ARTICLE: PKG1α Cysteine-42 Redox State Controls mTORC1 Activation in Pathological Cardiac Hypertrophy
AUTHORS: Christian U Oeing, Taishi Nakamura, Shi Pan, Sumita Mishra, Brittany Dunkerly-Eyring, Kristen M Kokkonen-Simon, Brian Leei Lin, Anna Chen, Guangshuo Zhu, Djahida Bedja, Dong I Lee, David A Kass and Mark J Ranek
JOURNAL: Circ Res. 2020 May 12. doi: 10.1161/CIRCRESAHA.119.315714. Online ahead of print.
Rationale: Stimulated protein kinase G-1α (PKG1α) phosphorylates tuberous sclerosis complex 2 (TSC2) at serine 1365, potently suppressing mTORC1 activation by neuro-hormonal and hemodynamic stress. This reduces pathological hypertrophy and dysfunction and increases autophagy. PKG1α oxidation at cysteine 42 is also induced by these stressors, which blunts its cardioprotective effects.
Objective: We tested the dependence of mTORC1 activation on PKG1α C42-oxidation, and its capacity to suppress such activation by soluble guanylyl cyclase-1 (GC-1) activation.
Methods and Results: Cardiomyocytes expressing WT PKG1α (PKG1αWT) or C42S redox-dead PKG1αCS/CS were exposed to endothelin-1 (ET-1). Cells expressing PKG1αWT exhibited substantial mTORC1 activation (p70 S6K, 4EBP1, and Ulk1 phosphorylation), reduced autophagy/autophagic flux, and abnormal protein aggregation; all were markedly reversed by PKG1αCS/CS expression. Mice with global knock-in of PKG1αCS/CS subjected to pressure-overload (PO) also displayed markedly reduced mTORC1 activation, protein aggregation, hypertrophy, and ventricular dysfunction versus PO in PKG1αWT mice. Cardioprotection against PO was equalized between groups by co-treatment with the mTORC1 inhibitor everolimus. TSC2 S1365 phosphorylation increased in PKG1αCS/CS more than PKG1αWT myocardium following PO. TSC2S1365A/S1365A KI mice lack TSC2 phosphorylation by PKG1α, and when genetically crossed with PKG1αCS/CS mice, protection against PO-induced mTORC1 activation, cardio-depression, and mortality in PKG1αCS/CS mice was lost. Direct stimulation of GC-1 (BAY-602770) offset disparate mTORC1 activation between PKG1αWT and PKG1αCS/CS after PO, and blocked ET-1 stimulated mTORC1 in TSC2S1365A expressing myocytes.
Conclusions: Oxidation of PKG1α at C42 reduces its phosphorylation of TSC2, resulting in amplified PO-stimulated mTORC1 activity and associated hypertrophy, dysfunction, and depressed autophagy. This is ameliorated by direct GC-1 stimulation.
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