The bands were visualized using ECL. ThS staining Coronal, 45-m brain sections were prepared using a DIPQUO Microm HM 360 microtome (Harlow Scientific, Arlington, VA), immersed for 3 min each in 95% and 70% ethanol followed by 5-min incubation in 1% ThS in deionized water (Sigma) and quick rinses in 80% ethanol and deionized water. the reverse reaction is catalyzed by the methionine-sulfoxide reductase (Msr) system, comprising peptide-methionine (and enantiomers of the sulfoxide group, respectively, providing protection against oxidative stress (22). Mammalian MsrA is encoded by a single gene (23) and is found DIPQUO in both the cytosol and mitochondria due to alternative splicing of an N-terminal mitochondrial signal sequence and myristoylation of the cytosolic form (24). MsrA levels decrease with aging (25) and in AD (26). Studies in mice have shown increased vulnerability to oxidative stress (27) and oxidative pathology associated with AD (28) and PD (29). Conversely, overexpression of MsrA in various organisms has been shown to provide enhanced protection against oxidative stress and extend survival rate (30C32). Several laboratories have reported lower toxicity of A-Met(O) relative to WT A (33). This lower toxicity largely has been attributed to the Rabbit Polyclonal to DNAI2 tendency of A-Met(O) to aggregate with slower kinetics (34) and/or form smaller oligomers relative to WT A (14), which correlate with structural differences between native and oxidized A in the C-terminal region (35, 36). However, recent examination of the sulfoxide and sulfone forms of A alongside the WT form DIPQUO found that although A-Met(O) showed reduced toxicity, as expected, the toxicity of A-Met(O2), which was used as a control, was surprisingly similar to that of WT A in assays of neuronal apoptosis, dendritic spine morphology, and Ca2+ homeostasis (37). These data suggested that the lower activity of A-Met(O) might result not only from an altered structure in the C-terminal region of A or alteration of A oligomerization, but also from other mechanisms, possibly Msr activation, which might be unique to the sulfoxide form, despite the similarity in the structure and calculated dipole moment between Met(O) and Met(O2) (14, 38). Consistent with this hypothesis, a recent study has reported elevated MsrA activity and mRNA levels in human neuroblastoma (IMR-32) cells in response to treatment with A42-Met(O) suggesting that the cells sensed the presence of Met(O) in A and upregulated MsrA to provide enhanced cellular protection (39). To test the hypothesis that Msr activation contributes to the lower toxicity observed for A-Met(O) relative to A-Met(O2) and WT A, here, we compared the effect of the WT, sulfoxide, and sulfone forms of A40 and A42 on the viability and Msr activity of rat primary cortical neurons. The findings led us to explore the role of the different Msr isoforms in the cellular response to A by using the same experimental paradigm in primary neurons from WT and by immunization with a Met(O)-rich antigen. Materials and Methods Peptides synthesis A40, [Met(O)35]A40, [Met(O2)35]A40, A42, [Met(O)35]A42, and [Met(O2)35]A42 were synthesized by incorporating FMOC-Met(O) or FMOC-Met(O2) (EMD Biosciences, San Diego, CA) in position 35 where appropriate, purified, and characterized in the UCLA Biopolymers Laboratory. Quantitative amino acid analysis and mass spectrometry were used to characterize the expected compositions and molecular weights, respectively, for each peptide. mice were bred and maintained in house. Cell culture Primary cortical or hippocampal neurons were prepared as described previously (37). Briefly, E18 pregnant rats or mice were euthanized with CO2 and the pups were collected immediately. The brains were dissected DIPQUO DIPQUO in chilled Leibovitzs L-15 medium (ATCC, Manassas, VA) in the presence of 1 g/ml penicillin/streptomycin (Invitrogen, Carlsbad, CA) and the cells were suspended in Dulbeccos Modified Eagles Medium (DMEM, obtained from ATCC) containing 10% heat-inactivated fetal bovine serum (ATCC) and penicillin/streptomycin (1 g/ml), and plated in poly D-lysine (0.1 mg/ml, Sigma)-coated 96-well COSTAR plates (Corning, Lowell, MA) at a density of 3105 cells/ml. The cultures were maintained for 6 d before treatment with peptides. Twenty-four hours after plating, the medium was replaced with.