Selective neuronal vulnerability and inadequate stress response in superoxide dismutase mutant mice.

To understand the role of oxidative stress and mitochondrial defects in the development of neurodegeneration, we examined the age-related pathological changes and corresponding gene expression profiles in homozygous mutant mice deficient in the mitochondrial form of superoxide dismutase (MnSOD, SOD2). These Sod2-/- mice, generated on a B6D2F1 background, developed ataxia at Postnatal Day (P) 11 and progressively deteriorated with frequent seizures by P14. Histopathological examination revealed neurodegenerative changes consistent with the neurological signs. Vacuolar degeneration was observed in neurons and neuropil throughout the brainstem and rostral cortex. The motor trigeminal nucleus in brainstem and the deeper layers of the motor cortex were the earliest regions to degenerate, with the thalamus and hippocampus affected at later stages. Oligonucleotide microarrays were used to compare gene expression profiles in the brainstem and thalamus of Sod2+/+ and -/- mice from birth to P18. Notably, a large set of heat-shock protein genes was transcriptionally down regulated, and this was most likely due to a reduction in the heat-shock transcription factor 1 (HSF1). Other major classes of differentially expressed genes include lipid biosynthesis and ROS metabolism.

Identification of biomarkers associated with the development of hepatocellular carcinoma in CuZn superoxide dismutase deficient mice.

To identify biomarkers associated with the development of hepatocellular carcinoma (HCC) in CuZn superoxide dismutase (CuZnSOD, Sod1) deficient mice, 2-DE followed by MS analysis was carried out with liver samples obtained from 18-month-old Sod1-/- and +/+ mice. The intracellular Ca binding protein, regucalcin (RGN), showed a divergent alteration in Sod1-/- samples. Whereas elevated RGN levels were observed in -/- samples with no obvious neoplastic changes, marked reduction in RGN was observed in -/- samples with fully developed HCC. GST mu1 (GSTM1), on the other hand, showed a significant increase only in the neoplastic regions obtained from Sod1-/- livers. No change in GSTM1 was observed in the surrounding normal tissues. Marked reduction was observed in two intracellular lipid transporters, fatty acid binding protein 1 (FABP1) and major urinary protein 11 and 8 (MUP 11&8), in Sod1-/- samples. Analysis of additional samples at 18-22 months of age showed a three-fold increase in enolase activities in Sod1-/- livers. Consistent with previous findings, carbonic anhydrase 3 (CAIII) levels were significantly reduced in Sod1-/- samples, and immunohistochemical analysis revealed that the reduction was not homogenous throughout the lobular structure in the liver.

Genetic modifiers of the phenotype of mice deficient in mitochondrial superoxide dismutase.

Sod2-/- mice, which are deficient in the mitochondrial form of superoxide dismutase (MnSOD), have a short survival time that is strongly affected by genetic background. This suggests the existence of genetic modifiers that are capable of modulating the degree of mitochondrial oxidative damage caused by the MnSOD deficiency, thereby altering longevity. To identify these modifier(s), we generated recombinant congenic mice with quantitative trait loci (QTL) containing the putative genetic modifiers on the short-lived C57BL/6J genetic background. MnSOD deficient C57BL/6J mice with a QTL from the distal region of chromosome 13 from DBA/2J were able to survive for as long as those generated on the long-lived DBA/2J background. Within this region, the gene encoding nicotinamide nucleotide transhydrogenase (Nnt) was found to be defective in C57BL/6J mice, and no mature NNT protein could be detected. The forward reaction of NNT, a nuclear-encoded mitochondrial inner membrane protein, couples the generation of NADPH to proton transport and provides NADPH for the regeneration of two important antioxidant compounds, glutathione and thioredoxin, in the mitochondria. This action of NNT could explain its putative protective role in MnSOD-deficient mice.