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Background/Aim: Pathological accumulation of the extracellular matrix component hyaluronan (HA) occurs in the kidney cortex in immune-system mediated tissue injury. The purpose of the present study was to examine the pattern of HA deposition and the mechanisms of HA synthesis in the MRL-Faslpr mouse model of lupus nephritis. Methods: Kidneys from normal and autoimmune mice were examined for HA content by immunofluorescence staining. Steady state mRNA levels for key enzymes involved in HA synthesis – uridine diphosphate-glucose dehydrogenase (UDPGDH) and HA synthases (HAS) 1, 2 and 3 – were assessed by reverse-transcriptase polymerase chain reaction (RT-PCR). Using cultured mouse tubular epithelial cells, the regulation of the HA production in vitro in response to tumor necrosis factor alpha and interferon gamma was also examined. Results: By immunofluorescence staining, large amounts of HA were detected in the cortical interstitium of MRL-Faslpr mice with autoimmune renal injury, but not in congenic MRL-++ mice. By RT-PCR the presence of transcripts for several genes involved in the synthesis of HA in normal and autoimmune kidneys could be demonstrated, including mRNA for UDPGDH and HAS1 and HAS2, but not for HAS3. Except for HAS2, steady state mRNA levels for these enzymes did not correlate with disease activity. Analyzing a kidney tubular epithelial cell line in vitro, it was found that tumor necrosis factor alpha and interferon gamma, and particularly the combination of these two cytokines, markedly enhanced the synthesis of HA. The expression of HAS2 mRNA was also enhanced in response to cytokine treatment. Conclusions: HA deposition is prominent in MRL-Faslpr mice with renal disease and could be mediated by local synthesis through HAS1 and HAS2. We hypothesize that the enhanced synthesis of HA could be promoted by proinflammatory cytokines in vivo. The functional significance of HA accumulation in autoimmune renal injury remains to be determined.

The accumulation of hyaluronan (HA) in the renal cortex is a characteristic feature of inflammatory renal diseases. Fragments of HA derived from high molecular weight precursors are known to display inflammatory effects in vitro and could, therefore, participate in immune renal injury. To understand the mechanisms of HA fragmentation in vivo we examined the expression of recently characterized mammalian hyaluronidases in normal and autoimmune kidneys and in cell lines. We found that transcripts for the lysosomal–type hyaluronidases Hyal1 and Hyal2 were constitutively expressed in normal and autoimmune kidneys as well as in tubular epithelial cells and in a macrophage cell line. The expression of hyaluronidase genes in the cell lines did not increase in response to treatment with tumor necrosis factor alpha or gamma interferon. Interestingly, transcripts for the testicular–type hyaluronidase PH–20 (Spam1, Hyal3) were also detected in normal and autoimmune kidneys as well as in tubular cells and macrophages. Transcript levels were higher in kidneys from male mice as compared with age–matched females. Again, transcript levels did not change in vitro in response to cytokines. We conclude that mRNA for three different hyaluronidases is found in murine kidneys. The functional role played by these hyaluronidases in the degradation and metabolism of HA remains to be investigated further.