Protein changes associated with embryonic stem cell differentiation to vascular smooth muscle cells
Embryonic stem (ES) cells can differentiate into many different cell lines, including vascular smooth muscle cells (SMCs). The aim of this project is to characterize protein changes during this differentiation process. Mouse ES cells are pre-differentiated by withdrawal of the leukemia inhibitory factor-1 from the culture medium. Subsequently, stem cell antigen-1 positive (Sca-1) cells are sorted by magnetic labelling cell sorting with anti-Sca-1 microbeads and cultured in differentiation medium with or without platelet-derived growth factor (PDGF). Protein extracts of ES cells and Sca-1+ cells are separated by two-dimensional electrophoresis. About 300 protein species of each cell lines are analyzed by mass spectrometry. Proteome maps are available online (http:/ /vwvw.v ascular-proteomicsc. om). After stimulation with PDGF for 5 passages, Sca-1+ cells differentiate into SMCs (esSMCs) with 95% staining positive for SMC markers such as smooth muscle a-actin, calponin, and smooth muscle myosin heavy chain. Protein profiles of esSMCs and mouse aortic SMCs are compared using the difference gel electrophoresis approach. esSMCs display decreased expression of myofilaments but increased oxidation of redox-sensitive proteins due to higher levels of reactive oxgen species (ROS). While immunoblotting reveals an upregulation of numerous antioxidants in esSMCs, enzymatic assays demonstrate lower glutathione concentrations compared to aortic SMCs despite a 3-fold increase in glutathione reductase activity. Mitochondrial superoxide measurement revealed the mitochondria-derived superoxide is the main source of ROS in esSMCs and inhibition of electron transport chain complex III by antimycin A showed remarkable increase of ROS in esSMCs. Moreover, depletion of glutathione by diethyl maleate or inhibition of glutathione reductase by carmustine (BCNU) results in a remarkable loss of cell viability in esSMCs compared to aortic SMCs while adding 2-mercaptoethanol increased esSMCs survival. These results indicate that esSMCs require additional antioxidant protection for survival and consequently, treatment with anti-oxidants could be beneficial for tissue repair from ES cells.
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