The role of hyaluronan in the pathogenesis of lupus nephritis

Abstract

Lupus nephritis is a severe organ manifestation of systemic lupus erythematosus, characterized by the production of autoantibodies and immune-mediated injury to the kidney.

Hyaluronan (HA) is a major component of the extracellular matrix, which is involved in immune-mediated renal injury. We have previously demonstrated that HA expression is increased in the glomerulus of patients with severe lupus nephritis, attributed in part to anti-dsDNA antibody-mediated induction of low molecular weight (LMW) HA and high molecular weight (HMW) HA synthesis in mesangial cells. The causal role of HA and its fragments in the pathogenesis of lupus nephritis has not been explored.

In this project, two separate in vivo studies were undertaken to delineate the role of HA in disease progression in NZBWF1/J mice. In the first study, we determined the effect of 4-methylumbelliferone (MU), a specific inhibitor of HA synthesis, on renal function and histology in NZBWF1/J mice with active disease, with particular emphasis on inflammatory and fibrotic processes. In the second study, we investigated whether exogenous HA could exacerbate disease manifestations in pre-disease NZBWF1/J mice. The mechanisms underlying the effects of MU and exogenous LMW HA and HMW HA were investigated in mesangial cells isolated from NZBWF1/J mice.

Female NZBWF1/J mice with established nephritis were randomized into 3 groups and treated with (1) PBS, (2) Arabic gum (Gum) or (3) MU (3g/kg/day) for 2, 4, 8 and 12 weeks. Treatment of mice with MU for 12 weeks reduced serum HA levels and abrogated intra-renal expression of HA compared to PBS and Gum treated mice. Inhibition of HA synthesis in the kidney resulted in decreased IgG and C3 deposition, reduced B cell, T cell and macrophage infiltration, matrix accumulation and TNF-, IL-6 and MCP-1 expression, which was associated with improved renal functions.

To confirm that HA influenced pathogenesis of lupus nephritis, pre-disease NZBWF1/J mice were randomized to receive (1) PBS, (2) LMW HA or (3) HMW HA for periods up to 24 weeks. Administration of LMW HA and HMW HA into NZBWF1/J mice by tail-vein injection induced intra-glomerular deposition of IgG and C3, B cell infiltration, glomerular hypercellularity and tubular atrophy, which was accompanied by induction of MAPK signaling pathways, enhanced MCP-1 expression, and increased matrix deposition in the glomerular and tubular basement membranes.

In vitro studies showed that exogenous IL-6, IL-1, TGF-1 and TNF- induced HA synthesis in murine mesangial cells (MMC), with over 80% secreted into the conditioned medium. This was accompanied by an increase in pro-inflammatory cytokine secretion and synthesis of fibronectin and laminin. Inhibition of HA synthesis with MU significantly decreased cytokine secretion and fibronectin synthesis. The ability of HA to induce inflammatory and fibrotic processes in mesangial cells was confirmed in separate studies in which MMC were incubated with exogenous LMW HA and HMW HA.

In summary, these original findings provide evidence of a direct effect of HA on intra-renal inflammation and fibrosis in lupus nephritis. Approaches to inhibit HA synthesis may offer novel therapeutic strategies to delay disease progression.