RNA-seq Analysis Of The Hypothalamic Transcriptome Reveals The Networks Regulating Physiopathological Progress In The Diabetic GK Rat

Type 2 diabetes(T2D),which is characterized by hyperglycaemia,insulin resistance of target tissues and insufficient insulin secretion from pancreatic ?-cells,is a worldwide epidemic that affects more than 415 million people.Approximately one in four cases of diabetes worldwide occur in China.Moreover,T2 D develops at considerably lower BMI values in the Chinese population compared with that of Western white populations.Diabetes caused 5 million deaths in 2015.A suitable animal model is necessary for the research of diabetes.The Goto-Kakizaki(GK)rat is an animal model of non-obese type 2 diabetes.The GK rat is not only characterized by non-obese but also displayed hyperglycaemia,?-cell defects and insulin resistance.GK rats spontaneously develop diabetes and were generated through repeated inbreeding of Wistar rats selected at the upper limit of the normal distribution for glucose tolerance,is one of the best characterized animal models of non-obese T2 D.The mutated genes in GK rats may play key roles in the regulation of diabetes.The hypothalamus controls food intake and plays a central role in energy homeostasis.Additionally,the hypothalamus influences peripheral organs to control the degree of energy expenditure and feeding behaviour by sensing hormones released from peripheral tissues and nutrients from the circulatory system.Dysfunction of the hypothalamus may result in a series of metabolic disorders.A previous study reported that increased Npy m RNA levels in the hypothalamus led to hyperphagia in the GK rats,but the regulatory network in the GK rat hypothalamus is unclear.To investigate the role of the hypothalamus in T2 D pathogenesis in GK rats,we analysed the transcriptomes of the GK rat hypothalamus at 4,8 and 12 weeks by RNA-seq.The results were shown as follows:(1)In total,there were approximately 13,600 genes detected with expression in the hypothalamus.Specifically,compared with Wistar rats,1119,1381 and 1702 differentially expressed genes in GK rats were found at 4,8 and 12 weeks,respectively.The differential gene expression analysis indicated that GK rats had a dysfunctional hypothalamic melanocortin system and attenuation of the hypothalamic glucose-sensing pathway,that may result in the increased food intake and disrupt energy homeostasis in GK rats.(2)Besides,we found 22,783 and 25,582 common variants in 15 Wistar rats and 15 GK rats(reference to Rattus norvegicus),respectively.Overall,there were 5831 and 8630 specific variants in Wistar and GK rats,respectively.Among all the mutation genes,1316 genes with variants were detected only in GK rats,which were defined as GK-specific genes;whereas the number of Wistar-specific genes was 767.The fixed mutations and differentially expressed genes were analysed.The number of variants identified from GK rats was significantly greater than that of Wistar rats,indicating that many variants were fixed and heritable in GK rats after selective inbreeding.(3)In addition,we generated integrated gene network modules by combining the protein-protein interaction(PPI)network,co-expression network and mutations in GK and Wistar rats.In the modules,GK-specific genes,such as Bad,Map2k2,Adcy3,Adcy2 and Gstm6,may play key roles in hypothalamic regulation in GK rats.Our research provides a comprehensive map of the abnormalities in the GK rat hypothalamus,which reveals the new mechanisms of pathogenesis of T2 D.The main innovation points in the present study are listed as follows:(1).We displayed the transcriptomes and mutations of the GK rat hypothalamus at 4,8 and 12 weeks at the first time.We detected the disorder of the melanocortin system and the impairment of the glucose-sensing pathway in GK rats,which may lead to hyperphagia,obstruct signals to glucose-sensitive neurons and further influence the energy homeostasis in GK rats.(2).Several gene network modules,which combined by the PPI network,coexpression network,and enriched for mutations in GK rats,revealed the biological changes from 4 to 12 weeks in the hypothalamus and contributed to diabetes development in GK rats.