The effects of low dose X-irradiation on osteoblastic MC3T3-E1 cells in vitro

Irradiation affects the structural, cellular and molecular components of jawbones

PURPOSE

Emerging evidence shows that changes in the bone and its microenvironment following radiotherapy are associated with either an inhibition or a state of low bone formation. Ionizing radiation is damaging to the jawbone as it increases the complication rate due to the development of hypovascular, hypocellular, and hypoxic tissue. This review summarizes and correlates the current knowledge on the effects of irradiation on the bone with an emphasis on jawbone, as these have been a less extensively studied area.

CONCLUSIONS

The stringent regulation of bone formation and bone resorption can be influenced by radiation, causing detrimental effects at structural, cellular, vascular, and molecular levels. It is also associated with a high risk of damage to surrounding healthy tissues and an increased risk of fracture. Technological advances and research on animal models as well as a few human bone tissue studies have provided novel insights into the ways in which bone can be affected by high, low and sublethal dose of radiation. The influence of radiation on bone metabolism, cellular properties, vascularity, collagen, and other factors like inflammation, reactive oxygen species are discussed.

Pilot investigation on the dose-dependent impact of irradiation on primary human alveolar osteoblasts in vitro

Radiotherapy of head and neck squamous cell carcinoma can lead to long-term complications like osteoradionecrosis, resulting in severe impairment of the jawbone. Current standard procedures require a 6-month wait after irradiation before dental reconstruction can begin. A comprehensive characterization of the irradiation-induced molecular and functional changes in bone cells could allow the development of novel strategies for an earlier successful dental reconstruction in patients treated by radiotherapy. The impact of ionizing radiation on the bone-forming alveolar osteoblasts remains however elusive, as previous studies have relied on animal-based models and fetal or animal-derived cell lines. This study presents the first in vitro data obtained from primary human alveolar osteoblasts. Primary human alveolar osteoblasts were isolated from healthy donors and expanded. After X-ray irradiation with 2, 6 and 10 Gy, cells were cultivated under osteogenic conditions and analyzed regarding their proliferation, mineralization, and expression of marker genes and proteins. Proliferation of osteoblasts decreased in a dose-dependent manner. While cells recovered from irradiation with 2 Gy, application of 6 and 10 Gy doses not only led to a permanent impairment of proliferation, but also resulted in altered cell morphology and a disturbed structure of the extracellular matrix as demonstrated by immunostaining of collagen I and fibronectin. Following irradiation with any of the examined doses, a decrease of marker gene expression levels was observed for most of the investigated genes, revealing interindividual differences. Primary human alveolar osteoblasts presented a considerably changed phenotype after irradiation, depending on the dose administered. Mechanisms for these findings need to be further investigated. This could facilitate improved patient care by re-evaluating current standard procedures and investigating faster and safer reconstruction concepts, thus improving quality of life and social integrity.

0.5‑Gy X‑ray irradiation induces reorganization of cytoskeleton and differentiation of osteoblasts

Osteoblasts are sensitive to ionizing radiation. The small GTPase RhoA and its effector Rho-associated protein kinase (ROCK) are critical to several cellular functions, including cytoskeleton reorganization, cell survival, and cell differentiation. However, whether the RhoA/ROCK signaling pathway is involved in the regulation of osteoblast cytoskeleton reorganization and differentiation induced by low-dose X-ray irradiation remains to be determined. The aim of the present study was to investigate the role of the RhoA/ROCK signaling pathway in mediating differentiation of osteoblasts and reorganization of the cytoskeleton under low-dose X-ray irradiation. Osteoblasts were pretreated with the ROCK kinase-specific inhibitor (Y-27632) before exposure to low-dose X-ray irradiation. The changes of F-actin in MC3T3 cells were observed at different time points following X-ray irradiation. Cell Counting Kit-8 assay, alkaline phosphatase activity, Alizarin red staining and western blotting were used to detect the proliferation and differentiation of osteoblasts after 0.5-Gy X-ray irradiation. In the present study, low-dose X-ray irradiation promoted the expression of genes associated with the cytoskeleton reorganization. Indeed, the results showed that, 0.5-Gy X-ray irradiation can induce reorganization of cytoskeleton and promote differentiation of osteoblasts through the RhoA/ROCK signaling pathway. Additionally, inhibiting ROCK activity blocked low-dose X-ray irradiation-induced LIMK2 phosphorylation, stress fiber formation and cell differentiation. Thus, these results demonstrated the excitatory effects of low-dose X-ray irradiation on MC3T3-E1 cells, including reorganization of the cytoskeleton and differentiation of osteoblasts.

Low-dose X-ray irradiation induces morphological changes and cytoskeleton reorganization in osteoblasts

Recently, research into the biological effects of low dose X-ray irradiation (LDI) has been a focus of interest. Numerous studies have suggested that cells exhibit different responses and biological effects to LDI compared with high doses. Preliminary studies have demonstrated that LDI may promote osteoblast proliferation and differentiation in vitro, thereby accelerating fracture healing in mice. However, the exact mechanism of action by which LDI exerts its effects remains unclear. Previous studies using microarrays revealed that LDI promoted the expression of genes associated with the cytoskeleton. In the current study, the effect of X-ray irradiation (0.5 and 5 Gy) on the morphology of MC3T3-E1 cells and fiber actin organization was investigated. Osteoblasts were treated with 0, 0.5 and 5 Gy X- ray irradiation, following which changes in the actin cytoskeleton were observed. The levels of RhoA, ROCK, cofilin and phosphorylated-cofilin were measured by reverse transcription-quantitative PCR and western blotting. Subsequently, osteoblasts were pretreated with ROCK specific inhibitor Y27632 to observe the changes of actin skeleton after X-ray irradiation. The results demonstrated that the cellular morphological changes were closely associated with radiation dose and exposure time. Furthermore, the gene expression levels of small GTPase RhoA and its effectors were increased following LDI. These results indicated that the RhoA/Rho-associated kinase pathway may serve a significant role in regulating LDI-induced osteoblast cytoskeleton reorganization.

Organ-Specific Effects of Low Dose Radiation Exposure: A Comprehensive Review

Ionizing radiation (IR) is a high-energy radiation whose biological effects depend on the irradiation doses. Low-dose radiation (LDR) is delivered during medical diagnoses or by an exposure to radioactive elements and has been linked to the occurrence of chronic diseases, such as leukemia and cardiovascular diseases. Though epidemiological research is indispensable for predicting and dealing with LDR-induced abnormalities in individuals exposed to LDR, little is known about epidemiological markers of LDR exposure. Moreover, difference in the LDR-induced molecular events in each organ has been an obstacle to a thorough investigation of the LDR effects and a validation of the experimental results in in vivo models. In this review, we summarized the recent reports on LDR-induced risk of organ-specifically arranged the alterations for a comprehensive understanding of the biological effects of LDR. We suggested that LDR basically caused the accumulation of DNA damages, controlled systemic immune systems, induced oxidative damages on peripheral organs, and even benefited the viability in some organs. Furthermore, we concluded that understanding of organ-specific responses and the biological markers involved in the responses is needed to investigate the precise biological effects of LDR.

Effect of autophagy on irradiation‑induced damage in osteoblast‑like MC3T3‑E1 cells

Autophagy is activated under radiation stress, which serves an important role in maintaining bone homeostasis. However, the underlying mechanisms of irradiation-induced autophagy in bone homeostasis is not well understood. The present study aimed to determine the effects of radiation-activated autophagy on pre-osteoblastic MC3T3-E1 cells. X-ray irradiation activated autophagy in a dose-dependent manner, with an increased fluorescence intensity of monodansylcadaverine staining, increased ratio of microtubule-associated protein 1 light chain 3β (LC3)-II/LC3-I, decreased p62 expression, and increased ATG5 and beclin-1 expression levels in MC3T3-E1 cells 72 h after irradiation compared with those in non-irradiated MC3T3-E1 cells. Irradiation reduced colony formation and mineralization in a dose-dependent manner in MC3T3-E1 cells at 2 and 3 weeks after irradiation, respectively. Decreased levels of alkaline phosphatase activity and runt-related transcription factor 2 expression were observed at 72 h post-irradiation. In addition, irradiation-induced apoptosis was accompanied by a decreased ratio of Bcl-2/BAX protein and increased the activity of caspase-3. By contrast, doxycycline (DOX)-inhibited autophagy attenuated the decreased colony formation and mineralization, and aggravated the increased cell apoptosis in irradiated MC3T3-E1 cells. Furthermore, the ratio of phosphorylated P38/P38 was observed to be higher following DOX treatment within 1 week of irradiation, which was reversed 2 weeks post-irradiation. In conclusion, DOX-inhibited autophagy aggravated X-ray irradiation-induced apoptosis at an early stage, but maintained cell proliferation and mineralization at a late stage in irradiated MC3T3-E1 cells.

The Influence of Radiation on Bone and Bone Cells-Differential Effects on Osteoclasts and Osteoblasts

The bone is a complex organ that is dependent on a tight regulation between bone formation by osteoblasts (OBs) and bone resorption by osteoclasts (OCs). These processes can be influenced by environmental factors such as ionizing radiation (IR). In cancer therapy, IR is applied in high doses, leading to detrimental effects on bone, whereas radiation therapy with low doses of IR is applied for chronic degenerative and inflammatory diseases, with a positive impact especially on bone homeostasis. Moreover, the effects of IR are of particular interest in space travel, as astronauts suffer from bone loss due to space radiation and microgravity. This review summarizes the current state of knowledge on the effects of IR on bone with a special focus on the influence on OCs and OBs, as these cells are essential in bone remodeling. In addition, the influence of IR on the bone microenvironment is discussed. In summary, the effects of IR on bone and bone remodeling cells strongly depend on the applied radiation dose, as differential results are provided from in vivo as well as in vitro studies with varying doses of IR. Furthermore, the isolated effects of IR on a single cell type are difficult to determine, as the bone cells and bone microenvironment are building a tightly regulated network, influencing on one another. Therefore, future research is necessary in order to elucidate the influence of different bone cells on the overall radiation-induced effects on bone.

Effects of low-dose irradiation on human osteoblasts and periodontal ligament cells

OBJECTIVE

To investigate the effects of dental x-ray on proliferation and mineralization in human primary osteoblasts as well as on proliferation and apoptotic potential in human periodontal ligament (PDL) cells.

DESIGN

Primary osteoblasts and PDL cells were irradiated with various doses of periapical radiography by repeated exposures and further incubated for 1, 3 or 7 days. Cell proliferation was assayed by BrdU incorporation. The effect of dental x-ray on mineralization in osteoblasts either before or after x-ray exposures was determined by Alizarin red staining. Both mRNA and protein expressions of BCL-2, an anti-apoptotic gene, and BAX, a pro-apoptotic gene, in PDL cells were analyzed by RT-qPCR and immunoblotting analysis, respectively.

RESULTS

Neither the proliferative nor the mineralization ability of irradiated osteoblasts was different from that of non-irradiated osteoblasts at any doses or time points. By contrast, there was a significant decrease in the proliferation of PDL cells on day 3 after repeated exposures to dental x-ray for 20 times (P < 0.05), whereas the ratio of BCL-2 to BAX mRNA and protein expressions in these irradiated PDL cells was significantly increased (P < 0.05).

CONCLUSIONS

Upon multiple exposures to dental x-ray used in intraoral radiography up to 20 times, there is no effect on the proliferation or the mineralization of osteoblasts, whereas the proliferative and apoptotic potentials of PDL cells are transiently decreased.

Therapeutic ionizing radiation induced bone loss: a review of in vivo and in vitro findings

Radiation therapy is one of the routine treatment modalities for cancer patients. Ionizing radiation (IR) can induce bone loss, and consequently increases the risk of fractures with delayed and nonunion of the bone in the cancer patients who receive radiotherapy. The orchestrated bone remodeling can be disrupted due to the affected behaviors of bone cells, including bone mesenchymal stem cells (BMSCs), osteoblasts and osteoclasts. BMSCs and osteoblasts are relatively radioresistant compared with osteoclasts and its progenitors. Owing to different radiosensitivities of bone cells, unbalanced bone remodeling caused by IR is closely associated with the dose absorbed. For doses less than 2 Gy, osteoclastogenesis and adipogenesis by BMSCs are enhanced, while there are limited effects on osteoblasts. High doses (>10 Gy) induce disrupted architecture of bone, which is usually related to decreased osteogenic potential. In this review, studies elucidating the biological effects of IR on bone cells (BMSCs, osteoblasts and osteoclasts) are summarized. Several potential preventions and therapies are also proposed.

Differences in responses to X-ray exposure between osteoclast and osteoblast cells

Radiation-induced bone loss is a potential health concern for cancer patients undergoing radiotherapy. Enhanced bone resorption by osteoclasts and decreased bone formation by osteoblasts were thought to be the main reasons. In this study, we showed that both pre-differentiating and differentiating osteoclasts were relatively sensitive to X-rays compared with osteoblasts. X-rays decreased cell viability to a greater degree in RAW264.7 cells and in differentiating cells than than in osteoblastic MC3T3-E1 cells. X-rays at up to 8 Gy had little effects on osteoblast mineralization. In contrast, X-rays at 1 Gy induced enhanced osteoclastogenesis by enhanced cell fusion, but had no effects on bone resorption. A higher dose of X-rays at 8 Gy, however, had an inhibitory effect on bone resorption. In addition, actin ring formation was disrupted by 8 Gy of X-rays and reorganized into clusters. An increased activity of Caspase 3 was found after X-ray exposure. Actin disorganization and increased apoptosis may be the potential effects of X-rays at high doses, by inhibiting osteoclast differentiation. Taken together, our data indicate high radiosensitivity of osteoclasts. X-ray irradiation at relatively low doses can activate osteoclastogenesis, but not osteogenic differentiation. The radiosensitive osteoclasts are the potentially responsive cells for X-ray-induced bone loss.

Exposure to Low-Dose X-Ray Radiation Alters Bone Progenitor Cells and Bone Microarchitecture

Exposure to high-dose ionizing radiation during medical treatment exerts well-documented deleterious effects on bone health, reducing bone density and contributing to bone growth retardation in young patients and spontaneous fracture in postmenopausal women. However, the majority of human radiation exposures occur in a much lower dose range than that used in the radiation oncology clinic. Furthermore, very few studies have examined the effects of low-dose ionizing radiation on bone integrity and results have been inconsistent. In this study, mice were irradiated with a total-body dose of 0.17, 0.5 or 1 Gy to quantify the early (day 3 postirradiation) and delayed (day 21 postirradiation) effects of radiation on bone microarchitecture and bone marrow stromal cells (BMSCs). Female BALBc mice (4 months old) were divided into four groups: irradiated (0.17, 0.5 and 1 Gy) and sham-irradiated controls (0 Gy). Micro-computed tomography analysis of distal femur trabecular bone from animals at day 21 after exposure to 1 Gy of X-ray radiation revealed a 21% smaller bone volume (BV/TV), 22% decrease in trabecular numbers (Tb.N) and 9% greater trabecular separation (Tb.Sp) compared to sham-irradiated controls (P < 0.05). We evaluated the differentiation capacity of bone marrow stromal cells harvested at days 3 and 21 postirradiation into osteoblast and adipocyte cells. Osteoblast and adipocyte differentiation was decreased when cells were harvested at day 3 postirradiation but enhanced in cells isolated at day 21 postirradiation, suggesting a compensatory recovery process. Osteoclast differentiation was increased in 1 Gy irradiated BMSCs harvested at day 3 postirradiation, but not in those harvested at day 21 postirradiation, compared to controls. This study provides evidence of an early, radiation-induced decrease in osteoblast activity and numbers, as well as a later recovery effect after exposure to 1 Gy of X-rays, whereas osteoclastogenesis was enhanced. A better understanding of the effects of radiation on osteoprogenitor cell populations could lead to more effective therapeutic interventions that protect bone integrity for individuals exposed to low-dose ionizing radiation.

High density lipoprotein promoting proliferation and migration of type II alveolar epithelial cells during inflammation state

BACKGROUND

To investigate the effect and mechanism of high density lipoprotein (HDL) on type II alveolar epithelial cells during inflammation state.

METHODS

The original generation of type II alveolar epithelial cells were separated in rats and treated with PBS/LPS/HDL/HDL + LPS. To observe the proliferation and migration of type II alveolar epithelial cells with bromodeoxyuridine(BrdU) assay, transwell assay and wound healing experiments. In addition, western blot detected the expression of TP-binding cassette transporter A1 (ABCA1), cystic fibrosis transmembrane conductance regulator (CFTR) and the phosphorylation of AKT/extracellular signal-regulated kinase(ERK)/mitogen-activated protein kinase(MAPK). Enzyme-linked immunosorbent assay (ELISA) tested the secretion of tumor necrosis factor a(TNF-a)/interleukin 1a(IL-1a)/IL-6.

RESULTS

HDL promoted the proliferation (↑17%, p < 0.001 HDL+ LPS vs. LPS) and migration (wounding healing: ↑93%, p < 0.001 HDL+ LPS vs. LPS; transwell migration: ↑154%, p < 0.001 HDL+ LPS vs. LPS) of type II alveolar epithelial cells. Furthermore, HDL increased the phosphorylation of MAPK, but not AKT/ERK. And HDL decreased the secretion of TNF-a (↓46%, p < 0.01 HDL+ LPS vs. LPS) and IL-1a (↓45%, p < 0.001 HDL+ LPS vs. LPS), but not IL-6. In addition, HDL up-regulated the expression of ABCAI (↑99%, p < 0.001 HDL vs. CON) and down-regulated the expression of CFTR (↓25%, p < 0.05 HDL vs. CON) in type II alveolar epithelial cells.

CONCLUSIONS

HDL increases the phosphorylation of MAPK, which promotes the proliferation and migration of type II alveolar epithelial cells. And it decreased the secretion of TNF-a/IL-1a and the expression of CFTR. All these suggest that HDL plays an important role in anti-inflammatory effect in inflammation state of lung.

G protein-coupled receptor kinase 6 is overexpressed in glioma and promotes glioma cell proliferation

The expression and potential biological functions of G protein-coupled receptor kinase 6 (GRK6) in human glioma are tested in this study. We show that protein and mRNA expression of GRK6 in human glioma tissues was significantly higher than that in the normal brain tissues. Further immunohistochemistry assay analyzing total 118 human glioma tissues showed that GRK6 over-expression was correlated with glioma pathologic grade and patients’ Karnofsky performance status (KPS) score. At the molecular level, in the GRK6-low H4 glioma cells, forced over-expression of GRK6 promoted cell proliferation. Reversely, siRNA-mediated knockdown of GRK6 in the U251MG (GRK6-high) cells led to proliferation inhibition and cell cycle arrest. Intriguingly, GRK6 could also be an important temozolomide resistance factor. Temozolomide-induced cytotoxicity was prominent only in GRK6-low H4 glioma cells. On the other hand, knockdown of GRK6 by targeted siRNA sensitized U251MG cells (GRK6-high) to temozolomide. Thus, GRK6 over-expression in glioma is important for cell proliferation and temozolomide resistance.

Effect of low-dose X-ray irradiation and Ti particles on the osseointegration of prosthetic

Low-dose irradiation (LDI) exhibits a positive effect on osteoblasts and inhibitory effect of inflammation. Here, we test the hypothesis that LDI can promote osseointegration and inhibit the inflammatory membrane formation in the presence of titanium (Ti) particles. Endotoxin-free titanium particles were injected into rabbit, prior to the insertion of a Ti6-Al-4-V sticks pre-coated with hydroxyapatite. Two days after operation, both distal femurs of the animal were exposed to 0.5 Gy X-ray irradiation. All ani-mals were euthanized 8 weeks after the operation. The PINP concentration was determined at day 0, 2, 4, and 8 weeks after operation. Trabecular morphology around the implants 8 weeks after operation was assessed using micro-CT, then the maximum push out force of simples was assessed using biomechanics test. Five samples in each group were chosen for bone histomorphology study without decalcification 8 weeks after operation. The results confirmed that the LDI can significantly improve ingrowth of bone into the prosthetic interface and stability of the prosthesis when there was no wear particles. Although promotion effects for bone formation induced by LDI can be counteracted by wear particles, LDI can significantly inhibit the interface membrane formation around the implant induced by wear particles. Based on these results, we conclude that LDI may be useful for enhancing the stability of prosthesis when there are no wear particles and for inhibiting the interface membrane formation during the early stage of aseptic loosening in the presence of wear particles. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1688-1696, 2016.

X-ray radiation effect of C-arm on adipose tissue-mesenchymal stem cell viability and population doubling time

Background: Adipose tissue derived mesenchymal stem cells (AT-MSCs) are relatively easy in isolation procedure compared to bone marrow-derived. Minimally invasive MSC injections need C-arm as guidance that potentially influence the cell viability and doubling time. This study aimsed to determine the effect of C-arm X-ray exposure on AT-MSC viability and population doubling time (PDT).Methods: This experimental study used cryopreserved adipose tissue derived MSCs stored in Stem Cell Medical Technology Integrated Service Unit Cipto Mangunkusumo Hospital. Cells were thawed, propagated, and exposed to varying doses of C-arm X-ray radiation. Stem cell viability was measured, and then the cells were cultured to assess their PDT. Generalized linear models test was used to compare cell viability between post-thaw, post-propagation, post-radiation, post-culture post-radiation, and control and between radiation dose groups. Kruskal-Wallis test assessed PDT between various radiation doses in post-radiation groups. Wilcoxon test was used to assess PDT between pre-radiation and post-radiation groups.Results: Mean confluence period of adipose MSCs post- irradiation was 4.33 days. There was no statistically significant difference in MSC viability after X-ray exposure between pre- and post-irradiation groups (p=0.831). There was no correlation between post-irradiation viability and radiation dose (p=0.138, r=0.503). There were no significant differences in PDT between pre- and post-culture post-irradiation groups and between various radiation doses in post-irradiation groups (p=0.792).  Conclusion: MSC viability and PDT were not influenced by radiation exposure up to 32.34 mgray.

Bone Marrow Stress Decreases Osteogenic Progenitors

Age-related bone loss may be a result of declining levels of stem cells in the bone marrow. Using the Col2.3Δtk (DTK) transgenic mouse, osteoblast depletion was used as a source of marrow stress in order to investigate the effects of aging on osteogenic progenitors which reside in the marrow space. Five-month-old DTK mice were treated with one or two cycles of ganciclovir to conditionally ablate differentiated osteoblasts, whereas controls were saline-treated. Treatment cycles were two weeks in length followed by four weeks of recovery. All animals were sacrificed at 8 months of age; bone marrow stromal cells (BMSCs) were harvested for cell culture and whole bones were excised for bone quality assessment. Colony-forming unit (CFU) assays were conducted to investigate the osteogenic potential of BMSC in vitro, and RNA was extracted to assess the expression of osteoblastic genes. Bone quality assessments included bone histomorphometry, TRAP staining, microcomputed tomography, and biomechanical testing. Osteoblast depletion decreased CFU-F (fibroblast), CFU-ALP (alkaline phosphatase), and CFU-VK (von Kossa) counts and BMSC osteogenic capacity in cell culture. Ex vivo, there were no differences in bone mineral density of vertebrae or femurs between treatment groups. Histology showed a decrease in bone volume and bone connectivity with repeated osteoblast depletion; however, this was accompanied by an increase in bone formation rate. There were no notable differences in osteoclast parameters or observed bone marrow adiposity. We have developed a model that uses bone marrow stress to mimic age-related decrease in osteogenic progenitors. Our data suggest that the number of healthy BMSCs and their osteogenic potential decline with repeated osteoblast depletion. However, activity of the remaining osteoblasts increases to compensate for this loss in progenitor osteogenic potential.

The Effect of OSM on MC3T3-E1 Osteoblastic Cells in Simulated Microgravity with Radiation

Bone deterioration is a challenge in long-term spaceflight with significant connections to patients experiencing disuse bone loss. Prolonged unloading and radiation exposure, defining characteristics of space travel, have both been associated with changes in inflammatory signaling via IL-6 class cytokines in bone. While there is also evidence for perturbed IL-6 class signaling in spaceflight, there has been scant examination of the connections between microgravity, radiation, and inflammatory stimuli in bone. Our lab and others have shown that the IL-6 class cytokine oncostatin M (OSM) is an important regulator of bone remodeling. We hypothesize that simulated microgravity alters osteoblast OSM signaling, contributing to the decoupling of osteolysis and osteogenesis in bone homeostasis. To test this hypothesis, we induced OSM signaling in murine MC3T3-E1 pre-osteoblast cells cultured in modeled microgravity using a rotating wall vessel bioreactor with and without exposure to radiation typical of a solar particle event. We measured effects on inflammatory signaling, osteoblast activity, and mineralization. Results indicated time dependent interactions among all conditions in the regulation of IL-6 production. Furthermore, OSM induced the transcription of OSM receptor ß, IL 6 receptor α subunits, collagen α1(I), osteocalcin, sclerostin, RANKL, and osteoprotegerin. Measurements of osteoid mineralization suggest that the spatial organization of the osteoblast environment is an important consideration in understanding bone formation. Taken together, these results support a role for altered OSM signaling in the mechanism of microgravity-induced bone loss.

DNA-PKcs-SIN1 complexation mediates low-dose X-ray irradiation (LDI)-induced Akt activation and osteoblast differentiation

Low-dose irradiation (LDI) induces osteoblast differentiation, however the underlying mechanisms are not fully understood. In this study, we explored the potential role of DNA-dependent protein kinase catalytic subunit (DNA-PKcs)-Akt signaling in LDI-induced osteoblast differentiation. We confirmed that LDI promoted mouse calvarial osteoblast differentiation, which was detected by increased alkaline phosphatase (ALP) activity as well as mRNA expression of type I collagen (Col I) and runt-related transcription factor 2 (Runx2). In mouse osteoblasts, LDI (1Gy) induced phosphorylation of DNA-PKcs and Akt (mainly at Ser-473). The kinase inhibitors against DNA-PKcs (NU-7026 and NU-7441) or Akt (LY294002, perifosine and MK-2206), as well as partial depletion of DNA-PKcs or Akt1 by targeted-shRNA, dramatically inhibited LDI-induced Akt activation and mouse osteoblast differentiation. Further, siRNA-knockdown of SIN1, a key component of mTOR complex 2 (mTORC2), also inhibited LDI-induced Akt Ser-473 phosphorylation as well as ALP activity increase and Col I/Runx2 expression in mouse osteoblasts. Co-immunoprecipitation (Co-IP) assay results demonstrated that LDI-induced DNA-PKcs-SIN1 complexation, which was inhibited by NU-7441 or SIN1 siRNA-knockdown in mouse osteoblasts. In summary, our data suggest that DNA-PKcs-SIN1 complexation-mediated Akt activation (Ser-473 phosphorylation) is required for mouse osteoblast differentiation.

Low-dose X-ray irradiation promotes osteoblast proliferation, differentiation and fracture healing

Great controversy exists regarding the biologic responses of osteoblasts to X-ray irradiation, and the mechanisms are poorly understood. In this study, the biological effects of low-dose radiation on stimulating osteoblast proliferation, differentiation and fracture healing were identified using in vitro cell culture and in vivo animal studies. First, low-dose (0.5 Gy) X-ray irradiation induced the cell viability and proliferation of MC3T3-E1 cells. However, high-dose (5 Gy) X-ray irradiation inhibited the viability and proliferation of osteoblasts. In addition, dynamic variations in osteoblast differentiation markers, including type I collagen, alkaline phosphatase, Runx2, Osterix and osteocalcin, were observed after both low-dose and high-dose irradiation by Western blot analysis. Second, fracture healing was evaluated via histology and gene expression after single-dose X-ray irradiation, and low-dose X-ray irradiation accelerates fracture healing of closed femoral fractures in rats. In low-dose X-ray irradiated fractures, an increase in proliferating cell nuclear antigen (PCNA)-positive cells, cartilage formation and fracture calluses was observed. In addition, we observed more rapid completion of endochondral and intramembranous ossification, which was accompanied by altered expression of genes involved in bone remodeling and fracture callus mineralization. Although the expression level of several osteoblast differentiation genes was increased in the fracture calluses of high-dose irradiated rats, the callus formation and fracture union were delayed compared with the control and low-dose irradiated fractures. These results reveal beneficial effects of low-dose irradiation, including the stimulation of osteoblast proliferation, differentiation and fracture healing, and highlight its potential translational application in novel therapies against bone-related diseases.

A report from Fukushima: an assessment of bone health in an area affected by the Fukushima nuclear plant incident

Bone health was assessed for inhabitants of an area affected by the Fukushima nuclear plant incident. Osteoporotic patients, who had been treated with active vitamin D3 and/or bisphosphonate at Soma Central Hospital before the Fukushima incident, were enrolled. Changes in bone turnover markers and bone mineral density were retrospectively analyzed. Serum levels of a bone resorption marker, serum type I collagen cross-linked N-telopeptide were decreased in all the treated groups, whereas those of a bone formation marker, bone-specific alkaline phosphatase, were increased. Accordingly, bone mineral density, estimated by dual-energy X-ray absorptiometry, was increased in the lumbar spine of all groups, but bone mass increase in the proximal femur was detected only in the group treated with the two agents in combination. From the degree of these parameter changes, the antiosteoporotic treatments looked effective and were equivalent to the expected potency of past observations. At this stage, the present study implies that the Fukushima nuclear incident did not bring an acute risk to bone health in the affected areas.

High-density lipoprotein nitration and chlorination catalyzed by myeloperoxidase impair its effect of promoting endothelial repair

High-density lipoprotein (HDL) plays a key role in protecting against atherosclerosis. In cardiovascular disease, HDL can be nitrated and chlorinated by myeloperoxidase (MPO). In this study, we discovered that MPO-oxidized HDL is dysfunctional in promoting endothelial repair compared to normal HDL. Proliferation assay, wound healing, and transwell migration experiments showed that MPO-oxidized HDL was associated with a reduced stimulation of endothelial cell (EC) proliferation and migration. In addition, we found that Akt and ERK1/2 phosphorylation in ECs was significantly lower when ECs were incubated with oxidized HDL compared with normal HDL. To further determine whether oxidized HDL diminished EC migration through the PI3K/Akt and MEK/ERK pathways, we performed experiments with inhibitors of both these pathways. The transwell experiments performed in the presence of these inhibitors showed that the migration capacity was reduced and the differences observed between normal HDL and oxidized HDL were diminished. Furthermore, to study the effects of oxidized HDL on endothelial cells in vivo, we performed a carotid artery electric injury model on nude mice injected with either normal or oxidized HDL. Oxidized HDL inhibited reendothelialization compared to normal HDL in vivo. These findings implicate a key role for MPO-oxidized HDL in the pathogenesis of cardiovascular disease.

Diabetic HDL is dysfunctional in stimulating endothelial cell migration and proliferation due to down regulation of SR-BI expression

BACKGROUND

Diabetic HDL had diminished capacity to stimulate endothelial cell (EC) proliferation, migration, and adhesion to extracellular matrix. The mechanism of such dysfunction is poorly understood and we therefore sought to determine the mechanistic features of diabetic HDL dysfunction.

METHODOLOGY/PRINCIPAL FINDINGS

We found that the dysfunction of diabetic HDL on human umbilical vein endothelial cells (HUVECs) was associated with the down regulation of the HDL receptor protein, SR-BI. Akt-phosphorylation in HUVECs was induced in a biphasic manner by normal HDL. While diabetic HDL induced Akt phosphorylation normally after 20 minutes, the phosphorylation observed 24 hours after diabetic HDL treatment was reduced. To determine the role of SR-BI down regulation on diminished EC responses of diabetic HDL, Mouse aortic endothelial cells (MAECs) were isolated from wild type and SR-BI (-/-) mice, and treated with normal and diabetic HDL. The proliferative and migratory effects of normal HDL on wild type MAECs were greatly diminished in SR-BI (-/-) cells. In contrast, response to diabetic HDL was impaired in both types suggesting diminished effectiveness of diabetic HDL on EC proliferation and migration might be due to the down regulation of SR-BI. Additionally, SR-BI down regulation diminishes diabetic HDL's capacity to activate Akt chronically.

CONCLUSIONS/SIGNIFICANCE

Diabetic HDL was dysfunctional in promoting EC proliferation, migration, and adhesion to matrix which was associated with the down-regulation of SR-BI. Additionally, SR-BI down regulation diminishes diabetic HDL's capacity to activate Akt chronically.