Abstract 168: Drp1 Accumulates in Mitochondria and Plays a Protective Role in the Heart in Response to Pressure Overload

Abstract

Dynamin-related protein 1 (Drp1) plays an essential role in maintaining the quality control of mitochondria through mitochondrial (Mt) fission and mitophagy. We investigated how Mt function, autophagy and Drp1 are regulated in the heart during pressure overload (PO) and whether endogenous Drp1 plays an important role in regulating cardiac function. Mice were subjected to transverse aortic constriction (TAC) at multiple time points between 6 hours and 30 days. Left ventricular (LV) weight/tibial length (LVW/TL) was significantly elevated at Day 5 (TAC vs Baseline; 6.21 ± 0.28 vs 4.59 ± 0.36, p<0.05). Ejection fraction (EF) was maintained at Day 5 (79±5 vs 82±7%), but gradually decreased thereafter (30 days; 51±12%, p<0.05). LC3-II was decreased (-40.0%, p<0.05) while p62 accumulated (1.84 fold, p<0.05) significantly at Day 5. Both Mt ATP content (-65.6%, p<0.05) and production (-90.3%, p<0.05) were reduced significantly at Days 7 and 14, respectively, and thereafter. Mt mass, evaluated by electron microscopy, was also reduced (-19.9%, p<0.05) at Day 7. Drp1 accumulated in mitochondria at Day 7, and S616 phosphorylation of Drp1, associated with increased activity, was increased at Day 7. Thus, PO suppresses autophagy and induces Mt dysfunction by Day 7, at which time Drp1 accumulates in mitochondria and Mt mass is decreased. To examine the functional significance of endogenous Drp1 during PO, cardiac-specific heterozygous Drp1 knock out (Drp-hetCKO) mice were subjected to TAC. At Day 7, decreases in EF (57± 11 vs 80 ± 7%, p<0.05) and increases in LVW/TL (7.22 ± 0.26 vs 5.86 ± 0.65, p<0.05) and lung weight/TL (13.03 ± 1.09 vs 7.00 ± 1.31, p<0.05) were exacerbated in Drp-hetCKO compared to in control mice. LV end diastolic pressure was significantly higher (20.0 ± 5.7 vs 7.4 ± 3.1 mmHg, p<0.05) and myocardial fibrosis (14.1 ± 2.5 vs 6.2 ± 4.3 %, p<0.05) was greater, and Mt mass was also significantly greater in Drp-hetCKO than in control mice (relative Mt mass, 1.21 ± 0.46 vs 1.00 ± 0.02, p<0.05). These results suggest that PO inhibits autophagy and induces mitochondrial dysfunction by Day7, which coincides with Mt accumulation of Drp1. Drp1 plays an adaptive role in this condition, mediating decreases in Mt mass and protecting the heart from dysfunction.