Memantine improves spatial learning and memory impairments by regulating NGF signaling in APP/PS1 transgenic mice

- MEM treatment increased endogenous NGF level in APP/PS1 mice.
- NGF/TrkA signaling is activated after MEM treatment, accompanied with the inhibition of p75NTR signaling.
- Our research revealed a new NGF-related mechanism of MEM for improving cognitive deficits and amyloidosis.
- The new mechanism suggests that NGF signaling is a potential target of MEM treatment for AD therapy.

Memantine (MEM) is used for improving the cognitive impairments of the patients suffering from Alzheimer's disease (AD) by multiple neuroprotective mechanisms. However, it is still not clear whether nerve growth factor (NGF) signaling is involved in the mechanisms of MEM. The present study investigated the neuroprotective effects of MEM treatment on the cognitive performance and amyloidosis in APP/PS1 transgenic mice, and disclosed the NGF-related mechanism of MEM. We found that MEM treatment improved the cognitive performance by decreasing the escape latency and path length in the navigation test, by shortening the duration in target quadrant and reducing the frequency to pass through the target in probe trial, and by prolonging the latency and decreasing the frequencies of entering the dark compartment in passive avoidance test. The over-expressions of Aβ(1-42) and amyloid precursor protein (APP) were also decreased in the brains of APP/PS1 mice. Interestingly, MEM treatment improved the decreased NGF levels in APP/PS1 mice. Furthermore, NGF/TrkA signaling was activated by increasing the phosphorylation levels of tyrosine kinase (TrkA), proto-oncogene serine/threonine-protein kinase, Raf1 (c-Raf), extracellular regulated protein kinases (ERK)1/2 and cAMP-response element binding protein (CREB) after MEM treatment. Simultaneously, MEM also inhibited NGF/p75NTR signaling via decreasing the cleavage substrate of p75NTR, increasing the JNK2 phosphorylation and decreasing the levels of p53 and cleaved-caspase 3. Therefore, the dual-regulation on NGF signaling was attributed to the improvements of cognitive deficits and Aβ depositions in APP/PS1 mice. In conclusion, MEM treatment activated the NGF/TrkA signaling, and inhibited the p75NTR signaling in APP/PS1 mice to ameliorate the behavioral deficits and amyloidosis, indicating that NGF signaling was a new potential target of MEM treatment for AD therapy.