Spermine Alleviates Hippocampal Neuronal Aging by Targeting Tlr4 Receptors to Regulate Erk1/Mek5 Expression

Abstract

BackgroundCerebral ischemia can trigger vascular dementia (VaD), which is characterized by memory loss, cognitive deficits, and cerebrovascular damage and is the second most common cause of cognitive impairment. Toll-like receptor 4 (TLR4) plays a crucial role in various cerebrovascular diseases. Spermine (SPM) is a natural aliphatic polyvalent cationic amine, a kind of polyamine, which can participate in a variety of biological processes and play an important role in neurodegenerative diseases. The objective of this study was to investigate the improvement of cognitive function in VD rats by SPM and to explore its potential mechanisms in vivo and in vitro.MethodsIn this study, we investigated the in vivo and in vitro mechanisms of the ameliorative effect of SPM on VaD in SD rats, primary hippocampal neurons, C57 mice, and TLR4-/- mice. The VaD rat model was established by bilateral common carotid artery occlusion and treated with SPM for 30 days. Morris water maze was used to evaluate the protective effect of SPM on nerves. Hematoxylin-eosin (HE) and NeuN staining were used to observe the number and structure of neurons in CA1 region of rat hippocampus. The number of dendritic spines and the length of dendrites in hippocampal CA1 neurons were detected by Golgi cox staining. The morphology and structure of mitochondria and nuclei in CA1 region of rat hippocampus were detected by transmission electron microscopy. Cell senescence was detected by β-galactosidase staining. BRDU proliferation assay and MAP2 fluorescence assay were used to detect cell proliferation. The expression of aging markers p-21, p-53, γ-H2A.X, proliferation marker Ki67, TLR4, EphA2, p-MEK5, and p-ERK1 in neurons in hippocampal CA1 region of rats were detected by immunofluorescence and Western Blotting. Intracellular Ca2+ concentration was detected by calcium imaging.ResultThe results showed that SPM could significantly improve the spatial memory ability of VaD rats. The length and number of normal neurons in CA1 region of hippocampus of VaD rats were increased, and the morphology and structure of neurons were improved. Significantly improve the structure and morphology of mitochondria and nuclei. Calcium ion imaging showed that SPM significantly reduced Ca2+ concentration in primary hippocampal neurons, BRUD and MPA2 detection showed that SPM promoted western blot and immunofluorescence results showed that SPM could reduce senescence. The expression of p-21, p-53 and γ-H2A.X and the expression of TLR4, EphA2, p-MEK5 and p-ERK1 were significantly decreased.ConclusionIn summary, our results prove that the neuroprotective effect of SPM on VaD rats may be achieved through the regulation and regulation of TLR4/EphA2/MEK5/ERK1 pathway.

Note:
Funding declaration: This work was supported by Henan Province Outstanding Youth Science Fund Project (242300421025).

Conflict of Interests: All other authors declare they have no competing interests.

Ethical Approval: Animal research is carried out in strict accordance with the recommendations of the National Institutes of Health “Guidelines for the Care and Use of Experimental Animals,” and all protocols of animal experiments were approved by the Institutional Animal Care and Use Committee of Henan Xinxiang Medical University (Xinxiang, China).

Keywords: Vascular dementia, Spermine, TLR4, EphA2, ERK1, MEK5