Tuesday, February 26, 2013

Stem cells shown to repair liver after transplantation

Theoretically, stem cells should be able to regenerate all damaged tissues in our body. Basically every organ has its own mature stem cells that are able to produce new cells when needed, although some are more active than others. So far, we have seen limited success with the use of stem cells. A prime example was the generation of an artificial kidney based on stem cells, which was successfully transplanted. Now, scientists have shown capable of growing liver cells out of specific stem cells, and also transplanted them successfully, paving the way for a cure for liver disease.

Stem cells in different organs have different characteristics. Because they have already 'committed' to a particular cell line, they all have the characteristics of the organ they reside in, and are therefore different from the embryonic stem cells that are regarded as the 'true' stem cells. Those of the liver are marked by expression of a gene known as Lgr5, which is induced by a signalling molecule called Wnt. While that may not sound very interesting, this mechanism has been proven to be very important in the artificial generation of liver tissue.

Building on previous work that identified the Lgr5 class of stem cells, scientists from the United States and the Netherlands discovered that these particular cells not only aid in the regeneration of liver cells, but also become active once the liver is damaged. One particularly important feature of certain stem cells is that they act as a repair mechanism: that means they do not only reside in the target organ and produce a bunch of cells now and then, they also act accordingly when the organ asks for it. Such is the case with Lgr5 stem cells.

It is possible to grow Lgr5 stem cells in the lab. The American and Dutch scientists found a way to accelerate their growth, which is an important first step in the creation of artificial tissues. Thereafter, they found a way to transplant the cultured cells into a mouse model that has been specifically 'designed' to mimic liver disease. Interestingly, they found that injection of the Lgr5 stem cells resulted in liver repair and a modest relieve of the symptoms.
From stem cell in the lab to fully functional liver cell in the mouse. The arrows indicate the different genetic markers that either go up or down in activity. (source)
Obviously, when a therapy has been tried in mice, it does not mean it will work in humans, although it is a good first step. Next, the scientists will try to improve the percentage of stem cells that is converted to hepatocytes after transplantation. Hepatocytes are the actual liver cells, and are therefore needed to perform the tasks that the organ has. The scientists themselves believe that their method will eventually find its way into the clinic, but this is of course still years away.

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