A low calcium environment enhances AP-1 transcription factor-mediated gene expression in the development of osteoblastic MC3T3-E1 cells

Hair and Serum Trace Element and Mineral Levels Profiles in Women with Premenopausal and Postmenopausal Osteoporosis

The objective of the present study was to evaluate serum and hair trace element and mineral levels in women with osteoporosis, as well as to estimate the impact of menopausal status on the profile of trace element and mineral status in women with osteoporosis. 207 women with diagnosed osteoporosis 22-85 years-of-age, and 197 healthy women of the respective age participated in the present study. Analysis of the levels of mineral and trace element in hair and serum samples was performed by inductively-coupled plasma mass-spectrometry (ICP-MS). Women with osteoporosis were characterized by significantly lower hair Ca, Mg, Co, I, Li, and Mn levels, as well as serum Ca, Mg, Co, Fe, V, and Zn concentrations compared to women in the control group. After additional grouping according to menopausal status, the lowest hair Ca and Mg content was observed in postmenopausal osteoporotic women, whereas serum Ca and Mg concentrations were the lowest in premenopausal osteoporotic women. Hair Co, Mn, and Zn levels in postmenopausal osteoporotic women were lower than in healthy postmenopausal women. The lowest circulating Zn levels were observed in osteoporotic postmenopausal women. Taken together, decreased hair and serum levels in osteoporotic women are indicative of increased risk of Ca, Mg, Co, and Zn deficiency in women with osteoporosis. In turn, alterations in hair trace element and mineral levels in osteoporosis are more profound in postmenopausal women. Hypothetically, improvement in trace element and mineral metabolism especially in postmenopausal women may be considered as a potential strategy for mitigating osteoporosis.

Sustained local ionic homeostatic imbalance caused by calcification modulates inflammation to trigger heterotopic ossification

Heterotopic ossification (HO) is a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues. Despite being a frequent complication of orthopedic and trauma surgery, brain and spinal injury, the etiology of HO is poorly understood. The aim of this study is to evaluate the hypothesis that a sustained local ionic homeostatic imbalance (SLIHI) created by mineral formation during tissue calcification modulates inflammation to trigger HO. This evaluation also considers the role SLIHI could play for the design of cell-free, drug-free osteoinductive bone graft substitutes. The evaluation contains five main sections. The first section defines relevant concepts in the context of HO and provides a summary of proposed causes of HO. The second section starts with a detailed analysis of the occurrence and involvement of calcification in HO. It is followed by an explanation of the causes of calcification and its consequences. This allows to speculate on the potential chemical modulators of inflammation and triggers of HO. The end of this second section is devoted to in vitro mineralization tests used to predict the ectopic potential of materials. The third section reviews the biological cascade of events occurring during pathological and material-induced HO, and attempts to propose a quantitative timeline of HO formation. The fourth section looks at potential ways to control HO formation, either acting on SLIHI or on inflammation. Chemical, physical, and drug-based approaches are considered. Finally, the evaluation finishes with a critical assessment of the definition of osteoinduction. STATEMENT OF SIGNIFICANCE: The ability to regenerate bone in a spatially controlled and reproducible manner is an essential prerequisite for the treatment of large bone defects. As such, understanding the mechanism leading to heterotopic ossification (HO), a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues, would be very useful. Unfortunately, the mechanism(s) behind HO is(are) poorly understood. The present study reviews the literature on HO and based on it, proposes that HO can be caused by a combination of inflammation and calcification. This mechanism helps to better understand current strategies to prevent and treat HO. It also shows new opportunities to improve the treatment of bone defects in orthopedic and dental procedures.

A somatic proteoglycan controls Notch-directed germ cell fate

Communication between the soma and germline optimizes germ cell fate programs. Notch receptors are key determinants of germ cell fate but how somatic signals direct Notch-dependent germ cell behavior is undefined. Here we demonstrate that SDN-1 (syndecan-1), a somatic transmembrane proteoglycan, controls expression of the GLP-1 (germline proliferation-1) Notch receptor in the Caenorhabditis elegans germline. We find that SDN-1 control of a somatic TRP calcium channel governs calcium-dependent binding of an AP-2 transcription factor (APTF-2) to the glp-1 promoter. Hence, SDN-1 signaling promotes GLP-1 expression and mitotic germ cell fate. Together, these data reveal SDN-1 as a putative communication nexus between the germline and its somatic environment to control germ cell fate decisions.

How much medium do you use for cell culture? Medium volume influences mineralization and osteoclastogenesis in vitro

Bone is maintained by a balance between bone formation and resorption. This remodeling is controlled by a wide variety of systemic and local factors including hormones, cytokines and mechanical stresses. The present in vitro study examined the impact of medium volume, using 0.4, 0.6, 0.8, 1.0, 1.5 and 2.0 ml/well in a 24‑well plate, on the differentiation of osteoblasts and osteoclasts. There were no differences in the alkaline phosphatase activity of osteoblasts amongst the groups; however, the area of mineral deposition was decreased in a media volume‑dependent manner. A co‑culture of osteoblastic cells with bone marrow cells revealed a reduction in the total number of osteoclastic tartrate‑resistant acid phosphatase (TRAP)‑positive multinuclear cells (≥2 nuclei), whereas the formation of large osteoclastic TRAP‑positive multinuclear cells (≥8 nuclei) was increased, in a media volume‑dependent manner. There were also no differences in receptor activator of nuclear factor‑κB ligand mRNA and total osteoprotegerin (OPG) protein expression levels amongst the groups, however the concentration of OPG decreased in a media volume‑dependent manner. In conclusion, the present study demonstrated that the suppression of mineralization in osteoblastic cells and the stimulation of osteoclast fusion are dependent on the medium volume, indicating that media volume is an important factor in in vitro cell culture systems.

The calcium-sensing receptor in bone metabolism: from bench to bedside and back

The calcium-sensing receptor (CaSR), a key player in the maintenance of calcium homeostasis, can influence bone modeling and remodeling by directly acting on bone cells, as demonstrated by in vivo and in vitro evidence. The modulation of CaSR signaling can play a role in bone anabolism.

INTRODUCTION

The calcium-sensing receptor (CaSR) is a key player in the maintenance of calcium homeostasis through the regulation of PTH secretion and calcium homeostasis, thus indirectly influencing bone metabolism. In addition to this role, in vitro and in vivo evidence points to direct effects of CaSR in bone modeling and remodeling. In addition, the activation of the CaSR is one of the anabolic mechanisms implicated in the action of strontium ranelate, to reduce fracture risk.

METHODS

This review is based upon the acquisition of data from a PubMed enquiry using the terms "calcium sensing receptor," "CaSR" AND "bone remodeling," "bone modeling," "bone turnover," "osteoblast," "osteoclast," "osteocyte," "chondrocyte," "bone marrow," "calcilytics," "calcimimetics," "strontium," "osteoporosis," "skeletal homeostasis," and "bone metabolism."

RESULTS

A fully functional CaSR is expressed in osteoblasts and osteoclasts, so that these cells are able to sense changes in the extracellular calcium and as a result modulate their behavior. CaSR agonists (calcimimetics) or antagonists (calcilytics) have the potential to indirectly influence skeletal homeostasis through the modulation of PTH secretion by the parathyroid glands. The bone anabolic effect of strontium ranelate, a divalent cation used as a treatment for postmenopausal and male osteoporosis, might be explained, at least in part, by the activation of CaSR in bone cells.

CONCLUSIONS

Calcium released in the bone microenvironment during remodeling is a major factor in regulating bone cells. Osteoblast and osteoclast proliferation, differentiation, and apoptosis are influenced by local extracellular calcium concentration. Thus, the calcium-sensing properties of skeletal cells can be exploited in order to modulate bone turnover and can explain the bone anabolic effects of agents developed and employed to revert osteoporosis.

[Extracellular calcium sensing under normal and pathological conditions]

Ionic calcium has been known as an important intracellular second messenger for many decades. In addition, a whole series of experimental and clinical studies from the past fifteen years have provided evidence that extracellular ionic calcium itself is also a first messenger, since it is the ligand of a cell surface G-protein coupled receptor called calcium-sensing receptor. This review summarizes the current knowledge on the role of calcium-sensing receptor in the maintenance of calcium homeostasis, its functions in various tissues and some of the most important disorders characterized by defective calcium sensing. The inherited disorders of the calcium-sensing receptors may be classified as the results of loss-of-function and gain-of-function mutations of the calcium-sensing receptor gene. Loss-of-function heterozygous mutations lead to familial hypocalciuric hypercalcemia while homozygous mutations result in the frequently life-threatening disorder called neonatal severe hyperparathyroidism. Gain-of-function mutations of this receptor's gene cause the disorder called autosomal dominant hypocalcemia. The authors briefly highlight the clinical features, laboratory characteristics and therapeutic implications of these disorders. Also, they discuss briefly the molecular mechanisms resulting defective calcium-sensing in of patients with primary and secondary hyperparathyroidism, and summarize the results of some recent investigations on the functional consequences of genetic variants of the calcium-sensing receptor gene.

Ca2+ as an extracellular signal in bone

Bone is the major sink and store for calcium and it fulfils essential roles in the maintenance of extracellular free ionised calcium concentration ([Ca2+]e) within its homeostatic range (1.1-1.3 mM). In response to acute hypercalcaemia or hypocalcaemia, Ca2+ is rapidly transported into or out of bone. Bone turnover (and therefore bone Ca2+ turnover) achieves the long-term correction of the [Ca2+]e by the metabolic actions of osteoblasts and osteoclasts, as they respectively incorporate or release Ca2+ from bone. These processes are regulated by the actions of hormones, such as parathyroid hormone (PTH), the release of which is a function of the [Ca2+]e, and is regulated by the action of the Ca2+-sensing receptor (CaR) in the parathyroid gland. Tissue culture studies indicate that bone cells also directly respond to increasing and decreasing [Ca2+]e in their vicinity, independently of the systemic factors. Nevertheless, further studies are necessary to identify how the acute and long-term local changes in [Ca2+]e affect bone cells and the physiological processes they are involved in. Also, the molecular mechanisms which enable the bone cells to sense and respond to [Ca2+]e are not clear. Like the parathyroid cells, bone cells also express the CaR, and accumulating evidence indicates the involvement of this receptor in their responses to the changing extracellular ionic environment.

Phosphate decreases osteoclastogenesis in coculture of osteoblast and bone marrow

Alkaline phosphatase (ALP) activity increases dramatically during osteoblast maturation, a phenomenon that is related to calcification of teeth and bone. Although the relation between ALP and calcification is widely known, there is a paucity of date relating ALP and osteoclast formation. Very recently, we showed that osteoblast maturation suppresses osteoclast formation. However, the relation between osteoblast maturation and osteoclastogenesis remains unclear. In the present study, we examined the effect of extracellular phosphate on osteoclastogenesis. As osteoblasts matured, osteoclast formation decreased, and ALP activity and inorganic phosphate in extracellular matrix increased. Inorganic phosphate in extracellular matrix and extracellular phosphate was suppressed osteoclast formation. These results suggest that phosphate released by ALP may be related not only to calcification but also to suppression of osteoclastogenesis.

Osteoblast maturation suppressed osteoclastogenesis in coculture with bone marrow cells

The analysis of co-culture system using osteoblast and bone marrow indicated that the mineralized osteoblast decreased osteoclast formation. This finding was an incentive to better investigate the relation of osteoblast development and osteoclastogenesis. The expression of osteoclast differentiation factor (ODF/RANKL) mRNA and protein dramatically decreased. Alternatively, macropharge colony stimulation factor (M-CSF/CSF-1) transcription and protein secreted in media slightly decreased as the development of osteoblast. On the other hands, mRNA expression and the secretion to the culture medium of osteoclastogenesis inhibitory factor (OPG/OCIF) didn't significantly change depending on osteoblast differentiation. We conclude that osteoblast development might suppress osteoclastogenesis especially with the decrease of ODF/RANKL.