ATP6V1H Deficiency Impairs Bone Development through Activation of MMP9 and MMP13

Zebrafish as a Model for Osteoporosis: Functional Validations of Genome-Wide Association Studies

PURPOSE OF REVIEW

GWAS, as a largely correlational analysis, requires in vitro or in vivo validation. Zebrafish (Danio rerio) have many advantages for studying the genetics of human diseases. Since gene editing in zebrafish has been highly valuable for studying embryonic skeletal developmental processes that are prenatally or perinatally lethal in mammalian models, we are reviewing pros and cons of this model.

RECENT FINDINGS

The true power for the use of zebrafish is the ease by which the genome can be edited, especially using the CRISPR/Cas9 system. Gene editing, followed by phenotyping, for complex traits such as BMD, is beneficial, but the major physiological differences between the fish and mammals must be considered. Like mammals, zebrafish do have main bone cells; thus, both in vivo stem cell analyses and in vivo imaging are doable. Yet, the "long" bones of fish are peculiar, and their bone cavities do not contain bone marrow. Partial duplication of the zebrafish genome should be taken into account. Overall, small fish toolkit can provide unmatched opportunities for genetic modifications and morphological investigation as a follow-up to human-first discovery.

Heritability and recursive influence of host genetics on the rumen microbiota drive body weight variance in male Hu sheep lambs

BACKGROUND

Heritable rumen microbiota is an important modulator of ruminant growth performance. However, no information exists to date on host genetics-rumen microbiota interactions and their association with phenotype in sheep. To solve this, we curated and analyzed whole-genome resequencing genotypes, 16S rumen-microbiota data, and longitudinal body weight (BW) phenotypes from 1150 sheep.

RESULTS

A variance component model indicated significant heritability of rumen microbial community diversity. Genome-wide association studies (GWAS) using microbial features as traits identified 411 loci-taxon significant associations (P < 10-8). We found a heritability of 39% for 180-day-old BW, while also the rumen microbiota likely played a significant role, explaining that 20% of the phenotypic variation. Microbiota-wide association studies (MWAS) and GWAS identified four marker genera (Bonferroni corrected P < 0.05) and five novel genetic variants (P < 10-8) that were significantly associated with BW. Integrative analysis identified the mediating role of marker genera in genotype influencing phenotype and unravelled that the same genetic markers have direct and indirect effects on sheep weight.

CONCLUSIONS

This study reveals a reciprocal interplay among host genetic variations, the rumen microbiota and the body weight traits of sheep. The information obtained provide insights into the diverse microbiota characteristics of rumen and may help in designing precision microbiota management strategies for controlling and manipulating sheep rumen microbiota to increase productivity. Video Abstract.

ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy

The vacuolar H+-ATPase is an enzymatic complex that functions in an ATP-dependent manner to pump protons across membranes and acidify organelles, thereby creating the proton/pH gradient required for membrane trafficking by several different types of transporters. We describe heterozygous point variants in ATP6V0C, encoding the c-subunit in the membrane bound integral domain of the vacuolar H+-ATPase, in 27 patients with neurodevelopmental abnormalities with or without epilepsy. Corpus callosum hypoplasia and cardiac abnormalities were also present in some patients. In silico modelling suggested that the patient variants interfere with the interactions between the ATP6V0C and ATP6V0A subunits during ATP hydrolysis. Consistent with decreased vacuolar H+-ATPase activity, functional analyses conducted in Saccharomyces cerevisiae revealed reduced LysoSensor fluorescence and reduced growth in media containing varying concentrations of CaCl2. Knockdown of ATP6V0C in Drosophila resulted in increased duration of seizure-like behaviour, and the expression of selected patient variants in Caenorhabditis elegans led to reduced growth, motor dysfunction and reduced lifespan. In summary, this study establishes ATP6V0C as an important disease gene, describes the clinical features of the associated neurodevelopmental disorder and provides insight into disease mechanisms.

Unveiling the Time Course Mechanism of Bone Fracture Healing by Transcriptional Profiles

BACKGROUND

Bone fracture healing is a time-consuming and high-priority orthopedic problem worldwide.

OBJECTIVE

Discovering the potential mechanism of bone healing at a time course and transcriptional level may better help manage bone fracture.

METHODS

In this study, we analyze a time-course bone fracture healing transcriptional dataset in a rat model (GSE592, GSE594, and GSE1371) of Gene Expression Omnibus (GEO). RNA was obtained from female Sprague-Dawley rats with a femoral fracture at the initial time (day 3) as well as early (week 1), middle (week 2), and late (week 4) time periods, with nonfracture rats used as control. Gene Ontology (GO) functional analysis and pathway examinations were performed for further measurements of GSEA and hub genes.

RESULTS

Results indicated that the four stages of bone fracture healing at the initial, early, middle, and late time periods represent the phases of hematoma formation, callus formation, callus molding, and mature lamellar bone formation, respectively. Extracellular organization was positively employed throughout the four stages. At the hematoma formation phase, the muscle contraction process was downregulated. Antibacterial peptide pathway was downregulated at all phases. The upregulation of Fn1 (initial, early, middle, and late time periods), Col3a1 (initial, early, and middle time periods), Col11a1 (initial and early time periods), Mmp9 (middle and late time periods), Mmp13 (early, middle, and late time periods) and the downregulation of RatNP-3b (initial, early, middle, and late time periods) were possible symbols for bone fracture healing and may be used as therapeutic targets.

CONCLUSION

These findings suggest some new potential pathways and genes in the process of bone fracture healing and further provide insights that can be used in targeted molecular therapy for bone fracture healing.

A minimally invasive fin scratching protocol for fast genotyping and early selection of zebrafish embryos

Current genetic modification and phenotyping methods in teleost fish allow detailed investigation of vertebrate mechanisms of development, modeling of specific aspects of human diseases and efficient testing of drugs at an organ/organismal level in an unparalleled fast and large-scale mode. Fish-based experimental approaches have boosted the in vivo verification and implementation of scientific advances, offering the quality guaranteed by animal models that ultimately benefit human health, and are not yet fully replaceable by even the most sophisticated in vitro alternatives. Thanks to highly efficient and constantly advancing genetic engineering as well as non-invasive phenotyping methods, the small zebrafish is quickly becoming a popular alternative to large animals' experimentation. This approach is commonly associated to invasive procedures and increased burden. Here, we present a rapid and minimally invasive method to obtain sufficient genomic material from single zebrafish embryos by simple and precise tail fin scratching that can be robustly used for at least two rounds of genotyping already from embryos within 48 h of development. The described protocol betters currently available methods (such as fin clipping), by minimizing the relative animal distress associated with biopsy at later or adult stages. It allows early selection of embryos with desired genotypes for strategizing culturing or genotype-phenotype correlation experiments, resulting in a net reduction of "surplus" animals used for mutant line generation.

CRISPR/Cas9 system: a reliable and facile genome editing tool in modern biology

Genome engineering has always been a versatile technique in biological research and medicine, with several applications. In the last several years, the discovery of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas9 technology has swept the scientific community and revolutionised the speed of modern biology, heralding a new era of disease detection and rapid biotechnology discoveries. It enables successful gene editing by producing targeted double-strand breaks in virtually any organism or cell type. So, this review presents a comprehensive knowledge about the mechanism and structure of Cas9-mediated RNA-guided DNA targeting and cleavage. In addition, genome editing via CRISPR-Cas9 technology in various animals which are being used as models in scientific research including Non-Human Primates Pigs, Dogs, Zebra, fish and Drosophila has been discussed in this review. This review also aims to understand the applications, serious concerns and future perspective of CRISPR/Cas9-mediated genome editing.

Transcriptome Profiling of Osteoblasts in a Medaka (Oryzias latipes) Osteoporosis Model Identifies Mmp13b as Crucial for Osteoclast Activation

Matrix metalloproteases (MMPs) play crucial roles in extracellular matrix (ECM) modulation during osteoclast-driven bone remodeling. In the present study, we used transcriptome profiling of bone cells in a medaka model for osteoporosis and bone regeneration to identify factors critical for bone remodeling and homeostasis. This identified mmp13b, which was strongly expressed in osteoblast progenitors and upregulated under osteoporotic conditions and during regeneration of bony fin rays. To characterize the role of mmp13b in bone remodeling, we generated medaka mmp13b mutants by CRISPR/Cas9. We found that mmp13b mutants form normal numbers of osteoblasts and osteoclasts. However, osteoclast activity was severely impaired under osteoporotic conditions. In mmp13b mutants and embryos treated with the MMP13 inhibitor CL-82198, unmineralized collagens and mineralized bone matrix failed to be degraded. In addition, the dynamic migratory behavior of activated osteoclasts was severely affected in mmp13b mutants. Expression analysis showed that maturation genes were downregulated in mmp13b deficient osteoclasts suggesting that they remain in an immature and non-activated state. We also found that fin regeneration was delayed in mmp13b mutants with a concomitant alteration of the ECM and reduced numbers of osteoblast progenitors in regenerating joint regions. Together, our findings suggest that osteoblast-derived Mmp13b alters the bone ECM to allow the maturation and activation of osteoclasts during bone remodeling in a paracrine manner. Mmp13b-induced ECM alterations are also required to facilitate osteoblast progenitor recruitment and full regeneration of bony fin rays.

Perspective of the GEMSTONE Consortium on Current and Future Approaches to Functional Validation for Skeletal Genetic Disease Using Cellular, Molecular and Animal-Modeling Techniques

The availability of large human datasets for genome-wide association studies (GWAS) and the advancement of sequencing technologies have boosted the identification of genetic variants in complex and rare diseases in the skeletal field. Yet, interpreting results from human association studies remains a challenge. To bridge the gap between genetic association and causality, a systematic functional investigation is necessary. Multiple unknowns exist for putative causal genes, including cellular localization of the molecular function. Intermediate traits ("endophenotypes"), e.g. molecular quantitative trait loci (molQTLs), are needed to identify mechanisms of underlying associations. Furthermore, index variants often reside in non-coding regions of the genome, therefore challenging for interpretation. Knowledge of non-coding variance (e.g. ncRNAs), repetitive sequences, and regulatory interactions between enhancers and their target genes is central for understanding causal genes in skeletal conditions. Animal models with deep skeletal phenotyping and cell culture models have already facilitated fine mapping of some association signals, elucidated gene mechanisms, and revealed disease-relevant biology. However, to accelerate research towards bridging the current gap between association and causality in skeletal diseases, alternative in vivo platforms need to be used and developed in parallel with the current -omics and traditional in vivo resources. Therefore, we argue that as a field we need to establish resource-sharing standards to collectively address complex research questions. These standards will promote data integration from various -omics technologies and functional dissection of human complex traits. In this mission statement, we review the current available resources and as a group propose a consensus to facilitate resource sharing using existing and future resources. Such coordination efforts will maximize the acquisition of knowledge from different approaches and thus reduce redundancy and duplication of resources. These measures will help to understand the pathogenesis of osteoporosis and other skeletal diseases towards defining new and more efficient therapeutic targets.

The application of genome editing technology in fish

The advent and development of genome editing technology has opened up the possibility of directly targeting and modifying genomic sequences in the field of life sciences with rapid developments occurring in the last decade. As a powerful tool to decipher genome data at the molecular biology level, genome editing technology has made important contributions to elucidating many biological problems. Currently, the three most widely used genome editing technologies include: zinc finger nucleases (ZFN), transcription activator like effector nucleases (TALEN), and clustered regularly interspaced short palindromic repeats (CRISPR). Researchers are still striving to create simpler, more efficient, and accurate techniques, such as engineered base editors and new CRISPR/Cas systems, to improve editing efficiency and reduce off-target rate, as well as a near-PAMless SpCas9 variants to expand the scope of genome editing. As one of the important animal protein sources, fish has significant economic value in aquaculture. In addition, fish is indispensable for research as it serves as the evolutionary link between invertebrates and higher vertebrates. Consequently, genome editing technologies were applied extensively in various fish species for basic functional studies as well as applied research in aquaculture. In this review, we focus on the application of genome editing technologies in fish species detailing growth, gender, and pigmentation traits. In addition, we have focused on the construction of a zebrafish (Danio rerio) disease model and high-throughput screening of functional genes. Finally, we provide some of the future perspectives of this technology.

Loss of vacuolar-type H+-ATPase induces caspase-independent necrosis-like death of hair cells in zebrafish neuromasts

The vacuolar-type H+-ATPase (V-ATPase) is a multi-subunit proton pump that regulates cellular pH. V-ATPase activity modulates several cellular processes, but cell-type-specific functions remain poorly understood. Patients with mutations in specific V-ATPase subunits can develop sensorineural deafness, but the underlying mechanisms are unclear. Here, we show that V-ATPase mutations disrupt the formation of zebrafish neuromasts, which serve as a model to investigate hearing loss. V-ATPase mutant neuromasts are small and contain pyknotic nuclei that denote dying cells. Molecular markers and live imaging show that loss of V-ATPase induces mechanosensory hair cells in neuromasts, but not neighboring support cells, to undergo caspase-independent necrosis-like cell death. This is the first demonstration that loss of V-ATPase can lead to necrosis-like cell death in a specific cell type in vivo. Mechanistically, loss of V-ATPase reduces mitochondrial membrane potential in hair cells. Modulating the mitochondrial permeability transition pore, which regulates mitochondrial membrane potential, improves hair cell survival. These results have implications for understanding the causes of sensorineural deafness, and more broadly, reveal functions for V-ATPase in promoting survival of a specific cell type in vivo.

Fish Models of Induced Osteoporosis

Osteopenia and osteoporosis are bone disorders characterized by reduced bone mineral density (BMD), altered bone microarchitecture and increased bone fragility. Because of global aging, their incidence is rapidly increasing worldwide and novel treatments that would be more efficient at preventing disease progression and at reducing the risk of bone fractures are needed. Preclinical studies are today a major bottleneck to the collection of new data and the discovery of new drugs, since they are commonly based on rodent in vivo systems that are time consuming and expensive, or in vitro systems that do not exactly recapitulate the complexity of low BMD disorders. In this regard, teleost fish, in particular zebrafish and medaka, have recently emerged as suitable alternatives to study bone formation and mineralization and to model human bone disorders. In addition to the many technical advantages that allow faster and larger studies, the availability of several fish models that efficiently mimic human osteopenia and osteoporosis phenotypes has stimulated the interest of the academia and industry toward a better understanding of the mechanisms of pathogenesis but also toward the discovery of new bone anabolic or antiresorptive compounds. This mini review recapitulates the in vivo teleost fish systems available to study low BMD disorders and highlights their applications and the recent advances in the field.

Radiation induces primary osteocyte senescence phenotype and affects osteoclastogenesis in vitro

Irradiation-induced bone remodeling imbalances arise as a consequence of the dysregulation of bone formation and resorption. Due to the abundance of osteocytes, their long life and their dual-regulatory effects on both osteoblast and osteoclast function, they serve as critical coordinators of bone remolding. In the present study, femur and tibia-derived primary osteocytes were cultured and irradiated to observe the functional changes and the cellular senescence phenotype in vitro. Irradiation directly reduced cell viability, affected the crucial dendritic morphology and altered the expression of functional proteins, including upregulation of receptor activator of nuclear factor-κB ligand and sclerostin, and downregulation of osteoprotegerin. Irradiated osteocytes were shown to exhibit notable DNA damage, which resulted in the initiation of a typical cellular senescence phenotype. Furthermore, it was found that irradiation-induced prematurely senescent osteocytes stimulate molecular secretion, referred to as senescence-associated secretory phenotype (SASP), which may be involved in modulation of the bone microenvironment, including the promotion of osteoclastogenesis. Taken together, the results showed that irradiation triggered osteocyte senescence and the acquisition of an associated secretory phenotype. This further resulted in an imbalance of bone remodeling through senescent influence on proliferation, morphology and marker protein production, but also indirectly via a paracrine pathway through SASP secretion. The results of the present study may highlight the potential of SASP-targeted interventions for the management of radiation-induced bone loss.

MEK1/2 Inhibitor (GDC0623) Promotes Osteogenic Differentiation of Primary Osteoblasts Inhibited by IL-1β through the MEK-Erk1/2 and Jak/Stat3 Pathways

OBJECTIVE

We evaluated the effects and mechanisms of GDC0623 on osteogenic differentiation of osteoblasts induced by IL-1β. Methodology. Osteoblasts were treated with 20 ng/ml IL-1β and 0.1 µM GDC0623. Cell proliferation levels were evaluated by the cell counting kit 8 (CCK8), EdU assay, and western blotting [proliferating cell nuclear antigen (PCNA) and Cyclin D1]. Osteoblasts were cultured in an osteogenic induction medium for 1-3 weeks after which their differentiations were assessed by alkaline phosphatase (ALP) staining, Alizarin Red staining, calcium concentration, immunocytochemistry staining, real-time quantitative PCR (RT-qPCR), and immunofluorescence staining. The osteogenesis-associated mechanisms were further evaluated by western blotting using appropriate antibodies.

RESULTS

Relative to the control group, IL-1β induced the rapid proliferation of osteoblasts and suppressed their osteogenic differentiations by upregulating the activities of MEK-Erk1/2 as well as Jak-Stat3 pathways and by elevating MMP13 and MMP9 levels. However, blocking of the MEK-Erk1/2 signaling pathway by GDC0623 treatment reversed these effects.

CONCLUSION

Inhibition of Jak-Stat3 pathway by C188-9 downregulated the expression levels of MMP9 and MMP13, activated MEK-Erk1/2 pathway, and inhibited osteogenic differentiation.

Investigation of alpl expression and Tnap-activity in zebrafish implies conserved functions during skeletal and neuronal development

Hypophosphatasia (HPP) is a rare genetic disease with diverse symptoms and a heterogeneous severity of onset with underlying mutations in the ALPL gene encoding the ectoenzyme Tissue-nonspecific alkaline phosphatase (TNAP). Considering the establishment of zebrafish (Danio rerio) as a new model organism for HPP, the aim of the study was the spatial and temporal analysis of alpl expression in embryos and adult brains. Additionally, we determined functional consequences of Tnap inhibition on neural and skeletal development in zebrafish. We show that expression of alpl is present during embryonic stages and in adult neuronal tissues. Analyses of enzyme function reveal zones of pronounced Tnap-activity within the telencephalon and the mesencephalon. Treatment of zebrafish embryos with chemical Tnap inhibitors followed by axonal and cartilage/mineralized tissue staining imply functional consequences of Tnap deficiency on neuronal and skeletal development. Based on the results from neuronal and skeletal tissue analyses, which demonstrate an evolutionary conserved role of this enzyme, we consider zebrafish as a promising species for modeling HPP in order to discover new potential therapy strategies in the long-term.

Applications of CRISPR for musculoskeletal research

The ability to edit DNA at the nucleotide level using clustered regularly interspaced short palindromic repeats (CRISPR) systems is a relatively new investigative tool that is revolutionizing the analysis of many aspects of human health and disease, including orthopaedic disease. CRISPR, adapted for mammalian cell genome editing from a bacterial defence system, has been shown to be a flexible, programmable, scalable, and easy-to-use gene editing tool. Recent improvements increase the functionality of CRISPR through the engineering of specific elements of CRISPR systems, the discovery of new, naturally occurring CRISPR molecules, and modifications that take CRISPR beyond gene editing to the regulation of gene transcription and the manipulation of RNA. Here, the basics of CRISPR genome editing will be reviewed, including a description of how it has transformed some aspects of molecular musculoskeletal research, and will conclude by speculating what the future holds for the use of CRISPR-related treatments and therapies in clinical orthopaedic practice.

Cite this article: Bone Joint Res 2020;9(7):351–359.

Genome editing methods in animal models

Genetically engineered animal models that reproduce human diseases are very important for the pathological study of various conditions. The development of the clustered regularly interspaced short palindromic repeats (CRISPR) system has enabled a faster and cheaper production of animal models compared with traditional gene-targeting methods using embryonic stem cells. Genome editing tools based on the CRISPR-Cas9 system are a breakthrough technology that allows the precise introduction of mutations at the target DNA sequences. In particular, this accelerated the creation of animal models, and greatly contributed to the research that utilized them. In this review, we introduce various strategies based on the CRISPR-Cas9 system for building animal models of human diseases and describe various in vivo delivery methods of CRISPR-Cas9 that are applied to disease models for therapeutic purposes. In addition, we summarize the currently available animal models of human diseases that were generated using the CRISPR-Cas9 system and discuss future directions.

Zebrafish: A Resourceful Vertebrate Model to Investigate Skeletal Disorders

Animal models are essential tools for addressing fundamental scientific questions about skeletal diseases and for the development of new therapeutic approaches. Traditionally, mice have been the most common model organism in biomedical research, but their use is hampered by several limitations including complex generation, demanding investigation of early developmental stages, regulatory restrictions on breeding, and high maintenance cost. The zebrafish has been used as an efficient alternative vertebrate model for the study of human skeletal diseases, thanks to its easy genetic manipulation, high fecundity, external fertilization, transparency of rapidly developing embryos, and low maintenance cost. Furthermore, zebrafish share similar skeletal cells and ossification types with mammals. In the last decades, the use of both forward and new reverse genetics techniques has resulted in the generation of many mutant lines carrying skeletal phenotypes associated with human diseases. In addition, transgenic lines expressing fluorescent proteins under bone cell- or pathway- specific promoters enable in vivo imaging of differentiation and signaling at the cellular level. Despite the small size of the zebrafish, many traditional techniques for skeletal phenotyping, such as x-ray and microCT imaging and histological approaches, can be applied using the appropriate equipment and custom protocols. The ability of adult zebrafish to remodel skeletal tissues can be exploited as a unique tool to investigate bone formation and repair. Finally, the permeability of embryos to chemicals dissolved in water, together with the availability of large numbers of small-sized animals makes zebrafish a perfect model for high-throughput bone anabolic drug screening. This review aims to discuss the techniques that make zebrafish a powerful model to investigate the molecular and physiological basis of skeletal disorders.

Development and Genome Sequencing of a Laboratory-Inbred Miniature Pig Facilitates Study of Human Diabetic Disease

Pig has been proved to be a valuable large animal model used for research on diabetic disease. However, their translational value is limited given their distinct anatomy and physiology. For the last 30 years, we have been developing a laboratory Asian miniature pig inbred line (Bama miniature pig [BM]) from the primitive Bama xiang pig via long-term selective inbreeding. Here, we assembled a BM reference genome at full chromosome-scale resolution with a total length of 2.49 Gb. Comparative and evolutionary genomic analyses identified numerous variations between the BM and commercial pig (Duroc), particularly those in the genetic loci associated with the features advantageous to diabetes studies. Resequencing analyses revealed many differentiated gene loci associated with inbreeding and other selective forces. These together with transcriptome analyses of diabetic pig models provide a comprehensive genetic basis for resistance to diabetogenic environment, especially related to energy metabolism.

Using zebrafish to study skeletal genomics

While genome-wide association studies (GWAS) have revolutionized our understanding of the genetic architecture of skeletal diseases, animal models are required to identify causal mechanisms and to translate underlying biology into new therapies. Despite large-scale knockout mouse phenotyping efforts, the skeletal functions of most genes residing at GWAS-identified loci remain unknown, highlighting a need for complementary model systems to accelerate gene discovery. Over the past several decades, zebrafish (Danio rerio) has emerged as a powerful system for modeling the genetics of human diseases. In this review, our goal is to outline evidence supporting the utility of zebrafish for accelerating our understanding of human skeletal genomics, as well as gaps in knowledge that need to be filled for this purpose. We do this by providing a basic foundation of the zebrafish skeletal morphophysiology and phenotypes, and surveying evidence of skeletal gene homology and the use of zebrafish for post-GWAS analysis in other tissues and organs. We also outline challenges in translating zebrafish mutant phenotypes. Finally, we conclude with recommendations of future directions and how to leverage the large body of tools and knowledge of skeletal genetics in zebrafish for the needs of human skeletal genomic exploration. Due to their amenability to rapid genetic approaches, as well as the large number of conserved genetic and phenotypic features, there is a strong rationale supporting the use of zebrafish for human skeletal genomic studies.

ATP6V1H facilitates osteogenic differentiation in MC3T3-E1 cells via Akt/GSK3β signaling pathway

Type 2 diabetes mellitus (T2DM) accounts for approximately 90% of all diabetic patients, and osteoporosis is one of the complications during T2DM process. ATP6V1H (V-type proton ATPase subunit H) displays crucial roles in inhibiting bone loss, but its role in osteogenic differentiation remains unknown. Therefore in this study, we aimed to explore the biological role of ATP6V1H in osteogenic differentiation. OM (osteogenic medium) and HG (high glucose and free fatty acids) were used to induce the MC3T3-E1 cells into osteogenic differentiation in a T2DM simulating environment. CCK8 assay was used to detect cell viability. Alizarin Red staining was used to detect the influence of ATP6V1H on osteogenic differentiation. ATP6V1H expression increased in OM-MC3T3-E1 cells, while decreased in OM+HG-MC3T3-E1 cells. ATP6V1H promoted osteogenic differentiation of OM+HG-MC3T3-E1 cells. Overexpression of ATP6V1H inhibited Akt/GSK3β signaling pathway, while knockdown of ATP6V1H promoted Akt/GSK3β signaling pathway. ATP6V1H overexpression promoted osteogenic differentiation of OM+HG-MC3T3-E1 cells. The role of ATP6V1H in osteogenic differentiation in a T2DM simulating environment involved in Akt/GSK3β signaling pathway. These data demonstrated that ATP6V1H could serve as a potential target for osteogenic differentiation in a T2DM simulating environment.

The Progress of CRISPR/Cas9-Mediated Gene Editing in Generating Mouse/Zebrafish Models of Human Skeletal Diseases

Genetic factors play a substantial role in the etiology of skeletal diseases, which involve 1) defects in skeletal development, including intramembranous ossification and endochondral ossification; 2) defects in skeletal metabolism, including late bone growth and bone remodeling; 3) defects in early developmental processes related to skeletal diseases, such as neural crest cell (NCC) and cilia functions; 4) disturbance of the cellular signaling pathways which potentially affect bone growth. Efficient and high-throughput genetic methods have enabled the exploration and verification of disease-causing genes and variants. Animal models including mouse and zebrafish have been extensively used in functional mechanism studies of causal genes and variants. The conventional approaches of generating mutant animal models include spontaneous mutagenesis, random integration, and targeted integration via mouse embryonic stem cells. These approaches are costly and time-consuming. Recent development and application of gene-editing tools, especially the CRISPR/Cas9 system, has significantly accelerated the process of gene-editing in diverse organisms. Here we review both mice and zebrafish models of human skeletal diseases generated by CRISPR/Cas9 system, and their contributions to deciphering the underpins of disease mechanisms.

Zebrafish as an Emerging Model for Osteoporosis: A Primary Testing Platform for Screening New Osteo-Active Compounds

Osteoporosis is metabolic bone disease caused by an altered balance between bone anabolism and catabolism. This dysregulated balance is responsible for fragile bones that fracture easily after minor falls. With an aging population, the incidence is rising and as yet pharmaceutical options to restore this imbalance is limited, especially stimulating osteoblast bone-building activity. Excitingly, output from large genetic studies on people with high bone mass (HBM) cases and genome wide association studies (GWAS) on the population, yielded new insights into pathways containing osteo-anabolic players that have potential for drug target development. However, a bottleneck in development of new treatments targeting these putative osteo-anabolic genes is the lack of animal models for rapid and affordable testing to generate functional data and that simultaneously can be used as a compound testing platform. Zebrafish, a small teleost fish, are increasingly used in functional genomics and drug screening assays which resulted in new treatments in the clinic for other diseases. In this review we outline the zebrafish as a powerful model for osteoporosis research to validate potential therapeutic candidates, describe the tools and assays that can be used to study bone homeostasis, and affordable (semi-)high-throughput compound testing.

V-ATPases and osteoclasts: ambiguous future of V-ATPases inhibitors in osteoporosis

Vacuolar ATPases (V-ATPases) play a critical role in regulating extracellular acidification of osteoclasts and bone resorption. The deficiencies of subunit a3 and d2 of V-ATPases result in increased bone density in humans and mice. One of the traditional drug design strategies in treating osteoporosis is the use of subunit a3 inhibitor. Recent findings connect subunits H and G1 with decreased bone density. Given the controversial effects of ATPase subunits on bone density, there is a critical need to review the subunits of V-ATPase in osteoclasts and their functions in regulating osteoclasts and bone remodeling. In this review, we comprehensively address the following areas: information about all V-ATPase subunits and their isoforms; summary of V-ATPase subunits associated with human genetic diseases; V-ATPase subunits and osteopetrosis/osteoporosis; screening of all V-ATPase subunits variants in GEFOS data and in-house data; spectrum of V-ATPase subunits during osteoclastogenesis; direct and indirect roles of subunits of V-ATPases in osteoclasts; V-ATPase-associated signaling pathways in osteoclasts; interactions among V-ATPase subunits in osteoclasts; osteoclast-specific V-ATPase inhibitors; perspective of future inhibitors or activators targeting V-ATPase subunits in the treatment of osteoporosis.

Use of zebrafish models to investigate rare human disease

Rare diseases are collectively common and often extremely debilitating. Following the emergence of next-generation sequencing (NGS) technologies, the variants underpinning rare genetic disorders are being unearthed at an accelerating rate. However, many rare conditions lack effective treatments due to their poorly understood pathophysiology. There is therefore a growing demand for the development of novel experimental models of rare genetic diseases, so that potentially causative variants can be validated, pathogenic mechanisms can be investigated and therapeutic targets can be identified. Animal models of rare diseases need to be genetically and physiologically similar to humans, and well-suited to large-scale experimental manipulation, considering the vast number of novel variants that are being identified through NGS. The zebrafish has emerged as a popular model system for investigating these variants, combining conserved vertebrate characteristics with a capacity for large-scale phenotypic and therapeutic screening. In this review, we aim to highlight the unique advantages of the zebrafish over other in vivo model systems for the large-scale study of rare genetic variants. We will also consider the generation of zebrafish disease models from a practical standpoint, by discussing how genome editing technologies, particularly the recently developed clustered regularly interspaced repeat (CRISPR)/CRISPR-associated protein 9 system, can be used to model rare pathogenic variants in zebrafish. Finally, we will review examples in the literature where zebrafish models have played a pivotal role in confirming variant causality and revealing the underlying mechanisms of rare diseases, often with wider implications for our understanding of human biology.

GAG and collagen II attenuate glucocorticoid-induced osteoporosis by regulating NF-κB and MAPK signaling

As a component of collagen II, glycosaminoglycan (GAG) has a relatively close relationship with bone metabolism. GAG and collagen II have been proven to promote connection of the bone trabecular structure. However, the exact mechanism remains unknown. In this study, we aimed to determine the concrete effect and the mechanism of GAG and collagen II on glucocorticoid-induced osteoporosis. We implanted prednisolone pellets subcutaneously in mice to mimic glucocorticoid-induced osteoporosis. GAG was administered intragastrically every day for 60 days. The results demonstrated a protective effect of GAG and collagen II on glucocorticoid-induced osteoporosis. Trabecular number and connection density increased after treatment with GAG and collagen II. We generated bone marrow-derived macrophages to explore the effect of GAG and collagen II on osteoclast differentiation. We collected cell protein and RNA in the presence of macrophage colony-stimulating factor (M-CSF) and receptor activator for nuclear factor-κB ligand (RANKL) and found that GAG and collagen II inhibited the NF-κB and MAPK pathways, thereby down-regulating osteoclast differentiation molecules such as matrix metallopeptidase 9 (MMP 9) and nuclear factor of activated T-cells, cytoplasmic 1 (NFATc-1). Our findings suggest that GAG and collagen II may have therapeutic potential of patients with glucocorticoid-induced osteoporosis in clinical settings.

Toxic effects and foundation of proton radiation on the early-life stage of zebrafish development

Proton is a major particle of space radiation environment and a prospective radiotherapy beam. However, its risk needs to be fully evaluated for the understanding and to establish the better protective strategy for astronaut and patient. Zebrafish is an ideal model for the toxicity studies on medicines and environmental genetic toxicants. In the current study, embryos of zebrafish at 24 h post-fertilization (hpf) were exposed to proton beam. Some toxic parameters of embryo-larval development were investigated. Microarray combining with qRT-PCR were used to detect the gene expression situation. Generally, fractions of a variety of abnormal phenotypes of embryos and larvae increased in a dose-dependent manner after irradiation. The copy number of mitochondria, the basal respiration rate and the maximum respiration rate of embryos significantly decreased after irradiation. Microarray data demonstrated that MAPK signaling pathway, cell communication, glycolysis and TGF-β signaling pathway were significantly affected in the irradiated group. The expressions of matrix metallopeptidase 9 (mmp9) and TIMP metallopeptidase inhibitor 2b (timp2b) genes, and enzymatic activity of MMP9 were significantly upregulated in irradiated group. Overall, these results suggest that acute radiation of proton severely affects the development of organism and results in aberration occurrence in the early stage of zebrafish development, which may relates to mitochondrial and glycolytic dysfunction.

Matrix metalloproteinases (MMPs) mediate leukocyte recruitment during the inflammatory phase of zebrafish heart regeneration

In zebrafish, the role of matrix metalloproteinases (MMPs) in the inflammatory phase of heart regeneration following cryoinjury remains poorly understood. Here, we demonstrated an increase in MMP enzymatic activity and elevated expression of mmp9 and mmp13 in the injured area (IA) of hearts from as early as 1 day post-cryoinjury (dpc). Treatment with the broad-spectrum MMP inhibitor, GM6001, during the first week after cryoinjury resulted in impaired heart regeneration, as indicated by the larger scar and reduced numbers of proliferating cardiomyocytes. GM6001 also significantly reduced the number of leukocytes to the IA at 0.5 dpc to 4 dpc. Specific inhibition of both MMP-9 and MMP-13 also resulted in impaired regeneration and leukocyte recruitment. However, chemokine rescue with recombinant CXCL8 and CCL2 restored the recruitment of macrophages and the cardiac regenerative capability in GM6001-treated fish. MMP-9 and MMP-13 cleaved zebrafish CXCL8 at the same site, and the truncated form was more chemotactic than the intact form. In contrast, CCL2 did not have an MMP-9 or MMP-13 cleavage site. Together, these data suggest that MMPs might play a key role in the inflammatory phase of heart regeneration in zebrafish, by mediating leukocyte recruitment via the activation of chemokines.

Genome editing in fishes and their applications

There have been revolutionary progresses in genome engineering in the past few years. The newly-emerged genome editing technologies including zinc-finger nuclease (ZFN), transcription activator-like effector nuclease (TALEN) and clustered regularly interspaced short palindromic repeats associated with Cas9 (CRISPR/Cas9) have enabled biological scientists to perform efficient and precise targeted genome editing in different species. Fish represent the largest group of vertebrates with many species having values for both scientific research and aquaculture industry. Genome editing technologies have found extensive applications in different fish species for basic functional studies as well asapplied research in such fields as disease modeling and aquaculture. This mini-review focuses on recent advancements and applications of the new generation of genome editing technologies in fish species, with particular emphasis on their applications in understanding reproductive functions because the reproductive axis has been most systematically and best studied among others and its function has been difficult to address with reverse genetics approach.

Defining Disease, Diagnosis, and Translational Medicine within a Homeostatic Perturbation Paradigm: The National Institutes of Health Undiagnosed Diseases Program Experience

Traditionally, the use of genomic information for personalized medical decisions relies on prior discovery and validation of genotype-phenotype associations. This approach constrains care for patients presenting with undescribed problems. The National Institutes of Health (NIH) Undiagnosed Diseases Program (UDP) hypothesized that defining disease as maladaptation to an ecological niche allows delineation of a logical framework to diagnose and evaluate such patients. Herein, we present the philosophical bases, methodologies, and processes implemented by the NIH UDP. The NIH UDP incorporated use of the Human Phenotype Ontology, developed a genomic alignment strategy cognizant of parental genotypes, pursued agnostic biochemical analyses, implemented functional validation, and established virtual villages of global experts. This systematic approach provided a foundation for the diagnostic or non-diagnostic answers provided to patients and serves as a paradigm for scalable translational research.