Hyperactive Adverse Mechanical Stress Responses in Dystrophic Heart Are Coupled to Transient Receptor Potential Canonical 6 and Blocked by cGMP–Protein Kinase G Modulation

Abstract

Rationale The heart is exquisitely sensitive to mechanical stimuli in order to rapidly adapt to physiological demands. In muscle lacking dystrophin, such as Duchenne muscular dystrophy (DMD), increased load during contraction triggers pathological responses thought to worsen the disease. The relevant mechano-transducers and therapies to target them remain unclear. Objectives We tested the role of transient receptor potential canonical channels TRPC3 and TRPC6 and their modulation by protein kinase G in controlling cardiac systolic mechano-sensing, and determined their pathophysiological relevance in an experimental model of DMD. Methods and Results Contracting isolated papillary muscles and/or cardiomyocytes from controls and mice genetically lacking either TRPC3 or TRPC6 were subjected to auxotonic load to induce stress-stimulated contractility (SSC, gradual rise in force and intracellular Ca2+). Incubation with cGMP (PKG activator) markedly blunted SSC in controls and Trpc3−/−; whereas in Trpc6−/−, the resting SSC response was diminished and cGMP had no impact. In DMD myocytes (mdx/utrophin deficient), the SSC was excessive and arrhythmogenic. Gene deletion or selective drug blockade of TRPC6, or cGMP/PKG activation, all reversed this phenotype. Chronic PDE5A inhibition also normalized abnormal mechano-sensing while blunting progressive chamber hypertrophy in DMD mice. Conclusion PKG is a potent negative-modulator of cardiac systolic mechano-signaling that requires TRPC6 as the target effector. In dystrophic hearts, excess SSC and arrhythmia are coupled to TRPC6 and are ameliorated by its targeted suppression or PKG activation. These results highlight novel therapeutic targets for this disease.

Prevention of PKG1α oxidation augments cardioprotection in the stressed heart

“…Reduced channel suppression by PKG1α oxidation fits this observation. Redox sensitivity of PKG1α suppression of TRPC6 may also have therapeutic implications beyond the heart, including in dystrophinopathies (24) and glomerulosclerosis (26,27), where ROS and TRPC6 play a pathophysiological role. Future studies are needed to identify the protein partners that control PKG1α translocation and develop strategies to selectively sustain its reduced state to maximize the efficacy of its activation against myocardial disease.…”

Tadalafil Treatment Delays the Onset of Cardiomyopathy in Dystrophin‐Deficient Hearts

“…26,47 We suspect that activation of TRPC6 is a major player in initiating this PDE5-medated cascade; however, difficulties in the measurement of murine TRPC6 leave us unable to draw that conclusion from this study. We chose the GRMD model of DMD to test the prophylactic efficacy of tadalafil on delaying cardiomyopathy because this model better recapitulates the severity of the cardiomyopathy seen in DMD compared with mdx mice, which show clinical signs of cardiomyopathy typically after age 12 months.…”

“…In a recent report, Seo et al 26 demonstrated that both genetic deletion of the nonspecific cation channel TRPC6 and sildenafil provide nearly equivalent protection against acute stretch-induced arrhythmias, an effect of calcium dysregulation in isolated mdx cardiomyocytes, suggesting that PDE5 inhibition deactivates TRPC6 permeability, thereby reducing TRPC6-mediated Ca 2+ influx. This effect is likely a result of PKG-dependent phosphorylation of TRPC6 on Thr69 (in mice; Thr70 in humans and dogs).…”

TRP Channels: Their Function and Potentiality as Drug Targets

“…TRPC1 and TRPC6 have been suggested to be a component of the tarantula toxin-sensitive mechanosensitive cation channels [ 132 , 133 ]. For example, the excessive mechanical stress-induced muscle contractility in myocytes with Duchenne muscular dystrophy was blunted by inhibition or deletion of TRPC6 [ 134 ]. On the other hand, intracellular lipid mediators, such as DAG and 12-hydroxy-eicosatetraenoic acid (12-HETE), reportedly mediate TRPC6 channel activation induced by oxidative stress [ 135 ] and mechanical stretch [ 136 ].…”