Osteoblast Survival Research Articles

Enhancing osteoblast survival through pulsed electrical stimulation and implications for osseointegration

Electrical stimulation has been suggested as a means for promoting the direct structural and functional bonding of bone tissue to an artificial implant, known as osseointegration. Previous work has investigated the impact of electrical stimulation in different models, both in vitro and in vivo, using various electrode configurations for inducing an electric field with a wide range of stimulation parameters. However, there is no consensus on optimal electrode configuration nor stimulation parameters. Here, we investigated a novel approach of delivering electrical stimulation to a titanium implant using parameters clinically tested in a different application, namely peripheral nerve stimulation. We propose an in vitro model comprising of Ti6Al4V implants precultured with MC3T3-E1 preosteoblasts, stimulated for 72 h at two different pulse amplitudes (10 µA and 20 µA) and at two different frequencies (50 Hz and 100 Hz). We found that asymmetric charge-balanced pulsed electrical stimulation improved cell survival and collagen production in a dose-dependent manner. Our findings suggest that pulsed electrical stimulation with characteristics similar to peripheral nerve stimulation has the potential to improve cell survival and may provide a promising approach to improve peri-implant bone healing, particularly to neuromusculoskeletal interfaces in which implanted electrodes are readily available.

Bone Regeneration Using MMP-Cleavable Peptides-Based Hydrogels.

Accumulating evidence has suggested the significant potential of chemically modified hydrogels in bone regeneration. Despite the progress of bioactive hydrogels with different materials, structures and loading cargoes, the desires from clinical applications have not been fully validated. Multiple biological behaviors are orchestrated precisely during the bone regeneration process, including bone marrow mesenchymal stem cells (BMSCs) recruitment, osteogenic differentiation, matrix calcification and well-organized remodeling. Since matrix metalloproteinases play critical roles in such bone metabolism processes as BMSC commitment, osteoblast survival, osteoclast activation matrix calcification and microstructure remodeling, matrix metalloproteinase (MMP) cleavable peptides-based hydrogels could respond to various MMP levels and, thus, accelerate bone regeneration. In this review, we focused on the MMP-cleavable peptides, polymers, functional modification and crosslinked reactions. Applications, perspectives and limitations of MMP-cleavable peptides-based hydrogels for bone regeneration were then discussed.

Fabrication, characterization, and optimization of a novel copper-incorporated chitosan/gelatin-based scaffold for bone tissue engineering applications.

Introduction: Fabricating composite scaffolds with improved physicochemical properties as artificial microenvironments are of great interest in bone tissue engineering. Given advantageous properties of nano-hydroxyapatite/chitosan/gelatin (nHA/Cs/Gel) scaffolds, the present study aimed to synthesize a modified nHA/Cs/Gel biomimetic scaffold with improved features. Methods: Pure and copper (Cu)-substituted nHA was synthesized using the chemical precipitation method under controlled pH and temperature. Pure and Cu-substituted nHA/Cs/Gel scaffolds were fabricated by salt-leaching/freeze-drying method. Physicochemical characteristics of nanoparticles and scaffolds were explored using XRD, FTIR, FE-SEM/EDX, and ICP. Besides, scaffold mechanical strength, degradation, porosity, swelling, biomineralization, and cytocompatibility were assessed. Results: Pure and Cu-substituted nHA were synthesized and characterized with appropriate Cu substitution and improved physical properties. All scaffolds were highly porous (porosity > 98%) and Cu incorporation reduced porosity from 99.555 ± 0.394% to 98.69 ± 0.80% while enlarged the pore size to more than100 µm. Cu-substitution improved the scaffold mechanical strength and the best result was observed in nHA.Cu5%/Cs/Gel scaffolds by the compressive strength 88.869 ± 19.574 MPa. Furthermore, 3% and 5% Cu-substituted nHA enhanced the scaffold structural stability and supported osteoblast spread, adhesion, survival, mineralization, and proliferation. Moreover, long-term and sustainable Cu release from scaffolds was observed within 28 days. Conclusion: Cu-substituted nHA/Cs/Gel scaffolds mimic the porous structure and mechanical strength of cancellous bone, along with prolonged degradation and Cu release, osteoblast attachment, viability, calcium deposition, and proliferation. Taken together, our results indicate the upgraded properties of nHA.Cu5%/Cs/Gel scaffolds for future applications in bone tissue engineering.

Possible Protective Role of Deferoxamine in Ameliorating Osteoporosis in a Rat Model of Liver Cirrhosis via Iron Metabolism Regulation

Abstract Background Liver cirrhosis is considered the terminal stage of many hepatic diseases of different etiologies. Liver cirrhosis was associated with increased incidence rates of some extrahepatic manifestations such as osteoporosis. Regardless of the liver disease etiology, the presence of cirrhosis implies a twofold risk of bone fractures higher than non-cirrhotic patients. The liver is the main storage depot for iron and is the primary organ that is responsible for clearing excess iron in conditions of iron overload. When the iron storage and antioxidant capacity of the liver is overwhelmed, iron overload can lead to marked oxidantmediated liver and bone injury and iron overload was a risk factor for osteoporosis via affecting osteoblast survival. Aim of the work to examine the possible protective effect of Deferoxamine (DFO) on liver cirrhosis rat model induced osteoporosis. Material and Method rats was divided into 4 groups Animal Groups: Naïve control, DFO-treated group, TAA-treated group received Thioacetamide (TAA) ip (200 mg/kg/rat) twice weekly for 12 weeks, TAA+DFO treated group received TAA intra-peritoneal in addition to DFO intraperitoneal injections (300 mg/kg/3 times/week, for the last 4 weeks of TAA injections. Results and Conclusion Deferoxamine produced significant improvement in bone mineralization alongside its significant effect on liver function test in a rat model of liver cirrhosis induced osteoporosis.

A Neuroprotective Bovine Colostrum Attenuates Apoptosis in Dexamethasone-Treated MC3T3-E1 Osteoblastic Cells.

Glucocorticoid-induced osteoporosis (GIO) is one of the most common secondary forms of osteoporosis. GIO is partially due to the apoptosis of osteoblasts and osteocytes. In addition, high doses of dexamethasone (DEX), a synthetic glucocorticoid receptor agonist, induces neurodegeneration by initiating inflammatory processes leading to neural apoptosis. Here, a neuroprotective bovine colostrum against glucocorticoid-induced neuronal damage was investigated for its anti-apoptotic activity in glucocorticoid-treated MC3T3-E1 osteoblastic cells. A model of apoptotic osteoblastic cells was developed by exposing MC3T3-E1 cells to DEX (0–700 μM). Colostrum co-treated with DEX was executed at 0.1–5.0 mg/mL. Cell viability was measured for all treatment schedules. Caspase-3 activation was assessed to determine both osteoblast apoptosis under DEX exposure and its potential prevention by colostrum co-treatment. Glutathione reduced (GSH) was measured to determine whether DEX-mediated oxidative stress-driven apoptosis is alleviated by colostrum co-treatment. Western blot was performed to determine the levels of p-ERK1/2, Bcl-XL, Bax, and Hsp70 proteins upon DEX or DEX plus colostrum exposure. Colostrum prevented the decrease in cell viability and the increase in caspase-3 activation and oxidative stress caused by DEX exposure. Cells, upon colostrum co-treated with DEX, exhibited higher levels of p-ERK1/2 and lower levels of Bcl-XL, Bax, and Hsp70. Our data support the notion that colostrum may be able to reduce DEX-induced apoptosis possibly via the activation of the ERK pathway and modulation of the Hsp70 system. We provided preliminary evidence on how bovine colostrum, as a complex and multi-component dairy product, in addition to its neuroprotective action, may affect osteoblastic cell survival undergoing apoptosis.

E3 Ubiquitin Ligase-Mediated Regulation of Osteoblast Differentiation and Bone Formation.

The ubiquitin–proteasome system (UPS) is an essential pathway that regulates the homeostasis and function of intracellular proteins and is a crucial protein-degradation system in osteoblast differentiation and bone formation. Abnormal regulation of ubiquitination leads to osteoblast differentiation disorders, interfering with bone formation and ultimately leading to osteoporosis. E3 ubiquitin ligases (E3) promote addition of a ubiquitin moiety to substrate proteins, specifically recognizing the substrate and modulating tyrosine kinase receptors, signaling proteins, and transcription factors involved in the regulation of osteoblast proliferation, differentiation, survival, and bone formation. In this review, we summarize current progress in the understanding of the function and regulatory effects of E3 ligases on the transcription factors and signaling pathways that regulate osteoblast differentiation and bone formation. A deep understanding of E3 ligase-mediated regulation of osteoblast differentiation provides a scientific rationale for the discovery and development of novel E3-targeting therapeutic strategies for osteoporosis.

Defects of cohesin loader lead to bone dysplasia associated with transcriptional disturbance.

Cohesin loader nipped-B-like protein (Nipbl) is increasingly recognized for its important role in development and cancer. Cornelia de Lange Syndrome (CdLS), mostly caused by heterozygous mutations of Nipbl, is an autosomal dominant disease characterized by multiorgan malformations. However, the regulatory role and underlying mechanism of Nipbl in skeletal development remain largely elusive. In this study, we constructed a Nipbl-a Cas9-knockout (KO) zebrafish, which displayed severe retardation of global growth and skeletal development. Deficiency of Nipbl remarkably compromised cell growth and survival, and osteogenic differentiation of mammalian osteoblast precursors. Furthermore, Nipbl depletion impaired the cell cycle process, and caused DNA damage accumulation and cellular senescence. In addition, nucleolar fibrillarin expression, global rRNA biogenesis, and protein translation were defective in the Nipbl-depleted osteoblast precursors. Interestingly, an integrated stress responseinhibitor (ISRIB), partially rescued Nipbl depletion-induced cellular defects in proliferation and apoptosis, osteogenesis, and nucleolar function. Simultaneously, we performed transcriptome analysis of Nipbl deficiency on human neural crest cells and mouse embryonic fibroblasts in combination withNipbl ChIP-Seq. We found that Nipbl deficiency caused thousands of differentially expressed genes including some important genes in bone and cartilage development. In conclusion, Nipbl deficiency compromised skeleton development through impairing osteoblast precursor cell proliferation and survival, and osteogenic differentiation, and also disturbing the expression of some osteogenesis-regulatory genes. Our study elucidated that Nipbl played a pivotal role in skeleton development, and supported the fact that treatment of ISRIB may provide an early intervention strategy to alleviate the bone dysplasia of CdLS.

Strontium gluconate potently promotes osteoblast development and restores bone formation in glucocorticoid-induced osteoporosis rats

Glucocorticoid-induced osteoporosis (GIOP) has emerged as a challenge after long-term glucocorticoid administration during the clinical therapy of diverse diseases. Although some candidates for GIOP treatment have been explored, there is still a lack of reliable drugs for GIOP prevention. In this study, rat bone marrow stem cells (rBMSCs) were utilized to investigate the feasibility of applying strontium gluconate (GluSr), which displays mild activity, easy absorption and good biocompatibility, for GIOP prevention. Thirty-two SD rats were divided into 4 groups to explore the effects of GluSr on osteoporosis rescue in vivo. Our results suggested that GluSr markedly alleviated dexamethasone (DEX)-induced apoptosis of osteoblast precursor cells and rBMSCs and enhanced rBMSC osteogenesis differentiation in vitro. GluSr also effectively promoted osteoblast survival, inhibited osteoclast differentiation and restored bone formation in GIOP rat models. Microarray analysis of the femora from GIOP rats treated with GluSr revealed that the signalling pathways of the glucocorticoid receptor (GR), oestrogen receptor gene (ESR) and vitamin D receptor (VDR) were involved in bone restoration by GluSr. In summary, our study proved that GluSr enhanced osteoblast differentiation and suppressed osteoclast activity both in vitro and in vivo. GluSr might function as a novel strontium reagent for GIOP prevention.

Phenanthrenoid Coelogin Isolated from Coelogyne cristata Exerts Osteoprotective Effect Through MAPK-Mitogen-Activated Protein Kinase Signaling Pathway.

Osteoporosis is a major health problem in postmenopausal women globally. This study determined the mechanism through which coelogin stimulates osteoblastogenesis and its osteoprotective and bone regenerating potential. Coelogin effect on primary calvarial osteoblast cells was determined by measuring alkaline phosphatase activity, mineralization, osteoblast survival, and apoptosis and protein expression studies. The osteoprotective effect of coelogin was also evaluated on osteopenic adult female Swiss mice. At autopsy, bones were collected for dynamic and histomorphometry studies. Serum samples were also collected for assessment of serum parameters. Coelogin treatment led to increased osteoblast proliferation, survival, differentiation, and mineralization in osteoblast cells. Coelogin supplementation to Ovx mice promoted new bone formation, prevented Ovx-induced deterioration of bone microarchitecture, and enhanced bone regeneration. In addition, signaling studies revealed that coelogin treatment activates the ER-Erk and Akt-dependent signaling pathways which stimulate the osteoblastogenesis in osteoblast cells.

Diabetic oxidative stress and bone loss complications

Diabetes mellitus is a group of metabolic disorder characterize by and absolute or partial insulin deficiency. Diabetic hyperglycemia is produce by the effect of homeostasis between proteolytic enzymes, their inhibitors and the antioxidants defense that protect and repair vital tissues and molecular components. Bone consist of both component and trabecular bone tissue. Organic matrix and albumin form part of noncollagenous of bone .Initiation of mineralization and collagen fibrils form the phase of mineral matrix. Calcium flux into and out of bone depend of osteoclastic and osteoblastic activity. The remodeling is initiated by resorption and new bone formation at the resorption site. Diabetic complication is a critical factor for bone pathology and could start early inflammatory stage even before hyperglycemia. Diabetic produces bone loss from reduce osteoblast activity. Partly insulin deficiency produce defective bone remodeling indirect by oxidative stress. The current treatment for defective bone in diabetes state include biophosphonate and cinaciguat. Biphosphonate inhibit bone resorption, but may worsen bone quality. A novel type of activation of sGMP is cinaciguat an NO independent activator of oxidative GC, increase c GMP synthesis on diabetic and restore proliferation and survival of osteoblasts. Chronic hyperglycemia interferes with the oseointegration of implants in diabetics. Both diabetic and aging plays a role in abnormal differentiation of osteroblasts. In diabetic patients may improve the oral health to have a positive impact if optimal glycemic control is emphasized. However with cinaciguat present as a novel paradigm enhancing bone formation under hyperglycemia and protect bone implants.

Genotypic Analyses of the Sclerostin rs851056 and Dickkopf rs1569198 Polymorphisms in Mexican-Mestizo Postmenopausal Osteoporosis: A Case-Control Study.

Background: The Wnt/β catenin pathway promotes bone mineralization stimulating proliferation, differentiation, and survival of osteoblasts; it also inhibits osteoclast differentiation and osteocyte activity. Sclerostin (SOST) and Dickkopf 1 (DKK1) are Wnt/β catenin pathway inhibitors. Genetic variability in the expression of SOST and DKK1 might be involved in the development of postmenopausal osteoporosis (OP). Aim: To determine whether the SOST rs851056 and DKK1 rs1569198 polymorphisms are associated with OP in Mexican-Mestizo postmenopausal women. Materials and Methods: Two hundred and eighty Mexican-Mestizo postmenopausal women were assessed for their bone mineral density by dual-energy X-ray absorptiometry (DXA). Patients were classified as OP or non-OP. Genomic DNA was extracted from peripheral blood leukocytes. Genetic polymorphisms were analyzed by quantitative polymerase chain reaction using TaqMan probes. Results: The frequency of OP was 40% among the study population. Osteoporotic patients were older (p < 0.001), had a higher frequency of smoking (p = 0.01), and lower body mass index (p < 0.001) compared with the non-osteoporotic patients. The genotypic frequencies of the rs851056 locus of the SOST gene were GG 19%, GC 45%, and CC 35%, whereas the genotypic frequencies of the rs1569198 locus of the DKK1 gene were GG 15%, GA 40%, and AA 44%. In relation to rs851056 locus of the SOST gene, no differences were observed between the OP and non-OP cohorts in the frequencies of the GC polymorphism (48.7% vs. 43.1%). Similarly, analyses of the DKK1 rs1569198 does not demonstrate differences in the GA genotypic frequencies between the OP and non-OP cohorts (42.5% vs. 38.9%). Conclusion: Polymorphisms SOST rs851056 and DKK1 rs1569198 polymorphisms are not associated with OP in Mexican-Mestizo postmenopausal women.

Sclerostin inhibition: A novel target for the treatment of postmenopausal osteoporosis

Osteoporosis, a widespread skeletal disorder with a substantial economic load, is characterized by increased porosity of the bones resulting in vulnerability to fractures. When activated, the canonical Wnt signaling pathway results in osteoblastogenesis and bone formation. A Wnt ligand forms a complex with low-density lipoprotein receptor-related proteins 5 and 6 (Lrp5/6) and stimulates intracellular signaling cascades, leading to nuclear translocation of β-catenin and transcription of downstream molecules involved in osteoblast differentiation, maturation, and survival. Sclerostin (SOST), a glycoprotein produced by osteocytes, is an extracellular Wnt antagonist that blocks the binding of Wnt ligands to Lrp5/6, preventing the activation of the pathway and osteoblast-mediated bone formation subsequently. Inhibition of SOST represents a new therapeutic paradigm for the treatment of osteoporosis. Monoclonal antibodies to SOST include romosozumab, blosozumab, and setrusumab. With its unique dual effect of increasing bone formation (anabolic action) and decreasing bone resorption, the Food and Drug Administration approved romosozumab, a promising new treatment for postmenopausal osteoporosis. Its efficacy and safety have been established in trials. However, patients at high risk of cardiovascular or cerebrovascular events should not be prescribed romosozumab.

Apelin-13 induces mitophagy in bone marrow mesenchymal stem cells to suppress intracellular oxidative stress and ameliorate osteoporosis by activation of AMPK signaling pathway

Osteoporosis is characterized by impaired bone metabolism. Current estimates show that it affects millions of people worldwide and causes a serious socioeconomic burden. Mitophagy plays key roles in bone marrow mesenchymal stem cells (BMSCs) osteoblastic differentiation, mineralization, and survival. Apelin is an endogenous adipokine that participates in bone homeostasis. This study was performed to determine the role of Apelin in the osteoporosis process and whether it affects mitophagy, survival, and osteogenic capacity of BMSCs in in vitro and in vivo models of osteoporosis. Our results demonstrated that Apelin was down-regulated in ovariectomized-induced osteoporosis rats and Apelin-13 treatment activated mitophagy in BMSCs, ameliorating oxidative stress and thereby reviving osteogenic function via AMPK-α phosphorylation. Besides, Apelin-13 administration restored bone mass and microstructure as well as reinstated mitophagy, enhanced osteogenic function in OVX rats. Collectively, our findings reveal the intrinsic mechanisms underlying Apelin-13 regulation in BMSCs and its potential therapeutic values in the treatment of osteoporosis.

Effects of inhibiting PDK‑1 expression in bone marrow mesenchymal stem cells on osteoblast differentiation invitro.

Osteoblasts are the main functional cells in bone formation, which are responsible for the synthesis, secretion and mineralization of bone matrix. The PI3K/AKT signaling pathway is strongly associated with the differentiation and survival of osteoblasts. The 3-phosphoinositide-dependent protein kinase-1 (PDK-1) protein is considered the master upstream lipid kinase of the PI3K/AKT cascade. The present study aimed to investigate the role of PDK-1 in the process of mouse osteoblast differentiation in vitro. In the BX-912 group, BX-912, a specific inhibitor of PDK-1, was added to osteoblast induction medium (OBM) to treat bone marrow mesenchymal stem cells (BMSCs), whereas the control group was treated with OBM alone. Homozygote PDK1flox/flox mice were designed and generated, and were used to obtain BMSCsPDK1flox/flox. Subsequently, an adenovirus containing Cre recombinase enzyme (pHBAd-cre-EGFP) was used to disrupt the PDK-1 gene in BMSCsPDK1flox/flox; this served as the pHBAd-cre-EGFP group and the efficiency of the disruption was verified. Western blot analysis demonstrated that the protein expression levels of phosphorylated (p)-PDK1 and p-AKT were gradually increased during the osteoblast differentiation process. Notably, BX-912 treatment and disruption of the PDK-1 gene with pHBAd-cre-EGFP effectively reduced the number of alkaline phosphatase (ALP)-positive cells and the optical density value of ALP activity, as well as the formation of cell mineralization. The mRNA expression levels of PDK-1 in the pHBAd-cre-EGFP group were significantly downregulated compared with those in the empty vector virus group on days 3–7. The mRNA expression levels of the osteoblast-related genes RUNX2, osteocalcin and collagen I were significantly decreased in the BX-912 and pHBAd-cre-EGFP groups on days 7 and 21 compared with those in the control and empty vector virus groups. Overall, the results indicated that BX-912 and disruption of the PDK-1 gene in vitro significantly inhibited the differentiation and maturation of osteoblasts. These experimental results provided an experimental and theoretical basis for the role of PDK-1 in osteoblasts.

Protein Kinase G2 Is Essential for Skeletal Homeostasis and Adaptation to Mechanical Loading in Male but Not Female Mice.

We previously showed that the NO/cGMP/protein kinase G (PKG) signaling pathway positively regulates osteoblast proliferation, differentiation, and survival in vitro, and that cGMP-elevating agents have bone-anabolic effects in mice. Here, we generated mice with an osteoblast-specific (OB) knockout (KO) of type 2 PKG (gene name Prkg2) using a Col1a1(2.3 kb)-Cre driver. Compared to wild type (WT) littermates, 8-week-old male OB Prkg2-KO mice had fewer osteoblasts, reduced bone formation rates, and lower trabecular and cortical bone volumes. Female OB Prkg2-KO littermates showed no bone abnormalities, despite the same degree of PKG2 deficiency in bone. Expression of osteoblast differentiation- and Wnt/β-catenin-related genes was lower in primary osteoblasts and bones of male KO but not female KO mice compared to WT littermates. Osteoclast parameters were unaffected in both sexes. Since PKG2 is part of a mechano-sensitive complex in osteoblast membranes, we examined its role during mechanical loading. Cyclical compression of the tibia increased cortical thickness and induced mechanosensitive and Wnt/β-catenin-related genes to a similar extent in male and female WT mice and female OB Prkg2-KO mice, but loading had a minimal effect in male KO mice. We conclude that PKG2 drives bone acquisition and adaptation to mechanical loading via the Wnt/β-catenin pathway in male mice. The striking sexual dimorphism of OB Prkg2-KO mice suggests that current U.S. Food and Drug Administration-approved cGMP-elevating agents may represent novel effective treatment options for male osteoporosis. © 2022 American Society for Bone and Mineral Research (ASBMR).

Osteoprotective Roles of Green Tea Catechins.

Osteoporosis is the second most common disease only secondary to cardiovascular disease, with the risk of fracture increasing with age. Osteoporosis is caused by an imbalance between osteoblastogenesis and osteoclastogenesis processes. Osteoclastogenesis may be enhanced, osteoblastogenesis may be reduced, or both may be evident. Inflammation and high reactive oxygen enhance osteoclastogenesis while reducing osteoblastogenesis by inducing osteoblast apoptosis and suppressing osteoblastic proliferation and differentiation. Catechins, the main polyphenols found in green tea with potent anti-oxidant and anti-inflammatory properties, can counteract the deleterious effects of the imbalance of osteoblastogenesis and osteoclastogenesis caused by osteoporosis. Green tea catechins can attenuate osteoclastogenesis by enhancing apoptosis of osteoclasts, hampering osteoclastogenesis, and prohibiting bone resorption in vitro. Catechin effects can be directly exerted on pre-osteoclasts/osteoclasts or indirectly exerted via the modulation of mesenchymal stem cells (MSCs)/stromal cell regulation of pre-osteoclasts through activation of the nuclear factor kB (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG) system. Catechins also can enhance osteoblastogenesis by enhancing osteogenic differentiation of MSCs and increasing osteoblastic survival, proliferation, differentiation, and mineralization. The in vitro effects of catechins on osteogenesis have been confirmed in several animal models, as well as in epidemiological observational studies on human subjects. Even though randomized control trials have not shown that catechins provide anti-fracture efficacy, safety data in the trials are promising. A large-scale, placebo-controlled, long-term randomized trial with a tea regimen intervention of optimal duration is required to determine anti-fracture efficacy.

Osteoblast-Osteoclast Communication and Bone Homeostasis.

Bone remodeling is tightly regulated by a cross-talk between bone-forming osteoblasts and bone-resorbing osteoclasts. Osteoblasts and osteoclasts communicate with each other to regulate cellular behavior, survival and differentiation through direct cell-to-cell contact or through secretory proteins. A direct interaction between osteoblasts and osteoclasts allows bidirectional transduction of activation signals through EFNB2-EPHB4, FASL-FAS or SEMA3A-NRP1, regulating differentiation and survival of osteoblasts or osteoclasts. Alternatively, osteoblasts produce a range of different secretory molecules, including M-CSF, RANKL/OPG, WNT5A, and WNT16, that promote or suppress osteoclast differentiation and development. Osteoclasts also influence osteoblast formation and differentiation through secretion of soluble factors, including S1P, SEMA4D, CTHRC1 and C3. Here we review the current knowledge regarding membrane bound- and soluble factors governing cross-talk between osteoblasts and osteoclasts.

Ovotransferrin Exhibits Osteogenic Activity Partially via Low-Density Lipoprotein Receptor-Related Protein 1 (LRP1) Activation in MC3T3-E1 Cells.

Ovotransferrin, a major protein in egg white, induces osteoblast proliferation and survival in vitro. However, it is unclear which receptor(s) drive the beneficial activities of this bioactive glycoprotein. We examined the role of the low-density lipoprotein receptor-related protein 1 (LRP1) in the actions of ovotransferrin on osteoblasts. Here, we showed that LRP1 in part regulates osteogenic action of ovotransferrin. Mouse osteoblasts, MC3T3-E1, with LRP1 deletion displayed diminished osteogenic activity. Our findings indicate that the bone-stimulatory impact of ovotransferrin on RUNX2, COL1A2, and Ca2+ signaling is LRP1-dependent. This shows that LRP1 not only acts as a scavenger receptor but also participates in ovotransferrin-mediated gene transcription. However, some of the key bone formatting factors such as ALP synthesis and serine residue phosphorylation of Akt by ovotransferrin remained independent of LRP1. Overall, this study shows that LRP1-ovotransferrin interaction might underline in part the ability of ovotransferrin to promote bone formation.

Vitamin K2 Can Rescue the Dexamethasone-Induced Downregulation of Osteoblast Autophagy and Mitophagy Thereby Restoring Osteoblast Function In Vitro and In Vivo.

Chronic long-term glucocorticoids (GC) use is associated with glucocorticoid-induced osteoporosis (GIOP) by inhibiting the survival and impairing the functions of osteoblasts. Autophagy and mitophagy play key roles in osteoblast differentiation, mineralization and survival, and mounting evidence have implicated osteoblast autophagy and mitophagy as a novel mechanism in the pathogenesis of GIOP. Vitamin K2 (VK2) is an essential nutrient supplement that have been shown to exert protective effects against osteoporotic bone loss including GIOP. In this study, we showed that the glucocorticoid dexamethasone (Dex) deregulated osteoblast autophagy and mitophagy by downregulating the expression of autophagic and mitophagic markers LC3-II, PINK1, Parkin. This consequently led to inhibition of osteoblast differentiation and mineralization function in vitro. Interestingly, co-treatment with VK2 significantly attenuated the Dex-induced downregulation of LC3-II, PINK1, Parkin, thereby restoring autophagic and mitophagic processes and normal osteoblastic activity. In addition, using an established rat model of GIOP, we showed that VK2 administration can protect rats against the deleterious effects of Dex on bone by reinstating autophagic and mitophagic activities in bone tissues. Collectively, our results provide new insights into the role of osteoblast autophagy and mitophagy in GIOP. Additionally, the use of VK2 supplementation to augment osteoblast autophagy/mitophagy may significantly improve clinical outcomes of GIOP patients.

Bone defect reconstruction with a novel biomaterial containing calcium phosphate and aluminum oxide reinforcement

BackgroundReconstruction of metaphyseal fractures represents a clinical challenge for orthopedic surgeons. Especially in osteoporotic bone, these fractures are frequently accompanied by osseous substance defects. In order to ensure rapid mobilization of patients, high stability requirements must be met by osteosynthesis. Various bone graft materials have been introduced in the past, such as autologous bone or exogenous bone substitute materials. These are used as bone void fillers or as augmentation techniques to ensure safe fixation of osteosynthesis. New calcium phosphate-based bone void-filling materials could be a promising alternative to autologous bone or to the currently and widely used polymethylmethacrylate (PMMA)-based cement. The aim of this study was to evaluate a novel paste-like bone void filler in vivo and in vitro with regard to biocompatibility and osteoconductivity.MethodsIn addition to in vitro testing of cell compatibility using pre-osteoblasts (MC3T3-E1), 35 Wistar rats were treated in vivo with implantation of various material mixtures based on calcium phosphate and aluminum oxide reinforcement in a metaphyseal drill hole defect. After 4 weeks, an examination by micro-computed tomography (μCT) and histology was performed.ResultsThe in vitro analysis showed good biocompatibility with a high cell survival of osteoblasts. In the in vivo experiments, a significantly higher bone ingrowth compared to the empty defect was shown by μCT and histological analysis. Here, the group receiving material reinforced with aluminum oxide (Al2O3) showed a bone volume/tissue volume (BV/TV) of 89.19% compared to a BV/TV of 83.14% for the empty defect (p = 0.0013). In the group treated with a polysaccharide matrix, no increase in BV/TV was observed given a mean ratio of 80.14%. Scoring of histological sections did not reveal a significant difference between CaP and CaP that was substituted with Al2O3.ConclusionThe results of this study show an encouraging first step towards the development of new pasty, bone void-filling materials. We demonstrated that a new paste-like bone-filling material, based on calcium phosphate granulates and aluminum oxide to provide strength, exhibits good biocompatibility and osteoconductivity. Further biomechanical test in an osteoporotic animal model will have to be performed, to prove feasibility in metaphyseal defects.