Successive changes in hyaluronan (HA) synthesis and fragmentation in the rat post‐ischemic kidney

Abstract

The precise time‐course of HA accumulation and fragmentation in inflammatory tissues remains uncertain. We examined the expression of the main hyaluronidases (HYAL1 and HYAL2) and HA synthases (HAS1, HAS2 and HAS3) by real‐time PCR in the outer [OSOM] and inner stripes [ISOM] of the renal outer medulla up to Day 14 after ischemia/reperfusion (IR) injury. We also assessed hyaluronidase activity by zymography and HA fragmentation by membrane filtration and pseudo‐ELISA. HAS1 was up‐regulated more than 100‐fold 12 h post‐IR, returning to baseline faster in the ISOM than in the OSOM. HAS2 increased only after a 2‐day delay and remained elevated. The mRNA for HAS3 could not be detected. Both HYAL1 and HYAL2 were strongly but transiently (12‐48 h) repressed in parallel with a reduction in hyaluronidase activity. HA accumulation was detected as early as 12 h and increased steadily thereafter. However, the amount of low molecular weight (MW) HA (i.e., HA fragments) decreased by 60% from baseline to Day 1 in the ISOM. Later, HA fragments amassed in both zones (×100 in OSOM and ×5 in ISOM vs baseline). In summary, within 24 h post‐IR, there is a massive activation of HAS1 combined with a repression of hyaluronidases, leading to a pool of predominantly high MW HA. Significant amounts of HA fragments appear later (Day 7‐14) when HAS2 is induced and HYAL1 and HYAL2 levels are back to baseline. HA fragments are possibly involved in regeneration.