Co-transplantation of plasmid-transfected myoblasts and myotubes into rat brains enables high levels of gene expression long-term

Migration and differentiation of myogenic precursors following transplantation into the developing rat brain

There is increasing evidence that muscle-derived precursor cells can, under appropriate conditions, give rise to other than myogenic cell types. Transplantation into the embryonic ventricular zone provides a unique opportunity to study the migration and differentiation of non-neural somatic progenitor cells in response to instructive cues within the developing neuroepithelium. Here, we demonstrate that myogenic cell lines grafted into the ventricles of rat embryos showed widespread migration into several host brain compartments. In contrast to incorporation patterns observed after transplantation of neural cells, grafted myoblasts incorporated virtually exclusively along endogenous blood vessels. Preferential incorporation sites included cortex, olfactory bulb, hippocampus, striatum, thalamus, hypothalamus, and tectum. While the engrafted myoblasts showed no evidence of neural differentiation, a fraction exhibited pronounced coexpression of endothelial marker antigens. These findings support the concept of a close developmental relationship between the myogenic and the endothelial lineages. Used as a delivery system, transfected myoblasts may be exploited for widespread gene transfer to the perivascular compartment of the perinatal central nervous system.

The effect of bone morphogenetic protein-2 expression on the early fate of skeletal muscle-derived cells

The identification of bone morphogenetic proteins (BMPs) has stimulated intense interest in BMP delivery approaches. Ex vivo BMP-2 gene delivery has recently been described using skeletal muscle-derived cells. Skeletal muscle-derived cells, because of proven efficient transgene delivery and osteocompetence, represent an attractive cell population on which to base ex vivo BMP-2 gene delivery. However, the early in vivo fate of BMP-2-expressing muscle-derived cells is unknown. This study investigates the in vivo effects of BMP-2 secretion on skeletal muscle-derived cells in terms of cell survival and cell differentiation. The first experiment compared survival of BMP-2-expressing cells with control cells during the first 48 h after in vivo implantation. The results demonstrate that BMP-2 secretion did not adversely affect cell survival 8, 24, or 48 h after intramuscular implantation. The second experiment histologically compared the fate of BMP-2-expressing muscle-derived cells to the same cells not expressing BMP-2. The results show that BMP-2 expression prevented in vivo myogenic differentiation and promoted osteogenic differentiation of the transduced cells. This study further supports the existence of osteoprogenitor cells residing within skeletal muscle. Moreover, it is demonstrated that BMP-2 secretion does not adversely affect early cell survival of muscle-derived cells. These data are important for future investigations into BMP-2 gene delivery approaches to the musculoskeletal system.

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.

Use of muscle cells to mediate gene transfer to the bone defect

Segmental bone defects and nonunions are relatively common problems facing all orthopaedic surgeons. Osteogenic proteins, i.e., BMP-2, can promote bone healing in segmental bone defects. However, a large quantity of the human recombinant protein is needed to enhance the bone healing potential. Cell mediated gene therapy in the bone defect can allow a sustained expression of the osteogenic proteins and further enhance bone healing. Muscle cells can be easily isolated and cultivated, and they are known to be an efficient gene delivery vehicle to muscle and nonmuscle tissues. Furthermore, they are capable of transforming into osteoblasts when stimulated by BMP-2. Thus, the utilization of muscle cells as the gene delivery vehicle to a bone defect would be an important step in establishing a less invasive treatment for non-unions and segmental bone defects. Muscle cells were transduced when the adenoviral-lacZ vector and injected into the bone defect and the muscles surrounding the defect. Expression of the marker gene was visualized 7 days after the injection, both macroscopically and microscopically, using lacZ histochemistry. The lacZ expressing cells in the defect tissue were also stained for desmin, a muscle specific marker, indicating the presence of muscle cells that have fused into myofibers in this nonmuscle bone defect area. With successful myoblast mediated gene delivery into the segmental bone defect, future experiments would focus on delivering viral vectors expressing osteogenic proteins to eventually improve bone healing postinjury.

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.

Tissue-engineered skeletal muscle organoids for reversible gene therapy

Genetically modified murine skeletal myoblasts were tissue engineered in vitro into organ-like structures (organoids) containing only postmitotic myofibers secreting pharmacological levels of recombinant human growth hormone (rhGH). Subcutaneous organoid implantation under tension led to the rapid and stable appearance of physiological sera levels of rhGH for up to 12 weeks, whereas surgical removal led to its rapid disappearance. Reversible delivery of bioactive compounds from postmitotic cells in tissue engineered organs has several advantages over other forms of muscle gene therapy.

Plasmid DNA entry into postmitotic nuclei of primary rat myotubes

These studies were initiated to elucidate the mechanism of DNA nuclear transport in mammalian cells. Biotin- or gold-labeled plasmid and plasmid DNA expression vectors for Escherichia coli beta-galactosidase or firefly luciferase were microinjected into the cytoplasm of primary rat myotubes in culture. Plasmid DNA was expressed in up to 70% of the injected myotubes, which indicates that it entered intact, postmitotic nuclei. The nuclear transport of plasmid DNA occurred through the nuclear pore by a process common to other large karyophilic macromolecules. The majority of the injected plasmid DNA was sequestered by cytoplasmic elements. This understanding of plasmid DNA nuclear transport provides a basis for increasing the efficiency of gene transfer.

Postnatal gene transfer into the central nervous system

Substantial progress has been made in the development of techniques for the expression of foreign genes in the central nervous system of postnatal animals. Fetal and adult brain cells and other cells, including fibroblasts and muscle cells, have been successfully employed as vehicles for foreign gene expression in the central nervous system. Direct gene transfer strategies, such as those using herpes and adenoviral vectors, are presently under intense and fruitful investigation.