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Estrogen signaling in stroke: genetic and experimental studies
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Stroke is a common and multifactorial disease influenced by genetic and environmental risk factors. It is a highly heterogeneous entity consisting of two main types, ischemic (80%) and hemorrhagic (20%) stroke. The most common form of hemorrhagic stroke is intracerebral hemorrhage (ICH). Ischemic stroke mainly results from thrombotic or embolic events, while ICH is caused by the rupture of an artery in the brain.

The mean age of first-ever stroke is 75 years (73 vs. 78 years, for men and women, respectively) and the age-specific stroke incidence is higher for men as compared to women, suggesting that hormonal factors confer protection. A large body of experimental and observational studies shows that estrogens exert beneficial effects in the cardiovascular system. However, large, recent, clinical randomized trials have failed to demonstrate a lower risk of stroke with hormone replacement therapy (HRT) in elderly postmenopausal women. It is possible that HRT may only protect a subgroup of women. Here, genetic predisposition might be involved. Stroke incidence is 50% higher in northern compared to southern Sweden, suggesting a genetic predisposition in this population. This relatively homogeneous population displays founder effects, making it well suited for genetic studies. Since 1985, the MONICA and VIP projects have conducted large-scale cardiovascular health surveys in this population. Information about conventional stroke risk determinants and also DNA have been collected, and two prospective, nested case-referent cohorts (113 cases and 226 controls; 275 cases and 549 controls) have been sampled.

To investigate whether genes of the estrogen signaling system may be important in stroke development, we performed genetic association studies, including specific functional single nucleotide polymorphisms in the genes for estrogen receptor alpha (ERα, ESR1), and its target genes osteoprotegerin (OPG, TNFRS11B) and interleukin-6 (IL-6, IL6). We found a significant association between the common c.454-397T/T genotype in ESR1 and ICH, remaining after adjustments for conventional stroke risk factors. The c.454-397T/T genotype also associated with increased systolic (SBP) and diastolic blood pressure (DBP). The combination of c.454- 397T/T and either hypertension, increased SBP, or increased DBP boosted this association substantially and significant synergistic effects on ICH risk between this genotype and increased blood pressure were demonstrated. In a second study, we found a similar association between the common OPG-1181C/C genotype and ICH.

Cognitive impairments, including spatial memory and learning deficiencies, are common after stroke. Estrogens improve cognitive functions, including memory and learning processes, in postmenopausal women and ovariectomized rodents. Post-ischemic housing of rats in an enriched environment (EE) improves recovery of spatial memory and learning impairments. Both estrogen and EE induce neuroplasticity in the hippocampus. We hypothesized that 17β- estradiol combined with EE would accelerate recovery after experimental focal brain ischemia in ovariectomized rats and that such improvements could be related to expression of nerve growth factor-induced gene A (NGFI-A) in the hippocampus. Five to six weeks after middle cerebral artery occlusion, 17β-estradiol–treated rats housed in an EE showed significant improvements in cognitive function (i.e., shorter latency and path in the Morris water maze task) and significantly higher NGFI-A mRNA expression in bilateral cornu ammonis 1 (CA1) and ipsilateral dentate gyrus (DG) compared to placebo-treated animals in EE.

In conclusion, we present evidence for the association between polymorphic variants in the ESR1 and TNFRS11B genes and ICH and show that 17β-estradiol in combination with EE accelerates cognitive functions in a rat stroke model, putatively through upregulation of NGFI-A in hippocampal subregions. These findings may contribute to an increased understanding of the underlying genetic etiology of ICH and may be informative for the primary prevention of this disease. They also provide hope for 17β-estradiol combined with early environmental enrichment as a novel therapeutic option following ischemic stroke.

Place, publisher, year, edition, pages
Umeå: Folkhälsa och klinisk medicin , 2007. , 83 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1131
Keyword [en]
intracerebral hemorrhage, ischemic stroke, genetics, ERα, OPG, 17β-estradiol, enriched environment, learning and memory, hippocampus, NGFI-A
National Category
Clinical Science
Identifiers
URN: urn:nbn:se:umu:diva-1397ISBN: 978-91-7264-426-7 (print)OAI: oai:DiVA.org:umu-1397DiVA: diva2:140885
Public defence
2007-11-09, Sal B, 9 tr, Tandläkarhögskolan, Umeå universitetssjukhus, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2007-10-19 Created: 2007-10-19 Last updated: 2016-08-19Bibliographically approved
List of papers
1. Estrogen Receptor Alpha Gene Polymorphisms and First-Ever Intracerebral Hemorrhage.
Open this publication in new window or tab >>Estrogen Receptor Alpha Gene Polymorphisms and First-Ever Intracerebral Hemorrhage.
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2007 (English)In: Cerebrovascular Diseases, ISSN 1015-9770, E-ISSN 1421-9786, Vol. 24, no 6, 500-508 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: Signaling through estrogen receptor alpha (ER alpha) regulates vasodilatation and atherogenesis. Since hypertension and atherosclerosis are major mechanisms in stroke development, we hypothesized that genetic variants of the ER alpha gene (ESR1) are determinants of future ischemic stroke or intracerebral hemorrhage (ICH). METHODS: In a population-based prospective nested case-control study, the relationships between ESR1 polymorphisms (c.454-397T>C and c.454-351A>G) and ischemic stroke and ICH were examined in univariate and multivariate models using conditional logistic regression, which included established risk factors.Definitive first-ever stroke events (n = 388), including ischemic stroke (n = 320), ICH (n = 61), and unspecified stroke (n = 7) cases, and controls without cardiovascular disease (n = 773), matched for age, sex, and geographical region were included. RESULTS: Carriers of the c.454-397T/T genotype had a significantly (p = 0.017) increased risk of ICH (OR 2.31, 95% CI 1.16-4.60) in a univariate analysis. This association persisted (OR 3.94, 95% CI 1.54-10.03), after adjustment for stroke risk determinants. Carriers of c.454-397T/T or c.454-397T/C genotypes had significantly (p = 0.002 and p = 0.004, respectively) higher mean systolic blood pressure (SBP), than carriers of c.454-397C/C, and a similar relationship was observed for diastolic blood pressure (DBP). The combinations of c.454-397T/T genotype and hypertension (OR 21.46, 95% CI 5.20-88.51), or high SBP (OR 18.17, 95% CI 4.91-67.31) or DBP (OR 11.94, 95% CI 3.75-38.03), were strongly associated with increased risk of ICH. CONCLUSIONS: In this population,the c.454-397T/T genotype associates with first-ever ICH, particularly in combination with hypertension. This implies that alterations in ER alpha-mediated signaling may be involved in the pathophysiology of this disease, with a putative impact on primary prevention.

Identifiers
urn:nbn:se:umu:diva-17976 (URN)10.1159/000110419 (DOI)17971628 (PubMedID)
Available from: 2007-12-03 Created: 2007-12-03 Last updated: 2017-12-14Bibliographically approved
2. Polymorphisms at the osteoprotegerin and interleukin-6 genes in relation to first-ever stroke.
Open this publication in new window or tab >>Polymorphisms at the osteoprotegerin and interleukin-6 genes in relation to first-ever stroke.
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2007 (English)In: Cerebrovascular Diseases, ISSN 1015-9770, E-ISSN 1421-9786, Vol. 24, no 5, 418-425 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: Arterial calcification and osteoporosis often coexist, especially in postmenopausal women. Osteoporosis associates with a substantially increased risk of stroke in elderly women, suggesting that impaired estrogen signaling may link stroke and osteoporosis. Osteoprotegerin (OPG, TNFRSF11B) and interleukin-6 (IL-6, IL6) are putative target genes for estrogen signaling and have been implicated in both cardiovascular diseases and osteoporosis. We hypothesized that specific polymorphisms in these genes may be associated with increased risk of ischemic stroke or intracerebral hemorrhage (ICH). METHODS: We performed a population-based prospective nested case-control study, in which the relationships between polymorphisms (OPG-1181G/C, OPG-950T/C and IL6-174G/C) and ischemic stroke and ICH were examined. Definitive first-ever stroke events (n = 388), i.e. ischemic stroke (n = 320), ICH (n = 61) and unspecified stroke (n = 7) cases, and controls without cardiovascular disease (n = 773), matched for age, sex and geographical region were studied. Univariate and multivariate models using conditional logistic regression, which included traditional risk factors, were used to test for association. RESULTS: Carriers of the OPG-1181C/C genotype had a significantly (p = 0.018) increased risk of ICH (OR, 2.69; 95% CI, 1.19-6.12) in the univariate analysis. After adjustments (hypertension, diabetes, BMI and triglycerides), this genotype remained significantly (p = 0.005) associated with ICH (OR, 6.04; 95% CI, 1.71-21.29). By contrast, no correlations were found between this genotype and ischemic stroke, nor between the OPG-950T/C or IL6-174G/C polymorphisms and stroke subtypes. CONCLUSIONS: In this population, the OPG-1181C/C genotype associates with first-ever ICH, implying that alterations in OPG-mediated signaling in the vasculature may be involved in the pathophysiology of this disease.

Identifiers
urn:nbn:se:umu:diva-18209 (URN)10.1159/000108431 (DOI)17878722 (PubMedID)
Available from: 2008-01-08 Created: 2008-01-08 Last updated: 2017-12-14Bibliographically approved
3. 17beta-estradiol and enriched environment accelerate cognitive recovery after focal brain ischemia
Open this publication in new window or tab >>17beta-estradiol and enriched environment accelerate cognitive recovery after focal brain ischemia
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2009 (English)In: European Journal of Neuroscience, ISSN 0953-816X, E-ISSN 1460-9568, Vol. 29, no 6, 1215-1224 p.Article in journal (Refereed) Published
Abstract [en]

Cognitive impairments, including spatial memory and learning deficiencies, are common after ischemic stroke. Estrogen substitution improves cognitive functions in post-menopausal women and ovariectomized rodents, partially through induction of neuroplasticity in the hippocampal formation. Post-ischemic housing of male rats in an enriched environment (EE) improves functional outcome, without changing infarct volume. We hypothesized that 17beta-estradiol combined with an EE would accelerate cognitive recovery after focal brain ischemia in ovariectomized rats and that recovery would be related to altered expression of nerve growth factor-induced gene (NGFI)-A in the hippocampus. 17beta-estradiol or placebo pellets were implanted 6 h after transient middle cerebral artery occlusion. Two days later, rats were placed in an EE or a deprived environment (DE) for 6 weeks. At 5 weeks after middle cerebral artery occlusion, 17beta-estradiol-treated rats housed in an EE showed improvements in cognitive function (i.e. shorter latency and path in the Morris water maze task) compared with placebo-treated animals housed in an EE. Furthermore, beneficial effects on latency and path were observed when comparing EE-housed vs. DE-housed 17beta-estradiol-treated rats. When comparing 17beta-estradiol-treated EE-housed rats vs. placebo-treated DE-housed rats, pronounced effects on latency and path were observed. Infarct volumes did not differ between groups. 17beta-estradiol-treated EE-housed rats had significantly higher NGFI-A mRNA expression bilaterally in the cornu ammonis 1 region and in the ipsilateral dentate gyrus of the hippocampus, compared with placebo-treated EE-housed rats. In conclusion, 17beta-estradiol treatment combined with an EE improved recovery of cognitive function after experimental brain ischemia, putatively through the upregulation of NGFI-A in hippocampal subregions.

Place, publisher, year, edition, pages
Hoboken: Wiley-Blackwell, 2009
Keyword
environmental enrichment, estrogen, hippocampus, ischemic stroke, learning and memory, rat
National Category
Neurology Neurosciences
Identifiers
urn:nbn:se:umu:diva-32402 (URN)10.1111/j.1460-9568.2009.06662.x (DOI)000264065500012 ()19302156 (PubMedID)
Available from: 2010-03-11 Created: 2010-03-11 Last updated: 2017-12-12Bibliographically approved

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