Effects Of Different Fatty Acids On Central Fatty Acid Sensing System And Appetite Regulation Of Chinese Perch(Siniperca Chuatsi)

The fatty acid sensing mechanism of the central nervous system is an important regulatory mechanism to detect circulating fatty acid levels,participate in physiological metabolism,regulate food intake,and maintain energy balance and homeostasis in fish.Chinese perch(Siniperca chuatsi)is a typical freshwater carnivorous fish because of its special feeding behavior,that is,it eats live bait from the beginning,usually refusing to eat dead bait and artificial compound feed.In addition,Chinese perch have a lower ability to utilize carbohydrates,so lipids are an important source of energy.Therefore,in this study,Chinese perch was used as a model of typical fierce freshwater fish.The effects of different fatty acids on the central fatty acid sensing system and appetite regulation mechanism of Chinese perch were investigated in vivo and cell experiments,respectively.First,the effects of different fatty acids on Chinese perch feeding and lipid metabolite levels were evaluated in vivo experiments.Secondly,the molecular mechanism of central nervous system sensing of different fatty acids and feeding regulation was analyzed from the m RNA level by RTPCR technology.Finally,at the cellular level,RT-PCR detection and PPARα specific inhibitor treatment and other biological technologies were used to verify the direct perception of unsaturated fatty acids(UFAs)by the central nervous system of Chinese perch and the key role of PPARα in the process of fatty acid sensing.This study aims to provide theoretical support for fatty acid metabolism and feeding regulation mechanism of Chinese perch.In experiment one,in order to study fatty acid sensing systems of Chinese perch hypothalamus and its sensitivity to fatty acids with different saturation levels.The effects of Stearate(SA;C18:0),oleate(OA;C18:1 n-9),linoleic acid(LA;C18:2 n-6),and α-linolenic acid(ALA;C18:3 n-3)on hypothalamus of Chinese perch were evaluated by intracerebroventricular administration.Food intake was calculated at 2,4,6,8,and 12 hours after intraventricular injection.The expression of genes related to fatty acid sensing mechanisms such as cd36,cpt1 c,pparα and srebp1 c,and hypothalamic appetite-related neuropeptides,such as pomc,cart,agrp and npy were detected 6 hours after intraventricular injection.The results showed that intraventricular injection of OA,LA and ALA can activate FAT / CD36 and PPARα in the fatty acid sensing signal pathway and regulate the expression level of hypothalamic appetite-related neuropeptide genes.Furthermore,a significant decrease in food intake was observed 6 and 8 hours after intraventricular injection of OA,LA and ALA,which was consistent with the activation of the hypothalamus fatty acid sensing system.Studies showed that some mechanisms of hypothalamic fatty acid sensing systems observed in mammals also existed in Chinese perch,that is,it can also be activated by monounsaturated fatty acids(MUFA).It is worth noting that polyunsaturated fatty acids(PUFA)can also activate the hypothalamus fatty acid perception system of Chinese perch.In addition,the unsaturation of fatty acid appears to be extremely important for fatty acid sensing mechanisms,since no major influences in Chinese perch after SA treatment.Our findings will contribute to the study of the fatty acids sensing in fish hypothalamus and highlight the important role of polyunsaturated fatty acids in fish.In experiment two,in order to verify that the catfish central nervous system fatty acid sensing system can directly sense UFAs without relying on peripheral signal transduction and other hormones,we conducted further research at the cellular level.We stimulated Chinese perch brain cells by adding 100 μM OA,LA and ALA to the cell culture medium,extracting cellular RNA after 6 h incubation,and detecting the expression of genes related to fatty acid perception mechanisms,such as fas,cpt1 c,cd36,pparα and srebp1 c,And the gene expression of appetite-related neuropeptides npy in brain cells of Chinese perch.The results show that OA,LA,and ALA can directly activate fatty acid sensing signal pathways and regulate the gene expression level of npy.Therefore,our research has shown that UFAs can directly act on fatty acid-sensing neurons in the brain of Chinese perch.In the third experiment,in order to further explore the function of PPARα in the fatty acid perception of Chinese perch brain neurons and the effect on other fatty acid metabolic factors.By adding 100 μM of OA,LA and ALA plus PPARα-specific inhibitors to the cell culture medium and incubating brain cells for 6 hours,we also extracted cellular RNA to detect fatty acid sensing mechanism-related genes(fas,cpt1 c,cd36,pparα and srebp1c)and the expression level of the appetite neuropeptide npy.The results showed that after the nuclear receptor PPARα function was inhibited,OA,LA,and ALA could not activate the fatty acid sensing signal pathway of catfish brain cells,resulting in no significant change in the expression level of npy.Therefore,PPARα as a key transcription factor for fatty acid metabolism,plays an important role in the fatty acid sensing mechanism of catfish.To sum up,we explored the action mechanisms of different fatty acids on the central fatty acid perception system and feeding regulation of Chinese perch from the living level and the cellular level,respectively.The results found that fatty acid saturation is the key to whether fatty acids can be sensed by the central nervous system.In addition,unsaturated fatty acids may activate the central fatty acid sensing system through fatty acid metabolism(fas,cpt1c)and fatty acid transport(FAT/CD36)pathways,which can regulate the expression of downstream appetite genes(pomc,cart,agrp and npy),thereby regulating the appetite of Chinese perch.This will provide an important theoretical basis for the study of fish fatty acid sensing and food regulation mechanism.