Cytokines promote motoneuron survival through the Janus kinase-dependent activation of the phosphatidylinositol 3-kinase pathway

ERK MAPK signaling pathway inhibition as a potential target to prevent autophagy alterations in Spinal Muscular Atrophy motoneurons

Spinal Muscular Atrophy (SMA) is a severe genetic neuromuscular disorder that occurs in childhood and is caused by misexpression of the survival motor neuron (SMN) protein. SMN reduction induces spinal cord motoneuron (MN) degeneration, which leads to progressive muscular atrophy and weakness. The link between SMN deficiency and the molecular mechanisms altered in SMA cells remains unclear. Autophagy, deregulation of intracellular survival pathways and ERK hyperphosphorylation may contribute to SMN-reduced MNs collapse, offering a useful strategy to develop new therapies to prevent neurodegeneration in SMA. Using SMA MN in vitro models, the effect of pharmacological inhibition of PI3K/Akt and ERK MAPK pathways on SMN and autophagy markers modulation was studied by western blot analysis and RT-qPCR. Experiments involved primary cultures of mouse SMA spinal cord MNs and differentiated SMA human MNs derived from induced pluripotent stem cells (iPSCs). Inhibition of the PI3K/Akt and the ERK MAPK pathways reduced SMN protein and mRNA levels. Importantly, mTOR phosphorylation, p62, and LC3-II autophagy markers protein level were decreased after ERK MAPK pharmacological inhibition. Furthermore, the intracellular calcium chelator BAPTA prevented ERK hyperphosphorylation in SMA cells. Our results propose a link between intracellular calcium, signaling pathways, and autophagy in SMA MNs, suggesting that ERK hyperphosphorylation may contribute to autophagy deregulation in SMN-reduced MNs.

Signal Transduction Regulators in Axonal Regeneration

Intracellular signal transduction in response to growth factor receptor activation is a fundamental process during the regeneration of the nervous system. In this context, intracellular inhibitors of neuronal growth factor signaling have become of great interest in the recent years. Among them are the prominent signal transduction regulators Sprouty (SPRY) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN), which interfere with major signaling pathways such as extracellular signal-regulated kinase (ERK) or phosphoinositide 3-kinase (PI3K)/Akt in neurons and glial cells. Furthermore, SPRY and PTEN are themselves tightly regulated by ubiquitin ligases such as c-casitas b-lineage lymphoma (c-CBL) or neural precursor cell expressed developmentally down-regulated protein 4 (NEDD4) and by different microRNAs (miRs) including miR-21 and miR-222. SPRY, PTEN and their intracellular regulators play an important role in the developing and the lesioned adult central and peripheral nervous system. This review will focus on the effects of SPRY and PTEN as well as their regulators in various experimental models of axonal regeneration in vitro and in vivo. Targeting these signal transduction regulators in the nervous system holds great promise for the treatment of neurological injuries in the future.

Role of IL-6 in the regulation of neuronal development, survival and function

The pleiotropic cytokine interleukin-6 (IL-6) is emerging as a molecule with both beneficial and destructive potentials. It can exert opposing actions triggering either neuron survival after injury or causing neurodegeneration and cell death in neurodegenerative or neuropathic disorders. Importantly, neurons respond differently to IL-6 and this critically depends on their environment and whether they are located in the peripheral or the central nervous system. In addition to its hub regulator role in inflammation, IL-6 is recently emerging as an important regulator of neuron function in health and disease, offering exciting possibilities for more mechanistic insight into the pathogenesis of mental, neurodegenerative and pain disorders and for developing novel therapies for diseases with neuroimmune and neurogenic pathogenic components.

Intracellular pathways involved in cell survival are deregulated in mouse and human spinal muscular atrophy motoneurons

Spinal Muscular Atrophy (SMA) is a severe neuromuscular disorder caused by loss of the Survival Motor Neuron 1 gene (SMN1). Due to this depletion of the survival motor neuron (SMN) protein, the disease is characterized by the degeneration of spinal cord motoneurons (MNs), progressive muscular atrophy, and weakness. Nevertheless, the ultimate cellular and molecular mechanisms leading to cell loss in SMN-reduced MNs are only partially known. We have investigated the activation of apoptotic and neuronal survival pathways in several models of SMA cells. Even though the antiapoptotic proteins FAIM-L and XIAP were increased in SMA MNs, the apoptosis executioner cleaved-caspase-3 was also elevated in these cells, suggesting the activation of the apoptosis process. Analysis of the survival pathway PI3K/Akt showed that Akt phosphorylation was reduced in SMA MNs and pharmacological inhibition of PI3K diminished SMN and Gemin2 at transcriptional level in control MNs. In contrast, ERK phosphorylation was increased in cultured mouse and human SMA MNs. Our observations suggest that apoptosis is activated in SMA MNs and that Akt phosphorylation reduction may control cell degeneration, thereby regulating the transcription of Smn and other genes related to SMN function.

Retracted: Knockdown of long noncoding RNA GAS5 attenuates H2 O2 -induced damage in retinal ganglion cells through upregulating miR-124: Potential role in traumatic brain injury

BACKGROUND

Optic nerve injury is one of the most common and serious complications in traumatic brain injury (TBI). Alleviating degree of optic nerve injury is important to cure of TBI. This study explored the role of long noncoding RNA (lncRNA) GAS5 in mice retinal ganglion cells (RGCs) suffered to H₂ O ₂ injury.

METHODS

Primary RGC (PRGCs) were treated with H₂ O ₂ to simulate an in vitro oxidation stress model. LncRNA GAS5 and miR-124 expressions were knocked down by cell transfection with short-hairpin RNA against GAS5 and miR-124 inhibitor, and the transfection efficiency was determined by qRT-PCR. Cell viability, apoptotic cell rate, and production of reactive oxygen species (ROS) was analyzed by CCK-8 assay, PI/FITC-Annexin V method, and DCFH-DA fluorometric assay. Cell apoptosis-associated proteins as well as activations of JAK/STAT3 signaling and JNK signaling were analyzed by Western blot.

RESULTS

H₂ O ₂ treatment-induced cell injury was inhibited by lncRNA GAS5 silence. Specifically, knockdown of GAS5 improved viability of primary PRGCs, inhibited apoptosis, decreased ROS expression, increased antiapoptosis proteins' expressions, and decreased proapoptosis proteins' expressions. It was also found that miR-124 inhibitor treatment impaired the cell protective effect of GAS5 silence, indicating low level of GAS5 protected PRGCs via upregulating miR-124. GAS5 silence might exert cytoprotection effect via activating JAK/STAT3 signaling pathway and inhibiting activation of JNK signaling pathway.

CONCLUSION

Knocking down lncRNA GAS5 alleviated H₂ O ₂ -induced injury in PRGCs via upregulation of miR-124, which might dependent on activation of JAK/STAT3 signaling pathway and inhibition of JNK signaling pathway.

Cardiotrophin-1 attenuates experimental colitis in mice

Cardiotrophin-1 (CT-1) holds potent anti-inflammatory, cytoprotective, and anti-apoptotic effects in the liver, kidneys, and heart. In the present study, the role of endogenous CT-1 and the effect of exogenous CT-1 were evaluated in experimental ulcerative colitis. Colitis was induced in CT-1 knockout and wild-type (WT) mice by administration of dextran sulphate sodium (DSS) in the drinking water during 7 days. CT-1 knockout mice showed higher colon damage and disease severity than WT mice. In addition, CT-1 (200 µg/kg/day, iv) or vehicle (as control) was administered during 3 days to WT, colitic mice, starting on day 4 after initiation of DSS. Disease activity index (DAI), inflammatory markers (tumor necrosis factor α (TNF-α), INFγ, IL-17, IL-10, inducible nitric oxide synthase (iNOS)), colon damage, apoptosis (cleaved caspase 3), nuclear factor κB (NFκB) and STAT-3 activation, and bacterial translocation were measured. Compared with mice treated with DSS, mice also treated with exogenous CT-1 showed lower colon damage, DAI, plasma levels of TNFα, colon expression of TNF-α, INFγ, IL-17, iNOS and cleaved caspase 3, higher NFκB and signal transducer and activator of transcription 3 (STAT3) pathways activation, and absence of bacterial translocation. We conclude that endogenous CT-1 plays a role in the defense and repair response of the colon against ulcerative lesions through an anti-inflammatory and anti-apoptotic effect. Supplementation with exogenous CT-1 ameliorates disease symptoms, which opens a potentially new therapeutic strategy for ulcerative colitis.

Upregulation of Vesicular Glutamate Transporter 2 and STAT3 Activation in the Spinal Cord of Mice Receiving 3,3'-Iminodipropionitrile

Chronic administration of 3,3'-iminodipropionitrile (IDPN) causes axonal impairment. Although controversy still remains, it has been suggested that IDPN intoxication mimics the axonopathy of amyotrophic lateral sclerosis (ALS). Interestingly, recent studies including our own showed that signal transducer and activator of transcription 3 (STAT3) in spinal α-motoneurons was activated in both IDPN-treated mice and SOD1 ^G93A mice, a genetic model of familial ALS. Because activation of STAT3 occurs in response to various stimuli, such as axonal injury, ischemia, and excessive glutamate, here we focused on a potential link between phosphorylated STAT3 (pSTAT3, an active form) and vesicular glutamate transporter 2 (VGluT2, a regulator of glutamate storage and release) in IDPN-treated mice and SOD1 ^G93A mice. Impairment of axonal transport was confirmed by western blot analysis: the expression levels of phosphorylated neurofilament H were elevated in both models. As shown in SOD1 ^G93A mice, the expression frequencies of VGluT2 in synaptophysin-positive (SYP)⁺ presynaptic terminals around spinal α-motoneurons were significantly higher in IDPN-treated mice than in vehicle controls. The coverages of spinal α-motoneurons by VGluT2⁺ presynaptic terminals were more elevated around pSTAT3⁺ cells than around pSTAT3^- cells in IDPN-treated mice and SOD1 ^G93A mice. Considering that excessive glutamate is shown to be involved in axonal impairment and STAT3 activation, the present results suggest that IDPN-induced upregulation of VGluT2 may result in an increase in glutamate, which might cause axonopathy and induction of pSTAT3. The link between upregulation of VGluT2 and activation of STAT3 via glutamate may represent a common pathological feature of IDPN-treated mice and SOD1 ^G93A mice.

Cardiotrophin-1 stimulates the neural differentiation of human umbilical cord blood-derived mesenchymal stem cells and survival of differentiated cells through PI3K/Akt-dependent signaling pathways

Cardiotrophin-1 (CT1) plays an important role in the differentiation, development, and survival of neural stem cells. In this study, we analyzed its effects on the stimulation of human umbilical cord blood-derived mesenchymal stem cells in terms of their potential to differentiate into neuron-like cells, their survival characteristics, and the molecular mechanisms involved. The treatment of cells with neural induction medium (NIM) and CT1 generated more cells that were neuron-like and produced stronger expression of neural-lineage markers than cells treated with NIM and without CT1. Bcl-2 and Akt phosphorylation (p-Akt) expression levels increased significantly in cells treated with both NIM and CT1. This treatment also effectively blocked cell death following neural induction and decreased Bax, Bak and cleaved-caspase 3 expression compared with cells treated with NIM without CT1. In addition, the inhibition of phosphatidylinositol 3-kinase (PI3K) abrogated p-Akt and Bcl-2 expression. Thus, PI3K/Akt contribute to CT1-stimulated neural differentiation and to the survival of differentiated cells.

Cardiotrophin-1 therapy prevents gentamicin-induced nephrotoxicity in rats

Aminoglycosides are very effective antibiotics for the treatment of severe infections, but they rank among the most frequent causes of drug-induced nephrotoxicity. Thus, prevention of aminoglycoside nephrotoxicity is an unmet therapeutic objective. Cardiotrophin-1 (CT-1), a member of the IL-6 family of cytokines, has been reported to protect the kidney against toxic and ischemic acute kidney injury (AKI). We have assessed the effect of rat CT-1 in the severity of gentamicin (G)-induced AKI. Groups of male Wistar rats received the following for 6 consecutive days: i) isotonic saline solution (group CONT), ii) G, 150mg/kg/day, i.p. (group G), iii) CT-1, 100μg/kg/day i.v. (group CT-1), or iv) G and CT-1 at the doses described above. The G group showed a manifest AKI characterized by low creatinine clearance, high plasma creatinine and urea levels, increased urinary excretion of proteins, glucose and AKI markers such as N-acetyl-glucosaminidase, neutrophil gelatinase-associated lipocalin, kidney-injury molecule-1 and T-gelsolin, increased kidney levels of CD-68, iNOS, IL-1β and TNF-α, and markedly higher histological renal damage and leukocyte infiltration than the CONT and CT-1 groups. Administration of CT-1 together with G reduced almost all of the above-described manifestations of G-induced AKI. The results of this study have potential clinical application, as CT-1 is near to being used as a drug for organ protection.

Muscle A-Kinase Anchoring Protein-α is an Injury-Specific Signaling Scaffold Required for Neurotrophic- and Cyclic Adenosine Monophosphate-Mediated Survival

Neurotrophic factor and cAMP-dependent signaling promote the survival and neurite outgrowth of retinal ganglion cells (RGCs) after injury. However, the mechanisms conferring neuroprotection and neuroregeneration downstream to these signals are unclear. We now reveal that the scaffold protein muscle A-kinase anchoring protein-α (mAKAPα) is required for the survival and axon growth of cultured primary RGCs. Although genetic deletion of mAKAPα early in prenatal RGC development did not affect RGC survival into adulthood, nor promoted the death of RGCs in the uninjured adult retina, loss of mAKAPα in the adult increased RGC death after optic nerve crush. Importantly, mAKAPα was required for the neuroprotective effects of brain-derived neurotrophic factor and cyclic adenosine-monophosphate (cAMP) after injury. These results identify mAKAPα as a scaffold for signaling in the stressed neuron that is required for RGC neuroprotection after optic nerve injury.

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mAKAPα is a stress-specific mediator of RGC survival.

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mAKAP deletion does not affect RGC survival in development or in the uninjured adult retina.

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mAKAP is downregulated after optic nerve injury, and its further deletion exacerbates RGC death.

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mAKAP deletion suppresses the neuroprotective effects of cAMP and BDNF after injury.

After injury or in degenerative diseases, neurons of the central nervous system (CNS) fail to regenerate and often die partly due to a lack of pro-survival, trophic signaling. Better understanding of such signaling is important for the development of therapies that enhance survival and regeneration of neurons after injury. Here we identify a critical regulator of such signaling, mAKAPα, a scaffold protein that coordinates pro-survival signaling to enhance survival and regeneration in CNS neurons after injury. The neuroprotective role of mAKAPα will likely lead to further future insights into the detailed nature of survival signaling in adult neurons.

Neuronal Survival, Morphology and Outgrowth of Spiral Ganglion Neurons Using a Defined Growth Factor Combination

Objectives

The functionality of cochlear implants (CI) depends, among others, on the number and excitability of surviving spiral ganglion neurons (SGN). The spatial separation between the SGN, located in the bony axis of the inner ear, and the CI, which is inserted in the scala tympani, results in suboptimal performance of CI patients and may be decreased by attracting the SGN neurites towards the electrode contacts. Neurotrophic factors (NTFs) can support neuronal survival and neurite outgrowth.

Methods

Since brain-derived neurotrophic factor (BDNF) is well known for its neuroprotective effect and ciliary neurotrophic factor (CNTF) increases neurite outgrowth, we evaluated if the combination of BDNF and CNTF leads to an enhanced neuronal survival with extended neurite outgrowth. Both NTFs were added in effective high concentrations (BDNF 50ng/ml, CNTF 100ng/ml), alone and in combination, to cultured dissociated SGN of neonatal rats for 48 hours.

Results

The neuronal survival and neurite outgrowth were significantly higher in SGN treated with the combination of the two NTFs compared to treatment with each factor alone. Additionally, with respect to the morphology, the combination of BDNF and CNTF leads to a significantly higher number of bipolar neurons and a decreased number of neurons without neurites in culture.

Conclusion

The combination of BDNF and CNTF shows a great potential to increase the neuronal survival and the number of bipolar neurons in vitro and to regenerate retracted nerve fibers.

The MAPK and PI3K pathways mediate CNTF-induced neuronal survival and process outgrowth in hypothalamic organotypic cultures

While collateral sprouting has been shown to occur in a variety of neuronal populations, the factor or factors responsible for mediating the sprouting response remain largely un-defined. There is evidence indicating that ciliary neurotrophic factor (CNTF) may play an important role in promoting neuronal survival and process outgrowth in neuronal phenotypes tested to date. We previously demonstrated that the astrocytic Jak-STAT pathway is necessary to mediate CNTF-induced oxytocinergic (OT) neuronal survival; however, the mechanism (s) of CNTF-mediated process outgrowth remain unknown. Our working hypothesis is that CNTF mediates differential neuroprotective responses via different intracellular signal transduction pathways. In order to test this hypothesis, we utilized stationary hypothalamic organotypic cultures to assess the contribution of the MAPK-ERK and PI3-AKT pathways to OT neuron survival and process outgrowth. Our results demonstrate that the MAPK-ERK½ pathway mediates CNTF-induced neuronal survival. Moreover, we show that inhibition of the p38-, JNK-MAPK, and mTOR pathways prevents loss OT neurons following axotomy. We also provide quantitative evidence indicating that CNTF promotes process outgrowth of OT neurons via the PI3K-AKT pathway. Together, these data indicate that distinct intracellular signaling pathways mediate diverse neuroprotective processes in response to CNTF.

The protective effect of growth hormone on Cu/Zn superoxide dismutase-mutant motor neurons

Background

Amyotrophic lateral sclerosis (ALS) is characterized by selective degeneration of motor neurons. The gene encoding Cu/Zn superoxide dismutase (SOD1) is responsible for 20% of familial ALS cases. Growth hormone (GH) concentrations are low in the cerebrospinal fluid of patients with ALS; however, its association with motoneuronal death is not known. We tested the neuroprotective effects of GH on human SOD-1-expressing cultured motor neurons and SOD1G93A transgenic mice.

Results

In cultured motor neurons, cytotoxicity was induced by A23187, GNSO, or homocysteine, and the effects of GH were determined by MTT, bax, PARP cleavage pattern, Hoechst nuclear staining, MAPK, and PI3K assay. In SOD-1 transgenic mice, rotarod motor performance was evaluated. Survival analysis of motoneuronal loss was done using cresyl violet, GFAP, and Bcl-2 staining. GH prevents motorneuronal death caused by GSNO and homocysteine, but not that by A23187. It activates MAPK and PI3K. GH-treated mice showed prolonged survival with improved motor performance and weight loss. GH decreased cresyl violet positive motoneuronal loss with strong Bcl-2 and less GFAP immunoreactivity.

Conclusions

Our results demonstrate that GH has a protective effect on mutant SOD-1-expressing motor neurons.

Plasticity versus specificity in RTK signalling modalities for distinct biological outcomes in motor neurons

BACKGROUND

Multiple growth factors are known to control several aspects of neuronal biology, consecutively acting as morphogens to diversify neuronal fates, as guidance cues for axonal growth, and as modulators of survival or death to regulate neuronal numbers. The multiplicity of neuronal types is permitted by the combinatorial usage of growth factor receptors, each of which is expressed in distinct and overlapping subsets of neurons, and by the multitasking role of growth factor receptors, which recruit multiple signalling cascades differentially required for distinct biological outcomes. We have explored signalling robustness in cells where a given receptor tyrosine kinase (RTK) elicits qualitatively distinct outcomes. As the HGF/Met system regulates several biological responses in motor neurons (MN) during neuromuscular development, we have investigated the signalling modalities through which the HGF/Met system impacts on MN biology, and the degree of robustness of each of these functions, when challenged with substitutions of signalling pathways.

RESULTS

Using a set of mouse lines carrying signalling mutations that change the Met phosphotyrosine binding preferences, we have asked whether distinct functions of Met in several MN subtypes require specific signalling pathways, and to which extent signalling plasticity allows a pleiotropic system to exert distinct developmental outcomes. The differential ability of signalling mutants to promote muscle migration versus axonal growth allowed us to uncouple an indirect effect of HGF/Met signalling on nerve growth through the regulation of muscle size from a direct regulation of motor growth via the PI3 kinase (PI3K), but not Src kinase, pathway. Furthermore, we found that HGF/Met-triggered expansion of Pea3 expression domain in the spinal cord can be accomplished through several alternative signalling cascades, differentially sensitive to the Pea3 dosage. Finally, we show that the regulation of MN survival by HGF/Met can equally be achieved in vitro and in vivo by alternative signalling cascades involving either PI3K-Akt or Src and Mek pathways.

CONCLUSIONS

Our findings distinguish MN survival and fate specification, as RTK-triggered responses allowing substitutions of the downstream signalling routes, from nerve growth patterning, which depends on a selective, non-substitutable pathway.

Growth Hormone Deteriorates the Functional Outcome in an Experimental Model of Huntington's Disease Induced by 3-Nitropionic Acid

Background and Purpose:

Growth hormone (GH) has been frequently used to control the aging process in healthy individuals, probably due to its slowing effect on senescence-associated degeneration. Mitochondrial dysfunction is related to the aging process, and one of the chemical models of Huntington’s disease is that it can be induced by mitochondrial toxin. To investigate the potential application of GH to modify the progression of Huntington’s disease (HD), we examined whether GH can protect the functional deterioration by striatal damage induced by 3-nitropropionic acid (3NP).

Methods:

3NP (63 mg/kg/day) was delivered to Lewis rats by osmotic pumps for five consecutive days, and the rats received intraperitoneal administration of GH or vehicle (saline) throughout the experiment. Neurological deficits and body weight were monitored. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test was performed to further determine the mitochondrial activity in cultured N18TG2 neuroblastoma cells in vitro.

Results:

3NP-treated rats showed progressive neurologic deficits with striatal damage. Application of GH accelerated behavioral deterioration, particularly between day 3 and day 5, resulting in reduced survival outcome. The body weights of rats given 3NP were decreased, but GH did not affect such decrease compared to the non-treated control group. The effect of GH on cultured neuronal cells was a decrease in the MTT absorbance, suggesting a lower number of cells in a dose dependent pattern.

Conclusions:

Those results suggest that application of GH to a 3NP-induced experimental model of HD deteriorates the progress of functional deficits, possibly disturbing mitochondrial activities.

Critical assessment of implantable drug delivery devices in glaucoma management

Glaucoma is a group of heterogeneous disorders involving progressive optic neuropathy that can culminate into visual impairment and irreversible blindness. Effective therapeutic interventions must address underlying vulnerability of retinal ganglion cells (RGCs) to degeneration in conjunction with correcting other associated risk factors (such as elevated intraocular pressure). However, realization of therapeutic outcomes is heavily dependent on suitable delivery system that can overcome myriads of anatomical and physiological barriers to intraocular drug delivery. Development of clinically viable sustained release systems in glaucoma is a widely recognized unmet need. In this regard, implantable delivery systems may relieve the burden of chronic drug administration while potentially ensuring high intraocular drug bioavailability. Presently there are no FDA-approved implantable drug delivery devices for glaucoma even though there are several ongoing clinical studies. The paper critically assessed the prospects of polymeric implantable delivery systems in glaucoma while identifying factors that can dictate (a) patient tolerability and acceptance, (b) drug stability and drug release profiles, (c) therapeutic efficacy, and (d) toxicity and biocompatibility. The information gathered could be useful in future research and development efforts on implantable delivery systems in glaucoma.

Cardiotrophin-1 (CTF1) ameliorates glucose-uptake defects and improves memory and learning deficits in a transgenic mouse model of Alzheimer's disease

Cardiotrophin-1 (CTF1) has been reported to act as a trophic factor for a few neurons, such as sensory, cholinergic, dopaminergic, motor and cortical neurons. Studies have indicated that CTF1 delays degenerative disease progression in motor neuron disease. However, little is known about the effects of CTF1 on degenerative disease in the brain. We have shown that expression of CTF1 is strongly down-regulated in the brain of the APPswe/PS1dE9 transgenic mouse model of Alzheimer's disease (AD). Transgenic mice with brain tissue-specific CTF1 expression alone or in combination with APPswe/PS1dE9 transgenic mice were produced to study the effects of CTF1 on AD. CTF1 expressing APPswe/PS1dE9 transgenic mice exhibited improvements in learning and memory, less severe abnormalities in locomotor activity, reduced scattered senile plaques and ameliorated disturbances of brain energy metabolism compared to APPswe/PS1dE9 transgenic mice. Furthermore, CTF1 inhibited the activity of glycogen synthase kinase-3β (GSK-3β) in SH-SY5Y cell line and in the brain tissues of APPswe/PS1dE9 transgenic mice. The transgenic expression of CTF1 compensated for the loss of CTF1 expression and brought about a marked improvement on cognitive functioning in the APPswe/PS1dE9 transgenic mouse model of Alzheimer's disease, suggesting that the inhibition of GSK-3β activity might play an important role.

Inhibition of the Jak-STAT pathway prevents CNTF-mediated survival of axotomized oxytocinergic magnocellular neurons in organotypic cultures of the rat supraoptic nucleus

Previous studies have demonstrated that ciliary neurotrophic factor (CNTF) enhances survival and process outgrowth from magnocellular neurons in the paraventricular (PVN) and the supraoptic (SON) nuclei. However, the mechanisms by which CNTF facilitates these processes remain to be determined. Therefore, the aim of this study was to identify the immediate signal transduction events that occur within the rat SON following administration of exogenous rat recombinant CNTF (rrCNTF) and to determine the contribution of those intracellular signaling pathway(s) to neuronal survival and process outgrowth, respectively. Immunohistochemical and Western blot analyses demonstrated that axonal injury and acute unilateral pressure injection of 100 ng/μl of rrCNTF directly over the rat SON resulted in a rapid and transient increase in phosphorylated-STAT3 (pSTAT3) in astrocytes but not neurons in the SON in vivo. Utilizing rat hypothalamic organotypic explant cultures, we then demonstrated that administration of 25 ng/ml rrCNTF for 14days significantly increased the survival and process outgrowth of OT magnocellular neurons. In addition, pharmacological inhibition of the Jak-STAT pathway via AG490 and cucurbitacin I significantly reduced the survival of OT magnocellular neurons in the SON and PVN; however, the contribution of the Jak-STAT pathway to CNTF-mediated process outgrowth remains to be determined. Together, these data indicate that CNTF-induced survival of OT magnocellular neurons is mediated indirectly through astrocytes via the Jak-STAT signaling pathway.

Eph and ephrin signaling: lessons learned from spinal motor neurons

In nervous system assembly, Eph/ephrin signaling mediates many axon guidance events that shape the formation of precise neuronal connections. However, due to the complexity of interactions between Ephs and ephrins, the molecular logic of their action is still being unraveled. Considerable advances have been made by studying the innervation of the limb by spinal motor neurons, a series of events governed by Eph/ephrin signaling. Here, we discuss the contributions of different Eph/ephrin modes of interaction, downstream signaling and electrical activity, and how these systems may interact both with each other and with other guidance molecules in limb muscle innervation. This simple model system has emerged as a very powerful tool to study this set of molecules, and will continue to be so by virtue of its simplicity, accessibility and the wealth of pioneering cellular studies.

Motor neuron trophic factors: therapeutic use in ALS?

The modest effects of neurotrophic factor (NTF) treatment on lifespan in both animal models and clinical studies of Amyotropic Lateral Sclerosis (ALS) may result from any one or combination of the four following explanations: 1.) NTFs block cell death in some physiological contexts but not in ALS; 2.) NTFs do not rescue motoneurons (MNs) from death in any physiological context; 3.) NTFs block cell death in ALS but to no avail; and 4.) NTFs are physiologically effective but limited by pharmacokinetic constraints. The object of this review is to critically evaluate the role of both NTFs and the intracellular cell death pathway itself in regulating the survival of spinal and cranial (lower) MNs during development, after injury and in response to disease. Because the role of molecules mediating MN survival has been most clearly resolved by the in vivo analysis of genetically engineered mice, this review will focus on studies of such mice expressing reporter, null or other mutant alleles of NTFs, NTF receptors, cell death or ALS-associated genes.

The canonical nuclear factor-κB pathway regulates cell survival in a developmental model of spinal cord motoneurons

In vivo and in vitro motoneuron survival depends on the support of neurotrophic factors. These factors activate signaling pathways related to cell survival or inactivate proteins involved in neuronal death. In the present work, we analyzed the involvement of the nuclear factor-κB (NF-κB) pathway in mediating mouse spinal cord motoneuron survival promoted by neurotrophic factors. This pathway comprises ubiquitously expressed transcription factors that could be activated by two different routes: the canonical pathway, associated with IKKα/IKKβ kinase phosphorylation and nuclear translocation RelA (p65)/p50 transcription factors; and the noncanonical pathway, related to IKKα kinase homodimer phosphorylation and RelB/p52 transcription factor activation. In our system, we show that neurotrophic factors treatment induced IKKα and IKKβ phosphorylation and RelA nuclear translocation, suggesting NF-κB pathway activation. Protein levels of different members of the canonical or noncanonical pathways were reduced in a primary culture of isolated embryonic motoneurons using an interference RNA approach. Even in the presence of neurotrophic factors, selective reduction of IKKα, IKKβ, or RelA proteins induced cell death. In contrast, RelB protein reduction did not have a negative effect on motoneuron survival. Together these results demonstrated that the canonical NF-κB pathway mediates motoneuron survival induced by neurotrophic factors, and the noncanonical pathway is not related to this survival effect. Canonical NF-κB blockade induced an increase of Bim protein level and apoptotic cell death. Bcl-x(L) overexpression or Bax reduction counteracted this apoptotic effect. Finally, RelA knockdown causes changes of CREB and Smn protein levels.

Caspase inhibition by cardiotrophin-1 prevents neuronal death in vivo and in vitro

Our previous studies showed that cardiotrophin-1 (CT-1), a cytokine in the interleukin-6 family, protected the developing rat brain against focal cerebral ischemia (FCI) in vivo and prevented cortical neuron death in vitro. However, the mechanisms by which CT-1 prevents neuronal death are not clearly understood. This in vivo study focused on whether CT-1 treatment prevented FCI-induced brain injuries in the postnatal day 7 (P7) rat through modulating activation of the initiator caspase-8 (C-8) and the downstream effector caspase-3 (C-3). FCI caused a significant increase in expressions of cleaved C-8 and C-3 and, meanwhile, a significant decrease in expression of microtubule-associated protein-2 (MAP2) in the left ischemic cortex of the P7 rat brain after FCI. Exogenous treatment of CT-1 significantly reduced the expression of cleaved C-8 or C-3 and attenuated the decline in MAP2 expression in the ischemic cortex from 12 to 24 hr after FCI. Subsequent in vitro experiments demonstrated that CT-1 treatment inhibited sodium nitroprusside (SNP)-induced activation of C-8 and C-3 and loss of MAP2-positive neurons in cortical neuron cultures. More importantly, CT-1 activated several pathways, including Janus kinase 2, signal transducers and activators of transcription 3, nuclear factor kappa B, mitogen-activated protein kinase (MAPK), and MAPK kinase in the cultures exposed to SNP. This is the first suggestion that CT-1 prevents neuronal injury in the developing central nervous system possibly through mediating multiple signal pathways, inhibiting activation of C-8 and C-3.

STAT3 signalling pathway is involved in the activation of microglia induced by 2.45 GHz electromagnetic fields

PURPOSE

Microglia activation plays a pivotal role in the initiation and progression of central nervous system (CNS) insult. The aim of the present work was to investigate the activation of microglia and involvement of signal transducer and activator of transcription 3 (STAT3) in microglia activation after 2.45 GHz electromagnetic fields (EMF) exposure.

MATERIALS AND METHODS

In this study, murine N9 microglial cells were exposed to 2.45 GHz EMF, the protein expressions of STAT3, Janus Tyrosine kinase 1 and 2(JAK1 and JAK2), phosphor-(Try705)STAT3 and DNA binding activity of STAT3 were examined by Western blot analysis and electrophoresis mobility shift assay (EMSA). Levels of the nitric oxide (NO) derivative nitrite were determined in the culture medium by the Griess reaction. The mRNA expression of tumour necrosis factor alpha (TNF-alpha) and inducible nitric oxide synthase (iNOS) were detected by reverse transcription and polymerase chain reaction (RT-PCR).

RESULTS

A significant increase of STAT3 DNA-binding ability was noted after exposure. Consistent with this, EMF rapidly induced phosphorylation of STAT3 and activated JAK1 and JAK2. In addition, EMF exposure increased transcription levels of the inflammation-associated genes, iNOS and TNF-alpha, which are reported to contain STAT-binding elements in their promoter region. P6, a JAK inhibitor, reduced induction of iNOS and TNF-alpha, nuclear factor binding activity, and activation of STAT3 in EMF-stimulated microglia.

CONCLUSION

These results provide evidence that EMF exposure can initiate the activation of microglia cells and STAT3 signalling involves in EMF-induced microglial activation.

Developing a novel serum-free cell culture model of skeletal muscle differentiation by systematically studying the role of different growth factors in myotube formation

This work describes the step-by-step development of a novel, serum-free, in vitro cell culture system resulting in the formation of robust, contracting, multinucleate myotubes from dissociated skeletal muscle cells obtained from the hind limbs of fetal rats. This defined system consisted of a serum-free medium formulation developed by the systematic addition of different growth factors as well as a nonbiological cell growth promoting substrate, N-1[3-(trimethoxysilyl) propyl] diethylenetriamine. Each growth factor in the medium was experimentally evaluated for its effect on myotube formation. The resulting myotubes were evaluated immunocytochemically using embryonic skeletal muscle, specifically the myosin heavy chain antibody. Based upon this analysis, we propose a new skeletal muscle differentiation protocol that reflects the roles of the various growth factors which promote robust myotube formation. Further observation noted that the proposed skeletal muscle differentiation technique also supported muscle-nerve coculture. Immunocytochemical evidence of nerve-muscle coculture has also been documented. Applications for this novel culture system include biocompatibility and skeletal muscle differentiation studies, understanding myopathies, neuromuscular disorders, and skeletal muscle tissue engineering.

Cytokine-induced SOCS expression is inhibited by cAMP analogue: impact on regeneration in injured retina

Injured adult retinal ganglion cells (RGCs) regrow axons into peripheral nerve (PN) grafted onto cut optic nerve. Survival and regeneration of RGCs is increased by intraocular injections of ciliary neurotrophic factor (CNTF) and axonal regeneration is further enhanced by co-injection of a cyclic AMP analogue (CPT-cAMP). Based on these data, and because cytokine signaling is negatively regulated by suppressor of cytokine signaling (SOCS) proteins, we set out to determine whether CNTF injections increase retinal SOCS expression and whether any changes are attenuated by co-injection with CPT-cAMP. Using quantitative PCR we found increased SOCS1, SOCS2 and SOCS3 mRNA levels at various times after a single CNTF injection. Expression remained high for many days. SOCS protein levels were also increased. In situ hybridization revealed that RGCs express SOCS3 mRNA, and SOCS expression in cultured RGCs was increased by CNTF. Co-injection of CPT-cAMP reduced CNTF induced expression of SOCS1 and SOCS3 mRNA and decreased SOCS3 protein expression. CNTF injection also transiently increased retinal leukemia inhibitory factor (LIF) expression, an effect that was also moderated by CPT-cAMP. We propose that, along with known reparative effects of elevated cAMP on neurons, reducing SOCS upregulation may be an additional way in which cyclic nucleotides augment cytokine-induced regenerative responses in the injured CNS.

Neurotrophic modulation of motor neuron development

Neurotrophic factors (NTFs) are a pleiotropic group of secreted growth factors that regulate multiple aspects of neuronal development, including the regressive event of cell death. Skeletal muscleinnervating lower motoneurons (MNs) of the brain stem and spinal cord comprise one population of central neurons in which programmed cell death (PCD) during embryogenesis has been actively investigated, as much for reasons of technical facility as clinical relevance. The precise identity of NTF-dependent MNs has remained unclear, with most studies simply reporting losses or gains across the entire spinal cord or individual brain-stem nuclei. However, MNs are grouped into highly heterogenous populations based on transcriptional identity, target innervation, and physiological function. Therefore, recent work has focused on the effects of NTF overexpression or deletion on the survival of these MN subpopulations. Together with the recent progress attained in the generation of conditional mutant mice, in which the function of an NTF or its receptor can be eliminated specifically in MNs, these recent studies have begun to define the differential trophic requirements for MN subpopulations during PCD. The intent of this review is to summarize these recent findings and to discuss their significance with respect to neurotrophic theory.

Neurotrophic support and oxidative stress: converging effects in the normal and diseased nervous system

Oxidative stress and loss of neurotrophic support play major roles in the development of various diseases of the central and peripheral nervous systems. In disorders of the central nervous system such as Alzheimer's, Parkinson's, and Huntington's diseases, oxidative stress appears inextricably linked to the loss of neurotrophic support. A similar situation is seen in the peripheral nervous system in diseases of olfaction, hearing, and vision. Neurotrophic factors act to up-regulate antioxidant enzymes and promote the expression of antioxidant proteins. On the other hand, oxidative stress can cause down-regulation of neurotrophic factors. We propose that normal functioning of the nervous systems involves a positive feedback loop between antioxidant processes and neurotrophic support. Breakdown of this feedback loop in disease states leads to increased oxidative stress and reduced neurotrophic support.

Exogenous CNTF stimulates axon regeneration of retinal ganglion cells partially via endogenous CNTF

Intravitreal injections of exogenous CNTF stimulate axon regeneration of RGCs in vivo. Nevertheless, controversy exists over the ability of exogenous CNTF to directly stimulate axon regeneration of mature RGCs. Here we demonstrate that CNTF potently stimulated axon outgrowth of mature RGCs in culture in a JAK/STAT3- and PI3K/AKT-signaling pathway-dependent fashion and stronger than oncomodulin. Additional cAMP elevation or inhibition of MAPK activity increased these effects. In vivo intravitreal injections of exogenous CNTF induced endogenous CNTF expression in astrocytes in a manner that depended on the MAPK/ERK-signaling pathway activation. Reduction of endogenous CNTF expression by MAPK/ERK pathway inhibitors or its absence in CNTF deficient mice markedly reduced the neurite growth-promoting effects of exogenous CNTF. These data demonstrate that CNTF is a potent axon growth-promoting factor for mature RGCs. However, exogenously applied CNTF stimulates RGCs in vivo partially indirectly via a mechanism that depends on astrocyte-derived CNTF.

Cardiotrophin-1. Review

BACKGROUND

Cardiotrophin-1 is newly discovered chemokin with a lot of functions. Aim of our work was to describe most important of them.

METHODS

systematically scan of available scientific resources.

RESULTS

Cardiotrophin-1 stimulates the proliferation of cardiomyocytes. Cardiotrophin-1 expression and plasma values are elevated in individuals with heart failure and have high diagnostic efficacy for the heart failure. Plasma values are also an independent prognostic factor. Preliminary findings suggest that the determination of plasma cardiotrophin-1 may be useful for the follow-up of hypertensive heart disease in routine clinical practice. Cardiotrophin-1 also plays an important cardioprotective effect on myocardial damage, is a potent regulator of signaling in adipocytes in vitro and in vivo and potentiates the elevation the acute-phase proteins. Cardiotrophin-1 may play also an important protective role in other organ systems (such as hematopoietic, neuronal, developmental).

CONCLUSION

Cardiotrophin is a newly discovered chemokin with a lot of system effects and is stable in system circulation hence permitting its development in the routine clinical investigation.

Roles of PI3K and JAK pathways in viability of retinal ganglion cells after acute elevation of intraocular pressure in rats with different autoimmune backgrounds

Background

We recently showed that whereas inhibition of PI3K/akt or JAK/STAT pathway promoted retinal ganglion cell (RGC) survival after optic nerve (ON) injury in Fischer 344 (F344) rats, the same inhibition resulted in aggravated RGC loss after acute intraocular pressure (IOP) elevation in Sprague Dawley (SPD) rats. In addition, the responses of macrophages to ON injury and acute IOP elevation were different between F344 and Lewis rats, i.e., different autoimmune profiles. Using an acute IOP elevation paradigm in this study, we investigated 1) whether autoimmune background influences PI3K/akt and JAK/STAT functions by examining the effect of PI3K/akt and JAK/STAT pathway inhibition on RGC survival in F344 and Lewis rats, and 2) whether differential actions of macrophages occur in PI3K/akt and JAK/STAT pathways-dependent modulation of RGC survival. IOP elevation was performed at 110 mmHg for 2 hours. PI3K/akt and JAK/STAT pathway inhibitors were applied intravitreally to block their respective pathway signaling transduction. Because macrophage invasion was seen in the eye after the pathway inhibition, to examine the role of these pathways independent of macrophages, macrophages in the retina were removed by intravitreal application of clodronate liposomes. Viable RGCs were retrogradely labelled by FluoroGold 40 hours before animal sacrifice.

Results

Similar to what was previously observed, significantly more RGCs were lost in Lewis than F344 rats 3 weeks after acute IOP elevation. As in SPD rats, inhibition of the PI3K/akt or JAK/STAT pathway increased the loss of RGCs in both F344 and Lewis rats. Removal of macrophages in the eye by clodronate liposomes reduced RGC loss due to pathway inhibition in both strains.

Conclusion

This study demonstrates that following acute IOP elevation 1) PI3K/akt and JAK/STAT pathways mediate RGC survival in both F344 and Lewis rats, 2) autoimmune responses do not influence the functions of these two pathways, and 3) PI3K/akt and JAK/STAT pathway inhibition-dependent activation of macrophages is detrimental to RGCs.

Neuroprotective properties of ciliary neurotrophic factor for cultured adult rat dorsal root ganglion neurons

We observed that recombinant ciliary neurotrophic factor (CNTF) enhanced survival and neurite outgrowth of cultured adult rat dorsal root ganglion (DRG) neurons. Among other neurotrophic factors (NGF and GDNF) and interleukin (IL)-6 cytokine members [IL-6, LIF, cardiotrophin-1, and oncostatin M (OSM)] at the same concentration (50 ng/ml), CNTF, as well as LIF and OSM, displayed high efficacy for the promotion of the number of viable neurons and neurite-bearing cells. CNTF enhanced the number of neurite-bearing cells in both small neurons (soma diameter <30 microm) and large neurons (soma diameter > or =30 microm), whereas NGF and GDNF promoted that in only small neurons. Western blot analysis revealed that CNTF induced phosphorylation of STAT3, Akt, and ERK1/2 in the neurons. Furthermore, the neurite outgrowth-promoting activity of CNTF was diminished by co-treatment with Janus kinase (JAK) 2 inhibitor, AG490; STAT3 inhibitor, STA-21; phosphatidyl inositol-3'-phosphate-kinase (PI3K) inhibitor, LY294002; and mitogen-activated protein kinase kinase (MEK) inhibitor, PD98059, in a concentration-dependent manner. Its survival-promoting activity was also affected by AG490, STA-21, and LY294002 at higher concentrations, but not by PD98059. These findings suggest the involvement of JAK2/STAT3, PI3K/Akt, and MEK/ERK signaling pathways in CNTF-induced neurite outgrowth, where the former two pathways are thought to play major roles in mediating the survival response of neurons to CNTF.

Differential roles of phosphatidylinositol 3-kinase/akt pathway in retinal ganglion cell survival in rats with or without acute ocular hypertension

Intraocular pressure (IOP) elevation has often been used as an experimental model to study mechanisms underlying retinal ganglion cell (RGC) death associated with ocular ischemic injury and glaucoma. The aim of the present study, using both in vitro and in vivo approaches, was to investigate the role of phosphatidylinositol 3-kinase (PI3K)/akt pathway in RGC viability in normal rats and rats following transient IOP elevation. For in vivo studies, pathway inhibitors were administered intravitreally on days 3, 9, and 15 post-2-h IOP elevation at 110 mm Hg. Toward the end of the 3-week examination period, the fluorescent dye Fluorogold was used to retrogradely label surviving RGCs. In order to examine the role of macrophages that were recruited into the eye following the pathway inhibition, clodronate liposomes were used to deplete phagocytic cells in the eye. PI3K/akt pathway activity and location in the retina were examined using Western blot and immunohistochemistry, respectively. Here we showed that PI3K/akt inhibitors 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride (LY294002) and KY12420 at low concentrations (2 microM or 20 microM) did not influence RGC survival but caused RGC loss at high concentration (200 muM) in retinal explants derived from intact rats. In contrast, both LY294002 and KY12420 at 20 microM led to RGC loss in retinal explants derived from IOP-elevated eyes. A detrimental action of phagocytic cells on RGC survival was also seen in these retinas. In vivo results confirmed the detrimental actions of PI3K/akt inhibition and macrophages on RGC survival in IOP-elevated, but not intact eyes even with high concentration of LY294002. Low level of PI3K/akt activity was detected in the ganglion cell layer (GCL) in intact retina. Acute IOP elevation activated PI3K/akt pathway in the inner nuclear layer and GCL including RGCs. This study thus demonstrates that PI3K/akt pathway mediates RGC survival after IOP elevation but not under normal condition.

PI3K/akt, JAK/STAT and MEK/ERK pathway inhibition protects retinal ganglion cells via different mechanisms after optic nerve injury

Recently we unexpectedly found that PI3K/akt, JAK/STAT and MEK/ERK pathway inhibitors enhanced retinal ganglion cell (RGC) survival after optic nerve (ON) axotomy in adult rat, a phenomenon contradictory to conventional belief that these pathways are pro-survival. In this study we showed that: (i) the RGC protection was pathway inhibition-dependent; (ii) inhibition of PI3K/akt and JAK/STAT, but not MEK/ERK, activated macrophages in the eye, (iii) macrophage removal from the eye using clodronate liposomes significantly impeded PI3K/akt and JAK/STAT inhibition-induced RGC survival and axon regeneration whereas it only slightly affected MEK/ERK inhibition-dependent protection; (iv) in the absence of recruited macrophages in the eye, inhibition of PI3K/akt or JAK/STAT did not influence RGC survival; and (v) strong PI3K/akt, JAK/STAT and MEK/ERK pathway activities were located in RGCs but not macrophages after ON injury. In retinal explants, in which supply of blood-derived macrophages is absent, MEK/ERK inhibition promoted RGC survival whereas PI3K/akt or JAK/STAT inhibition had no effect on RGC viability. However, MEK/ERK inhibition exerted opposite effects on the viability of purified adult RGCs at different concentrations in vitro, suggesting that this pathway may be bifunctional depending on the level of pathway activity. Our data thus demonstrate that inhibition of the PI3K/akt or JAK/STAT pathway activated macrophages to facilitate RGC protection after ON injury whereas the two pathways per se did not modulate RGC viability under the injury conditions (in the absence of the pathway activators). In contrast, the MEK/ERK pathway inhibition protected RGCs via macrophage-independent mechanism(s).

Emerging role of mitogen-activated protein kinases in peripheral neuropathies

Among the different families of intracellular molecules that can be modulated during cell damage and repair, mitogen-activated protein kinases (MAPKs) are particularly interesting because they are involved in several intracellular pathways activated by injury and regeneration signals. Despite most of the studies have been performed in non-neurological models, recently a causal role for MAPKs has been postulated in central nervous system disorders. However, also in some peripheral neuropathies, MAPK changes can occur and these modifications might be relevant in the pathogenesis of the damage as well as during regeneration and repair. In this review, the current knowledge on the role of MAPKs in peripheral neuropathies will be discussed.

JAK/STAT pathway mediates retinal ganglion cell survival after acute ocular hypertension but not under normal conditions

Intraocular pressure (IOP) elevation is an important cause of glaucoma. Animal models of ocular hypertension have been widely used to mimic glaucoma to investigate the mechanisms underlying retinal ganglion cell (RGC) death and search for possible cure. The aim of the present study was to examine the role of JAK/STAT pathway in RGC viability in normal condition or after acute IOP elevation. Retinal explants obtained from intact or IOP-elevated eyes were firstly used to examine the effect of the JAK/STAT pathway inhibitors, AG490 and Jak Inhibitor I, on RGC viability in vitro. The role of this signal pathway was further investigated and confirmed in vivo. AG490 and Jak Inhibitor I were applied into the left eye on days 3, 9, and 15 post 2-h IOP elevation at 110mmHg. Fluorescence dye Fluorogold was used to retrogradely label surviving RGCs. Because macrophage recruitment was seen in the IOP-elevated eyes after inhibition of this pathway, clodronate liposomes were used to remove phagocytic cells in the eye and examine the role of JAK/STAT pathway in RGC survival independent of macrophages. Activities and location of JAK/STAT pathway in the retina were examined using Western blotting and immunohistochemistry. We found that inhibition of JAK/STAT pathway did not affect RGC survival in the retinal explants derived from intact eye but caused RGC death in the retinal explants that were derived from IOP-elevated eye. Importantly, the detrimental effect of JAK/STAT pathway inhibition on RGC survival was also observed in vivo following acute IOP elevation, but not in intact eye. In addition, both in vitro and in vivo experiments confirmed a detrimental action of phagocytic cells following acute IOP elevation and the pathway inhibition. Compatible with what were observed in vivo, Western blotting and immunohistochemistry showed that JAK/STAT activities were not present in intact retina, but acute IOP elevation activated JAK/STAT pathway in the retina, in the regions of inner nuclear layer and ganglion cell layer, including RGCs. The IOP elevation-induced JAK/STAT activities were effectively abolished by intravitreal application of AG490. This study thus shows that (1) acute IOP elevation activates JAK/STAT pathway in RGCs, and (2) JAK/STAT pathway mediates RGC survival following IOP elevation but not under normal condition.

Role of signal transducer and activator of transcription-3 in estradiol-mediated neuroprotection

Estradiol is protective in experimental cerebral ischemia, but the precise mechanisms remain unknown. Signal transducer and activator of transcription-3 (STAT3) is a transcription factor that is activated by estrogen, translocates to the nucleus, and induces the transcription of neuroprotective genes, such as bcl-2. We determined whether estradiol increases STAT3 activation in female rat brain after focal cerebral ischemia and whether STAT3 activation contributes to estradiol-mediated neuroprotection against ischemic brain injury. Ovariectomized (OVX) female rats with and without estradiol replacement were subjected to 2 h of middle cerebral artery occlusion (MCAO), and phosphorylated STAT3 (P-STAT3) and total STAT3 (T-STAT3) were quantified by Western blot analysis at 3 and 22 h of reperfusion. STAT3 activation was colocalized with neuronal and survival markers microtubule-associated protein 2 (MAP2) and Bcl-2 using immunohistochemistry. Infarct size was measured at 22 h after MCAO in estradiol-treated OVX animals in the presence and absence of STAT3 inhibitor cucurbitacin I (JSI-124) using 2,3,5-triphenyltetrazolium chloride staining. Estradiol increased P-STAT3 in the ischemic cortex cytosolic fraction at 3 h after MCAO without affecting T-STAT3. This was associated with increased P-STAT3 in the nuclear fraction, which remained elevated at 22 h after MCAO. The nuclear P-STAT3 colocalized with MAP2 and Bcl-2 within the peri-infarct zone. The P-STAT3 inhibitor JSI-124 abolished the protective effect of estradiol without affecting infarct size in untreated OVX rats. We conclude that estradiol increases STAT3 phosphorylation in neurons after MCAO and that STAT3 activation plays an important role in estradiol-mediated neuroprotection.

Dose-specific or dose-dependent effect of growth hormone treatment on the proliferation and differentiation of cultured neuronal cells

OBJECTIVE

GH controls the proliferation of cartilage, fibroblasts or the differentiation of adipose and muscle tissue. However, the effect of GH on neuronal cells remains unknown. The present study was conducted to determine the proliferative or differentiating effect of GH on the nervous system in vitro.

DESIGN

Neuronal hybrid cells (VSC4.1) were cultured with GH. The concentration ranged from 0.134 microg/ml up to 1.34 mg/ml. A cell confluency and MTT assay, cell cycle phase analysis with flow cytometry, extracellular receptor kinase (ERK) phosphorylation and mitogen activated protein kinase (MAPK) inhibitor (PD98050) assays were all performed to determine the effect on proliferation. Differentiation was evaluated by neurite outgrowth and neurofilament expression. Terminally differentiated neurons were stained by Hoechst 33342 for apoptotic nuclear fragmentation by degeneration. Poly-adenosyl ribose polymerase (PARP) expression and its cleavage products were evaluated.

RESULTS

Cells at concentrations between 0.134 microg/ml and 1.34 microg/ml of GH proliferated with ERK phosphorylation, which was attenuated by MAPK inhibitors. Proliferation decreased at concentrations higher than 13.4 microg/ml; however, neurite outgrowth was observed at these concentrations. Terminally differentiated cells underwent apoptosis and showed nuclear fragmentation by Hoechst 33342 staining. PARP expression was increased with caspase-3 dependent-cleaved fragment.

CONCLUSIONS

Our in vitro data demonstrate that GH exerts dual effects; proliferation with a specific GH dose window, or differentiation in a dose-dependent manner in cultured neuronal hybrid cells.

Alteration of retinal intrinsic survival signal and effect of α2–adrenergic receptor agonist in the retina of the chronic ocular hypertension rat

The purpose of this study is to examine the retinal expression of intrinsic cell survival molecules and to elucidate the effect of an α2-adrenergic receptor agonist in the chronic ocular hypertensive rat model. Chronic ocular hypertension was induced in both eyes of each rat by episcleral vein cauterization. Two five-microliter drops of the selective α2-adrenoceptor agonist brimonidine 0.2% (Alphagan; Allergan Inc., Irvine, CA, USA) were topically administered twice daily for up to eight weeks in one eye. The fellow eye received balanced salt solution as a control. Protein and mRNA expression were evaluated at 1, 4, and 8 weeks after injury. Retinal expression of BDNF, Akt, and GFAP was assessed using immunohistochemistry. Retinal levels of mRNA for BDNF, bcl-2, and bcl-xL were determined using semi-quantitative RT-PCR. Retinal ganglion cell (RGC) density was evaluated after retrograde labeling with 4-Di-10-ASP (DiA). A significant decrease in RGC density was observed in ocular hypertensive eyes. Cauterized eyes showed an increase in GFAP expression from one week after injury, and the expression of bcl-2, bcl-xL, and BDNF mRNA was also increased. Treatment of ocular hypertensive eyes with brimonidine resulted in a reduction in RGC loss, a decrease in the level of GFAP immunoreactivity, and an increment in BDNF mRNA and p-Akt expression. Brimonidine appears to protect RGCs from neurodegeneration through mechanisms involving α2-adrenergic receptor mediated survival signal activation and up-regulation of endogenous neurotrophic factor expression in the chronic ocular hypertensive rat retina.

Injury-induced Janus kinase/protein kinase C-dependent phosphorylation of growth-associated protein 43 and signal transducer and activator of transcription 3 for neurite growth in dorsal root ganglion

Elevation of corticosteroids and excessive glutamate release are the two major stress responses that occur sequentially during traumatic CNS injury. We have previously reported that sequential application of corticosterone and kainic acid (CORT + KA) mimicking the nerve injury condition results in synergistic enhancement of neurite outgrowth and expression of growth-associated protein 43 (GAP-43) in cultured dorsal root ganglion (DRG). GAP-43 is known to promote neurite extension when phosphorylated by protein kinase C (PKC). In addition, PKC can phosphorylate the signal transducer and activator of transcription 3 (STAT3) at Ser727, which is phosphorylated primarily by Janus kinase (JAK) at Tyr705. In this study, we further examine the role of PKC in this stress-induced growth-promoting effect. In the cultured DRG neurons, the JAK inhibitor AG-490 and the PKC inhibitor Ro-318220 reduced the CORT + KA-enhanced neurite growth effect when applied prior to CORT and KA treatment, respectively. Both AG-490 and Ro-318220 diminished the CORT + KA-enhanced GAP-43 expression, phosphorylation, and axonal localization. Furthermore, CORT + KA treatment synergistically phosphorylated STAT3 at Ser727 but not at Tyr705. Similar phenomena were observed in an animal model of acute spinal cord injury (SCI), in which phosphorylation of GAP-43 and phospho-Ser727-STAT3 was elevated in the injured DRG 4 hr after the impact injury. Further treatment with the therapeutic glucocorticoid methylprednisolone enhanced the phosphorylation of GAP-43 in both the DRG and the spinal cord of SCI rats. These results suggest that elevated glucocorticoids and overexcitation following CNS injury contribute to nerve regeneration via induction of JAK/PKC-mediated GAP-43 and STAT3 activities.

Cardiotrophin-1 defends the liver against ischemia-reperfusion injury and mediates the protective effect of ischemic preconditioning

Ischemia-reperfusion (I/R) liver injury occurs when blood flow is restored after prolonged ischemia. A short interruption of blood flow (ischemic preconditioning [IP]) induces tolerance to subsequent prolonged ischemia through ill-defined mechanisms. Cardiotrophin (CT)-1, a cytokine of the interleukin-6 family, exerts hepatoprotective effects and activates key survival pathways like JAK/STAT3. Here we show that administration of CT-1 to rats or mice protects against I/R liver injury and that CT-1-deficient mice are exceedingly sensitive to this type of damage. IP markedly reduced transaminase levels and abrogated caspase-3 and c-Jun-NH2-terminal kinase activation after I/R in normal mice but not in CT-1-null mice. Moreover, the protective effect afforded by IP was reduced by previous administration of neutralizing anti-CT-1 antibody. Prominent STAT3 phosphorylation in liver tissue was observed after IP plus I/R in normal mice but not in CT-1-null mice. Oxidative stress, a process involved in IP-induced hepatoprotection, was found to stimulate CT-1 release from isolated hepatocytes. Interestingly, brief ischemia followed by short reperfusion caused mild serum transaminase elevation and strong STAT3 activation in normal and IL-6-deficient mice, but failed to activate STAT3 and provoked marked hypertransaminasemia in CT-1-null animals. In conclusion, CT-1 is an essential endogenous defense of the liver against I/R and is a key mediator of the protective effect induced by IP.