Mitochondria are devoid of amyloid ß-protein (Aß)-producing secretases: Evidence for unlikely occurrence within mitochondria of Aß generation from amyloid precursor protein.

Mitochondrial dysfunction is implicated in the pathological mechanism of Alzheimer's disease (AD). Amyloid ß-protein (Aß), which plays a central role in AD pathogenesis, is reported to accumulate within mitochondria. However, a question remains as to whether Aß is generated locally from amyloid precursor protein (APP) within mitochondria. We investigated this issue by analyzing the expression patterns of APP, APP-processing secretases, and APP metabolites in mitochondria separated from human neuroblastoma SH-SY5Y cells and those expressing Swedish mutant APP. APP, BACE1, and PEN-2 protein levels were significantly lower in crude mitochondria than microsome fractions while those of ADAM10 and the other γ-secretase complex components (presenilin 1, nicastrin, and APH-1) were comparable between fractions. The crude mitochondrial fraction containing substantial levels of cathepsin D, a lysosomal marker, was further separated via iodixanol gradient centrifugation to obtain mitochondria- and lysosome-enriched fractions. Mature APP, BACE1, and all γ-secretase complex components (in particular, presenilin 1 and PEN-2) were scarcely present in the mitochondria-enriched fraction, compared to the lysosome-enriched fraction. Moreover, expression of the ß-C-terminal fragment (ß-CTF) of APP was markedly low in the mitochondria-enriched fraction. Additionally, immunocytochemical analysis showed very little co-localization between presenilin 1 and Tom20, a marker protein of mitochondria. In view of the particularly low expression levels of BACE1, γ-secretase complex proteins, and ß-CTF in mitochondria, we propose that it is unlikely that Aß generation from APP occurs locally within this organelle.

Topographical disorientation in a patient with right parahippocampal infarction.

We here describe a patient showing topographical disorientation (TD) after infarction of the right medial occipital lobe; the lesion included the parahippocampal gyrus. Clinical and neuropsychological observations demonstrated a specific pattern of impairment in terms of visual and visuospatial (topographical) learning, and memory. He had no landmark agnosia. His defective route finding resulted from impaired allocentric and egocentric spatial representations. Drawing illustrations of both familial and unfamiliar place and orientation tasks in an egocentric coordination context is a useful means of recognizing the influence of egocentric and/or allocentric spatial disturbance. The definition of "allocentric" or "egocentric" is confusing, and requires a standard for differentiating TD types.

TFEB-mediated Enhancement of the Autophagy-lysosomal Pathway Dually Modulates the Process of Amyloid ß-Protein Generation in Neurons.

Abnormalities of the autophagy-lysosomal pathway (ALP) have been implicated in the pathology of Alzheimer's disease (AD). Activation of TFEB (transcription factor EB), a master regulator of the ALP, leads to ALP facilitation. The present study sought to clarify whether TFEB-mediated ALP facilitation influences the process of amyloid ß-protein (Aß) generation in neurons. TFEB was overexpressed in mature rat primary cortical neurons via recombinant adenoviruses, without (basal conditions) or with co-overexpression of wild-type amyloid precursor protein (APP) or its ß-C-terminal fragment (ß-CTF). We confirmed that TFEB overexpression upregulated the lysosomal proteins, cathepsin D and LAMP-1. In TFEB-expressing neurons, protein levels of ADAM10 were profoundly increased, whereas those of APP, BACE1, or γ-secretase complex proteins were unaffected. However, TFEB did not affect ADAM10 mRNA levels. TFEB overexpression had different effects on Aß production depending on the expression level of APP or ß-CTF: TFEB slightly decreased Aß secretion under basal conditions; clearly increased α-CTF levels and marginally increased ß-CTF levels with modest increases in secreted Aß in APP-expressing neurons; and caused a remarkable increase in ß-CTF levels with a significant increase in secreted Aß in ß-CTF-expressing neurons. Inhibition of proteasomes, but not lysosomes, markedly increased ß-CTF levels in ß-CTF-expressing neurons. These results collectively indicate that TFEB modulates Aß production not only by increasing α-secretase processing of APP through ADAM10 upregulation but also by augmenting ß-CTF levels possibly via altered proteasome-mediated catabolism. Thus, TFEB-mediated ALP enhancement appears to have dual, but opposite, effects on Aß production in neurons.

Tyrosol Reduces Amyloid-ß Oligomer Neurotoxicity and Alleviates Synaptic, Oxidative, and Cognitive Disturbances in Alzheimer's Disease Model Mice.

Soluble amyloid-ß (Aß) oligomers (AßOs), which elicit neurotoxicity and synaptotoxicity, are thought to play an initiating role in the pathology of Alzheimer's disease (AD). Since AßOs are a key therapeutic target, we attempted to identify natural agents that reduce AßO neurotoxicity. Using an assay system in which primary cultured neurons are treated with AßOs, we found that Rhodiola rosea extracts and one of its main constituents, tyrosol, significantly inhibited AßO-induced caspase-3 activation. We then assessed the in vivo efficacy of tyrosol by oral administration of the compound into AD model (5XFAD) transgenic and non-transgenic mice from either 2 or 4 to 7 months of age. In both paradigms, tyrosol treatment did not affect body weights of mice. Immunohistochemical analysis revealed that the immunoreactivity of spinophilin, a dendritic synaptic protein, was significantly reduced in three hippocampal subregions of vehicle-treated AD mice compared with non-transgenic mice, which was reversed in tyrosol-treated AD mice. Tyrosol treatment also prevented the enhancement of 4-hydroxy-2-nonenal immunoreactivity in the hippocampal CA3 region of AD mice. By contrast, tyrosol administration did not affect Aß accumulation, as evaluated by immunohistochemical and biochemical analyses. Moreover, the Barnes maze test showed that tyrosol administration modestly mitigated spatial memory impairment in AD mice. These findings collectively indicate that the natural agent tyrosol protects neurons against AßO neurotoxicity in vitro and ameliorates synaptic disturbance, oxidative stress responses, and cognitive impairment in vivo. We thus suggest that tyrosol is potentially an effective, safe, and unique drug candidate for AD.

GDF-15, a mitochondrial disease biomarker, is associated with the severity of multiple sclerosis.

GDF-15, a member of the transforming growth factor beta superfamily, regulates inflammatory and apoptotic pathways in various diseases, such as heart failure, kidney dysfunction, and cancer. We aimed to clarify potentially confounding variables affecting GDF-15 and demonstrate its utility as a mitochondrial biomarker using serum samples from 15 patients with mitochondrial diseases (MD), 15 patients with limbic encephalitis (LE), 10 patients with multiple sclerosis/neuromyelitis optica spectrum disorders (MS/NMOSD), and 19 patients with amyotrophic lateral sclerosis (ALS). GDF-15 and FGF-21 were significantly elevated in MD. GDF-15 and FGF-21 showed a good correlation in MD but not in LE, MS, and ALS. GDF-15 was potentially influenced by age in LE, MS/NMOSD, and ALS but not in MD. FGF-21 was not correlated with age in MS/NMOSD, ALS, LE, and MD. GDF-15 was not correlated with clinical features in LE or BMI or body weight in ALS. GDF-15 positively correlated with the Expanded Disability Status Scale (EDSS) in MS/NMOSD, while EDSS showed no correlation with age. In conclusion, the results revealed that GDF-15 may be influenced by EDSS in MS/NMOPSD and by age in LE, MS/NMOSD, and ALS but not in MD. Mitochondrial damage in MS/NMOSD is a potentially confounding variable affecting GDF-15.

The neurotoxicity of amyloid ß-protein oligomers is reversible in a primary neuron model.

Alzheimer's disease (AD) is characterized by the accumulation of extracellular amyloid ß-protein (Aß) and intracellular hyperphosphorylated tau proteins. Recent evidence suggests that soluble Aß oligomers elicit neurotoxicity and synaptotoxicity, including tau abnormalities, and play an initiating role in the development of AD pathology. In this study, we focused on the unclarified issue of whether the neurotoxicity of Aß oligomers is a reversible process. Using a primary neuron culture model, we examined whether the neurotoxic effects induced by 2-day treatment with Aß42 oligomers (Aß-O) are reversible during a subsequent 2-day withdrawal period. Aß-O treatment resulted in activation of caspase-3 and eIF2α, effects that were considerably attenuated following Aß-O removal. Immunocytochemical analyses revealed that Aß-O induced aberrant phosphorylation and caspase-mediated cleavage of tau, both of which were mostly reversed by Aß-O removal. Furthermore, Aß-O caused intraneuronal dislocation of ß-catenin protein and a reduction in its levels, and these alterations were partially reversed upon Aß-O withdrawal. The dislocation of ß-catenin appeared to reflect synaptic disorganization. These findings indicate that removal of extracellular Aß-O can fully or partially reverse Aß-O-induced neurotoxic alterations in our neuron model. Accordingly, we propose that the induction of neurotoxicity by Aß oligomers is a reversible process, which has important implications for the development of AD therapies.

Enlargement of the brachial plexus on magnetic resonance imaging: a novel finding in adult-onset Krabbe disease.

Adult-onset Krabbe disease is an autosomal recessive degenerative leukodystrophy that presents with bilateral corticospinal tract involvement on MRI. Although peripheral nerve involvement is a known manifestation of Krabbe disease, MRI findings of peripheral nerve abnormalities are limited to the cranial nerves and spinal nerve roots. In this case report, we discuss two cases of adult-onset Krabbe disease with brachial plexus enlargement on MRI. Adult-onset Krabbe disease should be included in the differential diagnoses when brachial plexus enlargement and white matter lesions involving corticospinal tracts present simultaneously.

Amyloid ß-protein oligomers upregulate the ß-secretase, BACE1, through a post-translational mechanism involving its altered subcellular distribution in neurons.

BACKGROUND: ß-Site amyloid precursor protein cleaving enzyme 1 (BACE1) is a membrane-bound aspartyl protease that initiates amyloid ß-protein (Aß) generation. Aberrant elevation of BACE1 levels in brains of Alzheimer's disease (AD) patients may involve Aß. In the present study, we used a neuron culture model system to investigate the effects of Aß on BACE1 expression as well as the underlying mechanisms. RESULTS: Rat primary cortical neurons were treated with relatively low concentrations (2.5 µM) of Aß42 oligomers (Aß-O) or fibrils (Aß-F) for 2-3 days. Aß-O induced a significant increase in protein levels of BACE1, while Aß-F only had a marginal effect. Levels of amyloid precursor protein (APP) and the major α-secretase, ADAM10, remained unaltered upon treatment with both types of Aß. Aß-O treatment resulted in activation of eIF2α and caspase 3 in a time-dependent manner, with no changes in the endoplasmic reticulum (ER) stress marker, GRP78, indicating that a typical ER stress response is not induced under our experimental conditions. Furthermore, Aß-O did not affect BACE1 mRNA expression but augmented the levels of exogenous BACE1 expressed via recombinant adenoviruses, indicating regulation of BACE1 protein expression, not at the transcriptional or translational but the post-translational level. Immunocytochemical analysis revealed that Aß-O causes a significant increase in BACE1 immunoreactivity in neurites (both axons and dendrites), but not soma of neurons; this change appears relevant to the mechanism of Aß-O-induced BACE1 elevation, which may involve impairment of BACE1 trafficking and degradation. In contrast, Aß-O had no effect on APP immunoreactivity. CONCLUSION: Our results collectively suggest that Aß oligomers induce BACE1 elevation via a post-translational mechanism involving its altered subcellular distribution in neurons, which possibly triggers a vicious cycle of Aß generation, thus contributing to the pathogenetic mechanism of AD.

LRP1 Downregulates the Alzheimer's ß-Secretase BACE1 by Modulating Its Intraneuronal Trafficking

The ß-secretase called BACE1 is a membrane-associated protease that initiates the generation of amyloid ß-protein (Aß), a key event in Alzheimer's disease (AD). However, the mechanism of intraneuronal regulation of BACE1 is poorly understood. Here, we present evidence that low-density lipoprotein receptor-related protein 1 (LRP1), a multi-functional receptor, has a previously unrecognized function to regulate BACE1 in neurons. We show that deficiency of LRP1 exerts promotive effects on the protein expression and function of BACE1, whereas expression of LRP-L4, a functional LRP1 mini-receptor, specifically decreases BACE1 levels in both human embryonic kidney (HEK) 293 cells and rat primary neurons, leading to reduced Aß production. Our subsequent analyses further demonstrate that (1) both endogenous and exogenous BACE1 and LRP1 interact with each other and are colocalized in soma and neurites of primary neurons, (2) LRP1 reduces the protein stability and cell-surface expression of BACE1, and (3) LRP1 facilitates the shift in intracellular localization of BACE1 from early to late endosomes, thereby promoting lysosomal degradation. These findings establish that LRP1 specifically downregulates BACE1 by modulating its intraneuronal trafficking and stability through protein interaction and highlight LRP1 as a potential therapeutic target in AD.

Recurrent isolated abducens nerve paresis associated with persistent trigeminal artery variant.

We report a 74-year-old woman who presented with recurrent isolated abducens nerve paresis. Cranial magnetic resonance imaging revealed that the right abducens nerve was sandwiched between the right internal carotid artery and a persistent trigeminal artery (PTA) variant, which might have led to neurovascular compression of the abducens nerve, resulting in abducens nerve damage. Normal variants of PTA, which are cerebellar arteries originating from a precavernous portion of the internal carotid artery, must be carefully observed as such variants can potentially cause a neurovascular compression of the abducens nerve.