Kinga G. Blecharz

Glucocorticoid Insensitivity at the Hypoxic Blood–Brain Barrier Can Be Reversed by Inhibition of the Proteasome

Background and Purpose— Glucocorticoids potently stabilize the blood–brain barrier and ameliorate tissue edema in certain neoplastic and inflammatory disorders of the central nervous system, but they are largely ineffective in patients with acute ischemic stroke. The reasons for this discrepancy are unresolved. Methods— To address the molecular basis for the paradox unresponsiveness of the blood–brain barrier during hypoxia, we used murine brain microvascular endothelial cells exposed to O2/glucose deprivation as an in vitro model. In an in vivo approach, mice were subjected to transient middle cerebral artery occlusion to induce brain infarctions. Blood–brain barrier damage and edema formation were chosen as surrogate markers of glucocorticoid sensitivity in the presence or absence of proteasome inhibitors. Results— O2/glucose deprivation reduced the expression of tight junction proteins and transendothelial resistance in murine brain microvascular endothelial cells in vitro. Dexamethasone treatment failed to reverse these effects during hypoxia. Proteasome-dependent degradation of the glucocorticoid receptor impaired glucocorticoid receptor transactivation thereby preventing physiological glucocorticoid activity. Inhibition of the proteasome, however, fully restored the blood–brain barrier stabilizing properties of glucocorticoid during O2/glucose deprivation. Importantly, mice treated with the proteasome inhibitor Bortezomib in combination with steroids several hours after stroke developed significantly less brain edema and functional deficits, whereas respective monotherapies were ineffective. Conclusions— We for the first time show that inhibition of the proteasome can overcome glucocorticoid resistance at the hypoxic blood–brain barrier. Hence, combined treatment strategies may help to combat stroke-induced brain edema formation in the future and prevent secondary clinical deterioration.

Glucocorticoids increase VE-cadherin expression and cause cytoskeletal rearrangements in murine brain endothelial cEND cells

Recent studies have shown the influence of glucocorticoids on the expression of the tight junction protein occludin in the brain capillary endothelial cell line cEND, contributing to improvement in endothelial barrier functions. In this study, we investigated glucocorticoid effects on the expression of the adherens junction proteins VE- (vascular-endothelial) cadherin, α-catenin and β-catenin as well as that of ZO-1, the plaque protein shared by both adherens and tight junctions on stimulation with dexamethasone. We were able to show a positive influence of dexamethasone administration on VE-cadherin protein levels as well as a rearrangement of VE-cadherin protein to the cytoskeleton after dexamethasone treatment. Investigation of transcriptional activation of the VE-cadherin promoter by dexamethasone, however, did not point to direct glucocorticoid-mediated VE-cadherin gene induction but rather suggested indirect steroid effects leading to increased VE-cadherin protein synthesis. Dexamethasone was further shown to induce cellular differentiation into a cobblestone cellular morphology and reinforcement of adherens junctions concomitant with the increased anchorage of VE-cadherin to the actin cytoskeleton. We thus propose that glucocorticoid effects on VE-cadherin protein synthesis and organization are important for the formation of both adherens and tight junction, and for improved barrier properties in microvascular brain endothelial cells.

Glucocorticoid effects on endothelial barrier function in the murine brain endothelial cell line cEND incubated with sera from patients with multiple sclerosis

Compromised blood—brain barrier integrity is a major hallmark of active multiple sclerosis (MS). Alterations in brain endothelial tight junction protein and gene expression occur early during neuroinflammation but there is little known about the underlying mechanisms. In this study, we analysed barrier compromising effects of sera from MS patients and barrier restoring effects of glucocorticoids on blood—brain barrier integrity in vitro. cEND murine brain microvascular endothelial cell monolayers were incubated with sera from patients in active phase of disease or in relapse. Data were compared with effects of the glucocorticoid dexamethasone alone or in combination with MS sera on barrier integrity. Tight junction protein levels and gene expression were evaluated concomitant with barrier integrity. We reveal downregulation of claudin-5 and occludin protein and mRNA and an accompanying upregulation in expression of matrix metalloproteinase MMP-9 after incubation with serum from active disease and remission and also a minor reconstitution of barrier functions related to dexamethasone treatment. Moreover, we for the first time describe downregulation of claudin-5 and occludin protein after incubation of cEND cells with sera from patients in remission phase of MS. Our findings reveal direct and differential effects of MS sera on blood-brain barrier integrity.

TWIST1 regulates the activity of ubiquitin proteasome system via the miR-199/214 cluster in human end-stage dilated cardiomyopathy.

BACKGROUND The transcription factor TWIST1 has been described to regulate the microRNA (miR)-199/214 cluster. Genetic disruption of TWIST1 resulted in a cachectic phenotype and early death of the knock-out mice. This might be connected to the activity of the ubiquitin-proteasome-system (UPS), as miR-199a has been suggested to regulate the ubiquitin E2 ligases Ube2i and Ube2g1. METHODS Cardiac tissue from explanted hearts of 42 patients with dilated cardiomyopathy and 20 healthy donor hearts were analysed for protein expression of TWIST1 and its inhibitors Id-1, MuRF-1 and MAFbx, the expression of miR-199a, -199b and -214, as well as the activity of the UPS by using specific fluorogenic substrates. RESULTS TWIST1 was repressed in patients with dilated cardiomyopathy by 43% (p=0.003), while Id1 expression was unchanged. This was paralleled by a reduced expression of miR-199a by 38 ± 9% (p=0.053), miR-199b by 36 ± 13% (p=0.019) and miR-214 by 41 ± 11% (p=0.0158) compared to donor hearts. An increased peptidylglutamyl-peptide-hydrolysing activity (p<0.0001) was observed in the UPS, while the chymotrypsin-like and trypsin-like activities were unchanged. The protein levels of the rate limiting ubiquitin E3-ligases MuRF-1 and MAFbx were up-regulated (p=0.005 and p=0.0156, respectively). Mechanistically silencing of TWIST1 using siRNA in primary rat cardiomyocytes led to a down-regulation of the miR-199/214 cluster and to a subsequent up-regulation of Ube2i. CONCLUSION The TWIST1/miR-199/214 axis is down-regulated in dilated cardiomyopathy, which is likely to play a role in the increased activity of the UPS. This may contribute to the loss of cardiac mass during dilatation of the heart.

Control of the blood–brain barrier function in cancer cell metastasis

Cerebral metastases are the most common brain neoplasms seen clinically in the adults and comprise more than half of all brain tumours. Actual treatment options for brain metastases that include surgical resection, radiotherapy and chemotherapy are rarely curative, although palliative treatment improves survival and life quality of patients carrying brain‐metastatic tumours. Chemotherapy in particular has also shown limited or no activity in brain metastasis of most tumour types. Many chemotherapeutic agents used systemically do not cross the blood–brain barrier (BBB), whereas others may transiently weaken the BBB and allow extravasation of tumour cells from the circulation into the brain parenchyma. Increasing evidence points out that the interaction between the BBB and tumour cells plays a key role for implantation and growth of brain metastases in the central nervous system. The BBB, as the tightest endothelial barrier, prevents both early detection and treatment by creating a privileged microenvironment. Therefore, as observed in several in vivo studies, precise targetting the BBB by a specific transient opening of the structure making it permeable for therapeutic compounds, might potentially help to overcome this difficult clinical problem. Moreover, a better understanding of the molecular features of the BBB, its interrelation with metastatic tumour cells and the elucidation of cellular mechanisms responsible for establishing cerebral metastasis must be clearly outlined in order to promote treatment modalities that particularly involve chemotherapy. This in turn would substantially expand the survival and quality of life of patients with brain metastasis, and potentially increase the remission rate. Therefore, the focus of this review is to summarise the current knowledge on the role and function of the BBB in cancer metastasis.

Vasculogenic and angiogenic pathways in moyamoya disease

BACKGROUND Moyamoya disease (MMD) is a slowly progressing steno-occlusive cerebrovascular disease. The typical moyamoya vessels, which originate from an initial stenosis of the internal carotid, highlight that increased and/or abnormal angiogenic, vasculogenic and arteriogenic processes are involved in the disease pathophysiology. OBJECTIVE Herein, we summarize the current knowledge on the most important signaling pathways involved in MMD vessel formation, particularly focusing on the expression of growth factors and function of endothelial progenitor cells (EPCs). METHODS AND RESULTS Higher plasma concentrations of vascular endothelial growth factor, matrix metalloproteinase, hepatocyte growth factor, and interleukin-1β were reported in MMD. A specific higher level of basic fibroblast growth factor was also found in the cerebrospinal fluid of these patients. Finally, the number and the functionality of EPCs were found to be increased. In spite of the available data, the approaches and findings reported so far do not give an evident correlation between the expression levels of the aforementioned growth factors and MMD severity. Furthermore, the controversial results provided by studies on EPCs, do not permit to understand the true involvement of these cells in MMD pathophysiology. CONCLUSION Further studies should thus be implemented to extend our knowledge on processes regulating both the arterial stenosis and the excessive formation of collateral vessels. Moreover, we suggest advances of integrated approaches and functional assays to correlate biological and clinical data, arguing for the development of new therapeutic applications for MMD.

Autocrine release of angiopoietin-2 mediates cerebrovascular disintegration in Moyamoya disease.

Moyamoya disease is a rare steno-occlusive cerebrovascular disorder often resulting in hemorrhagic and ischemic strokes. Although sharing the same ischemic stimulus with atherosclerotic cerebrovascular disease, Moyamoya disease is characterized by a highly instable cerebrovascular system which is prone to rupture due to pathological neovascularization. To understand the molecular mechanisms underlying this instability, angiopoietin-2 gene expression was analyzed in middle cerebral artery lesions obtained from Moyamoya disease and atherosclerotic cerebrovascular disease patients. Angiopoietin-2 was significantly up-regulated in Moyamoya vessels, while serum concentrations of soluble angiopoietins were not changed. For further evaluations, cerebral endothelial cells incubated with serum from these patients in vitro were applied. In contrast to atherosclerotic cerebrovascular disease serum, Moyamoya disease serum induced an angiopoietin-2 overexpression and secretion, accompanied by loss of endothelial integrity. These effects were absent or inverse in endothelial cells of non-brain origin suggesting brain endothelium specificity. The destabilizing effects on brain endothelial cells to Moyamoya disease serum were partially suppressed by the inhibition of angiopoietin-2. Our findings define brain endothelial cells as the potential source of vessel-destabilizing factors inducing the high plasticity state and disintegration in Moyamoya disease in an autocrine manner. We also provide new insights into Moyamoya disease pathophysiology that may be helpful for preventive treatment strategies in future.

Inhibition of proteasome-mediated glucocorticoid receptor degradation restores nitric oxide bioavailability in myocardial endothelial cells in vitro.

Glucocorticoids (GCs), including the synthetic GC derivate dexamethasone, are widely used as immunomodulators. One of the numerous side effects of dexamethasone therapy is hypertension arising from reduced release of the endothelium‐derived vasodilator nitric oxide (NO).

Glucocorticoids cause VE-cadherin upregulation and cytoskeletal rearrangements in the blood-brain barrier endothelial cEND cell line

The demonstration that glucocorticoid-mediated activation can control occludin expression in brain capillary endothelial cells has provided a new avenue of research in the field of blood brain-barrier (BBB) permeability regulation. In order to identify more key genes involved in glucocorticoid-mediated regulation of BBB permeability, we used cDNA microarrays to study changes in gene expression in dexamethasone-treated brain capillary endothelial cEND cells: Primarily, we observed changes in expression of the VE-cadherin gene involved in cell adhesion. Vascular-endothelial-cadherin (VE-cadherin) is an endothelial cell-specific adhesion protein localized in cell-cell contacts. It is known as an important determinant of vascular architecture and endothelial cell survival. Quantitative real-time PCR showed an upregulation of VE-cadherin expression exclusively in cEND cells, in accordance to previous observations made for the occludin gene. Subsequently, we verified divergent transcriptional activation of the VE-cadherin gene by dexamethasone. Furthermore, we measured the change in protein levels of VE-cadherin and demonstrated a transactivation of the VE-cadherin promoter in cEND cells via dexamethasone. Dexamethasone was further shown to induce cellular differentiation into a cobblestone cellular morphology and reinforcement of adherens junctions concomitant with the increased anchorage of VE-cadherin to the actin cytoskeleton. We thus propose that glucocorticoid effects on VE-cadherin protein synthesis and organization are important for the formation of both adherens and tight junction, and for improved barrier properties in microvascular brain endothelial cells. To find cell- or tissue-specific ligands that could be used in therapeutic regime of barrier disorder diseases it is necessary to study and understand the molecular mechanisms of beneficial effects of glucocorticoid action on BBB-genes involved in BBB-permeability regulation.