Yuan Liu

α7 nicotinic acetylcholine receptor-mediated neuroprotection against dopaminergic neuron loss in an MPTP mouse model via inhibition of astrocyte activation

BackgroundAlthough evidence suggests that the prevalence of Parkinson’s disease (PD) is lower in smokers than in non-smokers, the mechanisms of nicotine-induced neuroprotection remain unclear. Stimulation of the α7 nicotinic acetylcholine receptor (α7-nAChR) seems to be a crucial mechanism underlying the anti-inflammatory potential of cholinergic agonists in immune cells, including astrocytes, and inhibition of astrocyte activation has been proposed as a novel strategy for the treatment of neurodegenerative disorders such as PD. The objective of the present study was to determine whether nicotine-induced neuroprotection in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model occurs via α7-nAChR-mediated inhibition of astrocytes.MethodsBoth in vivo (MPTP) and in vitro (1-methyl-4-phenylpyridinium ion (MPP+) and lipopolysaccharide (LPS)) models of PD were used to investigate the role(s) of and possible mechanism(s) by which α7-nAChRs protect against dopaminergic neuron loss. Multiple experimental approaches, including behavioral tests, immunochemistry, and stereology experiments, astrocyte cell cultures, reverse transcriptase PCR, laser scanning confocal microscopy, tumor necrosis factor (TNF)-α assays, and western blotting, were used to elucidate the mechanisms of the α7-nAChR-mediated neuroprotection.ResultsSystemic administration of nicotine alleviated MPTP-induced behavioral symptoms, improved motor coordination, and protected against dopaminergic neuron loss and the activation of astrocytes and microglia in the substantia nigra. The protective effects of nicotine were abolished by administration of the α7-nAChR-selective antagonist methyllycaconitine (MLA). In primary cultured mouse astrocytes, pretreatment with nicotine suppressed MPP+-induced or LPS-induced astrocyte activation, as evidenced by both decreased production of TNF-α and inhibition of extracellular regulated kinase1/2 (Erk1/2) and p38 activation in astrocytes, and these effects were also reversed by MLA.ConclusionTaken together, our results suggest that α7-nAChR-mediated inhibition of astrocyte activation is an important mechanism underlying the protective effects of nicotine.

Activation of α7 nicotinic acetylcholine receptors protects astrocytes against oxidative stress-induced apoptosis: implications for Parkinson's disease.

Astrocytes have been implicated in the immune responses associated with Parkinsons disease (PD). Inhibition of astrocyte apoptosis is a novel strategy for the treatment of PD. Recent studies suggest that α7 nicotinic acetylcholine receptors (α7-nAChRs) expressed in glial cells are critical links between inflammation and neurodegeneration in PD. However, little is known about their contribution to astrocyte apoptosis during the development of this disorder. In the present study, we showed that nicotine exerts a protective effect on H2O2-induced astrocyte apoptosis and glial cell-derived neurotrophic factor (GDNF) downregulation, and this effect was abolished by an α7-nAChR-selective antagonist. The underlying mechanisms might involve alleviation of mitochondrial membrane potential loss, stabilization of the Bax/Bcl-2 balance, and inhibition of cleaved caspase-9 activity through α7-nAChR activation. Systemic administration of nicotine dramatically alleviated MPTP-induced symptoms, protected dopaminergic neurons against degeneration, inhibited astrocytes and microglia activation in the substantia nigra pars compacta (SNpc) and blocked the decrease of GDNF in the striatum by activating α7-nAChRs. Taken together these findings demonstrate, for the first time, that nicotine suppresses H2O2-induced astrocyte apoptosis via the mitochondrial pathway through the stimulation of α7-nAChRs. Targeting α7-nAChRs expressed in astrocytes may be a novel therapeutic strategy for the treatment of neurodegenerative disorders.

Regulation of B7-H1 expression on peripheral monocytes and IFN-γ secretion in T lymphocytes by HBeAg

This study is to observe the expression of B7-H1, PD-1 and TLR2 on peripheral blood monocytes (PBMCs) regulated by HBeAg in chronic hepatitis B (CHB), and to illustrate the relation between HBeAg and persistent infection of HBV. In both CHB patients and healthy controls, the expression of B7-H7 was significantly increased on CD14(+) monocytes incubated with HBeAg, while that of TLR2 was significantly reduced; the expression of specific IFN-γ was significantly decreased in CD3(+)CD4(+) T lymphocytes incubated with HBeAg, while IL-6 and IL-10 in conditioned media were significantly increased. HBeAg is able to significantly up-regulate B7-H1, down-regulate TLR2 on monocytes, reduce IFN-γ produced by T lymphocytes and increase Th2-type cytokines secretion. These findings suggest that HBeAg suppresses the specific cellular immunity to clear the virus, and eventually lead to immune tolerance to HBV infection. Therefore, HBeAg plays an important role in immune suppression in chronic HBV patients.

Activation of α7 Nicotinic Acetylcholine Receptors Prevents Monosodium Iodoacetate-Induced Osteoarthritis in Rats

Background/Aims: Although some evidence suggests that the prevalence of osteoarthritis (OA) is lower in smokers compared to nonsmokers, the mechanisms of nicotine-induced protection remain unclear. Stimulation of the a7 nicotinic acetylcholine receptor (a7-nAChR) appears to be a critical mechanism underlying the anti-inflammatory potential of cholinergic agonists in immune cells. The inhibition of secreted inflammatory molecules and the subsequent inflammatory processes have been proposed as a novel strategy for the treatment of OA. The objective of the present study was to determine whether nicotine-induced protection in a monosodium iodoacetate (MIA) rat model of OA occurs via a7-nAChR-mediated inhibition of chondrocytes. Methods: Both in vivo (MIA) and in vitro (MIA; Interleukin-1ß, IL-1ß) models of OA were used to investigate the roles and the possible mechanisms whereby a7-nAChRs protect against knee joint degradation. Multiple experimental approaches, including macroscopic, histological analysis, chondrocyte cell cultures, confocal microscopy, and western blotting, were employed to elucidate the mechanisms of a7-nAChR-mediated protection. Results: Systemic administration of nicotine alleviated MIA-induced joint degradation. The protective effects of nicotine were abolished by administration of the a7-nAChR-selective antagonist methyllycaconitine (MLA). In primary cultured rat chondrocytes, pretreatment with nicotine suppressed both p38, extracellular regulated kinase (Erk) 1/2 and c-Jun-N-terminal kinase (JNK) mitogen-activated protein kinases (MAPK) phosphorylation and phosphorylated nuclear factor-kappa B (NF-κB) p65 activation induced by MIA- or IL-1ß, and these effects were also reversed by MLA. Conclusion: Taken together, our results suggest that activation a7-nAChRs is an important mechanism underlying the protective effects of nicotine.

Wnt/β-catenin signaling plays an essential role in α7 nicotinic receptor-mediated neuroprotection of dopaminergic neurons in a mouse Parkinson’s disease model

&NA; Parkinsons disease (PD) is a neurodegenerative disorder with an incidence second only to Alzheimers disease. The main pathological feature of PD is the death of dopaminergic neurons in the substantia nigra pars compacta. Nicotinic receptor agonists are neuroprotective in several PD models and there is considerable evidence that &agr;7 nicotinic acetylcholine receptors (&agr;7‐nAChRs) are important therapeutic targets for neurodegenerative diseases. However, the involvement of &agr;7‐nAChRs and underlying signaling mechanisms in PD pathogenesis are unclear. The objective of the present study was to explore the potential functions of &agr;7‐nAChRs in PD pathology, and to determine whether these effects are exerted via Wnt/&bgr;‐catenin signaling in a mouse PD model. In the in vivo study, &agr;7‐nAChR knockout (&agr;7‐KO) reversed the beneficial effects of nicotine on motor deficits, dopaminergic neuron loss, astrocyte and microglia activation, and reduced striatal dopamine release induced by 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine. Injury to SH‐SY5Y cells by 1‐methyl‐4‐phenylpyridinium treatment was also ameliorated by nicotine, and this effect was abolished by methyllycaconitine (MLA), a selective &agr;7‐nAChR antagonist, or by siRNA‐mediated &agr;7‐nAChR knockdown. Furthermore, nicotine increased expression levels of Wnt/&bgr;‐catenin signaling proteins in the PD mouse model or in the SH‐SY5Y cells treated by 1‐methyl‐4‐phenylpyridinium, and these effects were also reversed by MLA or &agr;7‐siRNA treatment in vivo or in vitro. These results suggest that endogenous &agr;7‐nAChR mechanisms play a crucial role in a mouse PD model via regulation of Wnt/&bgr;‐catenin signaling.

Dynamic alterations of gene expression of nicotinic acetylcholine receptor α7, α4 and β2 subunits in an acute MPTP-lesioned mouse model

Epidemiologic studies show that the prevalence of Parkinsons disease (PD) is lower in smokers than in nonsmokers. Nicotine, a potent agonist of nicotinic acetylcholine receptors (nAChRs), excites midbrain dopaminergic neurons and this may contribute to the anti-parkinsonian effects. However, the alterations in gene expression of nAChR subunits using an acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse PD model remain unclear. In the present study, we profile the time course of nAChR α7, α4 and β2 subunit expression levels using a comparative RT-PCR approach after acute MPTP injection. The results fall into four categories. (1) MPTP treatment transiently increased nAChR α7 (after last injection of MPTP 3 and 24 h), α4 and β2 (24 h) mRNA expression in the substantia nigra (SN) and striatum. (2) Compared to cortical and hippocampal tissues, this transient increase of nAChR subunit expression specifically occurred in the SN and striatum. (3) In the acute MPTP model, time-courses of altered expression for nAChR α7, α4 and β2 subunits closely mirrored the deficits observed in animal motor activity. (4) Stereological data showed that after administration of MPTP for 24h, there was a robust astrogliosis in the SN associated with significant dopaminergic neurodegeneration. These changes followed or paralleled MPTP-induced elevation in the levels of α7, α4 and β2 mRNAs. Collectively, our results demonstrate that nAChRs are important targets in the MPTP neurotoxic process. These data suggest that therapeutic strategies targeted toward nAChR α7, α4 and β2 subunits may have potential for developing new treatments for PD.

MicroRNA-132 and microRNA-212 mediate doxorubicin resistance by down-regulating the PTEN-AKT/NF-κB signaling pathway in breast cancer

Breast cancer is a serious health problem worldwide. Acquisition of multi-drug resistance (MDR) during the treatment of breast cancer is still considered a major clinical obstacle. Despite the biological functions of miRNAs becoming increasingly apparent, the function of miRNAs in regulating drug resistance of breast cancer remains under investigation. Quantitative real-time PCR (qRT-PCR) was used to quantify the expression of miR-132/-212 (miR-132 and miR-212) in doxorubicin (DOX)-resistant and -sensitive breast cancer tumors and cells. The function of miR-132/-212 in drug resistance was investigated in vitro (MTT assay, TUNEL assay, fluorescence, immunohistochemistry, luciferase reporter assay, Western blotting). We found that miR-132/-212 were commonly overexpressed in DOX-resistant breast cancer tumors and cells. Silenced miR-132/-212 expression induced DOX accumulation in MCF-7/ADR cells, while overexpression of miR-132/-212 led to breast cancer resistance protein (BCRP)-based DOX efflux in MCF-7 cells. Further study showed that up-regulation of miR-132/-212 in MCF-7/ADR cells suppressed the expression of PTEN, a target gene of miR-132/-212, which activated AKT phosphorylation and the NF-κB pathway and led to increased BCRP expression. Down-regulation of miR-132/-212 sensitized MCF-7/ADR cells to DOX. Mechanistic investigations suggested that miR-132/-212 enhancement was a result of NF-κB-mediated transactivation of the pri-miR-132/-212 gene. Taken together, our findings are among the first to demonstrate a novel aspect of the miR-132/-212-PTEN-AKT/NF-κB-BCRP pathway in the generation of breast cancer resistance and provides a potential method to reverse drug resistance.

Pre-operative radiographic findings predicting concomitant posterior malleolar fractures in tibial shaft fractures: a comparative retrospective study

BackgroundA concomitant tibial shaft and posterior malleolar fracture is a type of regular compound fracture. The associated posterior malleolar fractures are mostly occult fractures, which often do not show a fracture line on ordinary films, and thus lead to a high rate of misdiagnosis. The aim of the present study was to investigate factors helpful for the pre-operative detection of concomitant posterior ankle fractures using the ipsilateral radiographic tibia and fibula shaft fracture characteristics.MethodsOne hundred eleven adult patients with tibial shaft fractures were selected using inclusion and exclusion criteria. Pre-operative ankle radiographs and computed tomography (CT) scans were obtained for all patients, and clinical data, including age and gender, were collected. Patients were divided into two groups (posterior malleolar fracture and no posterior malleolar fracture groups). Fracture height, fracture length, fracture shape, and Haraguchi type of posterior malleolar fracture were measured on radiographs and CT images, and were compared between the two groups. Multiple logistic regression analysis was performed to identify the factors that significantly contributed to concomitant posterior malleolar fractures. Receiver operating characteristic curves were calculated, and cut-off values were used to predict posterior malleolar fractures on pre-operative imaging measurements.ResultsOf the 111 patients with tibial shaft fractures, 42 (37.8%) had a concurrent posterior malleolar fracture. Age, gender and affected side were not significantly different, but tibial fracture location, fracture length, and fibular and tibial fracture shape were significantly different between the two groups. In the multiple logistic analysis, tibial fracture location, fracture length, and tibial fracture shape were shown to be significant factors contributing to posterior malleolar fractures. Receiver operating characteristic curves showed that the status of tibial shaft fractures is closely related to the associated posterior malleolar fracture.ConclusionIpsilateral posterior ankle fractures are commonly associated with tibial shaft fractures, especially spiral-type injuries. An analysis of the imaging features of such fractures and evaluation of the diagnostic value of various methods can provide imaging basics for the development of accurate and appropriate treatment options.