The Relationship Of Calcium Homeostasis And Oxidative Stress In Neurodegeneration

Calcium(Ca²⁺)plays critical role in fundamental functions of neurons,from the regulation of neurite outgrowth,synaptogenesis,synaptic transmission and plasticity to cell survival.Although it is essential for neurons,excessively high level of intracellular Ca²⁺is toxic to the cell.During aging,and especially in neurodegenerative disorders,cellular Ca²⁺homeostasis is interrupted,which leads to synaptic dysfunction,impaired plasticity and oxidative stress.All these factors contribute to neuronal degeneration and apoptosis.Oxidative stress,resulting in metabolic disorder of energy and aggregation of disease-related proteins,adversely affect Ca²⁺homeostasis in return.It causes Ca²⁺fluxes into the cytoplasm from the extracelluar environment and from the endoplasmic reticulum through the Ca²⁺ channels.Alterations of Ca²⁺-regulating proteins in the plasma membrane, endoplasmic reticulum,and mitochondria are involved in age-related neurodegeneration.The harm of aging on neuronal Ca²⁺regulation are subject to genetic and environmental factors that may cause or affect the risk of neurodegenerative disease.A good understanding of the cellular and molecular mechanisms of oxidative stress and cellular Ca²⁺dyshomeostasis during aging may be helpful to find novel therapies in neurological disorders such as Alzheimer's and Parkinson's diseases.1.The Relationship of Calcium Homeostasis and Oxidative Stress in VitroTo investigate the influence of oxidative stress on the calcium homeostasis,we used a model of oxidative stress on SH-SY5Y cells with H₂O₂.Fluo-4 calcium indicator and Flexstation were used to detect intracellular calcium flux.As a result, H₂O₂ caused Ca²⁺influx into the cytoplasm from the extracellular environment and from the endoplasmic reticulum(ER),depending on the concentration of H₂O₂.And L-ascorbic acid was proved of being effective to reduce the Ca²⁺influx caused by H₂O₂.Synthesized curcumin(CCM)and one of its derivatives(CCM-2)were studied as well.The results showed that these compounds could significantly protect the cells from intracellular Ca²⁺increase caused by H₂O₂,while another natural compound, EUK4010,was demonstrated to have no such effect on Ca²⁺homeostasis.2.Oxidative Stress in PS Knockout Mouse Model of ADForebrain-specific and conditional presenilin-1(PS1)and presenilin-2(PS2) double knock-out mouse exhibits some usual hallmarks of Alzheimer's disease(AD), such as progressive memory dysfunction,forebrain degeneration and ventricle enlargemen,without the accumulation of Aβ.Oxidative stress mechanism has been long implicated predominantly in amyloidosis-mediated AD pathologies;however,its role in the pathogenic mechanism of loss-of-function of PS in AD remains unclear.It is believed that presenilins form ER Ca²⁺leak channels and elevated Ca²⁺levels in the cytoplasm can also indirectly cause oxidative stress.To identify and understand oxidative imbalance as an important mechanism of AD in response to PS loss-of-function,we examined oxidative stress status,using F₂-isoprostanes(iPF_2α-â…¢) as the marker of lipid peroxidation in vivo,in both brain tissues and circulation of 4-, 8-,12-,and 16-month PS cDKO,PS1 cKO,PS2 KO and the age-,gender-matched wide-type control mice(WT).Enhanced lipid peroxidation was occurred in a genderand age-related manner in PS KO mice,and the enhancement of iPF_2α-â…¢in PS cDKO mice are dependent on both PS1 and PS2 deficiency.Western blot analysis of a-CaMKII revealed a significant increase of this protein in the brain of 12-month-old PS cDKO mice,implicating an involvement of calcium dyshomeostasis in the PS loss-of-function mechanism.In conclusion,the interaction of oxidative stree and calcium dyshomeostasis might have important role in response to the loss-of-function of PS in AD pathogenesis.3.The Effect of EUK4010 on Lipid Peroxidation in PS cDKO miceEUK4010 is a natural compound isolated from a herb,which has been used frequently in China for the treatment of cardiovascular diseases.EUK4010 has been identified to exhibit an inhibitory effect on beta-amyloid(Aβ)-induced loss of neuronal cell viability.To investigate if there is an anti-oxidative mechanism for EUK4010 in protecting neurons from neurodegeneration in PS cDKO mice,we administrated the 6-month-old PS cDKO mice with EUK4010 for 6 months and iPF_2α-â…¢was detected in both cerebral cortex and circulation after treatment.The results showed that there was no significant difference in production of iPF_2α-â…¢between the EUK4010-treated animals and their controls,suggesting that neuronal pharmacological protecting role of EUK4010 might be not oxidative stress-related.