Direct rAAV SOX9 administration for durable articular cartilage repair with delayed terminal differentiation and hypertrophy in vivo

Engineering gene-activated bioprinted scaffolds for enhancing articular cartilage repair

Untreated articular cartilage injuries often result in severe chronic pain and dyskinesia. Current repair strategies have limitations in effectively promoting articular cartilage repair, underscoring the need for innovative therapeutic approaches. A gene-activated matrix (GAM) is a promising and comprehensive therapeutic strategy that integrates tissue-engineered scaffold-guided gene therapy to promote long-term articular cartilage repair by enhancing gene retention, reducing gene loss, and regulating gene release. However, for effective articular cartilage repair, the GAM scaffold must mimic the complex gradient structure of natural articular cartilage. Three-dimensional (3D) bioprinting technology has emerged as a compelling solution, offering the ability to precisely create complex microstructures that mimic the natural articular cartilage. In this review, we summarize the recent research progress on GAM and 3D bioprinted scaffolds in articular cartilage tissue engineering (CTE), while also exploring future challenges and development directions. This review aims to provide new ideas and concepts for the development of gene-activated bioprinted scaffolds with specific properties tailored to meet the stringent requirements of articular cartilage repair.

Visualized trends and bibliometric analysis in ankle cartilage repair from 2004 to 2024

Ankle cartilage injuries are a common sports-related condition that significantly impairs patients' daily activities and imposes substantial economic burdens on both families and society. Effective cartilage repair strategies are crucial to addressing this pathological condition. Current conservative treatments include muscle strengthening, use of ankle braces, physical therapy, and the administration of NSAIDs. In cases of severe injury, surgical interventions such as osteophyte resection and cartilage transplantation may be necessary. However, the inherent regenerative capacity of articular cartilage is limited, and conventional treatments are insufficient to promote cartilage regeneration and repair. Consequently, innovative therapies such as stem cell therapy, exosome therapy, and cartilage regeneration scaffolds are prioritized for future development. In recent years, significant progress has been made in ankle cartilage repair. While bibliometric studies on cartilage repair exist, specific analyses focused on ankle cartilage repair are lacking. This study aims to address this gap by conducting a bibliometric analysis of 131 articles published over the past two decades, highlighting development trajectories, research hotspots, and evolutionary trends through knowledge mapping. Our findings indicate growing global interest, with the United States leading in international collaboration, funding, publication output, and citation frequency. Foot & Ankle International emerges as the leading journal for publication and dissemination in this field, with Kerkhoffs GMMJ identified as the most influential author. Notable hotspot keywords include "osteochondral lesions" and "platelet-rich plasma." By highlighting critical research hotspots and collaboration patterns, this study not only enriches the existing literature on ankle cartilage repair but also serves as a foundational resource for clinicians and researchers aiming to develop innovative strategies for improving patient outcomes. Furthermore, our findings underscore the necessity of interdisciplinary collaboration in advancing the understanding and treatment of ankle cartilage injuries. Ultimately, the visual characterization of these trends provides valuable insights into the field's evolutionary trajectory, offering guidelines for future research directions and encouraging further exploration of this promising area.

SOX family transcription factors as therapeutic targets in wound healing: A comprehensive review

The SOX family plays a vital role in determining the fate of cells and has garnered attention in the fields of cancer research and regenerative medicine. It also shows promise in the study of wound healing, as it actively participates in the healing processes of various tissues such as skin, fractures, tendons, and the cornea. However, our understanding of the mechanisms behind the SOX family's involvement in wound healing is limited compared to its role in cancer. Gaining insight into its role, distribution, interaction with other factors, and modifications in traumatized tissues could provide valuable new knowledge about wound healing. Based on current research, SOX2, SOX7, and SOX9 are the most promising members of the SOX family for future interventions in wound healing. SOX2 and SOX9 promote the renewal of cells, while SOX7 enhances the microvascular environment. The SOX family holds significant potential for advancing wound healing research. This article provides a comprehensive review of the latest research advancements and therapeutic tools related to the SOX family in wound healing, as well as the potential benefits and challenges of targeting the SOX family for wound treatment.

SOX9 Inhibits the Progression of Osteonecrosis of the Femoral Head via the Activation of the Wnt/Beta-Catenin Pathway

Background: In this study, we aimed to explore whether the SRY-box transcription factor 9 (SOX9) can play protective roles against the occurrence and development of osteonecrosis of the femoral head (ONFH) by regulating the proliferation, apoptosis, and osteogenic differentiation of human bone marrow stromal cells (hBMSCs) via the Wnt/β-catenin pathway.Methods: We used 1600 mg of glucocorticoid (GC) to induce hBMSCs to establish an ONFH cell model and performed various experiments. Reverse transcription-quantitative polymerase chain reaction and western blotting assays were used to determine the expression levels of SOX9 and osteoblast markers, such as the RUNX family transcription factor 2 (RUNX2), alkaline phosphatase (ALP), osterix, Wnt3a, and β-catenin. An ALP detection kit was used to measure the ALP activity. Flow cytometry and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays were performed to determine the cell viability.Results: GC treatment decreased the expression levels of RUNX2, ALP, and osterix, suppressed ALP activity, and inhibited SOX9 expression. SOX9 overexpression promoted GC-induced cell proliferation and decreased cell apoptosis. Additionally, hBMSCs were transfected with SOX9-small interfering RNA in GC treatment, and SOX9 knockdown was found to suppress the osteogenic differentiation of cells and decrease their viability.Conclusion: Our results revealed that SOX9 is related to the Wnt/β-catenin pathway in ONFH. Moreover, SOX9 participated in ONFH development by activating the Wnt/β-catenin pathway.

Gene-activated hyaluronic acid-based cryogels for cartilage tissue engineering

Articular cartilage injuries are very frequent lesions that if left untreated may degenerate into osteoarthritis. Gene transfer to mesenchymal stem cells (MSCs) provides a powerful approach to treat these lesions by promoting their chondrogenic differentiation into the appropriate cartilage phenotype. Non-viral vectors constitute the safest gene transfer tools, as they avoid important concerns of viral systems including immunogenicity and insertional mutagenesis. However, non-viral gene transfer usually led to lower transfection efficiencies when compared with their viral counterparts. Biomaterial-guided gene delivery has emerged as a promising alternative to increase non-viral gene transfer efficiency by achieving sustained delivery of the candidate gene into cellular microenvironment. In the present study, we designed hyaluronic acid-based gene-activated cryogels (HACGs) encapsulating a novel formulation of non-viral vectors based on niosomes (P80PX) to promote MSCs in situ transfection. The developed HACG P80PX systems showed suitable physicochemical properties to promote MSCs in situ transfection with very low cytotoxicity. Incorporation of a plasmid encoding for the transcription factor SOX9 (psox9) into HACG P80PX systems led to an effective MSCs chondrogenic differentiation with reduced expression of fibrocartilage and hypertrophic markers. The capacity of the developed systems to restore cartilage extracellular matrix was further confirmed in an ex vivo model of chondral defect.

In vivo rAAV-mediated human TGF-β overexpression reduces perifocal osteoarthritis and improves osteochondral repair in a large animal model at one year

OBJECTIVE

Osteoarthritis (OA) is a serious consequence of focal osteochondral defects. Gene transfer of human transforming growth factor beta (hTGF-β) with recombinant adeno-associated virus (rAAV) vectors offers a strategy to improve osteochondral repair. However, the long-term in vivo effects of such rAAV-mediated TGF-β overexpression including its potential benefits on OA development remain unknown.

METHOD

Focal osteochondral defects in minipig knees received rAAV-lacZ (control) or rAAV-hTGF-β in vivo. After one year, osteochondral repair and perifocal OA were visualized using validated macroscopic scoring, ultra-high-field MRI at 9.4 T, and micro-CT. A quantitative estimation of the cellular densities and a validated semi-quantitative scoring of histological and immunohistological parameters completed the analysis of microarchitectural parameters.

RESULTS

Direct rAAV-hTGF-β application induced and maintained significantly improved defect filling and safranin O staining intensity and overall cartilage repair at one year in vivo. In addition, rAAV-hTGF-β led to significantly higher chondrocyte densities within the cartilaginous repair tissue without affecting chondrocyte hypertrophy and minimized subarticular trabecular separation. Of note, rAAV-hTGF-β significantly improved the adjacent cartilage structure and chondrocyte density and reduced overall perifocal OA development after one year in vivo.

CONCLUSIONS

rAAV-hTGF-β treatment improves long-term osteochondral repair and delays the progression of perifocal OA in a translational model. These findings have considerable potential for targeted molecular approaches to treat focal osteochondral defects.

Gene Therapy for Regenerative Medicine

The development of biological methods over the past decade has stimulated great interest in the possibility to regenerate human tissues. Advances in stem cell research, gene therapy, and tissue engineering have accelerated the technology in tissue and organ regeneration. However, despite significant progress in this area, there are still several technical issues that must be addressed, especially in the clinical use of gene therapy. The aims of gene therapy include utilising cells to produce a suitable protein, silencing over-producing proteins, and genetically modifying and repairing cell functions that may affect disease conditions. While most current gene therapy clinical trials are based on cell- and viral-mediated approaches, non-viral gene transfection agents are emerging as potentially safe and effective in the treatment of a wide variety of genetic and acquired diseases. Gene therapy based on viral vectors may induce pathogenicity and immunogenicity. Therefore, significant efforts are being invested in non-viral vectors to enhance their efficiency to a level comparable to the viral vector. Non-viral technologies consist of plasmid-based expression systems containing a gene encoding, a therapeutic protein, and synthetic gene delivery systems. One possible approach to enhance non-viral vector ability or to be an alternative to viral vectors would be to use tissue engineering technology for regenerative medicine therapy. This review provides a critical view of gene therapy with a major focus on the development of regenerative medicine technologies to control the in vivo location and function of administered genes.

Intra-articular injection of rAAV-hFGF-2 ameliorates monosodium iodoacetate-induced osteoarthritis in rats via inhibiting TLR-4 signaling and activating TIMP-1

Osteoarthritis (OA) is a chronic debilitating degenerative disorder leading to structural, and functional anomaly of the joint. The present study tests the hypothesis that overexpression of the basic fibroblast growth factor (FGF-2) via direct rAAV-mediated gene transfer suppresses monosodium iodoacetate (MIA)-induced knee OA in rats relative to control (reporter rAAV-lacZ vector) gene transfer by intra-articular injection. Rats were treated with 20 μl rAAV-hFGF-2 on weekly basis; on days 7, 14, and 21 after single intra-articular injection of MIA (3 mg/50 μl saline). FGF-2 reduced knee joint swelling and improved motor performance and muscle coordination as evidenced by increased distance travelled, mean speed, rearing frequency in open field test (OFT) as well as fall-off latency in rotarod test together with reduced immobility time in OFT. Moreover, FGF-2 attenuated MIA-related radiological and histological alterations. Indeed, FGF-2 decreased knee joint inflammatory biomarker as demonstrated by reduced mRNA expression of toll like receptor (TLR)-4 and its downstream mediators such as tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β) and high motility group box (HMGB) 1. In parallel, FGF-2 attenuated knee joint degradation biomarkers as reflected by the downregulation of ADAMTS-5 mRNA expression and matrix metalloproteinase 13 (MMP-13) content together with the up-regulation of tissue inhibitor of metalloproteinase (TIMP)-1 mRNA expression. These findings suggest a potential therapeutic role for FGF-2 against MIA-induced knee OA in rats via inhibition of TLR4 signaling and activating TIMP-1, resulting in down-regulation of ADAMTS-5 and MMP-13.

Gene Delivery to Chondrocytes

Delivering genes to chondrocytes offers new possibilities both clinically, for treating conditions that affect cartilage, and in the laboratory, for studying the biology of chondrocytes. Advances in gene therapy have created a number of different viral and non-viral vectors for this purpose. These vectors may be deployed in an ex vivo fashion, where chondrocytes are genetically modified outside the body, or by in vivo delivery where the vector is introduced directly into the body; in the case of articular and meniscal cartilage in vivo delivery is typically by intra-articular injection. Ex vivo delivery is favored in strategies for enhancing cartilage repair as these can be piggy-backed on existing cell-based technologies, such as autologous chondrocyte implantation, or used in conjunction with marrow-stimulating techniques such as microfracture. In vivo delivery to articular chondrocytes has proved more difficult, because the dense, anionic, extra-cellular matrix of cartilage limits access to the chondrocytes embedded within it. As Grodzinsky and colleagues have shown, the matrix imposes strict limits on the size and charge of particles able to diffuse through the entire depth of articular cartilage. Empirical observations suggest that the larger viral vectors, such as adenovirus (~100 nm), are unable to transduce chondrocytes in situ following intra-articular injection. However, adeno-associated virus (AAV; ~25 nm) is able to do so in horse joints. AAV is presently in clinical trials for arthritis gene therapy, and it will be interesting to see whether human chondrocytes are also transduced throughout the depth of cartilage by AAV following a single intra-articular injection. Viral vectors have been used to deliver genes to the intervertebral disk but there has been little research on gene transfer to chondrocytes in other cartilaginous tissues such as nasal, auricular or tracheal cartilage.

MiR-539-3p inhibited chondrogenic differentiation in human adipose stem cells by targeting Sox9

Background

Mesenchymal stem cells (MSCs) have emerged as the attractive candidates for cell therapy for cartilage repair in clinical therapy of osteoarthritis (OA). MiR-539-3p was reported to differentially express during chondrogenic differentiation of adipose stem cells (ASCs) by miRNA microarrays. The aim of the study was to investigate the effects and underlying mechanisms of miR-539-3p on chondrogenic differentiation of ASCs.

Methods

Human ASCs (hASCs) were obtained from liposuction and transfected with miR-539-3p mimic or inhibitor. Then, the cells were cultured in chondrogenic differentiation medium including transforming growth factor-β1 (TGF-β1).

Results

Our results found that miR-539-3p was gradually down-regulated during chondrogenic differentiation of hASCs. MiR-539-3p overexpression inhibited TGF-β1-induced chondrogenic differentiation of hASCs, as supported by reducing the gene and protein expression of chondrogenic differentiation markers type II collagen alpha 1 (COL2A1), aggrecan (ACAN), and type II collagen. In contrast, miR-539-3p inhibitor significantly promoted the chondrogenic differentiation of hASCs. Dual luciferase reporter assay demonstrated that Sox9 was a direct target gene of miR-539-3p. The expression of SRY-box transcription factor 9 (Sox9) was up-regulated progressively over time during chondrogenic differentiation of hASCs. Additionally, Sox9 overexpression notably reversed chondrogenic differentiation of hASCs inhibited by miR-539-3p mimic, as demonstrated by the decreased expression of COL2A1, ACAN, and type II collagen.

Conclusions

Altogether, miR-539-3p inhibited chondrogenic differentiation of hASCs by targeting Sox9. MiR-539-3p may have significant clinical applications for use as a targeted therapy of OA.

rAAV-Mediated sox9 Overexpression Improves the Repair of Osteochondral Defects in a Clinically Relevant Large Animal Model Over Time In Vivo and Reduces Perifocal Osteoarthritic Changes

BACKGROUND

Gene transfer of the transcription factor SOX9 with clinically adapted recombinant adeno-associated virus (rAAV) vectors offers a powerful tool to durably enhance the repair process at sites of osteochondral injuries and counteract the development of perifocal osteoarthritis (OA) in the adjacent articular cartilage.

PURPOSE

To examine the ability of an rAAV sox9 construct to improve the repair of focal osteochondral defects and oppose perifocal OA development over time in a large translational model relative to control gene transfer.

STUDY DESIGN

Controlled laboratory study.

METHODS

Standardized osteochondral defects created in the knee joints of adult sheep were treated with rAAV-FLAG-hsox9 relative to control (reporter) rAAV-lacZ gene transfer. Osteochondral repair and degenerative changes in the adjacent cartilage were monitored using macroscopic, histological, immunohistological, and biochemical evaluations after 6 months. The microarchitecture of the subchondral bone was assessed by micro-computed tomography.

RESULTS

Effective, prolonged sox9 overexpression via rAAV was significantly achieved in the defects after 6 months versus rAAV-lacZ treatment. The application of rAAV-FLAG-hsox9 improved the individual parameters of defect filling, matrix staining, cellular morphology, defect architecture, surface architecture, subchondral bone, and tidemark as well as the overall score of cartilage repair in the defects compared with rAAV-lacZ. The overexpression of sox9 led to higher levels of proteoglycan production, stronger type II collagen deposition, and reduced type I collagen immunoreactivity in the sox9- versus lacZ-treated defects, together with decreased cell densities and DNA content. rAAV-FLAG-hsox9 enhanced semiquantitative histological subchondral bone repair, while the microstructure of the incompletely restored subchondral bone in the sox9 defects was not different from that in the lacZ defects. The articular cartilage adjacent to the sox9-treated defects showed reduced histological signs of perifocal OA changes versus rAAV-lacZ.

CONCLUSION

rAAV-mediated sox9 gene transfer enhanced osteochondral repair in sheep after 6 months and reduced perifocal OA changes. These results underline the potential of rAAV-FLAG-hsox9 as a therapeutic tool to treat cartilage defects and afford protection against OA.

CLINICAL RELEVANCE

The delivery of therapeutic rAAV sox9 to sites of focal injuries may offer a novel, convenient tool to enhance the repair of osteochondral defects involving both the articular cartilage and the underlying subchondral bone and provide a protective role by reducing the extent of perifocal OA.

Etomidate ameliorated advanced glycation end-products (AGEs)-induced reduction of extracellular matrix genes expression in chondrocytes

Osteoarthritis (OA) is a rheumatic disease common in the elderly. AGEs are the end products of glycation reactions and play an important role in the development of OA. Etomidate is a general anesthesia-inducing agent recently reported to exert significant anti-inflammatory effects. The present study aims to explore the protective effect of Etomidate against advanced glycation end-products (AGEs)-induced reduction of extracellular matrix gene expression in chondrocytes. In the present study, we found that AGEs significantly reduced the expression of Collagen II (COL2A1) and Aggrecan (ACAN) at the gene level. Furthermore, AGEs inhibited the expression of SRY-related high mobility group-box gene 9 (SOX-9), promoting the expression of COL2A1 and ACAN. COL2A1, ACAN, and SOX-9 in chondrocytes were significantly elevated by treatment with Etomidate alone. Consistently, Etomidate ameliorated AGEs-induced downregulation of COL2A1, ACAN, and SOX-9 in a dose-dependent manner. Importantly, we found that knockdown of SOX-9 eliminated the beneficial effects of Etomidate against AGEs-induced decrease in COL2A1 and ACAN genes. Based on these findings, we demonstrated that Etomidate could ameliorate AGEs-induced reduction of extracellular matrix gene expression in chondrocytes by upregulating SOX-9.

An Overview of RNA-Based Scaffolds for Osteogenesis

Tissue engineering provides new hope for the combination of cells, scaffolds, and bifactors for bone osteogenesis. This is achieved by mimicking the bone's natural behavior in recruiting the cell's molecular machinery for our use. Many researchers have focused on developing an ideal scaffold with specific features, such as good cellular adhesion, cell proliferation, differentiation, host integration, and load bearing. Various types of coating materials (organic and non-organic) have been used to enhance bone osteogenesis. In the last few years, RNA-mediated gene therapy has captured attention as a new tool for bone regeneration. In this review, we discuss the use of RNA molecules in coating and delivery, including messenger RNA (mRNA), RNA interference (RNAi), and long non-coding RNA (lncRNA) on different types of scaffolds (such as polymers, ceramics, and metals) in osteogenesis research. In addition, the effect of using gene-editing tools-particularly CRISPR systems-to guide RNA scaffolds in bone regeneration is also discussed. Given existing knowledge about various RNAs coating/expression may help to understand the process of bone formation on the scaffolds during osseointegration.

Hydrogel-Guided, rAAV-Mediated IGF-I Overexpression Enables Long-Term Cartilage Repair and Protection against Perifocal Osteoarthritis in a Large-Animal Full-Thickness Chondral Defect Model at One Year In Vivo

The regeneration of focal articular cartilage defects is complicated by the reduced quality of the repair tissue and the potential development of perifocal osteoarthritis (OA). Biomaterial-guided gene therapy may enhance cartilage repair by controlling the release of therapeutic sequences in a spatiotemporal manner. Here, the benefits of delivering a recombinant adeno-associated virus (rAAV) vector coding for the human insulin-like growth factor I (IGF-I) via an alginate hydrogel (IGF-I/AlgPH155) to enhance repair of full-thickness chondral defects following microfracture surgery after one year in minipigs versus control (lacZ/AlgPH155) treatment are reported. Sustained IGF-I overexpression is significantly achieved in the repair tissue of defects treated with IGF-I/AlgPH155 versus those receiving lacZ/AlgPH155 for one year and in the cartilage surrounding the defects. Administration of IGF-I/AlgPH155 significantly improves parameters of cartilage repair at one year relative to lacZ/AlgPH155 (semiquantitative total histological score, cell densities, matrix deposition) without deleterious or immune reactions. Remarkably, delivery of IGF-I/AlgPH155 also significantly reduces perifocal OA and inflammation after one year versus lacZ/AlgPH155 treatment. Biomaterial-guided rAAV gene transfer represents a valuable clinical approach to promote cartilage repair and to protect against OA.

rAAV-Mediated Human FGF-2 Gene Therapy Enhances Osteochondral Repair in a Clinically Relevant Large Animal Model Over Time In Vivo

BACKGROUND

Osteochondral defects, if left untreated, do not heal and can potentially progress toward osteoarthritis. Direct gene transfer of basic fibroblast growth factor 2 (FGF-2) with the clinically adapted recombinant adeno-associated viral (rAAV) vectors is a powerful tool to durably activate osteochondral repair processes.

PURPOSE

To examine the ability of an rAAV-FGF-2 construct to target the healing processes of focal osteochondral injury over time in a large translational model in vivo versus a control gene transfer condition.

STUDY DESIGN

Controlled laboratory study.

METHODS

Standardized osteochondral defects created in the knee joints of adult sheep were treated with an rAAV human FGF-2 (hFGF-2) vector by direct administration into the defect relative to control (reporter) rAAV-lacZ gene transfer. Osteochondral repair was monitored using macroscopic, histological, immunohistological, and biochemical methods and by micro-computed tomography after 6 months.

RESULTS

Effective, localized prolonged FGF-2 overexpression was achieved for 6 months in vivo relative to the control condition without undesirable leakage of the vectors outside the defects. Such rAAV-mediated hFGF-2 overexpression significantly increased the individual histological parameter "percentage of new subchondral bone" versus lacZ treatment, reflected in a volume of mineralized bone per unit volume of the subchondral bone plate that was equal to a normal osteochondral unit. Also, rAAV-FGF-2 significantly improved the individual histological parameters "defect filling,""matrix staining," and "cellular morphology" and the overall cartilage repair score versus the lacZ treatment and led to significantly higher cell densities and significantly higher type II collagen deposition versus lacZ treatment. Likewise, rAAV-FGF-2 significantly decreased type I collagen expression within the cartilaginous repair tissue.

CONCLUSION

The current work shows the potential of direct rAAV-mediated FGF-2 gene therapy to enhance osteochondral repair in a large, clinically relevant animal model over time in vivo.

CLINICAL RELEVANCE

Delivery of therapeutic (hFGF-2) rAAV vectors in sites of focal injury may offer novel, convenient tools to enhance osteochondral repair in the near future.

Exploiting Joint-Resident Stem Cells by Exogenous SOX9 for Cartilage Regeneration for Therapy of Osteoarthritis

The lack of effective treatment options for osteoarthritis (OA) is mostly due to the very limited regenerative capacity of articular cartilage. Mesenchymal stem cells (MSCs) have been most extensively explored for cell-based therapy to induce cartilage regeneration for OA. However, current in vitro expanded MSC-based approaches have significant drawbacks. On the other hand, osteoarthritic joints contain chondrocyte progenitors and MSCs in several niches which have the potential yet fail to differentiate into chondrocytes for cartilage regeneration. One of the underlying mechanisms of the failure is that these chondrocyte progenitors and MSCs in OA joints are deficient in the activity of chondrogenic transcription factor SOX9 (SRY-type high-mobility group box-9). Thereby, replenishing with exogenous SOX9 would reactivate the potential of these stem cells to differentiate into chondrocytes. Cell-permeable, super-positively charged SOX9 (scSOX9) protein is able to promote hyaline-like cartilage regeneration by inducing chondrogenic differentiation of bone marrow derived MSCs in vivo. This scSOX9 protein can be administered into osteoarthritic joints by intra-articular injection. This one-step, cell-free supplement of exogenous SOX9 may harness the regenerative potential of the intrinsic MSCs within the joint cavity to stimulate cartilage regeneration in OA.

Genetics in Cartilage Lesions: Basic Science and Therapy Approaches

Cartilage lesions have a multifactorial nature, and genetic factors are their strongest determinants. As biochemical and genetic studies have dramatically progressed over the past decade, the molecular basis of cartilage pathologies has become clearer. Several homeostasis abnormalities within cartilaginous tissue have been found, including various structural changes, differential gene expression patterns, as well as altered epigenetic regulation. However, the efficient treatment of cartilage pathologies represents a substantial challenge. Understanding the complex genetic background pertaining to cartilage pathologies is useful primarily in the context of seeking new pathways leading to disease progression as well as in developing new targeted therapies. A technology utilizing gene transfer to deliver therapeutic genes to the site of injury is quickly becoming an emerging approach in cartilage renewal. The goal of this work is to provide an overview of the genetic basis of chondral lesions and the different approaches of the most recent systems exploiting therapeutic gene transfer in cartilage repair. The integration of tissue engineering with viral gene vectors is a novel and active area of research. However, despite promising preclinical data, this therapeutic concept needs to be supported by the growing body of clinical trials.

Therapeutic Delivery of rAAV sox9 via Polymeric Micelles Counteracts the Effects of Osteoarthritis-Associated Inflammatory Cytokines in Human Articular Chondrocytes

Osteoarthritis (OA) is a prevalent joint disease linked to the irreversible degradation of key extracellular cartilage matrix (ECM) components (proteoglycans, type-II collagen) by proteolytic enzymes due to an impaired tissue homeostasis, with the critical involvement of OA-associated pro-inflammatory cytokines (interleukin 1 beta, i.e., IL-1β, and tumor necrosis factor alpha, i.e., TNF-α). Gene therapy provides effective means to re-establish such degraded ECM compounds by rejuvenating the altered OA phenotype of the articular chondrocytes, the unique cell population ubiquitous in the articular cartilage. In particular, overexpression of the highly specialized SOX9 transcription factor via recombinant adeno-associated viral (rAAV) vectors has been reported for its ability to readjust the metabolic balance in OA, in particular via controlled rAAV delivery using polymeric micelles as carriers to prevent a possible vector neutralization by antibodies present in the joints of patients. As little is known on the challenging effects of such naturally occurring OA-associated pro-inflammatory cytokines on such rAAV/polymeric gene transfer, we explored the capacity of polyethylene oxide (PEO) and polypropylene oxide (PPO)-based polymeric micelles to deliver a candidate rAAV-FLAG-hsox9 construct in human OA chondrocytes in the presence of IL-1β and TNF-α. We report that effective, micelle-guided rAAV sox9 overexpression enhanced the deposition of ECM components and the levels of cell survival, while advantageously reversing the deleterious effects afforded by the OA cytokines on these processes. These findings highlight the potentiality of polymeric micelles as effective rAAV controlled delivery systems to counterbalance the specific contribution of major OA-associated inflammatory cytokines, supporting the concept of using such systems for the treatment for chronic inflammatory diseases like OA.

rAAV-Mediated Overexpression of SOX9 and TGF-β via Carbon Dot-Guided Vector Delivery Enhances the Biological Activities in Human Bone Marrow-Derived Mesenchymal Stromal Cells

Scaffold-assisted gene therapy is a highly promising tool to treat articular cartilage lesions upon direct delivery of chondrogenic candidate sequences. The goal of this study was to examine the feasibility and benefits of providing highly chondroreparative agents, the cartilage-specific sex-determining region Y-type high-mobility group 9 (SOX9) transcription factor or the transforming growth factor beta (TGF-β), to human bone marrow-derived mesenchymal stromal cells (hMSCs) via clinically adapted, independent recombinant adeno-associated virus (rAAV) vectors formulated with carbon dots (CDs), a novel class of carbon-dominated nanomaterials. Effective complexation and release of a reporter rAAV-lacZ vector was achieved using four different CDs elaborated from 1-citric acid and pentaethylenehexamine (CD-1); 2-citric acid, poly(ethylene glycol) monomethyl ether (MW 550 Da), and N,N-dimethylethylenediamine (CD-2); 3-citric acid, branched poly(ethylenimine) (MW 600 Da), and poly(ethylene glycol) monomethyl ether (MW 2 kDa) (CD-3); and 4-citric acid and branched poly(ethylenimine) (MW 600 Da) (CD-4), allowing for the genetic modification of hMSCs. Among the nanoparticles, CD-2 showed an optimal ability for rAAV delivery (up to 2.2-fold increase in lacZ expression relative to free vector treatment with 100% cell viability for at least 10 days, the longest time point examined). Administration of therapeutic (SOX9, TGF-β) rAAV vectors in hMSCs via CD-2 led to the effective overexpression of each independent transgene, promoting enhanced cell proliferation (TGF-β) and cartilage matrix deposition (glycosaminoglycans, type-II collagen) for at least 21 days relative to control treatments (CD-2 lacking rAAV or associated to rAAV-lacZ), while advantageously restricting undesirable type-I and -X collagen deposition. These results reveal the potential of CD-guided rAAV gene administration in hMSCs as safe, non-invasive systems for translational strategies to enhance cartilage repair.

Enhanced Chondrogenic Differentiation Activities in Human Bone Marrow Aspirates via sox9 Overexpression Mediated by pNaSS-Grafted PCL Film-Guided rAAV Gene Transfer

BACKGROUND

The delivery of therapeutic genes in sites of articular cartilage lesions using non-invasive, scaffold-guided gene therapy procedures is a promising approach to stimulate cartilage repair while protecting the cargos from detrimental immune responses, particularly when targeting chondroreparative bone marrow-derived mesenchymal stromal cells in a natural microenvironment like marrow aspirates.

METHODS

Here, we evaluated the benefits of providing a sequence for the cartilage-specific sex-determining region Y-type high-mobility group box 9 (SOX9) transcription factor to human marrow aspirates via recombinant adeno-associated virus (rAAV) vectors delivered by poly(ε-caprolactone) (PCL) films functionalized via grafting with poly(sodium styrene sulfonate) (pNaSS) to enhance the marrow chondrogenic potential over time.

RESULTS

Effective sox9 overexpression was observed in aspirates treated with pNaSS-grafted or ungrafted PCL films coated with the candidate rAAV-FLAG-hsox9 (FLAG-tagged rAAV vector carrying a human sox9 gene sequence) vector for at least 21 days relative to other conditions (pNaSS-grafted and ungrafted PCL films without vector coating). Overexpression of sox9 via rAAV sox9/pNaSS-grafted or ungrafted PCL films led to increased biological and chondrogenic differentiation activities (matrix deposition) in the aspirates while containing premature osteogenesis and hypertrophy without impacting cell proliferation, with more potent effects noted when using pNaSS-grafted films.

CONCLUSIONS

These findings show the benefits of targeting patients' bone marrow via PCL film-guided therapeutic rAAV (sox9) delivery as an off-the-shelf system for future strategies to enhance cartilage repair in translational applications.

Reduced hypertrophy in vitro after chondrogenic differentiation of adult human mesenchymal stem cells following adenoviral SOX9 gene delivery

Background

Mesenchymal stem cell (MSC) based-treatments of cartilage injury are promising but impaired by high levels of hypertrophy after chondrogenic induction with several bone morphogenetic protein superfamily members (BMPs). As an alternative, this study investigates the chondrogenic induction of MSCs via adenoviral gene-delivery of the transcription factor SOX9 alone or in combination with other inducers, and comparatively explores the levels of hypertrophy and end stage differentiation in a pellet culture system in vitro.

Methods

First generation adenoviral vectors encoding SOX9, TGFB1 or IGF1 were used alone or in combination to transduce human bone marrow-derived MSCs at 5 × 10² infectious particles/cell. Thereafter cells were placed in aggregates and maintained for three weeks in chondrogenic medium. Transgene expression was determined at the protein level (ELISA/Western blot), and aggregates were analysed histologically, immunohistochemically, biochemically and by RT-PCR for chondrogenesis and hypertrophy.

Results

SOX9 cDNA was superior to that encoding TGFB1, the typical gold standard, as an inducer of chondrogenesis in primary MSCs as evidenced by improved lacuna formation, proteoglycan and collagen type II staining, increased levels of GAG synthesis, and expression of mRNAs associated with chondrogenesis. Moreover, SOX9 modified aggregates showed a markedly lower tendency to progress towards hypertrophy, as judged by expression of the hypertrophy markers alkaline phosphatase, and collagen type X at the mRNA and protein levels.

Conclusion

Adenoviral SOX9 gene transfer induces chondrogenic differentiation of human primary MSCs in pellet culture more effectively than TGFB1 gene transfer with lower levels of chondrocyte hypertrophy after 3 weeks of in vitro culture. Such technology might enable the formation of more stable hyaline cartilage repair tissues in vivo.

Thermosensitive Hydrogel Based on PEO-PPO-PEO Poloxamers for a Controlled In Situ Release of Recombinant Adeno-Associated Viral Vectors for Effective Gene Therapy of Cartilage Defects

Advanced biomaterial-guided delivery of gene vectors is an emerging and highly attractive therapeutic solution for targeted articular cartilage repair, allowing for a controlled and minimally invasive delivery of gene vectors in a spatiotemporally precise manner, reducing intra-articular vector spread and possible loss of the therapeutic gene product. As far as it is known, the very first successful in vivo application of such a biomaterial-guided delivery of a potent gene vector in an orthotopic large animal model of cartilage damage is reported here. In detail, an injectable and thermosensitive hydrogel based on poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-PEO poloxamers, capable of controlled release of a therapeutic recombinant adeno-associated virus (rAAV) vector overexpressing the chondrogenic sox9 transcription factor in full-thickness chondral defects, is applied in a clinically relevant minipig model in vivo. These comprehensive analyses of the entire osteochondral unit with multiple standardized evaluation methods indicate that rAAV-FLAG-hsox9/PEO-PPO-PEO hydrogel-augmented microfracture significantly improves cartilage repair with a collagen fiber orientation more similar to the normal cartilage and protects the subchondral bone plate from early bone loss.

Scaffoldless tissue-engineered cartilage for studying transforming growth factor beta-mediated cartilage formation

Reduced transforming growth factor beta (TGF-β) signaling is associated with osteoarthritis (OA). TGF-β is thought to act as a chondroprotective agent and provide anabolic cues to cartilage, thus acting as an OA suppressor in young, healthy cartilage. A potential approach for treating OA is to identify the factors that act downstream of TGF-β's anabolic pathway and target those factors to promote cartilage regeneration or repair. The aims of the present study were to (a) develop a scaffoldless tissue-engineered cartilage model with reduced TGF-β signaling and disrupted cartilage formation and (b) validate the system for identifying the downstream effectors of TGF-β that promote cartilage formation. Sox9 was used to validate the model because Sox9 is known to promote cartilage formation and TGF-β regulates Sox9 activity. Primary bovine articular chondrocytes were grown in Transwell supports to form cartilage tissues. An Alk5/TGF-β type I receptor inhibitor, SB431542, was used to attenuate TGF-β signaling, and an adenovirus encoding FLAG-Sox9 was used to drive the expression of Sox9 in the in vitro-generated cartilage. SB431542-treated tissues exhibited reduced cartilage formation including reduced thicknesses and reduced proteoglycan staining compared with control tissue. Expression of FLAG-Sox9 in SB431542-treated cartilage allowed the formation of cartilage despite antagonism of the TGF-β receptor. In summary, we developed a three-dimensional in vitro cartilage model with attenuated TGF-β signaling. Sox9 was used to validate the model for identification of anabolic agents that counteract loss of TGF-β signaling. This model has the potential to identify additional anabolic factors that could be used to repair or regenerate damaged cartilage.

Current Trends in Viral Gene Therapy for Human Orthopaedic Regenerative Medicine

Background

Viral vector-based therapeutic gene therapy is a potent strategy to enhance the intrinsic reparative abilities of human orthopaedic tissues. However, clinical application of viral gene transfer remains hindered by detrimental responses in the host against such vectors (immunogenic responses, vector dissemination to nontarget locations). Combining viral gene therapy techniques with tissue engineering procedures may offer strong tools to improve the current systems for applications in vivo.

Methods

The goal of this work is to provide an overview of the most recent systems exploiting biomaterial technologies and therapeutic viral gene transfer in human orthopaedic regenerative medicine.

Results

Integration of tissue engineering platforms with viral gene vectors is an active area of research in orthopaedics as a means to overcome the obstacles precluding effective viral gene therapy.

Conclusions

In light of promising preclinical data that may rapidly expand in a close future, biomaterial-guided viral gene therapy has a strong potential for translation in the field of human orthopaedic regenerative medicine.

Scaffold-Based Delivery of Nucleic Acid Therapeutics for Enhanced Bone and Cartilage Repair

Recent advances in tissue engineering have made progress toward the development of biomaterials capable of the delivery of growth factors, such as bone morphogenetic proteins, in order to promote enhanced tissue repair. However, controlling the release of these growth factors on demand and within the desired localized area is a significant challenge and the associated high costs and side effects of uncontrolled delivery have proven increasingly problematic in clinical orthopedics. Gene therapy may be a valuable tool to avoid the limitations of local delivery of growth factors. Following a series of setbacks in the 1990s, the field of gene therapy is now seeing improvements in safety and efficacy resulting in substantial clinical progress and a resurgence in confidence. Biomaterial scaffold-mediated gene therapy provides a template for cell infiltration and tissue formation while promoting transfection of cells to engineer therapeutic proteins in a sustained but ultimately transient fashion. Additionally, scaffold-mediated delivery of RNA-based therapeutics can silence specific genes associated with orthopedic pathological states. This review will provide an overview of the current state-of-the-art in the field of gene-activated scaffolds and their use within orthopedic tissue engineering applications. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1671-1680, 2019.

miRNA-101 promotes chondrogenic differentiation in rat bone marrow mesenchymal stem cells

Effect and related mechanisms of miR-101 on the chondrogenic differentiation of rat bone marrow mesenchymal stem cells (MSCs) were investigated. The expression level of miR-101 was detected during chondrogenic differentiation. Three groups were established to study the potential function between miR-101 and chondrogenic differentiation: miR-NC group (negative control), miR-101 mimics (BMSCs transfected by miR-101 mimics) and mimics + inhibitor (BMSCs transfected by miR-101 mimics and inhibitor), after the induction of chondrogenic differentiation, the cell viability of MSCs and chondrogenic markers were determined, further, the expression level of Sox9 and Runx2 were detected. In our present research, miR-101 was found upregulated during chondrogenic differentiation of MSCs. Compared with the miR-NC group, the cell viability of MSCs was enhanced and the expression level of chondrogenic markers were respectively gained. The expression level of Sox9 was increased but the expression level of Runx2 was decreased by treatment of miR-101 mimics after induction of chondrogenic differentiation. However, these variations of the indicators were reversed by the intervention using the miR-101 inhibitor. Collectively, our research revealed promotion function of miR-101 on chondrogenic differentiation of MSCs, indicating that miR-101 could be a potential therapeutic strategy for the treatment of osteoarthritis (OA).

Improved Chondrogenic Differentiation of rAAV SOX9-Modified Human MSCs Seeded in Fibrin-Polyurethane Scaffolds in a Hydrodynamic Environment

The repair of focal articular cartilage defects remains a problem. Combining gene therapy with tissue engineering approaches using bone marrow-derived mesenchymal stem cells (MSCs) may allow the development of improved options for cartilage repair. Here, we examined whether a three-dimensional fibrin-polyurethane scaffold provides a favorable environment for the effective chondrogenic differentiation of human MSCs (hMSCs) overexpressing the cartilage-specific SOX9 transcription factor via recombinant adeno-associated virus (rAAV) -mediated gene transfer cultured in a hydrodynamic environment in vitro. Sustained SOX9 expression was noted in the constructs for at least 21 days, the longest time point evaluated. Such spatially defined SOX9 overexpression enhanced proliferative, metabolic, and chondrogenic activities compared with control (reporter lacZ gene transfer) treatment. Of further note, administration of the SOX9 vector was also capable of delaying premature hypertrophic and osteogenic differentiation in the constructs. This enhancement of chondrogenesis by spatially defined overexpression of human SOX9 demonstrate the potential benefits of using rAAV-modified hMSCs seeded in fibrin-polyurethane scaffolds as a promising approach for implantation in focal cartilage lesions to improve cartilage repair.

Effects of TGF-β Overexpression via rAAV Gene Transfer on the Early Repair Processes in an Osteochondral Defect Model in Minipigs

BACKGROUND

Application of the chondrogenic transforming growth factor beta (TGF-β) is an attractive approach to enhance the intrinsic biological activities in damaged articular cartilage, especially when using direct gene transfer strategies based on the clinically relevant recombinant adeno-associated viral (rAAV) vectors.

PURPOSE

To evaluate the ability of an rAAV-TGF-β construct to modulate the early repair processes in sites of focal cartilage injury in minipigs in vivo relative to control (reporter lacZ gene) vector treatment.

STUDY DESIGN

Controlled laboratory study.

METHODS

Direct administration of the candidate rAAV-human TGF-β (hTGF-β) vector was performed in osteochondral defects created in the knee joint of adult minipigs for macroscopic, histological, immunohistochemical, histomorphometric, and micro-computed tomography analyses after 4 weeks relative to control (rAAV- lacZ) gene transfer.

RESULTS

Successful overexpression of TGF-β via rAAV at this time point and in the conditions applied here triggered the cellular and metabolic activities within the lesions relative to lacZ gene transfer but, at the same time, led to a noticeable production of type I and X collagen without further buildup on the subchondral bone.

CONCLUSION

Gene therapy via direct, local rAAV-hTGF-β injection stimulates the early reparative activities in focal cartilage lesions in vivo.

CLINICAL RELEVANCE

Local delivery of therapeutic (TGF-β) rAAV vectors in focal defects may provide new, off-the-shelf treatments for cartilage repair in patients in the near future.

Chondrogenic Differentiation Processes in Human Bone-Marrow Aspirates Seeded in Three-Dimensional-Woven Poly(ɛ-Caprolactone) Scaffolds Enhanced by Recombinant Adeno-Associated Virus-Mediated SOX9 Gene Transfer

Combining gene therapy approaches with tissue engineering procedures is an active area of translational research for the effective treatment of articular cartilage lesions, especially to target chondrogenic progenitor cells such as those derived from the bone marrow. This study evaluated the effect of genetically modifying concentrated human mesenchymal stem cells from bone marrow to induce chondrogenesis by recombinant adeno-associated virus (rAAV) vector gene transfer of the sex-determining region Y-type high-mobility group box 9 (SOX9) factor upon seeding in three-dimensional-woven poly(ɛ-caprolactone; PCL) scaffolds that provide mechanical properties mimicking those of native articular cartilage. Prolonged, effective SOX9 expression was reported in the constructs for at least 21 days, the longest time point evaluated, leading to enhanced metabolic and chondrogenic activities relative to the control conditions (reporter lacZ gene transfer or absence of vector treatment) but without affecting the proliferative activities in the samples. The application of the rAAV SOX9 vector also prevented undesirable hypertrophic and terminal differentiation in the seeded concentrates. As bone marrow is readily accessible during surgery, such findings reveal the therapeutic potential of providing rAAV-modified marrow concentrates within three-dimensional-woven PCL scaffolds for repair of focal cartilage lesions.

Gene therapy for chondral and osteochondral regeneration: is the future now?

Gene therapy might represent a promising strategy for chondral and osteochondral defects repair by balancing the management of temporary joint mechanical incompetence with altered metabolic and inflammatory homeostasis. This review analysed preclinical and clinical studies on gene therapy for the repair of articular cartilage defects performed over the last 10 years, focussing on expression vectors (non-viral and viral), type of genes delivered and gene therapy procedures (direct or indirect). Plasmids (non-viral expression vectors) and adenovirus (viral vectors) were the most employed vectors in preclinical studies. Genes delivered encoded mainly for growth factors, followed by transcription factors, anti-inflammatory cytokines and, less frequently, by cell signalling proteins, matrix proteins and receptors. Direct injection of the expression vector was used less than indirect injection of cells, with or without scaffolds, transduced with genes of interest and then implanted into the lesion site. Clinical trials (phases I, II or III) on safety, biological activity, efficacy, toxicity or bio-distribution employed adenovirus viral vectors to deliver growth factors or anti-inflammatory cytokines, for the treatment of osteoarthritis or degenerative arthritis, and tumour necrosis factor receptor or interferon for the treatment of inflammatory arthritis.

The role of Sox9 in collagen hydrogel-mediated chondrogenic differentiation of adult mesenchymal stem cells (MSCs)

Sox9 is a transcription factor that regulates chondrogenesis, but its role in the chondrogenic differentiation of mesenchymal stem cells (MSCs) triggered by materials is poorly understood.

Downregulated SOX9 mediated by miR-206 promoted cell apoptosis in Legg-Calvé-Perthes disease

Legg-Calvé-Perthes disease (LCPD) commonly onsets in adolescents, and threatens their health. However, the potential mechanism underlying LCPD remains unclear. MicroRNA (miR)-206 and SRY-box 9 (SOX9) serve an important role in chondrocytes; however, their role in LCPD remains ambiguous. In the present study, whether miR-206 and SOX9 mediated cell apoptosis in dexamethasone (DEX)-induced LCPD was investigated. The chondrocytes of the LCPD and normal control group were isolated from clinical tissues. Reverse transcription-quantitative polymerase chain reaction was used to evaluate the expression of miR-206 and SOX9 mRNA. Western blotting was used to measure the protein level of SOX9. A combination of Annexin V-fluorescein isothiocyanate flow cytometry was used to assess cell apoptosis. The association between miR-206 and SOX9 was detected using a luciferase reporter assay. miR-206 was overexpressed while SOX9 was downregulated in chondrocytes treated with DEX obtained from patients with LCPD. miR-206 targeted SOX9 to regulate its expression. Overexpression of miR-206 promoted cell apoptosis in TC28, while it was reversed by SOX9 overexpression. TC28 cells pretreated with DEX significantly promoted cell apoptosis, while cells transfected with miR-206 inhibitor significantly reversed the effect; however, downregulated SOX9 abolished the effects of miR-206 inhibitor. SOX9 mediated by miR-206 possibly contributed to the pathogenesis of LCPD. The results of the present study suggest that miR-206 and SOX9 function as important therapeutic targets for the future of clinical therapy.

BMP-2 gene activated muscle tissue fragments for osteochondral defect regeneration in the rabbit knee

BACKGROUND

Previously published data indicate that BMP-2 gene activated muscle tissue grafts can repair large bone defects in rats. This innovative abbreviated ex vivo gene therapy is appealing because it does not require elaborative and time-consuming extraction and expansion of cells. Hence, in the present study, we evaluated the potential of this expedited tissue engineering approach for regenerating osteochondral defects in rabbits.

METHODS

Autologous muscle tissue grafts from female White New Zealand rabbits were directly transduced with an adenoviral BMP-2 vector or remained unmodified. Osteochondral defects in the medial condyle of rabbit knees were treated with either BMP-2 activated muscle tissue implants or unmodified muscle tissue or remained empty. After 13 weeks, repair of osteochondral defects was examined by biomechanical indentation testing and by histology/imunohistochemistry applying an extended O'Driscoll scoring system and histomorphometry.

RESULTS

Biomechanical investigations revealed a trend towards slightly improved mechanical properties of the group receiving BMP-2 activated muscle tissue compared to unmodified muscle treatment and empty defect controls. However, a statistically significant difference was noted only between BMP-2 muscle and unmodified muscle treatment. Also, histological evaluation resulted in slightly higher histological scores and improved collagen I/II ratio without statistical significance in the BMP-2 treatment group. Histomorphometry indicated enhanced repair of subchondral bone after treatment with BMP-2 muscle, with a significantly larger bone area compared to untreated defects.

CONCLUSIONS

Gene activated muscle tissue grafts showed potential for osteochondral defect repair. There is room for improvement via the use of appropriate growth factor combinations.

Irx3 and Bmp2 regulate mouse mesenchymal cell chondrogenic differentiation in both a Sox9-dependent and -independent manner

Sox9, a master regulator of cartilage development, controls the cell fate decision to differentiate from mesenchymal to chondrogenic cells. In addition, Sox9 regulates the proliferation and differentiation of chondrocytes, as well as the production of cartilage-specific proteoglycans. The existence of Sox9-independent mechanisms in cartilage development remains to be determined. Here, we attempted to identify genes involved in such putative mechanisms via microarray analysis using a mouse chondrogenic cell line, N1511. We first focused on transcription factors that exhibited upregulated expression following Bmp2 treatment, which was not altered by subsequent treatment with Sox9 siRNA. Among these, we selected positive regulators for chondrogenesis and identified Iroquois-related homeobox 3 (Irx3) as one of the candidate genes. Irx3 expression gradually increased with chondrocyte terminal differentiation in a reciprocal manner to Sox9 expression, and promoted the chondrogenic differentiation of mesenchymal cells upon Bmp2 treatment. Furthermore, Irx3 partially rescued impaired chondrogenesis by upregulating the expression of epiphycan and lumican under reduced Sox9 expression. Finally, Irx3 was shown to act in concert with Bmp2 signaling to activate the p38 MAPK pathway, which in turn stimulated Sox9 expression, as well as the expression of epiphycan and lumican in a Sox9-independent manner. These results indicate that Irx3 represents a novel chondrogenic factor of mesenchymal cells, acts synergistically with Bmp2-mediated signaling, and regulates chondrogenesis independent of the transcriptional machinery associated with Sox9-mediated regulation.

Recent tissue engineering-based advances for effective rAAV-mediated gene transfer in the musculoskeletal system

Musculoskeletal tissues are diverse and significantly different in their ability to repair upon injury. Current treatments often fail to reproduce the natural functions of the native tissue, leading to an imperfect healing. Gene therapy might improve the repair of tissues by providing a temporarily and spatially defined expression of the therapeutic gene(s) at the site of the injury. Several gene transfer vehicles have been developed to modify various human cells and tissues from musculoskeletal system among which the non-pathogenic, effective, and relatively safe recombinant adeno-associated viral (rAAV) vectors that have emerged as the preferred gene delivery system to treat human disorders. Adapting tissue engineering platforms to gene transfer approaches mediated by rAAV vectors is an attractive tool to circumvent both the limitations of the current therapeutic options to promote an effective healing of the tissue and the natural obstacles from these clinically adapted vectors to achieve an efficient and durable gene expression of the therapeutic sequences within the lesions.

rAAV-mediated combined gene transfer and overexpression of TGF-β and SOX9 remodels human osteoarthritic articular cartilage

Direct administration of therapeutic candidate gene sequences using the safe and effective recombinant adeno-associated virus (rAAV) vectors is a promising strategy to stimulate the biologic activities of articular chondrocytes as an adapted tool to treat human osteoarthritic (OA) cartilage. In the present study, we developed a combined gene transfer approach based on the co-delivery of the pleiotropic transformation growth factor beta (TGF-β) with the specific transcription factor SOX9 via rAAV to human normal and OA chondrocytes in vitro and cartilage explants in situ in light of the mitogenic and pro-anabolic properties of these factors. Effective, durable co-overexpression of TGF-β and SOX9 significantly enhanced the levels of cell proliferation both in human normal and OA chondrocytes and cartilage explants over an extended period of time (21 days), while stimulating the biosynthesis of key matrix components (proteoglycans, type-II collagen) compared with control conditions (reporter lacZ gene transfer, absence of vector treatment). Of further note, expression of hypertrophic type-X collagen significantly decreased following co-treatment by the candidate vectors. The present findings show the value of combining the transfer and expression of potent candidate factors in human OA cartilage as a means to re-establish essential features of normal cartilage and counteract the pathological shift of homeostasis. These observations support the concept of developing dual therapeutic rAAV gene transfer strategies as future, adapted tools for the direct treatment of human OA. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2181-2190, 2016.

Genetic Modification of Human Peripheral Blood Aspirates Using Recombinant Adeno-Associated Viral Vectors for Articular Cartilage Repair with a Focus on Chondrogenic Transforming Growth Factor-β Gene Delivery

Transplantation of genetically modified peripheral blood aspirates that carry chondrogenically competent progenitor cells may offer new, convenient tools to treat articular cartilage lesions compared with the more complex and invasive application of bone marrow concentrates or of bone marrow‐derived mesenchymal stem cells. Here, we show that recombinant adeno‐associated viral (rAAV) vectors are powerful gene vehicles capable of successfully targeting primary human peripheral blood aspirates in a stable and safe manner, allowing for an efficient and long‐term transgene expression in such samples (up to 63 days with use of a lacZ reporter gene and for at least 21 days with application of the pleiotropic, chondrogenic factor transforming growth factor‐β [TGF‐β]). rAAV‐mediated overexpression of TGF‐β enhanced both the proliferative and metabolic properties of the peripheral blood aspirates, also increasing the chondrogenic differentiation processes in these samples. Hypertrophy and osteogenic differentiation events were also activated by production of TGF‐β via rAAV, suggesting that translation of the current approach in vivo will probably require close regulation of expression of this candidate gene. However, these results support the concept of directly modifying peripheral blood as a novel approach to conveniently treat articular cartilage lesions in patients. Stem Cells Translational Medicine2017;6:249–260

Effects of rAAV-mediated FGF-2 gene transfer and overexpression upon the chondrogenic differentiation processes in human bone marrow aspirates

Background

Application of genetically modified bone marrow concentrates in articular cartilage lesions is a promising approach to enhance cartilage repair by stimulating the chondrogenic differentiation processes in sites of injury.

Method

In the present study, we examined the potential benefits of transferring the proliferative and pro-chondrogenic basic fibroblast growth factor (FGF-2) to human bone marrow aspirates in vitro using the clinically adapted recombinant adeno-associated virus (rAAV) vectors to monitor the biological and chondrogenic responses over time to the treatment compared with control (lacZ) gene application.

Results

Effective, significant FGF-2 gene transfer and expression via rAAV was established in the aspirates relative to the lacZ condition (from ~ 97 to 36 pg rhFGF-2/mg total proteins over an extended period of 21 days). Administration of the candidate FGF-2 vector led to prolonged increases in cell proliferation, matrix synthesis, and chondrogenesis but also to hypertrophic and terminal differentiation in the aspirates.

Conclusion

The present evaluation shows the advantages of rAAV-mediated FGF-2 gene transfer to conveniently modify bone marrow concentrates as a future approach to directly treat articular cartilage lesions, provided that expression of the growth factor is tightly regulated to prevent premature hypertrophy in vivo.

Role of sox9 in growth factor regulation of articular chondrocytes

Chondrogenic polypeptide growth factors influence articular chondrocyte functions that are required for articular cartilage repair. Sox9 is a transcription factor that regulates chondrogenesis, but its role in the growth factor regulation of chondrocyte proliferation and matrix synthesis is poorly understood. We tested the hypotheses that selected chondrogenic growth factors regulate sox9 gene expression and protein production by adult articular chondrocytes and that sox9 modulates the actions of these growth factors. To test these hypotheses, we delivered insulin-like growth factor-I (IGF-I), fibroblast growth factor-2 (FGF-2), bone morphogenetic protein-2 (BMP-2) and/or bone morphogenetic protein-7 (BMP-7), or their respective transgenes to adult bovine articular chondrocytes, and measured changes in sox9 gene expression and protein production. We then knocked down sox9 gene expression with sox9 siRNA, and measured changes in the expression of the genes encoding aggrecan and types I and II collagen, and in the production of glycosaminoglycan, collagen and DNA. We found that FGF-2 or the combination of IGF-I, BMP-2, and BMP-7 increased sox9 gene expression and protein production and that sox9 knockdown modulated growth factor actions in a complex fashion that differed both with growth factors and with chondrocyte function. The data suggest that sox9 mediates the stimulation of matrix production by the combined growth factors and the stimulation of chondrocyte proliferation by FGF-2. The mitogenic effect of the combined growth factors and the catabolic effect of FGF-2 appear to involve sox9-independent mechanisms. Control of these molecular mechanisms may contribute to the treatment of cartilage damage.

TGF-β gene transfer and overexpression via rAAV vectors stimulates chondrogenic events in human bone marrow aspirates

Genetic modification of marrow concentrates may provide convenient approaches to enhance the chondrogenic differentiation processes and improve the repair capacities in sites of cartilage defects following administration in the lesions. Here, we provided clinically adapted recombinant adeno‐associated virus (rAAV) vectors to human bone marrow aspirates to promote the expression of the potent transforming growth factor beta (TGF‐β) as a means to regulate the biological and chondrogenic activities in the samples in vitro. Successful TGF‐β gene transfer and expression viarAAV was reached relative to control (lacZ) treatment (from 511.1 to 16.1 pg rhTGF‐β/mg total proteins after 21 days), allowing to durably enhance the levels of cell proliferation, matrix synthesis, and chondrogenic differentiation. Strikingly, in the conditions applied here, application of the candidate TGF‐β vector was also capable of reducing the hypertrophic and osteogenic differentiation processes in the aspirates, showing the potential benefits of using this particular vector to directly modify marrow concentrates to generate single‐step, effective approaches that aim at improving articular cartilage repair in vivo.

Controlled release strategies for rAAV-mediated gene delivery

The development of efficient and safe gene transfer vectors capable of achieving appropriate levels of therapeutic gene expression in a target is one of the most challenging issues in clinical gene therapy. Diverse nonviral and viral gene vehicles have been developed to modify human cells and tissues that may be affected in a variety of diseases, among which the nonpathogenic, effective, and relatively safe recombinant adeno-associated viral (rAAV) vectors that make them a preferred gene delivery system to treat human disorders. Yet, their adapted clinical application is still limited by several hurdles including the presence of immune responses in the host organism and the existence of rate-limiting steps associated with physiological barriers. The use of controlled release strategies to deliver gene vectors such as rAAV may provide powerful tools to enhance the temporal and spatial presentation of therapeutic agents in a defined target and to overcome such obstacles in vivo. The goal of this review is to provide an overview of the most recent advances in gene therapy with a focus on rAAV vectors for clinical translation based on the controlled release from adapted biomaterials as a means to improve the performance of the gene transfer procedure. We also discuss the challenges that remain to be addressed for a safe and efficient adaptation and use of such approaches in the patient.

STATEMENT OF SIGNIFICANCE

The development of effective gene vectors to achieve suitable levels of a therapeutic agent in a target is a critical issue in clinical gene therapy and regenerative medicine. Diverse vehicles are currently available among which the nonpathogenic recombinant adeno-associated virus (rAAV) vectors, a preferred system to effectively treat human disorders. Yet, the clinical use of rAAV is impaired by the host immune responses and by rate-limiting steps of transgene expression. Controlled rAAV delivery systems may provide workable approaches to overcome such obstacles. Here, we give an overview of the most recent advances on the controlled release of vectors with a focus on rAAV using adapted biomaterials and discuss the key challenges for a safe translation in patients.

rAAV-mediated overexpression of sox9, TGF-β and IGF-I in minipig bone marrow aspirates to enhance the chondrogenic processes for cartilage repair

Administration of therapeutic gene sequences coding for chondrogenic and chondroreparative factors in bone marrow aspirates using the clinically adapted recombinant adeno-associated virus (rAAV) vector may provide convenient, single-step approaches to improve cartilage repair. Here, we tested the ability of distinct rAAV constructs coding for the potent SOX9, transforming growth factor beta (TGF-β) and insulin-like growth factor I (IGF-I) candidate factors to modify marrow aspirates from minipigs to offer a preclinical large animal model system adapted for a translational evaluation of cartilage repair upon transplantation in sites of injury. Our results demonstrate that high, prolonged rAAV gene transfer efficiencies were achieved in the aspirates (up to 100% for at least 21 days) allowing to produce elevated amounts of the transcription factor SOX9 that led to increased levels of matrix synthesis and chondrogenic differentiation and of the growth factors TGF-β and IGF-I that both increased cell proliferation, matrix synthesis and chondrogenic differentiation (although to a lower level than SOX9) compared with control (lacZ) condition. Remarkably, application of the candidate SOX9 vector also led to reduced levels of hypertrophic differentiation in the aspirates, possibly by modulating the β-catenin, Indian hedgehog and PTHrP pathways. The present findings show the benefits of modifying minipig marrow concentrates via rAAV gene transfer as a future means to develop practical strategies to promote cartilage repair in a large animal model.

Ordinary and Activated Bone Grafts: Applied Classification and the Main Features

Bone grafts are medical devices that are in high demand in clinical practice for substitution of bone defects and recovery of atrophic bone regions. Based on the analysis of the modern groups of bone grafts, the particularities of their composition, the mechanisms of their biological effects, and their therapeutic indications, applicable classification was proposed that separates the bone substitutes into “ordinary” and “activated.” The main differential criterion is the presence of biologically active components in the material that are standardized by qualitative and quantitative parameters: growth factors, cells, or gene constructions encoding growth factors. The pronounced osteoinductive and (or) osteogenic properties of activated osteoplastic materials allow drawing upon their efficacy in the substitution of large bone defects.

Effective genetic modification and differentiation of hMSCs upon controlled release of rAAV vectors using alginate/poloxamer composite systems

Viral vectors are common tools in gene therapy to deliver foreign therapeutic sequences in a specific target population via their natural cellular entry mechanisms. Incorporating such vectors in implantable systems may provide strong alternatives to conventional gene transfer procedures. The goal of the present study was to generate different hydrogel structures based on alginate (AlgPH155) and poloxamer PF127 as new systems to encapsulate and release recombinant adeno-associated viral (rAAV) vectors. Inclusion of rAAV in such polymeric capsules revealed an influence of the hydrogel composition and crosslinking temperature upon the vector release profiles, with alginate (AlgPH155) structures showing the fastest release profiles early on while over time vector release was more effective from AlgPH155+PF127 [H] capsules crosslinked at a high temperature (50°C). Systems prepared at room temperature (AlgPH155+PF127 [C]) allowed instead to achieve a more controlled release profile. When tested for their ability to target human mesenchymal stem cells, the different systems led to high transduction efficiencies over time and to gene expression levels in the range of those achieved upon direct vector application, especially when using AlgPH155+PF127 [H]. No detrimental effects were reported on either cell viability or on the potential for chondrogenic differentiation. Inclusion of PF127 in the capsules was also capable of delaying undesirable hypertrophic cell differentiation. These findings are of promising value for the further development of viral vector controlled release strategies.

PEO-PPO-PEO micelles as effective rAAV-mediated gene delivery systems to target human mesenchymal stem cells without altering their differentiation potency

Recombinant adeno-associated viral (rAAV) vectors are clinically adapted gene transfer vectors for direct human cartilage regenerative medicine. Their appropriate use in patients is still limited by a relatively low efficacy of vector penetration inside the cells, by the pre-existing humoral immune responses against the viral capsid proteins in a large part of the human population, and by possible inhibition of viral uptake by clinical compounds such as heparin. The delivery of rAAV vectors to their targets using optimized vehicles is therefore under active investigation. Here, we evaluated the possibility of providing rAAV to human bone marrow-derived mesenchymal stem cells (hMSCs), a potent source of cartilage regenerative cells, via self-assembled poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) triblock copolymers as linear poloxamers or X-shaped poloxamines. Encapsulation in poloxamer PF68 and poloxamine T908 polymeric micelles allowed for an effective, durable, and safe modification of hMSCs via rAAV to levels similar to or even higher than those noted upon direct vector application. The copolymers were capable of restoring the transduction of hMSCs with rAAV in conditions of gene transfer inhibition, i.e. in the presence of heparin or of a specific antibody directed against the rAAV capsid, enabling effective therapeutic delivery of a chondrogenic sox9 sequence leading to an enhanced chondrocyte differentiation of the cells. The present findings highlight the value of PEO-PPO copolymers as powerful tools for rAAV-based cartilage regenerative medicine.

STATEMENT OF SIGNIFICANCE

While recombinant adeno-associated viral (rAAV) vectors are adapted vectors to treat a variety of human disorders, their clinical use is still restricted by pre-existing antiviral immune responses, by a low efficacy of natural vector entry in the target cells, and by inhibition of viral uptake by clinically used compounds like heparin. The search for alternative routes of rAAV delivery is thus becoming a new field of investigation. In the present study, we describe the strong benefits of providing rAAV to human mesenchymal stem cells, a potent source of cells for regenerative medicine, encapsulated in polymeric micelles based on poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) triblock copolymers as novel, effective and safe delivery systems for human gene therapy.