Protective effects of phosphodiesterase 2 inhibitor on depression- and anxiety-like behaviors: involvement of antioxidant and anti-apoptotic mechanisms

Abstract

Stress occurs in everyday life, but the relationship between stress and the onset or development of depression/anxiety remains unknown. Increasing evidence suggests that the impairment of antioxidant defense and the neuronal cell death are important in the process of emotional disorders. Chronic stress impairs the homeostasis of antioxidants/oxidation, which results in the aberrant stimulation of the cell cycle proteins where cGMP-PKG signaling is thought to have an inhibitory role. Phosphodiesterase 2 (PDE2) is linked to cGMP-PKG signaling and highly expressed in the limbic brain regions including hippocampus and amygdala, which may play important roles in the treatment of depression and anxiety. To address the possible effects of PDE2 inhibitors on depression-/anxiety-like behaviors and the underlying mechanisms, Bay 60-7550 (0.75, 1.5 and 3 mg/kg, i.p.) was administered 30 min before chronic stress. The results suggested that Bay 60-7550 not only restored the behavioral changes but also regulated Cu/Zn superoxide dismutase (SOD) levels differentially in hippocampus and amygdala, which were increased in the hippocampus while decreased in the amygdala. It was also significant that Bay 60-7550 regulated the abnormalities of pro- and anti-apoptotic components, such as Bax, Caspase 3 and Bcl-2, and the indicator of PKG signaling characterized by pVASP(ser239), in these two brain regions. The results suggested that Bay 60-7550 is able to alleviate oxidative stress and mediate part of the apoptotic machinery in neuronal cells possibly through SOD-cGMP/PKG-anti-apoptosis signaling and that inhibition of PDE2 may represent a novel therapeutic target for psychiatric disorders, such as depression and anxiety.

Keywords: Cyclic GMP; Neuronal apoptosis; Oxidative damage; Phosphodiesterase 2.

Fig. 1

CUS-induced depressive behaviors. Mice were subjected to CUS or not, and stressed animals were administered vehicle, Bay 60-7550 (0.75, 1.5 and 3 mg/kg), or desipramine (10mg/kg). A) The immobility time in mouse tail suspension test (TST). B) The immobility time in mouse forced swim test (FST). Values are means ± S.E.M. with 10 mice in each group. **p<0.01 vs. non-stressed control group and ***p<0.001 vs. non-stressed control group. ^#p<0.05, ^##p<0.01 and ^###p<0.001 vs. vehicle-treated CUS group.

Figure 2

CUS-induced anxious behaviors. Mice were subjected to CUS or not, and stressed animals were administered vehicle, Bay 60-7550 (0.75, 1.5 and 3 mg/kg), or diazepam (1.5 mg/kg). A) % open arm entries in the elevated plus maze test (EPM). B) % time spent in open arms in the elevated plus maze test (EPM). C) Numbers of marbles buried in the marble burying test (MBT). Values are means ± S.E.M. with 10 mice in each group. *p<0.05, **p<0.01 and ***p<0.001 vs. non-stressed control group. ^#p<0.05, ^##p<0.01 and ^###p<0.001 vs. vehicle-treated CUS group.

Figure 3

Effects of Bay 60-7550 on Cu/Zn SOD protein expression in control and CUS-exposed mice, in hippocampus and amygdala. Mice were subjected to CUS or not, and stressed animals were administered vehicle, Bay 60-7550 (0.75, 1.5 and 3 mg/kg), desipramine (10mg/kg) or diazepam (1.5 mg/kg). A) Expression of Cu/Zn SOD in hippocampus. B) Expression of Cu/Zn SOD in amygdala. Values are means ± S.E.M. with 10 mice in each group. **p<0.01 vs. non-stressed control group. ^#p<0.05 and ^##p<0.01 vs. vehicle-treated CUS group.

Figure 4

Effects of Bay 60-7550 on p-VASP^Ser239 protein expression in control and CUS-exposed mice, in hippocampus and amygdala. Mice were subjected to CUS or not, and stressed animals were administered vehicle, Bay 60-7550 (0.75, 1.5 and 3 mg/kg), desipramine (10mg/kg) or diazepam (1.5 mg/kg). A) Expression of p-VASP^Ser239 in hippocampus. B) Expression of p-VASP^Ser239 in amygdala. Values are means ± S.E.M. with 10 mice in each group. **p<0.01 vs. non-stressed control group. ^#p<0.05 and ^##p<0.01 vs. vehicle-treated CUS group.

Figure 5

Effects of Bay 60-7550 on Bcl-2 mRNA and protein expression in control and CUS-exposed mice, in hippocampus and amygdala. Mice were subjected to CUS or not, and stressed animals were administered vehicle, Bay 60-7550 (0.75, 1.5 and 3 mg/kg), desipramine (10mg/kg) or diazepam (1.5 mg/kg). A) mRNA expression of Bcl-2 in hippocampus. B) Protein expression of Bcl-2 in hippocampus. C) mRNA expression of Bcl-2 in amygdala. D) Protein expression of Bcl-2 in amygdala. Values are means ± S.E.M. with 10 mice in each group. *p<0.05, **p<0.01 and ***p<0.001 vs. non-stressed control group. ^#p<0.05 and ^##p<0.01 vs. vehicle-treated CUS group.

Figure 6

Effects of Bay 60-7550 on Bax mRNA and protein expression in control and CUS-exposed mice, in hippocampus and amygdala. Mice were subjected to CUS or not, and stressed animals were administered vehicle, Bay 60-7550 (0.75, 1.5 and 3 mg/kg), desipramine (10mg/kg) or diazepam (1.5 mg/kg). A) mRNA expression of Bax in hippocampus. B) Protein expression of Bax in hippocampus. C) mRNA expression of Bax in amygdala. D) Protein expression of Bax in amygdala. Values are means ± S.E.M. with 10 mice in each group. **p<0.01 and ***p<0.001 vs. non-stressed control group. ^#p<0.05 and ^##p<0.01 vs. vehicle-treated CUS group.

Figure 7

Effects of Bay 60-7550 on Caspase 3 mRNA and protein expression in control and CUS-exposed mice, in hippocampus and amygdala. Mice were subjected to CUS or not, and stressed animals were administered vehicle, Bay 60-7550 (0.75, 1.5 and 3 mg/kg), desipramine (10mg/kg) or diazepam (1.5 mg/kg). A) mRNA expression of Caspase 3 in hippocampus. B) Protein expression of Caspase 3 in hippocampus. C) mRNA expression of Caspase 3 in amygdala. D) Protein expression of Caspase 3 in amygdala. Values are means ± S.E.M. with 10 mice in each group. **p<0.01 and ***p<0.001 vs. non-stressed control group. ^#p<0.05 and ^##p<0.01 vs. vehicle-treated CUS group.