Zebrafish scales respond differently to in vitro dynamic and static acceleration: Analysis of interaction between osteoblasts and osteoclasts

Reduced ossification caused by 3D simulated microgravity exposure is short-term in larval zebrafish

Understanding how skeletal tissues respond to microgravity is ever more important with the increased interest in human space travel. Here, we exposed larval Danio rerio at 3.5 dpf to simulated microgravity (SMG) using a 3D mode of rotation in a ground-based experiment and then studied different cellular, molecular, and morphological bone responses both immediately after exposure and one week later. Our results indicate an overall decrease in ossification in several developing skeletal elements immediately after SMG exposure with the exception of the otoliths, however ossification returns to normal levels seven days after exposure. Coincident with the reduction in overall ossification tnfsf11 (RANKL) expression is highly elevated after 24 h of SMG exposure and also returns to normal levels seven days after exposure. We also show that genes associated with osteoblasts are unaffected immediately after SMG exposure. Thus, the observed reduction in ossification is primarily the result of a high level of bone resorption. This study sheds insight into the nuances of how osteoblasts and osteoclasts in the skeleton of a vertebrate organism respond to an external environmental disturbance, in this case simulated microgravity.

Transcriptomic and proteomic strategies to reveal the mechanism of Gymnocypris przewalskii scale development

BACKGROUND

Fish scales are typical products of biomineralization and play an important role in the adaptation of fish to their environment. The Gymnocypris przewalskii scales are highly specialized, with scales embedded in only specific parts of the dermis, such as the areas around the anal fin and branchiostegite, making G. przewalskii an ideal material for biomineralization research. In this study, we aimed to unveil genes and pathways controlling scale formation through an integrated analysis of both transcriptome and proteome, of which G. przewalskii tissues of the dorsal skin (no scales) and the rump side skin (with scales) were sequenced. The sequencing results were further combined with cellular experiments to clarify the relationship between genes and signaling pathways.

RESULTS

The results indicated the following: (1) a total of 4,904 differentially expressed genes were screened out, including 3,294 upregulated genes and 1,610 downregulated genes (with a filtering threshold of |log2Fold-Change|> 1 and p-adjust < 0.05). The identified differentially expressed genes contained family members such as FGF, EDAR, Wnt10, and bmp. (2) A total of 535 differentially expressed proteins (DEPs) were filtered out from the proteome, with 204 DEPs downregulated and 331 DEPs upregulated (with a filtering threshold of |Fold-Change|> 1.5 and p < 0.05). (3) Integrated analyses of transcriptome and proteome revealed that emefp1, col1a1, col6a2, col16a1, krt8, and krt18 were important genes contributing to scale development and that PI3K-AKT was the most important signaling pathway involved. (4) With the use of the constructed G. przewalskii fibroblast cell line, emefp1, col1a1, col6a2, col16a1, krt8, and krt18 were confirmed to be positively regulated by the PI3K-AKT signaling pathway.

CONCLUSION

This study provides experimental evidence for PI3K-AKT controlled scale development in G. przewalskii and would benefit further study on stress adaptation, scale biomineralization, and the development of skin appendages.

Attenuative effects of collagen peptide from milkfish (Chanos chanos) scales on ovariectomy-induced osteoporosis

Osteoporosis is characterized by low bone mass, bone microarchitecture disruption, and collagen loss, leading to increased fracture risk. In the current study, collagen peptides were extracted from milkfish scales (MS) to develop potential therapeutic candidates for osteoporosis. MS was used to synthesize a crude extract of fish scales (FS), collagen liquid (COL), and hydroxyapatite powder (HA). COL samples were further categorized according to the peptide size of total COL (0.1 mg/mL), COL < 1 kDa (0.1 mg/mL), COL: 1-10 kDa (0.1 mg/mL), and COL > 10 kDa (0.1 mg/mL) to determine it. Semi-quantitative reverse transcription polymerase chain reaction (sqRT-PCR) and immunofluorescence labeling were used to assess the expression levels of specific mRNA and proteins in vitro. For in vivo studies, mice ovariectomy (OVX)-induced postmenopausal osteoporosis were developed, while the sham surgery (Sham) group was treated as a control. Collagen peptides (CP) from MS inhibited osteoclast differentiation in RAW264.7 cells following an insult with nuclear factor kappa-B ligand (RANKL). CP also enhanced osteoblast proliferation in MG-63 cells, possibly through downregulating NFATc1 and TRAP mRNA expression and upregulating ALP and OPG mRNA levels. Furthermore, COL1 kDa also inhibited bone density loss in osteoporotic mice. Taken together, CP may reduce RANKL-induced osteoclast activity while promoting osteoblast synthesis, and therefore may act as a potential therapeutic agent for the prevention and control of osteoporosis.

Leptin and melatonin's effects on OVX rodents' bone metabolism

Purpose

This study aims to examine the effects of leptin and melatonin intervention on bone metabolism in ovariectomize (OVX) rodents, as well as their potential mechanisms of action.

Methods

Prepare an OVX model of osteoporosis in rodents and validate the model by collecting bilateral tibia samples for Micro-CT scanning and histological analysis. A control group of normal size, the OVX group, the OVX+Sema4D (Semaphorin 4D) group, the OVX+Sema4D+Leptin group, the OVX+Sema4D+ Melatonin(MT) group and the OVX+Sema4D+Leptin+ MT group were the experimental groups. Adenovirus vector construction and tibial medullary injection validation were conducted in accordance with the aforementioned experimental groups. Four groups of rats were injected with the Sema4D overexpression adenovirus vector into the tibial medullary cavity, and two groups were injected with the Leptin overexpression adenovirus vector. The repair of osteoporosis was observed using micro-CT and histological analysis. Immunohistochemical detection of bone morphogenetic protein-2 (BMP-2) expression in bone tissue was employed to ascertain the amount of osteoclasts in the upper tibial metaphysis, utilizing TRAP(tartrate-resistant acid phosphatase) staining.

Results

Increased levels of BV/TV, Tb.N, BMD, and BMC were seen in the OVX+ Sema4D+Leptin, OVX+ Sema4D+MT, and OVX+ Sema4D+Leptin+ MT groups compared to the OVX group, whereas Tb. Sp levels were lowered. When compared to the Sema4D overexpression group, the trabecular bone structure of the OVX + Sema4D + Leptin, OVX + Sema4D + MT, and OVX + Sema4D + Leptin + MT groups is largely intact, tends to be closer, and the amount of trabecular bone increases. The OVX + Sema4D + Leptin + MT group in particular.The expression of BMP-2 was dramatically upregulated (p<0.05), the number of TRAP-stained osteoclasts was significantly reduced (p<0.05), and BALP(bone-derived alkaline phosphatase) and TRAP-5b(tartrate-resistant acid phosphatase-5b) activities were significantly downregulated (p<0.05).

Conclusion

In rats with osteoporosis, leptin and melatonin can be seen to augment the trabecular microstructure of the bone, augment bone growth, diminish trabecular harm, and mend the bone. The combined effect is more powerful.

Isoorientin ameliorates osteoporosis and oxidative stress in postmenopausal rats

CONTEXT

Isoorientin has many biological activities, including antioxidant, anti-inflammatory, antitumor. However, the effect of isoorientin on postmenopausal osteoporosis remains unclear.

OBJECTIVE

To evaluate the effect of isoorientin on postmenopausal osteoporosis.

MATERIALS AND METHODS

Sprague-Dawley rats were divided into five groups (n = 5): sham, model, 17-β-oestradiol (E2, 10 μg/kg/day), low-dose isoorientin (L-Iso, 50 mg/kg), and high-dose isoorientin (H-Iso, 100 mg/kg). The rats were ovariectomized, treated by gavage daily for 12 weeks, and serum and femur samples were collected. Bone mineral density, bone metabolism, and oxidative stress were assessed. H&E staining, immunohistochemistry, and western blotting were employed.

RESULTS

Isoorientin improved the bone mineral density of the lumbar vertebrae (2.01 ± 0.05 g/cm³ in H-Iso group vs. 1.74 ± 0.07 g/cm³ in model group) and femur (1.46 ± 0.06 g/cm³ vs. 1.19 ± 0.03 g/cm³), increased the trabecular bone number (1.97 ± 0.03 vs. 1.18 ± 0.13) and thickness (0.27 ± 0.02 vs. 0.16 ± 0.03 mm). Isoorientin decreased the separation degree of trabecular bone, ameliorated bone histomorphology changes, and significantly improved the mechanical properties. Isoorientin diminished MDA (by 60%) and increased SOD (by 49.2%), and GSH-Px (by 159%) activity. Furthermore, osteoprotegerin (OPG), nuclear factor erythroid 2-like 2 (Nrf2), haem oxygenase (HO-1), NAD(P)H quinone dehydrogenase 1(NQO1), and oestrogen receptor 1(ESR1) protein expression increased, while receptor activator of nuclear factor-κB ligand (RANKL) protein expression decreased after treatment.

CONCLUSIONS

Isoorientin ameliorates osteoporosis via upregulating OPG and Nrf2/ARE signalling, suggesting isoorientin maybe a potential therapeutic drug for PMOP.

Expression variations in ectodysplasin-A gene (eda) may contribute to morphological divergence of scales in haplochromine cichlids

BACKGROUND

Elasmoid scales are one of the most common dermal appendages and can be found in almost all species of bony fish differing greatly in their shape. Whilst the genetic underpinnings behind elasmoid scale development have been investigated, not much is known about the mechanisms involved in moulding of scales. To investigate the links between gene expression differences and morphological divergence, we inferred shape variation of scales from two different areas of the body (anterior and posterior) stemming from ten haplochromine cichlid species from different origins (Lake Tanganyika, Lake Malawi, Lake Victoria and riverine). Additionally, we investigated transcriptional differences of a set of genes known to be involved in scale development and morphogenesis in fish.

RESULTS

We found that scales from the anterior and posterior part of the body strongly differ in their overall shape, and a separate look on scales from each body part revealed similar trajectories of shape differences considering the lake origin of single investigated species. Above all, nine as well as 11 out of 16 target genes showed expression differences between the lakes for the anterior and posterior dataset, respectively. Whereas in posterior scales four genes (dlx5, eda, rankl and shh) revealed significant correlations between expression and morphological differentiation, in anterior scales only one gene (eda) showed such a correlation. Furthermore, eda displayed the most significant expression difference between species of Lake Tanganyika and species of the other two younger lakes. Finally, we found genetic differences in downstream regions of eda gene (e.g., in the eda-tnfsf13b inter-genic region) that are associated with observed expression differences. This is reminiscent of a genetic difference in the eda-tnfsf13b inter-genic region which leads to gain or loss of armour plates in stickleback.

CONCLUSION

These findings provide evidence for cross-species transcriptional differences of an important morphogenetic factor, eda, which is involved in formation of ectodermal appendages. These expression differences appeared to be associated with morphological differences observed in the scales of haplochromine cichlids indicating potential role of eda mediated signal in divergent scale morphogenesis in fish.

Fermented Oyster (Crassostrea gigas) Extract Cures and Prevents Prednisolone-Induced Bone Resorption by Activating Osteoblast Differentiation

Osteoporosis is a bone resorptive disease characterized by the loss of bone density, causing an increase in bone fragility. In our previous study, we demonstrated that gamma aminobutyric acid-enriched fermented oyster (Crassostrea gigas) extract (FO) stimulated osteogenesis in MC3T3-E1 preosteoblast cells and vertebral formation in zebrafish. However, the efficacy of FO in prednisolone (PDS)-induced bone resorption remains unclear. In this study, we evaluated the osteogenic potential of FO in MC3T3-E1 preosteoblast cells and zebrafish larvae under both PDS-pretreated and PDS-post-treated conditions. We found that FO recovered osteogenic activity by upregulating osteoblast markers, such as alkaline phosphatase (ALP), runt-related transcription factor 2, and osterix, in both PDS-pretreated and post-treated MC3T3-E1 osteoblast cells and zebrafish larvae. In both conditions, PDS-induced decrease in calcification and ALP activity was recovered in the presence of FO. Furthermore, vertebral resorption in zebrafish larvae induced by pretreatment and post-treatment with PDS was restored by treatment with FO, along with the recovery of osteogenic markers and downregulation of osteoclastogenic markers. Finally, whether FO disturbs the endocrine system was confirmed according to the Organization for Economic Cooperation and Development guideline 455. We found that FO did not stimulate estrogen response element-luciferase activity or proliferation in MCF7 cells. Additionally, in ovariectomized mice, no change in uterine weight was observed during FO feeding. These results indicate that FO effectively prevents and treats PDS-induced osteoporosis without endocrine disturbances.

Fisetin promotes osteoblast differentiation and osteogenesis through GSK-3β phosphorylation at Ser9 and consequent β-catenin activation, inhibiting osteoporosis

Fisetin is a bioactive flavonol that inhibits osteoclastogenesis and promotes osteoblastogenesis. However, the osteogenic activity of fisetin needs to be comprehensively elucidated. In the present study, we observed that fisetin significantly increased alkaline phosphatase (ALP) activity and bone mineralization in MC3T3-E1 preosteoblasts, accompanied by a significant increase in runt-related transcription factor 2 (RUNX2), ALP, collagen type Ⅰ alpha 1 (Col1α1), osterix (OSX), osteocalcin (OCN), and bone morphogenetic protein 4 (BMP4) expression. Furthermore, fisetin promoted vertebral formation in zebrafish larvae, with the highest fisetin concentration comparable with that observed in β-glycerophosphate treatment. Fisetin also inhibited prednisolone (PDS)-induced anti-osteoblastic genes, including nuclear factor of activated T-cells cytoplasmic 1 (NFATc1), tartrate-resistant acid phosphatase-6 (ACP6), dendritic cell-specific transmembrane protein (DC-STAMP), and cathepsin K (CTSK). Fisetin potently mitigated the PDS-induced inhibition of ALP activity and bone mineralization, as well as vertebral resorption in zebrafish larvae. Moreover, we confirmed that fisetin-induced osteogenic effect was activated through phosphorylation of glycogen synthase kinase-3β (GSK-3β) at Ser9, consequently releasing β-catenin from the destructive complex to promote its nuclear translocation. β-Catenin inhibition by FH535 and the stabilization of GSK-3β by DOI hydrochloride remarkably inhibited fisetin-induced osteogenic activities, indicating that the GSK-3β/β-catenin signaling pathway plays a vital role in fisetin-induced osteogenesis. Collectively, our findings suggest that fisetin stimulates osteogenic activity and could be used as an effective strategy to prevent bone resorption.

Zebrafish as a potential biomaterial testing platform for bone tissue engineering application: A special note on chitosan based bioactive materials

Biomaterials function as an essential aspect of tissue engineering and have a profound impact on cell growth and subsequent tissue regeneration. The development of new biomaterials requires a potential platform to understand the host-biomaterial interaction, which is crucial for successful biomaterial implantation. Biomaterials analyzed in rodent models for in vivo research are cost-effective but tedious, and the practice has many technical difficulties. As an alternative, zebrafish provide an excellent biomaterial testing platform over the current rodent models. During growth and recovery, zebrafish bone morphogenesis shows a variety of inductive signals involved in the cycle that are close to those influencing differentiation of bone and cartilage in mammals, including humans. This platform is cheap, optically transparent, quick to change genes, and provides reliable reproducibility on short life cycles. Chitosan is a well-known biomaterial in the field of tissue engineering. In view of its documented use in bone regeneration, the biological characterization of chitosan-based bioactive materials in the zebrafish model has been featured in an outstanding note. We, therefore, outlined this review of the zebrafish as a potential in vivo research model for the rapid characterization of the biological properties of new biomaterials for bone tissue engineering applications.

Age-dependent modulation of bone metabolism in zebrafish scales as new model of male osteoporosis in lower vertebrates

After middle age, in human bone, the resorption usually exceeds formation resulting in bone loss and increased risk of fractures in the aged population. Only few in vivo models in higher vertebrates are available for pathogenic and therapeutic studies about bone aging. Among these, male Danio rerio (zebrafish) can be successfully used as low vertebrate model to study degenerative alterations that affect the skeleton during aging, reducing the role of sex hormones.

In this paper, we investigated the early bone aging mechanisms in male zebrafish (3, 6, 9 months old) scales evaluating the physiological changes and the effects of prednisolone, a pro-osteoporotic drug.

The results evidentiated an age-dependent reduction of the mineralization rate in the fish scales, as highlighted by growing circle measurements. Indeed, the osteoblastic ALP activity at the matrix deposition site was found progressively downregulated.

The higher TRAP activity was found in 63% of 9-month-old fish scales associated with resorption lacunae along the scale border. Gene expression analysis evidentiated that an increase of the tnfrsf1b (homolog of human rank) in aging scales may be responsible for resorption stimulation.

Interestingly, prednisolone inhibited the physiological growth of the scale and induced in aged scales a more significant bone resorption compared with untreated fish (3.8% vs 1.02%). Bone markers analysis shown a significant reduction of ALP/TRAP ratio due to a prednisolone-dependent stimulation of tnfsf11 (homolog of human rankl) in scales of older fish.

The results evidentiated for the first time the presence of a senile male osteoporosis in lower vertebrate. This new model could be helpful to identify the early mechanisms of bone aging and new therapeutic strategies to prevent age-related bone alterations in humans.

Zebrafish: A Suitable Tool for the Study of Cell Signaling in Bone

In recent decades, many studies using the zebrafish model organism have been performed. Zebrafish, providing genetic mutants and reporter transgenic lines, enable a great number of studies aiming at the investigation of signaling pathways involved in the osteoarticular system and at the identification of therapeutic tools for bone diseases. In this review, we will discuss studies which demonstrate that many signaling pathways are highly conserved between mammals and teleost and that genes involved in mammalian bone differentiation have orthologs in zebrafish. We will also discuss as human diseases, such as osteogenesis imperfecta, osteoarthritis, osteoporosis and Gaucher disease can be investigated in the zebrafish model.

Terrestrial acclimation and exercise lead to bone functional response in Polypterus senegalus pectoral fins

The ability of bones to sense and respond to mechanical loading is a central feature of vertebrate skeletons. However, the functional demands imposed on terrestrial and aquatic animals differ vastly. The pectoral girdle of the basal actinopterygian fish Polypterus senegalus was previously shown to exhibit plasticity following terrestrial acclimation, but the pectoral fin itself has yet to be examined. We investigated skeletal plasticity in the pectoral fins of P. senegalus after exposure to terrestrial loading. Juvenile fish were divided into three groups: a control group was kept under aquatic conditions without intervention, an exercised group was also kept in water but received daily exercise on land, and a terrestrial group was kept in a chronic semi-terrestrial condition. After 5 weeks, the pectoral fins were cleared and stained with Alcian Blue and Alizarin Red to visualize cartilage and bone, allowing measurements of bone length, bone width, ossification and curvature to be taken for the endochondral radial bones. Polypterus senegalus fin bones responded most strongly to chronic loading in the terrestrial condition. Fish that were reared in a terrestrial environment had significantly longer bones compared with those of aquatic controls, wider propterygia and metapterygia, and more ossified metapterygia and medial radials, and they showed changes in propterygial curvature. Exercised fish also had longer and more ossified medial radials compared with those of controls. Polypterus senegalus fin bones exhibit plasticity in response to novel terrestrial loading. Such plasticity could be relevant for transitions between water and land on evolutionary scales, but key differences between fish and tetrapod bone make direct comparisons challenging.

A role for G protein-coupled receptor 137b in bone remodeling in mouse and zebrafish

G protein-coupled receptor 137b (GPR137b) is an orphan seven-pass transmembrane receptor of unknown function. In mouse, Gpr137b is highly expressed in osteoclasts in vivo and is upregulated during in vitro differentiation. To elucidate the role that GPR137b plays in osteoclasts, we tested the effect of GPR137b deficiency on osteoclast maturation and resorbing activity. We used CRISPR/Cas9 gene editing in mouse-derived ER-Hoxb8 immortalized myeloid progenitors to generate GPR137b-deficient osteoclast precursors. Decreasing Gpr137b in these precursors led to increased osteoclast differentiation and bone resorption activity. To explore the role of GPR137b during skeletal development, we generated zebrafish deficient for the ortholog gpr137ba. Gpr137ba-deficient zebrafish are viable and fertile and do not display overt morphological defects as adults. However, analysis of osteoclast function in gpr137ba^-/- mutants demonstrated increased bone resorption. Micro-computed tomography evaluation of vertebral bone mass and morphology demonstrated that gpr137ba-deficiency altered the angle of the neural arch, a skeletal site with high osteoclast activity. Vital staining of gpr137ba^-/- fish with calcein and alizarin red indicated that bone formation in the mutants is also increased, suggesting high bone turnover. These results identify GPR137b as a conserved negative regulator of osteoclast activity essential for normal resorption and patterning of the skeleton. Further, these data suggest that coordination of osteoclast and osteoblast activity is a conserved process among vertebrates and may have similar regulation.

Liquiritigenin Reduces Blood Glucose Level and Bone Adverse Effects in Hyperglycemic Adult Zebrafish

Diabetes mellitus is a metabolic disease characterized by chronic hyperglycemia that induces other pathologies including diabetic retinopathy and bone disease. Adult Danio rerio (zebrafish) represents a powerful model to study both glucose and bone metabolism. Then, the aim of this study was to evaluate the effects of liquiritigenin (LTG) on blood glucose level and diabetes complications in hyperglycemic adult zebrafish. LTG is a flavonoid extracted from Glycyrrhiza glabra roots which possess important antioxidant, anti-inflammatory, and anti-diabetic properties. During four weeks of glucose treatment, LTG significantly prevented the onset of the hyperglycemia in adult zebrafish. Moreover, hyperglycemic fish showed increased advanced glycation end-products (AGEs) and parathormone levels whereas LTG completely prevented both of these metabolic alterations. Large bone-loss areas were found in the scales of glucose-treated fish whereas only small resorption lacunae were detected after glucose/LTG treatment. Biochemical and histological tartrate resistant acid phosphatase (TRAP) assays performed on explanted scales confirmed that LTG prevented the increase of osteoclastic activity in hyperglycemic fish. The osteoblastic alkaline phosphatase (ALP) activity was clearly lost in scales of glucose-treated fish whereas the co-treatment with LTG completely prevented such alteration. Gene expression analysis showed that LTG prevents the alteration in crucial bone regulatory genes. Our study confirmed that LTG is a very promising natural therapeutic approach for blood glucose lowering and to contrast the development of bone complications correlated to chronic hyperglycemia.

Involvement of Bone in Systemic Endocrine Regulation

The skeleton shows an unconventional role in the physiology and pathophysiology of the human organism, not only as the target tissue for a number of systemic hormones, but also as endocrine tissue modulating some skeletal and extraskeletal systems. From this point of view, the principal cells in the skeleton are osteocytes. These cells primarily work as mechano-sensors and modulate bone remodeling. Mechanically unloaded osteocytes synthetize sclerostin, the strong inhibitor of bone formation and RANKL, the strong activator of bone resorption. Osteocytes also express hormonally active vitamin D (1,25(OH)2D) and phosphatonins, such as FGF23. Both 1,25(OH)2D and FGF23 have been identified as powerful regulators of the phosphate metabolism, including in chronic kidney disease. Further endocrine cells of the skeleton involved in bone remodeling are osteoblasts. While FGF23 targets the kidney and parathyroid glands to control metabolism of vitamin D and phosphates, osteoblasts express osteocalcin, which through GPRC6A receptors modulates beta cells of the pancreatic islets, muscle, adipose tissue, brain and testes. This article reviews some knowledge concerning the interaction between the bone hormonal network and phosphate or energy homeostasis and/or male reproduction.

Sanggenon C Stimulates Osteoblastic Proliferation and Differentiation, Inhibits Osteoclastic Resorption, and Ameliorates Prednisone-Induced Osteoporosis in Zebrafish Model

Sanggenon C (SC), which is a natural flavonoid found in the stem bark of Cortex Mori, has been discovered to have the antioxidant, anti-inflammatory, and antitumor properties. However, its effect in osteoporosis has not yet been reported. In this research, the effect of SC on the proliferation of MC3T3-E1 cells was evaluated by using the MTT assay. Alkaline phosphatase (ALP) activity and the mRNA expression of Runx2, Collagen I, OPG, and RANKL were examined. TRAP-positive cell counting and bone resorption pits were adopted to observe the effect of SC on the formation and function of osteoclasts. Next, the mRNA level of TRAP, CTSK, NFATc1, and TRAF6 of osteoclasts were measured by real-time qPCR. In addition, the anti-osteoporosis activity of SC in vivo was evaluated in the zebrafish model. Our study indicated that SC exhibited a significant stimulatory effect on MC3T3-E1 cell proliferation at 1 to 10 μM and caused an increase in ALP activity at 0.3 to 10 μM. It could upregulate the expression of Runx2, Collagen I, and increases the OPG/RANKL ratio. Furthermore, SC was found to inhibit the formation and function of osteoclasts, which is demonstrated by a lower number of TRAP-positive multinuclear cells and a fewer area of bone resorption pits compared to the control group. TRAP, CTSK, and NFATc1 were downregulated in 0.3 to 10 μM SC treated groups. In addition, 3 to 10 μM SC also inhibited the expression of TRAF6 mRNA. When prednisone-induced zebrafish was treated with 0.3, 1, 3, and 10 μM SC, higher mineralization of vertebrate column was discovered in a dose-dependent pattern, which suggests that SC could reverse the bone loss of zebrafish caused by prednisone. In summary, these findings indicated that SC has the potential to prevent or treat osteoporosis.

Metabolic and bone effects of high-fat diet in adult zebrafish

An increase of visceral fat affects human bone health causing fragility, mechanical strength reduction, and increased propensity to fractures because of impaired bone matrix microstructure and aberrant bone cell function. Adult Danio rerio (zebrafish) represents a powerful model to study both metabolic diseases and bone metabolism. The aim of this study was to generate an obese adult zebrafish by high-fat diet and evaluate metabolic and bone tissue effects. Fish blood glucose and insulin levels were found to be altered in high-fat diet fish revealing a failure in β-cells insulin production. Blood analysis of adipokines revealed significant alterations in adiponectin and leptin levels that are common in human and other obesity animal models. Advanced glycation end products (AGEs), derived from hyperglycemia condition, were found to be altered too. All these alterations were associated with an impaired bone metabolism. The scales of high-fat diet fish shown bone resorption lacunae associated with an intense osteoclastic tartrate-resistant acid phosphatase (TRAP) activity, whereas alkaline phosphatase (ALP) decreased. These data suggest that an imbalance of fat metabolism alters energy metabolism generating an osteoporosis-like phenotype in adult zebrafish scales. The zebrafish obesity model can contribute to elucidate in vivo the molecular mechanisms of metabolic changes in human obese patients.

RANKL, Ephrin-Eph and Wnt10b are key intercellular communication molecules regulating bone remodeling in autologous transplanted goldfish scales

This study aimed to investigate the precise data of gene expression, functions, and chronological relationships amongst communication molecules involved in the bone remodeling process with an in vivo model using autologous transplanted scales of goldfish. Autotransplantation of methanol-fixed cell-free scales triggers scale resorption and regeneration, as well as helps elucidate the process of bone remodeling. We investigated osteoclastic markers, osteoblastic markers, and gene expressions of communicating molecules (RANKL, ephrinB2, EphB4, EphA4, Wnt10b) by qPCR, in situ hybridization for Wnt10b, and immunohistochemistry for EphrinB2 and EphA4 proteins to elucidate the bone remodeling process. Furthermore, functional inhibition experiments for the signaling of ephrinB2/Eph, ephrin/EphA4, and Wnt10b using specific antibodies, revealed that these proteins are involved in key signaling pathways promoting normal bone remodeling. Our data suggests that the remodeling process comprises of two successive phases. In the first absorption phase, differentiation of osteoclast progenitors by RANKL is followed by the bone absorption by mature, active osteoclasts, with the simultaneous induction of osteoblast progenitors by multinucleated osteoclast-derived Wnt10b, and proliferation of osteoblast precursors by ehprinB2/EphB4 signaling. Subsequently, during the second formation phase, termination of bone resorption by synergistic cooperation occurs, with downregulation of RANKL expression in activated osteoblasts and Ephrin/EphA4-mediated mutual inhibition between neighboring multinucleated osteoclasts, along with simultaneous activation of osteoblasts via forward and reverse EphrinB2/EphB4 signaling between neighboring osteoblasts. In addition, the present study shows that autologous transplantation of methanol-fixed cell-free scale is an ideal in vivo model to study bone remodeling.

Contact of myeloma cells induces a characteristic transcriptome signature in skeletal precursor cells -Implications for myeloma bone disease

Physical interaction of skeletal precursors with multiple myeloma cells has been shown to suppress their osteogenic potential while favoring their tumor-promoting features. Although several transcriptome analyses of myeloma patient-derived mesenchymal stem cells have displayed differences compared to their healthy counterparts, these analyses insufficiently reflect the signatures mediated by tumor cell contact, vary due to different methodologies, and lack results in lineage-committed precursors. To determine tumor cell contact-mediated changes on skeletal precursors, we performed transcriptome analyses of mesenchymal stem cells and osteogenic precursor cells cultured in contact with the myeloma cell line INA-6. Comparative analyses confirmed dysregulation of genes which code for known disease-relevant factors and additionally revealed upregulation of genes that are associated with plasma cell homing, adhesion, osteoclastogenesis, and angiogenesis. Osteoclast-derived coupling factors, a dysregulated adipogenic potential, and an imbalance in favor of anti-anabolic factors may play a role in the hampered osteoblast differentiation potential of mesenchymal stem cells. Angiopoietin-Like 4 (ANGPTL4) was selected from a list of differentially expressed genes as a myeloma cell contact-dependent target in skeletal precursor cells which warranted further functional analyses. Adhesion assays with full-length ANGPTL4-coated plates revealed a potential role of this protein in INA-6 cell attachment. This study expands knowledge of the myeloma cell contact-induced signature in the stromal compartment of myelomatous bones and thus offers potential targets that may allow detection and treatment of myeloma bone disease at an early stage.

Chronic hyperglycemia affects bone metabolism in adult zebrafish scale model

Type II diabetes mellitus is a metabolic disease characterized by chronic hyperglycemia that induce other pathologies including diabetic retinopathy and bone disease. The mechanisms implicated in bone alterations induced by type II diabetes mellitus have been debated for years and are not yet clear because there are other factors involved that hide bone mineral density alterations. Despite this, it is well known that chronic hyperglycemia affects bone health causing fragility, mechanical strength reduction and increased propensity of fractures because of impaired bone matrix microstructure and aberrant bone cells function. Adult Danio rerio (zebrafish) represents a powerful model to study glucose and bone metabolism. Then, the aim of this study was to evaluate bone effects of chronic hyperglycemia in a new type II diabetes mellitus zebrafish model created by glucose administration in the water. Fish blood glucose levels have been monitored in time course experiments and basal glycemia was found increased. After 1 month treatment, the morphology of the retinal blood vessels showed abnormalities resembling to the human diabetic retinopathy. The adult bone metabolism has been evaluated in fish using the scales as read-out system. The scales of glucose-treated fish didn't depose new mineralized matrix and shown bone resorption lacunae associated with an intense osteoclast activity. In addition, hyperglycemic fish scales have shown a significant decrease of alkaline phosphatase activity and increase of tartrate-resistant acid phosphatase activity, in association with alterations in other bone-specific markers. These data indicates an imbalance in bone metabolism, which leads to the osteoporotic-like phenotype visualized through scale mineral matrix staining. The zebrafish model of hyperglycemic damage can contribute to elucidate in vivo the molecular mechanisms of metabolic changes, which influence the bone tissues regulation in human diabetic patients.

Effects of hyperglycemia on bone metabolism and bone matrix in goldfish scales

Increased risk of fracture associated with type 2 diabetes has been a topic of recent concern. Fracture risk is related to a decrease in bone strength, which can be affected by bone metabolism and the quality of the bone. To investigate the cause of the increased fracture rate in patients with diabetes through analyses of bone metabolism and bone matrix protein properties, we used goldfish scales as a bone model for hyperglycemia. Using the scales of seven alloxan-treated and seven vehicle-treated control goldfish, we assessed bone metabolism by analyzing the activity of marker enzymes and mRNA expression of marker genes, and we measured the change in molecular weight of scale matrix proteins with SDS-PAGE. After only a 2-week exposure to hyperglycemia, the molecular weight of α- and β-fractions of bone matrix collagen proteins changed incrementally in the regenerating scales of hyperglycemic goldfish compared with those of euglycemic goldfish. In addition, the relative ratio of the γ-fraction significantly increased, and a δ-fraction appeared after adding glyceraldehyde-a candidate for the formation of advanced glycation end products in diabetes-to isolated type 1 collagen in vitro. The enzymatic activity and mRNA expression of osteoblast and osteoclast markers were not significantly different between hyperglycemic and euglycemic goldfish scales. These results indicate that hyperglycemia is likely to affect bone quality through glycation of matrix collagen from an early stage of hyperglycemia. Therefore, non-enzymatic glycation of collagen fibers in bone matrix may lead to the deterioration of bone quality from the onset of diabetes.

Targeted disruption of sp7 and myostatin with CRISPR-Cas9 results in severe bone defects and more muscular cells in common carp

The common carp (Cyprinus carpio) as one of the most important aquaculture fishes produces over 3 million metric tones annually, approximately 10% the annual production of the all farmed freshwater fish worldwide. However, the tetraploidy genome and long generation-time of the common carp have made its breeding and genetic studies extremely difficult. Here, TALEN and CRISPR-Cas9, two versatile genome-editing tools, are employed to target common carp bone-related genes sp7, runx2, bmp2a, spp1, opg, and muscle suppressor gene mstn. TALEN were shown to induce mutations in the target coding sites of sp7, runx2, spp1 and mstn. With CRISPR-Cas9, the two common carp sp7 genes, sp7a and sp7b, were mutated individually, all resulting in severe bone defects; while mstnba mutated fish have grown significantly more muscle cells. We also employed CRISPR-Cas9 to generate double mutant fish of sp7a;mstnba with high efficiencies in a single step. These results demonstrate that both TALEN and CRISPR-Cas9 are highly efficient tools for modifying the common carp genome, and open avenues for facilitating common carp genetic studies and breeding.

The role of Sema4D/CD100 as a therapeutic target for tumor microenvironments and for autoimmune, neuroimmune and bone diseases

INTRODUCTION

Semaphorin 4D (Sema4D), also known as CD100, has been implicated in physiologic roles in the immune and nervous systems. However, the interaction of Sema4D with its high affinity receptor, Plexin-B1, reveals a novel role for Sema4D produced by the tumor microenvironment in tumor angiogenesis and metastasis.

AREAS COVERED

The ligation of Sema4D/CD100 with CD72 on immune and inflammatory cells is known to stimulate immune responses and regulation. Because CD100 and CD72 are expressed on lung immune and nonimmune cells, as well as on mast cells, the CD100/CD72 interaction plays another important role in allergic airway inflammation and mast cell functions. A better understanding of Sema4D-mediated cell signaling in physiological and pathological processes may be crucial for crafting new Sema4D-based therapeutics for human disease and tumor microenvironments. Strategies to achieve effective management through treatment with Sema4D include special siRNAs, neutralizing antibodies and knockdown.

EXPERT OPINION

This review focuses on the links between Sema4D and human diseases such as cancer, bone metabolism, immune responses and organ development. The current knowledge regarding the expression of Sema4D and its receptors and its functional roles is systemically reviewed to explore Sema4D as both a target and a therapeutic in human diseases.

Effects of bioactive fatty acid amide derivatives in zebrafish scale model of bone metabolism and disease

The endocannabinoid system (which includes fatty acid derivatives, receptors, and metabolizing enzymes) is involved in a variety of physiological processes, including bone metabolism in which it regulates the function of osteoblasts and osteoclasts, as well as differentiation of their precursors. The zebrafish (Danio rerio) provides a useful animal model for bone research since zebrafish bones develop rapidly and are anatomically similar to mammalian bones. Putative orthologues and paralogs of endocannabinoid genes have recently been identified in zebrafish, demonstrating the presence of cannabinoid type 1 (CB1) and type 2 (CB2) receptors with affinity to endocannabinoid ligands. To identify therapeutic molecules potentially useful in bone-related diseases, we evaluated the in vivo effects of exposure to long-chain fatty acid amides in adult zebrafish. Using a well-established zebrafish scale model, we found that anandamide and N-linoleoylethanolamine are able to stimulate bone formation by increasing alkaline phosphatase activity in physiological conditions. In addition, they prevent the alteration of bone markers in a prednisolone-induced osteoporosis model in adult zebrafish scales, whereas their esterified forms do not. These data suggest that long-chain fatty acid amides are involved in regulating bone metabolism in zebrafish scales and that the CB2 receptor is a key mediator in this process.

Danio rerio: the Janus of the bone from embryo to scale

Danio rerio (zebrafish), like the Roman god Janus, is an old animal model which is recently emerged and looks to the future with an increasing scientific success. Unlike other traditional animal models, zebrafish represents a versatile way to approach the study of the skeleton. Transparency of the larval stage, genetic manipulability and unique anatomical structures (scales) makes zebrafish a powerful and versatile instrument to investigate the bone tissue in terms of structure and function. Like Janus, zebrafish offers two different faces, or better, two models in one animal: larval and adult stage. The embryo can be used to isolate new genes involved in osteogenesis by large-scale mutagenesis screenings. The behavior of bone cells and genes in osteogenesis can be investigate by using transgenic lines, vital dyes, mutants and traditional molecular biology techniques. The adult zebrafish represents an important resource to study the pathways related to the bone metabolism and turnover. In particular, the properties of the caudal fin allow to study mechanisms of bone regeneration and reparation whereas the elasmoid scale represents an unique tool to investigate the bone metabolism under physiological or pathological conditions.

Alendronate rescued osteoporotic phenotype in a model of glucocorticoid-induced osteoporosis in adult zebrafish scale

Long-term effects of glucocorticoid treatment in humans induce bone loss and increase the risk of fracture in the skeleton. The pathogenic mechanisms of glucocorticoid-induced osteoporosis (GIOP) are still unclear. The GIOP and its effects have been reproduced in several animal models including Danio rerio (zebrafish) embryo. The treatment of adult fish with prednisolone (PN) has shown a dose-dependent decrease of mineralized matrix in the scales. Large resorption lacunae are characterized by single TRAP-positive cells which migrate to the margin of the scale merging into a multinucleated structures. The treatment with PN of cultured scales did not increase TRAP activity suggesting that the massive presence of osteoclasts in the resorption sites could be likely the result of a systemic recruitment of monocyte-macrophage precursors. We observed that treatment with PN induced a significant decrease of the alkaline phosphatase (ALP) activity in scale scleroblasts if compared with untreated controls. Then, we investigated the total mineral balance under prednisolone treatment using a time-dependent double live staining. The untreated fish fully repaired the resorption lacuna induced by prednisolone, whereas treated fish failed. The presence of osteoclast resorption fingerprints on new matrix suggested that the osteoclast activity counterbalances the osteodepositive activity exerted by scleroblasts. The treatment with PN in association with alendronate (AL) has surprisingly resulted in a significant decrease of TRAP activity and increase of ALP compared to PN-treated fish in biochemical and histological assays confirming the action of alendronate against GIOP in fish as well in humans.

Holmgren's principle of delamination during fin skeletogenesis

During fin morphogenesis, several mesenchyme condensations occur to give rise to the dermal skeleton. Although each of them seems to create distinctive and unique structures, they all follow the premises of the same morphogenetic principle. Holmgren's principle of delamination was first proposed to describe the morphogenesis of skeletal elements of the cranium, but Jarvik extended it to the development of the fin exoskeleton. Since then, some cellular or molecular explanations, such as the "flypaper" model (Thorogood et al.), or the evolutionary description by Moss, have tried to clarify this topic. In this article, we review new data from zebrafish studies to meet these criteria described by Holmgren and other authors. The variety of cell lineages involved in these skeletogenic condensations sheds light on an open discussion of the contributions of mesoderm- versus neural crest-derived cell lineages to the development of the head and trunk skeleton. Moreover, we discuss emerging molecular studies that are disclosing conserved regulatory mechanisms for dermal skeletogenesis and similarities during fin development and regeneration, which may have important implications in the potential use of the zebrafish fin as a model for regenerative medicine.

Bone tissue as a systemic endocrine regulator

Bone is a target tissue for hormones, such as the sex steroids, parathormon, vitamin D, calcitonin, glucocorticoids, and thyroid hormones. In the last decade, other "non-classic" hormones that modulate the bone tissue have been identified. While incretins (GIP and GLP-1) inhibit bone remodeling, angiotensin acts to promote remodeling. Bone morphogenetic protein (BMP) has also been found to have anabolic effects on the skeleton by activating bone formation during embryonic development, as well as in the postnatal period of life. Bone has also been identified as an endocrine tissue that produces a number of hormones, that bind to and modulate extra-skeletal receptors. Osteocalcin occupies a central position in this context. It can increase insulin secretion, insulin sensitivity and regulate metabolism of fatty acids. Moreover, osteocalcin also influences phosphate metabolism via osteocyte-derived FGF23 (which targets the kidneys and parathyroid glands to control phosphate reabsorption and metabolism of vitamin D). Finally, osteocalcin stimulates testosterone synthesis in Leydig cells and thus may play some role in male fertility. Further studies are necessary to confirm clinically important roles for skeletal tissue in systemic regulations.