The Anti-Hepatic Fibrosis Effect Of Docosahexaenoic Acid Targeting PPARγ

Hepatic fibrosis is caused by the imbalance of extracellular matrix(ECM)formation and degradation,which lead to deposition of large amount of type Ⅰ and Ⅲ fibrillar collagen in portal and hepatic lobule.Hepatic fibrosis is the common clinicopathological stage of chronic liver diseases.It might develop to cirrhosis and hepatocellular carcinoma if left untreated.Hepatic fibrosis is reported to be reversible.During the process of hepatic fibrosis,hepatic stellate cells(HSCs)are activated and transformed into fibroblasts,which is the pivotal event of hepatic fibrosis.HSCs are located at Disse gaps and their activation and conversion is modulated by multi-factors and pathways.Our prior studies focusing on antifibrotic potential of curcumin,the main bioactive ingredient of traditional Chinese medicine Curcuma Tonga L.have confirmed that peroxisome proliferator-activated receptor gamma(PPARγ)is a "switch" molecule controlling HSCs activation.Since marine compound docosahexaenoic acid(DHA)is the natural ligand of PPARy,we hypothesized that DHA can inhibit HSCs activation by activating PPARy to improve hepatic fibrosis.To prove our hypothesis,we first evaluated the anti-fibrotic effects of DHA on carbon tetrachloride-induced hepatic fibrosis in rats.DHA was given as a preventive medicine.Our data showed that DHA significantly alleviated CCl4-induced liver damage,evidenced by ameliorated hepatic fibrogenesis,suppressed inflammatory and oxidative stress.On the mRNA and protein levels,DHA treatment significantly increased PPARy expression and decreased transforming growth factor-β receptor I(Tβ-RI),transforming growth factor-β receptor Ⅱ(Tβ-RⅡ)and Platelet-derived growth factor β receptor(PDGF-βR).Therefore,we inferred that DHA may attenuate liver fibrosis by enhancing PPAR-y expression to inhibit TGF-β and PDGF pathway.Based on the in vivo study,the mechanism of DHA inhibition of HSCs activation was investigated.Our data showed that DHA inhibited the proliferation of HSCs by modulating AKT/FOXO1/p27 signaling pathway.On the other hand,DHA upregulated BAX and downregulated Bcl-2 at protein levels.Antagonism of PPARy basically abrogated the inhibition of DHA to HSCs.Therefore,we concluded that DHA inhibits the activation of HSCs by blocking proliferation pathway and by inducing apoptotic pathway of HSCs in a PPARy dependent manner.The results of computer-aided molecular docking showed that DHA had a good binding effect with the active sites of PPARy,thus PPARy might be the direct target of DHA.We further overexpressed Ser289 mutant PPARy in LX-2 cell line with plasmid transfection and investigated the fibrotic maker modulation to verify the molecular docking data,and the results showed that Ser289 residue was required for DHA to activate PPARy to exert its inhibiting effect on activated HSCs.At last,we used a CC14 treated mice model to confirm that PPARy activation is required for DHA to attenuate hepatic fibrosis.The study of this thesis clarifies the protective effect of marine original compound DHA on the liver.In this thesis,we further demostrated that DHA alleviate liver fibrosis via PPARy activation,which provided a theoretical and experimental basis for the research and development of marine original anti-fibrotic drugs.