Thioredoxin 1 (Trx1) is a 12-kDa oxidoreductase that catalyzes thiol-disulfide exchange reactions to reduce proteins with disulfide bonds. As such, Trx1 helps protect the heart against stresses, such as ischemia and pressure overload. Mechanistic target of rapamycin (mTOR) is a serine/threonine kinase that regulates cell growth, metabolism, and survival. We have shown previously that mTOR activity is increased in response to myocardial ischemia-reperfusion injury. However, whether Trx1 interacts with mTOR to preserve heart function remains unknown. Using a substrate-trapping mutant of Trx1 (Trx1C35S), we show here that mTOR is a direct interacting partner of Trx1 in the heart. In response to HO treatment in cardiomyocytes, mTOR exhibited a high molecular weight shift in non-reducing SDS-PAGE in a 2-mercaptoethanol-sensitive manner, suggesting that mTOR is oxidized and forms disulfide bonds with itself or other proteins. The mTOR oxidation was accompanied by reduced phosphorylation of endogenous substrates, such as S6 kinase (S6K) and 4E-binding protein 1 (4E-BP1) in cardiomyocytes. Immune complex kinase assays disclosed that HO treatment diminished mTOR kinase activity, indicating that mTOR is inhibited by oxidation. Of note, Trx1 overexpression attenuated both HO-mediated mTOR oxidation and inhibition, whereas Trx1 knockdown increased mTOR oxidation and inhibition. Moreover, Trx1 normalized HO-induced down-regulation of metabolic genes and stimulation of cell death, and an mTOR inhibitor abolished Trx1-mediated rescue of gene expression. HO-induced oxidation and inhibition of mTOR were attenuated when Cys-1483 of mTOR was mutated to phenylalanine. These results suggest that Trx1 protects cardiomyocytes against stress by reducing mTOR at Cys-1483, thereby preserving the activity of mTOR and inhibiting cell death.

Background: Proper dynamics of RNA polymerase II, such as promoter recruitment and elongation, are essential for transcription. PGC-1α (peroxisome proliferator-activated receptor [PPAR]-γ coactivator-1α), also termed PPARGC1a, is a transcriptional coactivator that stimulates energy metabolism, and PGC-1α target genes are downregulated in the failing heart. However, whether the dysregulation of polymerase II dynamics occurs in PGC-1α target genes in heart failure has not been defined. Methods and Results: Chromatin immunoprecipitation-sequencing revealed that reduced promoter occupancy was a major form of polymerase II dysregulation on PGC-1α target metabolic gene promoters in the pressure-overload–induced heart failure model. PGC-1α-cKO (cardiac-specific PGC-1α knockout) mice showed phenotypic similarity to the pressure-overload–induced heart failure model in wild-type mice, such as contractile dysfunction and downregulation of PGC-1α target genes, even under basal conditions. However, the protein levels of PGC-1α were neither changed in the pressure-overload model nor in human failing hearts. Chromatin immunoprecipitation assays revealed that the promoter occupancy of polymerase II and PGC-1α was consistently reduced both in the pressure-overload model and PGC-1α-cKO mice. In vitro DNA binding assays using an endogenous PGC-1α target gene promoter sequence confirmed that PGC-1α recruits polymerase II to the promoter. Conclusions: These results suggest that PGC-1α promotes the recruitment of polymerase II to the PGC-1α target gene promoters. Downregulation of PGC-1α target genes in the failing heart is attributed, in part, to a reduction of the PGC-1α occupancy and the polymerase II recruitment to the promoters, which might be a novel mechanism of metabolic perturbations in the failing heart.

Exchanging cryptographic keys has been a problem with respect to security. Whitfield Diffie and Martin Hellman proposed the Diffie-Hellman key exchange algorithm to overcome the problem. Since then, the concept of key exchange over an unsecured network has completely been revolutionized. The algorithm is based on using arithmetic calculations for transmission of the shared session keys. The purpose of this algorithm is to enable users to securely exchange keys which can be used for later encryptions. This ability to securely exchange session keys dynamically and publicly between a group of users has become the foundation for secure group applications such as distributed computing, distributed databases and conference calls. Man-in-the-middle attacks are better secured using the Diffie-Hellman algorithm. Over time, Diffie-Hellman algorithm has been altered several times by various authors. However, some limitations to the Diffie-Hellman algorithm still persist. One of the limitations of the Diffie-Hellman algorithm is that it is computationally intensive thereby increasing the time complexity when generating public keys. The proposed algorithm has similar grounds with the Diffie-Hellman algorithm, and a new technique is used for sharing session keys which overcome the time complexity limitation of the Diffie-Hellman algorithm. The proposed "Multiplicative Key Exchange Algorithm" uses simple arithmetic equations to generate and exchange keys over an insecure network.