Elevated level of ambient glucose stimulates the synthesis of high-molecular-weight hyaluronic acid by human mesangial cells. The involvement of transforming growth factor beta1 and its activation by thrombospondin-1.

Abstract

The dysregulation of the metabolism of glycosaminoglycan and protein components of extracellular matrix (ECM) is a typical feature of diabetic complications. High glucose-induced enrichment of ECM with hyaluronan (HA) not only affects tissue structural integrity, but influences cell metabolic response due to the variety of effects depending on the HA polymer molecular weight. TSP-1-dependent activation of TGFbeta1 axis is known to mediate numerous matrix disorders in diabetes, but its role concerning HA has not been studied so far. In this work we demonstrated that 30 mM D-glucose increased the incorporation of [(3)H]glucosamine in high-molecular-weight (> 2000 kDa) HA of medium and matrix compartments of human mesangial cultures. Simultaneously, the synthesis of HA with lower molecular weight and HA degradation were not altered. The cause of the increased high-molecular-weight HA synthesis consisted in the up-regulation of hyaluronan synthase (HAS) 2 mRNA without alterations of the expression of HAS3, which generates HA of lower molecular weight. D-Glucose at 30 mM also stimulated the production of transforming growth factor beta1 (TGFbeta1), the excessive activation of which was determined by the up-regulation of thrombospondin-1 (TSP-1). The blockage of TGFbeta1 action either by neutralizing anti-TGFbeta1 antibodies or by quenching the TGFbeta1 activation (with TSP-1-derived synthetic GGWSHW peptide) abolished the effect of high glucose on HAS2 mRNA expression and normalized the synthesis of HA. Exogenous human TGFbeta1 had the same effect on HAS2 expression and HA synthesis as high glucose treatment. Therefore, we supposed that TSP-1-dependent TGFbeta1 activation is involved in the observed high glucose effect on HA metabolism. Since high-molecular-weight HA polymers, unlike middle- and low-molecular weight HA oligosaccharides, are known to possess anti-inflammatory and anti-fibrotic functions, we suppose that the enrichment of mesangial matrix with high-molecular-weight HA may represent an endogenous mechanism to limit renal injury in diabetes.