The fibroproliferative response of arterial smooth muscle cells to balloon catheter injury is associated with increased hyaluronidase production and hyaluronan degradation

Hyaluronan - a functional and structural sweet spot in the tissue microenvironment

Transition from homeostatic to reactive matrix remodeling is a fundamental adaptive tissue response to injury, inflammatory disease, fibrosis, and cancer. Alterations in architecture, physical properties, and matrix composition result in changes in biomechanical and biochemical cellular signaling. The dynamics of pericellular and extracellular matrices, including matrix protein, proteoglycan, and glycosaminoglycan modification are continually emerging as essential regulatory mechanisms underlying cellular and tissue function. Nevertheless, the impact of matrix organization on inflammation and immunity in particular and the consequent effects on tissue healing and disease outcome are arguably under-studied aspects of adaptive stress responses. Herein, we review how the predominant glycosaminoglycan hyaluronan (HA) contributes to the structure and function of the tissue microenvironment. Specifically, we examine the evidence of HA degradation and the generation of biologically active smaller HA fragments in pathological settings in vivo. We discuss how HA fragments versus nascent HA via alternate receptor-mediated signaling influence inflammatory cell recruitment and differentiation, resident cell activation, as well as tumor growth, survival, and metastasis. Finally, we discuss how HA fragmentation impacts restoration of normal tissue function and pathological outcomes in disease.

Role of hyaluronan in angiogenesis and its utility to angiogenic tissue engineering

Angiogenesis represents the outgrowth of new blood vessels from existing ones, a physiologic process that is vital to supply nourishment to newly forming tissues during development and tissue remodeling and repair (wound healing). Regulation of angiogenesis in the healthy body occurs through a fine balance of angiogenesis-stimulating factors and angiogenesis inhibitors. When this balance is disturbed, excessive or deficient angiogenesis can result and contribute to development of a wide variety of pathological conditions. The therapeutic stimulation or suppression of angiogenesis could be the key to abrogating these diseases. In recent years, tissue engineering has emerged as a promising technology for regenerating tissues or organs that are diseased beyond repair. Among the critical challenges that deter the practical realization of the vision of regenerating functional tissues for clinical implantation, is how tissues of finite size can be regenerated and maintained viable in the long-term. Since the diffusion of nutrients and essential gases to cells, and removal of metabolic wastes is typically limited to a depth of 150-250 microm from a capillary (3-10 cells thick), tissue constructs must mandatorily permit in-growth of a blood capillary network to nourish and sustain the viability of cells within. The purpose of this article is to provide an overview of the role and significance of hyaluronan (HA), a glycosaminoglycan (GAG) component of connective tissues, in physiologic and pathological angiogenesis, its applicability as a therapeutic to stimulate or suppress angiogenesis in situ within necrotic tissues in vivo, and the factors determining its potential utility as a pro-angiogenic stimulus that will enable tissue engineering of neo-vascularized and functional tissue constructs for clinical use.

The enzymatic degradation of hyaluronan is associated with disease progression in experimental pulmonary hypertension

Hyaluronan (HA) degradation fragments have been linked to inflammation in a wide range of lung diseases. In idiopathic pulmonary arterial hypertension, HA accumulation has been associated with advanced disease. In this study, we investigated the potential role of HA degradation in the early stages of disease by examining HA distribution, molecular mass, synthesis, and enzymatic degradation at different stages of disease progression in a rat model of monocrotaline (MCT)-induced pulmonary hypertension (PH). At 28 days post-MCT, severe PH was associated with increased total lung HA (P = 0.04). In contrast, a significant decrease in total lung HA was observed on day 10, before the onset of PH (P = 0.02). Molecular mass analysis revealed a loss of high molecular mass (HMM) HA at 10 and 24 days post-MCT, followed by an increase in HMM HA at 28 days. Expression of HA synthase 2 (HAS2) was elevated in MCT-challenged animals at 24 and 28 days, consistent with increased synthesis of HMM HA. Analysis by Morgan Elson assay and zymography demonstrated increased hyaluronidase-1 activity in the lungs of MCT-challenged rats, indicating that the observed increases in HAS2 expression and HA synthesis were counterbalanced, in part, by enhanced degradation. The present data demonstrate that, in the MCT model, early-stage PH is associated with enhanced hyaluronidase-1 activity, while both degradation and synthesis are increased at later stages. Thus an early increase in the generation of proinflammatory HA fragments may play a role in the onset and progression of pulmonary arterial hypertension.

Hyaluronan accumulation is elevated in cultures of low density lipoprotein receptor-deficient cells and is altered by manipulation of cell cholesterol content

The extracellular matrix molecule hyaluronan (HA) accumulates in human atherosclerotic lesions. Yet the reasons for this accumulation have not been adequately addressed. Because abnormalities in lipid metabolism promote atherosclerosis, we have asked whether disrupted cholesterol homeostasis alters HA accumulation in low density lipoprotein receptor-deficient cell cultures. Cultured aortic smooth muscle cells (ASMC) from Watanabe heritable hyperlipidemic (WHHL) rabbits and skin fibroblasts from homozygous patients with familial hypercholesterolemia accumulated 2-4-fold more HA than corresponding cells from age- and sex-matched normolipidemic rabbits and individuals. This occurred in both cell-associated and secreted HA fractions and was independent of cell density or medium serum concentration. WHHL ASMC cultures synthesized twice the proportion of high molecular mass HA (>2x10(6) Da) as normal rabbit ASMC but showed a lower capacity to degrade exogenous [3H]HA. Most importantly, cholesterol depletion or blocking cholesterol synthesis markedly reduced HA accumulation in WHHL ASMC cultures, whereas cholesterol replenishment or stimulation of cholesterol synthesis restored elevated HA levels. We conclude the following: 1) maintaining normal HA levels in cell cultures requires normal cell cholesterol homeostasis; 2) HA degradation may contribute to but is not the predominant mechanism to increase high molecular mass HA accumulation in low density lipoprotein receptor-deficient WHHL ASMC cultures; and 3) elevated accumulation of HA depends on cellular or membrane cholesterol content and, potentially, intact cholesterol-rich microdomains.

Aortic adventitial angiogenesis and lymphangiogenesis promote intimal inflammation and hyperplasia

INTRODUCTION

Adventitial inflammation is known to influence neointimal formation and vascular remodeling. The present study was aimed to clarify the relationship between neointima hyperplasia and adventitial angiogenesis and lymphangiogenesis after balloon-induced aortic endothelial injury.

METHODS

Seventy male Wistar rats were randomly divided into six interventional groups and one control group. The intimal area/medial area ratio (I/M ratio), the adventitial macrophage index, and the number of adventitial microvessels (Ad-MV) and lymphatic vessels (Ad-LV) in the aorta were measured, and the mRNA expressions of VEGF-A, VEGFR-1, VEGF-C, VEGFR-3, PDGF-B, and PDGFR-beta in the aortic wall were quantified by real-time RT-PCR.

RESULTS

Compared with the control group, the I/M ratio, macrophage index, Ad-MV, Ad-LV, and the mRNA expressions of VEGF-A, VEGFR-1, VEGF-C, VEGFR-3, PDGF-B, and PDGFR-beta in interventional groups increased significantly after balloon-induced injury. I/M ratio showed significant correlations with Ad-MV and Ad-LV after balloon intervention. Multiple linear regression analysis indicated that Ad-MV and Ad-LV were independent factors of intimal hyperplasia.

CONCLUSION

Adventitial angiogenesis and lymphangiogenesis are induced by intimal inflammation after balloon injury, and these neogenetic vessels in turn promote intimal inflammation and hyperplasia probably via delivery and activation of inflammatory cells.

Differential effects of hyaluronan and its fragments on fibroblasts: relation to wound healing

Hyaluronan (HA) is involved in wound healing and its biological properties depend on its molecular size. The effects of native HA and HA-12 and HA-880 saccharide fragments on human fibroblast proliferation and expression of matrix-related genes were studied. The three HA forms promoted cell adhesion and proliferation. Matrix metalloproteinase-1 and -3 mRNA were increased by all HA forms, whereas only HA-12 stimulated the expression of the tissue inhibitor of metalloproteinase 1. HA-12 enhanced type I collagen and transforming growth factor-beta (TGF-beta) 1 expression. Interestingly, HA-12 and native HA stimulated type III collagen and TGF-beta3. HA and its fragments activated Akt and extracellular-regulated kinases 1/2 and p38. Inhibition of these signaling pathways suggested their implication in most of the effects. Only native HA activated nuclear factor-kappaB and activating protein 1. Use of CD44 siRNA suggests that this HA receptor is partly implicated in the effects, although it does not rule out the involvement of other receptors. Depending on its size, HA may exert differential regulation on the wound-healing process. Furthermore, the HA up-regulation of type III collagen and TGF-beta3 expression suggests that it may promote a fetal-like cell environment that favors scarless healing.

Gene expression profile of oxidant stress and neurodegeneration in transgenic mice deficient in alpha-tocopherol transfer protein

Alpha-tocopherol transfer protein (TTP) regulates the retention and secretion of alpha-tocopherol (alpha-T) by the liver. Deletion of the TTP gene (Ttpa) in mice results in systemic deficiency of alpha-T and neurological dysfunctions described in patients with mutated Ttpa. We have explored genome-wide changes in mRNAs from brain cortex and liver of Ttpa-deficient (Ttpa(-/-)) mice and wild-type (Ttpa(+/+)) mice. Selective inductions of genes regulated by antioxidant response elements were detected in Ttpa(-/-) livers compared to Ttpa(+/+) livers, suggesting increased oxidant stress in Ttpa(-/-) livers. The activation of cell proliferation pathways in Ttpa(-/-) livers was indicated by the induction of genes that encode growth factor-binding proteins, mitogen-activated protein kinase kinase 3, and apoptosis inhibitor 6. The induction of synuclein-alpha and repression of synuclein-beta genes was detected in Ttpa(-/-) cortex. This may predispose Ttpa(-/-) cortex to increased formation of synuclein-alpha aggregates and Lewy body, often associated with oxidant stress. Cortex of Ttpa(-/-) mice revealed repression of genes encoding synaptic proteins, protein kinase C family members, and myelin proteins. A 13-fold decrease in the expression of retinoic acid receptor-related orphan receptor-alpha mRNA predicts staggerer-like phenotype (ataxia and deficits of motor coordination) of Ttpa(-/-) mice. The repression of specific genes that determine synaptic plasticity and neuronal development may account for suppressed electrophysiological activities of cortex and impaired behavior in Ttpa(-/-) mice.