종설 J Korean Neurol Assoc / Volume 24 / August, 2006 간질과뉴런손상기전 성균관대학교의과대학신경과학교실 서대원 Mechanism of Neuronal Damage in Epilepsy Dae-Won Seo, M.D., Ph.D. Department of Neurology, Samsung Medicial Center, Sungkyunkwan University School of Medicine, Seoul, Korea Epilepsy is one of the most common episodic neurological diseases, and patients with epilepsy may experience a range of neurological, psychological, and behavioral problems. Recurring seizures potentially contribute to the progressive severity of epilepsy, cognitive and behavioral consequences. The clinical and experimental evidences involving radiological, pathological, and biochemical studies suggest that seizures can potentially injure the brain via a number of diverse molecular, cellular, and network mechanisms. The damage includes neuronal death, axodendritic changes, molecular changes of synaptic membrane, and gliosis and increased neurogenesis. Those changes induce rewiring of the network and reorganization of synapses, causing alteration of the functional and morphological properties as the mechanism of epilepsy. As the most overt form of alterations, the neuronal death may result from the execution of cellular programs that are similar to the molecular machinery of programmed cell death including the caspases and bcl-2 family proteins. In epileptic seizure, the neurons are overexcited and run out of energy. The low energy state is closely related with the necrotic pathway. The features suggest that the neuronal death in epilepsy may follow characteristic mechanism, suggesting necrotic programmed cell death pathway. Therapeutic modification of seizure-induced death could open new strategy in epilepsy treatment. J Korean Neurol Assoc 24(4):301-310, 2006 Key Words: Epilepsy, Seizure, Neuron, Damage, Cell death 서 론 간질은돌발적임상양상 (paroxysmal event) 을나타내는흔한신경계질환이다. 유럽에서는전체인구의 5% 가평생 1회이상의간질발작을경험하게되며, 간질의발병률은 10만명중 50~70 명, 유병률은 0.5~1.0% 이며, 진단및치료의발전에도불구하고 30% 는여전히약제내성간질증후군 (pharmacoresistance epilepsy syndrome) 인것으로보고되고있다. 1 간질의평균이환기간은 10 년정도이지만, 장애를겪는생활 (disabilityadjusted life) 정도는신경계질환중우울증, 치매, 알코올중 *Dae-Won Seo, M.D., Ph.D. Department of Neurology, Samsung Medical Center, Sungkyunkwan University School of Medicine 50 Irwon-dong, Gangnam-gu, Seoul, 135-710, Korea Tel: +82-2-3140-3595 Fax: +82-2-3410-6540 E-mail: daewon3.seo@samsung.com 독에이어네번째로크며, 남성의폐암과여성의유방암과같은정도로간질환자들은신체적, 정신적, 사회적으로많은어려움을겪게된다. 2 간질발작은뇌뉴런집단의비정상적동기화 (synchronization) 에의해서발생하며, 발작직후뉴런은 fos 유전자의발현을포함한다양한변화를일으키며, 3 기능을악화시키는비가역적변화를겪을수있고, 이것을간질발작에의한뉴런의손상으로볼수있다. 뉴런손상은뇌기능의장애를유발하며, 흥분과억제의불균형을초래해간질발생을더욱악화시킬수있다. 4 이와같이간질발작의손상은다양한영향을초래할수있지만어떻게손상이이루어지는지에대해서자세히알려져있지않다. 임상적으로간질발작이신경계에미치는손상으로뇌영상의발달, 전자현미경연구결과, 세포사망기전에대한분자생물학적연구에힘입어새로운여러변화들이알려졌다. MRI 의발전으로간질중첩증후뇌위축을쉽게확인할수있었으며, J Korean Neurol Assoc Volume 24 No. 4, 2006 301
서대원 측두엽간질후해마의용적감소를확인할수있었다. 5 전자현미경으로간질발작후수상돌기의형태변화도확인할수있었다. 6 이러한변화는미세한시냅스변화부터뉴런의사망까지다양하지만, 가장심한형태는뉴런의사망이다. 최근뉴런의사망기전에대한형태적생화학적변화가간질발작후에도관찰된다고보고되었다. 7,8 본글에서는뉴런사망의형태적분자생물학적변화를포함한간질발작에의한손상을살펴보겠다. 본론 1. 괴사 (necrosis), 아포토시스 (apotptosis) 및사망기전 (death mechanism) 과거에뉴런은세포막항상성 (homeostasis) 을유지하는데장애가발생하여세포외액이유입되며팽창하다터져염증반응을일으키며사망하는것으로알려져왔다. 이러한사망기전을사망시거치게되는유일한최종공통단계로보았고 괴사 라명명해왔다. 괴사는세포막의항상성이파괴되어시작되며, 수동적이며비가역적으로진행하는유일한사망기전으로생각되어왔다. 그러나괴사의수동적팽창과는달리능동적수축이일어나며조용히소실되는사망형태가관찰되었고, 이러한사망기전을 아포토시스 라명명하였다. 7 생화학적면에서괴사는단백분해효소들과자유라디칼 (free radical) 들이연쇄반응을일으키지만, 아포토시스는세포내시스테인의존성아스파르탄산염특이적단백분해효소 (cysteine-dependent aspartatedirected proteases: caspase) 가관여한다. 또한세포막의여 러사망수용체 (death receptors; TNFR, Fas) 를통해시작되는외부경로나마이토콘드리아에서 cytochrome c가유리되면서시작되는내부경로를통하며, 핵내뉴클레오솜간분단 (internucleosomal fragmentation) 을보이며, 아포토시스체 (apoptotic body) 를형성한다. 7 결국뉴런사망은괴사나아포토시스형태의사망경로를밟으며, 서로다른생화학적물질들이관여한다고생각했다 (Table 1). 그러나괴사모양을띄면서생화적으로아포토시스의특징을보이는경우도알려졌고, 세포내수포 (vacuole) 을형성하는경우도있고, 전형적인핵내변화인뉴클레오솜간분단을보이지는않지만대단위 DNA 분단 [large scale DNA fragmentation (>50 kbp)] 을보이면서 caspase 관여없이사망하는세포들도관찰되었다. 8 이런다양성때문에아직까지세포사망기전에대해논란이있다. 현재흔한사망형태에따른분류방법은비프로그램세포사망 (non-programmed cell death: non-pcd) 과프로그램세포사망 (programmed cell death: PCD) 으로나누는것이다. 프로그램세포사망은 caspase 의존성과 caspase 비의존성으로나눌수있다 (Fig. 1). Caspase 의존성경로는 caspase-dependent DNase (CAD) 활성화와뉴클레오솜간분단을보이는데, 이경로는사망수용체경로또는마이토콘드리아경로로나눌수있다. Caspase 비의존성은다시유사- 아포토시스프로그램세포사망 (apoptosis-like PCD) 과유사-괴사프로그램세포사망 (necrosis-like PCD) 으로나눌수있다. 전자는 apoptosisinducing factor (AIF) 가관여하는데마이토콘드리아에서유리된 AIF가핵내로이동하여 endonuclease G와상호작용하며대단위 DNA 분단을일으킨다. 후자는세포내 mutated Ras 나 insulin-like growth factor 1 receptor (IGFIR) 활성화를통 Table 1. Comparison of necrosis and apoptosis in terms of morphology and biochemistry Morphological change During death Volume Membrane Mitochondria Nucleus DNA degradation After death Cell fragmentation Others Necrosis Swelling Rupture (early) Swollen Pyknosis Random No (lysis) Inflammation Apoptosis Shrinkage Intact (until late) Normal Chromatin margination Controlled (condensation) Yes (apoptotic body) Phagocytosis Biochemical change Energy state ATP depletion (%) Laboratory tests Calcium increase (um) Caspase requirement Pattern on gels 70~100 >1 No Smear 25~75 0.2~0.4 Yes Ladder (internucleosomal cleavage) 302 J Korean Neurol Assoc Volume 24 No. 4, 2006
간질과뉴런손상기전 Figure 1. Schematic drawing of proposed cell death pathway after epileptic seizure. The neuronal cell death after epileptic seizures occurs through non-programmed necrotic pathway, programmed caspase-independent necrotic pathway, programmed caspase-dependent extrinsic apoptotic pathway, and programmed caspase-dependent intrinsic apoptotic pathway. In non-programmed pathway, seizure induces disturbances in intracellular ion homeostasis through NMDA receptors, inducing mitochondria rupture and surrounding inflammation. In programmed necrosis, the swollen mitochondria induce cytochrome c release and caspase activation. In extrinsic pathway, binding of ligand to death receptors activates caspase-8, which makes truncated Bid (tbid) and activates intrinsic cascades through Bax and executor caspases like caspase-3. In intrinsic pathway, mitochondria release cytochrome c, Smac, Omni and AIF. Forkhead (FKHR in rhabdomyosarcoma) activates Bim, causing Bax translocation into mitochondria. Dephosphorylated Bad dissociates Bax from Bcl-xl, causing Bax translocation. Bax translocation induces cytochrome c release from intramembranous portion of mitochondria. The released cytochrome c binds to APAF-1 forming apoptosome. The intrinsic cascade is triggered by the apoptosome, which is inhibited by inhibitors of apoptosis pathway (IAP). Smac and Omi give negative feedback to IAP. In programmed death pathway, the activated executors (caspase-3, 6, 7) cause DNA fragmentation in nucleus. 해수포를형성한다. 이러한사망형태는전자현미경으로가장잘구분할수있다. 괴사의전형적인형태인비프로그램세포사망에서는비교적늦게까지핵내변화가관찰되지않으며, 아포토시스의전형적인형태인 caspase 의존성프로그램세포사망에서는초생달모양크로마틴응집 (crescent-like chromatin condensation) 이관찰되고, caspase 비의존성프로그램세포사망에서는부분적및주변부크로마틴응집 (partial and peripheral chromatin condensation) 이관찰된다. 특히유사-괴사세포사망 에서는크로마틴응집보다는분절된 DNA 덩어리 (lumpy DNA fragmentation) 가관찰된다. 9,10 따라서사망기전을언급할때는형태적구분과생화학적변화를동시에언급하는것이필요하다. 프로그램세포사멸은간질환자의조직에서도관찰되었다. 11 2. 간질발작에서뉴런사망기전간질발작에서뉴런의사망에는글루탄산염흥분독성 (gluta- J Korean Neurol Assoc Volume 24 No. 4, 2006 303
서대원 mate excitotoxicity) 이선두유발인자 (initial trigger) 로보인다. 12 글루탄삼염흥분독성작용은 ROS 를적절히제거하지못하는 oxidative stress 경로와 NMDA 수용체의개방에따른세포내칼슘증가경로를통해일어난다. 13 Oxidative stress 경로에대한뉴런배양실험에의하면글루탄산염에의해 neuronal NOS 가활성화되며, 산화질소 (nitric oxide: NO) 가증가되고, 결국 ROS 인 peroxynitrite 가증가되어세포내단백질의질화 (nitration) 가발생한다. 14 또한마이토콘드리아세포막의탈분극을촉진시켜마이토콘드리아세포막전위소실이발생하며이것은 ROS 생산을증가시키게한다. 이러한 oxidative stress 경로를통해핵내 DNA 손상이발생하며, 15-17 DNA 손상을수리하는효소인 poly-adp-ribose polymerase-1 (PARP-1) 이과도하게증가되고, AIF 가마이토콘드리아에서유리되고핵내로이동되어 caspase 비의존성세포사망경로를밟는다. 17 결국간질발작후글루탄산염흥분독성에서 oxidative pathway 중에 PRAP-1 이나 AIF 가중요한역할을할것으로생각된다. 세포내칼슘증가경로는간질발작후마이토콘드리아의칼슘농도가증가되면서시작된다. 이로인한마이토콘드리아의 membrane permeability transition (MPT) 이증가되면서막간 (intermembraneous space) 에있던 cytochrome c가세포질로방출된다. 그후순차적으로 apoptosome 형성, caspase-9 활성, caspase-3 활성을초래한다 (Fig. 1). Caspase-9 및 caspase-3 억제제를처치할경우이러한과정은억제될수있었다. 18 마이토콘드리아막간에서세포질로방출된 cytochrome c는 APAF-1 및 ATP 와결합하여칠면체 (heptamor) 의 apoptosome 을형성하고주위에있는 caspase-9 을활성화시킨다. 19 활성화된 caspase-9 에의해 caspase-3 가활성화되며이것은면역화학조직염색법이나 DEVDase 활성도를측정하여확인할수있다. 19 Caspase-3 는많은기질을분해시키지만, 실제뉴런사망에는 casapse-6 가더욱중요하다. 그이유는뇌에는 caspase-6 가 caspase-3 보다고농도로존재하고 caspase-6 는 caspase-3 보다먼저작동하며, 아포토시스전구체 (inhibitor of apoptosis precursor: IAP) 는 caspase-6 의작용을억제시키지못하기때문이다. 15 간질발작흰쥐모델에서발작후해마에서 caspase-6 의증가를확인할수있으며, 특히발작으로손상된해마의수상돌기에서 caspase-6 가강하게염색되는것을확인할수있었다. 15 이러한칼슘증가후 caspase 의존성마이토콘드리아내부계경로를통한세포사망이발생한다. Bax 증가를발작후 2시간내에관찰할수있으며, 이것은 cytochrome c가방출되는시기와비슷하다. 20 Bax 는 Bcl-xl 과결합된이중체 (dimmer) 로있다가, Bad 가 chaperone protein 14-3-3 에서떨어져 Bcl-xl 과결합하면 Bcl-xl 로부터유리되어마이토콘드리아외막에박히게 (translocation) 되면서 cytochrome c의방출과 caspase-9 및 caspase-3 의활성화를일으켜아포토시스내부계를활성화시킨다 (Fig. 1). Calcineurin 의억제제인 FK506 을투여하면 Bad의탈인산화 (dephosphorylation) 를차단해서 14-3-3 단백질로부터의유리를막을수있게된다. 결국내부계의활성화를차단하여보호작용을나타나게된다. 21 그러나해마뉴런의배양연구에서 kynurenic acid 를제거할때간질파와같은파형을관찰할수있고내부계의활성화를관찰할수있지만 Bad 의탈인산화를막는다고아포토시스를막을수는없었다. 결국 Bax 의증가에관여하는 Bad 는중간단계정도에작용하는단백질로생각할수있다. 22 Bim은세포체 (endoplasmic reticulum) 에서 dynein 과복합체를형성하거나 14-3-3 단백질과결합된상태 22 로있다가활성화되면 Bcl-w 와복합체 (oligomer) 를형성하여, Bcl-w 와결합되어안정된상태로있던 Bax 를유리시키고, 유리된 Bax 는미토콘드리아외막에박히게된다. 23 세포배양연구에서 Bim antisense oligonucleotides 로 Bim 유리를억제하면뉴런생존률이증가되었다. 24 그러나뇌실내카이닉산주사후유발한흰쥐의간질중첩증모델에서 Bim 은해마손상에기여하지못하고빠르게소실되었다. 25 따라서아직 Bad와 Bim 경로는간질발작으로인한세포의사멸에관여할것으로는생각되지만어느정도기여할지는모르고있다. Bim 의유리는전사인자인 forkhead in rhabdomyosarcoma (FKHR) 계에의해서조절된다. 흰쥐의카이닉산모델에서간질발작후 FKHR 과 FKHRL-1 의불활성화상태인인산화상태 (phosphorylated state) 가감소하고, 활성화상태인탈인산화상태 (dephosphorylated state) 가증가하며핵내로이동해 Bim 의발현을증가시키는것으로생각되고있다. 21 세포배양연구에서간질발작과같은전기적현상후에 FKHR 은 Bim 의 promoter 와더욱많이결합하였다. 그리고억제제인 sodium orthovanate 를투여하면세포의생존율을증가시킬수있었다. 또한 PI3K (phosphatidylinositol 3-kinase) 억제제인 LY294002 는 Akt 활성화를억제시키고, FKHR 의전사를유발하며, Bim 발현을증가시켜세포의생존율이감소하였다. 이런작용은허혈증모델에서허혈성내성 (ischemic tolerance) 과같이간질발작에서도 Akt 경로가같은보호작용을갖는것으로비교할수있다. 15 난치성측두엽간질환자의조직에서 Akt 활성화, FKHR 비활성화상태의증가, Bim 의감소를관찰할수있다. 20 이러한결과는일종의간질내성 (epileptic tolerance) 으로볼수있다. 즉 Akt 가활성화되면 FHKR 의인산화가증가하고 Bim 의발현은감소하여세포생존율이증가한다. 따라서 Akt 활성화는강력한치료의한부분으로고려할수 304 J Korean Neurol Assoc Volume 24 No. 4, 2006
간질과뉴런손상기전 있다. 그러나 FK506 은세포배양모델 26 에서는효과가있었지만, 동물실험모델 26-28 에서는효과가없어좀더세부적인연구가필요하다. 간질발작에의한 caspase 의존성프로그램세포사망외부계의활성화는사망수용체에리간드가붙어서수용체간의연결이일어나면서시작된다. Caspase-2, 8, 10의활성화가일어날수있으며, 간질발작으로동물실험에서 caspase-2 와 8의활성화가아주초기에일어나는것을알수있었지만, 27 아직정확한경로는확인되지않고있다. 뇌에는 TNFR1, Fas 및 DR4 가존재하며간질발작으로 TNFR1 과 Fas 수용체와 DR 리간드가결합하여나타난다. 29,30 사망수용체의신호전달과정은 FLIP (FADD-like interleukin converting enzyme inhibitory protein) 과 SODD (silence of death domains) 에의해서억제된다. 간질발작후 FLIP 의변화는아직밝혀져있지않지만, SODD 는해마제 3 아몬체방추세포 (pyramidal cell) 에서발현이감소되었다. 26 따라서사망수용체의결합이있고이로인한 caspase-8 이활성화되는외부계가작동할수있다는것을알수있다. 그러나전형적인프로그램 caspase 의존성세포사망의형태를보이는경우는매우드물다는보고도있다. 31 결국간질발작후다양한기전으로뉴런의사망이이루어질수있으며아포토시스의생화학적특징은쉽게발견할수있으나, 형태학적특징은잘관찰되지않는다고볼수있다. 오히려괴사형태의세포사망이흔히관찰되는점을고려할때프로그램 caspase 비의존성세포사멸과관련있을가능성이높다. 일부는 programmed necrosis 라기도하며이에대한연구가좀더필요하다. 3. 뉴런사망경로간의연결뉴런사망기전에는마이토콘드리아가초기에중요한역할을한다. 카이닉산 (kainite) 으로간질발작을일으킨후발생한뉴런사망에서 Bim, Bid, 및 Bad 가관여되어마이토콘드리아의막전위변화를유발하며, 허혈성뇌질환에서도 Bim, Bad 및 Bid 가관여하여마이토콘드리아경로를초기에활성화시킨다. 그러나초기의프로그램이활성화하며마이토콘드리아의영향이발생한이후에 caspase 는다양한되먹임경로 (feedback loop) 를통해서로활성화시킨다. 예를들면인도자 (initiator) 인 caspase- 8과 9이활성화되어실행자 (executor) 인 caspase-3 과 7이활성화된다. 마이토콘드리아에서 cytochrome c가유리되어 caspase-9 이활성화되고, 활성화된 caspase-9 은 caspase- 3를활성화시키고 caspase-2, 6, 8, 10, 그리고다시 caspase- 9이활성화되면서 caspase 계를증폭시킨다. 외부계에의한 caspase-8 은 Bid 를활성화시키고활성화형태인 truncated Bid (tbid) 는 cytochrome c의유출을촉진시키며내부계의 caspase-9 을활성화시키게된다. 결국외부계의인도자는내부계의활성화와연결되게된다. 따라서특정 caspase 억제제는효과를나타내지못하게된다. 32 또한내부계와외부계의활성화로세포사망경로에관여하는주요물질들은새로이합성되기보다는인산화와탈인산화또는단백질 -단백질상호간의작용 ( 결합, 이중체, 복합체 ) 을통해세포사망의중요한역할을수행한다. 33 이러한기전은전통적인아포토시스의연쇄반응보다에너지소모율이낮아서간질중첩증, 간질발작과같이에너지가고갈되는상황에서잘작동할수있는특성을가지고있다. 4. 선택적억제성중간뉴런소실억제성중간뉴런은뉴런집단의동기화에매우중요하다. 간질발작이뉴런집단의비정상적동기화로발생하므로동기화에영향을미치는억제성중간뉴런은간질발작에서매우중요한역할을할것으로생각된다. 해마연구에의하면 GABA 계중간뉴런들은주요세포세포체주변의신경지배 (perisomatic innervation) 를통해주요세포 (principal cell) 네트웍진동 (network oscillation) 에영향을주어주요세포들의동기화에중요한역할을하며, 수상돌기신경지배 (dendritic innervation) 를통해흥분성입력을조절하는역할을한다. 34 또한억제성중간뉴런은상위억제성 (disinhibitory) 중간뉴런의수상돌기신경지배를받는다. 35 억제성중간뉴런들은특정표지자에선택적인면역반응성을나타내므로, 면역조직염색법을통해각각의중간뉴런을확인할수있다. 세포체주변억제 (perisomatic inhibition) 는칼슘결합단백질 (calcium binding protein) 인 paralbumin (PV) 과면역반응 (immunoreactivity) 을나타내며, 36 수상돌기억제 (dendritic inhibition) 는 calbindin (CB), somatostatin 37 이나 neuropeptide Y (NPY) 와면역반응 (immunoreactivity) 을나타내고, 중간뉴런에작용 (interneuron selective: IS) 하는상위중간뉴런은 calretinin (CR) 과면역반응 (immunoreactivity) 을나타낸다 (Fig. 2). 전자현미경연구에의하면내측두엽간질환자의해마는중간뉴런에다양한변화가관찰된다. 면역반응성에따른억제성중간뉴런의변화를살펴보면 PV 면역반응성바구니세포 (basket cell) 는보존되며, 과립세포 (granule cell) 시냅스는증가한다. CB- 면역반응성뉴런도보존되지만, 수상돌기및세포체의팽창, 수상돌기가시 (dendritic spine) 및세포체가시 (somatic spine) 증가가관찰된다. SOM- 면역반응성, 또는 NPY- 면역반응성수상돌기억제성중간뉴런 (dendritic inhibitory interneuron) 은소실되며, 보상성가지 J Korean Neurol Assoc Volume 24 No. 4, 2006 305
서대원 Figure 2. Selective inhibitory interneuronal loss and rewiring of network. Interrupted lines indicate the death cells by epileptic seizures. The mossy cells, ST/NY interneuron and CR interneurons shows neuronal loss. The synaptic changes are seen dendritic synapses between PC and CB. The sprouting of dendrite of interneuron is drawn from intact ST/NY neuron in red. The sprouting of mossy fiber from granule cell (GC) is also drawn in red. PC: pyramidal neurons in CA3, GC: granule cells in dentate gyrus, MC: mossy cells in hilus, PV, CB, ST/NY: inhibitory GABAergic interneurons having positive immunoreactivity with paralbumin, calbindin, substance P/neuropeptide irrespectively. 치기 (compensatory sprouting) 도관찰된다. CR- 면역반응성뉴런은매우약하여한번의발작에서도소실된다. 38 이러한결과는간질발작후초기에는 CR- 면역반응성뉴런소실이발생해서상위억제성중간뉴런의억제성중간뉴런에대한억제능력이감소되어결국간질조직의과도한흥분이일어날수있는조건이된다. 그후생존한중간뉴런의축삭은가지치기등의보상적작용을보이지만이전과같은적절한억제적조절을나타내지못한다. 오히려지나친억제작용으로주요세포의동기화에기여하게된다. 결국간질발작에의한글루탄산염적흥분이주요세포에전달될때세포체주변과수상돌기주변억제성중간뉴론의소실로적절한억제성조절을받지못하여과도한흥분을나타내며, 살아남은억제성중간뉴런의축삭성장에의해부적절한동기화까지일으켜간질발작을강화하는데기여하게된다. 5. 수상돌기변화뉴런수상돌기가시 (spine) 들은흥분성글루타민산염적 (glutaminergic) 시냅스를가지고있으며흥분성신경전달의중요한구조물이다. 39 전자현미경적관찰에의하면가시를두부 40 와경부 (neck) 로나누어볼때길쭉한두부와가는경부형태부터버섯모양의두부와짧은경부형태까지다양하다 (Fig. 3). 지속촬영영상 (time-lapse imaging) 에의하면가시는아주빠르게움직이며그모양이변한다. 41 기능적으로전기적신호를수상돌기를거쳐세포체에전달하는회로 (circuit) 역할이외에수용체 (receptors), 이차신경전달물질 (second messenger) 및기타다른전달물질 (other transduction molecules) 을조절하는생화학적역할을수행한다. 42,43 이러한가시의기능은학습및기억과관련이있다. 즉새로운학습이나 long-term potentiation 이일어날때새로운가시가형성되며, 관찰할때 306 J Korean Neurol Assoc Volume 24 No. 4, 2006
간질과뉴런손상기전 Figure 3. Schematic drawings of change of spine. The dendritic spines are composed of presynaptic terminal, head, and neck. The types of spine changes are enlargement of heads, neck elongation, spine loss, and new spine formation. 두부의확대와경부의단축이관찰되기도하였다. 44 간질발작에의해가시의소실이나수상돌기의팽창 (swelling) 이수시간에걸쳐서서히나타나며, 글루탄산염길항제에의해억제되므로글루탄산염독성작용이중요한역할을한다고생각된다. 45 가시의두부와경부구조는 GTPase 가관여하는 actin 의 polymerization 에의해일어난다. 발작후글루탄산염독성작용에의해증가된세포내칼슘은 GTPase 를활성화시키고 actin 의 polymerization 을억제해서가시는자신의구조를유지할수게된다. 또한소디움, 염화물 (chloride) 및수분의유입에의해수상돌기의팽창이이루어지는것으로생각된다. 46 간질발작후수상돌기가시의소실및수상돌기의팽창은간질발작의원인인지단순한이차적변화인지확실하지는않지만, 시냅스의기능장애를유발할수있으며비정상적동기화를일으키는간질발작의원인으로생각할수있어서, 이에대해좀더자세한연구가필요하다. 6. 뉴런생성과교세포증식 출생후에도뉴런생성 (neurogenesis) 이일어나는치상회과립하층 (dentate subgranular layer) 에서간질발작후에는뉴런생성이 75~140% 증가하는것이관찰되었다. 47 뉴런생성증가의임상적의미는아직확실히알려져있지않지만, 기존에있던신경회로망이상을초래할가능성이높아진다. 발작후 GFAP (glial fibrillary acidic protein) 염색에의한교세포증식 (glial proliferation) 을관찰할수있다. 48 교세포는글루탄산염의재흡수에중요한역할을하며, 교세포증식은발작후비교적초기에확인할수있다. 이러한변화는단지이차적변화일수있지만뉴런의흥분도및동기화를변화시킬수있는환경을조성할가능성도있다. 7. 손상과기능적변화간질발작의손상으로일어나는영향은간질이진행되는점과기능이감소되는점으로나누어볼수있다. 측두엽간질에서 Gowers 의 발작은발작을초래한다 (seizures beget J Korean Neurol Assoc Volume 24 No. 4, 2006 307
서대원 Figure 4. Brain MRI and schematic drawing of hippocampal formation. (A) T2 weighted image of a normal subject shows normal hippocampal structure, which looks like a sea-horse shape. (B) T2-weighted image of a patient with mesial temporal lobe epilepsy reveals atrophic hippocampal formation. (C) Schematic drawing of the chief cells and trisynaptic circuit includes perforant pathway (PP) from subiculum, mossy fiber (Mf) from dentate granule cell, and schaffer collateral (SC) from CA3 pyramidal cell. (D) Mossy fiber of dentate granule cell has axonal spouting into inner molecular layer of dentate gyrus, indicating mossy fiber sprouting, and selective neuronal loss in CA4, CA3, CA1, and subiculum. seizures) 는격언처럼 1회의발작이후발작이강화되는것을볼수있었다. 49 또한측두엽간질이나신피질간질에서전신발작이많을수록해마의용적감소와인지기능감소가심하게관찰되었다. 50-54 간질발작후관찰한동물과사람의뇌조직에서주로 CA1 과 CA3 에서심한선택적신경세포의소실과함께치상회 (dentate gyrus) 과립세포 (granule cell) 의축삭인모시섬유 (mossy fiber) 가비정상적으로분자층내측부위 (inner molecular layer) 로성장하는것을볼수있다 (Fig. 4). 이러한발작후뉴런소실과모시섬유성장 (mossy fiber sprouting) 은간질의발생과기억기능의장애와관계가있다고보고되었다. 55 8. 신경보호작용세포사멸중프로그램세포사망에관여하는 Bcl-2 계, Akt, caspase, AIF 등을효과적으로억제한다면간질발작후난치성간질로의진행이나뇌기능의감퇴를막을수있다. GABA 는억제작용을나타낸다고알려져있지만, K-Cl cotransporter 인 KCC2 는 chloride 이온의세포외배출을억제시켜오히려 GABA 가흥분작용을나타낸다. 따라서일반적인 GABA 작용약제보다는수상돌기및세포체의특정부위에작용하는 GABA 계약제를통해효과적인신경보호작용을기대할수있다. 또한수상돌기가시의구조변화를막을수있는 actin 의 polymerization 을조절하는약제의개발을통해신경보호작용을기 308 J Korean Neurol Assoc Volume 24 No. 4, 2006
간질과뉴런손상기전 대할수있겠다. 요 약 간질발작의영향을소실, 변화및생성현상으로구분해볼수있다. 소실은주로뉴런에서확인되고, 간질발작의진행과인지기능저하에가장중요한소견이다. 특히선택적중간뉴런소실은간질발생기전의중요한부분으로생각된다. 변화는수상돌기및그가시들에서주로일어나며, 시냅스의기능적변화를초래하여간질발생을강화시키는원인으로생각된다. 생성은치상회하부에정상적으로존재하는뉴런의생성증가및교세포의증식에서알수있으며, 그의미는아직정확히모르고있다. 이러한변화중가장심한형태인뉴런사망은간질발작에서관찰되는프로그램세포사망의생화학적변화를고려할때주로프로그램괴사성세포사망형태를보이는것으로생각된다. 이러한간질발작으로발생하는뉴런의손상을조절할수있다면, 발작후간질발생이강화되는현상을예방할수있으며, 뇌의기능적보호도이루어질수있을것으로생각된다. 따라서간질발작에의한뇌손상의연구를통해새로운치료개념을도입할수있을것이다. REFERENCES 1. Brodie MJ, Shorvon SD, Canger R, Halasz P, Johannessen S, Thompson P, et al. Commission on European Affairs: appropriate standards of epilepsy care across Europe. ILEA. Epilepsia 1997; 38:1245-1250. 2. Engel J Jr. Bringing epilepsy out of the shadows. Neurology 2003; 60:1412. 3. Kim Y, Lee KS, Kim BS, Kim YJ, Chun MH, Kim MS. Characteristics of Lithium-Pilocarpine Seizure Model: Behaviors, Electroencephalography, Fos Expression and Neuropathologic changes. J Korean Neurol Assoc 1996;14:74-88. 4. Kim JM. Epilpetogenesis. J Korean Neurol Assoc 2002;20:101-109. 5. Bernasconi N, Natsume J, Bernasconi A. Progression in temporal lobe epilepsy: differential atrophy in mesial temporal structures. Neurology 2005;65:223-228. 6. Wong M. Modulation of dendritic spines in epilepsy: cellular mechanisms and functional implications. Epilepsy Behav 2005;7: 569-577. 7. Krantic S, Mechawar N, Reix S, Quirion R. Molecular basis of programmed cell death involved in neurodegeneration. Trends Neurosci 2005;28:670-6. 8. Henshall DC, Simon RP. Epilepsy and apoptosis pathways. J Cereb Blood Flow Metab 2005;25:1557-1572. 9. Kim MK, Kim KB, Sohn EJ, Cho KH, Lee MC. The Temporospatial Distribution of Glutamate Receptors and the Effect of MK-801 on Glutamate Receptors Activation in Kainateinduced Seizure Model: Quantitative Receptor Autoradiography of Ionotropic Glutamate Receptors. J Korean Neurol Assoc 2002;20: 179-186. 10. Aarts MM, Tymianski M. Molecular mechanisms underlying specificity of excitotoxic signaling in neurons. Curr Mol Med 2004;4:137-147. 11. Mazarati AM. Galanin and galanin receptors in epilepsy. Neuropeptides 2004;38:331-343. 12. Stewart VC, Heales SJ. Nitric oxide-induced mitochondrial dysfunction: implications for neurodegeneration. Free Radic Biol Med 2003; 34:287-303. 13. Vergun O, Sobolevsky AI, Yelshansky MV, Keelan J, Khodorov BI, Duchen MR. Exploration of the role of reactive oxygen species in glutamate neurotoxicity in rat hippocampal neurones in culture. J Physiol 2001;531:147-163. 14. Yu SW, Wang H, Dawson TM, Dawson VL. Poly (ADP-ribose) polymerase-1 and apoptosis inducing factor in neurotoxicity. Neurobiol Dis 2003;14:303-317. 15. Henshall DC, Araki T, Schindler CK, Lan JA, Tiekoter KL, Taki W, et al. Activation of Bcl-2- associated death protein and counterresponse of Akt within cell populations during seizure-induced neuronal death. J Neurosci 2002;22:8458-8465. 16. Henshall DC, Chen J, Simon RP. Involvement of caspase-3-like protease in the mechanism of cell death following focally evoked limbic seizures. J Neurochem 2000;74:1215-1223. 17. Henshall DC, Bonislawski DP, Skradski SL, Araki T, Lan JQ, Schindlen CK, et al. Formation of the Apaf-1/cytochrome c complex precedes activation of caspase-9 during seizure-induced neuronal death. Cell Death Differ 2001;8:1169-1181. 18. Weise J, Engelhorn T, Dorfler A, Aker S, Bahr M, Hufnagel A. Expression time course and spatial distribution of activated caspase-3 after experimental status epilepticus: contribution of delayed neuronal cell death to seizure-induced neuronal injury. Neurobiol Dis 2005;18:582-590. 19. Narkilahti S, Pitkanen A. Caspase 6 expression in the rat hippocampus during epileptogenesis and epilepsy. Neuroscience 2005;131: 887-897. 20. Meller R, Schindler CK, Chu XP, Xiong ZG, Carmeron JA, Simon RP, et al. Seizure-like activity leads to the release of BAD from 14-3-3 protein and cell death in hippocampal neurons in vitro. Cell Death Differ 2003;10:539-547. 21. Shinoda S, Schindler CK, Meller R, So NK, Araki Y, Yamamoto A, et al. Bim regulation may determine hippocampal vulnerability after injurious seizures and in temporal lobe epilepsy. J Clin Invest 2004;113:1059-1068. 22. Wilson-Annan J, O Reilly LA, Crawford SA, Hausmann G, Beaumont JG, Parma LP, et al. Proapoptotic BH3-only proteins trigger membrane integration of prosurvival Bcl-w and neutralize its activity. J Cell Biol 2003;162:877-887. 23. Korhonen L, Belluardo N, Mudo G, Lindholm D. Increase in Bcl-2 phosphorylation and reduced levels of BH3-only Bcl-2 family proteins in kainic acid-mediated neuronal death in the rat brain. Eur J Neurosci 2003;18:1121-1134. 24. Burgering BM, Kops GJ. Cell cycle and death control: long live Forkheads. Trends Biochem Sci 2002;27:352-360. 25. Yano S, Morioka M, Fukunaga K, Kawano T, Hara T, Kai Y, et al. Activation of Akt/protein kinase B contributes to induction of ischemic tolerance in the CA1 subfield of gerbil hippocampus. J J Korean Neurol Assoc Volume 24 No. 4, 2006 309
서대원 Cereb Blood Flow Metab 2001;21:351-360. 26. Henshall DC, Bonislawski DP, Skradski SL, Lan JQ, Meller R, Simon RP. Cleavage of bid may amplify caspase-8-induced neuronal death following focally evoked limbic seizures. Neurobiol Dis 2001; 8:568-580. 27. Shinoda S, Skradski SL, Araki T, Schindler CK, Meller R, Lan JQ, et al. Formation of a tumour necrosis factor receptor 1 molecular scaffolding complex and activation of apoptosis signal-regulating kinase 1 during seizure- induced neuronal death. Eur J Neurosci 2003;17:2065-2076. 28. Henshall DC, Skradski SL, Bonislawski DP, Lan JQ, Simon RP. Caspase-2 activation is redundant during seizure-induced neuronal death. J Neurochem 2001;77:886-895. 29. Fujikawa DG, Shinmei SS, Cai B. Kainic acid-induced seizures produce necrotic, not apoptotic, neurons with internucleosomal DNA cleavage: implications for programmed cell death mechanisms. Neuroscience 2000;98:41-53. 30. Fujikawa DG, Shinmei SS, Cai B. Seizure-induced neuronal necrosis: implications for programmed cell death mechanisms. Epilepsia 2000;41 Suppl 6:9-13. 31. Liou AK, Clark RS, Henshall DC, Yin XM, Chen J. To die or not to die for neurons in ischemia, traumatic brain injury and epilepsy: a review on the stress-activated signaling pathways and apoptotic pathways. Prog Neurobiol 2003;69:103-142. 32. Miles R, Toth K, Gulyas AI, Hajos N, Freund TF. Differences between somatic and dendritic inhibition in the hippocampus. Neuron 1996;16:815-823. 33. Gulyas AI, Hajos N, Freund TF. Interneurons containing calretinin are specialized to control other interneurons in the rat hippocampus. J Neurosci 1996;16:3397-411. 34. Sloviter RS, Sollas AL, Barbaro NM, Laxer KD. Calcium-binding protein (calbindin-d28k) and parvalbumin immunocytochemistry in the normal and epileptic human hippocampus. J Comp Neurol 1991;308:381-396. 35. Magloczky Z, Freund TF. Impaired and repaired inhibitory circuits in the epileptic human hippocampus. Trends Neurosci 2005;28:334-340. 36. Gray EG. Electron microscopy of synaptic contacts on dendrite spines of the cerebral cortex. Nature 1959;183:1592-1593. 37. Reutens DC, Bye AM, Hopkins IJ, Danks A, Somerville E, Walsh J, et al. Corpus callosotomy for intractable epilepsy: seizure outcome and prognostic factors. Epilepsia 1993;34:904-909. 38. Nimchinsky EA, Sabatini BL, Svoboda K. Structure and function of dendritic spines. Annu Rev Physiol 2002;64:313-353. 39. Koch C, Zador A. The function of dendritic spines: devices subserving biochemical rather than electrical compartmentalization. J Neurosci 1993;13:413-422. 40. Zhao M, Su J, Head E, Cotman CW. Accumulation of caspase cleaved amyloid precursor protein represents an early neurodegenerative event in aging and in Alzheimer's disease. Neurobiol Dis 2003;14:391-403. 41. Segal M. Dendritic spines and long-term plasticity. Nat Rev Neurosci 2005;6:277-284. 42. Mizrahi A, Crowley JC, Shtoyerman E, Katz LC. High-resolution in vivo imaging of hippocampal dendrites and spines. J Neurosci 2004;24:3147-51. 43. Rensing N, Ouyang Y, Yang XF, Yamada KA, Rothman SM, Wong M. In vivo imaging of dendritic spines during electrographic seizures. Ann Neurol 2005;58:888-898. 44. Kennedy MB, Beale HC, Carlisle HJ, Washburn LR. Integration of biochemical signalling in spines. Nat Rev Neurosci 2005;6:423-434. 45. Al-Noori S, Swann JW. A role for sodium and chloride in kainic acid-induced beading of inhibitory interneuron dendrites. Neuroscience 2000;101:337-348. 46. Kim YI, Lee KS, Kim BS, Kim YJ, Chun MH, Kim MS. Characteristics of Lithium-Pilocarpine Seizure Model: Behaviors, Electroencephalography, Fos Expression and Neuropathologic changes. J Korean Neurol Assoc 1996;14:74-88. 47. Liu ZL, Xu RX, Yang ZJ, Dai YW, Luo CY, Ru MX, et al. [Responses of neurons and astrocytes in rat hippocampus to kainic acid-induced seizures]. Di Yi Jun Yi Da Xue Xue Bao 2003;23: 1151-1155. 48. Cohen I, Navarro V, Clemenceau S, Baulac M, Miles R. On the origin of interictal activity in human temporal lobe epilepsy in vitro. Science 2002;298:1418-1421. 49. Pitkanen A, Sutula TP. Is epilepsy a progressive disorder? Prospects for new therapeutic approaches in temporal-lobe epilepsy. Lancet Neurol 2002;1:173-181. 50. Briellmann RS, Wellard RM, Jackson GD. Seizure-associated abnormalities in epilepsy: evidence from MR imaging. Epilepsia 2005;46:760-766. 51. Fuerst D, Shah J, Shah A, Watson C. Hippocampal sclerosis is a progressive disorder: a longitudinal volumetric MRI study. Ann Neurol 2003;53:413-416. 52. Liu RS, Lemieux L, Bell GS, Hannmers A, Sisodiya SM, Bartlett PA, et al. Progressive neocortical damage in epilepsy. Ann Neurol 2003;53:312-324. 53. Thompson PJ, Duncan JS. Cognitive decline in severe intractable epilepsy. Epilepsia 2005;46:1780-1787. 54. Oyegbile TO, Dow C, Jones J, Bell B, Rutecki P, Sheth R, et al. The nature and course of neuropsychological morbidity in chronic temporal lobe epilepsy. Neurology 2004;62:1736-1742. 55. Hengartner MO. The biochemistry of apoptosis. Nature 2000;407: 770-776. 310 J Korean Neurol Assoc Volume 24 No. 4, 2006