Inverse correlation of protein oxidation and proteasome activity in liver and lung.

Several studies have demonstrated that proteasome activity decreases whereas protein oxidation increases with aging in various tissues. However, no studies are available correlating both parameters directly comparing different tissues of one organism. Therefore, we determined whether there is an age-related change in proteasome activity and protein oxidation in heart, lung, liver, kidney and skeletal muscle samples of 6-, 10-, 18- and 26-month-old rats. There was a significant age-related increase in protein carbonyls at 18 and 26 months compared to young rats. Thereby, protein carbonyl formation was rather due to a general than a specific protein carbonylation as shown by immunblot studies. The highest increase in protein carbonyl formation was found in liver, lung and kidney samples. Proteasome activity decreased significantly with age in lung and liver samples. Proteasome activity in liver and lung decreased by factor five compared to young rats. Strong correlations between proteasome activity and protein oxidation were found in liver and lung, whereas in other tissues only a trend was found. These results demonstrate that the increase in protein oxidation and the decline in proteasome activity are correlating. Further studies are needed to determine the mechanisms which cause organ-specific aging-rates and their consequences.

Effect of oxidative stress on the junctional proteins of cultured cerebral endothelial cells.

(1) There is increasing evidence that the cerebral endothelium and the blood-brain barrier (BBB) plays an important role in the oxidative stress-induced brain damage. The aim of the present study was to investigate the role of interendothelial junctional proteins in the BBB permeability increase induced by oxidative stress. (2) For the experiments, we have used cultured cerebral endothelial cells exposed to hypoxia/reoxygenation or treated with the redox cycling quinone 2,3-Dimethoxy-1,4-naphthoquinone (DMNQ) in the presence or absence of glucose. The expression of junctional proteins and activation of mitogen activated protein kinases (MAPK) was followed by Western-blotting, the interaction of junctional proteins was investigated using coimmunoprecipitation. (3) Oxidative stress induces a downregulation of the tight junction protein occludin expression which is more pronounced in the absence of glucose. Furthermore, oxidative stress leads to disruption of the cadherin-beta-catenin complex and an activation of extracellular signal-regulated kinase (ERK1/2), which is more intense in the absence of glucose. (4) We have shown that one of the causes of the BBB breakdown is probably the structural alteration of the junctional complex caused by oxidative stress, a process in which ERK1/2 may play an important role.