Mechanism Of Epididymal Delipidation In Mice Induced By Dietary Administration Of Conjugated Linoleic Acid

The objective of this study was to explore the mechanism of epididymaldelipidation in mice induced by dietary administration of conjugated linoleic acid. Inour experiment kunming male mice were randomized into two groups (n=12) withone group receiving a diet supplemented with LA (1.5%w/w) and another receiving adiet with CLA (1.5%w/w) for13days and then sacrificed,collecting epididymal fattissue(EPI) for mechanism exploitation of fat loss in lipodystrophic mice, weinvestigated lipolysis, lipogenesis, adipogenesis and apoptosis involved in thisprocess.Body weight and food intake have no significant changes between the twogroups(P>0.05).Compared to that in LA group wet weight of WAT normalized bybody weight and the mRNA level of leptin reduced significantly (P<0.01), but thelevel of plasma TG increased significantly (P<0.01) in CLA group.The insulintolerance test showed CLA induced insulin resistance, and Sections of EPI adiposetissues were stained with hematoxylin/eosinand illustrating the histologicalalternations, in which the size of adipocytes was relatively uniform in LA group butdivergent in CLA group. These data demonstrated CLA have caused lipodystrophy.Owing to the importance of Perilipin1pathway in the droplet formation and lipolysisin adipocytes, the expression of this gene was studied for the interpretation of theimpaired lipolysis. In EPI WAT of CLA mice the mRNA level of perilipin1significantly reduced compared to that in LA mice (P<0.01); parallel with thisobservation, Western blotting showed that the protein Perilipin1remarkablydecreased.The mRNA levels of TNFα, the negative regulator of perilipin, increasedsignificantly (P<0.01), while that of PPARγ, the positive regulator, lost significantly(P<0.01). We also transiently transfected3T3-L1cells with a luciferase reporterconstruct containing the proximal promoter of the mouse perilipin1gene. The resultof luciferase assay showed that the addition of t10c12in the culture medium dramatically inhibited the promoter activity in cells compared to that of LA. In orderto find the mechanism of perilipin1,we conducted the ex vivo experiment.The dataindicated that the WAT of CLA mice had an increased basal lipolysis but lost theability to respond to epinephrine treatment.Real-time PCR be used in lipogenic study,and we found the expression of lipogenic genes such as ACC and SCD as well as theirmaster activator SREBP-1c was suppressed significantly (P<0.01) in EPI WAT ofCLA mice, suggesting the impairment of de novo synthesis of fatty acids.Furthermore, the mRNA level of LPL also diminished significantly (P<0.01),signifying the shortage of material provision from blood for fat synthesis in WAT ofCLA mice. Regarding the adipogenesis, the dramatic reduction of PPARγ coupledwith the morphological abnormality of adipocytes indicated that the dysfunction ofadipocyte differentiation.Moreover, the activity of Caspase3/7in the lysates of WATwas measured by monitoring the luminescent signals in the Caspase-Glo3/7Assaywith a luminometer, the promotion of apoptosis was also evidenced by theenhancement of Caspase3/7activity in this experiment in CLA mice. Collectively weconcluded that CLA-mediated fat loss may be resulted from the alternations ofbiological activities like adipocyte lipolysis, adipogenesis, lipogenesis and apoptosis.