Iron Aggravates The Depressive Phenotype Of Stressed Mice By Compromising Glymphatic System

Objective:Glymphatic system is a flow system of cerebrospinal fluid-brain tissue fluid exchange mediated by astrocytes,which can promote the clearance of metabolic waste in the brain parenchyma and play an important role in maintaining the homeostasis of the extracellular microenvironment.In previous studies,we have reported unpredicted chronic mild stress(CUMS)treatment decreased the function of Glymphoid system and increased the level of amyloid-b 42(Ab 42)in the brain which related with Alzheimer's disease protein.Fluoxetine could improve the circulatory function of Glymphoid system and decrease the level of amyloid-b 42 by increasing the expression of aquaporin 4(Aquaporin4;AQP4)in astrocytes.However,in the behavioral experiment,we found that CUMS could only increase the depression-like or anxiety-like behavior of mice,and the cognitive function was not significantly affected.Recent studies have found that iron overload can affect the pathological mechanism of neurodegenerative diseases.Clinically,patients with major depressive disorders(MDD)are more likely to be associated with neurodegenerative diseases,such as Alzheimer's disease and Parkinson's disease,but the related pathological mechanism is unclear.Moreover,the effect of iron overload on the function of Glymphatic system is not known.In this study,we studied the effect of iron overload on the circulatory function of Glymphoid system in CUMS model mice,and revealed the effect of iron overload on the cognitive function of MDD patients.Methods:1.C57BL/6 male mice were randomly divided into CUMS group and control group.CUMS model mice were established by chronic unpredictable stress.Five weeks after CUMS treatment,we performed sucrose preference test.The mice were successfully modeled were randomly divided into control group and iron overload group.They were injected with dextran or iron dextran for 6 days,respectively: control group,(Control);iron overload group,(Iron);CUMS treatment group(CUMS)and CUMS+iron co-treatment group(CUMS+Iron).2.The accumulation of iron in the brain was detected by Perl's staining.3.The tracer was infused into the subarachnoid CSF via cisterna magna puncture at a rate of 2ml/min for 5 minutes to measure the function of Glymphatic system.4.The expression of transferrin receptor(TFR)in cortex and hippocampus was detected by immunofluorescence.5.TUNEL staining was used to detect the effect of CUMS and iron overload on apoptosis.6.The behavior of mice was tested to explore the effect of iron overload on depression-like behavior.Results: 1.Compared with the control group,Perl's positive iron deposition was found in the iron overload group and the CUMS and iron co-treatment group,but not in the mice treated with CUMS alone.2.CUMS or iron overload alone can affect the circulatory function of glymphoid system,but iron overload further aggravate this effect.3.Excess iron or CUMS instigates astrogliosis in cortex,but iron overload further promote astrogliosis in the CUMS modle mice.4.CUMS treatment promotes neuronal expression of TFR stimulated by overload with iron.5.Treatment with CUMS enhances neuronal apoptosis triggered by overload with iron.6.At the behavioural level iron overload exacerbated depressive like phenotype of stressed mice,and added motor and cognitive impairments absent in mice treated with CUMS alone.Conclusion: Iron overload aggravates the depression-like behavior of CUMS treated mice by inhibiting the function of Glymphoid system,and further causes motor and cognitive dysfunction in mice.At the same time,iron overload enhanced the expression of transferrin receptor(TFR)in neurons,and pre-treated with CUMS increased the expression of TFR induced by iron overload,which in turn aggravated the apoptosis level of neurons in cortex and hippocampus.Our results show that iron overload in CUMS-treated model mice can further aggravate depression-like performance and induce motor and cognitive impairment.This study suggests that patients with MDD should pay attention to intake of iron.Excessive iron in the body will not only aggravate the depressive symptoms,but also increase the risk of neurodegenerative diseases.