Renal Ischemia-Induced Cholesterol Loading

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-B, 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-B) 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 (␤-actin and ␤-globin). In conclusion, I/R activates the HMGCR gene via multiple stress-activated transcriptional and epigenetic pathways, contributing to renal cholesterol loading.

Functional Promoter Polymorphisms Govern Differential Expression of HMG-CoA Reductase Gene in Mouse Models of Essential Hypertension

“…A recent study reported recruitment of c-Fos to the Hmgcr promoter for transcriptional regulation under acute kidney injury in mice [43]. The transcription factor n-Myc is a basic helix-loop-helix leucine zipper (bHLH-ZIP) protein that heterodimerizes with the transcription factor Max and play important roles in neuronal differentiation and cell proliferation [44]–[48].…”

Early Growth Response 1 (Egr1) Regulates Cholesterol Biosynthetic Gene Expression

“…One of the best studied cholesterol biosynthetic promoters is that of the Hmgcr gene (56,57). Hmgcr activity is the ratelimiting step for cholesterol synthesis; consequently, many regulatory molecules affect this gene and gene product as a means of regulating the cholesterol biosynthetic pathway.…”

Role of Cellular Cholesterol in Pharmacologic Preconditioning with Cyclosporine in Experimental Kidney Transplantation

“…In a maleate nephrotoxicity model, renal cortical cholesterol content increased in response to injury along with doubling of HMG CoA reductase (HMGCR) mRNA levels, indicating an increase in synthesis [20,26]. Similarly, in a model of renal IRI, cholesterol loading was associated with elevated recruitment of RNA polymerase II to HMGCR and increased expression of HMGCR protein and mRNA [21,27]. Finally, dysregulation in the cholesterol efflux proteins SR-B1 and ABCA-1 and in LDL receptor was also shown to contribute to a cholesterol overload state in the injured kidney [22,28].…”