Porcine placental extract facilitates memory and learning in aged mice

Abstract

Aging induces a decline in both memory and learning ability without predisposing an individual to diseases of the central nervous system, such as dementia. This decline can have a variety of adverse effects on daily life, and it can also gradually affect the individual and the people they are surrounded by. Since recent evidence indicated that placental extract has effects on brain function such as memory, we hypothesized that placental extract could ameliorate the age-associated reduction in cognitive function in aging. Here, we investigated the effect of new modified porcine placental extract (SD-F) on memory ability in aged mice at both the behavioral and molecular levels. Our results revealed that SD-F significantly enhanced memory ability in the object recognition and object location tasks in a dose-dependent manner in aged mice relative to controls. The numbers of Nissl-positive cells in the hippocampal cornu ammonis 3 (CA3) and dentate gyrus (DG) regions were increased in SD-F-treated aged mice relative to controls. RNA-seq analysis of the hippocampus of aged mice identified 542 differentially expressed genes, of which 216 were up-regulated and 326 were down-regulated in SD-F-treated mice relative to controls. Of the 216 up-regulated genes, we identified four characteristic genes directly related to memory, including early growth response protein 1 (Egr1), growth arrest and DNA-damage-inducible, beta (Gadd45b), NGFI-A binding protein 2 (Nab2), and vascular endothelial growth factor a (Vegfa). These results suggest that the efficacy of SD-F involves upregulation of these genes.

Keywords: RNA‐seq; aging; hippocampus; memory; porcine placental extract.

Figure 1

Experimental protocol and effect of SD‐F on food intake and body weight in aged mice. Schematic drawing of experimental protocol. After normal diet for one week, mice were divided into four groups (n = 9 per group), and then SD‐F (500, 1,000, or 5,000 mg/kg) or control (normal diet) was provided ad libitum for 4 weeks. Four weeks after ingestion, behavioral tests were carried out (a). Effect of SD‐F on food intake (b) and body weight (c). (closed circle) control group; (closed triangle) 500 mg/kg SD‐F‐treated group; (closed square) 1,000 mg/kg treated SD‐F group; (crosses) 5,000 mg/kg SD‐F‐treated group. There were no significant differences among the groups. Results represent means ± SEM

Figure 2

Effect of SD‐F in the object recognition test (ORT) and object location test (OLT) in aged mice. Four weeks after ingestion of SD‐F, behavioral tests were carried out. Result of the ORT (a). Preference index for the new object in the training and test sessions is shown. Result of the OLT. Preference index for the new object location in the training and test sessions is shown (b). Results represent means ± SEM (^a p < .05, ^b p < .001 vs. 0 mg/kg SD‐F‐treated group)

Figure 3

Representative photomicrographs displaying Nissl staining of hippocampal CA1, CA3, and dentate gyrus (DG) subfields of control and SD‐F‐treated aged mice. Nissl‐positive cells were visualized using cresyl violet staining. There was no significant difference between the groups. Results represent means ± SEM (control group: n = 6, 1,000 mg/kg SD‐F‐treated group: n = 6). Scale bars: Hippocampus = 1 mm; CA1, CA3, and DG = 0.2 mm (a). Cell numbers in the CA1, CA3, and DG subregions in aged mice treated with or without SD‐F (b)

Figure 4

Genes involved in memory function in the hippocampus of aged mice treated with SD‐F. Volcano plot highlighting differentially expressed genes (a). Up‐regulated and down‐regulated genes are shown in green and red, respectively. Pie chart showing the percentage of genes up‐ and down‐regulated in control versus SD‐F (1,000 mg/kg) groups. Of the 542 differentially expressed genes, 216 were up‐regulated and 326 were down‐regulated (b). Heatmap of differentially expressed genes in control versus SD‐F (1,000 mg/kg) groups. High expression is shown by the red color spectrum, and low expression is shown by the green color spectrum (c). Two gene networks related to neurological function are shown. The networks are shown as pictures for genes and lines for biological relationship. Solid lines represent a direct interaction, and dotted lines represent indirect interactions between the genes. The shapes of genes indicate their molecular functions. Up‐regulated and down‐regulated genes are shown in red and green colors, respectively. Data are shown as means ± SEM (control group: n = 3, 1,000 mg/kg SD‐F‐treated group: n = 3) (d, e)

Figure 5

qPCR analysis. Relative expression of early growth response protein 1 (Egr1), growth arrest and DNA‐damage‐inducible, beta (Gadd45b), kallikrein‐8 (Klk8), NGFI‐A binding protein 2 (Nab2), nerve growth factor (Ngf), ryanodine receptor 3 (Ryr3), and vascular endothelial growth factor (Vegfa) in the hippocampus of aged mice treated with and without SD‐F (1,000 mg/kg). All data (mean ± SD, n = 9) were normalized to GAPDH expression. ^a p < .01, ^b p < .001 versus control group