A team of researchers from Italy, Israel and the United Kingdom has succeeded in generating mature, functional skeletal muscles in mice using a new approach for tissue engineering. The scientists grew a leg muscle starting from engineered cells cultured in a dish to produce a graft. The subsequent graft was implanted close to a normal, contracting skeletal muscle where the new muscle was nurtured and grown. In time, the method could allow for patient-specific treatments for a large number of muscle disorders. The results are published in EMBO Molecular Medicine .
The study of the growth of new connective tissues, or organs, from cells and a collagenous scaffold to produce a fully functional organ for implantation back into the donor host. This technique will allow organs to be grown from implantation (rather than transplantation) and hence free from immunological rejection. The starting point for any tissue-engineered organ is the harvesting of small amounts of tissue from the future recipient of the Tissue Engineered organ.
Mesoangioblast: A mesenchymal-like cell, associated with the walls of the large vessels. Mesoangioblasts exhibit many similarities to pericytes found in the small vessels. Mesoangioblasts are relatively undifferentiated cells with the potential to progress down the endothelial or mesodermal lineages. Mesoangioblasts express the endothelial marker Flk-1, but not haematopoietic markers such as Tal-1.
The scientists used muscle precursor cells - mesoangioblasts - grown in the presence of a hydrogel (support matrix) in a tissue culture dish.
The cells were also genetically modified to produce a growth factor that stimulates blood vessel and nerve growth from the host. Cells engineered in this way express a protein growth factor that attracts other essential cells that give rise to the blood vessels and nerves of the host, contributing to the survival and maturation of newly formed muscle fibers.
After the graft was implanted onto the surface of the skeletal muscle underneath the skin of the mouse, mature muscle fibers formed a complete and functional muscle within several weeks. Replacing a damaged muscle with the graft also resulted in a functional artificial muscle very similar to a normal Tibialis anterior.
Tissue engineering of skeletal muscle is a significant challenge but has considerable potential for the treatment of the various types of irreversible damage to muscle that occur in diseases like Duchenne muscular dystrophy. So far, attempts to re-create a functional muscle either outside or directly inside the body have been unsuccessful. In vitro-generated artificial muscles normally do not survive the transfer in vivo because the host does not create the necessary nerves and blood vessels that would support the muscle's considerable requirements for oxygen.
"The morphology and the structural organization of the artificial organ are extremely similar to if not indistinguishable from a natural skeletal muscle," says Cesare Gargioli of the University of Rome, one of the lead authors of the study.
In future, irreversibly damaged muscles could be restored by implanting the patient's own cells within the hydrogel matrix on top of a residual muscle, adjacent to the damaged area.
"While we are encouraged by the success of our work in growing a complete intact and functional mouse leg muscle we emphasize that a mouse muscle is very small and scaling up the process for patients may require significant additional work," comments EMBO Member Giulio Cossu, one of the authors of the study. The next step in the work will be to use larger animal models to test the efficacy of this approach before starting clinical studies.
In vivo generation of a mature and functional artificial skeletal muscle
Claudia Fuoco, Roberto Rizzi, Antonella Biondo, Emanuela Longa, Anna Mascaro, Keren Shapira-Schweitzer, Olga Kossovar, Sara Benedetti, Maria L Salvatori, Sabrina Santoleri, Stefano Testa, Sergio Bernardini, Roberto Bottinelli, Claudia Bearzi, Stefano M Cannata, Dror Seliktar, Giulio Cossu and Cesare Gargioli.
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The paper is available at embomolmed.embopress.org
Further information on EMBO Molecular Medicine is available at embomolmed.embopress.org
Tissue engineering utilizes living cells as engineering materials. Examples include using living fibroblasts in skin replacement or repair, cartilage repaired with living chondrocytes, or other types of cells used in other ways. Cells became available as engineering materials when scientists at Geron Corp. discovered how to extend telomeres in 1998, producing immortalized cell lines. Before this, laboratory cultures of healthy, noncancerous mammalian cells would only divide a fixed number of times, up to the Hayflick limit.