Trideoxycytidine Diphosphate Promotes Neural Stem Cell Proliferation and Neurogenesis in Mice

Background

Food-derived nucleic acids exhibit various biological activities and may act as nutrients. Oral ingestion of the nucleic acid fraction (NAF) of salmon milt extract hydrolysates enhances cognitive function in mice, although their active ingredients have not yet been identified, and detailed mechanisms of action are unknown.

Objectives

To identify active ingredients enhancing cognitive function contained in the NAF and its possible underlying mechanism.

Methods

Because the NAF is rich in trinucleotides, proliferative effects of all 64 types of trideoxyribonucleotides were examined in primary cultured neural stem cells (pcNSCs). The active trideoxyribonucleotide was administered intrahippocampally (5 μg) in 7-wk-old male Institute of Cancer Research (ICR) mice (n = 4–6) or orally (1 mg) 3 times a week for 2 wk in 6-wk-old male ICR mice (n = 5), followed by evaluating neurogenesis and cognitive function by immunohistochemical analysis and spatial recognition test, respectively. The mechanism of action was examined by proteomic analysis of trideoxyribonucleotide-treated pcNSCs using the software DAVID, followed by western blot analysis in pcNSCs and hippocampus.

Results

Among all trideoxyribonucleotides, only trideoxycytidine diphosphate (CCC) significantly promoted NSC proliferation (P < 0.05), whereas exposure to putative metabolites of CCC did not affect the proliferation. Intrahippocampal or oral CCC administration in mice increased doublecortin-positive cells in hippocampus (P < 0.05) and enhanced spatial memory (P < 0.05). Proteomic analysis revealed significant alterations in expression of PI3K-Akt signaling-related proteins, including eEF1A2 (P < 0.05). Intrahippocampal CCC administration significantly increased the Akt phosphorylation (p-Akt/Akt) (P < 0.05), which was abolished with the PI3K-Akt inhibitor, LY294002 (P < 0.05). CCC exposure increased p-Akt/Akt (P < 0.05) in pcNSCs, whereas LY294002 or small interfering RNA for eef1a2 suppressed CCC-induced increase in p-Akt/Akt (P < 0.05) and cell proliferation (P < 0.05).

Conclusions

A simple food-derived structural molecule CCC promotes NSC proliferation through eEF1A2/PI3K-Akt signaling pathway, thereby enhancing neurogenesis.