ABSTRACT: Estrogen is a reproductive steroid hormone that has both beneficial and detrimental effects on the cardiovascular system. Selective estrogen receptor modulators (SERMs) exhibit partial estrogen agonist/antagonist activity in estrogen target tissues. Since we still have an incomplete picture of the gene targets of estrogen in the vasculature, and our understanding of SERM gene targets in the vasculature is even less well-developed, it is important to broaden the available information on this subject. The present study tested the hypothesis that estrogens (ethinyl estradiol, estradiol benzoate, and equilin) and SERMs (tamoxifen and raloxifene) cause differential gene and protein expression in the vasculature. DNA microarray and real-time RT-PCR were used to investigate gene expression in the mesenteric arteries of estrogen and SERM treated ovariectomized rats. The genes shown to be differentially expressed included stearoyl-CoA desaturase (SCD), soluble epoxide hydrolase (sEH), secreted frizzled related protein-4 (SFRP-4), insulin-like growth factor-1 (IGF-1), phospholipase A2 group 1B (PLA2-G1B), and fatty acid synthase (FAS). Western blot further confirmed the differential expression of sEH, SFRP-4, FAS, and SCD protein. These results reveal that estrogens and SERMs cause differential gene and protein expression in the mesenteric artery. Consequently, the use of these agents may be associated with a unique profile of functional and structural changes in the mesenteric arterial circulation. Goal of the experiment: To examine the effects of three formulations of estrogen (ethinyl estradiol, equilin, and estradiol benzoate) and of the selective estrogen receptor modulators, tamoxifen and raloxifene, on gene expression in the mesenteric arteries of the rat. Keywords: rat, artery, gene expression, mesentery, estrogen, tamoxifen, raloxifene Experimental factors: hormone treatment, drug treatment Experimental design: Prepubertal female Sprague Dawley rats (Harlan, Indianapolis, IN) were ovariectomized at 4 weeks of age, prior to the initiation of regular ovarian cycles. The animals were allowed to recover for 2 weeks before the experimental protocol was initiated. The rats were randomly divided into 6 groups (n=3-4/group) and treated by daily gavage for 3 weeks with the vehicle (20% 2-hydroxypropyl-β-cyclodextrin, Sigma, St Louis, MO), ethinyl estradiol (EE, 0.15 mg/kg; Sigma), estradiol benzoate (EB, 0.15 mg/kg; Sigma), equilin (EQ, 0.15 mg/kg; Sigma), tamoxifen (TAM, 3 mg/kg; Sigma), or raloxifene (RAL, 3 mg/kg; Eli Lilly & Co., Indianapolis, IN). After 3 weeks of treatment, the rats were euthanized and the mesentery obtained. Total RNA was extracted from each individual sample and used for the synthesis of labeled cRNA for microarray analysis. After the final gavage treatment on day 21, the rats were deeply anesthetized with isoflurane and euthanized by decapitation. The mesenteric arterial tree was isolated and harvested and stored in RNAlater (Ambion) at -80ºC. The mesenteric arteries were dissected free from veins and surrounding fat and homogenized in TRI reagent (MRC, Cincinnati, OH). Mesenteric artery RNA was extracted and purified using an RNeasy Mini Kit (Qiagen). Any potentially contaminating DNA was removed by treatment with RNase-free DNase (Qiagen) on the RNeasy column. Total RNA was quantified and RNA integrity was assessed using the Agilent Bioanalyzer (Santa Clara, CA). Following analysis, the RNA was stored at -80ºC until it was used for gene expression studies. DNA microarray: CodeLink Whole Rat Genome Bioarrays (Applied Microarrays, Tempe, AZ) were used. Five μg total RNA was used from each mesenteric arterial sample for the microarray analysis. Complementary RNA was synthesized per company protocol (Ambion). A set of bacterial RNAs was added to each total RNA sample and carried through the synthesis and labeling reactions as controls and for nor¬malization of the data. The microarrays were scanned with the GenePix 4000B (Axon Instruments, Union City, CA) with GenePix Pro 5.0 software (Axon Instruments). Analysis of the microar¬rays was performed with the CodeLink Expression Analysis software (Applied Microarrays) and Acuity 3.1 software (Axon), and statistical analysis was performed with GeneSpring 7.1 software (Agilent, Santa Clara, CA). A sample of n=3 was completed with the microarrays for each treatment. Quality control steps: The cRNA that was synthesized from each mesenteric artery treatment sample was used for hybridization to a single CodeLink (Applied Microarrays) whole rat genome microarray. Only one sample was hybridized with each slide and only one dye (streptavidin-Alexa 647) was used so no dye swaps were used. Bacterial control spikes were used per manufacturer's instructions. Samples used, extract preparation and labeling: The origin of each biological sample: The samples were isolated mesenteric arteries from individual Sprague Dawley rats that had been treated by daily gavage for 3 weeks with the vehicle (20% 2-hydroxypropyl-β-cyclodextrin, Sigma, St Louis, MO), ethinyl estradiol (EE, 0.15 mg/kg; Sigma), estradiol benzoate (EB, 0.15 mg/kg; Sigma), equilin (EQ, 0.15 mg/kg; Sigma), tamoxifen (TAM, 3 mg/kg; Sigma), or raloxifene (RAL, 3 mg/kg; Eli Lilly & Co., Indianapolis, IN). Manipulations of biological samples and protocols used: Ovariectomized female rats were treated by daily gavage for 3 weeks with the vehicle (20% 2-hydroxypropyl-β-cyclodextrin, Sigma, St Louis, MO), ethinyl estradiol (EE, 0.15 mg/kg; Sigma), estradiol benzoate (EB, 0.15 mg/kg; Sigma), equilin (EQ, 0.15 mg/kg; Sigma), tamoxifen (TAM, 3 mg/kg; Sigma), or raloxifene (RAL, 3 mg/kg; Eli Lilly & Co., Indianapolis, IN). After the final gavage treatment on day 21, the rats were deeply anesthetized with isoflurane and euthanized by decapitation. The mesenteric arterial tree was isolated, harvested, and stored in RNAlater (Ambion) at -80ºC. The mesenteric arteries were dissected free from veins and surrounding fat and homogenized in TRI reagent (MRC, Cincinnati, OH). Experimental factor: hormone treatment, drug treatment Technical protocols: The mesenteric arteries were minced with scalpels and TRI reagent (MRC) was added. The tissue was homogenized with a Polytron homogenizer. Bromochloropropane and sodium acetate were added, and the samples were centrifuged to separate the phases. The RNA-containing layer was removed and the RNA purified on an RNeasy extraction column (Qiagen). The sample was treated with an on-column DNase treatment (RNase-free DNase, Qiagen). The purity and quantity were evaluated by an Agilent Bioanalyzer using the RNA 6000 Nanoassay LabChip. Labeled cRNA was prepared using the Message Amp II-Biotin Enhanced Kit from Ambion, following the manufacturer's Instruction Protocol. 5.0 microgram of rat mesenteric artery total RNA was mixed with bacterial control RNA spikes and primed with T7 oligo(dT) primer for 10 min at 70C. (The bacterial control spikes included araB, entF, fixB, gnd, hisB, and leuB.) The first strand of cDNA was synthesized with first strand buffer, dNTP mix, RNase inhibitor, and reverse transcriptase for 2 h at 42C. The second strand cDNA synthesis reaction was prepared using second strand buffer, dNTP mix, DNA polymerase mix, and RNase H; the reaction was carried out for 2h at 16C. The double-stranded cDNA was purified on spin columns included in the Ambion kit. The double-stranded cDNA was mixed with T7 reaction buffer, T7 ATP, T7 GTP, T7 UTP, T7 CTP, biotin-11-UTP, and T7 enzyme mix for the synthesis of cRNA. The cRNA synthesis reaction was terminated after 14h at 37C by purifying the cRNA on spin columns from the Ambion kit. The concentration of cRNA was determined by spectrophotometry. Hybridization procedures and parameters: 10 micrograms of biotinylated cRNA was mixed with fragmentation buffer and heated to 94C for 20 min. The fragmented cRNA was mixed with CodeLink hybridization buffer, loaded on the microarray slides (CodeLink Whole Rat Genome Bioarrays), and hybridized for 18 hours at 37C. The slides were washed in 0.75x TNT (Tris-HCl, NaCl, Tween-20) at 46C for 1h then incubated with streptavidin-Alexa 647 fluorescent dye for 30 min at room temperature. The streptavidin-Alexa 647 fluor was prepared in TNB blocking buffer (0.1M Tris-HCl, 0.15M NaCL, 0.5% NEN Blocking Reagent-PerkinElmer) The slides were then washed 4 times for 5 min each in 1x TNT and twice in 0.05% Tween 20 for 5 sec each. The slides were dried by centrifugation and scanned in an Axon GenePix 4000B scanner.
