Changes in hyaluronan production and metabolism following ischaemic stroke in man

Hyaluronan benzyl ester as a scaffold for tissue engineering

Tissue engineering is a multidisciplinary field focused on in vitro reconstruction of mammalian tissues. In order to allow a similar three-dimensional organization of in vitro cultured cells, biocompatible scaffolds are needed. This need has provided immense momentum for research on “smart scaffolds” for use in cell culture. One of the most promising materials for tissue engineering and regenerative medicine is a hyaluronan derivative: a benzyl ester of hyaluronan (HYAFF^®). HYAFF^® can be processed to obtain several types of devices such as tubes, membranes, non-woven fabrics, gauzes, and sponges. All these scaffolds are highly biocompatible. In the human body they do not elicit any adverse reactions and are resorbed by the host tissues. Human hepatocytes, dermal fibroblasts and keratinocytes, chondrocytes, Schwann cells, bone marrow derived mesenchymal stem cells and adipose tissue derived mesenchymal stem cells have been successfully cultured in these meshes. The same scaffolds, in tube meshes, has been applied for vascular tissue engineering that has emerged as a promising technology for the design of an ideal, responsive, living conduit with properties similar to that of native tissue.

Stress-dependent Daxx-CHIP interaction suppresses the p53 apoptotic program

Our previous studies have implicated CHIP (carboxyl terminus of Hsp70-interacting protein) as a co-chaperone/ubiquitin ligase whose activities yield protection against stress-induced apoptotic events. In this report, we demonstrate a stress-dependent interaction between CHIP and Daxx (death domain-associated protein). This interaction interferes with the stress-dependent association of HIPK2 with Daxx, blocking phosphorylation of serine 46 in p53 and inhibiting the p53-dependent apoptotic program. Microarray analysis confirmed suppression of the p53-dependent transcriptional portrait in CHIP(+/+) but not in CHIP(-/-) heat shocked mouse embryonic fibroblasts. The interaction between CHIP and Daxx results in ubiquitination of Daxx, which is then partitioned to an insoluble compartment of the cell. In vitro ubiquitination of Daxx by CHIP revealed that ubiquitin chain formation utilizes non-canonical lysine linkages associated with resistance to proteasomal degradation. The ubiquitination of Daxx by CHIP utilizes lysines 630 and 631 and competes with the sumoylation machinery of the cell at these residues. These studies implicate CHIP as a stress-dependent regulator of Daxx that counters the pro-apoptotic influence of Daxx in the cell. By abrogating p53-dependent apoptotic pathways and by ubiquitination competitive with Daxx sumoylation, CHIP integrates the proteotoxic stress response of the cell with cell cycle pathways that influence cell survival.

Airway smooth muscle cells synthesize hyaluronan cable structures independent of inter-alpha-inhibitor heavy chain attachment

The covalent association of inter-alpha-inhibitor-derived heavy chains (HCs) with hyaluronan was first described in synovial fluid from arthritic patients and later described as a structural and functional component of hyaluronan "cable" structures produced by many different cells and stimuli. HC transfer has been shown to be mediated by the protein product of TSG-6 (tumor necrosis factor-stimulated gene 6). Considering the accumulation of hyaluronan in airways following asthmatic attacks and the subsequent infiltration of leukocytes, we sought to characterize HC substitution of hyaluronan "cables" in primary mouse airway smooth muscle cells (MASM) and primary human airway smooth muscle cells (HASM). We found that cells derived from mice lacking TSG-6 had no defect in hyaluronan production or hyaluronan-mediated leukocyte adhesion when treated with the viral mimic poly(I,C). Functional hyaluronan cables were induced by cycloheximide in the confirmed absence of protein synthesis, with or without simultaneous treatment with poly(I,C). We characterized the species specificity of the antibody other investigators used to describe the HC-hyaluronan complex of hyaluronan cables and found minimal affinity to bovine-derived HCs in contrast to HCs from mouse and human sera. Thus, we cultured MASM and HASM cells in serum from these three sources and analyzed hyaluronan extracts for HCs and other hyaluronan-binding proteins, using parallel cumulus cell-oocyte complex (COC) extracts as positive controls. We conclude that, if hyaluronan cables derived from MASM and HASM cells are substituted with HCs, the amount of substitution is significantly below the limit of detection when compared with COC extracts of similar hyaluronan mass.

High levels of hyaluronan in idiopathic pulmonary arterial hypertension

Hyaluronan (HA), a large glycosaminoglycan found in the ECM, has major roles in lung and vascular biology and disease. However, its role in idiopathic pulmonary arterial hypertension (IPAH) is unknown. We hypothesized that HA metabolism is abnormal in IPAH. We measured the plasma levels of HA in IPAH and healthy individuals. We also evaluated HA synthesis and the expression of HA synthases and hyaluronidases in pulmonary artery smooth muscle cells (PASMCs) from explanted lungs. Plasma HA levels were markedly elevated in IPAH compared with controls [HA (ng/ml, mean +/- SD): IPAH 325 +/- 80, control 28 +/- 9; P = 0.02]. In vitro, unstimulated IPAH PASMCs produced high levels of HA compared with control cells [HA in supernatant (microg/ml, mean +/- SD): IPAH 12 +/- 2, controls 6 +/- 0.9; P = 0.04]. HA levels were also higher in IPAH PASMC lysates. The increased HA was biologically relevant as shown by tissue staining and increased HA-specific binding of mononuclear cells to IPAH compared with control PASMCs [number of bound cells x 10(4) (mean +/- SD): IPAH 9.5 +/- 3, control 3.0 +/- 1; P = 0.01]. This binding was abrogated by the addition of hyaluronidase. HA synthase-2 and hyaluronidase-2 were predominant in control and IPAH PASMCs. Interestingly, the expressions of HA synthase-2 and hyaluronidase-2 were approximately 2-fold lower in IPAH compared with controls [HA synthase-2 (relative expression mean +/- SE): IPAH 4.3 +/- 0.02, control 7.8 +/- 0.1; P = 0.0004; hyaluronidase-2 (relative expression mean +/- SE): IPAH 4.2 +/- 0.06, control 7.6 +/- 0.07; P = 0.008]. Thus patients with IPAH have higher circulating levels of HA, and PASMCs derived from IPAH lungs produce more HA compared with controls. This is associated with increased tissue levels and increased binding of inflammatory cells suggesting a role for HA in remodeling and inflammation in IPAH.

Brain extracellular matrix in neurodegeneration

The role of extracellular matrix (ECM) in neurological development, function and degeneration has evolved from a simplistic physical adhesion to a system of intricate cellular signaling. While most cells require ECM adhesion to survive, it is now clear that differentiated function is intimately dependent upon cellular interaction with the ECM. Therefore, it is not surprising that the ECM is increasingly found to be involved in the enigmatic process of neurodegeneration. Descriptive studies of human neurodegenerative disorders and experimental studies of animal models of neurodegeneration have begun to define potential mechanisms of ECM disruption that can lead to synaptic and neuronal loss.

Toll-like receptor-4 mediates neuronal apoptosis induced by amyloid beta-peptide and the membrane lipid peroxidation product 4-hydroxynonenal

The innate immune system senses the invasion of pathogenic microorganisms and tissue injury through Toll-like receptors (TLR), a mechanism thought to be limited to immune cells. We recently found that neurons express several TLRs, and that the levels of TLR2 and TLR4 are increased in neurons in response to energy deprivation. Here we report that TLR4 expression increases in neurons when exposed to amyloid beta-peptide (Abeta1-42) or the lipid peroxidation product 4-hydroxynonenal (HNE). Neuronal apoptosis triggered by Abeta and HNE was mediated by jun N-terminal kinase (JNK); neurons from TLR4 mutant mice exhibited reduced JNK and caspase-3 activation and were protected against apoptosis induced by Abeta and HNE. Levels of TLR4 were decreased in inferior parietal cortex tissue specimens from end-stage AD patients compared to aged-matched control subjects, possibly as the result of loss of neurons expressing TLR4. Our findings suggest that TLR4 signaling increases the vulnerability of neurons to Abeta and oxidative stress in AD, and identify TLR4 as a potential therapeutic target for AD.

Hyaluronan in tissue injury and repair

A hallmark of tissue injury and repair is the turnover of extracellular matrix components. This review focuses on the role of the glycosaminoglycan hyaluronan in tissue injury and repair. Both the synthesis and degradation of extracellular matrix are critical contributors to tissue repair and remodeling. Fragmented hyaluronan accumulates during tissue injury and functions in ways distinct from the native polymer. There is accumulating evidence that hyaluronan degradation products can stimulate the expression of inflammatory genes by a variety of immune cells at the injury site. CD44 is the major cell-surface hyaluronan receptor and is required to clear hyaluronan degradation products produced during lung injury; impaired clearance of hyaluronan results in persistent inflammation. However, hyaluronan fragment stimulation of inflammatory gene expression is not dependent on CD44 in inflammatory macrophages. Instead, hyaluronan fragments utilize both Toll-like receptor (TLR) 4 and TLR2 to stimulate inflammatory genes in macrophages. Hyaluronan also is present on the cell surface of lung alveolar epithelial cells and provides protection against tissue damage by interacting with TLR2 and TLR4 on these parenchymal cells. The simple repeating structure of hyaluronan appears to be involved in a number of important aspects of noninfectious tissue injury and repair that are dependent on the size and location of the polymer as well as the interacting cells. Thus, the interactions between the endogenous matrix component hyaluronan and its signaling receptors initiate inflammatory responses, maintain structural cell integrity, and promote recovery from tissue injury.

The effect of vestibular nerve section on the expression of the hyaluronan in the frog, Rana esculenta

Following postganglionic lesion of the eighth cranial nerve, the changes in the expression of hyaluronan (HA), one of the extracellular matrix macromolecules, were examined in the medial (MVN) and lateral (LVN) vestibular nuclei and in the entry or transitional zone (TZ) of the nerve in the frog. HA was detected in different survival times by using a specific biotinylated hyaluronan-binding probe. HA expression was defined by the area-integrated optical density (AIOD), calculated from pixel intensities of digitally captured images. During the first postoperative days the perineuronal net (PN), a HA-rich area around the neurons, was not distinguishable from the surrounding neuropil in the MVN and LVN, characterized by a bilateral drop of AIOD specifically on the operated side. From postoperative day 14 onwards AIOD increased whilst the PN reorganized. In contrast, the AIOD wobbled up and down bilaterally without any trend in the TZ. Statistical analysis indicated that AIOD changes in the structures studied ran parallel bilaterally presumably because of the operation. Our results demonstrated for the first time that (1) the lesion of the eighth cranial nerve is accompanied by the modification of AIOD reflected HA expression in the MVN, LVN and TZ, (2) different tendencies exist in the time course of AIOD in the structures studied and (3) these tendencies are similar on the intact and operated sides. Our findings may suggest an area dependent molecular mechanism of HA in the restoration of vestibular function.

Pivotal role for neuronal Toll-like receptors in ischemic brain injury and functional deficits

The innate immune system senses the invasion of pathogenic microorganisms and tissue injury through Toll-like receptors (TLR), a mechanism thought to be limited to immune cells. We now report that neurons express several TLRs, and that the levels of TLR2 and -4 are increased in neurons in response to IFN-gamma stimulation and energy deprivation. Neurons from both TLR2 knockout and -4 mutant mice were protected against energy deprivation-induced cell death, which was associated with decreased activation of a proapoptotic signaling cascade involving jun N-terminal kinase and the transcription factor AP-1. TLR2 and -4 expression was increased in cerebral cortical neurons in response to ischemia/reperfusion injury, and the amount of brain damage and neurological deficits caused by a stroke were significantly less in mice deficient in TLR2 or -4 compared with WT control mice. Our findings establish a proapoptotic signaling pathway for TLR2 and -4 in neurons that may render them vulnerable to ischemic death.

The molecular basis of inter-α-inhibitor heavy chain transfer on to hyaluronan

The inflammation-associated protein TSG-6 (the product of tumour necrosis factor-stimulated gene-6) can form covalent complexes with the heavy chains (HC1 and HC2) of IαI (inter-α-inhibitor); namely, TSG-6·HC1 and TSG-6·HC2, which act as intermediates in the covalent transfer of HCs on to the GAG (glycosaminoglycan) HA (hyaluronan). HC·HA, which is formed for example in the synovial fluids of arthritis patients, is more aggregated than unmodified HA and has altered mechanical and cell-binding properties. The expansion of the HA-rich cumulus ECM (extracellular matrix) during ovulation is critically dependent on the catalysis of HC·HA generation by TSG-6, with TSG-6−/− mice being female infertile because of failure of HA cross-linking. It has been shown recently that TSG-6-mediated HC·HA formation is essential for the formation of HA-rich pericellular matrix and for cell migration in a model of wound healing. In contrast, in this model, the formation of cell-associated HA cable-like structures, although requiring the transfer of HCs on to HA, might not involve TSG-6. TSG-6-mediated HC transfer involves two sequential transesterification processes, where HCs are transferred from the CS (chondroitin sulfate) of IαI first on to TSG-6 and then on to HA. TSG-6 is an essential co-factor and catalyst in this chain of events, with both TSG-6·HC formation and HC transfer being dependent on the presence of Mg2+ or Mn2+ ions.

Hyaluronan export by the ABC transporter MRP5 and its modulation by intracellular cGMP

Hyaluronan must be exported from its site of synthesis, the inner side of plasma membrane, to the extracellular matrix. Here, we identified the multidrug-associated protein MRP5 as the principle hyaluronan exporter from fibroblasts. The expression of the MRP5 (ABC-C5) transporter was silenced in fibroblasts using RNA interference, and a dose-dependent inhibition of hyaluronan export was observed. Hyaluronan oligosaccharides introduced into the cytosol competed with the export of endogenously labeled hyaluronan and the MRP5 substrate fluorescein. Because cGMP is a physiological substrate of MRP5, the intracellular concentrations of cGMP were modulated by the drugs 3-isobutyl-1-methylxanthin, propentofyllin, L-NAME, zaprinast, and bromo-cGMP, and the effects on hyaluronan export were analyzed. Increasing the cGMP levels inhibited hyaluronan export and decreasing it afforded higher concentrations of zaprinast to inhibit the export. Thus, cGMP may be a physiological regulator of hyaluronan export at the level of the export MRP5.

Cellular prion protein is increased in the plasma and peri-infarcted brain tissue after acute stroke

The physiologic properties of the normal cellular prion protein (PrP(C)) have not been established fully, although recent evidence showed its upregulation in cerebral ischaemia. Using patients, animal models, and in vitro studies we aimed to identify in detail the expression and localization of PrP(C) in ischemic stroke. Patients in acute phase of ischaemic stroke had increased plasma levels of circulating PrP(C) as compared to healthy age- and gender-matched controls (3.1 +/- 1.4 vs. 1.9 +/- 0.7 ng/ml, P = 0.002). Immunohistochemistry showed increased expression of PrP(C) in the soma of peri-infarcted neurones as well as in the endothelial cells (EC) of micro-vessels and inflammatory cells in peri-infarcted brain tissue from patients who survived for 2-34 days after an initial stroke. The same pattern was repeated 1-48 hr after MCAO. RT-PCR showed increased gene expression of PrP(C) by human foetal neurons (HFN) after 12 hr of oxygen glucose deprivation (OGD), which remained increased after 24 hr reperfusion. Western blotting confirmed that protein expression was similarly upregulated, and fluorescent labeling showed a notable increase in peri-nuclear and axonal PrP(C) staining intensity. Increased plasma PrP(C) seems to reflect endogenous expression in acute stroke-affected brain tissue. Increased cellular expression in peri-infarcted regions may influence hypoxia-induced cell damage, although the effects on EC survival and angiogenesis remain to be elucidated.

The magic glue hyaluronan and its eraser hyaluronidase: a biological overview

Hyaluronan (HA) is a multifunctional high molecular weight polysaccharide found throughout the animal kingdom, especially in the extracellular matrix (ECM) of soft connective tissues. HA is thought to participate in many biological processes, and its level is markedly elevated during embryogenesis, cell migration, wound healing, malignant transformation, and tissue turnover. The enzymes that degrade HA, hyaluronidases (HAases) are expressed both in prokaryotes and eukaryotes. These enzymes are known to be involved in physiological and pathological processes ranging from fertilization to aging. Hyaluronidase-mediated degradation of HA increases the permeability of connective tissues and decreases the viscosity of body fluids and is also involved in bacterial pathogenesis, the spread of toxins and venoms, acrosomal reaction/ovum fertilization, and cancer progression. Furthermore, these enzymes may promote direct contact between pathogens and the host cell surfaces. Depolymerization of HA also adversely affects the role of ECM and impairs its activity as a reservoir of growth factors, cytokines and various enzymes involved in signal transduction. Inhibition of HA degradation therefore may be crucial in reducing disease progression and spread of venom/toxins and bacterial pathogens. Hyaluronidase inhibitors are potent, ubiquitous regulating agents that are involved in maintaining the balance between the anabolism and catabolism of HA. Hyaluronidase inhibitors could also serve as contraceptives and anti-tumor agents and possibly have antibacterial and anti-venom/toxin activities. Additionally, these molecules can be used as pharmacological tools to study the physiological and pathophysiological role of HA and hyaluronidases.

Changes in Hyaluronan Metabolism and RHAMM Receptor Expression Accompany Formation of Complicated Carotid Lesions and May be Pro-Angiogenic Mediators of Intimal Neovessel Growth

Previous studies have shown that changes in expression of the glycosaminoglycan, hyaluronan (HA) were associated with erosion in areas of post-mortem coronary artery liable to rupture. Angiogenesis is an important feature of ulcerating haemorrhagic plaques prone to rupture. HA is a glycosaminoglycan known to possess potent angiogenic properties on metabolism to oligosaccharides of HA (o-HA) in the presence of hyaluronidase (HYAL) enzymes. In this study we have examined HA receptor and HYAL enzyme expression in a series of carotid artery specimens used as vascular transplants and exhibiting various stages of atherosclerotic lesions as determined by anatomo-pathology. Our results demonstrated dramatically increased expression of HYAL-1 in regions of inflammation associated with complicated plaques. Receptor for HA-mediated motility (RHAMM), which is known to be important in transducing angiogenic signals in vascular endothelium, was strongly expressed on intimal blood vessels from complicated lesions but almost absent from other regions including adventitial vessels. Metabolism of HA, together with up-regulation of RHAMM in complicated plaque lesions might be partly responsible for over-production of leaky neovessels and predisposition to plaque rupture.

Hyaluronan-mediated angiogenesis in vascular disease: uncovering RHAMM and CD44 receptor signaling pathways

The correct formation of new blood vessels from existing vasculature (angiogenesis) is essential for embryogenesis and the effective repair of damaged or wounded tissues. However, excessive and detrimental vascularization also occurs in neoplasia, promoting tumour growth and metastasis, as well as in proliferative diabetic retinopathy and atherosclerosis. Greater understanding of the mechanisms controlling the angiogenic process will allow optimization of wound healing, and provide mechanisms to inhibit vascularization in tumours and other diseases. Evidence supports a cascade of events in which the perturbation of one of the steps is sufficient to significantly inhibit neovascularization. The extracellular macromolecules, notably glycosaminoglycans (GAGs), are important mediators of angiogenesis. Hyaluronan (HA), a large, non-sulphated GAG, was first discovered in the vitreous of the eye [.], and is ubiquitously expressed in the extracellular matrix (ECM) of tissues. Native high molecular weight HA (n-HA) is anti-angiogenic, whereas HA degradation products (o-HA; 3-10 disaccharides) stimulate endothelial cell (EC) proliferation, migration and tube formation following activation of specific HA receptors in particular, CD44 and Receptor for HA-Mediated Motility (RHAMM, CD168). The involvement of HA in the regulation of angiogenesis makes it an attractive therapeutic target. We review the role of o-HA in modulation of angiogenesis during tissue injury, and vascular disease, focusing on receptor-mediated signal transduction pathways that have been evaluated.