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Hung VKL, Yeung PKK, Lai AKW, Ho MCY, Lo ACY, Chan KC, Wu EXK, Chung SSM, Cheung CW, Chung SK. Selective astrocytic endothelin-1 overexpression contributes to dementia associated with ischemic stroke by exaggerating astrocyte-derived amyloid secretion. J Cereb Blood Flow Metab 2015; 35:1687-96. [PMID: 26104290 PMCID: PMC4640314 DOI: 10.1038/jcbfm.2015.109] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/04/2014] [Revised: 04/26/2015] [Accepted: 04/28/2015] [Indexed: 12/27/2022]
Abstract
Endothelin-1 (ET-1) is synthesized by endothelial cells and astrocytes in stroke and in brains of Alzheimer's disease patients. Our transgenic mice with ET-1 overexpression in the endothelial cells (TET-1) showed more severe blood-brain barrier (BBB) breakdown, neuronal apoptosis, and glial reactivity after 2-hour transient middle cerebral artery occlusion (tMCAO) with 22-hour reperfusion and more severe cognitive deficits after 30 minutes tMCAO with 5 months reperfusion. However, the role of astrocytic ET-1 in contributing to poststroke cognitive deficits after tMCAO is largely unknown. Therefore, GET-1 mice were challenged with tMCAO to determine its effect on neurologic and cognitive deficit. The GET-1 mice transiently displayed a sensorimotor deficit after reperfusion that recovered shortly, then more severe deficit in spatial learning and memory was observed at 3 months after ischemia compared with that of the controls. Upregulation of TNF-α, cleaved caspase-3, and Thioflavin-S-positive aggregates was observed in the ipsilateral hemispheres of the GET-1 brains as early as 3 days after ischemia. In an in vitro study, ET-1 overexpressing astrocytic cells showed amyloid secretion after hypoxia/ischemia insult, which activated endothelin A (ETA) and endothelin B (ETB) receptors in a PI3K/AKT-dependent manner, suggesting role of astrocytic ET-1 in dementia associated with stroke by astrocyte-derived amyloid production.
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Affiliation(s)
- Victor K L Hung
- Department of Anatomy, The University of Hong Kong, HKSAR, China
| | - Patrick K K Yeung
- Department of Anatomy, The University of Hong Kong, HKSAR, China.,School of Biomedical Sciences, The University of Hong Kong, HKSAR, China
| | - Angela K W Lai
- Department of Anatomy, The University of Hong Kong, HKSAR, China
| | - Maggie C Y Ho
- Department of Anatomy, The University of Hong Kong, HKSAR, China
| | - Amy C Y Lo
- Department of Anatomy, The University of Hong Kong, HKSAR, China
| | - Kevin C Chan
- University of Biomedical Imaging and Signal Processing, The University of Hong Kong, HKSAR, China
| | - Ed X K Wu
- University of Biomedical Imaging and Signal Processing, The University of Hong Kong, HKSAR, China
| | | | - Chi W Cheung
- Department of Anaesthesiology, The University of Hong Kong, HKSAR, China.,Research Center of Heart, Brain, Hormone and Healthy Aging, The University of Hong Kong, HKSAR, China
| | - Sookja K Chung
- Department of Anatomy, The University of Hong Kong, HKSAR, China.,School of Biomedical Sciences, The University of Hong Kong, HKSAR, China.,Research Center of Heart, Brain, Hormone and Healthy Aging, The University of Hong Kong, HKSAR, China.,The State Key Laboratory of Pharmaceutical Biotechnology, Zhuhai, Guandong, China
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Hung VKL, Tai LW, Luo X, Wang XM, Chung SK, Cheung CW. Targeted Overexpression of Astrocytic Endothelin-1 Attenuates Neuropathic Pain by Upregulating Spinal Excitatory Amino Acid Transporter-2. J Mol Neurosci 2015; 57:90-6. [PMID: 25994587 DOI: 10.1007/s12031-015-0581-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2015] [Accepted: 05/14/2015] [Indexed: 12/11/2022]
Abstract
We previously demonstrated that endogenous endothelin-1 (ET-1) inhibits pathological pain in a transgenic mouse model with astrocyte-specific ET-1 overexpression (GET-1 mice); however, the underlying mechanism is unclear. ET-1 regulates excitatory amino acid transporter-2 (EAAT-2), a predominant subtype of glutamate transporters that plays critical role in pain modulation in spinal astrocytes. We hypothesized that astrocytic ET-1 overexpression alleviates neuropathic pain through modulating EAAT-2. GET-1 or nontransgenic (NTg) mice either received sham operation or sciatic nerve ligation (SNL) with or without ceftriaxone (CEF, an EAAT-2 inducer, for 4 days before termination). In GET-1 mice, mRNA and protein expressions of EAAT-2, but not EAAT-1, were upregulated associated with reduced SNL-induced neuropathic pain. Despite that SNL induced a significant reduction of EAAT-2 mRNA expression in both genotypes of mice, post-SNL EAAT-2 mRNA expression was higher in GET-1 mice than that in NTg mice. EAAT-2 induction by CEF reduced SNL-induced neuropathic pain in both NTg and GET-1 mice. In cultured rat astrocytic cell line, overexpression of ET-1 mRNA expression also elevated EAAT-2 mRNA expression, which was reversed by ET receptor antagonists. In conclusion, overexpressed astrocytic ET-1 suppressed neuropathic pain by upregulating spinal EAAT-2 expression via ET receptors.
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Affiliation(s)
- Victor K L Hung
- Department of Anaesthesiology, The University of Hong Kong, Rm 424, 4/F, Block K, Queen Mary Hospital, 102, Pokfulam, HKSAR, China
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Wong DPK, Chu JMT, Hung VKL, Lee DKM, Cheng CHK, Yung KKL, Yue KKM. Modulation of endoplasmic reticulum chaperone GRP78 by high glucose in hippocampus of streptozotocin-induced diabetic mice and C6 astrocytic cells. Neurochem Int 2013; 63:551-60. [PMID: 24056253 DOI: 10.1016/j.neuint.2013.09.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2013] [Revised: 09/09/2013] [Accepted: 09/12/2013] [Indexed: 12/15/2022]
Abstract
Diabetes mellitus is known to increase the risk of neurodegeneration, and both diseases are reported to be linked to dysfunction of endoplasmic reticulum (ER). Astrocytes are important in the defense mechanism of central nervous system (CNS), with great ability of tolerating accumulation of toxic substances and sensitivity in Ca(2+) homeostasis which are two key functions of ER. Here, we investigated the modulation of the glucose-regulated protein 78 (GRP78) in streptozotocin (STZ)-induced diabetic mice and C6 cells cultured in high glucose condition. Our results showed that more reactive astrocytes were presented in the hippocampus of STZ-induced diabetic mice. Simultaneously, decrease of GRP78 expression was found in the astrocytes of diabetic mice hippocampus. In in vitro study, C6 cells were treated with high glucose to investigate the role of high glucose in GRP78 modulation in astrocytic cells. GRP78 as well as other chaperones like GRP94, calreticulin and calnexin, transcription levels were down-regulated after high glucose treatment. Also C6 cells challenged with 48h high glucose were activated, as indicated by increased level of glial fibrillary acidic protein (GFAP). Activated C6 cells simultaneously exhibited significant decrease of GRP78 level and was followed by reduced phosphorylation of Akt. Moreover, unfolded protein response was induced as an early event, which was marked by the induction of CHOP with high glucose treatment, followed by the reduction of GRP78 after 48h. Finally, the upsurge of ROS production was found in high glucose treated C6 cells and chelation of ROS could partially restore the GRP78 expression. Taken together, these data provide evidences that high glucose induced astrocytic activation in both in vivo and in vitro diabetic models, in which modulation of GRP78 would be an important event in this activation.
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Affiliation(s)
| | - John M T Chu
- School of Chinese Medicine, Hong Kong Baptist University, Hong Kong; Department of Biology, Hong Kong Baptist University, Hong Kong
| | - Victor K L Hung
- Department of Anaestheiology, The University of Hong Kong, Hong Kong
| | - Dicky K M Lee
- School of Chinese Medicine, Hong Kong Baptist University, Hong Kong
| | | | - Ken K L Yung
- Department of Biology, Hong Kong Baptist University, Hong Kong
| | - Kevin K M Yue
- School of Chinese Medicine, Hong Kong Baptist University, Hong Kong.
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Lo ACY, Cheung AKH, Hung VKL, Yeung CM, He QY, Chiu JF, Chung SSM, Chung SK. Deletion of aldose reductase leads to protection against cerebral ischemic injury. J Cereb Blood Flow Metab 2007; 27:1496-509. [PMID: 17293845 DOI: 10.1038/sj.jcbfm.9600452] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Previously, we reported that transgenic mice overexpressing endothelin-1 in astrocytes showed more severe neurological deficits and increased infarct after transient focal ischemia. In those studies, we also observed increased level of aldose reductase (AR), the first and rate-limiting enzyme of the polyol pathway, which has been implicated in osmotic and oxidative stress. To further understand the involvement of the polyol pathway, the mice with deletion of enzymes in the polyol pathway, AR, and sorbitol dehydrogenase (SD), which is the second enzyme in this pathway, were challenged with similar cerebral ischemic injury. Deletion of AR-protected animals from severe neurological deficits and large infarct, whereas similar protection was not observed in mice with SD deficiency. Most interestingly, AR(-/-) brains showed lowered expression of transferrin and transferrin receptor with less iron deposition and nitrotyrosine accumulation. The protection against oxidative stress in AR(-/-) brain was also associated with less poly(adenosine diphosphate-ribose) polymerase (PARP) and caspase-3 activation. Pharmacological inhibition of AR by Fidarestat also protected animals against cerebral ischemic injury. These findings are the first to show that AR contributes to iron- and transferrin-related oxidative stress associated with cerebral ischemic injury, suggesting that inhibition of AR but not SD may have therapeutic potential against cerebral ischemic injury.
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Affiliation(s)
- Amy C Y Lo
- Department of Anatomy, The University of Hong Kong, Hong Kong SAR, China
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Mak CKM, Hung VKL, Wong JTY. Type II topoisomerase activities in both the G1 and G2/M phases of the dinoflagellate cell cycle. Chromosoma 2005; 114:420-31. [PMID: 16252092 DOI: 10.1007/s00412-005-0027-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2005] [Revised: 08/31/2005] [Accepted: 09/01/2005] [Indexed: 11/28/2022]
Abstract
Dinoflagellate genomes are large (up to 200 pg) and are encoded in histoneless chromosomes that are quasi-permanently condensed. This unique combination of chromosomal characteristics presents additional topological and cell cycle control problems for a eukaryotic cell, potentially exhibiting novel regulatory requirements of topoisomerase II. The heterotrophic dinoflagellate Crypthecodinium cohnii was used in this study. The topoisomerase II activities throughout its cell cycle were investigated by DNA flow cytometry following enzyme deactivation. Fluorescence microscopy was also used for studying the chromosome morphology of the treated cells. Two classes of topoisomerase II inhibitors were applied in our study, both of which caused G1 delay as well as G2/M arrest in the C. cohnii cell cycle. At high doses, the topoisomerase poisons amsacrine and ellipticine induced DNA fragmentation in C. cohnii cells. Topoisomerase II activities, as measured by the ability to decatenate kinetoplastid DNA (kDNA), are normally detected throughout the cell cycle in C. cohnii. Our results suggest that the requirement of type II topoisomerase activities during the G1 phase of the cell cycle may relate to the unwinding of quasi-permanently condensed chromosomes for the purpose of transcription. This was also the first time that topoisomerase II activity in dinoflagellate cells was detected.
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Affiliation(s)
- Carmen K M Mak
- Biology Department, Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong SAR, People's Republic of China
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Lo ACY, Chen AYS, Hung VKL, Yaw LP, Fung MKL, Ho MCY, Tsang MCS, Chung SSM, Chung SK. Endothelin-1 overexpression leads to further water accumulation and brain edema after middle cerebral artery occlusion via aquaporin 4 expression in astrocytic end-feet. J Cereb Blood Flow Metab 2005; 25:998-1011. [PMID: 15815585 DOI: 10.1038/sj.jcbfm.9600108] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Stroke patients have increased levels of endothelin-1 (ET-1), a strong vasoconstrictor, in their plasma or cerebrospinal fluid. Previously, we showed high level of ET-1 mRNA expression in astrocytes after hypoxia/ischemia. It is unclear whether the contribution of ET-1 induction in astrocytes is protective or destructive in cerebral ischemia. Here, we generated a transgenic mouse model that overexpress ET-1 in astrocytes (GET-1) using the glial fibrillary acidic protein promoter to examine the role of astrocytic ET-1 in ischemic stroke by challenging these mice with transient middle cerebral artery occlusion (MCAO). Under normal condition, GET-1 mice showed no abnormality in brain morphology, cerebrovasculature, absolute cerebral blood flow, blood-brain barrier (BBB) integrity, and mean arterial blood pressure. Yet, GET-1 mice subjected to transient MCAO showed more severe neurologic deficits and increased infarct, which were partially normalized by administration of ABT-627 (ET(A) antagonist) 5 mins after MCAO. In addition, GET-1 brains exhibited more Evans blue extravasation and showed decreased endothelial occludin expression after MCAO, correlating with higher brain water content and increased cerebral edema. Aquaporin 4 expression was also more pronounced in astrocytic end-feet on blood vessels in GET-1 ipsilateral brains. Our current data suggest that astrocytic ET-1 has deleterious effects on water homeostasis, cerebral edema and BBB integrity, which contribute to more severe ischemic brain injury.
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Affiliation(s)
- Amy C Y Lo
- Institute of Molecular Biology, The University of Hong Kong, Hong Kong Special Administrative Region, Hong Kong, China
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Wong JTY, New DC, Wong JCW, Hung VKL. Histone-like proteins of the dinoflagellate Crypthecodinium cohnii have homologies to bacterial DNA-binding proteins. Eukaryot Cell 2003; 2:646-50. [PMID: 12796310 PMCID: PMC161454 DOI: 10.1128/ec.2.3.646-650.2003] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The dinoflagellates have very large genomes encoded in permanently condensed and histoneless chromosomes. Sequence alignment identified significant similarity between the dinoflagellate chromosomal histone-like proteins of Crypthecodinium cohnii (HCCs) and the bacterial DNA-binding and the eukaryotic histone H1 proteins. Phylogenetic analysis also supports the origin of the HCCs from histone-like proteins of bacteria.
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Affiliation(s)
- J T Y Wong
- Department of Biology, Hong Kong University of Science and Technology, Kowloon, Hong Kong, People's Republic of China.
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