The anti-oxidative property of mesoporous silica nanoparticles (MSNs) has been proposed previously, which prompted us to investigate the potential protective effect of MSNs on human embryonic stem cells (hESCs) against oxidative stress. To this purpose, the cell viability was determined by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assay. Apoptosis was analyzed by Annexin V/propidium iodide double-staining method. The intracellular glutathione, superoxide dismutase and malondialdehyde were measured with commercial assay kits. The reactive oxygen species was detected by staining with fluorescent dye DCFH-DA. The relative levels of Nkx2.5, Mef2c, Tbx5, dHand and α-MHC transcripts were measured by real-time polymerase chain reaction. The protein levels of Connexin 43, Troponin C1 and GAPDH were determined by immunoblotting. The beating behavior of embryoid bodies (EBs) was visually examined. Our results demonstrated that MSNs reversed hydrogen peroxide (H2O2)-inhibited cell viability and ameliorated H2O2-induced cell apoptosis in vitro. The H2O2-elicited intracellular oxidative stress was significantly relieved in the presence of MSNs. Furthermore, MSNs improved H2O2-suppressed differentiation of hESC-derived EBs and the maturation of the cardiomyocytes. In addition, MSNs treatment enhanced the beating properties of EBs. MSNs effectively conferred protection on hESCs against oxidative stress with respect to cardiac differentiation.
Key words: Mesoporous silica nanoparticles, hydrogen peroxide, human embryonic stem cells, differentiation
The Golgi apparatus is a central station for protein trafficking in eukaryotic cells. A widely accepted model of protein transport within the Golgi apparatus is cisternal maturation. Each cisterna has specific resident proteins, which are thought to be maintained by COPI-mediated transport. However, the mechanisms underlying specific sorting of these Golgi-resident proteins remain elusive. To obtain a clue to understand the selective sorting of vesicles between the Golgi cisterenae, we investigated the molecular arrangements of the conserved oligomeric Golgi (COG) subunits in yeast cells. Mutations in COG subunits cause defects in Golgi trafficking and glycosylation of proteins and are causative of Congenital Disorders of Glycosylation (CDG) in humans. Interactions among COG subunits in cytosolic and membrane fractions were investigated by co-immunoprecipitation. Cytosolic COG subunits existed as octamers, whereas membrane-associated COG subunits formed a variety of subcomplexes. Relocation of individual COG subunits to mitochondria resulted in recruitment of only a limited number of other COG subunits to mitochondria. These results indicate that COG proteins function in the forms of a variety of subcomplexes and suggest that the COG complex does not comprise stable tethering without other interactors.
Key words: The Golgi apparatus, COG complex, yeast, membrane trafficking, multi-subunit tethering complex