Cyclin dependent kinase inhibitors prevent apoptosis of postmitotic mouse motoneurons

Cell cycle deregulation in neurodegenerative diseases

Background: Cell cycle is critical for a wide range of cellular processes such as proliferation, differentiation and apoptosis in dividing cells. Neurons are postmitotic cells which have withdrawn from the cell division cycle. Recent data show us that inappropriate activation of cell cycle regulators including cyclins, cyclin dependent kinases (CDKs) and endogenous cyclin dependent kinase inhibitors (CDKIs) may take part in the aetiology of neurodegenerative diseases. However, the mechanisms for cell cycle reentry in neurodegenerative disease remain unclear.Methods: Electronic databases such as Pubmed, Science Direct, Directory of Open Access Journals, PLOS were searched for relevant articles.Conclusion: The present work reviews basic aspects of cell cycle mechanism, as well as the evidence showing the expression of cell cycle proteins in neurodegenerative disease. We provide a brief summary of these findings and hope to highlight the interaction between the cell cycle reentry and neurodegenerative diseases. Moreover, we outline the possible signaling pathways. However more understanding of the mechanism of cell cycle is of great importance. Because these represents an alternative target for therapeutic interventions, leading to novel treatments of neurodegenerative diseases.

Protein kinase inhibitors for amyotrophic lateral sclerosis therapy

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder that causes the progressive loss of motoneurons and, unfortunately, there is no effective treatment for this disease. Interconnecting multiple pathological mechanisms are involved in the neuropathology of this disease, including abnormal aggregation of proteins, neuroinflammation and dysregulation of the ubiquitin proteasome system. Such complex mechanisms, together with the lack of reliable animal models of the disease have hampered the development of drugs for this disease. Protein kinases, a key pharmacological target in several diseases, have been linked to ALS as they play a central role in the pathology of many diseases. Therefore several inhibitors are being currently trailed for clinical proof of concept in ALS patients. In this review, we examine the recent literature on protein kinase inhibitors currently in pharmaceutical development for this diseaseas future therapy for AS together with their involvement in the pathobiology of ALS. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.6/issuetoc.

Sustained (S)-roscovitine delivery promotes neuroprotection associated with functional recovery and decrease in brain edema in a randomized blind focal cerebral ischemia study

Stroke is a devastating disorder that significantly contributes to death, disability and healthcare costs. In ischemic stroke, the only current acute therapy is recanalization, but the narrow therapeutic window less than 6 h limits its application. The current challenge is to prevent late cell death, with concomitant therapy targeting the ischemic cascade to widen the therapeutic window. Among potential neuroprotective drugs, cyclin-dependent kinase inhibitors such as (S)-roscovitine are of particular relevance. We previously showed that (S)-roscovitine crossed the blood-brain barrier and was neuroprotective in a dose-dependent manner in two models of middle cerebral artery occlusion (MCAo). According to the Stroke Therapy Academic Industry Roundtable guidelines, the pharmacokinetics of (S)-roscovitine and the optimal mode of delivery and therapeutic dose in rats were investigated. Combination of intravenous (IV) and continuous sub-cutaneous (SC) infusion led to early and sustained delivery of (S)-roscovitine. Furthermore, in a randomized blind study on a transient MCAo rat model, we showed that this mode of delivery reduced both infarct and edema volume and was beneficial to neurological outcome. Within the framework of preclinical studies for stroke therapy development, we here provide data to improve translation of pre-clinical studies into successful clinical human trials.

Amyotrophic lateral sclerosis: recent genetic highlights

PURPOSE OF REVIEW

Amyotrophic lateral sclerosis (ALS), like other neurodegenerative diseases, remains incurable, but gene mutations linked to ALS are providing clues as to how to target therapies. It is important for researchers to keep abreast of the rapid influx of new data in ALS, and we aim to summarize the major genetic advances made in the field over the past 2 years.

RECENT FINDINGS

Significant variation in seven genes has recently been found in ALS: TBK1, CCNF, GLE1, MATR3, TUBA4A, CHCHD10 and NEK1. These have mostly been identified through large exome screening studies, though traditional linkage approaches and candidate gene screening remain important. We briefly update C9orf72 research, noting in particular the development of reagents to better understand the normal role of C9orf72 protein.

SUMMARY

Striking advances in our understanding of the genetic heterogeneity of ALS continue to be made, year on year. These implicate proteostasis, RNA export, nuclear transport, the cytoskeleton, mitochondrial function, the cell cycle and DNA repair. Functional studies to integrate these hits are needed. By building a web of knowledge with interlinked genes and mechanisms, it is hoped we can better understand ALS and work toward effective therapies.

Bilateral gene interaction hierarchy analysis of the cell death gene response emphasizes the significance of cell cycle genes following unilateral traumatic brain injury

BACKGROUND

Delayed or secondary cell death that is caused by a cascade of cellular and molecular processes initiated by traumatic brain injury (TBI) may be reduced or prevented if an effective neuroprotective strategy is employed. Microarray and subsequent bioinformatic analyses were used to determine which genes, pathways and networks were significantly altered 24 h after unilateral TBI in the rat. Ipsilateral hemi-brain, the corresponding contralateral hemi-brain, and naïve (control) brain tissue were used for microarray analysis.

RESULTS

Ingenuity Pathway Analysis showed cell death and survival (CD) to be a top molecular and cellular function associated with TBI on both sides of the brain. One major finding was that the overall gene expression pattern suggested an increase in CD genes in ipsilateral brain tissue and suppression of CD genes contralateral to the injury which may indicate an endogenous protective mechanism. We created networks of genes of interest (GOI) and ranked the genes by the number of direct connections each had in the GOI networks, creating gene interaction hierarchies (GIHs). Cell cycle was determined from the resultant GIHs to be a significant molecular and cellular function in post-TBI CD gene response.

CONCLUSIONS

Cell cycle and apoptosis signalling genes that were highly ranked in the GIHs and exhibited either the inverse ipsilateral/contralateral expression pattern or contralateral suppression were identified and included STAT3, CCND1, CCND2, and BAX. Additional exploration into the remote suppression of CD genes may provide insight into neuroprotective mechanisms that could be used to develop therapies to prevent cell death following TBI.

Transcriptional analysis reveals distinct subtypes in amyotrophic lateral sclerosis: implications for personalized therapy

Amyotrophic lateral sclerosis (ALS) is an incurable disease, caused by the loss of the upper and lower motor neurons. The lack of therapeutic progress is mainly due to the insufficient understanding of complexity and heterogeneity underlying the pathogenic mechanisms of ALS. Recently, we analyzed whole-genome expression profiles of motor cortex of sporadic ALS patients, classifying them into two subgroups characterized by differentially expressed genes and pathways. Some of the deregulated genes encode proteins, which are primary targets of drugs currently in preclinical or clinical studies for several clinical conditions, including neurodegenerative diseases. In this review, we discuss in-depth the potential role of these candidate targets in ALS pathogenesis, highlighting their possible relevance for personalized ALS treatments.

Cyclin-dependent kinases regulate apoptosis of intestinal epithelial cells

Homeostasis of the gastrointestinal epithelium is dependent upon a balance between cell proliferation and apoptosis. Cyclin-dependent kinases (Cdks) are well known for their role in cell proliferation. Previous studies from our group have shown that polyamine-depletion of intestinal epithelial cells (IEC-6) decreases cyclin-dependent kinase 2 (Cdk2) activity, increases p53 and p21Cip1 protein levels, induces G1 arrest, and protects cells from camptothecin (CPT)-induced apoptosis. Although emerging evidence suggests that members of the Cdk family are involved in the regulation of apoptosis, their roles directing apoptosis of IEC-6 cells are not known. In this study, we report that inhibition of Cdk1, 2, and 9 (with the broad range Cdk inhibitor, AZD5438) in proliferating IEC-6 cells triggered DNA damage, activated p53 signaling, inhibited proliferation, and induced apoptosis. By contrast, inhibition of Cdk2 (with NU6140) increased p53 protein and activity, inhibited proliferation, but had no effect on apoptosis. Notably, AZD5438 sensitized, whereas, NU6140 rescued proliferating IEC-6 cells from CPT-induced apoptosis. However, in colon carcinoma (Caco-2) cells with mutant p53, treatment with either AZD5438 or NU6140 blocked proliferation, albeit more robustly with AZD5438. Both Cdk inhibitors induced apoptosis in Caco-2 cells in a p53-independent manner. In serum starved quiescent IEC-6 cells, both AZD5438 and NU6140 decreased TNF-α/CPT-induced activation of p53 and, consequently, rescued cells from apoptosis, indicating that sustained Cdk activity is required for apoptosis of quiescent cells. Furthermore, AZD5438 partially reversed the protective effect of polyamine depletion whereas NU6140 had no effect. Together, these results demonstrate that Cdks possess opposing roles in the control of apoptosis in quiescent and proliferating cells. In addition, Cdk inhibitors uncouple proliferation from apoptosis in a p53-dependent manner.

Repair of oxidative DNA damage, cell-cycle regulation and neuronal death may influence the clinical manifestation of Alzheimer's disease

Alzheimer’s disease (AD) is characterized by progressive cognitive decline associated with a featured neuropathology (neuritic plaques and neurofibrillary tangles). Several studies have implicated oxidative damage to DNA, DNA repair, and altered cell-cycle regulation in addition to cell death in AD post-mitotic neurons. However, there is a lack of studies that systematically assess those biological processes in patients with AD neuropathology but with no evidence of cognitive impairment. We evaluated markers of oxidative DNA damage (8-OHdG, H2AX), DNA repair (p53, BRCA1, PTEN), and cell-cycle (Cdk1, Cdk4, Cdk5, Cyclin B1, Cyclin D1, p27^Kip1, phospho-Rb and E2F1) through immunohistochemistry and cell death through TUNEL in autopsy hippocampal tissue samples arrayed in a tissue microarray (TMA) composed of three groups: I) “clinical-pathological AD” (CP-AD) - subjects with neuropathological AD (Braak≥IV and CERAD = B or C) and clinical dementia (CDR≥2, IQCODE>3.8); II) “pathological AD” (P-AD) - subjects with neuropathological AD (Braak≥IV and CERAD = B or C) and without cognitive impairment (CDR 0, IQCODE<3.2); and III) “normal aging” (N) - subjects without neuropathological AD (Braak≤II and CERAD 0 or A) and with normal cognitive function (CDR 0, IQCODE<3.2). Our results show that high levels of oxidative DNA damage are present in all groups. However, significant reductions in DNA repair and cell-cycle inhibition markers and increases in cell-cycle progression and cell death markers in subjects with CP-AD were detected when compared to both P-AD and N groups, whereas there were no significant differences in the studied markers between P-AD individuals and N subjects. This study indicates that, even in the setting of pathological AD, healthy cognition may be associated with a preserved repair to DNA damage, cell-cycle regulation, and cell death in post-mitotic neurons.

Retinal degeneration depends on Bmi1 function and reactivation of cell cycle proteins

The epigenetic regulator Bmi1 controls proliferation in many organs. Reexpression of cell cycle proteins such as cyclin-dependent kinases (CDKs) is a hallmark of neuronal apoptosis in neurodegenerative diseases. Here we address the potential role of Bmi1 as a key regulator of cell cycle proteins during neuronal apoptosis. We show that several cell cycle proteins are expressed in different models of retinal degeneration and required in the Rd1 photoreceptor death process. Deleting E2f1, a downstream target of CDKs, provided temporary protection in Rd1 mice. Most importantly, genetic ablation of Bmi1 provided extensive photoreceptor survival and improvement of retinal function in Rd1 mice, mediated by a decrease in cell cycle markers and regulators independent of p16(Ink4a) and p19(Arf). These data reveal that Bmi1 controls the cell cycle-related death process, highlighting this pathway as a promising therapeutic target for neuroprotection in retinal dystrophies.

Inactivation of CDK/pRb pathway normalizes survival pattern of lymphoblasts expressing the FTLD-progranulin mutation c.709-1G>A

BACKGROUND

Mutations in the progranulin (PGRN) gene, leading to haploinsufficiency, cause familial frontotemporal lobar degeneration (FTLD-TDP), although the pathogenic mechanism of PGRN deficit is largely unknown. Allelic loss of PGRN was previously shown to increase the activity of cyclin-dependent kinase (CDK) CDK6/pRb pathway in lymphoblasts expressing the c.709-1G>A PGRN mutation. Since members of the CDK family appear to play a role in neurodegenerative disorders and in apoptotic death of neurons subjected to various insults, we investigated the role of CDK6/pRb in cell survival/death mechanisms following serum deprivation.

METHODOLOGY/PRINCIPAL FINDINGS

We performed a comparative study of cell viability after serum withdrawal of established lymphoblastoid cell lines from control and carriers of c.709-1G>A PGRN mutation, asymptomatic and FTLD-TDP diagnosed individuals. Our results suggest that the CDK6/pRb pathway is enhanced in the c.709-1G>A bearing lymphoblasts. Apparently, this feature allows PGRN-deficient cells to escape from serum withdrawal-induced apoptosis by decreasing the activity of executive caspases and lowering the dissipation of mitochondrial membrane potential and the release of cytochrome c from the mitochondria. Inhibitors of CDK6 expression levels like sodium butyrate or the CDK6 activity such as PD332991 were able to restore the vulnerability of lymphoblasts from FTLD-TDP patients to trophic factor withdrawal.

CONCLUSION/SIGNIFICANCE

The use of PGRN-deficient lymphoblasts from FTLD-TDP patients may be a useful model to investigate cell biochemical aspects of this disease. It is suggested that CDK6 could be potentially a therapeutic target for the treatment of the FTLD-TDP.

Microvesicles: novel biomarkers for neurological disorders

Microvesicles (MVs) are released by most cell types in physiological conditions, but their number is often increased upon cellular activation or neoplastic transformation. This suggests that their detection may be helpful in pathological conditions to have information on activated cell types and, possibly, on the nature of the activation. This could be of paramount importance in districts and tissues that are not accessible to direct examination, such as the central nervous system. Increased release of MVs has been described to be associated to the acute or active phase of several neurological disorders. While the subcellular origin of MVs (exosome or ectosomes) is basically never addressed in these studies because of technical limitations, the cell of origin is always identified. Endothelium- or platelet-derived MVs, detected in plasma or serum, are linked to neurological pathologies with a vascular or ischemic pathogenic component, and may represent a very useful marker to support therapeutic choices in stroke. In neuroinflammatory disorders, such as multiple sclerosis, MVs of oligodendroglial, or microglial origin have been described in the cerebrospinal fluid and may carry, in perspective, additional information on the biological alterations in their cell of origin. Little specific evidence is available in neurodegenerative disorders and, specifically, MVs of neural origin have never been investigated in these pathologies. Few data have been reported for neuroinfection and brain trauma. In brain tumors, despite the limited number of studies performed, results are very promising and potentially close to clinical translation. We here review all currently available data on the detection of MVs in neurological diseases, limiting our search to exclusively human studies. Current literature and our own data indicate that MVs detection may represent a very promising strategy to gain pathogenic information, identify therapeutic targets, and select specific biomarkers for neurological disorders.

The post-mitotic state in neurons correlates with a stable nuclear higher-order structure

Neurons become terminally differentiated (TD) post-mitotic cells very early during development yet they may remain alive and functional for decades. TD neurons preserve the molecular machinery necessary for DNA synthesis that may be reactivated by different stimuli but they never complete a successful mitosis. The non-reversible nature of the post-mitotic state in neurons suggests a non-genetic basis for it since no set of mutations has been able to revert it. Comparative studies of the nuclear higher-order structure in neurons and cells with proliferating potential suggest that the non-reversible nature of the post-mitotic state in neurons has a structural basis in the stability of the nuclear higher-order structure.

Cross-talk between cell cycle induction and mitochondrial dysfunction during oxidative stress and nerve growth factor withdrawal in differentiated PC12 cells

Neuronal death has been reported to involve mitochondrial dysfunction and cell cycle reentry. In this report, we used Nerve Growth Factor (NGF)-differentiated PC12 cells to investigate mechanisms linking mitochondrial dysfunction and cell cycle activation during neuronal death induced by NGF withdrawal and/or oxidative stress. We found that loss of survival following H(2) O(2) -induced oxidative stress or NGF deprivation was preceded by a decrease in mitochondrial membrane potential (ΔΨm), increase in reactive oxygen species (ROS), and up-regulation of cyclin D1 and phosphorylation (Ser-780) of protein retinoblastoma (P-pRb), without an increase of proliferation rates. Treatment with H(2) O(2) , but not NGF deprivation, also induced the phosporylation (Ser-10) of p27(kip1) and the appearance of a cleaved P-p27(kip1) fragment of about 15 kDa. The extent of cell cycle activation appeared to be inversely correlated to the duration of toxic stimuli (pulse/continuous). H(2) O(2) -induced mitogenic responses appeared to be mediated by induction of P-MAPK and P-Akt and were blocked by p38MAPK and JNK inhibitors as well as by the CDK inhibitor flavopiridol (Flav) and by sodium selenite (Sel), a component of selenoproteins, including glutathione peroxidases. Inhibition of p38MAPK and JNK, instead, did not affect cyclin D1 changes following NGF deprivation. Finally, both Flav hydrochloride and Sel partially prevented mitochondrial dysfunction and cell death following NGF withdrawal or H(2) O(2) toxicity, but not during oxidative stress in the absence of NGF. Taken together, these data suggest that H(2) O(2) -induced oxidative stress can determine distinct patterns of mitogenic responses as a function of mitochondrial dysfunction depending on 1) intensity/duration of stress stimuli and/or 2) presence of NGF.

Flavopiridol reduces the impedance of neural prostheses in vivo without affecting recording quality

We hypothesized that re-entry into the cell cycle may be associated with reactive gliosis surrounding neural prostheses, and that administration of a cell cycle inhibitor (flavopiridol) at the time of surgery would reduce this effect. We investigated the effects of flavopiridol on recording quality and impedance over a 28-day time period and conducted histology at 3 and 28 days post-implantation. Flavopiridol reduced the expression of a cell cycle protein (cyclin D1) in microglia surrounding probes at the 3-day time point. Impedance at 1 kHz was decreased by drug administration across the study period compared to vehicle controls. Correlations between recording (SNR, units) and impedance metrics revealed a small, but statistically significant, inverse relationship between these variables. However, the relationship between impedance and recording quality was not sufficiently strong for flavopiridol to result in an improvement in SNR or the number of units detected. Our data indicate that flavopiridol is an effective, easily administered treatment for reducing impedance in vivo, potentially through inhibiting microglial encapsulation of implanted devices. This strategy may be useful in stimulation applications, where reduced impedance is desirable for achieving activation thresholds and prolonging the lifetime of the implanted power supply. While improvements in recording quality were not observed, a combination of flavopiridol with a second strategy which enhances neuronal signal detection may enhance these results in future studies.

Interaction of Akt-phosphorylated SRPK2 with 14-3-3 mediates cell cycle and cell death in neurons

Terminally differentiated neurons are unable to reenter the cell cycle. Aberrant cell cycle activation provokes neuronal cell death, whereas cell cycle inhibition elevates neuronal survival. However, the molecular mechanism regulating the cell cycle and cell death in mature neurons remains elusive. Here we show that SRPK2, a protein kinase specific for the serine/arginine (SR) family of splicing factors, triggers cell cycle progression in neurons and induces apoptosis through regulation of nuclear cyclin D1. Akt phosphorylates SRPK2 on Thr-492 and promotes its nuclear translocation leading to cyclin D1 up-regulation, cell cycle reentry, and neuronal apoptosis. In addition, SRPK2 phosphorylates SC35 and, thus, inactivates p53, resulting in cyclin D1 up-regulation. 14-3-3 binding to SRPK2, regulated by Akt phosphorylation, inhibits these events. We find that SRPK2 is phosphorylated in ischemia-attacked brain, correlating with the observed increase in cyclin D1 levels. Hence, phosphatidylinositol 3-kinase/Akt mediates the cell cycle and cell death machinery in the nervous system through phosphorylation of SRPK2.

A human spinal cord cell promotes motoneuron survival and maturation in vitro

Primary cultures of motoneurons represent a good experimental model for studying mechanisms underlying certain spinal cord pathologies, such as amyotrophic lateral sclerosis and spinal bulbar muscular atrophy (Kennedy's disease). However, a major problem with such culture systems is the relatively short cell survival times, which limits the extent of motoneuronal maturation. In spite of supplementing culture media with various growth factors, it remains difficult to maintain motoneurons viable longer than 10 days in vitro. This study employs a new approach, in which rat motoneurons are plated on a layer of cultured cells derived from newborn human spinal cord. For all culture periods, more motoneurons remain viable in such cocultures compared with control monocultures. Moreover, although no motoneurons survive in control cultures after 22 days, viable motoneurons were observed in cocultures even after 7 weeks. Although no significant difference in neurite length was observed between 8-day mono- and cocultures, after 22 and 50 days in coculture motoneurons had a very mature morphology. They extended extremely robust, very long neurites, which formed impressive branched networks. Data obtained using a system in which the spinal cord cultures were separated from motoneurons by a porous polycarbonate filter suggest that soluble factors released from the supporting cells are in part responsible for the beneficial effects on motoneurons. Several approaches, including immunocytochemistry, immunoblotting, and electron microscopy, indicated that these supporting cells, capable of extending motoneuron survival and enhancing neurite growth, had an undifferentiated or poorly differentiated, possibly mesenchymal phenotype.

Effect of seliciclib (CYC202, R-roscovitine) on lymphocyte alloreactivity and acute kidney allograft rejection in rat

BACKGROUND

T cell stimulation by alloantigens is followed by cell cycle progression, an event that is critically dependent on cyclin-dependent kinases.

METHODS

We conducted a study to evaluate whether the cyclin-dependent kinase inhibitor seliciclib affected rat lymph node cells (LNc) activation and proliferation induced by either concanavalin A or allogeneic splenocytes in vitro and studied the mechanisms underlying the suppressive effect. We also investigated the immunosuppressive properties of seliciclib in vivo.

RESULTS

Seliciclib completely inhibited in vitro proliferation of LNc and CD8 T cells, in response to either concanavalin A or allogeneic splenocytes. The percentage of activated LNc was lower in mixed leukocyte reactions (MLR) added with seliciclib than in MLR added with vehicle. The percentages of viable and apoptotic cells at the end of MLR with seliciclib were comparable to those of MLR with vehicle. LNc pre-exposed in MLR to seliciclib did not respond to further stimulation with alloantigens, and neither IL-2 nor IL-15 restored proliferation. These data indicate that the inhibitory effect of seliciclib on T cell alloreactivity is not because of cytotoxic effect but is associated with induction of profound T cell anergy. LNc harvested at the end of the primary MLR with seliciclib did not suppress the proliferation of syngeneic LNc cells toward allogeneic splenocytes, thus excluding that seliciclib induced the formation of regulatory cells. Finally, seliciclib partially prolonged grafted animal survival in a rat model of fully major histocompatibility complex-mismatched kidney transplantation.

CONCLUSIONS

Altogether these results document that seliciclib regulates lymphocyte reactivity and may exert an immunosuppressive effect in vivo in the setting of transplantation.

Dual roles of NF-kappaB in cell survival and implications of NF-kappaB inhibitors in neuroprotective therapy

NF-kappaB is a well-characterized transcription factor with multiple physiological and pathological functions. NF-kappaB plays important roles in the development and maturation of lymphoids, regulation of immune and inflammatory response, and cell death and survival. The influence of NF-kappaB on cell survival could be protective or destructive, depending on types, developmental stages of cells, and pathological conditions. The complexity of NF-kappaB in cell death and survival derives from its multiple roles in regulating the expression of a broad array of genes involved in promoting cell death and survival. The activation of NF-kappaB has been found in many neurological disorders, but its actual roles in pathogenesis are still being debated. Many compounds with neuroprotective actions are strongly associated with the inhibition of NF-kappaB, leading to speculation that blocking the pathological activation of NF-kappaB could offer neuroprotective effects in certain neurodegenerative conditions. This paper reviews the recent developments in understanding the dual roles of NF-kappaB in cell death and survival and explores its possible usefulness in treating neurological diseases. This paper will summarize the genes regulated by NF-kappaB that are involved in cell death and survival to elucidate why NF-kappaB promotes cell survival in some conditions while facilitating cell death in other conditions. This paper will also focus on the effects of various NF-kappaB inhibitors on neuroprotection in certain pathological conditions to speculate if NF-kappaB is a potential target for neuroprotective therapy.

Microarray analysis of the cellular pathways involved in the adaptation to and progression of motor neuron injury in the SOD1 G93A mouse model of familial ALS

The cellular pathways of motor neuronal injury have been investigated in the SOD1 G93A murine model of familial amyotrophic lateral sclerosis (ALS) using laser-capture microdissection and microarray analysis. The advantages of this study include the following: analysis of changes specifically in motor neurons (MNs), while still detecting effects of interactions with neighboring cells; the ability to profile changes during disease progression, an approach not possible in human ALS; and the use of transgenic mice bred on a homogeneous genetic background, eliminating the confounding effects arising from a mixed genetic background. By using this rigorous approach, novel changes in key cellular pathways have been detected at both the presymptomatic and late stages, which have been validated by quantitative reverse transcription-PCR. At the presymptomatic stage (60 d), MNs extracted from SOD1 G93A mice show a significant increase in expression of genes subserving both transcriptional and translational functions, as well as lipid and carbohydrate metabolism, mitochondrial preprotein translocation, and respiratory chain function, suggesting activation of a strong cellular adaptive response. Mice 90 d old still show upregulation of genes involved in carbohydrate metabolism, whereas transcription and mRNA processing genes begin to show downregulation. Late in the disease course (120 d), important findings include the following: marked transcriptional repression, with downregulation of multiple transcripts involved in transcriptional and metabolic functions; upregulation of complement system components; and increased expression of key cyclins involved in cell-cycle regulation. The changes described in the motor neuron transcriptome evolving during the disease course highlight potential novel targets for neuroprotective therapeutic intervention.

Implication of the transcription factor E2F-1 in the modulation of neuronal apoptosis

Neurodegenerative diseases as Alzheimer's disease, Parkinson's disease and other neurological disorders remain major problem worldwide since is currently no effective treatment. Thus, studying the mechanisms involved in neuronal apoptotic pathways is imperative if drugs that might stop or delay these disease processes are to be synthesized. In recent years it has become evident that mitochondria are key component of the neuronal apoptotic route. In addition to mitochondria, other intracellular components have been implicated in this process. Thus, DNA damage and re-entry into the cell cycle may constitute a common pathway in apoptosis in neurological diseases. The implication of cell cycle in neurodegenerative disorders is supported by data on the brain of patients who showed an increase in cell cycle protein expression. Indeed, studies performed in neuronal cell preparations indicate that re-entry into the cell cycle and, more specifically, an increase in the expression of E2F-1 transcription role of DNA damage/repair as a potential mechanism in cell cycle re-entry. In this context, ataxia telangiectasia mutated protein could be the enzyme responsible for neuronal apoptosis activation. Furthermore, the potential routes involved in E2F-1 induced apoptosis, p53-dependent and p53-independent, are similarly reviewed. Under this hypothesis, multiple pathways have been suggested, including the route of caspases. Finally, given the increasing experimental data on the neuroprotective and antiapoptotic effects of cyclin dependent kinase CDK inhibitory drugs, including flavopiridol, their application for the treatment of neurological disorders is proposed.

Nuclear factor-kappaB-dependent cyclin D1 induction and DNA replication associated with N-methyl-D-aspartate receptor-mediated apoptosis in rat striatum

Cell cycle reentry has been found during apoptosis of postmitotic neurons under certain pathological conditions. To evaluate whether nuclear factor-kappaB (NF-kappaB) activation promotes cell cycle entry and neuronal apoptosis, we studied the relation among NF-kappaB-mediated cyclin induction, bromodeoxyuridine (BrdU) incorporation, and apoptosis initiation in rat striatal neurons following excitotoxic insult. Intrastriatally injected N-methyl-D-aspartate receptor agonist quinolinic acid (QA, 60 nmol) elicited a rise in cyclin D1 mRNA and protein levels (P<0.05). QA-induced NF-kappaB activation occurred in striatal neurons and nonneuronal cells and partially colocalized with elevated cyclin D1 immunoreactivity and TUNEL-positive nuclei. QA triggered DNA replication as evidenced by BrdU incorporation; some striatal BrdU-positive cells were identified as neurons by colocalization with NeuN. Blockade of NF-kappaB nuclear translocation with the recombinant peptide NF-kappaB SN50 attenuated the QA-induced elevation in cyclin D1 and BrdU incorporation. QA-induced internucleosomal DNA fragmentation was blunted by G(1)/S-phase cell cycle inhibitors. These findings suggest that NF-kappaB activation stimulates cyclin D1 expression and triggers DNA replication in striatal neurons. Excitotoxin-induced neuronal apoptosis may thus result from, at least partially, a failed cell cycle attempt.

The nature of the cell cycle in neurons: Focus on a “non-canonical” pathway of DNA replication causally related to death

The mechanism whereby a reactivation of cell cycle in neurons causes cell death is beginning to be identified. In cellular models of Alzheimer's disease, activation of a non-canonical pathway of DNA replication contributes to neuronal death. This pathway involves the repair enzyme DNA polymerase-beta, which is highly expressed in neurons of the Alzheimer's brain at early stages of the disease. Loading of DNA polymerase-beta into the replication forks generates a death signal, which involves the tumor suppressor p53. The increasing knowledge of the main actors of the unscheduled DNA replication in neurons will pave the way for novel therapeutic interventions in Alzheimer's disease and other neurodegenerative disorders.

Cell division in the CNS: protective response or lethal event in post-mitotic neurons?

Cell cycle events have been documented to be associated with several human neurodegenerative diseases. This review focuses on two diseases--Alzheimer's disease and ataxia telangiectasia--as well as their mouse models. Cell cycle studies have shown that ectopic expression of cell cycle markers is spatially and regional correlated well with neuronal cell death in both disease conditions. Further evidence of ectopic cell cycling is found in both human diseases and in its mouse models. These findings suggest that loss of cell cycle control represents a common pathological root of disease, which underlies the defects in the affected brain tissues in both human and mouse. Loss of cell cycle control is a unifying hypothesis for inducing neuronal death in CNS. In the disease models we have examined, cell cycle markers appear before the more well-recognized pathological changes and thus could serve as early stress markers--outcome measures for preclinical trials of potential disease therapies. As a marker these events could serve as a new criterion in human pathological diagnosis. The evidence to date is compatible with the requirement for a second "hit" for a neuron to progress cell cycle initiation and DNA replication to death. If this were true, any intervention of blocking 'second' processes might prevent or slow the neuronal cell death in the process of disease. What is not known is whether, in an adult neuron, the cell cycle event is part of the pathology or rather a desperate attempt of a neuron under stress to protect itself.

Cell-specific responses to loss of cyclin-dependent kinases

Inactivation of cyclin-dependent kinases (Cdks) and/or cyclins in mice has changed our view of cell cycle regulation. In general, cells are far more resistant to the loss of Cdks than originally anticipated, suggesting widespread compensation among the Cdks. Early embryonic cells are, so far, not sensitive to the lack of multiple Cdks or cyclins. In contrast, differentiated cells are more dependent on Cdk/cyclin complexes and the functional redundancy is more limited. Our challenge is to better understand these cell-type specific differences in cell cycle regulation that can be used to design efficient cancer therapy. Indeed, tumor cells seem to respond to inhibition of Cdk activities, however, with different outcome depending on the tumor cell type. Tumor cells share some proliferation features with stem cells, but appear more sensitive to loss of Cdk activity, somewhat resembling differentiated cells. We summarize the current knowledge of cell cycle regulation in different cell types and highlight their sensitivity to the lack of Cdk activities.

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

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

c-Jun induces apoptosis of starved BM2 monoblasts by activating cyclin A-CDK2

c-Jun is one of the major components of the activating protein-1 (AP-1), the transcription factor that participates in regulation of proliferation, differentiation, and apoptosis. In this study, we explored functional interactions of the c-Jun protein with several regulators of the G1/S transition in serum-deprived v-myb-transformed chicken monoblasts BM2. We show that the c-Jun protein induces expression of cyclin A, thus up-regulating activity of cyclin A-associated cyclin-dependent kinase 2 (CDK2), and causing massive programmed cell death of starved BM2cJUN cells. Specific inhibition of CDK2 suppresses frequency of apoptosis of BM2cJUN cells. We conclude that up-regulation of cyclin A expression and CDK2 activity can represent important link between the c-Jun protein, cell cycle machinery, and programmed cell death pathway in leukemic cells.