Elevated extracellular calcium increases fibroblast growth factor-2 gene and protein expression levels via a cAMP/PKA dependent pathway in cementoblasts

Cross Talk Between Cells and the Current Bioceramics in Bone Regeneration: A Comprehensive Review

The conventional approach for addressing bone defects and stubborn non-unions typically involves the use of autogenous bone grafts. Nevertheless, obtaining these grafts can be challenging, and the procedure can lead to significant morbidity. Three primary treatment strategies for managing bone defects and non-unions prove resistant to conventional treatments: synthetic bone graft substitutes (BGS), a combination of BGS with bioactive molecules, and the use of BGS in conjunction with stem cells. In the realm of synthetic BGS, a multitude of biomaterials have emerged for creating scaffolds in bone tissue engineering (TE). These materials encompass biometals like titanium, iron, magnesium, and zinc, as well as bioceramics such as hydroxyapatite (HA) and tricalcium phosphate (TCP). Bone TE scaffolds serve as temporary implants, fostering tissue ingrowth and the regeneration of new bone. They are meticulously designed to enhance bone healing by optimizing geometric, mechanical, and biological properties. These scaffolds undergo continual remodeling facilitated by bone cells like osteoblasts and osteoclasts. Through various signaling pathways, stem cells and bone cells work together to regulate bone regeneration when a portion of bone is damaged or deformed. By targeting signaling pathways, bone TE can improve bone defects through effective therapies. This review provided insights into the interplay between cells and the current state of bioceramics in the context of bone regeneration.

Therapeutic and Metagenomic Potential of the Biomolecular Therapies against Periodontitis and the Oral Microbiome: Current Evidence and Future Perspectives

The principles of periodontal therapy are based on the control of microbial pathogens and host factors that contribute to biofilm dysbiosis, with the aim of modulating the progression of periodontitis and periodontal tissue destruction. It is currently known how differently each individual responds to periodontal treatment, depending on both the bacterial subtypes that make up the dysbiotic biofilm and interindividual variations in the host inflammatory response. This has allowed the current variety of approaches for the management of periodontitis to be updated by defining the goals of target strategies, which consist of reducing the periodontopathogenic microbial flora and/or modulating the host-mediated response. Therefore, this review aims to update the current variety of approaches for the management of periodontitis based on recent target therapies. Recently, encouraging results have been obtained from several studies exploring the effects of some targeted therapies in the medium- and long-term. Among the most promising target therapies analyzed and explored in this review include: cell-based periodontal regeneration, mediators against bone resorption, emdogain (EMD), platelet-rich plasma, and growth factors. The reviewed evidence supports the hypothesis that the therapeutic combination of epigenetic modifications of periodontal tissues, interacting with the dysbiotic biofilm, is a key step in significantly reducing the development and progression of disease in periodontal patients and improving the therapeutic response of periodontal patients. However, although studies indicate promising results, these need to be further expanded and studied to truly realize the benefits that targeted therapies could bring in the treatment of periodontitis.

The role of Ca2+ /Calcineurin/NFAT signalling pathway in osteoblastogenesis

The bone remodelling process is closely related to bone health. Osteoblasts and osteoclasts participate in the bone remodelling process under the regulation of various factors inside and outside. Excessive activation of osteoclasts or lack of function of osteoblasts will cause occurrence and development of multiple bone‐related diseases. Ca²⁺/Calcineurin/NFAT signalling pathway regulates the growth and development of many types of cells, such as cardiomyocyte differentiation, angiogenesis, chondrogenesis, myogenesis, bone development and regeneration, etc. Some evidences indicate that this signalling pathway plays an extremely important role in bone formation and bone pathophysiologic changes. This review discusses the role of Ca²⁺/Calcineurin/NFAT signalling pathway in the process of osteogenic differentiation, as well as the influence of regulating each component in this signalling pathway on the differentiation and function of osteoblasts, whereby the relationship between Ca²⁺/Calcineurin/NFAT signalling pathway and osteoblastogenesis could be deeper understood.

Protein adsorption/desorption dynamics on Ca-enriched titanium surfaces: biological implications

Calcium ions are used in the development of biomaterials for the promotion of coagulation, bone regeneration, and implant osseointegration. Upon implantation, the time-dependent release of calcium ions from titanium implant surfaces modifies the physicochemical characteristics at the implant-tissue interface and thus, the biological responses. The aim of this study is to examine how the dynamics of protein adsorption on these surfaces change over time. Titanium discs with and without Ca were incubated with human serum for 2 min, 180 min, and 960 min. The layer of proteins attached to the surface was characterised using nLC-MS/MS. The adsorption kinetics was different between materials, revealing an increased adsorption of proteins associated with coagulation and immune responses prior to Ca release. Implant-blood contact experiments confirmed the strong coagulatory effect for Ca surfaces. We employed primary human alveolar osteoblasts and THP-1 monocytes to study the osteogenic and inflammatory responses. In agreement with the proteomic results, Ca-enriched surfaces showed a significant initial inflammation that disappeared once the calcium was released. The distinct protein adsorption/desorption dynamics found in this work demonstrated to be useful to explain the differential biological responses between the titanium and Ca-ion modified implant surfaces.

Tissue response to white mineral aggregate-based cement containing barium sulfate as alternative radiopacifier: A randomized controlled animal study

The purpose of this study was to investigate the tissue reaction stimulated by BaSO4 - and Bi2 O3 -containing White MTA Angelus, in comparison with Bi2 O3 -containing white Portland cement, and white ProRoot MTA. Thirty-six adult male Wistar rats (Rattus norvegicus), weighing between 250 and 300 g, were distributed into three groups (n = 12) in accordance with the period of sacrifice (15, 30, and 60 days). Four polyethylene tubes filled with the tested cements were implanted into the dorsum of each rat. Lateral wall of the tubes served as the negative control. After the experimental periods, the animals were euthanized by overdose of pentobarbital anesthetic solution, and the specimens were prepared for microscopic analysis under ×50, ×100, and ×400 magnifications. Inflammatory scores (0-3) were used to grade the tissue reaction. Data were analyzed by the Kruskal-Wallis test and Dunn's test for individual comparisons (p < .05). A mild to moderate inflammatory tissue reaction was observed at the 15-day period, which decreased over the course of the periods for all cements, except for Portland cement. There was no significant difference among the tissue responses for ProRoot MTA, BaSO4 - and Bi2 O3 -containing White MTA Angelus at the 60-day period (p > .05). The Portland group had moderate inflammatory reaction at the final period of analysis, which was statistically different when compared to the other groups (p < .05). The microscopic findings of this animal study suggest that the addition of BaSO4 to White MTA Angelus does not hampers the biocompatibility of the cement.

Intermittent parathyroid hormone promotes cementogenesis in a PKA- and ERK1/2-dependent manner

BACKGROUND

Intermittent parathyroid hormone (PTH) promotes cementogenesis and provides a promising biotherapeutic to rehabilitate resorbed roots. However, the underlying mechanisms remain inconclusive. Cyclic aenosine monophosphate (AMP)-dependent protein kinases A (PKA) and extracellular signal-regulated MAP kinases 1/2 (ERK1/2) are key regulators of bone remodeling. The present study aims to investigate whether PKA and ERK1/2 are involved in the process of intermittent PTH-promoted cementogenesis.

METHODS

Sprague-Dawley rats in experimental group (n = 30) received a daily subcutaneous injection of PTH and the control (n = 30) received placebo vehicle for 1, 2, 3, 4, and 5 weeks. Results were evaluated by hematoxylin and eosin and immunohistochemistry staining. In vitro, OCCM-30 cells were incubated with intermittent PTH. H89 and U0126 were used to determine the role of PKA and ERK1/2, respectively. The cementogenic results were analyzed by reverse transcription-polymerase chain reaction (RT-PCR), western blotting, alkaline phosphatase activity assay and Alizarin Red S staining. The interaction of PKA and p-ERK1/2 was determined by co-immunoprecipitation (Co-IP).

RESULTS

Intermittent PTH exerted anabolic effect on cellular cementum in developing teeth with elevated expression of osteocalcin, osteopontin, and PKA (catalytic subunit) in PTH injection group. The promoting effects of intermittent PTH on cementogenesis and osteogenic differentiation were abrogated by H89 and U0126 in vitro, respectively. Blocking of PKA pathway downregulated intermittent PTH-induced ERK1/2 phosphorylation.

CONCLUSIONS

Intermittent PTH promotes cementogenesis in a PKA- and ERK1/2-dependent manner. In this process, PKA and p-ERK1/2 interact with each other. These results support the future biotherapeutic applications of PTH in cementum resorption.

Repair of Bone Defects with Chitosan-Collagen Biomembrane and Scaffold Containing Calcium Aluminate Cement

Innovative biomaterials can provide a promising new direction for the treatment of bone defects, stimulating a proper repair process, with no damage to adjacent tissues. The purpose of this in vivo study was to evaluate the biocompatibility and the osteoinductive capacity of chitosan-collagen biomembrane and scaffold containing calcium aluminate cement. Eighteen New Zealand white rabbits (Oryctolagus cuniculus) were distributed according to the experimental times of analysis (7, 15 and 30 days). Four bone defects were created in the rabbits calvaria, which were individually filled with the biomembrane, scaffold, blood clot (negative control) and autologous bone (positive control). Histopathological analysis was performed using optical microscope at 32´, 64´, 125´ and 320´ magnifications. Cell response to inflammation and new bone tissue formation was quantified using a score system. The biomembrane group presented greater inflammatory response at 15 days, with significant difference to autologous bone group (p<0.05). There was no statistically significant difference for foreign body type reaction among groups (p>0.05). Concerning new bone formation, linear closure of the defect area was observed more evidently in the group with autologous bone. The scaffold group presented similar results compared with the autologous bone group at 30 days (p>0.05). Both tested biomaterials presented similar biocompatibility compared with the control groups. In addition, the biomembrane and scaffold presented similar osteoinductive capacity, stimulating bone repair process in the course of the experimental time intervals.

Clinical and Molecular Perspectives of Reparative Dentin Formation: Lessons Learned from Pulp-Capping Materials and the Emerging Roles of Calcium

The long-term use of calcium hydroxide and the recent increase in the use of hydraulic calcium-silicate cements as direct pulp-capping materials provide important clues in terms of how reparative dentin may be induced to form a "biological seal" to protect the underlying pulp tissues. In this review article, we discuss clinical and molecular perspectives of reparative dentin formation based on evidence learned from the use of these pulp-capping materials. We also discuss the emerging role of calcium as an odontoinductive component in these pulp-capping materials.

Extracellular calcium increases fibroblast growth factor 2 gene expression via extracellular signal-regulated kinase 1/2 and protein kinase A signaling in mouse dental papilla cells

We previously reported that elevated extracellular calcium (Ca²⁺) levels increase bone morphogenetic protein 2 expression in human dental pulp (hDP) cells. However, it is unknown whether extracellular Ca²⁺ affects the expression of other growth factors such as fibroblast growth factor 2 (FGF2).

Effects of different Ca2+ level on fluoride-induced apoptosis pathway of endoplasmic reticulum in the rabbit osteoblast in vitro

In reviewing the literature, the cellular mechanism of fluoride F-induced osteoblast OB cells apoptosis is diverse and perplexing, but detailed regulatory pathway, targets and role of extracellular Ca²⁺ remains still unclear. Hence, in the present study, we investigated the effects of F (9 mg/L F ion) and different Ca²⁺ (0.5, 1, 2, 4, 8 mmol/L) levels treatment on the proliferation rate of osteoblast cells, intracellular free Ca²⁺ ([Ca²⁺]i) and endoplasmic reticulum (ER) stress apoptosis pathway related gene levels of rabbit OB cells. Our results demonstrated that F exposure had a pronounced negative effect on osteoblast survival, further different Ca²⁺ levels treatment suggested that low concentration of Ca²⁺ (0.5-1 mmol/L) relieved the damaged effect, on the contrary, high concentration of Ca²⁺ (2-8 mmol/L) enhanced the effect. In addition, F significantly increased [Ca²⁺]i levels and the expression of ER stress-induced cell apoptosis pathway related genes. Treatment with 0.5-1 mmol/L Ca²⁺ markedly reversed the F-induced harmful effects, but high dose Ca²⁺ (2-8 mmol/L) enhanced these effects. In summary, 0.5-1 mmol/L Ca²⁺ can alleviate F-induced OB cells injure through ER stress apoptosis pathway, which provided a dose basis for the future study on the treatment of skeletal fluorosis with Ca²⁺.

Harnessing cAMP signaling in musculoskeletal regenerative engineering

This paper reviews the most recent findings in the search for small molecule cyclic AMP analogues regarding their potential use in musculoskeletal regenerative engineering.

Bioactive Polymeric Nanoparticles for Periodontal Therapy

Aims

to design calcium and zinc-loaded bioactive and cytocompatible nanoparticles for the treatment of periodontal disease.

Methods

PolymP-nActive nanoparticles were zinc or calcium loaded. Biomimetic calcium phosphate precipitation on polymeric particles was assessed after 7 days immersion in simulated body fluid, by scanning electron microscopy attached to an energy dispersive analysis system. Amorphous mineral deposition was probed by X-ray diffraction. Cell viability analysis was performed using oral mucosa fibroblasts by: 1) quantifying the liberated deoxyribonucleic acid from dead cells, 2) detecting the amount of lactate dehydrogenase enzyme released by cells with damaged membranes, and 3) by examining the cytoplasmic esterase function and cell membranes integrity with a fluorescence-based method using the Live/Dead commercial kit. Data were analyzed by Kruskal-Wallis and Mann-Whitney tests.

Results

Precipitation of calcium and phosphate on the nanoparticles surfaces was observed in calcium-loaded nanoparticles. Non-loaded nanoparticles were found to be non-toxic in all the assays, calcium and zinc-loaded particles presented a dose dependent but very low cytotoxic effect.

Conclusions

The ability of calcium-loaded nanoparticles to promote precipitation of calcium phosphate deposits, together with their observed non-toxicity may offer new strategies for periodontal disease treatment.

Effect of Combined Action of Extracellular ATP and Elevated Calcium on Osteogenic Differentiation of Primary Cultures From Rat Calvaria

The in vitro osteogenic differentiation has been intensively studied. However, it is not yet clear precisely how osteogenesis can be optimized. Changes in extracellular Ca(2+) concentration ([Ca(2+) ]e ), as well as modulation of purinergic receptors play an important role in the regulation of osteoblasts differentiation and bone formation. In this study, we investigated the effects of a combined treatment of ATPγ-S and high [Ca(2+) ]e (5.35 mM) on osteogenic differentiation and function of primary cell cultures from rat calvaria. Our results indicate that ATPγ-S stimulates cell transition from the G0 to S phase of cell cycle, involving the PI3K signaling pathway. Treatment with 10 or 100 µM ATPγ-S and [Ca(2+) ]e (ATP-[Ca(2+) ]e ) for 48 h increases cell number significantly above the control. ATPγ-S treatment in osteogenic medium containing [Ca(2+) ]e stimulates the gene expression of BMP-4, BMP-5, and OPN at 16, 48, and 72 h, respectively, above control. In same conditions, treatment for 6 days with 10 µM UTP or 100 µM UDP significantly increased the ALP activity respect to control. Cells grown in osteogenic medium showed a statistically significant increase in calcium deposits at 15 and 18 days, for 10 µM ATPγ-S treatment, and at 18 and 22 days, for [Ca(2+) ]e treatment, respect to control but ATP-[Ca(2+) ]e treatment shown a significant greater mineralization at 15 days respect to ATPγ-S, and at 18 days respect to both agonists. In conclusion, we demonstrated that an osteogenic medium containing 10 µM ATPγ-S and 5.35 mM [Ca(2+) ]e enhance osteogenesis and mineralization by rat primary calvarial cells cultures. J. Cell. Biochem. 117: 2658-2668, 2016. © 2016 Wiley Periodicals, Inc.

TGF-β1 and FGF2 stimulate the epithelial-mesenchymal transition of HERS cells through a MEK-dependent mechanism

Hertwig's epithelial root sheath (HERS) cells participate in cementum formation through epithelial-mesenchymal transition (EMT). Previous studies have shown that transforming growth factor beta 1 (TGF-β1) and fibroblast growth factor 2 (FGF2) are involved in inducing EMT. However, their involvement in HERS cell transition remains elusive. In this study, we confirmed that HERS cells underwent EMT during the formation of acellular cementum. We found that both TGF-β1 and FGF2 stimulated the EMT of HERS cells. The TGF-β1 regulated the differentiation of HERS cells into periodontal ligament fibroblast-like cells, and FGF2 directed the differentiation of HERS cells into cementoblast-like cells. Treatment with TGF-β1 or FGF2 inhibitor could effectively suppress HERS cells differential transition. Combined stimulation with both TGF-β1 and FGF-2 did not synergistically accelerate the EMT of HERS. Moreover, TGF-β1/FGF2-mediated EMT of HERS cells was reversed by the MEK1/2 inhibitor U0126. These results suggest that TGF-β1 and FGF2 induce the EMT of HERS through a MAPK/ERK-dependent signaling pathway. They also exert their different tendency of cellular differentiation during tooth root formation. This study further expands our knowledge of tooth root morphogenesis and provides more evidence for the use of alternative cell sources in clinical treatment of periodontal diseases.

Elevation of extracellular Ca2+ induces store-operated calcium entry via calcium-sensing receptors: a pathway contributes to the proliferation of osteoblasts

Aims

The local concentration of extracellular Ca²⁺ ([Ca²⁺]_o) in bone microenvironment is accumulated during bone remodeling. In the present study we investigated whether elevating [Ca²⁺]_o induced store-operated calcium entry (SOCE) in primary rat calvarial osteoblasts and further examined the contribution of elevating [Ca²⁺]_o to osteoblastic proliferation.

Methods

Cytosolic Ca²⁺ concentration ([Ca²⁺]_c) of primary cultured rat osteoblasts was detected by fluorescence imaging using calcium-sensitive probe fura-2/AM. Osteoblastic proliferation was estimated by cell counting, MTS assay and ATP assay. Agonists and antagonists of calcium-sensing receptors (CaSR) as well as inhibitors of phospholipase C (PLC), SOCE and voltage-gated calcium (Cav) channels were applied to study the mechanism in detail.

Results

Our data showed that elevating [Ca²⁺]_o evoked a sustained increase of [Ca²⁺]_c in a dose-dependent manner. This [Ca²⁺]_c increase was blocked by TMB-8 (Ca²⁺ release inhibitor), 2-APB and BTP-2 (both SOCE blockers), respectively, whereas not affected by Cav channels blockers nifedipine and verapamil. Furthermore, NPS2143 (a CaSR antagonist) or U73122 (a PLC inhibitor) strongly reduced the [Ca²⁺]_o-induced [Ca²⁺]_c increase. The similar responses were observed when cells were stimulated with CaSR agonist spermine. These data indicated that elevating [Ca²⁺]_o resulted in SOCE depending on the activation of CaSR and PLC in osteoblasts. In addition, high [Ca²⁺]_o significantly promoted osteoblastic proliferation, which was notably reversed by BAPTA-AM (an intracellular calcium chelator), 2-APB, BTP-2, TMB-8, NPS2143 and U73122, respectively, but not affected by Cav channels antagonists.

Conclusions

Elevating [Ca²⁺]_o induced SOCE by triggering the activation of CaSR and PLC. This process was involved in osteoblastic proliferation induced by high level of extracellular Ca²⁺ concentration.

Nanostructured titanate with different metal ions on the surface of metallic titanium: a facile approach for regulation of rBMSCs fate on titanium implants

Titanium (Ti) is widely used for load-bearing bio-implants, however, it is bio-inert and exhibits poor osteo-inductive properties. Calcium and magnesium ions are considered to be involved in bone metabolism and play a physiological role in the angiogenesis, growth, and mineralization of bone tissue. In this study, a facile synthesis approach to the in situ construction of a nanostructure enriched with Ca(2+) and Mg(2+) on the surface of titanium foil is proposed by inserting Ca(2+) and Mg(2+) into the interlayers of sodium titanate nanostructures through an ion-substitution process. The characteriz 0.67, and 0.73 nm ation results validate that cations can be inserted into the interlayer regions of the layered nanostructure without any obvious change of morphology. The cation content is positively correlated to the concentration of the solutions employed. The biological assessments indicate that the type and the amount of cations in the titanate nanostructure can alter the bioactivity of titanium implants. Compared with a Na(+) filled titanate nanostructure, the incorporation of divalent ions (Mg(2+) , Ca(2+) ) can effectively enhance protein adsorption, and thus also enhance the adhesion and differentiation ability of rat bone-marrow stem cells (rBMSCs). The Mg(2+) /Ca(2+) -titanate nanostructure is a promising implantable material that will be widely applicable in artificial bones, joints, and dental implants.

The influence of biodegradable magnesium alloys on the osteogenic differentiation of human mesenchymal stem cells

The postdegradation effect of pure Mg, Mg-1Y, Mg-5Al, and Mg-2Ca alloys on the differentiation, proliferation and gene expression of human mesenchymal stem cells (hMSCs) was investigated. It was revealed that that Mg(2+) ions result in an increase in cell proliferation. However, we observed a maximum concentration (approximately 8.0 × 10(-4) M) that was favourable to ATP production, above which ATP production began to decrease. In contrast to proliferation, no maximum concentration for osteogenic differentiation was observed, with increasing concentration of Mg(2+) ions resulting in an increase in osteogenic differentiation across the entire tested range. Interestingly, the Mg-2Ca alloy had minimal effect on osteogenic differentiation, with Mg-1Y and pure Mg having a superior effect on the proliferation and differentiation of hMSCs. This was also observed from gene expression data, where these alloys upregulated TGFβ-1, SMAD4, FGF-2, FGF-10, and BMP-2, while SOX-2, SOX-9, and TNF-α were downregulated. Increased expression of TGFβ-1, SMAD4, BMPs, and COLIA1 protein provided further evidence to support osteogenic differentiation and that the influence of the alloying extracts on differentiation may be via the SMAD signaling pathway.

Calcium-mediated increased expression of fibroblast growth factor-2 acts through NF-κB and PGE2/EP4 receptor signaling pathways in cementoblasts

We reported previously that cementoblasts are provided with sensing mechanisms for extracellular Ca2+ and that elevated extracellular Ca2+ increases fibroblast growth factor-2 (FGF-2) gene and protein expression levels via a cyclic AMP/protein kinase A (PKA) dependent pathway. In the present study, we found that stimulation of murine cementoblasts with 10 mM CaCl2 induced cyclooxygenase-2 (COX-2) gene expression and prostaglandin E2 (PGE2) biosynthesis. NS-398, a COX-2 inhibitor, significantly reduced CaCl2-induced increase in Fgf-2 gene expression, indicating that PGE2 synthesized by COX-2 may be involved in FGF-2 induction. The inhibitory effect of NS-398 was restored completely by the addition of PGE2 receptor 4 (E-prostanoid receptor 4, called EP4) agonist, but not agonists for EP1, EP2, and EP3. Furthermore, EP4 antagonist significantly reduced CaCl2-induced Fgf-2 induction, suggesting that it is mediated by EP4 activation. However, stimulation with EP4 agonist alone in the absence of CaCl2 had no effect on the Fgf-2 induction, indicating that EP4 signaling alone is not sufficient. CaCl2 also upregulated gene expression levels of Ep4 and Cox-2, as well as Fgf-2 and induction of these genes was abolished by pretreatment with BMS-345541, a nuclear factor-κB (NF-κB) inhibitor, indicating that NF-κB signaling triggered by CaCl2 is indispensable for FGF-2 induction. Furthermore, CaCl2-induced Fgf-2 induction was synergistically enhanced by the addition of EP4 agonist. This indicates that the signaling triggered via CaCl2 and its combination with EP4 agonist may be useful as a novel strategy for periodontal regeneration.

Extracellular calcium chronically induced human osteoblasts effects: specific modulation of osteocalcin and collagen type XV

Fluctuation in extracellular calcium (Ca(2+)) concentration occurs during bone remodeling. Free ionized Ca(2+) plays a critical role in regulating osteoblast functions. We analyzed the effects of different concentrations of free ionized Ca(2+) (0.5, 1.3, and 2.6 mM) on human osteoblasts and we evaluated osteoblastic phenotype (marker expression and cell morphology) and functions (osteogenic differentiation, cell proliferation, and cell signaling). Our data show human osteoblasts that chronically stimulated with 0.5, 1.3, or 2.6 mM Ca(2+) significantly increase intracellular content of alkaline phosphatase, collagen type I, osteocalcin, and bone sialoprotein, whereas collagen type XV was down-modulated and RUNX2 expression was not affected. We also found a Ca(2+) concentration-dependent increase in osteogenic differentiation and cell proliferation, associated to an increase of signaling protein PLCβ1 and p-ERK. Human osteoblast morphology was affected by Ca(2+) as seen by the presence of numerous nucleoli, cells in mitosis, cell junctions, and an increased number of vacuoles. In conclusion, our data show a clear phenotypical and functional effect of extracellular Ca(2+) on human osteoblasts and support the hypothesis of a direct role of this cation in the bone remodeling processes.

A calcium-induced signaling cascade leading to osteogenic differentiation of human bone marrow-derived mesenchymal stromal cells

The response of osteoprogenitors to calcium (Ca(2+)) is of primary interest for both normal bone homeostasis and the clinical field of bone regeneration. The latter makes use of calcium phosphate-based bone void fillers to heal bone defects, but it is currently not known how Ca(2+) released from these ceramic materials influences cells in situ. Here, we have created an in vitro environment with high extracellular Ca(2+) concentration and investigated the response of human bone marrow-derived mesenchymal stromal cells (hMSCs) to it. Ca(2+) enhanced proliferation and morphological changes in hMSCs. Moreover, the expression of osteogenic genes is highly increased. A 3-fold up-regulation of BMP-2 is observed after only 6h and pharmaceutical interference with a number of proteins involved in Ca(2+) sensing showed that not the calcium sensing receptor, but rather type L voltage-gated calcium channels are involved in mediating the signaling pathway between extracellular Ca(2+) and BMP-2 expression. MEK1/2 activity is essential for the effect of Ca(2+) and using microarray analysis, we have identified c-Fos as an early Ca(2+) response gene. We have demonstrated that hMSC osteogenesis can be induced via extracellular Ca(2+), a simple and economic way of priming hMSCs for bone tissue engineering applications.