Myoblast-MediatedEx VivoGene Transfer to Mature Muscle

Development of Approaches to Improve the Healing following Muscle Contusion

Muscle injuries are a challenging problem in traumatology, and the most frequent occurrence in sports medicine. Muscle contusions are among the most common muscle injuries. Although this injury is capable of healing, an incomplete functional recovery often occurs, depending on the severity of the blunt trauma. We have developed an animal model of muscle contusion in mice (high energy blunt trauma) and characterized the muscle's ability to heal following this injury using histology and immunohistochemistry to determine the level of muscle regeneration and the development of scar tissue. We have observed a massive muscle regeneration occurring in the first 2 wk postinjury that is subsequently followed by the development of muscle fibrosis. Based on these observations, we propose that the enhancement of muscle growth and regeneration, as well as the prevention of fibrotic development, could be used as approach(es) to improve the healing of muscle injuries. In fact, we have identified three growth factors (bFGF, IGF-1, and NGF) capable of enhancing myoblast proliferation and differentiation in vitro and improving the healing of the injured muscle in vivo. Furthermore, the ability of adenovirus to mediate direct and ex vivo gene transfer of β-galactosidase into the injured site opens possibilities of delivering an efficient and persistent expression of these growth factors in the injured muscle. These studies should help in the development of strategies to promote efficient muscle healing with complete functional recovery following muscle contusion. © 1998 Elsevier Science Inc.

NADPH Oxidase-Dependent NLRP3 Inflammasome Activation and its Important Role in Lung Fibrosis by Multiwalled Carbon Nanotubes

The purpose of this paper is to elucidate the key role of NADPH oxidase in NLRP3 inflammasome activation and generation of pulmonary fibrosis by multi-walled carbon nanotubes (MWCNTs). Although it is known that oxidative stress plays a role in pulmonary fibrosis by single-walled CNTs, the role of specific sources of reactive oxygen species, including NADPH oxidase, in inflammasome activation remains to be clarified. In this study, three long aspect ratio (LAR) materials (MWCNTs, single-walled carbon nanotubes, and silver nanowires) are used to compare with spherical carbon black and silver nanoparticles for their ability to trigger oxygen burst activity and NLRP3 assembly. All LAR materials but not spherical nanoparticles induce robust NADPH oxidase activation and respiratory burst activity in THP-1 cells, which are blunted in p22(phox) -deficient cells. The NADPH oxidase is directly involved in lysosomal damage by LAR materials, as demonstrated by decreased cathepsin B release and IL-1β production in p22(phox) -deficient cells. Reduced respiratory burst activity and inflammasome activation are also observed in bone marrow-derived macrophages from p47(phox) -deficient mice. Moreover, p47(phox) -deficient mice have reduced IL-1β production and lung collagen deposition in response to MWCNTs. Lung fibrosis is also suppressed by N-acetyl-cysteine in wild-type animals exposed to MWCNTs.

Adenovirus mediated gene transfer to skeletal muscle

Transfer of therapeutic genes into muscle tissue has promise for the treatment of a variety of muscular dystrophies. Various vectors have been used to deliver genes to skeletal muscle but their application has faced several major limitations including: (1) the lack of transgene persistence caused by the immune rejection of transduced myofibers and/or vector toxicity, and (2) the maturation dependence of viral transduction. While the immunorejection and/or cytotoxic problems are being overcome with the development of new vectors, maturation-dependent viral transduction is still a major hurdle in gene transfer to skeletal muscle. Poor adenoviral transduction in mature myofibers has been attributed to: (1) the extracellular matrix of mature myofibers may form a physical barrier and prevent the passage of large viral particles; (2) viral receptors are down-regulated with muscle maturation; and (3) loss of myoblasts with muscle maturation, which serve as intermediaries in the viral transduction. In this review, we will focus on recent developments in overcoming those hurdles of gene therapy in skeletal muscle, especially to adenovirus (Ad), including: (1) new mutant vectors lacking all viral genes to decrease immunogenicity, and hence, improve persistence of transgene expression in muscle in vivo; (2) using tissue specific promoters to evade immunorejection; (3) permeabilization of the extracellular matrix; (4) modifying the viral receptors in mature myofibers; and (5) myoblast or muscle stem cell mediated ex vivo gene transfer.

Muscle-based gene therapy and tissue engineering for the musculoskeletal system

The recent expansion of molecular biology techniques has opened the gates for a rapid advancement in our knowledge of disease mechanisms. These techniques, in addition to advances in cell biology and polymer chemistry, are resulting in novel approaches to treating musculoskeletal disorders. Surgeons, who have traditionally used the tools of excision and reconstruction to treat patients, might now serve as surgical 'gardeners', who create microenvironments that are conducive for tissue regeneration. This review will update readers on the principles and current advances in muscle-based gene therapy and tissue engineering for the musculoskeletal system.

Transplantation of virally transduced cells into the dermis of immunocompetent and immunodeficient (SCID) mice to determine gene expression profile and differential donor cell survival

Cell therapy and bioengineering hold great promise as therapeutic approaches using cells and cell-derived factors to treat various pathologic or trauma-induced states. One possible application is the transplantation of cells into wounded tissue to help regulate tissue repair. Cells engineered for optimal wound healing may help to minimize scarring following surgery or to enhance the rate of healing of chronic wounds. The purpose of the current study was to determine the effect of a viral insert, the LacZ-bearing, first generation adenovirus AdRGD, on the survival of dermally transplanted murine skin allogenic fibroblasts. The LacZ insert facilitated quantitation of both cell survival and gene expression and was used here to measure viable cell number. In addition to bearing the LacZ marker, the AdRGD vector is capable of carrying therapeutic gene inserts, so this study tested the feasibility of gene therapy for wound healing. Murine skeletal muscle PP6 (i.e., Pre-Plate 6) myogenic stem cells served as an alternate donor cell type. Cells were labeled with the LacZ-bearing AdRGD adenovirus vector and injected (50,000 cells/site) into the dorsal skin of adult normal, immunocompetent mice as well as in immunodeficient SCID mice. Skin biopsies were taken on days 0, 1, 2, 3, and 7 post-transplant, and assayed for LacZ expression. Soon after transplant (day 1), cell numbers underwent a transient decrease, but by day 2 post-transplant they were present in appreciable numbers. Between days 2-7 post-transplant, both allogenic fibroblasts and PP6 myogenic stem cells maintained survivability in similar numbers. Further, survival of transplanted cell types was similar in both normal, immunocompetent as well as SCID mice during this time period. There were no signs of acute inflammation or rejection in any of the samples. This study shows that AdRGD-transduced cells are not immunogenic in the mouse skin model and the cells show similar survival for the first 7 days post-transplantation independent of the cell type or immunocompetence of the host.

The influence of muscle fiber type in myoblast-mediated gene transfer to skeletal muscles

Myoblast transplantation has been hindered by immune rejection problems, as well as the poor survival and spread of transplanted cells. Our recent study has shown that the poor survival of the injected cells can be totally overcome by the use of specific populations of muscle-derived cells. In the present study, we have investigated whether a relationship exists between the fate of transplanted cells and the muscle fiber types. Four kinds of myogenic cells [primary myoblasts at a high purity (PMb), myoblasts isolated from fast single fibers (FMb), mdx (MCL), and MtMd-1 cell lines] were infected with an adenoviral vector carrying a LacZ reporter gene and injected into mdx hindlimb muscle. The LacZ transduced myofibers formed by the fusion of the injected myoblasts at 2-10 days postinjection were colocalized with MyHC stainings. The PMb cells, which expressed both slow and fast MyHCs in vitro, displayed the same phenotypes when injected into the m. soleus and m. gastrocnemius (white) muscles, which contained 70% and 0% of slow myofibers, respectively, and showed a high degree of fusion with host muscle fibers. In contrast, the FMb cells only expressed fast MyHCs in vitro and fused exclusively with each other or with host fast muscle fibers when injected in the m. gastrocnemius. Injected MCL and MtMd-1 fused predominantly with each other and displayed a similar expression of MyHCs to those they expressed in vitro. Just a few host myofibers were found to express the reporter gene product following implantation of both cell lines, indicating that these myogenic cell lines display an intrinsic potential to fuse together rather than with host myofibers. Based on the data, we concluded that 1) the essential key to survival is the ability of the donor cells to fuse with the host myofibers, and 2) the most successful combination is achieved between donor primary muscle cells that express both fast and slow MyHC and a host muscle type that facilitates fusion.

Preliminary results of myoblast injection into the urethra and bladder wall: a possible method for the treatment of stress urinary incontinence and impaired detrusor contractility

The purpose of this study is to explore the feasibility of myoblasts, the precursors of muscle fibers, injected periurethrally as a potential treatment of stress urinary incontinence. We also studied myoblast injection into the bladder wall to potentially improve detrusor contractility. A myoblast cell line was transduced with adenovirus carrying the expression of the beta-galactosidase reporter gene while in culture. The cells were incubated with fluorescent latex microspheres (FLMs) to follow the outcome of the injected cells. The tissue was harvested 3-4 days after injection; sectioned, fixed, assayed for beta-galactosidase expression, and counterstained with H+E. Photographs of the slides were taken under light and fluorescence microscopy. We have noted a large number of cells expressing beta-galactosidase and containing FLMs in the urethral and bladder walls under fluorescent microscopy (8 animals). Many regenerative myofibers expressing beta-galactosidase were also seen in the urethral and bladder walls. The fusion of injected myoblasts to form myotubes was seen in both the urethral and bladder walls. The introduction of myoblasts into the urethral and bladder wall is feasible and results in formation of myotubes and myofibers in the smooth muscle layers of the lower urinary tract. We hypothesize that myoblast injections can be used as a non-allergenic agent to enhance urethral closure and bladder function.

Matching host muscle and donor myoblasts for myosin heavy chain improves myoblast transfer therapy

Intensive efforts have been made to develop an effective therapy for Duchenne muscular dystrophy (DMD). Although myoblast transplantation has been found capable of transiently delivering dystrophin and improving the strength of the injected dystrophic muscle, this approach has been hindered by the immune rejection problems as well as the poor survival and limited spread of the injected cells. In the present study, we have investigated whether the careful selection of donor myoblasts and host muscle for the myosin heavy chain expression (MyHCs) plays a role in the success of myoblast transfer. Highly purified normal myoblasts derived from the m. soleus and m. gastrocnemius white of normal mice were transplanted into the m. soleus (containing 70% of type I fibers) and gastrocnemius white (100% of type II fibers) of dystrophin deficient mdx mice. At several time-points after injection (10, 20 and 30 days), the number of dystrophin-positive fibers was monitored and compared among the different groups. A significantly higher number and better persistence of dystrophin-positive myofibers were observed when the injected muscle and donor myoblasts expressed a similar MyHC in comparison with myoblast transfer between host muscle and donor myoblasts that were not matched for MyHC. These results suggest that careful matching between the injected myoblasts and injected muscle for the MyHC expression can improve the efficiency of myoblast-mediated gene transfer to skeletal muscle. Gene Therapy (2000) 7, 428-437.

Use of growth factors to improve muscle healing after strain injury

Muscle injuries represent a large number of professional and recreational sports injuries. Muscle strains habitually occur after an eccentric contraction, which often leads to an injury located in the myotendinous junction. Treatment varies widely, depending on the severity of the trauma, but has remained limited mostly to rest, ice, compression, elevation, antiinflammatory drugs, and mobilization. The authors' research group aims to develop new biologic approaches to improve muscle healing after injuries, including muscle strains. To achieve this goal, the authors investigated several parameters that will lead to the development of new strategies to enhance muscle healing. The authors first evaluated natural muscle healing after strain injuries and showed that muscle regeneration occurs in the early phase of healing but becomes impaired with time by the development of tissue fibrosis. Several growth factors capable of improving muscle regeneration were investigated; basic fibroblast growth factor, insulin-like growth factor, and nerve growth factors were identified as substances capable of enhancing muscle regeneration and improving muscle force in the strained injured muscle. The current study should aid in the development of strategies to promote efficient muscle healing and complete recovery after strain injury.

Development of approaches to improve cell survival in myoblast transfer therapy

Myoblast transplantation has been extensively studied as a gene complementation approach for genetic diseases such as Duchenne Muscular Dystrophy. This approach has been found capable of delivering dystrophin, the product missing in Duchenne Muscular Dystrophy muscle, and leading to an increase of strength in the dystrophic muscle. This approach, however, has been hindered by numerous limitations, including immunological problems, and low spread and poor survival of the injected myoblasts. We have investigated whether antiinflammatory treatment and use of different populations of skeletal muscle-derived cells may circumvent the poor survival of the injected myoblasts after implantation. We have observed that different populations of muscle-derived cells can be isolated from skeletal muscle based on their desmin immunoreactivity and differentiation capacity. Moreover, these cells acted differently when injected into muscle: 95% of the injected cells in some populations died within 48 h, while others richer in desmin-positive cells survived entirely. Since pure myoblasts obtained from isolated myofibers and myoblast cell lines also displayed a poor survival rate of the injected cells, we have concluded that the differential survival of the populations of muscle-derived cells is not only attributable to their content in desmin-positive cells. We have observed that the origin of the myogenic cells may influence their survival in the injected muscle. Finally, we have observed that myoblasts genetically engineered to express an inhibitor of the inflammatory cytokine, IL-1, can improve the survival rate of the injected myoblasts. Our results suggest that selection of specific muscle-derived cell populations or the control of inflammation can be used as an approach to improve cell survival after both myoblast transplantation and the myoblast-mediated ex vivo gene transfer approach.

Muscle maturation: implications for gene therapy

Skeletal muscle is a promising target tissue for gene therapy, for both muscle and non-muscle disorders. A variety of methods have been studied to transfer genes into skeletal muscle, including retroviral, adenoviral and herpes simplex viral vectors. However, various factors impede muscle-based viral gene therapy. Here, we discuss why some viral vectors cannot efficiently transduce mature muscle fibers, and describe some new approaches to overcome this barrier.

Implications of maturation for viral gene delivery to skeletal muscle

Different viral vectors have been analyzed as gene delivery vehicles to skeletal muscle for potentially therapeutic purposes. In this review, we evaluate the application of retroviral, adenoviral, and herpes simplex viral vectors to deliver genes to skeletal muscle and focus on the dramatic loss of viral transduction detected throughout muscle maturation. Recent results suggested that there are several factors involved in the reduced viral transducibility of mature skeletal muscle: muscle cells become post-mitotic in an early stage, the extracellular matrix develops into a physical barrier, and a loss of myoblast mediation occurs since myoblasts progressively become quiescent. Approaches to improve viral gene delivery to mature skeletal muscle may include the use of particular enzymes to increase the permeability of the extracellular matrix, the pre-treatment of the muscle with a myonecrotic agent to induce myoblast mediation, or the application of the myoblast-mediated ex vivo gene transfer.

Myoblast-mediated gene transfer to the joint

Several genetic and acquired pathologic conditions of the musculoskeletal system, such as arthritis and damage to ligament, cartilage, and meniscus, may be amenable to gene therapy. Even though ex vivo gene transfer with synovial cells has been shown to deliver genes encoding for anti-arthritic proteins into the rabbit knee joint, its success has been limited by a transient transgene expression. In this study, data were investigated regarding the use of muscle cells as an alternative gene-delivery vehicle to the joint in newborn rabbit and adult severe combined immunodeficiency mice. We demonstrated that myoblasts were transduced more efficiently than synovial cells with use of the same adenoviral preparation in vitro. After intra-articular injection, the engineered muscle cells adhered to several structures in the joint, including the ligament, capsule, and synovium. In addition, myoblasts fused to form many post-mitotic myotubes and myofibers at different locations of the joint of the newborn rabbit 5 days after the injection. In the knee of the adult mouse, myoblasts fused and expressed the reporter gene for at least 35 days after the injection. The presence of post-mitotic myofibers in the knee joint raises the possibility of long-term expression of the secreted protein. Currently, numerous tissues in the joint (ligament, meniscus, and cartilage) have poor intrinsic healing capacity and frequently need surgical corrections. A stable gene-delivery vehicle to the joint producing proteins that ameliorate these different musculoskeletal conditions may change the clinical implications of these pathologies.