| ObjectiveAlzheimer’s disease (AD), a kind of age-related neurodegenerative disease that is characterized with progressive worsening of memory and cognition, accounts for about 50%-70% of all cases of dementia and which is the most common type of dementia in China. The global incidence of AD is increased year by year as the ageing of population worldwide and in China. The typical neuropathological lesions include the formation of senile plaques resulted from accumulation of extracellular Aβ. the formation of neurofibrillary tangles resulted from intracellular hyperphosphorylated tau, neuron and synapse loss and dysfunction of cholinergic neurons. In recent years, emerging data have demonstrated that AD is fundamentally a metabolic disease which has close relationship with brain insulin signaling pathway injury. In light of the fact that features of AD overlap with both type 1 diabetes mellitus (DM) and T2DM, some researchers prefer to use the term "T3DM" or "brain diabetes" to refer to AD. Insulin and IGF-1 play a vital role in regulation of neuronal growth, survival and key process of learning ability and memory via activating insulin signaling pathways. The major molecular pathological lesion of brain insulin signaling pathways that occurs in AD is close associated with a number of abnormal expressing and processing of key proteins. Thus, the growing progression of molecular biology provides useful tools to reveal the mechanisms of protein synthesis, protein transportation and protein accumulation in brain.The present study was designed to observe and quantify the effects of curcumin on expression of relevant molecules of insulin signaling pathways in 9-month-old APPswe/PS1dE9 double transgenic mice, and compare the observation data with that of 6-month-old transgenic mice by contrastive analysis, further investigate the neuroprotective mechanism of curcumin on different ages, objectively evaluate the therapeutic effects of curcumin and provide theoretical evidence for TCM prevention and treatment of AD.Materials and methods1. The experimental subjects were 3-month-old APPswe/PS1dE9 double transgenic mice and wild type C57BL/6J littermates with the same background.60 transgenic mice were randomly divided into five groups, with 12 in each group. The gavage administration were respectively put on each group:model group (b, VEH); rosiglitazone maleate group (c, RSG), dosage of RSG was 10mg/(kg·d); high dose curcumin group (d, HDC), medium dose curcumin group (e, MDC) and low dose curcumin group (f, LDC), dosage of curcumin respectively was 400mg/(kg·d),200mg/(kg·d) and 100mg/(kg·d).12 wild type C57/BL6J littermates were used for the normal control group (a, CON). The successive administration was carried out on mice for 6 months and one time every day.2. Using Morris water maze to test the effects of curcumin on spatial learning and memory of APPswe/PS1dE9 double transgenic mice, and further evaluate the therapeutic effects on cognitive function.3. To evaluate the regulation effects of curcumin on insulin signaling pathways, we investigate the distribution and expression of relevant proteins in upstream and downstream of insulin signaling pathways including InR, IRS-1, p-IRS-1, PI3K, p-PI3K, Akt and p-Akt by immunohistochemistry and western blot methods.Results1. Curcumin improves spatial learning ability and memory of APPswe/PS1dE9 double transgemc miceIn place navigation test, swimming distance of all six groups of mice are shortened along with the training time increase. Compared with the normal control group, swimming distance of mice in VEH group increased significantly (p<0.05). While compared to the VEH group, swimming distance of mice in all the treated groups are decreased, and on the 5th day, which decrease are significant (p<0.05). In spatial probe test, residence time in target quadrant of the VEH group mice is significant shortened than the normal control group (p<0.05), in comparison with the VEH group, residence time in target quadrant of other groups are significant increase (p<0.05).2. Curcumin regulates and improves the expression level of key molecules in insulin signaling pathwaysThe results of immunohistochemistry:In contrast with the CON group, there is a significant increase on the number of positive cells of InR and IRS-1 in hippocampal CA1 area of the VEH group mice (p<0.05 or p<0.01). On the contrary, the number of positive cells of p-IRS-1, PI3K, p-PI3K, Akt and p-Akt are decreased significantly (p<0.05 or p<0.01). Compared to the VEH group, InR and IRS-1 positive cells in hippocampal CA1 area of the RSG group and all the curcumin treated groups mice have a significant decrease (p<0.05 or p<0.01), and p-IRS-1, PI3K, p-PI3K, Akt and p-Akt positive cells increased significantly (p<0.05 or/?<0.01).The results of western blot:The expression levels of each protein are well consistent with results of immunohistochemistry.ConclusionCurcumin exerts neuroprotective effect by improving insulin signaling pathways, regulating brain energy metabolism and further ameliorating cognitive functions and memory. |
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