Global gene expression profiling on renal scarring in rat model of pyelonephritis

Renal scarring is a serious complication of chronic pyelonephritis due to vesicoureteral reflux, and requires specific biomarker for indication of early intervention. We investigated global expression profile of kidney during renal scarring formation using rat pyelonephritis model. An inoculum of the DS-17 strain Escherchia coli was injected directly into renal cortex of Wister rat. Histologically, renal scarring developed during 3 and 4 weeks after injection. The time course expression profile of approximately 20,500 genes was analyzed using high density oligonucleotide microarray followed by validation using real time RT-PCR. Most of up-regulated genes during this experimental renal scarring were associated with immune and defense response, including cytokines, chemokines, their receptors, complements, and adhesion molecules as well as proteins related to extra cellular matrix. These genes were up-regulated as early as 1 week after injection when histological examination did not show fibrotic change yet, peaked at 2 weeks and gradually decreased thereafter. However, a subset of cytokine genes is persistently activated even in 6 weeks after the injection, which are involved in TGF-β related tissue regeneration pathway or IL-1β related pathway. The products of these genes may potentially be the source of novel non-invasive diagnostic or prognostic biomarkers for renal scarring. Keywords: renal scarring, TGF-β , IL-1β Experimental pyelonephritis was produced by standard method of direct infection of rat kidney. In brief, animals were anesthetized with pentobarbital intraperitoneally. The kidneys were exposed through a midline abdominal incision. An inoculum of 1x109 colony-forming units / 0.1 ml of Escherchia coli was injected directly into bilateral renal cortex of Wister rat using 26-gauge needle. We used DS-17 or NU-14 strains, both of which has type 1 and P pili, and SEC strain, which has only type 1 pili. Control rats received isotonic saline instead of bacterial solution. Both test and control kidneys were harvested at 1, 2, 4 and 6 weeks after injection. The kidney samples (1x1x2 mm each) were obtained including the injection site, which was easily identified by surface color change. Then we cut the kidney into half; one was used for microscopic examination and the other half was immediately frozen in liquid nitrogen for later RNA extraction.