Evidence of a significant role of glutathione reductase in the sulfur assimilation pathway

With the objective of studying the role of glutathione reductase (GR) in the accumulation of cysteine and methionine, we generated transgenic tobacco and Arabidopsis lines overexpressing the cytosolic AtGR1 and the plastidic AtGR2 genes. The transgenic plants had higher contents of cysteine and glutathione. To understand why cysteine levels increased in these plants, we also used gr1 and gr2 mutants. The results showed that the transgenic plants have higher levels of sulfite, cysteine, glutathione and methionine, which are downstream to adenosine 5′ phosphosulfate reductase (APR) activity. However, the mutants had lower levels of these metabolites, while the sulfate content increased. A feeding experiment using ³⁴SO₄^2– also showed that the levels of APR downstream metabolites increased in the transgenic lines and decreased in gr1 compared with their controls. These findings, and the results obtained from the expression levels of several genes related to the sulfur pathway, suggest that GR plays an essential role in the sulfur assimilation pathway by supporting the activity of APR, the key enzyme in this pathway. GR recycles the oxidized form of glutathione (GSSG) back to reduce glutathione (GSH), which serves as an electron donor for APR activity. The phenotypes of the transgenic plants and the mutants are not significantly altered under non‐stress and oxidative stress conditions. However, when germinating on sulfur‐deficient medium, the transgenic plants grew better, while the mutants were more sensitive than the control plants. The results give substantial evidence of the yet unreported function of GR in the sulfur assimilation pathway.     

Activation of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) by atorvastatin is mediated by 15-deoxy-delta-12,14-PGJ2

Several studies suggested that 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) activate peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Atorvastatin (ATV) increases myocardial levels of prostaglandins (PG) by upregulating and activating cytosolic-phospholipase-A(2) and cycloxygenase-2 (COX2). We investigated whether ATV activates PPAR-gamma via 15-deoxy-delta-12,14-PGJ(2) (15DPGJ(2)) an endogenous ligand of PPAR-gamma and a product of PGD(2), and to compare the effects of pioglitazone (PIO), a known direct PPAR-gamma activator, to that of ATV. First we measured myocardial 15DPGJ(2) levels in the rat heart after a 3-day pretreatment with oral ATV (10 mg/(kg d)), PIO (10 mg/(kg d)), ATV+PIO, ATV+COX1 inhibitor, and ATV+COX2 inhibitor. We also assessed in human umbilical venous endothelial cells (HUVEC) whether ATV and PIO activate PPAR-gamma via 15DPGJ(2) using siRNA targeted to PGD(2) synthase. Both 15DPGJ(2) levels and PPAR-gamma activation were assessed. ATV and PIO increased myocardial 15DPGJ(2) levels in the rat myocardium and HUVEC. siRNA inhibited this increase in both groups. Both ATV and PIO augmented PPAR-gamma activation while co-treatment with siRNA completely blocked the ATV effect but only partially inhibited the PIO effect. In conclusion, both ATV and PIO activate PPAR-gamma and increase myocardial 15DPGJ(2) levels. Activation of PPAR-gamma by ATV is mediated solely by 15DPGJ(2), whereas PIO activates PPAR-gamma both directly and indirectly via 15DPGJ(2).