Selected reaction monitoring mass spectrometry for relative quantification of proteins involved in cellular life and death processes

Increased antioxidant response in medium-chain acyl-CoA dehydrogenase deficiency: does lipoic acid have a protective role?

BACKGROUND

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency (MCADD) is the most frequent fatty acid oxidation (FAO) defect in humans. MCAD-deficient fibroblasts are more resistant to oxidative stress-induced cell death than other FAO defects and healthy controls.

METHODS

Herein we investigate the antioxidant response and mitochondrial function in fibroblasts from MCAD-deficient patients (c.985 A>G/c.985 A>G) and healthy controls.

RESULTS

MCAD-deficient fibroblasts showed increased level of mitochondrial superoxide, while lipids were less oxidatively damaged, and higher amount of manganese superoxide dismutase were detected compared to healthy controls, showing forceful antioxidant system in MCADD. We showed increased maximal respiration and reserve capacity in MCAD-deficient fibroblasts compared to controls, indicating more capacity through the tricarboxylic acid (TCA) cycle and subsequently respiratory chain. This led us to study the pyruvate dehydrogenase complex (PDC), the key enzyme in the glycolysis releasing acetyl-CoA to the TCA cycle. MCAD-deficient fibroblasts displayed not only significantly increased PDC but also increased lipoylated PDC protein levels compared to healthy controls.

CONCLUSIONS

Based on these findings, we raise the interesting hypothesis that increased PDC-bound lipoic acid, synthesized from accumulated octanoic acid in MCADD, may affect the cellular antioxidant pool in MCADD.

The zinc transporter Zip14 (SLC39a14) affects Beta-cell Function: Proteomics, Gene expression, and Insulin secretion studies in INS-1E cells

Insulin secretion from pancreatic beta-cells is dependent on zinc ions as essential components of insulin crystals, zinc transporters are thus involved in the insulin secretory process. Zip14 (SLC39a14) is a zinc importing protein that has an important role in glucose homeostasis. Zip14 knockout mice display hyperinsulinemia and impaired insulin secretion in high glucose conditions. Endocrine roles for Zip14 have been established in adipocytes and hepatocytes, but not yet confirmed in beta-cells. In this study, we investigated the role of Zip14 in the INS-1E beta-cell line. Zip14 mRNA was upregulated during high glucose stimulation and Zip14 silencing led to increased intracellular insulin content. Large-scale proteomics showed that Zip14 silencing down-regulated ribosomal mitochondrial proteins, many metal-binding proteins, and others involved in oxidative phosphorylation and insulin secretion. Furthermore, proliferation marker Mki67 was down-regulated in Zip14 siRNA-treated cells. In conclusion, Zip14 gene expression is glucose sensitive and silencing of Zip14 directly affects insulin processing in INS-1E beta-cells. A link between Zip14 and ribosomal mitochondrial proteins suggests altered mitochondrial RNA translation, which could disturb mitochondrial function and thereby insulin secretion. This highlights a role for Zip14 in beta-cell functioning and suggests Zip14 as a future pharmacological target in the treatment of beta-cell dysfunction.

The clinical outcome of LMNA missense mutations can be associated with the amount of mutated protein in the nuclear envelope

AIMS

Lamin A/C mutations are generally believed to be associated with a severe prognosis. The aim of this study was to investigate disease expression in three affected families carrying different LMNA missense mutations. Furthermore, the potential molecular disease mechanisms of the mutations were investigated in fibroblasts obtained from mutation carriers.

METHODS AND RESULTS

A LMNA-p.Arg216Cys missense mutation was identified in a large family with 36 mutation carriers. Disease expression was unusual with a late onset and a favourable prognosis. Two smaller families with severe disease expression were shown to carry a LMNA-p.Arg471Cys and LMNA-p.Arg471His mutation, respectively. LMNA gene and protein expression was investigated in eight different mutation carriers by quantitative reverse transcriptase polymerase chain reaction, Western blotting, immunohistochemistry, and protein mass spectrometry. The results showed that all mutation carriers incorporated mutated lamin protein into the nuclear envelope. Interestingly, the ratio of mutated to wild-type protein was only 30:70 in LMNA-p.Arg216Cys carriers with a favourable prognosis while LMNA-p.Arg471Cys and LMNA-p.Arg471His carriers with a more severe outcome expressed significantly more of the mutated protein by a ratio of 50:50.

CONCLUSION

The clinical findings indicated that some LMNA mutations may be associated with a favourable prognosis and a low risk of sudden death. Protein expression studies suggested that a severe outcome was associated with the expression of high amounts of mutated protein. These findings may prove to be helpful in counselling and risk assessment of LMNA families.