癲癇重積狀態 (status epilepticus; SE) 為一種嚴重並且可能會危及到生命的神經性急症。當個體所產生的癲癇時間過長或短時間內不斷的產生癲癇反應就即稱之為癲癇重積狀態，並且會因為大腦中興奮性神經元過度的放電造成麩胺酸 (glutamate) 釋放增加進而導致神經毒性 (neurotoxicity) 的發生，而受損神經元產生的異常電脈衝 (abnormal electrical impulses ) 則進一步的提高了其後癲癇復發之機率。截至目前為止，癲癇重積狀態如何造成神經元損傷的分子機制仍尚未被完全了解。組織蛋白酶S (Ctss) 為一種溶酶體半胱氨酸蛋白酶與創傷性腦損傷後的繼發性損傷有關。 在此研究中，我們主要探討組織蛋白酶 S 是否參與癲癇重積狀態誘導之海馬迴 (hippocampus) 神經元損傷。 我們主要的發現為在正常生理情況下，成熟型的組織蛋白酶 S 在成年（12週齡）小鼠海馬迴中組織不易被觀察到，然而其表達量在 50 週齡時則顯著地被上調。 在成年小鼠中，紅藻胺酸 (kainic acid; KA) 誘導癲癇重積狀態後 16 小時，可以觀察到海馬迴中組織蛋白酶 S 蛋白質明顯地表達，並持續到發作後 4 週。組織蛋白酶 S 蛋白的表現增加主要發現於紅藻胺酸誘導癲癇重積狀態後的小膠質細胞(microglia)中。透過 Fluoro-Jade C 染色觀察紅藻胺酸誘導癲癇重積狀態後 16 小時，在海馬迴 CA3 區域就可以看到明顯的 FJC 訊號。組織蛋白酶 S 剔除 (knockdown) 對紅藻胺酸誘導的癲癇發作特性上沒有影響，但顯著降低了癲癇重積狀態誘導的小膠質細胞活化和神經元損傷之程度。此外紅藻胺酸誘導的癲癇重積狀態後，小膠質細胞上的趨化因子 C-X3-C 基序配體 1 (CXC3L1) 的表現量也隨之增加。 總結，此等結果顯示組織蛋白酶 S 可能透過CXC3L1介導的小膠質細胞活化在癲癇重積狀態誘導的神經元損傷中扮演著重要的角色，並且可以用來作為防止癲癇重積狀態誘導的神經元損傷的標的分子。

Status epilepticus (SE) is a serious and potentially life-threatening neurological emergency that exhibits persistent seizures and results in brain damage that increases the risk of recurrent seizures due to abnormal electrical impulses produced by damaged neurons. Nonetheless, the molecular mechanism by which convulsive SE results in the progressive neuronal damage is not completely understood. Cathepsin S (Ctss), a lysosomal cysteine protease, has been implicated in the secondary injury after traumatic brain injury. In this study, we investigated whether Ctss is also involved in SE-induced neuronal damage in the hippocampus. We found that the mature form of Ctss is not visible in adult (12-week-old) mouse hippocampus under normal condition but its expression level is significantly upregulated at 50 weeks of age. In adult mice, the expression of Ctss in the hippocampus was increased as early as 16 h after kainic acid (KA)-induced SE, with constant expression for 4 weeks. The increased Ctss immunoreactivity was mainly found in microglia following KA-induced SE. The degenerative neurons visualized by Fluoro-Jade C staining was already prominent in the hippocampal CA3 region 16 h after KA-induced SE. Ctss knockdown had no effect on KA-induced seizure properties but significantly reduced the levels of SE-induced microglia activation and neuronal degeneration. Additionally, chemokine C-X3-C motif ligand 1 (CXC3L1) immunoreactivity is elevated on microglia following KA-induced SE. These results indicate a crucial role of Ctss in SE-induced neuronal damage possibly via a CXC3L1-mediated microglial activation and provide a new perspective for preventing SE-induced neuronal damage.

Akahoshi N, Murashima YL, Himi T, Ishizaki Y, Ishii I (2007) Increased expression of the lysosomal protease cathepsin S in hippocampal microglia following kainate-induced seizures. Neuroscience Letter 429:136-141.
Ali I, Chugh D, Ekdahl CT (2015) Role of fractalkine-CX3CR1 pathway in seizure-induced microglial activation, neurodegeneration, and neuroblast production in the adult rat brain. Neurobiology of Disease 74:194-203.
Banerjee M, Sasse VA, Wang Y, Maulik M, Kar S (2015) Increased levels and activity of cathepsins B and D in kainate-induced toxicity. Neuroscience 284:360-373.
Barker-Haliski M, White HS (2015) Glutamatergic Mechanisms Associated with Seizures and Epilepsy. Cold Spring Harbor Perspectives in Medicine 5:a022863.
Bromfield EB, Cavazos JE, Sirven JI, editors (2006) An Introduction to Epilepsy [Internet] West Hartford (CT): American Epilepsy Society.
Brömme D, Bonneau PR, Lachance P, Wiederanders B, Kirschke H, Peters C, Thomas DY, Storer AC, Vernet T (1993) Functional expression of human cathepsin S in Saccharomyces cerevisiae. Purification and characterization of the recombinant enzyme. Journal of Biological Chemistry 268: 4832-4838.
Brophy GM, Bell R, Claassen J, Alldredge B, Bleck TP, Glauser T, Laroche SM, Riviello JJ Jr, Shutter L, Sperling MR, Treiman DM, Vespa PM (2012) Neurocritical Care Society Status Epilepticus Guideline Writing Committee. Guidelines for the evaluation and management of status epilepticus. Neurocritical Care 17:3-23.
Catalano M, Lauro C, Cipriani R, Chece G, Ponzetta A, Di Angelantonio S, Ragozzino D, Limatola C (2013) CX3CL1 protects neurons against excitotoxicity enhancing GLT-1 activity on astrocytes. Journal of Neuroimmunology 263:75-82.
Chen KL, Chang WS, Cheung CH, Lin CC, Huang CC, Yang YN, Kuo CP, Kuo CC, Chang YH, Liu KJ, Wu CM, Chang JY (2012) Targeting cathepsin S induces tumor cell autophagy via the EGFR-ERK signaling pathway. Cancer Letters 317:89-98.
Clark AK, Malcangio M (2012) Microglial signalling mechanisms: Cathepsin S and Fractalkine. Experimental Neurology 234:283-92.
Cooper GM (2000) The Cell: A Molecular Approach. 2nd edition.
Ekdahl CT, Claasen JH, Bonde S, Kokaia Z, Lindvall O (2003) Inflammation is detrimental for neurogenesis in adult brain. Proceedings of the National Academy of Sciences 100:13632-13637.
Ekdahl CT, Kokaia Z, Lindvall O (2009) Brain inflammation and adult neurogenesis: the dual role of microglia. Neuroscience 158:1021-1029.
Elmore S (2007) Apoptosis: a review of programmed cell death. Toxicologic Pathology 35:495-516.
Fonović UP, Jevnikar Z, Kos J (2013) Cathepsin S generates soluble CX3CL1 (fractalkine) in vascular smooth muscle cells. Biological Chemistry 394:1349-1352.
Fu R, Guo H, Janga S, Choi M, Klinngam W, Edman MC, Hamm-Alvarez SF (2020) Cathepsin S activation contributes to elevated CX3CL1 (fractalkine) levels in tears of a Sjögren’s syndrome murine model. Science Reports 10:1455.
Grudkowska M, Zagdańska B (2004) Multifunctional role of plant cysteine proteinases. Acta Biochimica Polonica 51:609-624.
Ginhoux F, Prinz M (2015) Origin of microglia: current concepts and past controversies. Cold Spring Harbor Perspectives in Biology 7: a020537.
Gu B, Huang YZ, He XP, Joshi RB, Jang W, McNamara JO (2015) A Peptide Uncoupling BDNF Receptor TrkB from Phospholipase Cγ1 Prevents Epilepsy Induced by Status Epilepticus. Neuron 88:484-491.
Hickman S, Izzy S, Sen P, Morsett L, El Khoury J (2018) Microglia in neurodegeneration. Nature Neuroscience 21:1359-1369.
Hiragi T, Ikegaya Y, Koyama R (2018) Microglia after Seizures and in Epilepsy. Cells 7:26.
Huang CC, Lee CC, Lin HH, Chen MC, Lin CC, Chang JY (2015) Autophagy-Regulated ROS from Xanthine Oxidase Acts as an Early Effector for Triggering Late Mitochondria-Dependent Apoptosis in Cathepsin S-Targeted Tumor Cells. PLoS One 10:e0128045.
Jing ZT, Liu W, Xue CR, Wu SX, Chen WN, Lin XJ, Lin X (2019) AKT activator SC79 protects hepatocytes from TNF-α-mediated apoptosis and alleviates d-Gal/LPS-induced liver injury. American Journal of Physiology-Gastrointestinal and Liver Physiology 316:G387-G396.
Jones BA, Beamer M, Ahmed S (2010) Fractalkine/CX3CL1: a potential new target for inflammatory diseases. Molecular Interventions 10:263-270.
Kinoshita S, Koyama R (2021) Pro- and anti-epileptic roles of microglia. Neural Regeneration Research 16:1369-1371.
Lee H, Lee DH, Oh JH, Chung JH (2021) Skullcapflavone II Suppresses TNF-α/IFN-γ-Induced TARC, MDC, and CTSS Production in HaCaT Cells. International Journal of Molecular Sciences 22:6428.
Lemere CA, Munger JS, Shi GP, Natkin L, Haass C, Chapman HA, Selkoe DJ (1995) The lysosomal cysteine protease, cathepsin S, is increased in Alzheimer's disease and Down syndrome brain. An immunocytochemical study. American Journal of Pathology 146:848-60.
Nakanishi H (2020) Cathepsin regulation on microglial function. Biochim Biophys Acta Proteins Proteomics 1868:140465.
Pawelec P, Ziemka-Nalecz M, Sypecka J, Zalewska T (2020) The Impact of the CX3CL1/CX3CR1 Axis in Neurological Disorders. Cells 9:2277.
Perera RM, Zoncu R (2016) The Lysosome as a Regulatory Hub. Annual Review of Cell and Developmental Biology 32:223-253.
Petanceska S, Burke S, Watson SJ, Devi L (1994) Differential distribution of messenger RNAs for cathepsins B, L and S in adult rat brain: an in-situ hybridization study. Neuroscience 59:729-738.
Pišlar A, Bolčina L, Kos J (2021) New Insights into the Role of Cysteine Cathepsins in Neuroinflammation. Biomolecules 11:1796.
Bose SJ, Ayagama T, Burton RAB (2022) Chapter 3 - Lysosomal proteases and their role in signaling pathways, Proteolytic Signaling in Health and Disease, Academic Press 41-61.
Cormican S, Griffin MD (2021) Fractalkine (CX3CL1) and Its Receptor CX3CR1: A Promising Therapeutic Target in Chronic Kidney Disease? Frontiers in Immunology 12:664202.
Salvi V, Sozio F, Sozzani S, Del Prete A (2017) Role of Atypical Chemokine Receptors in Microglial Activation and Polarization. Frontiers in Aging Neuroscience 9:148.
Smyth P, Sasiwachirangkul J, Williams R, Scott CJ (2022) Cathepsin S (CTSS) activity in health and disease - A treasure trove of untapped clinical potential. Molecular Aspects of Medicine 88:101106.
Song H, Mylvaganam SM, Wang J, Mylvaganam SMK, Wu C, Carlen PL, Eubanks JH, Feng J, Zhang L (2018) Contributions of the Hippocampal CA3 Circuitry to Acute Seizures and Hyperexcitability Responses in Mouse Models of Brain Ischemia. Frontiers in Cellular Neuroscience 12:278.
Tran AP, Silver J (2021) Cathepsins in neuronal plasticity. Neural Regeneration Research 16:26-35.
Traynelis SF, Wollmuth LP, McBain CJ, Menniti FS, Vance KM, Ogden KK, Hansen KB, Yuan H, Myers SJ, Dingledine R (2010) Glutamate receptor ion channels: structure, regulation, and function. Pharmacological Reviews 62:405-496.
Velíšek L (2017) Models of Generalized Seizures in Freely Moving Animals. Reference Module in Neuroscience and Biobehavioral Psychology.
Villadangos JA, Riese RJ, Peters C, Chapman HA, Ploegh HL (1997) Degradation of mouse invariant chain: roles of cathepsins S and D and the influence of major histocompatibility complex polymorphism. Journal of Experimental Medicine 186:549-560.
Wang YC, Chen CH, Yang CY, Ling P, Hsu KS (2023) High-Fat Diet Exacerbates Autistic-Like Restricted Repetitive Behaviors and Social Abnormalities in CC2D1A Conditional Knockout Mice. Molecular Neurobiology 60:1331-1352.
Wasterlain CG, Fujikawa DG, Penix L, Sankar R (1993) Pathophysiological mechanisms of brain damage from status epilepticus. Epilepsia 34:S37-53.
Wasterlain CG, Niquet J, Thompson KW, Baldwin R, Liu H, Sankar R, Mazarati AM, Naylor D, Katsumori H, Suchomelova L, Shirasaka Y (2002) Seizure-induced neuronal death in the immature brain. Progress in Brain Research 135:335-353.
Wendt W, Lübbert H, Stichel CC (2008) Upregulation of cathepsin S in the aging and pathological nervous system of mice. Brain Research 1232:7-20.
Wendt W, Zhu XR, Lübbert H, Stichel CC (2007) Differential expression of cathepsin X in aging and pathological central nervous system of mice. Experimental Neurology 204:525-540.
Wiederanders B, Kaulmann G, Schilling K (2003) Functions of Propeptide Parts in Cysteine Proteases. Current Protein and Peptide Science 4:309-326.
Wilkinson RD, Williams R, Scott CJ, Burden RE (2015) Cathepsin S: therapeutic, diagnostic, and prognostic potential. Biological Chemistry 396:867-82.
Wolf Y, Yona S, Kim KW, Jung S (2013) Microglia, seen from the CX3CR1 angle. Frontiers in Cellular Neuroscience 7:26.
Wolters PJ, Chapman HA (2000) Importance of lysosomal cysteine proteases in lung disease. Respiratory Research 1:170-177.
Wylie T, Sandhu DS, Murr N (2023) Status Epilepticus. StatPearls [Internet].
Xu J, Wang H, Ding K, Lu X, Li T, Wang J, Wang C, Wang J (2013) Inhibition of cathepsin S produces neuroprotective effects after traumatic brain injury in mice. Mediators of Inflammation 2013:187873.
Xu L, Wang J, Ding Y, Wang L, Zhu YJ (2022) Current Knowledge of Microglia in Traumatic Spinal Cord Injury. Frontiers in Neurology 12:796704.
Xu Y, Zeng K, Han Y, Wang L, Chen D, Xi Z, Wang H, Wang X, Chen G (2012) Altered expression of CX3CL1 in patients with epilepsy and in a rat model. American Journal of Pathology 180:1950-1962.
Yadati T, Houben T, Bitorina A, Shiri-Sverdlov R (2020) The Ins and Outs of Cathepsins: Physiological Function and Role in Disease Management. Cells 9:1679.
Zhao X, Liao Y, Morgan S, Mathur R, Feustel P, Mazurkiewicz J, Qian J, Chang J, Mathern GW, Adamo MA, Ritaccio AL, Gruenthal M, Zhu X, Huang Y (2018) Noninflammatory Changes of Microglia Are Sufficient to Cause Epilepsy. Cell Reports 22:2080-2093.
Zieger M, Ahnelt PK, Uhrin P (2014) CX3CL1 (fractalkine) protein expression in normal and degenerating mouse retina: in vivo studies. PLoS One 9:e106562.