Neuron PPARγ In Medial Prefrontal Cortex Modulates Depressive-like Behavior In Mice

Depression is a kind of mood disorder that is characterized by anhedonia,low self-evaluation,and associated with cognitive impairment and sleep disorders,eating disorders.According to the world health organization(WHO),the latest statistics found that the global prevalence of depression and dysthymia is as high as 12.8%,and is predicts that by 2020 depression will become the world’s second largest mental illness that serious influence human physical and mental health.However,the clinical commonly used antidepressant drugs has certain limitation,such as low effective,classical antidepressant drug include monoamine oxidase inhibitors,tricyclic antidepressants,and selective serotonin reuptake inhibitors and NE reuptake inhibitors,which biggest remission rate is about 60%-70%;in addition to the need to administer the drug for 3-6 week to see clinical bennefit;About 50%of the patients experienced side effects.so there is still great need for faster acting,low side effect and new antidepressant drugs.More importantly,the pathogenesis of depression is still not clear so far.Peroxisome proliferator-activated receptor gamma(PPARy)is a ligand-activated transcription factor that belongs to the nuclear receptor family.PPARs possess the classic domain structure of other nuclear receptors(e.g.,steroid or thyroid hormone receptors).They have an NH2-terminal region with a ligand-independent transactivation domain(AF-1),followed by a DNA-binding domain(two zinc fingers)and,at the COOH-terminus,a ligand and dimerization domain and a ligand-activation domain(AF-2).The two proteins form a heterodimer in the nucleus.The ligand-free complex interacts with corepressor proteins and blocks the expression of the genes.With the activating ligands and coactivator segments of regulating proteins,the heterodimer becomes active and allows translation of the genes under its controlRecent studies showed that PPARy signaling plays a crucial role in neuronal survival and many agonists of PPARy implicate a neuroprotective effect.Recent epidemiological investigation and preclinical studies indicate that PPARy agonists also show certain antidepressant effect.But it is difficult to distinguish PPARγ’s antidepressant effect from the peripheral or the central nervous system.Therefore,we will study whether the brain PPARy is involved in the high-fat diet-induced depression and The pyramidal neuron specificity knockout PPARy mice-induced depression,the neuronal PPARy is also changed in the universality pathogenesis of depression.7-8weeks old C57BL/6J mice were purchased from Southern Medical University Animal Center.One week after arrival,mice were divided into two groups and were fed either a high-fat diet(10%kcal fat,D12450B,Research Diets Inc.)or received continuous feeding of a normal diet(60%kcal fat,D12492,Research Diets Inc.)for up to 16 weeks.The data showed that the weight of high fat diet group increased remarkably compared with the control group after 16 weeks’high fat diet.We had also tested the fasting plasma glucose.The data showed that the fasting plasma glucose of the high fat diet group were significantly higher than the control.The high fat diet group had reached the standard of diabetes,Suggest that the model of obesity or diabetes model is successful.After the animal model was completed,the two groups were conducted to a series of behavioral tests:first with The force swimming test,the high fat diet mice was also significantly longer than the control group about immobility time;The tail suspension test,which is used to detect immobility time during 6min,the immobility time of the high fat diet mice was significantly longer than the control group;open-field test(Open field test,OFT)to detect the total distance in 5min or 30min,the total distance exhibited no difference between the high fat diet mice and the control group.It is suggested that long-time high-fat diet may induced depressive-like behavior.The western blotting were used to detect the expression of brain PPARy,and found that high-fat diet gourp PPARγ level were decreased in the mPFC compared to CD-fed miceTo determine whether depression-like behaviors were due to a neuronal PPARy decrease or whether neuronal PPARy deficiency was sufficient to induce depression-like behaviors,we generated neuron-specific PPARy knockout mice(KO)using a Cre lox-p recombination system.To achieve neuronal selectively for PPARy deletion,we crossed PPARyfl/fl mice with mice expressing Cre under a well-characterized αCaM-KⅡ promoter to drive Cre expression.PPARyfl/fl(f/f)mice were used as the control.The force swimming test,the duration of immobility increased in the KO mice compared with the f/f mice.The tail suspension test,which is used to detect immobility time during 6min,the immobility time of the KO mice was significantly longer than the control group.The open field test show that the total distance exhibited no difference between the f/f mice and KO mice.These results indicated that neuronal PPARy deficiency induced depression-like behaviors in adult miceTo verify whether knockout the pyramidal neuron PPARy vector in mPFC can induce depressive-like behavior in mice,we bilaterally injected AAV-GFP or AAV-CRE vectors into the mPFC in f/f mice.After 3 weeks,the force swimming test and the tail suspension test all show that the immobility time increased in f/f+AAV-CRE gourp compared with f/f+AAV-GFP group.To verify whether overexpress PPARγ vector in mPFC can reverce depressive-like behavior in KO gourp.we unbilaterally stereotaxically injected AAV-GFP or AAV-PPARγ vectors into the mPFC in f/f group or KO group,f/f gourp and KO group were randomly divided into three groups,include:f/f-AAV、KO-AAV、KO-PPARγ.After 3 weeks,the force swimming test show that the immobility time decreased in KO-PPARy gourp,but not in KO-AAV group.In the tail suspension test,the duration of immobility increased in the KO-AAV mice compared with the f/f-AAV mice which was rescued by overexpress PPARy vector in mPFC.In order to test whether the role of PPARy in mPFC modulate depressive-like behavior in high fat mice,we unbilaterally stereotaxically injected AAV-GFP or AAV-PPARy vectors into the mPFC in high-fat diet group or control group.The high-fat diet group and the control group were randomly divided into four groups,includ:CD-AAV,CD-PPAy,HFD-AAV,HFD-PPARy.After 3 weeks,the tail suspension test and the force swimming test both show that the immobility time decreased in HFD-PPARy gourp,but not in HFD-AAV group.Next,after a HFD-feeding regimen of 16 consecutive weeks,all mice were placed in a stereotaxic frame.A brain infusion cannula(Plastics One)was unbilaterally implanted in the mPFC.The high-fat diet group and the control group were randomly divided into four groups,include CD-saline、CD-rosiglizatone、HFD-saline、HFD-rosiglizatone.Seven days after implantation,the force swimming test show that rosiglitazone in the mPFC abolished the increase in immobility time in the HFD-fed mice.All of the data indicated that neuronal PPARγ deficiency in the mPFC is responsible for the depression-like behavior in chronic HFD-fed mice.Conclusion:1.16weeks high-fat diet lead to depressive-like behavior;2.16weeks high-fat diet decreased the protein level of PPARy in mPFC.3.The pyramidal neuron specificity knockout mice showed depressive-like behavior 4.knockout the pyramidal neuron PPARy in mPFC induced depressive-like bahaviors in mice.5.PPARγ overexpression in mPFC can reverse the depressive-like behavior in knockout mice.6.PPARy overexpression or the PPARy agonist in mPFC can reverse the depressive-like behavior induced by high-fat diet.