Immunohistochemical Investigation for Renal Tubules in Adaptive and Maladaptive Repair Process after Renal Tubular Injury in the Kidney of Rats

Acute kidney injury (AKI) have been thought to be reversible condition, however, emerging evidence demonstrated association between AKI and subsequent development of irreversible fibrosis and chronic kidney disease. In the present study, since recovery of AKI depends on renal tubular regeneration, factors expressing in renal tubules in adaptive or maladaptive repair process were investigated to predict reversibility of kidney injury. In the kidney of female F344 rats subjected to ischemia/reperfusion (I/R), regenerative tubules and dilated tubules were observed at 3 and 7 days after I/R. In fibrotic areas of the kidney of male SD rats subjected to I/R, renal tubules were dilated or atrophied. From microarray data of regenerative tubules, survivin, sex-determining region Y (SRY)-box 9 (SOX9), and CD44 were extracted as factors possibly relating to tubular regeneration or fibrosis. Immunohistochmical analysis demonstrated that survivin and SOX9 expressed in regenerative tubules, while SOX9 also expressed in renal tubules in fibrotic area, indicating that survivin and SOX9 contribute renal tubular regeneration, but sustained SOX9 expression may lead fibrosis. CD44 expressed in dilated tubules at day 3 and 7, and tubules in fibrotic area, suggesting that CD44 expressed in maladaptive tubules. These information will be helpful to consider reversibility of kidney injury.