Inhibition of Mitochondrial Clearance and Cu/Zn-SOD Activity Enhance 6-Hydroxydopamine-Induced Neuronal Apoptosis.

Parkinson's disease (PD) is a common movement disorder among neurodegenerative diseases, involving neuronal cell death in the substantia nigra of the midbrain. Although mechanisms of cell death in PD have been studied, the exact molecular pathogenesis is still unclear. Here, we explore the relationship between two types of cell death, autophagy and apoptosis, which have been studied separately in parkinsonian mimetic model of 6-hydroxydopamine (6-OHDA). 6-OHDA induced autophagy firstly and then later inhibition of autophagy flux occurred with apoptosis. The apoptosis was prevented by treatment of pan-caspase inhibitor, zVAD-fmk (benzyloxycarbonyl-VAD-fluoromethylketone (zVAD)), or early phase inhibitor of autophagy, 3-methyladenine (3-MA), indicating that autophagic induction was followed by the apoptosis. Interestingly, late step inhibitor of autophagy, bafilomycin A1 (BafA), aggravated 6-OHDA-induced apoptosis. This was associated with mitochondrial abnormality such as the inhibition of damaged mitochondrial clearance and aberrant increase of extracellular oxygen consumption. Furthermore, treatment of BafA did not inhibit 6-OHDA-mediated superoxide formation but strongly reduced the hydrogen peroxide production to below basal levels, indicating failure from superoxide to hydrogen peroxide. These results were accompanied by a lowered expression and activity of copper/zinc superoxide dismutase (Cu/Zn-SOD) but not of manganese SOD (MnSOD) and catalase. Thus, the present study suggests that crosstalk among apoptosis, autophagy, and oxidative stress is a causative factor of 6-OHDA-induced neuronal death and provides a mechanistic understanding of PD pathogenesis.

Beta-amyloid oligomers induce early loss of presynaptic proteins in primary neurons by caspase-dependent and proteasome-dependent mechanisms.

Beta-amyloid is a major pathogenic molecule for Alzheimer's disease (AD) and can be aggregated into a soluble oligomer, which is a toxic intermediate, before amyloid fibril formation. Beta-amyloid oligomers are associated closely with early synaptic loss in AD. However, it is still unknown which synaptic proteins are involved in the synaptotoxicity, and a direct comparison among the synaptic proteins should also be addressed. Here, we investigated changes in the expression of several presynaptic and postsynaptic proteins in primary neurons after treatment with a low-molecular weight and a high-molecular weight beta-amyloid oligomer. Both oligomers induced early neuronal dysfunction after 4 h and significantly reduced presynaptic protein (synaptophysin, syntaxin, synapsin, and synaptotagmin) expression. However, the expression of postsynaptic proteins (PSD95, NMDAR2A/B, and GluR2/3), except NMDAR1 was not reduced, and some protein expression levels were increased. Glutamate treatment, which is correlated with postsynaptic activation, showed more postsynaptic-specific protein loss compared with beta-amyloid oligomer treatment. Finally, the caspase inhibitor zVAD and the proteasomal inhibitor MG132 attenuated presynaptic protein loss. Thus, our data showed changes in synaptic proteins by beta-amyloid oligomers, which provides an understanding of early synaptotoxicity and suggests new approaches for AD treatment.

Phlorotannin-rich Ecklonia cava reduces the production of beta-amyloid by modulating alpha- and gamma-secretase expression and activity.

Beta-amyloid (Aß) is a major pathogenic peptide in Alzheimer's disease (AD) and is generated by the processing of amyloid precursor protein (APP). We have previously reported that the brown algae Ecklonia cava, which has anti-oxidant and anti-inflammatory functions, decreased Aß production and further aggregation in HEK293 cells expressing the APP Swedish mutation. Here, we show the reduction mechanism of Aß production using the butanol extract of Ecklonia cava through the examination of expression and activity of alpha-, beta-, and gamma-secretase. Treatment with the extract resulted in the activation of alpha-secretase with a contrasting decrease in its mRNA and protein expression. This activation was consistent with the translocation of the extract into the plasma membrane of the secretase. Gamma-secretase activity was lowered by E. cava, and this effect may be due to the decreased expression of PSEN1 mRNA and protein. In addition, the basal nuclear location of PSEN1, which may affect chromosome missegregation in neurodegenerative disease, was reduced by the extract, despite the significance of this finding remains unclear. Taken together, these results led us to conclude that E. cava regulated the expression and activity of gamma-secretase and alpha-secretase, leading to a reduction in Aß production by the stable cells. Our data indicate that E. cava is a novel natural-product candidate for AD treatment, although further in vivo studies are needed.

Nicotinamide induces male-specific body weight loss in the postnatal period through molecular regulation of the hypothalamus and liver.

Molecular mechanisms of body weight control have been discovered recently and much research focuses on the hypothalamic regulation of food intake and the hepatic regulation of glucose utility. We previously reported that postnatal nicotinamide treatment reduced brain dopamine and body weight. To further investigate the differential effects of nicotinamide-mediated body weight loss, nicotinamide (i.p. 100mg/kg) was injected into postnatal and adult mice twice a week for 4 weeks. Interestingly, following nicotinamide treatment, male postnatal mice displayed reduced body weight and spontaneous motor activity. No significant changes were observed in adult and postnatal female mice or adult male mice following nicotinamide treatment. In male postnatal mice, hypothalamic agouti-related peptide (AGRP) and proopiomelanocortin (POMC) levels were increased in the arcuate nucleus following nicotinamide treatment. Neuropeptide Y (NPY) levels were unchanged in both male and female mice. Additionally, nicotinamide-injected male postnatal mice had increased glucose 6-phosphatase (G6Pase) and decreased phosphoenolpyruvate carboxykinase (PEPCK) expression in liver. These results indicate that hypothalamic POMC and hepatic PEPCK are important molecules that mediate nicotinamide-induced weight loss in postnatal male mice.