Amyloid Precursor Protein mRNA Levels Research Articles

Abstract W P359: Activation of Prostacyclin Receptor (IP) in Human Brain Microvascular Endothelial Cells Stimulates Production of SAPPa

Previous studies have established that cerebral blood vessels possess high capacity to synthesize prostacyclin (PGI 2 ). Substantial evidence indicates that amyloid precursor protein (APP) and soluble APPα (sAPPα) have neurotrophic and nueroprotective properties. We hypothesized that activation of IP-cAMP pathway stimulates non-amyloidogenic processing of APP in cerebral endothelial cells. Western blotting was used to detect protein expression; real time RT-PCR was employed to measure mRNA levels of APP, and a disintegrin and metalloprotease 10 (ADAM10, an α processing enzyme); sAPPα secretion was detected in condition medium derived from culturing human brain microvascular endothelial cells (BMVECs), by ELISA. After human BMVECs were treated with PGI 2 analog iloprost (0.01, 0.05, 0.1, or 0.5 μM) for 3 days, protein levels of ADAM10 (n=7-9, P<0.05) and APP (n=6, P<0.05) were significantly increased in a concentration dependent manner, while β amyloidogenic processing enzyme BACE1, and other α processing enzymes such as ADAM9 and ADAM17 were not changed. mRNA levels of APP (n=7, P<0.05) and ADAM10 (n=4, P<0.05), as well as sAPPα production in human BMVECs (n=6, P<0.05) were also significantly augmented in response to iloprost treatment. Moreover, stimulation of human BMVECs with forskolin (40μM) significantly enhanced APP and ADAM10 protein expression. Most notably, iloprost significantly augmented protein expression of peroxisome proliferation-activated receptor-δ (PPARδ) and SIRT1. We further explored the role of PPARδ in APP processing. ADAM10 expression (n=6, P<0.05), but not APP and BACE1, was significantly increased in human BMVECs treated with PPARδ ligand GW501516 (30 or 100 nM). GW501516 (100 nM) also significantly increase sAPPα production (n=9-10, P<0.05). siRNA against PPARδ significantly suppressed basal levels of ADAM10, and blocked iloprost-induced ADAM10 expression (n=4, P<0.05). These findings suggest that activation of IP-cAMP pathway enhances non-amyloidogenic processing of APP and consequently increases production of neurotrophic molecule sAPPα in human BMVECs. Activation of PPARδ in part mediates iloprost-induced α processing of APP.

Effects of Nerve Growth Factor and Nitric Oxide Synthase Inhibitors on Amyloid Precursor Protein mRNA Levels and Protein Stability

We determined previously that nitric oxide (NO) modulates the nerve growth factor (NGF)-mediated increases in amyloid precursor protein (APP) levels in PC12 cells. To elucidate potential mechanisms, the effects of NGF and NO synthase (NOS) inhibitors on APP mRNA levels and protein stability were evaluated. Surprisingly, treatment of PC12 cells with NGF resulted in decreased levels of APP695 and APP751/770 mRNA. Therefore, the effect of NGF on APP protein stability was examined using the translation inhibitor, cycloheximide. Under these conditions, NGF did not alter the rate of APP degradation, suggesting that NGF may be enhancing the translation rate of APP. Since NOS inhibitors attenuate the NGF-mediated increase in APP levels, their effect on APP mRNA levels and protein stability was also assessed. S-methylisothiourea (S-MIU), selective for inducible NOS, decreased both APP695 and APP751/770 mRNA levels while the non-selective NOS inhibitor, Nω-nitro-L-arginine methylester (L-NAME) had no effect. In both control and NGF-treated PC12 cells, S-MIU increased the half-life of APP, with the greatest effect observed with the APP695 isoform. Based on these data we propose that in PC12 cells, NGF increases APP levels through enhanced translation rate and that NO, which modulates the NGF-induced increase in APP protein, also regulates APP mRNA levels and could play a role in APP processing.

Amyloid precursor protein mRNA levels in Alzheimer's disease brain

Insoluble β-amyloid deposits in Alzheimer's disease (AD) brain are proteolytically derived from the membrane bound amyloid precursor protein (APP). The APP gene is differentially spliced to produce isoforms that can be classified into those containing a Kunitz-type serine protease inhibitor domain (K +, APP 751, APP 770, APRP 365 and APRP 563), and those without (K −, APP 695 and APP 714,). Given the hypothesis that Aβ is a result of aberrant catabolism of APP, differential expression of mRNA isoforms containing protease inhibitors might play an active role in the pathology of AD. We took 513 cerebral cortex samples from 90 AD and 81 control brains and quantified the mRNA isoforms of APP with TaqMan™ real-time RT-PCR. After adjustment for age at death, brain pH and gender we found a change in the ratio of KPI+ to KPI− mRNA isoforms of APP. Three separate probes, designed to recognise only KPI+ mRNA species, gave increases of between 28% and 50% in AD brains relative to controls ( p=0.002). There was no change in the mRNA levels of KPI-(APP 695) ( p=0.898). Therefore, whilst KPI-mRNA levels remained stable the KPI+species increased specifically in the AD brains.

Induction of tyrosine kinase receptor b by retinoic acid allows brain-derived neurotrophic factor-induced amyloid precursor protein gene expression in human sh-sy5y neuroblastoma cells

Retinoic acid (RA) is a potent regulator of morphogenesis, growth and cell differentiation. Incubation with RA causes arrest of proliferation and neurite extension in SH-SY5Y cells, a neuroblastoma cell line of human origin. In these cells, RA regulates the expression of the β-amyloid precursor protein. The retinoid increases the levels of intracellular and secreted forms of APP (amyloid precursor protein), APP–mRNA levels and the activity of the APP promoter in transient transfection studies. These responses require long periods of exposition to the ligand, thus suggesting a nondirect effect of the RA receptors on the APP gene. Also in these cells, RA induces the expression of TrkB, the tyrosine kinase receptor for brain-derived neurotrophic factor (BDNF), and 4 days of pretreatment with retinoic acid confers BDNF responsiveness to the APP promoter.

Amyloid precursor protein mRNA levels in the mononuclear blood cells of Alzheimer's and Down's patients

Amyloid precursor protein (APP) is expressed by many non-neural tissues and it is possible that over-expression of the APP gene in non-neural tissue is responsible for the deposition of amyloid β-protein in the brain and elsewhere. One possible source of β-protein is circulating mononuclear blood cells which have previously been shown to express APP. To test this hypothesis. RNA was isolated from the mononuclear blood cells of patients suffering from Alzheimer's disease ( n = 27), Down's syndrome ( n = 13), senile dementia non-Alzheimer type ( n = 14) and from normal individuals ( n = 48). The relative abundance of mRNA coding for different splicing variants of the amyloid precursor protein (APP) mRNA was measured using multiprobe oligonucleotide solution hybridisation (MOSH). There was no significant difference in APP mRNA levels between any of the groups. This indicates that Alzheimer's disease is not characterised by an increase in production of APP in circulating mononuclear blood cells.