Abstract 14660: Severe Pulmonary Hypertension and Right Ventricular Dysfunction in Rats are Associated with Changes in Ubiquitin Proteasome System
Introduction. Ubiquitin-proteasome system (UPS) is responsible for degradation of intracellular proteins. UPS maintains a dynamic equilibrium of proteins and prevents accumulation of damaged and misfolded proteins, yet its role in pulmonary hypertension (PH) and right ventricular (RV) dysfunction is not fully understood.
Methods. To induce PH, male rats received monocrotaline (MCT, 60mg/kg, s.c.). Severe PH was well established by day 21 and progressed to severe RV failure (RVF, n=10) by day 30. Saline treated rats served as control (CTRL, n=10). Serial echocardiography was performed to monitor cardiopulmonary hemodynamics. Cardiac catheterisation was terminally performed to record RV pressure (RVP). Proteasome subunits were determined by Western blot. Proteasome activity was measured in lungs with fluorescent substrates. Subcellular localization of proteasomal subunits was determined in isolated RV myocytes by high-resolution confocal microscopy. P<0.05 was considered significant. Values were mean±SE.
Results. Rats developed severe PH 21 days after MCT, which progressed to RVF by day 30 [RVP=72±1 vs. 30±1mmHg in CTRL, P<0.01; RV ejection fraction=30±1 vs 66±1%, P<0.01; RV/(LV+IVS)=0.68±0.05 vs. 0.24±0.02, P<0.01]. Western blot of lung revealed that RVF was associated with significant downregulation of a7 (a subunit of 20S, 0.05±0.001 in CTRL vs 0.04±0.002 in RVF, P<0.05), RPT4 (the 19S regulatory proteasomal subunit, 0.25±0.008 in CTRL vs. 0.18±0.01 in RVF, P<0.05) and PA28a (4.83±0.17 in CTRL vs 3.17±0.17 in RVF, P<0.01) protein levels. The activity of b1 26S and b2 26S subunits increased whereas activity of b1 20S and b2 20S decreased in RVF lungs. The activity of b5 26S and b5 20S subunits remained unchanged. In RV myocytes, microscopy showed that RVF was associated with disappearance of Core 20S in the nuclei as well as in the t-tubules. The expression of RPT4 was also reduced both in the nucleus as well as in the t-tubules in isolated myocytes from RVF group only.
Conclusions. Severe PH is associated with decreased protein levels of a7, PA28a and RPT4, increased activity of b1 and b2 26S and decreased activity of b1 and b2 20S proteasomal subunits in the lungs. PH-induced RV failure is associated with decreased Core and RPT4 expression in RV myocytes.
- © 2011 by American Heart Association, Inc.