Epigenetics: an expanding new piece of the stroke puzzle

Tet Enzymes-Mediated DNA 5hmC Modification in Cerebral Ischemic and Hemorrhagic Injury

5-Hydroxymethylcytosine (5hmC) has recently been found that plays an important role in many diseases; however, there are still few studies in the field of stroke. The purpose of this review is to introduce the influence and function of 5hmC in stroke, in order for more people can study it. In this review, we introduced the role of 5hmC in ischemia and hemorrhage stroke, and summarized the possible therapeutic prospects of 5hmC in stroke. In conclusion, we suggest that 5hmC may serve as a biomarker or therapeutic target for the treatment of stroke.

Clinical Pharmacokinetics and Pharmacodynamics of Desmoteplase

Desmoteplase is a bat (Desmodus rotundus) saliva-derived fibrinolytic enzyme resembling a urokinase and tissue plasminogen activator. It is highly dependent on fibrin and has some neuroprotective attributes. Intravenous administration of desmoteplase is safe and well tolerated in healthy subjects. Plasma fibrinolytic activity is linearly related to its blood concentration, its terminal elimination half-life ranges from 3.8 to 4.92 h (50 vs. 90 μg/kg dose). Administration of desmoteplase leads to transitory derangement of fibrinogen, D-dimer, alpha2-antiplasmin, and plasmin and antiplasmin complex which normalize within 4–12 h. It does not alter a prothrombin test, international normalized ratio, activated partial thromboplastin time, and prothrombin fragment 1.2. Desmoteplase was tested in myocardial infarction and pulmonary embolism and showed promising results versus alteplase. In ischemic stroke trials, desmoteplase was linked to increased rates of symptomatic intracranial hemorrhages and case fatality. However, data from “The desmoteplase in Acute Ischemic Stroke” Trials, DIAS-3 and DIAS-J, suggest that the drug is well tolerated and its safety profile is comparable to placebo. Desmoteplase is theoretically a superior thrombolytic because of high fibrin specificity, no activation of beta-amyloid, and lack of neurotoxicity. It was associated with better outcomes in patients with significant stenosis or occlusion of a proximal precerebral vessels. However, DIAS-4 was stopped as it might have not reached its primary endpoint. Due to its promising properties, desmoteplase may be added into treatment of ischemic stroke with extension of the time window and special emphasis on patients presenting outside the 4.5-h thrombolysis window, with wake-up strokes and strokes of unknown onset.

Circulating miR-155 and JAK2/STAT3 Axis in Acute Ischemic Stroke Patients and Its Relation to Post-Ischemic Inflammation and Associated Ischemic Stroke Risk Factors

Background

“Micro RNAs and their target genes recently have been identified to play a crucial role in the molecular pathogenesis of post-stroke ischemic cellular injury, which elucidates their new role in ischemic stroke diagnosis and therapy”. Thus, we evaluated the relative serum expression of miR-155, an inflammatory micro RNA, and the mRNAs (JAK2/STAT3) in acute ischemic stroke patients and its associations with the inflammatory cytokine TNF-α and different stroke risk factors.

Subjects and Methods

The relative expression of serum miR-155 and mRNAs (JAK2/STAT3) was assessed using RT-PCR, serum TNF-α was measured using ELIZA in 46 acute ischemic stroke patients and 50 control subjects. Receiver operating characteristic (ROC) curve was constructed to assess the specificity and sensitivity of circulating miR-155, JAK2/STAT3 as biomarkers for acute ischemic stroke.

Results

Circulating miR-155, JAK2/STAT3 were significantly up-regulated among stroke patients (8.5, 2.9, 4.2 fold respectively, P<0.001) with significant increase in TNF-α (263.8 ± 10.7 pg/mL, P <0.001). MiR-155, JAK2/STAT3 were positively correlated with TNF-α. MiR-155, JAK2/STAT3 were significantly increased in stroke patients and associated with risk factors such as hypertension, carotid atherosclerosis, and atrial fibrillation. Our study revealed that miR-155 has diagnostic accuracy for acute ischemic stroke where AUC=0.9, (P<0.001).

Conclusion

The elevated expressions of circulating miR-155, JAK2/STAT3, and TNF-α in acute ischemic stroke patients could trigger post-stroke cellular inflammation. MiR-155 could be used as potential inflammatory biomarker for acute ischemic stroke. However, further clinical studies are still needed to determine the exact role of miRNAs and different signal transduction expressions in the stage of acute ischemic stroke.

Silencing a Multifunctional microRNA Is Beneficial for Stroke Recovery

Stroke-induced endothelial cell injury leads to destruction of cerebral microvasculature and significant damage to the brain tissue. A subacute phase of cerebral ischemia is associated with regeneration involving the activation of vascular remodeling, neuroplasticity, neurogenesis, and neuroinflammation processes. Effective restoration and improvement of blood supply to the damaged brain tissue offers a potential therapy for stroke. microRNAs (miRNAs) are recently identified small RNA molecules that regulate gene expression and significantly influence the essential cellular processes associated with brain repair following stroke. A number of specific miRNAs are implicated in regulating the development and propagation of the ischemic tissue damage as well as in mediating post-stroke regeneration. In this review, I discuss the functions of the miRNA miR-155 and the effect of its in vivo inhibition on brain recovery following experimental cerebral ischemia. The article introduces new and unexplored approach to cerebral regeneration: regulation of brain tissue repair through a direct modulation of specific miRNA activity.

Endothelial depletion of murine SRF/MRTF provokes intracerebral hemorrhagic stroke

Intracerebral hemorrhagic stroke and vascular dementia are age- and hypertension-associated manifestations of human cerebral small vessel disease (SVD). Cerebral microvessels are formed by endothelial cells (ECs), which are connected through tight junctions, adherens junctions, and stabilizing basement membrane structures. These endothelial connections ensure both vessel stability and blood-brain barrier (BBB) functions, the latter enabling selective exchange of ions, bioactive molecules, and cells between the bloodstream and brain tissue. Srf(iECKO) mice, permitting conditional EC-specific depletion of the transcription factor Serum Response Factor (SRF), suffer from loss of BBB integrity and intracerebral hemorrhaging. Cerebral microbleeds and larger hemorrhages developed upon postnatal and adult depletion of either SRF or its cofactors Myocardin Related Transcription Factor (MRTF-A/-B), revealing essential requirements of ongoing SRF/MRTF activity for maintenance of cerebral small vessel integrity. In vivo magnetic resonance imaging allowed detection, localization, and time-resolved quantification of BBB permeability and hemorrhage formation in Srf(iECKO) brains. At the molecular level, direct and indirect SRF/MRTF target genes, encoding structural components of tight junctions (Claudins and ZO proteins), adherens junctions (VE-cadherin, α-Actinin), and the basement membrane (Collagen IV), were down-regulated upon SRF depletion. These results identify SRF and its MRTF cofactors as major transcriptional regulators of EC junctional stability, guaranteeing physiological functions of the cerebral microvasculature. We hypothesize that impairments in SRF/MRTF activity contribute to human SVD pathology.

The fetal cerebral circulation: three decades of exploration by the LLU Center for Perinatal Biology

For more than three decades, research programs in the Center of Perinatal Biology have focused on the vascular biology of the fetal cerebral circulation. In the 1980s, research in the Center demonstrated that cerebral autoregulation operated over a narrower pressure range, and was more vulnerable to insults, in fetuses than in adults. Other studies were among the first to establish that compared to adult cerebral arteries, fetal cerebral arteries were more hydrated, contained smaller smooth muscle cells and less connective tissue, and had endothelium less capable of producing NO. Work in the 1990s revealed that pregnancy depressed reactivity to NO in extra-cerebral arteries, but elevated it in cerebral arteries through effects involving changes in cGMP metabolism. Comparative studies verified that fetal lamb cerebral arteries were an excellent model for cerebral arteries from human infants. Biochemical studies demonstrated that cGMP metabolism was dramatically upregulated, but that contraction was far more dependent on calcium influx, in fetal compared to adult cerebral arteries. Further studies established that chronic hypoxia accelerates functional maturation of fetal cerebral arteries, as indicated by increased contractile responses to adrenergic agonists and perivascular adrenergic nerves. In the 2000s, studies of signal transduction established age-dependent roles for PKG, PKC, PKA, ERK, ODC, IP3, myofilament calcium sensitivity, and many other mechanisms. These diverse studies clearly demonstrated that fetal cerebral arteries were functionally quite distinct compared to adult cerebral arteries. In the current decade, research in the Center has expanded to a more molecular focus on epigenetic mechanisms and their role in fetal vascular adaptation to chronic hypoxia, maternal drug abuse, and nutrient deprivation. Overall, the past three decades have transformed thinking about, and understanding of, the fetal cerebral circulation due in no small part to the sustained research efforts by faculty and staff in the Center for Perinatal Biology.

MS-275, a class I histone deacetylase inhibitor, protects the p53-deficient mouse against ischemic injury

The administration of pan histone deacetylase (HDAC) inhibitors reduces ischemic damage to the CNS, both in vitro and in animal models of stroke, via mechanisms which we are beginning to understand. The acetylation of p53 is regulated by Class I HDACs and, because p53 appears to play a role in ischemic pathology, the purpose of this study was to discover, using an in vitro white matter ischemia model and an in vivo cerebral ischemia model, if neuroprotection mediated by HDAC inhibition depended on p53 expression. Optic nerves were excised from wild-type and p53-deficient mice, and then subjected to oxygen-glucose deprivation in the presence and absence of a specific inhibitor of Class I HDACs (MS-275, entinostat) while compound action potentials were recorded. Furthermore, transient focal ischemia was imposed on wild-type and p53-deficient mice, which were subsequently treated with MS-275. Interestingly, and in both scenarios, the beneficial effects of MS-275 were most pronounced when p53 was absent. These results suggest that modulation of p53 activity is not responsible for MS-275-mediated neuroprotection, and further illustrate how HDAC inhibitors variably influence p53 and associated apoptotic pathways. Optic nerves from wild-type and p53-deficient mice, engineered to express cyan fluorescent protein (CFP) in neuronal mitochondria, were subjected to oxygen-glucose deprivation (OGD) in the presence and absence of a specific inhibitor of Class I histone deacetylases. The protective effect of MS-275 was evidenced by mitochondrial preservation, and this was most pronounced in the absence of p53.

Novel protective effects of histone deacetylase inhibition on stroke and white matter ischemic injury

Understanding how epigenetics influences the process and progress of a stroke could yield new targets and therapeutics for use in the clinic. Experimental evidence suggests that inhibitors of zinc-dependent histone deacetylases can protect neurons, axons, and associated glia from the devastating effects of oxygen and glucose deprivation. While the specific enzymes involved have yet to be clearly identified, there are hints from somewhat selective chemical inhibitors and also from the use of specific small hairpin RNAs to transiently knockdown protein expression. Neuroprotective mechanisms implicated thus far include the upregulation of extracellular glutamate clearance, inhibition of p53-mediated cell death, and maintenance of mitochondrial integrity. The histone deacetylases have distinct cellular and subcellular localizations, and discrete substrates. As a number of chemical inhibitors are already in clinical use for the treatment of cancer, repurposing for the stroke clinic should be expedited.

Emerging molecular targets for brain repair after stroke

The field of neuroprotection generated consistent preclinical findings of mechanisms of cell death but these failed to be translated into clinics. The approaches that combine the modulation of the inhibitory environment together with the promotion of intrinsic axonal outgrowth needs further work before combined therapeutic strategies will be transferable to clinic trials. It is likely that only when some answers have been found to these issues will our therapeutic efforts meet our expectations. Stroke is a clinically heterogeneous disease and combinatorial treatments require much greater work in pharmacological and toxicological testing. Advances in genetics and results of the Whole Human Genome Project (HGP) provided new unknown information in relation to stroke. Genetic factors are not the only determinants of responses to some diseases. It was recognized early on that "epigenetic" factors were major players in the aetiology and progression of many diseases like stroke. The major players are microRNAs that represent the best-characterized subclass of noncoding RNAs. Epigenetic mechanisms convert environmental conditions and physiological stresses into long-term changes in gene expression and translation. Epigenetics in stroke are in their infancy but offer great promise for better understanding of stroke pathology and the potential viability of new strategies for its treatment.