When they harvested the brain tissue of the mice two months later (at 6 months), the researchers discovered that both variants of Hsp27 interacted with tau. However, only the wild-type Hsp27 cleared tau from the brain, reducing neuronal tau levels. The genetically-altered Hsp27 was associated with increased tau levels.
In another experiment, the researchers examined the physiological effects of Hsp27 overexpression in the brain. Both variants of Hsp27 were administered to 2-month-old Alzheimer's mice. At 4 months, their brain tissue was examined to evaluate whether Hsp27 improved any neuron deficiencies brought on by the accumulation of abnormal tau over the previous 2-month period. The researchers found that overexpression of wild-type Hsp27 succeeded in rescuing the mice from neuron damage. The genetically altered (perpetually activated) Hsp27 did not.
The researchers concluded that Hsp27 must be able to fluctuate between activated and de-activated states to succeed at clearing abnormal tau, thus preventing the protein from sticking together and building up excessively in the brain. In addition, Hsp27 can only be effective in helping maintain healthy tau turnover if the chaperone protein interacts with tau while it's still soluble -- before tau has developed into solid nerve-killing tangles. The chaperone protein cannot disrupt already formed tau tangles.
"In some circumstances, the activated chaperone protein may help stabilize and recycle tau, restoring the protein so it can do its normal job of supporting nerve cell structure," Dr. Dickey said. "But when tau has become abnormally folded, activated Hsp27 may actually
|Contact: Anne DeLotto Baier|
University of South Florida (USF Health)