Do c-Jun, c-Fos, and amyloid precursor protein play a role in neuronal death or survival?

Effects of Probiotics on Colitis-Induced Exacerbation of Alzheimer's Disease in AppNL-G-F Mice

Alzheimer's disease (AD) is characterized by progressive cognitive decline and is a leading cause of death in the United States. Neuroinflammation has been implicated in the progression of AD, and several recent studies suggest that peripheral immune dysfunction may influence the disease. Continuing evidence indicates that intestinal dysbiosis is an attribute of AD, and inflammatory bowel disease (IBD) has been shown to aggravate cognitive impairment. Previously, we separately demonstrated that an IBD-like condition exacerbates AD-related changes in the brains of the AppNL-G-F mouse model of AD, while probiotic intervention has an attenuating effect. In this study, we investigated the combination of a dietary probiotic and an IBD-like condition for effects on the brains of mice. Male C57BL/6 wild type (WT) and AppNL-G-F mice were randomly divided into four groups: vehicle control, oral probiotic, dextran sulfate sodium (DSS), and DSS given with probiotics. As anticipated, probiotic treatment attenuated the DSS-induced colitis disease activity index in WT and AppNL-G-F mice. Although probiotic feeding significantly attenuated the DSS-mediated increase in WT colonic lipocalin levels, it was less protective in the AppNL-G-F DSS-treated group. In parallel with the intestinal changes, combined probiotic and DSS treatment increased microglial, neutrophil elastase, and 5hmC immunoreactivity while decreasing c-Fos staining compared to DSS treatment alone in the brains of WT mice. Although less abundant, probiotic combined with DSS treatment demonstrated a few similar changes in AppNL-G-F brains with increased microglial and decreased c-Fos immunoreactivity in addition to a slight increase in Aβ plaque staining. Both probiotic and DSS treatment also altered the levels of several cytokines in WT and AppNL-G-F brains, with a unique increase in the levels of TNFα and IL-2 being observed in only AppNL-G-F mice following combined DSS and probiotic treatment. Our data indicate that, while dietary probiotic intervention provides protection against the colitis-like condition, it also influences numerous glial, cytokine, and neuronal changes in the brain that may regulate brain function and the progression of AD.

Chemotherapy Resistance: Role of Mitochondrial and Autophagic Components

Simple Summary

Chemotherapy resistance is a common occurrence during cancer treatment that cancer researchers are attempting to understand and overcome. Mitochondria are a crucial intracellular signaling core that are becoming important determinants of numerous aspects of cancer genesis and progression, such as metabolic reprogramming, metastatic capability, and chemotherapeutic resistance. Mitophagy, or selective autophagy of mitochondria, can influence both the efficacy of tumor chemotherapy and the degree of drug resistance. Regardless of the fact that mitochondria are well-known for coordinating ATP synthesis from cellular respiration in cellular bioenergetics, little is known its mitophagy regulation in chemoresistance. Recent advancements in mitochondrial research, mitophagy regulatory mechanisms, and their implications for our understanding of chemotherapy resistance are discussed in this review.

Abstract

Cancer chemotherapy resistance is one of the most critical obstacles in cancer therapy. One of the well-known mechanisms of chemotherapy resistance is the change in the mitochondrial death pathways which occur when cells are under stressful situations, such as chemotherapy. Mitophagy, or mitochondrial selective autophagy, is critical for cell quality control because it can efficiently break down, remove, and recycle defective or damaged mitochondria. As cancer cells use mitophagy to rapidly sweep away damaged mitochondria in order to mediate their own drug resistance, it influences the efficacy of tumor chemotherapy as well as the degree of drug resistance. Yet despite the importance of mitochondria and mitophagy in chemotherapy resistance, little is known about the precise mechanisms involved. As a consequence, identifying potential therapeutic targets by analyzing the signal pathways that govern mitophagy has become a vital research goal. In this paper, we review recent advances in mitochondrial research, mitophagy control mechanisms, and their implications for our understanding of chemotherapy resistance.

Transcriptional changes in the hypothalamus, pituitary, and mammary gland underlying decreased lactation performance in mice under heat stress

Because of climate change, heat stress (HS) causes more and more impacts on dairy animals to decrease lactation performance. The neuroendocrine system is key in regulating systemic physiological processes and milk synthesis. However, the hypothalamic-pituitary axis response to HS is still unclear. In this study, a group of lactating mice underwent a daily 2-h heat treatment (36°C) for 14 d to explore possible cross-talk between the hypothalamic-pituitary axis and mammary gland under HS. Transcriptome analyses by multitissue RNA-Seq indicated the possible mechanisms of reduced lactation performance in animals under HS. In the hypothalamus, the cAMP signaling pathway was activated to resist neuronal death, and the expression of downstream genes was increased to promote cell survival under HS. Reduced food intake might be caused by down-regulated appetite-related peptide, whereas up-regulated neuropeptide Y acted to attenuate reduced food intake. In pituitary, energy stress from lower food intake might result in reduced secretion of prolactin and growth hormone. Under HS, the mammary gland may undergo hypoxic stress, causing mammary epithelial cell apoptosis. Together, these data showed systemic changes in tissues to accommodate the effects of HS on lactation.-Han, J., Shao, J., Chen, Q., Sun, H., Guan, L., Li, Y., Liu, J., Liu, H. Transcriptional changes in the hypothalamus, pituitary, and mammary gland underlying decreased lactation performance in mice under heat stress.

Continuous neurodegeneration and death pathway activation in neurons and glia in an experimental model of severe chronic epilepsy

Whether seizures might determine the activation of cell death pathways and what could be the relevance of seizure-induced cell death in epilepsy are still highly debated issues. We recently developed an experimental model of acquired focal cortical dysplasia (the MAM-pilocarpine or MP rat) in which the occurrence of status epilepticus--SE--and subsequent seizures induced progressive cellular/molecular abnormalities and neocortical/hippocampal atrophy. Here, we exploited the same model to verify when, where, and how cell death occurred in neurons and glia during epilepsy course. We analyzed Fluoro Jade (FJ) staining and the activation of c-Jun- and caspase-3-dependent pathways during epilepsy, from few hours post-SE up to six months of spontaneous recurrent seizures. FJ staining revealed that cell injury in MP rats was not temporally restricted to SE, but extended throughout the different epileptic stages. The region-specific pattern of FJ staining changed during epilepsy, and FJ(+) neurons became more prominent in the dorsal and ventral hippocampal CA at chronic epilepsy stages. Phospho-c-Jun- and caspase-3-dependent pathways were selectively activated respectively in neurons and glia, at early but even more conspicuously at late chronic stages. Phospho-c-Jun activation was associated with increased cytochrome-c staining, particularly at chronic stages, and the staining pattern of cytochrome-c was suggestive of its release from the mitochondria. Taken together, these data support the content that at least in the MP rat model the recurrence of seizures can also sustain cell death mechanisms, thus continuously contributing to the pathologic process triggered by the occurrence of SE.

The senescence hypothesis of disease progression in Alzheimer disease: an integrated matrix of disease pathways for FAD and SAD

Alzheimer disease (AD) is a progressive, neurodegenerative disease characterised in life by cognitive decline and behavioural symptoms and post-mortem by the neuropathological hallmarks including the microtubule-associated protein tau-reactive tangles and neuritic plaques and amyloid-beta-protein-reactive senile plaques. Greater than 95 % of AD cases are sporadic (SAD) with a late onset and <5 % of AD cases are familial (FAD) with an early onset. FAD is associated with various genetic mutations in the amyloid precursor protein (APP) and the presenilins (PS)1 and PS2. As yet, no disease pathway has been fully accepted and there are no treatments that prevent, stop or reverse the cognitive decline associated with AD. Here, we review and integrate available environmental and genetic evidence associated with all forms of AD. We present the senescence hypothesis of AD progression, suggesting that factors associated with AD can be seen as partial stressors within the matrix of signalling pathways that underlie cell survival and function. Senescence pathways are triggered when stressors exceed the cells ability to compensate for them. The APP proteolytic system has many interactions with pathways involved in programmed senescence and APP proteolysis can both respond to and be driven by senescence-associated signalling. Disease pathways associated with sporadic disease may be different to those involving familial genetic mutations. The interpretation we provide strongly points to senescence as an additional underlying causal process in dementia progression in both SAD and FAD via multiple disease pathways.

Molecular mechanisms that enhance synapse stability despite persistent disruption of the spectrin/ankyrin/microtubule cytoskeleton

Neuromuscular junctions crippled by a disrupted microtubule cytoskeleton are rescued by stress-induced activation of MAPK-JNK-Fos signaling.

Loss of spectrin or ankyrin in the presynaptic motoneuron disrupts the synaptic microtubule cytoskeleton and leads to disassembly of the neuromuscular junction (NMJ). Here, we demonstrate that NMJ disassembly after loss of α-spectrin can be suppressed by expression of a Wld^S transgene, providing evidence for a Wallerian-type degenerative mechanism. We then identify a second signaling system. Enhanced MAPK-JNK-Fos signaling suppresses NMJ disassembly despite loss of presynaptic α-spectrin or ankyrin2-L. This signaling system is activated after an acute cytoskeletal disruption, suggesting an endogenous role during neurological stress. This signaling system also includes delayed, negative feedback via the JNK phosphatase puckered, which inhibits JNK-Fos to allow NMJ disassembly in the presence of persistent cytoskeletal stress. Finally, the MAPK-JNK pathway is not required for baseline NMJ stabilization during normal NMJ growth. We present a model in which signaling via JNK-Fos functions as a stress response system that is transiently activated after cytoskeletal disruption to enhance NMJ stability, and is then shut off allowing NMJ disassembly during persistent cytoskeletal disruption.

Differential activation of c-fos and caspase-3 in hippocampal neuron subpopulations following neonatal hypoxia-ischemia

Neonatal hypoxia-ischemia (HI) induces immediate early gene (IEG) c-fos expression as well as neuron death. The precise role of IEGs in neonatal HI is unclear. We investigated the temporal and spatial patterns of c-Fos expression in postnatal day 7 mice after unilateral carotid ligation and exposure to 8% oxygen. mRNA levels of c-fos quantitated by real-time polymerase chain reaction (PCR) increased nearly 40-fold (log 1.2 +/- 0.4) in the ipsilateral hippocampus 3 hr following neonatal HI, then returned to basal levels within 12 hr, although no change was observed in c-jun mRNA. Frozen coronal brain sections were stained with cresyl violet or used for immunohistochemical detection of c-Fos, cleaved caspase-3, glial fibrillary acidic protein (GFAP), and the mature neuron marker NeuN. c-Fos immunoreactivity increased throughout the injured hippocampus 3 hr after HI but became restricted to the CA2-3 subregion and the dentate gyrus (DG) at 6-12 hr and declined by 24 hr. In contrast, cleaved (activated) caspase-3 immunoreactivity was most abundant in the ipsilateral CA1 region at 3-6 hr after neonatal HI, then became more prominent in CA2-3 and DG. Double-labeling experiments showed c-Fos and cleaved caspase-3 immunoreactivity localized in spatially distinct neuron subpopulations. Prominent c-Fos immunoreactivity was observed in surviving CA2-3 and external granular DG neurons, and robust cleaved caspase-3 immunoreactivity was observed in pyknotic CA1, CA2-3, and subgranular DG neurons. The differential expression of c-Fos in HI-resistant hippocampal subpopulations vs. cleaved caspase-3 in dying neurons suggests a neuroprotective role for c-Fos expression in neonatal HI.

Neuronal and astroglial alterations in the hippocampus of a mouse model for type 1 diabetes

The influence of diabetes mellitus on brain pathology is increasingly recognized. Previous contributions of our laboratory demonstrated in models of type 1 diabetes (nonobese diabetic and streptozotocin (STZ)-treated mice), a marked astrogliosis and neurogenesis deficit in hippocampus and increased expression of hypothalamic neuropeptides. In the present investigation, we further analyzed alterations of astroglia and neurons in the hippocampus of mice 1 month after STZ-induced diabetes. Results showed that these STZ-diabetic mice presented: (a) increased number of astrocytes positive for apolipoprotein-E (Apo-E), a marker of ongoing neuronal dysfunction; (b) abnormal expression of early gene products associated with neuronal activation, including a high number of Jun + neurons in CA1 and CA3 layers and dentate gyrus, and of Fos-expressing neurons in CA3 layer; (c) augmented activity of NADPH-diaphorase, linked to oxidative stress, in CA3 region. These data support the concept that uncontrolled diabetes leads to hippocampal pathology, which adjoin to changes in other brain structures such as hypothalamus and cerebral cortex.

Astrocyte protection of neurons: role of transforming growth factor-beta signaling via a c-Jun-AP-1 protective pathway

Astrocytes have become a focal point for research in neurobiology, especially regarding their purported ability to regulate neuronal communication and survival. The present study addressed a poorly understood but important focus in this area, the mechanism(s) underlying astrocyte-induced survival of neurons. The results of the study show that soluble factors in astrocyte-conditioned media (ACM) protect murine GT1-7 neurons from serum deprivation-induced cell death and that this neuroprotection is correlated with enhanced activation/phosphorylation of the AP-1 transcription factor, c-JunSer-63. A parallel and correlated activation of the upstream kinases, c-Jun N-terminal kinase (JNK) and mitogen-activated protein kinase kinase-4 (MKK4) was also demonstrated. Furthermore, co-administration of JNK inhibitors, but not a MEK inhibitor, significantly attenuated ACM-induced phosphorylation of c-JunSer-63 and blocked its neuroprotective action. Gel shift analysis demonstrated that ACM enhanced AP-1 binding, an effect that appears functionally important, since an AP-1 binding inhibitor significantly attenuated the neuroprotective action of ACM. Further studies implicated transforming growth factor (TGF)-beta1 and TGF-beta2 as critical active soluble factors released by astrocytes, since both were demonstrated in ACM, and immunoneutralization of the conditioned media with a panspecific TGF-beta antibody significantly attenuated the enhanced AP-1 binding and neuroprotective action of the ACM. Furthermore, exogenous application of TGF-beta1 and TGF-beta2 was found to enhance c-JunSer-63 phosphorylation and to be neuroprotective, and co-administration of JNK inhibitors or an AP-1 binding inhibitor blocked TGF-beta-induced neuroprotection. Taken together, these studies suggest that astrocytes can protect neurons from serum deprivation-induced cell death, at least in part, by release of TGF-beta and activation of a c-Jun/AP-1 protective pathway.

Effect of intra-ischemic hypothermia on the expression of c-Fos and c-Jun, and DNA binding activity of AP-1 after focal cerebral ischemia in rat brain

It is unknown whether immediate early gene (IEG) induction and subsequent late gene regulation after ischemia is beneficial or deleterious. The aim of this study was to examine the effect of hypothermia on expression of c-Fos and c-Jun, and AP-1 DNA binding activity, after transient focal cerebral ischemia in rat brain, and clarify the role of IEGs and AP-1 after insults. Male Wistar rats underwent right middle cerebral artery occlusion for 1 h with the intraluminal suture method. During ischemia, animals were assigned to either normothermic (NT) or hypothermic (HT) groups. In the NT group, brain temperature was observed to spontaneously increase to 40 degrees C during ischemia. In the HT group, brain temperature decreased to 30 degrees C. Infarct volume in cortex was decreased in the HT group, compared with that in the NT group (P<0.001). Increased c-Fos immunoreactivity in the cortex was observed at 3 h after reperfusion in the HT, but not the NT group, while c-Jun expression was not affected by HT treatment. There was also a significant increase in AP-1 DNA binding activity at 3 h in the HT group when compared to the NT group (P<0.01). In conclusion, hypothermia decreased cerebral infarction in association with early increases in c-Fos expression and AP-1 DNA binding activity in peri-infarct cortex. It remains to be established whether such responses are a cause or consequence of cell survival, but these results clearly establish that altered transcription is a key feature of tissue spared following hypothermic focal ischemia.

Contribution of the Atm protein to maintaining cellular homeostasis evidenced by continuous activation of the AP-1 pathway in Atm-deficient brains

Maintenance of genome stability is essential for keeping cellular homeostasis. The DNA damage response is a central component in maintaining genome integrity. Among of the most cytotoxic DNA lesions are double strand breaks (DSBs) caused by ionizing radiation or radiomimetic chemicals. ATM is missing or inactivated in patients with ataxia-telangiectasia. Ataxia-telangiectasia patients display a pleiotropic phenotype and suffer primarily from progressive ataxia caused by degeneration of cerebellar Purkinje and granule neurons. Additional features are immunodeficiency, genomic instability, radiation sensitivity, and cancer predisposition. Disruption of the mouse Atm locus creates a murine model of ataxia-telangiectasia that exhibits most of the clinical features of the human disease but very mild neuronal abnormality. The ATM protein is a multifunctional protein kinase, which serves as a master regulator of cellular responses to DSBs. There is growing evidence that ATM may be involved in addition to the DSB response in other processes that maintain processes in cellular homeostasis. For example, mounting evidence points to increased oxidative stress in the absence of ATM. Here we report that the AP-1 pathway is constantly active in the brains of Atm-deficient mice not treated with DNA damaging agents. A canonical activation (increased phosphorylation of mitogen-activated protein kinase kinase-4, c-Jun N-terminal kinase, and c-Jun) of the AP-1 pathway was found in Atm-deficient cerebra, whereas induction of the AP-1 pathway in Atm-deficient cerebella is likely to mediate elevated expression of c-Fos and c-Jun. Although Atm(+/+) mice are capable of responding to ionizing radiation by activating stress responses such as the AP-1 pathway, Atm-deficient mice display higher basal AP-1 activity but gradually lose their ability to activate AP-1 DNA-binding activity in response to ionizing radiation. Our results further demonstrate that inactivation of the ATM gene results in a state of constant stress.

Hypothermia suppresses inducible nitric oxide synthase and stimulates cyclooxygenase-2 in lipopolysaccharide stimulated BV-2 cells

Hypothermia is neuroprotective, possibly through suppression of microglial activation. We investigated the effects of hypothermia on lipopolysaccharide (LPS) stimulated BV-2 cells. At 37 degrees C, LPS elicited strong increases in inducible nitric oxide synthase (iNOS), nitric oxide (NO), cyclooxygenase-2 (COX-2), tumour necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6), accompanied by translocation of nuclear factor-kappaB (NF-kappaB) to the nucleus. Hypothermia (33 degrees C) caused complete suppression of iNOS and NO, a partial reduction of IL-6 but did not prevent TNF-alpha production or NF-kappaB translocation. In contrast, LPS induced cyclooxygenase-2 (COX-2) to higher levels under hypothermic conditions. These results show that hypothermia selectively suppresses iNOS in microglia.

Expression of c-Fos and c-Myc and deposition of beta-APP in neurons in the adult rat brain as a result of exposure to short-lasting impulse noise

There is increasing evidence that impulse noise causes brain damage, but little is known about the mechanisms and extent of the response. Here, rat brains were investigated immunohistochemically for the expression of c-Fos, c-Myc, and beta-APP during the first 3 weeks postexposure to impulse noise of 198 or 202 dB. The expression of c-Fos and c-Myc increased at 2 h after exposure in neurons of the cerebral cortex, thalamus, and hippocampus, and this c-Fos immunoreactivity remained elevated for the entire observation period. The c-Myc immunoreactivity peaked at 18 h in both neurons and astrocytes but returned to control levels at 7 days. Abnormal deposition of beta-APP was evident within 6 h in the same brain regions. The beta-APP immunoreactivity was most prominent at 18 h and remained increased over the 21-day period assessed. The observed effects were similar to those described in humans following traumatic brain injury and in Alzheimer's disease. We conclude that impulse noise influences the brain in a fashion similar to that in cases with progressive CNS degeneration.

Behavioral and anatomical correlates of chronic episodic hypoxia during sleep in the rat

The role played by chronic episodic hypoxia (EHYP) in the neurocognitive morbidity of obstructive sleep apnea (OSA) is unknown. Sleep recordings, Morris water maze experiments, and immunohistochemistry for NMDA NR1 glutamate receptor, c-fos protein, and apoptosis [nuclear immunoreactivity for single-stranded DNA and terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling assay] were conducted in EHYP-exposed Sprague Dawley male rats. Exposures consisted of up to14 d in an environmental chamber in which O(2) concentrations were cycled between 10 and 21% every 90 sec or 30 min during 12 hr of daylight. For the remaining 12 hr, EHYP rats breathed room air, while controls spent 14 d in room air. Although EHYP induced significant disruption of sleep architecture during the initial day of exposure, sleep patterns normalized thereafter. Marked increases in apoptosis occurred in the CA1 hippocampal region (sevenfold) and cortex (Cx; eightfold) after 1-2 d of EHYP but not in CA3 and were followed by decreases toward normoxic levels by 14 d. Double labeling for NMDA NR1 and c-fos revealed marked architectural disorganization in CA1 and Cx with increases in c-fos over time. Rats exposed to EHYP displayed significantly longer escape latencies and swim path lengths to escape a hidden platform during 12 training trials given over 2 d. Differences in the performances of EHYP and control rats, although reduced, persisted after 14 d of recovery. We conclude that EHYP is associated with marked cellular changes over time within neural regions associated with cognitive functions. Furthermore, EHYP impaired performance during acquisition of a cognitive spatial task without affecting sensorimotor function. Such changes may underlie components of the learning and memory impairments found in OSA.

The functions of the amyloid precursor protein gene

The amyloid precursor protein (APP) gene and its protein products have multiple functions in the central nervous system and fulfil criteria as neuractive peptides: presence, release and identity of action. There is increased understanding of the role of secretases (proteases) in the metabolism of APP and the production of its peptide fragments. The APP gene and its products have physiological roles in synaptic action, development of the brain, and in the response to stress and injury. These functions reveal the strategic importance of APP in the workings of the brain and point to its evolutionary significance.

Early differential induction of C-jun in the central nervous system of hens treated with diisopropylphosphorofluoridate (DFP)

Diisopropyl phosphorofluoridate (DFP) produces organophosphorus-ester induced delayed neurotoxicity (OPIDN) in the hen, human and other sensitive species. We studied the effect of a single dose of DFP (1.7 mg/kg/sc) on the expression of c-jun, which is one of the heterodimerizing ITFs (Inducible Transcriptional Factors) of the AP-1 family. The hens were sacrificed at different time points ie 0.25, .0.50, 1 and 2 hrs. Total RNA was extracted from the following brain regions: cerebrum, cerebellum, brainstem, midbrain and as well as spinal cord. Northern blots prepared using standard protocols were hybridized with c-jun as well as b-actin and 18S RNA cDNA (control) probes. The results indicate differential regulation of c-jun levels which may be due to the activation of both cholinergic and non-cholinergic pathways of CNS, besides changing roles of c-jun (as mediator of degeneration or regeneration) depending on heterodimerization with other ITFs. In the highly susceptible tissues like brainstem and spinal cord c-jun transcript levels increased at 15 minutes and continued to increase gradually till it reached the maximum at 2 hrs. Overall spinal cord showed the maximum levels of c-jun induction (207%) at 2 hrs time point of all the CNS tissues. The enhancement of cholinergic transmisson by the inhibition of cholinestrase may be responsible for the gradual increase mediated by neural and vascular factors. In contrast, less susceptible tissue, cerebellum showed almost immediate induction to high level of (179%) at 15 minutes and the levels stayed more or less the same until it peaked to 185% at 2 hrs. Relatively low abundance of cholinergic neurons and high number of sensitized specialized cell types like Bergman glia and Purkinje cells may be responsible for the immediate higher induction. Non-susceptible tissue cerebrum did not show any changes in the c-jun levels. In midbrain the induction pattern was very similar to that of brainstem. This differential induction pattern of c-jun encomposing the differences in the quantity and time course was directly proportionate to the degree of susceptibility and cellular heterogeneity of different regions of CNS. The significant increase in c-jun levels along with our earlier observation on the increased c-fos levels indicate that AP-1 family of genes may be one of the IEGs involved in the long term changes which eventually lead to OPIDN.

c-Jun promotes neurite outgrowth and survival in PC12 cells

We investigated the function of c-Jun in PC12 cells by transfecting them with a plasmid containing a c-Jun cDNA transcription cassette. Transfected cells expressed high levels of c-Jun mRNA and protein and demonstrated an increase in both AP-1 DNA binding and gene activation. The c-Jun over-expressing cells showed marked neurite outgrowth but no evidence of spontaneous cell death. In fact, c-Jun over-expressing cells were more resistant to okadaic acid-induced apoptosis. The process outgrowth was not indicative of a full neuronal differentiation response as the transfected PC12 cells did not display action potentials when examined with whole-cell patch-clamping. The phosphorylation of c-Jun on serine 73 appears to be important for this neurite sprouting effect as mutagenesis at this site reduced sprouting whereas a serine 63 mutant tended to increase sprouting. Thus, in PC12 cells c-Jun expression does not induce apoptosis, but rather functions as a neurite outgrowth and neuronal survival signal.

CROC-4: a novel brain specific transcriptional activator of c-fos expressed from proliferation through to maturation of multiple neuronal cell types

A novel, brain-specific cDNA, denoted CROC-4, was cloned from human brain by a contingent replication of cDNA procedure capable of detecting transcriptional activators of the human c-fos proto-oncogene promoter. CROC-4 encoded an 18-kDa serine/threonine-rich polypeptide containing a P-loop motif and an SH3-binding region with phosphorylation sites for a variety of protein kinases (cdc2, CDK2, MAPK, CDK5, protein kinase C, Ca(2+)/calmodulin protein kinase 2, casein kinase 2) involved in cell proliferation and differentiation. Immunohistochemistry revealed that during early development, expression was associated with proliferating and migrating cells throughout the rodent brain, initially appearing in the proliferative ventricular zones. During late development and in adult human brain, CROC-4 was expressed in diverse brain regions including the thalamus, subthalamic nucleus, corpus callosum, substantia nigra, caudate nucleus, amygdala, and hippocampus. The association of CROC-4 expression with proliferating regions of developing brain and retention in regions of the adult brain, as well as the punctate nuclear location, suggest that CROC-4 participates in brain-specific c-fos signaling pathways involved in cellular remodeling of brain architecture.

β -amyloid precursor protein positive axonal bulbs may form in non-head-injured patients

Since the early 1980s axonal bulbs staining positively for beta-amyloid precursor protein (betaAPP) have been used as a marker of diffuse axonal injury (DAI), bulb formation been attributed to shearing forces generated during rotational acceleration/deceleration head injury. This study draws attention to the observation that they may form in the absence of a head injury and, thus, axonal injury cannot be assumed to result from mechanical injury alone. Out of 20 cases with no history of head injury studied, which only showed evidence of neuronal hypoxic change, 11 (55%) showed variable positive staining for betaAPP in a similar anatomical distribution to that previously described for DAI. The role of hypoxia in the formation of axonal bulbs, as well as the possible role of betaAPP as an acute phase protein, are discussed. These observations further clarify the pattern and relationship between neuronal and axonal staining observed following a brain insult and emphasize the possible role of betaAPP as a neuroprotective protein.

Neuronal death and survival in two models of hypoxic-ischemic brain damage

Two unilateral hypoxic-ischemia (HI) models (moderate and severe) in immature rat brain have been used to investigate the role of various transcription factors and related proteins in delayed neuronal death and survival. The moderate HI model results in an apoptotic-like neuronal death in selectively vulnerable regions of the brain while the more severe HI injury consistently produces widespread necrosis resulting in infarction, with some necrosis resistant cell populations showing evidence of an apoptotic type death. In susceptible regions undergoing an apoptotic-like death there was not only a prolonged induction of the immediate early genes, c-jun, c-fos and nur77, but also of possible target genes amyloid precursor protein (APP751) and CPP32. In contrast, increased levels of BDNF, phosphorylated CREB and PGHS-2 were found in cells resistant to the moderate HI insult suggesting that these proteins either alone or in combination may be of importance in the process of neuroprotection. An additional feature of both the moderate and severe brain insults was the rapid activation and/or proliferation of glial cells (microglia and astrocytes) in and around the site of damage. The glial response following HI was associated with an upregulation of both the CCAAT-enhancer binding protein alpha (microglia only) and NFkappaB transcription factors.

Inducible transcription factor expression in a cell culture model of apoptosis

We have developed a model of nerve cell death based on the toxicity of okadaic acid, a compound that triggers apoptosis in PC12 cells via a protein synthesis-dependent mechanism. The cell death process is accompanied by induction of JunB, c-Jun, JunD and Fos proteins. Phosphorylation-specific antibodies were used to demonstrate that c-Jun is phosphorylated at serine 63 and serine 73. Electrophoretic gel mobility shift and pAP1-Luc luciferase assays showed that expression of ITFs is associated with increases in AP-1 binding and in AP-1 transcriptional activity. In addition, dose response and time course studies provided strong correlative evidence that Fos and Jun proteins are involved in the apoptotic death cascades. Thus, this model provides a useful system to investigate the role of inducible transcription factor proteins in apoptosis.

c-fos expression in brains of patients with Down syndrome

c-fos is a protooncogene serving in multiple physiological processes in brain from signalling to proliferation and synaptic plasticity. We therefore decided to determine this transcription factor in control and Down Syndrome (DS) brain with the Rationale that c-fos may be linked to brain damage in DS. We determined mRNA steady state levels in frontal, parietal, occipital, temporal cortex and cerebellum of 9 patients with DS and 9 controls using RT-PCT. Significantly increased levels of mRNA c-fos normalized versus the housekeeping gene beta-actin mRNA were found in frontal, parietal and temporal cortex of DS brain. c-fox mRNA levels comparable to controls were found in occipital cortex and cerebellum. Deteriorated c-fos expression in the individual brain regions may be linked to increased apoptosis and neurodegeneration, overexcitation by excitatory amino acids of reactive oxygen species.

ATF-2 phosphorylation in apoptotic neuronal death

Activating transcription factor (ATF-2) is a basic region-leucine zipper transcription factor that can mediate a diverse range of transcriptional responses including those generated by various forms of cellular stress. Activation of ATF-2 in response to these stimuli requires post-translational modification, in particular the phosphorylation of Thr69 and Thr71. To investigate whether ATF-2 activation also has a role in neuronal apoptosis, immunocytochemistry using a phospho-specific ATF-2 (Thr71) antibody was carried out in the 21 day old rat brain following a unilateral hypoxic-ischemic (HI) insult and PC12 cells cultured in the presence of okadaic acid. In both models a dramatic increase in phosphorylated ATF-2 was found within cells undergoing apoptosis.

CCAAT-enhancer binding protein alpha is expressed in activated microglial cells after brain injury

Microglial cells play important roles in brain injury and repair and are implicated in diseases such as Alzheimer's disease, Creutzfeldt-Jacob disease, multiple sclerosis, the Aids Dementia Complex and stroke. Despite their importance in neuropathology, the underlying molecular basis for the activation of microglia after brain injury is not understood. We show, using RT-PCR, in situ hybridisation, immunocytochemistry, and electrophoretic mobility shift assay, that the CCAAT-enhancer binding protein alpha (C/EBP alpha), a sequence specific DNA-binding protein, is induced in microglial cells, but not astrocytes or neurons, after hypoxic-ischemic brain injury. These results suggest that C/EBP alpha might regulate gene expression and consequentially have a role in the activation and/or proliferation of microglia following brain injury.