Upregulation of EphA4 deteriorate brain damage by shifting microglia M1-polarization via NF-κB signaling after focal cerebral ischemia in rats.

Ischemic stroke is the main reason of disability and mortality in many countries, and currently has limited treatments. The post-stroke inflammation characterized with microglia activation and polarization has been regarded as a promising therapeutic target for ischemic stroke. After ischemia, the activated microglia polarize to classical (M1) phenotype or alternative (M2) phenotype and exhibit biphasic function. Promoting microglia phenotype shift from deleterious M1 phenotype to neuroprotective M2 phenotype will be promising in stroke treatment. Increasing evidence indicates that the erythropoietin-producing human hepatocellular (Eph) receptor A4 (EphA4), a kind of abundant Eph receptor, distributes mainly in neuron and participates in multiple links of pathological changes after ischemia. This paper discussed the hypothesis that EphA4 receptor could affect ischemic brain injury through EphA4/ephrin bidirectional signaling between neuron and microglia, and then explored its underlying mechanisms. We manipulated EphA4/ephrin signaling with either EphA4 overexpression lentiviral vectors or the short hairpin RNA (shRNA) to upregulate or knock down neuronal EphA4 expression. NF-κB inhibitor pyrrolidine dithiocarbamate ammonium salt (PDTC) was applied to block NF-κB pathway. According to the experimental results, upregulated neuronal EphA4 induced by ischemia deteriorated neurological function as well as brain damage by shifting microglia M1-polarization via promoting NF-κB signaling.

Neuronal EphA4 Regulates OGD/R-Induced Apoptosis by Promoting Alternative Activation of Microglia.

Accumulating evidence indicates that post-injury inflammation characterized by activated microglia contributes much to the neuropathology of ischemic injury. Several studies have demonstrated that microglia exhibit two entirely different functional activation states, referred to as classically activated (M1) and alternatively activated (M2) phenotype. Promoting microglial phenotype to switch from M1 dominant to M2 dominant might be a promising approach for handling ischemic injury. However, the comprehensive mechanism that underlines microglia polarization in ischemic brain remains unclear. Neuronal erythropoietin-producing human hepatocellular carcinoma cell receptor 4 (EphA4), the richest Eph receptor in the central nervous system (CNS), upregulate after ischemia and may have the potential to regulate microglia activation. We hypothesized that modulating EphA4/ephrin signaling could affect ischemic injury through controlling microglia polarization. We therefore knocked down neuronal EphA4 with short hairpin RNA (shRNA) and determined the role of EphA4/ephrin signaling in oxygen-glucose deprivation and reperfusion (OGD/R)-induced injury. We found that EphA4 shRNA treatment attenuated OGD/R-induced apoptosis and microglia proliferation. Neuronal EphA4 knockdown also promoted microglial M2 polarization, which reduced pro-inflammatory mediators and released anti-inflammatory cytokines as well as neurotrophic factors. We further revealed that EphA4 shRNA treatment functioned through RhoA/Rho-associated kinase 2 (ROCK2) signaling, a key mediator of microglia alternative activation. Together, these data suggested that blockage of EphA4/ephrin signaling between neuron and microglia decreased OGD/R-induced injury by promoting alternative activation of microglia via RhoA/ROCK2 signaling.

Roles of Eph/ephrin bidirectional signaling in central nervous system injury and recovery.

Multiple cellular components are involved in the complex pathological process following central nervous system (CNS) injury, including neurons, glial cells and endothelial cells. Previous studies and neurotherapeutic clinical trials have assessed the molecular mechanisms that underlie neuronal cell death following CNS injury. However, this approach has largely failed to reduce CNS damage or improve the functional recovery of patients. Erythropoietin-producing human hepatocellular (Eph) receptors and ephrin ligands have attracted considerable attention since their discovery, due to their extensive distribution and unique bidirectional signaling between astrocytes and neurons. Previous studies have investigated the roles of Eph/ephrin bidirectional signaling in the developing central nervous system. It was determined that Eph/ephrin bidirectional signaling is expressed in various CNS regions and cell types, and that it serves diverse roles in the adult CNS. In the present review, the roles of Eph/ephrin bidirectional signaling in CNS injuries are assessed.

Deduction of regional cerebral blood flow loss index after stenosis in cerebral artery.

OBJECTIVE: To study the calculation of cerebral blood flow loss ratio after cerebral artery stenosis using the data obtained from transcranial Doppler sonography (TCD), by deducing regional cerebral blood flow loss index (rCBFLI). METHODS AND RESULTS: The data of TCD performed in 31 cases of unilateral stenosis in the middle cerebral artery (MCA) were collected and analyzed for deducing the formula for calculating the MCA stenosis index (STI): STI=1 (Vm(0)/Vm(1)) x (PI(1)/PI(0)), where Vm(0) is the mean normal velocity of MCA blood flow (derived from the measurements in 908 normal subjects at varied ages receiving TCD) and Vm(1) the mean velocity at the stenosed MCA, and PI(0) and PI(1) stand for the pulsatility index before and after stenosis. The ratio of PI(1) to PI(0) is likely to be equivalent to the ratio of Q(1) to Q(0) (Q(0) and Q(1) represent the volume of blood flow in the MCA in normal condition and after stenosis, respectively), thus the equivalence can be extended as rCBFLI=(1 Q(1)/Q(0)) x 100%=(1 PI(1)/PI(0)) x 100%. rCBFLI after MCA stenosis was calculated in 31 cases accordingly, and by means of correlation analysis, we found positive correlation between rCBFLI and Vm(1) (r=0.76, P < 0.001) and between Vm(1) and STI (r=0.85, P < 0.001). In the same way, rCBFLI of 55 sides with MCA stenosis in 43 cases were analyzed, and positive correlation between rCBFLI and Vm (r=0.76, P < 0.001) and between rCBFLI and STI (r=0.83, P < 0.001) was found. CONCLUSION: rCBFLI can be used to evaluate the degree of regional cerebral blood flow loss due to artery stenosis, and the combination of rCBFLI and STI may provide an insight into the changes of cerebral hemodynamics in this pathologic condition.

[Analysis of the clinical manifestations and electrophysiological changes in 32 patients with atypical myasthenia gravis].

OBJECTIVE: To study the clinical characteristics and electrophysiological changes in patients with atypical myasthenia gravis (MG). METHODS: The characteristics of the clinical symptoms and electrophysiological changes were investigated in 32 patients with atypical MG diagnosed in our hospital from January 2004 to December 2008. RESULTS: The ages of the patients ranged from 7 to 70 years. Five patients were diagnosed to have ocular MG (OMG), among whom 2 patient only complained of eye discomfort and blurred vision. Twenty-seven patients had generalized MG, and 6 of them showed muscle weakness of the limbs with or without mild difficulty in swallowing or respiratory muscles, but free of muscle dysfunctions in muscles of eyes, head, neck or face. Another 2 patients manifested muscular atrophy. Twenty-three patients (71.9%) displayed both fluctuating symptoms and positive results of fatigue test. Twenty-nine patients (90.6%) have positive results in the neostigmine test. Two patients in the OMG group (40.0%) showed positive results in the low frequency repetitive nerve stimulation (LFRNS), as compared with the 21 patients in the generalized MG group (71.9%) showing positive results. The total positivity rate of LFRNS was 71.9% in the total patients, consistent with the published data. CONCLUSIONS: In MG patients with atypical clinical symptoms, negative results of neostigmine test and fatigue test, LFRNS test can be an indispensable method to increase detection rate of MG and reduce erroneous or missed diagnosis.