The Study Of The Metabolic And Physiological Characteristics Of Adipose Tissue And Adipocytes In Nile Tilapia,Oreochromis Niloticus

This study used the technology and methods related to nutrition,biochemistry,molecular biology and cell biology,combining with the magnetic resonance imaging(MRI)technology to study the the differences in different adipose tissues in Tilapia and the effects of exogenous fatty acids on the proliferation and differentiation of adipocyte.In this study,we used magnetic resonance imaging and H&E staining to determine the differences in the distribution and morphological structure of visceral adipose tissue(VAT)and subcutaneous adipose tissue(SCAT)in Tilapia.After the experiments in vivo and in vitro,we determined the different metabolic functions between VAT and SCAT.We found that SCAT is active in metabolism,while VAT has a negative impact on fish life activities.In order to further understand the effects of nutrient conditions on fat deposition in Tilapia,we established the adipocyte model to explore the role of exogenous fatty acids on the proliferation and differentiation of adipocyte.In the study,we provide a new technical method for current fish aquaculture in the excessive deposition of fat.The main research results and conclusions are as follows:1.The physiological and metabolic differences between VAT and SCAT in TilapiaIn mammals,it has been confirmed that VAT and SCAT are different in the distribution,morphology and metabolism.VAT are closely related to diabetes,hypertension and hyperlipidemia;on the contrary,SCAT can improve insulin sensitivity.However,researches on differences between VAT and SCAT have not seen in fish.In order to explore the differences between VAT and SCAT in Tilapia,we firstly used the MRI and H&E staining to determine the differences in the distribution and morphological structure of VAT and SCAT.After that,we determined the differences of cell metabolism in different adipose tissues with vivo and vitro experiments.Our results showed that SCAT contains the larger adipocyte,higher lipolysis efficiency,concentration of mitochondria fatty acid oxidation,lipid synthesis and expression of marker gene of brown fat but the inflammation gene and adipocyte differentiation gene expression was lower compared with VAT.In conclusion,the metabolic activity of SCAT is more exuberant,and the excessive deposition of VAT has a negative impact on the activities of life.To be same with mammals,in Tilapia,VAT could cause the hyperglycemia,hypertension and other metabolic diseases while SCAT can improve insulin sensitivity.2.Establishment of primary adipocytes culture model in TilapiaIn the first part of our experiments,we have confirmed that VAT deposition has a negative impact on the metabolic activity of Tilapia.As we know that the fat deposition is mainly include hyperplasia of adipose tissue(proliferation of fat cells)and hypertrophy of adipose tissue(differentiation of fat cells).Therefore,the main contents of this part of the work is to establish the tilapia fat cells in vitro.Nextly,we would discusses the effects of exogenous nutrients on the proliferation and differentiation of adipocytes.Through aseptic operation,preadipocytes is isolated from VAT in Tilapia,cultured in grow medium(DMEM/F12 containing 15%fetal bovine serum).The density was 2～3 ×105 cell/ml,under the condition of 28 ℃,5%CO2.After cultured for 7 days,cells can grow to confluence.Then the cell were cultured in the differentation medium for 12 days.At last,the cells were stained with oil red O dye.The establishment of the cell model was used to pave the way for the study of the effects of exogenous fatty acids on the proliferation and differentiation of adipocytes.3 Effects of different fatty acids on the proliferation and differentiation of tilapia primary adipocytesIn the front of the experiments,we had established the model of adipocyte.In this part,first of all,we added four kinds of exogenous fatty acid including palmitic acid(PA),oleic acid(OA),linoleic acid(LA),linolenic acid(LNA)in the process proliferation to discuss the impact of fatty acids on the proliferation of adipocyte.The results showed that:1)Fatty acids can promote cell proliferation especially unsaturated fatty acid;2)Increasing the concentration of exogenous fatty acid could decline the fatty acid synthesis in adipocyte;3)Adding exogenous fatty acids in the process of adipocyte proliferation,the adipocyte could absorb the fatty acid and store the lipid intracellularly,then the excess lipid could be consumed by hydrolysis.Nextly,in the process of differentiation,we used different concentration OA(0,10,100,200 M).The rsults showed that 100 M and 200 M OA can inhibit adipocyte differentiation.Therefore,in the following experiment,we use four different kinds of fatty acids:palmitic acid(PA),oleic acid(OA),linoleic acid(LA),linolenic acid(LNA)in the process of adipocyte differentiation.The concentration of fatty acid is 100 M.The results showed that:1)Exogenous fatty acids can inhibit adipocyte differentiation;2)Exogenous fatty acid could inhibite the volume of lipid droplets increasing and prevent small lipid droplets fused into larger droplets;3)Fatty acid can inhibit lipid synthesis and promote lipid metabolism(β oxidation).We also found thatβ oxidation can resolve the excess intracellular lipid,prior to hydrolysis.In summary,we believe that VAT and SCAT are different in distribution,morphology and metabolism in Tilapia.The SCAT is more active in metabolism while VAT has a negative impact on the metabolism.Although exogenous fatty acids can promote the proliferation and differentiation of adipocyte,when the excessive deposition of fat tissue,the number of preadipocytes would be decreased,decreasing the ability of fatty acid absorbing and transforming in adipocyte.Generally speaking,the polyunsaturated fatty acids(LA,LNA)have much more cell proliferation promting than the single unsaturated fatty acid(OA)and saturated fatty acids(PA).The proliferation promting of unsaturated fatty acids(OA,LA,LNA)is positively correlated with the concentration,while saturated fatty acid(PA)showed the opposite trend.All kinds of the fatty acids can inhibit adipocyte differentiation,saturated fatty acid most.The study is the first one to reveals the nutritional and metabolic characteristics of adipose tissue and adipocytes of tilapia,and provides new evidence for further understanding of the nutrient metabolism mechanism of fish.