Endogenous hippocampal leptin in mediating strong potentiation by Astaxanthin supplementation for mild exercise-enhanced neurogenesis and memory functions

Although exercise and dietary interventions on cognitive function have been investigated, synergistic interactions remain unclear. As tested on hippocampus-dependent functions, mild exercise (ME) or astaxanthin (AX), a naturally-occurring antioxidant and cognitive enhancer, each boost the hippocampus-related memory and neurogenesis. Here we show that leptin (LEP) is required for the synergistic enhancement of hippocampal function by a combination of ME and AX. In C57BL/6J mice, ME or AX alone enhanced spatial memory and neurogenesis, but the enhancement was greater with their combination. DNA microarray analysis showed that the up-regulation of the Lep gene by ME alone was further elevated when combined with AX. The combined interventions synergistically increased hippocampal LEP protein, which was positively correlated with memory enhancement. In LEP-deficient mice, the combined interventions did not enhance memory compared to ME alone, leading us to suggest that the brain-derived LEP has an essential role for the synergistic effect on hippocampal functions. Male C57BL/6J mice (11-weeks-old) were obtained from SLC (Shizuoka, Japan). Based on the ventilatory threshold (VT), we determined the intensity of treadmill running for the WT mice. Their running speed at VT value was found to be 12.29 m/min and 8.66 m/min for the WT mice. AX diets were made by mixing the MF powder with either AX or a placebo powder (AstaREAL-20F based on 2% content of AX derived from Haematococcus pluvialis; Fuji Chemical Industry, Japan) at concentrations of 0.5% (wt:wt). For DNA microarray and sqRT-PCR, the total RNA was extracted from finely powdered hippocampal tissue of WT mice (n=8/group- SED, ME, AX, and AX+ME) using the RNeasy Mini Kit (QIAGEN) according to the manufacturer’s protocol. DNA microarray was performed using A SurePrint G3 Mouse GE 8X60K Microarray Kit (Agilent Technologies). All samples were labeled with eitehr Cy3 (4 samples) or Cy5 (4 samples). The 1 chip conatined all the 8 samples.