The Molecular Pathways Of Morphine Regulating Thioredoxin Expression

Drug addiction is a chronic, relapsing brain disease, which is induced by one or various psychostimulants. It is characterized by compulsive drug use and seeking, and loss of ability to control behaviour.Morphine addiction has become a worldwide problem, but its mechanism is not fully understood. Previous studies have shown that morphine can cause changes in intracellular molecules, such as Cyclin-dependent kinase5(CDK5), cAMP responsive element binding (CREB) and Ca2+related molecules. These molecules play very important roles in the process of morphine dependence and withdrawal syndrome. Cyclin-dependent kinase5(CDK5) is a serine/threonine protein kinase belonging to the cyclin-dependent kinase family, but it has no report that CDK5is related with cell cycle. In the study of morphine addiction, CDK5phosphorylates the delta receptor of morphine, and has effects on the relief of morphine tolerance. CREB is one of the most in-depth studied addiction-related molecules so far and plays an important role in drug addiction. CREB is activated when its serine133residue (Ser133) is phosphorylated, called p-CREB. p-CREB can participate in the regulation of gene transcription and induce a variety of biological effects in cells. The act of opioids can induce the generation of p-CREB and the formation of drug dependence. NR2B is subunit of the N-methyl-D-aspartate (NMDA) receptor which plays important roles in synaptic plasticity and learning and memory processes. It was proved that the overexpression NR2B transgenic mice performed better than their wild-type littermates in learning and memory aspects. Drug addiction is an abnormal learning and memory process. Thus, NR2B is associated with addiction. Ca2+is an important second messenger in cells and plays a vital role in morphine addiction. In morphine-dependent animals, the withdrawal symptoms can be eliminated by using calcium channel blockers. Chronic exposure to morphine-like substances can increase the calcium ion channels of nerve cells. NMDA receptors, Calcium/calmodulin-dependent protein kinase II (CaMKII) and extracellular signal-regulated kinase (ERK) are important Ca2+regulatory molecules, which play key roles in the regulation of Ca2+In addition, it has been reported that morphine addiction can lead to oxidative stress and imbalance of the redox state. Thioredoxin (Trx) is a small molecular weight protein of12kDa. It can regulate redox state and has multiple functions. Trx widely exists in prokaryotes and eukaryotes. The thioredoxin system, which is consist of Trx, thioredoxin reductase and nicotinamide adenine dinucleotide phosphate (NADPH), has many physiological functions, including anti-oxidation, inhibiting apoptosis, promoting cell proliferation and regulating gene transcription and so on. Therefore, in this paper, we use antagonists of NMDAR/CaMKII/ERK to study molecule pathways on morphine regulating Trx in PC12cells.In our study we used poorly differentiated PC12pheochromocytoma cells. Our data suggested that the expression of Trx was increased after morphine traetment in PC12cells. We also found that the NMDA receptor inhibitor MK-801、CaMKII inhibitor KN-62and ERK inhibitor PD98059suppressed the expression of Trx induced by morphine. In addition, the expression of p-CREB decreased after morphine treatment. Overexpression of Trx blocked the morphine-induced suppression of p-CREB. As well as morphine inhibited the expression of CDK5. Interestingly, the expression of NR2B is increased in the hippocampus of Trx overexpression mice.In summary, our study showed that morphine induced the expression of Trx and inhibited CDK5and p-CREB expressions, the inhibitors of NMDA, MK-801and the inhibitors of CaMKII, KN-62suppressed the increase of Trx by morphine. This study preliminarily clarify signaling pathways on morphine regulating Trx. Overexpression of Trx restored the expression of p-CREB and induced the expression of NR2B in the hippocampus of mice suggesting Trx plays roles in addiction by morphine. Therefore, the further study on relationship between morphine and Trx may provide a new theoretical basis for drug addiction treatment.