Insulin resistance in skeletal muscle is a hallmark feature of type 2 diabetes. An increasing number of enzymes and metabolic pathways have been implicated in the development of insulin resistance. However, the primary cellular cause of insulin resistance remains uncertain. Proteome analysis can quantitate a large number of proteins and their post-translational modifications simultaneously and is a powerful tool to study polygenic diseases like type 2 diabetes. Using this approach on human skeletal muscle biopsies, we have identified eight potential protein markers for type 2 diabetes in the fasting state. The observed changes in protein expression indicate increased cellular stress, e.g. up-regulation of two heat shock proteins, and perturbations in ATP (re)synthesis and mitochondrial metabolism, e.g. down-regulation of ATP synthase ␤-subunit and creatine kinase B, in skeletal muscle of patients with type 2 diabetes. Phosphorylation appears to play a key, potentially coordinating role for most of the proteins identified in this study. In particular, we demonstrated that the catalytic ␤-subunit of ATP synthase is phosphorylated in vivo and that the levels of a down-regulated ATP synthase ␤-subunit phosphoisoform in diabetic muscle correlated inversely with fasting plasma glucose levels. These data suggest a role for phosphorylation of ATP synthase ␤-subunit in the regulation of ATP synthesis and that alterations in the regulation of ATP synthesis and cellular stress proteins may contribute to the pathogenesis of type 2 diabetes.Insulin resistance in skeletal muscle, defined as reduced insulin-stimulated glucose disposal, is a characteristic feature of type 2 diabetes mellitus (T2DM) 1 and is believed to be largely accounted for by reduced non-oxidative glucose metabolism (1-3). Furthermore, insulin stimulation of glucose oxidation and suppression of lipid oxidation is significantly impaired in patients with T2DM (2, 3). Conversely, in the basal, fasting state increased glucose oxidation and reduced lipid oxidation is seen in skeletal muscle of insulin resistant subjects, whether caused by T2DM or obesity alone (4). These defects suggest an impaired capacity to switch between carbohydrate and fat as oxidative energy sources in insulin-resistant subjects. Together with reports of reduced oxidative enzyme activity and dysfunction of mitochondria in skeletal muscle of patients with T2DM (4 -6) and the fact that mitochondrial DNA defects cause T2DM through impairment of oxidative phosphorylation (7, 8), these abnormalities in fuel metabolism have led to the hypotheses that perturbations in skeletal muscle mitochondrial metabolism (6, 9, 10) and defects in the signaling pathways of AMP-activated protein kinase (AMPK) are implicated in the pathogenesis of T2DM (11). That rates of fuel oxidation and mitochondrial function can affect glucose uptake and glycogen synthesis has been reported earlier (12, 13). In addition, both chronic activation of AMPK and induced expression of the transcriptional co-activator of peroxisom...

Moderate heat response involves proteins related to lipid biogenesis, cytoskeleton structure, sulfate assimilation, thiamine and hydrophobic amino acid biosynthesis, and nuclear transport. Photostasis is achieved through carbon metabolism adjustment, a decrease of photosystem II (PSII) abundance and an increase of PSI contribution to photosynthetic linear electron flow. Thioredoxin h may have a special role in this process in P. euphratica upon moderate heat exposure.

No abstract

Detection of phosphorylated proteins as well as assignment of the phosphorylated sites in such proteins is a major challenge in proteomics. In the present study we evaluate the use of enzymatic de-phosphorylation in combination with differential peptide mass mapping for identification of phosphorylated peptides in peptide mixtures derived from in-gel digested phospho-proteins. Phospho-peptides could be identified provided that improved sample preparation methods prior to mass spectrometric analysis were used. An attempt to identify the proteins visualized by [32P] autoradiography in a proteomics study and their phosphorylation sites, demonstrated that protein identification was possible whereas reliable identification of the phospho-peptides requires more protein than normally available in our proteomics studies.

The intracellular molecular events involved in the ␤-cell death process are complex but poorly understood. Cytokines, e.g., interleukin (IL)-1␤, may play a crucial role in inducing this process. Protein synthesis is necessary for the deleterious effect of IL-1, and induction of both protective and deleterious proteins has been described. To characterize the rather complex pattern of islet protein expression in rat islets in response to IL-1, we have attempted to identify proteins of altered expression level after IL-1 exposure by 2D gel electrophoresis and mass spectrometry. Of 105 significantly changed (i.e., up-or downregulated or de novo-induced) protein spots, we obtained positive protein identification for 60 protein spots. The 60 identifications corresponded to 57 different proteins. Of these, 10 proteins were present in two to four spots, suggesting that posttranslatory modifications had occurred. In addition, 11 spots contained more than one protein. The proteins could be classified according to their function into the following groups: 1) energy transduction; 2) glycolytic pathway; 3) protein synthesis, chaperones, and protein folding; and 4) signal transduction, regulation, differentiation, and apoptosis. In conclusion, valuable information about the molecular mechanisms involved in cytokine-mediated ␤-cell destruction was obtained by this approach. Protein synthesis inhibitors (e.g., cycloheximide) effectively protect IL-1-exposed islets from destruction (12). Hence, protein synthesis is necessary for the deleterious effect of IL-1. Previous studies have shown that IL-1 induces the synthesis of members of the heat shock protein (HSP) family, like heme oxygenase (13) and HSPs 70 and 90 (14,15), and hyperexpression of HSPs in islets is partially protective against cytokine-induced ␤-cell destruction (16). Furthermore, it has been reported that IL-1 may induce the synthesis of unknown proteins with molecular weights of 45,50, 75, 85, 95, and 120 kDa (17). It has previously been shown that rat islets exposed to IL-1 release NO into the culture media (18). iNOS has been cloned from islets (19) in which it has been shown to be inducible in ␤-cells only (20). We have further shown that IL-1 also upregulates IL-1 converting enzyme mRNA transcription (21) in rat islets. Also, SOD is shown to be upregulated in islets by cytokines (15,22).Based on ␤-cell-selective toxic effects, we hypothesized that IL-1 induces a rather complex pattern of both protective and deleterious events and mechanisms in islets cells, and that in ␤-cells the deleterious events seem to prevail (23). We further suggested that this might be reflected at the level of islet protein expression (24). To examine this hypothesis, we used 2D gel electrophoresis to produce a database of rat islet proteins containing about 2,200 protein spots characterized by molecular weight and isoelectric point (pI). The data presented here provide the first global assessment of the IL-1-mediated ␤-cell-damaging processes at the protein level. We could demonstra...