A Study About The Correlation Between The PHG-OFC/POR-vlOFC Neuronal Circuit And Visuospatial Dysfunction In Alzheimer’s Disease

BacgroundAlzheimer’s disease(AD)is a neurodegenerative disease with progressive cognitive decline,behavioral impairment,associated psychiatric disorders,and eventual loss of ultimate daily living ability.It is the most common type of dementia,accounting for 60-80%of the dementia.The problem of dementia is a major problem for human beings and a global issue of great concern.With the aging of the population,the prevalence of AD has increased year by year.According to the 2018 AD Global Report,there is a case of dementia every 3 seconds in the world.In 2018,about 50 million people worldwide suffer from dementia.The cost will reach 1 trillion US dollars By 2050,the global population of dementia will increase to 152 million,and the related costs will increase to 2 trillion US dollars.However,so far,the pathogenesis of AD is still unclear.Once the disease begins,there is no effective drug reversal.Drugs targeting the characteristic pathological changes of AD always failed in the clinical trials.Solanezumab,a drug targeting Abeita failed in the phase III of clinical trials as well.Therefore,for decades,it is important to find the mechanism of the onset of AD for improving the early diagnostic of AD.One of the means,early diagnosis and early intervention of AD has always been the focus of attention and an important problem to be solved in the world.The human beings have about 1011 neurons and 1015 synaptic connections.They interact with each other to form multiple neural networks to control our behavior,emotions and memory.But changes of the connection patterns between neural networks underlies psychiatric disorders and neurodegenerative diseases remains unclear.In 2016,academician Pu Muming and others proposed the concept of "one body and two wings" in the brain plan of china for exploring the neural basis underling cognitive function,early diagnosis and intervention of brain diseases and development and ampplication of brain-computer interface in the field of rehabilitation.It provided us a new idea for the study of AD.Episodic memory impairment is one of the core clinical symptoms of AD.In addition,in recent years,visuospatial memory deficit was also found in the early stage of AD,and it would get worse with the progression of disease.With the development of neuroimaging technology,the function of the brain is gradually visualized.Previous studies by visuospatial task dependent magmatic resonance imaging(MRI)showed that the dorsal pathway and ventral pathway contributed to visuospatial function.The dorsal pathway delivery information from visual cortex to inferior parietal lobule and superior parietal lobule,while,the ventral pathway sending message from the visual cortex to the inferotemporal cortex.Studies in rodents and primates showed that the hippocampus,the parahippocampus,and frontal cortex make close interaction with the dorsal and ventral pathway in visuospatial function.The parahippocampus is a key region contributing to visuospatial memory.It has numerous fibers including inferior longitudinal fasciculus,superior longitudinal fasciculus,unciform fasciculus(UF),joint fasciculus and the thalamus peduncle.The uncinate fasciculus is a hook shaped long-range association pathway which creates a monosynaptic connection from the anterior temporal lobes to the orbitofrontal cortex(OFC),contributing to visuospatial memory,episodic memory,social emotional processing and language function.In rodents,the postrhinal cortex(POR)-central lateral orbitofrontal cortex(vlOFC)pathway is homologous to PHG-OFC circuit in primate.Our previous study showed that the deficit of UF was associated with episodic memory impairment in aMCI patients.In wilde mice,the glutamatergic POR-v1OFCpathway modulates the retrieval of visuospatial memory.Therefore,the anatomical and functional impairment of the PHG-OFC circuit plays important role in the pathogenesis of AD,which may be one of the initiating factors of visuospatial memory deficit.Therefore,in this study,we combine the aMCI patients and 5XFAD transgenic mice to explored that how the PHG-OFC or the POR-vlOFCcircuit modulates visuospatial function deficit in AD through neuroimaging in human and mice.First,in a three-year longitudinal follow-up study,conbininga multi-dimensional cognitive neuropsychological assessment and neuroimaging studies,we assess cognitive function of aMCI patients and its correlation with brain structural and functional brain network;Second,micro-MRI was performed to detect the structural and functional alteration of brain network in visuospatial memory-impaired 5XFAD mice;(3)Third,combination of in vivo c-Fos mapping,neurotropic virus tracing,in vivo electrophysiology and opotogentics,to explore the structural and functional integrity of POR-vlOFC projection in 5XFAD mice.Finally,the study is expected to advance our understanding of the modulation pattern of the PHG-OFC projection on visuospatial memory in AD,and shed lights on exploring the biological markers of AD in the future.Part Ⅰ Damage of the PHG-OFC neural circuit in aMCI patients and its relationship with visuospatial memoryObjective:To investigate the relationship between structural and functional integrity of PHG-OFC circuit and visuospatial function scores in aMCI patients,and its changes with disease progression.Methods:Multi-dimensional cognitive neuropsychological assessment and multi-modal rest-state functional magnetic resonance imaging(R-fMRI)were performed in 146 subjects[aged 60-80 years,including 64 aMCI patients and 82 healthy controls(HCs)at baseline].Seed-based analysis was used to investigate the differences of cortical thickness,volume of gray matters(GM),regional cerebral blood flow,functional connectivity and integrity of white matters(WM)in PHG and OFC between aMCI patients and healthy controls(HC s).Further we explored the correlation between each neuroimaging indexes with visuospatial memory scores by covariance analysis.Additionally,50 of 82 HC and 57 of 64 aMCI subjects received follow-up clinical evaluations after a 3-year interval.16 aMCI subjects(28%)progressed to probable Alzheimer’s disease(pMCI),whereas 34(60%)remained cognitively stable(sMCI)over successive clinical evaluations;46 HC subjects remained cognitive stable(sHC).At the 3-year follow-up,six of the 16 pMCI and 6 six of the 34 sMCI were excluded due to excessive motion artifacts,poor quality of image(i.e.,ghost intensity)or incomplete image coverage.4 HC subjects progressed to aMCI and 7 aMCI subjects revert to a normal state at the 3-year follow-up,whowere not recruited into the secondary follow-up study.Hence,46 sHC,10 pMCI and 28 sMCI participants underwent baseline and follow-up multi-modal MRI scans.To determine whether the longitudinal changes in the neuropsychological tests and neuroimaging measures were significantly different among the sHC,sMCI and pMCI groups,general linear models with“diagnosis" as predictor variable were performed on the longitudinal change estimates(i.e.,A values,follow-up subtracted from those at baseline)with an FDR-corrected P<0.05 were considered as significant.Results:(1)At baseline,the scores in visuospatial function in aMCI patients was significantly decreased.ROI-based analysis showed that compared with HCs,the cortical thickness of bilateral PHG and GM volume of right PHG were significantly reduced in aMCI patients.In addition,WM tracts of interest(TOI)-based analysis showed impaired integrity of right UF in aMCI patients(P<0.05,FDR correction).However,no significant between-group differences were observed in rCBF values in the orbitofrontal and parahippocampal ROIs,and reste state FCs(RSFCs)in ROI pairs.Correlation analyses revealed that the mean GM volume in the parahippocampal ROIs(i.e.,left A35/36r[r=0.334,P=0.008]and A28/34[r=0.305,P=0.017],and right TI[r=0.295,P=0.021])positively correlated with the CDT scores in the aMCI group.(2)The pMCI group showed a significant greater decrease in GM volume over time than did sHC and sMCI groups in the right PHG[i.e,right A28/34(FDR corrected,F=6.515,P=0.002)].In addition,the pMCI group showed greater longitudinal deficits in the bilateral UF integrity,compared with the sHC and sMCI groups(FDR corrected,P<0.05).However,there were no statistically significant longitudinal rCBF and RSFC differences among the three groups.Finally,within the pMCI group,the longitudinal deficits in the left UF integrity(i.e.,MD value[r=-0.639,P=0.047])correlated with the longitudinal decreases in the CFT scores.Conclusion:Visuospatial dysfunction was shown in aMCI patients which may related to the structural damage of PHG-OFC neural circuit,and it is aggravated with the progress of the disease.Part Ⅱ Neuroimaging characteristics of the POR-v1OFC circuit in 5XFAD mice:evidence from multi-modality 7.0T MRIObjective:To investigate the damage pattern of microstructural and functional integrity of POR-v1OFCpathway in 5XFAD mice.Methods:First,Morris water maze(MWM)test was performed in 5-month 5XFAD mice and age-matched WT mice,to detect the spatial learning and memory;(2)using 7.0T micro-MRI,ROI-based analysis was performed to evaluate the T2 relaxation time(T2-RT),DTI index[diffusion anisotropy(FA),mean diffusivity(MD),axial diffusivity(DA)and DR]and Mn2+enhanced T1 signals in the POR and v1OFC between 5XFAD and WT mice.Results:(1)Compared to the age mathced WT mice,the 5XFAD mice showed significantly prolonged escape latency on the 3rd(adjusted P=0.002),4th(adjusted P=0.022)and 5th(adjusted P=0.047)days of training.In the pilot MWM test,the 5XFAD mice had significantly decreased crossovers of initial platform position(t=2.616,P=0.012)and percentage of time spent in the quadrant(t=2.522,P=0.016)without abnormal swimming velocity,compared to age-matched controls.(2)The age-matched 5XFAD and WT mice showed no significant differences in terms of GM volume,Mn2+enhanced T1 signal and four DTI indices[diffusion anisotropy(FA),MD,DA and DR]with voxel-based analysis(P>0.005,uncorrected,cluster size>30).In atlas-based analysis,the ROI of the POR and v1OFC were generated and normalized to the template.While,the POR of 5XFAD mice showed significant lower T2-RT and higher Mn2+enhanced T1 signal,no significant differences were observed in the v1OFC of WT and 5XFAD mice.In addition,neither areas showed any difference in the GM volume and DTI indices between the two groups.Taken together,the 5XFAD mice showed clear deficits in spatial and memory functions compared to the WT mice,which were likely related to their neuroanatomical differences.Conclusion:5-month 5XFAD mice showed spatial learning and memory impairment,and the micro-structure and function in the POR of these mouse are significantly damaged,which may be the anatomical basis of spatial learning and memory impairment in 5XFAD mice.PartⅢ The anatomical and founctionalcharacteristics of the POR-vlOFCprojection in 5XFAD miceObjective:The POR and OFC play important roles in spatial memory.Our previous study showed that the POR-v1OFCpathway is a glutamatergic projection,and it involved in the retrieval of visuospatial memory in wild mice.Visuospatial memory deficit is one of the core symptoms in AD,but whether the structure and function of POR-OFC pathway is damaged in 5XFAD mice and whether its intervention could rescue the visuospatial memory deficit remains unclear.In the present study,virus tracing,c-Fos mapping and in vivo electrophysiology recording were performed to explore the structural and functional alteration of POR-vlOFC projection in 5XFAD mice,and optogenetic manipulation were applied to detect whether it could improve the visuospatial memory in 5XFAD mice.Methods:The visuospatial memory was determined by novel object place recognition test(NOPRT);immunofluorescence was performed to detect the expression of CamKIIa,GAD67 and their co-expression with c-Fos protein;in vivo recording of the local field potential(LFP)was performed to explore the functional connection between the POR and v1OFC regions.Retrograde anatomical tracing with cholera toxin B(CTB)labeling was performed to detect the structural integrity of the POR-OFC projection;Furthermore,optogenetically,we probed whether opto-stimulation of the neuron-specific POR-v1OFC pathway significantly improved the visuospatial memory deficit.Results:(1)Compared with WT mice,6-month 5XFAD mice showed visuospatial memory deficit rather than 4-month 5XFAD mice;(2)During NOPRT,the deactivation of the glutamatergic neurons in the v1OFC region was shown in 5XFAD mice.(3)5XFAD mice showed decreased power of beta band in the vlOFC region and increased coherence at 15HZ between the POR and v1OFC regions during exploring the displaced object,as compared with WT mice.(4)Retrograde anatomical tracing with CTB labeling revealed that 5XFAD mice had a slightly lower ratio of the CamKIIa-positive CTB neurons in the POR to the v1OFC;(5)Effective rescue of the impaired visuospatial memory deficit by opto-stimulation of glutamatergic POR-vlOFC terminals was found in 5XFAD mice.Conclusion:It further suggested that the disruption of the glutamatergic POR-vlOFC pathway may be the anatomical foundation of the visuospatial memory deficit providing a potential target for intervention of AD.