Phosphorylation and Glycosylation of Amyloid-ß Protein Precursor: The Relationship to Trafficking and Cleavage in Alzheimer's Disease.

Alzheimer's disease (AD) is a neurodegenerative disorder in the central nervous system, and this disease is characterized by extracellular senile plaques and intracellular neurofibrillary tangles. Amyloid-ß (Aß) peptide is the main constituent of senile plaques, and this peptide is derived from the amyloid-ß protein precursor (AßPP) through the successive cleaving by ß-site AßPP-cleavage enzyme 1 (BACE1) and γ-secretase. AßPP undergoes the progress of post-translational modifications, such as phosphorylation and glycosylation, which might affect the trafficking and the cleavage of AßPP. In the recent years, about 10 phosphorylation sites of AßPP were identified, and they play complex roles in glycosylation modification and cleavage of AßPP. In this article, we introduced the transport and the cleavage pathways of AßPP, then summarized the phosphorylation and glycosylation sites of AßPP, and further discussed the links and relationship between phosphorylation and glycosylation on the pathways of AßPP trafficking and cleavage in order to provide theoretical basis for AD research.

Inhibitory effects of curcumin on H2O2-induced cell damage and APP expression and processing in SH-SY5Y cells transfected with APP gene with Swedish mutation.

Alzheimer's disease (AD) is a neurodegenerative disorder, and the pathological mechanism of the disease is still far to understand. According to the amyloid cascade hypothesis in AD, Amyloid-ß (Aß) is considered as a key substance that contributes AD development. Aß is a ß-cleaving product from Amyloid-ß protein precursor (APP). Mutations of APP including APPKM670/671670NL (Swedish mutation) result in Aß overproduction and the development of early-onset familial AD. Increase of oxidative stress and damage also occurs in early stage of AD. In this study, we used a SH-SY5Y cell line that stably expresses APP gene with Swedish mutation (SH-SY5Y-APPswe), and the inhibitory effects of curcumin on H2O2-induced cell damage and APP processing were investigated. Cells were treated with curcumin (0 ~ 5 µM) for 4 h before hydrogen peroxide (H2O2). Cell growth was detected with CCK-8 assay, and cell damage was determined through the evaluation of release of lactate dehydrogenase (LDH) from the cytosol to the culture medium and the morphological change of nucleus. The ability of mitochondrial stress and the depolarization of mitochondrial membrane potential were assayed through the measuring the oxygen consumption rate (OCR) and the green/red fluorescence ratio of JC-1 dye respectively. The protein levels of APP, sAPPα, sAPPß, and BACE1 were analyzed with Western blot assay. Aß production was measured with enzyme-linked immunosorbent assay (ELISA). The results indicated that curcumin inhibits H2O2-induced decrease of cell growth and cell damage. Curcumin attenuates H2O2-induced damage on the ability to mitochondrial oxidative phosphorylation and membrane potential. Curcumin inhibits H2O2-induced increase of APP cleavage through ß-cleavage pathway and of intracellular Aß production. These results imply that curcumin can be used to treat AD through inhibiting oxidative damage-induced APP ß-cleavage and intracellular Aß generation.

Variations in blood pressure and heart rate in conscious rats with cervical lymphatic blockade.

The possible effects of cervical lymphatic blockade (CLB) on a series of parameters in conscious freely moving rats were analysed. Blood pressure (BP) and heart rate (HR) for conscious male Sprague-Dawley rats at 1, 3, 7, 11, 15 and 21 days after a CLB or a sham operation were monitored continuously for 24 hours with a computerized recording system. Since BP and HR were subjected to spontaneous variations, blood pressure variability (BPV) and heart rate variability (HRV) were expressed as the standard deviation of beat-to-beat BP and HR values. The baroreflex sensitivities (BRS) were determined by measuring the heart period (HP = 60,000/HR) prolongation in response to the elevation in BP induced by an intravenous administration of phenylephrine at 1, 7, 15 and 21 days after the CLB or sham operation. Compared with those in sham-operated rats, the values of systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial blood pressure (MAP), HR and BRS in CLB rats were significantly lower, whereas the values of BPV and HRV were markedly raised in CLB rats at different time points. Furthermore, the impaired ultrastructure in the dorsomedial nucleus of the solitary tract (dmNTS) including degeneration, apoptosis and necrosis in neurons and gliacytes, were apparent from the 1st to 15th day but the changes were most significant at 7th day after CLB operation. Structural changes appeared to be closely related to functional changes of the dmNTS at each time point. Thus, in CLB conscious rats, a significant decline in blood pressure accompanied by dysfunction in its regulation might be due to the impaired structure in the dmNTS.

Changes of nitric oxide, oxide free radicals, and systolic arterial blood pressure in rats with experimental lymphatostatic encephalopathy.

The model of lymphatostatic encephalopathy was established by occluding and removing profound cervical nodes in rats, and the kinetic alteration of nitric oxide (NO), maleic dialdehyde (MDA), free radical scavenger (CuZn-SOD) and arterial systolic blood pressure were determined on different days after the blockage. The results showed that the level of NO significantly decreased at 1 day (P<0.05) and further decreased at 3, 5 and 7 day (P<0.01). The levels of MDA at 1, 3, 5 and 7 day significantly increased, but the contents of CuZn-SOD significantly decreased compared with the control (P<0.01). There was negative correlation between the levels of MDA and CuZn-SOD, but there was no relationship between MDA an NO. Arterial systolic blood pressure decreased progressively after cervical lymphatic blockage. The results showed that NO, oxide free radicals and the disturbances of the cardiovascular regulation may play important roles in lymphatostatic encephalopathy.

Identification of two critical amino acid residues of the severe acute respiratory syndrome coronavirus spike protein for its variation in zoonotic tropism transition via a double substitution strategy.

Severe acute respiratory syndrome coronavirus (SARS-CoV) is a recently identified human coronavirus. The extremely high homology of the viral genomic sequences between the viruses isolated from human (huSARS-CoV) and those of palm civet origin (pcSARS-CoV) suggested possible palm civet-to-human transmission. Genetic analysis revealed that the spike (S) protein of pcSARS-CoV and huSARS-CoV was subjected to the strongest positive selection pressure during transmission, and there were six amino acid residues within the receptor-binding domain of the S protein being potentially important for SARS progression and tropism. Using the single-round infection assay, we found that a two-amino acid substitution (N479K/T487S) of a huSARS-CoV for those of pcSARS-CoV almost abolished its infection of human cells expressing the SARS-CoV receptor ACE2 but no effect upon the infection of mouse ACE2 cells. Although single substitution of these two residues had no effects on the infectivity of huSARS-CoV, these recombinant S proteins bound to human ACE2 with different levels of reduced affinity, and the two-amino acid-substituted S protein showed extremely low affinity. On the contrary, substitution of these two amino acid residues of pcSARS-CoV for those of huSRAS-CoV made pcSARS-CoV capable of infecting human ACE2-expressing cells. These results suggest that amino acid residues at position 479 and 487 of the S protein are important determinants for SARS-CoV tropism and animal-to-human transmission.