Transcriptome profiling of visceral adipose tissue in a novel obese rat model, WNIN/Ob & its comparison with other animal models.

BACKGROUND & OBJECTIVES: Adipose tissue dysfunction in obesity is linked to the development of type 2 diabetes and cardiovascular diseases. We studied the differential gene expression in retroperitoneal adipose tissue of a novel obese rat model, WNIN/Ob, to understand the possible underlying transcriptional changes involved in the development of obesity and associatedcomorbidities in this model. METHODS: Four month old, male WNIN/Ob lean and obese rats were taken, blood was collected and tissues were dissected. Body composition analysis and adipose tissue histology were performed. Global gene expression in retroperitoneal adipose tissue of lean and obese rats was studied by microarray using Affymetrix GeneChips. RESULTS: One thousand and seventeen probe sets were downregulated and 963 probe sets were upregulated (more than two-fold) in adipose tissue of WNIN/Ob obese rats when compared to that of lean rats. Small nucleolar RNA (SnoRNA) made most of the underexpressed probe sets, whereas immune system-related genes werethe most overexpressed in the adipose tissues of obese rats. Genes coding for cytoskeletal proteinswere downregulated, whereas genes related to lipid biosynthesis were elevated in the adipose tissue of obese rats. INTERPRETATION & CONCLUSIONS: Majority of the altered genes and pathways in adipose tissue of WNIN/Ob obese rats were similar to the observations in other obese animal models and human obesity. Based on these observations, it is proposed that WNIN/Ob obese rat model may be a good model to study the mechanisms involved in the development of obesity and its comorbidities. Downregulation of SnoRNA appears to be a novel feature in this obese rat model.

Vitamin A supplementation ameliorates obesity-associated retinal degeneration in WNIN/Ob rats.

OBJECTIVE: Obesity is associated with various health afflictions, including ocular complications such as diabetic retinopathy, high intraocular pressure, cataracts, and macular degeneration. We previously reported progressive retinal degeneration after the onset of obesity in the spontaneously obese rat (WNIN/Ob) model. In the present study, we investigated vitamin A supplementation to ameliorate obesity-associated retinal degeneration in the WNIN/Ob rat. METHODS: Five-month-old male WNIN/Ob obese (O) and lean (L) control rats were fed with vitamin A 2.6 mg (L/O-I), 26 mg (L/O-II), 52 mg (L/O-III), and 129 mg (L/O-IV) per kilogram of diet as retinyl palmitate for 4 mo 2 wk. Retinal morphology and retinal gene expression were assessed by histologic, immunohistochemical, and real-time polymerase chain reaction methods. RESULTS: Supplementation of vitamin A at 26 or 52 mg significantly modulated the expression of retinal genes in the O but not in the L phenotype. Vitamin A supplementation significantly upregulated the expression of genes, such as rhodopsin, rod arrestin, phosphodiesterase, transducins, and fatty acid elongase-4, that were otherwise downregulated in O rat retina. The expression of glial fibrillary acidic protein was downregulated by vitamin A feeding in O rat retina. The immunohistochemical and histologic findings corroborated the gene expression data. The effects were significant at a 26- or 52-mg dose of vitamin A. CONCLUSION: Vitamin A supplementation alleviated obesity-associated retinal degeneration in the WNIN/Ob rat.

Carbenoxolone treatment ameliorated metabolic syndrome in WNIN/Ob obese rats, but induced severe fat loss and glucose intolerance in lean rats.

BACKGROUND: 11beta-hydroxysteroid dehydrogenase type 1 (11ß-HSD1) regulates local glucocorticoid action in tissues by catalysing conversion of inactive glucocorticoids to active glucocorticoids. 11ß-HSD1 inhibition ameliorates obesity and associated co-morbidities. Here, we tested the effect of 11ß-HSD inhibitor, carbenoxolone (CBX) on obesity and associated comorbidities in obese rats of WNIN/Ob strain, a new animal model for genetic obesity. METHODOLOGY/PRINCIPAL FINDINGS: Subcutaneous injection of CBX (50 mg/kg body weight) or volume-matched vehicle was given once daily for four weeks to three month-old WNIN/Ob lean and obese rats (n = 6 for each phenotype and for each treatment). Body composition, plasma lipids and hormones were assayed. Hepatic steatosis, adipose tissue morphology, inflammation and fibrosis were also studied. Insulin resistance and glucose intolerance were determined along with tissue glycogen content. Gene expressions were determined in liver and adipose tissue. CBX significantly inhibited 11ß-HSD1 activity in liver and adipose tissue of WNIN/Ob lean and obese rats. CBX significantly decreased body fat percentage, hypertriglyceridemia, hypercholesterolemia, insulin resistance in obese rats. CBX ameliorated hepatic steatosis, adipocyte hypertrophy, adipose tissue inflammation and fibrosis in obese rats. Tissue glycogen content was significantly decreased by CBX in liver and adipose tissue of obese rats. Severe fat loss and glucose- intolerance were observed in lean rats after CBX treatment. CONCLUSIONS/SIGNIFICANCE: We conclude that 11ß-HSD1 inhibition by CBX decreases obesity and associated co-morbidities in WNIN/Ob obese rats. Our study supports the hypothesis that inhibition of 11ß-HSD1 is a key strategy to treat metabolic syndrome. Severe fat loss and glucose -intolerance by CBX treatment in lean rats suggest that chronic 11ß-HSD1 inhibition may lead to insulin resistance in normal conditions.

Vitamin A decreases pre-receptor amplification of glucocorticoids in obesity: study on the effect of vitamin A on 11beta-hydroxysteroid dehydrogenase type 1 activity in liver and visceral fat of WNIN/Ob obese rats.

BACKGROUND: 11ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1) catalyzes the conversion of inactive glucocorticoids to active glucocorticoids and its inhibition ameliorates obesity and metabolic syndrome. So far, no studies have reported the effect of dietary vitamin A on 11ß-HSD1 activity in visceral fat and liver under normal and obese conditions. Here, we studied the effect of chronic feeding of vitamin A-enriched diet (129 mg/kg diet) on 11ß-HSD1 activity in liver and visceral fat of WNIN/Ob lean and obese rats. METHODS: Male, 5-month-old, lean and obese rats of WNIN/Ob strain (n = 16 for each phenotype) were divided into two subgroups consisting of 8 rats of each phenotype. Control groups received stock diet containing 2.6 mg vitamin A/kg diet, where as experimental groups received diet containing 129 mg vitamin A/Kg diet for 20 weeks. Food and water were provided ad libitum. At the end of the experiment, tissues were collected and 11ß-HSD1 activity was assayed in liver and visceral fat. RESULTS: Vitamin A supplementation significantly decreased body weight, visceral fat mass and 11ß-HSD1 activity in visceral fat of WNIN/Ob obese rats. Hepatic 11ß-HSD1 activity and gene expression were significantly reduced by vitamin A supplementation in both the phenotypes. CCAAT/enhancer binding protein α (C/EBPα), the main transcription factor essential for the expression of 11ß-HSD1, decreased in liver of vitamin A fed-obese rats, but not in lean rats. Liver × receptor α (LXRα), a nuclear transcription factor which is known to downregulate 11ß-HSD1 gene expression was significantly increased by vitamin A supplementation in both the phenotypes. CONCLUSIONS: This study suggests that chronic consumption of vitamin A-enriched diet decreases 11ß-HSD1 activity in liver and visceral fat of WNIN/Ob obese rats. Decreased 11ß-HSD1 activity by vitamin A may result in decreased levels of active glucocorticoids in adipose tissue and possibly contribute to visceral fat loss in these obese rats. Studying the role of various nutrients on the regulation of 11ß-HSD1 activity and expression will help in the evolving of dietary approaches to treat obesity and insulin resistance.