Citations

We report a technique to simultaneously measure fractional synthesis rates (FSR) of several muscle proteins that facilitate further understanding of translational regulation, a key step involved in gene expression in a tissue. Skeletal muscle samples were collected from five rats following bolus injection of [ring 13 C 6 ] phenylalanine. Muscle proteins were fractionated by differential centrifugation followed by separation of individual proteins by high resolution two‐dimensional gel electrophoresis. We identified 60 mitochondrial and 30 non‐mitochondrial proteins by liquid chromatography tandem mass spectrometry. Isotope enrichment of these 90 proteins was measured by gas chromatography tandem mass spectrometry, and FSR was calculated using the muscle tissue fluid isotopic enrichment as the precursor. Approximately 25 fold differences in the FSR of muscle proteins were observed, (e.g. FSR of structural protein such as myosin heavy chain‐1 = 0.19 %/h ± 0.03 and tropomysin‐4 = 0.16 ± 03 and that of mitochondrial proteins such as cytochrome c oxidase Va = 0.64 ± 0.07 and dihydrolipoamide dehydrogenase = 4.3 %/h ± 0.53). The current approach, based on in‐vivo metabolic labeling, to simultaneously measure FSR of multiple muscle proteins offers tremendous opportunity to study the regulation of skeletal muscle mitochondrial and non‐mitochondrial protein synthesis in various physiologic and pathologic states. Funding: NIH RO1 DK41973

Insulin regulates many cellular processes, but the full impact of insulin deficiency on cellular functions remains to be defined. Applying a mass spectrometry–based nontargeted metabolomics approach, we report here alterations of 330 plasma metabolites representing 33 metabolic pathways during an 8-h insulin deprivation in type 1 diabetic individuals. These pathways included those known to be affected by insulin such as glucose, amino acid and lipid metabolism, Krebs cycle, and immune responses and those hitherto unknown to be altered including prostaglandin, arachidonic acid, leukotrienes, neurotransmitters, nucleotides, and anti-inflammatory responses. A significant concordance of metabolome and skeletal muscle transcriptome–based pathways supports an assumption that plasma metabolites are chemical fingerprints of cellular events. Although insulin treatment normalized plasma glucose and many other metabolites, there were 71 metabolites and 24 pathways that differed between nondiabetes and insulin-treated type 1 diabetes. Confirmation of many known pathways altered by insulin using a single blood test offers confidence in the current approach. Future research needs to be focused on newly discovered pathways affected by insulin deficiency and systemic insulin treatment to determine whether they contribute to the high morbidity and mortality in T1D despite insulin treatment.

It remains to be determined whether systemic insulin replacement normalizes synthesis rates of different plasma proteins and whether there are differential effects on various plasma proteins. We tested a hypothesis that insulin deprivation differentially affects individual plasma protein synthesis and that systemic insulin treatment may not normalize synthesis of all plasma proteins. We measured synthesis rates of 41 plasma proteins in seven each of type 1 diabetic (T1DM) and nondiabetic participants (ND) using [ ring-13C6]phenylalanine as a tracer. T1DM were studied while on chronic insulin treatment and during 8 h insulin deprivation. Insulin treatment normalized glucose levels, but plasma insulin levels were higher during insulin treatment than during insulin deprivation in T1DM and ND. Individual plasma proteins were purified by affinity chromatography and two-dimensional gel electrophoresis. Only 41 protein gel spots from over 300 were chosen based on their protein homogeneity. Insulin deprivation and hyperglycemia either significantly increased ( n = 12) or decreased ( n = 12) synthesis rates of 24 of 41 plasma proteins in T1DM compared with ND. Insulin treatment normalized synthesis rates of 13 of these 24 proteins, which were altered during insulin deprivation. However, insulin treatment significantly altered the synthesis of 14 additional proteins. In conclusion, acute insulin deprivation caused both a decrease and increase in synthesis rates of many plasma proteins with various functions. Moreover, chronic systemic insulin treatment not only did not normalize synthesis of all plasma proteins but also altered synthesis of several additional proteins that were unaltered during insulin deprivation.