p53-Dependent pathways in neurite outgrowth and axonal regeneration

P53-induced GAP-43 Upregulation in Primary Cortical Neurons of Rats

OBJECTIVES

In this study, we employed an in vitro culturing technique to investigate the impact of p53 on the modulation of growth-associated protein-43 (GAP-43) within the primary cortical neurons of rat specimens.

METHODS

(1) Within the first 24 hours after birth, the bilateral cortex was extracted from newborn Wistar rats and primary cortical neurons were cultured and identified. (2) The changes in the mRNA and protein expressions of GAP-43 induced by p53 in rat primary cortical neurons cultured in vitro were identified utilizing real-time polymerase chain reaction and western blot techniques.

RESULTS

(1) Lentiviral transfection of p53 within primary cortical neurons of rats elicited elevated levels of both mRNA and protein expressions of GAP-43, consequently culminating in a noteworthy augmentation of p53 expression. (2) The introduction of a p53 inhibitor in rat primary cortical neurons resulted in a reduction in both mRNA and protein expressions of GAP-43.

CONCLUSION

Within primary rat cortical neurons, p53 has the potential to prompt an augmentation in both the transcriptional and protein expression levels of the GAP-43 protein.

The Role of Hydrogen Sulfide in the Localization and Expression of p53 and Cell Death in the Nervous Tissue in Traumatic Brain Injury and Axotomy

Traumatic brain injury (TBI) is one of the leading causes of disability and death worldwide. It is characterized by various molecular-cellular events, with the main ones being apoptosis and damage to axons. To date, there are no clinically effective neuroprotective drugs. In this study, we examined the role of hydrogen sulfide (H2S) in the localization and expression of the key pro-apoptotic protein p53, as well as cell death in the nervous tissue in TBI and axotomy. We used a fast donor (sodium sulphide, Na2S) H2S and a classic inhibitor (aminooxyacetic acid, AOAA) of cystathionine β-synthase (CBS), which is a key enzyme in H2S synthesis. These studies were carried out on three models of neurotrauma in vertebrates and invertebrates. As a result, it was found that Na2S exhibits a pronounced neuroprotective effect that reduces the number of TUNEL-positive neurons and glial cells in TBI and apoptotic glia in axotomy. This effect could be realized through the Na2S-dependent decrease in the level of p53 in the cells of the nervous tissue of vertebrates and invertebrates, which we observed in our study. We also observed the opposite effect when using AOAA, which indicates the important role of CBS in the regulation of p53 expression and death of neurons and glial cells in TBI and axotomy.

Contributions of circadian clock genes to cell survival in fibroblast models of lithium-responsive bipolar disorder

Bipolar disorder (BD) is characterized by mood episodes, disrupted circadian rhythms and gray matter reduction in the brain. Lithium is an effective pharmacotherapy for BD, but not all patients respond to treatment. Lithium has neuroprotective properties and beneficial effects on circadian rhythms that may distinguish lithium responders (Li-R) from non-responders (Li-NR). The circadian clock regulates molecular pathways involved in apoptosis and cell survival, but how this overlap impacts BD and/or lithium responsiveness is unknown. In primary fibroblasts from Li-R/Li-NR BD patients and controls, we found patterns of co-expression among circadian clock and cell survival genes that distinguished BD vs. control, and Li-R vs. Li-NR cells. In cellular models of apoptosis using staurosporine (STS), lithium preferentially protected fibroblasts against apoptosis in BD vs. control samples, regardless of Li-R/Li-NR status. When examining the effects of lithium treatment of cells in vitro, caspase activation by lithium correlated with period alteration, but the relationship differed in control, Li-R and Li-NR samples. Knockdown of Per1 and Per3 in mouse fibroblasts altered caspase activity, cell death and circadian rhythms in an opposite manner. In BD cells, genetic variation in PER1 and PER3 predicted sensitivity to apoptosis in a manner consistent with knockdown studies. We conclude that distinct patterns of coordination between circadian clock and cell survival genes in BD may help predict lithium response.

Exploring the mechanisms under Zuogui Pill's treatment of ischemic stroke through network pharmacology and in vitro experimental verification

Due to its high mortality, incidence and disability rates, ischemic stroke poses heavy economic burdens to families and society. Zuogui Pill (ZGP) is a classic Chinese medicine for tonifying the kidney, which is effective for the recovery of neurological function after ischemic stroke. However, Zuogui Pill has not been evaluated for its potential effects on ischemic strokes. Using network pharmacology, the research aimed to explore the mechanisms of Zuogui Pill on ischemic stroke, which were further validated in SH-SY5Y cells injured by oxygen and glucose deprivation/reperfusion (OGD/R). Network analysis of Zuogui Pill identified 86 active ingredients and 107 compound-related targets correlated with ischemic stroke. Additionally, 11 core active compounds were obtained, such as Quercetin, beta sitosterol, and stigmasterol. Most of the compounds have been proven to have pharmacological activities. Based on pathway enrichment studies, Zuogui Pill may exert neuroprotection through MAPK signaling, PI3K-Akt signaling and apoptosis, as well as enhance neurite outgrowth and axonal regeneration effect via mTOR signaling, p53 signaling and Wnt signaling pathways. In vitro experiment, the viability of ischemic neuron treated with Zuogui Pill was increased, and the ability of neurite outgrowth was significantly improved. Western blot assays shown that the pro-neurite outgrowth effect of Zuogui Pill on ischemic stroke may be relate to PTEN/mTOR signal pathway. The results of the study provided new insights into Zuogui Pill's molecular mechanism in treatment of ischemic stroke, as well as clinical references for its use.

VRK1 variants at the cross road of Cajal body neuropathogenic mechanisms in distal neuropathies and motor neuron diseases

Distal hereditary neuropathies and neuro motor diseases are complex neurological phenotypes associated with pathogenic variants in a large number of genes, but in some the origin is unknown. Recently, rare pathogenic variants of the human VRK1 gene have been associated with these neurological phenotypes. All VRK1 pathogenic variants are recessive, and their clinical presentation occurs in either homozygous or compound heterozygous patients. The pathogenic VRK1 gene pathogenic variants are located in three clusters within the protein sequence. The main, and initial, shared clinical phenotype among VRK1 pathogenic variants is a distal progressive loss of motor and/or sensory function, which includes diseases such as spinal muscular atrophy, Charcot-Marie-Tooth, amyotrophic lateral sclerosis and hereditary spastic paraplegia. In most cases, symptoms start early in infancy, or in utero, and are slowly progressive. Additional neurological symptoms vary among non-related patients, probably because of their different VRK1 variants and their genetic background. The underlying common pathogenic mechanism, by its functional impairment, is a likely consequence of the roles that the VRK1 protein plays in the regulation on the stability and assembly of Cajal bodies, which affect RNA maturation and processing, neuronal migration of RNPs along axons, and DNA-damage responses. Alterations of these processes are associated with several neuro sensory or motor syndromes. The clinical heterogeneity of the neurological phenotypes associated with VRK1 is a likely consequence of the protein complexes in which VRK1 is integrated, which include several proteins known to be associated with Cajal bodies and DNA damage responses. Several hereditary distal neurological diseases are a consequence of pathogenic variants in genes that alter these cellular functions. We conclude that VRK1-related distal hereditary neuropathies and motor neuron diseases represent a novel subgroup of Cajal body related neurological syndromes.

Downregulation of UBE4B promotes CNS axon regrowth and functional recovery after stroke

The limited intrinsic regrowth capacity of corticospinal axons impedes functional recovery after cortical stroke. Although the mammalian target of rapamycin (mTOR) and p53 pathways have been identified as the key intrinsic pathways regulating CNS axon regrowth, little is known about the key upstream regulatory mechanism by which these two major pathways control CNS axon regrowth. By screening genes that regulate ubiquitin-mediated degradation of the p53 proteins in mice, we found that ubiquitination factor E4B (UBE4B) represses axonal regrowth in retinal ganglion cells and corticospinal neurons. We found that axonal regrowth induced by UBE4B depletion depended on the cooperative activation of p53 and mTOR. Importantly, overexpression of UbV.E4B, a competitive inhibitor of UBE4B, in corticospinal neurons promoted corticospinal axon sprouting and facilitated the recovery of corticospinal axon-dependent function in a cortical stroke model. Thus, our findings provide a translatable strategy for restoring corticospinal tract-dependent functions after cortical stroke.

Anti-Oxidative, Anti-Inflammatory and Anti-Apoptotic Effects of Flavonols: Targeting Nrf2, NF-κB and p53 Pathways in Neurodegeneration

Neurodegenerative diseases are one of the leading causes of disability and death worldwide. Intracellular transduction pathways that end in the activation of specific transcription factors are highly implicated in the onset and progression of pathological changes related to neurodegeneration, of which those related to oxidative stress (OS) and neuroinflammation are particularly important. Here, we provide a brief overview of the key concepts related to OS- and neuroinflammation-mediated neuropathological changes in neurodegeneration, together with the role of transcription factors nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor-κB (NF-κB). This review is focused on the transcription factor p53 that coordinates the cellular response to diverse genotoxic stimuli, determining neuronal death or survival. As current pharmacological options in the treatment of neurodegenerative disease are only symptomatic, many research efforts are aimed at uncovering efficient disease-modifying agents. Natural polyphenolic compounds demonstrate powerful anti-oxidative, anti-inflammatory and anti-apoptotic effects, partially acting as modulators of signaling pathways. Herein, we review the current understanding of the therapeutic potential and limitations of flavonols in neuroprotection, with emphasis on their anti-oxidative, anti-inflammatory and anti-apoptotic effects along the Nrf2, NF-κB and p53 pathways. A better understanding of cellular and molecular mechanisms of their action may pave the way toward new treatments.

p53 regulates katanin-p60 promoter in HCT 116 cells

Tumor suppressor protein p53, which functions in the cell cycle, apoptosis and neuronal differentiation via transcriptional regulations of target genes or interactions with several proteins, has been associated with neurite outgrowth through microtubule re-organization. We previously demonstrated in neurons that upon p53 induction, the level of microtubule severing protein Katanin-p60 increases, indicating that p53 might be a transcriptional regulator of the KATNA1 gene encoding Katanin-p60. In this context, we firstly elucidated the activity of KATNA1 regulatory regions and endogenous KATNA1 mRNA levels in the presence or absence of p53 using HCT 116 WT and HCT 116 p53 (-/-) cells. Next, we demonstrated the binding of p53 to the KATNA1 promoter and then investigated the role of p53 on KATNA1 gene expression by ascertaining KATNA1 mRNA and Katanin-p60 protein levels upon p53 overexpression and activation in both cells. Moreover, we showed changes in microtubule network upon increased Katanin-p60 level due to p53 overexpression. Also, the changes in KATNA1 mRNA and Katanin-p60 protein levels upon p53 knockdown were investigated. Our results indicate that p53 is an activator of KATNA1 gene expression and we show that both p53 and Katanin-p60 expression have strict regulations and are maintained at balanced levels as they are vital proteins to orchestrate either survival and apoptosis or differentiation.

Telomerase Reverse Transcriptase and p53 Regulate Mammalian Peripheral Nervous System and CNS Axon Regeneration Downstream of c-Myc

Although several genes have been identified to promote axon regeneration in the CNS, our understanding of the molecular mechanisms by which mammalian axon regeneration is regulated is still limited and fragmented. Here by using female mouse sensory axon and optic nerve regeneration as model systems, we reveal an unexpected role of telomerase reverse transcriptase (TERT) in regulation of axon regeneration. We also provide evidence that TERT and p53 act downstream of c-Myc to control sensory axon regeneration. More importantly, overexpression of p53 in sensory neurons and retinal ganglion cells is sufficient to promote sensory axon and optic never regeneration, respectively. The study reveals a novel c-Myc-TERT-p53 signaling pathway, expanding horizons for novel approaches promoting CNS axon regeneration.SIGNIFICANCE STATEMENT Despite significant progress during the past decade, our understanding of the molecular mechanisms by which mammalian CNS axon regeneration is regulated is still fragmented. By using sensory axon and optic nerve regeneration as model systems, the study revealed an unexpected role of telomerase reverse transcriptase (TERT) in regulation of axon regeneration. The results also delineated a c-Myc-TERT-p53 pathway in controlling axon growth. Last, our results demonstrated that p53 alone was sufficient to promote sensory axon and optic nerve regeneration in vivo Collectively, the study not only revealed a new mechanisms underlying mammalian axon regeneration, but also expanded the pool of potential targets that can be manipulated to enhance CNS axon regeneration.

Mild Therapeutic Hypothermia Protects the Brain from Ischemia/Reperfusion Injury through Upregulation of iASPP

Mild therapeutic hypothermia, a robust neuroprotectant, reduces neuronal apoptosis, but the precise mechanism is not well understood. Our previous study showed that a novel inhibitor of an apoptosis-stimulating protein of p53 (iASPP) might be involved in neuronal death after stroke. The aim of this study was to confirm the role of iASPP after stroke treated with mild therapeutic hypothermia. To address this, we mimicked ischemia/reperfusion injury in vitro by using oxygen-glucose deprivation/reperfusion (OGD/R) in primary rat neurons. In our in vivo approach, we induced middle cerebral artery occlusion (MCAO) for 60 min in C57/B6 mice. From the beginning of ischemia, focal mild hypothermia was applied for two hours. To evaluate the role of iASPP, small interfering RNA (siRNA) was injected intracerebroventricularly. Our results showed that mild therapeutic hypothermia increased the expression of iASPP and decreased the expression of its targets, Puma and Bax, and an apoptosis marker, cleaved caspase-3, in primary neurons under OGD/R. Increased iASPP expression and decreased ASPP1/2 expression were observed under hypothermia treatment in MCAO mice. iASPP siRNA (iASPPi) or hypothermia plus iASPPi application increased infarct volume, apoptosis and aggravated the neurological deficits in MCAO mice. Furthermore, iASPPi downregulated iASPP expression, and upregulated the expression of proapoptotic effectors, Puma, Bax and cleaved caspase-3, in mice after stroke treated with mild therapeutic hypothermia. In conclusion, mild therapeutic hypothermia protects against ischemia/reperfusion brain injury in mice by upregulating iASPP and thus attenuating apoptosis. iASPP may be a potential target in the therapy of stroke.

Turning Death to Growth: Hematopoietic Growth Factors Promote Neurite Outgrowth through MEK/ERK/p53 Pathway

Stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF) are the essential hematopoietic growth factors to control hematopoiesis. However, the role of SCF and G-CSF in the central nervous system remains poorly understood. Here, we have demonstrated the involvement of MEK/ERK/p53 signaling in SCF + G-CSF-enhanced neurite extension. Cortical neurons dissected from embryonic rat brains were seeded onto the membranes of transwell inserts, and neurite outgrowth was determined by using both the neurite outgrowth quantification assay kit and immunostaining of β III tubulin. Quantitative RT-PCR and western blotting were used for determining gene and protein expression of ERK and p53, respectively. p53 small interfering RNA (siRNAs) were introduced into neurons for examining the involvement of p53 in SCF + G-CSF-mediated neurite outgrowth. We observed that both SCF and G-CSF alone increased activation of MEK/ERK and gene expression of p53, while SCF + G-CSF synergistically activated the MEK/ERK signaling and upregulated p53 expression. MEK specific inhibitors (PD98059 and U0126) blocked the SCF + G-CSF-increased ERK phosphorylation and p53 gene and protein expression, and the MEK specific inhibitors also eliminated the SCF + G-CSF-promoted neurite outgrowth. p53 siRNAs knocked down the SCF + G-CSF-elevated p53 protein and prevented the SCF + G-CSF-enhanced neurite outgrowth. These findings suggest that activation of MEK/ERK/p53 signaling is required for SCF + G-CSF-promoted neurite outgrowth. Through the pro-apoptotic pathway of the MEK/ERK/p53, SCF + G-CSF turns neuronal fate from apoptotic commitment toward neural network generation. This observation provides novel insights into the putative role of SCF + G-CSF in supporting generation of neural connectivity during CNS development and in brain repair under pathological or neurodegenerative conditions.

The age factor in axonal repair after spinal cord injury: A focus on neuron-intrinsic mechanisms

Age is an important consideration for recovery and repair after spinal cord injury. Spinal cord injury is increasingly affecting the middle-aged and aging populations. Despite rapid progress in research to promote axonal regeneration and repair, our understanding of how age can modulate this repair is rather limited. In this review, we discuss the literature supporting the notion of an age-dependent decline in axonal growth after central nervous system (CNS) injury. While both neuron-intrinsic and extrinsic factors are involved in the control of axon growth after injury, here we focus on possible intrinsic mechanisms for this age-dependent decline.

p53 on the crossroad between regeneration and cancer

Regeneration and tumorigenesis share common molecular pathways, nevertheless the outcome of regeneration is life, whereas tumorigenesis leads to death. Although the process of regeneration is strictly controlled, malignant transformation is unrestrained. In this review, we discuss the involvement of TP53, the major tumor-suppressor gene, in the regeneration process. We point to the role of p53 as coordinator assuring that regeneration will not shift to carcinogenesis. The fluctuation in p53 activity during the regeneration process permits a tight control. On one hand, its inhibition at the initial stages allows massive proliferation, on the other its induction at advanced steps of regeneration is essential for preservation of robustness and fidelity of the regeneration process. A better understanding of the role of p53 in regulation of regeneration may open new opportunities for implementation of TP53-based therapies, currently available for cancer patients, in regenerative medicine.

Differentiation Induces Dramatic Changes in miRNA Profile, Where Loss of Dicer Diverts Differentiating SH-SY5Y Cells Toward Senescence

MicroRNAs (miRNAs) are generated by endonuclease activity of Dicer, which also helps in loading of miRNAs to their target sequences. SH-SY5Y, a human neuroblastoma and a cellular model of neurodevelopment, consistently expresses genes related to neurodegenerative disorders at different biological levels (DNA, RNA, and proteins). Using SH-SY5Y cells, we have studied the role of Dicer and miRNAs in neuronal differentiation and explored involvement of P53, a master regulator of gene expression in differentiation-induced induction of miRNAs. Knocking down Dicer gene induced senescence in differentiating SH-SY5Y cells, which indicate the essential role of Dicer in brain development. Differentiation of SH-SY5Y cells by retinoic acid (RA) or RA + brain-derived neurotrophic factor (BDNF) induced dramatic changes in global miRNA expression. Fully differentiated SH-SY5Y cells (5-day RA followed by 3-day BDNF) significantly (p < 0.05 and atleast >3-fold change) upregulated and downregulated the expression of 77 and 17 miRNAs, respectively. Maximum increase was observed in the expression of miR-193-5p, miR-199a-5p, miR-192, miR-145, miR-28-5p, miR-29b, and miR-222 after RA exposure and miR-193-5p, miR-146a, miR-21, miR-199a-5p, miR-153, miR-29b, and miR-222 after RA + BDNF exposure in SH-SY5Y cells. Exploring the role of P53 in differentiating SH-SY5Y cells, we have observed that induction of miR-222, miR-192, and miR-145 is P53 dependent and expression of miR-193a-5p, miR-199a-5p, miR-146a, miR-21, miR-153, and miR-29b is P53 independent. In conclusion, decreased Dicer level enforces differentiating cells to senescence, and differentiating SH-SY5Y cells needs increased expression of P53 to cope up with changes in protein levels of mature neurons.

Enhanced Transcriptional Activity and Mitochondrial Localization of STAT3 Co-induce Axon Regrowth in the Adult Central Nervous System

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor central to axon regrowth with an enigmatic ability to act in different subcellular regions independently of its transcriptional roles. However, its roles in mature CNS neurons remain unclear. Here, we show that along with nuclear translocation, STAT3 translocates to mitochondria in mature CNS neurons upon cytokine stimulation. Loss- and gain-of-function studies using knockout mice and viral expression of various STAT3 mutants demonstrate that STAT3's transcriptional function is indispensable for CNS axon regrowth, whereas mitochondrial STAT3 enhances bioenergetics and further potentiates regrowth. STAT3's localization, functions, and growth-promoting effects are regulated by mitogen-activated protein kinase kinase (MEK), an effect further enhanced by Pten deletion, leading to extensive axon regrowth in the mouse optic pathway and spinal cord. These results highlight CNS neuronal dependence on STAT3 transcriptional activity, with mitochondrial STAT3 providing ancillary roles, and illustrate a critical contribution for MEK in enhancing diverse STAT3 functions and axon regrowth.

Identification of novel radiation-induced p53-dependent transcripts extensively regulated during mouse brain development

Ionizing radiation is a potent activator of the tumor suppressor gene p53, which itself regulates the transcription of genes involved in canonical pathways such as the cell cycle, DNA repair and apoptosis as well as other biological processes like metabolism, autophagy, differentiation and development. In this study, we performed a meta-analysis on gene expression data from different in vivo and in vitro experiments to identify a signature of early radiation-responsive genes which were predicted to be predominantly regulated by p53. Moreover, we found that several genes expressed different transcript isoforms after irradiation in a p53-dependent manner. Among this gene signature, we identified novel p53 targets, some of which have not yet been functionally characterized. Surprisingly, in contrast to genes from the canonical p53-regulated pathways, our gene signature was found to be highly enriched during embryonic and post-natal brain development and during in vitro neuronal differentiation. Furthermore, we could show that for a number of genes, radiation-responsive transcript variants were upregulated during development and differentiation, while radiation non-responsive variants were not. This suggests that radiation exposure of the developing brain and immature cortical neurons results in the p53-mediated activation of a neuronal differentiation program. Overall, our results further increase the knowledge of the radiation-induced p53 network of the embryonic brain and provide more evidence concerning the importance of p53 and its transcriptional targets during mouse brain development.

p53 inhibition provides a pivotal protective effect against ischemia-reperfusion injury in vitro via mTOR signaling

Tumor suppressor p53 has recently been reported to have numerous functions independent of tumorigenesis, including neuronal survival during ischemia. The mammalian target of rapamycin (mTOR) signaling pathway plays a central role in the regulation of metabolism, cell growth, development, and cell survival. Our recent work has demonstrated the neuroprotective effects of the mTOR pathway. Considering that p53 is also an important regulator of mTOR, to further clarify the role of p53 and the mTOR signaling pathway in neuronal ischemic-reperfusion injury, we used mouse primary mixed cultured neurons with an oxygen glucose deprivation (OGD) model to mimic an ischemic-reperfusion injury in vitro. A lentiviral system was also used to inhibit or overexpress p53 to determine whether p53 alteration affects OGD and reperfusion injury. Our results show that activated p53 was induced and it suppressed mTOR expression in primary mixed cultured neurons after OGD and reperfusion. Inhibiting p53, using either a chemical inhibitor or lentiviral-mediated shRNA, exhibited neuroprotective effects in primary cultured neurons against OGD and reperfusion injury through the upregulation of mTOR activity. Such protective effects could be reversed by rapamycin, an mTOR inhibitor. Conversely, p53 overexpression tended to exacerbate the detrimental effects of OGD injury by downregulating mTOR activity. These results suggest that p53 inhibition has a pivotal protective effect against an in vitro ischemia-reperfusion injury via mTOR signaling and provides a potential and promising therapeutic target for stroke treatment.

P53 protein in proliferation, repair and apoptosis of cells

The p53 protein is an important factor of many intra- and extracellular processes. This protein regulates the repair of cellular DNA and induces apoptosis. It is also responsible for the regulation of the senescence and the cell entering the subsequent stages of the cellular cycle. The protein p53 is also involved in inhibiting angiogenesis and the induction of oxidative shock. In our study, we examined the activity of p53 protein in the uterine epithelial cells in rats treated with cladribine. Its action is mainly based on apoptosis induction. We compared the activity of p53 protein in cells with a high apoptosis index and in cells with active repair mechanisms and high proliferation index. We observed stronger p53 protein expression in the epithelial cells of the materials taken 24 h after the last dose of 2-CdA associated with the active process of apoptosis and inhibition of proliferation. After 4 weeks from the last dose of cladribine, the stronger expression of p53 protein was associated with both the existing changes in the cell's genome, the effects of the ongoing repair mechanisms, as well as the high proliferation activity.

Carbamylated erythropoietin promotes neurite outgrowth and neuronal spine formation in association with CBP/p300

Both erythropoietin (EPO) and carbamylated EPO (cEPO) have been shown to increase the length of neurites and spine density in neurons. However, the molecular mechanism underlying the EPO- and cEPO-induced neuronal differentiation has yet to be investigated. To address this issue, we investigated epigenetic modifications that regulate gene expression in neurons. Neurons treated with EPO or cEPO display an upregulation of E1A-binding protein (p300) and p300-mediated p53 acetylation, possibly increasing the transactivation activity of p53 on growth-associated protein 43 (GAP43). Treatment of cells with cEPO markedly increases spine formation and potentiates p300-mediated transactivation of PSD95, Shank2 and 3 compared to EPO. These results demonstrate that cEPO controls neuronal differentiation via acetylation of transcription factors and subsequent transactivation of target genes. These findings have important medical implications because cEPO is of interest in the development of therapeutic agents against neuropsychiatric disorders.

Subtractive screen of potential limb regeneration related genes from Pachytriton brevipes

Regeneration capacity varies greatly among different animal species. In vertebrate, amphibian especially the Urodela, has been used as a powerful model system to study the mechanism of tissue regeneration because of the strong ability to regenerate their damaged or lost appendages. Pachytriton brevipes, a species of newt, which is widely distributed in south of China, can completely restore their damaged limbs within several months. In this study, we use modified suppression subtractive hybridization assay and dot-blot screening to identify candidate genes involved in tissue regeneration in P. brevipes. We successfully isolated 81 ESTs from a forward regeneration subtraction library. And we further verified the differential expression of four candidate genes, Rpl11, Cirbp, Ag2 and Trimx, between regenerating blastema and non-regeneration tissues by in situ hybridization. These genes were also be further characterized by phylogenetic and bioinformatic analysis. In general, we provided a comparative experimental approach to study the mechanisms of vertebrate regeneration.

Characterization of neurite outgrowth and ectopic synaptogenesis in response to photoreceptor dysfunction

In the mammalian retina, light signals generated in photoreceptors are passed to bipolar and horizontal cells via synaptic contacts. In various pathological conditions, these second-order neurons extend neurites into the outer nuclear layer (ONL). However, the molecular events associated with this neurite outgrowth are not known. Here, we characterized the morphological synaptic changes in the CNGA3/CNGB1 double-knockout (A3B1) mouse, a model of retinitis pigmentosa. In these mice, horizontal cells looked normal until postnatal day (p) 11, but started growing neurites into the ONL 1 day later. At p28, the number of sprouting processes decreased, but the remaining sprouts developed synapse-like contacts at rod cell bodies, with an ultrastructural appearance reminiscent of ribbon synapses. Hence, neurite outgrowth and ectopic synaptogenesis in the A3B1 retina were precisely timed events starting at p12 and p28, respectively. We therefore performed microarray analysis of retinal gene expression in A3B1 and wild-type mice at those ages to evaluate the genomic response underlying these two events. This analysis identified 163 differentially regulated genes in the A3B1 retina related to neurite outgrowth or plasticity of synapses. The global changes in gene expression in the A3B1 retina were consistent with activation of signaling pathways related to Tp53, Smad, and Stat3. Moreover, key molecules of these signaling pathways could be localized at or in close proximity to outgrowing neurites. We therefore propose that Tp53, Smad, and Stat3 signaling pathways contribute to the synaptic plasticity in the A3B1 retina.

ASPP1/2 regulate p53-dependent death of retinal ganglion cells through PUMA and Fas/CD95 activation in vivo

The transcription factor p53 mediates neuronal death in a variety of stress-related and neurodegenerative conditions. The proapoptotic activity of p53 is tightly regulated by the apoptosis-stimulating proteins of p53 (ASPP) family members: ASPP1 and ASPP2. However, whether ASPP1/2 play a role in the regulation of p53-dependent neuronal death in the CNS is currently unknown. To address this, we asked whether ASPP1/2 contribute to the death of retinal ganglion cells (RGCs) using in vivo models of acute optic nerve damage in mice and rats. Here, we show that p53 is activated in RGCs soon after injury and that axotomy-induced RGC death is attenuated in p53 heterozygote and null mice. We demonstrate that ASPP1/2 proteins are abundantly expressed by injured RGCs, and that short interfering (si)RNA-based ASPP1 or ASPP2 knockdown promotes robust RGC survival. Comparative gene expression analysis revealed that siASPP-mediated downregulation of p53-upregulated-modulator-of-apoptosis (PUMA), Fas/CD95, and Noxa depends on p53 transcriptional activity. Furthermore, siRNA against PUMA or Fas/CD95 confers neuroprotection, demonstrating a functional role for these p53 targets in RGC death. Our study demonstrates a novel role for ASPP1 and ASPP2 in the death of RGCs and provides evidence that blockade of the ASPP-p53 pathway is beneficial for central neuron survival after axonal injury.

Conformational altered p53 affects neuronal function: relevance for the response to toxic insult and growth-associated protein 43 expression

The role of p53 in neurodegenerative diseases is essentially associated with neuronal death. Recently an alternative point of view is emerging, as altered p53 conformation and impaired protein function have been found in fibroblasts and blood cells derived from Alzheimer's disease patients. Here, using stable transfected SH-SY5Y cells overexpressing APP751wt (SY5Y-APP) we demonstrated that the expression of an unfolded p53 conformation compromised neuronal functionality. In particular, these cells showed (i) augmented expression of amyloid precursor protein (APP) and its metabolites, including the C-terminal fragments C99 and C83 and β-amyloid peptide (ii) high levels of oxidative markers, such as 4-hydroxy-2-nonenal Michael-adducts and 3-nitro-tyrosine and (iii) altered p53 conformation, mainly due to nitration of its tyrosine residues. The consequences of high-unfolded p53 expression resulted in loss of p53 pro-apoptotic activity, and reduction of growth-associated protein 43 (GAP-43) mRNA and protein levels. The role of unfolded p53 in cell death resistance and lack of GAP-43 transcription was demonstrated by ZnCl₂ treatment. Zinc supplementation reverted p53 wild-type tertiary structure, increased cells sensitivity to acute cytotoxic injury and GAP-43 levels in SY5Y-APP clone.

Connective tissue growth factor regulates retinal neovascularization through p53 protein-dependent transactivation of the matrix metalloproteinase (MMP)-2 gene

BACKGROUND

The role of connective tissue growth factor (CTGF/CCN2) in pathological angiogenesis in the retina is unknown.

RESULTS

CTGF/CCN2 stimulates retinal neovascularization through transactivation of p53 target genes such as matrix metalloproteinase (MMP)-2.

CONCLUSION

CTGF/CCN2 effects on abnormal vessel formation in the retina are mediated by p53 and MMP-2.

SIGNIFICANCE

CTGF/CCN2 and its downstream effectors are potential targets in the development of new antiangiogenic treatments. Pathological angiogenesis in the retina is driven by dysregulation of hypoxia-driven stimuli that coordinate physiological vessel growth. How the various components of the neovascularization signaling network are integrated to yield pathological changes has not been defined. Connective tissue growth factor (CTGF/CCN2) is an inducible matricellular protein that plays a major role in fibroproliferative disorders. Here, we show that CTGF/CCN2 was dynamically expressed in the developing murine retinal vasculature and was abnormally increased and localized within neovascular tufts in the mouse eye with oxygen-induced retinopathy. Consistent with its propitious vascular localization, ectopic expression of the CTGF/CCN2 gene further accelerated neovascularization, whereas lentivirus-mediated loss-of-function or -expression of CTGF/CCN2 harnessed ischemia-induced neovessel outgrowth in oxygen-induced retinopathy mice. The neovascular effects of CTGF/CCN2 were mediated, at least in part, through increased expression and activity of matrix metalloproteinase (MMP)-2, which drives vascular remodeling through degradation of matrix and non matrix proteins, migration and invasion of endothelial cells, and formation of new vascular patterns. In cultured cells, CTGF/CCN2 activated the MMP-2 promoter through increased expression and tethering of the p53 transcription factor to a highly conserved p53-binding sequence within the MMP-2 promoter. Concordantly, the neovascular effects of CTGF/CCN2 were suppressed by p53 inhibition that culminated in reduced enrichment of the MMP-2 promoter with p53 and decreased MMP-2 gene expression. Our data identified new gene targets and downstream effectors of CTGF/CCN2 and provided the rational basis for targeting the p53 pathway to curtail the effects of CTGF/CCN2 on neovessel formation associated with ischemic retinopathy.

Effects of PACAP on intracellular signaling pathways in human retinal pigment epithelial cells exposed to oxidative stress

The integrity of retinal pigment epithelial cells is critical for photoreceptor survival and vision. Pituitary adenylate cyclase activating polypeptide (PACAP) exerts retinoprotective effects against several types of injuries in vivo, including optic nerve transection, retinal ischemia, excitotoxic injuries, UVA-induced lesion, and diabetic retinopathy. In a recent study, we have proven that PACAP is also protective in oxidative stress-induced injury in human pigment epithelial cells (ARPE-19 cells). The aim of the present study was to investigate the possible mechanisms of this protection. ARPE cells were exposed to a 24-h hydrogen peroxide treatment. Expressions of kinases and apoptotic markers were studied by complex array kits and Western blot. Oxidative stress induced the activation of several apoptotic markers, including Bad, Bax, HIF-1α, several heat shock proteins, TNF-related apoptosis-inducing ligand, and Fas-associated protein with death domain, while PACAP treatment decreased them. The changes in the expression of MAP kinases showed that PACAP activated the protective ERK1/2 and downstream CREB, and decreased the activation of the pro-apoptotic p38MAPK and c-Jun N-terminal kinase, an effect opposite to that observed with only oxidative stress. Furthermore, PACAP increased the activation of the protective Akt pathway. In addition, the effects of oxidative stress on several other signaling molecules were counteracted by PACAP treatment (Chk2, Yes, Lyn, paxillin, p53, PLC, STAT4, RSK). These play a role in cell death, cell cycle, inflammation, adhesion, differentiation and proliferation. In summary, PACAP, acting at several levels, influences the balance between pro- and anti-apoptotic factors in favor of anti-apoptosis, thereby providing protection in oxidative stress-induced injury of human retinal pigment epithelial cells.

Gatekeeper between quiescence and differentiation: p53 in axonal outgrowth and neurogenesis

The transcription factor and tumor suppressor gene p53 regulates a wide range of cellular processes including DNA damage/repair, cell cycle progression, apoptosis, and cell metabolism. In the past several years, a specific novel role for p53 in neuronal biology has emerged. p53 orchestrates the polarity of self-renewing divisions in neural stem cells both during embryonic development and in adulthood and coordinates the timing for cell fate specification. In postmitotic neurons, p53 regulates neurite outgrowth and postinjury axonal regeneration via neurotrophin-dependent and -independent signaling by both transcriptional and posttranslational control of growth cone remodeling. This review provides an insight into the molecular mechanisms upstream and downstream p53 both during neural development and following axonal injury. Their understanding may provide therapeutic targets to enhance neuroregeneration following nervous system injury.