Modification of Epidermal Growth Factor Receptor (EGFR) Expression after Aminoglycoside-induced Acute Tubular Necrosis in Rat

Rhee, Hong Woo; Kang, Sung Hak; Shin, Myung Sik; Lee, Dong Hwan

Abstract

Acute tubular necrosis induced by aminoglycoside-antibiotics is followed by a regenerative Process which leads to the restoration of damaged tubules. It is well known that tubular regeneration is mediated by polypeptide growth factors such as epidermal growth factor (EGF) In the absence of nephrotoxic alterations, EGF is immunolocalized in distal tubules, whereas epidermal growth factor receptor(EGFR) immunostaining is localized in proximal tubules. After acute tubular necrosis, the sign of regeneration is accompanied by redistribution of EGF immunoreactivity from distal to proximal tubules and a reduction of total immunoreactive EGF due to a decrease of tissue-bound proEGF. However, it is controversial whether EGFR is down- or up-regulated during this regenerative process. We evaluated the time course of the regenerative response subsequent to tubular damage induced by aminoglycoside, with a particular attention paid to EGFR in order to examine whether it is down- or up-regulated. Female Sprague-Dawley rats were treated during 4 and 8 consecutive days with a daily dose of 80 mg/kg gentamicin i.p. Groups of experimental animals (n=10) were terminated at increasing time intervals (5, 9, 12, 16 days) after cessation of treatment. One hour before sacrifice, each individual received i.p. 200mg/kg Blood for the immunohistochemical demonstration of cell proliferation (S-phase cell). Blood was collected at the time of sacrifice to measure serum creatinine and BUN levels. EGFR immunoreactivity was revealed on paraffin-embedded tissue section by immunohistochemical staining using polyclonal anti-EGFR antibody. Upon immunostaining sections in control kidneys, immunoreactive EGFRs exhibited a quite specific and restricted distribution since they were confined to proximal tubules. But proximal tubules undergoing regenerative repair were characterized by a disappearance of EGFR, which expressed BrdU in immunohistochemical sections for BrdU. Beyond the episode of tubular regeneration, proximal tubules recovered immunoreactive EGFR. The results suggest that the apparent loss of EGFR could be due to a process of receptor down-regulation in proximal tubules displaying evidence of regenerative response.