No abstract

Mammalian members of the forkhead box protein O (FoxO) class of transcription factors are implicated in the regulation of oxidative stress, and FoxO proteins are negatively regulated by the phosphatidylinositol 3-kinase (PI3K)–AKT signaling pathway. We examined the effect of Klotho on the PI3K/AKT pathway and manganese superoxide dismutase (MnSOD) during tacrolimus (Tac)-induced oxidative stress. Klotho-treated mice showed decreased Tac-induced oxidative stress accompanied by functional and histological improvements. Klotho inhibited the PI3K/AKT-mediated phosphorylation of FoxO3a and enhanced FoxO3a binding to the MnSOD promoter. Klotho increased MnSOD mRNA and protein expression in mitochondria. In addition, Klotho reduced Tac-induced mitochondrial dysfunction and decreased mitochondrial reactive oxygen species production, and these effects were enhanced by blocking PI3K activity with LY294002. Collectively, our data showed that Klotho protects Tac-induced oxidative stress by negatively regulating the PI3K/AKT pathway and subsequently enhancing FoxO3a-mediated MnSOD expression.

The polypurine/polypyrimidine (pPu/pPy) tract of the human vascular endothelial growth factor (VEGF) gene is proposed to be structurally dynamic and to have potential to adopt non-B DNA structures. In the present study, we further provide evidence for the existence of the G-quadruplex structure within this tract both in vitro and in vivo using the dimethyl sulfate (DMS) footprinting technique and nucleolin as a structural probe specifically recognizing G-quadruplex structures. We observed that the overall reactivity of the guanine residues within this tract toward DMS was significantly reduced compared with other guanine residues of the flanking regions in both in vitro and in vivo footprinting experiments. We also demonstrated that nucleolin, which is known to bind to G-quadruplex structures, is able to bind specifically to the G-rich sequence of this region in negatively supercoiled DNA. Our chromatin immunoprecipitation analysis further revealed binding of nucleolin to the promoter region of the VEGF gene in vivo. Taken together, our results are in agreement with our hypothesis that secondary DNA structures, such as G-quadruplexes, can be formed in supercoiled duplex DNA and DNA in chromatin in vivo under physiological conditions similar to those formed in single-stranded DNA templates.

ABSTRACT:Ferroelectric tunnel junctions (FTJs) have attracted increasing research interest as a promising candidate for non-volatile memories. Recently, significant enhancements of tunneling electroresistance (TER) have been realized through modifications of electrode materials.However, direct control of the FTJ performance through modifying the tunneling barrier has not been adequately explored. Here, adding a new direction to FTJ research, we fabricated FTJs with Ferroelectric tunnel junctions (FTJs), composed of a thin ferroelectric (FE) layer sandwiched in between two metallic electrodes, have been intensively investigated in recent years. This device is considered to be a promising candidate for next-generation nonvolatile memories, because it combines the advantages of both ferroelectric random-access-memory and resistiveswitching memory. 1-3 The concept of FTJ was first proposed by Esaki in 1971, 4 but the research activities have not flourished untixl this decade. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] The operation of FTJs has been mainly explained in terms of interfacial screening of polarization charges. [5][6][7][8] In a metal 1(M1)/FE/metal 2 (M2) structured FTJ (Figure 1a), the two asymmetric electrodes lead to unequal screen lengths and potential changes at metal/FE interfaces. Depending on the polarizations, the electrostatic potential profile of tunneling barrier will be varied. As a result, the tunneling resistance can be switched between low (ON) and high (OFF) values by polarization reversal, leading to the socalled tunneling electroresistance (TER) effect.Extensive experimental works based on this asymmetric screening scenario have been reported during the last decade. In 2009, the TER effect was first demonstrated using conducting atomic force microscopy (CAFM). 9-11 Subsequently, FTJs with highly reproducible performance were realized in capacitor geometry, which will be useful for practical applications. 12,13 Up to recently, most studies of FTJs have focused on improving device performance by modifying the electrode materials. [14][15][16][17][18][19][20] Typical examples include the use of lightly doped semiconductors, [14][15][16] For a thick barrier, these obstacles can be avoided, but the tunneling current becomes too small for realizing a practically useful device. As an alternative, several groups have theoretically proposed a new kind of FTJ using an FE/paraelectric (FE/PE) composite barrier. 27,28 The PE layer provides a new route to control the tunneling barrier potentials, and thus the TER can be tuned and significantly enhanced. However, there have been few experimental efforts to systematically attest this theoretical prediction. 29 In this paper, we report experimental control of the TER effect by directly manipulating the tunneling barrier thickness and composition. For this purpose, we fabricated two types of FTJs: Figure S5), which further confirm good epitaxial film qualities.We estimated the lattice constants of the oxide layers from XRD reci...