Abstract 582: Obg-like Atpase 1 (OLA1) Regulates Cardiomyocyte Hypertrophic Response via Gsk3β Signaling

Background: OLA1 that possesses both GTP and ATP hydrolyzing activities has been reported as a translational regulator of cell growth and survival. However, its role in cardiac hypertrophy, a process involving enhanced protein synthesis and increased cell size has not been studied. Hence, we hypothesized that OLA1 expression is regulated by oxidative stress and inflammatory responses in angiotensin-II induced cardiac hypertrophy and its aberrant expression mediates altered GSK3β-β-Catenin signaling. Methods: Protein expression of OLA1, GSK3β/P-GSK3β, β-Catenin/P-β-Catenin in total protein extracts of human cardiomyocytes with and without angiotensin II (500nM) treatment were studied. Knockdown of OLA1 expression in cardiomyocytes was achieved by SiRNA transfection and total protein extracts were isolated. In addition, phosphokinase array in OLA1 knockdown cells with and without angiotensin II was performed. H 2 O 2 and LPS treatment in cardiomyocytes for 24h was performed in culture and their total protein extracts were isolated to study the expression of OLA1, GSK3β/P-GSK3β and β-Catenin/P-β-Catenin. Results: A significant increase in OLA1 expression from 1 to 3.86±0.72 in angiotensin II treated cells was observed. GSK3β phosphorylation was also increased to 1.27±.10 in angiotensin II treated cells. While, β-Catenin phosphorylation was reduced, total β-Catenin level was significantly increased to 2.26±.34 in angiotensin II treated cells. OLA1 knockdown cells showed a significant reduction (0.12±0.0006) in GSK3β phosphorylation both with and without angiotensin II treatment. Also, phosphorylation of β-Catenin (1.28±.16) was induced in OLA1 knockdown cells. OLA1 expression was up-regulated in both H 2 O 2 and LPS treated cardiomyocytes after 24h. GSK3β phosphorylation and total β-Catenin levels were increased in these cells similar to angiotensin II treated cells. We also found cell proliferation and survival-related phosphoproteins were up-regulated in OLA1 knockdown cells with and without angiotensin II treatment. Conclusion: OLA1 was up-regulated during inflammation and reactive oxygen species production which then lead to GSK3β phosphorylation and β-Catenin accumulation in angiotensin II treated cardiomyocytes.