The Molecular Mechanism Of LIMK1/Cofilin Regulation The Pathological Changes Of Dendritic Spines In The Process Of Brain Development In APP/PS1 Mice

Alzheimer’s disease, the most common form of dementia, currently has no effective treatment. The clinical manifestations of the Alzhermer’s disease are the progressive decline of cognitive function and the short-term memory impairment. The primary pathological changes are those such as senile plaques formed by β-amyloid protein deposition in neuronal outside, neurofibrillary tangle in the neuron, and the loss of neurons and synapsis. Synapsis is the important structure of information transmission between neurons. In the brain of the animal models and Parkinson’s patients, the synaptic loss is more closely related to cognitive impairment, which occurs earlier than that of SP, NFT and the loss of neurons. Therefore,synaptic dysfunction and loss are widely assumed to be the cellular mechanisms of cognitive impairment.The dendritic spine is the main structure in the formation of excitatory synapse. In the pathogenesis of AD,morphological and pathological alterations of dendritic spines are closely related to the loss and dysfunction of synapsis. Preliminary findings indicated that Aβ depositon in the brain of APP/PS1 mice could result in the significant decrease in the density of dendritic spine in hippocampal pyramidal cells, and this change was age-dependent. Yet, it is not clear as to the the cellular and molecular mechanisms of morphological and pathologic changes of dendritic spines caused by the overproduction of Aβ. Thus, we conducted the experiments on the basis of preliminary investigations. The methods of morphological and molecular biological techniques with immunofluorescence, Western blot and RT-PCR were employed to systematically test the expression of Cofilin and LIMK1 in the dendritic spine of hippocampal pyramidal cells during the course of APP/PS1 mice development. These proteins could regulate and control the pathological changes of dendritic spines. The purpose was to finally clarify the phenomena that the molecular mechanisms of age-dependent pathologic changes of dendritic spines which was the results from overproduction of Aβ in the pathogenesis of AD.Results:(1) Compared with wild-type mice, APP/PS1 mice aged three months, nine months and one year had significantly higher levels of pCofilin protein(P<0.01) in the hippocampal CA1 region and brain by the test of immunofluorescence and Western blot. While the level of pCofilin protein in six-month micedecreased slightly(P<0.05), which required further verification.(2) Compared with wild-type mice, APP/PS1 mice aged three months, nine months and one year had higher levels of p LIMK1(P<0.01) by the test of immunofluorescence in the hippocampal CA1 region. The expresson of this protein was mice decreased slightly in six-moth mice, and this diferrenc did not reach statistical significance(P>0.05). The interesting fact was that it’s similar with the pattern of expression of pCofilin. It suggested that age of six months might be the turning point in the process of brain aging in APP/PS1 mice. It remains to be further confirmed. The levels of pLIMK1 by the test of Western blot were not consistent with the results by the test of immunofluorescence. It might be related to the difference in the measuring parts.(3) The age-dependent rise in levels of Cofilin phosphorylation would occur during the brain development of both wild-type and AD-type mice, revealing that there was a close relationship between the tendency of Cofilin phosphorylation and pathologic changes of dendritic spines.With the summary of the above results, it showed that phosphorylation of LIMK1(activation) and phosphorylation of Cofilin(inactivation) were involved in the regulation of pathological changes of dendritic spines in hippocampal neurons during the development of APP/PS1 mice’s brain. The PCofilin is likely to be the new target linking senile and the molecular mechanisms of AD. These findings provide valuable morphological basis for understanding the cause of cognitive impairment in AD patients. It also provides valuable reference for the AD drug development based on dendritic spines or Cofilin.