BackgroundThe PGC-1α/PPAR axis has been proposed as a potential therapeutic target for several metabolic disorders. The aim was to evaluate the efficacy of the pan-PPAR agonist, bezafibrate, in tafazzin knockdown mice (TazKD), a mouse model of Barth syndrome that exhibits age-dependent dilated cardiomyopathy with left ventricular (LV) dysfunction.ResultsThe effect of bezafibrate on cardiac function was evaluated by echocardiography in TazKD mice with or without beta-adrenergic stress. Adrenergic stress by chronic isoproterenol infusion exacerbates the cardiac phenotype in TazKD mice, significantly depressing LV systolic function by 4.5 months of age. Bezafibrate intake over 2 months substantially ameliorates the development of LV systolic dysfunction in isoproterenol-stressed TazKD mice. Without beta-adrenergic stress, TazKD mice develop dilated cardiomyopathy by 7 months of age. Prolonged treatment with suprapharmacological dose of bezafibrate (0.5% in rodent diet) over a 4-month period effectively prevented LV dilation in mice isoproterenol treatment. Bezafibrate increased mitochondrial biogenesis, however also promoted oxidative stress in cardiomyocytes. Surprisingly, improvement of systolic function in bezafibrate-treated mice was accompanied with simultaneous reduction of cardiolipin content and increase of monolysocardiolipin levels in cardiac muscle.ConclusionsThus, we demonstrate that bezafibrate has a potent therapeutic effect on preventing cardiac dysfunction in a mouse model of Barth syndrome with obvious implications for treating the human disease. Additional studies are needed to assess the potential benefits of PPAR agonists in humans with Barth syndrome.

Age represents a major risk factor for multiple organ failure, including cardiac dysfunction, in patients with sepsis. AMP-activated protein kinase (AMPK) is a crucial regulator of energy homeostasis that controls mitochondrial biogenesis by activation of peroxisome proliferator-activated receptor-γ coactivator-1α and disposal of defective organelles by autophagy. We investigated whether AMPK dysregulation contributes to age-dependent cardiac injury in young (2-3 mo) and mature adult (11-13 mo) male mice subjected to sepsis by cecal ligation and puncture and whether AMPK activation by 5-amino-4-imidazole carboxamide riboside affords cardioprotective effects. Plasma proinflammatory cytokines and myokine follistatin were similarly elevated in vehicle-treated young and mature adult mice at 18 h after sepsis. However, despite equivalent troponin I and T levels compared with similarly treated young mice, vehicle-treated mature adult mice exhibited more severe cardiac damage by light and electron microscopy analyses with more marked intercellular edema, inflammatory cell infiltration, and mitochondrial derangement. Echocardiography revealed that vehicle-treated young mice exhibited left ventricular dysfunction after sepsis, whereas mature adult mice exhibited a reduction in stroke volume without apparent changes in load-dependent indexes of cardiac function. At molecular analysis, phosphorylation of the catalytic subunits AMPK-α/α was associated with nuclear translocation of peroxisome proliferator-activated receptor-γ coactivator-1α in vehicle-treated young but not mature adult mice. Treatment with 5-amino-4-imidazole carboxamide riboside ameliorated cardiac architecture derangement in mice of both ages. These cardioprotective effects were associated with attenuation of the systemic inflammatory response and amelioration of cardiac dysfunction in young mice only, not in mature adult animals. NEW & NOTEWORTHY Our data suggest that sepsis-induced cardiac dysfunction manifests with age-dependent characteristics, which are associated with a distinct regulation of AMP-activated protein kinase-dependent metabolic pathways. Consistent with this age-related deterioration, pharmacological activation of AMP-activated protein kinase may afford cardioprotective effects allowing a partial recovery of cardiac function in young but not mature age.

The nuclear transcription factor peroxisome proliferator-activated receptor-γ (PPARγ) is a key regulator of the inflammatory response to an array of biologic insults. We have previously demonstrated that PPARγ ligands reduce myocardial ischemia-reperfusion injury in rodents. In the current study, we directly determined the role of cardiomyocyte PPARγ in ischemia-reperfusion injury, employing a model of conditional cardiomyocyte-specific deletion of PPARγ in vivo. In mice, α-myosin heavy chain-restricted Cre-mediated PPARγ deficiency was induced by tamoxifen treatment (30 mg/kg intraperitoneally) for 4 days (PPARγ−/− mice); whereas controls included mice treated with the oil diluent vehicle (PPARγ+/+ mice). Western blot and histochemical analyses confirmed that expression of PPARγ protein was abolished in cardiomyocytes of mice treated with tamoxifen, but not with vehicle. After tamoxifen or vehicle treatment, animals were subjected to 30 min ligation of the left anterior descending coronary artery followed by 2 hrs reperfusion. In PPARγ−/− mice, myocardial ischemia and reperfusion induced extensive myocardial damage, which was associated with elevated tissue activity of myeloperoxidase, indicating infiltration of neutrophils, and elevated plasma levels of troponin-I when compared to PPARγ+/+ mice. PPARγ−/− mice also demonstrated ventricular dilatation and systolic dysfunction upon echocardiographic analysis. Plasma levels of the pro-inflammatory cytokines interleukin-1β and interleukin-6 were higher in PPARγ−/− mice when compared to PPARγ+/+ mice. These pathological events in PPARγ−/− mice were associated with enhanced nuclear factor-κB DNA binding in the infarcted hearts. Thus, our data suggests that cardiomyocyte PPARγ is a crucial protective receptor and may prevent reperfusion injury by modulating mechanisms of inflammation.