RNAi of COL1A1 in mesenchymal progenitor cells

New Perspectives of Therapies in Osteogenesis Imperfecta-A Literature Review

(1) Background: Osteogenesis imperfecta (OI) is a rare skeletal dysplasia characterized as a heterogeneous disorder group with well-defined phenotypic and genetic features that share uncommon bone fragility. The current treatment options, medical and orthopedic, are limited and not efficient enough to improve the low bone density, bone fragility, growth, and mobility of the affected individuals, creating the need for alternative therapeutic agents. (2) Methods: We searched the medical database to find papers regarding treatments for OI other than conventional ones. We included 45 publications. (3) Results: In reviewing the literature, eight new potential therapies for OI were identified, proving promising results in cells and animal models or in human practice, but further research is still needed. Bone marrow transplantation is a promising therapy in mice, adults, and children, decreasing the fracture rate with a beneficial effect on structural bone proprieties. Anti-RANKL antibodies generated controversial results related to the therapy schedule, from no change in the fracture rate to improvement in the bone mineral density resorption markers and bone formation, but with adverse effects related to hypercalcemia. Sclerostin inhibitors in murine models demonstrated an increase in the bone formation rate and trabecular cortical bone mass, and a few human studies showed an increase in biomarkers and BMD and the downregulation of resorption markers. Recombinant human parathormone and TGF-β generated good results in human studies by increasing BMD, depending on the type of OI. Gene therapy, 4-phenylbutiric acid, and inhibition of eIF2α phosphatase enzymes have only been studied in cell cultures and animal models, with promising results. (4) Conclusions: This paper focuses on eight potential therapies for OI, but there is not yet enough data for a new, generally accepted treatment. Most of them showed promising results, but further research is needed, especially in the pediatric field.

Identification and implication of tissue-enriched ligands in epithelial-endothelial crosstalk during pancreas development

Development of the pancreas is driven by an intrinsic program coordinated with signals from other cell types in the epithelial environment. These intercellular communications have been so far challenging to study because of the low concentration, localized production and diversity of the signals released. Here, we combined scRNAseq data with a computational interactomic approach to identify signals involved in the reciprocal interactions between the various cell types of the developing pancreas. This in silico approach yielded 40,607 potential ligand-target interactions between the different main pancreatic cell types. Among this vast network of interactions, we focused on three ligands potentially involved in communications between epithelial and endothelial cells. BMP7 and WNT7B, expressed by pancreatic epithelial cells and predicted to target endothelial cells, and SEMA6D, involved in the reverse interaction. In situ hybridization confirmed the localized expression of Bmp7 in the pancreatic epithelial tip cells and of Wnt7b in the trunk cells. On the contrary, Sema6d was enriched in endothelial cells. Functional experiments on ex vivo cultured pancreatic explants indicated that tip cell-produced BMP7 limited development of endothelial cells. This work identified ligands with a restricted tissular and cellular distribution and highlighted the role of BMP7 in the intercellular communications contributing to vessel development and organization during pancreas organogenesis.

Developmental and sexual dimorphic atlas of the prenatal mouse external genitalia at the single-cell level

Birth defects of the external genitalia are among the most common in the world. Proper formation of the external genitalia requires a highly orchestrated process that involves special cell populations and sexually dimorphic hormone signaling. It is clear what the end result of the sexually dimorphic development is (a penis in the male versus clitoris in the female); however, the cell populations involved in the process remain poorly defined. Here, we used single-cell messenger RNA sequencing in mouse embryos to uncover the dynamic changes in cell populations in the external genitalia during the critical morphogenetic window. We found that overall, male and female external genitalia are largely composed of the same core cellular components. At the bipotential stage of development (embryonic day or E14.5), few differences in cell populational composition exist between male and female. Although similar in cell population composition, genetic differences in key sexual differentiation developmental pathways arise between males and females by the early (E16.5) and late (E18.5) differentiation stages. These differences include discrete cell populations with distinct responsiveness to androgen and estrogen. By late sexual differentiation (E18.5), unique cell populations in both male and female genitalia become apparent and are enriched with androgen- and estrogen-responsive genes, respectively. These data provide insights into the morphogenesis of the external genitalia that could be used to understand diseases associated with defects in the external genitalia.

Mesenchymal stromal cells and rheumatic diseases: new tools from pathogenesis to regenerative therapies

In recent years, mesenchymal stromal cells (MSCs) have been largely investigated and tested as a new therapeutic tool for several clinical applications, including the treatment of different rheumatic diseases. MSCs are responsible for the normal turnover and maintenance of adult mesenchymal tissues as the result of their multipotent differentiation abilities and their secretion of a variety of cytokines and growth factors. Although initially derived from bone marrow, MSCs are present in many different tissues such as many peri-articular tissues. MSCs may exert immune-modulatory properties, modulating different immune cells in both in vitro and in vivo models, and they are considered immune-privileged cells. At present, these capacities are considered the most intriguing aspect of their biology, introducing the possibility that these cells may be used as effective therapy in autoimmune diseases. Therefore, stem cell therapies may represent an innovative approach for the treatment of rheumatic diseases, especially for the forms that are not responsive to standard treatments or alternatively still lacking a definite therapy. At present, although the data from scientific literature appear to suggest that such treatments might be more effective whether administered as soon as possible, the use of MSCs in clinical practice is likely to be restricted to patients with a long history of a severe refractory disease. Further results from larger clinical trials are needed to corroborate preclinical findings and human non-controlled studies, and advancement in the knowledge of MSCs might provide information about the therapeutic role of these cells in the treatment of many rheumatic diseases.

Treatment of osteogenesis imperfecta in adults

BACKGROUND

Osteogenesis imperfecta (OI) is a heterogeneous rare connective tissue disorder commonly caused by mutations in the collagen type I genes. Pharmacological treatment has been most extensively studied in children, and there are only few studies comprising adult OI patients.

OBJECTIVES

i) To review the literature on the current medical management of OI in children and adults, and thereby identify unmet medical needs and ii) to present an overview of possible future treatment options.

RESULTS

Individualization and optimization of OI treatment in adults remain a challenge, because available treatments do not target the underlying collagen defect, and available literature gives weak support for treatment decisions for adult patients.

CONCLUSIONS

Bisphosphonates are still the most widely used pharmacological treatment for adult OI, but the current evidence supporting this is sparse and investigations on indications for choice and duration of treatment are needed.

Cartilage tissue engineering: molecular control of chondrocyte differentiation for proper cartilage matrix reconstruction

BACKGROUND

Articular cartilage defects are a veritable therapeutic problem because therapeutic options are very scarce. Due to the poor self-regeneration capacity of cartilage, minor cartilage defects often lead to osteoarthritis. Several surgical strategies have been developed to repair damaged cartilage. Autologous chondrocyte implantation (ACI) gives encouraging results, but this cell-based therapy involves a step of chondrocyte expansion in a monolayer, which results in the loss in the differentiated phenotype. Thus, despite improvement in the quality of life for patients, reconstructed cartilage is in fact fibrocartilage. Successful ACI, according to the particular physiology of chondrocytes in vitro, requires active and phenotypically stabilized chondrocytes.

SCOPE OF REVIEW

This review describes the unique physiology of cartilage, with the factors involved in its formation, stabilization and degradation. Then, we focus on some of the most recent advances in cell therapy and tissue engineering that open up interesting perspectives for maintaining or obtaining the chondrogenic character of cells in order to treat cartilage lesions.

MAJOR CONCLUSIONS

Current research involves the use of chondrocytes or progenitor stem cells, associated with "smart" biomaterials and growth factors. Other influential factors, such as cell sources, oxygen pressure and mechanical strain are considered, as are recent developments in gene therapy to control the chondrocyte differentiation/dedifferentiation process.

GENERAL SIGNIFICANCE

This review provides new information on the mechanisms regulating the state of differentiation of chondrocytes and the chondrogenesis of mesenchymal stem cells that will lead to the development of new restorative cell therapy approaches in humans. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Allele-specific Col1a1 silencing reduces mutant collagen in fibroblasts from Brtl mouse, a model for classical osteogenesis imperfecta

Gene silencing approaches have the potential to become a powerful curative tool for a variety of monogenic diseases caused by gain-of-function mutations. Classical osteogenesis imperfecta (OI), a dominantly inherited bone dysplasia, is characterized in its more severe forms by synthesis of structurally abnormal type I collagen, which exerts a negative effect on extracellular matrix. Specific suppression of the mutant (Mut) allele would convert severe OI forms to the mild type caused by a quantitative defect in normal collagen. Here, we describe the in vitro and ex vivo investigation of a small interfering RNA (siRNA) approach to allele-specific gene silencing using Mut Col1a1 from the Brtl mouse, a well-characterized model for classical human OI. A human embryonic kidney cell line, which expresses the firefly luciferase gene, combined with either wild-type or Mut Brtl Col1a1 exon 23 sequences, was used for the first screening. The siRNAs selected based on their specificity and the corresponding short hairpin RNAs (shRNAs) subcloned in a lentiviral vector were evaluated ex vivo in Brtl fibroblasts for their effect on collagen transcripts and protein. A preferential reduction of the Mut allele of up to 52% was associated with about 40% decrease of the Mut protein, with no alteration of cell proliferation. Interestingly, a downregulation of HSP47, a specific collagen chaperone known to be upregulated in some OI cases, was detected. Our data support further testing of shRNAs and their delivery by lentivirus as a strategy to specifically suppress the Mut allele in mesenchymal stem cells of OI patients for autologous transplantation.

Control of collagen production in mouse chondrocytes by using a combination of bone morphogenetic protein-2 and small interfering RNA targeting Col1a1 for hydrogel-based tissue-engineered cartilage

Because articular cartilage does not self-repair, tissue-engineering strategies should be considered to regenerate this tissue. Autologous chondrocyte implantation is already used for treatment of focal damage of articular cartilage. Unfortunately, this technique includes a step of cell amplification, which results in dedifferentiation of chondrocytes, with expression of type I collagen, a protein characteristic of fibrotic tissues. Therefore, the risk of producing a fibrocartilage exists. The aim of this study was to propose a new strategy for authorizing the recovery of the differentiated status of the chondrocytes after their amplification on plastic. Because the bone morphogenetic protein (BMP)-2 and the transforming growth factor (TGF)-β1 are cytokines both proposed as stimulants for cartilage repair, we undertook a detailed comparative analysis of their biological effects on chondrocytes. As a cellular model, we used mouse chondrocytes after their expansion on plastic and we tested the capability of BMP-2 or TGF-β1 to drive their redifferentiation, with special attention given to the nature of the proteins synthesized by the cells. To prevent any fibrotic character of the newly synthesized extracellular matrix, we silenced type I collagen by transfecting small interfering RNA (siRNA) into the chondrocytes, before their exposure to BMP-2 or TGF-β1. Our results showed that addition of siRNA targeting the mRNA encoded by the Col1a1 gene (Col1a1 siRNA) and BMP-2 represents the most efficient combination to control the production of cartilage-characteristic collagen proteins. To go one step further toward scaffold-based cartilage engineering, Col1a1 siRNA-transfected chondrocytes were encapsulated in agarose hydrogel and cultured in vitro for 1 week. The analysis of the chondrocyte-agarose constructs by using real-time polymerase chain reaction, Western-blotting, immunohistochemistry, and electron microscopy techniques demonstrated that the BMP-2/Col1a1 siRNA combination is effective in reinitializing correct production and assembly of the cartilage-characteristic matrix in agarose hydrogel, without production of type I collagen. Because agarose is known to favor long-term expression of the chondrocyte phenotype and agarose-based hydrogels are approved for clinical trials, this strategy appears very promising to repair hyaline cartilage.

Allele dependent silencing of collagen type I using small interfering RNAs targeting 3'UTR Indels - a novel therapeutic approach in osteogenesis imperfecta

Osteogenesis imperfecta, also known as "brittle bone disease", is a heterogeneous disorder of connective tissue generally caused by dominant mutations in the genes COL1A1 and COL1A2, encoding the α1 and α2 chains of type I (pro)collagen. Symptomatic patients are usually prescribed bisphosphonates, but this treatment is neither curative nor sufficient. A promising field is gene silencing through RNA interference. In this study small interfering RNAs (siRNAs) were designed to target each allele of 3'UTR insertion/deletion polymorphisms (indels) in COL1A1 (rs3840870) and COL1A2 (rs3917). For both indels, the frequency of heterozygous individuals was determined to be approximately 50% in Swedish cohorts of healthy controls as well as in patients with osteogenesis imperfecta. Cultures of primary human bone derived cells were transfected with siRNAs through magnet-assisted transfection. cDNA from transfected cells was sequenced in order to measure targeted allele/non-targeted allele ratios and the overall degree of silencing was assessed by quantitative PCR. Successful allele dependent silencing was observed, with promising results for siRNAs complementary to both the insertion and non-insertion harboring alleles. In COL1A1 cDNA the indel allele ratios were shifted from 1 to 0.09 and 0.19 for the insertion and non-insertion allele respectively while the equivalent resulting ratios for COL1A2 were 0.05 and 0.01. Reductions in mRNA abundance were also demonstrated; in cells treated with siRNAs targeting the COL1A1 alleles the average COL1A1 mRNA levels were reduced 65% and 78% compared to negative control levels and in cells treated with COL1A2 siRNAs the average COL1A2 mRNA levels were decreased 26% and 49% of those observed in the corresponding negative controls. In conclusion, allele dependent silencing of collagen type I utilizing 3'UTR indels common in the general population constitutes a promising mutation independent therapeutic approach for osteogenesis imperfecta.

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.

Recessive osteogenesis imperfecta: clinical, radiological, and molecular findings

Osteogenesis imperfecta (OI) or "brittle bone disease" is currently best described as a group of hereditary connective tissue disorders related to primary defects in type I procollagen, and to alterations in type I procollagen biosynthesis, both associated with osteoporosis and increased susceptibility to bone fractures. Initially, the autosomal dominant forms of OI, caused by mutations in either COL1A1 or COL1A2, were described. However, for decades, the molecular defect of a small percentage of patients clinically diagnosed with OI has remained elusive. It has been in the last 6 years that the genetic causes of several forms of OI with autosomal recessive inheritance have been characterized. These comprise defects of collagen chaperones, and proteins involved in type I procollagen assembly, processing and maturation, as well as proteins involved in the formation and homeostasis of bone tissue. This article reviews the recently characterized forms of recessive OI, focusing in particular on their clinical and molecular findings, and on their radiological characterisation. Clinical management and treatment of OI in general will be discussed, too.

Allele-specific siRNA knockdown as a personalized treatment strategy for vascular Ehlers-Danlos syndrome in human fibroblasts

The vascular type of the Ehlers-Danlos syndrome (vEDS) is caused by dominant-negative mutations in the procollagen type III (COL3A1) gene. Patients with this autosomal dominant disorder have a shortened life expectancy due to complications from ruptured vessels or hollow organs. We tested the effectiveness of allele-specific RNA interference (RNAi) to reduce the mutated phenotype in fibroblasts. Small-interfering RNAs (siRNAs) discriminating between wild-type and mutant COL3A1 allele were identified by a luciferase reporter gene assay and in primary fibroblasts from a normal donor and a patient with vEDS. The best discriminative siRNA with the mutation at position 10 resulted in >90% silencing of the mutant allele without affecting the wild-type allele. Transmission and immunogold electron microscopy of extracted extracellular matrices from untreated fibroblasts of the patient with vEDS revealed structurally abnormal fibrils. After siRNA treatment, collagen fibrils became similar to fibrils from fibroblasts of normal and COL3A1 haploinsufficient donors. In addition, it was shown that expression of mutated COL3A1 activates the unfolded protein response and that reduction of the amount of mutated protein by siRNA reduces cellular stress. Taken together, the results provide evidence that allele-specific siRNAs are able to reduce negative effects of mutated COL3A1 proteins. Thus, the application of allele-specific RNAi may be a promising direction for future personalized therapies to reduce the severity of vEDS.

Osteogenesis Imperfecta: A Review with Clinical Examples

Osteogenesis imperfecta (OI) is characterized by susceptibility to bone fractures, with a severity ranging from subtle increase in fracture frequency to prenatal fractures. The first scientific description of OI dates from 1788. Since then, important milestones in OI research and treatment have, among others, been the classification of OI into 4 types (the 'Sillence classification'), the discovery of defects in collagen type I biosynthesis as a cause of most cases of OI and the use of bisphosphonate therapy. Furthermore, in the past 5 years, it has become clear that OI comprises a group of heterogeneous disorders, with an estimated 90% of cases due to a causative variant in the COL1A1 or COL1A2 genes and with the remaining 10% due to causative recessive variants in the 8 genes known so far, or in other currently unknown genes. This review aims to highlight the current knowledge around the history, epidemiology, pathogenesis, clinical/radiological features, management, and future prospects of OI. The text will be illustrated with clinical descriptions, including radiographs and, where possible, photographs of patients with OI.

In vivo cellular adaptation to ER stress: survival strategies with double-edged consequences

Disturbances to the balance of protein synthesis, folding and secretion in the endoplasmic reticulum (ER) induce stress and thereby the ER stress signaling (ERSS) response, which alleviates this stress. In this Commentary, we review the emerging idea that ER stress caused by abnormal physiological conditions and/or mutations in genes that encode client proteins of the ER is a key factor underlying different developmental processes and the pathology of diverse diseases, including diabetes, neurodegeneration and skeletal dysplasias. Recent studies in mouse models indicate that the effect of ERSS in vivo and the nature of the cellular strategies induced to ameliorate pathological ER stress are crucial factors in determining cell fate and clinical disease features. Importantly, ERSS can affect cellular proliferation and the differentiation program; cells that survive the stress can become 'reprogrammed' or dysfunctional. These cell-autonomous adaptation strategies can generate a spectrum of context-dependent cellular consequences, ranging from recovery to death. Secondary effects can include altered cell-extracellular-matrix interactions and non-cell-autonomous alteration of paracrine signaling, which contribute to the final phenotypic outcome. Recent reports showing that ER stress can be alleviated by chemical compounds suggest the potential for novel therapeutic approaches.

Current and emerging treatments for the management of osteogenesis imperfecta

Osteogenesis imperfecta (OI) is the most common bone genetic disorder and it is characterized by bone brittleness and various degrees of growth disorder. Clinical severity varies widely; nowadays eight types are distinguished and two new forms have been recently described although not yet classified. The approach to such a variable and heterogeneous disease should be global and therefore multidisciplinary. For simplicity, the objectives of treatment can be reduced to three typical situations: the lethal perinatal form (type II), in which the problem is survival at birth; the severe and moderate forms (types III-IX), in which the objective is 'autonomy'; and the mild form (type I), in which the aim is to reach 'normal life'. Three types of treatment are available: non-surgical management (physical therapy, rehabilitation, bracing and splinting), surgical management (intramedullary rod positioning, spinal and basilar impression surgery) and medical-pharmacological management (drugs to increase the strength of bone and decrease the number of fractures as bisphosphonates or growth hormone, depending on the type of OI). Suggestions and guidelines for a therapeutic approach are indicated and updated with the most recent findings in OI diagnosis and treatment.

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.

Potential implications of cell therapy for osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a brittle-bone disease whose hallmark is bone fragility. Since the disease is genetic, there is currently no available cure. Several pharmacological agents have been tried with not much success, except the recent use of bisphosphonates. Stem cells have been suggested as an alternative OI treatment, but many hurdles remain before this technology can be applied for treating patients with OI. This review summarizes what is known at present regarding the application of stem cells to treat OI using animal models, clinical trials using mesenchymal stem cells to treat patients with OI and the knowledge gained from the clinical trials. Application of gene therapy in combination with stem cells is also discussed. The hurdles to be overcome to bring stem cells close to the clinic and future perspectives are discussed.

Allele dependent silencing of COL1A2 using small interfering RNAs

Osteogenesis imperfecta (OI) is generally caused by a dominant mutation in Collagen I, encoded by the genes COL1A1 and COL1A2. To date there is no satisfactory therapy for OI, but inactivation of the mutant allele through small interfering RNAs (siRNA) is a promising approach, as siRNAs targeting each allele of a polymorphism could be used for allele-specific silencing irrespective of the location of the actual mutations. In this study we examined the allele dependent effects of several tiled siRNAs targeting a region surrounding an exonic COL1A2 T/C polymorphism (rs1800222) in heterozygous primary human bone cells. Relative abundances of COL1A2 alleles were determined by cDNA sequencing and overall COL1A2 abundance was analyzed by quantitative PCR. One of the siRNAs decreased overall COL1A2 abundance by 71% of which 75% was due to silencing of the targeted T-allele. In conclusion, allele-preferential silencing of Collagen type I genes may be a future therapeutic approach for OI.

Reference gene selection for real-time rtPCR in human epidermal keratinocytes

BACKGROUND

RNA interference represents a powerful tool with which to achieve suppression of specific target mRNA. Real-time rtPCR is a useful technique for assessing levels of mRNA expression. Critically, for real-time rtPCR to yield meaningful results, it is necessary to normalise expression of the gene of interest to stably expressed endogenous control genes.

OBJECTIVES

The study involved establishing expression profiles for 11 housekeeping genes in human epidermal keratinocyte cell lines determining their relative stability. Furthermore, the effect of the presence of shRNA on these expression profiles has been established.

METHODS

Keratinocytes were transfected using lipid-based transfection or AMAXA nucleofection. Real-time rtPCR was used to establish RNA expression levels. Data analysis was carried out using geNORM.

RESULTS

When using HaCaT or adult NHEK cells any combination of 8 of the housekeeping genes would be appropriate for normalisation. In contrast, with juvenile NHEK cells only 4 of the housekeeping genes were found to be sufficiently stable to be deemed appropriate for normalisation of expression data. Furthermore data demonstrated that the expression of housekeeping genes may sometimes be affected by the induction of the RNAi pathway.

CONCLUSIONS

The data obtained highlight the importance of characterising housekeeping gene expression profiles in each specific cell type prior to choosing a set of housekeeping genes for expression studies. The results from this study are applicable to researchers working with human epidermal keratinocytes and the experimental approach is more broadly applicable to any researcher carrying out real-time rtPCR.

Modulating the expression of disease genes with RNA-based therapy

Conventional gene therapy has focused largely on gene replacement in target cells. However, progress from basic research to the clinic has been slow for reasons relating principally to the challenges of heterologous DNA delivery and regulation in vivo. Alternative approaches targeting RNA have the potential to circumvent some of these difficulties, particularly as the active therapeutic molecules are usually short oligonucleotides and the target gene transcript is under endogenous regulation. RNA-based strategies offer a series of novel therapeutic applications, including altered processing of the target pre-mRNA transcript, reprogramming of genetic defects through mRNA repair, and the targeted silencing of allele- or isoform-specific gene transcripts. This review examines the potential of RNA therapeutics, focusing on antisense oligonucleotide modification of pre-mRNA splicing, methods for pre-mRNA trans-splicing, and the isoform- and allele-specific applications of RNA interference.

RNAi-mediated inhibition of COL1A1 and COL3A1 in human skin fibroblasts

Types I and III collagens are the major collagens comprising skin connective tissue. Defects in these collagens lead to diseases of dermal connective tissue and fibre hyperplasia. RNA interference (RNAi) provides a powerful tool to inhibit specific gene expression. In this study, we generated small interfering RNAs (siRNA) expression cassettes (SECs) by polymerase chain reaction (PCR) as a method to quickly screen the efficacy of siRNAs. We then cloned the most efficient SECs into vectors, using a rapid and novel method intrinsic to the design of the SEC, and transfected human skin fibroblasts (HSF) to generate stable lines. We show that the transfection of SECs into HSFs resulted in specific and effective repression of COL1A1 and COL3A1 expression (5.00% and 6.48% of control levels) provided a rapid method for testing candidate siRNA sequences. We report the use of vector-based RNAi to establish stable HSF cell lines with persistent knockdown over at least 30 days (25.21% and 22.12% of control levels). These stably modified HSF cell lines may be used for the study of other types of collagen or proteins of the extracellular matrix (ECM).

RNA interference-mediated suppression and replacement of human rhodopsin in vivo

Mutational heterogeneity represents a significant barrier to development of therapies for many dominantly inherited diseases. For example, >100 mutations in the rhodopsin gene (RHO) have been identified in patients with retinitis pigmentosa (RP). The development of therapies for dominant disorders that correct the primary genetic lesion and overcome mutational heterogeneity is challenging. Hence, therapeutics comprising two elements--gene suppression in conjunction with gene replacement--have been investigated. Suppression is targeted to a site independent of the mutation; therefore, both mutant and wild-type alleles are suppressed. In parallel with suppression, a codon-modified replacement gene refractory to suppression is provided. Both in vitro and in vivo validation of suppression and replacement for RHO-linked RP has been undertaken in the current study. RNA interference (RNAi) has been used to achieve ~90% in vivo suppression of RHO in photoreceptors, with use of adeno-associated virus (AAV) for delivery. Demonstration that codon-modifed RHO genes express functional wild-type protein has been explored transgenically, together with in vivo expression of AAV-delivered RHO-replacement genes in the presence of targeting RNAi molecules. Observation of potential therapeutic benefit from AAV-delivered suppression and replacement therapies has been obtained in Pro23His mice. Results provide the first in vivo indication that suppression and replacement can provide a therapeutic solution for dominantly inherited disorders such as RHO-linked RP and can be employed to circumvent mutational heterogeneity.

Treatment of children with osteogenesis imperfecta

Children with moderate to severe forms of osteogenesis imperfecta (OI) require adequate physiotherapy, rehabilitation and orthopedic surgery. Supportive treatment with bisphosphonates can improve the effects of these nonmedicinal treatment modalities. Benefits of bisphosphonate treatment include decreased pain, lower fracture incidence, and better mobility. Among the various bisphosphonates, intravenous pamidronate has been studied in most detail. However, the optimal treatment regimen and the long-term consequences of pamidronate treatment in children are currently unknown. Given these uncertainties, treatment with bisphosphonates during growth should be reserved for patients who have significant clinical problems, such as vertebral compression fractures or long-bone deformities. Medical therapies other than bisphosphonates play a minor role at present. Gene-based therapy currently remains in the realm of preclinical research.

Osteogenesis imperfecta, current and future medical treatment

Physiotherapy, rehabilitation, and orthopedic surgery are the mainstay of treatment in moderate to severe forms of osteogenesis imperfecta (OI). Nevertheless, medical treatment with bisphosphonates can bring significant additional improvements. Benefits include decreased pain, lower fracture incidence, and better mobility. Among the various bisphosphonates, intravenous pamidronate has been studied in most detail. It is unclear whether oral bisphosphonates are as effective as intravenous pamidronate. As the effect of bisphosphonates on the skeleton is largest during growth, it appears logical to start medical therapy of OI patients as early as possible. However, the optimal treatment regimen and the long-term consequences of pamidronate treatment in children are currently unknown. Given these uncertainties, treatment with bisphosphonates during growth should be reserved for patients who have significant clinical problems, such as vertebral compression fractures or long bone deformities. Medical therapies other than bisphosphonates, such as growth hormone and parathyroid hormone, play a minor role at present. Gene-based therapy currently remains in the early stages of preclinical research.

RNAi-based suppression and replacement of rds-peripherin in retinal organotypic culture

Extensive mutational heterogeneity presents a significant barrier to the development of therapeutics for RDS-peripherin-linked autosomal-dominant retinitis pigmentosa (RP), for which more than 50 disease-related mutations have been identified to date. Mutation-independent suppression, using RNA interference (RNAi), together with simultaneous expression of a replacement rds gene (r-rds, which has been altered to escape suppression but nevertheless encodes wild-type protein) has been explored in COS-7 cells and mouse retinal explants. The efficacy of small interfering and short hairpin RNAs (si/shRNAs) silencing mouse rds, and the function of r-rds (containing degenerate substitutions in the RNAi target sequence) were analyzed at transcript (RT-PCR) and protein (ELISA) levels in COS-7 cells. "Dual-" and "triple-expression" constructs carrying the shRNA suppressor and the marker EGFP with or without the r-rds cassette were electroporated in vitro into retinal explants from 1-day-old pups. The retinae were dissociated at day 14, and transduced cells were FACS-sorted using the coexpressed EGFP marker and analyzed by RT-PCR. si/shRNAs decreased rds mRNA and protein expression by up to 82%, while r-rds was protected from suppression in COS-7 cells. Similarly, efficient RNAi-mediated suppression of endogenous rds was detected in retinal explants, while concomitant rescue of r-rds was also achieved. These data validate the concept of RNAi-based suppression coupled with replacement technology for the development of therapies targeting RDS-linked autosomal-dominant RP, and suggest that such approaches could potentially be used for other autosomal-dominant diseases with similarly extensive intragenic heterogeneity.

Toward a gene therapy for dominant disease: validation of an RNA interference-based mutation-independent approach

The intragenic heterogeneity encountered in many dominant disease-causing genes represents a significant challenge with respect to development of economically viable therapeutics. For example, 25% of autosomal dominant retinitis pigmentosa is caused by over 100 different mutations within the gene encoding rhodopsin, each of which could require a unique gene therapy. We describe here an RNA interference (RNAi)-based mutation-independent approach, targeting as an example murine rhodopsin. Native transcripts are suppressed by a single RNAi molecular species, whereas transcripts from replacement genes engineered at degenerate third-codon wobble positions are resistant to suppression. We demonstrate suppression of murine rhodopsin transcript by up to 90% with full concomitant expression of replacement transcript and establish the validity of this approach in cell culture, retinal explants, and mouse liver in vivo.

Correction of a mineralization defect by overexpression of a wild-type cDNA for COL1A1 in marrow stromal cells (MSCs) from a patient with osteogenesis imperfecta: a strategy for rescuing mutations that produce dominant-negative protein defects

Gene therapy for dominant-negative disorders presents a more difficult challenge than gene therapy for recessive disorders, since even partial replacement of a protein for a recessive disorder can reverse symptoms. Osteogenesis imperfecta (OI) has frequently served as a model disorder for dominant-negative defects of structural proteins. The disease is caused by mutations in type I collagen (COL1A1), the major structural component of bone, skin and other connective tissues. The severity of the phenotype is largely dependent on the ratio of normal to mutant type I procollagen synthesized by cells. Recently, attempts have been made to develop strategies for cell and gene therapies using the adult stem cells from bone marrow referred to as mesenchymal stem cells or marrow stromal cells (MSCs). In this study, we used MSCs from a patient with type III OI who was heterozygous for an IVS 41A+4C mutation in COL1A1. A hybrid genomic / cDNA construct of COL1A1 was transfected into the MSCs and the transfectants were expanded over a 200-fold. Transfected MSCs showed increased expression of the wild-type mRNA and protein. In vitro assays demonstrated that the transfected cells more efficiently differentiated into mineralizing cells. The results indicated that it is possible to overexpress COL1A1 cDNA in OI MSCs and thereby to correct partially the dominant-negative protein defect.

Intrastriatal rAAV-mediated delivery of anti-huntingtin shRNAs induces partial reversal of disease progression in R6/1 Huntington's disease transgenic mice

Huntington's disease (HD) is a fatal neurodegenerative disorder caused by the presence of an abnormally expanded polyglutamine domain in the N-terminus of huntingtin. We developed a recombinant adeno-associated viral serotype 5 (rAAV5) gene transfer strategy to posttranscriptionally suppress the levels of striatal mutant huntingtin (mHtt) in the R6/1 HD transgenic mouse via RNA interference. Transient cotransfection of HEK293 cells with plasmids expressing a portion of human mHtt derived from R6/1 transgenic HD mice and a short-hairpin RNA directed against the 5' UTR of the mHtt mRNA (siHUNT-1) resulted in reduction in the levels of mHtt mRNA (-75%) and protein (-60%). Long-term in vivo rAAV5-mediated expression of siHUNT-1 in the striatum of R6/1 mice reduced the levels of mHtt mRNA (-78%) and protein (-28%) as determined by quantitative RT-PCR and Western blot analysis, respectively. The reduction in mHtt was concomitant with a reduction in the size and number of neuronal intranuclear inclusions and a small but significant normalization of the steady-state levels of preproenkephalin and dopamine- and cAMP-responsive phosphoprotein 32 kDa mRNA. Finally, bilateral expression of rAAV5-siHUNT-1 resulted in delayed onset of the rear paw clasping phenotype exhibited by the R6/1 mice. These results suggest that a reduction in the levels of striatal mHtt can ameliorate the HD phenotype of R6/1 mice.

Emerging therapeutic approaches for osteogenesis imperfecta

Osteogenesis imperfecta (OI) is an incurable genetic brittle-bone disease. Although drug therapy, surgery and physiotherapy represent current treatments for OI, the search is ongoing for effective and innovative new therapies targeting the underlying causes of the disease. In this regard, recent advances in the fields of gene and stem-cell therapies have been considerable. In spite of the many challenges that remain, potential new therapies for OI, which have been tested in cell culture systems, animal models and patients, offer hope for the future development of successful therapies. Recent progress in the field is reviewed here.

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.