Association Of Polymorphisms Of COMT And DAT Gene In Dopamine Metabolism System With Post-stroke Depression

IntroductionStroke can not only causing a variety of nerve dysfunction, but also leading a series of emotional changes, depression is the most common and important neuropsychiatric complications after stroke, and have an adverse effect on the patient's cognitive,neurological recovery and the quality of life. Post-stroke depression is defined as a common complication after stroke, which is characteristic of depression and interest decline that happened following apparently clinical symptoms after stroke. Its morbidity is different on clinical reports, domestic reports is 31.2% to 63.1%, foreign reports is 25% to 79%, more focus on the rate from 40% to 50%, which can be seen from the large number of clinical reports. With the bio-medical model to biological-psycho logical-social medical model of conversion, post-stroke depression, antidepressant drugs after stroke are both taken more seriously.The pathogenesis of PSD is not yet explicit, generally regard that it is caused by social psychology, neural anatomy, neurobiology and other factors, among them, the neurobiology factor is the hotspot of research in recent years. The primary endogenous theories of PSD thought that its happened was a result of the injury in a particular area of the brain and the change of neurotransmitter, specifically, the brain frontal lobe,limbic system,thalamus and brainstem blue spot nuclear etc could induce depression of human, but the communication of these nerve structure was primarily through neurotransmitters transfer. NE and 5-HT is an important neurotransmitter of the nervous system, its neurons locate in brainstem, the axons go through the hypothalamus and the basal ganglia area, forming frontal/temporal lobe- basal ganglia - brain stem ventral loop, the loop is responsible for regulating mood, sleep and cognition. When stroke destroy the above loop can cause the synthesis,metabolism and conduction obstacles of many neurotransmitters relating to neural psychological activity, and can reduce the synthesis of 5-HT,NE, or induce the change of postsynaptic membrane receptor number and/or sensitivity change, all of this can cause depression. Dopamine also participates in human mental and emotional activities, it contains the midbrain-the cerebral cortex and the midbrain-edge leaf system are closely to human mental and emotional activities.The research of primary depression suggested that the occurrence of depression was relating with low activity of brain monoamine neural transmitter, especially 5-HT,NE, their relationship with depression might have been widely recognized as the conclusion, but because many new antidepressant drugs have obvious function on the DA metabolic, which enable researchers think DA play an important role in depression biochemical mechanism. Randrup firstly suggested dopamine may be involved in the pathogenesis of depression in 1975. Schwaninger also believed that patients with depression was not only have 5-HT,NE nerve conduction abnormal, DA neurons conduction anomaly was also related to the pathophysiology of depression. Recently, Maj discovered that we used agonists,rather than inhibitor Apomorphine antidepressant treatment might increase the active state of D2,D3 receptor density, patients with DA receptor response surface perceptual decline, use paroxetine antidepressant treatment effect will be better. This suggested that perhaps SSRIS is playing a role by increasing DA receptor sensitivity. This would mean that the dopamine plays a very important role in primary depression. In recent years, Lv Luxian pointed out that the dopamine concentration in plasma,cerebrospinal fluid of PSD patients below the stroke without depression group even though the normal control group; Yan Bin studied the monoamine neural transmitter and its metabolites change rule of the hippocampal,striatum,cortex of cerebral ischemia reperfusion mice, and thought that the occurrence of PSD were closely linked to the NE,DA system anomalies after hippocampal cerebral ischemia reperfusion. The PSD patients who used the antidepressant drug therapy that could increase the monoamine neurotransmitter concentrations, could alleviate symptoms of depression, to further support the above theory. That suggests us that the dopamine metabolic system dysfunction after stroke may also play an important position in PSD happening.DA in the brain can be used as the neurotransmitter influence on the motion,behavior,emotion and pituitary hormone release, some drugs that can affect DA metabolism have anti-depression roles, such as Bupropion, it is a relatively selective DA recycling inhibitors, it also plays an excited role in DA receptor, Double Blinded Randomized and Controlled Study suggests that the effect of this second generation of antidepressants is better than placebo, and equivalent to amitriptyline. Recently, someone proposed that there were two kinds of theories of the correlation between DA metabolism system dysfunction and depression: one thought that people with depression might exist lower DA D1 receptor function; the other thought that people who suffered depression might exist the damage of brain reward pathways, the midbrain edge DA pathways composed of the midbrain ventral tegmentum area and the nucleus accumbens play a key role in reward processing. Recently, people gradually realized that the reward pathway plays an important role in regulating power, sleep, appetite, circadian rhythms and cheerful or disgust stimulation reaction, Almost all of the long-term antidepressant treatment of patients will increase DA induction reward reaction.COMT is widely existed in one of the body's metabolic enzymes, which mainly degradate forehead cortical synaptic inside above 60% DA through methylation directly and selectively, it is biologically active or toxic catecholamine main metabolic enzymes, and also the most key enzyme. The gene locates in 22q11.2, is a mutation more gene. Now, more research focus on a G-A point mutations in exon 4, it makes the coding of 108 or 158 amino acid Val instead by Met, and cause enzyme activity reduced 3-4 times, thus causing a different genotypes of individual body neurotransmitter content appears obvious difference. The Val/Val genotype has high-activity, the Val/Met genotype has moderate-activity, the Met/Met genotype has low-activity, this is decided by the high-active allele G and low-active allele A, it is codominant inheritance. Massat study found highly active COMT Val allele, especially Val/Val genotype was concerned with early onset depression, and pointed out that COMT gene might play more complex and learning effect in many susceptibility and symptoms of neural mental illness. The neurotransmitter theory of PSD thought that the happen of acute PSD was relating to the functional active reduced of the serum monoamine transmitters, studies proved that the DA functional reduced in PSD patients, this might because DA generating reduce or degradation increase, also the reduction of effective precursor tyrosine or the mechanism change of enzyme, or might be caused by amine transfer function abate.The high-activity COMT enzyme can accelerate the degradation and elimination of neurotransmitter as substrate such as DA, thus will shorten the function time of neurotransmitter DA, then reduce the DA signal transduction in prefrontal cortex and enhance the DA signal transduction in subcortical, thus increase the risk of cognitive impairment of depressed patients. So, this mutant site which can trigger the activity change of COMT will cause some related biology change or not, whether it is associated with the onset of PSD, all of them are well worth researching of genetics subject.DAT is a transmembrane protein which located in DA neurons presynapic,it can reuptake the DA between synapses,terminate the DA signal transmission,and is the most important factor that can maintain DA neural function stable, especially very important to maintain normal brain function. It restricts dopaminergic receptor activated time,degree,limits, adjusts DA concentration,moreover the number of dapamine is concerned with many nerve disease. If the aborb function of transporter is abnormal, that will cause the neurotransmitter concentrations high or low in the synaptic space, thus cause the change of the corresponding neurotransmitter system function activities, a lot of drug therapies for neurological diseases will make transporters as its direct acting targets, and adjust the schedule of the neurotransmitter between the synaptic by adjusting the transporters function, thus change the nervous system signaling pathways and achieve the remedial effect.Human DAT gene located in 5p15.3, the 3'UTR 40bp VNTR is the most studied. This VNTR polymorphism is located in the non-coding areas, It may not directly change the structure and function of DAT itself, but studies find that it is concerned with the expression and utilization of DAT in brain. The points of DAT is not slient, can affect gene produce high level mRNA expression, studies found that 10 times repeat allele had stronger enhancement effect than other alleles, the individuals with 10/10 genotypes had more-than 20% DAT protein content in striatum compare with 9/10 ones. But the other two studies thought that the nine times repeat allele had higher expression and utilization. Among the studies about depression, Brunswick found that the affinity of dopamine transporter protein mightbe higher in basal ganglia of depression patients than normal controls, these suggested that dopamine function was changeable in depression patients, this mightbe the reason of effect of antidepressant drugs. Animal studies have confirmed that all types of antidepressant drugs can cause dopamine transporter affinity changes. Joyce PR thought that DAT-9 repeat gene polymorphism was the risk factor of borderline personality disorder of depression patients, particularly obvious in older people with depression.Stroke destroys DA signal pathway can also change the activitie and affinity of DAT, we speculate it may also play a role in PSD happening.Objective:To investigate the associaton of post-stroke depression with gene polymorphisms of COMT Val108/158Met,DAT 40 bp VNTR in dopamine metabolic system.Methods:The blood samples were from the neurology Department of Zhu Jiang Hospital and it was diagnosized of the Fourth National cerebrovascular Conference and Hamilton depression scale. Patients were divided into two groups:91 cases of pure stroke patients (59 cases of male and 32 cases of female) and 68 cases of post-stroke depression patients (40 cases of male and 30 cases of female). Polymerase chain reaction-restriction fragment length polymorphism technology was applied, Blood was pumped about 2mL, and then it was anticoagulated and extracted peripheral blood leukocyte genomic DNA by phenol-chloroform extraction method.5'-ACT GTG GCT ACT CAG CTG TG-3'in upstream and 5'-CCT TTT TCC AGG TCT GAC AA-3'in downstream were used for amplification of COMT gene. NlaⅢenzyme was used for detecting Val108/158Met polymorphism of COMT gene. Meanwhile 5'-TGT GGT GTA GGG AAC GGC CTG AG-3'in upstream and 5'-CTT CCT GGA GGT CAC GGC TCA AGG-3'in downstream were used for amplification of DAT gene, and compared the augmentation segment size. SPSS 13.0 statistical package was employed in the comparison of genotype frequency. Chi-square test was used to compare each allele and genotype frequency in pure stroke and post-stroke depression patients.When theory frequency was behind 5,we used Fisher's Exact Test.Results:(1)COMT Val108/158Met polymorphism analysis:The frequence of A allele was lower in PSD group(21.3%) than in pure stroke group(33.5%),and G allele was higher in PSD group(78.7%) than in pure stroke group(66.5%), there were significantly different between two group patients comparison of populations (χ2=5.703, P=0.017, OR=1.860,95%CI=1.114-3.107). But if compared by sex, the frequency of COMT G,A alleles were significantly different between the two female groups(χ2=4.610, P=0.032, OR=2.455,95%CI=1.069-5.635), but no significant difference was found between the two male groups(χ2=1.864, P=0.172); The wildtype G/G occupied 63.2%, mutation type A/A only occupied 5.9% in PSD group, but the heterozygous type occupiede 47.3%, and mutation type A/A occupied 9.9%, the frequency of COMT three genotypes were significantly different between two group patients comparison of populations(χ2=6.489, P=0.039), but if compared by sex, the frequency of COMT three genotypes were significantly different between the two female groups (χ2=6.547, P=0.024), but no significant difference was found between the two male groups(χ2=1.701, P=0.476).(2) DAT 40bp VNTR polymorphism analysis:10 repeats (480bp) variant was the dominant allele of DAT 40bp VNTR polymorphisms with the allelic frequency 91.9% in PSD group and 90.7% in pure stroke group, then was the 9 repeats (440bp), which separately occupyed 5.9%.5.5% in the two groups. These alleles,genotypes and heterozygosity frequency differences between the two groups were no significant difference (χ2=1.966, P=0.634;χ2=2.248, P=1.000;χ2=0.125, P=0.724). We divided the DAT genotypes and alleles gene into four groups,10/10 genotypes,non-10/10 genotypes,10 repeat alle,non-10 repeat allele, there was no statistical significance between the two group 10 repeat allele and non-10 repeat allele (χ2 =0.145, P= 0.703); also the 10/10 genotypes and non-10/10 genotypes (χ2=0.152, P= 0.697)Conclussion:(1) It was suggested from the results that COMT Val108/158Met gene polymorphism mightbe associated with post-stroke depression in our study, and this correlation mainly reflected in female patients.We also found that this gene polymorphism might play a bigger role in the genetic pathogenesis of PSD of women.(2) Maybe there was no relationship between the polymorphism of DAT 40bp VNTR gene polymorphism and PSD, it needed further research.