Levent M. Akyürek

Filamins in cell signaling, transcription and organ development

Filamins are large actin-binding proteins that stabilize delicate three-dimensional actin filament networks and link them to cellular membranes where they integrate cell architectural and signaling functions important for cell locomotion. Filamins have been shown to bind to proteins with diverse functions and are implicated in human genetic diseases including malformations of the skeleton, brain, and heart. Mouse models of filamin deficiency have advanced our understanding of the important roles filamins play in embryonic development and disease progression. These studies provide clear evidence that cytoskeletal filamin proteins integrate cell signaling, transcription and organ development. This review focuses on the emerging roles of filamins in cell signaling and transcription, with emphasis on cell motility and organ development.

Antioxidants can increase melanoma metastasis in mice

Antioxidants increase migration and invasion of human melanoma cells and accelerate metastasis in an endogenous mouse model of malignant melanoma. Another strike against antioxidants Antioxidants are found in a variety of foods and dietary supplements and are frequently used with the goal of preventing cancer, but mounting evidence suggests that they may not be as beneficial as once thought. Clinical studies have shown mixed or no benefits, and other works demonstrated that antioxidants may accelerate the progression of lung cancer. Now, Le Gal et al. discovered that some common antioxidants increase the rate of melanoma cell migration and invasion and increase metastasis in a mouse model. These are early findings, and additional work will be required to confirm the generalizability of this observation. Nevertheless, the results suggest a need for caution in the use of antioxidants, especially for patients with existing cancer. Antioxidants in the diet and supplements are widely used to protect against cancer, but clinical trials with antioxidants do not support this concept. Some trials show that antioxidants actually increase cancer risk and a study in mice showed that antioxidants accelerate the progression of primary lung tumors. However, little is known about the impact of antioxidant supplementation on the progression of other types of cancer, including malignant melanoma. We show that administration of N-acetylcysteine (NAC) increases lymph node metastases in an endogenous mouse model of malignant melanoma but has no impact on the number and size of primary tumors. Similarly, NAC and the soluble vitamin E analog Trolox markedly increased the migration and invasive properties of human malignant melanoma cells but did not affect their proliferation. Both antioxidants increased the ratio between reduced and oxidized glutathione in melanoma cells and in lymph node metastases, and the increased migration depended on new glutathione synthesis. Furthermore, both NAC and Trolox increased the activation of the small guanosine triphosphatase (GTPase) RHOA, and blocking downstream RHOA signaling abolished antioxidant-induced migration. These results demonstrate that antioxidants and the glutathione system play a previously unappreciated role in malignant melanoma progression.

The Risk-Associated Long Noncoding RNA NBAT-1 Controls Neuroblastoma Progression by Regulating Cell Proliferation and Neuronal Differentiation

Neuroblastoma is an embryonal tumor of the sympathetic nervous system and the most common extracranial tumor of childhood. By sequencing transcriptomes of low- and high-risk neuroblastomas, we detected differentially expressed annotated and nonannotated long noncoding RNAs (lncRNAs). We identified a lncRNA neuroblastoma associated transcript-1 (NBAT-1) as a biomarker significantly predicting clinical outcome of neuroblastoma. CpG methylation and a high-risk neuroblastoma associated SNP on chromosome 6p22 functionally contribute to NBAT-1 differential expression. Loss of NBAT-1 increases cellular proliferation and invasion. It controls these processes via epigenetic silencing of target genes. NBAT-1 loss affects neuronal differentiation through activation of the neuronal-specific transcription factor NRSF/REST. Thus, loss of NBAT-1 contributes to aggressive neuroblastoma by increasing proliferation and impairing differentiation of neuronal precursors.

Filamin B deficiency in mice results in skeletal malformations and impaired microvascular development.

Mutations in filamin B (FLNB), a gene encoding a cytoplasmic actin-binding protein, have been found in human skeletal disorders, including boomerang dysplasia, spondylocarpotarsal syndrome, Larsen syndrome, and atelosteogenesis phenotypes I and III. To examine the role of FLNB in vivo, we generated mice with a targeted disruption of Flnb. Fewer than 3% of homozygous embryos reached term, indicating that Flnb is important in embryonic development. Heterozygous mutant mice were indistinguishable from their wild-type siblings. Flnb was ubiquitously expressed; strong expression was found in endothelial cells and chondrocytes. Flnb-deficient fibroblasts exhibited more disorganized formation of actin filaments and reduced ability to migrate compared with wild-type controls. Flnb-deficient embryos exhibited impaired development of the microvasculature and skeletal system. The few Flnb-deficient mice that were born were very small and had severe skeletal malformations, including scoliotic and kyphotic spines, lack of intervertebral discs, fusion of vertebral bodies, and reduced hyaline matrix in extremities, thorax, and vertebrae. These mice died or had to be euthanized before 4 weeks of age. Thus, the phenotypes of Flnb-deficient mice closely resemble those of human skeletal disorders with mutations in FLNB.

Tolerance induction ameliorates allograft vasculopathy in rat aortic transplants. Influence of Fas-mediated apoptosis.

Based on successful induction of donor-specific unresponsiveness by alloantigenic stimulation in several animal models of acute rejection, we hypothesized that similar immune manipulations would also inhibit the evolution of chronic rejection and transplant vasculopathy. To induce immune tolerance, DA rats received a PVG heart allograft and were immunosuppressed with cyclosporine for 30 d. At day 100 the animals were challenged with a PVG aortic allograft after either 1 or 18 h of cold ischemia. 8 wk after the aortic transplantation, the grafts were investigated for morphological changes, infiltrating cells, apoptosis, and Fas-Fas ligand expression. Control allografts showed advanced transplant arteriosclerosis, whereas tolerance-induced aortic allografts displayed reduced neointimal formation, less medial atrophy, fewer apoptotic cells, and fewer Fas- and FasL-expressing cells. Prolonged ischemic storage time did not profoundly alter the morphological changes of the allografts. Fas expression was found in T cells, macrophages, vascular smooth muscle cells, and endothelial cells, whereas FasL was expressed mainly by T cells and macrophages. FasL mRNA expression was evident throughout the entire allograft wall. In conclusion, induction of allospecific tolerance can effectively prevent transplant arteriosclerosis. Cold ischemia damage does not abrogate the beneficial effect of tolerance, but creates a separate identity of mainly endothelial lesions. Furthermore, Fas-mediated apoptosis appears to be involved in the pathological lesions seen in chronic rejection.

Differences in Lesion Severity and Cellular Composition between in vivo Assessed Upstream and Downstream Sides of Human Symptomatic Carotid Atherosclerotic Plaques

Background: The heterogeneous structure of carotid atherosclerotic plaques may be better understood if it is related to blood flow variations, influencing gene expression and cellular functions. Upstream of the maximum stenosis there is laminar blood flow and high shear stress, downstream there is turbulence and low shear stress. We studied if these variations were associated with differences in plaque morphology and composition between sites located up- and downstream of the maximum stenosis in symptomatic carotid plaques. Methods: Patients with symptomatic carotid stenosis were examined with magnetic resonance angiography to localize the maximum stenosis in-vivo, prior to endarterectomy. In 41 endarterectomized specimens, transverse tissue sections prepared up- and downstream of the maximum stenosis were compared using histopathology and immunohistochemistry. Results: The location of maximum stenosis relative the carotid bifurcation varied considerably between plaques. Compared with the downstream side, the upstream side of the stenosis had higher incidence of severe lesions with cap rupture and intraplaque hemorrhage, more macrophages, less smooth muscle cells and more collagen. Conclusions: The up- and downstream sides of symptomatic carotid plaques differed in plaque morphology and composition. This implies that the intraplaque location of sampling sites may be a confounding factor in studies of atherosclerotic plaques.

Cyclosporine Does Not Reduce Myocardial Infarct Size in a Porcine Ischemia-Reperfusion Model

Cyclosporine A (CsA) has been shown to protect against myocardial ischemia and reperfusion (I/R) injury in small animal models. The aim of the current study was to evaluate the effects of CsA on myocardial I/R injury in a porcine model. Pigs were randomized between CsA (10mg/kg; n = 12) or placebo (n = 15) and anesthetized with either isoflurane (phase I) or pentobarbital (phase II). By catheterization, the left descending coronary artery was occluded for 45 minutes, followed by reperfusion for 2 hours. Hearts were stained to quantify area at risk (AAR) and infarct size (IS). Myocardial biopsies were obtained for terminal dUTP nick end labeling and immunoblot analysis of proapoptotic proteins (apoptosis-inducing factor [AIF], BCL2/adenovirus E1B 19-kd interacting protein 3 [BNIP-3], and active caspase-3). Cyclosporine A did not reduce IS/AAR compared with placebo (49% vs 41%, respectively; P = .21). Pigs anesthetized with isoflurane had lower IS/AAR than pigs anesthetized with pentobarbital (39% vs 51%, respectively; P = .03). This reduction in IS/AAR seemed to be attenuated by CsA. Apoptosis-inducing factor protein expression was higher after CsA administration than after placebo (P = .02). Thus, CsA did not protect against I/R injury in this porcine model. The data suggest a possible deleterious interaction of CsA and isoflurane.

Smooth muscle cell migration into intima and adventitia during development of transplant vasculopathy.

Smooth muscle cell (SMC) migration from the medial layer into the intima is a characteristic feature of transplant vasculopathy and is thought to be regulated by locally produced cytokines. We studied the expression of smooth muscle alpha-actin, PDGF B-ligand and, PDGF alpha- and beta-receptors in rat aortic allografts with transplant vasculopathy using immunohistochemistry. At two weeks, an intense expression of PDGF B-ligand and, PDGF alpha- and beta-receptors was found in the neointima and adventitia. Medial SMC expression decreased with time in parallel with accumulation of smooth muscle alpha-actin in the neointima and adventitia. PDGF expression persisted in the adventitia. Prolonged ischemic storage time resulted in an increase in the number of alpha-actin-positive SMCs in the intima of syngeneic grafts. These data indicate that SMCs migrate into both the intima and adventitia. This migration may be induced, at least in part, by PDGF produced by graft invading monocyte-derived macrophages.

Endothelial cells are activated during hypoxia via endoglin/ALK-1/SMAD1/5 signaling in vivo and in vitro.

Endoglin (ENG) promotes angiogenesis by enhancing activation of TGF-beta type I receptors ALK-1 and ALK-5. ALK-1 phosphorylates transcription factors SMAD1/5, which bind to BMP-responsive elements (BRE), whereas ALK-5 phosphorylates SMAD3, which binds to CAGA elements. Expression of ENG is increased during myocardial infarction (MI). We investigated which ENG signaling pathway is activated in endothelial cells during hypoxia. Expression of ENG, ALK-1, ALK-5, and phosphorylated SMAD1/3/5 by immunostaining and immunoblotting in a mouse model of myocardial infarction (MI) and in hypoxic human aortic endothelial cells (HAECs) was evaluated. Activation of BRE and CAGA was measured by luciferase assays in cells transfected with plasmids expressing ENG or ALK-1 and the number of cells was quantified. mRNA expression of the target genes of TGF-beta signaling, ID1 and BCL-X, was quantified by real-time RT-PCR. Expression of ENG, ALK-1 and phosphorylated SMAD1/5, but not ALK-5 or phosphorylated SMAD3, was significantly increased in hypoxic endothelial cells in vivo and in vitro. Overexpression of both ENG and ALK-1 significantly increased BRE but not CAGA activity, expression of ID1 and BCL-X and the number of HAECs at hypoxia. ENG/ALK-1 signaling is one of the factors that regulate endothelial cell activity during adaptive cardiac angiogenesis.

Gene Transfer Strategies to Inhibit Neointima Formation

Vascular smooth muscle cell (VSMC) proliferation after arterial injury results in neointima formation and plays an important role in the pathogenesis of restenosis after angioplasty, in-stent restenosis, vascular bypass graft occlusion, and allograft vasculopathy. Major progress has been made recently in elucidating the cellular and molecular mechanisms underlying neointima formation. However, no known curative treatment currently exists. In cases in which pharmacologic and surgical interventions have had limited success, gene therapy remains a potential strategy for the treatment of such vascular proliferative diseases. To date, recombinant adenoviral vectors continue to be the most efficient methods of gene transfer into the arterial wall. However, concerns over the safety of using viral vectors in a clinical situation have inspired the considerable progress that has been made in improving both viral and nonviral modes of gene transfer. This review discusses some of the recent insights and outstanding progress in vascular gene therapeutic approaches to inhibit neointima both from a biologic and therapeutic perspective.