Charles C. Matouk

Epigenetic Regulation of Vascular Endothelial Gene Expression

Epigenetics refers to chromatin-based pathways important in the regulation of gene expression and includes 3 distinct, but highly interrelated, mechanisms: DNA methylation, histone density and posttranslational modifications, and RNA-based mechanisms. Together, they offer a newer perspective on transcriptional control paradigms in vascular endothelial cells and provide a molecular basis for how the environment impacts the genome to modify disease susceptibility. This review provides an introduction to epigenetic concepts for vascular biologists. Using endothelial nitric oxide synthase (NOS3) as an example, we examine the growing body of evidence implicating epigenetic pathways in the control of vascular endothelial gene expression in health and disease.

Vessel Wall MRI to Differentiate Between Reversible Cerebral Vasoconstriction Syndrome and Central Nervous System Vasculitis Preliminary Results

Background and Purpose— Prospective differentiation between reversible cerebral vasoconstriction syndrome and central nervous system vasculitis can be challenging. We hypothesized that high-resolution vessel wall MRI would demonstrate arterial wall enhancement in central nervous system vasculitis but not in reversible cerebral vasoconstriction syndrome. Methods— We identified all patients with multifocal segmental narrowing of large intracranial arteries who had high-resolution vessel wall MRI and follow-up angiography at our institute over a 4-year period and performed a detailed chart review. Results— Three patients lacked arterial wall enhancement, and these all had reversal of arterial narrowing within 3 months. Four patients demonstrated arterial wall enhancement, and these had persistent or progressive arterial narrowing at a median follow-up of 17 months (range, 6–36 months) with final diagnoses of central nervous system vasculitis (3) and cocaine vasculopathy (1). Conclusions— Preliminary results suggest that high-resolution contrast-enhanced vessel wall MRI may enable differentiation between reversible cerebral vasoconstriction syndrome and central nervous system vasculitis.

Hypoxic Repression of Endothelial Nitric-oxide Synthase Transcription Is Coupled with Eviction of Promoter Histones

Hypoxia elicits endothelial dysfunction, in part, through reduced expression of endothelial nitric-oxide synthase (eNOS). Here we present evidence that hypoxia causes a rapid decrease in the transcription of the eNOS/NOS3 gene, accompanied by decreased acetylation and lysine 4 (histone H3) methylation of eNOS proximal promoter histones. Surprisingly, we demonstrate that histones are rapidly evicted from the eNOS proximal promoter during hypoxia. We also demonstrate endothelium-specific H2A.Z incorporation at the eNOS promoter and find that H2A.Z is also evicted by hypoxic stimulation. After longer durations of hypoxia, histones are reincorporated at the eNOS promoter, but these histones lack substantial histone acetylation. Additionally, we identify a key role for the chromatin remodeler, BRG1, in re-establishing eNOS expression following reoxygenation of hypoxic cells. We posit that post-translational histone modifications are required to maintain constitutive eNOS transcriptional activity and that histone eviction rapidly resets histone marks and is a proximal event in the hypoxic repression of eNOS. Although nucleosome eviction has been reported in models of transcriptional activation, the observation that eviction can also accompany transcriptional repression in hypoxic mammalian cells argues that eviction may be broadly relevant to both positive and negative changes in transcription.

Hypoxia-inducible expression of a natural cis-antisense transcript inhibits endothelial nitric-oxide synthase.

The destabilization of endothelial nitric-oxide synthase (eNOS) mRNA in hypoxic endothelial cells may be important in the etiology of vascular diseases, such as pulmonary hypertension. Recently, an overlapping antisense transcript to eNOS/NOS3 was implicated in the post-transcriptional regulation of eNOS. We demonstrate here that expression of sONE, also known as eNOS antisense (NOS3AS) or autophagy 9-like 2 (APG9L2), is robustly induced by hypoxia or functional deficiency of von Hippel-Lindau protein. sONE is also up-regulated in the aortas of hypoxic rats. In hypoxic endothelial cells, sONE expression negatively correlates with eNOS expression. Blocking the hypoxic induction of sONE by RNA interference attenuates the fall in both eNOS RNA and protein. We provide evidence that the induction of sONE primarily involves transcript stabilization rather than increased transcriptional activity and is von Hippel-Lindaubut not hypoxia-inducible factor 2α-dependent. We also demonstrate that sONE transcripts are enriched in the nucleus of normoxic cells and that hypoxia promotes an increase in the level of cytoplasmic and polyribosome-associated, sONE mRNA. The finding that eNOS expression can be regulated by an overlapping cis-antisense transcript in a stimulus-dependent fashion provides evidence that sense/antisense interactions may play a previously unappreciated role in vascular disease pathogenesis.

Vessel wall magnetic resonance imaging identifies the site of rupture in patients with multiple intracranial aneurysms: proof of principle.

BACKGROUND High-resolution magnetic resonance vessel wall imaging (MR-VWI) is increasingly used to study steno-occlusive cerebrovascular disease, but has not yet been applied to patients with aneurysmal subarachnoid hemorrhage (SAH). OBJECTIVE To study the ability of high-resolution MR-VWI to determine the site of rupture in patients with aneurysmal SAH. METHODS Medical records of patients admitted with aneurysmal SAH between December 2011 and May 2012 were reviewed. MR-VWI was routinely performed for patients treated in the IMRIS Neurovascular Suite immediately before definitive treatment of the ruptured aneurysm. RESULTS We report for the first time high-resolution MR-VWI in 5 patients with aneurysmal SAH. Three patients harbored multiple intracranial aneurysms. The ruptured aneurysms demonstrated thick vessel wall enhancement in all cases. None of the associated unruptured aneurysms demonstrated this MR imaging finding. CONCLUSION High-resolution MR-VWI identified the site of rupture in patients with aneurysmal SAH, including those patients harboring multiple intracranial aneurysms. It may represent a useful tool in the investigation of aneurysmal SAH.

Epigenetics of the vascular endothelium

Classical models of transcription in vascular endothelial cells, specifically the cis/trans paradigm, have limitations. For instance, how does the environment have chronic effects on gene expression in endothelial cells after weeks or years? When an endothelial cell divides, how is this information transmitted to daughter cells? Epigenetics refers to chromatin-based pathways important in the regulation of gene expression and includes three distinct, but highly interrelated, mechanisms: DNA methylation, histone density and posttranslational modifications, and RNA-based mechanisms. Together they offer a newer perspective on transcriptional control paradigms in vascular endothelial cells and provide a molecular basis for understanding how the environment impacts the genome to modify disease susceptibility. This alternative viewpoint for transcriptional regulation allows a reassessment of the cis/trans model and even helps explain some of its limitations. This review provides an introduction to epigenetic concepts for vascular biologists and uses topical examples in cell biology to provide insight into how cell types or even whole organisms, such as monozygotic human twins with the same DNA sequence, can exhibit heterogeneous patterns of gene expression, phenotype, or diseases prevalence. Using endothelial nitric oxide synthase (NOS3) as an example, we examine the growing body of evidence implicating epigenetic pathways in the control of vascular endothelial gene expression in health and disease.

The CXCR4/CXCR7/SDF-1 pathway contributes to the pathogenesis of Shiga toxin–associated hemolytic uremic syndrome in humans and mice

Hemolytic uremic syndrome (HUS) is a potentially life-threatening condition. It often occurs after gastrointestinal infection with E. coli O157:H7, which produces Shiga toxins (Stx) that cause hemolytic anemia, thrombocytopenia, and renal injury. Stx-mediated changes in endothelial phenotype have been linked to the pathogenesis of HUS. Here we report our studies investigating Stx-induced changes in gene expression and their contribution to the pathogenesis of HUS. Stx function by inactivating host ribosomes but can also alter gene expression at concentrations that minimally affect global protein synthesis. Gene expression profiling of human microvascular endothelium treated with Stx implicated a role for activation of CXCR4 and CXCR7 by their shared cognate chemokine ligand (stromal cell-derived factor-1 [SDF-1]) in Stx-mediated pathophysiology. The changes in gene expression required a catalytically active Stx A subunit and were mediated by enhanced transcription and mRNA stability. Stx also enhanced the association of CXCR4, CXCR7, and SDF1 mRNAs with ribosomes. In a mouse model of Stx-mediated pathology, we noted changes in plasma and tissue content of CXCR4, CXCR7, and SDF-1 after Stx exposure. Furthermore, inhibition of the CXCR4/SDF-1 interaction decreased endothelial activation and organ injury and improved animal survival. Finally, in children infected with E. coli O157:H7, plasma SDF-1 levels were elevated in individuals who progressed to HUS. Collectively, these data implicate the CXCR4/CXCR7/SDF-1 pathway in Stx-mediated pathogenesis and suggest novel therapeutic strategies for prevention and/or treatment of complications associated with E. coli O157:H7 infection.

The pipeline flow-diverting stent for exclusion of ruptured intracranial aneurysms with difficult morphologies.

BACKGROUND: The Pipeline Embolization Device (PED) is a flow-diverting stent that may represent a new therapeutic tool for difficult-to-treat intracranial aneurysms, including those that present with subarachnoid hemorrhage (SAH). OBJECTIVE: To demonstrate the feasibility of utilizing the PED as a primary treatment for ruptured aneurysms with challenging morphologies. METHODS: Three patients with ruptured intracranial aneurysms presented with SAH. Three distinct and difficult-to-treat aneurysm morphologies were encountered: (1) a small basilar trunk pseudoaneurysm, (2) a carotid artery blister aneurysm, and (3) an A1/A2 junction-dissecting-type aneurysm. All were treated with deployment of one or more PEDs across the aneurysm. RESULTS: PEDs were successfully deployed in all 3 cases. Two patients were treated with 2 overlapping PEDs, and the third patient was treated with a single device. Aneurysm obliteration was achieved in all 3 cases with no early rehemorrhage or other clinically adverse event. CONCLUSION: Endovascular treatment with the pipeline flow-diverting stent may be a viable treatment option for otherwise difficult-to-treat aneurysm morphologies in the context of acute SAH.

Seizure control for intracranial arteriovenous malformations is directly related to treatment modality: a meta-analysis

Object Seizures are a common presenting sign of intracranial arteriovenous malformations (AVMs). The object of this meta-analysis was to determine if the modality selected to treat AVMs affects the rate of seizure outcomes. Methods All published data describing seizure status as an outcome goal over the past 20 years were included in this study. Seizure outcomes following microsurgery (MS), endovascular embolization for cure (EVE), or stereotactic radiosurgery (SRS) were compared using a validated random effect logistic regression approach. Results 24 studies, with a total of 1157 patients, were analyzed. Overall, the microsurgical group had the best seizure control (p<0.01), with the relative predicted rates of seizure outcome as follows: MS 78.3% (95% CI 70.1% to 85.8%); SRS 62.8% (95% CI 55.0% to 70.0%); and EVE 49.3% (95% CI 32.1% to 66.6%). Patients in the SRS group who had complete obliteration of their AVMs achieved the highest rate of seizure control (85.2% (95% CI 79.1% to 91.2%); p<0.01). The development of new onset seizures occurred more frequently in patients undergoing EVE (39.4% (95% CI 8.1% to 67.8%)) compared with MS (9.1% (95% CI 5.0% to 13.1%)) and SRS (5.4% (95% CI 3.0% to 7.8%)) (p<0.3 and p<0.01, respectively). Conclusions This is the first meta-analysis designed to study relative rates of seizure outcomes following the currently utilized AVM treatment modalities. In general, MS results in the highest proportion of seizure control. However, if SRS results in successful obliteration of the AVM, then this modality is the most effective in achieving seizure control.

Intracranial Vessel Wall MRI: Principles and Expert Consensus Recommendations of the American Society of Neuroradiology

SUMMARY: Intracranial vessel wall MR imaging is an adjunct to conventional angiographic imaging with CTA, MRA, or DSA. The technique has multiple potential uses in the context of ischemic stroke and intracranial hemorrhage. There remain gaps in our understanding of intracranial vessel wall MR imaging findings and research is ongoing, but the technique is already used on a clinical basis at many centers. This article, on behalf of the Vessel Wall Imaging Study Group of the American Society of Neuroradiology, provides expert consensus recommendations for current clinical practice.