Dietary Restriction-induced Fto Expression Alternation And Its Machanisms

OBJECTIVENowdays obesity has reached epidemic proportions in worldwide. The etiology of obesity is complex, and seems to be based on both environmental and multiple genetic factors. Heritability of obesity is high and genetic factors contribute 40-70% to the development of obesity. Genome-wide association, the latest gene-finding strategy, has led to the first major success in the field of obesity genetics with the discovery of FTO (fat mass and obesity associated gene) as an obesity-susceptibility gene.Although the genetic variants of FTO is found to be associated with obesity and type 2 diabetes, the functional role of FTO and the regulation of FTO expression in peripheral metabolic tissues and central nervous system (CNS) remain elusive. We investigated the influence of dietary restriction (DR) on FTO expression in periphery and CNS,and the potential relationship between FTO and STAT3 signaling pathway.RESEARCH DESIGN AND METHODS1.FTO mRNA and FTO protein expression in various tissues were examined by RT-PCR, real-time PCR and western blotting.2.The changes of FTO expression after 8 weeks and 50 weeks of DR were examined by real-time PCR and western blotting.3.Double-immunofluorescence staining and co-immunoprecipitation were performed to investigate the association between FTO and leptin receptor long isoform (OB-Rb).4. The underlying mechanisms were further explored using db/db mice in vivo. The mice ware divided into 4 groups:db/db-AL group,db/db-DR group,WT-AL group and WT-DR group.we determined the FTO expression in db/db mice and their WT control mice. We investigated the STAT3,GSK3 and JAK2 pathways under DR stimulation in hypothalamus and brainstem of WT and db/db mice.5.Culture C57 mouse isolated arcuate nucleus of hypothalamus (ARH) in vitro. Give leptin and STAT3,GSK3 and JAK2 circuits' inhibitors, and then examine FTO protein with western blotting.RESULTS1.FTO is ubiquitously expressed in animal tissues with high abundance in the brain and skeletal muscle.2.Two kinds of DR (8 and 50 weeks) decreased the FTO expression in hypo-thalamus and brainstem rather than in periphery in rats.3.FTO colocalized with OB-Rb in the arcuate nucleus of hypothalamus and the nucleus of the solitary tract, whereas the direct interaction between these two proteins were not observed.4. In OB-Rb mutant db/db mice, the FTO downregulation in CNS and weight loss induced by DR (8 weeks) were totally abolished. Moreover, the activation of STAT3 signaling pathway induced by DR was impaired in db/db mice, but the activation of GSK3,JAK2 signaling pathway induced by DR was unimpaired in db/db mice.5.In WT mice,8 weeks of DR induced conspicuous weight loss. Surprisingly, this effect was totally abolished in db/db mice.6.Culture C57 mouse isolated arcuate nucleus of hypothalamus (ARH) in vitro. leptin treatment downregulated FTO in ARH cultures in vitro, which was prevented by STAT3 specific inhibitor, but not GSK-3 or JAK2 inhibitor.CONCLUSIONSOur results provide the first evidence that DR modulates FTO expression in an OB-Rb-dependent manner in CNS.We found that the OB-Rb was essential for the effect of DR on FTO expression, and STAT3 signaling pathway might contribute to this process.We also used different methods to evaluate the expression of FTO in several metabolic sensitive tissues both in periphery and CNS.FTO is high expressed in brain and skeletal muscle.DR decreased the FTO expression in hypothalamus and brainstem.