Role Of Adult Neurogenesis And Inflammatory Regulation Involved In Cognitive And Depressive Behaviors Related To Chronic Cerebral Hypoperfusion

PartⅠThe Biological Mechanisms of Adult Hippocampal Neurogenesis and Neuroinflammation Involved in Cognitive and Depression in Chronic Cerebral Hypoperfusion RatsBackground Chronic cerebral hypoperfusion（CCH）has been gradually regarded as a common etiologic mechanism for cognitive and psychiatric disturbances,which accelerates potential new therapeutic avenue benefiting from it.The regulation of adult hippocampal neurogenesis（AHN）,neuroinflammation and systemic inflammation might be potential pathological mechanisms for cognitive and depressive disorders caused by CCH.Ten-eleven translocation methylcytosine dioxygenase 1（TET1）was suggested to stimulate neuronal stem cells（NSCS）proliferation,active AHN and participate in multiple processes such as synaptic plasticity,axonal growth,and neural circuit formation.However,whether TET1 could be an important regulatory factor for CCH-related cognition and depressive-like behavior still needed to be investigated.Enriched environment（EE）could effectively activate AHN, improve synaptic plasticity,and reduce neuroinflammation,thus devoting protection to central nervous system insult.In this study,we generated a rat model of chronic cerebral hypoperfusion through bilateral occlusion of common carotid artery（2-VO）surgery,and compared regular EE and novel genetical treatment with h TET1 hippocampal microinjection to observe which one was more suitable for the cognitive and depressive disturbance treatment and to investigate the underlying mechanism from standpoint of AHN and glial activation,which would provide clues for clinical prevention and therapy.Method All adult male Sprague-Dawley rats（220-240g）were subjected to stereotaxic injection of phosphate-buffered saline（PBS）or Adeno-associated virus（AAV）-human TET1（h TET1）.The 2VO and sham surgery was carried out 10 days later.After 3 days recovery,rats were subjected to standard environment or enriched environment with free access to food and water.3-4 rats in each group underwent 5-bromo-2-deoxyuridine（Brd U）injection（200 mg/kg,i.p.once daily）per day for five consecutive days from the 12^th and 34^th after 2-VO or sham surgery,respectively.3-4 rats in each group were injected with Brd U once for 3 days,and rats were sacrificed 4h after the last injection.Behavioral tests were used to appraise depression and cognition before sacrifice.All rats were sacrificed on the 47^th day after 2-VO or sham surgery.Then epigenetic molecules,synaptic proteins,glial activation of the dorsal hippocampus were determined.Results In the present study,we found both enriched environment（EE）and genetical treatment with overexpressing a catalytic domain of human TET1（AAV-h TET1）were sufficient for stimulating adult hippocampal neurogenesis（AHN）.However,promoting AHN could not deal with the cognitive dysfunction and depressive-like behaviors in CCH rats. Notably,a healthy local brain environment with elevated BDNF and astrocytes was conducive to improving cognitive dysfunction.Meanwhile,astrocytes were involved in the cognitive regulating process of neurons,presynaptic function and microglia.In general,we held that depressive disturbances were determined by BDNF levels,neuronal and presynaptic function,as well as glial activation containing astrocytes and microglia.To further support this point,we investigated severe depressive symptoms was strongly correlated with activation of astroglia and microglia.Importantly,causal mediation analysis showed significant mediation by the presence of reactive glial cells in the relation between neural plasticity and depressive symptoms.Finally,we compared the efficiency of genetical therapy and EE to treat cognitive dysfunction and depressive-related disorders in CCH rats.We showed EE performed better than h TET1 treatment for cognitive deficits and depression.EE with less glial reactivity was much more resistant to depression,while h TET1 with more glial activation was more vulnerable to depressive disorders.Conclusion A healthy local brain environment（e.g elevated BDNF expression and increased astrocytes）was contribute to renovating cognitive dysfunction.Moreover,less glial reactivity,and fewer depressive-like disturbances.These results were important for our understanding of disease mechanisms and provided valuable tools for the overall management of CCH patients.PartⅡ The Causal Effect of Peripheral Inflammation on Vascular Cognitive Impairment:A MendelianRandomization StudyBackground Systemic inflammation has been suggested to be involved in the etiology for Alzheimer’s disease（AD）,depression and other vascular related diseases,such as hypertension,but their specificity and causality remain mostly unclear.This study aims to determine the causal effect of systemic inflammatory regulators on vascular cognitive impairment using Mendelian-randomization（MR）approach.Method 38 systemic inflammatory regulators in 8293 Finnish individuals were obtained from a recent genome-wide association study（GWAS）.A total of 23 outcomes were obtained from UK biobank,Finn Gen biobank or recent GWAS studies.The inverse variance weighted method（IVW）was used to evaluate the causal estimate and regard alternate methods using MR-Egger,weighted median,weighted mode and simple mode methods as sensitivity analyses to avoid the presence of the heterogeneity and horizontal pleiotropy.Results In this study,we found that peripheral inflammatory factors could participate in the regulation of cardiovascular related diseases and pathological conditions.For example,genetically predicted macrophage colony stimulating factor（MCSF）,interleukin（IL）-13,and TNF-related apoptosis-inducing ligand（TRAIL）were associated with higher odds of hypertension,while interleukin-1-receptor antagonist（IL-1ra）showed the opposite.Three inflammatory exposures could increase the risk of ischemic heart disease,including macrophage inflammatory protein 1b（MIP1b）,platelet-derived growth factor B（PDGFbb）,and IL-16.Chemokine Eotaxin causally related to higher risk of atrial fibrillation,and higher cutaneous T-cell attracting chemokine（CTACK）and regulated on activation,normal T cell expressed and secreted（RANTES）levels also displayed positive relationship to type 2 diabetes.Meanwhile,systemic inflammation might be associated with the mechanisms of lipid metabolism.Out of all the circulating inflammatory factors,seven inflammatory genetically relate to lower levels of apolipoprotein A1,such as interferon gamma-induced protein 10（IP10）,MIP1 b,beta-nerve growth factor（b NGF）,stem cell growth factor beta（SCGFb）,IL-1b,IL-16 and predicted interferon gamma（IFNg）,but IL-5 decreased the levels of apolipoprotein A1.Certain factors containing MIP1 b,stromal-cell-derived factor 1 alpha（SDF1a）,IL-5 and IL-6 could reduce the risk of apolipoprotein B,with the granulocytecolony stimulating factor（GCSF）and tumor necrosis factor alpha（TNFa）increased the levels of apolipoprotein B.Some inflammatory regulators [e.g MIP1 b and monocyte chemoattractant protein-1（MCP1）,SCGFb,IL-9 and IFNg] showed negative causation with high-density lipoprotein cholesterol,while IL-5 showed the opposite direction.Three systemic inflammatory exposures containing MCP1,IL16 and TNFa reduced the level of triglyceride,and MIP1 b increased the concentration of triglyceride.Furthermore,systemic inflammation might be involved in the pathogenesis of dementia.14 inflammatory factors causally associated with variations of vascular dementia（Va D）and its subtype.For instance,lower risk of Va D might be genetically determined by MIP1 b,MCSF,IL-2ra,IL-8,and TRAIL.Certain inflammatory factors,such as IP10,SCGFb and IL-8,were related to higher odds of multiple infarct Va D,but MIP1 b and PDGFbb causally reduced the odds of multiple infarct Va D.For subcortical Va D,genetically determined CTACK and TRAIL increased its prevalence,but MIP1 a reduced its risk.Genetically predicted IL-1b increased the risk of mixed Va D.For undefined Va D,Eotaxin,MIP1 b and TNFa could reduce its risk,but SCGFb and IL-1ra showed the opposite causal effect.In our study,we observed IP10 made a negatively causal effect on AD,and fibroblast growth factor basic（FGFBasic）and macrophage migration inhibitory factor（MIF）displayed positively causal effect on AD risk.Genetically related TRAIL reduced the risk of frontotemporal dementia（FTD）-TDP subtype.Genetically determined PDGFbb and MIF reduced the risk of dementia in Lewy body（DLB）.At the same time,interleukins such as IL-2ra,IL-4 and IL-16 could reduce the risk of Parkinson disease related dementia.Peripheral inflammation might constitute the etiological mechanisms of depression and anxiety disorders.MIP1 a and MCP1 made a causal effect on the depression risk,and MIP1 b could reduce the risk of depression.Genetic determined MIP1 b and IL-7 were related to higher anxiety risk,and IL-9 reduced its risk.Furthermore,peripheral inflammation might be regarded as biomarkers of cerebrovascular disease.For lacunar stroke,IL-1ra made an increased casually effect on its risk,but IL-12p70 manifested opposite direction.For circumscribed brain atrophy,genetically predicted MIP1 b and IFNg decreased its risk,and SCGFb and IL-2 increased the risk.Conclusion Specific systemic inflammatory factors were genetically associated with vascular cognitive impairment.Our results warrant further studies to be verified through clinical trials and elucidate the underlying mechanisms of these reported causal associations.