Gene therapy for osteoporosis: evaluation in a murine ovariectomy model

Inflammatory bowel disease and osteoporosis: Common genetic effects, pleiotropy, and causality

INTRODUCTION

Previous studies have shown that inflammatory bowel disease (IBD) is associated with osteoporosis (OP) and bone mineral density (BMD), but the underlying genetic mechanisms are unclear. Our study wanted to explore the genetic and causal relationship between IBD and OP.

MATERIALS AND METHODS

Based on large-scale genome-wide association summary statistics and individual-level datasets (i.e., the UK Biobank), this study performed linkage disequilibrium score regression (LDSC), pleiotropic analysis under the composite null hypothesis (PLACO), and Mendelian randomization (MR) analyses to explore the genetic association, the pleiotropic genes and the causal relationship between IBD and BMD.

RESULTS

LDSC revealed significant genetic correlations between IBD and BMD (e.g., forearm BMD (rg = -0.3479, P = 0.019) and femoral neck BMD (rg = -0.1335, P = 0.0307). PLACO identified 14 overlapping pleiotropic loci, 1 shared risk gene (CDYL), and multiple shared pathways, revealing possible mechanisms for IBD and OP. MR analysis demonstrated a causal association between IBD and BMD.

CONCLUSIONS

Our study indicates that IBD may increase the risk of OP and reveals a complex genetic mechanism linking IBD and the risk of osteoporosis, which has important implications for diagnosing and treating IBD and OP.

FoxO3 Regulates Mouse Bone Mesenchymal Stem Cell Fate and Bone-Fat Balance During Skeletal Aging

Age-related osteoporosis is characterized by an imbalance between osteogenic and adipogenic differentiation in bone mesenchymal stem cells (BMSCs). Forkhead box O 3 (FoxO3) transcription factor is involved in lifespan and cell differentiation. In this study, we explore whether FoxO3 regulates age-related bone loss and marrow fat accumulation. The expression levels of FoxO3 in BMSCs during aging were detected in vivo and in vitro. To explore the role of FoxO3 in osteogenic and adipogenic differentiation, primary BMSCs were isolated from young and aged mice. FoxO3 expression was modulated by adenoviral vector transfection. The role of FoxO3 in bone-fat balance was evaluated by alizarin red S staining, oil red O staining, quantitative reverse transcription-polymerase chain reaction, Western blot, and histological analysis. Age-related bone loss and fat deposit are associated with downregulation of FoxO3. Overexpression of FoxO3 alleviated age-related bone loss and marrow fat accumulation in aged mice. Mechanistically, FoxO3 reduced adipogenesis and enhanced osteogenesis of BMSCs via downregulation of PPAR-γ and Notch signaling, respectively. In conclusion, FoxO3 is an essential factor controlling the fate of BMSCs and is a potential target for the prevention of age-related osteoporosis.

Bone regeneration in osteoporosis: opportunities and challenges

Osteoporosis is a bone disorder characterised by low bone mineral density, reduced bone strength, increased bone fragility, and impaired mineralisation of bones causing an increased risk of bone fracture. Several therapies are available for treating osteoporosis which include bisphosphonates, anti-resorptive agents, oestrogen modulators, etc. These therapies primarily focus on decreasing bone resorption and do not assist in bone regeneration or offering permanent curative solutions. Additionally, these therapies are associated with severe adverse events like thromboembolism, increased risk of stroke, and hypocalcaemia. To overcome these limitations, bone regenerative pathways and approaches are now considered to manage osteoporosis. The bone regenerative pathways involved in bone regeneration include wingless-related integration site/β-catenin signalling pathway, notch signalling pathway, calcium signalling, etc. The various regenerative approaches which possess potential to heal and replace the bone defect site include scaffolds, cements, cell therapy, and other alternative medicines. The review focuses on describing the challenges and opportunities in bone regeneration for osteoporosis.

Inflammasomes and the IL-1 Family in Bone Homeostasis and Disease

PURPOSE OF REVIEW

Inflammasomes are multimeric protein structures with crucial roles in host responses against infections and injuries. The importance of inflammasome activation goes beyond host defense as a dysregulated inflammasome and subsequent secretion of IL-1 family members is believed to be involved in the pathogenesis of various diseases, some of which also produce skeletal manifestations. The purpose of this review is to summarize recent developments in the understanding of inflammasome regulation and IL-1 family members in bone physiology and pathology and current therapeutics will be discussed.

RECENT FINDINGS

Small animal models have been vital to help understand how the inflammasome regulates bone dynamics. Animal models with gain or loss of function in various inflammasome components or IL-1 family signaling have illustrated how these systems can impact numerous bone pathologies and have been utilized to test new inflammasome therapeutics. It is increasingly clear that a tightly regulated inflammasome is required not only for host defense but for skeletal homeostasis, as a dysregulated inflammasome is linked to diseases of pathological bone accrual and loss. Given the complexities of inflammasome activation and redundancies in IL-1 activation and secretion, targeting these pathways is at times challenging. Ongoing research into inflammasome-mediated mechanisms will allow the development of new therapeutics for inflammasome/IL-1 diseases.

Nanoscale Imaging and Analysis of Bone Pathologies

Understanding the properties of bone is of both fundamental and clinical relevance. The basis of bone’s quality and mechanical resilience lies in its nanoscale building blocks (i.e., mineral, collagen, non-collagenous proteins, and water) and their complex interactions across length scales. Although the structure–mechanical property relationship in healthy bone tissue is relatively well characterized, not much is known about the molecular-level origin of impaired mechanics and higher fracture risks in skeletal disorders such as osteoporosis or Paget’s disease. Alterations in the ultrastructure, chemistry, and nano-/micromechanics of bone tissue in such a diverse group of diseased states have only been briefly explored. Recent research is uncovering the effects of several non-collagenous bone matrix proteins, whose deficiencies or mutations are, to some extent, implicated in bone diseases, on bone matrix quality and mechanics. Herein, we review existing studies on ultrastructural imaging—with a focus on electron microscopy—and chemical, mechanical analysis of pathological bone tissues. The nanometric details offered by these reports, from studying knockout mice models to characterizing exact disease phenotypes, can provide key insights into various bone pathologies and facilitate the development of new treatments.

Osthole improves therapy for osteoporosis through increasing autophagy of mesenchymal stem cells

Osteoporosis is a common skeletal disorder resulting in elevated fracture risk. Improvement of osteogenic differentiation is thought to be the top priority in osteoporosis treatment projects. Significant characteristics of bone marrow mesenchymal stem cells (BMMSCs), especially attractive ability to differentiate into osteoblasts, have made them alternatives for osteoporosis treatment. However, therapeutic effect with BMMSCs remains to be improved. Here, osthole, a bioactive simple coumarin derivative extracted from many medicinal plants, was introduced to pre-stimulate BMMSCs and then applied in osteoporosis therapy. The results showed that osthole-treated-BMMSCs (OBMMSCs) brought a better outcome than BMMSCs alone in estrogen deficiency-induced osteoporosis model. And elevated autophagy level was suggested to be the underlying mechanism of the ability of osthole to promote osteoblast differentiation, which is indicated by the upregulation of protein and mRNA expression level of autophagy-associated genes, Beclin1 and LC3. We concluded from these experiments that OBMMSCs are more effective than BMMSCs in osteoporosis treatment maybe through upregulation level of autophagy level induced by osthole.

Anabolic Therapies in Osteoporosis and Bone Regeneration

Osteoporosis represents the most common bone disease worldwide and results in a significantly increased fracture risk. Extrinsic and intrinsic factors implicated in the development of osteoporosis are also associated with delayed fracture healing and impaired bone regeneration. Based on a steadily increasing life expectancy in modern societies, the global implications of osteoporosis and impaired bone healing are substantial. Research in the last decades has revealed several molecular pathways that stimulate bone formation and could be targeted to treat both osteoporosis and impaired fracture healing. The identification and development of therapeutic approaches modulating bone formation, rather than bone resorption, fulfils an essential clinical need, as treatment options for reversing bone loss and promoting bone regeneration are limited. This review focuses on currently available and future approaches that may have the potential to achieve these aims.

Autophagy activation facilitates mechanical stimulation-promoted osteoblast differentiation and ameliorates hindlimb unloading-induced bone loss

Autophagy has been indicated to be involved in regulating bone metabolism. However, little is known about the role of autophagy in mechanical stimulation-influenced osteoblast differentiation and bone formation. In the present study, we first demonstrated that autophagy activation was essential for cyclic mechanical stretching-promoted osteoblast differentiation of bone marrow mesenchymal stem cells. To explore the in vivo role of autophagy in osteoblast differentiation, the hindlimb unloading-induced disuse osteoporosis model was used. Compared to the normal controls, hindlimb unloading led to abundant bone loss as well as lessened autophagy activation of osteoblasts. However, the activation of autophagy by ULK1 overexpression or in the presence of rapamycin significantly increased osteoblast differentiation activity and restored the bone volume. The findings implicate autophagy as a novel mechanosensitive pathway that regulates osteoblast differentiation. The pharmacological activation of autophagy may be an interesting approach for the prevention and treatment of disuse osteoporosis.

New horizons in treatment of osteoporosis

BACKGROUND

Prevalence of osteoporosis is increasing both in developed and developing countries. Due to rapid growth in the burden and cost of osteoporosis, worldwide, it seems reasonable to focus on the reduction of fractures as the main goal of treatment. Although, efficient pharmacological agents are available for the treatment of osteoporosis, there still remains a need to more specific drugs with less adverse effects.

MAIN BODY

This review article provides a brief update on the pathogenesis, presenting current pharmacological products approved by the US Food and Drug Administration (FDA) or Europe, and also newer therapeutic agents to treat osteoporosis according to the clinical trial data available at PubMed, UpToDate, International Osteoporosis Foundation (IOF), and clinical practice guidelines. As well, the effect of combination therapy and recommendations for future research will be further discussed.

SHORT CONCLUSION

The use of current antiresorptive and anabolic agents alone or in combinations for the treatment of osteoporosis entails several limitations. Mainly, their efficacy on non-vertebral fracture reduction is lower than that observed on vertebral fracture. In addition, they have potential adverse events on long time usage. Development of newer agents such as cathepsin k inhibitor and strontium ranelate not only have increased the available options for treating osteoporosis, but also have opened doors of opportunity to improvements in the effective treatment. However, the high cost of new agents have restricted their usage in selective patients who are at high risk of fracture or whom failed response to first line treatment options. Thus, personalized medicine should be considered for future evaluation of genetic risk score and also for environmental exposure assessment. In addition to permanent attention to early diagnosis of osteoporosis and understanding of the pathophysiology of osteoporosis for novel approach in drug discovery, there seems a need to more well-designed clinical trials with larger sample sizes and longer duration on current as well as on newer agents. Also, continuous research on plant-derived components as the source of discovering new agents, and conducting more clinical trials with combination of two or more synthetic drugs, plants, or drug-plant for the treatment of osteoporosis are recommended. Summary of treatment modalities for osteoporosis.

Gout increases risk of fracture: A nationwide population-based cohort study

There is still debate on whether high uric acid increases bone mineral density (BMD) against osteoporotic fracture or bone resorption caused by gout inflammation. This study aimed to evaluate whether gout offers a protective effect on bone health or not. We conducted a nationwide population-based retrospective cohort study to evaluate the association between gout history and risk factors of fracture.A retrospective cohort study was designed using the claim data from Longitudinal Health Insurance Database (LHID). A total of 43,647 subjects with gout and a cohort of 87,294 comparison subjects without gout were matched in terms of age and sex between 2001 and 2009, and the data were followed until December 31, 2011. The primary outcome of the study was the fracture incidence, and the impacts of gout on fracture risks were analyzed using the Cox proportional hazards model.After an 11-year follow-up period, 6992 and 11,412 incidents of fracture were reported in gout and comparison cohorts, respectively. The overall incidence rate of fracture in individuals with gout was nearly 23%, which was higher than that in individuals without gout (252 vs 205 per 10,000 person-years) at an adjusted hazard ratio of 1.17 (95% confidence interval = 1.14-1.21). Age, sex, and fracture-associated comorbidities were adjusted accordingly. As for fracture locations, patients with gout were found at significant higher fracture risks for upper/lower limbs and spine fractures. In gout patient, the user of allopurinol or benzbromarone has significantly lower risk of facture than nonusers.Gout history is considered as a risk factor for fractures, particularly in female individuals and fracture sites located at the spine or upper/lower limbs.

Differentiation of Bone Marrow Mesenchymal Stem Cells in Osteoblasts and Adipocytes and its Role in Treatment of Osteoporosis

Osteoporosis is a systemic metabolic bone disorder characterized by a decrease in bone mass and degradation of the bone microstructure, leaving bones that are fragile and prone to fracture. Most osteoporosis treatments improve symptoms, but to date there is no quick and effective therapy. Bone marrow mesenchymal stem cells (BMMSCs) have pluripotent potential. In adults, BMMSCs differentiate mainly into osteoblasts and adipocytes in the skeleton. However, if this differentiation is unbalanced, it may lead to a decrease in bone mass. If the number of adipocyte cells increases and that of osteoblast cells decreases, osteoporosis can result. A variety of hormones and cytokines play an important role in the regulation of BMMSCs bidirectional differentiation. Therefore, a greater understanding of the regulation mechanism of BMMSC differentiation may provide new methods to prevent and treat osteoporosis. In addition, autologous, allogeneic BMMSCs or genetically modified BMMSC transplantation can effectively increase bone mass and density, increase bone mechanical strength, correct the imbalance in bone metabolism, and increase bone formation, and is expected to provide a new strategy and method for the treatment of osteoporosis.

Macrophage subsets and osteoimmunology: tuning of the immunological recognition and effector systems that maintain alveolar bone

Chronic and aggressive periodontal diseases are characterized by the failure to resolve local inflammation against periodontopathogenic bacteria in the subgingival biofilm. Alveolar bone resorption is associated with altered innate and adaptive immune responses to periodontal pathogens. Macrophage-derived cytokines, chemokines and growth factors, present in both destructive and reparative phases of periodontitis, are elevated in numerous animal and human studies. Macrophage polarization to either a predominantly pro-inflammatory or anti-inflammatory phenotype may be a critical target for monitoring disease activity, modulating immune responses to subgingival biofilms in patients at risk and reducing alveolar bone loss.

Role of inflammation in the aging bones

Chronic inflammation in aging is characterized by increased inflammatory cytokines, bone loss, decreased adaptation, and defective tissue repair in response to injury. Aging leads to inherent changes in mesenchymal stem cell (MSC) differentiation, resulting in impaired osteoblastogenesis. Also, the pro-inflammatory cytokines increase with aging, leading to enhanced myelopoiesis and osteoclastogenesis. Bone marrow macrophages (BMMs) play pivotal roles in osteoblast differentiation, the maintenance of hematopoietic stem cells (HSCs), and subsequent bone repair. However, during aging, little is known about the role of macrophages in the differentiation and function of MSC and HSC. Aged mammals have higher circulating pro-inflammatory cytokines than young adults, supporting the hypothesis of increased inflammation with aging. This review will aid in the understanding of the potential role(s) of pro-inflammatory (M1) and anti-inflammatory (M2) macrophages in differentiation and function of osteoblasts and osteoclasts in relation to aging.

Role of angiogenesis in bone repair

Bone vasculature plays a vital role in bone development, remodeling and homeostasis. New blood vessel formation is crucial during both primary bone development as well as fracture repair in adults. Both bone repair and bone remodeling involve the activation and complex interaction between angiogenic and osteogenic pathways. Interestingly studies have demonstrated that angiogenesis precedes the onset of osteogenesis. Indeed reduced or inadequate blood flow has been linked to impaired fracture healing and old age related low bone mass disorders such as osteoporosis. Similarly the slow penetration of host blood vessels in large engineered bone tissue grafts has been cited as one of the major hurdle still impeding current bone construction engineering strategies. This article reviews the current knowledge elaborating the importance of vascularization during bone healing and remodeling, and the current therapeutic strategies being adapted to promote and improve angiogenesis.

RNA therapeutics targeting osteoclast-mediated excessive bone resorption

RNA interference (RNAi) is a sequence-specific post-transcriptional gene silencing technique developed with dramatically increasing utility for both scientific and therapeutic purposes. Short interfering RNA (siRNA) is currently exploited to regulate protein expression relevant to many therapeutic applications, and commonly used as a tool for elucidating disease-associated genes. Osteoporosis and their associated osteoporotic fragility fractures in both men and women are rapidly becoming a global healthcare crisis as average life expectancy increases worldwide. New therapeutics are needed for this increasing patient population. This review describes the diversity of molecular targets suitable for RNAi-based gene knock down in osteoclasts to control osteoclast-mediated excessive bone resorption. We identify strategies for developing targeted siRNA delivery and efficient gene silencing, and describe opportunities and challenges of introducing siRNA as a therapeutic approach to hard and connective tissue disorders.

Gene delivery to bone

Gene delivery to bone is useful both as an experimental tool and as a potential therapeutic strategy. Among its advantages over protein delivery are the potential for directed, sustained and regulated expression of authentically processed, nascent proteins. Although no clinical trials have been initiated, there is a substantial pre-clinical literature documenting the successful transfer of genes to bone, and their intraosseous expression. Recombinant vectors derived from adenovirus, retrovirus and lentivirus, as well as non-viral vectors, have been used for this purpose. Both ex vivo and in vivo strategies, including gene-activated matrices, have been explored. Ex vivo delivery has often employed mesenchymal stem cells (MSCs), partly because of their ability to differentiate into osteoblasts. MSCs also have the potential to home to bone after systemic administration, which could serve as a useful way to deliver transgenes in a disseminated fashion for the treatment of diseases affecting the whole skeleton, such as osteoporosis or osteogenesis imperfecta. Local delivery of osteogenic transgenes, particularly those encoding bone morphogenetic proteins, has shown great promise in a number of applications where it is necessary to regenerate bone. These include healing large segmental defects in long bones and the cranium, as well as spinal fusion and treating avascular necrosis.

Inflammatory bone loss: pathogenesis and therapeutic intervention

Bone is a tissue undergoing continuous building and degradation. This remodelling is a tightly regulated process that can be disturbed by many factors, particularly hormonal changes. Chronic inflammation can also perturb bone metabolism and promote increased bone loss. Inflammatory diseases can arise all over the body, including in the musculoskeletal system (for example, rheumatoid arthritis), the intestine (for example, inflammatory bowel disease), the oral cavity (for example, periodontitis) and the lung (for example, cystic fibrosis). Wherever inflammatory diseases occur, systemic effects on bone will ensue, as well as increased fracture risk. Here, we discuss the cellular and signalling pathways underlying, and strategies for therapeutically interfering with, the inflammatory loss of bone.

Terapia gênica para osteoporose

A osteoporose é considerada um dos problemas de saúde mais comuns e sérios da população idosa mundial. É uma doença crônica e progressiva, caracterizada pela diminuição da massa óssea e deterioração da microarquitetura do tecido ósseo. A terapia gênica representa uma nova abordagem para o tratamento da osteoporose e tem como princípio devolver a função comprometida pelo metabolismo. Esta revisão visa focar os trabalhos relevantes desenvolvidos nos últimos anos, disponibilizados nas bases de dados médicas, e que utilizaram a terapia gênica para o tratamento da osteoporose em modelos animais, bem como, as perspectivas futuras desta terapia. A maioria dos estudos utiliza os genes BMPs, PTH e OPG na tentativa de restabelecer a massa óssea. Apesar da carência de novas moléculas, todos os genes empregados nos estudos se mostraram eficientes no tratamento da doença. Os benefícios que a terapia gênica proporcionará aos pacientes no futuro devem contribuir substancialmente para o aumento na qualidade de vida dos idosos. Em breve, protocolos clínicos envolvendo humanos irão beneficiar os indivíduos com osteoporose.

Periprosthetic osteolysis: characterizing the innate immune response to titanium wear-particles

Osteolysis of bone following total hip replacement is a major clinical problem. Examination of the areas surrounding failed implants has indicated an increase in the bone-resorption-inducing cytokine, interleukin 1β (IL-1β). NALP3, a NOD-like receptor protein located in the cytosol of macrophages, signals the cleavage of pro-IL-1β into its mature, secreted form, IL-1β. Here we showed that titanium particles stimulate the NALP3 inflammasome. We demonstrated that titanium induces IL-1β secretion from macrophages. This response depended on the expression of components of the NALP3 inflammasome, including NALP3, ASC, and Caspase-1. We also showed that titanium particles trigger the recruitment of neutrophils and that this acute inflammatory response depends on the expression of the IL-1 receptor and IL-1α/β. Moreover, administration of the IL-1 receptor antagonist (IL-1Ra) diminished neutrophil recruitment in response to titanium particles. Together, these results suggest that titanium particle-induced acute inflammation is due to activation of the NALP3 inflammasome, which leads to increased IL-1β secretion and IL-1-associated signaling, including neutrophil recruitment. Efficacy of IL-1Ra treatment introduces the potential for antagonist-based therapies for implant osteolysis.

Gene therapy for bone healing

Clinical problems in bone healing include large segmental defects, spinal fusions, and the nonunion and delayed union of fractures. Gene-transfer technologies have the potential to aid healing by permitting the local delivery and sustained expression of osteogenic gene products within osseous lesions. Key questions for such an approach include the choice of transgene, vector and gene-transfer strategy. Most experimental data have been obtained using cDNAs encoding osteogenic growth factors such as bone morphogenetic protein-2 (BMP-2), BMP-4 and BMP-7, in conjunction with both nonviral and viral vectors using in vivo and ex vivo delivery strategies. Proof of principle has been convincingly demonstrated in small-animal models. Relatively few studies have used large animals, but the results so far are encouraging. Once a reliable method has been developed, it will be necessary to perform detailed pharmacological and toxicological studies, as well as satisfy other demands of the regulatory bodies, before human clinical trials can be initiated. Such studies are very expensive and often protracted. Thus, progress in developing a clinically useful gene therapy for bone healing is determined not only by scientific considerations, but also by financial constraints and the ambient regulatory environment.

Orthopedic gene therapy in 2008

Orthopedic disorders, although rarely fatal, are the leading cause of morbidity and impose a huge socioeconomic burden. Their prevalence will increase dramatically as populations age and gain weight. Many orthopedic conditions are difficult to treat by conventional means; however, they are good candidates for gene therapy. Clinical trials have already been initiated for arthritis and the aseptic loosening of prosthetic joints, and the development of bone-healing applications is at an advanced, preclinical stage. Other potential uses include the treatment of Mendelian diseases and orthopedic tumors, as well as the repair and regeneration of cartilage, ligaments, and tendons. Many of these goals should be achievable with existing technologies. The main barriers to clinical application are funding and regulatory issues, which in turn reflect major safety concerns and the opinion, in some quarters, that gene therapy should not be applied to nonlethal, nongenetic diseases. For some indications, advances in nongenetic treatments have also diminished enthusiasm. Nevertheless, the preclinical and early clinical data are impressive and provide considerable optimism that gene therapy will provide straightforward, effective solutions to the clinical management of several common debilitating disorders that are otherwise difficult and expensive to treat.

Radiation effects on bone architecture in mice and rats resulting from in vivo micro-computed tomography scanning

Recently established techniques for performing in vivo micro-computed tomography (micro-CT) provide the capability of monitoring bone changes in a living animal at various points in time. However, radiation exposure from repeated micro-CT scans may have an effect on skeletal growth in normal or disease-model animals. The purpose of this study is to test a high resolution (approximately 10 microm) in vivo micro-CT protocol on mice and rats used for bone research to understand the impact of micro-CT radiation exposure on bone architecture. Ovariectomy (OVX) or sham-OVX surgery was performed on groups (n=6-8/group) of 12-week-old C3H/HeJ, C57BL/6J, and BALB/cByJ mice, and one strain of rat (Wistar, retired breeders). The right proximal tibiae were scanned at weekly intervals while the contralateral left limbs were not scanned until the endpoint of the protocol. Trabecular and cortical bone morphology was compared between radiated and non-radiated limbs at the endpoint to quantify the radiation effect. No effects of radiation were observed in OVX or sham rats. Lower trabecular bone volume was observed in the radiated limbs (-8 to -20% relative to non-radiated limb) of all mice groups except sham BALB/cByJ mice and normal control C57BL/6J mice, however, the observed effects were much less than the observed effects of ovariectomy ( approximately 40-50% total bone volume reduction, depending on mouse strain), and no interactions between radiation and OVX treatment were observed (p>0.2). Using an internal non-radiated control within each animal is a potential method to elucidate the effect of radiation exposure for any in vivo protocol. Thus, although in vivo micro-CT is a valuable tool for bone-related research, the impact of radiation in skeletally immature mice should be considered, particularly for strains with low bone volume at the measured site.

Knocking down dickkopf-1 alleviates estrogen deficiency induction of bone loss. A histomorphological study in ovariectomized rats

Dickkopf-1 (DKK1) has been found to act as a potent Wnt signaling-inhibitory factor for regulating skeletal disorders. We investigated whether modulation of DKK1 expression by end-capped phosphorothioate DKK1 antisense oligonucleotide could alter estrogen loss-induced bone loss. Ovariectomized or sham-operated rats were given 20 microg/kg/day DKK1 sense or antisense oligonucleotide or vehicle for 28 days. Femurs and tibiae were dissected to assess bone mass, biomechanical strength, immunohistochemistry and ex vivo osteoclast formation. We found that DKK1 antisense oligonucleotide significantly abrogated the suppressing effect of ovariectomy on weight, mineral content, mineral density and peak load of femurs. DKK1 antisense oligonucleotide treatment reduced ovariectomy promotion of ex vivo osteoclast differentiation of primary M-CSF-dependent bone marrow macrophages. Histomorphometric observation demonstrated that DKK1 antisense oligonucleotide treatment increased osteoblast number and impaired ovariectomy-promoted trabecular bone loss and osteoclast number in bone tissue. Osteoblastic cells adjacent to endosteum of trabecular bone and chondrocytes at calcified cartilage expressed intensive DKK1 and RANKL and weak OPG immunostaining in ovariectomized rat bone microenvironments. Osteogenic cells and chondral cells displayed weak DKK1, RANKL and OPG expression of bone tissue after DKK1 antisense oligonucleotide treatment. Taken together, attenuation of DKK1 expression in ovariectomized rat bone tissue alleviated loss of bone mass and biomechanical property. The regulatory action of DKK1 antisense oligonucleotide treatment on bone tissue appeared to suppress the promoting effect of estrogen deficiency on osteoclastogenesis-stimulatory factor RANKL expression and osteoclast differentiation. Control of DKK1 signaling can be used in the future as an alternative strategy for protecting estrogen deficiency induction of bone loss.

Direct adenoviral transfer of bone morphogenetic protein-2 cDNA enhances fracture healing in osteoporotic sheep

Osteoporosis, a major public health burden, is associated with increased fracture risk. Fracture healing in osteoporosis is delayed, with reduced callus formation and impaired biomechanical properties of newly formed bone leading to high risk of fixation failure. Adenoviral gene transfer of bone morphogenetic protein-2 (BMP-2) has been shown to enhance fracture healing. This study evaluated the ability of gene transfer to enhance bone healing in osteoporosis. An established sheep model of osteoporosis with well-characterized alterations in fracture healing was used. Osteotomies were created surgically in the tibias of adult female sheep and monitored for 8 weeks, using radiographic, biomechanical, and histological methods. For pilot experiments, primary ovine osteoblasts and mesenchymal stem cells were transduced with a recombinant adenovirus carrying BMP-2 cDNA (Ad.BMP-2). Large increases in alkaline phosphatase production and mineralization confirmed the ability of human BMP-2 to stimulate osteoblastic differentiation in sheep. In vivo bending stiffness measurements during fracture healing as well as ex vivo torsional stiffness measurements demonstrated stiffer callus tissue after treatment with Ad.BMP-2. The differences were found mainly in the early fracture-healing period. Computed tomography demonstrated that animals receiving the BMP-2 cDNA had larger cross-sectional callus area and higher callus density. Histological examination of the tibias confirmed enhanced callus formation. Direct, local adenoviral delivery of an osteogenic gene thus led to enhanced healing of fractures in an ovine model of osteoporosis. These promising data encourage the further development of genetic approaches to enhance bone healing in patients suffering osteoporosis-associated fractures.

BMP2 gene therapy on the repair of bone defects of aged rats

Age-related decline in the number of mesenchymal stem cells (MSCs) and their reduced capability to differentiate osteogenically, along with diminished availability of growth factors, may be major factors accounting for reduced bone formation in the aging mammalian body. In the first part of the study, we compared the number of MSCs in bone marrow (BM) and the content of bone morphogenetic protein 2 (BMP2) in cortical bone tissue in juvenile, adult, and aged (1, 9, and 24 months, respectively) male rats. To assay the influence of aging on osteogenic differentiation ability, MSCs from the three age groups were transduced with the BMP2 gene. Following gene transduction, the production of BMP2 in culture media, expression of osteogenic proteins (e.g., alkaline phosphatase, type Ialpha1 collagen, osteopontin, and bone sialoprotein), as well as ectopic bone formation in athymic mice were compared. Results showed that the number of MSCs in BM as well as the content of BMP2 in cortical bone tissue decreased with age, but no significant differences between the three age groups were found with regard to production of BMP2 or capability of BMP2 gene-modified MSCs to differentiate osteogenically. The second part of the study applied BMP2 gene-modified autologous MSCs/beta-tricalcium phosphate for repair of bone defects in aged rats with positive results. Our data indicate that the osteogenic potential of MSCs of aged rats can be restored following BMP2 gene transduction and that this technique may be a useful approach in the future planning of gene therapy for age-related osteoporotic fractures.

Gene therapy for the treatment of musculoskeletal diseases

Research into the orthopaedic applications of gene therapy has resulted in progress toward managing chronic and acute genetic and nongenetic disorders. Gene therapy for arthritis, the original focus of research, has progressed to the initiation of several phase I clinical trials. Preliminary findings support the application of gene therapy in the treatment of additional chronic conditions, including osteoporosis and aseptic loosening, as well as musculoskeletal tumors. The most rapid progress is likely to be in tissue repair because it requires neither long-term transgene expression nor closely regulated levels of transgene expression. Moreover, healing probably can be achieved with existing technology. In preclinical studies, genetically modulated stimulation of bone healing has shown impressive results in repairing segmental defects in the long bones and cranium and in improving the success of spinal fusions. An increasing amount of evidence indicates that gene transfer can aid the repair of articular cartilage, menisci, intervertebral disks, ligaments, and tendons. These developments have the potential to transform many areas of musculoskeletal care, leading to treatments that are less invasive, more effective, and less expensive than existing modalities.

The potential of gene therapy for fracture healing in osteoporosis

Osteoporosis-associated fractures impair a patient's function and quality of life and represent one of the major public health burdens. Demographic changes predict a dramatic increase in osteoporotic fractures. Experimental data have shown that osteoporosis impairs fracture healing. Clinical observations demonstrate high failure rates of implant fixation in osteoporosis. The reduced healing capacity, including impaired bone formation, in osteoporotic humans might be due to defects in mesenchymal stem cells that lead to reduced proliferation and osteoblastic differentiation. Growth factors show remarkable promise as agents that can improve the healing of bone or increase the proliferation and differentiation capacities of mesenchymal stem cells. Their clinical utility is limited by delivery problems. The attraction of gene-transfer approaches is the unique ability to deliver authentically processed gene products to precise anatomical locations at therapeutic levels for sustained periods of time. Unlike the treatment of chronic diseases, it is neither necessary nor desirable for transgene expression to persist beyond the few weeks or months needed to achieve healing. This review presents different approaches of gene therapy to enhance fracture healing and summarizes the promising results of preclinical studies. It focuses on applications of this new technique to fracture healing in osteoporosis. In our opinion, these applications represent some of the few examples in which gene therapy has a good chance of early clinical success.

The 2003 Nicolas Andry Award. Orthopaedic gene therapy

We review progress in the field of orthopaedic gene therapy since the concept of using gene transfer to address orthopaedic problems was initiated approximately 15 years ago. The original target, arthritis, has been the subject of two successful Phase I clinical trials, and additional human studies are pending in rheumatoid arthritis and osteoarthritis. The repair of damaged musculoskeletal tissues also has proved to be a fruitful area of research, and impressive enhancement of bone healing has been achieved in preclinical models. Rapid progress also is being made in the use of gene transfer to improve cartilage repair, ligament healing, and restoration of various additional tissues, including tendon and meniscus. Other applications include intervertebral disc degeneration, aseptic loosening, osteoporosis, genetic diseases, and orthopaedic tumors. Of these various orthopaedic targets of gene therapy, tissue repair is likely to make the earliest clinical impact because it can be achieved with existing technology. Tissue repair may become one of the earliest clinical successes for gene therapy as a whole. Orthopaedics promises to be a leading discipline for the use of human gene therapy.

Gene therapy in orthopaedic surgery: the current status

The first successful gene therapy trial was reported in 1991. Since then, successful gene transfer in cultured cells and small animals has been reported by many studies, with achievement of at least transitory high levels of exogenous gene expression. Over 400 clinical protocols for gene therapy have been approved, involving over 4000 patients. However, publication of the results of these gene therapy trials has been limited, with only 80 published reports as of 2002. The majority of clinical gene therapy trials reported so far have been phase I or phase II trials, which are concerned mainly with safety issues and have focused on the treatment of malignancies and other potentially fatal conditions. The death of a patient in 1999 from systemic administration of an adenoviral vector and recent reports of leukaemia in two patients in a clinical gene therapy trial have led to a further re-evaluation of the safety of gene therapy and the role for gene therapy in clinical practice. This review outlines the current status of gene therapy as it relates to orthopaedic diseases and highlights the areas where progress is still to be made.