Osteonectin-null mutation compromises osteoblast formation, maturation, and survival

Exercise improves load bearing bone structural properties in female secreted protein acidic and rich in cysteine (SPARC) null mice but not in males

Secreted protein acidic and rich in cysteine (SPARC) is the most abundant glycoprotein in bone and is thought to play a critical role in bone remodeling and homeostasis. However, the effect of SPARC in relation to gender and exercise on bone quality is not well understood. The purpose of this study was to quantify differences in the structural and biomechanical properties between calvarial and femoral bone from male and female wild-type (WT) and SPARC null (SPARC(-/-)) mice as well as the ability of exercise to rescue bone health. Male and female WT and transgenic SPARC(-/-) mice were given either a fixed or rotating running wheel for exercise. Bone structural, biomechanical, and morphological parameters were quantified using micro computed tomography, push out testing for the calvaria, three-point flexural testing for the femurs, histological and immunofluorescent staining. Similar reductions in structural and biomechanical strength were observed in both male and female SPARC(-/-) calvaria, most of which were not significantly affected by exercise. In femurs, SPARC(-/-) had a significant effect on structural parameters in both sexes, but was more pronounced in females with some properties being rescued with running. Interestingly, the effect of SPARC(-/-) on bone mineral density was only detected in female SPARC(-/-) mice, not males, and was subsequently rescued with exercise. This study emphasizes the differences between sexes in WT and SPARC(-/-) mice in regard to structural parameters and biomechanical properties. Research into gender differences can help inform and personalize treatment options to more accurately meet patient needs.

Notch activation promotes bone metastasis via SPARC inhibition in adenoid cystic carcinoma

OBJECTIVES

We aimed to investigate bone metastasis induced by Notch signalling pathway dysregulation and to demonstrate that SPARC is a potential therapeutic target in adenoid cystic carcinoma (AdCC) with Notch dysregulation.

MATERIALS AND METHODS

This retrospective study enrolled 144 AdCC patients. RNA-sequencing and enrichment analyses were performed using 32 AdCC samples. Osteonectin/SPARC and the Notch activation indicator Notch intracellular domain (NICD) were detected using immunohistochemistry. Cell proliferation and migration assays were conducted using stably NICD over-expressing cells. The effect of SPARC on osteoclast differentiation in NICD cells was investigated using western blotting, quantitative reverse transcription PCR, tartrate-resistant acid phosphatase staining and resorption assays.

RESULTS

RNA-sequencing analysis showed that genes down-regulated in Notch-mutant AdCCs, such as SPARC, were enriched in ossification and osteoblast differentiation. Most (75/110, 68.2%) Notch1-wild-type AdCCs showed SPARC over-expression, whereas 30 out of 34 (88.2%) Notch1-mutant tumours showed low SPARC expression. SPARC over-expression was then found negatively to be correlated with NICD expression in 144 AdCCs. NICD over-expression promoted cell growth, migration and osteoclast differentiation, which could be partly reversed by exogenous SPARC.

CONCLUSIONS

Notch activation in AdCC contributes to bone metastasis through SPARC inhibition. The study results suggest that SPARC may represent a prognostic biomarker and potential therapeutic target.

Kisspeptin (Kp-10) inhibits in vitro osteogenic differentiation of multipotent mesenchymal stromal cells extracted from the bone marrow of adult rats

Kisspeptin (Kp-10) is a neuropeptide that binds to GPR54 receptors, exerting several functions mainly in the nervous and reproductive systems of the body. However, its effects and mechanisms of action on the skeletal system remain poorly understood. This study evaluated the effects of different concentrations of Kp-10 on in vitro osteogenic differentiation of multipotent mesenchymal stromal cells (MSCs) extracted from the bone marrow (BM) of adult Wistar rats. Two-month-old female rats were euthanized to extract BM from long bones to obtain MSCs. Four experimental groups were established in vitro: a control and Kp-10 at concentrations of 0.01, 0.05 and, 0.1 µg/mL. After induction of osteogenic differentiation, cell viability was evaluated using the 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyl tetrazolium bromide (MTT) assay, alkaline phosphatase activity, collagen synthesis, percentage of area covered by MSCs/field and mineralized nodules/field, and immunocytochemistry of the GPR54 receptor tests. Furthermore, evaluation of gene transcripts for type I collagen, Runx-2, Bmp-2, bone sialoprotein, osteocalcin and osteopontin was performed using real-time RT-qPCR. It was observed that MSCs expressed GPR54 receptor to which Kp-10 binds during osteogenic differentiation, promoting a negative effect on osteogenic differentiation. This effect was observed at all the Kp-10 concentrations in a concentration-dependent manner, characterized by a decrease in the activity of alkaline phosphatase, collagen synthesis, mineralized nodules, and decreased expression of gene transcripts for type I collagen, osteocalcin, osteopontin, and Runx-2. Thus, Kp-10 inhibits in vitro osteogenic differentiation of MSCs extracted from the BM of adult Wistar rats.

Obesity and Bone Mineral Density Protection Paradox in Chronic Kidney Disease: Secreted Protein Acidic and Rich in Cysteine as a Piece of the Puzzle?

Obesity is a health condition that represents a risk factor for numerous diseases and complications. However, obesity might also have-to some extent-some "benefits" in certain situations. This includes potential bone protection in patients suffering from chronic kidney disease. In an attempt to explain such a paradox, we highlight secreted protein acidic and rich in cysteine (SPARC) as a hypothetical mediator of this protection. Indeed, SPARC properties provide a logical rationale to describe such bone protection via its overexpression combined with its calcium-binding and collagen-binding properties. We believe that exploring such hypotheses could open new doors to elucidate unknown pathways towards developing a new generation of molecular therapies.

Giant Cells of Various Lesions Are Characterised by Different Expression Patterns of HLA-Molecules and Molecules Involved in the Cell Cycle, Bone Metabolism, and Lineage Affiliation: An Immunohistochemical Study with a Review of the Literature

Giant cells (GCs) are thought to originate from the fusion of monocytic lineage cells and arise amid multiple backgrounds. To compare GCs of different origins, we immunohistochemically characterised the GCs of reactive and neoplastic lesions (n = 47). We studied the expression of 15 molecules including HLA class II molecules those relevant to the cell cycle, bone metabolism and lineage affiliation. HLA-DR was detectable in the GCs of sarcoidosis, sarcoid-like lesions, tuberculosis, and foreign body granuloma. Cyclin D1 was expressed by the GCs of neoplastic lesions as well as the GCs of bony callus, fibroid epulis, and brown tumours. While cyclin E was detected in the GCs of all lesions, p16 and p21 showed a heterogeneous expression pattern. RANK was expressed by the GCs of all lesions except sarcoid-like lesions and xanthogranuloma. All GCs were RANK-L-negative, and the GCs of all lesions were osteoprotegerin-positive. Osteonectin was limited to the GCs of chondroblastoma. Osteopontin and TRAP were detected in the GCs of all lesions except xanthogranuloma. RUNX2 was heterogeneously expressed in the reactive and neoplastic cohort. The GCs of all lesions except foreign body granuloma expressed CD68, and all GCs were CD163- and langerin-negative. This profiling points to a functional diversity of GCs despite their similar morphology.

Persicae Semen Promotes Bone Union in Rat Fractures by Stimulating Osteoblastogenesis through BMP-2 and Wnt Signaling

Fractures cause extreme pain to patients and impair movement, thereby significantly reducing their quality of life. However, in fracture patients, movement of the fracture site is restricted through application of a cast, and they are reliant on conservative treatment through calcium intake. Persicae semen (PS) is the dried mature seeds of Prunus persica (L.) Batsch, and in this study the effects of PS on osteoblast differentiation and bone union promotion were investigated. The osteoblast-differentiation-promoting effect of PS was investigated through alizarin red S and Von Kossa staining, and the regulatory role of PS on BMP-2 (Bmp2) and Wnt (Wnt10b) signaling, representing a key mechanism, was demonstrated at the protein and mRNA levels. In addition, the bone-union-promoting effect of PS was investigated in rats with fractured femurs. The results of the cell experiments showed that PS promotes mineralization and upregulates RUNX2 through BMP-2 and Wnt signaling. PS induced the expression of various osteoblast genes, including Alpl, Bglap, and Ibsp. The results of animal experiments show that the PS group had improved bone union and upregulated expression of osteogenic genes. Overall, the results of this study suggest that PS can promote fracture recovery by upregulating osteoblast differentiation and bone formation, and thus can be considered a new therapeutic alternative for fracture patients.

Creating an atlas of the bone microenvironment during oral inflammatory-related bone disease using single-cell profiling

Oral inflammatory diseases such as apical periodontitis are common bacterial infectious diseases that may affect the periapical alveolar bone tissues. A protective process occurs simultaneously with the inflammatory tissue destruction, in which mesenchymal stem cells (MSCs) play a primary role. However, a systematic and precise description of the cellular and molecular composition of the microenvironment of bone affected by inflammation is lacking. In this study, we created a single-cell atlas of cell populations that compose alveolar bone in healthy and inflammatory disease states. We investigated changes in expression frequency and patterns related to apical periodontitis, as well as the interactions between MSCs and immunocytes. Our results highlight an enhanced self-supporting network and osteogenic potential within MSCs during apical periodontitis-associated inflammation. MSCs not only differentiated toward osteoblast lineage cells but also expressed higher levels of osteogenic-related markers, including Sparc and Col1a1. This was confirmed by lineage tracing in transgenic mouse models and human samples from oral inflammatory-related alveolar bone lesions. In summary, the current study provides an in-depth description of the microenvironment of MSCs and immunocytes in both healthy and disease states. We also identified key apical periodontitis-associated MSC subclusters and their biomarkers, which could further our understanding of the protective process and the underlying mechanisms of oral inflammatory-related bone disease. Taken together, these results enhance our understanding of heterogeneity and cellular interactions of alveolar bone cells under pathogenic and inflammatory conditions. We provide these data as a tool for investigators not only to better appreciate the repertoire of progenitors that are stress responsive but importantly to help design new therapeutic targets to restore bone lesions caused by apical periodontitis and other inflammatory-related bone diseases.

SPARC is a decoy counterpart for c‑Fos and is associated with osteoblastic differentiation of bone marrow stromal cells by inhibiting adipogenesis

Secreted protein acidic and rich in cysteine (SPARC), also called basement‑membrane protein 40 or osteonectin, is a matricellular protein that is abundant not only in bone tissue as a non‑collagenous protein but is also ubiquitously expressed in non‑calcified tissue. SPARC is located intracellularly and disruption of the Sparc gene has been reported to reduce bone formation and increase fat tissue; however, the mechanism by which SPARC inhibits adipogenesis remains unclear. The present study evaluated the intracellular function of SPARC in adipogenesis using the bone marrow stromal cell line ST2. When ST2 cells with low SPARC production were cloned, intrinsic activator protein‑1 (AP‑1) activity was markedly higher, mineralized nodule formation was significantly lower and lipid accumulation was significantly increased compared with in the parental ST2 cells. Forced expression of secreted SPARC with the signal peptide‑coding sequences of wild‑type Sparc or preprotrypsin in SPARC‑low ST2 cells significantly reduced AP‑1 transcription activity; however, these reductions were not observed in the absence of signal peptide sequences. Recombinant SPARC, produced using Brevibacillus brevis, specifically bound to c‑Fos but not c‑Jun and inhibited the binding of c‑Fos/c‑Jun to a TPA‑response element sequence. These data suggested that SPARC was incorporated into the cells from the extracellular spaces and serves an intracellular role as a decoy counterpart for c‑Fos, as well as being associated with osteoblastogenesis through the inhibition of adipogenesis. These findings may provide new insights into regenerative medicine.

An In Vitro Engineered Osteochondral Model as Tool to Study Osteoarthritis Environment

Osteoarthritis (OA) is a joint degenerative pathology characterized by mechanical and inflammatory damages affecting synovium, articular cartilage (AC), and subchondral bone (SB). Several in vitro, in vivo, and ex vivo models are developed to study OA, but to date the identification of specific pharmacological targets seems to be hindered by the lack of models with predictive capabilities. This study reports the development of a biomimetic in vitro model of AC and SB interface. Gellan gum methacrylated and chondroitin sulfate/dopamine hydrogels are used for the AC portion, whereas polylactic acid functionalized with gelatin and nanohydroxyapatite for the SB. The physiological behavior of immortalized stem cells (Y201s) and Y201s differentiated in chondrocytes (Y201-Cs), respectively, for the SB and AC, is demonstrated over 21 days of culture in vitro in healthy and pathological conditions, whilst modeling the onset of cytokines-induced OA. The key metrics are: lower glycosaminoglycans production and increased calcification given by a higher Collagen X content, in the AC deep layer; higher expression of pro-angiogenic factor (vegf) and decreased expression of osteogenic markers (coll1, spp1, runx2) in the SB. This novel approach provides a new tool for studying the development and progression of OA.

Platelets and osteoblasts: secretome connections

Megakaryocyte hyperplasia associated with myeloproliferative neoplasms commonly leads to abnormal bone tissue deposition in the bone marrow, known as osteosclerosis. In this study, we aimed to synthesize the known proteomics literature describing factors released by megakaryocytes and platelets and to examine if any of the secreted factors have a known ability to stimulate the bone-forming cells, osteoblasts. Using a systematic search of Medline, we identified 77 articles reporting on factors secreted by platelets and megakaryocytes. After a full-text screening and analysis of the studies, we selected seven papers that reported proteomics data for factors secreted by platelets from healthy individuals. From 60 proteins reported in at least two studies, we focused on 23 that contained a putative signal peptide, which we searched for a potential osteoblast-stimulatory function. From nine proteins with a positive effect on osteoblast formation and function, two extracellular matrix (ECM) proteins, secreted protein acidic and rich in cysteine (SPARC) and tissue inhibitor of metalloproteinase-1 (TIMP1), and three cellular proteins with known extracellular function, the 70-kDa heat shock protein (HSP70), thymosin-β4 (TB4), and super dismutase (SOD), were identified as hypothetical candidate molecules to be examined as potential mediators in mouse models of osteomyelofibrosis. Thus, careful analysis of prior literature can be beneficial in assisting the planning of future experimental studies.

Secreted Protein Acidic and Rich in Cysteine as an Exercise-Induced Gene: Towards Novel Molecular Therapies for Immobilization-Related Muscle Atrophy in Elderly Patients

Long periods of immobilization, among other etiologies, would result is muscle atrophy. Exercise is the best approach to reverse this atrophy. However, the limited or the non-ability to perform the required physical activity for such patients and the limited pharmacological options make developing novel therapeutic approaches a necessity. Within this context, secreted protein acidic and rich in cysteine (SPARC) has been characterized as an exercise-induced gene. Whereas the knock-out of this gene leads to a phenotype that mimics number of the ageing-induced and sarcopenia-related changes including muscle atrophy, overexpressing SPARC in mice or adding it to muscular cell culture produces similar effects as exercise including enhanced muscle mass, strength and metabolism. Therefore, this piece of writing aims to provide evidence supporting the potential use of SPARC/SPARC as a molecular therapy for muscle atrophy in the context of immobilization especially for elderly patients.

Secreted Protein Acidic and Rich in Cysteine (Sparc) KO Leads to an Accelerated Ageing Phenotype Which Is Improved by Exercise Whereas SPARC Overexpression Mimics Exercise Effects in Mice

Secreted protein acidic and rich in cysteine (SPARC) is a matricellular glycoprotein implicated in various functions, including metabolism, tissue regeneration, and functional homeostasis. SPARC/Sparc declines with ageing but increases with exercise. We aim to verify two hypotheses: (1) SPARC deficiency leads to an ageing-like phenotype (metabolic decline, muscle loss, etc.), and (2) SPARC overexpression would mimic exercise, counteract ageing, and improve age-related changes. Our mice experiments are divided into two parts. First, we explore the consequences of Sparc knockout (KO) and compare them to the ageing effects. We also observe the effects of exercise. In the second part, we study the effects of SPARC overexpression and compare them to the exercise benefits. At the end, we make an analysis of the results to point out the analogies between Sparc KO and the ageing-like phenotype on the one hand and make comparisons between SPARC overexpression and exercise in the context of exercise counteracting ageing. The measurements were mainly related to tissue weights, adiposity, metabolism, and muscle strength. The main findings are that Sparc KO reduced glucose tolerance, muscle glucose transporter expression, and abdominal adipose tissue weight but increased glycogen content in the muscle. SPARC overexpression increased muscle strength, muscle mass, and expressions of the muscle glucose transporter and mitochondrial oxidative phosphorylation but lowered the glycemia and the adiposity, especially in males. Collectively, these findings, and the data we have previously reported, show that Sparc KO mice manifest an ageing-like phenotype, whereas SPARC overexpression and exercise generate similar benefits. The benefits are towards counteracting both the SPARC deficiency-induced ageing-like phenotype as well as reversing the age-related changes. The potential applications of these findings are to build/optimize Sparc KO-based animal models of various health conditions and, on the other hand, to develop therapies based on introducing SPARC or targeting SPARC-related pathways to mimic exercise against age-related and metabolic disorders.

Absorbance or organization into ankylosis: a microarray analysis of haemarthrosis in a sheep model of temporomandibular joint trauma

Background

Traumatic haemarthrosis was hypothesized to be the etiology of temporomandibular (TMJ) ankylosis. Here, taking haematoma absorbance as a control, we aimed to reveal the molecular mechanisms involved in haematoma organizing into ankylosis using transcriptome microarray profiles.

Material/methods

Disk removal was performed to building haematoma absorbance (HA) in one side of TMJ, while removal of disk and articular fibrous layers was performed to induced TMJ ankylosis through haematoma organization (HO) in the contralateral side in a sheep model. Haematoma tissues harvested at days 1, 4 and 7 postoperatively were examined by histology, and analyzed by Affymetrix OviGene-1_0-ST microarrays. The DAVID were recruited to perform the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis for the different expression genes (DEGs). The DEGs were also typed into protein–protein interaction (PPI) networks to get the interaction data. Six significant genes screened from PPI analysis, were confirmed by real-time PCR.

Results

We found 268, 223 and 17 DEGs at least twofold at days 1, 4 and 7, respectively. At day 1, genes promoting collagen ossification (POSTN, BGN, LUM, SPARC), cell proliferation (TGF-β), and osteogenic differentiation of mesenchymal stem cells (BMP-2) were up-regulated in the HO side. At day 4, several genes involved in angiogenesis (KDR, FIT1, TEK) shower higher expression in the HO side. While HA was characterized by a continuous immune and inflammatory reaction.

Conclusions

Our results provide a comprehensive understanding of the role of haematoma in the onset and progress of TMJ ankylosis. The study will contribute to explaining why few injured TMJs ankylose and most do not from the molecular level.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-021-02033-w.

Advances in bone turnover markers

Bone fragility fractures remain an important worldwide health and economic problem due to increased morbidity and mortality. The current methods for predicting fractures are largely based on the measurement of bone mineral density and the utilization of mathematical risk calculators based on clinical risk factors for bone fragility. Despite these approaches, many bone fractures remain undiagnosed. Therefore, current research is focused on the identification of new factors such as bone turnover markers (BTM) for risk calculation. BTM are a group of proteins and peptides released during bone remodeling that can be found in serum or urine. They derive from bone resorptive and formative processes mediated by osteoclasts and osteoblasts, respectively. Potential use of BTM in monitoring these phenomenon and therefore bone fracture risk is limited by physiologic and pathophysiologic factors that influence BTM. These limitations in predicting fractures explain why their inclusion in clinical guidelines remains limited despite the large number of studies examining BTM.

Mechanical and chemical cues synergistically promote human venous smooth muscle cell osteogenesis through integrin β1-ERK1/2 signaling: A cell model of hemodialysis fistula calcification

Arteriovenous fistula (AVF) is the vascular access of choice for renal replacement therapy. However, AVF is susceptible to calcification with a high prevalence of 40%-65% in chronic hemodialysis patients. Repeated needle puncture for hemodialysis cannulation results in intimal denudation of AVF. We hypothesized that exposure to blood shear stress in the medial layer promotes venous smooth muscle cell (SMC) osteogenesis. While previous studies of shear stress focused on arterial-type SMCs, SMCs isolated from the vein had not been investigated. This study established a venous cell model of AVF using the fluid shear device, combined with a high phosphate medium to mimic the uremic milieu. Osteogenic gene expression of venous SMCs upon mechanical and chemical cues was analyzed in addition to the activated cell signaling pathways. Our findings indicated that upon shear stress and high phosphate environment, mechanical stimulation (shear stress) had an additive effect in up-regulation of an early osteogenic marker, Runx2. We further identified that the integrin β1-ERK1/2 signaling pathway was responsible for the molecular basis of venous SMC osteogenesis upon shear stress exposure. Mitochondrial biogenesis also took part in the early stage of this venopathy pathogenesis, evident by the up-regulated mitochondrial transcription factor A and mitochondrial DNA polymerase γ in venous SMCs. In conclusion, synergistic effects of fluid shear stress and high phosphate induce venous SMC osteogenesis via the ERK1/2 pathway through activating the mechanosensing integrin β1 signaling. The present study identified a promising druggable target for reducing AVF calcification, which deserves further in vivo investigations.

Different grinding speeds affect induced regeneration capacity of human treated dentin matrix

Human-treated dentin matrix (hTDM) is a biomaterial scaffold, which can induce implant cells to differentiate into odontoblasts and then form neo-dentin. However, hTDM with long storage or prepared by high-speed handpiece would not to form neo-dentin. In this research, we developed two fresh hTDM with different grinding speeds, which were low-speed hTDM (LTDM) with maximum speed of 500 rpm and high-speed hTDM (HTDM) with a speed of 3,80,000 rpm. Here, we aim to understand whether there were induced regeneration capacity differences between LTDM and HTDM. Scanning electron microscope showed that DFCs grew well on both materials, but the morphology of DFCs and the extracellular matrix was different. Especially, the secreted extracellular matrixes on the inner surface of LTDM were regular morphology and ordered arrangement around the dentin tubules. The transcription-quantitative polymerase chain reaction (qRT-PCR), western blot and immunofluorescence assay showed that the dentin markers DSPP and DMP-1 were about 2× greater in DFCs induced by LTDM than by HTDM, and osteogenic marker BSP was about 2× greater in DFCs induced by HTDM than by LTDM. Histological examinations of the harvested grafts observed the formation of neo-tissue were different, and there were neo-dentin formed on the inner surface of LTDM and neo-cementum formed on the outer surface of HTDM. In summary, it found that the induction abilities of LTDM and HTDM are different, and the dentin matrix is directional. This study lays a necessary foundation for searching the key factors of dentin regeneration in future.

miR-433-3p suppresses bone formation and mRNAs critical for osteoblast function in mice

MicroRNAs (miRNAs) are key posttranscriptional regulators of osteoblastic commitment and differentiation. miR-433-3p was previously shown to target Runt-related transcription factor 2 (Runx2) and to be repressed by bone morphogenetic protein (BMP) signaling. Here, we show that miR-433-3p is progressively decreased during osteoblastic differentiation of primary mouse bone marrow stromal cells in vitro, and we confirm its negative regulation of this process. Although repressors of osteoblastic differentiation often promote adipogenesis, inhibition of miR-433-3p did not affect adipocyte differentiation in vitro. Multiple pathways regulate osteogenesis. Using luciferase-3' untranslated region (UTR) reporter assays, five novel miR-433-3p targets involved in parathyroid hormone (PTH), mitogen-activated protein kinase (MAPK), Wnt, and glucocorticoid signaling pathways were validated. We show that Creb1 is a miR-433-3p target, and this transcription factor mediates key signaling downstream of PTH receptor activation. We also show that miR-433-3p targets hydroxysteroid 11-β dehydrogenase 1 (Hsd11b1), the enzyme that locally converts inactive glucocorticoids to their active form. miR-433-3p dampens glucocorticoid signaling, and targeting of Hsd11b1 could contribute to this phenomenon. Moreover, miR-433-3p targets R-spondin 3 (Rspo3), a leucine-rich repeat-containing G-protein coupled receptor (LGR) ligand that enhances Wnt signaling. Notably, Wnt canonical signaling is also blunted by miR-433-3p activity. In vivo, expression of a miR-433-3p inhibitor or tough decoy in the osteoblastic lineage increased trabecular bone volume. Mice expressing the miR-433-3p tough decoy displayed increased bone formation without alterations in osteoblast or osteoclast numbers or surface, indicating that miR-433-3p decreases osteoblast activity. Overall, we showed that miR-433-3p is a negative regulator of bone formation in vivo, targeting key bone-anabolic pathways including those involved in PTH signaling, Wnt, and endogenous glucocorticoids. Local delivery of miR-433-3p inhibitor could present a strategy for the management of bone loss disorders and bone defect repair. © 2021 American Society for Bone and Mineral Research (ASBMR).

Albiflorin Promotes Osteoblast Differentiation and Healing of Rat Femoral Fractures Through Enhancing BMP-2/Smad and Wnt/β-Catenin Signaling

Fracture healing is related to osteogenic differentiation and mineralization. Recently, due to the unwanted side effects and clinical limitations of existing treatments, various natural product-based chemical studies have been actively conducted. Albiflorin is a major ingredient in Paeonia lactiflora, and this study investigated its ability to promote osteogenic differentiation and fracture healing. To demonstrate the effects of albiflorin on osteoblast differentiation and calcified nodules, alizarin red S staining and von Kossa staining were used in MC3T3-E1 cells. In addition, BMP-2/Smad and Wnt/β-catenin mechanisms known as osteoblast differentiation mechanisms were analyzed through RT-PCR and western blot. To investigate the effects of albiflorin on fracture healing, fractures were induced using a chainsaw in the femur of Sprague Dawley rats, and then albiflorin was intraperitoneally administered. After 1, 2, and 3 weeks, bone microstructure was analyzed using micro-CT. In addition, histological analysis was performed by staining the fractured tissue, and the expression of osteogenic markers in serum was measured. The results demonstrated that albiflorin promoted osteoblastogenesis and the expression of RUNX2 by activating BMP-2/Smad and Wnt/β-catenin signaling in MC3T3-E1 cells. In addition, albiflorin upregulated the expression of various osteogenic genes, such as alkaline phosphatase, OCN, bone sialoprotein, OPN, and OSN. In the femur fracture model, micro-CT analysis showed that albiflorin played a positive role in the formation of callus in the early stage of fracture recovery, and histological examination proved to induce the expression of osteogenic genes in femur tissue. In addition, the expression of bone-related genes in serum was also increased. This suggests that albiflorin promotes osteogenesis, bone calcification and bone formation, thereby promoting the healing of fractures in rats.

Signaling Pathway and Transcriptional Regulation in Osteoblasts during Bone Healing: Direct Involvement of Hydroxyapatite as a Biomaterial

Bone defects and periodontal disease are pathological conditions that may become neglected diseases if not treated properly. Hydroxyapatite (HA), along with tricalcium phosphate and bioglass ceramic, is a biomaterial widely applied to orthopedic and dental uses. The in vivo performance of HA is determined by the interaction between HA particles with bone cells, particularly the bone mineralizing cells osteoblasts. It has been reported that HA-induced osteoblastic differentiation by increasing the expression of osteogenic transcription factors. However, the pathway involved and the events that occur in the cell membrane have not been well understood and remain controversial. Advances in gene editing and the discovery of pharmacologic inhibitors assist researchers to better understand osteoblastic differentiation. This review summarizes the involvement of extracellular signal-regulated kinase (ERK), p38, Wnt, and bone morphogenetic protein 2 (BMP2) in osteoblastic cellular regulation induced by HA. These advances enhance the current understanding of the molecular mechanism of HA as a biomaterial. Moreover, they provide a better strategy for the design of HA to be utilized in bone engineering.

Integrated analysis of miRNA and mRNA transcriptomic reveals antler growth regulatory network

The growth of antler is driven by endochondral ossification in the growth center of the apical region. Antler grows faster than cancer tissues, but it can be stably regulated and regenerated periodically. To elucidate the molecular mechanisms of how antler grows rapidly without carcinogenesis, in this study, we used RNA-seq technology to evaluate the changes of miRNA and mRNA profiles in antler at four different developmental stages, including 15, 60, 90, and 110 days. We identified a total of 55004 unigenes and 246 miRNAs of which, 10182, 13258, 10740 differentially expressed (DE) unigenes and 35, 53, 27 DE miRNAs were identified in 60-day vs. 15-day, 90-day vs. 60-day, and 110-day vs. 90-day. GO and KEGG pathway analysis indicated that DE unigenes and DE miRNA were mainly associated with chondrogenesis, osteogenesis and inhibition of oncogenesis, that were closely related to antler growth. The interaction networks of mRNA-mRNA and miRNA-mRNA related to chondrogenesis, osteogenesis and inhibition of oncogenesis of antler were constructed. The results indicated that mRNAs (COL2A1, SOX9, WWP2, FGFR1, SPARC, LOX, etc.) and miRNAs (miR-145, miR-199a-3p, miR-140, miR-199a-5p, etc.) might have key roles in chondrogenesis and osteogenesis of antler. As well as mRNA (TP53, Tpm3 and ATP1A1, etc.) and miRNA (miR-106a, miR-145, miR-1260b and miR-2898, etc.) might play important roles in inhibiting the carcinogenesis of antler. In summary, we constructed the mRNA-mRNA and miRNA-mRNA regulatory networks related to chondrogenesis, osteogenesis and inhibition of oncogenesis of antler, and identified key candidate mRNAs and miRNAs among them. Further developments and validations may provide a reference for in-depth analysis of the molecular mechanism of antler growth without carcinogenesis.

Effect of rosmarinic acid on differentiation and mineralization of MC3T3-E1 osteoblastic cells on titanium surface

Titanium (Ti) is a widely used biomaterial for dental implants because of its outstanding biocompatibility for hard tissues. Osseointegration, the interaction between implanted biomaterials and living cells in bone, is essential for successful implantation. Rosmarinic acid (RA) is a plant-derived phytochemical with low toxicity and side effects and has various effects that can be applied as a therapeutic substance. The MC3T3-E1 osteoblastic cells on the Ti surface in medium with or without 14 μg/ml RA were used to test RA effects on osteoblast differentiation, cell viability and mineralization during differentiation. RA treatment increased osteoblast differentiation, cell viability and mineralization in MC3T3-E1 osteoblastic cells on Ti surface during differentiation, upregulating Runx-2 and OPG, but downregulating RANKL. This study suggest that RA should be applied as an effective functional and therapeutic substance to enhance osseointegration of osteoblast cells by increasing differentiation, mineralization, and bone formation through the RANKL/RANK/OPG pathway during the differentiation in MC3T3-E1 osteoblastic cells on the Ti surface.

Bone-like ceramic scaffolds designed with bioinspired porosity induce a different stem cell response

Biomaterial science increasingly seeks more biomimetic scaffolds that functionally augment the native bone tissue. In this paper, a new concept of a structural scaffold design is presented where the physiological multi-scale architecture is fully incorporated in a single-scaffold solution. Hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) bioceramic scaffolds with different bioinspired porosity, mimicking the spongy and cortical bone tissue, were studied. In vitro experiments, looking at the mesenchymal stem cells behaviour, were conducted in a perfusion bioreactor that mimics the physiological conditions in terms of interstitial fluid flow and associated induced shear stress. All the biomaterials enhanced cell adhesion and cell viability. Cortical bone scaffolds, with an aligned architecture, induced an overexpression of several late stage genes involved in the process of osteogenic differentiation compared to the spongy bone scaffolds. This study reveals the exciting prospect of bioinspired porous designed ceramic scaffolds that combines both cortical and cancellous bone in a single ceramic bone graft. It is prospected that dual core shell scaffold could significantly modulate osteogenic processes, once implanted in patients, rapidly forming mature bone tissue at the tissue interface, followed by subsequent bone maturation in the inner spongy structure.

Deciphering the Relevance of Bone ECM Signaling

Bone mineral density, a bone matrix parameter frequently used to predict fracture risk, is not the only one to affect bone fragility. Other factors, including the extracellular matrix (ECM) composition and microarchitecture, are of paramount relevance in this process. The bone ECM is a noncellular three-dimensional structure secreted by cells into the extracellular space, which comprises inorganic and organic compounds. The main inorganic components of the ECM are calcium-deficient apatite and trace elements, while the organic ECM consists of collagen type I and noncollagenous proteins. Bone ECM dynamically interacts with osteoblasts and osteoclasts to regulate the formation of new bone during regeneration. Thus, the composition and structure of inorganic and organic bone matrix may directly affect bone quality. Moreover, proteins that compose ECM, beyond their structural role have other crucial biological functions, thanks to their ability to bind multiple interacting partners like other ECM proteins, growth factors, signal receptors and adhesion molecules. Thus, ECM proteins provide a complex network of biochemical and physiological signals. Herein, we summarize different ECM factors that are essential to bone strength besides, discussing how these parameters are altered in pathological conditions related with bone fragility.

Adipokines: New Potential Therapeutic Target for Obesity and Metabolic, Rheumatic, and Cardiovascular Diseases

Besides its role as an energy storage organ, adipose tissue can be viewed as a dynamic and complex endocrine organ, which produces and secretes several adipokines, including hormones, cytokines, extracellular matrix (ECM) proteins, and growth and vasoactive factors. A wide body of evidence showed that adipokines play a critical role in various biological and physiological functions, among which feeding modulation, inflammatory and immune function, glucose and lipid metabolism, and blood pressure control. The aim of this review is to summarize the effects of several adipokines, including leptin, diponectin, resistin, chemerin, lipocalin-2 (LCN2), vaspin, omentin, follistatin-like 1 (FSTL1), secreted protein acidic and rich in cysteine (SPARC), secreted frizzled-related protein 5 (SFRP5), C1q/TNF-related proteins (CTRPs), family with sequence similarity to 19 member A5 (FAM19A5), wingless-type inducible signaling pathway protein-1 (WISP1), progranulin (PGRN), nesfatin-1 (nesfatin), visfatin/PBEF/NAMPT, apelin, retinol binding protein 4 (RPB4), and plasminogen activator inhibitor-1 (PAI-1) in the regulation of insulin resistance and vascular function, as well as many aspects of inflammation and immunity and their potential role in managing obesity-associated diseases, including metabolic, osteoarticular, and cardiovascular diseases.

Two-day-treatment of Activin-A leads to transient change in SV-HFO osteoblast gene expression and reduction in matrix mineralization

Activins regulate bone formation by controlling osteoclasts and osteoblasts. We investigated Activin‐A mechanism of action on human osteoblast mineralization, RNA and microRNA (miRNA) expression profile. A single 2‐day treatment of Activin‐A at Day 5 of osteoblast differentiation significantly reduced matrix mineralization. Activin A‐treated osteoblasts responded with transient change in gene expression, in a 2‐wave‐fashion. The 38 genes differentially regulated during the first wave (within 8 hr after Activin A start) were involved in transcription regulation. In the second wave (1–2 days after Activin A start), 65 genes were differentially regulated and related to extracellular matrix. Differentially expressed genes in both waves were associated to transforming growth factor beta signaling. We identified which microRNAs modulating osteoblast differentiation were regulated by Activin‐A. In summary, 2‐day treatment with Activin‐A in premineralization period of osteoblast cultures influenced miRNAs, gene transcription, and reduced matrix mineralization. Modulation of Activin A signaling might be useful to control bone quality for therapeutic purposes.

Secreted protein acidic and rich in cysteine and bioenergetics: Extracellular matrix, adipocytes remodeling and skeletal muscle metabolism

The extracellular matrix (ECM) remodeling plays important roles in both adipocytes shape/expansion remodeling and the skeletal muscle (SM) metabolism. Secreted protein acidic and rich in cysteine (SPARC) is expressed in divers tissues including adipose tissue (AT) and SM where it impacts a variety of remodeling as well as metabolic functions. SPARC, also known as osteonectin or BM-40, is a glycoprotein associated with the ECM. Numerous researches attempted to elucidate the implications of SPARC in these two key metabolic tissues under different conditions. Whereas SPARC deficiency tends to shape the remodeling of the adipocytes and the fat distribution, this deficiency decreases SM metabolic properties. On the other hand, SPARC seems to be an enhancer of the metabolism and a mediator of the exercise-induced adaptation in the SM and as well as an adipogenesis inhibitor. Some findings about the SPARC effects on AT and SM seem "contradictory" in terms of tissue development and energy profile therefore highlighting the mechanistic role of SPARC in both is a priority. Yet, within this review, we expose selected researches and compare the results. We conclude with explanations to "reconcile" the different observations, hypothesize the feedback and regulatory character of SPARC and put its roles within the energetic and structural maps of both adipocytes and myocytes in homeostasis and in situations such as obesity or exercise. These properties explain the modifications and the remodeling seen in AT and SM undergoing adaptive changes (obesity, exercise, etc.) and represent a starting point for precise therapeutic targeting of SPARC-related pathways is conditions such as obesity, sarcopenia and diabetes.

Collagen and non-collagenous proteins molecular crosstalk in the pathophysiology of osteoporosis

Collagenous and non-collagenous proteins (NCPs) in the extracellular matrix, as well as the coupling mechanisms between osteoclasts and osteoblasts, work together to ensure normal bone metabolism. Each protein plays one or more critical roles in bone metabolism, sometimes even contradictory, thus affecting the final mechanical, physical and chemical properties of bone tissue. Anomalies in the amount and structure of one or more of these proteins can cause abnormalities in bone formation and resorption, which consequently leads to malformations and defects, such as osteoporosis (OP). The connections between key proteins involved in matrix formation and resorption are far from being elucidated. In this review, we resume knowledge on the crosstalk between collagen type I and selected NCPs (Transforming Growth Factor-β, Insulin-like Growth Factor-1, Decorin, Osteonectin, Osteopontin, Bone Sialoprotein and Osteocalcin) of bone matrix, focusing on their possible involvement and role in OP. The different elements of this network can be pharmacologically targeted or used for the design/development of innovative regenerative strategies to modulate a feedback loop in bone remodelling.

Osteonectin regulates the extracellular matrix mineralization of osteoblasts through P38 signaling pathway

Osteonectin binds strongly to type I collagen and hydroxyapatite and plays a crucial role in extracellular matrix mineralization. Previous studies have also shown that p38 signaling pathway is an important regulator for osteoblast mineralization. This study focused on the role of osteonectin in regulating extracellular matrix mineralization via the p38 signaling pathway. Osteoblasts were isolated and cultured from parietal bones of neonatal Sprague-Dawley rats. The gene and protein expressions of noncollagen proteins (BSP, bone sialoprotein; OCN, osteocalcin; OPN, osteopontin), p38 mitogen-activated protein kinase, and SIBLINGs (Small Integrin-Binding LIgand N-linked Glycoproteins) members (DMP1, dentine matrix protein 1, DSPP, dentin sialophosphoprotein, and MEPE, matrix extracellular phosphoglycoprotein) were detected by reverse-transcription quantitative polymerase chain reaction and western blot analysis. Alizarin red staining, intracellular calcium assay, and transmission electron microscopy were used to detect mineralization. Initially, by adding osteonectin at different concentrations in osteoblasts and detecting the above mineralization indexes, 1 µg/ml was determined to be the optima osteonectin concentration, which significantly increased gene expressions of BSP, OPN, OCN, DMP1, MEPE, DSPP, and p38 in osteoblasts, p38 and p-p38 protein expressions were also significantly increased, mineralized nodules were significantly enhanced; when added with SB203580 (a specific inhibitor for p38) these effects were inhibited. Furthermore, osteoblasts transfected with Ad-p38 also significantly upregulated the protein and gene expressions of noncollagens and SIBLINGs members, whereas transfection of p38-rhRNA showed the opposite effect. Our data suggest that osteonectin regulates the extracellular matrix mineralization of osteoblasts through the P38 signaling pathway.

Bone biology: insights from osteogenesis imperfecta and related rare fragility syndromes

The limited accessibility of bone and its mineralized nature have restricted deep investigation of its biology. Recent breakthroughs in identification of mutant proteins affecting bone tissue homeostasis in rare skeletal diseases have revealed novel pathways involved in skeletal development and maintenance. The characterization of new dominant, recessive and X-linked forms of the rare brittle bone disease osteogenesis imperfecta (OI) and other OI-related bone fragility disorders was a key player in this advance. The development of in vitro models for these diseases along with the generation and characterization of murine and zebrafish models contributed to dissecting previously unknown pathways. Here, we describe the most recent advances in the understanding of processes involved in abnormal bone mineralization, collagen processing and osteoblast function, as illustrated by the characterization of new causative genes for OI and OI-related fragility syndromes. The coordinated role of the integral membrane protein BRIL and of the secreted protein PEDF in modulating bone mineralization as well as the function and cross-talk of the collagen-specific chaperones HSP47 and FKBP65 in collagen processing and secretion are discussed. We address the significance of WNT ligand, the importance of maintaining endoplasmic reticulum membrane potential and of regulating intramembrane proteolysis in osteoblast homeostasis. Moreover, we also examine the relevance of the cytoskeletal protein plastin-3 and of the nucleotidyltransferase FAM46A. Thanks to these advances, new targets for the development of novel therapies for currently incurable rare bone diseases have been and, likely, will be identified, supporting the important role of basic science for translational approaches.

Leonurus sibiricus L. ethanol extract promotes osteoblast differentiation and inhibits osteoclast formation

Leonurus sibiricus L. (LS) is a medicinal plant used in East Asia, Europe and the USA. LS is primarily used in the treatment of gynecological diseases, and recent studies have demonstrated that it exerts anti-inflammatory and antioxidant effects. To the best of our knowledge, the present study demonstrated for the first time that LS may promote osteoblast differentiation and suppress osteoclast differentiation in vitro, and that it inhibited lipopolysaccharide (LPS)-induced bone loss in a mouse model. LS was observed to promote the osteoblast differentiation of MC3T3-E1 cells and upregulate the expression of runt-related transcription factor 2 (RUNX2), a key gene involved in osteoblast differentiation. This resulted in the induction of the expression of various osteogenic genes, including alkaline phosphatase (ALP), osteonectin (OSN), osteopontin (OPN), type I collagen (COL1) and bone sialoprotein (BSP). LS was also observed to inhibit osteoclast differentiation and bone resorption. The expression levels of nuclear factor of activated T-cells 1 (NFATc1) and c-Fos were inhibited following LS treatment. NFATc1 and c-Fos are key markers of osteoclast differentiation that inhibit receptor activator of nuclear factor-κB ligand (RANKL)-induced mitogen-activated protein kinase (MAPKs) and nuclear factor (NF)-κB. As a result, LS suppressed the expression of osteoclast-associated genes, such as matrix metallopeptidase-9 (MMP-9), cathepsin K (Ctsk), tartrate-resistant acid phosphatase (TRAP), osteoclast-associated immunoglobulin-like receptor (OSCAR), c-src, c-myc, osteoclast stimulatory transmembrane protein (OC-STAMP) and ATPase H+ transporting V0 subunit d2 (ATP6v0d2). Consistent with the in vitro results, LS inhibited the reduction in bone mineral density and the bone volume/total volume ratio in a mouse model of LPS-induced osteoporosis. These results suggest that LS may be a valuable agent for the treatment of osteoporosis and additional bone metabolic diseases.

Regulation of the bi-directional cross-talk between ovarian cancer cells and adipocytes by SPARC

Ovarian cancer (OvCa) exhibits a specific predilection for metastasis to the omentum. Our earlier studies highlighted the tumour-suppressor effect of secreted protein acidic and rich in cysteine (SPARC) in OvCa through multi-faceted roles inhibiting cancer cell interactions within the peritoneal milieu. The goal of this study is to investigate the role of SPARC in OvCa interactions with omental adipocytes and its role in OvCa colonization in the omentum. We employed multi-pronged approach using primary omental adipocytes from Sparc knockout mice, genetically engineered human omental adipocytes in 3D co-cultures with OvCa cells, as well as treatment with recombinant SPARC protein. We show that SPARC suppresses multistep cascade in OvCa omental metastasis. SPARC inhibited in vivo and adipocyte-induced homing, proliferation, and invasion of OvCa cells. SPARC suppressed metabolic programming of both adipocytes and OvCa cells and exerted an inhibitory effect of adipocyte differentiation and their phenotypic switch to cancer-associated phenotype. Mechanistic studies revealed that this effect is mediated through inhibition of cEBPβ-NFkB-AP-1 transcription machinery. These findings define a novel and functionally important role of SPARC in OvCa and not only bridge the knowledge gap but highlight the need to consider SPARC protein expression in therapeutic development.

Bone physiology as inspiration for tissue regenerative therapies

The development, maintenance of healthy bone and regeneration of injured tissue in the human body comprise a set of intricate and finely coordinated processes. However, an analysis of current bone regeneration strategies shows that only a small fraction of well-reported bone biology aspects has been used as inspiration and transposed into the development of therapeutic products. Specific topics that include inter-scale bone structural organization, developmental aspects of bone morphogenesis, bone repair mechanisms, role of specific cells and heterotypic cell contact in the bone niche (including vascularization networks and immune system cells), cell-cell direct and soluble-mediated contact, extracellular matrix composition (with particular focus on the non-soluble fraction of proteins), as well as mechanical aspects of native bone will be the main reviewed topics. In this Review we suggest a systematic parallelization of (i) fundamental well-established biology of bone, (ii) updated and recent advances on the understanding of biological phenomena occurring in native and injured tissue, and (iii) critical discussion of how those individual aspects have been translated into tissue regeneration strategies using biomaterials and other tissue engineering approaches. We aim at presenting a perspective on unexplored aspects of bone physiology and how they could be translated into innovative regeneration-driven concepts.

Human Osteoblast-Derived Extracellular Matrix with High Homology to Bone Proteome Is Osteopromotive

Efficient osteogenic differentiation of mesenchymal stromal cells (MSCs) is crucial to accelerate bone formation. In this context, the use of extracellular matrix (ECM) as natural 3D framework mimicking in vivo tissue architecture is of interest. The aim of this study was to generate a devitalized human osteogenic MSC-derived ECM and to investigate its impact on MSC osteogenic differentiation to improve MSC properties in bone regeneration. The devitalized ECM significantly enhanced MSC adhesion and proliferation. Osteogenic differentiation and mineralization of MSCs on the ECM were quicker than in standard conditions. The presence of ECM promoted in vivo bone formation by MSCs in a mouse model of ectopic calcification. We analyzed the ECM composition by mass spectrometry, detecting 846 proteins. Of these, 473 proteins were shared with the human bone proteome we previously described, demonstrating high homology to an in vivo microenvironment. Bioinformatic analysis of the 846 proteins showed involvement in adhesion and osteogenic differentiation, confirming the ECM composition as key modulator of MSC behavior. In addition to known ECM components, proteomic analysis revealed novel ECM functions, which could improve culture conditions. In summary, this study provides a simplified method to obtain an in vitro MSC-derived ECM that enhances osteogenic differentiation and could be applied as natural biomaterial to accelerate bone regeneration.

Microcalcifications in breast cancer: From pathophysiology to diagnosis and prognosis

The implementation of mammographic screening programmes in many countries has been linked to a marked increase in early detection and improved prognosis for breast cancer patients. Breast tumours can be detected by assessing several features in mammographic images but one of the most common are the presence of small deposits of calcium known as microcalcifications, which in many cases may be the only detectable sign of a breast tumour. In addition to their efficacy in the detection of breast cancer, the presence of microcalcifications within a breast tumour may also convey useful prognostic information. Breast tumours with associated calcifications display an increased rate of HER2 overexpression as well as decreased survival, increased risk of recurrence, high tumour grade and increased likelihood of spread to the lymph nodes. Clearly, the presence of microcalcifications in a tumour is a clinically significant finding, suggesting that a detailed understanding of their formation may improve our knowledge of the early stages of breast tumourigenesis, yet there are no reports which attempt to bring together recent basic science research findings and current knowledge of the clinical significance of microcalcifications. This review will summarise the most current understanding of the formation of calcifications within breast tissue and explore their associated clinical features and prognostic value.

Structural and functional maturation of skin during metamorphosis in the Atlantic halibut (Hippoglossus hippoglossus)

To establish if the developmental changes in the primary barrier and osmoregulatory capacity of Atlantic halibut skin are modified during metamorphosis, histological, histochemical, gene expression and electrophysiological measurements were made. The morphology of the ocular and abocular skin started to diverge during the metamorphic climax and ocular skin appeared thicker and more stratified. Neutral mucins were the main glycoproteins produced by the goblet cells in skin during metamorphosis. Moreover, the number of goblet cells producing neutral mucins increased during metamorphosis and asymmetry in their abundance was observed between ocular and abocular skin. The increase in goblet cell number and their asymmetric abundance in skin was concomitant with the period that thyroid hormones (THs) increase and suggests that they may be under the control of these hormones. Several mucin transcripts were identified in metamorphosing halibut transcriptomes and Muc18 and Muc5AC were characteristic of the body skin. Na⁺, K⁺-ATPase positive (NKA) cells were observed in skin of all metamorphic stages but their number significantly decreased with the onset of metamorphosis. No asymmetry was observed between ocular and abocular skin in NKA cells. The morphological changes observed were linked to modified skin barrier function as revealed by modifications in its electrophysiological properties. However, the maturation of the skin functional characteristics preceded structural maturation and occurred at stage 8 prior to the metamorphic climax. Treatment of Atlantic halibut with the THs disrupter methimazole (MMI) affected the number of goblet cells producing neutral mucins and the NKA cells. The present study reveals that the asymmetric development of the skin in Atlantic halibut is TH sensitive and is associated with metamorphosis and that this barrier's functional properties mature earlier and are independent of metamorphosis.

Osteogenic commitment and differentiation of human mesenchymal stem cells by low-intensity pulsed ultrasound stimulation

Low-intensity pulsed ultrasound (LIPUS) as an adjuvant therapy in in vitro and in vivo bone engineering has proven to be extremely useful. The present study aimed at investigating the effect of 30 mW/cm² LIPUS stimulation on commercially available human mesenchymal stem cells (hMSCs) cultured in basal or osteogenic medium at different experimental time points (7, 14, 21 days). The hypothesis was that LIPUS would improve the osteogenic differentiation of hMSC and guarantying the maintenance of osteogenic committed fraction, as demonstrated by cell vitality and proteomic analysis. LIPUS stimulation (a) regulated the balance between osteoblast commitment and differentiation by specific networks (activations of RhoA/ROCK signaling and upregulation of Ribosome constituent/Protein metabolic process, Glycolysis/Gluconeogenesis, RNA metabolic process/Splicing and Tubulins); (b) allowed the maintenance of a few percentage of osteoblast precursors (21 days CD73+/CD90+: 6%; OCT-3/4+/NANOG+/SOX2+: 10%); (c) induced the activation of osteogenic specific pathways shown by gene expression (early: ALPL, COL1A1, late: RUNX2, BGLAP, MAPK1/6) and related protein release (COL1a1, OPN, OC), in particular in the presence of osteogenic soluble factors able to mimic bone microenvironment. To summarize, LIPUS might be able to improve the osteogenic commitment of hMSCs in vitro, and, at the same time, enhance their osteogenic differentiation.

Associations between FGF21, osteonectin and bone turnover markers in type 2 diabetic patients with albuminuria

AIM

We measured the levels of bone turnover markers (BTMs) in patients with early diabetic nephropathy from type 2 diabetes mellitus (T2DM), and investigated the associations of BTMs with adipokines, serum fibroblast growth factor-21 (FGF21) and osteonectin.

METHODS

We included 159 males and 300 females with T2DM in this cross-sectional study. Clinical characteristics, BTMs and adipokines levels were measured.

RESULTS

One-hundred and ninety-two (41.8%) patients presented with albuminuria. Patients with albuminuria had significantly higher levels of serum osteonectin (P<0.0001) and FGF21 (P=0.0125) than those with normoalbuminuria. Serum levels of P1NP were slightly lower among patients with albuminuria (P=0.031), but the difference disappeared after adjusting for FBG, PBG, and HbA1c. Serum FGF21 levels were independently and negatively related to eGFR (overall β=-0.161, P=0.001; albuminuria group β=-0.240, P=0.001) but not related to uACR. While Osteonectin was independently and positively related to uACR (overall β=0.209, P=0.001; albuminuria group β=0.170, P=0.021). The levels of serum FGF21 were independently inversely related with P1NP (overall β=-0.192, P<0.0001; albuminuria group β=-0.195, P=0.031).

CONCLUSIONS

Our results suggest that persistent hyperglycemia may inhibit bone formation. Both osteonectin and FGF21 were associated with early nephropathy in T2DM patients, albeit with different patterns.

Characterisation of Cultured Mesothelial Cells Derived from the Murine Adult Omentum

The human omentum has been long regarded as a healing patch, used by surgeons for its ability to immunomodulate, repair and vascularise injured tissues. A major component of the omentum are mesothelial cells, which display some of the characteristics of mesenchymal stem/stromal cells. For instance, lineage tracing studies have shown that mesothelial cells give rise to adipocytes and vascular smooth muscle cells, and human and rat mesothelial cells have been shown to differentiate into osteoblast- and adipocyte-like cells in vitro, indicating that they have considerable plasticity. However, so far, long-term cultures of mesothelial cells have not been successfully established due to early senescence. Here, we demonstrate that mesothelial cells isolated from the mouse omentum could be cultured for more than 30 passages. While epithelial markers were downregulated over passages in the mesothelial cells, their mesenchymal profile remained unchanged. Early passage mesothelial cells displayed clonogenicitiy, expressed several stem cell markers, and up to passage 5 and 13, respectively, could differentiate along the adipogenic and osteogenic lineages, demonstrating stem/progenitor characteristics and differentiation potential.

MicroRNA variants as genetic determinants of bone mass

Single nucleotide polymorphisms (SNPs) are the most abundant genetic variants that contribute to the heritability of bone mass. MicroRNAs (miRNAs, miRs) are key post-transcriptional regulators that modulate the differentiation and function of skeletal cells by targeting multiple genes in the same or distinct signaling pathways. SNPs in miRNA genes and miRNA binding sites can alter miRNA abundance and mRNA targeting. This review describes the potential impact of miRNA-related SNPs on skeletal phenotype. Although many associations between SNPs and bone mass have been described, this review is limited to gene variants for which a function has been experimentally validated. SNPs in miRNA genes (miR-SNPs) that impair miRNA processing and alter the abundance of mature miRNA are discussed for miR-146a, miR-125a, miR-196a, miR-149 and miR-27a. SNPs in miRNA targeting sites (miR-TS-SNPs) that alter miRNA binding are described for the bone remodeling genes bone morphogenetic protein receptor 1 (Bmpr1), fibroblast growth factor 2 (Fgf2), osteonectin (Sparc) and histone deacetylase 5 (Hdac5). The review highlights two aspects of miRNA-associated SNPs: the mechanism for altering miRNA mediated gene regulation and the potential of miR-associated SNPs to alter osteoblast, osteoclast or chondrocyte differentiation and function. Given the polygenic nature of skeletal diseases like osteoporosis and osteoarthritis, validating the function of additional miRNA-associated SNPs has the potential to enhance our understanding of the genetic determinants of bone mass and predisposition to selected skeletal diseases.

SPARC/osteonectin in mineralized tissue

Secreted protein acidic and rich in cysteine (SPARC/osteonectin/BM40) is one of the most abundant non-collagenous protein expressed in mineralized tissues. This review will focus on elucidating functional roles of SPARC in bone formation building upon results from non-mineralized cells and tissues, the phenotype of SPARC-null bones, and recent discoveries of human diseases with either dysregulated expression of SPARC or mutations in the gene encoding SPARC that give rise to bone pathologies. The capacity of SPARC to influence pathways involved in extracellular matrix assembly such as procollagen processing and collagen fibril formation as well as the capacity to influence osteoblast differentiation and osteoclast activity will be addressed. In addition, the potential for SPARC to regulate cross-linking of extracellular matrix proteins by members of the transglutaminase family of enzymes is explored. Elucidating defined biological functions of SPARC in terms of bone formation and turnover are critical. Further insight into specific cellular mechanisms involved in the formation and homeostasis of mineralized tissues will lead to a better understanding of disease progression.

Matricellular proteins as regulators of cancer metastasis to bone

Metastasis is the major cause of death in cancer patients, and a frequent site of metastasis for many cancers is the bone marrow. Therefore, understanding the mechanisms underlying the metastatic process is necessary for future prevention and treatment. The tumor microenvironment is now known to play a role in the metastatic cascade, both at the primary tumor and in metastatic sites, and includes both cellular and non-cellular components. The extracellular matrix (ECM) provides structural support and signaling cues to cells. One particular group of molecules associated with the ECM, known as matricellular proteins, modulate multiple aspects of tumor biology, including growth, migration, invasion, angiogenesis and metastasis. These proteins are also important for normal function in the bone by regulating bone formation and bone resorption. Recent studies have described a link between some of these proteins and metastasis of various tumors to the bone. The aim of this review is to summarize what is currently known about matricellular protein influence on bone metastasis. Particular attention to the contribution of both tumor cells and non-malignant cells in the bone has been given.

The secreted protein acidic and rich in cysteine is a critical mediator of cell death program induced by WIN/TRAIL combined treatment in osteosarcoma cells

Secreted protein acidic and rich in cysteine (SPARC) is a multi-functional protein which modulates cell-cell and cell-matrix interactions. In cancer cells, SPARC behaves as a tumor promoter in a number of tumors, but it can also act as a tumor suppressor factor. Our previous results showed that the synthetic cannabinoid WIN55,212-2 (WIN), a potent cannabinoid receptor agonist, is able to sensitize osteosarcoma MG63 cells to TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis which is accompanied with endoplasmic reticulum (ER)-stress induction and the increase in autophagic markers. In the present investigation, we studied the role of SPARC in WIN/TRAIL-induced apoptosis demonstrating that WIN increased the level of SPARC protein and mRNA in a time-dependent manner. This event was functional to WIN/TRAIL-dependent apoptosis as demonstrated by RNA interfering analysis which indicated that SPARC-silenced cells were less sensitive to cytotoxic effects induced by the combined treatment. Our experiments also demonstrate that SPARC interacts with caspase-8 thus probably favoring its translocation to plasma membrane and the activation of extrinsic apoptotic pathway. In conclusion, to the best of our knowledge, our results are the first to show that WIN-dependent increase in the level of SPARC plays a critical role in sensitizing osteosarcoma cells to TRAIL action.

Decreased Mechanical Strength and Collagen Content in SPARC-Null Periodontal Ligament Is Reversed by Inhibition of Transglutaminase Activity

The periodontal ligament (PDL) is a critical tissue that provides a physical link between the mineralized outer layer of the tooth and the alveolar bone. The PDL is composed primarily of nonmineralized fibrillar collagens. Expression of secreted protein acidic and rich in cysteine (SPARC/osteonectin), a collagen-binding matricellular protein, has been shown to be essential for collagen homeostasis in PDL. In the absence of SPARC, PDL collagen fibers are smaller and less dense than fibers that constitute WT PDL. The aim of this study was to identify cellular mechanisms by which SPARC affected collagen fiber assembly and morphology in PDL. Cross-linking of fibrillar collagens is one parameter that is known to affect insoluble collagen incorporation and fiber morphology. Herein, the reduction in collagen fiber size and quantity in the absence of SPARC expression was shown to result in a PDL with reduced molar extraction force in comparison to that of WT mice (C57Bl/6J). Furthermore, an increase in transglutaminase activity was found in SPARC-null PDL by biochemical analyses that was supported by immunohistochemical results. Specifically, collagen I was identified as a substrate for transglutaminase in PDL and transglutaminase activity on collagen I was found to be greater in SPARC-null tissues in comparison to WT. Strikingly, inhibition of transglutaminase activity in SPARC-null PDL resulted in increases in both collagen fiber thickness and in collagen content, whereas transglutaminase inhibitors injected into WT mice resulted in increases in collagen fiber thickness only. Furthermore, PDL treated with transglutaminase inhibitors exhibited increases in molar extraction force in WT and in SPARC-null mice. Thus, SPARC is proposed to act as a critical regulator of transglutaminase activity on collagen I with implications for mechanical strength of tissues.

OP9 Stromal Cells Proteins Involved in Hematoendothelial Differentiation from Human Embryonic Stem Cells

Hematopoietic cells (HCs) and endothelial cells (ECs) can be produced in vitro from human embryonic stem cells (hESCs), but the differentiation systems used are still inefficient. To overcome this obstacle, it is necessary to understand the differentiation process. One of the methods used to obtain HCs and ECs from hESCs is their co-culture with stromal cells. The soluble factors secreted by these cells and cell-cell contact have a great impact on the differentiation process. Here, we performed comparative proteomic analyses of proteins obtained from the total extract of OP9 stromal cells and secreted by these cells before and during in vitro generation of HCs and ECs (hematoendothelial) from hESCs. We identified a total of 83 secreted and 759 intracellular proteins during differentiation. Twenty-five secreted and 181 proteins from the total extract were more abundant. Some secreted proteins are involved in cell-matrix interactions and HC and/or EC development. Moreover, 13 proteins of the total extract from OP9 cells that were exclusive/or more abundant during differentiation are involved in the Nrf2/Nfe2l2 gene pathway, that is, they are described to have a key role in oxidative stress and in hematopoietic development and maturation. Our proteomic profiles provide valuable insight about the proteins involved in in vitro hematoendothelial cell generation and in the future they might be used to optimize the differentiation process and produce both cell types in vitro.

An Attempt to Evaluate Selected Aspects of "Bone-Fat Axis" Function in Healthy Individuals and Patients With Pancreatic Cancer

Recently, much attention has been paid to a potential biochemical cross-talk between the metabolism of the adipose tissue (AT) and bone (marrow), termed "bone-fat axis." We hypothesized that selected substances, participating in this "dialog," are associated with body mass and peripheral trafficking of bone marrow-derived stem cells (BMSCs) in both healthy individuals and patients with obesity-associated malignancies such as pancreatic adenocarcinoma.We performed an analysis of the systemic levels of selected substances involved in the regulation of bone (marrow) homeostasis (parathormone, calcitonin, osteopontin, osteonectin, stem cell factor [SCF], and fibroblast growth factor-23) in 35 generally healthy volunteers and 35 patients with pancreatic cancer. Results were correlated with the absolute number of circulating BMSCs and body mass values. Additionally, subcutaneous and visceral/omental AT levels of the aforementioned molecules were analyzed in lean and overweight/obese individuals.Intensified steady-state trafficking of only Lin-CD45 + CD133 + hematopoietic stem/progenitor cells was observed in overweight/obese individuals and this was associated with BMI values and elevated levels of both osteonectin and SCF, which also correlated with BMI. In comparison to healthy individuals, patients with cancer had significantly higher osteopontin levels and lower values of both osteonectin and osteonectin/osteopontin ratio. While no significant correlation was observed between BMI and the number of circulating BMSCs in patients with cancer, peripheral trafficking of CD34 + KDR + CD31 + CD45-endothelial progenitor cells and CD105 + STRO-1 + CD45-mesenchymal stem cells was associated with the osteonectin/osteopontin ratio, which also correlated with BMI (r = 0.52; P < 0.05). AT levels of the examined substances were similar to those measured in the plasma, except for osteonectin, which was about 10 times lower.Our study highlights the potential role of osteonectin, osteopontin, and SCF as communication signals between the bone (marrow) and AT in both healthy individuals and patients with pancreatic cancer. We postulate that these molecules may be overlooked biochemical players linking body mass and BMSCs with obesity-associated cancer development and/or progression in humans.