Exogenous regucalcin stimulates osteoclastogenesis and suppresses osteoblastogenesis through NF-κB activation

Functional pleiotropy of calcium binding protein Regucalcin in signaling and diseases

Regucalcin (Mr ∼ 33.38 kDa) is a calcium binding protein, discovered in rat liver. In humans, gene for regucalcin is located on chromosome-11 (p11.3-q11.2) consisting of seven exons and six introns. The protein differs from other calcium binding protein in the way that it lacks EF-hand motif of calcium binding domain. It is also called as Senescence Marker Protein-30 (SMP-30) as previously its weight assumes to be 30 kDa and expression of this protein decreases with aging in androgen independent manner. Among vertebrates, it is a highly conserved protein showing gene homology in Drosophila, Xenopus, fireflies and others too. It is primarily expressed in liver and kidney in addition to brain, lungs, and skeletal muscles. Regucalcin acts as a Ca²⁺ regulatory protein and controls various cellular functions in liver and other organs. It suppresses protein phosphatase, protein kinase, DNA and RNA synthesis. Published evidences suggest regucalcin to be a reliable biomarker in various disorders of liver, kidney, brain and ocular. In over expressed state, it subdues apoptosis in cloned rat hepatoma cells and also induces hyperlipidemia and osteoblastogenesis by regulating various factors. Owing to the multi-functionality of regucalcin this review is presented to elaborate its importance in order to understand its involvement in cellular signaling during various pathologies.

C. R. Twelve Weeks of Whole Body Vibration Training Improve Regucalcin, Body Composition and Physical Fitness in Postmenopausal Women: A Pilot Study

(1) Background: Regucalcin or senescence marker protein 30 (SMP30) is a Ca2+ binding protein discovered in 1978 with multiple functions reported in the literature. However, the impact of exercise training on SMP30 in humans has not been analyzed. Aging is associated with many detrimental physiological changes that affect body composition, functional capacity, and balance. The present study aims to investigate the effects of whole body vibration (WBV) in postmenopausal women. (2) Methods: A total of 13 women (aged 54.3 ± 3.4 years) participated in the study. SMP30, body composition (fat mass, lean mass, and bone mass) and physical fitness (balance, time up and go (TUG) and 6-min walk test (6MWT)) were measured before and after the 12 weeks of WBV training. (3) Results: The WBV training program elicited a significant increase in SPM30 measured in plasma (27.7%, p = 0.004) and also in 6MWT (12.5%, p < 0.001). The WBV training also significantly reduced SPM30 measured in platelets (38.7%, p = 0.014), TUG (23.1%, p < 0.001) and total body fat mass (4.4%, p = 0.02). (4) Conclusions: There were no significant differences in balance, lean mass or bone mass. The present study suggests that 12 weeks of WBV has the potential to improve SPM30, fat mass, TUG and 6MWT in postmenopausal women.

A simple and robust reporter gene assay for measuring the bioactivity of anti-RANKL therapeutic antibodies

RANKL (receptor activator of nuclear factor κB ligand) plays a key role in the differentiation, activation and survival of osteoclasts. Denosumab, which targets RANKL, is approved for osteoporosis or bone loss that has a high risk for fracture and bone metastases from solid tumors. Bioactivity determination is essential for the safety and efficacy of therapeutic antibodies. At present, the mechanism of action (MOA) based bioassay for anti-RANKL monoclonal antibodies (mAbs) is the measurement of tartrate resistant acid phosphatase (TRAP) activity, which takes about five days and has complex operation and relatively high variation. In this study, we developed a reporter gene assay (RGA) based on a RAW264.7 cell line stably expressing luciferase reporter under the control of nuclear factor-κB (NF-κB) response elements. After optimizing the key parameters, the validation results based on ICH-Q2 not only show superior specificity, precision, linearity, accuracy and passage stability, but also a short duration and simple operation. These results demonstrate the RGA based on the RANKL-RANK-NF-κB pathway can be an excellent alternative for measuring the bioactivity of anti-RANKL mAbs.

Extracellular Signal-regulated Kinase Mitogen-activated Protein Kinase and Phosphatidylinositol 3-Kinase/Akt Signaling Are Required for Lipopolysaccharide-mediated Mineralization in Murine Odontoblast-like Cells

INTRODUCTION

Odontoblasts play an important role in post-developmental control of mineralization in response to external stimuli in the tooth. The present study investigated whether lipopolysaccharide (LPS), a major bacterial cell wall component, influenced mineralization in a murine odontoblast-like cell (OLC) line and the related intracellular signaling pathways involved.

METHODS

Alizarin red S staining was used to assess mineralized nodule formation in OLCs in response to LPS. The effects of LPS on gene expression of odontoblastic markers were investigated by using quantitative real-time reverse-transcriptase polymerase chain reaction. The potential involvement of toll-like receptor 4 (TLR4), nuclear factor kappa B (NF-κB), mitogen-activated protein kinase (MAPK), or phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathways in the mineralized nodule formation, and mRNA expression of several odontoblastic markers of OLCs induced by LPS was assessed by using alizarin red S staining and quantitative real-time reverse-transcriptase polymerase chain reaction. Moreover, LPS stimulation resulted in phosphorylation of protein that was determined by Western blot analysis.

RESULTS

OLCs showed reduced mineralized nodule formation and several odontoblastic markers expression in response to LPS exposure. Furthermore, inhibition of TLR4, extracellular signal-regulated kinase (ERK), and PI3K/Akt signaling noticeably antagonized LPS-mediated mineralization in OLCs. However, p38 MAPK, c-Jun N-terminal kinase, and NF-κB signaling inhibitors did not affect LPS-mediated mineralization in OLCs. Notably, LPS treatment resulted in a time-dependent phosphorylation of ERK and PI3K/Akt in OLCs, which was abrogated by their specific inhibitors.

CONCLUSIONS

LPS decreased mineralization in OLCs via TLR4, ERK MAPK, and PI3K/Akt signaling pathways, but not p38, c-Jun N-terminal kinase, or NF-κB signaling.

The role of regucalcin in bone homeostasis: involvement as a novel cytokine

Regucalcin, which was discovered as a calcium-binding protein in 1978, has been demonstrated to play a multifunctional role in the regulation of various tissues and cell types. Regucalcin plays a pivotal role in the regulation of intracellular calcium homeostasis, various enzyme activities, cell signal transduction, nuclear function and gene expression, and cell proliferation and apoptosis. Moreover, regucalcin has been found to play a role in the regulation of bone homeostasis. Overexpression of regucalcin induces bone loss in regucalcin transgenic rats in vivo and deficiency causes osteomalacia in vivo. Regucalcin mRNA and its protein are expressed in rat femoral tissues, bone marrow cells, and osteoblastic cells. Exogenous regucalcin has suppressive effects on the differentiation and mineralization of osteoblastic MC3T3-E1 cells and stimulates osteoclastogenesis in mouse bone marrow culture in vitro. Moreover, regucalcin has been found to suppress osteoblastogenesis and stimulate adipogenesis in the bone marrow culture system in vitro. Regucalcin shows enhancing effects on activation of NF-κB, which is mediated through tumor necrosis factor-α (TNF-α) or the receptor activator of the NF-κB ligand (RANKL) in preosteoblastic cells and preosteoclastic cells. Exogenous regucalcin may play a pivotal role in the regulation of bone homeostasis as a suppressor in osteoblastogenesis and an enhancer in osteoclastogenesis, suggesting its role as a cytokine.

The diverse roles of calcium-binding protein regucalcin in cell biology: from tissue expression and signalling to disease

Regucalcin (RGN) is a calcium (Ca(2+))-binding protein widely expressed in vertebrate and invertebrate species, which is also known as senescence marker protein 30, due to its molecular weight (33 kDa) and a characteristically diminished expression with the aging process. RGN regulates intracellular Ca(2+) homeostasis and the activity of several proteins involved in intracellular signalling pathways, namely, kinases, phosphatases, phosphodiesterase, nitric oxide synthase and proteases, which highlights its importance in cell biology. In addition, RGN has cytoprotective effects reducing intracellular levels of oxidative stress, also playing a role in the control of cell survival and apoptosis. Multiple factors have been identified regulating the cell levels of RGN transcripts and protein, and an altered expression pattern of this interesting protein has been found in cases of reproductive disorders, neurodegenerative diseases and cancer. Moreover, RGN is a serum-secreted protein, and its levels have been correlated with the stage of disease, which strongly suggests the usefulness of this protein as a potential biomarker for monitoring disease onset and progression. The present review aims to discuss the available information concerning RGN expression and function in distinct cell types and tissues, integrating cellular and molecular mechanisms in the context of normal and pathological conditions. Insight into the cellular actions of RGN will be a key step towards deepening the knowledge of the biology of several human diseases.

Exogenous regucalcin suppresses osteoblastogenesis and stimulates adipogenesis in mouse bone marrow culture

Regucalcin plays a pivotal role in regulating intracellular calcium homeostasis and consequently has a profound effect on multiple intracellular signal transduction pathways. The regucalcin transgenic rat displays pronounced bone loss and hyperlipidemia. Consistent with these effects exogenous regucalcin has been shown to promote osteoclastogenesis in mouse bone marrow cultures and to suppress the differentiation and mineralization of MC3T3 osteoblast precursors. Regucalcin may induce hyperlipidemia in vivo by suppressing osteoblast differentiation and stimulating adipogenesis in bone marrow mesenchymal stem cells. The present study demonstrates that exogenous regucalcin suppresses differentiation to osteoblasts and stimulates adipogenesis in mouse bone marrow cell culture ex vivo. Moreover, exogenous regucalcin was found to enhance adipogenesis stimulated by insulin which is involved in the extracellular signal-related kinase pathway in 3T3-L1 adipocytes in vitro.

Pathways for bone loss in inflammatory disease

Chronic inflammation including autoimmune disease is an important risk factor for the development of osteoporosis. Receptor activator of nuclear factor-κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF) play a central role in osteoclast differentiation and function, and the molecular pathways by which M-CSF and RANKL induce osteoclast differentiation have been analyzed in detail. Proinflammatory cytokines directly or indirectly regulate osteoclastogenesis and bone resorption providing a link between inflammation and osteoporosis. Tumor necrosis factor-α, interleukin (IL)-1, IL-6, and IL-17 are the most important proinflammatory cytokines triggering inflammatory bone loss. Inhibition of these cytokines has provided potent therapeutic effects in the treatment of diseases such as rheumatoid arthritis. Further investigation is needed to understand the pathophysiology and to develop new strategies to treat inflammatory bone loss. This review summarizes new data on inflammatory bone loss obtained in 2011.