Abstract 207: Differential Regulation of Ubiquitin-Proteasomal System in Right Ventricular Versus Left Ventricular Hypertrophy and Failure
Background: While the role of Ubiquitin-Proteasomal System (UPS) in left ventricular hypertrophy (LVH) and failure (LVF) has been controversial, the role of UPS in the right, RVH/RVF is unknown. Given the greater percent increase in RV mass and protein with RV vs. LV afterload stress, we hypothesized that UPS alterations could play an important role in RVH and RVF.
Methods: Using our pulmonary artery constriction (PAC) model to induce RVH/RVF by 8d (n=13-14), UPS gene and protein expression, ubiquitination, oxidation (carbonylation), and enzyme activity were measured in PAC vs. sham controls. Proteasomal inhibitors epoxomicin (0.5 mg/kg/d) or MG132 (10 µg/kg/d) were administered from 1d before to 7d after surgery (n=3-6).
Results: RVW/BW was increased by 109.3% in PAC mice. All mice developed progressive RV dilation, septal shift and decrease in RV function. UPS function, measured as 26S ß5 chymotrypsin-like activity (71.3±3.9 vs. 100±8.3%; p<0.05) and 20S ß1 caspase-like activity (66.9±3.2 vs. 100±6.9%; p<0.001), was decreased. 20S protein expression was unchanged whereas the 19S regulatory subunit Rpt5 was increased (3.3±0.5 vs. 1.4±0.2; p<0.05). UCHL1 deubiquitinase (0.3±0.04 vs. 0.05±0.004; p<0.0001) and Smurf1 E3 ubiquitin ligase (3369±538 vs. 1249±75.6; p<0.01) were increased and both poly-ubiquitinated proteins (877600±50550 vs. 639700±45050; p<0.05) and free-ubiquitins (373102±65859 vs. 177318±24188) were also increased. Carbonylation was unchanged. Pro-apoptotic Bax was increased (0.06±0.004 vs. 0.02±0.001; p<0.0001), and anti-apoptotic Bcl-2 decreased (0.2±0.03 vs. 0.5±0.08; p<0.05) with a 6-fold increase in Bax/Bcl-2 ratio. Proteasomal inhibition further increased free ubiquitin levels 2.6-fold (p<0.0001). However, neither the degree of RVH, nor decrease in RV function was altered.
Conclusion: UPS has been shown to be both activated/inhibited and cardioprotective/cardiotoxic in LVH/LVF. In RVH/RVF, despite a doubling in RV mass, UPS activity is decreased, associated with increased ubiquitinated proteins and Bax/Bcl-2 ratio. Further proteasomal inhibition does not hasten RVF, suggesting that the failing RV is resistant to further proteasomal inhibition, or a limited role for the UPS in the progression from RVH to RVF.
- © 2012 by American Heart Association, Inc.