Tabony Alexander Michael, Yoshida Tadashi, Sukhanov Sergiy, Delafontaine Patrice
Tulane University Department of Medicine, Heart and Vascular Institute, New Orleans, LA 70112, USA.
Tulane University Department of Medicine, Heart and Vascular Institute, New Orleans, LA 70112, USA ; Heart and Vascular Institute, Tulane University School of Medicine, 1430 Tulane Ave. SL-48, New Orleans, LA, USA.
Skelet Muscle. 2014 Oct 30;4:20. doi: 10.1186/2044-5040-4-20. eCollection 2014.
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, blocked AngII upregulation of PP2Cα, increased p-T172-AMPK, and inhibited AngII-mediated reductions in peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), nuclear respiratory factor 1 (NRF1), mitochondrial transcription factor A (TFAM), in complex IV activity, and in ATP levels. AngII impaired the rate of autophagy as determined by a 2.4-fold increase in p62/SQSTM1 (p62) accumulation. This induction was reduced by PP2Cα knockdown, which also increased beclin-1 expression and microtubule-associated protein 1 light chain 3 (LC3)-II conversion in AngII-infused Gas. AngII reduced activating S555 phosphorylation of UNC-51-like kinase 1 (ULK1), a critical regulator of autophagosome formation, and increased inhibitory S757 ULK1 phosphorylation and these effects were prevented by PP2Cα siRNA.
AngII inhibited AMPK activity and reduced PGC-1α and TFAM expression (thereby inhibiting mitochondrial biogenesis) and impaired ULK1 activation and autophagy (thereby also inhibiting clearance of damaged mitochondria), resulting in mitochondrial dysfunction, decreased ATP, and wasting. Knockdown of PP2Cα normalized AMPK activity, PGC-1α, NRF1, and TFAM 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 AngII on cellular metabolism that are likely critical in mediating the muscle wasting that is a hallmark of CHF.
充血性心力衰竭（CHF）患者循环血管紧张素II（AngII）水平升高，可导致骨骼肌萎缩，这与患者预后不良密切相关。我们之前发现，AngII可上调骨骼肌中蛋白磷酸酶2C-α（PP2Cα）并使细胞代谢关键调节因子AMP活化蛋白激酶（AMPK）去磷酸化。
为确定PP2Cα在AngII诱导的萎缩中的作用，向FVB小鼠的腓肠肌注射乱序或PP2Cα小干扰RNA（siRNA），并向小鼠输注生理盐水或AngII，持续4天。
敲低PP2Cα可减轻AngII诱导的萎缩，阻断AngII对PP2Cα的上调，增加p-T172-AMPK水平，并抑制AngII介导的过氧化物酶体增殖物激活受体γ共激活因子1α（PGC-1α）、核呼吸因子1（NRF1）、线粒体转录因子A（TFAM）水平降低以及复合物IV活性和ATP水平降低。AngII使自噬速率受损，表现为p62/SQSTM1（p62）积累增加2.4倍。PP2Cα敲低可减少这种诱导作用，还可增加AngII灌注的腓肠肌中贝林1（beclin-1）表达和微管相关蛋白1轻链3（LC3）-II转化。AngII降低自噬体形成关键调节因子UNC-样激酶1（ULK1）的S555磷酸化激活水平，并增加ULK1的S757磷酸化抑制水平，而PP2Cα siRNA可阻止这些效应。
AngII抑制AMPK活性，降低PGC-1α和TFAM表达（从而抑制线粒体生物合成），损害ULK1激活和自噬（从而也抑制受损线粒体的清除），导致线粒体功能障碍、ATP减少和萎缩。敲低PP2Cα可使AMPK活性、PGC-1α、NRF1和TFAM水平恢复正常，并阻断AngII对ULK1的抑制，从而改善线粒体生物合成/再循环/功能、能量产生，并抑制AngII诱导的萎缩。这些结果证明了AngII对细胞代谢的新作用，这可能在介导CHF标志性的肌肉萎缩中起关键作用。
