Selenium-deficient diet enhances protein oxidation and affects methionine sulfoxide reductase (MsrB) protein level in certain mouse tissues

Abstract

Mammals contain two methionine sulfoxide (MetO) reductases, MsrA and MsrB, that catalyze the thioredoxin-dependent reduction of the S-MetO and R-MetO derivatives, respectively, to methionine. The major mammalian MsrB is a selenoprotein (except in the heart). Here, we show that there is a loss of MsrB activity in the MsrA-/- mouse that correlates with parallel losses in the levels of MsrB mRNA and MsrB protein, suggesting that MsrA might have a role in MsrB transcription. Moreover, mice that were grown on a selenium-deficient (SD) diet showed a substantial decrease in the levels of MsrB-catalytic activity, MsrB protein, and MsrB mRNA in liver and kidney tissues of both WT and MsrA-/- mouse strains. Whereas no significant protein-MetO could be detected in tissue proteins of young mature mice grown on a selenium-adequate diet, growth on the SD diet led to substantial accumulations of MetO in proteins and also of protein carbonyl derivatives in the liver, kidney, cerebrum, and cerebellum, respectively. In addition, accumulation of protein-MetO derivatives increased with age in tissues of mice fed with a selenium-adequate diet. It should be pointed out that even though the total Msr level is at least 2-fold higher in WT than in MsrA-/- mice, SD diet causes an equal elevation of protein-MetO (except in brain cerebellum) and carbonyl levels in both strains, suggesting involvement of other selenoproteins in regulation of the level of cellular protein-MetO accumulation. Furthermore, the development of the "tip-toe" walking behavior previously observed in the MsrA-/- mice occurred earlier when they were fed with the SD diet.

Fig. 1.

Expression of MsrA and MsrB in livers taken from mice fed with SA or SD diet. (Top and Middle) Equal amounts of liver proteins (20 μg) were separated by SDS/PAGE followed by Western blot analysis using specific antibodies against MsrA or MsrB, respectively. Lanes 1 and 3 represent WT samples, and lanes 2 and 4 represent MT samples. Lanes 1 and 2 are liver proteins taken from mice fed the SA diet, and lanes 3 and 4 are liver proteins taken from mice fed the SD diet. Each lane contains pooled proteins collected from five mice at 6 months of age. (Bottom) Quantitation of the MsrB mRNA levels on a 1% agar gel after RT-PCR of mRNA sample from each liver tissue, as described in Materials and Methods. The agar gel is aligned according to lanes 1–4 of the Western blots described above.

Fig. 2.

Msr activities in extracts of tissues taken from mice fed with SA or SD diet. MsrA or MsrB activity was measured by using Dabsyl-MetO as substrate as described in Materials and Methods. Solid bars represent SA diet, and hatched bars represent SD diet. R and S represent MsrB and MsrA activity, respectively. Proteins from five mice at 6 months of age were used for each analysis.

Fig. 3.

MetO accumulations in various tissues of mice fed with SD or SA diet. Protein-bound MetO levels were analyzed according to the procedure described in Materials and Methods. Solid bars and cross-hatched bars represent WT and MT, respectively. Proteins from five mice were used for each analysis. SD (6 months) or SA (13 months) represents mice at age 6 or 13 months fed the SD or SA diet, respectively. Brain,Cr and Brain,Cl represent cerebrum and cerebellum, respectively.

Fig. 4.

Protein carbonyl accumulations in various mouse tissues fed the SA or SD diet. Protein carbonyl was measured according to the method described previously (24). L, K, and B represent liver, kidney, and brain, respectively. Solid bars and cross-hatched bars represent WT and MT, respectively. Proteins from five mice were used for each analysis.