| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
(Stroke. 2005;36:189.)
© 2005 American Heart Association, Inc.
Advances in Stroke 2004 |
From the Neuroprotection Research Laboratory (E.H.L.), Departments of Radiology and Neurology, Massachusetts General Hospital, and Program in Neuroscience, Harvard Medical School, Charlestown, Mass; the Neurovascular Regulation and Stroke Laboratory (M.A.M.), Departments of Radiology and Neurology, Massachusetts General Hospital, Harvard Medical School, Charlestown, Mass; and the Neural Environment Cluster (T.P.J.), National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Md.
Correspondence to Dr Eng H. Lo, Neuroprotection Research Laboratory, Harvard Medical School, MGH East 149-2401, Charlestown, MA 02129. E-mail Lo{at}helix.mgh.harvard.edu
Key Words: Advances in Stroke apoptosis erythopoietin ischemia neuroprotective agents
| Introduction |
|---|
|
|
|---|
Although the precise timing and cellular pathways involved are not fully understood, it is believed that mechanisms actively promoting cell death are triggered after stroke. Remarkable progress has been made in dissecting these mechanisms over the past 3 decades. Three major pathways have emerged: excitotoxicity, oxidative stress, and apoptosis, and they are inextricably linked. Here, we explore the notion that stroke is most fruitfully investigated by an integrative "systems biology" approach that encompasses cell death and survival signaling within all components of the neurovascular unit.
| Cell Death: A Convergence of Factors |
|---|
|
|
|---|
Just how did these notions about ischemic cell death evolve over the past 30 years? A PubMed search is very revealing. From 1975 to 2003, the number of articles on stroke increased from about 900 to almost 7000 (Figure A). Within this subset (Figure B), those studying excitotoxicity or oxidative stress appeared in the mid 1980s, appeared to peak in the late 1990s, and showed trends of decreasing thereafter. Publications on apoptosis began to increase in 1993 and continued until the present time. Those publications implicating multiple mechanisms (ie, at least 2 out of the 3) only appeared recently and are slowly increasing in number. Based on the complexity of intracellular prolife and prodeath signaling and the death of multiple cell types, we anticipate the trend to continue in this direction.
|
Although the original model of excitotoxicity emphasized calcium influx through glutamate receptor-coupled ion channels, ionic imbalance may also proceed via other routes. Energy deprivation triggers acidosis, which activates novel classes of acid-sensing ion channels that further perturb sodium and calcium homeostasis.10 Importantly, glutamate receptors are also coupled to multiple intracellular kinase signals that subserve the cells stress response repertoire. For example, NMDA receptor activation engages Ras-GRF exchange factors and upregulates ERK and CREB pathways that mediate endogenous prosurvival responses to cellular stress. Double knockout mice lacking both Ras-GRF1 and Ras-GRF2 are less resistant to ischemic injury and show increased infarction after focal cerebral ischemia.11 The net effect of ERK activation, however, may also depend on the severity of ischemia. Whereas ERK may be beneficial after moderate ischemia, sustained overactivation of ERK after severe ischemia may paradoxically promote cell death.12 Another important mediator that has emerged is Akt, a serinethreonine kinase that phosphorylates and inactivates cell death mediators such as BAD, caspase-9, and glycogen synthase kinase-3. In cultured neurons, Akt protects against a wide array of excitotoxic, oxidative, and apoptotic insults.13 In a mouse model of focal cerebral ischemia, Akt is rapidly downregulated in the dying ischemic core, whereas increased Akt and neuronal survival in the cortex accompanies SOD1 overexpression, a superoxide radical scavenging protein.14
In addition to prosurvival responses, neuronal stress also triggers deleterious intracellular signals. The 2 stress-activated protein kinases, c-jun-N-terminal kinase (JNK) and p38, have been intensely investigated in recent years. JNK phosphorylates Bax and enhances its mitochondrial translocation, where it then augments pro-apoptotic caspase activation. Elevated phospho-JNK colocalizes with TUNEL-positive apoptotic neurons in mouse focal cerebral ischemia and inhibition of JNK protects injured brain.15 Consistent with these pharmacologic data, ischemic brain injury is reduced in knockout mice lacking the neuron-specific JNK3 isoform.16 Because these stress kinase signals play key roles in the cross-talk between multiple cell death pathways,17 they are attractive targets in the context of stroke where excitotoxicity, oxidative stress, and apoptosis may converge. Perhaps most importantly, such targets may afford a longer therapeutic window. At least in experimental rat and mouse models, JNK and p38 inhibitors are reportedly effective up to 6 hours after ischemic onset.18,19 Ultimately, multiple pathways are involved, so targeting the overall imbalance between prodeath versus prolife signaling mechanisms may be required.20
| The Neurovascular Unit: More Than Just Neurons? |
|---|
|
|
|---|
This fundamental concept of the neurovascular unit emphasizes that neurons participate as part of an integrative brain response in which signaling between cells and between cells and matrix are important determinants of tissue outcome in neurological disorders.21,22 How has the stroke literature reflected this concept? Although most publications remain focused on cell death specifically within neurons, there is an emerging and important recognition that glia and endothelial cells are also key players in stroke (Figure C). In this context, an ideal therapeutic target would be one active in multiple brain cell types. For example, the stress-activated protein kinase p38 not only mediates neuronal death but also may augment caspase-3mediated cell death in cerebral endothelial cells after hypoxic injury.23 Another multicell mediator might be the arachidonic acid cascade enzyme 12/15-lipoxygenase, which has recently been shown to contribute to glutamate-induced oxidative cell death in both neurons24 and oligodendrocytes,25 thus making it a potential target for both gray and white matter injury in stroke.
These past 2 years witnessed the emergence of erythropoietin (EPO) as a potential cerebroprotectant for stroke. A very limited clinical trial suggested that EPO may be safe and possibly efficacious in acute ischemic stroke.26 The mechanisms of EPOs actions are complex, but precisely because it targets multiple pathways of cross-talk signaling in cell death, EPO may become an especially potent therapeutic approach. Importantly, EPO is protective in both neurons27 and cerebral endothelial cells.28 EPO may even enhance neurogenesis and angiogenesis during stroke recovery.29 The recent development of an EPO derivative that is not erythropoietic yet retains its neuroprotective properties may further enhance its potential clinical importance.30
In contrast to many failures in trials of clinical neuroprotectants, the only Food and Drug Administration-approved stroke therapy targets the vasculature, ie, thrombolysis, using recombinant tissue plasminogen activator. It makes good sense to develop combination therapies for ischemia that combine vascular and parenchymal actions,31 especially because preclinical data suggest that many drug combinations improve neuroprotection and extend the therapeutic window in ways not possible with a single agent. It has been proposed that co-administering recombinant tissue plasminogen activator with activated protein C (APC) may be one rational approach. APC may enhance thrombolysis, decrease bloodbrain barrier perturbations, and salvage brain. By inactivating factors Va and VIIIa and by binding the tissue plasminogen activator antagonist PAI-1, APC may promote thrombolysis by preventing downstream microvascular thrombosis. APC may also reduce inflammation based on successful experience with recombinant APC (drotrecogin alpha, activated) in severe sepsis.32 APC appears to downregulate endothelial cell adhesion molecules such as intracellular adhesion molecules and selectins, thereby reducing leukocyte infiltration and secondary tissue injury. APC reduces glutamate and oxidative stress-induced apoptosis in both cultured neurons and cerebral endothelial cells,33,34 and decreases recombinant tissue plasminogen activatorassociated worsening of infarction and neurological deficits in a mouse stroke model.35 Taken together, these data suggest that combination approaches that simultaneously target vascular and parenchymal injury might increase the safety and lengthen the time window for effective thrombolytic reperfusion in stroke.
The pathophysiology and treatment of stroke remains a daunting scientific and clinical problem. Despite impressive advances in elucidating the complexity of cell death mechanisms, the way forward may entail deciphering those intracellular signals that mediate cross-talk between multiple pathways, and perhaps between multiple cell types. Targeting prodeath versus prolife signals within all cells of the neurovascular unit may eventually lead us to improved methods to treat salvageable brain tissue after ischemic insult.
Received December 1, 2004; accepted December 1, 2004.
| References |
|---|
|
|
|---|
2. Sharp FR, Lu A, Tang Y, Millhorn DE. Multiple molecular penumbras after focal cerebral ischemia. J Cereb Blood Flow Metab. 2000; 20: 10111032.[CrossRef][Medline] [Order article via Infotrieve]
3. Astrup J, Symon L, Branston NM, Lassen NA. Cortical evoked potential and extracellular K+ and H+ at critical levels of brain ischemia. Stroke. 1977; 8: 5157.
4. Lipton P. Ischemic cell death in brain neurons. Physiol Rev. 1999; 79: 14311568.
5. Graham SH, Chen J. Programmed cell death in cerebral ischemia. J Cereb Blood Flow Metab. 2001; 21: 99109.[CrossRef][Medline] [Order article via Infotrieve]
6. Chan PH. Reactive oxygen radicals in signaling and damage in the ischemic brain. J Cereb Blood Flow Metab. 2001; 21: 214.[CrossRef][Medline] [Order article via Infotrieve]
7. Driscoll M, Gerstbrein B. Dying for a cause: invertebrate genetics takes on human neurodegeneration. Nat Rev Genet. 2003; 4: 181194.[Medline] [Order article via Infotrieve]
8. De Keyser J, Sulter G, Luiten PG. Clinical trials with neuroprotective drugs in acute ischaemic stroke: are we doing the right thing? Trends Neurosci. 1999; 22: 535540.[CrossRef][Medline] [Order article via Infotrieve]
9. Gladstone DJ, Black SE, Hakim AM. Toward wisdom from failure: lessons from neuroprotective stroke trials and new therapeutic directions. Stroke. 2002; 33: 21232136.
10. Xiong ZG, Zhu XM, Chu XP, Minami M, Hey J, Wei WL, MacDonald JF, Wemmie JA, Price MP, Welsh MJ, Simon RP. Neuroprotection in ischemia: blocking calcium-permeable acid-sensing ion channels. Cell. 2004; 118: 687698.[CrossRef][Medline] [Order article via Infotrieve]
11. Tian X, Gotoh T, Tsuji K, Lo EH, Huang S, Feig LA. Developmentally regulated role for Ras-GRFs in coupling NMDA glutamate receptors to Ras, Erk and CREB. EMBO J. 2004; 23: 15671575.[CrossRef][Medline] [Order article via Infotrieve]
12. Chu CT, Levinthal DJ, Kulich SM, Chalovich EM, DeFranco DB. Oxidative neuronal injury. The dark side of ERK1/2. Eur J Biochem. 2004; 271: 20602066.[Medline] [Order article via Infotrieve]
13. Luo HR, Hattori H, Hossain MA, Hester L, Huang Y, Lee-Kwon W, Donowitz M, Nagata E, Snyder SH. Akt as a mediator of cell death. Proc Natl Acad Sci U S A. 2003; 100: 1171211717.
14. Noshita N, Sugawara T, Lewen A, Hayashi T, Chan PH. Copper-zinc superoxide dismutase affects Akt activation after transient focal cerebral ischemia in mice. Stroke. 2003; 34: 15131518.
15. Okuno S, Saito A, Hayashi T, Chan PH. The c-Jun N-terminal protein kinase signaling pathway mediates bax activation and subsequent neuronal apoptosis through interaction with bim after transient focal cerebral ischemia. J Neurosci. 2004; 24: 78797887.
16. Kuan CY, Whitmarsh AJ, Yang DD, Liao G, Schloemer AJ, Dong C, Bao J, Banasiak KJ, Haddad GG, Flavell RA, Davis RJ, Rakic P. A critical role of neural-specific JNK3 for ischemic apoptosis. Proc Natl Acad Sci U S A. 2003; 100: 1518415189.
17. Bossy-Wetzel E, Talantova MV, Lee WD, Scholzke MN, Harrop A, Mathews E, Gotz T, Han J, Ellisman MH, Perkins GA, Lipton SA. Crosstalk between nitric oxide and zinc pathways to neuronal cell death involving mitochondrial dysfunction and p38-activated K+ channels. Neuron. 2004; 41: 351365.[CrossRef][Medline] [Order article via Infotrieve]
18. Borsello T, Clarke PG, Hirt L, Vercelli A, Repici M, Schorderet DF, Bogousslavsky J, Bonny C. A peptide inhibitor of c-Jun N-terminal kinase protects against excitotoxicity and cerebral ischemia. Nat Med. 2003; 9: 11801186.[CrossRef][Medline] [Order article via Infotrieve]
19. Piao CS, Kim JB, Han PL, Lee JK. Administration of the p38 MAPK inhibitor SB203580 affords brain protection with a wide therapeutic window against focal ischemic insult. J Neurosci Res. 2003; 73: 537544.[CrossRef][Medline] [Order article via Infotrieve]
20. Chan PH. Future targets and cascades for neuroprotective strategies. Stroke. 2004; 35 (Suppl 1): 27482750.
21. Lo EH, Dalkara T, Moskowitz MA. Mechanisms, challenges and opportunities in stroke. Nat Rev Neurosci. 2003; 4: 399415.[Medline] [Order article via Infotrieve]
22. Iadecola C. Neurovascular regulation in the normal brain and in Alzheimers disease. Nat Rev Neurosci. 2004; 5: 347360.[CrossRef][Medline] [Order article via Infotrieve]
23. Lee SR, Lo EH. Interactions between p38 mitogen-activated protein kinase and caspase-3 in cerebral endothelial cell death after hypoxia-reoxygenation. Stroke. 2003; 34: 27042709.
24. Li Y, Maher P, Schubert D. A role for 12-lipoxygenase in nerve cell death caused by glutathione depletion. Neuron. 1997; 19: 453463.[CrossRef][Medline] [Order article via Infotrieve]
25. Wang H, Li J, Follett PL, Zhang Y, Cotanche DA, Jensen FE, Volpe JJ, Rosenberg PA. 12-Lipoxygenase plays a key role in cell death caused by glutathione depletion and arachidonic acid in rat oligodendrocytes. Eur J Neurosci. 2004; 20: 20492058.[CrossRef][Medline] [Order article via Infotrieve]
26. Ehrenreich H, Hasselblatt M, Dembowski C, Cepek L, Lewczuk P, Stiefel M, Rustenbeck HH, Breiter N, Jacob S, Knerlich F, Bohn M, Poser W, Ruther E, Kochen M, Gefeller O, Gleiter C, Wessel TC, De Ryck M, Itri L, Prange H, Cerami A, Brines M, Siren AL. Erythropoietin therapy for acute stroke is both safe and beneficial. Mol Med. 2002; 8: 495505.[Medline] [Order article via Infotrieve]
27. Digicaylioglu M, Lipton SA. Erythropoietin-mediated neuroprotection involves cross-talk between Jak2 and NF-kappaB signalling cascades. Nature. 2001; 412: 641647.[CrossRef][Medline] [Order article via Infotrieve]
28. Chong ZZ, Kang JQ, Maiese K. Apaf-1, Bcl-xL, cytochrome c, and caspase-9 form the critical elements for cerebral vascular protection by erythropoietin. J Cereb Blood Flow Metab. 2003; 23: 320330.[CrossRef][Medline] [Order article via Infotrieve]
29. Wang L, Zhang Z, Wang Y, Zhang R, Chopp M. Treatment of stroke with erythropoietin enhances neurogenesis and angiogenesis and improves neurological function in rats. Stroke. 2004; 35: 17321737.
30. Leist M, Ghezzi P, Grasso G, Bianchi R, Villa P, Fratelli M, Savino C, Bianchi M, Nielsen J, Gerwien J, Kallunki P, Larsen AK, Helboe L, Christensen S, Pedersen LO, Nielsen M, Torup L, Sager T, Sfacteria A, Erbayraktar S, Erbayraktar Z, Gokmen N, Yilmaz O, Cerami-Hand C, Xie QW, Coleman T, Cerami A, Brines M. Derivatives of erythropoietin that are tissue protective but not erythropoietic. Science. 2004; 305: 239242.
31. Lo EH. Combination stroke therapy: easy as APC? Nat Med. 2004; 10: 12951296.[CrossRef][Medline] [Order article via Infotrieve]
32. Bernard GR, Vincent JL, Laterre PF, LaRosa SP, Dhainaut JF, Lopez-Rodriguez A, Steingrub JS, Garber GE, Helterbrand JD, Ely EW, Fisher CJ Jr; Recombinant human protein C Worldwide Evaluation in Severe Sepsis (PROWESS) study group. Efficacy and safety of recombinant human activated protein C for severe sepsis. N Engl J Med. 2001; 344: 699709.
33. Guo H, Liu D, Gelbard H, Cheng T, Insalaco R, Fernandez JA, Griffin JH, Zlokovic BV. Activated protein C prevents neuronal apoptosis via protease activated receptors 1 and 3. Neuron. 2004; 41: 563572.[CrossRef][Medline] [Order article via Infotrieve]
34. Cheng T, Liu D, Griffin JH, Fernandez JA, Castellino F, Rosen ED, Fukudome K, Zlokovic BV. Activated protein C blocks p53-mediated apoptosis in ischemic human brain endothelium and is neuroprotective. Nat Med. 2003; 9: 338342.[CrossRef][Medline] [Order article via Infotrieve]
35. Liu D, Cheng T, Guo H, Fernandez JA, Griffin JH, Song X, Zlokovic BV. Tissue plasminogen activator neurovascular toxicity is controlled by activated protein C. Nat Med. 2004; 10: 13791383.[CrossRef][Medline] [Order article via Infotrieve]
This article has been cited by other articles:
![]() |
M. O. Breckwoldt, J. W. Chen, L. Stangenberg, E. Aikawa, E. Rodriguez, S. Qiu, M. A. Moskowitz, and R. Weissleder Tracking the inflammatory response in stroke in vivo by sensing the enzyme myeloperoxidase PNAS, November 25, 2008; 105(47): 18584 - 18589. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. Bull, J. P. Finkelstein, J. Galvez, G. Sanchez, P. Donoso, M. I. Behrens, and C. Hidalgo Ischemia Enhances Activation by Ca2+ and Redox Modification of Ryanodine Receptor Channels from Rat Brain Cortex J. Neurosci., September 17, 2008; 28(38): 9463 - 9472. [Abstract] [Full Text] [PDF] |
||||
![]() |
G. Jin, K. Arai, Y. Murata, S. Wang, M. F. Stins, E. H. Lo, and K. van Leyen Protecting Against Cerebrovascular Injury: Contributions of 12/15-Lipoxygenase to Edema Formation After Transient Focal Ischemia Stroke, September 1, 2008; 39(9): 2538 - 2543. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. L. Sacchetti Is It Time to Definitely Abandon Neuroprotection in Acute Ischemic Stroke? Stroke, June 1, 2008; 39(6): 1659 - 1660. [Full Text] [PDF] |
||||
![]() |
S. Guo, W. J. Kim, J. Lok, S.-R. Lee, E. Besancon, B.-H. Luo, M. F. Stins, X. Wang, S. Dedhar, and E. H. Lo Neuroprotection via matrix-trophic coupling between cerebral endothelial cells and neurons PNAS, May 27, 2008; 105(21): 7582 - 7587. [Abstract] [Full Text] [PDF] |
||||
![]() |
L. Sun, H. H. Marti, and R. Veltkamp Hyperbaric Oxygen Reduces Tissue Hypoxia and Hypoxia-Inducible Factor-1{alpha} Expression in Focal Cerebral Ischemia Stroke, March 1, 2008; 39(3): 1000 - 1006. [Abstract] [Full Text] [PDF] |
||||
![]() |
T. N. Nagaraja, K. Karki, J. R. Ewing, R. L. Croxen, and R. A. Knight Identification of Variations in Blood-Brain Barrier Opening After Cerebral Ischemia by Dual Contrast-Enhanced Magnetic Resonance Imaging and T1sat Measurements Stroke, February 1, 2008; 39(2): 427 - 432. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. Chu, S.-T. Lee, D.-I. Sinn, S.-Y. Ko, E.-H. Kim, J.-M. Kim, S.-J. Kim, D.-K. Park, K.-H. Jung, E.-C. Song, et al. Pharmacological Induction of Ischemic Tolerance by Glutamate Transporter-1 (EAAT2) Upregulation Stroke, January 1, 2007; 38(1): 177 - 182. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. van Leyen, H. Y. Kim, S.-R. Lee, G. Jin, K. Arai, and E. H. Lo Baicalein and 12/15-Lipoxygenase in the Ischemic Brain Stroke, December 1, 2006; 37(12): 3014 - 3018. [Abstract] [Full Text] [PDF] |
||||
![]() |
O. Wu, S. Christensen, N. Hjort, R. M. Dijkhuizen, T. Kucinski, J. Fiehler, G. Thomalla, J. Rother, and L. Ostergaard Characterizing physiological heterogeneity of infarction risk in acute human ischaemic stroke using MRI Brain, September 1, 2006; 129(9): 2384 - 2393. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. B. Tatro Melanocortins Defend their Territory: Multifaceted Neuroprotection in Cerebral Ischemia. Endocrinology, March 1, 2006; 147(3): 1122 - 1125. [Full Text] [PDF] |
||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Stroke Home | Subscriptions | Archives | Feedback | Authors | Help | AHA Journals Home | Search Copyright © 2005 American Heart Association, Inc. All rights reserved. Unauthorized use prohibited. |