The effect of soybean isoflavone on the dysregulation of NMDA receptor signaling pathway induced by β-amyloid peptides 1-42 in rats

Abstract

Synaptic damage is the key factor of cognitive impairment. The purpose of this study was to understand the effect of soybean isoflavone (SIF) on synaptic damage induced by β-amyloid peptide 1-42 (Aβ1-42) in rats. Adult male Wistar rats were randomly divided into control, Aβ1-42, SIF, and SIF + Aβ1-42 (SIF pretreatment) groups according to body weight. SIF was treated orally by gavage in SIF and SIF + Aβ1-42 groups. After 14 days pretreatment with SIF or vehicle, Aβ1-42 was injected into the lateral cerebral ventricle of rats in Aβ1-42 and SIF + Aβ1-42 groups using miniosmotic pump. The level of Aβ1-42 and the expression of N-methyl-D-aspartic-acid receptor (NMDAR) were observed by immunohistochemistry. Reverse transcriptase polymerase chain reaction was used to detect the mRNA levels of NMDAR, calmodulin (CaM), calcium/CaM-dependent protein kinase II (CaMKII), cAMP-response element binding protein (CREB), and brain-derived neurotrophic factor (BDNF). The results showed that Aβ1-42 down-regulated mRNA and protein expression of the NR1 and NR2B subunits of NMDAR, SIF pretreatment could reverse these changes. The mRNA expression of CaM, CaMKII, CREB, and BDNF were down-regulated by Aβ1-42, but they were all regulated by SIF pretreatment. These results suggest that SIF pretreatment could antagonize the neuron damage in rats induced by Aβ1-42, and its mechanism might be associated with the NMDA receptor and CaM/CaMKII/CREB/BDNF signaling pathway, which are the synaptic plasticity-related molecules.

Fig. 1

The relative protein expression of Aβ1-42 in the rat brain tissue. After 14 days pretreatment with SIF or vehicle, a surgery was performed to inject Aβ1-42 (20 μg/200 μl) into the lateral cerebral ventricle in the rats of Aβ1-42 and SIF + Aβ1-42 groups using the miniosmotic pump every day, whereas the rats in control and SIF groups were treated with equivalent amount of normal saline. The relative protein expression of Aβ1-42 was measured by immunohistochemistry (n = 3 rats; four sections per rat). All the data were shown as mean ± SE. *P < 0.05 compared with Control group; ^† P < 0.05 compared with Aβ1-42 group. Scale bar 50 μm

Fig. 2

The mRNA expression of NR1 in the rat brain tissue. After 14 days pretreatment with SIF or vehicle, a surgery was performed to inject Aβ1-42 (20 μg/200 μl) into the lateral cerebral ventricle in the rats of Aβ1-42 and SIF + Aβ1-42 groups using the miniosmotic pump every day, whereas the rats in control and SIF groups were treated with equivalent amount of normal saline. The mRNA expression of NR1 (NMDAR1) was measured by RT-PCR. β-Actin was amplified as an internal control. All the experiments were repeated three times (n = 3). All the data were shown as mean ± SE. *P < 0.05 compared with control group; ^† P < 0.05 compared with Aβ1-42 group

Fig. 3

The relative protein expression of NR1 in the rat brain tissue. After 14 days pretreatment with SIF or vehicle, a surgery was performed to inject Aβ1-42 (20 μg/200 μl) into the lateral cerebral ventricle in the rats of Aβ1-42 and SIF + Aβ1-42 groups using the miniosmotic pump every day, whereas the rats in control and SIF groups were treated with equivalent amount of normal saline. The relative protein expression of NR1 (NMDAR1) was measured by immunohistochemistry (n = 3 rats; four sections per rat). All the data were shown as mean ± SE. *P < 0.05 compared with Control group; ^† P < 0.05 compared with Aβ1-42 group. Scale bar 50 μm

Fig. 4

The mRNA expression of NR2B in the rat brain tissue. After 14 days pretreatment with SIF or vehicle, a surgery was performed to inject Aβ1-42 (20 μg/200 μl) into the lateral cerebral ventricle in the rats of Aβ1-42 and SIF + Aβ1-42 groups using the miniosmotic pump every day, whereas the rats in control and SIF groups were treated with equivalent amount of normal saline. The mRNA expression of NR2B (NMDAR2B) was measured by RT-PCR. β-Actin was amplified as an internal control. All the experiments were repeated three times (n = 3). All the data were shown as mean ± SE. *P < 0.05 compared with control group; ^† P < 0.05 compared with Aβ1-42 group

Fig. 5

The relative protein expression of NR2B in the rat brain tissue. After 14 days pretreatment with SIF or vehicle, a surgery was performed to inject Aβ1-42 (20 μg/200 μl) into the lateral cerebral ventricle in the rats of Aβ1-42 and SIF + Aβ1-42 groups using the miniosmotic pump every day, whereas the rats in control and SIF groups were treated with equivalent amount of normal saline. The relative protein expression of NR2B (NMDAR2B) was measured by immunohistochemistry (n = 3 rats; four sections per rat). a Control group; b Aβ1-42 group; c SIF group; d SIF + Aβ1-42 group. All the data were shown as mean ± SE. *P < 0.05 compared with control group; ^† P < 0.05 compared with Aβ1-42 group. Scale bar 50 μm

Fig. 6

The mRNA of CaM, CaMKII, CREB, and BDNF in the rat brain tissue. After 14 days pretreatment with SIF or vehicle, a surgery was performed to inject Aβ1-42 (20 μg/200 μl) into the lateral cerebral ventricle in the rats of Aβ1-42 and SIF + Aβ1-42 groups using the miniosmotic pump every day, whereas the rats in control and SIF groups were treated with equivalent amount of normal saline. The mRNA of CaM, CaMKII, CREB, and BDNF was measured by RT-PCR. β-Actin was amplified as an internal control. All the experiments were repeated three times (n = 3). All the data were shown as mean ± SE. *P < 0.05 compared with Control group; ^† P < 0.05 compared with Aβ1-42 group