Hong-Qi Yang

Protective effects of erythropoietin on tau phosphorylation induced by β-amyloid

Neuropathological studies have demonstrated that the presence of neurofibrillary tangles (NFTs) is one of the most prominent pathologic characteristics of Alzheimers disease (AD). The microtubule‐associated protein tau is the major component of NFTs, and its abnormal hyperphosphorylation leads to the destabilization of microtubules, impaired axonal transport, and eventual death of the neurons. The hematopoietic cytokine erythropoietin (Epo) is now considered as a viable agent with regard to central nervous system injury in a variety of cellular systems. Here we report that Epo prevented tau hyperphosphorylation in SH‐SY5Y cells exposed to the β‐amyloid peptide and that this effect may depend on the PI3K/Akt‐GSK‐3β pathway. This study provides new molecular insight into the neuroprotective effect of Epo and suggests its possible therapeutic role in the management of AD.

Blockade of the translocation and activation of c-Jun N-terminal kinase 3 (JNK3) attenuates dopaminergic neuronal damage in mouse model of Parkinson's disease

Increasing evidence suggests that c-Jun N-terminal kinase (JNK) is an important kinase mediating neuronal death in Parkinsons disease (PD) model induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). JNK3, the only neural-specific isoform, may play an important role in mediating the neurotoxic effects of MPTP in dopaminergic neuronal injury. To analyze the variation in JNK3 activation, the levels of phospho-JNK3 were measured at the various time points of occurrence of MPTP-induced lesions. In our study, we observed that during MPTP intoxication, two peaks of JNK3 activation appeared at 8 and 24h. To further define the mechanism of JNK3 activation and translocation, the antioxidant N-acetylcysteine (NAC), the N-methyl-D-aspartate (NMDA) receptor antagonist ketamine, and the alpha-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate (KA) receptor antagonist 6,7-dinitroquinoxaline-2,3(1H,4H)-dione (DNQX) were administered to the mice 30 min after each of the four MPTP injections. The results revealed that NAC clearly inhibited JNK3 activation during the early intoxication, whereas ketamine preferably attenuated JNK3 activation during the latter intoxication. DNQX had no significant effects on JNK3 activation during intoxication. Consequently, reactive oxygen species (ROS) and the NMDA receptor were closely associated with JNK3 activation following MPTP intoxication. NAC and ketamine exerted a preventive effect against MPTP-induced loss of tyrosine hydroxylase-positive neurons and suppressed the nuclear translocation of JNK3, suggesting that NAC and ketamine can prevent MPTP-induced dopaminergic neuronal death by suppressing JNK3 activation.

New protein kinase C activator regulates amyloid precursor protein processing in vitro by increasing α‐secretase activity

The beta amyloid (Aβ) cascade has been at the forefront of the hypothesis used to describe the pathogenesis of Alzheimers disease (AD). It is generally accepted that drugs that can regulate the processing of the amyloid precursor protein (APP) toward the non‐amyloidogenic pathway may have a therapeutic potential. Previous studies have shown that protein kinase C (PKC) hypofunction has an important role in AD pathophysiology. Therefore, the effects of a new PKC activator, α‐APP modulator [(2S,5S)‐(E,E)‐8‐(5‐(4‐(trifluoromethyl)phenyl)‐2,4‐pentadienoylamino)benzolactam (TPPB)], on APP processing were investigated. Using PC12 cells and SH‐SY5YAPP695 cells, it was found that TPPB promoted the secretion of sAPPα without affecting full‐length expression of APP. The increase in sAPPα by TPPB was blocked by inhibitors of PKC, extracellular signal‐regulated kinase (ERK), c‐Jun N‐terminal kinase (JNK) and tyrosine kinase, suggesting the involvement of these signal transduction pathways. TPPB increased α‐secretase activity [a disintegrin and metalloproteinase (ADAM)10 and 17], as shown by direct fluorescence activity detection and Western blot analysis. TPPB‐induced sAPPα release was blocked by the metalloproteinase inhibitor TAPI‐2, furin inhibitor CMK and by the protein‐trafficking inhibitor brefeldin. The results also showed that TPPB decreased β‐secretase activity, Aβ40 release and beta site APP‐cleaving enzyme 1 (BACE1) expression, but did not significantly affect neprilysin (NEP) and insulin‐degrading enzyme (IDE) expression. Our data indicate that TPPB could direct APP processing towards the non‐amyloidogenic pathway by increasing α‐secretase activity, and suggest its therapeutic potential in AD.

K252a Prevents Nigral Dopaminergic Cell Death Induced by 6-Hydroxydopamine through Inhibition of Both Mixed-Lineage Kinase 3/c-Jun NH2-Terminal Kinase 3 (JNK3) and Apoptosis-Inducing Kinase 1/JNK3 Signaling Pathways

It is well documented that the mitogen-activated protein kinase pathway plays a pivotal role in rats with 6-hydroxydopamine (6-OHDA)-induced unilateral lesion in the nigrostriatal system. Our recent studies have shown that mixed-lineage kinase 3 (MLK3) and apoptosis-inducing kinase 1 (ASK1) are all involved in neuronal cell death induced by ischemia, which is mediated by the MLK3/c-Jun NH2-terminal kinase 3 (JNK3) and ASK1/JNK signaling pathway. To investigate whether these pathways are correlated with 6-OHDA-induced lesion as well, we examined the phosphorylation of MLK3, ASK1, and JNK3 in 6-OHDA rats. The results showed that both MLK3 and ASK1 could activate JNK3 and then subsequently enhance the neuronal death through its downstream pathways (i.e., nuclear and non-nuclear pathway). K252a have wide-range effects including Trk inhibition, MLK3 inhibition, and activation of phosphatidylinositol 3 kinase and mitogen-activated protein kinase kinase signaling pathways through interactions with distinct targets and is a well known neuroprotective compound. We found that K252a could protect dopaminergic neurons against cell program death induced by 6-OHDA lesion, and the phenotypes of 6-OHDA rat model treated with K252a were partial rescued. The inhibition of K252a on the activation of MLK3/JNK3 and ASK1/JNK3 provided a link between 6-OHDA lesion and stress-activated kinases. It suggested that both proapoptotic MLK3/JNK3 and ASK1/JNK3 cascade may play an important role in dopaminergic neuronal death in 6-OHDA insult. Thus, the JNK3 signaling may eventually emerge as a prime target for novel therapeutic approaches to treatment of Parkinson disease, and K252a may serve as a potential and important neuroprotectant in therapeutic aspect in Parkinson disease.

Cellular and behavioral effects of 5-HT1A receptor agonist 8-OH-DPAT in a rat model of levodopa-induced motor complications

5-HT1A autoreceptor stimulation can act to attenuate supraphysiological swings in extracellular dopamine levels following long-term levodopa treatment and may be useful in the treatment and prevention of the motor complications. The purpose of this study was to investigate cellular and behavioral effects of 5-HT1A receptor agonist 8-OH-DPAT in a rat model of levodopa-induced motor complications. Two sets of experiments were performed. First, animals were treated with levodopa (50 mg/kg with benserazide 12.5 mg/kg, twice daily), intraperitoneally (i.p.) for 22 days. On day 23, animals received either 8-OH-DPAT (1 mg/kg, i.p.) or 8-OH-DPAT plus WAY-100635 (0.1 mg/kg, i.p) or vehicle with each levodopa dose. In the second set, animals were treated either with levodopa (50 mg/kg, i.p.) plus 8-OH-DPAT (1 mg/kg, i.p.) or levodopa (50 mg/kg, i.p.) plus vehicle, administered twice daily for 22 consecutive days. Our study showed that 8-OH-DPAT plus levodopa both prolonged the duration of the motor response and reduced peak turning. 8-OH-DPAT plus levodopa also decreased the frequency of failures to levodopa. Co-administration of WAY-100635, a 5-HT1A receptor antagonist, with 8-OH-DPAT eliminated the effect of 8-OH-DPAT on motor complications indicating that the observed 8-OH-DPAT responses were probably mediated at the 5-HT1A autoreceptor. Moreover, 8-OH-DPAT plus levodopa significantly reduced hyperphosphorylation of GluR1 at serine 845, which was closely associated with levodopa-induced motor complications.

Involvement of protein trafficking in deprenyl-induced α-secretase activity regulation in PC12 cells

Deprenyl is a selective B-type monoamine oxidase inhibitor and a neuroprotective agent that has been used to slow the progress of Alzheimers disease for many years. We previously demonstrated that deprenyl could stem amyloid precursor protein processing (APP) toward the non-amyloidogenic pathway through mitogen activated protein kinase (MAPK) and protein kinase C (PKC)-dependent signaling pathways [Yang, H.Q., Ba, M.W., Ren, R.J., Zhang, Y.H., Ma, J.F., Pan, J., Lu, G.Q., Chen, S.D., 2007a. Mitogen activated protein kinase and protein kinase C mediated promotion of sAPPalpha by deprenyl. Neurochem. Int. 50, 74-82.]. The experiment here further showed that deprenyl could increase alpha-secretase activity in a dose-dependent manner in PC12 cells. Deprenyl increased alpha-secretase activity can be partially blocked by pretreatment with brefeldin A, an intracellular protein transport inhibitor, suggesting involvement of protein trafficking in deprenyl regulated alpha-secretase activity. In accordance with this, the experiment showed that brefeldin A also decreased sAPPalpha release induced by deprenyl. Deprenyl promoted ADAM10 transported to the membrane fraction, and this effect was blocked by pretreatment with brefeldin A. The immunocytochemistry staining revealed that deprenyl promoted colocalization of ADAM10 with PKCalpha and PKCepsilon isoforms. These data suggest a novel pharmacological mechanism in which deprenyl increased alpha-secretase activity via protein trafficking related mechanism.