SCAP/SREBP-2 Mediated Disorder Of Glucose And Lipid Result In Type 2 Diabetes Mellitus Associated Cognitive Dysfunction

Part Ⅰ Association between peripheral levels of LDL-C and mild cognitive function in T2 DM patientsBackgrounds: Cholesterol is one of the most important contents of neurons.However,excess cholesterol is also a risk factor of cognitive dysfunction.In previous study,the disorder of cholesterol metabolism is involved in the occurrence of cognitive impairment.Nether the less,the relationship between cognitive function and disorder of LDL-C,which is common in T2 DM patients is still need further explore.Objectives: We aim to explore the relationship between cognitive impairment and LDL-C levels in T2 DM patients,especially in diabetic patients with different levels of LDL-C.Methods: We recruited 497 patients with T2 DM in this present cross-section study.Firstly,sociodemographic,clinical characteristics and cognitive performances were extensively assessed.All patients were divided into MCI group and NC group according to the results of Mo CA scores,reflecting the global cognitive function.In addition,correlation analysis,goodness of fitting,binary logistic regression analysis and multiple linear regression analysis were used to access the relationship between levels of LDL-C and cognitive function in patients with T2 DM.Results: There is not only no significance between LDL-C levels of patients in MCI group and NC group,but also no significant liner relation between LDL-C levels and Mo CA in all patients enrolled in this present work.However,inverted-U-shaped correlation between serum LDL-C levels and Mo CA were found in all patients.Moreover,the cutoff point of this U-shaped curve is 2.686 mmol/l.In patients with LDL-levels over 2.686 mmol/l,LDL-C levels is negatively associated with Mo CA.Further binary logistic regression analysis showed that increased LDL-C is an independent risk factor of MCI in patients with T2 DM adjusted by age,gender,education levels and hypertension duration.Additionally,multiple linear regression analysis suggested that LDL-C is positively associated with TMT-B,which is reflecting executive function,in patients with LDL-C levels higher than 2.686 mmol/l,while LDL-C is positively related to CDT,which showing the visual space function,in patients with LDL-C levels lower than 2.686 mmol/l.Conclusion: Excessive or deficient LDL-C may result in the cognitive dysfunction.Excessive LDL-C seems to damage the executive function of T2 DM patients.Patients with T2 DM may benefit from suitable levels of LDL-C.Part Ⅱ SCAP/SREBP-2 activated by CML involves in the cognitive dysfunction of KK-Ay mice with the disorder of glucose and lipidBackground: CML is one of the most important content of AGEs,involves in the occurrence and development of diabetic complications including neurological complications.SREBP-2 is an important transcription factor associated with cholesterol.SCAP,a couple protein of SREBP-2,could sense the concentration of cholesterol in the cytoplasm and transport SREBP-2 from endoplasmic reticulum to Golgi as the lack of cholesterol.SREBP-2 could be cleaved to mature SREBP-2,get into nuclear to regulate the expression of target genes and involve in cognitive impairment directly or via the metabolism of cholesterol.Objectives: We aim to investigate that whether CML active SCAP/SREBP-2,and involve in cognitive dysfunction of KK-Ay mice with the disorder of glucose and lipid in vivo.Methods: In this present study,KK-Ay mice with the disorder of glucose and lipid were considered as models of cognitive impairment.C57BL/6 mice with HFD and ND were used as control.Peripheral levels of cholesterol and CML were measured,RAGE,SCAP,SREBP-2,BACE1 and Aβ were observed in hippocampus.Additionally,the cognitive function of mice was analyzed.Moreover,FPS-ZM1,a specific blocker of RAGE,were used to block the effect of CML on RAGE.And then,the effect of FPS-ZM1 on the activation of SCAP/SREBP-2 and the cognitive function of KK-Ay mice were monitored.Results: Compared to C57BL/6 mice with ND,KK-Ay mice and C57BL/6 mice with HFD showed increased peripheral levels of cholesterol and significant cognition decline.While KK-Ay mice exhibited impaired cognitive function,there is no significant cognition decline in C57BL/6 mice with HFD.Additionally,activated SCAP/SREBP-2 were measured in the hippocampus of KK-Ay mice.Hippocampal expression levels of BACE1 and deposition of Aβ were detected in KK-Ay mice rather than C57BL/6 mice with HFD.However,FPS-ZM1 inhibited the activation of SCAP/SREBP-2,down-regulated the expression of BACE1 and decreased the deposition of Aβ in hippocampus of KK-Ay mice.Conclusion: CML may activate SCAP/SREBP-2 by RAGE,and involves in the occurrence and development of cognitive dysfunction in KK-Ay mice with disorder of glucose and lipid.Part Ⅲ CML activated SCAP/SREBP-2,regulated the expression of BACE1,and increased the produce of Aβ in HT22 cellsBackgrounds: SREBP-2 could be transported from endoplasmic reticulum to Golgi by SCAP as the low concentration of cholesterol in cytoplasm.Since SREBP-2 was transport to Golgi,it will be cleaved to mature SREBP-2,entering nuclear to regulate the expression of its target genes including gene involves in metabolism.However,as cholesterol is excessive,SREBP-2 could be bind on endoplasmic reticulum and cannot be transported to Golgi.The cholesterol homeostasis is regulated by this kind of “negative feedback balance”.Previous study showed that matured SREBP-2 could get into nuclear and regulate the expression of BACE1.Our previously research suggested that CML could induce apoptosis of neurons and involve in diabetic cognition decline.However,it is not clear that CML could break this kind of “negative feedback balance”,promote SREBP-2 transported to Golgi and cleaved to mature SREBP-2,regulate the expression of BACE1 and increase the produce of Aβ in HT22 cells.Objectives: We aim to clarify that if CML break the above “negative feedback balance”,promote the transport from SREBP-2 from endoplasmic reticulum to Golgi and regulate the expression of BACE1 and the produce of Aβ in vitro。Methods: In this part,HT22 cells were used.First of all,LDL-C was used to treat HT22 cells.The effect of LDL-C upon SCAP/SREBP-2 was monitored.In addition,CML was used to treat HT22 cells with LDL-C.SCAP,SREBP-2,BACE1 and Aβ were measured.SREBP-2 on Golgi and nuclear was detected by immunofluorescence and observed by confocal microscope.The direct interactive between SREBP-2 and promoter sequence of BACE1 was inspected by chromatin immunoprecipitation.Moreover,FPS-ZM1 was used to block the effect of CML.The activation of SCAP/SREBP-2,the expression of BACE1 and the produce of Aβ were measured.Finally,the overexpression of RAGE in HT22 cells was performed.Results: LDL-C significantly decreased the levels of SCAP and SREBP-2 in HT22 cells.LDL-C and CML treated HT22 cells not only showed increased SACP and SREBP-2,but also up-regulated BACE1 expression and Aβ producing.Additionally,the amount of SREBP-2 on Golgi and nuclear increased.Moreover,we detected the sequence of BACE1 promoter in the mixture pulled by SREBP-2 antibody by PCR.FPS-ZM1 reduced the levels of SCAP and SREBP-2,decreased the amount of SREBP-2 on Golgi and nuclear,meanwhile,down-regulated the expression of BACE1 and the producing of Aβ.Compared to transfection with control plasmid,the transfection with RAGE overexpression plasmid reversed the effect of FPS-ZM1 on HT22 cells with LDL-C and CML.Conclusion: CML could activate SCAP/SREBP-2,promote the transport of SREBP-2 to Golgi.SREBP-2 transported to Golgi could be cleaved,enter nuclear and involve in the expression of BACE1 result in the producing of Aβ.