Researchers identify age-dependent beta cell proliferation pathway

Oct 13 2011

As a person ages, the ability of their beta cells to divide and make new beta cells declines. By the time children reach the age of 10 to 12 years, the ability of their insulin-producing cells to replicate greatly diminishes. If these cells, called beta cells, are destroyed-as they are in type 1 diabetes-treatment with the hormone insulin becomes essential to regulate blood glucose levels and get energy from food. Now, longtime JDRF-funded researchers at Stanford University have identified a pathway responsible for this age-related decline, and have shown that they can tweak it to get older beta cells to act young again-and start dividing.

The work, to appear in the October12 issue of Nature, provides the most complete picture to date of the molecular and biochemical mechanisms that bring beta cell regeneration to a near halt as beta cells age. These findings may help pave a path for developing strategies to restore beta cell number to treat both type 1 and type 2 diabetes.

In their work, the researchers, led by Seung Kim, M.D., Ph.D., of Stanford University, found that a protein called PDGF, or platelet derived growth factor, and its receptor send beta cells signals to start dividing via an intricate pathway that controls the levels of two proteins in the beta cell nucleus, where cell division occurs. Working with young mice, Dr. Kim and his team found that PDGF binds to its receptor on the beta cell's surface and controls the level of these regulating proteins allowing cells to divide. However, in older mice, they discovered that beta cells lose PDGF receptors, and that this age-related change prevents beta cells from dividing. Dr. Kim and his colleagues further found that by artificially increasing the number of PDGF receptors, they can restore the ability of the beta cell to divide and generate new cells.

The researchers also show that this age-dependent beta cell proliferation pathway is also present in human beta cells. Similar to the findings with mice beta cells, the researchers found that juvenile human islet beta cells proliferate in response to PDGF, but adult human islet beta cells do not due to a reduced level of PDGF receptors.

In the past, researchers have used other techniques to trigger older beta cells to start dividing, but they have been met with challenging results, explains Dr. Kim, who is also a Howard Hughes Medical Institute investigator. "You can get these cells to grow but they will literally lose their specific identity as a beta cell," he says. "They will either stop making insulin, or they'll grow just fine but they will grow uncontrollably or into other cell types."

But with the advent of better genetic tools and the completion of the human genome project, that era has come to pass, he explains. "With these advanced technologies, we are now able to get a comprehensive view-at the genetic level-of the changes beta cells undergo as they age, and we can track these changes and study them in a systematic way," he adds. "By understanding what genes are turned on and off in a young beta cell, we can try to recreate that genetic environment in older beta cells such that they divide in a desirable, controlled manner."

By better understanding the mechanisms that control and govern pancreatic β-cell proliferation, researchers could transform treatments for diabetes. The cascade leading from PDGF binding to its receptor on the beta cell's surface to changes in protein levels within the nucleus could inspire scientists with new ideas on how to discover new drugs to safely promote beta cell regeneration to replace those lost in diabetes.

"A major goal of JDRF's regeneration program is to find ways to preserve and restore functional beta cells as a cure for type 1 diabetes. One of the challenges is that adult beta cells do not readily replicate, and these new findings provide key insight on how the body regulates beta cell growth and replication," says Patricia Kilian, Ph.D., JDRF's scientific program director of regeneration research. "Based on these key scientific insights, we hope the new findings will help enable the discovery of safe therapies to promote beta cell regeneration."

Source: Juvenile Diabetes Research Foundation International