The Role Of Prolylcarboxypeptidase In Chronic Social Defeat Stress-induced Depression-like Behaviors Of Mice

Part IThe expression of PRCP mRNA and protein after chronic social defeat stressObjective: MC4R(Melanocortin-4 receptor)plays an important role in the pathophysiology of mood disorders.Previous research hasshown that activation of MC4 R acts as important determinants of anhedonia in accumbens nucleus(NAc).?-melanocyte stimulating hormon(?-MSH)is an activator of MC4 R.PRCP has the ability to cleave the last proline from ?-MSH C-terminus.PRCP-degraded ?-MSH is not neuroactive.Hippocampus and m PFC(medial prefrontal cortex),the two highly PRCP-expressed brain regions,play an important role in major depression disorder.In order to illuminate the relationship between PRCP and major depressive disorder,we explore the change of PRCP protein and mRNA in these 3 brain regions after chronic social defeat stress(CSDS).Methods: CSDS was utilized to establish mice model of depression;sucrose preference test(SPT)and social interaction test(SIT)were performed to evaluate depression-like behaviors;The expression levels of PRCP mRNA were quantified by real-time RT q-PCR(real-time quantitative PCR);Western blotting was used to analyze the level of PRCP protein.Results:(1)CSDS displayed an ability to induce a significant increase in depression-like behavior.Significantly decreased sucrose preference ratio was observed in CSDS group compared with control group(control: 84.25 ± 3.47%,n = 8;susceptible: 66.50 ± 2.89%,n = 8,P< 0.01);Social interaction ratio was higher in CSDS group compared with control group(n = 7-8,P< 0.01).Time in interaction zone was decreased insusceptible group compared with control group(n = 7-8,P<0.05).(2)There were no statistical differences in mRNA expression between susceptible group and control group in hippocampus(n = 6)and m PFC(n = 4).Significantly decreased mRNA expression in NAc was observed in susceptible group compared with control group(n = 7-10,P< 0.05).(3)PRCP protein in hippocampus had no differences between susceptible group and control group(n = 8).The trend in m PFC was similar(n = 6).(4)Alhough there was no significant statistical difference between the two groups,a descending tendency showed that PRCP levels was 90 ± 3% of control in NAc core(n = 12).(5)In NAc shell,susceptible group displayed a significant decrease in PRCP protein levels when compared with control group(n = 7-8,P< 0.05).The signal of fluorescence in NAc shell wasmuch stronger than the signal in NAc core.Conclusion: CSDS has ability to induce remarked depressive like behaviors.Through the behavioral tests after CSDS,susceptible mice could be identified.According to the comparison of hippocampus,m PFC and NAc,the decreaseof mRNA and protein levels of NAc in susceptible mice are the most significant.Part IIThe regulationof PRCP on chronic social defeat stress induced depression-likebehavior of miceObjective: Nucleus accumbens(NAc)is a critical part of the brain's reward circuitry,which mediates rewarding behavior and major depressive disorder.As describedin part I,there was a significant decrease of PRCP protein and mRNA levels in NAcof susceptible mice.Thus,we investigated the potential regulation effect of PRCP on depression-like behavior.Methods: CSDS was used to establish mice models of depression;SPT and SIT were performed to evaluate depression-like behaviors and identify susceptible mice after CSDS;Stereotaxic injections were used to inject AAV(Adeno-associated virus)into NAc;Western blotting was performed to test the levels of PRCP-e GFP protein;Fluorescence microscope was used to detect fluorescence signal;PRCP inhibitor ZPP(Z-Pro-prolinal)was injected to investigate the effect of PRCP on depression-like behavior induced by subthreshold social defeat stress in normal mice.Results:(1)AAV-mediated PRCP overexpression(AAV-PRCP-e GFP)in NAc can be detected by Fluorescence microscope after 14 days of injection,PRCP-e GFP protein was verified to be increased by western blotting.(2)AAV-mediated PRCP overexpression in NAc improved depression-like behaviour.PRCPoverexpression reversed the decreased social interaction time in susceptible mice.(3)ZPP facilitated theinducement ofdepression-like behaviour bysubthreshold social defeat stress.The effect of ZPP could be blocked by SHU9119,which wasthe antagonist of MC4 R.24h food intake wasnot changed among all the groups during the subthreshold social defeat stress test.Social interaction ratio supported the result,social interaction time also showed the effect of SHU9119.There was no significant difference of SPT in each group.Conclusion:PRCP overexpression in NAcimproves depression-like behaviors.Whereas pharmacological inhibition of PRCP facilitates the subthreshold social defeat stress-induceddepression-like behavior,which could be prevented byantagonist of MC4R.