Abstract 14366: Pulmonary Hypertension-Induced RV Hypertrophy and Dysfunction is Associated With Reduced Activity and Abundance of Complex IV in Respiratory Supercomplexes

Abstract

Introduction: PH results in RV hypertrophy, fibrosis and impaired function resulting in RV failure. PH is associated with impaired heart metabolism and mitochondrial respiration. Mitochondrial supercomplexes (mSC) are assemblies of multiple electron transport chain (ETC) complexes that consist of physically associated complex I, III and IV to enhance respiration. We determined if activity and/or abundance of mSC’s is altered in a rat model of PH. Methods: PH was induced in SD-rats by Sugen-Hypoxia (3 weeks) followed by normoxia (4 weeks) . Control (n=11) and PH (n=10) were subjected to echocardiography and isolation of LV and RV mitochondria. Clear native PAGE with equal amounts mitochondrial protein was used for SC abundance and activity with immunoblot or in gel activity with specific substrates. Results: PH animals had significantly reduced PAT and TAPSE, increased RV wall thickness and hypertrophy (RV/LVS). Western analysis of total protein fractions demonstrated reductions in representative CI, II, III, and IV proteins in RV indicating reduced mitochondrial content in PH. Assays with normalized mitochondrial protein showed activity (100+/- 3.6 vs 64.0+/-3.8 %, p<.01) and abundance (100+/-1.8 vs 49.3 +/-1.1, p=.02) of complex IV in mitochondrial SCs was severely reduced in PH animals compared to control. There were no differences in total CIV activity or abundance in lower order ETC assemblies (100 vs 97.5%, p=.78). TAPSE, PAT and RV Wall thickness significantly correlated with CIV SC activity (r=.71, .66, and -.80 respectively P<.01). CIII abundance was lower in SCs (P=.01) but total CIII unchanged. CI activity in SC assemblies was reduced in PH but this was not significant (100+/-12 vs 77.4 +/-8.2, p=.14). Overall levels of CI were unchanged. There were no changes in CII activity or abundance in RV or LV. In the LV, activity of CIV in SC was reduced in PH (100+/-6 vs 78+/-6, p=.02) but to a lesser extent than RV. There were also decreases in overall abundance of CIII and CIV assemblies in the LV in PH. Conclusion: The data support the concept that although mitochondrial abundance may be altered, there are also significant alterations associated with assembly and activity of mitochondrial SCs in the RV with pronounced differences in complex IV assembled into SCs.