The way the liver renews itself may be simpler than what scientists had been assuming.
A new study, appearing in the April 13 issue of The Journal of Biological Chemistry, provides new information on the inner workings of cells from regenerating livers that could significantly affect the way physicians make livers regrow in patients with liver diseases such as cirrhosis, hepatitis, or cancer.
"The human liver is one of the few organs in the body that can regenerate from as little as 25 percent of its tissue," says Seth Karp, assistant professor of surgery at Harvard Medical School, Boston, and main author of the study. "It is not known how the liver does it, but our results provide some details of what makes the liver so unique."
Although organ regeneration has been observed in many animals, the details of how it happens at the cellular level are still not completely understood. So far, scientists have shown that cells that participate in tissue regeneration behave as if they were part of a growing organ in an embryo. In other words, the cells act as if the liver is growing, as do other organs in a developing embryo.
Many of the proteins that induce organ regeneration have been identified and scientists are now trying to make organs regrow by stimulating these proteins. Regrowing livers this way would be especially useful for patients whose livers are so damaged , say, by a tumor that has spread to most of the liver , that a large part would be removed. Unless such patients receive the right amount of liver transplant from an organ donor, they do not always survive. Quickly stimulating the growth of the remaining portion of their liver could be their only chance of survival.
To investigate how the liver regenerates, Karp and his colleagues set out to determine which proteins are involved in the regenerating cells. The scientists were also interested in testing whether regenerating cells behave like embryonic ones, as is commonly assumed for other organs. New processes may explain why the liver is so uniquely capable of renewal and repair after injury, the scientists thought.
Karp's team considered two samples of mice. The first consisted of embryonic mice at various stages of development while the second was composed of adult mice to which two-thirds of their liver were removed. Using techniques such as DNA microarrays , which determine which genes are active in a cells , and software programs that analyze the collected information, the scientists listed all the proteins that help the cells grow and proliferate in both samples.