Degradation of hydroxyapatite in vivo and in vitro requires osteoclastic sodium-bicarbonate co-transporter NBCn1

Dissolution of the inorganic bone matrix releases not only calcium and phosphate ions, but also bicarbonate. Electroneutral sodium-bicarbonate co-transporter (NBCn1) is expressed in inactive osteoclasts, but its physiological role in bone resorption has remained unknown. We show here that NBCn1, encoded by the SLC4A7 gene, is directly involved in bone resorption. NBCn1 protein was specifically found at the bone-facing ruffled border areas, and metabolic acidosis increased NBCn1 expression in rats in vivo. In human hematopoietic stem cell cultures, NBCn1 mRNA expression was observed only after formation of resorbing osteoclasts. To further confirm the critical role of NBCn1 during bone resorption, human hematopoietic stem cells were transduced with SLC4A7 shRNA lentiviral particles. Downregulation of NBCn1 both on mRNA and protein level by lentiviral shRNAs significantly inhibited bone resorption and increased intracellular acidification in osteoclasts. The lentiviral particles did not impair osteoclast survival, or differentiation of the hematopoietic or mesenchymal precursor cells into osteoclasts or osteoblasts in vitro. Inhibition of NBCn1 activity may thus provide a new way to regulate osteoclast activity during pathological bone resorption.     

Chordin knockdown enhances the osteogenic differentiation of human mesenchymal stem cells

Introduction

Bone morphogenetic proteins (BMPs) are critical growth factors in the osteogenic differentiation of progenitor cells during development in embryos and fracture repair in adults. Although recombinant BMPs are in use clinically, their clinical efficiency needs to be improved. The biological activities of BMPs are naturally regulated by extracellular binding proteins. The specific hypotheses tested in this study were as follows: the BMP inhibitor chordin is produced endogenously during the osteogenic differentiation of human mesenchymal stem cells (MSCs); and blockade of the activity of the BMP inhibitor increases the rate of osteogenic differentiation of human MSCs in vitro.

Methods

Human MSCs were derived from bone marrow from an iliac crest aspirate and from patients undergoing hip hemiarthroplasty. The MSCs were induced down the osteogenic pathway using standard osteogenic differentiation media, and expressions of BMP-2 and chordin were determined by gene expression analysis. During osteogenic differentiation, chordin knockdown was induced using RNA interference. Osteogenic differentiation was assessed by measuring the expression of alkaline phosphatase and calcium deposition. The differences in expression of osteogenic makers between groups were compared by analysis of variance, followed by Gabriel post hoc test.

Results

We demonstrate the expression of BMP-2 and chordin in human MSCs during osteogenic differentiation. Knockdown of chordin by RNA interference in vitro resulted in a significant increase in the expression of the osteogenic marker alkaline phosphatase and the deposition of extracellular mineral, in response to osteogenic stimulation.

Conclusion

We conclude that endogenously produced chordin constrains the osteogenic differentiation of human MSCs. The targeting of BMP inhibitors, such as chordin, may provide a novel strategy for enhancing bone regeneration.     

The Spatiotemporal Role of COX-2 in Osteogenic and Chondrogenic Differentiation of Periosteum-Derived Mesenchymal Progenitors in Fracture Repair

Periosteum provides a major source of mesenchymal progenitor cells for bone fracture repair. Combining cell-specific targeted Cox-2 gene deletion approaches with in vitro analyses of the differentiation of periosteum-derived mesenchymal progenitor cells (PDMPCs), here we demonstrate a spatial and temporal role for Cox-2 function in the modulation of osteogenic and chondrogenic differentiation of periosteal progenitors in fracture repair. Prx1Cre-targeted Cox-2 gene deletion in mesenchyme resulted in marked reduction of intramembraneous and endochondral bone repair, leading to accumulation of poorly differentiated mesenchyme and immature cartilage in periosteal callus. In contrast, Col2Cre-targeted Cox-2 gene deletion in cartilage resulted in a deficiency primarily in cartilage conversion into bone. Further cell culture analyses using Cox-2 deficient PDMPCs demonstrated reduced osteogenic differentiation in monolayer cultures, blocked chondrocyte differentiation and hypertrophy in high density micromass cultures. Gene expression microarray analyses demonstrated downregulation of a key set of genes associated with bone/cartilage formation and remodeling, namely Sox9, Runx2, Osx, MMP9, VDR and RANKL. Pathway analyses demonstrated dysregulation of the HIF-1, PI3K-AKT and Wnt pathways in Cox-2 deficient cells. Collectively, our data highlight a crucial role for Cox-2 from cells of mesenchymal lineages in modulating key pathways that control periosteal progenitor cell growth, differentiation, and angiogenesis in fracture repair.     

Mesenchymal Stromal Cell Proliferation,Gene Expression and Protein Production in Human Platelet-Rich Plasma-Supplemented Media

Background

Platelet-rich plasma (PRP) is increasingly used as a cell culture supplement, in order to reduce the contact of human cells with animal-derived products during in vitro expansion. The effect of supplementation changes on cell growth and protein production is not fully characterized.

Methods

Human mesenchymal stromal cells from bone marrow, adipose tissue and Wharton''s Jelly were isolated and cultured in PRP-supplemented media. Proliferation, in vitro differentiation, expression of cell surface markers, mRNA expression of key genes and protein secretion were quantified.

Results

10% PRP sustained five to tenfold increased cell proliferation as compared to 10% fetal bovine serum. Regarding cell differentiation, PRP reduced adipogenic differentiation and increased calcium deposits in bone marrow and adipose tissue-mesenchymal stromal cells. Wharton''s Jelly derived mesenchymal stromal cells secreted higher concentrations of chemokines and growth factors than other mesenchymal stromal cells when cultured in PRP-supplemented media. Bone marrow derived mesenchymal stromal cells secreted higher concentrations of pro-inflammatory and pro-angiogenic proteins. Mesenchymal stromal cells isolated from adipose tissue secreted higher amounts of extracellular matrix components.

Conclusions

Mesenchymal stromal cells purified from different tissues have distinct properties regarding differentiation, angiogenic, inflammatory and matrix remodeling potential when cultured in PRP supplemented media. These abilities should be further characterized in order to choose the best protocols for their therapeutic use.     

Ultrastructural evidence for calcium phosphate deposition by isolated corn shoot mitochondria

This study demonstrates that isolated corn (Zea mays L. Wf9 xM14) shoot mitochondria will accumulate calcium phosphate crystals in vitro that are comparable to those observed in both in vivo and in vitro animal mitochondria. The intensity of deposition, as observed by electron microscopy, increased with incubation time, substrate concentration, and concentration of calcium and inorganic phosphate. Calcium phosphate deposits were initially observed as amorphous, nearly spherical areas that lacked sharp or clear edges, but which were crystalline in nature under heavier loading conditions and longer incubation times.     

The effect of medium composition on deposition of collagen type 1 and expression of osteogenic genes in mesenchymal stem cells derived from human adipose tissue and bone marrow

The two mesenchymal stem cell (MSC) populations that have gained most attention in relation to bone tissue engineering are adipose tissue (AT) MSCs and bone marrow (BM) MSCs. The purpose of this study was to investigate the ability of human BM-MSCs and AT-MSCs to survive, proliferate and deposit collagen type 1 when cultured on polycaprolactone nanofiber scaffolds and to ascertain the effect of medium composition on collagen type 1 formation and expression of osteogenic genes. The cells were seeded on polycaprolactone nanofiber scaffolds and cultured in three different types of media that differed by the presence of ascorbic acid, β-glycerophosphate and dexamethasone, that are typical components used for osteogenic differentiation of MSCs in vitro.In summary, AT-MSCs were proliferating significantly faster than BM-MSCs. AT-MSCs also showed better ability to deposit collagen type 1 and had a higher expression of early osteogenic markers, whereas BM-MSCs had higher expression of late osteogenic markers. This suggests that MSCs from diverse sources have different attributes and with respect to osteogenic differentiation, AT-MSCs are more immature compared to BM-MSCs. Collagen formation was depending on medium composition and the organization of collagen type 1 appeared to be influenced by the presence of dexamethasone.     

Validation of a simple and fast method to quantify in vitro mineralization with fluorescent probes used in molecular imaging of bone

Alizarin Red S staining is the standard method to indicate and quantify matrix mineralization during differentiation of osteoblast cultures. KS483 cells are multipotent mouse mesenchymal progenitor cells that can differentiate into chondrocytes, adipocytes and osteoblasts and are a well-characterized model for the study of bone formation. Matrix mineralization is the last step of differentiation of bone cells and is therefore a very important outcome measure in bone research. Fluorescently labelled calcium chelating agents, e.g. BoneTag and OsteoSense, are currently used for in vivo imaging of bone. The aim of the present study was to validate these probes for fast and simple detection and quantification of in vitro matrix mineralization by KS483 cells and thus enabling high-throughput screening experiments.     

Human Wharton’s Jelly Mesenchymal Stem Cells Plasticity Augments Scar-Free Skin Wound Healing with Hair Growth

Human mesenchymal stem cells (MSCs) are a promising candidate for cell-based transplantation and regenerative medicine therapies. Thus in the present study Wharton’s Jelly Mesenchymal Stem Cells (WJ-MSCs) have been derived from extra embryonic umbilical cord matrix following removal of both arteries and vein. Also, to overcome the clinical limitations posed by fetal bovine serum (FBS) supplementation because of xenogeneic origin of FBS, usual FBS cell culture supplement has been replaced with human platelet lysate (HPL). Apart from general characteristic features of bone marrow-derived MSCs, wharton jelly-derived MSCs have the ability to maintain phenotypic attributes, cell growth kinetics, cell cycle pattern, in vitro multilineage differentiation plasticity, apoptotic pattern, normal karyotype-like intrinsic mesenchymal stem cell properties in long-term in vitro cultures. Moreover, the WJ-MSCs exhibited the in vitro multilineage differentiation capacity by giving rise to differentiated cells of not only mesodermal lineage but also to the cells of ectodermal and endodermal lineage. Also, WJ-MSC did not present any aberrant cell state upon in vivo transplantation in SCID mice and in vitro soft agar assays. The immunomodulatory potential assessed by gene expression levels of immunomodulatory factors upon exposure to inflammatory cytokines in the fetal WJ-MSCs was relatively higher compared to adult bone marrow-derived MSCs. WJ-MSCs seeded on decellularized amniotic membrane scaffold transplantation on the skin injury of SCID mice model demonstrates that combination of WJ-MSCs and decellularized amniotic membrane scaffold exhibited significantly better wound-healing capabilities, having reduced scar formation with hair growth and improved biomechanical properties of regenerated skin compared to WJ-MSCs alone. Further, our experimental data indicate that indocyanin green (ICG) at optimal concentration can be resourcefully used for labeling of stem cells and in vivo tracking by near infrared fluorescence non-invasive live cell imaging of labelled transplanted cells, thus proving its utility for therapeutic applications.     

Role of MyD88 in TLR agonist-induced functional alterations of human adipose tissue-derived mesenchymal stem cells

In this study, we established an in vitro model of osteogenic-inductive differentiation of rat bone marrow mesenchymal stem cells (BMSCs) to determine the mechanisms and relative gene function underlying BMSCs osteogenesis. Osteoplastic differentiation of the third generation BMSCs was induced with the α-minimal essential medium containing β-glyceraldehyde-3-phosphate, l-ascorbic acid, dexamethasone and 1,25–2(OH)₂ vitamin D₃ prior to applying gene chip technology (also called microarray technology) for global gene expression screening. Real-time quantitative PCR (Real-time PCR) was used to determine the temporal profile of mRNA expression of regulated genes during osteogenic differentiation of BMSCs. A bioinformatic analysis was utilized to determine the functional significance of the identified osteogenic-related genes. Purkinje cell protein 4 (Pcp4) mRNA expression was identified by the gene chip screening as being up-regulated during osteoplastic differentiation of BMSCs. Real-time PCR analysis confirmed the increased expression of Pcp4 mRNA expression during osteoplastic differentiation of BMSCs with an upward trend that peaked at day 14. The bioinformatic analysis identified Pcp4 as a gene involved in the deposition of calcium and the modulation of CaM-dependent protein kinase. Thus, we hypothesize that Pcp4 osteoplastic differentiation of BMSCs is mediated in part via Pcp4-induced calcium deposition to form mineral nodules and modulation of certain signal transduction pathways of BMPs.     

Cartilage–Specific Over-Expression of CCN Family Member 2/Connective Tissue Growth Factor (CCN2/CTGF) Stimulates Insulin-Like Growth Factor Expression and Bone Growth

Previously we showed that CCN family member 2/connective tissue growth factor (CCN2) promotes the proliferation, differentiation, and maturation of growth cartilage cells in vitro. To elucidate the specific role and molecular mechanism of CCN2 in cartilage development in vivo, in the present study we generated transgenic mice overexpressing CCN2 and analyzed them with respect to cartilage and bone development. Transgenic mice were generated expressing a ccn2/lacZ fusion gene in cartilage under the control of the 6 kb-Col2a1-enhancer/promoter. Changes in cartilage and bone development were analyzed histologically and immunohistologically and also by micro CT. Primary chondrocytes as well as limb bud mesenchymal cells were cultured and analyzed for changes in expression of cartilage–related genes, and non-transgenic chondrocytes were treated in culture with recombinant CCN2. Newborn transgenic mice showed extended length of their long bones, increased content of proteoglycans and collagen II accumulation. Micro-CT analysis of transgenic bones indicated increases in bone thickness and mineral density. Chondrocyte proliferation was enhanced in the transgenic cartilage. In in vitro short-term cultures of transgenic chondrocytes, the expression of col2a1, aggrecan and ccn2 genes was substantially enhanced; and in long-term cultures the expression levels of these genes were further enhanced. Also, in vitro chondrogenesis was strongly enhanced. IGF-I and IGF-II mRNA levels were elevated in transgenic chondrocytes, and treatment of non-transgenic chondrocytes with recombinant CCN2 stimulated the expression of these mRNA. The addition of CCN2 to non-transgenic chondrocytes induced the phosphorylation of IGFR, and ccn2-overexpressing chondrocytes showed enhanced phosphorylation of IGFR. Our data indicates that the observed effects of CCN2 may be mediated in part by CCN2-induced overexpression of IGF-I and IGF-II. These findings indicate that CCN2-overexpression in transgenic mice accelerated the endochondral ossification processes, resulting in increased length of their long bones. Our results also indicate the possible involvement of locally enhanced IGF-I or IGF-II in this extended bone growth.     

Endothelial Differentiation of Mesenchymal Stromal Cells

Human mesenchymal stromal cells (hMSCs) are increasingly used in regenerative medicine for restoring worn-out or damaged tissue. Newly engineered tissues need to be properly vascularized and current candidates for in vitro tissue pre-vascularization are endothelial cells and endothelial progenitor cells. However, their use in therapy is hampered by their limited expansion capacity and lack of autologous sources. Our approach to engineering large grafts is to use hMSCs both as a source of cells for regeneration of targeted tissue and at the same time as the source of endothelial cells. Here we investigate how different stimuli influence endothelial differentiation of hMSCs. Although growth supplements together with shear force were not sufficient to differentiate hMSCs with respect to expression of endothelial markers such as CD31 and KDR, these conditions did prime the cells to differentiate into cells with an endothelial gene expression profile and morphology when seeded on Matrigel. In addition, we show that endothelial-like hMSCs are able to create a capillary network in 3D culture both in vitro and in vivo conditions. The expansion phase in the presence of growth supplements was crucial for the stability of the capillaries formed in vitro. To conclude, we established a robust protocol for endothelial differentiation of hMSCs, including an immortalized MSC line (iMSCs) which allows for reproducible in vitro analysis in further studies.     

Do novel cement-type biomaterials reveal ion reactivity that affects cell viability in vitro?

Calcium phosphate bioceramics have been studied as bone filler materials for years and have become a component of many commercial products. It is widely known that surface-reactive biomaterials may cause changes in the concentration of crucial ions in the surrounding environment, thereby affecting cell metabolism and viability. The aim of this study was to produce five cement-type biomaterials and characterize their phase composition using X-ray diffraction method, and porosity and pore size distribution using mercury intrusion porosimeter. We then evaluated ion interactions of the novel biomaterials with the surrounding environment (culture medium). A commercially available bone substitute, HydroSet? (Stryker®), was used as a reference. MTT and NRU cytotoxicity tests were performed to assess the effect of changes in the concentration of crucial ions (calcium, magnesium, phosphate) on osteoblast metabolism and viability in vitro. Our study clearly indicated that various biomaterials demonstrated different ion reactivity and consequently may cause changes in ion concentration in the local environment. Critically low or high values of calcium, magnesium, and phosphate concentrations in the medium exerted cytotoxic effects on the cultured cells. Moreover, we discovered that the chemical composition of the culture medium had a substantial influence on ion interactions with biomaterials.     

The Therapeutic Effect on Bone Mineral Formation from Biomimetic Zinc Containing Tricalcium Phosphate (ZnTCP) in Zinc-Deficient Osteoporotic Mice

The aim of this study was to evaluate the therapeutic efficacy of biomimetic zinc-containing tricalcium phosphate (ZnTCP) produced by hydrothermally converting calcium carbonate exoskeletons from foraminifera, in the treatment of osteoporotic mice. X-Ray powder diffraction showed crystallographic structures matching JCPDS profile for tricalcium phosphate. Mass spectroscopy used to calculate total composition amount showed similar amount of calcium (5×10⁴ µg/g) and phosphate (4×10⁴ ppm) after conversion and the presence of zinc (5.18×10³ µg/g). In vitro zinc release showed no release in PBS buffer and <1% zinc release in 7 days. In vivo evaluation was done in ovariectomized mice by implanting the ZnTCP samples in the soft tissues near the right femur bone for four weeks. Thirty ddY mice (5 weeks old, average weight of 21 g) were divided into six experimental groups (normal, sham, OVX, β-TCP, ZnTCP and direct injection of zinc). CT images were taken every two weeks where the bone mineral density (BMD) and bone mineral content (BMC) were calculated by software based on CT images. The ZnTCP group exhibits cortical and cancellous bone growth of 45% and 20% respectively. While sham, OVX and β-TCP suffered from bone loss. A correlation was made between the significant body weight increase in ZnTCP with the significant increase in plasma zinc level compared with OVX. The presented results indicate that biomimetic ZnTCP were effective in preventing and treating bone loss in osteoporotic mice model.     

Adipose-derived stem cells alleviate osteoporosis by enchancing osteogenesis and inhibiting adipogenesis in a rabbit model

Background aimsOsteoporosis (OP) is characterized by a reduction in bone quality, which is associated with inadequacies in bone marrow mesenchymal stromal cells (BMSCs). As an alternative cell source to BMSCs, adipose-derived stem cells (ASCs) have been investigated for bone repair because of their osteogenic potential and self-renewal capability. Nevertheless, whether autologous ASCs can be used to promote bone regeneration under osteoporotic conditions has not been elucidated.MethodsThe OP rabbit model was established by means of bilateral ovariectomy (OVX). Both BMSCs and ASCs were harvested from OVX rabbits and expanded in vitro. The effects of osteogenic-induced ASCs on the in vitro adipogenic and osteogenic capabilities of BMSCs were evaluated. Autologous ASCs were then encapsulated by calcium alginate gel and transplanted into the distal femurs of OVX rabbits (n = 12). Hydrogel without loading cells was injected into the contralateral femurs as a control. Animals were killed for investigation at 12 weeks after transplantation.ResultsOsteogenic-induced ASCs were able to promote osteogenesis and inhibit adipogenesis of osteoporotic BMSCs through activation of the bone morphogenetic protein 2/bone morphogenetic protein receptor type IB signal pathway. Local bone mineral density began to increase at 8 weeks after ASC transplantation (P < 0.05). At 12 weeks, micro–computed tomography and histological evaluation revealed more new bone formation in the cell-treated femurs than in the control group (P < 0.05).ConclusionsThis study demonstrated that ASCs could stimulate proliferation and osteogenic differentiation of BMSCs in vitro and enhance bone regeneration in vivo, which suggests that autologous osteogenic-induced ASCs might be useful to alleviate OP temporally.     

Knockout of Nuclear High Molecular Weight FGF2 Isoforms in Mice Modulates Bone and Phosphate Homeostasis

We previously reported that targeted overexpression of the fibroblast growth factor 2 (FGF2) high molecular weight (HMW) isoforms in osteoblastic lineage cells in mice resulted in phenotypic changes, including dwarfism, rickets, osteomalacia, hypophosphatemia, increased serum parathyroid hormone, and increased levels of the phosphatonin FGF23 in serum and bone. This study examined the effects of genetically knocking out the FGF2HMW isoforms (HMWKO) on bone and phosphate homeostasis. HMWKO mice were not dwarfed and had significantly increased bone mineral density and bone mineral content in femurs and lumbar vertebrae when compared with the wild-type (WT) littermates. Micro-computed tomography analysis of femurs revealed increased trabecular bone volume, thickness, number, and connective tissue density with decreased trabecular spacing compared with WT. In addition, there was significantly decreased cortical porosity and increased cortical thickness and sub-periosteal area in femurs of HMWKO. Histomorphometric analysis demonstrated increased osteoblast activity and diminished osteoclast activity in the HMWKO. In vitro bone marrow stromal cell cultures showed there was a significant increase in alkaline phosphatase-positive colony number at 1 week in HMWKO. At 3 weeks of culture, the mineralized area was also significantly increased. There was increased expression of osteoblast differentiation marker genes and reduced expression of genes associated with impaired mineralization, including a significant reduction in Fgf23 and Sost mRNA. Normal serum phosphate and parathyroid hormone were observed in HMWKO mice. This study demonstrates a significant negative impact of HMWFGF2 on biological functions in bone and phosphate homeostasis in mice.     

Comparative Characteristics of Porous Bioceramics for an Osteogenic Response In Vitro and In Vivo

Porous calcium phosphate ceramics are used in orthopedic and craniofacial applications to treat bone loss, or in dental applications to replace missing teeth. The implantation of these materials, however, does not induce stem cell differentiation, so suitable additional materials such as porous calcium phosphate discs are needed to influence physicochemical responses or structural changes. Rabbit adipose-derived stem cells (ADSC) and mouse osteoblastic cells (MC3T3-E1) were evaluated in vitro by the MTT assay, semi-quantitative RT-PCR, and immunoblotting using cells cultured in medium supplemented with extracts from bioceramics, including calcium metaphosphate (CMP), hydroxyapatite (HA) and collagen-grafted HA (HA-col). In vivo evaluation of the bone forming capacity of these bioceramics in rat models using femur defects and intramuscular implants for 12 weeks was performed. Histological analysis showed that newly formed stromal-rich tissues were observed in all the implanted regions and that the implants showed positive immunoreaction against type I collagen and alkaline phosphatase (ALP). The intramuscular implant region, in particular, showed strong positive immunoreactivity for both type I collagen and ALP, which was further confirmed by mRNA expression and immunoblotting results, indicating that each bioceramic material enhanced osteogenesis stimulation. These results support our hypothesis that smart bioceramics can induce osteoconduction and osteoinduction in vivo, although mature bone formation, including lacunae, osteocytes, and mineralization, was not prominent until 12 weeks after implantation.