Effects Of Hepcidin On Hippocampal Iron Deposition And Cognitive Impairment In T2DM Rats

With the acceleration of population aging process and the change of lifestyle brought by urbanization in our country,the prevalence of type 2 diabetes mellitus?T2DM?has gradually increased,and the cognitive impairment caused by it has become an increasingly prominent clinical and social problem.Cognitive impairment is a common complication of type 2 diabetes and has a2.5-fold risk of developing dementia than normal people,which imposes a heavy burden on families and society.Therefore,elucidating the underlying mechanism of cognitive impairment induced by T2DM is of great significance for its prevention and treatment.It is well known that the hippocampus plays a prominent role in cognitive functions and is responsible for memory.Emerging evidence indicates that cognitive impairment in T2DM is related to iron overload in the brain,especially the hippocampus.Hepcidin plays a negative role in iron homeostasis and is widely distributed in the brain and liver.Therefore,the purpose of this study was to investigate the role of Hepcidin in hippocampal iron deposition and cognitive impairment in type 2 diabetic rats.Therefore,this research was designed to explore the role of hepcidin in hippocampal iron deposition and cognitive impairment in T2DM rats.Based on the rat model of type 2 diabetes,this study investigated the role of hepcidin in hippocampal iron deposition and cognitive impairment in type 2 diabetes through two studies.The first part of this study is consisted of three experiments.For experiment one,the rat model of T2DM was induced by Streptozotocin?STZ?and high-fat diet?HFD?.To investigate whether ^T2DM_{nMaovrirgiast} ^rats_{iowna tt} ^develop_{erri alm,atzhee} ^ed_naup ^cogni_pmabreatr ^ti_uos._f^{v e}_cT ^impairment,_{rhoes sliantgesn cthyr ot} ^s_ou ^patial_{grhe atchhe} ^learni_{tphlaet f}h_oⁿi_rd_m^g d ^ae_dⁿn_u^d _{r i}p_nl^ma_g^et f_t^mo_hr_e^or m_p^{y were}_{rdoubrei nt} ^asse_{rgi atlh,}^ssed_{ea npdo s} ^usi_tihtieo ^ng_tniimn ^a_gee spent in the target quadrant during the probe trial were analyzed.The results indicated that STZ and HFD administration resulted in significantly reduced spatial learning and memory of rats.The latency to reach the platform in T2DM rats was significantly longer than that in control rats during the positioning navigation trial.The number of crossings through the platform in T2DM rats was significantly less than that in control rats during the probe trial.Compared to the control group,the diabetic group exhibited significantly reduced time spent in the target quadrant during the probe trial.These data demonstrated that cognitive impairment occurred after T2DM.In experiment two,blood samples of rats were collected and analyzed to investigate changes in body iron level reflected by serum ferritin concentration,as well as changes in glucose and insulin levels after diabetes.The results showed that HFD and STZ injection induced hyperglycemia,insulin resistance,and significantly increased serum ferritin concentrations in T2DM rats,indicating the stability of the T2DM model and an increase in body iron content in T2DM rats.In experiment three,susceptibility-weighted images?SWI?were obtained using magnetic resonance imaging?MRI?on the basis of experiment one.The hippocampal susceptibility values were examined using quantitative susceptibility mapping?QSM?method to investigate brain iron deposition in T2DM.The results showed that the susceptibility values of T2DM rats in the bilateral hippocampus was significantly increased,demonstrating that T2DM rats developed hippocampal iron deposition.The first part showed in three experiments that the development of type 2 diabetes resulted in hippocampal iron deposition and cognitive impairment in rats.Then,whether the hippocampal iron deposition and cognitive impairment in T2DM rats are caused by insufficient hepcidin levels in the brain needs further exploration.Therefore,we conducted the second study to investigate whether the level of hepcidin in the brain effect hippocampal iron content and cognitive function of T2DM rats.The second part of this study further explored the underlying mechanisms of hippocampal iron deposition and cognitive impairment in T2DM rats by intracerebroventricular?i.c.v.?injecting recombinant adeno-associated virus that overexpress hepcidin?AAV-hepcidin?.The second part of this study is consisted of four experiments.For experiment one,the escape latency during the positioning navigation trial,the number of crossings through the platform during the probe trial,and the time spent in the target quadrant during the probe trial in three groups of rats were analyzed to study whether AAV-hepcidin improved spatial learning and memory impairment of T2DM rats using MWM.The results indicated that rats injected with AAV-hepcidin showed increased spatial learning and memory.The latency to reach the platform in rats injected with AAV-hepcidin was significantly shorter during the positioning navigation trial.Rats injected with AAV-hepcidin had significantly increased crossings through the platform and time spent in the target quadrant during the probe trial.These results revealed that cognitive impairment in T2DM were improved after AAV-hepcidin injection.In experiment two,blood samples of rats were collected and analyzed to investigate the effect of the increased hepcidin levels on glucose,insulin resistance and serum ferritin concentration in type 2 diabetic rats.The results showed decreased serum ferritin concentration of rats injected with AAV-hepcidin,indicating that the increased hepcidin level reduced the iron content in the type 2 diabetic rats.For experiment three,susceptibility-weighted images were obtained using magnetic resonance imaging.The hippocampal susceptibility values were examined using QSM method to investigate the effect of increased hepcidin levels on hippocampal iron content of type 2 diabetic rats.The results showed decreased susceptibility values in the bilateral hippocampus of Rats injected with AAV-hepcidin,suggesting that the hepcidin therapy reduced iron deposition in T2DM.In experiment four,the expression of AAV-hepcidin was detected by rat brain tissue.The results showed that the AAV-hepcidin has been normally expressed in the brain of T2DM rats,and the target gene Hepc has also been expressed.The second study showed in four experiments that the hippocampal iron deposition and cognitive impairment in T2DM rats has been improvement by increased hepcidin level.In conclusion,the present research demonstrated that the cognitive impairment and hippocampal iron deposition in T2DM was associated with insufficient hepcidin levels,which could be improved by increasing the expression of hepcidin.Our study may help reveal the role of hepcidin in iron homeostasis in T2DM,which would provide a new basis for the diagnosis and treatment of T2DM-associated cognitive impairment.