Alexandra F. Trollope

Long-lasting behavioral responses to stress involve a direct interaction of glucocorticoid receptors with ERK1/2–MSK1–Elk-1 signaling

Stressful events are known to have a long-term impact on future behavioral stress responses. Previous studies suggested that both glucocorticoid hormones and glutamate acting via glucocorticoid receptors (GRs) and N-methyl d-aspartate (NMDA) receptors, respectively, are of critical importance for the consolidation of these long-lasting behavioral responses at the dentate gyrus, the gateway of the hippocampal formation. We found that an acute psychologically stressful event resulted in ERK1/2 phosphorylation (pERK1/2), which within 15 min led to the activation of the nuclear kinases MSK1 and Elk-1 in granule neurons of the dentate gyrus. Next, MSK1 and Elk-1 activation evoked serine-10 phosphorylation and lysine-14 acetylation in histone H3, resulting in the induction of the neuroplasticity-associated immediate-early genes c-Fos and Egr-1 in these neurons. The pERK1/2-mediated activation of MSK1 and Elk-1 required a rapid protein–protein interaction between pERK1/2 and activated GRs. This is a unique nongenomic mechanism of glucocorticoid hormone action in dentate gyrus granule neurons on long-lasting behavioral responses to stress involving direct cross-talk of GRs with ERK1/2–MSK1–Elk-1 signaling to the nucleus.

Whole genome expression analysis within the angiotensin II-apolipoprotein E deficient mouse model of abdominal aortic aneurysm

BackgroundAn animal model commonly used to investigate pathways and potential therapeutic interventions relevant to abdominal aortic aneurysm (AAA) involves subcutaneous infusion of angiotensin II within the apolipoprotein E deficient mouse. The aim of this study was to investigate genes differentially expressed in aneurysms forming within this mouse model in order to assess the relevance of this model to human AAA.ResultsUsing microarrays we identified genes relevant to aneurysm formation within apolipoprotein E deficient mice. Firstly we investigated genes differentially expressed in the aneurysm prone segment of the suprarenal aorta in these mice. Secondly we investigated genes that were differentially expressed in the aortas of mice developing aneurysms relative to those that did not develop aneurysms in response to angiotensin II infusion. Our findings suggest that a host of inflammation and extracellular matrix remodelling pathways are upregulated within the aorta in mice developing aneurysms. Kyoto Encyclopedia of Genes and Genome categories enriched in the aortas of mice with aneurysms included cytokine-cytokine receptor interaction, leukocyte transendothelial migration, natural killer cell mediated cytotoxicity and hematopoietic cell lineage. Genes associated with extracellular matrix remodelling, such as a range of matrix metalloproteinases were also differentially expressed in relation to aneurysm formation.ConclusionThis study is the first report describing whole genome expression arrays in the apolipoprotein E deficient mice in relation to aneurysm formation. The findings suggest that the pathways believed to be critical in human AAA are also relevant to aneurysm formation in this mouse model. The findings therefore support the value of this model to investigate interventions and mechanisms of human AAA.

Animal models of abdominal aortic aneurysm and their role in furthering management of human disease

Abdominal aortic aneurysm is a common degenerative disorder associated with sudden death due to aortic rupture. Current therapy is limited to open surgical repair of the aorta or endovascular placement of covered stents to exclude the abdominal aortic aneurysm from the circulation. A number of different animal models have been developed in order to study abdominal aortic aneurysm in an effort to advance current management deficiencies. Large animal models have been mostly used to assist in developing novel methods to surgically treat abdominal aortic aneurysms. Small animal models, particularly those developed in rodents, have been employed to further the understanding of the mechanisms involved in abdominal aortic aneurysm in order to identify potential new medical treatments. It is expected that findings from these animal models will contribute importantly to new treatments for human abdominal aortic aneurysm. This review explores the animal models which are used in abdominal aortic aneurysm research and highlights their advantages and disadvantages.

Epigenetic mechanisms in stress and adaptation

Epigenetic mechanisms are processes at the level of the chromatin that control the expression of genes but their role in neuro-immuno-endocrine communication is poorly understood. This review focuses on epigenetic modifications induced by a range of stressors, both physical and psychological, and examines how these variations can affect the biological activity of cells. It is clear that epigenetic modifications are critical in explaining how environmental factors, which have no effect on the DNA sequence, can have such profound, long-lasting influences on both physiology and behavior. A signaling pathway involving activation of MEK-ERK1/2, MSK1, and Elk-1 signaling molecules has been identified in the hippocampus which results in the phospho-acetylation of histone H3 and modification of gene expression including up-regulation of immediate early genes such as c-Fos. This pathway can be induced by a range of challenging experiences including forced swimming, Morris water maze learning, fear conditioning and exposure to the radial maze. Glucocorticoid (GC) hormones, released as part of the stress response and acting via glucocorticoid receptors (GRs), enhance signaling through the ERK1/2/MSK1-Elk-1 pathway and thereby increase the impact on epigenetic and gene expression mechanisms. The role of synergetic interactions between these pathways in adaptive responses to stress and learning and memory paradigms is discussed, in addition we speculate on their potential role in immune function.

Stress, epigenetic control of gene expression and memory formation.

Making memories of a stressful life event is essential for an organisms survival as it allows it to adapt and respond in a more appropriate manner should the situation occur again. However, it may be envisaged that extremely stressful events can lead to formation of traumatic memories that are detrimental to the organism and lead to psychiatric disorders such as post-traumatic stress disorder (PTSD). The neurotransmitter glutamate and the ERK MAPK signaling pathway play a principal role in learning and memory. Glucocorticoid hormones acting via the glucocorticoid receptor have been shown to strengthen the consolidation of memories of stressful events. The ERK MAPK signaling pathway and glucocorticoid receptor-mediated actions have recently been shown to drive epigenetic modifications and conformational changes in the chromatin, stimulating the expression of neuroplasticity-related genes involved in stress-related learning and memory processes. The main epigenetic regulatory mechanisms are histone modifications and DNA (de-)methylation. Recently, studies have demonstrated that these processes are acting together in concert to regulate gene expression required for memory consolidation. This review explores the role of stress in learning and memory paradigms and the participating signaling pathways and epigenetic mechanisms and the enzymes that control these modifications during the consolidation process of memory formation.

Stress-induced gene expression and behavior are controlled by DNA methylation and methyl donor availability in the dentate gyrus

Significance Appropriate behavioral responses to psychologically stressful events are important for maintaining mental health and well-being. The consolidation of these behavioral responses critically depends on the induction of the immediate-early gene products FBJ murine osteosarcoma viral oncogene homolog (c-Fos) and early growth response protein 1 (Egr-1) in dentate gyrus neurons. In this report, we found that an intricate balance between DNA methylation, DNA demethylation, and availability of the methyl donor S-adenosyl methionine governs the induction of these genes as well as the behavioral responses after stress. These findings provide insights into the epigenetic control of gene expression underlying stress-induced behavioral adaptation. Stressful events evoke long-term changes in behavioral responses; however, the underlying mechanisms in the brain are not well understood. Previous work has shown that epigenetic changes and immediate-early gene (IEG) induction in stress-activated dentate gyrus (DG) granule neurons play a crucial role in these behavioral responses. Here, we show that an acute stressful challenge [i.e., forced swimming (FS)] results in DNA demethylation at specific CpG (5′-cytosine–phosphate–guanine-3′) sites close to the c-Fos (FBJ murine osteosarcoma viral oncogene homolog) transcriptional start site and within the gene promoter region of Egr-1 (early growth response protein 1) specifically in the DG. Administration of the (endogenous) methyl donor S-adenosyl methionine (SAM) did not affect CpG methylation and IEG gene expression at baseline. However, administration of SAM before the FS challenge resulted in an enhanced CpG methylation at the IEG loci and suppression of IEG induction specifically in the DG and an impaired behavioral immobility response 24 h later. The stressor also specifically increased the expression of the de novo DNA methyltransferase Dnmt3a [DNA (cytosine-5-)-methyltransferase 3 alpha] in this hippocampus region. Moreover, stress resulted in an increased association of Dnmt3a enzyme with the affected CpG loci within the IEG genes. No effects of SAM were observed on stress-evoked histone modifications, including H3S10p-K14ac (histone H3, phosphorylated serine 10 and acetylated lysine-14), H3K4me3 (histone H3, trimethylated lysine-4), H3K9me3 (histone H3, trimethylated lysine-9), and H3K27me3 (histone H3, trimethylated lysine-27). We conclude that the DNA methylation status of IEGs plays a crucial role in FS-induced IEG induction in DG granule neurons and associated behavioral responses. In addition, the concentration of available methyl donor, possibly in conjunction with Dnmt3a, is critical for the responsiveness of dentate neurons to environmental stimuli in terms of gene expression and behavior.

Angiopoietins, abdominal aortic aneurysm and atherosclerosis.

Abdominal aortic aneurysm (AAA) and atherosclerosis are common causes of mortality and morbidity in an aging population. Angiogenesis is believed to contribute to the development and progression of these diseases. Angiopoietins (angpts) are known to be important regulators of angiogenesis. Angpts can also influence inflammation and have been shown to possess both pro-atherosclerotic and atheroprotective effects. This review explores the potential roles that the angpts play in the development and progression of AAA and atherosclerosis.

Rapid down‐regulation of glucocorticoid receptor gene expression in the dentate gyrus after acute stress in vivo: Role of DNA Methylation and microRNA Activity

Background: Although glucocorticoid receptors (GRs) in the hippocampus play a vital role in the regulation of physiological and behavioural responses to stress, the regulation of receptor expression remains unclear. This work investigates the molecular mechanisms underpinning stress-induced changes in hippocampal GR mRNA levels in vivo. Methods: Male Wistar rats were killed either under baseline conditions or after forced swim stress (FSS; 15 min in 25°C water). Rat hippocampi were micro-dissected (for mRNA, microRNA, and DNA methylation analysis) or frozen whole (for chromatin immunoprecipitation). In an additional experiment, rats were pre-treated with RU486 (a GR antagonist) or vehicle. Results: FSS evoked a dentate gyrus-specific reduction in GR mRNA levels. This was related to an increased DNMT3a protein association with a discreet region of the Nr3c1 (GR gene) promoter, shown here to undergo increased DNA methylation after FSS. FSS also caused a time-dependent increase in the expression of miR-124a, a microRNA known to reduce GR mRNA expression, which was inversely correlated with a reduction in GR mRNA levels 30 min after FSS. FSS did not affect GR binding to a putative negative glucocorticoid response element within the Nr3c1 gene. Conclusions: Acute stress results in decreased GR mRNA expression specifically in the dentate gyrus. Our results indicate that a complex interplay of multiple molecular mechanisms - including increased DNA methylation of discrete CpG residues within the Nr3c1 gene, most likely facilitated by DNMT3a, and increased expression of miR-124a - could be responsible for these changes.

The relevance of epigenetics to occlusive cerebral and peripheral arterial disease

Athero-thrombosis of the arteries supplying the brain and lower limb are the main causes of stroke and limb loss. New therapies are needed to improve the outcomes of athero-thrombosis. Recent evidence suggests a role for epigenetic changes in the development and progression of ischaemic injury due to atherosclerotic occlusion of peripheral arteries. DNA hypermethylation have been associated with cardiovascular diseases. Histone post-translational modifications have also been implicated in atherosclerosis. Oxidized low-density lipoprotein regulated pro-inflammatory gene expression within endothelial cells is controlled by phosphorylation/acetylation of histone H3 and acetylation of histone H4 for example. There are a number of challenges in translating the growing evidence implicating epigenetics in atherosclerosis to improved therapies for patients. These include the small therapeutic window in conditions such as acute stroke and critical limb ischaemia, since interventions introduced in such patients need to act rapidly and be safe in elderly patients with many co-morbidities. Pre-clinical animal experiments have also reported conflicting effects of some novel epigenetic drugs, which suggest that further in-depth studies are required to better understand their efficacy in resolving ischaemic injury. Effective ways of dealing with these challenges are needed before epigenetic approaches to therapy can be introduced into practice.

Angiopoietin-2 attenuates angiotensin II-induced aortic aneurysm and atherosclerosis in apolipoprotein E-deficient mice

Angiogenesis and inflammation are implicated in aortic aneurysm and atherosclerosis and regulated by angiopoietin-2 (Angpt2). The effect of Angpt2 administration on experimental aortic aneurysm and atherosclerosis was examined. Six-month-old male apolipoprotein E deficient (ApoE−/−) mice were infused with angiotensin II (AngII) and administered subcutaneous human Fc-protein (control) or recombinant Angpt2 (rAngpt2) over 14 days. Administration of rAngpt2 significantly inhibited AngII-induced aortic dilatation and rupture of the suprarenal aorta (SRA), and development of atherosclerosis within the aortic arch. These effects were blood pressure and plasma lipoprotein independent and associated with Tie2 activation and down-regulation of monocyte chemotactic protein-1 (MCP-1) within the SRA. Plasma concentrations of MCP-1 and interleukin-6 were significantly lower in mice receiving rAngpt2. Immunostaining for the monocyte/macrophage marker MOMA-2 and the angiogenesis marker CD31 within the SRA were less in mice receiving rAngpt2 than controls. The percentage of inflammatory (Ly6Chi) monocytes within the bone marrow was increased while that in peripheral blood was decreased by rAngpt2 administration. In conclusion, administration of rAngpt2 attenuated angiotensin II-induced aortic aneurysm and atherosclerosis in ApoE−/− mice associated with reduced aortic inflammation and angiogenesis. Up-regulation of Angpt2 may have potential therapeutic value in patients with aortic aneurysm and atherosclerosis.