The Role Of Liver X Receptor β In The Regulation Of Autistic-like Psychotic Behaviors In Inflammation Mice Model

BackgroundPsychosis is a generic term for injured emotion, cognition or willpower caused by brain dysfunction, which includes organic psychosis and affective psychosis. Many pathogenesis involve psychosis, such as biogenetic factors, physical factors, personality traits and social environmental factors. The main Psychosis are divided as manic disorder, depressive disorder, schizophrenia, paranoid disorder, menopause mental disorders, various organic mental disorders. Autistic disorder is a neurodevelopmental disorder characterized by impaired social interaction, verbal and non-verbal communication, and restricted and repetitive behavior. Due to ASD usually occurs in childhood, it is also called baby ASD or children ASD. Since 1980, scholars had divided ASD into the neurodevelopmental disease. Nowadays, the main pathogenesis of ASD are related to chromosomal inheritance, brain organic or neurotransmitter disorders, brain or intestinal immune responses. Current researches found the risk of ASD is increasing, but no exact clinical diagnosis or intervention treatments were found due to the complexity of its pathogenesis. Until now, the researches of ASD focus on studies the patients’ blood, chromosome and the postmortem organs, while systematic researches in molecular level via animal models are not fully confirmed. Current researches on ASD animal models discovered that(1) BTBR T+TF/J(BTBR) inbred mice partly carry the phenotypes of ASD and are used as a common ASD mice model;(2) Prenatal i.p. injection of Valproic acid(VPA) in mice can lead to significant autism-like behaviors and are used as a common ASD mice model;(3) Prenatal i.p. injection of Lipopolysaccharides(LPS) can lead to decreased communication or social behaviors and increased repetitive behaviors in male offspring during childhood or adulthood, which were considered to be associated with altered motivation state and increased anxiety. These rats are also regarded as a ASD research model;(4) Injection of Propionic acid(PPA) in the lateral ventricle can induce the abnormal social behaviors and are suggested as a ASD model;(5) Sepcifically knockout ASD related chromosome can induce specific ASD model, such as 16p11.2-/- mice model and 15q11-13-/- mice model etc.Liver X receptors(LXRs) belong to nuclear receptor superfamily. LXRs include two subtypes: LXRα(NRIH3) and LXRβ(NRIH2), which are located in 11p11.2 and 19q13.3 respectively. The expression of LXRα usually confine to lipid-metabolism-related organs such as liver, intestine and brown adipose tissue. However, LXRβ is widely expressed in the body, including the central nervous system. Our previous studies have demonstrated that LXRβ plays an important role in the development of the laminar structure such as cerebral cortex, cerebellum and hippocampus. Using LXRβ knockout mice, we discovered that(1) Activation of LXRβ could regulate the radial migration of newborn produced at later embryonic stage by maintaing the radial processes of radial glial cells(RGCs), and thus affect the formation of cortical lamina;(2) LXRβ affect the myelin formation by regulating the differentiation of RGCs in periventricular area and corpus collosum to the oligodendrocyte progenitors and further into the mature oligodendrocytes;(3) LXRβ can affect the development of hippocampal dentate gyrus, which thereby affect the neurogenesis occurred in hippocampal subgranular zone. In addition, we discovered that LXRβ knockout mice showed abnormal neuropsychological behaviors, such as decreased exploration, decreased nest building score and appeared anxiety to some extend. However, the underlying mechanism is still not clear.A large number of evidences showed that inflammation response is related to the abnormal neuropsychological behaviors in psychosis. LPS is a common inflammatory reagent and can be injected intraperitoneally or in the lateral ventricle, which could cause depression like behaviors, decreased social ability and anxiety. Also, some studies showed LXRβ could inhibit the inflammation in brains of Alzheimer’s disease(AD) by reversing the activated astrocytes into resting state and decreasing the inflammation microenvironment in brain; LXRβ could relieve the inflammation in midbrain by inhibition of microglia activation, suggesting its protective role in the treating Parkinson’s disease(PD). Additionally, activation of LXRs could also affect the brain inflammation in Encephalomyelitis(EAE) by regulation the activation of microglia. In conclusion, we could infer that LXRβ participate in the inflammation regulation in the central nervous system and might regulate the abnormal neuropsychological behaviors. Uncovering the underlying mechanism might provide a new target for the diagnosis and treatment of abnormal psychosis.This study adopted lateral ventricle injection of LPS to establish acute intracranial inflammation model of mice, using the in vivo bioluminescence imaging technique to test the distribution and intensity of inflammation in abdomen, brain and some abdominal organs of these inflammational mouse model respectively. The astrocytes marker GFAP and the microglial marker Iba1 were used to further evaluate inflammation occurred in the brain. The behavioral tests were used to determine the roles of LXRβ and LPS involved in the neuropsychic behaviors, including social intercourse experiment for testing the social intercourse, open field test for observing autonomous behavior and exploratory behavior, elevated plus maze for determining the anxious behavior, tail suspension test for analyzing the depressive emotion. Neurogenesis in hippocampal dentate gyrus(DG) was also explored investigated by both 5-bromo-2’-deoxyuridine(Brd U) and doublecortin(DCX) immunohistochemistry techniques. The content of monoamine neurotransmitter was detected in brains from WT and LXRβKO mouse with or without inflammation condition through electrochemicaltechniques. Both 5-HT and TPH immunostaining neurons in the dorsal raphe nucleus(DRN) were also analyzed to interpret the assocaiton of 5-HT and abnormal neuropsychological behaviors. WB technique was used to test the different expression of TPH in the midbrain to define the regulatory function of LXRβ in 5-HT expression in the nice subjected to inflammation insult. Finally, the expression of 5-HT in brain was further explored in the neonatal mice given LPS injection after pretreatment with synthetic LXRs against TO901317.The main results were as follows:1. Roles of LXRβ involved in the regulation of neuropsychic behaviour of mice with inflammation insult.(1) Compared with saline group, the mice treated with LPS show increased inflammation levels in the brain, liver and belly, loss of LXRβ enhanced this effect.(2) Compared with saline group, the mice treated with LPS have increased activated astrocytes and microglia in the midbrain. The number of Iba1 labeled microglia in the DRN was significantly increased in the mice from LXRβKO-LPS group compared with LXRβKO-Saline group(P<0.05).(3) Compared with LXRβKO-Saline mice, contact number((P<0.05) and duration time(P<0.05) with stranger mouse in 10 minutes were significantly lower in LXRβKO-LPS mice, while there is no significant difference in those between WT-Saline group and WT-LPS group.(4) Compared with mice from Saline group, mice from LPS group have a decreasing trend in the central area of distance and the central area of time activities in 10 minutes, whose difference has yet to be accepted by the statistics.(5) In the elevated plus maze assay, a one-way ANOVA revealed the percentages of open-arm entries for LPS treated WT(P<0.05) or LXRβKO(P<0.05) mice were less than that in saline treated mice. Similary, the percentage of open-arm time for LPS treated WT(P<0.01) or LXRβKO(P<0.05) mice mice were also less than that in saline treated mice. Additionally, and the percentage of open-arm time in mice from LXRβKO-Saline was significantly decreased compared with WT-Saline group(P<0.05).(6) Tail suspension experiment showed that immobolity time in mice from LXRβKO –Saline group was significantly reduced comparing with WT-Saline group.2. Mechanism of LXRβ involved in the regulation of autistic-like psychotic behaviors in mice subjected to LPS injection.(1) The contend of 5-HT in the brain was significantly increased in the LXRβKO mice compared with WT mice. LPS injection significantly increased the contend of DA(P<0.001), NE(P<0.01) and 5-HT(P<0.05) in the brains of LXRβKO mice, whereas did not alter them in the WT mice. Furthermore, there were significantly increased in the content of DA(P<0.001), NE(P<0.01)and 5-HT(P<0.05) in the brains of mice from LXRβKO-LPS group, compared with that in the mice of WT-LPS group.(2) The number of 5-HT positive neurons in the DRN of mice from LXRβKO-LPS was increased significantly compared with LXRβKO-Saline group(P<0.01). The number of TPH positive neurons in WT-LPS group are also increased significantly compared with that in WT-Saline group(P<0.05), LXRβ deletion enhanced this effect.Western blot showed LPS can increase the TPH expression in the mice of LXRβKO-LPS group(but not significantly) compared with that in LXRβKO-Saline group.(3) Loss of LXRβ decreased Brd U and DCX labeled cells in the DG compared with WT group, LPS stimulation had no obvious effect. Interestingly, LPS stimulation seemed to increased the GFAP expression in the DG, the highest number of GFAP positive cells in the LXRβKO-LPS group.3. The endogenous activation of LXR regulates 5-HT expression in the DRN of newborn mice subjected to LPS insult.(1) The expression of Iba1 expression in the midbrain was increased in the mice from LPS group compared with saline group(P<0.05), which can be reversed by pretreatment of TO901317 before suffering from LPS exposure(P<0.05). Meanwhile, the expression of 5-HT(P<0.01) and TPH(P<0.05) in the DRN were also increased in the mice from LPS group compared with saline group which can be inhibited by pretreatment of TO901317(P<0.05).(2) ELISA assay has indicated that the expression of TNF-α in the midbrain was increased by LPS injection(P<0.05), which can be inhited by pretreatment of TO901317 before suffering from LPS exposure(P<0.05).ConclusionsLXRβis engaged in the control of autistic-like psychotic behaviors in mice induced by LPS.Probably,LXRβaffects the autistic-like behaviors in mice by regulating 5-HT levels as well as influencing the hippocampal neurogenesis.Anti-rabbit荧光二抗瑞士Invitrogen公司Anti-mouse荧光二抗瑞士Invitrogen公司7)复染DAPI(5sec)。...