Aging influences segment-specific toxicity of the proximal tubule caused by chemicals. II. Gene expression in kidney tissue

Changes in mRNA of genes expressed in the injured kidney cells or that contribute to cellular repair or renal function recovery are some of the earliest events that accompany the injury. The aim of the present research was to measure levels of some of these genes by means of qRT-PCR mRNA after treatment with segment-specific nephrotoxicants. In addition, influence of aging on gene expression was studied. Male Wistar rats aged 6 or 14 weeks were treated with a single i.p. injection of hexachloro-1:3-butadiene (HCBD) 100 mg/kg b.w. in corn oil, or s.c. injection of potassium dichromate (Cr) in saline. Forty eight hours after treatment, the rats were sacrificed and the kidney cortex was processed to RNA extraction and qRT-PCR using the relative quantification method. The following genes were valuated: kidney injury molecule-1 (KIM-1), clusterin (Cln), regucalcin (Rgn), and osteopontin (Spp1) according to their function. At 6-week of age, HCBD causes marked over-expression of KIM-1, Cln, and Spp1, and down-expression of Rgn. All the genes appear significantly affected. Cr causes over-expression of KIM-1 and Cln, significantly (p<0.05) lower than HCBD, but not of Rgn and Spp1. At 14-week of age, HCBD further affects gene expression, increasing up-regulation of KIM-1. In contrast to the effects at 6-week of age, Cr causes a further significant (p<0.05) over-expression of KIM-1 and Cln but also down-regulation of Rgn and up-regulation of Spp1. Evaluation of gene expression appears a good and sensitive method to determine nephrotoxicity caused by chemicals. Segment-specific toxicity induced by HCBD (pars recta) or Cr (pars convoluta) is accompanied by modifications in gene expression. In fact, treatment at 6-week of age well differentiates the segment-specific response in expression of some genes such as Rgn and Spp1 that appear influenced by HCBD but not by Cr, suggesting a mainly localization of these genes in S3 segment. Effects of Cr at 14-week of age signify an extension of the damage with aging to the other segments. Aging highly influences the expression of these selected genes caused by HCBD and, above all, by Cr, indicating a major suffering by oxygen deprivation.