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.

Rationale Wound healing after myocardial infarction involves a highly regulated inflammatory response that is initiated by the appearance of neutrophils to clear out dead cells and matrix debris. Neutrophil infiltration is controlled by multiple secreted factors, including the master regulator transforming growth factor beta (TGFβ). Broad inhibition of TGFβ early post-infarction has worsened post-MI remodeling; however, this signaling displays potent cell-specificity and targeted suppression particularly in the myocyte could be beneficial. Objective To test the hypothesis that targeted suppression of myocyte TGFβ signaling suppresses post-infarct remodeling and inflammatory modulation, and identify mechanisms by which this may be achieved. Methods and Results Mice with TGFβ receptor-coupled signaling genetically suppressed only in cardiac myocytes (conditional TGFβ receptor 1 or 2 knockout) displayed marked declines in neutrophil recruitment and accompanying metalloproteinase-9 activation after infarction, and were protected against early onset mortality due to wall rupture. This was a cell-specific effect, as broader inhibition of TGFβ signaling led to 100% early mortality due to rupture. Rather than by altering fibrosis or reducing generation of pro-inflammatory cytokines/chemokines, myocyte-selective TGFβ-inhibition augmented synthesis of a constellation of highly protective cardiokines. These included thrombospondin 4 with associated endoplasmic reticulum stress responses, interleukin-33, follistatin-like 1, and growth and differentiation factor-15 (GDF-15), which is an inhibitor of neutrophil integrin activation and tissue migration. Conclusions These data reveal a novel role of myocyte canonical TGFβ signaling as a potent regulator of protective cardiokine and neutrophil mediated infarct remodeling.