Modulation of renal cell injury by heat shock proteins: Lessons learned from the immature kidney

Division of Pediatric Nephrology at Yale University School of Medicine, New Haven, CT 06520, USA.
Nature Clinical Practice Nephrology (Impact Factor: 6.08). 04/2006; 2(3):149-56. DOI: 10.1038/ncpneph0117
Source: PubMed


The mechanisms that underlie tolerance to injury in immature animals and tissues have been a subject of interest since 1670. Observations in neonatal units that premature infants are less prone to develop acute renal failure than adults in critical care units have prompted a series of investigations. Although initially attributed to metabolic adaptation such as increased glycolytic capacity and preservation of high energy phosphate, more recent studies have indicated a prominent role for the heat shock response. Observed modulations of injury by heat shock proteins in the immature kidney have significant implications for advancement of our understanding of renal cell injury in both adults and children.

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    • "The major underlying pathogenic mechanisms are apoptosis and necrosis of kidney tubular cells [6], in particular in the proximal convoluted tubuli. Many recent studies suggest that chaperones, in particular members of the Hsp70 family, may provide protection against AKI [7] (for recent reviews see [8], [9], [10]). "
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    ABSTRACT: Chronic hyperglycemia is known to increase renal injury, particularly during ischemia-reperfusion episodes. The goal of this study was to examine whether transient hyperglycemia during or after renal ischemia-reperfusion increased renal dysfunction. Male Lewis rats underwent sham operations or unilateral nephrectomies followed by contralateral renal ischemia-reperfusion. Hyperglycemic rats were given 25% dextrose to induce transient hyperglycemia lasting throughout the duration of ischemia (PI rats) or beginning 2 h after initiation of reperfusion (PR rats). Additional vehicle control rats received saline and underwent ischemia-reperfusion surgery as with PI and PR rats. Twenty-five minutes of mild renal ischemia followed by 24 h of reperfusion was induced by occluding the renal artery and vein. Terminal serum creatinine concentrations were significantly higher in the PI rats when compared with the PR or vehicle control rats. Histology demonstrated significantly increased necrosis in the PI rats relative to PR and control animals. Tissue analyses demonstrated significantly higher heat shock protein 70, heat shock protein 32, and cleaved caspase-3 protein levels in the PI rats. Oxidative stress generated through the xanthine pathway in the PI group was significantly increased compared with the oxidative stress in the PR and vehicle control rats. In contrast, vascular endothelial growth factor and erythropoietin were significantly decreased in the PI rats compared with the PR rats and controls. Hyperglycemia that occurred during renal ischemia-reperfusion resulted in severe functional injury compared with normoglycemia or with hyperglycemia that occurred after reperfusion. Investigated molecular pathways are more profoundly affected by hyperglycemia that occurs before renal ischemia-reperfusion.
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    ABSTRACT: Acute kidney injury evokes renal tubular cholesterol synthesis. However, the factors during acute kidney injury that regulate HMG CoA reductase (HMGCR) activity, the rate-limiting step in cholesterol synthesis, have not been defined. To investigate these factors, mice were subjected to 30 minutes of either unilateral renal ischemia or sham surgery. After 3 days, bilateral nephrectomy was performed and cortical tissue extracts were prepared. The recruitment of RNA polymerase II (Pol II), transcription factors (SREBP-1, SREBP-2, NF-kappaB, c-Fos, and c-Jun), and heat shock proteins (HSP-70 and heme oxygenase-1) to the HMGCR promoter and transcription region (start/end exons) were assessed by Matrix ChIP assay. HMGCR mRNA, protein, and cholesterol levels were determined. Finally, histone modifications at HMGCR were assessed. Ischemia/reperfusion (I/R) induced marked cholesterol loading, which corresponded with elevated Pol II recruitment to HMGCR and increased expression levels of both HMGCR protein and mRNA. I/R also induced the binding of multiple transcription factors (SREBP-1, SREBP-2, c-Fos, c-Jun, NF-kappaB) and heat shock proteins to the HMGCR promoter and transcription regions. Significant histone modifications (increased H3K4m3, H3K19Ac, and H2A.Z variant) at these loci were also observed but were not identified at either the 5' and 3' HMGCR flanking regions (+/-5000 bps) or at negative control genes (beta-actin and beta-globin). In conclusion, I/R activates the HMGCR gene via multiple stress-activated transcriptional and epigenetic pathways, contributing to renal cholesterol loading.
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