Mononuclear leukocytes preferentially bind via CD44 to hyaluronan on human intestinal mucosal smooth muscle cells after virus infection or treatment with poly(I.C)

Bone morphogenic protein-7 inhibits monocyte-stimulated TGF-beta1 generation in renal proximal tubular epithelial cells

It has been demonstrated that bone morphogenic protein-7 (BMP-7) stimulates formation of hyaluronan (HA)-based cables on the cell surface of renal proximal tubular cells and that these cables mediate monocyte binding. Furthermore, interaction of monocytes with proximal tubule cell (PTC) surface intracellular adhesion molecule (ICAM) stimulates the synthesis of TGF-beta1. This study examined the effect of BMP-7 on monocyte-stimulated TGF-beta1 synthesis under conditions of basal and stimulated ICAM expression. Monocyte (U937 cells)-dependent stimulation of TGF-beta1 promoter activity and protein synthesis was reduced by addition of BMP-7 for 24 h before addition of U937 cells. Removal of cell surface HA or inhibition of monocyte interaction with HA using antibody to CD44 prevented this effect of BMP-7. These data suggest that BMP-7 enhances HA-dependent binding and reduces ICAM-dependent binding, which is known to stimulate TGF-beta1 synthesis. This hypothesis was examined further by stimulation of PTC ICAM expression by TNF-alpha. After TNF-alpha stimulation, monocyte-dependent TGF-beta1 synthesis increased. This was abrogated by inhibition of ICAM-CD18 interactions. TNF-alpha stimulation alone did not increase TGF-beta1 synthesis. TNF-alpha stimulation of PTC in the presence of BMP-7 failed to increase monocyte-dependent TGF-beta1 stimulation. Although stimulation of PTC by BMP-7 alone decreased cell surface ICAM expression, it did not affect TNF-alpha-induced ICAM expression. The effect of BMP-7 on TGF-beta1 synthesis in TNF-alpha-stimulated cells was abrogated by disruption of CD44-HA interactions, suggesting that it was due to increased monocyte binding to HA on the cell surface.

Hyaluronan participates in the epidermal response to disruption of the permeability barrier in vivo

Hyaluronan (hyaluronic acid, HA) is a glycosaminoglycan in the extracellular matrix of tissues that plays a role in cellular migration, proliferation and differentiation. Injury to the stratum corneum elicits an epidermal hyperproliferative response, a pathogenic feature in many cutaneous diseases including eczema and psoriasis. Because HA is abundant in the matrix between keratinocytes, we asked whether the presence of HA is required for epidermal hyperplasia to occur in response to barrier injury. Disruption of the stratum corneum, by acetone application on the skin of hairless mice, led to a marked accumulation of HA in the matrix between epidermal basal and spinous keratinocytes, and also within keratinocytes of the upper epidermis. To test whether HA may have a functional role in epidermal hyperplasia, we used Streptomyces hyaluronidase (StrepH), delivered topically, to degrade epidermal HA and blunt the accumulation of epidermal HA after acetone. StrepH signficantly reduced epidermal HA levels, and also significantly inhibited the development of epidermal hyperplasia. This reduction in epidermal thickness was not attributable to any decrease in keratinocyte proliferation, but rather to an apparent acceleration in terminal differentiation (ie, increased keratin 10 and filaggrin expression). Overall, the data show that HA is a significant participant in the epidermal response to barrier injury.

Renal proximal tubular epithelial cell transforming growth factor-beta1 generation and monocyte binding

With increasing awareness of the importance of renal cortical interstitial fibrosis, interest has focused on the mechanisms that stimulate generation of profibrotic factors including transforming growth factor (TGF)-beta1, by resident cells, such as proximal tubular epithelial cells (PTCs). Infiltration of monocytes, has been implicated in the pathogenesis of a wide variety of renal diseases, however, how interaction between monocytes and PTCs may affect the generation of TGF-beta1 by the resident cell is unknown. We demonstrate that monocytes stimulate TGF-beta1 transcription and protein synthesis by PTCs. This was dependent on direct cell contact and TGF-beta1 transcriptional activation that was dependent on ICAM-1 binding of unstimulated monocytes. This was mimicked by antibody cross-linking of PTC surface ICAM-1. We have previously identified hyaluronan (HA)-based structures on the surface of PTCs, both primary cultures and the HK-2 cell line. Removal of cell-surface HA increased ICAM-1-dependent monocyte binding and stimulation of TGF-beta1 synthesis. Furthermore, we demonstrate that binding of monocytes to HA-based structures on the cell surface of HK-2 cells interferes with this response. In summary, we have demonstrated that HA-based pericellular structures down-regulate proinflammatory and profibrotic responses by modulation of monocyte-driven ICAM-1-dependent cell activation and TGF-beta1 generation.

Hyaluronan suppresses epidermal differentiation in organotypic cultures of rat keratinocytes

Hyaluronan (hyaluronic acid, HA) is an abundant matrix component between keratinocytes of the epidermis in vivo, but its function there remains unclear. We used a lift culture model, in which rat epidermal keratinocytes (REKs) stratify at an air-liquid interface, to ask whether HA may regulate epidermal proliferation and/or differentiation. In this model, early markers of differentiation (keratin 10), and later markers (profilaggrin, keratohyalin granules, cornified layers) are faithfully expressed, both temporally and spatially. HA, measured using two different analytical techniques, accumulated to high levels only in the presence of an intact basement membrane that seals the epidermal compartment. To test whether HA has a functional role in differentiation, Streptomyces hyaluronidase (StrepH, 1 U/ml; digests >95% of HA within 4 h) was added daily to lift cultures during stratification time-course experiments over 5 days. In StrepH-treated cultures, the expression of profilaggrin and the number and size of keratohyalin granules were significantly increased relative to controls using semiquantitative histological analyses. The StrepH-related accumulation of K10 protein and profilaggrin/filaggrin were confirmed by Western analyses. Thus, it appears that the presence of intercellular HA in the epidermis acts as a brake upon intracellular events that occur during keratinocyte differentiation.

Use of 15N-NMR to resolve molecular details in isotopically-enriched carbohydrates: sequence-specific observations in hyaluronan oligomers up to decasaccharides

The glycosaminoglycan hyaluronan is a vital structural component of extracellular matrices with diverse biological functions, a molecular understanding of which requires a detailed description of secondary and tertiary solution structures. Various models of these structures have been proposed on the basis of 1H and 13C natural-abundance nuclear magnetic resonance (NMR) experiments, but resonance overlap limits further progress with these techniques. We have therefore produced 15N- and 13C- isotopically-labeled hyaluronan oligosaccharides and applied triple-resonance and 3D experiments to overcome this restriction. Spectra recorded on oligosaccharides (of lengths 4, 6, 8, 10, and 12 sugar rings), reveal that the 15N nucleus allows resolution of the amide groups in a decamer at high magnetic field, whereas 13C natural-abundance NMR can only resolve internal groups up to hexamers. Complete 13N sequence- specific assignments of these oligosaccharides indicate that the chemical shift dispersion can be explained by end-effects, which are seen even in the middle of octamers. Triple- resonance and 15N-edited 3D experiments, among the first of their kind in oligosaccharides, have been used to achieve resolution of ring 1H and 13C nuclei where not possible previously. The subtle chemical shift perturbations resolved suggest that different conformations and dynamics occur at the ends, which may contribute to the range of biological activities displayed by varying lengths of hyaluronan. 15N-NMR in carbohydrates has not received much attention before, however, this study demonstrates it has clear advantages for achieving resolution and assessing dynamic motion. These conclusions are likely to be applicable to the study of the structure and dynamics of other nitrogen-containing carbohydrates.

Proteoglycans in Atherosclerosis and Restenosis

The proteoglycan versican is one of several extracellular matrix (ECM) molecules that accumulate in lesions of atherosclerosis and restenosis. Its unique structural features create a highly interactive molecule that binds growth factors, enzymes, lipoproteins, and a variety of other ECM components to influence fundamental events involved in vascular disease. Versican is one of the principal genes that is upregulated after vascular injury and is a prominent component in stented and nonstented restenotic lesions. The synthesis of versican is highly regulated by specific growth factors and cytokines and the principal source of versican is the smooth muscle cell. Versican interacts with hyaluronan, a long chain glycosaminoglycan, to create expanded viscoelastic pericellular matrices that are required for arterial smooth muscle cell (ASMC) proliferation and migration. Versican is also prominent in advanced lesions of atherosclerosis, at the borders of lipid-filled necrotic cores as well as at the plaque-thrombus interface, suggesting roles in lipid accumulation, inflammation, and thrombosis. Versican influences the assembly of ECM and controls elastic fiber fibrillogenesis, which is of fundamental importance in ECM remodeling during vascular disease. Collectively, these studies highlight the critical importance of this specific ECM component in atherosclerosis and restenosis.

Hyaluronan Structures Synthesized by Rat Mesangial Cells in Response to Hyperglycemia Induce Monocyte Adhesion

Mesangial expansion, the principal glomerular lesion in diabetic nephropathy, is preceded by a phenotypic activation and transient proliferation of the glomerular mesangial cells and by a prominent glomerular infiltration of monocytes and macrophages. Because this infiltration seems to play a key role in the subsequent mesangial matrix expansion, we tested the response of cultures of rat mesangial cells (RMCs) for monocyte adhesion in response to hyperglycemia. Increasing the medium glucose concentration from 5.6 mm (normal) to 25.6 mm (hyperglycemic) significantly increased hyaluronan in the cell matrix, with a concurrent 3- to 4-fold increase in adhesion of U937 monocytic leukemic cells to cultures of near confluent RMCs. These responses were attributed directly to the high glucose concentration and not to increased extracellular osmolality. The monocytes primarily bind directly to hyaluronan-based structures in vitro. Abnormal deposits of hyaluronan were found in glomeruli of kidney sections from diabetic rats 1 week after streptozotocin treatment, often with closely associated monocytes/macrophages, suggesting that similar structures are relevant in vivo. The monocyte adhesion response to high glucose concentration required growth stimulation of RMCs by serum and activation of protein kinase C, and was inhibited by prior passage of the RMCs in the presence of heparin. These results suggest that the response may be cell growth state and protein kinase C-dependent. When incubated with the viral mimetic, poly I:C, in the presence of normal glucose, heparin-passaged RMCs still increased cell-associated hyaluronan and exhibited hyaluronan-mediated adhesion of monocytes, indicating that the two stimuli, high glucose and viral mimetic, induce the production of the hyaluronan structures that promote monocyte adhesion by distinctly different intracellular signaling mechanisms.

Pro- and anti-inflammatory factors cooperate to control hyaluronan synthesis in lung fibroblasts

Hyaluronan (HA) is an important constituent of the extracellular matrix and accumulates during inflammatory lung diseases like asthma. Little is known about the factors that regulate HA synthesis by lung cells. Accordingly, we investigated the effect of T-helper 1 (TH1) and 2 (TH2) cytokines and the anti-inflammatory agents fluticasone and salmeterol on HA synthesis in human lung fibroblasts. Interleukin-1beta (IL-1beta) and tumor necrosis factor (TNF)-alpha were the most potent stimulators of HA synthesis and when combined, caused synergistic increases in HA accumulation. Time-course analysis of HA accumulation and [3H]-glucosamine incorporation into HA demonstrated continued synthesis over the 24 h of stimulation. Peak synthesis at 6-12 h coincided with an increased proportion of high molecular weight HA. Reverse transcriptase polymerase chain reaction (RT-PCR) revealed that IL-1beta and TNF-alpha induced HA synthase-2 messenger RNA (mRNA) 3 h following stimulation and remained elevated throughout the 24-h stimulation period. Fluticasone inhibited IL-1beta and TNF-alpha induced HA synthesis (44.5%) whereas salmeterol had no effect. When combined, fluticasone and salmeterol inhibited HA synthesis to a greater extent (85.2%). Further, fluticasone attenuated IL-1beta and TNF-alpha stimulated hyaluronan synthase-2 messenger RNA (mRNA), and the addition of salmeterol cooperatively enhanced this inhibition. These results indicate that enhanced synthesis of HA by the proinflammatory cytokines IL-1beta and TNF-alpha can be abrogated by specific corticosteroid and beta2 blocker combinations shown to be effective in the treatment of asthma.

Differential effect of transforming growth factor beta (TGF-beta) on the genes encoding hyaluronan synthases and utilization of the p38 MAPK pathway in TGF-beta-induced hyaluronan synthase 1 activation

Unfettered hyaluronan (HA) production is a hallmark of rheumatoid arthritis. The discovery of three genes encoding hyaluronan synthases (HASs) allows for the investigation of the signaling pathways leading to the activation of these genes. Our objective is to further understanding of the regulation of these genes as well as to find ways to prevent undesired gene activation. Human fibroblast-like synoviocytes were used in these experiments. mRNA levels of HAS were monitored by reverse transcriptase-PCR. A series of specific kinase inhibitors were used to investigate intracellular pathways leading to the up-regulation of HAS1. Our experiments, testing a series of stimuli including tumor necrosis factor alpha (TNFalpha), demonstrate that TGF-beta is the most potent stimulus for HAS1 transcription. TGF-beta activates HAS1 in a dose-dependent manner with a maximum effect at a concentration of 0.5-1 ng/ml. TGF-beta-induced HAS1 mRNA can be detected within 60 min and reaches maximal levels at 6 h. Furthermore, TGF-beta treatment leads to an increase in synthase activity as determined by HA ELISA and by in vitro HA synthase assays. In contrast to the activatory effect on HAS1, TGF-beta dose-dependently suppresses HAS3 mRNA. As to the mode of action of TGF-beta-induced HAS1 mRNA activation, our experiments reveal that blocking p38 MAPK inhibited the TGF-beta effect by 90%, blocking the MEK pathway led to an inhibition by 40%, and blocking the JNK pathway had no effect. The presented data might contribute to a better understanding of the role of TGF-beta and of HA in the pathology of diseases.

Endoplasmic reticulum stress induces hyaluronan deposition and leukocyte adhesion

There is mounting evidence that perturbations in endoplasmic reticulum (ER) function play a key role in the pathogenesis of a broad range of diseases. We have examined the ability of ER stress to modulate leukocyte binding to colonic and aortic smooth muscle cells. In vitro, control smooth muscle cells bind few leukocytes, but treatment with compounds that induce ER stress, including tunicamycin, A23187, and thapsigargin, promotes leukocyte binding. Likewise, dextran sulfate, another agent capable of inducing ER stress and promoting inflammation in vivo, strongly induces leukocyte adhesion. The bound leukocytes are released by hyaluronidase treatment, indicating a critical role for hyaluronan-containing structures in mediating leukocyte binding. Affinity histochemistry demonstrated that hyaluronan accumulates and is present in cable-like structures in the treated, but not the untreated, cultures and that these structures serve as attachment sites for leukocytes. Hyaluronan-rich regions of both murine and human inflamed colon contain numerous cells that stain intensely for ER-resident chaperones containing the KDEL sequence, demonstrating a relationship between ER stress and hyaluronan deposition in vivo. These results indicate that ER stress may contribute to chronic inflammation by forming a hyaluronan-rich extracellular matrix that is conducive to leukocyte binding.

Targeted deletion of CD44v7 exon leads to decreased endothelial cell injury but not tumor cell killing mediated by interleukin-2-activated cytolytic lymphocytes

In the current study, we investigated the nature and role of CD44 variant isoforms involved in endothelial cell (EC) injury and tumor cell cytotoxicity mediated by IL-2-activated killer (LAK) cells. Treatment of CD44 wild-type lymphocytes with IL-2 led to increased gene expression of CD44 v6 and v7 variant isoforms and to significant induction of vascular leak syndrome (VLS). CD44v6-v7 knockout (KO) and CD44v7 KO mice showed markedly reduced levels of IL-2-induced VLS. The decreased VLS in CD44v6-v7 KO and CD44v7 KO mice did not result from differential activation and expansion of CD8+ T cells, NK, and NK-T cells or from altered degree of perivascular lymphocytic infiltration in the lungs. LAK cells from CD44v7 KO mice showed a significant decrease in their ability to adhere to and mediate lysis of EC but not lysis of P815 tumor cells in vitro. CD44v7-mediated lysis of EC by LAK cells was dependent on the activity of phosphatidylinositol 3-kinase and tyrosine kinases. Interestingly, IL-2-activated LAK cells expressing CD44hi but not CD44lo were responsible for EC lysis. Furthermore, lysis of EC targets could be blocked by addition of soluble or enzymatic cleavage of CD44v6-v7-binding glycosaminoglycans. Finally, anti-CD44v7 mAbs caused a significant reduction in the adherence to and killing of EC and led to suppression of IL-2-induced VLS. Together, this study suggests that the expression of CD44v7 on LAK cells plays a specific role in EC injury and that it may be possible to reduce EC injury but not tumor cell killing by specifically targeting CD44v7.

Mononuclear leukocytes bind to specific hyaluronan structures on colon mucosal smooth muscle cells treated with polyinosinic acid:polycytidylic acid: inter-alpha-trypsin inhibitor is crucial to structure and function

Inflammatory bowel disease (IBD) is a chronic disorder whose etiology is linked to triggering events, including viral infections, that lead to immunoregulatory dysfunction in genetically susceptible people. Characteristic pathological changes include increased mononuclear leukocyte influx into the intestinal mucosa as well as mucosal smooth muscle cell (M-SMC) hyperplasia. Virus infection or viral mimic [polyinosinic acid:polycytidylic acid (polyI:C)] treatment of human colon M-SMCs in vitro increases cell surface hyaluronan (HA), and nonactivated mononuclear leukocytes bind to virus-induced HA structures by interactions that involve the HA-binding receptor CD44. In this study, confocal microscopy reveals increased HA on poly I:C-treated M-SMC surfaces within 3 hours, arrayed in coat-like structures. By 17 hours, novel, lengthy cable structures are evident, and these are primarily responsible for mediating leukocyte adhesion. Immunohistochemical staining demonstrates components of the inter-alpha-trypsin inhibitor (IalphaI) complex in both coat-like and cable structures. M-SMCs co-treated with polyI:C and a polyclonal antibody to IalphaI display HA in coats but with diminished cables, and they bind significantly fewer leukocytes than M-SMCs treated with polyI:C alone. Western blot data suggest that heavy chains of IalphaI are specifically associated with cable structures. Staining of tissue sections from patients with IBD demonstrates the presence of HA in inflamed colon tissue, and shows that HA-associated IalphaI staining increases in the mucosa of inflamed IBD specimens compared to noninflamed sections from the same patient, establishing a probable link between the observations in vitro and the progression of the inflammatory process in IBD.

Hyaluronan, a common thread

Hyaluronan, nature's simplest, but still exceptionally versatile glycosaminoglycan, is currently the focus of attention across a wide front of research; from cell biology, morphogenesis, matrix organization, pathobiology to tissue engineering. This macromolecule has entangled me in a number of puzzling and challenging projects over the past 3 decades. These entertaining encounters are outlined in this retrospective.