Regulation of the maturation of osteoblasts and osteoclastogenesis by glutamate

Dextromethorphan Inhibits Osteoblast Differentiation and Bone Regeneration of Rats With Subcritical-Sized Calvarial Defects

The glutamatergic signaling pathway, which is mediated by N-methyl-D-aspartate (NMDA) receptors, is crucial for osteoblast differentiation and bone function. Dextromethorphan (DXM), a widely used antitussive, is a noncompetitive antagonist of the NMDA receptor. However, the effects of DXM on osteoblast and bone regeneration remain unclear. The present study investigated the effects of DXM on osteogenesis in vitro and in vivo. A MC3T3-E1 preosteoblast cell line was treated with varying concentrations of DXM. Real-time-quantitative polymerase chain reaction (RT-qPCR) and Western-blot analysis were performed to evaluate the expression of osteogenesis-related runt-related transcription factor 2 (RUNX2), osterix (OSX), osteocalcin (OCN), collagen type 1α (Col-1α), and alkaline phosphatase (ALP) after DXM treatment. Zebrafish embryos were incubated with DXM, which had potential to affect the ossification of the vertebrae and skull, and analyzed using calcein staining. Furthermore, we used a rat calvarial defect model to assess the effects of DXM on bone regeneration by using microcomputed tomography. The results indicate that DXM inhibited extracellular mineralization, ALP activity, and the expression of osteogenic markers, namely RUNX2, OSX, OCN, Col-1α, and ALP, in MC3T3-E1 cells. DXM suppressed skeleton ossification in zebrafish and affected bone regeneration in rats with calvarial defects. However, the mineral density of the regenerated bones did not differ significantly between the DXM and control groups. The present study demonstrated that DXM negatively affects the osteogenic function of osteoblasts, leading to impaired skeletal development and bone regeneration. Thus, clinicians should consider the negative effects of DXM on bone regeneration.

Design and characterization of memantine and donepezil loaded 3D scaffolds

Memantine HCl (MEM) and Donepezil HCl (DON) are widely used separately and in combination to treat Alzheimer's disease, and some studies suggest that these drugs may also prevent bone fractures and promote bone regeneration. For this purpose, we formulated fiber-based 3D scaffolds for local delivery of MEM/DON to improve the regeneration process of bone fractures. First, Poly (ε-caprolactone) (PCL)-based MEM/DON-loaded nanofibrous membranes were produced by electrospinning, and then these nanofibrous membranes were transformed into 3D scaffolds using the thermally induced self-agglomeration (TISA) method. Encapsulation efficiency after these two steps was found to be around 20%. Analyses confirmed that the 3D scaffolds have a morphology similar to the extracellular matrix, and that their hydrophilicity, swelling ratio, porosity, and degradation rate were adequate for bone tissue regeneration. Release studies show that the scaffolds provide an initial burst release of the drugs, followed by a sustained release for 21 days. These 3D scaffolds did not show any cytotoxic effect on the L-929 cell line, and increased cell viability over time indicates that they can be used in tissue engineering applications.

The emerging role of tranexamic acid and its principal target, plasminogen, in skeletal health

The worldwide burden of skeletal diseases such as osteoporosis, degenerative joint disease and impaired fracture healing is steadily increasing. Tranexamic acid (TXA), a plasminogen inhibitor and anti-fibrinolytic agent, is used to reduce bleeding with high effectiveness and safety in major surgical procedures. With its widespread clinical application, the effects of TXA beyond anti-fibrinolysis have been noticed and prompted renewed interest in its use. Some clinical trials have characterized the effects of TXA on reducing postoperative infection rates and regulating immune responses in patients undergoing surgery. Also, several animal studies suggest potential therapeutic effects of TXA on skeletal diseases such as osteoporosis and fracture healing. Although a direct effect of TXA on the differentiation and function of bone cells in vitro was shown, few mechanisms of action have been reported. Here, we summarize recent findings of the effects of TXA on skeletal diseases and discuss the underlying plasminogen-dependent and -independent mechanisms related to bone metabolism and the immune response. We furthermore discuss potential novel indications for TXA application as a treatment strategy for skeletal diseases.

Dual targeting total saponins of Pulsatilla of natural polymer crosslinked gel beads with multiple therapeutic effects for ulcerative colitis

Oral colon targeted drug delivery system (OCTDDS) is desirable for the treatment of ulcerative colitis (UC). In this study, we designed a partially oxidized sodium alginate-chitosan crosslinked microsphere for UC treatment. Dissipative particle dynamics (DPD) was used to study the formation and enzyme response of gel beads from a molecular perspective. The formed gel beads have a narrow particle size distribution, a compact structure, low cytotoxicity and great colon targeting in vitro and in vivo. Animal experiments demonstrated that gel beads promoted colonic epithelial barrier integrity, decreased the level of pro-inflammatory factors, accelerated the recovery of intestinal microbial homeostasis in UC rats and restored the intestinal metabolic disorders. In conclusion, our gel bead is a promising approach for the treatment of UC and significant for the researches on the pathogenesis and treatment mechanism of UC.

Mechanisms of secondary biogenic coalbed methane formation in bituminous coal seams: a joint experimental and multi-omics study

Coal seam microbes, as endogenous drivers of secondary biogenic gas production in coal seams, might be related to methane production in coal seams. In this study, we carried out anaerobic indoor culture experiments of microorganisms from three different depths of bituminous coal seams in Huainan mining area, and revealed the secondary biogas generation mechanism of bituminous coal seams by using the combined analysis of macro-genome and metabolism multi-omics. The results showed that the cumulative mass molar concentrations (Molality) of biomethane production increased with the increase of the coal seam depth in two consecutive cycles. At the genus level, there were significant differences in the bacterial and archaeal community structures corresponding to the three coal seams 1#, 6#, and 9#(p < 0.05). The volatile matter of air-dry basis (Vad) of coal was significantly correlated with differences in genus-level composition of bacteria and archaea, with correlations of R bacterial = 0.368 and R archaeal = 0.463, respectively. Functional gene analysis showed that the relative abundance of methanogenesis increased by 42% before and after anaerobic fermentation cultivation. Meanwhile, a total of 11 classes of carbon metabolism homologues closely related to methanogenesis were detected in the liquid metabolites of coal bed microbes after 60 days of incubation. Finally, the fatty acid, amino acid and carbohydrate synergistic methanogenic metabolic pathway was reconstructed based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. The expression level of mcrA gene within the metabolic pathway of the 1# deep coal sample was significantly higher than that of the other two groups (p < 0.05 for significance), and the efficient expression of mcrA gene at the end of the methanogenic pathway promoted the conversion of bituminous coal organic matter to methane. Therefore, coal matrix compositions may be the key factors causing diversity in microbial community and metabolic function, which might be related to the different methane content in different coal seams.

Unfavorable effects of memantine on the skeletal system in female rats

Memantine is an N-methyl-D-aspartate (NMDA) receptor antagonist used in the treatment of Alzheimer's disease (AD). NMDA receptors are expressed on bone cells. The aim of the present study was to investigate the effects of memantine on the rat musculoskeletal system. Taking into account that most of female AD patients are postmenopausal, the study was carried out on intact and ovariectomized (estrogen-deficient) rats. Mature Wistar rats were divided into following groups: non-ovariectomized (NOVX) control rats, NOVX rats treated with memantine, ovariectomized (OVX) control rats, and OVX rats treated with memantine. Memantine (2 mg/kg p.o.) was administered once daily for four weeks, starting one week after ovariectomy. The serum bone turnover marker and cytokine levels, bone density, mass, mineralization, mechanical properties, histomorphometric parameters of compact and cancellous bone, skeletal muscle mass and grip strength were determined. In NOVX rats, memantine slightly decreased the strength of compact bone of the femoral diaphysis (parameters in the yield point) and unfavorably affected histomorphometric parameters of cancellous bone (the femoral epiphysis and metaphysis). In OVX rats, in which estrogen deficiency induced osteoporotic changes, memantine increased the phosphorus content in the femoral bone mineral. No other effects on bone were observed in the memantine-treated OVX rats. In conclusion, the results of the present study indicated slight damaging skeletal effects of memantine in rats with normal estrogen levels.

A Novel Prenylflavonoid Icariside I Ameliorates Estrogen Deficiency-Induced Osteoporosis via Simultaneous Regulation of Osteoblast and Osteoclast Differentiation

Regulation of osteoblast-mediated bone formation and osteoclast-mediated bone resorption is crucial for bone health. Currently, most clinical drugs for osteoporosis treatment such as bisphosphonates are commonly used to inhibit bone resorption but unable to promote bone formation. In this study, we discovered for the first time that icariside I (GH01), a novel prenylflavonoid isolated from Epimedium, can effectively ameliorate estrogen deficiency-induced osteoporosis with enhancement of trabecular and cortical bone in an ovariectomy (OVX) mouse model. Mechanistically, our in vitro results showed that GH01 repressed osteoclast differentiation and resorption through inhibition of RANKL-induced TRAF6-MAPK-p38-NFATc1 cascade. Simultaneously, we also found that GH01 dose-dependently promoted osteoblast differentiation and formation by inhibiting adipogenesis and accelerating energy metabolism of osteoblasts. In addition, both in vitro and in vivo studies also suggested that GH01 is not only a non-toxic natural small molecule but also beneficial for restoration of liver injury in OVX mice. These results demonstrated that GH01 has great potential for osteoporosis treatment by simultaneous regulation of osteoblast and osteoclast differentiation.

Downregulation of the Autism Spectrum Disorder Gene Shank2 Decreases Bone Mass in Male Mice

Mutations of the postsynaptic scaffold protein Shank2 lead to autism spectrum disorders (ASD). These patients frequently suffer from higher fracture risk. Here, we investigated whether Shank2 directly regulates bone mass. We show that Shank2 is expressed in bone and that Shank2 levels are increased during osteoblastogenesis. Knockdown of Shank2 by siRNA targeting the encoding regions for PDZ and SAM domain inhibits osteoblastogenesis of primary murine calvarial osteoblasts. Shank2 knockout mice (Shank2 ^-/-) have a decreased bone mass due to reduced osteoblastogenesis and bone formation, whereas bone resorption remains unaffected. Induced pluripotent stem cells (iPSCs)-derived osteoblasts from a loss-of-function Shank2 mutation in a patient showed a significantly reduced osteoblast differentiation potential. Moreover, silencing of known Shank2 interacting proteins revealed that a majority of them promote osteoblast differentiation. From this we conclude that Shank2 and interacting proteins known from the central nervous system are decisive regulators in osteoblast differentiation. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Amino acid metabolism in skeletal cells

Amino acid metabolism regulates essential cellular functions, not only by fueling protein synthesis, but also by supporting the biogenesis of nucleotides, redox factors and lipids. Amino acids are also involved in tricarboxylic acid cycle anaplerosis, epigenetic modifications, next to synthesis of neurotransmitters and hormones. As such, amino acids contribute to a broad range of cellular processes such as proliferation, matrix synthesis and intercellular communication, which are all critical for skeletal cell functioning. Here we summarize recent work elucidating how amino acid metabolism supports and regulates skeletal cell function during bone growth and homeostasis, as well as during skeletal disease. The most extensively studied amino acid is glutamine, and osteoblasts and chondrocytes rely heavily on this non-essential amino acid during for their functioning and differentiation. Regulated by lineage-specific transcription factors such as SOX9 and osteoanabolic agents such as parathyroid hormone or WNT, glutamine metabolism has a wide range of metabolic roles, as it fuels anabolic processes by producing nucleotides and non-essential amino acids, maintains redox balance by generating the antioxidant glutathione and regulates cell-specific gene expression via epigenetic mechanisms. We also describe how other amino acids affect skeletal cell functions, although further work is needed to fully understand their effect. The increasing number of studies using stable isotope labelling in several skeletal cell types at various stages of differentiation, together with conditional inactivation of amino acid transporters or enzymes in mouse models, will allow us to obtain a more complete picture of amino acid metabolism in skeletal cells.

Endo- and Exometabolome Crosstalk in Mesenchymal Stem Cells Undergoing Osteogenic Differentiation

This paper describes, for the first time to our knowledge, a lipidome and exometabolome characterization of osteogenic differentiation for human adipose tissue stem cells (hAMSCs) using nuclear magnetic resonance (NMR) spectroscopy. The holistic nature of NMR enabled the time-course evolution of cholesterol, mono- and polyunsaturated fatty acids (including ω-6 and ω-3 fatty acids), several phospholipids (phosphatidylcholine, phosphatidylethanolamine, sphingomyelins, and plasmalogens), and mono- and triglycerides to be followed. Lipid changes occurred almost exclusively between days 1 and 7, followed by a tendency for lipidome stabilization after day 7. On average, phospholipids and longer and more unsaturated fatty acids increased up to day 7, probably related to plasma membrane fluidity. Articulation of lipidome changes with previously reported polar endometabolome profiling and with exometabolome changes reported here in the same cells, enabled important correlations to be established during hAMSC osteogenic differentiation. Our results supported hypotheses related to the dynamics of membrane remodelling, anti-oxidative mechanisms, protein synthesis, and energy metabolism. Importantly, the observation of specific up-taken or excreted metabolites paves the way for the identification of potential osteoinductive metabolites useful for optimized osteogenic protocols.

Tryptophan-Kynurenine Pathway in COVID-19-Dependent Musculoskeletal Pathology: A Minireview

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19), affecting multiple organ systems, including the respiratory tract and lungs. Several studies have reported that the tryptophan-kynurenine pathway is altered in COVID-19 patients. The tryptophan-kynurenine pathway plays a vital role in regulating inflammation, metabolism, immune responses, and musculoskeletal system biology. In this minireview, we surmise the effects of the kynurenine pathway in COVID-19 patients and how this pathway might impact muscle and bone biology.

Treadmill exercise influences the microRNA profiles in the bone tissues of mice

As an important regulator involved in cell activity, microRNAs (miRNAs) are important in the process of exercise influencing bone metabolism. The present study aimed to detect and select differentially expressed miRNAs in the bone tissues of mice trained on a treadmill, predict the target genes of these differentially expressed miRNAs and lay a foundation for exploring the effect of treadmill training on bone metabolism through miRNAs. In this experiment, after the mice were trained on a treadmill for 8 weeks, the mechanical properties of mouse femur bone were assessed, and the alkaline phosphatase (ALP) activity and osteocalcin (OCN) protein levels of the bone were assayed. miRNA microarray and reverse transcription-quantitative (RT-q)PCR were performed to select and validate differentially expressed miRNAs in the bone, and the target genes of these miRNAs were predicted with bioinformatics methods. In addition, the differentially expressed miRNAs in the bone tissues were compared with those in mechanically strained osteocytes in vitro. Treadmill training improved the mechanical properties of the femur bones of mice, and elevated the ALP activity and OCN protein level in the bone. In addition, 122 differentially expressed miRNAs were detected in the bone, of which nine were validated via RT-qPCR. Among the target genes of these differentially expressed miRNAs, certain candidates were involved in bone metabolism. A total of eight miRNAs were differentially expressed in both bone tissue and osteocytes, exhibiting the same expression trends, and various target genes of these eight miRNAs were also involved in bone metabolism. Treadmill training resulted in altered miRNA expression profiles in the bones of mice (mainly in osteocytes) and the differentially expressed miRNAs may serve important roles in regulating bone metabolism and osteogenic differentiation.

Amino acid metabolism and autophagy in skeletal development and homeostasis

Bone is an active organ that is continuously remodeled throughout life via formation and resorption; therefore, a fine-tuned bone (re)modeling is crucial for bone homeostasis and is closely connected with energy metabolism. Amino acids are essential for various cellular functions as well as an energy source, and their synthesis and catabolism (e.g., metabolism of carbohydrates and fatty acids) are regulated through numerous enzymatic cascades. In addition, the intracellular levels of amino acids are maintained by autophagy, a cellular recycling system for proteins and organelles; under nutrient deprivation conditions, autophagy is strongly induced to compensate for cellular demands and to restore the amino acid pool. Metabolites derived from amino acids are known to be precursors of bioactive molecules such as second messengers and neurotransmitters, which control various cellular processes, including cell proliferation, differentiation, and homeostasis. Thus, amino acid metabolism and autophagy are tightly and reciprocally regulated in our bodies. This review discusses the current knowledge and potential links between bone diseases and deficiencies in amino acid metabolism and autophagy.

Neurogenic Obesity and Skeletal Pathology in Spinal Cord Injury

Spinal cord injury (SCI) results in dramatic changes in body composition, with lean mass decreasing and fat mass increasing in specific regions that have important cardiometabolic implications. Accordingly, the recent Consortium for Spinal Cord Medicine (CSCM) released clinical practice guidelines for cardiometabolic disease (CMD) in SCI recommending the use of compartmental modeling of body composition to determine obesity in adults with SCI. This recommendation is guided by the fact that fat depots impact metabolic health differently, and in SCI adiposity increases around the viscera, skeletal muscle, and bone marrow. The contribution of skeletal muscle atrophy to decreased lean mass is self-evident, but the profound loss of bone is often less appreciated due to methodological considerations. General-population protocols for dual-energy x-ray absorptiometry (DXA) disregard assessment of the sites of greatest bone loss in SCI, but the International Society for Clinical Densitometry (ISCD) recently released an official position on the use of DXA to diagnose skeletal pathology in SCI. In this review, we discuss the recent guidelines regarding the evaluation and monitoring of obesity and bone loss in SCI. Then we consider the possible interactions of obesity and bone, including emerging evidence suggesting the possible influence of metabolic, autonomic, and endocrine function on bone health in SCI.

Koh group influence on titanium surfaces and pure sol-gel silica for enhanced osteogenic activity

Although, the excellent level of success of titanium surfaces is based on the literature, there are some biological challenges such as unfavorable metabolic conditions or regions of poor bone quality where greater surface bioactivity is desired. Seeking better performance, we hypothesized that silica-based coating via sol-gel route with immersion in potassium hydroxide basic solution induces acceleration of bone mineralization. This in vitro experimental study coated titanium surfaces with bioactive glass synthesized by route sol-gel via hydrolysis and condensation of chemical alkoxide precursor, tetraethylorthosilicate (TEOS) and/or deposition of chemical compound potassium hydroxide (KOH) to accelerate bone apposition. The generated surfaces titanium(T), titanium with potassium hydroxide deposition (T + KOH), titanium with bioactive glass deposition synthesized by sol-gel route via tetraethylorthosilicate hydrolysis (TEOS), titanium with bioactive glass deposition synthesized by sol-gel route via tetraethylorthosilicate hydrolysis with potassium hydroxide deposition (TEOS + KOH) were characterized by 3D optical profilometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM), contact angle by the sessile drop method, x-ray excited photoelectron spectroscopy (XPS) and energy dispersive x-ray spectrometer (EDX). The addition of the KOH group on the pure titanium (T) or bioactive glass (TEOS) surfaces generated a tendency for better results for mineralization. Groups covered with bioactive glass (TEOS, TEOS + KOH) tended to outperform even groups with titanium substrate (T, T + KOH). The addition of both, bioactive glass and KOH, in a single pure titanium substrate yielded the best results for the mineralization process.

The kynurenine connection: how exercise shifts muscle tryptophan metabolism and affects energy homeostasis, the immune system, and the brain

Tryptophan catabolism through the kynurenine pathway generates a variety of bioactive metabolites. Physical exercise can modulate kynurenine pathway metabolism in skeletal muscle and thus change the concentrations of select compounds in peripheral tissues and in the central nervous system. Here we review recent advances in our understanding of how exercise alters tryptophan-kynurenine metabolism in muscle and its subsequent local and distal effects. We propose that the effects of kynurenine pathway metabolites on skeletal muscle, adipose tissue, immune system, and the brain suggest that some of these compounds could qualify as exercise-induced myokines. Indeed, some of the more recently discovered biological activities for kynurenines include many of the best-known benefits of exercise: improved energy homeostasis, promotion of an anti-inflammatory environment, and neuroprotection. Finally, by considering the tissue expression of the different membrane and cytosolic receptors for kynurenines, we discuss known and potential biological activities for these tryptophan metabolites.

Effects of Atractylodes Oil on Inflammatory Response and Serum Metabolites in Adjuvant Arthritis Rats

Atractylodes Rhizoma is one of two principal components in Ermiaosan, a well-known traditional Chinese medicine for the treatment of rheumatoid arthritis (RA). Atractylodes oil (AO) represents a potential alternative treatment for RA. The purpose of this study was to investigate the effect of AO in rats with Adjuvant Arthritis (AA) by exploration of changes in serum metabolites using gas chromatography-mass spectrometry (GC-MS). Foot thickness and arthritis score, ankle joint pathological structure, the concentrations of TNF-α, IL-1β, IL-6, IL-17 and the expression of MMPs in ankle joint tissue were measured as indicators of efficacy of treatment using AO. In addition, multivariate statistical analysis was used to identify differential production of metabolites and biomarkers, and to analyze metabolic pathways. The results demonstrate that administration of AO resulted in a good therapeutic effect in the AA rat model, with significantly improved joint swelling, reduced joint score, and inhibition of inflammation, synovial pannus hyperplasia, and bone and cartilage destruction. Furthermore, AO was found to exert its effect against rheumatoid arthritis principally by differentially affecting 11 metabolites and six metabolic pathways, predominantly related to abnormal amino acid metabolism, in addition to energy-related metabolic pathways. This study evaluated the capability of AO to effectively treat AA rats, providing a novel strategy for the treatment of RA.

Bioinspired by both mussel foot protein and bone sialoprotein: universal adhesive coatings for the promotion of mineralization and osteogenic differentiation

Natural protein bioinspired coatings are developed to promote the mineralization and osteogenic differentiation of MC3T3-E1 cells for implant material use.

Chronic dietary supplementation with kynurenic acid, a neuroactive metabolite of tryptophan, decreased body weight without negative influence on densitometry and mandibular bone biomechanical endurance in young rats

Kynurenic acid (KYNA) is a neuroactive metabolite of tryptophan. KYNA naturally occurs in breast milk and its content increases with lactation, indicating the role of neonatal nutrition in general growth with long-term health effects. KYNA is also an antagonist of ionotropic glutamate receptors expressed in bone cells. The aim of this study was to establish the effects of chronic KYNA supplementation on bone homeostasis in young rats, using mandible as a model bone. Female and male newborn Wistar rats were divided into control and KYNA-administered groups until 60 days of age (25x10¹ mg/L or 25x10² mg/L in drinking water). Hemimandibles were subjected to densitometry, computed tomography analysis and mechanical testing. Rats supplemented with KYNA at both doses showed a decrease in body weight. There were no effects of KYNA administration and mandible histomorphometry. In males, a significant quadratic effect (P < 0.001) was observed in the densitometry of the hemimandible, where BMD increased in the group supplemented with 2.5x10¹ mg/L of KYNA. Analysis of mechanical tests data showed that when fracture forces were corrected for bone geometry and rats body weight the improvement of bone material properties was observed in male and female rats supplemented with lower dose of KYNA. This study showed that chronic supplementation with KYNA may limit weight gain in the young, without adversely affecting the development of the skeleton.

Monosodium Glutamate Supplementation Improves Bone Status in Mice Under Moderate Protein Restriction

Adequate protein intake during development is critical to ensure optimal bone gain and to attain a higher peak bone mass later. Using a mild protein restriction model in Balb/C mice consuming 6% of their total energy intake as soy protein (LP-SOY)-for which we observed a significantly lower femoral cortical thickness, bone volume, trabecular number, and thickness reduction-we evaluated the effects of monosodium glutamate (MSG) supplementation at different concentrations (0.5, 1, 5, 10, and 20 g/kg of diet) on bone characteristics in LP-SOY-fed mice. After 6 and 12 weeks, LP-SOY-fed mice had lower BMD and reduced body weight related to lower lean mass, which was associated with a reduced IGF-1 level. The negative effect of the LP-SOY diet on BMD correlated with impaired bone formation. MSG supplementation, at 5, 10, and 20 g/kg of diet, and PTH injection, used as a positive control, were able to improve BMD and to increase osteoblast activity markers (P1NP and osteocalcin), as well as glutamine plasma concentration. An analysis of bone microarchitecture found that cortical bone was less sensitive to protein restriction than trabecular bone, and that MSG ingestion was able to preserve bone quality through an increase of collagen synthesis, although it did not allow normal bone growth. Our study reinforces the view that glutamate can act as a functional amino acid for bone physiology and support clinical investigation of glutamate supplementation in adults characterized by poor bone status, notably as a result of insufficient protein intake. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

The angiotensin converting enzyme 2/angiotensin-(1-7)/Mas Receptor axis as a key player in alveolar bone remodeling

The renin-angiotensin system (RAS), aside its classical hormonal properties, has been implicated in the pathogenesis of inflammatory disorders. The angiotensin converting enzyme 2/angiotensin-(1-7)/Mas Receptor (ACE2/Ang-(1-7)/MasR) axis owns anti-inflammatory properties and was recently associated with bone remodeling in osteoporosis. Thus, the aim of this study was to characterize the presence and effects of the ACE2/Ang-(1-7)/MasR axis in osteoblasts and osteoclasts in vitro and in vivo. ACE2 and MasR were detected by qPCR and western blotting in primary osteoblast and osteoclast cell cultures. Cells were incubated with different concentrations of Ang-(1-7), diminazene aceturate (DIZE - an ACE2 activator), A-779 (MasR antagonist) and/or LPS in order to evaluate osteoblast alkaline phosphatase and mineralized matrix, osteoclast differentiation and cytokine expression, and mRNA levels of osteoblasts and osteoclasts markers. An experimental model of alveolar bone resorption triggered by dysbiosis in rats was used to evaluate bone remodeling in vivo. Rats were treated with Ang-(1-7), DIZE and/or A-779 and periodontal samples were collected for immunohistochemistry, morphometric analysis, osteoblast and osteoclast count and cytokine evaluation. Human gingival samples from healthy and periodontitis patients were also evaluated for detection of ACE2 and MasR expression. Osteoblasts and osteoclasts expressed ACE2 and MasR in vitro and in vivo. LPS stimulation or alveolar bone loss induction reduced ACE2 expression. Treatment of bone cells with Ang-(1-7) or DIZE stimulated osteoblast ALP, matrix synthesis, upregulated osterix, osteocalcin and collagen type 1 transcription, reduced IL-6 expression, and decreased osteoclast differentiation, RANK and IL-1β mRNA transcripts, and IL-6 and IL-1β levels, in a MasR-dependent manner. In vivo, Ang-(1-7) and DIZE decreased alveolar bone loss through improvement of osteoblast/osteoclast ratio. A-779 reversed such phenotype. ACE2/Ang-(1-7)/MasR axis activation reduced IL-6 expression, but not IL-1β. ACE2 and MasR were also detected in human gingival samples, with higher expression in the healthy than in the inflamed tissues. These findings show that the ACE2/Ang-(1-7)/MasR is an active player in alveolar bone remodeling.

Avaliação topográfica e in vitro de superfícies de titânio revestidas com vidro bioativo

Resumo Objetivo Avaliar e comparar a rugosidade superficial e a atividade dos osteoblastos em contato com uma nova superfície bioativa e nanoestruturada de titânio grau 4 revestida com vidro bioativo contendo fosfato de cálcio, sintetizada pelo método sol-gel. Material e método Sessenta e três discos de titânio, medindo 4 mm de diâmetro por 2 mm de altura, foram preparados e divididos em três grupos: microtexturizado (Ticp - controle); revestido com vidro bioativo e seco a vácuo a 37 °C por 10 dias (BGTi37), e revestido com vidro bioativo e aquecido a 600 °C por cinco horas (BGTi600). Três espécimes de cada grupo foram utilizados para avaliação da topografia superficial e 18 espécimes, para cultura celular. Resultado O revestimento de vidro bioativo diminuiu a rugosidade média quando comparado ao titânio microtexturizado. A proporção de células viáveis, a produção de fosfatase alcalina e o grau de mineralização da matriz óssea em contato com os espécimes de titânio do grupo BGTi600 foram significativamente menores em relação aos grupos controle e do titânio microtexturizado. Conclusão Apesar de sua marcante menor rugosidade, a superfície BGTi37 apresentou comportamento biológico semelhante a uma superfície de titânio microtexturizada e moderadamente rugosa. A outra superfície experimental (BGTi600), a de menor rugosidade entre todas as testadas, apresentou os piores resultados de ativação dos osteoblastos.

Genetic architecture of bone quality variation in layer chickens revealed by a genome-wide association study

Skeletal problems in layer chickens are gaining attention due to animal welfare and economic losses in the egg industry. The genetic improvement of bone traits has been proposed as a potential solution to these issues; however, genetic architecture is not well understood. We conducted a genome-wide association study (GWAS) on bone quality using a sample of 1534 hens genotyped with a 600 K Chicken Genotyping Array. Using a linear mixed model approach, a novel locus close to GSG1L, associated with femur bone mineral density (BMD), was uncovered in this study. In addition, nine SNPs in genes were associated with bone quality. Three of these genes, RANKL, ADAMTS and SOST, were known to be associated with osteoporosis in humans, which makes them good candidate genes for osteoporosis in chickens. Genomic partitioning analysis supports the fact that common variants contribute to the variations of bone quality. We have identified several strong candidate genes and genomic regions associated with bone traits measured in end-of-lay cage layers, which accounted for 1.3–7.7% of the phenotypic variance. These SNPs could provide the relevant information to help elucidate which genes affect bone quality in chicken.

Neuronal Activity in Ontogeny and Oncology

The nervous system plays a central role in regulating the stem cell niche in many organs, and thereby pivotally modulates development, homeostasis, and plasticity. A similarly powerful role for neural regulation of the cancer microenvironment is emerging. Neurons promote the growth of cancers of the brain, skin, prostate, pancreas, and stomach. Parallel mechanisms shared in development and cancer suggest that neural modulation of the tumor microenvironment may prove a universal theme, although the mechanistic details of such modulation remain to be discovered for many malignancies. We review here what is known about the influences of active neurons on stem cell and cancer microenvironments across a broad range of tissues, and we discuss emerging principles of neural regulation of development and cancer.

Bidirectional communication between sensory neurons and osteoblasts in an in vitro coculture system

Recent studies have revealed that the sensory nervous system is involved in bone metabolism. However, the mechanism of communication between neurons and osteoblasts is yet to be elucidated. In this study, we investigated the signaling pathways between sensory neurons of the dorsal root ganglion (DRG) and the osteoblast-like MC3T3-E1 cells using an in vitro coculture system. Our findings indicate that signal transduction from DRG-derived neurons to MC3T3-E1 cells is suppressed by antagonists of the AMPA receptor and the NK₁ receptor. Conversely, signal transduction from MC3T3-E1 cells to DRG-derived neurons is suppressed by a P2X₇ receptor antagonist. Our results suggest that these cells communicate with each other by exocytosis of glutamate, substance P in the efferent signal, and ATP in the afferent signal.

Glutamate Receptor Agonists and Glutamate Transporter Antagonists Regulate Differentiation of Osteoblast Lineage Cells

Development and function of osteoblast lineage cells are regulated by a complex microenvironment consisting of the bone extracellular matrix, cells, systemic hormones and cytokines, autocrine and paracrine factors, and mechanical load. Apart from receptors that transduce extracellular signals into the cell, molecular transporters play a crucial role in the cellular response to the microenvironment. Transporter molecules are responsible for cellular uptake of nutritional components, elimination of metabolites, ion transport, and cell-cell communication. In this report, the expression of molecular transporters in osteoblast lineage cells was investigated to assess their roles in cell development and activity. Low-density arrays, covering membrane and vesicular transport molecules, were used to assess gene expression in osteoblasts representing early and late differentiation states. Receptors and transporters for the amino acid glutamate were found to be differentially expressed during osteoblast development. Glutamate is a neurotransmitter in the central nervous system, and the mechanisms of its release, signal transduction, and cellular reabsorption in the synaptic cleft are well understood. Less clear, however, is the control of equivalent processes in peripheral tissues. In primary osteoblasts, inhibition of glutamate transporters with nonselective inhibitors leads to an increase in the concentration of extracellular glutamate. This change was accompanied by a decrease in osteoblast proliferation, stimulation of alkaline phosphatase, and the expression of transcripts encoding osteocalcin. Enzymatic removal of extracellular glutamate abolished these pro-differentiation effects, as did the inhibition of PKC- and Erk1/2-signaling pathways. These findings demonstrate that glutamate signaling promotes differentiation and activation of osteoblast lineage cells. Consequently, the glutamate system may represent a putative therapeutic target to induce an anabolic response in the skeletal system. Known antagonists of glutamate transporters will serve as lead compounds in developing new and specific bioactive molecules.

Glutamate signalling: A multifaceted modulator of oligodendrocyte lineage cells in health and disease

Myelin is essential for the mammalian brain to function efficiently. Whilst many factors have been associated with regulating the differentiation of oligodendroglia and myelination, glutamate signalling might be particularly important for learning-dependent myelination. The majority of myelinated projection neurons are glutamatergic. Oligodendrocyte precursor cells receive glutamatergic synaptic inputs from unmyelinated axons and oligodendrocyte lineage cells express glutamate receptors which enable them to monitor and respond to changes in neuronal activity. Yet, what role glutamate plays for oligodendroglia is not fully understood. Here, we review glutamate signalling and its effects on oligodendrocyte lineage cells, and myelination in health and disease. Furthermore, we discuss whether glutamate signalling between neurons and oligodendroglia might lay the foundation to activity-dependent white matter plasticity. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

The Role of KV7.3 in Regulating Osteoblast Maturation and Mineralization

KCNQ (KV7) channels are voltage-gated potassium (KV) channels, and the function of KV7 channels in muscles, neurons, and sensory cells is well established. We confirmed that overall blockade of KV channels with tetraethylammonium augmented the mineralization of bone-marrow-derived human mesenchymal stem cells during osteogenic differentiation, and we determined that KV7.3 was expressed in MG-63 and Saos-2 cells at the mRNA and protein levels. In addition, functional KV7 currents were detected in MG-63 cells. Inhibition of KV7.3 by linopirdine or XE991 increased the matrix mineralization during osteoblast differentiation. This was confirmed by alkaline phosphatase, osteocalcin, and osterix in MG-63 cells, whereas the expression of Runx2 showed no significant change. The extracellular glutamate secreted by osteoblasts was also measured to investigate its effect on MG-63 osteoblast differentiation. Blockade of KV7.3 promoted the release of glutamate via the phosphorylation of extracellular signal-regulated kinase 1/2-mediated upregulation of synapsin, and induced the deposition of type 1 collagen. However, activation of KV7.3 by flupirtine did not produce notable changes in matrix mineralization during osteoblast differentiation. These results suggest that KV7.3 could be a novel regulator in osteoblast differentiation.

Excitatory amino acid glutamate: role in peripheral nociceptive transduction and inflammation in experimental and clinical osteoarthritis

Although a large proportion of patients with osteoarthritis (OA) show inflammation in their affected joints, the pathological role of inflammation in the development and progression of OA has yet to be clarified. Glutamate is considered an excitatory amino acid (EAA) neurotransmitter in the mammalian central nervous system (CNS). There are cellular membrane glutamate receptors and transporters for signal input modulation and termination as well as vesicular glutamate transporters (VGLUTs) for signal output through exocytotic release. Glutamate been shown to mediate intercellular communications in bone cells in a manner similar to synaptic transmission within the CNS. Glutamate-mediated events may also contribute to the pathogenesis and ongoing processes of peripheral nociceptive transduction and inflammation of experimental arthritis models as well as human arthritic conditions. This review will discuss the differential roles of glutamate signaling and blockade in peripheral neuronal and non-neuronal joint tissues, including bone remodeling systems and their potentials to impact OA-related inflammation and progression. This will serve to identify several potential targets to direct novel therapies for OA. Future studies will further elucidate the role of glutamate in the development and progression of OA, as well as its association with the clinical features of the disease.

MicroRNA-218, microRNA-191*, microRNA-3070a and microRNA-33 are responsive to mechanical strain exerted on osteoblastic cells

MicroRNA (miRNA) is an important regulator of cell differentiation and function. Mechanical strain is important in the growth and differentiation of osteoblasts. Therefore, mechanresponsive miRNA may be important in the response of osteoblasts to mechanical strain. The purpose of the present study was to select and identify the mechanoresponsive miRNAs of osteoblasts. Mouse osteoblastic MC3T3-E1 cells were cultured in cell culture dishes and stimulated with a mechanical tensile strain of 2,50 με at 0.5 Hz, and the activity of alkaline phosphatase (ALP), mRNA levels of ALP, osteocalcin (OCN), and collagen type I (Col I), and protein levels of bone morphogenetic proteins (BMPs) in the cell culture medium were assayed. Following miRNA microarray and reverse transcription-quantitative polymerase chain reaction analyses, differentially expressed miRNAs in the mechanically strained cells and unstrained cells were selected and identified. Using bioinformatics analysis, the target genes of the miRNAs were then predicted. The results revealed that the mechanical strain of 2,500 με increased the activity of ALP, the mRNA levels of ALP, OCN and Col I, and the protein levels of bone morphogenetic protein(BMP)-2 and BMP-4 Continuous mechanical stimulation for 8 h had the most marked stimulant effects. miR-218, miR-191*, miR-3070a and miR-33 were identified as differentially expressed miRNAs in the mechanically strained MC3T3-E1 cells. Certain target genes of these four miRNAs were involved in osteoblastic differentiation. These findings indicated that a mechanical strain of 2,500 με, particularly for a period of 8 h, promoted osteoblastic differentiation, and the four mechanoresponsive miRNAs identified may be a potential regulator of osteoblastic differentiation and their response to mechanical strain.

Shear stress-induced Ca(2+) elevation is mediated by autocrine-acting glutamate in osteoblastic MC3T3-E1 cells

Mechanical loading is an important regulatory factor in bone homeostasis. Neurotransmitters, such as glutamate and ATP, are known to be released from osteoblasts, but their roles have been less studied. In this study, we investigated the role of transmitter release in mechanotransduction. To identify from where transmitters were released, focal fluid flow was applied to a single cell of MC3T3-E1, mouse calvaria-derived osteoblastic cell line, by using a glass micropipette. Intracellular Ca(2+) elevation induced by the focal shear stress was eliminated by either GdCl3, a mechanosensing channel inhibitor, or removal of extracellular Ca(2+). On the other hand, the focal shear stress-induced Ca(2+) elevation was also significantly suppressed by inositol triphosphate receptor antagonist or vesicular release inhibitors. These results suggest that not only mechanosensitive channel-mediated Ca(2+) influx but also some autocrine transmitters are involved in mechanotransduction. Additionally, glutamate receptor antagonists, but not ATP receptor antagonist, suppressed most of the focal shear stress-induced Ca(2+) elevation. Therefore, it is suggested that glutamate is released from osteoblasts following the activation of mechanosensitive Ca(2+) channels and acts in an autocrine manner. The glutamate release may have a significant role in the initial event of mechanotransduction in bone tissue.

AMPA/kainate glutamate receptors contribute to inflammation, degeneration and pain related behaviour in inflammatory stages of arthritis

OBJECTIVES

Synovial fluid glutamate concentrations increase in arthritis. Activation of kainate (KA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors (GluRs) increase interleukin-6 (IL-6) release and cause arthritic pain, respectively. We hypothesised that AMPA and KA GluRs are expressed in human arthritis, and that intra-articular NBQX (AMPA/KA GluR antagonist) prevents pain and pathology in antigen-induced arthritis (AIA).

METHODS

GluR immunohistochemistry was related to synovial inflammation and degradation in osteoarthritis (OA) and rheumatoid arthritis (RA). A single intra-articular NBQX injection was given at induction, and knee swelling and gait of AIA and AIA+NBQX rats compared over 21 days, before imaging, RT-qPCR, histology and immunohistochemistry of joints. Effects of NBQX on human primary osteoblast (HOB) activity were determined.

RESULTS

AMPAR2 and KA1 immunolocalised to remodelling bone, cartilage and synovial cells in human OA and RA, and rat AIA. All arthritic tissues showed degradation and synovial inflammation. NBQX reduced GluR abundance, knee swelling (p<0.001, days 1-21), gait abnormalities (days 1-2), end-stage joint destruction (p<0.001), synovial inflammation (p<0.001), and messenger RNA expression of meniscal IL-6 (p<0.05) and whole joint cathepsin K (p<0.01). X-ray and MRI revealed fewer cartilage and bone erosions, and less inflammation after NBQX treatment. NBQX reduced HOB number and prevented mineralisation.

CONCLUSIONS

AMPA/KA GluRs are expressed in human OA and RA, and in AIA, where a single intra-articular injection of NBQX reduced swelling by 33%, and inflammation and degeneration scores by 34% and 27%, respectively, exceeding the efficacy of approved drugs in the same model. AMPA/KA GluR antagonists represent a potential treatment for arthritis.

The potential of targeting NMDA receptors outside the CNS

INTRODUCTION

NMDA receptor (NMDAR) is an ionotropic glutamate receptor with a high permeability to calcium and a unique feature of controlling numerous calcium-dependent processes. Apart from being widely distributed in the CNS, the presence of NMDAR and its potential significance in a variety of non-neuronal cells and tissues has become an interesting research topic.

AREAS COVERED

The current review summarizes prevailing knowledge on the role of NMDARs in the kidney, bone and parathyroid gland, three main organs responsible for calcium homeostasis, as well as in the heart, an organ whose function is highly dependable on balanced intracellular calcium concentrations. The review also examines studies that have advanced our understanding of the therapeutic potential of NMDAR agonists and antagonists in renal, cardiovascular and bone pathologies.

EXPERT OPINION

NMDARs have a preeminent role in many physiological and pathological processes outside the CNS. In certain organs and/or disease conditions, activating the NMDAR leads to beneficial effects for the target organ, whereas in other diseases cell signaling downstream of NMDAR activation can exacerbate their pathology. Therefore, targeting NMDARs therapeutically is rather intricate work, and surely requires more extensive investigation in order to properly tune up the diverse NMDAR's actions translating them into beneficial cellular responses.

Effects of glutamine on proliferation, migration, and differentiation of human dental pulp cells

INTRODUCTION

Although glutamine (Gln) is mitogenic in various cell types, little is known about its role in human dental pulp cells (HDPCs). This study investigated the effects of Gln on proliferation, migration, and odontoblastic differentiation of HDPCs and the underlying signal pathway mechanisms.

METHODS

Growth and migration were assessed by cell counting and colorimetric cell migration kits. Differentiation was measured as alkaline phosphatase activity, calcified nodule formation by alizarin red staining, and marker mRNA expression by reverse transcriptase-polymerase chain reaction (RT-PCR). Chemokine expression was also evaluated by RT-PCR. Signal transduction pathways were examined by RT-PCR and Western blot analysis.

RESULTS

Gln dose-dependently increased proliferation, migration, alkaline phosphatase activity, mineralized nodule formation, and odontoblast-marker mRNA of HDPCs. Gln also up-regulated expression of interleukin-6, interleukin-8, MCP-1, MIP-3α, CCL2, CCL20, and CXCL1. Gln increased BMP-2 and BMP-4 mRNA, phosphorylation of Smad 1/5/8, β-catenin, and key proteins of the Wnt signaling pathway. Furthermore, Gln resulted in up-regulation of extracellular signal-regulated kinase, p38, and c-Jun N-terminal kinase. In addition, noggin, DKK1, inhibitors of p38, ERK, and JNK significantly attenuatted Gln-induced growth, migration, and odontoblastic differentiation.

CONCLUSIONS

Collectively, this study demonstrated that Gln promoted growth, migration, and differentiation in HDPCs through the BMP-2, Wnt, and MAPK pathways, leading to improved pulp repair and regeneration.

Assessment of NMDA receptor genes (GRIN2A, GRIN2B and GRIN2C) as candidate genes in the development of degenerative lumbar scoliosis

Degenerative lumbar scoliosis (DLS) progresses with aging after 50–60 years. The genetic association of DLS remains largely unclear. In this study, the genetic association between glutamate receptor, ionotropic, N-methyl D-aspartate (NMDA, GRIN) receptor genes and DLS was investigated. A total of 9 coding single nucleotide polymorphisms (cSNPs) in NMDA receptor genes [GRIN2A (rs8049651, Leu425Leu; rs9806806, Tyr730Tyr); GRIN2B (rs7301328, Pro122Pro; rs35025065, Asp447Asp; rs1805522, Ile602Ile; rs1806201, Thr888Thr; rs1805247, His1399His); and GRIN2C (rs689730, Ala33Ala; rs3744215, Arg1209Ser)] were selected and genotyped using direct sequencing in 70 patients with DLS and 141 healthy controls. Multiple logistic models (codominant, dominant and recessive) were calculated for the odds ratio (OR), 95% confidence interval (CI) and corresponding P-values. The SNPStats, SNPAnalyzer and HelixTree programs were used for the evaluation of the genetic data. Among the SNPs examined, no significant associations were observed between the NMDA receptor genes and DLS. When the patients were divided into two groups according to clinical characteristics based on Cobb’s angle (<20° or ≥20°) and lateral listhesis (<6 mm or ≥6 mm), associations were observed between rs689730 of GRIN2C and Cobb’s angle (codominant, P=0.038; dominant, P=0.022) and between rs7301328 of GRIN2B and lateral listhesis (codominant, P=0.003; dominant, P=0.015; recessive, P=0.015). These results indicate that the GRIN2A, GRIN2B and GRIN2C genes do not affect the development of DLS. However, the GRIN2C gene may be associated with Cobb’s angle, while the GRIN2B gene may be associated with lateral listhesis.

Dietary nitrogen and fish welfare

Little research has been done in optimizing the nitrogenous fraction of the fish diets in order to minimize welfare problems. The purpose of this review is to give an overview on how amino acid (AA) metabolism may be affected when fish are under stress and the possible effects on fish welfare when sub-optimal dietary nitrogen formulations are used to feed fish. In addition, it intends to evaluate the current possibilities, and future prospects, of using improved dietary nitrogen formulations to help fish coping with predictable stressful periods. Both metabolomic and genomic evidence show that stressful husbandry conditions affect AA metabolism in fish and may bring an increase in the requirement of indispensable AA. Supplementation in arginine and leucine, but also eventually in lysine, methionine, threonine and glutamine, may have an important role in enhancing the innate immune system. Tryptophan, as precursor for serotonin, modulates aggressive behaviour and feed intake in fish. Bioactive peptides may bring important advances in immunocompetence, disease control and other aspects of welfare of cultured fish. Fishmeal replacement may reduce immune competence, and the full nutritional potential of plant-protein ingredients is attained only after the removal or inactivation of some antinutritional factors. This review shows that AA metabolism is affected when fish are under stress, and this together with sub-optimal dietary nitrogen formulations may affect fish welfare. Furthermore, improved dietary nitrogen formulations may help fish coping with predictable stressful events.

Glutamate signaling in healthy and diseased bone

Bone relies on multiple extracellular signaling systems to maintain homeostasis of its normal structure and functions. The amino acid glutamate is a fundamental extracellular messenger molecule in many tissues, and is used in bone for both neural and non-neural signaling. This review focuses on the non-neural interactions, and examines the evolutionarily ancient glutamate signaling system in the context of its application to normal bone functioning and discusses recent findings on the role of glutamate signaling as they pertain to maintaining healthy bone structure. The underlying mechanisms of glutamate signaling and the many roles glutamate plays in modulating bone physiology are featured, including those involved in osteoclast and osteoblast differentiation and mature cell functions. Moreover, the relevance of glutamate signaling systems in diseases that affect bone, such as cancer and rheumatoid arthritis, is discussed, and will highlight how the glutamate system may be exploited as a viable therapeutic target. We will identify novel areas of research where knowledge of glutamate communication mechanisms may aid in our understanding of the complex nature of bone homeostasis. By uncovering the contributions of glutamate in maintaining healthy bone, the reader will discover how this complex molecular signaling system may advance our capacity to treat bone pathologies.

Glutamate signaling in bone

Mechanical loading plays a key role in the physiology of bone, allowing bone to functionally adapt to its environment, however characterization of the signaling events linking load to bone formation is incomplete. A screen for genes associated with mechanical load-induced bone formation identified the glutamate transporter GLAST, implicating the excitatory amino acid, glutamate, in the mechanoresponse. When an osteogenic load (10 N, 10 Hz) was externally applied to the rat ulna, GLAST (EAAT1) mRNA, was significantly down-regulated in osteocytes in the loaded limb. Functional components from each stage of the glutamate signaling pathway have since been identified within bone, including proteins necessary for calcium-mediated glutamate exocytosis, receptors, transporters, and signal propagation. Activation of ionotropic glutamate receptors has been shown to regulate the phenotype of osteoblasts and osteoclasts in vitro and bone mass in vivo. Furthermore, glutamatergic nerves have been identified in the vicinity of bone cells expressing glutamate receptors in vivo. However, it is not yet known how a glutamate signaling event is initiated in bone or its physiological significance. This review will examine the role of the glutamate signaling pathway in bone, with emphasis on the functions of glutamate transporters in osteoblasts.

Absence of glutamine supplementation prevents differentiation of murine calvarial osteoblasts to a mineralizing phenotype

Osteoblasts in vitro differentiate from a proliferating to a mineralizing phenotype upon transfer to a medium rich in beta-glycerophosphate and ascorbic acid. The nutritional requirements of the cells at different stages of this differentiation process are not known. In other cell types, nutritional supplementation during surgery can improve the outcome in terms of speed of patient recovery and prognosis. There is therefore the potential for supplementation at the site of fracture repair or bone grafting with critical osteoblast nutritional factors to potentially accelerate healing. In this study we investigate which common cell nutrients are required for the proliferating and mineralizing stages of osteoblast differentiation. Medium containing 5.5 mM glucose was sufficient to achieve maximal proliferation of primary calvarial osteoblasts and human osteoblast cell lines, with some added benefit of additional glutamine supplementation. However, when cells were stimulated to mineralize, glucose was insufficient to support their energetic requirements. Only when cells were supplemented with glucose together with glutamine were high levels of osteocalcin expression observed together with mineralized nodules in culture, suggesting that this would be a useful combination to assess in cultures of primary human osteoblasts to determine whether it may have beneficial effects during fracture surgery, bone grafting, and fixation of uncemented arthroplasty implants.

The N-methyl-d-aspartic acid receptor antagonist memantine ameliorates and delays the development of arthritis by enhancing regulatory T cells

The neuroendocrine impact on rheumatoid arthritis is not yet fully described although numerous neurotransmitters are shown to act as inflammatory modulators. One of these is the excitatory transmitter glutamate (Glu). In this study, the influence of the Glu receptor (GluR)-mediated effects on collagen-induced arthritis (CIA) was investigated. CIA was induced in DBA/1 mice by immunization with chicken collagen type II (CII). Mice were exposed to the following GluR antagonists: group 1, the N-methyl-D-aspartic acid (NMDA) receptor channel blocker memantine; group 2, the metabotropic GluR antagonist AIDA, and group 3, the excitatory amino acid receptor antagonist kynurenic acid (KA). Arthritis was evaluated clinically and histologically and compared to PBS-treated controls. The effects of treatment on T cell populations and the levels of anti-CII and anti-citrullinated peptide antibodies were evaluated. Memantine treatment significantly improved the course of CIA, reducing synovitis (p = 0.007) and the frequency of erosions (p = 0.007). Memantine treatment up-regulated the expression of Foxp3 in spleen CD4+ T cells followed by an increase in CD4+CD25+ regulatory T cells. The other GluR antagonists, AIDA and KA, had no effect on CIA. These results demonstrate that blockade of the NMDA receptor channel with memantine delays and attenuates the development of arthritis, probably by promoting the development of regulatory T lymphocytes.

Extracellular glutamate alters mature osteoclast and osteoblast functions

Glutamatergic intercellular communication is involved in many aspects of metabolic homeostasis in normal bone. In bone metastasis, the balance between bone formation and degradation is disrupted. Although the responsible mechanisms are not clear, we have previously identified that cancer cell lines used in bone tumour models secrete glutamate, suggesting that tumour-derived glutamate may disrupt sensitive signalling systems in bone. This study examines the role of glutamate in mature osteoclastic bone resorption, osteoblast differentiation, and bone nodule formation. Glutamate was found to have no effect on the survival or activity of mature osteoclasts, although glutamate transporter inhibition and receptor blockade increased the number of bone resorption pits. Furthermore, transporter inhibition increased the area of resorbed bone while significantly decreasing the number of osteoclasts. Alkaline phosphatase activity and extracellular matrix mineralization were used as measurements of osteoblast differentiation. Glutamate significantly increased osteoblast differentiation and mineralization, but transport inhibitors had no effect. These studies support earlier findings suggesting that glutamate may be more important for osteoclastogenesis than for osteoclast proliferation or functions. Since glutamate is capable of changing the differentiation and activities of both osteoclast and osteoblast cell types in bone, it is reasonable to postulate that tumour-derived glutamate may impact bone homeostasis in bone metastasis.

A by-product of glutathione production in cancer cells may cause disruption in bone metabolic processes

Bone is a frequent site for metastasis of breast and prostate cancers, often resulting in pathologic changes in bone metabolism and severe pain. The mechanisms involved are not well understood, but tumour cells may release factors that interfere with bone homeostasis. Several observations have led us to hypothesize that the functional disruptions in bone metastasis are the result of a biological process common to many cell types. The high metabolic activity characteristic of cancer cells often upregulates oxidative stress protection mechanisms such as the antioxidant molecule glutathione. In maintaining redox balance, this normal metabolic response may result in unintended pathologic effects in certain sensitive organ sites. Malignant glioma cells kill surrounding neurons in the brain specifically by secreting the amino acid glutamate, an obligatory waste product of glutathione synthesis. We suggest that glutamate release is a plausible mechanism that may account for the pathologic changes in bone metastasis, since bone, like brain, is also highly sensitive to glutamatergic disruption. This report reviews the available evidence to draw a mechanistic connection between tumour cell oxidative stress and the pathology seen in patients with bone metastasis.

Sustained activation of renal N-methyl-D-aspartate receptors decreases vitamin D synthesis: a possible role for glutamate on the onset of secondary HPT

N-methyl-D-aspartate (NMDA) receptors (NMDAR) are tetrameric amino acid receptors that act as membrane calcium channels. The presence of the receptor has been detected in the principal organs responsible for calcium homeostasis (kidney, bone, and parathyroid gland), pointing to a possible role in mineral metabolism. The aim of this study was to test the effect of NMDAR activation in the kidney and on 1,25(OH)₂D₃ synthesis. We determined the presence of NMDAR subunits in HK-2 (human kidney cells) cells and proved its functionality. NMDA treatment for 4 days induced a decrease in 1α-hydroxylase levels and 1,25(OH)₂D₃ synthesis through the activation of the MAPK/ERK pathway in HK-2 cells. In vivo administration of NMDA for 4 days also caused a decrease in blood 1,25(OH)₂D₃ levels in healthy animals and an increase in blood PTH levels. This increase in PTH induced a decrease in the urinary excretion of calcium and an increase in urinary excretion of phosphorous and sodium as well as in diuresis. Bone turnover markers also increased. Animals with 5/6 nephrectomy showed low levels of renal 1α-hydroxylase as well as high levels of renal glutamate compared with healthy animals. In conclusion, NMDAR activation in the kidney causes a decrease in 1,25(OH)₂D₃ synthesis, which induces an increase on PTH synthesis and release. In animals with chronic kidney disease, high renal levels of glutamate could be involved in the downregulation of 1α-hydroxylase expression.

Upregulation of heme oxygenase-1 inhibits the maturation and mineralization of osteoblasts

Heme-oxygenase-1 (HO-1), an important enzyme involved in vascular disease, transplantation, and inflammation, catalyzes the degradation of heme into carbon monoxide and biliverdin. It has been reported that overexpression of HO-1 inhibits osteoclastogenesis. However, the effect of HO-1 on osteoblast differentiation is still not clear. We here used adenoviral vector expressing recombinant human HO-1 and HO-1 inducer hemin to study the effects of HO-1 in primary cultured osteoblasts. The results showed that induction of HO-1 inhibited the maturation of osteoblasts including mineralized bone nodule formation, alkaline phosphatase activity and decreased mRNA expression of several differentiation markers such as alkaline phosphatase, osteocalcin, and RUNX2. Furthermore, downstream products of HO-1, bilirubin, carbon monoxide, and iron, are involved in the inhibitory action of HO-1. HO-1 can be induced by H(2)O(2), lipopolysaccharide and inflammatory cytokines such as TNF-alpha and IL-1beta in osteoblasts and also in STZ-induced diabetic mice. In addition, endogenous PPARgamma ligand, 15-deoxy-Delta(12,14)-prostaglandin-J2 (15d-PGJ2) markedly increased both mRNA and protein levels of HO-1 in osteoblasts via PI3K-Akt and MAPK pathways. Blockade of HO activity by ZnPP IX antagonized the inhibitory action on osteocalcin expression by hemin and 15d-PGJ2. Our results indicate that upregulation of HO-1 inhibits the maturation of osteoblasts and HO-1 may be involved in oxidative- or inflammation-induced bone loss.