In 1998, the team published a paper on work that Hirotsune did in the Wynshaw-Boris laboratory, in which he produced a mouse with the same mutation that displayed defective brain development. They have continued to collaborate on understanding the mechanism of action of LIS1 since Hirotsune set up his independent laboratory in Japan.
The current research found, using these mice, that the protein calpain degrades the LIS1 protein to less than half its normal levels near the surface of the cells. The team then used a specific small-molecule protease inhibitor of calpain in these mice. At a cellular level, the protease inhibitors enabled LIS1 protein to be expressed at near-normal levels.
The team then gave daily injections of a calpain inhibitor to pregnant mice whose fetuses had the mouse-model of this defect. The resulting offspring had more normal brains and showed no sign of mental retardation.
"This study is really a proof-of-principle not only for treating complex developmental brain disorders, but also for any disorder with reduced protein levels where proteases normally play some role in breaking down that protein," Hirotsune said. "This will be much more difficult to apply to humans, because of the safety issues involved, but it could lead to new therapies that might be effective for a wide range of developmental disorders."
Scientists have known that loss of one of the two copies of the human form of the gene, known as LIS1, prevents immature nerve cells from migrating from deep in the brain up to the surface of the emerging cerebral cortex.
As a result, these immature cells stall at mid-point in their migration, causing the brain to develop a smooth surface, devoid of the convoluted nerve tissue that enables humans to think and function. The resulting disease, lissencephaly, varies in severity, but always leads to
|Contact: Kristen Bole|
University of California - San Francisco