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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 TGFβ1 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 [3H]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 β1 (TGFβ1), the excessive activation of which was determined by the up-regulation of thrombospondin-1 (TSP-1). The blockage of TGFβ1 action either by neutralizing anti-TGFβ1 antibodies or by quenching the TGFβ1 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 TGFβ1 had the same effect on HAS2 expression and HA synthesis as high glucose treatment. Therefore, we supposed that TSP-1-dependent TGFβ1 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.
Acute glomerulonephritis can lead to chronic glomerulonephritis or resolve without permanent damage to the kidneys. Differential gene expression was studied in a model of acute and chronic glomerulonephritis to identify factors influencing the course of glomerulonephritis towards healing or chronification. One of the differentially expressed genes was identified as SCL, encoding selenocysteine lyase. Its expression was higher in acute glomerulonephritis and lower in chronic glomerulonephritis. The transcriptional regulation of SCL was studied in vitro in rat mesangial cells (MC). SCL RNA expression increased eight-fold compared to the baseline after stimulation with interleukin-1β (IL-1β) for three hours. Luciferase expression and gel shift experiments revealed an enhancer element between bp −152 and −298 of the SCL 5’-regulatory region, with protein binding to an AP-1 binding site that may be involved in the regulation of SCL-RNA in vivo in an endogenous feedback mechanism to the inflammatory reaction in acute glomerulonephritis, leading to resolution of this disease.
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