Abstract 13912: Protein Phosphatase 2C-alpha Knockdown Reduces Angiotensin II-Mediated Skeletal Muscle Wasting via Restoration of Mitochondrial Recycling and Function
Circulating Angiotensin II (AngII) is elevated in congestive heart failure (CHF), and leads to skeletal muscle wasting, which is strongly associated with poor patient outcomes. We previously found that AngII upregulates protein phosphatase 2C-alpha (PP2Cα) and dephosphorylates AMP-Activated Protein Kinase (AMPK), a critical regulator of cellular metabolism, in skeletal muscle. To determine the role of PP2Cα in AngII-induced wasting, gastrocnemius (Gas) muscles of FVB mice were injected with scrambled or PP2Cα siRNA and mice were infused with saline or AngII for 4 days.
Knockdown of PP2Cα reduced AngII wasting by 50% (p<0.001), blocked AngII upregulation of PP2Cα by 62% (p<0.01), increased p-T172-AMPK by 60% versus scrambled siRNA (p<0.01), and inhibited AngII-mediated reductions in peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α, p<0.05), in complex IV activity (p<0.01), and in ATP (p<0.05) by 35-51%. AngII impaired autophagic flux as determined by a 165% increase in p62/SQSTM1 (p62) expression (p<0.001). This p62 induction was reduced by 96% with PP2Cα siRNA (p<0.05), which also increased beclin-1 expression by 122% (p<0.05) and microtubule-associated protein 1 light chain 3 (LC3)-I to LC3-II conversion by 182% (p<0.05) in AngII-infused Gas, consistent with reactivation of autophagy by PP2Cα knockdown. AngII reduced activating S555 phosphorylation of UNC-51-like kinase 1 (ULK1), a critical regulator of autophagosome formation, by 32% (p<0.05) and increased inhibitory S757 ULK1 phosphorylation by 86% (p<0.01) and these effects were completely prevented by PP2Cα siRNA (p<0.05).
AngII inhibited AMPK activity and reduced PGC-1α expression (thereby preventing mitochondrial biogenesis) and impaired autophagy (preventing clearance of damaged mitochondria), resulting in mitochondrial dysfunction, decreased ATP, and wasting. Knockdown of PP2Cα normalized AMPK activity/PGC-1α levels and blocked AngII inhibition of ULK1, leading to improved mitochondrial biogenesis/recycling/function, energy production, and inhibition of AngII-induced wasting. These results demonstrate novel effects of Ang II on cellular metabolism that are likely critical in mediating the muscle wasting that is a hallmark of CHF.
Author Disclosures: A.M. Tabony: None. T. Yoshida: None. P. Delafontaine: None.
- © 2014 by American Heart Association, Inc.