Strategies for gene transfer into muscle

Various approaches can be used to achieve gene transfer to the muscu-loskeletal system, including cell therapy (myoblast transplantation), gene therapy (based on viral and nonviral vectors), and a combination of both techniques. A description of the various approaches used to deliver growth factors into injured skeletal muscle follows. It is hoped that, through cell and gene therapy, substances such as growth factors can be delivered to promote efficient healing and complete functional recovery following injury.

4.1. Cell Therapy

MDSC transplantation is the implantation of MDSCs into damaged muscle for muscle regeneration. The transplantation of MDSCs into dystrophin-deficient muscle to create a reservoir of dystrophin-producing cells has been studied extensively in mdx mice (an animal model for DMD) and in patients with DMD (27). MDSC transplantation is capable of deliver ing dystrophin, the missing protein in DMD, and increasing muscle strength in DMD muscles. Yet, immune rejection as well as the poor survival and spread of injected MDSC posttransplantation have greatly limited the success of MDSC transplantation (28). As such, recent research has focused on using viral or nonviral vectors to deliver genes to skeletal muscle, an approach called ex vivo gene transfer.

4.2. Direct Gene Therapy

Direct gene therapy is another approach to deliver genes to skeletal muscle. Muscle cells have been successfully transduced in vitro and in vivo using the intramuscular inoculation of replicative-deficient adenovirus, retrovirus, and HSV carrying the -galactosidase (LacZ) reporter gene; however, a major limitation of using these viral vectors alone is the differential transducibility observed throughout skeletal muscle development (22,29).

The direct gene transfer of recombinant adenovirus carrying the LacZ reporter gene is capable of highly transducing injured muscle. Many LacZ-expressing myofibers have been found in the injured site of contused, lacerated, and strained muscles at 5 d following the direct gene transfer approach (30). Although the transient expression of the transgene is likely an immune reaction, the use of the new-generation adenovirus vectors and the adeno-associated virus vectors may reduce the immune response and allow persistent expression of the transgene into the injected muscle (23,31).

4.3. MDSC Transplantation Using Ex Vivo Gene Transfer

The ex vivo approach combines MDSC transplantation and gene therapy using an autologous MDSC transfer to deliver genes to skeletal muscle. This approach involves establishing a primary MDSC culture from dystrophic and injured muscles, which is then engineered by adequate transfection or transduction to produce dystrophin and growth factors in vitro. The engineered MDSCs are then injected into the same host to avoid immune rejection against the injured myoblasts. This method has been performed using adenovirus, retrovirus, and HSV-1-carrying reporter genes (20,32,33). The transduced MDSCs fuse and reintroduce the reporter genes into the injected muscle. The ex vivo approach was used to deliver dystrophin into dystro-phic muscle, and the efficiency of viral transduction using the ex vivo approach is greater than that of direct injection of the same amount of virus (34).

Also, the ex vivo approach has been used to deliver genes into injured muscle. Primary MDSCs have been isolated, engineered following transduction with an adenovirus carrying the LacZ reporter gene, and injected

Mdsc Transplantation

Fig. 2. MDSC-based tissue engineering in the lower urinary tract.

I Injection Cu|ture

Fig. 2. MDSC-based tissue engineering in the lower urinary tract.

into injured muscle. The LacZ-transduced myofibers persisted in the injured muscle for at least 35 d postinjection. This suggests that the ex vivo gene transfer of autologous MDSCs is feasible and leads to persistent expression of marker gene in injured muscle (30,35).

In summary, MDSC transplantation using ex vivo gene transfer may be advantageous for repairing muscle because the cells can be used as a reservoir for secreting growth factors. In addition, the engineered MDSCs can serve as a source of exogenous cells capable of participating in the healing process. The use of pluripotent MDSC in an ex vivo approach may become very attractive for the healing of damaged muscle.

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The Basics Of Body Building

The Basics Of Body Building

Bodybuilding is the process of developing muscle fibers through various techniques. It is achieved through muscle conditioning, weight training, increased calorie intake, and resting your body as it repairs and heals itself, before restarting your workout routine.

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