The inhibition, in mice, of the phosphodiesterase PDE9A, which specifically regulates natriuretic-peptide-coupled cGMP signalling, is independent of nitric oxide and is upregulated in failing human hearts, and can reverse pre-established stress-induced heart disease. Work in animals has shown that inhibition of phosphodiesterase type 5A (PDE5A) with, for example, Viagra, can protect the heart from pathological stress by preventing the degradation of nitric-oxide-generated cGMP. However, nitric oxide signalling is often depressed in cardiovascular disease, potentially explaining the disappointing results of PDE5A inhibition in clinical trials. David Kass and colleagues now identify an alternative target, PDE9A, which specifically regulates natriuretic-peptide-coupled cGMP signalling, and is independent of nitric oxide. They show that PDE9A is upregulated in failing human hearts and that its inhibition in mice can reverse pre-established stress-induced heart disease. PDE9A inhibitors seem to be well tolerated in humans and are being investigated in clinical trials for neurocognitive disease. The new results suggest that these inhibitors may also find an application in heart disease. Cyclic guanosine monophosphate (cGMP) is a second messenger molecule that transduces nitric-oxide- and natriuretic-peptide-coupled signalling, stimulating phosphorylation changes by protein kinase G. Enhancing cGMP synthesis or blocking its degradation by phosphodiesterase type 5A (PDE5A) protects against cardiovascular disease1,2. However, cGMP stimulation alone is limited by counter-adaptions including PDE upregulation3. Furthermore, although PDE5A regulates nitric-oxide-generated cGMP4,5, nitric oxide signalling is often depressed by heart disease6. PDEs controlling natriuretic-peptide-coupled cGMP remain uncertain. Here we show that cGMP-selective PDE9A (refs 7, 8) is expressed in the mammalian heart, including humans, and is upregulated by hypertrophy and cardiac failure. PDE9A regulates natriuretic-peptide- rather than nitric-oxide-stimulated cGMP in heart myocytes and muscle, and its genetic or selective pharmacological inhibition protects against pathological responses to neurohormones, and sustained pressure-overload stress. PDE9A inhibition reverses pre-established heart disease independent of nitric oxide synthase (NOS) activity, whereas PDE5A inhibition requires active NOS. Transcription factor activation and phosphoproteome analyses of myocytes with each PDE selectively inhibited reveals substantial differential targeting, with phosphorylation changes from PDE5A inhibition being more sensitive to NOS activation. Thus, unlike PDE5A, PDE9A can regulate cGMP signalling independent of the nitric oxide pathway, and its role in stress-induced heart disease suggests potential as a therapeutic target.

Cardiac troponins are often elevated in patients with skeletal muscle disease who have no evidence of cardiac disease. The goal of this study was to characterize cardiac troponin concentrations in patients with myopathies and derive insights regarding the source of elevated troponin T measurements. Cardiac troponin T (cTnT) and cardiac troponin I (cTnI) concentrations were determined by using high sensitivity assays in 74 patients with hereditary and acquired skeletal myopathies. Patients underwent comprehensive cardiac evaluation, including 12-lead electrocardiogram, 24-h electrocardiogram, cardiac magnetic resonance imaging, and coronary artery computed tomography. cTnT and cTnI protein expression was determined in skeletal muscle samples of 9 patients and in control tissues derived from autopsy using antibodies that are used in commercial assays. Relevant Western blot bands were subjected to liquid chromatography tandem mass spectrometry for protein identification. Levels of cTnT (median: 24 ng/l; interquartile range: 11 to 54 ng/l) were elevated (>14 ng/l) in 68.9% of patients; cTnI was elevated (>26 ng/l) in 4.1% of patients. Serum cTnT levels significantly correlated with creatine kinase and myoglobin (r = 0.679 and 0.786, respectively; both p < 0.001). Based on cTnT serial testing, 30.1% would have fulfilled current rule-in criteria for myocardial infarction. Noncoronary cardiac disease was present in 23%. Using cTnT antibodies, positive bands were found in both diseased and healthy skeletal muscle at molecular weights approximately 5 kDa below cTnT. Liquid chromatography tandem mass spectrometry identified the presence of skeletal troponin T isoforms in these bands. Measured cTnT concentrations were chronically elevated in the majority of patients with skeletal myopathies, whereas cTnI elevation was rare. Our data indicate that cross-reaction of the cTnT immunoassay with skeletal muscle troponin isoforms was the likely cause.

The NAD ⁺ precursor nicotinamide improves diastolic dysfunction caused by aging, hypertension, or metabolic syndrome in rodents.

Chronic neurohormonal and mechanical stresses are central features of heart disease. Increasing evidence supports a role for the transient receptor potential canonical channels TRPC3 and TRPC6 in this pathophysiology. Channel expression for both is normally very low but is increased by cardiac disease, and genetic gain- or loss-of-function studies support contributions to hypertrophy and dysfunction. Selective small-molecule inhibitors remain scarce, and none target both channels, which may be useful given the high homology among them and evidence of redundant signaling. Here we tested selective TRPC3/6 antagonists (GSK2332255B and GSK2833503A; IC₅₀, 3–21 nM against TRPC3 and TRPC6) and found dose-dependent blockade of cell hypertrophy signaling triggered by angiotensin II or endothelin-1 in HEK293T cells as well as in neonatal and adult cardiac myocytes. In vivo efficacy in mice and rats was greatly limited by rapid metabolism and high protein binding, although antifibrotic effects with pressure overload were observed. Intriguingly, although gene deletion of TRPC3 or TRPC6 alone did not protect against hypertrophy or dysfunction from pressure overload, combined deletion was protective, supporting the value of dual inhibition. Further development of this pharmaceutical class may yield a useful therapeutic agent for heart disease management. Significance Cardiac hypertrophy and dysfunction in response to sustained hormonal and mechanical stress are sentinel features of most forms of heart disease. Activation of non–voltage-gated transient receptor potential canonical channels TRPC3 and TRPC6 may contribute to this pathophysiology and provide a therapeutic target. Effects from combined selective inhibition have not been tested previously. Here we report the capability of highly selective TRPC3/6 inhibitors to block pathological hypertrophic signaling in several cell types, including adult cardiac myocytes. We show in vivo redundancy of each channel; individual gene deletion was not protective against sustained pressure overload, whereas combined deletion ameliorated the response. These data strongly support a role for both channels in cardiac disease and the utility of selective combined inhibition.