Effect of Cholesterol on Membrane Dipole Potential: Atomistic and Coarse-Grained Molecular Dynamics Simulations.

The effect of cholesterol on membrane dipole potential has been the subject of a great number of experimental and theoretical investigations, but these studies have yielded different findings and interpretations at high cholesterol concentrations. This suggests that the underlying mechanism of the cholesterol effect is not well addressed. Moreover, as far as we know, none of the previously proposed coarse-grained (CG) models (including MARTINI and its improved versions) have been successfully used to probe the effect of cholesterol on membrane dipole potential, owing to either an inaccurate description of water-cholesterol electrostatics or the neglect of the contribution of cholesterol to membrane dipole potential. In our previous works, we proposed a CG model CAVS (charge attached to virtual site) for lipid and water, showing the advantage of the CAVS model in the calculations of membrane dipole potential as compared to the MARTINI model. In this work, we present the CAVS model for cholesterol in order to enable us to investigate the effect of cholesterol on membrane dipole potential at large spatial scale. Our works showed that the CAVS and CHARMM models produced similar results in the study of the effects of cholesterol on lipid bilayer structures and membrane dipole potential. In particular, by combining the CHARMM and CAVS simulations, we explicitly calculated the individual contributions of membrane components (cholesterol, water, and lipid) to membrane dipole potential at different cholesterol concentrations, and we discovered that an increase in cholesterol content would result in a nonlinear variation of the individual contributions of water and lipid with cholesterol concentration. On the other side, we observed that the individual contribution of cholesterol to membrane dipole potential would nonlinearly increase with increasing cholesterol concentration. Thus, the effect of cholesterol on membrane dipole potential is complicated owing to the different variation of individual contributions of membrane components (water, lipid, and cholesterol) with cholesterol concentration.

miR-202 promotes the differentiation of 3T3-L1 preadipocyte via inhibiting PGC1β expression / 基础医学与临床

Objective To explore the effect and molecular mechanism of miR-202 on the differentiation of 3T3-L1 preadipocyte .Methods Through lentivirus infected with 3T3-L1 preadipocytes , we set up the AMO-miR-202 group and the random control group , then, these cells were induced to differentiate , nine days later, differentiation was assessed by Oil Red O staining and we examined the mRNA expression of PPARγ2 and aP2 by RT-PCR method. We examined the mRNA expression of PPARγ2,aP2 and PGC1βby Western blot method .Results After packa-ging lentivirus with AMO-miR-202 and random sequence control miRNA through cell line 293T, 80%-90%cells with fluorescence were found under fluorescence microscope; After these two lentivirus respectively infected with 3T3-L1 preadipocytes, About 70%-80%cells with fluorescence were found under fluorescence microscope .Oil Red O staining test showed that these cells with Oil Red O stained bright red fat droplets of AMO-miR-202 group and PPARγ2 and aP2 mRNA expression in the AMO-miR-202 group significantly lower than control groups (P<0.05). Western blot assay showed that the protein expression of PGC 1βin the AMO-miRNA-202 group was significantly increased(P<0.05), but the expression of aP 2 and PPARγ2 was significantly decreased (P<0.01).However, the random control group and the adipocyte group had no significant effect on the above indexes .Conclusions miR-202 can promote the differentiation of 3T3-L1 preadipocyte by inhibiting the protein expression of PGC 1βand im-proving the protein expression of PPARγ2 and aP2.