Jagadeesh K. Venkatesan

SOX9 gene transfer via safe, stable, replication-defective recombinant adeno-associated virus vectors as a novel, powerful tool to enhance the chondrogenic potential of human mesenchymal stem cells

IntroductionTransplantation of genetically modified human bone marrow-derived mesenchymal stem cells (hMSCs) with an accurate potential for chondrogenic differentiation may be a powerful means to enhance the healing of articular cartilage lesions in patients. Here, we evaluated the benefits of delivering SOX9 (a key regulator of chondrocyte differentiation and cartilage formation) via safe, maintained, replication-defective recombinant adeno-associated virus (rAAV) vector on the capability of hMSCs to commit to an adequate chondrocyte phenotype compared with other mesenchymal lineages.MethodsThe rAAV-FLAG-hSOX9 vector was provided to both undifferentiated and lineage-induced MSCs freshly isolated from patients to determine the effects of the candidate construct on the viability, biosynthetic activities, and ability of the cells to enter chondrogenic, osteogenic, and adipogenic differentiation programs compared with control treatments (rAAV-lacZ or absence of vector administration).ResultsMarked, prolonged expression of the transcription factor was noted in undifferentiated and chondrogenically differentiated cells transduced with rAAV-FLAG-hSOX9, leading to increased synthesis of major extracellular matrix components compared with control treatments, but without effect on proliferative activities. Chondrogenic differentiation (SOX9, type II collagen, proteoglycan expression) was successfully achieved in all types of cells but strongly enhanced when the SOX9 vector was provided. Remarkably, rAAV-FLAG-hSOX9 delivery reduced the levels of markers of hypertrophy, terminal and osteogenic/adipogenic differentiation in hMSCs (type I and type X collagen, alkaline phosphatise (ALP), matrix metalloproteinase 13 (MMP13), and osteopontin (OP) with diminished expression of the osteoblast-related transcription factor runt-related transcription factor 2 (RUNX2); lipoprotein lipase (LPL), peroxisome proliferator-activated receptor gamma 2 (PPARG2)), as well as their ability to undergo proper osteo-/adipogenic differentiation. These effects were accompanied with decreased levels of β-catenin (a mediator of the Wnt signaling pathway for osteoblast lineage differentiation) and enhanced parathyroid hormone-related protein (PTHrP) expression (an inhibitor of hypertrophic maturation, calcification, and bone formation) via SOX9 treatment.ConclusionsThis study shows the potential benefits of rAAV-mediated SOX9 gene transfer to propagate hMSCs with an advantageous chondrocyte differentiation potential for future, indirect therapeutic approaches that aim at restoring articular cartilage defects in the human population.

Current perspectives in stem cell research for knee cartilage repair

Protocols based on the delivery of stem cells are currently applied in patients, showing encouraging results for the treatment of articular cartilage lesions (focal defects, osteoarthritis). Yet, restoration of a fully functional cartilage surface (native structural organization and mechanical functions) especially in the knee joint has not been reported to date, showing the need for improved designs of clinical trials. Various sources of progenitor cells are now available, originating from adult tissues but also from embryonic or reprogrammed tissues, most of which have already been evaluated for their chondrogenic potential in culture and for their reparative properties in vivo upon implantation in relevant animal models of cartilage lesions. Nevertheless, particular attention will be needed regarding their safe clinical use and their potential to form a cartilaginous repair tissue of proper quality and functionality in the patient. Possible improvements may reside in the use of biological supplements in accordance with regulations, while some challenges remain in establishing standardized, effective procedures in the clinics.

Benefits of recombinant adeno-associated virus (rAAV)-mediated insulinlike growth factor I (IGF-I) overexpression for the long-term reconstruction of human osteoarthritic cartilage by modulation of the IGF-I axis

Administration of therapeutic genes to human osteoarthritic (OA) cartilage is a potential approach to generate effective, durable treatments against this slow, progressive disorder. Here, we tested the ability of recombinant adeno-associated virus (rAAV)-mediated overexpression of human insulinlike growth factor (hIGF)-I to reproduce an original surface in human OA cartilage in light of the pleiotropic activities of the factor. We examined the proliferative, survival and anabolic effects of the rAAV-hIGF-I treatment in primary human normal and OA chondrocytes in vitro and in explant cultures in situ compared with control (reporter) vector delivery. Efficient, prolonged IGF-I secretion via rAAV stimulated the biological activities of OA chondrocytes in all the systems evaluated over extended periods of time, especially in situ, where it allowed for the long-term reconstruction of OA cartilage (at least for 90 d). Remarkably, production of high, stable amounts of IGF-I in OA cartilage using rAAV advantageously modulated the expression of central effectors of the IGF-I axis by downregulating IGF-I inhibitors (IGF binding protein (IGFBP)-3 and IGFBP4) while upregulating key potentiators (IGFBP5, the IGF-I receptor and downstream mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 (MAPK/ERK-1/2) and phosphatidylinisitol-3/Akt (PI3K/Akt) signal transduction pathways), probably explaining the enhanced responsiveness of OA cartilage to IGF-I treatment. These findings show the benefits of directly providing an IGF-I sequence to articular cartilage via rAAV for the future treatment of human osteoarthritis.

rAAV-mediated overexpression of TGF-β stably restructures human osteoarthritic articular cartilage in situ

BackgroundTherapeutic gene transfer is of significant value to elaborate efficient, durable treatments against human osteoarthritis (OA), a slow, progressive, and irreversible disorder for which there is no cure to date.MethodsHere, we directly applied a recombinant adeno-associated virus (rAAV) vector carrying a human transforming growth factor beta (TGF-β) gene sequence to primary human normal and OA chondrocytes in vitro and cartilage explants in situ to monitor the stability of transgene expression and the effects of the candidate pleiotropic factor upon the regenerative cellular activities over time.ResultsEfficient, prolonged expression of TGF-β achieved via rAAV gene transfer enhanced both the proliferative, survival, and anabolic activities of cells over extended periods of time in all the systems evaluated (at least for 21xa0days in vitro and for up to 90xa0days in situ) compared with control (reporter) vector delivery, especially in situ where rAAV-hTGF-β allowed for a durable remodeling of OA cartilage. Notably, sustained rAAV production of TGF-β in OA cartilage advantageously reduced the expression of key OA-associated markers of chondrocyte hypertrophic and terminal differentiation (type-X collagen, MMP-13, PTHrP, β-catenin) while increasing that of protective TIMPs and of the TGF-β receptor I in a manner that restored a favorable ALK1/ALK5 balance. Of note, the levels of activities in TGF-β-treated OA cartilage were higher than those of normal cartilage, suggesting that further optimization of the candidate treatment (dose, duration, localization, presence of modulating co-factors) will most likely be necessary to reproduce an original cartilage surface in relevant models of experimental OA in vivo without triggering potentially adverse effects.ConclusionsThe present findings show the ability of rAAV-mediated TGF-β gene transfer to directly remodel human OA cartilage by activating the biological, reparative activities and by regulating hypertrophy and terminal differentiation in damaged chondrocytes as a potential treatment for OA or for other disorders of the cartilage that may require transplantation of engineered cells.

Determination of the chondrogenic differentiation processes in human bone marrow-derived mesenchymal stem cells genetically modified to overexpress transforming growth factor-β via recombinant adeno-associated viral vectors.

Genetic modification of bone marrow-derived mesenchymal stem cells (MSCs) for use in transplantation settings may be a valuable strategy to enhance the repair processes in articular cartilage defects. Here, we evaluated the potential of overexpressing the transforming growth factor (TGF)-β via recombinant adeno-associated viral (rAAV) vector-mediated gene transfer to promote the chondrogenic differentiation of human MSCs (hMSCs). A human TGF-β sequence was delivered to undifferentiated and chondrogenically induced primary hMSCs, using rAAV vectors to test the efficacy and duration of transgene expression and its effects on the chondrogenic, osteogenic, and adipogenic differentiation patterns of the cells compared with control (lacZ) treatment after 21 days in vitro. Significant, durable TGF-β expression was noted both in undifferentiated and chondrogenically induced hMSCs transduced with the candidate rAAV-hTGF-β vector for up to 21 days compared with rAAV-lacZ treatment, allowing for increased proliferative, metabolic, and chondrogenic activities via stimulation of the critical SOX9 (SRY [sex-determining region Y]-related HMG [high-mobility group] box 9) chondrogenic pathway. Overexpression of TGF-β under the conditions applied here also activated the hypertrophic and osteogenic differentiation processes in the treated cells. Such effects were noted in association with enhanced levels of β-catenin and Indian hedgehog and decreased parathyroid hormone-related protein expression. The current findings show that rAAV vectors provide advantageous vehicles for gene- and stem cell-based approaches to treat articular cartilage defects, requiring tight regulation of TGF-β expression to avoid hypertrophy as candidate treatment for future applications in clinically relevant animal models in vivo.

Influence of insulin-like growth factor I overexpression via recombinant adeno-associated vector gene transfer upon the biological activities and differentiation potential of human bone marrow-derived mesenchymal stem cells

IntroductionThe transplantation of genetically modified progenitor cells such as bone marrow-derived mesenchymal stem cells (MSCs) is an attractive strategy to improve the natural healing of articular cartilage defects. In the present study, we examined the potential benefits of sustained overexpression of the mitogenic and pro-anabolic insulin-like growth factor I (IGF-I) via gene transfer upon the biological activities of human MSCs (hMSCs).MethodsRecombinant adeno-associated vectors (rAAV) were used to deliver a human IGF-I coding sequence in undifferentiated and chondrogenically-induced primary hMSCs in order to determine the efficacy and duration of transgene expression and the subsequent effects of the genetic modification upon the chondrogenic versus osteogenic differentiation profiles of the cells relative to control (lacZ) treatment after 21xa0days in vitro.ResultsSignificant and prolonged expression of IGF-I was evidenced in undifferentiated and most importantly in chondrogenically-induced hMSCs transduced with the candidate rAAV-hIGF-I vector for up to 21xa0days, leading to enhanced proliferative, biosynthetic, and chondrogenic activities compared with rAAV-lacZ treatment. Overexpression of IGF-I as achieved in the conditions applied here also increased the expression of hypertrophic and osteogenic markers in the treated cells.ConclusionsThese results suggest that a tight regulation of rAAV expression may be necessary for further translation of the approach in clinically relevant animal models in vivo. However, the current findings support the concept of using this type of vector as an effective tool to treat articular cartilage defects via gene- and stem cell-based procedures.

Nicotinamide Adenine Dinucleotide-Dependent Binding of the Neuronal Ca2+ Sensor Protein GCAP2 to Photoreceptor Synaptic Ribbons

Guanylate cyclase activating protein 2 (GCAP2) is a recoverin-like Ca2+-sensor protein known to modulate guanylate cyclase activity in photoreceptor outer segments. GCAP2 is also present in photoreceptor ribbon synapses where its function is unknown. Synaptic ribbons are active zone-associated presynaptic structures in the tonically active photoreceptor ribbon synapses and contain RIBEYE as a unique and major protein component. In the present study, we demonstrate by various independent approaches that GCAP2 specifically interacts with RIBEYE in photoreceptor synapses. We show that the flexible hinge 2 linker region of RIBEYE(B) domain that connects the nicotinamide adenine dinucleotide (NADH)-binding subdomain with the substrate-binding subdomain (SBD) binds to the C terminus of GCAP2. We demonstrate that the RIBEYE–GCAP2 interaction is induced by the binding of NADH to RIBEYE. RIBEYE–GCAP2 interaction is modulated by the SBD. GCAP2 is strongly expressed in synaptic terminals of light-adapted photoreceptors where GCAP2 is found close to synaptic ribbons as judged by confocal microscopy and proximity ligation assays. Virus-mediated overexpression of GCAP2 in photoreceptor synaptic terminals leads to a reduction in the number of synaptic ribbons. Therefore, GCAP2 is a prime candidate for mediating Ca2+-dependent dynamic changes of synaptic ribbons in photoreceptor synapses.

Effective and durable genetic modification of human mesenchymal stem cells via controlled release of rAAV vectors from self-assembling peptide hydrogels with a maintained differentiation potency.

Controlling the release of recombinant adeno-associated virus (rAAV) vectors from biocompatible materials is a novel, attractive approach to increase the residence time and effectiveness of a gene carrier at a defined target site. Self-assembling peptides have an ability to form stable hydrogels and encapsulate cells upon exposure to physiological pH and ionic strength. Here, we examined the capacity of the peptide hydrogel RAD16-I in a pure (RAD) form or combined with hyaluronic acid (RAD-HA) to release rAAV vectors as a means to genetically modify primary human bone marrow-derived mesenchymal stem cells (hMSCs), a potent source of cells for regenerative medicine. Specifically, we demonstrate the ability of the systems to efficiently encapsulate and release rAAV vectors in a sustained, controlled manner for the effective transduction of hMSCs (up to 80%) without deleterious effects on cell viability (up to 100%) or on their potential for chondrogenic differentiation over time (up to 21days). The present study demonstrates that RAD16-I is an advantageous material with tunable properties to control the release of rAAV vectors as a promising tool to develop new, improved therapeutic approaches for tissue engineering in vivo.

Current Progress in Stem Cell-Based Gene Therapy for Articular Cartilage Repair

Administration of mesenchymal stem cells (MSCs) that have a reliable potential for chondrogenic differentiation is a promising approach currently employed to treat articular cartilage lesions (focal defects and osteoarthritis) in patients as a mean to enhance the poor intrinsic capabilities of this specialized tissue for self-repair. However, there is still a critical need for improved designs, as reproduction of a native structural and functional unit in sites of cartilage damage is not occurring upon implantation of such cells. With the availability of optimized gene transfer systems, gene therapy offers powerful tools to stimulate the chondrogenic process in MSCs via the effective, safe, and durable delivery of candidate sequences with chondroprotective and/or chondroregenerative properties, both in vitro and in experimental models of cartilage lesions in vivo. In the present article, we provide an overview of the current advances in gene- and stem cell-based treatments employed to promote cartilage repair in focal defects and for osteoarthritis, and discuss the challenges that remain to be addressed for a safe translation of such procedures into the clinics.

Human mesenchymal stem cells overexpressing therapeutic genes: From basic science to clinical applications for articular cartilage repair

Adult articular cartilage has a limited capacity for self repair. Reproduction of a native structure and functional integrity in damaged cartilage remains a major problem in orthopaedic surgery. Strategies based on the implantation of genetically modified cells to sites of injury may provide workable options to treat articular cartilage lesions like those resulting from acute trauma or associated with the progression of osteoarthritis. Mesenchymal stem cells have remarkable properties that make them an attractive source of cells to treat cartilage disorders due to their self-renewal capability, stemness maintenance, and chondrogenic differentiation potential. For these reasons, such progenitor cells might be further modified by gene transfer protocols to reinforce their potency and consequently, to enhance the healing processes in damaged tissue following transplantation in sites of cartilage injury. Here, we propose an overview of the current approaches employed for cell- and gene-based treatment of articular cartilage disorders using mesenchymal stem cells.