[acb-diabetics] new way of switching on insulin cells

[Patricia LaFrance-Wolf]

Insulin-Releasing Switch Discovered


Johns Hopkins researchers believe they have uncovered the molecular switch
for the secretion of insulin, providing for the first time an explanation of
this process.... 







Advertisement 

In a new published report, the researchers say the work solves a longtime
mystery and may lead to better treatments for Type 2 diabetes, the most
common form of the disease. 

Mehboob Hussain, M.D., associate professor of pediatrics, medicine and
biological chemistry stated that, "Before our discovery, the mechanism
behind how exactly the insulin-producing beta cells in the islets of
Langerhans of the pancreas fail in Type 2 diabetes was incompletely
understood, making it difficult to design new and better therapies." "Our
research cracks open a decades-long mystery." 

After a meal, the pancreas produces insulin to move glucose from the blood
into cells for fuel. People with Type 2 diabetes either don't secrete enough
insulin or their cells are resistant to its effects. 

In a study designed to figure out more precisely how the pancreas releases
insulin, Hussain's group looked at how other cells in the body release
chemicals. One particular protein, Snapin, found in nerve cells, caught
their eye because it's used by nerve cells to release chemicals necessary
for cell communication. Snapin also is found in the insulin-secreting
pancreatic beta cells. 

To test the role of Snapin, researchers engineered a change to the Snapin
gene in mice to keep Snapin permanently "on" in the pancreas. Researchers
removed the pancreas cells and grew them in a dish for a day, then added
glucose to the cells and took samples to measure how much insulin was
released. 

When the scientists compared that measurement to what was released by
pancreas cells in normal mice, they found that normal mice released about
2.8 billionths of a gram of insulin per cell, whereas the cells from
"Snapin-on" mice released 7.3 billionths of a gram of insulin per cell -
about three times the normal amount. 

"We were surprised to find that the Snapin-on mice didn't have more or
bigger pancreas cells, they just made more insulin naturally," says Hussain.
"This means all our insulin-secreting cells have this amazing reserve of
insulin that we didn't really know existed and a switch that controls it." 

To see if permanently turning off Snapin would reduce insulin release and
further demonstrate that Snapin controls the process, the researchers first
grew normal mouse pancreas cells in a dish, and treated them with a chemical
that stopped them from making the Snapin protein. They again bathed the
cells in glucose and measured how much insulin was released by the cells.
Normal cells released 5.8 billionths of a gram of insulin, whereas cells
with no Snapin only released 1.1 billionths of a gram of insulin - about 80
percent less. 

"These results convinced us that Snapin is indeed the switch that releases
insulin from the pancreas," says Hussain.

Cell Metabolism online March 1, 2011

 


 
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