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Aims Thioredoxin 1 (Trx1) is an evolutionarily conserved oxidoreductase that cleaves disulphide bonds in oxidized substrate proteins such as mechanistic target of rapamycin (mTOR) and maintains nuclear-encoded mitochondrial gene expression. The cardioprotective effect of Trx1 has been demonstrated via cardiac-specific overexpression of Trx1 and dominant negative Trx1. However, the pathophysiological role of endogenous Trx1 has not been defined with a loss-of-function model. To address this, we have generated cardiac-specific Trx1 knockout (Trx1cKO) mice. Methods and results Trx1cKO mice were viable but died with a median survival age of 25.5 days. They developed heart failure, evidenced by contractile dysfunction, hypertrophy, and increased fibrosis and apoptotic cell death. Multiple markers consistently indicated increased oxidative stress and RNA-sequencing revealed downregulation of genes involved in energy production in Trx1cKO mice. Mitochondrial morphological abnormality was evident in these mice. Although heterozygous Trx1cKO mice did not show any significant baseline phenotype, pressure-overload-induced cardiac dysfunction, and downregulation of metabolic genes were exacerbated in these mice. mTOR was more oxidized and phosphorylation of mTOR substrates such as S6K and 4EBP1 was impaired in Trx1cKO mice. In cultured cardiomyocytes, Trx1 knockdown inhibited mitochondrial respiration and metabolic gene promoter activity, suggesting that Trx1 maintains mitochondrial function in a cell autonomous manner. Importantly, mTOR-C1483F, an oxidation-resistant mutation, prevented Trx1 knockdown-induced mTOR oxidation and inhibition and attenuated suppression of metabolic gene promoter activity. Conclusion Endogenous Trx1 is essential for maintaining cardiac function and metabolism, partly through mTOR regulation via Cys1483. [ABSTRACT FROM AUTHOR]

Thioredoxin 1 (Trx1) is a major antioxidant that acts adaptively to protect the heart during the development of diabetic cardiomyopathy. The molecular mechanism(s) responsible for regulating the Trx1 level and/or activity during diabetic cardiomyopathy is unknown. β-hydroxybutyrate (βHB), a major ketone body in mammals, acts as an alternative energy source in cardiomyocytes under stress, but it also appears to be involved in additional mechanisms that protect the heart against stress. βHB upregulated Trx1 in primary cultured cardiomyocytes in a dose- and a time-dependent manner and a ketogenic diet upregulated Trx1 in the heart. βHB protected cardiomyocytes against H2O2-induced death, an effect that was abolished in the presence of Trx1 knockdown. βHB also alleviated the H2O2-induced inhibition of mTOR and AMPK, known targets of Trx1, in a Trx1-dependent manner, suggesting that βHB potentiates Trx1 function. It has been shown that βHB is a natural inhibitor of HDAC1 and knockdown of HDAC1 upregulated Trx1 in cardiomyocytes, suggesting that βHB may upregulate Trx1 through HDAC inhibition. βHB induced Trx1 acetylation and inhibited Trx1 degradation, suggesting that βHB-induced inhibition of HDAC1 may stabilize Trx1 through protein acetylation. These results suggest that βHB potentiates the antioxidant defense in cardiomyocytes through the inhibition of HDAC1 and the increased acetylation and consequent stabilization of Trx1. Thus, modest upregulation of ketone bodies in diabetic hearts may protect the heart through the upregulation of Trx1. [ABSTRACT FROM AUTHOR]

Proper RNA polymerase II (Pol II) dynamics, such as promoter recruitment and elongation, are essential for transcription. PGC-1α is a transcriptional coactivator that stimulates energy metabolism, and PGC-1α target genes are downregulated in the failing heart. However, whether and how PGC-1α regulates Pol II dynamics during the development of heart failure has not been defined. To elucidate whether Pol II dynamics are changed in the failing heart, chromatin immunoprecipitation-sequencing was performed in a pressure-overload (PO)-induced heart failure model. Reduced Pol II promoter occupancy was observed in 26 of the 29 genes involved in fatty acid metabolism and mitochondrial ATP production in the PO model, suggesting that impaired promoter recruitment is the major form of Pol II dysregulation. Cardiac-specific PGC-1α knockout (PGC-1α-cKO) mice showed failing heart phenotypes even under basal conditions (Ejection fraction: Wild-type (WT): 0.74; PGC-1α-cKO: 0.58*, p<0.05 vs. WT), accompanied by downregulation of metabolic genes and reduced Pol II occupancy in metabolic gene promoters (relative promoter occupancy of Pol II: Mcad: WT: 1; PGC-1α-cKO: 0.55*; Idh3a: WT: 1; PGC-1α-cKO: 0.45*; p<0.05 vs. WT). Thus, loss of PGC-1α diminishes Pol II promoter recruitment in the heart in vivo. An in vitro DNA binding assay with a biotin labeled endogenous Idh3a promoter sequence revealed that PGC-1α promoted Pol II recruitment to the promoter. These results suggest that PGC-1α promotes transcription partly through Pol II recruitment. Therefore, loss of PGC-1α reduces gene expression and Pol II recruitment. Importantly, despite the phenotypic similarity between the PO-induced heart failure model and PGC-1α-cKO mice, the protein level of PGC-1α was not significantly reduced in the PO model. Rather, promoter occupancy of PGC-1α in the target gene promoters was inhibited (relative promoter occupancy of PGC-1α: Mcad: WT: 1; PGC-1α-cKO: 0.34*; Idh3a: WT: 1; PGC-1α-cKO: 0.35*; p<0.05 vs. WT). These results show that recruitment of Pol II to metabolic gene promoters is inhibited under PO conditions, possibly due to dissociation of PGC-1α from the promoters, a mechanism which may be responsible for metabolic dysregulation in the failing heart. [ABSTRACT FROM AUTHOR]

Dual peroxisome proliferator-activated receptor (PPAR)α/γ agonists that were developed to target hyperlipidemia and hyperglycemia in type 2 diabetes patients, caused cardiac dysfunction or other adverse effects. We studied the mechanisms that underlie the cardiotoxic effects of a dual PPARα/γ agonist, tesaglitazar, in wild type and diabetic (leptin receptor deficient - db/db) mice. Mice treated with tesaglitazar-containing chow or high fat diet developed cardiac dysfunction despite lower plasma triglycerides and glucose levels. Expression of cardiac peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α), which promotes mitochondrial biogenesis, had the most profound reduction among various fatty acid metabolism genes. Furthermore, we observed increased acetylation of PGC1α, which suggests PGC1α inhibition and lowered sirtuin 1 (SIRT1) expression. This change was associated with lower mitochondrial abundance. Combined pharmacological activation of PPARα and PPARγ in C57BL/6 mice reproduced the reduction of PGC1α expression and mitochondrial abundance. Resveratrol-mediated SIRT1 activation attenuated tesaglitazar-induced cardiac dysfunction and corrected myocardial mitochondrial respiration in C57BL/6 and diabetic mice but not in cardiomyocyte-specific Sirt1-/- mice. Our data shows that drugs, which activate both PPARα and PPARγ lead to cardiac dysfunction associated with PGC1α suppression and lower mitochondrial abundance likely due to competition between these two transcription factors.