Trans-cinnamaldehyde improves neuroinflammation-mediated NMDA receptor dysfunction and memory deficits through blocking NF-κB pathway in presenilin1/2 conditional double knockout mice

A chronic neuroinflammatory response has been considered as a critical pathogenesis promoting neurodegenerative progression in Alzheimer's disease (AD). During neuroinflammatory process, microglia are excessively activated and simultaneously release numerous pro-inflammatory mediators that cause synaptic dysfunction in the forebrain prior to neuronal degeneration and memory deficits in AD. Thus, prevention of neuroinflammation-mediated synaptic dysfunction may be a potential therapeutic approach against neurodegenerative disorders. Trans-cinnamaldehyde (TCA) is a primary bioactive component derived from the stem bark of Cinnamomum cassia, and it possesses potent anti-inflammatory and neuroprotective activities in in vivo and in vitro experiments. However, the in-depth molecular mechanisms of TCA underlying anti-neuroinflammatory and neuroprotective effects on memory deficits in AD are still unclear. The presenilin 1 and 2 conditional double knockout (PS cDKO) mice exhibit AD-like phenotypes including obvious neuroinflammatory responses and synaptic dysfunction and memory deficits. Here, PS cDKO were used to evaluate the potential neuroprotective effects of TCA against neuroinflammation-mediated dementia by performing behavioral tests, electrophysiological recordings and molecular biology analyses. We observed that TCA treatment reversed abnormal expression of synaptic proteins and tau hyperphosphorylation in the hippocampus and prefrontal cortex of PS cDKO mice. TCA treatment also ameliorated NMDA receptor (NMDAR) dysfunction including impaired NMDAR-mediated responses and long-term potentiation (LTP) induction in the hippocampus of PS cDKO mice. Moreover, TCA possesses an ability to suppress neuroinflammatory responses by diminishing microglial activation and levels of pro-inflammatory mediators in the hippocampus and prefrontal cortex of PS cDKO mice. Importantly, improving NMDAR dysfunction and memory deficits of PS cDKO mice was due to the inhibition of neuroinflammatory responses through TCA's interruptive effect on the nuclear factor kappa B (NF-κB) signaling pathway. Therefore, TCA may be a potential anti-neuroinflammatory agent for deterring neurodegenerative progression of AD.