Intracellular localization of 73 kDa heat‐shock protein in rat kidneys with acute gentamicin nephropathy: an electron microscopic immunohistochemical study

Abstract

Summary: Recent in vitro studies have suggested a chaperone function of 73 kDa heat‐shock protein (HSP73) in targeting denatured proteins to lysosomes for degradation. We previously reported the induction of HSP73 in rat kidneys with gentamicin‐induced acute tubular injury, and suggested that HSP73 might accumulate in injured lysosomes by observations at light microscopic level. In this study, we examined serial intracellular localizations of HSP73 in this animal model at electron microscopic level. Sprague‐Dawley rats received gentamicin (80 mg/kg per day) for 14 days, and developed acute proximal tubular injury. After the gentamicin exposure, HSP73 moved from the nucleus to the cytoplasm, and was expressed within enlarged lysosomes in the injured proximal tubular epithelial cells. These accumulations started to appear from 36 h after the first gentamicin exposure, enlarged in size until day 12, and gradually diminished after day 18. At day 27, the HSP73 localization pattern returned to that of the normal kidney. We next observed serial intracellular localizations of a renal isoform of argininosuccinate synthetase (ASS), which is not a chaperone protein. Argininosuccinate synthetase was mainly expressed in the cytoplasm of normal proximal tubular epithelial cells. After the gentamicin exposure, ASS also accumulated within the lysosomes, but the magnitude of this lysosomal accumulation was less than that of HSP73. These findings in vivo support the suggested function of HSP73 in lysosomal protein degradation pathways. HSP73 may have a role in the disposition of damaged proteins for the repair of target cells from gentamicin nephrotoxicity.