28 August 2013

Cardiomyocytes from scar tissue: work continues

Transformed heart scar tissue cells contract like Cardiomyocytes

LifeSciencesToday by Gladstone Institutes:
Gladstone Scientists Transform Non-Beating Human Cells into Heart-Muscle Cells
Research findings lay foundation for one day regenerating damaged heart muscle

An image of a cell similar in its characteristics to a cardiomyocyte obtained by direct reprogramming from a human fibroblast; the cell is stained with a marker of a sarcomere – a contractile unit of striated muscles (photo: Stem Cell Reports).Immediately after a myocardial infarction, the cells of the most affected area of the heart muscle stop contracting.

They end up buried in scar tissue. But by finding a way to reprogram a class of cells that form scar tissue into cells close to cardiomyocytes, scientists from the Gladstone Institutes have demonstrated that today's science can make significant changes to this bleak picture.

Last year, in the laboratory of Deepak Srivastava, MD, cardiac fibroblasts forming scar tissue were reprogrammed into heart muscle cells contracting in the body of a living mouse. In the latest issue of the journal Stem Cell Reports, the same group reports that they managed to do the same with human cells in in vitro experiments (Fu et al., Direct Reprogramming of Human Fibroblasts towards a Cardiomyocyte-like State).

"Fibroblasts make up about 50% of all heart cells and, therefore, represent an extensive pool of cells that may one day be used for reprogramming into cells of a new muscle," explains Dr. Srivastava, professor at the University of California, San Francisco (University of California, San Francisco). "Our results serve as proof of the concept that human fibroblasts can be successfully reprogrammed into rhythmically contracting heart cells."

In 2012, in the journal Nature (In vivo reprogramming of murine cardiac fibroblasts into induced cardiomyocytes), Professor Srivastava and his group reported that fibroblasts can be reprogrammed into contracting heart cells by introducing just three genes, collectively known as GMT, into the post-infarction heart of a living mouse. They reasonably assumed that the same three genes could have the same effect on human cells. But the first experiments on human fibroblasts from three sources – fetal heart cells, embryonic stem cells and newborn skin cells – showed that one combination of GMT is not enough.

"The introduction of GMT into each of these three types of human fibroblasts did not lead to anything – they did not transform. Therefore, we returned to the search for additional genes that can help start the transformation," says Ji–dong Fu, PhD, a researcher at the Gladstone Institute, the first author of the article. "We narrowed our search to 16 potential genes and, in the hope of finding the right solution, screened them together with GMT."

Scientists began by introducing all candidate genes into human fibroblasts. Then they systematically removed one of them to find out which ones were needed for reprogramming and which ones could be dispensed with. In the end, it was found that the introduction of a cocktail of five genes – a 3-gene combination of GMT plus ESRRG and Mesp1 – was enough to reprogram fibroblasts into cells close to cardiomyocytes. In addition, the addition of two more genes – MYOCD and ZFPM2 – made the transformation even more complete. Finally, in the early stages of reprogramming, scientists initiated a chemical reaction known as the TGF-β signaling pathway, which allowed for even greater success.

"While almost all the cells in our study showed at least partial transformation, about 20 percent were able to transmit electrical signals – a key characteristic of the contracting heart cells –" continues Dr. Fu. "Obviously, there are barriers preventing a more complete transformation of most cells that have yet to be determined. For example, efficiency can be increased by transforming fibroblasts not in a Petri dish, but directly in a living heart, which we have already observed during our first experiments on mice."

In the very near future, scientists are planning to test a cocktail of five genes on larger animals, such as a pig. However, they hope that, eventually, to replace this cocktail, it will be possible to develop a combination of low–molecular compounds - a safer and simpler method.

"The hearts of more than five million American heart attack survivors are no longer able to contract at full strength, and our results – along with the recently published results of our colleagues – come at a turning point," concludes Dr. Srivastava. "We have laid a solid foundation for developing a way to reverse this disorder – which was previously considered impossible – and move in the future to radically new methods of treating myocardial infarction."

3-D image of a heart muscle cell obtained from fibroblast by direct reprogramming. Direct reprogramming makes it possible to transform a cell of one type into a cell of another without first returning it to the stem state.Portal "Eternal youth" http://vechnayamolodost.ru


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