Abstract 457: Dynamic Regulation of Mitochondrial Uncoupling Protein-2 during Endothelial Cell Growth
Background: Mitochondrial respiration, in addition to providing cellular energy, is now known to participate in many cellular functions. Uncoupling proteins (UCPs), a mitochondrial inner membrane transporter, are key regulators of mitochondrial respiration. To investigate the dynamic regulation of mitochondrial respiration, we examined UCPs (isoform 1, 2 and 3) in endothelial cells as a function of cell growth.
Methods and Results: Based on the expression levels determined by real-time RT-PCR, we focused on UCP-2 with the most abundant mRNA expression among the three isoforms in endothelial cells. We found that bovine aortic endothelial cells (BAECs) exposed to high serum (10%) for 24 hours showed 3.4-fold increase in UCP-2 protein expression compared to cells exposed to low serum (0.5%), and low confluence cells (60%) also showed 3.5-fold increase in UCP-2 protein expression compared to confluent cells (100%). Consistent with these data, rapid cell growth under low confluence was characterized by 36±7 % decrease of mitochondrial membrane potential (Δψ) in association with the higher UCP-2 protein expression level. Then, we examined cell growth rate by [3H]-thymidine incorporation assay for UCP-2 gene-manipulated cells in culture. We found that UCP-2 overexpressed cells by adenovirus showed significantly increased cell growth by 27±8 % (n=5; p<0.05 vs. both no treated cells and LacZ adenovirus treated cells), whereas UCP-2 knockdown cells by siRNA showed significantly decreased cell growth by 17±6 % (n=5; p<0.05 vs. both no treated cells and control siRNA treated cells).
Conclusions: These data indicate that mitochondrial uncoupling protein-2 expression is dynamically regulated as a function of endothelial cell growth conditions and support the notion that mitochondrial function is involved in the control of endothelial cell phenotype.