PKG1α Cysteine-42 Redox State Controls mTORC1 Activation in Pathological Cardiac Hypertrophy

Abstract

Rationale: Stimulated PKG1α (protein kinase G-1α) phosphorylates TSC2 (tuberous sclerosis complex 2) at serine 1365, potently suppressing mTORC1 (mechanistic [mammalian] target of rapamycin complex 1) activation by neurohormonal 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 GC-1 (guanylyl cyclase 1) activation.

Methods and results: Cardiomyocytes expressing wild-type (WT) PKG1α (PKG1α^WT) or cysteine-42 to serine mutation redox-dead (PKG1α^CS/CS) were exposed to ET-1 (endothelin 1). Cells expressing PKG1α^WT exhibited substantial mTORC1 activation (p70 S6K [p70 S6 kinase], 4EBP1 [elF4E binding protein-1], and Ulk1 [Unc-51-like kinase 1] phosphorylation), reduced autophagy/autophagic flux, and abnormal protein aggregation; all were markedly reversed by PKG1α^CS/CS expression. Mice with global knock-in of PKG1α^CS/CS subjected to pressure overload (PO) also displayed markedly reduced mTORC1 activation, protein aggregation, hypertrophy, and ventricular dysfunction versus PO in PKG1α^WT mice. Cardioprotection against PO was equalized between groups by co-treatment with the mTORC1 inhibitor everolimus. TSC2-S1365 phosphorylation increased in PKG1α^CS/CS more than PKG1α^WT myocardium following PO. TSC2^{S1365A/S1365A} (TSC2 S1365 phospho-null, created by a serine to alanine mutation) knock-in mice lack TSC2 phosphorylation by PKG1α, and when genetically crossed with PKG1α^CS/CS mice, protection against PO-induced mTORC1 activation, cardiodepression, and mortality in PKG1α^CS/CS mice was lost. Direct stimulation of GC-1 (BAY-602770) offset disparate mTORC1 activation between PKG1α^WT and PKG1α^CS/CS after PO and blocked ET-1 stimulated mTORC1 in TSC2^S1365A-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.

Keywords: autophagy; heart failure; hypertrophy; mice; phosphorylation.