Persisting expression of galanin in axotomized mamillary and septal neurons of adult rats labeled for c-Jun and NADPH-diaphorase

A non-functional galanin receptor-2 in a multiple sclerosis patient

Multiple Sclerosis (MS) is an inflammatory neurodegenerative disease that affects approximately 2.5 million people globally. Even though the etiology of MS remains unknown, it is accepted that it involves a combination of genetic alterations and environmental factors. Here, after performing whole exome sequencing, we found a MS patient harboring a rare and homozygous single nucleotide variant (SNV; rs61745847) of the G-protein coupled receptor (GPCR) galanin-receptor 2 (GALR2) that alters an important amino acid in the TM6 molecular toggle switch region (W249L). Nuclear magnetic resonance imaging showed that the hypothalamus (an area rich in GALR2) of this patient exhibited an important volumetric reduction leading to an enlarged third ventricle. Ex vivo experiments with patient-derived blood cells (AKT phosphorylation), as well as studies in recombinant cell lines expressing the human GALR2 (calcium mobilization and NFAT mediated gene transcription), showed that galanin (GAL) was unable to stimulate cell signaling in cells expressing the variant GALR2 allele. Live cell confocal microscopy showed that the GALR2 mutant receptor was primarily localized to intracellular endosomes. We conclude that the W249L SNV is likely to abrogate GAL-mediated signaling through GALR2 due to the spontaneous internalization of this receptor in this patient. Although this homozygous SNV was rare in our MS cohort (1:262 cases), our findings raise the potential importance of impaired neuroregenerative pathways in the pathogenesis of MS, warrant future studies into the relevance of the GAL/GALR2 axis in MS and further suggest the activation of GALR2 as a potential therapeutic route for this disease.

Differential expression of galanin in the cholinergic basal forebrain of patients with Lewy body disorders

INTRODUCTION

Depletion of cholinergic neurons within the nucleus basalis of Meynert (nbM) is thought to contribute to the development of cognitive impairments in both Alzheimer's disease (AD) and Lewy body disorders (LBD). It has been reported that, in late stage AD, a network of fibres that contain the neuropeptide galanin displays significant hypertrophy and 'hyperinnervates' the surviving cholinergic neurons. Galanin is considered as a highly inducible neuroprotective factor and in AD this is assumed to be part of a protective tissue response. The aim of this study was to determine if a similar galanin upregulation is present in the nbM in post-mortem tissue from patients with LBD. Gallatin immunohistochemistry was carried out on anterior nbM sections from 76 LBD cases (27 PD, 15 PD with mild cognitive impairment (MCI), 34 PD with dementia (PDD) and 4 aged-matched controls. Galaninergic innervation of cholinergic neurons was assessed on a semi-quantitative scale.

RESULTS

The LBD group had significantly higher galaninergic innervation scores (p = 0.016) compared to controls. However, this difference was due to increased innervation density only in a subgroup of LBD cases and this correlated positively with choline acetyltransferase-immunopositive neuron density.

CONCLUSION

Galanin upregulation within the basal forebrain cholinergic system in LBD, similar to that seen in AD, may represent an intrinsic adaptive response to neurodegeneration that is consistent with its proposed roles in neurogenesis and neuroprotection.

Increased expression of the neuroregenerative peptide galanin in the major pelvic ganglion following cavernous nerve injury

INTRODUCTION

Erectile dysfunction (ED) remains a frequent complication of radical prostatectomy due to injury to the cavernous nerves (CNs). A recent microarray showed the neuropeptide galanin to be one of the most strikingly upregulated genes in the rat major pelvic ganglion (MPG) after bilateral CN crush injury (BCNI).

AIM

The aim of this study is to evaluate the temporal regulation of galanin in the MPG after BCNI and its relationship to functional nerve regeneration.

METHODS

Changes in galanin, galanin receptor (galR), and c-JUN mRNA expression were assessed in Sprague-Dawley rats after sham operation (n = 10) and at 48 hours (n = 10), 7 (n = 10), 14 (n = 5), 21 (n = 5), 30 (n = 5), and 60 (n = 5) days after BCNI using quantitative PCR. Erectile function was assessed by measuring intracavernous pressure (ICP) divided by mean arterial pressure (MAP) during CN electrostimulation. Immunohistochemistry was performed on the MPG in sham-operated animals and 5 days after BCNI.

MAIN OUTCOME MEASURES

ICP/MAP upon CN stimulation; galanin, galR1, -2, -3, and c-JUN mRNA expression at various time points after BCNI; and nNOS, galanin, and galR distribution in the MPG of sham-operated rats and after BCNI.

RESULTS

After BCNI, ICP/MAP values quickly deteriorate, while after 60 days, spontaneous restoration of erectile responses to CN stimulation is observed, reflecting CN regeneration. Galanin mRNA in the MPG is up to 186-fold upregulated compared with sham-operated rats at 48 hours and 7 days after BCNI and gradually declines with increasing time from injury, whereas galanin receptor expressions decrease and c-JUN gradually increases. Galanin expression shows a strong inverse correlation with erectile responses to CN stimulation with time from injury. Injured MPGs show a colocalization between galanin- and nNOS-positive neuronal cell population in the MPG.

CONCLUSIONS

Galanin is upregulated in the MPG in the early phase after CN injury after which it gradually decreases and is present in nNOS-positive neurons of the ganglion. We hypothesize that galanin upregulation is an important factor in the endogenous neuroregenerative response to CN injury.

Galanin protects against nerve injury after shear stress in primary cultured rat cortical neurons

The neuropeptide galanin and its receptors (GalR) are found to be up-regulated in brains suffering from nerve injury, but the specific role played by galanin remains unclear. This study aimed to explore the neuroprotective role of galanin after shear stress induced nerve injury in the primary cultured cortical neurons of rats. Our results demonstrated that no significant changes in cell death and viability were found after galanin treatment when subjected to a shear stress of 5 dyn/cm(2) for 12 h, after increasing magnitude of shear stress to 10 dyn/cm(2) for 12 h, cell death was significantly increased, while galanin can inhibit the nerve injury induced by shear stress with 10 dyn/cm(2) for 12 h. Moreover, Gal2-11 (an agonist of GalR2/3) could also effectively inhibit shear stress-induced nerve injury of primary cultured cortical neurons in rats. Although GalR2 is involved in the galanin protection mechanism, there was no GalR3 expression in this system. Moreover, galanin increased the excitatory postsynaptic currents (EPSCs), which can effectively inhibit the physiological effects of shear stress. Galanin was also found to inhibit the activation of p53 and Bax, and further reversed the down regulation of Bcl-2 induced by shear stress. Our results strongly demonstrated that galanin plays a neuroprotective role in injured cortical neurons of rats.

Changes in galanin and GalR1 gene expression in discrete brain regions after transient occlusion of the middle cerebral artery in female rats

Injury to neurons results in up-regulation of galanin in some central and peripheral systems, and it has been suggested that this neuropeptide may play a protective and trophic role, primarily mediated by galanin receptor 2 (GalR2). The objective of the present study was to investigate galanin, GalR1, GalR2 and GalR3 gene expression in the female rat brain 7 days after a 60-min unilateral occlusion of the middle cerebral artery followed by reperfusion. Quantitative real-time PCR was employed in punch-biopsies from the locus coeruleus, somatosensory cortex and dorsal hippocampal formation, including sham-operated rats as controls. Galanin gene expression showed a ∼2.5-fold increase and GalR1 a ∼1.5-fold increase in the locus coeruleus of the ischemic hemisphere compared to the control side. Furthermore, the GalR1 mRNA levels decreased by 35% in somatosensory cortex of the ischemic hemisphere. Immunohistochemical analysis indicated a depletion of galanin from cell bodies and dendrites in the locus coeruleus after middle cerebral artery occlusion. The present results suggest that a stroke-induced forebrain lesion up-regulates synthesis of galanin and GalR1 in the locus coeruleus, a noradrenergic cell group projecting to many forebrain areas, including cortex and the hippocampal formation. These results support the notion that galanin may play a role in the response of the central nervous system to injury.

Galanin acts as a trophic factor to the central and peripheral nervous systems

The neuropeptide galanin is widely, but not ubiquitously, expressed in the adult nervous system. Its expression is markedly up-regulated in many neuronal tissues after nerve injury or disease. Over the last 10 years, we have demonstrated that the peptide plays a developmental survival role to subsets of neurons in the peripheral and central nervous systems with resulting phenotypic changes in neuropathic pain and cognition. Galanin also appears to play a trophic role to adult sensory neurons following injury, via activation of GalR2, by stimulating neurite outgrowth. Furthermore, galanin also plays a neuroprotective role to the hippocampus following excitotoxic injury, again mediated by activation of GalR2. Most recently, we have shown that galanin expression is markedly up-regulated in multiple sclerosis (MS) lesions and in the experimental autoimmune encephalomyelitis (EAE) model of MS. Over-expression of galanin in transgenic mice abolishes disease in the EAE model, whilst loss-of-function mutations in galanin or GalR2 increase disease severity. In summary, these studies demonstrate that a GalR2 agonist might have clinical utility in a variety of human diseases that affect the nervous system.

A role for galanin in human and experimental inflammatory demyelination

The neuropeptide galanin is widely expressed by many differing subsets of neurons in the nervous system. There is a marked upregulation in the levels of the peptide in a variety of nerve injury models and in the basal forebrain of humans with Alzheimer's disease. Here we demonstrate that galanin expression is specifically and markedly upregulated in microglia both in multiple sclerosis (MS) lesions and shadow plaques. Galanin expression is also upregulated in the experimental autoimmune encephalomyelitis (EAE) model of MS, although solely in oligodendrocytes. To study whether the observed increase in expression of galanin in inflammatory demyelination might modulate disease activity, we applied the EAE model to a panel of galanin transgenic lines. Over-expression of galanin in transgenic mice (Gal-OE) abolishes disease in the EAE model, whilst loss-of-function mutations in galanin or galanin receptor-2 (GalR2) increase disease severity. The pronounced effects of altered endogenous galanin or GalR2 expression on EAE disease activity may reflect a direct neuroprotective effect of the neuropeptide via activation of GalR2, similar to that previously described in a number of neuronal injury paradigms. Irrespective of the mechanism(s) by which galanin alters EAE disease activity, our findings imply that galanin/GalR2 agonists may have future therapeutic implications for MS.

Galanin decreases proliferation of PC12 cells and induces apoptosis via its subtype 2 receptor (GalR2)

Galanin is a neuropeptide with a wide range of effects in the nervous and endocrine systems, mediated through three G protein-coupled receptor subtypes (GalR1-3). Interestingly, galanin and its receptors are also expressed in certain tumors. Here we studied the effects of galanin in rat pheochromocytoma (PC12) cells stably transfected with GFP-tagged GalR2. Galanin at 100 nM inhibited cell proliferation in both nontransfected and transfected cells. Conversly, both galanin and the GalR2(R3)-agonist AR-M1896 induced caspase-dependent apoptotic cell death only in GalR2-transfected cells. Western-blot analyses of downstream mediators of the G(q/11)-type G protein showed down-regulation of pAkt and pBad in galanin-exposed transfected cells. Also, the specific PI3 kinase inhibitor LY-294002 increased the level of pBad and decreased activation of caspases. In addition, p21(cip1) levels were up-regulated in galanin-exposed PC12 cells and down-regulated in galanin-exposed GalR2-transfected cells. In agreement, FACS analyses of galanin exposed cells showed occurrence of cell cycle arrest in PC12 cells and cell death in transfected cells. Finally, as shown with real-time PCR, galanin and its receptors were expressed at very high levels in human pheochromocytoma tissues as compared with normal adrenal medulla. These findings point to GalR2 as a possible target for therapeuthic interventions in pheochromocytoma.

Contusive spinal cord injury evokes localized changes in NADPH-d activity but extensive changes in Fos-like immunoreactivity in the rat

The histological detection of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d), a marker for nitric oxide-producing cells, was used to evaluate ongoing changes in the neural biochemistry of the rat spinal cord 1 week following contusive spinal cord injury (SCI). In addition, the immunohistochemical detection of the immediate-early gene c-fos was used to identify basal patterns of neural activity at this time. The numbers and laminar locations of NADPH-d- and c-fos-positive cells were examined in spinal segments adjacent to the site of injury (T12-S3) as well as those distant from the injury (C3-C5) in both SCI and un-injured rats. Our data show that contusive SCI results in a significant reduction in NADPH-d labelling in the superficial dorsal horn, and a significant increase in NADPH-d expression in small bipolar neurons and large motoneurons in the ventral horn at the site of the injury. In spinal segments distant to the injury site (C3-C5), NADPH-d activity did not differ from that of uninjured controls. Furthermore, significant reductions in the levels of c-fos expression were observed in SCI rats, in spinal segments both at and distant to the site of injury for all spinal laminae. The only exception was a dramatic increase observed in the sacral parasympathetic nucleus. These data suggest that increased NADPH-d expression is related to conditions specific to the site of injury, whereas the changes in c-fos expression probably indicate more global changes in neuronal activity following SCI.

Activation of the galanin receptor 2 (GalR2) protects the hippocampus from neuronal damage

Expression of the neuropeptide galanin is up-regulated in many brain regions following nerve injury and in the basal forebrain of patients with Alzheimer's disease. We have previously demonstrated that galanin modulates hippocampal neuronal survival, although it was unclear which receptor subtype(s) mediates this effect. Here we report that the protective role played by galanin in hippocampal cultures is abolished in animals carrying a loss-of-function mutation in the second galanin receptor subtype (GalR2-MUT). Exogenous galanin stimulates the phosphorylation of the serine/threonine kinase Akt and extracellular signal-regulated kinase (ERK) in wild-type (WT) cultures by 435 +/- 5% and 278 +/- 2%, respectively. The glutamate-induced activation of Akt was abolished in cultures from galanin knockout animals, and was markedly attenuated in GalR2-MUT animals, compared with WT controls. In contrast, similar levels of glutamate-induced ERK activation were observed in both loss-of-function mutants, but were further increased in galanin over-expressing animals. Using specific inhibitors of either ERK or Akt confirms that a GalR2-dependent modulation in the activation of the Akt and ERK signalling pathways contributes to the protective effects of galanin. These findings imply that the rise in endogenous galanin observed either after brain injury or in various disease states is an adaptive response that reduces apoptosis by the activation of GalR2, and hence Akt and ERK.

Synaptogenesis regulates axotomy-induced activation of c-Jun-activator protein-1 transcription

The activator protein-1 (AP1) transcription complex remains active for long periods after axotomy, but its activity diminishes during target contact. This raises the possibility that the function of this complex is regulated by the synaptic connections. Using Aplysia californica, we found that crushing peripheral nerves in vivo enhanced AP1 binding in the sensory neurons that lasted for weeks and then declined as regeneration was completed. The AP1 complex in Aplysia is a c-Jun homodimer. Its activation, after axotomy, is mediated by Aplysia c-Jun-N-terminal kinase (apJNK), which enters the nucleus of sensory neurons and phosphorylates c-Jun at Ser-73 (p73-c-Jun). Active AP1 in the sensory neurons did not mediate apoptosis and was not involved in the appearance of the long-term hyperexcitability that develops in these cells after axotomy, and blocking the activation of apJNK in vitro did not influence neurite outgrowth. In contrast, the levels of activated apJNK and p73-c-Jun declined markedly when sensory neurons formed synapses with motor neuron L7 in vitro. Furthermore, inhibiting the pathway accelerated synaptogenesis between sensory neurons and L7. These data suggest that positive and negative modulation of the JNK-c-Jun-AP1 pathway functions in alerting the nucleus to the loss and gain of synapses, respectively.

Either nitric oxide or nerve growth factor is required for dorsal root ganglion neurons to survive during embryonic and neonatal development

During early embryonic (E12) development almost all dorsal root ganglion (DRG) neurons express the neuronal isoform of nitric oxide synthase (nNOS). At this stage, the axons of these neurons are rudimentary and have not made contact with peripheral tissue targets. As their axons establish contact with peripheral targets such as the skin, the number of neurons expressing nNOS decrease that correspond to increased immunoreactivity for nerve growth factor (NGF) in the skin, and its high affinity receptor, tyrosine kinase A (trkA) in both skin and DRG neurons. During late postnatal development, very few DRG neurons express nNOS; however, axotomy or NGF deprivation of cultured DRG neurons induce nNOS and NOS blockade causes neuronal death. In contrast, NGF-deprived embryonic and neonatal DRG neurons die by apoptosis, while NOS blockade has no effect. Overall, these observations suggest that NGF and nitric oxide (NO) interact during embryonic and postnatal development to facilitate neuronal selection and survival. The roles of NO, NGF and its receptor trkA in DRG neurons during different stages of development are discussed.

Galanin acts as a neuroprotective factor to the hippocampus

The expression of the neuropeptide galanin is markedly up-regulated in many areas of the central and peripheral nervous system after injury. We have recently demonstrated that peripheral sensory neurons depend on galanin for neurite extension after injury, mediated by activation of the second galanin receptor subtype (GALR2). We therefore hypothesized that galanin might also act in a similar manner in the CNS, reducing cell death in hippocampal models of excitotoxicity. Here we report that galanin acts an endogenous neuroprotective factor to the hippocampus in a number of in vivo and in vitro models of injury. Kainate-induced hippocampal cell death was greater in both the CA1 and CA3 regions of galanin knockout animals than in WT controls. Similarly, exposure to glutamate or staurosporine induced significantly more neuronal cell death in galanin knockout organotypic and dispersed primary hippocampal cultures than in WT controls. Conversely, less cell death was observed in the hippocampus of galanin overexpressing transgenic animals after kainate injection and in organotypic cultures after exposure to staurosporine. Further, exogenous galanin or the previously described high-affinity GALR2 agonist, both reduced cell death when coadministered with glutamate or staurosporine in WT cultures. These results demonstrate that galanin acts an endogenous neuroprotective factor to the hippocampus and imply that a galanin agonist might have therapeutic uses in some forms of brain injury.

Damage-induced neuronal endopeptidase (DINE/ECEL) expression is regulated by leukemia inhibitory factor and deprivation of nerve growth factor in rat sensory ganglia after nerve injury

Damage-induced neuronal endopeptidase (DINE) is a novel metallopeptidase and is expressed in response to various neuronal injuries. The expression regulation of DINE mRNA in the dorsal root ganglia (DRGs) after sciatic nerve injury is examined. A substantial increase of DINE mRNA expression was observed in relatively small-sized DRG neurons after nerve injury. The expression was observed in isolectin B4-negative and partly TrkA-positive neurons, and the expression profile was fairly similar to that of the neuropeptide galanin. More than 80% of DINE mRNA-positive neurons simultaneously demonstrated galanin immunoreactivity after nerve injury. In cultured DRG, DINE mRNA expression was enhanced by leukemia inhibitory factor (LIF) but not by other growth factors and cytokines. LIF treatment to rat sciatic nerve induced DINE mRNA expression in DRG without nerve injury, and, conversely, the intranerve injection of anti-gp130 antibody after sciatic nerve injury significantly inhibited the upregulation of DINE mRNA in DRG. Furthermore, nerve growth factor (NGF) deprivation, which can induce galanin expression, also enhanced DINE mRNA expression in vitro and in vivo. Both LIF application and NGF deprivation additively enhanced DINE expression in vitro. These results suggest that DINE gene expression is regulated separately by both LIF and NGF deprivation, and this regulation pattern is similar to that of galanin gene expression. Because both DINE and galanin have a neuroprotective function, their simultaneous induction may provide more successful protection for injured sensory neurons.

Distinct subcellular localization and mRNA expression of neuronal nitric oxide synthase in the nucleus dorsalis and red nucleus and their correlation with inducible transcription factors after spinal cord hemisection

We previously reported on the differential expression of neuronal nitric oxide synthase (nNOS) in neurons of the nucleus dorsalis (ND) and red nucleus (RN), as well as differential roles of nitric oxide (NO) in these two distinct groups' neurons characterized with different nNOS phenotypes after lower thoracic spinal cord hemisection. To further understand the enzyme, nNOS expression was studied at the subcellular and mRNA levels by using electron microscopic immunohistochemistry (EM-IHC) and in situ hybridization respectively. Possible transcriptional regulation by c-Jun or CREB in the differential nNOS expression in both ND and RN neurons was also studied. nNOS mRNA was not found in the normal ND neurons, but was shown in the normal RN neurons. After spinal cord hemisection, nNOS mRNA was induced in the ipsilateral ND, while upregulated on both sides of the RN, which preceded protein induction or upregulation. By EM-IHC, nNOS immunoreaction products were predominantly bound to the membrane of the mitochondria, rough endoplasmic reticulum (rER), Golgi apparatus, and nuclear envelope in the RN neurons of normal rats as well as rats subjected to spinal cord hemisection. In contrast, nNOS-immunoreactive deposits in the experimental ND neurons were found to be mainly granular, being dispersed throughout the cytoplasmic matrix. It is speculated that the differential subcellular localizationof nNOS indicates that axotomy may trigger different nNOS transcripts and lead to different nNOS isoform expression in the normally non-nNOS- and normally nNOS-containing neurons. c-Jun was induced in the ipsilateral ND neuronsand upregulated only in the contralateral RN neurons. Activation of CREB by phosphorylation was occasionally detectable in the ND neurons, but not in the RN neurons. Double-labeling data showed a large proportion of c-Jun and nNOS colocalization in neurons of the ipsilateral ND and contralateral RN after spinal cord hemisection. However, dissociation of nNOS expression kinetics with c-Jun was observed in the ipsilateral RN. The results implied that nNOS expression might not be under the direct transcriptional regulation by c-Jun, although it seemed to be closely related to the c-Jun expression.

Galanin in ascending systems. Focus on coexistence with 5-hydroxytryptamine and noradrenaline

Galanin can be synthesized in several ascending systems including cholinergic forebrain neurons, serotonergic dorsal raphe neurons, and the noradrenergic locus coeruleus system. Recent immunohistochemical studies suggest that of these three systems, the locus coeruleus neurons express the highest levels of galanin and that in cortex and hippocampus galanin peptide can only be detected in the noradrenergic projections. Electrophysiologic studies show that galanin hyperpolarizes both serotonergic dorsal raphe neurons and noradrenergic locus coeruleus neurons at fairly high concentrations (10(6)-10(-7) M). In addition, galanin at low concentrations (10(-9) M) enhances the 5-HT- and noradrenaline-induced hyperpolarization. Consequently, a galanin antagonist could attenuate an inhibitory tone on both dorsal raphe and locus coeruleus neurons and thus perhaps exert antidepressant activity.

Axotomy-induced c-JUN expression in young medial septal neurons is regulated by nerve growth factor

In the present study we investigated the axotomy-induced expression of the proto-oncogene c-jun in young rat medial septal neurons and its regulation by nerve growth factor. First, medial septal neurons were retrogradely labelled by Fast Blue injection into the hippocampus at postnatal day 1 (P1). Rats of different developmental ages (P6, P9, P14, P21, P28 and P42) were then subjected to bilateral fimbria-fornix transection resulting in the axotomy of septohippocampal projection neurons. After the lesion, c-JUN immunoreactivity was observed in the nuclei of axotomized medial septal neurons of all stages examined, suggesting that c-JUN induction is an age-independent feature of axotomized medial septal neurons. Double immunolabelling for choline acetyltransferase and c-JUN or parvalbumin and c-JUN, respectively, revealed that both cholinergic and GABAergic septohippocampal projection neurons express c-JUN after axotomy. In addition, a co-localization of immunostaining for c-JUN and the neuropeptide galanin was found after lesion, as both proteins were induced in the same medial septal neurons following fimbria-fornix transection. Next, the regulation of c-JUN expression in axotomized medial septal neurons was studied in organotypic cultures of the medial septum. Axotomized medial septal neurons in culture did not express c-JUN in contrast to the in vivo situation. With the concept that nerve growth factor suppresses c-JUN expression, slice cultures of the medial septum were treated with antibodies against nerve growth factor. This treatment caused a dose-dependent increase in c-JUN-positive cells in these slice cultures. Simultaneous addition of nerve growth factor and antibodies against nerve growth factor resulted in the reversal of this effect. These data suggest an age-independent induction of c-JUN in axotomized medial septal neurons and its regulation by nerve growth factor.

Role of NGF in axotomy-induced c-Jun expression in medial septal cholinergic neurons

The extent of neuronal regeneration after axotomy largely depends on the survival capacity of the injured cell. It has been shown for a long time that nerve fiber transection results in retrograde changes in the parent neuronal cell body, and that these changes may eventually lead to neuronal degeneration. At present, little is known about the sequence of events initiated in a nerve cell body by the transection of its axonal process. In this report, we will focus on an interaction of nerve growth factor (NGF) with the transcription factor c-Jun in intact and axotomized septohippocampal projection neurons.

Lasting N-terminal phosphorylation of c-Jun and activation of c-Jun N-terminal kinases after neuronal injury

Transcription factor c-Jun is proposed to control neuronal cell death and survival, but its activation by N-terminal phosphorylation and the underlying activity of the c-Jun N-terminal kinases (JNKs) remain to be elucidated in the adult mammalian brain. We generated a polyclonal antiserum that specifically recognizes c-Jun phosphorylated at its serine 73 (S73) residue after UV irradiation of 3T3 cells. Disruption of the c-jun locus in 3T3 cells abolished this reaction, and retransfection of the human c-jun at the c-jun-/- background restored it. The phospho-c-Jun antiserum was used to visualize N-terminally phosphorylated c-Jun in the adult rat brain with cellular resolution. Prolonged c-Jun S73 phosphorylation was detected in affected neurons up to 5 d after transient occlusion of medial cerebral artery or up to 50 d after transection of central nerve fiber tracts. After cerebral ischemia-reperfusion, phosphorylation of c-Jun was linked with induced expression of Fas-ligand (APO-1, CD95-ligand), whose gene is a putative c-Jun/AP-1 target, and with terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL) reactivity, a marker for apoptosis. After nerve fiber transection, however, lasting c-Jun phosphorylation occurred in axotomized neurons negative for Fas-ligand or TUNEL and regardless of degeneration or survival. In contrast to these lasting phosphorylation patterns, transient seizure activity by pentylenetetrazole provoked only a brief c-Jun phosphorylation and JNK activation. In extracts from ischemic or axotomized brain compartments, c-Jun phosphorylation correlated with enhanced long-term JNK activity, and in-gel kinase assays visualized proteins with sizes corresponding to JNK isoforms as the only c-Jun N-terminally phosphorylating enzymes. These results demonstrate that lasting c-Jun S73 phosphorylation and JNK activity are part of neuronal stress response after neurodegenerative disorders in the adult mammalian brain with Fas-ligand as a putative apoptotic effector.