c-Jun and the transcriptional control of neuronal apoptosis

Modulation of apoptosis pathways by oxidative stress and autophagy in β cells

Human islets isolated for transplantation are exposed to multiple stresses including oxidative stress and hypoxia resulting in significant loss of functional β cell mass. In this study we examined the modulation of apoptosis pathway genes in islets exposed to hydrogen peroxide, peroxynitrite, hypoxia, and cytokines. We observed parallel induction of pro- and antiapoptotic pathways and identified several novel genes including BFAR, CARD8, BNIP3, and CIDE-A. As BNIP3 is an inducer of autophagy, we examined this pathway in MIN6 cells, a mouse beta cell line and in human islets. Culture of MIN6 cells under low serum conditions increased the levels of several proteins in autophagy pathway, including ATG4, Beclin 1, LAMP-2, and UVRAG. Amino acid deprivation led to induction of autophagy in human islets. Preconditioning of islets with inducers of autophagy protected them from hypoxia-induced apoptosis. However, induction of autophagy during hypoxia exacerbated apoptotic cell death. ER stress led to induction of autophagy and apoptosis in β cells. Overexpression of MnSOD, an enzyme that scavenges free radicals, resulted in protection of MIN6 cells from cytokine-induced apoptosis. Ceramide, a mediator of cytokine-induced injury, reduced the active phosphorylated form of Akt and downregulated the promoter activity of the antiapoptotic gene bcl-2. Furthermore, cytokine-stimulated JNK pathway downregulated the bcl-2 promoter activity which was reversed by preincubation with SP600125, a JNK inhibitor. Our findings suggest that β cell apoptosis by multiple stresses in islets isolated for transplantation is the result of orchestrated gene expression in apoptosis pathway.

Chronic isolation stress compromises JNK/c-Jun signaling in rat brain

The c-Jun NH2-terminal kinases (JNKs) are important stress-responsive kinases. They regulate cellular activities by sequential phosphorylation and activation through a mitogen-activated protein kinase cascade, whereas JNKs activation is altered in response to various stressors. In the present study, we used immunoblotting to assess the effect of 21 day of social isolation as the chronic stressor, either sole and in combination with 2 h of acute immobilization or cold (4°C) stress on circulating corticosterone level and phosphorylation status of p46 (phospho-p46/total p46) and p54 (phospho-p54/total p54) JNK isoforms in the cytosolic and nuclear fraction of the prefrontal cortex and hippocampus of male Wistar rats. Also, the phosphorylation status of JNK nuclear down-stream target c-Jun (p-c-Jun/c-Jun) on Ser63 was examined. Both acute stressors with elevated CORT levels led to increased phosphorylation status of cytosolic p54 JNK isoforms but not p46 JNK isoforms only in the hippocampus and no change in phosphorylation status of c-jun in both brain regions. Chronic isolation with unaltered CORT level and reduced responsiveness to novel acute stressors, led to unchanged or reduced phosphorylation status of p46 and p54 JNK isoforms in both fractions and both brain regions, whereas the decrease of c-Jun phosphorylation status was found only in the prefrontal cortex. Our results suggest that compromised JNKs activation following chronic isolation may lead to interruption of JNK signaling, which could be related with neuropsychiatric disorders such as depression or long-lasting neuronal remodeling.

JNK2 and JNK3 are major regulators of axonal injury-induced retinal ganglion cell death

Glaucoma is a neurodegenerative disease characterized by the apoptotic death of retinal ganglion cells (RGCs). The primary insult to RGCs in glaucoma is thought to occur to their axons as they exit the eye in the optic nerve head. However, pathological signaling pathways that exert central roles in triggering RGC death following axonal injury remain unidentified. It is likely that the first changes to occur following axonal injury are signal relay events that transduce the injury signal from the axon to the cell body. Here we focus on the c-Jun N-terminal kinase (JNK1-3) family, a signaling pathway implicated in axonal injury signaling and neurodegenerative apoptosis, and likely to function as a central node in axonal injury-induced RGC death. We show that JNK signaling is activated immediately after axonal injury in RGC axons at the site of injury. Following its early activation, sustained JNK signaling is observed in axonally-injured RGCs in the form of JUN phosphorylation and upregulation. Using mice lacking specific Jnk isoforms, we show that Jnk2 and Jnk3 are the isoforms activated in injured axons. Combined deficiency of Jnk2 and Jnk3 provides robust long-term protection against axonal injury-induced RGC death and prevents downregulation of the RGC marker, BRN3B, and phosphorylation of JUN. Finally, using Jun deficient mice, we show that JUN-dependent pathways are important for axonal injury-induced RGC death. Together these data demonstrate that JNK signaling is the major early pathway triggering RGC death after axonal injury and may directly link axon injury to transcriptional activity that controls RGC death.

Loss of transcription factor early growth response gene 1 results in impaired endochondral bone repair

Transcription factors that play a role in ossification during development are expected to participate in postnatal fracture repair since the endochondral bone formation that occurs in embryos is recapitulated during fracture repair. However, inherent differences exist between bone development and fracture repair, including a sudden disruption of tissue integrity followed by an inflammatory response. This raises the possibility that repair-specific transcription factors participate in bone healing. Here, we assessed the consequence of loss of early growth response gene 1 (EGR-1) on endochondral bone healing because this transcription factor has been shown to modulate repair in vascularized tissues. Model fractures were created in ribs of wild type (wt) and EGR-1(-/-) mice. Differences in tissue morphology and composition between these two animal groups were followed over 28 post fracture days (PFDs). In wt mice, bone healing occurred in healing phases characteristic of endochondral bone repair. A similar healing sequence was observed in EGR-1(-/-) mice but was impaired by alterations. A persistent accumulation of fibrin between the disconnected bones was observed on PFD7 and remained pronounced in the callus on PFD14. Additionally, the PFD14 callus was abnormally enlarged and showed increased deposition of mineralized tissue. Cartilage ossification in the callus was associated with hyper-vascularity and -proliferation. Moreover, cell deposits located in proximity to the callus within skeletal muscle were detected on PFD14. Despite these impairments, repair in EGR-1(-/-) callus advanced on PFD28, suggesting EGR-1 is not essential for healing. Together, this study provides genetic evidence that EGR-1 is a pleiotropic regulator of endochondral fracture repair.

Caffeine induces beneficial changes in PKA signaling and JNK and ERK activities in the striatum and cortex of Alzheimer's transgenic mice

Caffeine intake has been associated with a lower incidence of Alzheimer's disease (AD) in humans. In AD mouse models, caffeine significantly decreases senile plaques and amyloid beta (Aβ) levels while also protecting against or reversing cognitive impairment. To understand the mechanism(s) underlying the protective effects of caffeine against AD pathology, we investigated the effects of a two-week treatment with caffeine (3mg/day) in transgenic (APPswe) mice and non-transgenic (NT) mice on signaling factors involved in neuronal plasticity and survival. We evaluated cAMP-dependent protein kinase A (PKA), phospho-cyclic AMP response-element binding protein (phospho-CREB), and the pro-apoptotic protein kinases extracellular signal-regulated kinase 1/2 (phospho-ERK) and phospho-c-Jun N-terminal kinase 1 (phospho-JNK) in the striatum and frontal cortex of caffeine-treated mice. In the striatum, APPswe control mice exhibited a significant decrease in phospho-CREB, as well as significant increases in phospho-JNK and phospho-ERK in comparison to NT mice. Caffeine treatment stimulated PKA activity, increased phospho-CREB levels, and decreased phospho-JNK and phospho-ERK expression in the striatum of APPswe mice, all of which are thought to be beneficial changes for brain function. Even caffeine-treated NT mice exhibited some of these changes in striatum. In the frontal cortex, caffeine did not significantly increase phospho-CREB and PKA activity, but significantly reduced phospho-JNK and phospho-ERK expression in both APPswe and NT mice. These results suggest that caffeine shifts the balance between neurodegeneration and neuronal survival toward the stimulation of pro-survival cascades and inhibition of pro-apoptotic pathways in the striatum and/or cortex, which may contribute to its beneficial effects against AD.

Mechanisms of mycotoxin-induced neurotoxicity through oxidative stress-associated pathways

Among many mycotoxins, T-2 toxin, macrocyclic trichothecenes, fumonisin B(1) (FB(1)) and ochratochin A (OTA) are known to have the potential to induce neurotoxicity in rodent models. T-2 toxin induces neuronal cell apoptosis in the fetal and adult brain. Macrocyclic trichothecenes bring about neuronal cell apoptosis and inflammation in the olfactory epithelium and olfactory bulb. FB(1) induces neuronal degeneration in the cerebral cortex, concurrent with disruption of de novo ceramide synthesis. OTA causes acute depletion of striatal dopamine and its metabolites, accompanying evidence of neuronal cell apoptosis in the substantia nigra, striatum and hippocampus. This paper reviews the mechanisms of neurotoxicity induced by these mycotoxins especially from the viewpoint of oxidative stress-associated pathways.

Early growth response gene 1 regulates bone properties in mice

Transcriptional regulation of the postnatal skeleton is incompletely understood. Here, we determined the consequence of loss of early growth response gene 1 (EGR-1) on bone properties. Analyses were performed on both the microscopic and molecular levels utilizing micro-computed tomography (micro-CT) and Fourier transform infrared imaging (FTIRI), respectively. Mice deficient in EGR-1 (Egr-1 (-/-)) were studied and compared to sex- and age-matched wild-type (wt) control animals. Femoral trabecular bone in male Egr-1 (-/-) mice demonstrated osteopenic characteristics marked by reductions in both bone volume fraction (BV/TV) and bone mineral density (BMD). Morphological analysis revealed fewer trabeculae in these animals. In contrast, female Egr-1 (-/-) animals had thinner trabeculae, but BV/TV and BMD were not significantly reduced. Analysis of femoral cortical bone at the mid-diaphysis did not show significant osteopenic characteristics but detected changes in cross-sectional geometry in both male and female Egr-1 (-/-) animals. Functionally, this resulted in decreased resistance to three-point bending as indicated by a reduction in maximum load, failure load, and stiffness. Assessment of compositional bone properties, including mineral-to-matrix ratio, carbonate-to-phosphate ratio, crystallinity, and cross-linking, in femurs by FTIRI did not show any significant differences or an appreciable trend between Egr-1 (-/-) and wt mice of either sex. Unexpectedly, rib bone from Egr-1 (-/-) animals displayed distinct osteopenic traits that were particularly pronounced in female mice. This study provides genetic evidence that both sex and skeletal site are critical determinants of EGR-1 activity in vivo and that its site-specific action may contribute to the mechanical properties of bone.

Diffuse traumatic axonal injury in the mouse induces atrophy, c-Jun activation, and axonal outgrowth in the axotomized neuronal population

Traumatic axonal injury (TAI) is a consistent component of traumatic brain injury (TBI) and is associated with much of its morbidity. Little is known regarding the long-term retrograde neuronal consequences of TAI and/or the potential that TAI could lead to anterograde axonal reorganization and repair. To investigate the repertoire of anterograde and retrograde responses triggered by TIA, Thy1-YFP-H mice were subjected to mild central fluid percussion injury and killed at various times between 15 min and 28 d post-injury. Based upon confocal assessment of the endogenous neuronal fluorescence, such injury was found to result in diffuse TAI throughout layer V of the neocortex within yellow fluorescent protein (YFP)-positive axons. When these fluorescent approaches were coupled with various quantitative and immunohistochemical approaches, we found that this TAI did not result in neuronal death over the 28 d period assessed. Rather, it elicited neuronal atrophy. Within these same axotomized neuronal populations, TAI was also found to induce an early and sustained activation of the transcription factors c-Jun and ATF-3 (activating transcription factor 3), known regulators of axon regeneration. Parallel ultrastructural studies confirmed that these reactive changes are consistent with atrophy in the absence of neuronal death. Concurrent with those events ongoing in the neuronal cell bodies, their downstream axonal segments revealed, as early as 1 d post-injury, morphological changes consistent with reactive sprouting that was accompanied by significant axonal elongation over time. Collectively, these TAI-linked events are consistent with sustained neuronal recovery, an activation of a regenerative genetic program, and subsequent axonal reorganization suggestive of some form of regenerative response.

Activity of all JNK isoforms contributes to neurite growth in spiral ganglion neurons

Jun N-terminal kinase (JNK) is a multifunctional protein kinase crucial for neuronal apoptosis as well as neurite growth. We have previously shown that JNK activity is correlated with spiral ganglion neuron (SGN) apoptosis following hair cell loss in rats (Alam et al., 2007) implying that JNK inhibition may have therapeutic potential to protect SGNs in deaf individuals. Here we investigated the role of JNK in neurite outgrowth from cultured neonatal rat and mouse SGNs. We show that JNK is required for initial growth of neurites and for continued extension of already established neurites. The effect of JNK inhibition on neurite growth is rapid and is also rapidly reversible after washout of the inhibitor. Using phosphoJNK immunoreactivity as an indicator, we show that JNK is activated in growth cones within 30 min after transfer to medium lacking neurotrophic stimuli (5 K medium) but activation in the nucleus and soma requires hours. By transfecting epitope-tagged JNK1, JNK2, or JNK3 isoforms into SGNs, we found that all are present in the nucleus and cytoplasm and that there is no preferential redistribution to the nucleus after transfer to 5 K medium. Cotransfection of dominant-negative (dn) JNK1 and JNK2 into SGNs reduced neurite growth, although transfection of dnJNK1 or dnJNK2 alone had no significant effect. SGNs cultured from JNK3(-/-) mice showed reduced neurite growth that was further reduced by transfection of dnJNK1 and dnJNK2. This indicates that all three JNK isoforms promote SGN neurite growth although there may be functional redundancy between JNK1 and JNK2.

Increased JNK1 activity contributes to the upregulation of ApoD in the apocrine secretory gland cells from axillary osmidrosis

Axillary osmidrosis is a benign disorder that causes functional and emotional problems in Asian patients. Recently, ApoD has been identified as an axillary odorant binding protein. The present study was designed to compare the expression of ApoD in normal and osmidrosis subjects. Compared with the normal subjects, osmidrosis subjects had a higher expression of AR and ApoD in the apocrine samples, both at mRNA and protein level. Further study showed that, consistent with the increased ApoD and AR, phosphorylated JNK1 was higher in apocrine samples from axillary osmidrosis subjects, while with no obvious differences of the total expression of JNK1. In the cultured apocrine epithelial cells from normal subjects, 5α-dihydrotestosterone (5α-DHT) increased the expression of ApoD in a dose dependent manner, which can be inhibited by the JNK1 inhibitor. In contrast, in the cultured apocrine epithelial cells from axillary osmidrosis subjects, inhibition of JNK1 significantly reduced the expression of ApoD. Taken together, our study here revealed that increased JNK1 activation in the apocrine cells from axillary osmidrosis contributes to the increased ApoD expression, which in turn involved in the process of axillary osmidrosis.

FoxG1 promotes the survival of postmitotic neurons

The transcription factor FoxG1 regulates neurogenesis in the embryonic telencephalon as well as a number of other neurodevelopmental processes. While FoxG1 continues to be expressed in neurons postnatally and through adulthood, its role in fully differentiated neurons is not known. The current study demonstrates that FoxG1 promotes the survival of postmitotic neurons. In cerebellar granule neurons primed to undergo apoptosis, FoxG1 expression is reduced. Ectopic expression of FoxG1 blocks neuronal death, whereas suppression of its expression induces death in otherwise healthy neurons. The first 36 residues of FoxG1 are necessary for its survival-promoting effect, while the C-terminal half of the protein is dispensable. Mutation of Asp219, a residue necessary for DNA binding, abrogates survival promotion by FoxG1. Survival promotion is also eliminated by mutation of Thr271, a residue phosphorylated by Akt. Pharmacological inhibition of Akt blocks the survival effects of wild-type FoxG1 but not forms in which Thr271 is replaced with phosphomimetic residues. Treatment of neurons with IGF-1, a neurotrophic factor that promotes neuronal survival by activating Akt, prevents the apoptosis-associated downregulation of FoxG1 expression. Moreover, the overexpression of dominant-negative forms of FoxG1 blocks the ability of IGF-1 to maintain neuronal survival suggesting that FoxG1 is a downstream mediator of IGF-1/Akt signaling. Our study identifies a new and important function for FoxG1 in differentiated neurons.

Neuroprotection by histone deacetylase-7 (HDAC7) occurs by inhibition of c-jun expression through a deacetylase-independent mechanism

Histone deacetylase (HDAC) 7 is a member of the HDAC family of deacetylases. Although some of the HDAC proteins have been shown to regulate neuronal survival and death, whether HDAC7 has a similar role is not known. In this study, we show that HDAC7 protects neurons from apoptosis. In cerebellar granule neurons (CGNs) primed to undergo apoptosis by low potassium treatment, expression of HDAC7 protein is reduced. Reduced expression is also observed in CGNs induced to die by pharmacological inhibition of the proteasome, in cortical neurons treated with homocysteic acid, and in the striatum of R6/2 transgenic mice, a commonly used genetic model of Huntington disease. Forced expression of HDAC7 in cultured CGNs blocks low potassium-induced death, and shRNA-mediated suppression of its expression induces death in otherwise healthy neurons. HDAC7-mediated neuroprotection does not require its catalytic domain and cannot be inhibited by chemical inhibitors of HDACs. Moreover, pharmacological inhibitors of the PI3K-Akt or Raf-MEK-ERK signaling pathways or that of PKA, PKC, and Ca(2+)/calmodulin-dependent protein kinase fail to reduce neuroprotection by HDAC7. We show that stimulation of c-jun expression, an essential feature of neuronal death, is prevented by HDAC7. shRNA-mediated suppression of HDAC7 expression leads to an increase in c-jun expression. Inhibition of c-jun expression by HDAC7 is mediated at the transcriptional level by its direct association with the c-jun gene promoter. Taken together, our results indicate that HDAC7 is a neuroprotective protein acting by a mechanism that is independent of its deacetylase activity but involving the inhibition of c-jun expression.

p75 neurotrophin receptor-mediated apoptosis in sympathetic neurons involves a biphasic activation of JNK and up-regulation of tumor necrosis factor-alpha-converting enzyme/ADAM17

During the development of the sympathetic nervous system, the p75 neurotrophin receptor (p75NTR) has a dual function: promoting survival together with TrkA in response to NGF, but inducing cell death upon binding pro or mature brain-derived neurotrophic factor (BDNF). Apoptotic signaling through p75NTR requires activation of the stress kinase, JNK. However, the receptor also undergoes regulated proteolysis, first by a metalloprotease, and then by gamma-secretase, in response to pro-apoptotic ligands and this is necessary for receptor mediated neuronal death (Kenchappa, R. S., Zampieri, N., Chao, M. V., Barker, P. A., Teng, H. K., Hempstead, B. L., and Carter, B. D. (2006) Neuron 50, 219-232). Hence, the relationship between JNK activation and receptor proteolysis remains to be defined. Here, we report that JNK3 activation is necessary for p75NTR cleavage; however, following release of the intracellular domain, there is a secondary activation of JNK3 that is cleavage dependent. Receptor proteolysis and apoptosis were prevented in sympathetic neurons from jnk3(-/-) mice, while activation of JNK by ectopic expression of MEKK1 induced p75NTR cleavage and cell death. Proteolysis of the receptor was not detected until 6 h after BDNF treatment, suggesting that JNK3 promotes cleavage through a transcriptional mechanism. In support of this hypothesis, BDNF up-regulated tumor necrosis factor-alpha-converting enzyme (TACE)/ADAM17 mRNA and protein in wild-type, but not jnk3(-/-) sympathetic neurons. Down-regulation of TACE by RNA interference blocked BDNF-induced p75NTR cleavage and apoptosis, indicating that this metalloprotease is responsible for the initial processing of the receptor. Together, these results demonstrate that p75NTR-mediated activation of JNK3 is required for up-regulation of TACE, which promotes receptor proteolysis, leading to prolonged activation of JNK3 and subsequent apoptosis in sympathetic neurons.

The expression of SIAH1 is downregulated and associated with Bim and apoptosis in human breast cancer tissues and cells

Seven in absentia homolog1 (SIAH1) was reported as a tumor suppressor and played an important role in regulating cell apoptosis. However, its effects on the breast carcinogenesis remain unclear. In this study, our aims were to examine the relationship between SIAH1 and Bcl-2-interacting mediator of cell death (Bim) and to explore the effects of SIAH1 on the breast carcinogenesis. Immunohistochemical analysis in 231 cases of breast tissues showed that the expression of SIAH1 and Bim were significantly decreased in the breast carcinogenesis. Moreover, SIAH1 expression was significantly correlated with Bim. Both SIAH1 and Bim expression were significantly higher in well to moderately differentiated and in early-stage breast cancer. Reverse transcription (RT)-polymerase chain reaction (PCR) and Western blot analysis in paired breast cancer tissues and breast cell lines found that the expression of SIAH1 was lower in the breast cancer tissues and cell lines. SIAH1 inducing apoptosis of the breast cancer cells was dependent on Bim. However, SIAH1 inhibiting invasion of the breast cancer cells was independent of Bim. The increase of the function of SIAH1 to upregulate the expression of Bim may play an important role in the progression of breast cancer. Restoration of the function of SIAH1 may be a new therapeutic target of human breast cancer.

Activation of c-Jun N-terminal kinase is required for the regulation of endoplasmic reticulum stress response in the rat dorsal striatum following repeated cocaine administration

Repeated exposure to cocaine upregulates endoplasmic reticulum (ER) stress response and c-Jun N-terminal kinase (JNK) phosphorylation is associated with the ER stress response in neurons. In this study, we investigated the involvement of JNK in the regulation of the ER stress response following repeated cocaine administration in the dorsal striatum in vivo. The results showed that systemic injections of cocaine (20 mg/kg) for seven consecutive days increased the induction of p46 JNK (JNK) phosphorylation, immunoglobulin heavy chain binding protein (BiP), the ER stress-associated protein caspase-12, and behavioral locomotor activity. This enhancement of BiP and caspase-12 expression and locomotor response was reduced by inhibiting JNK. Similar reduction of elevated JNK phosphorylation was induced by blocking dopamine D1 receptors, N-methyl-D-aspartate (NMDA) receptors, and group I metabotropic glutamate receptors (mGluRs). These data suggest that JNK activation following repeated cocaine administration is required for the regulation of the ER stress protein expression and behavioral alteration in the dorsal striatum. Stimulation of dopamine D1 receptors, NMDA receptors or group I mGluRs participates in the regulation of JNK activation.

Gestational zinc deficiency affects the regulation of transcription factors AP-1, NF-κB and NFAT in fetal brain

Transcription factors AP-1, nuclear factor κB (NF-κB) and NFAT are central to brain development by regulating the expression of genes that modulate cell proliferation, differentiation, apoptosis and synaptic plasticity. This work investigated the consequences of feeding zinc-deficient and marginal zinc diets to rat dams during gestation on the modulation of AP-1, NF-κB and NFAT in fetal brain. Sprague-Dawley rats were fed from gestation day (GD) 0 a control diet ad libitum (25 μg zinc/g diet, C), a zinc-deficient diet ad libitum (0.5 μg zinc/g diet, ZD), the control diet in the amounts eaten by the ZD rats (restrict fed, RF) or a diet containing a marginal zinc concentration ad libitum (10 μg zinc/g diet, MZD) until GD 19. AP-1-DNA binding was higher (50-190%) in nuclear fraction isolated from ZD, RF and MZD fetal brains compared to controls. In MZD fetal brain, high levels of activation of the upstream mitogen-activated protein kinases JNK and p38 and low levels of ERK phosphorylation were observed. Total levels of NF-κB and NFAT activation were higher or similar in the ZD and MZD groups than in controls, respectively. However, NF-κB- and NFAT-DNA binding in nuclear fractions was markedly lower in ZD and MZD fetal brain than in controls (50-80%). The latter could be related to zinc deficiency-associated alterations of the cytoskeleton, which is required for NF-κB and NFAT nuclear transport. In summary, suboptimal zinc nutrition during gestation could cause long-term effects on brain function, partially through a deregulation of transcription factors AP-1, NF-κB and NFAT.

DJ-1-deficient mice show less TH-positive neurons in the ventral tegmental area and exhibit non-motoric behavioural impairments

Loss of function of DJ-1 (PARK7) is associated with autosomal recessive early-onset Parkinson's disease (PD), one of the major age-related neurological diseases. In this study, we extended former studies on DJ-1 knockout mice by identifying subtle morphological and behavioural phenotypes. The DJ-1 gene trap-induced null mutants exhibit less dopamine-producing neurons in the ventral tegmental area (VTA). They also exhibit slight changes in behaviour, i.e. diminished rearing behaviour and impairments in object recognition. Furthermore, we detected subtle phenotypes, which suggest that these animals compensate for the loss of DJ-1. First, we found a significant upregulation of mitochondrial respiratory enzyme activities, a mechanism known to protect against oxidative stress. Second, a close to significant increase in c-Jun N-terminal kinase 1 phosphorylation in old DJ-1-deficient mice hints at a differential activation of neuronal cell survival pathways. Third, as no change in the density of tyrosine hydroxylase (TH)-positive terminals in the striatum was observed, the remaining dopamine-producing neurons likely compensate by increasing axonal sprouting. In summary, the present data suggest that DJ-1 is implicated in major non-motor symptoms of PD appearing in the early phases of the disease-such as subtle impairments in motivated behaviour and cognition-and that under basal conditions the loss of DJ-1 is compensated.

Dramatic co-activation of WWOX/WOX1 with CREB and NF-kappaB in delayed loss of small dorsal root ganglion neurons upon sciatic nerve transection in rats

BACKGROUND

Tumor suppressor WOX1 (also named WWOX or FOR) is known to participate in neuronal apoptosis in vivo. Here, we investigated the functional role of WOX1 and transcription factors in the delayed loss of axotomized neurons in dorsal root ganglia (DRG) in rats.

METHODOLOGY/PRINCIPAL FINDINGS

Sciatic nerve transection in rats rapidly induced JNK1 activation and upregulation of mRNA and protein expression of WOX1 in the injured DRG neurons in 30 min. Accumulation of p-WOX1, p-JNK1, p-CREB, p-c-Jun, NF-kappaB and ATF3 in the nuclei of injured neurons took place within hours or the first week of injury. At the second month, dramatic nuclear accumulation of WOX1 with CREB (>65% neurons) and NF-kappaB (40-65%) occurred essentially in small DRG neurons, followed by apoptosis at later months. WOX1 physically interacted with CREB most strongly in the nuclei as determined by FRET analysis. Immunoelectron microscopy revealed the complex formation of p-WOX1 with p-CREB and p-c-Jun in vivo. WOX1 blocked the prosurvival CREB-, CRE-, and AP-1-mediated promoter activation in vitro. In contrast, WOX1 enhanced promoter activation governed by c-Jun, Elk-1 and NF-kappaB. WOX1 directly activated NF-kappaB-regulated promoter via its WW domains. Smad4 and p53 were not involved in the delayed loss of small DRG neurons.

CONCLUSIONS/SIGNIFICANCE

Rapid activation of JNK1 and WOX1 during the acute phase of injury is critical in determining neuronal survival or death, as both proteins functionally antagonize. In the chronic phase, concurrent activation of WOX1, CREB, and NF-kappaB occurs in small neurons just prior to apoptosis. Likely in vivo interactions are: 1) WOX1 inhibits the neuroprotective CREB, which leads to eventual neuronal death, and 2) WOX1 enhances NF-kappaB promoter activation (which turns to be proapoptotic). Evidently, WOX1 is the potential target for drug intervention in mitigating symptoms associated with neuronal injury.

Zfh1 promotes survival of a peripheral glia subtype by antagonizing a Jun N-terminal kinase-dependent apoptotic pathway

In Drosophila subperineurial glia (SPG) ensheath and insulate the nerve. SPG is under strict cell cycle and survival control because cell division or death of such a cell type would compromise the integrity of the blood-nerve barrier. The mechanisms underlying the survival of SPG remain unknown. Here, we show that the embryonic peripheral glia expresses the Zfh1 transcription factor, and in zfh1 mutants a particular SPG subtype, ePG10, undergoes apoptosis. Our findings show that in ePG10, Zfh1 represses the pro-apoptotic RHG-motif gene reaper in a cell-autonomous manner. Zfh1 also blocks the activation of the Jun N-terminal kinase (JNK) pathway, and reducing or enhancing JNK signalling in zfh1 mutants prevents or promotes ePG10 apoptosis. Our study shows a novel function for Zfh1 as an anti-apoptotic molecule and uncovers a cryptic JNK-dependent apoptotic programme in ePG10, which is normally blocked by Zfh1. We propose that, in cells such as SPG that do not undergo self-renewal and survive long periods, transcriptional control of RHG-motif gene expression together with fine tuning of JNK signalling is crucial for cell survival.

Cbl negatively regulates JNK activation and cell death

Here, we explore the role of Cbl proteins in regulation of neuronal apoptosis. In two paradigms of neuron apoptosis - nerve growth factor (NGF) deprivation and DNA damage - cellular levels of c-Cbl and Cbl-b fell well before the onset of cell death. NGF deprivation also induced rapid loss of tyrosine phosphorylation (and most likely, activation) of c-Cbl. Targeting c-Cbl and Cbl-b with siRNAs to mimic their loss/inactivation sensitized neuronal cells to death promoted by NGF deprivation or DNA damage. One potential mechanism by which Cbl proteins might affect neuronal death is by regulation of apoptotic c-Jun N-terminal kinase (JNK) signaling. We demonstrate that Cbl proteins interact with the JNK pathway components mixed lineage kinase (MLK) 3 and POSH and that knockdown of Cbl proteins is sufficient to increase JNK pathway activity. Furthermore, expression of c-Cbl blocks the ability of MLKs to signal to downstream components of the kinase cascade leading to JNK activation and protects neuronal cells from death induced by MLKs, but not from downstream JNK activators. On the basis of these findings, we propose that Cbls suppress cell death in healthy neurons at least in part by inhibiting the ability of MLKs to activate JNK signaling. Apoptotic stimuli lead to loss of Cbl protein/activity, thereby removing a critical brake on JNK activation and on cell death.

A retrograde apoptotic signal originating in NGF-deprived distal axons of rat sympathetic neurons in compartmented cultures

Previous investigations of retrograde survival signaling by nerve growth factor (NGF) and other neurotrophins have supported diverse mechanisms, but all proposed mechanisms have in common the generation of survival signals retrogradely transmitted to the neuronal cell bodies. We report the finding of a retrograde apoptotic signal in axons that is suppressed by local NGF signaling. NGF withdrawal from distal axons alone was sufficient to activate the pro-apoptotic transcription factor, c-jun, in the cell bodies. Providing NGF directly to cell bodies, thereby restoring a source of NGF-induced survival signals, could not prevent c-jun activation caused by NGF withdrawal from the distal axons. This is evidence that c-jun is not activated due to loss of survival signals at the cell bodies. Moreover, blocking axonal transport with colchicine inhibited c-jun activation caused by NGF deprivation suggesting that a retrogradely transported pro-apoptotic signal, rather than loss of a retrogradely transported survival signal, caused c-jun activation. Additional experiments showed that activation of c-jun, pro-caspase-3 cleavage, and apoptosis were blocked by the protein kinase C inhibitors, rottlerin and chelerythrine, only when applied to distal axons suggesting that they block the axon-specific pro-apoptotic signal. The rottlerin-sensitive mechanism was found to regulate glycogen synthase kinase 3 (GSK3) activity. The effect of siRNA knockdown, and pharmacological inhibition of GSK3 suggests that GSK3 is required for apoptosis caused by NGF deprivation and may function as a retrograde carrier of the axon apoptotic signal. The existence of a retrograde death signaling system in axons that is suppressed by neurotrophins has broad implications for neurodevelopment and for discovering treatments for neurodegenerative diseases and neurotrauma.

Cytoplasmic inclusions of Htt exon1 containing an expanded polyglutamine tract suppress execution of apoptosis in sympathetic neurons

Proteins containing extended polyglutamine repeats cause at least nine neurodegenerative disorders, but the mechanisms of disease-related neuronal death remain uncertain. We show that sympathetic neurons containing cytoplasmic inclusions formed by 97 glutamines expressed within human huntingtin exon1-enhanced green fluorescent protein (Q97) undergo a protracted form of nonapoptotic death that is insensitive to Bax deletion or caspase inhibition but is characterized by mitochondrial dysfunction. By treating the neurons with combined cytosine arabinoside and NGF withdrawal, we demonstrate that Q97 confers a powerful resistance to apoptosis at multiple levels: despite normal proapoptotic signaling (elevation of P-ser15-p53 and BimEL), there is no increase of Puma mRNA or Bax activation, both necessary for apoptosis. Even restoration of Bax translocation with overexpressed Puma does not activate apoptosis. We demonstrate that this robust inhibition of apoptosis is caused by Q97-mediated accumulation of Hsp70, which occurs through inhibition of proteasomal activity. Thus, apoptosis is reinstated by short hairpin RNA-mediated knockdown of Hsp70. These findings explain the rarity of apoptotic death in Q97-expressing neurons. Given the proteasomal blockade, we test whether enhancing lysosomal-mediated degradation with rapamycin reduces Q97 accumulation. Rapamycin reduces the amount of nonpathological Q25 by 70% over 3 d, but Q97 accumulation is unaffected. Interestingly, Q47 inclusions form more slowly as a result of constitutive lysosomal degradation, but faster-forming Q97 inclusions escape lysosomal control. Thus, cytoplasmic Q97 inclusions are refractory to clearance by proteasomal and lysosomal systems, leading to a toxicity that dominates over neuroprotective Hsp70. Our findings may explain the rarity of apoptosis but the inevitable cell death associated with polyQ inclusion diseases.

Polyglutamine-expanded ataxin-3 causes cerebellar dysfunction of SCA3 transgenic mice by inducing transcriptional dysregulation

In the present study, we prepared a SCA3 animal model by generating transgenic mice expressing polyglutamine-expanded ataxin-3-Q79. Ataxin-3-Q79 was expressed in brain areas implicated in SCA3 neurodegeneration, including cerebellum, pontine nucleus and substantia nigra. Ataxin-3-Q79 transgenic mice displayed motor dysfunction with an onset age of 5-6 months, and neurological symptoms deteriorated in the following months. A prominent neuronal loss was not found in the cerebellum of 10 to 11-month-old ataxin-3-Q79 mice displaying pronounced ataxic symptoms, suggesting that instead of neuronal demise, ataxin-3-Q79 causes neuronal dysfunction of the cerebellum and resulting ataxia. To test the involvement of transcriptional dysregulation in ataxin-3-Q79-induced cerebellar malfunction, microarray analysis and real-time RT-PCR assays were performed to identify altered cerebellar mRNA expressions of ataxin-3-Q79 mice. Compared to non-transgenic mice or mice expressing wild-type ataxin-3-Q22, 10 to 11-month-old ataxin-3-Q79 mice exhibited downregulated mRNA expressions of proteins involved in glutamatergic neurotransmission, intracellular calcium signaling/mobilization or MAP kinase pathways, GABA(A/B) receptor subunits, heat shock proteins and transcription factor regulating neuronal survival and differentiation. Upregulated expressions of Bax, cyclin D1 and CDK5-p39, which may mediate neuronal death, were also observed in ataxin-3-Q79 transgenic mice. The involvement of transcriptional abnormality in initiating the pathological process of SCA3 was indicated by the finding that 4 to 5-month-old ataxin-3-Q79 mice, which did not display neurological phenotype, exhibited downregulated mRNA levels of genes involved in glutamatergic signaling and signal transduction. Our study suggests that polyglutamine-expanded ataxin-3 causes cerebellar dysfunction and ataxia by disrupting the normal pattern of gene transcriptions.

All JNKs can kill, but nuclear localization is critical for neuronal death

JNKs are implicated in a range of brain pathologies and receive considerable attention as potential therapeutic targets. However, JNKs also regulate physiological and homeostatic processes. An attractive hypothesis from the drug development perspective is that distinct JNK isoforms mediate "physiological" and "pathological" responses. However, this lacks experimental evaluation. Here we investigate the isoforms, subcellular pools, and c-Jun/ATF2 targets of JNK in death of central nervous system neurons following withdrawal of trophic support. We use gene knockouts, gene silencing, subcellularly targeted dominant negative constructs, and pharmacological inhibitors. Combined small interfering RNA knockdown of all JNKs 1, 2, and 3, provides substantial neuroprotection. In contrast, knockdown or knock-out of individual JNKs or two JNKs together does not protect. This explains why the evidence for JNK in neuronal death has to date been largely pharmacological. Complete knockdown of c-Jun and ATF2 using small interfering RNA also fails to protect, casting doubt on c-Jun as a critical effector of JNK in neuronal death. Nonetheless, the death requires nuclear but not cytosolic JNK activity as nuclear dominant negative inhibitors of JNK protect, whereas cytosolic inhibitors only block physiological JNK function. Thus any one of the three JNKs is capable of mediating apoptosis and inhibition of nuclear JNK is protective.

Distinct signaling pathways of microtubule inhibitors--vinblastine and Taxol induce JNK-dependent cell death but through AP-1-dependent and AP-1-independent mechanisms, respectively

Vinblastine and paclitaxel (Taxol) are widely used chemotherapeutic drugs that inhibit the normal function of microtubules causing mitotic arrest and cell death. Despite these similarities, the signaling pathways that mediate and regulate cell death induced by these agents remain incompletely understood. The purpose of this study was to directly compare the two drugs in terms of their ability to activate components of the c-Jun N-terminal protein kinase (JNK) pathway, and to establish the importance of these signaling events in apoptosis induced by these agents. We show that both drugs induce mitotic arrest and subsequent apoptotic cell death with highly similar kinetics and that both activate JNK and induce c-Jun protein and c-jun mRNA expression. Surprisingly, vinblastine induced c-Jun phosphorylation and c-jun transcriptional activation, although Taxol failed to do so. However, inhibition of JNK or an absence of JNK protected against both vinblastine- and Taxol-induced cell death. These results suggest that although JNK activation plays an important role in cell death induced by both agents, vinblastine and Taxol differ markedly with respect to signaling downstream of JNK, with AP-1-dependent and -independent mechanisms, respectively. In addition, these results show, contrary to popular belief, that JNK activation is not necessarily accompanied by c-Jun activation, and thus c-Jun is not an obligate substrate of JNK.

Genetic findings in Parkinson's disease and translation into treatment: a leading role for mitochondria?

Parkinson's disease (PD) is a progressive neurodegenerative movement disorder and in most patients its aetiology remains unknown. Molecular genetic studies in familial forms of the disease identified key proteins involved in PD pathogenesis, and support a major role for mitochondrial dysfunction, which is also of significant importance to the common sporadic forms of PD. While current treatments temporarily alleviate symptoms, they do not halt disease progression. Drugs that target the underlying pathways to PD pathogenesis, including mitochondrial dysfunction, therefore hold great promise for neuroprotection in PD. Here we summarize how the proteins identified through genetic research (alpha-synuclein, parkin, PINK1, DJ-1, LRRK2 and HTRA2) fit into and add to our current understanding of the role of mitochondrial dysfunction in PD. We highlight how these genetic findings provided us with suitable animal models and critically review how the gained insights will contribute to better therapies for PD.

Prosurvival and proapoptotic intracellular signaling in rat spiral ganglion neurons in vivo after the loss of hair cells

Neurons depend on afferent input for survival. Rats were given daily kanamycin injections from P8 to P16 to destroy hair cells, the sole afferent input to spiral ganglion neurons (SGNs). Most SGNs die over an approximately 14-week period after deafferentation. During this period, the SGN population is heterogeneous. At any given time, some SGNs exhibit apoptotic markers--TUNEL and cytochrome c loss--whereas others appear nonapoptotic. We asked whether differences among SGNs in intracellular signaling relevant to apoptotic regulation could account for this heterogeneity. cAMP response element binding protein (CREB) phosphorylation, which reflects neurotrophic signaling, is reduced in many SGNs at P16, P23, and P32, when SGNs begin to die. In particular, nearly all apoptotic SGNs exhibit reduced phospho-CREB, implying that apoptosis is due to insufficient neurotrophic support. However, >32% of SGNs maintain high phospho-CREB levels, implying access to neurotrophic support. By P60, when approximately 50% of the SGNs have died, phospho-CREB levels in surviving neurons are not reduced, and SGN death is no longer correlated with reduced phospho-CREB. Activity in the proapoptotic Jun N-terminal kinase (JNK)-Jun signaling pathway is elevated in SGNs during the cell death period. This too is heterogeneous: <42% of the SGNs exhibited high phospho-Jun levels, but nearly all SGNs undergoing apoptosis exhibited elevated phospho-Jun. Thus, heterogeneity among SGNs in prosurvival and proapoptotic signaling is correlated with apoptosis. SGN death following deafferentation has an early phase in which apoptosis is correlated with reduced phospho-CREB and a later phase in which it is not. Proapoptotic JNK-Jun signaling is tightly correlated with SGN apoptosis.

Pro-apoptotic Bim induction in response to nerve growth factor deprivation requires simultaneous activation of three different death signaling pathways

Bim is a pro-apoptotic member of the Bcl-2 family that is induced and contributes to neuron death in response to nerve growth factor (NGF) deprivation. Past work has revealed that Bim is downstream of multiple independent transcriptional pathways in neurons, including those culminating in activation of the c-Jun, FoxO, and Myb transcription factors. This study addresses the issue of whether the three signaling pathways are redundant with respect to Bim induction or whether they act cooperatively. Examination of the proximal Bim promoter reveals binding sites for FoxO, Mybs, and, as shown here, c-Jun. We find that mutation of any one of these types of sites abolishes induction of a Bim promoter-driven reporter in response to NGF deprivation. Moreover, down-regulation of either c-Jun, FoxOs, or Mybs by short hairpin RNAs blocks induction of Bim promoter-reporter activity triggered by withdrawal of NGF. This was the case for reporters driven by either the proximal promoter or a promoter that also includes additional regulatory elements in the first intron of the Bim gene. Such short hairpin RNAs also suppressed the induction of endogenous Bim protein. These findings thus indicate that the Bim promoter acts as a coincidence detector that optimally responds to the simultaneous activation of three different pro-apoptotic transcriptional pathways. Such a mechanism provides a "fail-safe" that prevents neurons from dying by accidental activation of any single pathway. It also permits neurons to utilize individual pathways such as JNK signaling for other purposes without risk of demise.

Neuroprotective function of thymosin-beta and its derivative peptides on the programmed cell death of chick and rat neurons

Thymosin-betas (Tbetas) are small polypeptides with various biological functions, including cytoskeletal remodeling, angiogenesis, cellular migration, wound healing, and regulation of apoptosis. Recently, we found that Tbeta is involved in the control of programmed cell death (PCD) of motoneurons (MNs) in chick embryo, and that the anti-apoptotic action of Tbeta is independent of its actin-sequestering activity. In this study, we observed that a synthetic peptide derived from Tbeta suppressed staurosporine-induced neuronal apoptosis in vitro, and PCD of chick or rat MNs in vivo. Furthermore, inhibition of Tbeta4 in chick embryo by antibody significantly augmented the PCD of MNs, suggesting that secreted form of Tbeta is physiological regulator of PCD. Based on these findings, we propose that extracellularly secreted Tbeta is involved in the control of PCD of neurons during development, and Tbeta-derived peptides could be useful for the anti-apoptotic therapy of neuropathologies related to neuronal apoptosis.

Neuronal apoptosis in neurodegeneration

Apoptosis mediates the precise and programmed natural death of neurons and is a physiologically important process in neurogenesis during maturation of the central nervous system. However, premature apoptosis and/or an aberration in apoptosis regulation is implicated in the pathogenesis of neurodegeneration, a multifaceted process that leads to various chronic disease states, such as Alzheimer's (AD), Parkinson's (PD), Huntington's (HD) diseases, amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), and diabetic encephalopathy. The current review focuses on two major areas (a) the fundamentals of apoptosis, which includes elements of the apoptotic machinery, apoptosis inducers, and emerging concepts in apoptosis research, and (b) apoptotic involvement in neurodegenerative disorders, neuroprotective treatment strategies/modalities, and the mechanisms of, and signaling in, neuronal apoptosis. Current and new experimental models for apoptosis research in neurodegenerative diseases are also discussed.

c-Jun N-terminal kinase signaling regulates events associated with both health and degeneration in motoneurons

The c-Jun N-terminal kinases (JNKs) are activated by various stimuli and are critical for neuronal development as well as for death following a stressful stimulus. Here, we have evaluated JNK activity in both healthy and dying motoneurons from developing chick embryos and found no apparent difference in overall JNK activity between the conditions, suggesting that this pathway maybe critical in both circumstances. Pharmacological inhibition of JNK in healthy motoneurons supplied with trophic support resulted in decreased mitochondrial membrane potential, neurite outgrowth, and phosphorylation of microtubule-associated protein 1B. On the other hand, in motoneurons deprived of trophic support, inhibition of JNK attenuated caspase activation, and nuclear condensation. We also examined the role of JNK's downstream substrate c-Jun in mediating these events. While c-Jun expression and phosphorylation were greater in cells supplied with trophic support as compared with those deprived, inhibition of c-Jun had no effect on nuclear condensation in dying cells or neurite outgrowth in healthy cells, suggesting that JNK's role in these events is independent of c-Jun. Together, our data underscore the dualistic nature of JNK signaling that is critical for both survival and degenerative changes in motoneurons.

Pin1 in neuronal apoptosis

While the role of the prolyl isomerase Pin1 in dividing cells has long been recognized, Pin1's function in postmitotic neurons is poorly understood. We have identified a novel mechanism by which Pin1 mediates activation of the mitochondrial cell death machinery specifically in neurons. This perspective presents a sophisticated signaling pathway that triggers neuronal apoptosis upon JNK-mediated phosphorylation of the BH3-only protein BIM(EL) at serine 65. Pin1 is enriched at the mitochondria in neurons together with BIM(EL) and components of a neuron-specific JNK signaling complex and functions as a molecular switch that couples the phosphorylation of BIM(EL) by JNK to apoptosis specifically in neurons. We discuss how these findings relate to our understanding of the development of the nervous system and the pathogenesis of neurologic disorders.

Apoptotic neuronal death in Parkinson's disease: Involvement of nitric oxide

Apoptosis of nigral dopaminergic neurons by various mechanisms is an emerging phenomenon involved in the degeneration of dopaminergic neurons in Parkinson's disease (PD). Both extrinsic and intrinsic pathways seems to be involved in death of nigral neurons, intrinsic pathway however, seems to be more important due to the energy crisis. Apoptosis by intrinsic pathway is executed by several initiators and effector caspases, which have been found activated in PD patients, experimental models as well as in neuronal cultures. Nitric oxide (NO) seems to be a central molecule due to its ability to modulate both pro and antiapoptotic phenomenon. The review focuses on the diverse extrinsic and intrinsic factors, signaling pathways and their modulation by NO leading to the death of dopaminergic neurons.

Deletion of the c-Jun N-terminal kinase 3 gene protects neonatal mice against cerebral hypoxic-ischaemic injury

c-Jun N-terminal kinase 3 (JNK3) is a member of the stress-activated group of mitogen-activated protein kinases. c-Jun N-terminal kinase 3 is a potent mediator of apoptosis and the use of JNK inhibitors or jnk3 gene deletion each protect against brain injury in adults. However, little is known about the role of JNK3 or its mechanism of action in neonatal brain injury. The aim of the present study was to compare the vulnerability of neonatal JNK3 knockout (JNK3 KO) mice and wild-type (WT) mice to cerebral hypoxic-ischaemic injury (HII) using unilateral-carotid occlusion combined with transient hypoxia. The degree of neural tissue loss in JNK3 KO mice was substantially reduced compared with WT mice (JNK3 KO 27.8%+/-2.8% versus WT 48.3%+/-2.0%, P<or=0.0001) after HII. Significant attenuation of injury was observed in the cerebral cortex, hippocampus, striatum, and thalamus of JNK3 KO compared with WT mice. Hypoxic-ischaemic injury increased JNK phosphorylation and activity, with JNK3 as the major isoform. Significantly, in JNK3 KO animals there was no difference in the activation of the upstream kinases mitogen-activated protein kinase kinase (MKK4) or MKK7. Downstream of JNK3, HII lead to increased phosphorylation of the transcription factors c-Jun and adenovirus transcription factor-2 (ATF-2), which was attenuated in JNK3 KO mice. c-Jun N-terminal kinase 3 deletion also decrease caspase-3 cleavage and Bim/PUMA expression, coupled with a upregulation of AKT/FOXO3a levels, linking JNK3 to apoptosis. These findings implicate JNK3 involvement in neural cell loss resulting from cerebral HII in the developing brain.

Pharmacological, behavioural and mechanistic analysis of HIV-1 gp120 induced painful neuropathy

A painful neuropathy is frequently observed in people living with human immunodeficiency virus type 1 (HIV-1). The HIV coat protein, glycoprotein 120 (gp120), implicated in the pathogenesis of neurological disorders associated with HIV, is capable of initiating neurotoxic cascades via an interaction with the CXCR4 and/or CCR5 chemokine receptors, which may underlie the pathogenesis of HIV-associated peripheral neuropathic pain. In order to elucidate the mechanisms underlying HIV-induced painful peripheral neuropathy, we have characterised pathological events in the peripheral and central nervous system following application of HIV-1 gp120 to the rat sciatic nerve. Perineural HIV-1 gp120 treatment induced a persistent mechanical hypersensitivity (44% decrease from baseline), but no alterations in sensitivity to thermal or cold stimuli, and thigmotactic (anxiety-like) behaviour in the open field. The mechanical hypersensitivity was sensitive to systemic treatment with gabapentin, morphine and the cannabinoid WIN 55,212-2, but not with amitriptyline. Immunohistochemical studies reveal: decreased intraepidermal nerve fibre density, macrophage infiltration into the peripheral nerve at the site of perineural HIV-1 gp120; changes in sensory neuron phenotype including expression of activating transcription factor 3 (ATF3) in 27% of cells, caspase-3 in 25% of cells, neuropeptide Y (NPY) in 12% of cells and galanin in 13% of cells and a spinal gliosis. These novel findings suggest that this model is not only useful for the elucidation of mechanisms underlying HIV-1-related peripheral neuropathy but may prove useful for preclinical assessment of drugs for the treatment of HIV-1 related peripheral neuropathic pain.

dp5/HRK is a c-Jun target gene and required for apoptosis induced by potassium deprivation in cerebellar granule neurons

In cerebellar granule neurons, a BH3-only Bcl-2 family member, death protein 5/harakiri, is up-regulated in a JNK-dependent manner during apoptosis induced by potassium deprivation. However, it is not clear whether c-Jun is directly involved in the induction of dp5. Here, we showed that the up-regulation of dp5, but not fas ligand and bim, after potassium deprivation was suppressed by the expression of a dominant negative form of c-Jun. Deletion analysis of the 5'-flanking sequence of the dp5 gene revealed that a major responsive element responsible for the induction by potassium deprivation is an ATF binding site located at -116 to -109 relative to the transcriptional start site. Mutation of this site completely abolished promoter activation. Furthermore, a gel shift assay showed that a specific complex containing c-Jun and ATF2 recognized this site and increased in potassium-deprived cerebellar granule neurons. Chromatin immunoprecipitation demonstrated that c-Jun was able to bind to this site in vivo. Finally, we demonstrated that knockdown of Dp5 by small interfering RNA rescued neurons from potassium deprivation-induced apoptosis. Taken together, these results suggest that dp5 is a target gene of c-Jun and plays a critical role in potassium deprivation-induced apoptosis in cerebellar granule neurons.

c-Jun N-terminal protein kinase signalling pathway mediates lovastatin-induced rat brain neuroblast apoptosis

We have previously shown that lovastatin, an HMG-CoA reductase inhibitor, induces apoptosis in rat brain neuroblasts. c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) are implicated in regulation of neuronal apoptosis. In this work, we investigated the role of JNK and p38 MAPK in neuroblast apoptosis induced by lovastatin. We found that lovastatin induced the activation of JNK, but not p38 MAPK. It also induced c-Jun phosphorylation with a subsequent increase in activator protein-1 (AP-1) binding, AP-1-mediated gene expression and BimEL protein levels. The effects of lovastatin were prevented by mevalonate. Pre-treatment with iJNK-I (a selective JNK inhibitor) prevented the effect of lovastatin on both neuroblast apoptosis and the activation of the JNK cascade. Furthermore, we found that the activation of the JNK signalling pathway triggered by lovastatin is accompanied by caspase-3 activation which is also inhibited by iJNK-I pre-treatment. Finally, a specific inhibitor of p38 MAPK, SB203580, had no effect on lovastatin-induced neuroblast apoptosis. Taken together, our data suggest that the activation of the JNK/c-Jun/BimEL signalling pathway plays a crucial role in lovastatin-induced neuroblast apoptosis. Our findings may also contribute to elucidate the intracellular mechanisms involved in the central nervous system side effects associated with statin therapy.

Cell cycle molecules define a pathway required for neuron death in development and disease

We review here evidence defining a molecular pathway that includes cell cycle-related molecules and that appears to play a required role in neuron death during normal development as well as in disease and trauma. The pathway starts with inappropriate activation of cyclin dependent kinase 4 (Cdk4) in neurons which leads to hyper-phosphorylation of the pRb family member p130. This in turn results in dissociation of p130 and its associated chromatin modifiers Suv39H1 and HDAC1 from the transcription factor E2F4. Dissociation of this complex results in de-repression of genes with E2F binding sites including those encoding the transcription factors B- and C-Myb. Once elevated in neurons, B- and C-Myb proteins bind to the promoter for the pro-apoptotic BH3-only protein Bim and promote its induction. Bim then interacts with the core cellular apoptotic machinery, leading to caspase activation and apoptotic death. This pathway is supported by a variety of observations and experimental findings that implicate it as a required element for neuron loss in development and in many nervous system traumas and disorders. The components of this pathway appear to represent potential therapeutic targets for prevention of disease-associated neuron death.

Ischemic preconditioning negatively regulates plenty of SH3s-mixed lineage kinase 3-Rac1 complex and c-Jun N-terminal kinase 3 signaling via activation of Akt

Activation of Akt/protein kinase B has been recently reported to play an important role in ischemic tolerance. We here demonstrate that the decreased protein expression and phosphorylation of phosphatase and tensin homolog deleted from chromosome 10 (PTEN) underlie the increased Akt-Ser-473 phosphorylation in the hippocampal CA1 subfield in ischemic preconditioning (IPC). Co-immunoprecipitation analysis reveals that Akt physically interacts with Rac1, a small Rho family GTPase required for mixed lineage kinase 3 (MLK3) autophosphorylation, and both this interaction and Rac1-Ser-71 phosphorylation induced by Akt are promoted in preconditioned rats. In addition, we show that Akt activation results in the disassembly of the plenty of SH3s (POSH)-MLK3-Rac1 signaling complex and down-regulation of the activation of MLK3/c-Jun N-terminal kinase (JNK) pathway. Akt activation results in decreased serine phosphorylation of 14-3-3, a cytoplasmic anchor of Bax, and prevents ischemia-induced mitochondrial translocation of Bax, release of cytochrome c, and activation of caspase-3. The expression of Fas ligand is also decreased in the CA1 region. Akt activation protects against apoptotic neuronal death as shown in TUNEL staining following IPC. Intracerebral infusion of LY294002 before IPC reverses the increase in Akt phosphorylation and the decrease in JNK signaling activation, as well as the neuroprotective action of IPC. Our results suggest that activation of pro-apoptotic MLK3/JNK3 cascade can be suppressed through activating anti-apoptotic phosphoinositide 3-kinase/Akt pathway induced by a sublethal ischemic insult, which provides a functional link between Akt and the JNK family of stress-activated kinases in ischemic tolerance.

Involvement of c-Jun-JNK pathways in the regulation of programmed cell death of developing chick embryo spinal cord motoneurons

Key features of developmentally regulated programmed cell death (PCD) have been described for the first time in the chick nervous system. JNK/c-Jun pathway was involved in early events determining normal and pathological neuronal death as shown in experimental models. In the chick embryo, PCD of motoneurons (MNs) in ovo occurs within a well-defined temporal window and can be subjected to experimental manipulation. Taking advantage of this in vivo system, we explored the role of c-Jun and JNK pathway in the regulation of PCD in MNs. By using specific antibodies against phospho-c-Jun (Ser 63, 73) and JNK we demonstrated that before MNs acquire apoptotic phenotype there is an increase in c-Jun. Blockage of neuromuscular activity by the GABA agonist muscimol reduces PCD and diminishes c-Jun immunoreactivity in MNs. Extensive induction of PCD, either due to injection of beta-bungarotoxin or limb bud removal, is also preceded by an increase in c-Jun immunoreactivity that is also associated with upregulation of phospho-c-Jun and JNK. Translocation of JNK from cytoplasm to MN nuclei was also detected. After acute application of beta-bungarotoxin, which is a strong apoptotic stimulus for MNs, c-Jun phosphorylation occurs on serine 73, whereas serine 63 is the main site for c-Jun phosphorylation after limb bud removal. These results demonstrated that the JNK/c-Jun pathway is involved in the decision phase of normal and induced apoptosis in MNs. Pharmacological interventions involving this pathway should be explored as a potential therapeutic target for promoting MN survival.

Inhibition of c-Jun N-terminal kinase rescues influenza epitope-specific human cytolytic T lymphocytes from activation-induced cell death

Cytolytic T lymphocytes (CTL) play an important role in defense against viral infections. Following clonal expansion and effector functions, a vast majority of the antigen-specific CTL undergoes programmed cell death to maintain homeostasis. We have shown earlier that melanoma epitope-specific CTL are quite sensitive to activation-induced cell death (AICD) even on the secondary encounter of the antigen. Excessive sensitivity of viral antigen-specific CTL to AICD, however, would be counterproductive. It might be argued that although CTL for a "self" epitope might be more prone to AICD for maintaining self-tolerance, viral antigen-specific CTL are likely to be less sensitive to AICD. We show here that influenza matrix protein-derived MP(58-66) epitope-specific CTL, activated in vitro and bearing a memory phenotype, are just as sensitive to AICD. The AICD in these CTL is not blocked by the pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp (OMe)-fluoromethylketone or by soluble Ig-Fc chimeras of the death receptors [Fas, TNF receptor (TNF-R), TRAIL-RI, TRAIL-RII]. However, the MP(58-66)-specific CTL can be rescued from AICD by the c-jun-N-terminal kinase (JNK) inhibitor SP600125. These results have implications for immunotherapeutic intervention in rescuing viral epitope-specific CTL from AICD.

A biphasic pattern of gene expression during mouse retina development

BACKGROUND

Between embryonic day 12 and postnatal day 21, six major neuronal and one glia cell type are generated from multipotential progenitors in a characteristic sequence during mouse retina development. We investigated expression patterns of retina transcripts during the major embryonic and postnatal developmental stages to provide a systematic view of normal mouse retina development,

RESULTS

A tissue-specific cDNA microarray was generated using a set of sequence non-redundant EST clones collected from mouse retina. Eleven stages of mouse retina, from embryonic day 12.5 (El2.5) to postnatal day 21 (PN21), were collected for RNA isolation. Non-amplified RNAs were labeled for microarray experiments and three sets of data were analyzed for significance, hierarchical relationships, and functional clustering. Six individual gene expression clusters were identified based on expression patterns of transcripts through retina development. Two developmental phases were clearly divided with postnatal day 5 (PN5) as a separate cluster. Among 4,180 transcripts that changed significantly during development, approximately 2/3 of the genes were expressed at high levels up until PN5 and then declined whereas the other 1/3 of the genes increased expression from PN5 and remained at the higher levels until at least PN21. Less than 1% of the genes observed showed a peak of expression between the two phases. Among the later increased population, only about 40% genes are correlated with rod photoreceptors, indicating that multiple cell types contributed to gene expression in this phase. Within the same functional classes, however, different gene populations were expressed in distinct developmental phases. A correlation coefficient analysis of gene expression during retina development between previous SAGE studies and this study was also carried out.

CONCLUSION

This study provides a complementary genome-wide view of common gene dynamics and a broad molecular classification of mouse retina development. Different genes in the same functional clusters are expressed in the different developmental stages, suggesting that cells might change gene expression profiles from differentiation to maturation stages. We propose that large-scale changes in gene regulation during development are necessary for the final maturation and function of the retina.

JNK signaling in neomycin-induced vestibular hair cell death

Mechanosensory hair cells are susceptible to apoptotic death in response to exposure to ototoxic drugs, including aminoglycoside antibiotics. The c-Jun n-terminal kinase (JNK) is a stress-activated protein kinase that can promote apoptotic cell death in a variety of systems. Inhibition of the JNK signaling pathway can prevent aminoglycoside-induced death of cochlear and vestibular sensory hair cells. We used an in vitro preparation of utricles from adult mice to examine the role of JNK activation in aminoglycoside-induced hair cell death. CEP-11004 was used as an indirect inhibitor of JNK signaling. Immunohistochemistry showed that both JNK and its downstream target c-Jun are phosphorylated in hair cells of utricles exposed to neomycin. CEP-11004 inhibited neomycin-induced phosphorylation of both JNK and c-Jun. CEP-11004 inhibited hair cell death in utricles exposed to moderate doses of neomycin. However, the results were not uniform across the dose-response function; CEP-11004 did not inhibit hair cell death in utricles exposed to high-dose neomycin. The CEP-11004-induced protective effect was not due to inhibition of PKC or p38, since neither Chelerythrine nor SB203580 could mimic the protective effect of CEP-11004. In addition, inhibition of JNK inhibited the activation of caspase-9 in hair cells. These results indicate that JNK plays an important role in neomycin-induced vestibular hair cell death and caspase-9 activation.

Akt inhibits MLK3/JNK3 signaling by inactivating Rac1: a protective mechanism against ischemic brain injury

The overall goal of this study was to determine the molecular basis by which mixed-lineage kinase 3 (MLK3) kinase and its signaling pathways are negatively regulated by the pro-survival Akt pathway in cerebral ischemia. We demonstrated that tyrosine phosphorylation of the phosphatase and tensin homolog deleted on chromosome 10 (PTEN) underlies the increased Akt-Ser473 phosphorylation by orthovanadate. Co-immunoprecipitation analysis revealed that endogenous Akt physically interacts with Rac1 in the hippocampal CA1 region, and this interaction is promoted on tyrosine phosphatase inhibition. The elevated Akt activation can deactivate MLK3 by phosphorylation at the Ser71 residue of Rac1, a small Rho family of guanidine triphosphatases required for MLK3 autophosphorylation. Subsequently, inhibition of c-Jun N-terminal kinase 3 (JNK3) results in decreased serine phosphorylation of 14-3-3, a cytoplasmic anchor of Bax, and prevents ischemia-induced mitochondrial translocation of Bax, release of cytochrome c and activation of caspase 3. At the same time, the expression of Fas-ligand decreases in the CA1 region after inhibition of c-Jun activation. The neuroprotective effect of Akt activation is significant in the CA1 region after global cerebral ischemia. Our results suggest that the activation of the pro-apoptotic MLK3/JNK3 cascade induced by ischemic stress can be suppressed through activation of the anti-apoptotic phosphatidylinositol 3-kinase/Akt pathway, which provides a direct link between Akt and the family of stress-activated kinases.

Anti-apoptotic function of thymosin-β in developing chick spinal motoneurons

Thymosin-betas (Tbetas) are water-soluble peptides abundantly present in the cytoplasm and extracellular compartment. The functions of Tbetas appear to be pleiotrophic, including actin-remodeling, wound healing, angiogenesis, etc. In the present study, we present the evidence that Tbetas have anti-apoptotic activity on developing chick motoneurons (MNs) in vivo. Using in ovo electroporation, we introduced three isoforms of Tbeta (Tbeta4, Tbeta10, and Tbeta15) and found the significantly diminished normal and limb bud removal (LBR)-induced programmed cell death. Such anti-apoptotic activity is independent of Tbeta's actin remodeling activity. On the other hand, overexpression of Tbetas substantially reduced early cell death initiation signal, such as phosphorylation of c-Jun. Collectively, these results suggest that Tbetas may prevent apoptosis of neurons via blockade of early apoptogenic signals independent of actin remodeling action.