Development of heart failure is known to be associated with changes in energy substrate metabolism. Information on the changes in energy substrate metabolism that occur in heart failure is limited and results vary depending on the methods employed. Our aim is to characterize the changes in energy substrate metabolism associated with pressure overload and ischaemia–reperfusion (I/R) injury. We used transverse aortic constriction (TAC) in mice to induce pressure overload-induced heart failure. Metabolic rates were measured in isolated working hearts perfused at physiological afterload (80 mmHg) using ³H- or ¹⁴C-labelled substrates. As a result of pressure-overload injury, murine hearts exhibited: (i) hypertrophy, systolic, and diastolic dysfunctions; (ii) reduction in LV work, (iii) reduced rates of glucose and lactate oxidations, with no change in glycolysis or fatty acid oxidation and a small decrease in triacylglycerol oxidation, and (iv) increased phosphorylation of AMPK and a reduction in malonyl-CoA levels. Sham hearts produced more acetyl CoA from carbohydrates than from fats, whereas TAC hearts showed a reverse trend. I/R in sham group produced a metabolic switch analogous to the TAC-induced shift to fatty acid oxidation, whereas I/R in TAC hearts greatly exacerbated the existing imbalance, and was associated with a poorer recovery during reperfusion. Pressure overload-induced heart failure and I/R shift the preference of substrate oxidation from glucose and lactate to fatty acid due to a selective reduction in carbohydrate oxidation. Normalizing the balance between metabolic substrate utilization may alleviate pressure-overload-induced heart failure and ischaemia.

Biomechanical stress and cytoskeletal remodeling are key determinants of cellular homeostasis and tissue responses to mechanical stimuli and injury. Here we document the increased activity of gelsolin, an actin filament severing and capping protein, in failing human hearts. Deletion of gelsolin prevents biomechanical stress-induced adverse cytoskeletal remodeling and heart failure in mice. We show that phosphatidylinositol (3,4,5)-triphosphate (PIP3) lipid suppresses gelsolin actin-severing and capping activities. Accordingly, loss of PI3Kα, the key PIP3-producing enzyme in the heart, increases gelsolin-mediated actin-severing activities in the myocardium in vivo, resulting in dilated cardiomyopathy in response to pressure-overload. Mechanical stretching of adult PI3Kα-deficient cardiomyocytes disrupts the actin cytoskeleton, which is prevented by reconstituting cells with PIP3. The actin severing and capping activities of recombinant gelsolin are effectively suppressed by PIP3. Our data identify the role of gelsolin-driven cytoskeletal remodeling in heart failure in which PI3Kα/PIP3 act as negative regulators of gelsolin activity.

Rationale:: The classic phagocyte nicotinamide adenine dinucleotide phosphate oxidase (gp91 ^phox or Nox2) is expressed in the heart. Nox2 activation requires membrane translocation of the p47 ^phox subunit and is linked to heart failure. We hypothesized that loss of p47 ^phox subunit will result in decreased reactive oxygen species production and resistance to heart failure. Objective:: To define the role of p47 ^phox in pressure overload–induced biomechanical stress. Methods and Results:: Eight-week-old male p47 ^phox null (p47 ^phox knockout [KO]), Nox2 null (Nox2KO), and wild-type mice were subjected to transverse aortic constriction–induced pressure overload. Contrary to our hypothesis, p47 ^phox KO mice showed markedly worsened systolic dysfunction in response to pressure overload at 5 and 9 weeks after transverse aortic constriction compared with wild-type–transverse aortic constriction mice. We found that biomechanical stress upregulated N-cadherin and β-catenin in p47 ^phox KO hearts but disrupted the actin filament cytoskeleton and reduced phosphorylation of focal adhesion kinase. p47 ^phox interacts with cytosolic cortactin by coimmunoprecipitation and double immunofluorescence staining in murine and human hearts and translocated to the membrane on biomechanical stress where cortactin interacted with N-cadherin, resulting in adaptive cytoskeletal remodeling. However, p47 ^phox KO hearts showed impaired interaction of cortactin with N-cadherin, resulting in loss of biomechanical stress–induced actin polymerization and cytoskeletal remodeling. In contrast, Nox2 does not interact with cortactin, and Nox2-deficient hearts were protected from pressure overload–induced adverse myocardial and intracellular cytoskeletal remodeling. Conclusions:: We showed a novel role of p47 ^phox subunit beyond and independent of nicotinamide adenine dinucleotide phosphate oxidase activity as a regulator of cortactin and adaptive cytoskeletal remodeling, leading to a paradoxically enhanced susceptibility to biomechanical stress and heart failure.