrates. Here we took advantage of recently released genomic and transcriptomic data in cartilaginous fishes and described the genomic loci and gene expression patterns of the Mgp/Bgp gene family. We identified three genes, Mgp1, Mgp2, and Bgp, in cartilaginous fishes instead of the single previously reported Mgp gene. We describe their genomic loci, resulting in a dynamic evolutionary scenario for this gene family including several events of local (tandem) duplications, but also of translocation events, along jawed vertebrate evolution. We describe the expression patterns of Mgp1, Mgp2, and Bgp in embryonic stages covering organogenesis in the small-spotted catshark Scyliorhinus canicula and present a comparative analysis with Mgp/Bgp family members previously described in bony vertebrates, highlighting ancestral features such as early embryonic, soft tissues, and neuronal expressions, but also derived features of cartilaginous fishes such as expression in fin supporting fibers. Our results support an ancestral function of Mgp in skeletal mineralization and a later derived function of Bgp in skeletal development that may be related to the divergence of bony vertebrates.

Identification of potential salivary biomarker panels for oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is one of the most prevalent cancers worldwide with the maximum number of incidences and deaths reported from India. One of the major causes of poor survival rate associated with OSCC has been attributed to late presentation due to non-availability of a biomarker. Identification of early diagnostic biomarker will help in reducing the disease morbidity and mortality. We validated 12 salivary proteins using targeted proteomics, identified initially by relative quantification of salivary proteins on LC-MS, in OSCC patients and controls. Salivary AHSG (p = 0.0041**) and KRT6C (p = 0.002**) were upregulated in OSCC cases and AZGP1 (p ≤ 0.0001***), KLK1 (p = 0.006**) and BPIFB2 (p = 0.0061**) were downregulated. Regression modelling resulted in a significant risk prediction model (p < 0.0001***) consisting of AZGP1, AHSG and KRT6C for which ROC curve had AUC, sensitivity and specificity of 82.4%, 78% and 73.5% respectively for all OSCC cases and 87.9%, 87.5% and 73.5% respectively for late stage (T3/T4) OSCC. AZGP1, AHSG, KRT6C and BPIFB2 together resulted in ROC curve (p < 0.0001***) with AUC, sensitivity and specificity of 94%, 100% and 77.6% respectively for N0 cases while KRT6C and AZGP1 for N+ cases with ROC curve (p < 0.0001***) having AUC sensitivity and specificity of 76.8%, 73% and 69.4%. Our data aids in the identification of biomarker panels for the diagnosis of OSCC cases with a differential diagnosis between early and late-stage cases.

Destroy to Rebuild: The Connection Between Bone Tissue Remodeling and Matrix Metalloproteinases

Bone is a dynamic organ that undergoes constant remodeling, an energetically costly process by which old bone is replaced and localized bone defects are repaired to renew the skeleton over time, thereby maintaining skeletal health. This review provides a general overview of bone’s main players (bone lining cells, osteocytes, osteoclasts, reversal cells, and osteoblasts) that participate in bone remodeling. Placing emphasis on the family of extracellular matrix metalloproteinases (MMPs), we describe how: (i) Convergence of multiple protease families (including MMPs and cysteine proteinases) ensures complexity and robustness of the bone remodeling process, (ii) Enzymatic activity of MMPs affects bone physiology at the molecular and cellular levels and (iii) Either overexpression or deficiency/insufficiency of individual MMPs impairs healthy bone remodeling and systemic metabolism. Today, it is generally accepted that proteolytic activity is required for the degradation of bone tissue in osteoarthritis and osteoporosis. However, it is increasingly evident that inactivating mutations in MMP genes can also lead to bone pathology including osteolysis and metabolic abnormalities such as delayed growth. We argue that there remains a need to rethink the role played by proteases in bone physiology and pathology.

Unexpected Role of Matrix Gla Protein in Osteoclasts: Inhibiting Osteoclast Differentiation and Bone Resorption

Matrix Gla protein (MGP) is an extracellular protein responsible for inhibiting mineralization. MGP inhibits osteoblast mineralization and bone formation by regulating the deposition of bone matrix. However, Mgp-/- mice display an osteopenic phenotype. To explain this contradiction, we investigated the role of MGP in osteoclastogenesis, the other side of bone remodeling. We found that MGP expression is markedly increased by osteoclastic commitment. Osteoclast differentiation and bone resorption are accelerated by MGP depletion while suppressed by MGP overexpression. The in vivo results confirmed its inhibitory role in osteoclastogenesis by the administration of Cre-dependent FLEX-On recombinant MGP-AAV to LysM Cre mice. Furthermore, we found that the expression and nuclear translocation of nuclear factor of activated T cells, cytoplasmic 1 (NFATc1), are under the control of MGP. MGP loss results in elevation of intracellular Ca2+ flux. Vitronectin-induced activation of Src/Rac1 is magnified in the absence of MGP but reduced when MGP is overexpressed. Inhibition of Src activation or NFATc1 nuclear import rescues the increased osteoclastogenesis induced by MGP deficiency. These observations (i) establish, for the first time to our knowledge, that MGP plays an essential role in osteoclast differentiation and function, (ii) enrich the current knowledge of MGP function, and (iii) indicate the potential of MGP as a therapeutic target for low-bone-mass disorders.

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

INTRODUCTION

AHSG, a serum glycoprotein with recognized anti-calcification activity, has also been suggested to modulate both bone formation and resorption. Though the bulk of AHSG is mostly synthesized in the liver, it has been claimed that also bone cells might produce it. However, the extent of the bone AHSG production and the potential controlling factors remain to be definitively proven. A relevant number of studies support the notion that FGF23, a bone-derived hormone, not only regulates the most important mineral metabolism (MM) related factors (phosphate, parathyroid hormone, vitamin D, etc.), but might be also involved in cardiovascular (CV) outcome, both in chronic kidney disease (CKD) patients and in the general population. Furthermore, in addition to some direct autocrine and paracrine effects in bone, FGF23 has been suggested to interact with AHSG. In this study we investigated if AHSG is really produced by bone cells, and if its bone production is related and/or controlled by FGF23, using cultured bone cells, according to a new method recently published by our group.

RESULTS

Our data show that AHSG is consistently produced in osteocytes and to a far lesser extent in osteoblasts. Both FGF23 addition to the culture medium and its over-expression in osteocytes were associated with a consistent increase of both AHSG mRNA and protein, while FGF23 silencing was followed by opposite effects. Though most of these results were largely affected by the blockage of FGF23 receptors, the role of these receptors in the different experimental sets is still not completely clarified. In addition, we found that FGF23 and AHSG proteins co-localized both in cytoplasm and nucleus, which suggests a possible reciprocal interactivity.

CONCLUSIONS

Our data not only confirm that AHSG is produced in bone, mainly in osteocytes, but show for the first time that its production is modulated by FGF23. Since both proteins play important roles in the bone and cardiovascular pathology, these results add new pieces to the puzzling relationship between bone and vascular pathology, in particular in CKD patients, prompting future investigations in this field.

Comparative analysis of mouse-induced pluripotent stem cells and mesenchymal stem cells during osteogenic differentiation in vitro

Induced pluripotent stem cells (iPSCs) can differentiate into mineralizing cells and are, therefore, expected to be useful for bone regenerative medicine; however, the characteristics of iPSC-derived osteogenic cells remain unclear. Here, we provide a direct in vitro comparison of the osteogenic differentiation process in mesenchymal stem cells (MSCs) and iPSCs from adult C57BL/6J mice. After 30 days of culture in osteogenic medium, both MSCs and iPSCs produced robustly mineralized bone nodules that contained abundant calcium phosphate with hydroxyapatite crystal formation. Mineral deposition was significantly higher in iPSC cultures than in MSC cultures. Scanning electron microscopy revealed budding matrix vesicles in early osteogenic iPSCs; subsequently, the vesicles propagated to exhibit robust mineralization without rich fibrous structures. Early osteogenic MSCs showed deposition of many matrix vesicles in abundant collagen fibrils that became solid mineralized structures. Both cell types demonstrated increased expression of osteogenic marker genes, such as runx2, osterix, dlx5, bone sialoprotein (BSP), and osteocalcin, during osteogenesis; however, real-time reverse transcription-polymerase chain reaction array analysis revealed that osteogenesis-related genes encoding mineralization-associated molecules, bone morphogenetic proteins, and extracellular matrix collagens were differentially expressed between iPSCs and MSCs. These data suggest that iPSCs are capable of differentiation into mature osteoblasts whose associated hydroxyapatite has a crystal structure similar to that of MSC-associated hydroxyapatite; however, the transcriptional differences between iPSCs and MSCs could result in differences in the mineral and matrix environments of the bone nodules. Determining the biological mechanisms underlying cell-specific differences in mineralization during in vitro iPSC osteogenesis may facilitate the development of clinically effective engineered bone.

The relationship of fetuin-A and lactoferrin with bone mass in elderly women

SUMMARY

The relationships of fetuin-A and lactoferrin to bone-related phenotypes were investigated in elderly women. Fetuin-A was associated not only with bone mineral density (BMD) but also with bone resorption marker suggesting an influence of fetuin-A on osteoclasts.

INTRODUCTION

The aim of this study is to investigate the relationship of bone-related phenotypes in elderly women with circulating fetuin-A and lactoferrin.

METHODS

Eighty-two elderly women were studied. Serum fetuin-A, lactoferrin, C-terminal telopeptide of type I collagen (CTx), total procollagen type 1 amino-terminal propeptide, and plasma intact parathyroid hormone (PTH) were analyzed. BMD of the lumbar spine at L2-4 and at the femoral neck was measured.

RESULTS

Serum fetuin-A was significantly associated with L2-4 BMD (r = 0.23, P < 0.05). After controlling for age and body weight, the association remained statistically significant. There was a significant association between serum fetuin-A and serum CTx (r = -0.37, P < 0.001). The association between fetuin-A and L2-4 BMD no longer existed after controlling for serum CTx. There were positive associations of circulating lactoferrin with plasma PTH (r = 0.24, P < 0.05) and serum CTx (r = 0.26, P < 0.05). No association between serum lactoferrin and BMD at the lumbar spine or femoral neck was detected.

CONCLUSIONS

Circulating fetuin-A is related to bone mass and bone resorption markers in elderly women. Lactoferrin, in contrast, is associated only with bone resorption markers.

Molecular characterization and methylation study of matrix gla protein in articular cartilage from pig with osteochondrosis

Osteochondrosis (OC) or leg weakness is an economically important disease of young fast growing pigs and is a concern of animal welfare. The etiology and pathogenesis of osteochondrosis is not fully understood yet, but any abnormalities in the formation of hypertrophic chondrocytes and disrupted blood supply to the growth cartilage are very important predisposing factors. Matrix gla protein (MGP) as a potential calcification inhibitor of extracellular matrix might contribute to the development of OC. Molecular characterization, polymorphisms analysis, methylation at promoter region and expression of MGP gene and protein were performed in both healthy and OC cartilage collected from a DurocxPietrain resource population. The porcine MGP gene consists of 4 exons and 3 introns. The full-length MGP cDNA isolated from articular cartilage consists of 606 bp with a 69-bp 5' UTR, a 312-bp open reading frame with a start codon, a 225-bp 3' UTR. Three single-nucleotide polymorphisms (SNP) were detected in the intron 1 (A-115G, C-1073T and C-1135A) and one in the 3'UTR (C-3767T). The relative abundance of MGP mRNA was lower (P<0.05) in OC compared with healthy cartilage. Moreover, the intensity of MGP band was lower (P<0.05) in OC group when quantified by western blot. Furthermore, one CpG region was identified in MGP promoter and DNA methylation of three CG sites were higher in OC compared with normal cartilage. This suggested that the high DNA methylation at specific CG sites in the MGP promoter might be involved in the down regulation of MGP in OC. Immunofluorescence of normal cartilage collected from pigs of different ages revealed that MGP signals were higher in younger pigs and decreased in the older pigs. The MGP protein was expressed more near to the cartilage canals. These results suggest that the MGP gene might be a potential candidate gene for the development of OC in pigs.