Oxidative stress has been shown to be an initiator and major contributor to both ER stress [9,15] and autophagy [19], although the mechanisms that promote the activation of these signaling routes and upstream targets are not completely defined

Oxidative stress has been shown to be an initiator and major contributor to both ER stress [9,15] and autophagy [19], although the mechanisms that promote the activation of these signaling routes and upstream targets are not completely defined. for these events are still unknown. Since IR is associated with numerous modern health problems, including type 2 diabetes and cardiovascular disease, it is an urgent priority to establish the molecular targets and upstream events that mediate the development of IR. Recently, we have reported that targeting the DNA repair protein human 8-oxoguanine (8-OxoG) glycosylase/AP lyase (hOGG1) to mitochondria protected mitochondrial DNA (mtDNA) from palmitate-induced damage, prevented mitochondrial reactive oxygen species (mtROS) generation and thus improved insulin sensitivity in L6 skeletal muscle cells [4]. Since we have recently shown that IR in skeletal muscle was associated with increased markers of both autophagy and endoplasmic reticulum (ER) stress [5], this study was designed to further evaluate the role of mtDNA damage in these processes. This study showed, for the first EGFR-IN-3 time, that mtDNA damage regulates ER stress and autophagy in L6 skeletal muscle cells. Since mitochondrial dysfunction [1,3], ER stress [6,7] and dysregulated autophagy [8,9] all contribute to the development of IR, this study sheds new light on the cause-effect relationships and sequence of events leading to IR, indicating that mtDNA damage is an early step in the chain of pathological events leading to IR. == Materials and Methods == == Materials == Dulbeccos modified Eagles medium (DMEM) was from Invitrogen (Carlsbad, CA), fetal bovine serum (FBS) was from Hyclone (Logan, UT). Palmitate, tunicamycin, bovine serum albumin (BSA) (fatty acid-free), insulin (from bovine pancreas), penicillin/streptomycin and NAC were from Sigma (St. Louis, MO). == Cell culture and treatment == Rat L6 skeletal muscle cells were obtained from ATCC (Manassa, VA). Cells were grown in DMEM supplemented with 10% FBS and 50 g/ml penicillin/streptomycin EGFR-IN-3 in 5% CO2at 37C. For these studies, L6 myoblasts were plated in EGFR-IN-3 culture dishes, 6-well or 24-well plates, and used at the EGFR-IN-3 myotube stage of differentiation as described previously [4,10,11]. Myogenic differentiation to myotubes was confirmed by light microscopy with morphological alignment, elongation, and fusion. A stock concentration of palmitate was prepared as discussed previously [4,10,11]. Control cells were treated with drug diluent only (2% BSA in the DMEM medium). For treatment with tunicamycin, cells were incubated with 5 g/ml of tunicamycin for indicated time. A stock concentration of tunicamycin (Sigma) was dissolved in dimethylsulfoxide (DMSO). Control cultures, not treated with tunicamycin, received the same Mouse monoclonal to CD45 concentration of DMSO as in the compound treated cultures. In the Akt (Ser473) phosphorylation experiments, L6 myotubes were incubated with tunicamycin (5 g/ml) or 1 mM palmitate for 16 h then serum starved for 2 h and incubated with 100 nM of insulin for 15 min [4]. == Adenovirus transduction of L6 myotubes == Adenoviruses containing MTS-hOGG1 and GFP were kindly provided by Dr. Mark Kelley (Indiana University) and all transductions and virus-containing culture techniques were done as described previously [4]. == Subcellular Fractionation, Protein isolation, Western Blot Analysis, and Protein carbonylation == Mitochondrial protein fractions were isolated from one 100 mm dish of each cell type (MTS-hOGG1 transduced and GFP-only transduced cells) by differential centrifugation as described previously [4]. Total protein isolation and Western blot analysis were performed as previously described [4]. Oxidative protein carbonylation (PCO) in mitochondrial fractions were performed after Western blot by using OxyBlot Protein Detection Kit according to the manufacturers instructions (Millipore) as described previously [5]. The antibodies used were to actin (Sigma); phospho-Akt (Ser 473), total Akt, pPERK, PERK, pEIF2, EIF2, pFox3Oa, Fox3Oa, Bnip3, ubiquitin (Cell Signaling), lamin A (Santa Cruz Biotechnology),.