Growth factor-induced morphological, physiological and molecular characteristics in cerebral endothelial cells

Tissue Augmentation in Wound Healing: the Role of Endothelial and Epithelial Cells

Introduction

Wounds and their complications present a frequent cause of morbidity and mortality in everyday clinical practice. In order to reduce the wound burden, much effort has been directed into the physiology of healing and new therapeutic approaches.

Aim

This paper provides an overview from the literature about the role of endothelial and epithelial cells in tissue filler employment for wound healing.

Material and Methods

The scientific literature was reviewed through PubMed, Medline and Science Direct. The articles were chosen in correlation with the study objective and their scientific relevance.

Results

Successful wound healing depends on many diverse processes, cell types and molecular mediators. The definitive aim of wound healing is a properly healed wound. Tissue fillers are becoming an important alternative in wound management, although augmentation of soft tissue can present a demanding problem due to the difficulties in tissue survival. In order to prevent its failure, an optimal vascular network needs to form from wound edges into the filler.

Conclusions

Because of the importance of chemotaxis and angiogenesis in various physiological and pathological processes, both events present an extensive area of intense research. Additionally, epithelial cells are needed to cover the wound defect and sealing the wound environment from outer world.

Pericytes in Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune inflammatory demyelinating disease that affects the central nervous system (CNS), particularly, in young adults. Current MS treatments aim to reduce demyelination; however, these have limited efficacy, display side effects and lack of regenerative activities. Oligodendrocyte progenitor cells (OPCs) represents the major source for new myelin. Upon demyelination, OPCs get activated, proliferate, migrate towards the lesion, and differentiate into remyelinating oligodendrocytes. Although myelin repair (remyelination) represents a robust response to myelin damage, during MS, this regenerative phenomenon decays in efficiency or even fails. CNS-resident pericytes (CNS-PCs) are essential for vascular homeostasis regulating blood-brain barrier (BBB) permeability and stability as well as endothelial cells (ECs) function during angiogenesis and neovascularization. Recent studies indicate that CNS-PCs also play a crucial role regulating OPC function during remyelination, and very importantly, these cells are substantially affected in MS. This chapter summarizes important aspects of MS and CNS remyelination as well as it provides new insights supporting the contribution of CNS-PCs to myelin regeneration and to MS pathology. Currently, there is evidence arguing in favor of CNS-PCs as novel therapeutic targets for the development of future treatments for MS.

Differences in the molecular structure of the blood-brain barrier in the cerebral cortex and white matter: an in silico, in vitro, and ex vivo study

The blood-brain barrier (BBB) is the main interface controlling molecular and cellular traffic between the central nervous system (CNS) and the periphery. It consists of cerebral endothelial cells (CECs) interconnected by continuous tight junctions, and closely associated pericytes and astrocytes. Different parts of the CNS have diverse functions and structures and may be subject of different pathologies, in which the BBB is actively involved. It is largely unknown, however, what are the cellular and molecular differences of the BBB in different regions of the brain. Using in silico, in vitro, and ex vivo techniques we compared the expression of BBB-associated genes and proteins (i.e., markers of CECs, brain pericytes, and astrocytes) in the cortical grey matter and white matter. In silico human database analysis (obtained from recalculated data of the Allen Brain Atlas), qPCR, Western blot, and immunofluorescence studies on porcine and mouse brain tissue indicated an increased expression of glial fibrillary acidic protein in astrocytes in the white matter compared with the grey matter. We have also found increased expression of genes of the junctional complex of CECs (occludin, claudin-5, and α-catenin) in the white matter compared with the cerebral cortex. Accordingly, occludin, claudin-5, and α-catenin proteins showed increased expression in CECs of the white matter compared with endothelial cells of the cortical grey matter. In parallel, barrier properties of white matter CECs were superior as well. These differences might be important in the pathogenesis of diseases differently affecting distinct regions of the brain.

Role of the blood-brain barrier in the formation of brain metastases

The majority of brain metastases originate from lung cancer, breast cancer and malignant melanoma. In order to reach the brain, parenchyma metastatic cells have to transmigrate through the endothelial cell layer of brain capillaries, which forms the morphological basis of the blood-brain barrier (BBB). The BBB has a dual role in brain metastasis formation: it forms a tight barrier protecting the central nervous system from entering cancer cells, but it is also actively involved in protecting metastatic cells during extravasation and proliferation in the brain. The mechanisms of interaction of cancer cells and cerebral endothelial cells are largely uncharacterized. Here, we provide a comprehensive review on our current knowledge about the role of junctional and adhesion molecules, soluble factors, proteolytic enzymes and signaling pathways mediating the attachment of tumor cells to brain endothelial cells and the transendothelial migration of metastatic cells. Since brain metastases represent a great therapeutic challenge, it is indispensable to understand the mechanisms of the interaction of tumor cells with the BBB in order to find targets of prevention of brain metastasis formation.

Brain pericyte plasticity as a potential drug target in CNS repair

Brain pericytes (BrPCs) are essential cellular components of the central nervous system neurovascular unit involved in the regulation of blood flow, blood-brain barrier function, as well as in the stabilization of the vessel architecture. More recently, it became evident that BrPCs, besides their regulatory activities in brain vessel function and homeostasis, have pleiotropic functions in the adult CNS ranging from stromal and regeneration promoting activities to stem cell properties. This special characteristic confers BrPC cell plasticity, being able to display features of other cells within the organism. BrPCs might also be causally involved in certain brain diseases. Due to these properties BrPCs might be potential drug targets for future therapies of neurological disorders. This review summarizes BrPC properties, disorders in which this cell type might be involved, and provides suggestions for future therapeutic developments targeting BrPCs.

Salvianolic acid B prevents epithelial-to-mesenchymal transition through the TGF-beta1 signal transduction pathway in vivo and in vitro

BACKGROUND

Salvianolic Acid B (Sal B) is a water-soluble component from Danshen (a traditional Chinese herb widely used for chronic renal diseases) with anti-oxidative and cell protective properties. Sal B also has potential protective effects on renal diseases. Tubular epithelial cells can undergo epithelial-to-mesenchymal transition (EMT), which plays an important role in the pathogenesis of renal interstitial fibrosis (RIF) and is mainly regulated by TGF-beta1/Smads pathway. The aims of the study are to investigate the effect of Sal B on tubular EMT in vivo and in vitro, and to elucidate its underlying mechanism against EMT related to TGF-beta1/Smads pathway.

RESULTS

For in vivo experiments, RIF was induced in rats by oral administration of HgCl2 and prophylaxised with Sal B and vitamin E. The protein expression of E-cadherin was down-regulated, while the expression of alpha-SMA, TGF-beta1, TbetaR-I, p-Smad2/3 and the activity of matrix metalloproteinase-2 (MMP-2) were up-regulated in kidneys of model rats when compared with those of normal rats. In contrast, Sal B and vitamin E significantly attenuated the expression of alpha-SMA, TGF-beta1, TbetaR-I, p-Smad2/3, and MMP-2 activity, but increased E-cadherin expression. For in vitro experiments, HK-2 cells were incubated with TGF-beta1 to induce EMT, and the cells were co-cultured with 1 and 10 microM Sal B or SB-431542 (a specific inhibitor of TbetaR-I kinase). TGF-beta1 induced a typical EMT in HK-2 cells, while it was blocked by Sal B and SB-431542, as evidenced by blocking morphologic transformation, restoring E-cadherin and CK-18 expression, inhibiting alpha-SMA expression and F-actin reorganization, and down-regulating MMP-2/9 activities in TGF-beta1 mediated HK-2 cells. Furthermore, Sal B and SB-431542 profoundly down-regulated the expressions of TbetaR-I and p-Smad2/3 but prevented the decreased expression of Smad7 in TGF-beta1 stimulated HK-2 cells.

CONCLUSIONS

Sal B can prevent tubular EMT in the fibrotic kidney induced by HgCl2 as well as HK-2 cells triggered by TGF-beta1, the mechanism of Sal B is closely related to the regulation of TGF-beta1/Smads pathway, manifested as the inhibition of TGF-beta1 expression, suppression of TbetaR-I expression and function, down-regulation of Smad2/3 phosphorylation, and restoration of the down-regulation of Smad7, as well as inhibition of MMP-2 activity.

The wound healing process: an overview of the cellular and molecular mechanisms

Wound healing remains a challenging clinical problem and correct, efficient wound management is essential. Much effort has been focused on wound care with an emphasis on new therapeutic approaches and the development of technologies for acute and chronic wound management. Wound healing involves multiple cell populations, the extracellular matrix and the action of soluble mediators such as growth factors and cytokines. Although the process of healing is continuous, it may be arbitrarily divided into four phases: (i) coagulation and haemostasis; (ii) inflammation; (iii) proliferation; and (iv) wound remodelling with scar tissue formation. The correct approach to wound management may effectively influence the clinical outcome. This review discusses wound classification, the physiology of the wound healing process and the methods used in wound management.

Effects of crystalline glucocorticoid triamcinolone acetonide on cultered human supraspinatus tendon cells

BACKGROUND

Rotator cuff tears are a common cause of shoulder pain and impairment. Subacromial glucocorticoid injections are widely used for treatment of epiphenomenons of chronic impingement syndrome with the possible side effects of tendon rupture and impaired tendon healing.

METHODS

Using qRT-PCR, western blot, immunoflourescence, and measurement of 3H-thymidine uptake we investigated the effects of the crystalline glucocorticoid triamcinolone acetonide (TAA) when added to the culture medium of isolated human rotator cuff tendon cells.

RESULTS

After 2 weeks of incubation, the cells had lost their fibroblastic appearance and parallel orientation, which is characteristic of cellular degeneration in vivo. Moreover, expression and secretion of collagen I was strongly reduced, and there was a decrease in proliferation rate. Cell migration was blocked and the rate of expression of the matrix metalloproteinases MMP2, MMP8, MMP9, and MMP13 was reduced, but expression of TIMP1 (a tissue inhibitor of MMPs) was upregulated, indicating a reduction in the cellular capacity for tendon repair. In addition, changes in cellular differentiation were observed: the number of adipocytes increased and levels of the protein Sox9-a marker of differentiating and mature chondrocytes-were elevated in triamcinolone acetonide treated cells.

INTERPRETATION

These results may indicate that the use of TAA is one reason for weaker mechanical tendon properties and for the high rate of re-rupture after supraspinatus tendon repair.

Sustained contraction and loss of NO production in TGFbeta1-treated endothelial cells

BACKGROUND AND PURPOSE

Transforming growth factor beta1 (TGFbeta1) is generated in atherosclerotic and injured vessel walls. We examined whether the endothelial-to-mesenchymal transdifferentiation induced by TGFbeta1 affects endothelial functions.

EXPERIMENTAL APPROACH

Bovine aortic endothelial cells (BAECs) were treated with 3 ng ml(-1) TGFbeta1 for 7 days. Contraction of TGFbeta1-treated BAECs was assessed by collagen gel contraction assay. Protein expression and phosphorylation were assessed by Western blotting. Intracellular Ca2+ concentration and NO production were measured using fura2 and DAF-2, respectively.

KEY RESULTS

TGFbeta1-treated BAECs showed dense actin fibers and expressed smooth muscle marker proteins; they also changed into smooth muscle-like, spindle-shaped cells in collagen gel cultures. ATP (10 microM) induced a gradual contraction of collagen gels containing TGFbeta1-treated BAECs but not of gels containing control BAECs. ATP-induced contraction of TGFbeta1-treated BAECs was not reversed by the removal of ATP but was partially suppressed by a high concentration of sodium nitroprusside (1 microM). TGFbeta1-treated BAECs showed sustained phosphorylation of myosin light chain in response to ATP and low levels of basal MYPT1 expression. ATP-induced Ca2+ transients as well as eNOS protein expression were not affected by TGFbeta1 in BAECs. However, ATP-induced NO production was significantly reduced in TGFbeta1-treated BAECs. Anti-TGFbeta1 antibody abolished all of these TGFbeta1-induced changes in BAECs.

CONCLUSIONS AND IMPLICATIONS

Mesenchymal transdifferentiation induced by TGFbeta1 leads to sustained contraction and reduced NO production in endothelial cells. Such effects, therefore, would not be beneficial for vascular integrity.

Effect of estrogen on the expression of occludin in ovariectomized mouse brain

The blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCSFB), formed by interactions of tight junctions (TJs) in the endothelia or the choroids plexus, respectively, are important diffusion barriers between systemic circulation and neural tissue of the central nervous system (CNS). Epidemiological incidence of degenerative changes in the CNS is significantly higher in postmenopausal women than in men, suggesting an important role of ovarian steroids for CNS integrity in women. To elucidate the role estrogen in the maintenance of paracellular diffusion barriers in the CNS, changes in the expression of occludin, a TJ protein, following ovariectomy (OVX), as well as the effect of estrogen on the expression of occludin in OVX female brain, were examined in mice. Immunoreactivity of occludin was found in brain endothelial capillaries, choroids plexus, ependyma, and aqueduct. In OVX brain, expression of occludin mRNA and protein was decreased a little but significantly relative to a sham control brain at the estrous stage. Estrogen (17beta estradiol) significantly up-regulated occludin mRNA levels in OVX mice. Together, these results suggest that occludin is an important structural element in both the BBB and BCSFB, and that expression of occludin in female brain tissue is sensitive to estrogen levels.

Functional adaptation: the key to plasticity of cardiovascular "stem" cells?

There is increasing evidence that cells of disparate phenotypes displaying various degrees of proliferative capacity engraft and function heterotopically in adult organisms. Efforts were made to reconcile these findings with the embryologic notions of pluripotent stem or progenitor cell, although the nature of the 'stemness' remained elusive. This topic is particularly important for the cardiovascular system, in which cytotrophoblasts, certain tumor cells, monocytes/macrophages, peritoneal mesothelial cells, and others acquire endothelial properties and/or perform endothelial functions. Here we suggest that this pluripotency reflects a fundamental characteristic of cellular diversity, which is manifested as the adaptive response to a functional pressure exerted by the cell's biochemical and biophysical microenvironments that would drive their differentiation. In this model, differentiation is a dynamic, reversible, and open-ended process where the cells would maintain the flexibility to respond to changing environmental clues with a fine tuning of their structure, a property that was previously called cellular plasticity. Pluripotent adult stem cells that display this property in culture, and, perhaps upon in vivo administration, were described. Therefore, we also suggest that differentiation of stem cells is a form of cellular plasticity within the larger context of functional adaptation, whereas their stemness remains associated with self-renewal.

Induction of aquaporin 1 but not aquaporin 4 messenger RNA in rat primary brain microvessel endothelial cells in culture

Aquaporins (AQPs) are a family of proteins that mediate water transport across cells, but the extent to which they are involved in water transport across endothelial cells of the blood-brain barrier is not clear. Expression of AQP1 and AQP4 in rat brain microvessel endothelial cells was investigated in order to determine whether these isoforms were present and, in particular, to examine the hypothesis that brain endothelial expression of AQPs is dynamic and regulated by astrocytic influences. Reverse-transcriptase-polymerase chain reaction (RT-PCR) and immunocytochemistry showed that AQP1 mRNA and protein are present at very low levels in primary rat brain microvessel endothelial cells, and are up-regulated in passaged cells. Upon passage, endothelial cell expression of mdr1a mRNA is decreased, indicating loss of blood-brain barrier phenotype. In passage 4 endothelial cells, AQP1 mRNA levels are reduced by coculture above rat astrocytes, demonstrating that astrocytic influences are important in maintaining the low levels of AQP1 characteristic of the blood-brain barrier endothelium. Reverse-transcriptase-PCR revealed very low levels of AQP1 mRNA present in the RBE4 rat brain microvessel endothelial cell line, with no expression detected in primary cultures of rat astrocytes or in the C6 rat glioma cell line. In contrast, AQP4 mRNA is strongly expressed in astrocytes, but no expression is found in primary or passaged brain microvessel endothelial cells, or in RBE4 or C6 cells. Our results support the concept that expression of AQP1, which is seen in many non-brain endothelia, is suppressed in the specialized endothelium of the blood-brain barrier.

Effects of hypoxia on endothelial/pericytic co-culture model of the blood-brain barrier

The blood-brain barrier (BBB) is composed of endothelial cells, pericytes and astrocytic foot processes. Most research for the in vitro BBB is performed endothelial cells with or without astrocytes. Hypoxia damage to the BBB induces vasogenic brain edema. We have generated a new model of the BBB with brain endothelial cells and pericytes and have examined the effects of hypoxia using this model. Brain microvascular endothelial cells and pericytes were isolated from three-week-old male Wister rats using enzyme and mechanical homogenization. Three models (A: only endothelial monolayer, B: endothelial monolayer with pericytes non-contact condition, and C: contact condition) were made by culturing these cells using Transwell co-culture system and were exposed to hypoxic condition. We evaluated barrier function with transendothelial electrical resistance (TEER) and permeability of Evans blue-albumin and sodium fluorescein. The tightest barrier was observed in the endothelial/pericytic contact model. Despite hypoxia-induced disruption of the barrier in endothelial monolayer and non-contact co-culture models, a minimum of dysfunction was seen in the contact co-culture model. Therefore, it is considered that pericytes effect on the endothelia by secreting factors or through a gap junction. In short, pericytes induce endothelial maturation and a tighter barrier function, which supports the function against the hypoxic injury. Intercellular communication might be important to keep the BBB functional and stabilize in hypoxia.

Changes in the expression of claudins and transepithelial electrical resistance of mouse Sertoli cells by Leydig cell coculture

In the testis, tight junctions (TJs) between adjacent Sertoli cells are important for the formation of blood-testis barrier (BTB). To verify the role of paracrine interactions between the Sertoli and Leydig cells in the structure and function of BTB in testis, the expression of claudin-1 and -11, and transepithelial electrical resistance (TER) of the mouse Sertoli cells were examined under the Leydig cell coculture. TER of Sertoli cell monolayer was significantly larger under the Leydig cell coculture in comparison with the control culture. Meanwhile, the expression of claudin-1 slightly decreased and claudin-11 significantly increased in the Sertoli cells in the Leydig cell coculture compared with control. Testosterone significantly increased claudin-11 expression in cultured Sertoli cells. Taken together, it suggested that Leydig cell coculture changed the structure and functions of inter-Sertoli TJs in vitro. Interactions between Leydig and Sertoli cells might be involved in the development of functional blood testis barrier in mouse testis.

A simple method for isolation and characterization of mouse brain microvascular endothelial cells

Brain endothelial cells, a site of the blood-brain barrier in vivo, regulate a number of physiological and pathophysiological processes in the brain including transport of nutrients, export of critical toxins, transmigration of circulating leukocytes and formation of new blood vessels. In this report, we describe a simple and reproducible method to isolate pure (>99%), functionally active endothelial cells from small quantities of adult mouse brain tissue. In vitro, these cells express typical phenotypic markers of differentiated brain endothelium such as von Willebrand factor, multiple drug resistant protein and glucose transporter-1, demonstrate uptake of acetylated low-density lipoprotein, and possess morphological and ultrastructural characteristics of microvascular endothelium. They form tight junctions and capillary-like tubes when stimulated by growth factors in an in vitro angiogenesis assay. In response to tumor necrosis factor-alpha, isolated mouse brain endothelial cells (MBEC) express vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1). The protocol described here provides an effective and reliable method to isolate pure cerebral endothelium from adult mouse brain that should offer a useful tool for studying the role of altered vascular biology in mice with genetically manipulated brain disorders.

Activation of ERK and Akt signaling in focal cerebral ischemia: modulation by TGF-alpha and involvement of NMDA receptor

Cerebral ischemia activates ERK and Akt pathways. We studied whether these activations were affected by treatment with the protective growth factor transforming growth factor-alpha (TGF-alpha), and whether they were mediated through N-methyl D-aspartate (NMDA) receptors. The middle cerebral artery was occluded in rats and signaling was studied 1 h later. Noncompetitive NMDA receptor antagonist MK-801 was injected i.p. before the occlusion, whereas in other rats TGF-alpha was given intraventricularly before and after occlusion. Ischemia caused ERK phosphorylation in the nucleus, localized in the endothelium and neurons. Phosphorylation of ERK was prevented by TGF-alpha, but it was enhanced in the nucleus and cytoplasm by MK-801. Also, MK-801 but not TGF-alpha increased p-Akt. Results suggest that preventing ERK activation is related to the protective effect of TGF-alpha, whereas the protective effect of MK-801 is associated with activation of pro-survival Akt. While results support that NMDA receptor signaling precludes Akt activation, we did not find evidence to support that it underlies ischemia-induced ERK phosphorylation. This study illustrates that neuroprotection results from a fine balance between death and survival signaling pathways.

Blockage of tubular epithelial to myofibroblast transition by hepatocyte growth factor prevents renal interstitial fibrosis

Activation of alpha-smooth muscle actin-positive myofibroblast cells is a key event in the progression of chronic renal diseases that leads to end-stage renal failure. Although the origin of these myofibroblasts in the kidney remains uncertain, emerging evidence suggests that renal myofibroblasts may derive from tubular epithelial cells by a process of epithelial to mesenchymal transition. It was demonstrated that hepatocyte growth factor (HGF) exhibited a remarkable ability to block this phenotypic transition both in vitro and in vivo. HGF abrogated the alpha-smooth muscle actin expression and E-cadherin depression triggered by transforming growth factor-beta1 in tubular epithelial cells in a dose-dependent manner. HGF also blocked morphologic transformation of tubular epithelial cells and inhibited the expression and extracellular deposition of fibronectin. In a mouse model of renal fibrosis disease induced by unilateral ureteral obstruction, transforming growth factor-beta type I receptor expression was specifically increased in renal tubules, and myofibroblastically phenotypic transition of the tubules was evident in vivo. Remarkably, injections of exogenous HGF blocked myofibroblast activation and drastically prevented renal interstitial fibrosis in the obstructed kidneys. These results suggest that tubular epithelial to myofibroblast conversion may play an important role in the pathogenesis of renal fibrosis and that blocking this phenotypic transition could provide a novel therapeutic strategy for the treatment of fibrotic diseases.

Dissection of key events in tubular epithelial to myofibroblast transition and its implications in renal interstitial fibrosis

Myofibroblast activation is a key event playing a critical role in the progression of chronic renal disease. Emerging evidence suggests that myofibroblasts can derive from tubular epithelial cells by an epithelial to mesenchymal transition (EMT); however, the details regarding the conversion between these two cell types are poorly understood. Here we dissect the key events during the process of EMT induced by transforming growth factor-beta1. Incubation of human tubular epithelial cells with transforming growth factor-beta1 induced de novo expression of alpha-smooth muscle actin, loss of epithelial marker E-cadherin, transformation of myofibroblastic morphology, and production of interstitial matrix. Time-course studies revealed that loss of E-cadherin was an early event that preceded other alterations during EMT. The transformed cells secreted a large amount of matrix metalloproteinase-2 that specifically degraded tubular basement membrane. They also exhibited an enhanced motility and invasive capacity. These alterations in epithelial phenotypes in vitro were essentially recapitulated in a mouse model of renal fibrosis induced by unilateral ureteral obstruction. Hence, these results indicate that tubular epithelial to myofibroblast transition is an orchestrated, highly regulated process involving four key steps including: 1) loss of epithelial cell adhesion, 2) de novo alpha-smooth muscle actin expression and actin reorganization, 3) disruption of tubular basement membrane, and 4) enhanced cell migration and invasion.