INDUCTION AND INTRACELLULAR-LOCALIZATION OF 90-KILODALTON HEAT-SHOCK PROTEIN IN RAT KIDNEYS WITH ACUTE GENTAMICIN NEPHROPATHY

BACKGROUND: We previously reported the induction of 73-kilodalton heat -shock protein (HSP73) in injured tubular epithelial cells in rat kidn eys with gentamicin-induced acute renal failure. In the present study, we examined serial expression of 90-kilodalton heat-shock protein (HS P90), another major HSP, in this animal model. EXPERIMENTAL DESIGN: Sp rague-Dawley rats received gentamicin (80 mg/kg/day) for 14 days and d eveloped acute proximal tubular injury. Serial immunohistochemical loc alization of HSP90 was observed at both light microscopic and electron microscopic levels, using a specific antibody against HSP90. In addit ion, serial renal extracts were analyzed by immunoblot. RESULTS: On li ght microscopy, HSP90 was induced in injured proximal tubular epitheli al cells and accumulated in fine granules 36 hours after the gentamici n exposure. The size and number of these granules gradually increased to Day 12 and decreased from Day 18, and the granules disappeared on D ay 27. Electron microscopy showed the accumulation of HSP90 in the swo llen lysosomes and the nucleoli of the injured proximal tubular epithe lial cells. On serial immunoblot analysis of renal extracts, increased amounts of HSP90 were found in association with the induction of HSP9 0 in injured cells. Furthermore, on immunoblot of nuclear fractions fr om kidneys at Days 0 and 6, HSP90 was detected in the fraction at Day 6. CONCLUSIONS: These results demonstrate that HSP90 is induced in the lysosomes and the nucleoli of damaged cells during the course of gent amicin-induced acute tubular injury. HSP90 may have roles in the dispo sition of degenerated proteins and in the new protein synthesis for th e protection and repair of target cells from gentamicin nephrotoxicity .