Deletion of a Single beta-Catenin Allele in Osteocytes Abolishes the Bone Anabolic Response to Loading

The Wnt/β-catenin signaling pathway is essential for bone cell viability and function and for skeletal integrity. To determine if β-catenin in osteocytes plays a role in the bone anabolic response to mechanical loading, 18- to 24-week-old osteocyte β-catenin haploinsufficient mice (Dmp1-Cre × β-catenin fl/ + ; HET cKO) were compared with their β-catenin fl/fl (control) littermates. Trabecular bone volume (BV/TV) was significantly less (58.3%) in HET cKO females versus controls, whereas male HET cKO and control mice were not significantly different. Trabecular number was significantly less in HET cKO mice compared with controls for both genders, and trabecular separation was greater in female HET cKO mice. Osteoclast surface was significantly greater in female HET cKO mice. Cortical bone parameters in males and females showed subtle or no differences between HET cKO and controls. The right ulnas were loaded in vivo at 100 cycles, 2 Hz, 2500 µϵ, 3 days per week for 3 weeks, and the left ulnas served as nonloaded controls. Calcein and alizarin complexone dihydrate were injected 10 days and 3 days before euthanization, respectively. Micro-computed tomography (µCT) analysis detected an 8.7% and 7.1% increase in cortical thickness in the loaded right ulnas of male and female control mice, respectively, compared with their nonloaded left ulnas. No significant increase in new cortical bone formation was observed in the HET cKO mice. Histomorphometric analysis of control mice showed a significant increase in endocortical and periosteal mineral apposition rate (MAR), bone-formation rate/bone surface (BFR/BS), BFR/BV, and BFR/TV in response to loading, but no significant increases were detected in the loaded HET cKO mice. These data show that deleting a single copy of β-catenin in osteocytes abolishes the anabolic response to loading, that trabecular bone in females is more severely affected and suggest that a critical threshold of β-catenin is required for bone formation in response to mechanical loading

Fatty Acid Excess Increases Lipid Droplet Size and Modifies Gene Expression in Osteocytes

The relationship between obesity and bone remains controversial, although recent studies suggest that obesity can confer an increased risk of osteoporosis resulting in bone fractures in skeletal sites such as the wrist. Osteocytes are the most numerous bone cells functioning as key regulators of bone formation, resorption, and renal phosphate homeostasis; therefore, they likely play an important role in obesity-induced skeletal pathology. Cells exposed to excess free fatty acids (FA) in obesity strive to detoxify the cytotoxic free FA by taking up and storing free FA into lipid droplets (LD). It is unknown how osteocytes respond to FA and how this would affect their functions. In this study, we assessed the effects of FA overload on osteocytes using two cell lines, MLO-Y4 and IDG-SW3. We hypothesized that normal osteocyte energy metabolism is disrupted by excess FA, resulting in increased lipid storage and abnormal osteocyte function. To study this, MLO-Y4 cells were treated with palmitate to induce LD accumulation, and then stained to quantify LD. To determine palmitate’s effects on osteocyte function, we performed qPCR analysis for lipid accumulation genes and osteocyte markers. To examine LD formation in IDG-SW3 mature osteocytes, LipidSpot fluorescent staining was performed; preliminary observations show LD accumulation. Using this in vitro system, MLO-Y4 cells under fatty acid overload demonstrated a greater percent area and size of LDs. RT-qPCR analysis showed an increase in lipid storage genes, Dgat2 (1.5- fold, p<0.001) and Cidec (4-fold, p<0.05). Opg, an inhibitor of osteoclast differentiation, was decreased (0.75-fold, p<0.01), whereas there was no change in Rankl, an inducer of osteoclast differentiation. Dmp1, an early osteocyte marker which plays a role in matrix mineralization, was increased (2-fold, p<0.05). This indicates that FA most likely disrupts osteocyte metabolism through increased lipid storage, which may alter osteocyte function to promote osteoclast activity leading to bone loss

Dynamic microtubules produce an asymmetric E-cadherin-Bazooka complex to maintain segment boundaries.

Distributing junctional components around the cell periphery is key for epithelial tissue morphogenesis and homeostasis. We discovered that positioning of dynamic microtubules controls the asymmetric accumulation of E-cadherin. Microtubules are oriented preferentially along the dorso-ventral axis in Drosophila melanogaster embryonic epidermal cells, and thus more frequently contact E-cadherin at dorso-ventral cell-cell borders. This inhibits RhoGEF2, reducing membrane recruitment of Rho-kinase, and increasing a specific E-cadherin pool that is mobile when assayed by fluorescence recovery after photobleaching. This mobile E-cadherin is complexed with Bazooka/Par-3, which in turn is required for normal levels of mobile E-cadherin. Mobile E-cadherin-Bazooka prevents formation of multicellular rosette structures and cell motility across the segment border in Drosophila embryos. Altogether, the combined action of dynamic microtubules and Rho signaling determines the level and asymmetric distribution of a mobile E-cadherin-Bazooka complex, which regulates cell behavior during the generation of a patterned epithelium

Soft X-ray absorption spectroscopy study of spin crossover Fe-compounds: Persistent high spin configurations under soft X-ray irradiation

Metal-organic complex exhibiting spin crossover (SCO) behavior has drawn attention for its functionality as a nanoscale spin switch. The spin states in the metal ions can be tuned by external stimuli such as temperature or light. This article demonstrates a soft X-ray?induced excited spin state trapping (SOXEISST) effect in Hofmann-like SCO coordination polymers of FeII (4-methylpyrimidine)2 [Au(CN)2 ]2 and FeII (pyridine)2 [Ni(CN)4 ]. A soft X-ray absorption spectroscopy (XAS) study on these polymers showed that the high spin configuration (HS; S = 2) was prevalent in Fe2+ ions during the measurement even at temperatures much lower than the critical temperatures (>170 K), manifesting HS trapping due to the X-ray irradiation. This is in strong contrast to the normal SCO behavior observed in FeII (1,10-phenanthroline)2 (NCS)2, implying that the structure of the ligand chains in the polymers with relatively loose Fe-N coordination might allow a structural adaptation to stabilize the metastable HS state under the soft X-ray irradiation. (C) 2018 by the authors. Licensee MDPI, Basel, Switzerlan

Simulated interventions to ameliorate age-related bone loss indicate the importance of timing

Bone remodeling is the continuous process of bone resorption by osteoclasts and bone formation by osteoblasts, in order to maintain homeostasis. The activity of osteoclasts and osteoblasts is regulated by a network of signaling pathways, including Wnt, parathyroid hormone (PTH), RANKL/OPG and TGF-β, in response to stimuli such as mechanical loading. During aging there is a gradual loss of bone mass due to dysregulation of signaling pathways. This may be due to a decline in physical activity with age and/or changes in hormones and other signaling molecules. In particular, hormones such as PTH have a circadian rhythm which may be disrupted in aging. Due to the complexity of the molecular and cellular networks involved in bone remodeling, several mathematical models have been proposed to aid understanding of the processes involved. However, to date there are no models which explicitly consider the effects of mechanical loading, the circadian rhythm of PTH and the dynamics of signaling molecules on bone remodeling. Therefore, we have constructed a network model of the system using a modular approach which will allow further modifications as required in future research. The model was used to simulate the effects of mechanical loading and also the effects of different interventions such as continuous or intermittent administration of PTH. Our model predicts that the absence of regular mechanical loading and/or an impaired PTH circadian rhythm leads to a gradual decrease in bone mass over time which can be restored by simulated interventions and that the effectiveness of some interventions may depend on their timing

Taurine, an osteocyte metabolite, protects against oxidative stress-induced cell death and decreases inhibitors of the Wnt/β-catenin signaling pathway

Taurine has been shown to have positive effects on bone mass, which are thought to be due in part to its cytoprotective effects on osteoblasts and here we show that taurine also protects osteocytes against cell death due to reactive oxygen species. Using the IDG-SW3 cell line, the expression of the taurine uptake transporter Taut/Slc6a6 is increased during osteoblast to osteocyte differentiation. Taurine had no effect on genes associated with osteoblast to osteocyte differentiation such as Dmp1, Phex or osteocalcin, even at high doses, but a slight yet significant inhibition of alkaline phosphatase was observed at the highest dose (50 mM). No effect was seen on the osteoclast regulatory genes Rankl and Opg, however the wnt antagonist Sost/sclerostin was potently and dose-dependently downregulated in response to taurine supplementation. Taurine also significantly inhibited Dkk1 mRNA expression, but only at 50 mM. Interestingly, osteocytes were found to also be able to synthesize taurine intracellularly, potentially as a self-protective mechanism, but do not secrete the metabolite. A highly significant increase in the expression of cysteine dioxygenase (Cdo), a key enzyme necessary for the production of taurine, was observed with osteoblast to osteocyte differentiation along with a decrease in methionine, the precursor of taurine. For the first time, we describe the synthesis of taurine by osteocytes, potentially to preserve viability and to regulate bone formation through inhibition of sclerostin

ACVR2B/Fc counteracts chemotherapy-induced loss of muscle and bone mass

Chemotherapy promotes the development of cachexia, a debilitating condition characterized by muscle and fat loss. ACVR2B/Fc, an inhibitor of the Activin Receptor 2B signaling, has been shown to preserve muscle mass and prolong survival in tumor hosts, and to increase bone mass in models of osteogenesis imperfecta and muscular dystrophy. We compared the effects of ACVR2B/Fc on muscle and bone mass in mice exposed to Folfiri. In addition to impairing muscle mass and function, Folfiri had severe negative effects on bone, as shown by reduced trabecular bone volume fraction (BV/TV), thickness (Tb.Th), number (Tb.N), connectivity density (Conn.Dn), and by increased separation (Tb.Sp) in trabecular bone of the femur and vertebra. ACVR2B/Fc prevented the loss of muscle mass and strength, and the loss of trabecular bone in femurs and vertebrae following Folfiri administration. Neither Folfiri nor ACVR2B/Fc had effects on femoral cortical bone, as shown by unchanged cortical bone volume fraction (Ct.BV/TV), thickness (Ct.Th) and porosity. Our results suggest that Folfiri is responsible for concomitant muscle and bone degeneration, and that ACVR2B/Fc prevents these derangements. Future studies are required to determine if the same protective effects are observed in combination with other anticancer regimens or in the presence of cancer

Perinatal Opioid Exposure Primes the Peripheral Immune System Toward Hyperreactivity

The increased incidence of opioid use during pregnancy warrants investigation to reveal the impact of opioid exposure on the developing fetus. Exposure during critical periods of development could have enduring consequences for affected individuals. Particularly, evidence is mounting that developmental injury can result in immune priming, whereby subsequent immune activation elicits an exaggerated immune response. This maladaptive hypersensitivity to immune challenge perpetuates dysregulated inflammatory signaling and poor health outcomes. Utilizing an established preclinical rat model of perinatal methadone exposure, we sought to investigate the consequences of developmental opioid exposure o

Abnormal urinalysis on day 7 in patients with IgA vasculitis (Henoch–Schönlein purpura)

2016-11Rare progression to renal failure imposes a burden on children with IgA vasculitis (Henoch–Schönlein purpura, HSP). An abnormal urinalysis on day 7 (7d-UA) may be a surrogate marker for persistent nephritis, but this has not been established. We retrospectively analyzed the risk factors for persistent nephritis in a cohort of 138 children. Of 35 children with abnormal 7d-UA, 24 (69%) had an abnormal urinalysis 6 months after the diagnosis of HSP, which was significantly more than 6 of 103 children (6%) with normal 7d-UA (P < 0.0001). The negative predictive values for normal urinalysis and negative proteinuria 6 months after diagnosis were 0.94 (95% confidence interval [CI], 0.90–0.97) and 0.98 (95% CI, 0.95–0.99), respectively. When children with abnormal urinalysis 6 months after diagnosis were compared with those without, the following factors were significantly associated: age at diagnosis, abnormal urinalysis at diagnosis, abnormal 7d-UA, complement C3, steroid treatment, and presence of abdominal pain. However, multivariate analysis revealed that abnormal 7d-UA was the only significant risk factor for abnormal urinalysis 6 months after diagnosis (odds ratio 54.3, 95% CI 15.3–275, P=1.89 × 10^−6). Abnormal 7d-UA may be an independent risk factor for persistent nephritis, but this should be confirmed in a prospective study.departmental bulletin pape