Synthesis and Surface Expression of Hyaluronan by Dendritic Cells and Its Potential Role in Antigen Presentation

Abstract

Hyaluronan (HA) is a large glycosaminoglycan consisting of repeating disaccharide units of glucuronic acid and N-acetylglucosamine. HA is known to act as a filling material of extracellular matrices and as an adhesive substrate for cellular migration. Here we report that dendritic cells (DC) express mRNAs for HA synthases and hyaluronidases, actively synthesize HA, and display HA on their surfaces. Interestingly, HA expression levels on DC were not significantly altered by their maturation states. With respect to physiological function, three specific HA inhibitors, i.e., bovine proteoglycan, a 12-mer HA-binding peptide (GAHWQFNALTVR) termed Pep-1, and an oligomeric Pep-1 formulation, all interfered with DC-induced activation of CD4+ T cells isolated from DO11.10 TCR transgenic mice. For example, Pep-1 oligomer efficiently inhibited DC-dependent cluster formation, IL-2 and IFN-γ production, and proliferation by DO11.10 T cells in vitro without affecting the viabilities of DC or T cells, DC function to uptake exogenous proteins, or DC-T cell conjugate formation at earlier time points. These observations suggest a paracrine mechanism by which DC-associated HA facilitates some of the late changes in T cell activation. Although T cells constitutively expressed mRNAs for HA synthases and hyaluronidases, their surface HA expression became detectable only after activation. Oligomeric Pep-1 and bovine proteoglycan both inhibited mitogen-triggered T cell activation in the absence of DC, suggesting an autocrine mechanism by which HA expressed by T cells assists their own activation processes. Finally, adoptively transferred DO11.10 T cells showed progressive mitosis when stimulated with Ag-pulsed DC in living animals, and this clonal expansion was inhibited significantly by administration of Pep-1 oligomer. Our findings may introduce a new concept that relatively simple carbohydrate moieties expressed on DC and perhaps T cells play an important immunomodulatory role during Ag presentation.

Identification and Analysis of the Promoter Region of the Human Hyaluronan Synthase 2 Gene

“…HA has been implicated in chondrogenesis and cartilage homeostasis, embryonic development, immunomodulation, wound healing, and a variety of disease processes, including arthritis, malignancies, and pulmonary and vascular disease, together with other immune and inflammatory disorders (27)(28)(29)(30)(31)(32)(33)(34)(35). In addition, the transcriptional regulation of HAS2 has potential significance in renal fibrosis (10 -12), diabetic nephropathy (13), and peritoneal inflammation (16).…”

Inhibition of Hyaluronan Synthesis Protects against Central Nervous System (CNS) Autoimmunity and Increases CXCL12 Expression in the Inflamed CNS

“…Possible mechanisms by which hyaluronan can stimulate T-cells have already been discussed by others (i) 4MU-mediated inhibition of hyaluronan synthesis in mitogen-stimulated T-cell cultures suppresses the production of the cytokine IL-2 that plays a crucial role in T-cell proliferation and differentiation (7). (ii) Hyaluronan produced and displayed on the surface of dendritic cells enhances antigen-specific T-cell activation by stabilizing T-cell receptor-APC interactions through functioning as an intracellular "glue" between T-cells and antigen-presenting cells (2,3).…”

“…Vivo-We used 4MU, a well established and specific inhibitor of hyaluronan production (3,7,(13)(14)(15)(16)(17)20), to modulate hyaluronan synthesis. First, we confirmed the inhibitory influence of 4MU on hyaluronan synthesis by in vitro experiments.…”

“…In the present study, we assessed the effect of hyaluronan in EAE by inhibiting hyaluronan synthesis with 4-methylumbelliferone (4MU) administration (3,(13)(14)(15)(16)(17). 4MU inhibits hyaluronan synthesis in a dose-dependent manner by two mechanisms: depletion of cellular UDP-glucuronic acid and down-regulation of hyaluronan synthases 2 and 3 (14).…”

“…HA exhibits diverse biological functions, including regulation of cell adhesion, cell proliferation, and diffusion of nutrients and growth factors (2), by its ability to interact with different proteins like CD44, brevican, aggrecan, versican, hyaluronectin, RHAMM, and neurocan (3,4). Several studies suggest that hyaluronan may have proinflammatory roles in the context of CNS autoimmunity: 1) it accumulates in demyelinated CNS lesions in MS and EAE (5,6); 2) HA production by dendritic cells and T-cells promotes antigen presentation and enhances T-cell activation and proliferation (2,3,7,8); 3) HA-CD44 interactions at the CNS vascular endothelium facilitate lymphocyte binding to vessels and CNS infiltration (9 -11); and 4) hyaluronan fragments signal through both Toll-like receptors (TLR) 2 and 4 and thereby stimulate inflammatory gene expression in immune cells (12).…”