The present study was conducted to develop a new animal model of neuropathic pain employing injury to the distal sciatic nerve branches. Under halothane anesthesia, the tibial, sural, and/or common peroneal nerves were injured and neuropathic pain behaviors were compared among different groups of rats. Different types of injury produced different levels of neuropathic pain. Rats with injury to the tibial and sural nerves showed the most vigorous mechanical allodynia, cold allodynia, and spontaneous pain. These neuropathic pain behaviors were not relieved by functional sympathectomy using guanethidine.The results suggested that injury to the tibial and sural nerves, while leaving the common peroneal nerve intact, can be used as a new animal model of neuropathic pain and that this model represents sympathetically independent pain (SIP). The present animal model is very simple to produce injury and can produce profound and reliable pain behaviors. These features enable the new animal model to be a useful tool in elucidating the mechanisms of neuropathic pain, especially SIP. NeuroReport

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As an essential protease in the generation of amyloid beta, gamma-secretase is believed to play an important role in the pathogenesis of Alzheimer's disease. Although a great deal of progress has been made in identifying the components of gamma-secretase complex, the endogenous regulatory mechanism of gamma-secretase is unknown. Here we show that gamma-secretase is endogenously regulated via extracellular signal regulated MAP kinase (ERK) 1/2-dependent mitogen-activated protein kinase (MAPK) pathway. The inhibition of ERK1/2 activity, either by a treatment with a MEK inhibitor or an ERK knockdown transfection, dramatically increased gamma-secretase activity in several different cell types. JNK or p38 kinase inhibitors had little effect, indicating that the effect is specific to ERK1/2-dependent MAPK pathway. Conversely, increased ERK1/2 activity, by adding purified active ERK1/2 or EGF-induced activation of ERK1/2, significantly reduced gamma-secretase activity, demonstrating down-regulation of gamma-secretase activity by ERK1/2. Whereas gamma-secretase expression was not affected by ERK1/2, its activity was enhanced by phosphatase treatment, indicating that ERK1/2 regulates gamma-secretase activity by altering the pattern of phophorylation. Among the components of isolated gamma-secretase complex, only nicastrin was phosphorylated by ERK1/2, and it precipitated with ERK1/2 in a co-immunoprecipitation assay, which suggests binding between ERK1/2 and nicastrin. Our results show that ERK1/2 is an endogenous regulator of gamma-secretase, which raises the possibility that ERK1/2 down-regulates gamma-secretase activity by directly phosphorylating nicastrin.

Myogenic differentiation plays an important role in muscle regeneration and is regulated by two transcription factor families, MRFs and MEF2, which induce differentiation of myoblasts through expression of the muscle-specific gene, myogenin. In addition, many intracellular signaling pathways are also involved in myogenic differentiation, including p38 MAPK, ERK/MAPK and PI3K/AKT. The JAK-STAT pathway is activated by various cytokines and positively or negatively regulates the differentiation of myoblasts. JAK1 plays a notable role in proliferation; whereas, JAK2 and JAK3 function mainly in differentiation. The STATs, molecules downstream of JAK, regulate myogenesis. With JAK1, STAT1 promotes proliferation, while STAT3 has a dual effect on proliferation and differentiation. The JAK-STAT negative regulator, SOCS, is also associated with myogenesis; although, its role is controversial. In this review, we will discuss the role of the JAK-STAT pathway on myogenic differentiation.

Wnt regulation of muscle development is thought to be mediated by the ␤-catenin-TCF/LEF-dependent canonical pathway. Here we demonstrate that ␤-catenin, not TCF/LEF, is required for muscle differentiation. We showed that ␤-catenin interacts directly with MyoD, a basic helix-loop-helix transcription factor essential for muscle differentiation and enhances its binding to E box elements and transcriptional activity. MyoDmediated transactivation is inhibited in muscle cells when ␤-catenin is deficient or the interaction between MyoD and ␤-catenin is disrupted. These results demonstrate that ␤-catenin is necessary for MyoD function, identifying MyoD as an effector in the Wnt canonical pathway.Canonical Wnt signaling via ␤-catenin (␤-Cat) has been shown to play a critical role in muscle development (5,16,34). Upon Wnt stimulation, activated Dishevelled prevents the destruction complex, including glycogen synthase kinase 3␤, axin, and adenomatous poliposis coli protein from targeting ubiquitinated ␤-Cat by ␤TrCP. Stabilized ␤-Cat translocates to nucleus and presumably via forming a complex with TCF/LEF and subsequently activates expression of basic helix-loop-helix (bHLH) myogenic regulatory factors (MRFs) such as Myf5 and MyoD for initiation of myogenesis (10, 47). The Wnt/␤-Cat pathway is also necessary for myogenic specification of muscle-derived CD45 ϩ stem cells in response to injury (37), vertebrate limb regeneration (18), and differentiation of multipotent cells into myogenic cells (3,35,42,48). These myogenic programs are thought to require TCF/LEF to activate MRF expression (36). While the canonical Wnt signaling pathway has been studied in earlier steps of muscle development, less is known about its role in muscle differentiation.bHLH factors bind to E box elements in the promoters of many tissue-specific genes and activate their gene expression (24,38,43). Cell fate determination and differentiation in a variety of tissues depend upon the function of different transcription factors, including bHLH factors (12, 17). For instance, MRFs such as MyoD, Myf5, myogenin, and MRF4 are essential for muscle cell fate determination and differentiation (24,38). When ectopically expressed in other cell types, MRFs including MyoD are able to initiate muscle differentiation (4). They may form complexes with other transcriptional activators (histone acetyltransferase, MEF2, SRF, and retinoblastoma protein) or repressors (mSin3A, NCoR, and histone deacetylase) to coordinate muscle differentiation (40). Deletion of the MyoD gene in mice has no notable defect in skeletal muscle (44), whereas mice deficient in both MyoD and Myf5, a member of the MyoD family, lack myoblasts and differentiated skeletal muscle (45). These observations suggest that MyoD and Myf5 may have functional redundancy in regulation of muscle-specific gene expression.In the present study, we investigated the role and underlying mechanisms of Wnt signaling during muscle differentiation. We show that ␤-Cat, but not TCF/LEF, was required for muscle differentiati...

Prostaglandin E 2 (PGE 2 ), a product of the cyclooxygenation of arachidonic acid released from membrane phospholipids, plays a critical role in inflammatory neurodegenerative conditions. Despite its classic role as a proinflammatory molecule, exogenous PGE 2 was suggested to have protective roles against neuronal death, although the exact protective mechanisms of PGE 2 are not yet defined. Thus, the aim of this study was to examine the effect of exogenous PGE 2 on inflammatory neurotoxicity. Lipopolysaccharide (LPS) induced neuronal toxicity, which was associated with terminal transferase dUTP nick end labeling (TUNEL)-positive neuronal death with increased caspase-3 activity. In neuron-glial coculture, LPS markedly induced inducible nitric oxide synthase/nitric oxide (iNOS/NO) release from microglial cells, but not from neurons; however, LPS-induced oxidative stress such as reactive oxygen species (ROS), measured with 2,7-dichlorofluorescein diacetate oxidation, was increased in neurons, but not in microglial cells. Exogenous PGE 2 (1 g/ml) rescued the neurons, reducing iNOS/NO release from microglial cells and ROS formation from neurons. PGE 2 has been known to increase intracelluar cyclic adenosine monophosphate (cAMP) levels. In this study, we found that intracellular cAMP elevating agents, forskolin, and cAMP analogue, dbcAMP and 8-Br-cAMP, also prevented LPS-induced neuronal death. Thus, these results indicate that exogenous PGE 2 protects against LPS-induced neuronal apoptotic cell death through the intracellular cAMP system, and is associated with the modulation of NO from microglial cells and ROS production from neurons.

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LIUS showed a potent anti-inflammatory effect in this animal arthritis model with reduced infiltration of inflammatory cells into the synovium.