Genetic Relatedness of WNIN and WNIN/Ob with Major Rat Strains in Biomedical Research

Prenatal exposure to bisphenol S and bisphenol A differentially affects male reproductive system in the adult offspring

Early exposure to bisphenol may result in adverse reproductive health in later life. The use of bisphenol S (BPS) has increased considerably after bisphenol A (BPA) is regulated worldwide. However, little is known about the fetal exposure to BPS compared with BPA and its effects on the reproductive system in the adult male offspring. Here, we investigated the effects of orally administered BPS and BPA (0.4, 4.0, 40.0 μg/kg bw/d) during gestation (gD4-21) on testicular development by evaluating the sperm DNA damage & methylation and testicular functions in the 90 d Wistar rats. Male offspring prenatally exposed to BPS (0.4 μg/kg) had higher plasma testosterone than BPA and control. The testis histology reveals thickened membrane by producing a wide interstitial gap between seminiferous tubules, increased testicular inflammation, oxidative stress, TIMP-1 expression, and decreased VCAM-1 expression. BPS promotes apoptosis by up-regulating IL-6, cleaved caspases, and a spike in sperm DNA fragmentation. Prenatal BPS exposure reduces sperm motility mediated via impaired PI3K-AKT signaling and increases testicular TEX11 expression in the offspring. Exposure of the fetus to BPS interferes developmental programming of the male reproductive system in the offspring. BPS could be an equally potent endocrine disruptor affecting male reproductive functions.

Advanced glycation end products in brain during aging

Aging is a main risk factor for many diseases including neurodegenerative disorders. Numerous theories and mechanisms including accumulation of advanced glycation end products (AGEs) have been put forward in explaining brain aging. However, a focused study on the status of AGEs in the brain during progressive aging in connection with interrelated cellular processes like ubiquitin-proteasome system (UPS), unfolded protein response, autophagy-lysosome system and apoptosis is lacking. Hence, in this study, we investigated the levels of AGEs in the brain of 5-, 10-, 15- and 20-months old WNIN rats. Endoplasmic reticulum (ER) stress response, UPS components, autophagy flux, neurotrophic and presynaptic markers along with cell death markers were analyzed by immunoblotting. The neuronal architecture was analyzed by H&E and Nissl staining. The results demonstrated progressive accumulation of AGEs in the brain during aging. Adaptive ER stress response was observed by 10-months while maladaptive ER stress response was seen at 15- and 20-months of age along with impaired UPS and autophagy, and perturbations in neuronal growth factors. All these disturbances intensify with age to further exaggerate cell death mechanisms. There was a shrinkage of the cell size with aging and Congo-red staining revealed β-amyloid accumulation in higher ages. Together these results suggest that progressive accumulation of AGEs with aging in the brain may lead to neuronal damage by affecting ER homeostasis, UPS, autophagic flux, and neuronal growth factors.

Strain specific variation underlines the disparity in stress response of rats to calorie dense diets in the pathophysiology of obesity

Obesity is a multifactorial disorder, caused mainly due to lifestyle changes, and increased consumption of calorie dense diets is not just limited to developed countries anymore. Chronic physiological stress and oxidative stress are known to be implicated in the etiology of obesity. However, the role of stress response towards obesity manifestation in genetically different rat strains is poorly understood. In the current study we have used obesity susceptible & resistant rat models to understand the role of both glucocorticoid and oxidativestress in the pathophysiology of obesity. Upon challenge with calorie dense diets, WNIN showed an increased glucocorticoid stress, resulting in increased oxidative stress; whereas such a phenomenon was not noticed in F-344 and SD. However, there was an increase in the circulatory melatonin levels in calorie dense fed groups of both F-344 and SD animals, which might have contributed to reduced oxidative stress. The molecular switch in the activation of melatonin could be possibly attributed to the genetic differences among these strains. It will be interesting to explore other molecular mechanisms for melatonin regulation, albeit increased corticosterone is implicated in the enhanced production of melatonin.

Rat Genome Assemblies, Annotation, and Variant Repository

The first and only published version of the rat reference genome sequence was RGSC3.1, accomplished by the Rat Genome Sequencing Project Consortium. Here we present the history of the community effort in the correction of sequence errors and filling missing gaps in the process of refining and providing researchers with a high-quality rat reference sequence. The genome assembly improvements, addition of different evidence resources over time, such as RNA-Seq data, and software development methodologies had a positive impact on the gene model annotations. Over the years we observed a great increase in the numbers of genes, protein coding sequences, predicted transcripts and transcript features. Before the sequencing of the rat genome was possible, first biochemical and next genomic markers like RAPD, AFLP, RFLP, and SSLP were fundamental in research studies involving cross-breeding between different rat strains, in finding the level of polymorphism, linkage mapping, and phylogeny. Linkage maps provide information on recombination rates, give insight into intra- and interspecies gene rearrangements, and help to identify Mendelian loci and Quantitative Trait Loci (QTL). In the 1990s many reports were published on the construction of rat linkage maps that incorporated increasing numbers of markers and facilitated the localization of disease loci. Current genetic monitoring and linkage mapping relies on single nucleotide polymorphisms (SNPs). The Rat Genome Database collects information on genetic variation from the worldwide community of rat researchers and provides tools for searching and retrieving these data. As of today we show details about almost 605 million variants coming from many studies in our Variant Visualizer tool.

Differential response of rat strains to obesogenic diets underlines the importance of genetic makeup of an individual towards obesity

Obesity, a multifactorial disorder, results from a chronic imbalance of energy intake vs. expenditure. Apart from excessive consumption of high calorie diet, genetic predisposition also seems to be equally important for the development of obesity. However, the role of genetic predisposition in the etiology of obesity has not been clearly delineated. The present study addresses this problem by selecting three rat strains (WNIN, F-344, SD) with different genetic backgrounds and exposing them to high calorie diets. Rat strains were fed HF, HS, and HFS diets and assessed for physical, metabolic, biochemical, inflammatory responses, and mRNA expression. Under these conditions: significant increase in body weight, visceral adiposity, oxidative stress and systemic pro-inflammatory status; the hallmarks of central obesity were noticed only in WNIN. Further, they developed altered glucose and lipid homeostasis by exhibiting insulin resistance, impaired glucose tolerance, dyslipidemia and fatty liver condition. The present study demonstrates that WNIN is more prone to develop obesity and associated co-morbidities under high calorie environment. It thus underlines the cumulative role of genetics (nature) and diet (nurture) towards the development of obesity, which is critical for understanding this epidemic and devising new strategies to control and manage this modern malady.