The renin-angiotensin system (RAS) and reactive oxygen species (ROS) have been implicated in the development of insulin resistance and its related complications. There is also evidence that angiotensin II (Ang II)-induced generation of ROS contributes to the development of insulin resistance in skeletal muscle, although the precise mechanisms remain unknown. In the present study, we found that Ang II markedly enhanced NADPH oxidase activity and consequent ROS generation in L6 myotubes. These effects were blocked by the angiotensin II type 1 receptor blocker losartan, and by the NADPH oxidase inhibitor apocynin. Ang II also promoted the translocation of NADPH oxidase cytosolic subunits p47 phox and p67 phox to the plasma membrane within 15 min. Furthermore, Ang II abolished insulin-induced tyrosine phosphorylation of insulin receptor substrate 1 (IRS1), activation of protein kinase B (Akt), and glucose transporter-4 (GLUT4) translocation to the plasma membrane, which was reversed by pretreating myotubes with losartan or apocynin. Finally, small interfering RNA (siRNA)-specific gene silencing targeted specifically against p47 phox (p47siRNA), in both L6 and primary myotubes, reduced the cognate protein expression, decreased NADPH oxidase activity, restored Ang II-impaired IRS1 and Akt activation as well as GLUT4 translocation by insulin. These results suggest a pivotal role for NADPH oxidase activation and ROS generation in Ang II-induced inhibition of insulin signaling in skeletal muscle cells.Insulin resistance and hypertension often coexist and frequently progress to diabetes and cardiovascular disease (1, 2). A reduced response by target tissues to insulin (3) is the hallmark of the metabolic syndrome (1-5), which is defined by a cluster of abnormalities including impaired glucose tolerance, hypertension, abdominal obesity, and dyslipidemia (6). Insulin signaling is a complex process involving multiple pathways and phosphorylation events. Phosphorylation of protein kinase B (Akt) is a key step leading to the translocation of glucose transporter 4 (GLUT4) 2 from intracellular compartments to the plasma membrane. GLUT4 helps mediate the increase in glucose uptake in skeletal muscle and adipose tissues in the presence of insulin (7,8). Skeletal muscle insulin receptor signaling is defective in metabolic syndrome and type 2 diabetes mellitus (T2DM) both in experimental models and humans (1-6;9). Many factors have been reported to induce insulin resistance in vitro and in vivo, including angiotensin II (Ang II), tumor necrosis factor (TNF)-␣, interleukin 6 (IL-6), and free fatty acids (10 -13).Ang II is an important physiological regulator of blood pressure, cardiac function, and salt and fluid homeostasis. Its hypertensive, growth, and remodeling effects are mediated through the Ang II receptor 1 (AT 1 R) (1, 5, 11). In addition, Ang II appears to be antagonistic to insulin action and contributes to insulin resistance. Several prospective clinical studies have shown that treating hypertensive patients with angiote...

In this report, we show that zinc is required for endoplasmic reticulum function in Saccharomyces cerevisiae. Zinc deficiency in this yeast induces the unfolded protein response (UPR), a system normally activated by unfolded ER proteins. Msc2, a member of the cation diffusion facilitator (CDF) family of metal ion transporters, was previously implicated in zinc homeostasis. Our results indicate that Msc2 is one route of zinc entry into the ER. Msc2 localizes to the ER when expressed at normal levels. UPR induction in low zinc is exacerbated in an msc2 mutant. Genetic and biochemical evidence indicates that this UPR induction is due to genuine ER dysfunction. Notably, we found that ER-associated protein degradation is defective in zinc-limited msc2 mutants. We also show that the vacuolar CDF proteins Zrc1 and Cot1 are other pathways of ER zinc acquisition. Finally, zinc deficiency up-regulates the mammalian ER stress response indicating a conserved requirement for zinc in ER function among eukaryotes.

Reduced insulin sensitivity is a key factor in the pathogenesis of type 2 diabetes and hypertension. Skeletal muscle insulin resistance is particularly important for its major role in insulin-mediated glucose disposal. Angiotensin II (ANG II) is integral in regulating blood pressure and plays a role in the pathogenesis of hypertension. In addition, we have documented that ANG II-induced skeletal muscle insulin resistance is associated with generation of reactive oxygen species (ROS). However, the linkage between ROS and insulin resistance in skeletal muscle remains unclear. To explore potential mechanisms, we employed the transgenic TG(mRen2)27 (Ren-2) hypertensive rat, which harbors the mouse renin transgene and exhibits elevated tissue ANG II levels, and skeletal muscle cell culture. Compared with Sprague-Dawley normotensive control rats, Ren-2 skeletal muscle exhibited significantly increased oxidative stress, NF-kappaB activation, and TNF-alpha expression, which were attenuated by in vivo treatment with an angiotensin type 1 receptor blocker (valsartan) or SOD/catalase mimetic (tempol). Moreover, ANG II treatment of L6 myotubes induced NF-kappaB activation and TNF-alpha production and decreased insulin-stimulated Akt activation and GLUT-4 glucose transporter translocation to plasma membranes. These effects were markedly diminished by treatment of myotubes with valsartan, the antioxidant N-acetylcysteine, NADPH oxidase-inhibiting peptide (gp91 ds-tat), or NF-kappaB inhibitor (MG-132). Similarly, NF-kappaB p65 small interfering RNA reduced NF-kappaB p65 subunit expression and nuclear translocation and TNF-alpha production but improved insulin-stimulated phosphorylation (Ser(473)) of Akt and translocation of GLUT-4. These findings suggest that NF-kappaB plays an important role in ANG II/ROS-induced skeletal muscle insulin resistance.

Background: Nutrient minerals are essential yet potentially toxic, and homeostatic mechanisms are required to regulate their intracellular levels. We describe here a genome-wide screen for genes involved in the homeostasis of minerals in Saccharomyces cerevisiae. Using inductively coupled plasma-atomic emission spectroscopy (ICP-AES), we assayed 4,385 mutant strains for the accumulation of 13 elements (calcium, cobalt, copper, iron, potassium, magnesium, manganese, nickel, phosphorus, selenium, sodium, sulfur, and zinc). We refer to the resulting accumulation profile as the yeast 'ionome'.