| Alzheimer’s disease (AD) is characterized by progressive memory and cognitive impairment in neurodegenerative disease. AD represents a huge socioeconomic problem that affects the health of human life, requires better diagnostic tools, management and effective therapies to ease the burden of this disease. One of the characteristic pathological markers of AD brains is senile plaques. Neprilysin (NEP), a86kda protein, also knwon as neutral endopeptidase or enkephalin enzyme, is composed of750amino acids. NEP is a membrane-bound glycoprotein, including a short N-terminal intercellular domain, a transmembrane domain and ectodomain containing HExxH of Zinc-binding catalytic motif, which degrades hydrophobic amino acid residues of extracellular Aβ oligomer(<5kda, such as Aβ40and Aβ42). NEP expresses in many tissues including intestinal, kidney, neutrophils, thymus cells, lung, prostate, testicles and brain tissue. NEP is abundant in the brush border membrane of renal tubular epithelial cells. In the human brains, NEP mainly exists in the membranes of neuron, synapse, pre-and postsynapses, and it is widely distributed in nigra-striatal pathway and the regions of Aβ deposition and susceptibility (such as the hippocampus). NEP degradates both monomer and polymer of Aβ. Experimental results indicate the changes in structure and function of the NEP is closely related to Aβ deposition.The aim of present study is to explore the relationship between the NEP regulation and the development of Alzheimer’s disease. Due to the limitation of sampling of human brain, the data obtained was generally the late stage of AD development. So, it is difficult to observe the earlier stages and the developing process. Thus, the AD mimic, APP/PS1double transgenic mouse model and normal wild type mice was used in our studies. Wildtyped C57mice and different age of transgenic mice were divided into four groups:3months,6months,9months,12months and WT control. Morris water maze performance was used to evaluate the cognitive disorder during AD development. After the water maze performance, all mice were sacrificed. The brains were taken out and sliced to detect Aβ depositon. Immunohistochemical/immunofluorescence staining was executed to detect subcellular NEP profile and the relationship with Aβ deposition. The brain homogenates were used to extract subcellular fractions inculing membrane and cytoplasm. The NEP activity was measured using above-mentioned homogenate extracts. Experimental results show that senile plaques developed after three months in the transgenic mice. The plaque is getting more and more with the growth of mice. However, there is no cognitive deficiency in3and6month’s mice from the data of water maze performance. The learning and memory disorder, the typical aspect of AD, was observed only in the age of9months. NEP activity test indicated that NEP increased at first and then decreased with a peak at6month.The results from this experiment suggested that NEP is a key factor that interfering Aβ-induced cognitive disorders and then slowing down AD development. Compensatory increase of NEP protein and activity might inhibit Aβ accumulation in the Aβ mice. While as the mice getting older, more and more AP produced and deposited which in turn inhibited NEP activity and induced cell lose. The decompensation of NEP regulation will induce a burden of Aβ deposition. Further studies are underway to address the mechanism in details... |
PDF Full Text Request