Naringenin Improve Cognition In Model Rats With Alzheimer’s Disease By Inhibiting MTOR/p70S6K/IRS-1 Signaling Pathway

Objective:This study was designed to investigate the role of mTOR/p70S6K/IRS-1 signaling pathway in AD pathogenesis, and to study whether naringenin can improve cognitive in model rats with AD through mTOR/p70S6K/IRS-1 signaling pathway, so as to provide new ideas for the treatment of AD.Methods:A total of 90 male adult SD rats were randomly divided into six groups of fifteen animals each, vehicle treated group (control group), STZ-induced and vehicle treated group (model group), STZ-induced and naringenin (100,50, or 25 mg/kg/d) treated groups and STZ-induced and rosiglitazone (5 mg/kg/d) treated group. STZ (3 mg/kg) was ICV injected twice within an interval of 48h to induce dementia model. Control rats were injected with the same volume of saline instead of STZ. Naringenin, rosiglitazone or sodium carboxymethylcellulose (NaCMC) was orally administered for five weeks by gavage immediately after the first STZ injection. Thirty-six days after STZ injection, spatial learning and memory of rats was determined by Morris water maze test. Deposition of Aβ was detected by Thioflavin S staining. The protein expression of BACE1, IRS-1, p-IRS-1Ser636, mTOR, p-mTORSer2448, p70S6K and p-p70S6KThr389 were measured by Western blot and immunohistochemistry. The mRNA expression of IRS-1, BACE1, ADAM10 and NEP were detected by RT-PCR.Results:(1) Morris water maze results. Compared with that in control group, the escape latency of model group and naringenin (25 mg/kg/d) treated group was significantly prolonged (P<0.01); number of crossings across the target and time spent in the target quadrant of model group and naringenin (25 mg/kg/d) treated group were significantly reduced (P<0.01). But naringenin (100 and 50 mg/kg/d) treated group and rosiglitazone treated group showed a marked improvement in escape latency, number of crossings across the target and time spent in the target quadrant (P<0.0l).(2) The deposition of Aβ detected by Thioflavin S staining in model group and naringenin (25 mg/kg/d) treated group were obviously more than those in control group. On the contrary, compared with those in model group and naringenin (25 mg/kg/d) treated group, the deposition of Aβ in naringenin (100 and 50 mg/kg/d) treated group and rosiglitazone treated group were significantly decreased.(3) Western blot and immunohistochemistry demonstrated that, compared with those in control group, the protein expression of BACE1 (P<0.05), the ratio of p-p70S6KThr389/p70S6K (P<0.01) and the ratio of p-IRS-1Ser636/IRS-1(P<0.01) in model group and naringenin (25 mg/kg/d) treated group were significantly escalated. Instead, naringenin (100 and 50 mg/kg/d) treated group and rosiglitazone treated group showed a notable improvement in all of the three signs (P<0.01). This suggests that there is excessive activation of mTOR/p70S6K/IRS-1 signaling pathway in model rats with AD. Moreover, naringenin (100 and 50 mg/kg/d) and rosiglitazone can inhibit increased activation of mTOR/p70S6K/IRS-1 signaling pathway.(4) Compared with that in control group, the mRNA expression of BACE1 measured by RT-PCR in model group and naringenin (25 mg/kg/d) treated group was obviously increased (P<0.01). Moreover, naringenin (100 and 50 mg/kg/d) treated group and rosiglitazone treated group showed a distinguished improvement in BACE1mRNA. This prompts that naringenin (100 and 50 mg/kg/d) and rosiglitazone can inhibit the mRNA expression of BACE1. There were no significant differences in the mRNA expression of ADAM 10 and NEP among six groups.Conclusion:(1) The increased activation of mTOR/P70S6K/IRS-1 signaling pathway may play important roles in AD pathogenesis.(2) Naringenin can ameliorate cognition in model rats with AD by inhibiting mTOR/P70S6K/IRS-1 signaling pathway.