No abstract

Oxidative stress is closely linked to the pathogenesis of neurodegeneration. Soluble amyloid ␤ (A␤) oligomers cause cognitive impairment and synaptic dysfunction in Alzheimer disease (AD). However, the relationship between oligomers, oxidative stress, and their localization during disease progression is uncertain. Our previous study demonstrated that mice deficient in cytoplasmic copper/zinc superoxide dismutase (CuZn-SOD, SOD1) have features of drusen formation, a hallmark of agerelated macular degeneration (Imamura, Y., Noda, S., Hashizume, K., Shinoda, K., Yamaguchi, M., Uchiyama, S., Shimizu, T., Mizushima, Y., Shirasawa, T., and Tsubota, K. (2006) Proc. Natl. Acad. Sci. U.S.A. 103, 11282-11287). Amyloid assembly has been implicated as a common mechanism of plaque and drusen formation. Here, we show that Sod1 deficiency in an amyloid precursor protein-overexpressing mouse model (AD mouse, Tg2576) accelerated A␤ oligomerization and memory impairment as compared with control AD mouse and that these phenomena were basically mediated by oxidative damage. The increased plaque and neuronal inflammation were accompanied by the generation of N ⑀ -carboxymethyl lysine in advanced glycation end products, a rapid marker of oxidative damage, induced by Sod1 gene-dependent reduction. The Sod1 deletion also caused Tau phosphorylation and the lower levels of synaptophysin. Furthermore, the levels of SOD1 were significantly decreased in human AD patients rather than non-AD agematched individuals, but mitochondrial SOD (Mn-SOD, SOD2) and extracellular SOD (CuZn-SOD, SOD3) were not. These findings suggest that cytoplasmic superoxide radical plays a critical role in the pathogenesis of AD. Activation of Sod1 may be a therapeutic strategy for the inhibition of AD progression. Alzheimer disease (AD)3 is characterized by amyloid deposits in senile plaques mainly consisting of 40-and 42-mer amyloid ␤ proteins (A␤40 and A␤42) (1, 2). These proteins are produced from amyloid precursor protein (APP) by ␤-and ␥-secretases. A␤42 plays a more important role in the pathogenesis of AD than A␤40 because of its greater aggregation propensity and higher neurotoxicity (3). It has been well demonstrated that oxidative stress is a contributing factor to neurodegenerative disease progression (4, 5). A␤-induced neurotoxicity has been linked to oxidative stress via protein radicalization in vitro (6, 7). Soluble oligomeric assemblies (50ϳ60 kDa; e.g. A␤-derived diffusible ligand, A␤ * 56, and globulomer) of A␤ rather than insoluble fibrils are believed to inhibit long term potentiation and induce neuronal loss (8, 9).Many defensive systems protect mammals from oxidative stress caused by reactive oxygen species, including superoxide radicals, hydrogen peroxide, hydroxyl radicals, and singlet oxygen. Superoxide dismutase (SOD) is one of the major antioxidant enzymes that catalyzes the conversion of superoxide radicals to hydrogen peroxide (10). SOD consists of three isozymes: copper/zinc SOD (CuZn-SOD, SOD1), which is localized in the cytosol, nucle...

Two motor neuron diseases, amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA), are caused by distinct genes involved in RNA metabolism, TDP-43 and FUS/TLS, and SMN, respectively. However, whether there is a shared defective mechanism in RNA metabolism common to these two diseases remains unclear. Here, we show that TDP-43 and FUS/TLS localize in nuclear Gems through an association with SMN, and that all three proteins function in spliceosome maintenance. We also show that in ALS, Gems are lost, U snRNA levels are up-regulated and spliceosomal U snRNPs abnormally and extensively accumulate in motor neuron nuclei, but not in the temporal lobe of FTLD with TDP-43 pathology. This aberrant accumulation of U snRNAs in ALS motor neurons is in direct contrast to SMA motor neurons, which show reduced amounts of U snRNAs, while both have defects in the spliceosome. These findings indicate that a profound loss of spliceosome integrity is a critical mechanism common to neurodegeneration in ALS and SMA, and may explain cell-type specific vulnerability of motor neurons.

The β-site amyloid precursor protein cleaving enzyme-1 (BACE1), an essential protease for the generation of amyloid-β (Aβ) peptide, is a major drug target for Alzheimer's disease (AD). However, there is a concern that inhibiting BACE1 could also affect several physiological functions. Here, we show that BACE1 is modified with bisecting N-acetylglucosamine (GlcNAc), a sugar modification highly expressed in brain, and demonstrate that AD patients have higher levels of bisecting GlcNAc on BACE1. Analysis of knockout mice lacking the biosynthetic enzyme for bisecting GlcNAc, GnT-III (Mgat3), revealed that cleavage of Aβ-precursor protein (APP) by BACE1 is reduced in these mice, resulting in a decrease in Aβ plaques and improved cognitive function. The lack of this modification directs BACE1 to late endosomes/lysosomes where it is less colocalized with APP, leading to accelerated lysosomal degradation. Notably, other BACE1 substrates, CHL1 and contactin-2, are normally cleaved in GnT-III-deficient mice, suggesting that the effect of bisecting GlcNAc on BACE1 is selective to APP. Considering that GnT-III-deficient mice remain healthy, GnT-III may be a novel and promising drug target for AD therapeutics.

Involvement of the peripheral autonomic nervous system is a core feature of Lewy body (LB) diseases, including Parkinson disease (PD), PD with dementia, and dementia with LBs. To investigate the potential use of skin biopsy for the diagnosis of LB diseases, we assessed anti-phosphorylated alpha-synuclein immunoreactivity in peripheral nerves in samples of skin from the abdominal wall and flexor surface of the upper arm in 279 prospectively studied consecutively autopsied patients whose data were registered at the Brain Bank for Aging Research between 2002 and 2005. Positive immunoreactivity was demonstrated in the unmyelinated fibers of the dermis in 20 of 85 patients with LB pathology in the CNS and the adrenal glands, the latter representing a substitute for peripheral autonomic nervous system sympathetic ganglia; no reactivity was seen in 194 patients without CNS LB pathology. In 142 retrospectively studied patients autopsied from 1995 onward who had subclinical or clinical LB disease, the sensitivity of the positive skin immunoreactivity was 70% in PD and PD with dementia and 40% in dementia with LBs. Skin immunoreactivity was absent in cases of multiple-system atrophy, progressive nuclear palsy, and corticobasal degeneration. We demonstrate for the first time that the skin is involved and may be a highly specific and useful biopsy site for the pathological diagnosis of LB diseases.