Epigenetic gene expression links heart failure to memory impairment
2021; Springer Nature; Volume: 13; Issue: 3 Linguagem: Inglês
10.15252/emmm.201911900
ISSN1757-4684
AutoresRezaul Islam, Dawid Lbik, M. Sadman Sakib, Raoul Maximilian Hofmann, Tea Berulava, Martí Jiménez Mausbach, Julia Cha, Maria Goldberg, Elerdashvili Vakhtang, Christian Schiffmann, Anke Zieseniß, Dörthe M. Katschinski, Farahnaz Sananbenesi, Karl Toischer, André Fischer,
Tópico(s)Hormonal Regulation and Hypertension
ResumoArticle20 January 2021Open Access Transparent process Epigenetic gene expression links heart failure to memory impairment Md Rezaul Islam Md Rezaul Islam Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Dawid Lbik Dawid Lbik Clinic of Cardiology and Pneumology, Georg-August-University, Göttingen, GermanyThese authors contributed equally to this work Search for more papers by this author M Sadman Sakib M Sadman Sakib Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, GermanyThese authors contributed equally to this workCorrection added on 05 March 2021, after first online publication: the author's name was changed from Md Sadman Sakib to M Sadman Sakib. Search for more papers by this author Raoul Maximilian Hofmann Raoul Maximilian Hofmann Clinic of Cardiology and Pneumology, Georg-August-University, Göttingen, Germany Search for more papers by this author Tea Berulava Tea Berulava Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Martí Jiménez Mausbach Martí Jiménez Mausbach Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Julia Cha Julia Cha Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Maria Goldberg Maria Goldberg Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Elerdashvili Vakhtang Elerdashvili Vakhtang Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Christian Schiffmann Christian Schiffmann Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Anke Zieseniss Anke Zieseniss German Center for Cardiovascular Research (DZHK), Göttingen, Germany Institute for Cardiovascular Physiology, University Medical Center, Georg-August University Göttingen, Göttingen, Germany Search for more papers by this author Dörthe Magdalena Katschinski Dörthe Magdalena Katschinski orcid.org/0000-0003-4630-9081 German Center for Cardiovascular Research (DZHK), Göttingen, Germany Institute for Cardiovascular Physiology, University Medical Center, Georg-August University Göttingen, Göttingen, Germany Search for more papers by this author Farahnaz Sananbenesi Farahnaz Sananbenesi Genome Dynamics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Karl Toischer Corresponding Author Karl Toischer [email protected] orcid.org/0000-0002-9644-3716 Clinic of Cardiology and Pneumology, Georg-August-University, Göttingen, Germany German Center for Cardiovascular Research (DZHK), Göttingen, Germany These authors contributed equally to this work Search for more papers by this author Andre Fischer Corresponding Author Andre Fischer [email protected] orcid.org/0000-0001-8546-1161 Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Department of Psychiatry and Psychotherapy, University Medical Center Göttingen, Göttingen, Germany Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Göttingen, Germany These authors contributed equally to this work Search for more papers by this author Md Rezaul Islam Md Rezaul Islam Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Dawid Lbik Dawid Lbik Clinic of Cardiology and Pneumology, Georg-August-University, Göttingen, GermanyThese authors contributed equally to this work Search for more papers by this author M Sadman Sakib M Sadman Sakib Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, GermanyThese authors contributed equally to this workCorrection added on 05 March 2021, after first online publication: the author's name was changed from Md Sadman Sakib to M Sadman Sakib. Search for more papers by this author Raoul Maximilian Hofmann Raoul Maximilian Hofmann Clinic of Cardiology and Pneumology, Georg-August-University, Göttingen, Germany Search for more papers by this author Tea Berulava Tea Berulava Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Martí Jiménez Mausbach Martí Jiménez Mausbach Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Julia Cha Julia Cha Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Maria Goldberg Maria Goldberg Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Elerdashvili Vakhtang Elerdashvili Vakhtang Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Christian Schiffmann Christian Schiffmann Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Anke Zieseniss Anke Zieseniss German Center for Cardiovascular Research (DZHK), Göttingen, Germany Institute for Cardiovascular Physiology, University Medical Center, Georg-August University Göttingen, Göttingen, Germany Search for more papers by this author Dörthe Magdalena Katschinski Dörthe Magdalena Katschinski orcid.org/0000-0003-4630-9081 German Center for Cardiovascular Research (DZHK), Göttingen, Germany Institute for Cardiovascular Physiology, University Medical Center, Georg-August University Göttingen, Göttingen, Germany Search for more papers by this author Farahnaz Sananbenesi Farahnaz Sananbenesi Genome Dynamics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Search for more papers by this author Karl Toischer Corresponding Author Karl Toischer [email protected] orcid.org/0000-0002-9644-3716 Clinic of Cardiology and Pneumology, Georg-August-University, Göttingen, Germany German Center for Cardiovascular Research (DZHK), Göttingen, Germany These authors contributed equally to this work Search for more papers by this author Andre Fischer Corresponding Author Andre Fischer [email protected] orcid.org/0000-0001-8546-1161 Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany Department of Psychiatry and Psychotherapy, University Medical Center Göttingen, Göttingen, Germany Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Göttingen, Germany These authors contributed equally to this work Search for more papers by this author Author Information Md Rezaul Islam1, Dawid Lbik2, M Sadman Sakib1, Raoul Maximilian Hofmann2, Tea Berulava1, Martí Jiménez Mausbach1, Julia Cha1, Maria Goldberg1, Elerdashvili Vakhtang1, Christian Schiffmann1, Anke Zieseniss3,4, Dörthe Magdalena Katschinski3,4, Farahnaz Sananbenesi5, Karl Toischer *,2,3 and Andre Fischer *,1,6,7 1Department for Systems Medicine and Epigenetics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany 2Clinic of Cardiology and Pneumology, Georg-August-University, Göttingen, Germany 3German Center for Cardiovascular Research (DZHK), Göttingen, Germany 4Institute for Cardiovascular Physiology, University Medical Center, Georg-August University Göttingen, Göttingen, Germany 5Genome Dynamics, German Center for Neurodegenerative Diseases (DZNE), Göttingen, Germany 6Department of Psychiatry and Psychotherapy, University Medical Center Göttingen, Göttingen, Germany 7Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Göttingen, Germany *Corresponding author. Tel: +49 551 3966318; E-mail: [email protected] *Corresponding author. Tel: +49 551 3961211; E-mail: [email protected] EMBO Mol Med (2021)13:e11900https://doi.org/10.15252/emmm.201911900 Correction added on 05 March 2021, after first online publication: the author's name was changed from Md Sadman Sakib to M Sadman Sakib. See also: G Condorelli & M Matteoli et al (March 2021) PDFDownload PDF of article text and main figures. Peer ReviewDownload a summary of the editorial decision process including editorial decision letters, reviewer comments and author responses to feedback. ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InMendeleyWechatReddit Figures & Info Abstract In current clinical practice, care of diseased patients is often restricted to separated disciplines. However, such an organ-centered approach is not always suitable. For example, cognitive dysfunction is a severe burden in heart failure patients. Moreover, these patients have an increased risk for age-associated dementias. The underlying molecular mechanisms are presently unknown, and thus, corresponding therapeutic strategies to improve cognition in heart failure patients are missing. Using mice as model organisms, we show that heart failure leads to specific changes in hippocampal gene expression, a brain region intimately linked to cognition. These changes reflect increased cellular stress pathways which eventually lead to loss of neuronal euchromatin and reduced expression of a hippocampal gene cluster essential for cognition. Consequently, mice suffering from heart failure exhibit impaired memory function. These pathological changes are ameliorated via the administration of a drug that promotes neuronal euchromatin formation. Our study provides first insight to the molecular processes by which heart failure contributes to neuronal dysfunction and point to novel therapeutic avenues to treat cognitive defects in heart failure patients. Synopsis Patients suffering from heart failure have an increased risk to develop age-associated dementia. This study elucidates the underlying mechanisms and provides evidence that heart-failure induced cognitive decline is linked to epigenetic changes that affect neuronal gene expression. Heart failure leads to hippocampal gene expression changes in mice. Heart failure induced aberrant neuronal gene expression was linked to hypoxia and ER stress pathways. Loss of H3K4me3 was identified as a key epigenetic change in heart failure induced cognitive impairment. Targeting H3K4me3 was able to reinstate memory function and transcriptome homeostasis in a mouse model for heart failure. The paper explained Problem Cognitive dysfunction is a severe burden in heart failure patients. Moreover, these patients have an increased risk for age-associated dementia. The underlying molecular mechanisms are presently unknown, and thus, corresponding therapeutic strategies to improve cognition in heart failure patients are missing. Results Using mice as model organisms, we show that heart failure leads to memory impairment and a profound alteration of gene expression in hippocampus, a brain region that is important for cognition and is affected early in Alzheimer's disease. Further analysis reveals that heart failure-related down-regulation of hippocampal genes is linked to reduced neuronal H3K4 methylation. These pathological changes are ameliorated via the systemic administration of an epigenetic drug via multiple mechanisms. Impact International organizations such as the European Society of Cardiology (ESC) recommend that cardiology and dementia research experts should team-up to identify therapeutic interventional options for managing cognitive impairment in subjects with heart failure. Our study provides first insight to the molecular processes by which heart failure contributes to neuronal dysfunction and points to novel therapeutic avenues to treat cognitive defects in heart failure patients. Introduction Traditionally, clinical medicine is organized by organ-centered disciplines which is reflected in the currently applied diagnostics and treatments of patients. This approach has been also commonly adopted in research strategies but it is becoming evident that novel interdisciplinary efforts are needed to improve therapies of complex diseases. For example, heart failure (HF) is a complex, debilitating condition afflicting millions of people worldwide (Savarese & Lund, 2017). However, in addition to the detrimental phenotypes linked directly to cardiac dysfunction, cognitive deficits present a major burden to patients with HF (Pressler et al, 2010; Hajduk et al, 2013; Ampadu & Morley, 2015; Doehner et al, 2017). Moreover, epidemiological studies have clearly demonstrated that HF significantly increases the risk for dementia and age-associated neurodegenerative diseases such as Alzheimer's disease (AD) (Angermann et al, 2012; Cermakova et al, 2015; Satizabal et al, 2016). In line with these observations, a consistent finding in HF patients is a substantially reduced cerebral blood flow (Roy et al, 2017) and imaging studies reveal subsequent structural and functional cerebral alterations including changes in key regions linked to memory formation, such as the hippocampus (Kumar et al, 2011; Pan et al, 2013; Kumar et al, 2015; Woo et al, 2015). However, how HF affects hippocampal function at the molecular level remains to be explored and thus effective therapies to manage cognitive impairment if HF patients do not exist yet. On the contrary, the therapeutic approaches currently used to treat cardiac phenotypes in HF patients lack evidence for improving cognition (Cleland et al, 2005; Frigerio & Roubina, 2005; Arnold et al, 2006) or have even been linked to an increased incidence of AD (Khachaturian et al, 2006; Pressler et al, 2010; Galli & Lombardi, 2014; Solomon et al, 2017), suggesting that HF may lead to long-lasting adaptive changes in neurons that can persist despite improvement of cardiac function. Thus, a better understanding of HF-mediated molecular alterations in neurons is of utmost importance but corresponding data are lacking. Consequently, international organizations such as the European Society of Cardiology (ESC) have recommended that cardiology and dementia research experts should team-up to identify therapeutic interventional options for managing cognitive impairment in subjects with HF (Ponikowski et al, 2018). In this study, we took on this challenge and show that HF leads to specific changes in hippocampal gene expression that are linked to memory impairment. Targeting aberrant gene expression via epigenetic drugs ameliorates these phenotypes suggesting a key role of this process in HF-mediated cognitive dysfunction. Moreover, our data suggest that therapeutic strategies directed toward epigenetic gene expression provide a therapeutic avenue to improve cognition in HF patients and ameliorate their risk to develop AD. Results Heart failure in CamkIIδc TG mice leads to hippocampal gene expression changes indicative of dementia With the aim to elucidate the molecular processes by which cardiovascular dysfunction leads to memory impairment and increases the risk for dementia, we decided to employ a well-established mouse model for HF in which cardiomyocyte-specific kinase CamkIIδc is overexpressed under the control of the alpha-MHC promoter (CamkIIδc TG mice) (Maier et al, 2003). Thus, overexpression of CamkIIδc is specific to cardiomyocytes and is not detected in other organs, including the brain (Maier et al, 2003), making it a bona fide model to study the impact of HF on brain function. In line with this, we confirmed that expression of the CamkIIδc transgene was absent in brain (Fig 1A). We reasoned that this well-defined genetic HF model would be superior to other experimental approaches linked for example to cerebral hypoperfusion such as carotid artery occlusion, since it allowed us to study brain function in response to the very precise and exclusive manipulation of cardiac tissue. Although CamkIIδc transgenic mice display early hypertrophy at 8 weeks of age, substantial functional and structural changes are observed at 3 months of age (Sossalla et al, 2011). Therefore, we investigated 3-month-old CamkIIδc TG mice, and in line with previous findings, these mice displayed HF with left ventricular dilatation, impaired ejection fraction, cardiac output, and cardiac index, while heart/body weight ratio and left ventricle/body weight ration as well as the lung/body weight ratio was increased (Fig 1B and C), whereas the overall body weight was not affected (P = 0.863 for CamkIIδc TG vs control mice, n = 8, unpaired t-test). As a first approach to study the impact of cardiac dysfunction on brain plasticity, we decided to analyze the transcriptome of the hippocampal CA1 region in 3-month-old CamkIIδc TG mice (Fig 1D). This was based on data showing that (i) gene expression is a sensitive molecular correlate of memory function and is deregulated in dementia patients and corresponding mouse models (Fischer, 2014a); (ii) the hippocampal CA1 regions is essential for spatial reference memory in rodents and humans and is affected early in AD (Fischer, 2014a); and (iii) imaging data show functional changes of the hippocampal CA1 region in patients with HF (Woo et al, 2015). RNA-seq analysis revealed substantial changes in the CA1 transcriptome of 3-month-old CamkIIδc TG and control mice that were obvious in a principal component analysis (PCA; Fig 1D). Namely, 1,780 genes were up-regulated and 2,014 genes were down-regulated in CamkIIδc TG when compared to the control group (Fig 1E; Dataset EV1). Comparison of the differentially expressed genes to previously reported cell type-specific gene expression datasets (Merienne et al, 2019) revealed that up-regulated genes were linked to neurons, microglia, and astrocytes, while down-regulated genes were mainly associated with neurons (Fig 1F). Further pathway analysis showed that up-regulated genes are related to cellular stress response pathways such as oxidative and endoplasmic reticulum (ER) stress (Fig 1G, Dataset EV1), while down-regulated genes are linked to cognition, protein folding, and processes related to protein methylation (Fig 1G, Dataset EV1). We decided to confirm the RNA-sequencing data by testing differential expression for selected genes representing changes related to increased cellular stress processes, in this case "ER stress" and down-regulated processes such as "protein methylation". qPCR analysis confirmed increased expression of the ER stress-related genes Fez1, Fez2, and Bcap31 (Fig 1H). We also tested the expression of several histone 3 lysine 4 (H3K4)-specific lysine methyltransferases (Kmts), since these pathways were detected in the RNA-seq data and several of the Kmt's, such as Kmt2a, were found to be essential for memory formation (Gupta et al, 2010; Kerimoglu et al, 2013; Jakovcevski et al, 2015; Kerimoglu et al, 2017). Indeed, we observed that Kmt2a and Kmt2d were significantly down-regulated in CamkIIδc TG mice (Fig 1H). Specificity of this observation was demonstrated by the fact that other H3K4 methyltransferases such as Kmt2b and Kmt2c were not differentially expressed. Figure 1. Heart failure in CamkIIδc TG mice is linked to aberrant hippocampal gene expression A. qPCR data comparing the expression of the CamkIIδc transgene in the brain and heart of 3-month-old CamkIIδc TG mice; n = 4/group; *P < 0.05, Unpaired t-test, two-tailed. Note that the transgene is not detected in the brain. B. Representative M-mode images from left ventricle from CamkIIδc TG and control mice. EDD, left ventricle diastolic diameter; ESD, left ventricle end-systolic diameter. C. Ejection fraction, cardiac output, and index are significantly decreased in CamkIIδc TG mice (n = 8) when compared to control mice (n = 5; *P < 0.05, **P < 0.01, ***P < 0.001, unpaired t-test, two-tailed). Heart to body ratio, left ventricle to body weight ratio, and lung to body weight ratio are increased in CamkIIδc TG (n = 8) compared to control (n = 5; *P < 0.05, **P < 0.01, unpaired t-test; two-tailed). D. Experimental scheme for RNA-seq analysis that was performed from hippocampal CA1 region of CamkIIδc TG mice (n = 6) and control mice (n = 5) at 3 months of age. Right panel shows principal component analysis (PCA) of the gene expression data. The first principal component (PC1) can explain 42% of the variation between two groups. E. Volcano plot showing differentially expressed genes (FDR < 0.05). Red color indicates up-regulation, while green represents down-regulation of transcripts. F. Hypergeometric overlap analysis comparing genes deregulated in CamkIIδc TG mice to genes uniquely expressed in neurons, astrocytes, or microglia. Numbers represent the P value after multiple adjustments with Benjamini–Hochberg (BH) method. Fisher's hypergeometric test; color represents fold enrichment. G. Dot plot showing Top GO biological processes after removing redundant GO terms using Rivago. H. qPCR quantification of selected genes reflecting ER stress or protein methylation-related processes in CamkIIδc TG mice (n = 4) and control mice (n = 5). *P < 0.05, ns, non-significant, unpaired t-test; two-tailed. Data are normalized to Hprt1 expression. I–K. Hypergeometric overlap analysis comparing genes deregulated in CamkIIδc TG mice to genes deregulated under (I) hypoxia conditions and (J) in response to tunicamycin-induced ER stress and (K) in hippocampal tissue from animal models of memory impairment and neurodegeneration. Benjamini–Hochberg (BH) adjusted P values after are denoted as numbers, and fold enrichment is represented as color heatmap. Fisher's hypergeometric test. Data information: Bars and error bars indicate average ± standard error mean. Download figure Download PowerPoint The observation that genes implicated with oxidative and ER stress are increased in the hippocampus of CamkIIδc TG mice is in line with previous findings linking HF to hypoxia as a consequence of cerebral hypoperfusion (Bikkina et al, 1994; Verdecchia et al, 2001; Perlman, 2007), although additional processes than hypoperfusion likely play a role. The concomitant down-regulation of genes linked to cognition let us to hypothesize about a potential link between the observed cellular stress-related gene expression changes and the decreased expression of genes associated with cognition. Namely, we wondered whether the decreased expression of genes linked to cognition could be a consequence of the activation of cellular stress pathways. We decided to test this hypothesis further with a focus on hypoxia and ER stress as key cellular stress pathways. Since data on the effects of hypoxia and ER stress on hippocampal gene expression at the genome-wide level are still rare, we decided to performed RNA sequencing from mixed hippocampal neuronal cultures that were subjected to either hypoxia or ER stress. First, we analyzed hypoxia. Differential expression analysis revealed a substantial amount of genes that were differentially expressed in response to hypoxic conditions (Dataset EV2). We then compared the genes up- and down-regulated in hippocampal cultures in response to hypoxia to the genes up- and down-regulated in the hippocampus of CamkIIδc TG mice. This analysis revealed a significant overlap of not only up- but also down-regulated genes suggesting that hypoxic conditions are sufficient to induce gene expression changes similar to that detected in the hippocampus of mice suffering from HF (Fig 1I). We employed the same experimental settings to test the impact of ER stress that can be modeled via the administration of tunicamycin. Thus, RNA sequencing was performed from mixed hippocampal neuronal cultures upon treatment with tunicamycin (Dataset EV3). Our data show that genes deregulated in response to tunicamycin also significantly overlap with genes affected in CamkIIδc TG mice, although to a lesser extend when compared to hypoxia (Fig 1I). In sum, these data suggest a scenario in which HF that is linked to cerebral hypoperfusion leads to hypoxia, oxidative, and ER stress-related hippocampal gene expression changes which are upstream of the reduced expression of neuronal genes important for cognition. Taken into account that impaired expression of genes essential for cognitive function is also a key hallmark of dementia, these data provide a plausible hypothesis to explain—at least in part—cognitive dysfunction in response to HF. To provide further evidence for this hypothesis, we first retrieved published datasets in which brain-specific gene expression changes were reported in mouse models with impaired memory function, namely models for aging-associated memory decline (Benito et al, 2015), models for AD (Gjoneska et al, 2015), and fronto-temporal dementia (FTLD) (Swarup et al, 2018). We compared these datasets to the transcriptional alterations observed in the hippocampus of CamkIIδc TG mice (Fig 1J). Interestingly, there was a significant overlap of genes up-regulated in the hippocampus of CamkIIδc TG mice and genes up-regulated in the hippocampus of cognitively impaired old mice, in CK-p25 mice representing a model for AD-like neurodegeneration and in the cortex of FVB mice, representing a mouse model for fronto-temporal dementia FTLD (Fig 1J). Similarly, genes down-regulated in the hippocampus of CamkIIδc TG mice significantly overlapped with the genes down-regulated in models for aging, AD-like neurodegeneration and FTLD (Fig 1J). Thus, the hippocampal gene expression signature observed in response to HF partly overlaps to the gene expression changes detected in cognitive diseases. On this basis, we hypothesized that aberrant hippocampal gene expression and especially the decreased expression of learning and memory genes could be a central process in HF mediated cognitive impairment and might therefore represent a suitable target for therapeutic intervention. To further substantialize and test this hypothesis, we decided to analyze memory function in CamkIIδc TG mice directly. Heart failure in CamkIIδc TG is associated with impaired hippocampus-dependent memory consolidation Three-month-old CamkIIδc TG (n = 16) and control mice (n = 13) were subjected to behavioral testing. Importantly, when subjected to the open field test, CamkIIδc TG and control mice traveled similar distances with the same speed, indicating that explorative behavior and basal motor function is normal (Fig 2A). Both groups also spent similar time in the center of the open field arena, suggesting that anxiety behavior is not affected in CamkIIδc TG mice (Fig 2A). Subsequently, mice were subjected to the Barnes Maze, a hippocampus-dependent spatial navigation-learning test (see Materials and Methods for details). Two-way ANOVA analysis revealed that CamkIIδc TG mice spent significantly more time to find the escape hole when compared to littermate controls (Fig 2B). These data suggest that hippocampus-dependent memory function is impaired in CamkIIδc TG mice. A detailed analysis of the different strategies to find the escape hole confirmed this observation and revealed that in comparison with control mice, CamkIIδc TG mice failed to adapt hippocampus-dependent strategies (direct, short, and long chaining approaches), which are generally considered to depend on higher cognitive abilities than the other strategies (Fig. 2C). To quantify this observation, we calculated the cumulative strategy score (see Materials and Methods for details) that was significantly reduced in CamkIIδc TG mice when compared to the control group (Fig 2D), further confirming that CamkIIδc TG mice exhibit impaired hippocampus-dependent learning abilities. We also assayed memory retrieval 24 h after the final day of training by placing the mice into the Barnes Maze arena with the escape hole being closed and measured the visits to the escape hole. The number of visits to the escape hole during the 120-s test period was significantly lower in CamkIIδc TG mice when compared to the control group, indicating impaired retrieval of spatial memories (Fig 2E). In summary, these findings are in line with our gene expression data (See Fig 1) and show that CamkIIδc overexpression-induced HF leads to cognitive deficits. To substantialize these observations, we analyzed an additional non-genetic model of HF, namely the myocardial infarction (MI) model. Our data show that MI mice also develop hippocampus-dependent memory impairments and exhibit a severe deregulation of hippocampal gene expression that is similar to our data obtained in CamkIIδc TG mice (Fig EV1; Dataset EV4). Figure 2. CamkIIδc TG mice display impaired hippocampus-dependent memory function The distance traveled (left panel), the speed (middle panel), and the time spent in the center region (right panel) during a 5-min open field test was similar among 3-month-old CamkIIδc TG (n = 16) and control mice (n = 13). Unpaired t
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