ABSTRACT: The renal mesangial cells play an important role in the development of diabetic glomerulosclerosis and renal failure. We have previously demonstrated some of the effects of high glucose are mediated via the hexosamine biosynthesis pathway (HBP) in which fructose-6-phosphate is converted to glucosamine-6-phosphate by the rate-limiting enzyme glutamine:fructose-6-phosphate amidotransferase (GFAT). Using Affymetrix murine expression U430 2.0 chips, we examined the global effects of high glucose (HG) and glucosamine (GlcN) on the transcriptomes of a mouse mesangial cell line (MES-13). Of the 34,000 genes on the chip, ~55-60% genes are detected in MES-13 cells. HG induces the expression of ~369 genes at >2-fold where 263 genes are up and 106 genes down regulated. Similarly, GlcN increases the expression of 120 genes and decreases 94 genes. Seventy-two genes are commonly regulated by HG and GlcN, in which 33 genes are up and 39 genes are down. The differential expressions of several genes found in the microarray are also confirmed by quantitative PCR. Significant pathways co-modulated by HG and GlcN are the thioredoxin system (a 20-fold increase in thioredoxin interacting protein expression), endoplasmic reticulum (ER) stress, extracellular matrix and interferon-inducible genes. Furthermore, HG and GlcN target various intracellular pathways including the mitogen-activated protein kinase, TOLL-like receptor, fructose and mannose metabolism, and the biosynthesis of steroids and N-glycans. We conclude from this microarray data and other experimental results that the HBP mediates several effects of high glucose on mesangial cell metabolism, which promotes ER stress, oxidative stress and the interferon-inducible gene expression to cause cell cycle arrest, ECM gene expression and apoptosis. Cell culture: Stable murine mesangial (MES-13) cells transformed with non-capsid-forming SV-40 virus were obtained from the ATCC, Manassas, VA. These cells display a differentiated mesangial cell phenotype including the typical spindle-like appearance, positive staining for vimentin and desmin, and contraction in response to ANG II and expression of AT1 receptor. The cells were maintained in DMEM and F-12 Nutrient Mixture (Ham's) (4:1 ratio) (GIBCO BRL, Gaithersburg, MD) containing a normal D-glucose concentration of 5.5 mmol/L, 2% FCS, 100 µg/ml streptomycin, 100 U/ml penicillin, and 2 mmol/L glutamine (26). The cells were incubated in a humidified incubator of 5% CO2 at 37 °C and routinely passaged at confluence every 3 days by trypsinization using 10-cm culture dishes. Approximately 50% confluent monolayers were starved in the above medium without FCS for 1 day and then incubated in the starvation medium with the desired concentrations of glucose and GlcN for 48h (LG, 5.5 mM; HG, 25 mM and GlcN, 1.5 mM + LG). Total RNA isolation, cDNA and cRNA synthesis and genechip hybridization: Total RNA was isolated using Trizol reagent (Life Technologies, Inc., Massachusetts). cDNA and cRNA synthesis, genechip hybridization, and scanning of the Affymetrix murine expression U430 2.0 chips (the Affymetrix U430 2.0 chip contains 39,000 transcripts targeted at 34,000 well characterized genes) were performed according to the manufacturer's protocol (Affymetrix, Santa Clara, CA). Briefly, 5 mg of RNA (from LG, HG and GlcN treated MES-13 cells) was converted into double-stranded cDNA by reverse transcription using a cDNA synthesis kit (SuperScript Choice, Life Technologies, Inc., MA) with an oligo(dT) 24 primer containing a T7 RNA polymerase promoter site added 3' of the poly(T) (Genset, La Jolla, CA). After second-strand synthesis, labeled cRNA was generated from the cDNA sample by an in vitro transcription reaction supplemented with biotin-11-CTP and biotin-16-UTP (Enzo, Farmingdale, NY). The labeled-cRNAs were purified in RNeasy spin columns (Qiagen, Valencia, CA). Fifteen mg of each cRNA was fragmented at 94 °C for 35 min in a fragmentation buffer (40 mM Tris acetate, pH 8.1, 100 mM potassium acetate, 30 mM magnesium acetate). These cRNA fragments were then used to prepare 300 ml of hybridization mixture (100 mM MES, 0.1 mg/ml herring sperm DNA (Promega), 1M sodium chloride, 10 mM Tris, pH 7.6, 0.005% Triton X-100). The solution was equilibrated at 45 °C for 5 min and clarified by centrifugation (14,000 x g) at room temperature for 5 min. Aliquots of each sample (10 mg of cRNA in 200 ml of the mater mix) were hybridized to GeneChip Mouse Genome U430 2.0 Array at 45 °C for 16 h in a rotisserie oven set at 60 rpm. After the overnight hybridization, the chips were washed with a non-stringent wash buffer (6x saline/sodium phosphate/EDTA) at 25 °C, followed by a stringent wash buffer (100 mM MES (pH 6.7), 0.1 M NaCl, 0.01% Tween-20) at 50 °C. The GeneChips were then stained with streptavidin-phycoerythrin (Molecular Probe), washed with 6x saline/sodium phosphate/EDTA, incubated with biotinylated anti-streptavidin lgG, followed by a second staining with streptavidin-phycoerythrin. Finally, a third wash with 6x saline/sodium phosphate/EDTA was performed using the GeneChip Fluidics Station 450. The arrays were then scanned in a GeneChip Scanner 3000 (Affymetrix). Each experiment was repeated twice. Microarray Data analysis: The chips were read with Affymetrix GCOS v1.2, and the probe intensity files were modeled with DChip 1.3 (Harvard School of Public Health) in both PM-only and PM-MM modes. Consensus differentially regulated genes were initially derived from repeat experiments on the bases of a 90% CI of greater than 2-fold change in expression and with p<0.05 of error in paired t-test across repeats. This was further validated through modeling of variance between sample groups (one-way ANOVA) conducted in GeneSpring 6 (Silicon Genetix). The consensus gene-set was clustered in DChip and GeneSpring 6.0, with OntoExpress (Wayne State University) to explore ontological associations. Further ontological and pathway analyses were conducted with the GeneGo software and NIH's DAVID bioinformatics programs (http://appls.niaid.nih.gov/david).
