June 21, 2006
Muscle Cells Shaped To Conduct Electric Pulses For Hearts

David Gobel, one of the folks behind the Methuselah Mouse Prize, points me to news of an experiment where regular muscle tissue was isolated from rats, shaped into heart tissue that can conduct electric impulses.

Patients with complete heart block, or disrupted electrical conduction in their hearts, are at risk for life-threatening rhythm disturbances and heart failure. The condition is currently treated by implanting a pacemaker in the patient's chest or abdomen, but these devices often fail over time, particularly in infants and small children who must undergo many re-operations. Researchers at Children's Hospital Boston have now taken preliminary steps toward using a patient's own cells instead of a pacemaker, marking the first time tissue-engineering methods have been used to create electrically conductive tissue for the heart. Results appear in the July issue of the American Journal of Pathology (published online on June 19).

The goal of this research is to develop living replacements for artificial pacemakers.

The scienitsts isolated myoblasts, a type of stem cells, from muscles. Then they grew up those cells on a structure made from collagen. The resulting tissue formed a structure implantable on hearts.

Cowan's team, including first author Yeong-Hoon Choi in Children's Department of Cardiac Surgery, obtained skeletal muscle from rats and isolated muscle precursor cells called myoblasts. They "seeded" the myoblasts onto a flexible scaffolding material made of collagen, creating a 3-dimensional bit of living tissue that could be surgically implanted in the heart.

The cells distributed themselves evenly in the tissue and oriented themselves in the same direction. Tested in the laboratory, the engineered tissue started beating when stimulated electrically, and its muscle cells produced proteins called connexins that channel ions from cell to cell, connecting the cells electrically.

The bioengineered tissue created pathways for conducting electricity.

When the engineered tissue was implanted into rats, between the right atrium and right ventricle, the implanted cells integrated with the surrounding heart tissue and electrically coupled to neighboring heart cells. Optical mapping of the heart showed that in nearly a third of the hearts, the engineered tissue had established an electrical conduction pathway, which disappeared when the implants were destroyed. The implants remained functional through the animals' lifespan (about 3 years).

"The advantage of using myoblasts is that they can be taken from skeletal muscle rather than the heart itself--which will be important for newborns whose hearts are so tiny they cannot spare any tissue for the biopsy--and that they're resistant to ischemia, meaning they can go without a good blood supply for a relatively long period of time," Cowan says.

The researchers are now working toward experiments with larger animals.

I like tissue engineering experiments that try to take existing tissue and rearrange it to solve problems. We certainly need advances in understanding of how embryonic stem cells go through series of steps to become much more specialized. However, as demonstrated by this report, not all applications of stem cells require the development of an enormous amount of understanding of how to control the differentiation (specialization) of stem cells through many steps. Existing non-embryonic cells have the potential to be rearranged and grown up into cells needed to solve many medical problems.

Share |      Randall Parker, 2006 June 21 08:41 PM  Biotech Tissue Engineering

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