Spatial transcriptomic analysis reveals local effects of intratumoral fusobacterial infection on DNA damage and immune signaling in rectal cancer

Mucinous colorectal cancer (CRC) is a common histological subtype of colorectal adenocarcinoma, associated with a poor response to chemoradiotherapy. The commensal facultative anaerobes fusobacteria, have been associated with poor prognosis specifically in mesenchymal CRC. Interestingly, fusobacterial infection is especially prevalent in mucinous CRC. The objective of this study was therefore to increase our understanding of beneficial and detrimental effects of fusobacterial infection, by contrasting host cell signaling and immune responses in areas of high vs. low infection, using mucinous rectal cancer as a clinically relevant example. We employed spatial transcriptomic profiling of 106 regions of interest from 8 mucinous rectal cancer samples to study gene expression in the epithelial and immune segments across regions of high versus low fusobacterial infection. Fusobacteria high regions were associated with increased oxidative stress, DNA damage, and P53 signaling. Meanwhile regions of low fusobacterial prevalence were characterized by elevated JAK-STAT, Il-17, Il-1, chemokine and TNF signaling. Immune masks within fusobacterial high regions were characterized by elevated proportions of cytotoxic (CD8+) T cells (p = 0.037), natural killer (NK) cells (p < 0.001), B-cells (p < 0.001), and gamma delta T cells (p = 0.003). Meanwhile, fusobacteria low regions were associated with significantly greater M2 macrophage (p < 0.001), fibroblast (p < 0.001), pericyte (p = 0.002), and endothelial (p < 0.001) counts.

Bcl-xL Is a Key Mediator of Apoptosis Following KRASG12C Inhibition in KRASG12C-mutant Colorectal Cancer

Novel covalent inhibitors of KRASG12C have shown limited response rates in patients with KRASG12C-mutant (MT) colorectal cancer. Thus, novel KRASG12C inhibitor combination strategies that can achieve deep and durable responses are needed. Small-molecule KRASG12C inhibitors AZ'1569 and AZ'8037 were used. To identify novel candidate combination strategies for AZ'1569, we performed RNA sequencing, siRNA, and high-throughput drug screening. Top hits were validated in a panel of KRASG12CMT colorectal cancer cells and in vivo. AZ'1569-resistant colorectal cancer cells were generated and characterized. We found that response to AZ'1569 was heterogeneous across the KRASG12CMT models. AZ'1569 was ineffective at inducing apoptosis when used as a single agent or combined with chemotherapy or agents targeting the EGFR/KRAS/AKT axis. Using a systems biology approach, we identified the antiapoptotic BH3-family member BCL2L1/Bcl-xL as a top hit mediating resistance to AZ'1569. Further analyses identified acute increases in the proapoptotic protein BIM following AZ'1569 treatment. ABT-263 (navitoclax), a pharmacologic Bcl-2 family inhibitor that blocks the ability of Bcl-xL to bind and inhibit BIM, led to dramatic and universal apoptosis when combined with AZ'1569. Furthermore, this combination also resulted in dramatically attenuated tumor growth in KRASG12CMT xenografts. Finally, AZ'1569-resistant cells showed amplification of KRASG12C, EphA2/c-MET activation, increased proinflammatory chemokine profile and cross-resistance to several targeted agents. Importantly, KRAS amplification and AZ'1569 resistance were reversible upon drug withdrawal, arguing strongly for the use of drug holidays in the case of KRAS amplification. Taken together, combinatorial targeting of Bcl-xL and KRASG12C is highly effective, suggesting a novel therapeutic strategy for patients with KRASG12CMT colorectal cancer.

Anti-angiogenic drug scheduling optimisation with application to colorectal cancer

Bevacizumab (bvz) is a first choice anti-angiogenic drug in oncology and is primarily administered in combination with chemotherapy. It has been hypothesized that anti-angiogenic drugs enhance efficacy of cytotoxic drugs by "normalizing" abnormal tumor vessels and improving drug penetration. Nevertheless, the clinical relevance of this phenomenon is still unclear with several studies over recent years suggesting an opposing relationship. Herein, we sought to develop a new computational tool to interrogate anti-angiogenic drug scheduling with particular application in the setting of colorectal cancer (CRC). Specifically, we have employed a mathematical model of vascular tumour growth which interrogates the impact of anti-angiogenic treatment and chemotherapeutic treatment on tumour volume. Model predictions were validated using CRC xenografts which underwent treatment with a clinically relevant combinatorial anti-angiogenic regimen. Bayesian model selection revealed the most appropriate term for capturing the effect of treatments on the tumour size, and provided insights into a switch-like dependence of FOLFOX delivery on the tumour vasculature. Our experimental data and mathematical model suggest that delivering chemotherapy prior to bvz may be optimal in the colorectal cancer setting.

Abstract 2579: Loss of chromosome 18q11.2-18q12.1 is predictive for progression-free survival in metastatic colorectal cancer patients treated with bevacizumab

Introduction: Most patients with metastatic colorectal cancer (mCRC) have a limited benefit from the addition of bevacizumab to standard combination chemotherapy. However, a subset of patients benefits substantially, highlighting an unmet clinical need for a predictive biomarker of response to bevacizumab. Previously, we demonstrated that losses in chromosome 5q34, 17q12 and 18q12.1-21.1 have a significant correlation with progression free survival (PFS) in patients treated with, but not without bevacizumab. These data warrant extensive validation. Patients: For validation, two cohorts of patients that received bevacizumab were analysed, one of 121 mCRC patient samples of the European multicenter study Angiopredict and one of 81 mCRC patient samples from the Italian multicenter study MoMA. A third cohort was included of 90 mCRC samples from patients that did not receive bevacizumab. Genome wide copy number aberrations were correlated with PFS, Results: Loss of chromosome 18q11.2-18q21.1 most significantly associated with PFS in both cohorts that received bevacizumab (Angiopredict: HR=0.61, p=0.016; MoMa: HR=0.55, p=0.019). No significant association with PFS was observed in the cohort that did not receive bevacizumab (HR=0.85, p=0.67). Patients of all three cohorts without an 18q11.2-21.1 loss had similar PFS regardless of treatment (Angiopredict, median PFS 211 days; MoMa, median PFS 232 days; no bevacizumab, median PFS 189 days). No significant associations with PFS were found for chromosome 5q34 and 17q for any of the cohorts. Conclusion: We conclude that loss of chromosomal region 18q11.2-18q21.1 is consistently predictive for PFS in patients receiving bevacizumab. 18q11.2 loss provides an increase in median PFS of 83 days, compared to patients without this loss. No significant increase was found for patients that did not received bevacizumab.

Citation Format: Erik van Dijk, Hedde Biesma, Martijn Cordes, Dominiek Smeets, Maarten Neerincx, Sudipto Das, Verena Murphy, Anna Barat, Orna Bacon, Jochen H.M. Prehn, Johannes Betge, Gaiser Timo, Bozena Fender, Gerrit A. Meijer, Deborah A. McNamara, Rut Klinger, Miriam Koopman, Matthias P.A. Ebert, Elaina W. Kay, Bryan T. Hennessey, Henk M.W. Verheul, William M. Gallagher, Darran P. O'Connor, Cornelis J.A. Punt, Fotios Loupakis, Diether Lambrechts, Annette Byrne, Nicole C.T. van Grieken, Bauke Ylstra. Loss of chromosome 18q11.2-18q12.1 is predictive for progression-free survival in metastatic colorectal cancer patients treated with bevacizumab [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2579.

Abstract 4924: Retrospective evaluation of a system model of the BCL2 family of proteins as a predictive and prognostic biomarker for the clinical outcome of stage II-IV colorectal cancer patients

With 1.4 million new cases every year, colorectal cancer (CRC) is the fourth most common cancer worldwide [Globocan 2012, WHO]. Despite therapeutic advances and improvements in overall care, TNM staging remains the best prognostic indicator for CRC patients’ clinical outcomes and is pivotal for deciding on use of adjuvant chemotherapy after resection of the tumour. Adjuvant chemotherapy is not recommended for many stage II patients and mostly high-risk patients receive chemotherapy. However, there is a lack of robust biomarkers for identifying patient response to chemotherapy, recurrence and mortality risk.

We developed a system model of the BCL2 family of proteins (DR_MOMP) to assess the sensitivity of cells to genotoxic stress and to induce apoptosis triggered by chemotherapy. It calculates the stress dose required to induce mitochondrial outer membrane permeabilization (MOMP) based on absolute protein levels and the interaction of pro- and anti-apoptotic BCL2 family proteins. Cells predicted to require a high stress dose showed decreased cell death rates after being exposed to 5FU and Oxaliplatin. Profiles of BAK, BAX, BCL2, BCL(X)L and MCL1 were determined by Reverse Phase Protein Array (RPPA) technology in FFPE primary tumours collected from two distinct cohorts: stage III CRC patients who underwent adjuvant 5FU-based chemotherapy (n = 128), and stage II CRC patients from a completed clinical trial with patients randomised to adjuvant 5FU-based chemotherapy or observation only (n = 138). Protein profiles were inputted into DR_MOMP to determine chemotherapy sensitivity and to classify patients into high- or low risk categories. Findings were validated on the TCGA COAD cohort using both protein (RPPA) and mRNA (SeqV2 RSEM) expression data.

Stage II patients classified as high-risk by DR_MOMP and randomised to observation only had approximately 2-fold increased risk of death from CRC compared to those classified as low-risk or received chemotherapy (HR 2.4; 95% CI 1.2-4.8; p-value = 0.0199). Among stage III patients treated with FOLFOX, those classified as high- versus low-risk had a more than 10-fold increased risk of death from CRC (HR 10.6; 95% CI 2.4-46.3; p-value &lt; 0.0001). We validated this finding in 261 stage II-IV patients of the TCGA COAD cohort (HR 10.6; 95% CI 1.2-12.5; p-value = 0.0125). DR_MOMP predicted mortality risk independent of TNM staging and KRAS mutation status.

Our system delivers a novel predictive and prognostic biomarker that could be combined with TNM staging when assessing initial risk and subsequent clinical management of CRC patients.

Citation Format: Andreas U. Lindner, Manuela Salvucci, Mattia Cremona, Naser Monsefi, Sarah Curry, Clare Morgan, Alexa Resler, Robert O’Byrne, Orna Bacon, Michael Stuehler, Lorna Flanagan, Richard Wilson, Patrick G. Johnston, Manuel Salto-Tellez, Sophie Camilleri-Broët, Deborah A. McNamara, Bryan T. Hennessy, Elaine W. Kay, Pierre Laurent-Puig, Sandra Van Schaeybroeck, Jochen H.M. Prehn. Retrospective evaluation of a system model of the BCL2 family of proteins as a predictive and prognostic biomarker for the clinical outcome of stage II-IV colorectal cancer patients. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4924.

Abstract LB-354: Investigating potential molecular biomarkers for cetuximab response in metastatic colorectal cancer tissue using reverse phase protein array

Colorectal cancer (CRC) is the third and second most commonly diagnosed cancer in males and females, and the second most common cause of cancer-related deaths in the developed world. Identifying the importance of epidermal growth factor (EGF) signalling pathways for the survival of CRC cells (Van Cutsem, Kohne et al. 2011) resulted in development of therapies that target EGF-receptors (EGFR). Late stage CRC patients are mainly treated with monoclonal anti-EGFR antibodies such as cetuximab. Although anti-EGFR therapies have significantly improved survival in CRC patients (Van Cutsem, Kohne et al. 2009), they are not effective in patients with activating KRAS, BRAF, NRAS and PI3KCA mutations (De Roock, Claes et al. 2010). Nevertheless, between 50-60% of patients will not benefit from the additional anti-EGFR treatment, even when these have a quadruple wild-type status (De Roock, De Vriendt et al. 2011), suggesting that novel biomarkers and targeted therapies are required.

In this study, we investigate potential biomarkers for cetuximab response in a panel of 93 quadruple wild-type, liver metastatic CRC samples from patient derived xenografts (PDX) with known responses to cetuximab. Matching PDXs were used to measure changes in tumour volumes post cetuximab treatment (Bertotti, Papp et al. 2015) and were later categorised as regressing, progressing or stabilised. Protein expression levels were measured in matched PDXs, using a reverse phase protein array (RPPA) with a panel of 72 antibodies targeting key cancer related proteins as previously described).

Statistical analysis of measured values showed significant correlation between high protein expression levels, such as Chk-1, PARP, HIAP-2 (cIAP-1), and PDX progression post cetuximab treatment. These proteins were significantly expressed lower in both regressing and stable PDXs. Interestingly, we found a high cross correlation between expression levels of these proteins across all the samples, giving them a great potential to act as predictive biomarkers for cetuximab response. Bioinformatics pathway enrichment of these proteins showed a significant enrichment of intrinsic apoptotic and cell cycle signalling pathways. These results have also been investigated in publically available patient data with cetuximab response and together will be used to construct a deterministic mathematical cell cycle model that will help to predict the outcome of cetuximab therapy in future.

Citation Format: Naser Monsefi, Robert O’Byrne, Steven Carberry, Eugenia R. Zanella, Ana Barat, Mattia Cremona, Clare Morgan, Bryan T. Hennessy, Andrea Bertotti, Livio Trusolino, Jochen H.M. Prehn. Investigating potential molecular biomarkers for cetuximab response in metastatic colorectal cancer tissue using reverse phase protein array. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-354.

Essential versus accessory aspects of cell death: recommendations of the NCCD 2015

Cells exposed to extreme physicochemical or mechanical stimuli die in an uncontrollable manner, as a result of their immediate structural breakdown. Such an unavoidable variant of cellular demise is generally referred to as ‘accidental cell death' (ACD). In most settings, however, cell death is initiated by a genetically encoded apparatus, correlating with the fact that its course can be altered by pharmacologic or genetic interventions. ‘Regulated cell death' (RCD) can occur as part of physiologic programs or can be activated once adaptive responses to perturbations of the extracellular or intracellular microenvironment fail. The biochemical phenomena that accompany RCD may be harnessed to classify it into a few subtypes, which often (but not always) exhibit stereotyped morphologic features. Nonetheless, efficiently inhibiting the processes that are commonly thought to cause RCD, such as the activation of executioner caspases in the course of apoptosis, does not exert true cytoprotective effects in the mammalian system, but simply alters the kinetics of cellular demise as it shifts its morphologic and biochemical correlates. Conversely, bona fide cytoprotection can be achieved by inhibiting the transduction of lethal signals in the early phases of the process, when adaptive responses are still operational. Thus, the mechanisms that truly execute RCD may be less understood, less inhibitable and perhaps more homogeneous than previously thought. Here, the Nomenclature Committee on Cell Death formulates a set of recommendations to help scientists and researchers to discriminate between essential and accessory aspects of cell death.

INS-1 cells undergoing caspase-dependent apoptosis enhance the regenerative capacity of neighboring cells

OBJECTIVE

In diabetes, β-cell mass is not static but in a constant process of cell death and renewal. Inactivating mutations in transcription factor 1 (tcf-1)/hepatocyte nuclear factor1a (hnf1a) result in decreased β-cell mass and HNF1A-maturity onset diabetes of the young (HNF1A-MODY). Here, we investigated the effect of a dominant-negative HNF1A mutant (DN-HNF1A) induced apoptosis on the regenerative capacity of INS-1 cells.

RESEARCH DESIGN AND METHODS

DN-HNF1A was expressed in INS-1 cells using a reverse tetracycline-dependent transactivator system. Gene(s)/protein(s) involved in β-cell regeneration were investigated by real-time quantitative RT-PCR, Western blotting, and immunohistochemistry. Pancreatic stone protein/regenerating protein (PSP/reg) serum levels in human subjects were detected by enzyme-linked immunosorbent assay.

RESULTS

We detected a prominent induction of PSP/reg at the gene and protein level during DN-HNF1A-induced apoptosis. Elevated PSP/reg levels were also detected in islets of transgenic HNF1A-MODY mice and in the serum of HNF1A-MODY patients. The induction of PSP/reg was glucose dependent and mediated by caspase activation during apoptosis. Interestingly, the supernatant from DN-HNF1A-expressing cells, but not DN-HNF1A-expressing cells treated with zVAD.fmk, was sufficient to induce PSP/reg gene expression and increase cell proliferation in naïve, untreated INS-1 cells. Further experiments demonstrated that annexin-V-positive microparticles originating from apoptosing INS-1 cells mediated the induction of PSP/reg. Treatment with recombinant PSP/reg reversed the phenotype of DN-HNF1A-induced cells by stimulating cell proliferation and increasing insulin gene expression.

CONCLUSIONS

Our results suggest that apoptosing INS-1 cells shed microparticles that may stimulate PSP/reg induction in neighboring cells, a mechanism that may facilitate the recovery of β-cell mass in HNF1A-MODY.

ALISSA: an automated live-cell imaging system for signal transduction analyses

Probe photobleaching and a specimen's sensitivity to phototoxicity severely limit the number of possible excitation cycles in time-lapse fluorescent microscopy experiments. Consequently, when a study of cellular processes requires measurements over hours or days, temporal resolution is limited, and spontaneous or rapid events may be missed, thus limiting conclusions about transduction events. We have developed ALISSA, a design framework and reference implementation for an automated live-cell imaging system for signal transduction analysis. It allows an adaptation of image modalities and laser resources tailored to the biological process, and thereby extends temporal resolution from minutes to seconds. The system employs online image analysis to detect cellular events that are then used to exercise microscope control. It consists of a reusable image analysis software for cell segmentation, tracking, and time series extraction, and a measurement-specific process control software that can be easily adapted to various biological settings. We have applied the ALISSA framework to the analysis of apoptosis as a demonstration case for slow onset and rapid execution signaling. The demonstration provides a clear proof-of-concept for ALISSA, and offers guidelines for its application in a broad spectrum of signal transduction studies.

Multiple kinetics of mitochondrial cytochrome c release in drug-induced apoptosis

We investigated cytochrome c release kinetics in response to three apoptosis-inducing agents (tumor necrosis factor-alpha, staurosporine, and valinomycin) in MCF-7/Casp-3 cells stably transfected with enhanced green fluorescent protein (EGFP)-tagged cytochrome c. All three agents induced significant caspase activation in the cultures determined by monitoring the cleavage of fluorigenic caspase substrates in extracts from drug-treated MCF-7/Casp-3 cells, albeit the valinomycin-induced activation was less pronounced. Time-lapse confocal microscopy showed that tumor necrosis factor-alpha and staurosporine caused rapid, one- or multiple-step release of cytochrome c-EGFP from mitochondria. In contrast, valinomycin-induced cytochrome c-EGFP release occurred slowly over several hours. Unlike staurosporine, the valinomycin-induced cytochrome c release was not associated with translocation of the proapoptotic Bax protein to the mitochondria, and was not accompanied by co-release of the proapoptotic Smac protein. Immunoprecipitation experiments revealed that cytochrome c was also released out of the cell into the extracellular space before loss of plasma membrane integrity. Our data indicate the existence of multiple kinetics of cytochrome c release in drug-induced apoptosis.

Dlk/ZIP kinase-induced apoptosis in human medulloblastoma cells: requirement of the mitochondrial apoptosis pathway

Dlk/ZIP kinase is a member of the Death Associated Protein (DAP) kinase family of pro-apoptotic serine/threonine kinases that have been implicated in regulation of apoptosis and tumour suppression. Expression of both Dlk/ZIP kinase and its interaction partner Par-4 is maintained in four medulloblastoma cell lines investigated, whereas three of seven neuroblastoma cell lines have lost expression of Par-4. Overexpression of a constitutively pro-apoptotic deletion mutant of Dlk/ZIP kinase induced significant apoptosis in D283 medulloblastoma cells. Cell death was characterized by apoptotic membrane blebbing, and a late stage during which the cells had ceased blebbing and were drastically shrunken or disrupted into apoptotic bodies. Over-expression of the anti-apoptotic Bcl-xL protein had no effect on Dlk/ZIP kinase-induced membrane blebbing, but potently inhibited Dlk/ZIP kinase-induced cytochrome c release and transition of cells to late stage apoptosis. Treatment with caspase inhibitors delayed, but did not prevent entry into late stage apoptosis. These results demonstrate that Dlk/ZIP kinase-triggered apoptosis involves the mitochondrial apoptosis pathway. However, cell death proceeded in the presence of caspase inhibitors, suggesting that Dlk/ZIP kinase is able to activate alternative cell death pathways. Alterations of signal transduction pathways leading to Dlk/ZIP kinase induced apoptosis or loss of expression of upstream activators could play important roles in tumour progression and metastasis of neural tumours.

Ca(2+)-induced inhibition of apoptosis in human SH-SY5Y neuroblastoma cells: degradation of apoptotic protease activating factor-1 (APAF-1)

During apoptotic and excitotoxic neuron death, challenged mitochondria release the pro-apoptotic factor cytochrome c. In the cytosol, cytochrome c is capable of binding to the apoptotic protease-activating factor-1 (APAF-1). This complex activates procaspase-9 in the presence of dATP, resulting in caspase-mediated execution of apoptotic neuron death. Many forms of Ca(2+)-mediated neuron death, however, do not lead to prominent activation of the caspase cascade despite significant release of cytochrome c from mitochondria. We demonstrate that elevation of cytosolic Ca(2+) induced prominent degradation of APAF-1 in human SH-SY5Y neuroblastoma cells and in a neuronal cell-free apoptosis system. Loss of APAF-1 correlated with a reduced ability of cytochrome c to activate caspase-3-like proteases. Ca(2+) induced the activation of calpains, monitored by the cleavage of full-length alpha-spectrin into a calpain-specific 150-kDa breakdown product. However, pharmacological inhibition of calpain activity indicated that APAF-1 degradation also occurred via calpain-independent pathways. Our data suggest that Ca(2+) inhibits caspase activation during Ca(2+)-mediated neuron death by triggering the degradation of the cytochrome c-binding protein APAF-1.

Dissipation of potassium and proton gradients inhibits mitochondrial hyperpolarization and cytochrome c release during neural apoptosis

Exposure of rat hippocampal neurons or human D283 medulloblastoma cells to the apoptosis-inducing kinase inhibitor staurosporine induced rapid cytochrome c release from mitochondria and activation of the executioner caspase-3. Measurements of cellular tetramethylrhodamine ethyl ester fluorescence and subsequent simulation of fluorescence changes based on Nernst calculations of fluorescence in the extracellular, cytoplasmic, and mitochondrial compartments revealed that the release of cytochrome c was preceded by mitochondrial hyperpolarization. Overexpression of the anti-apoptotic protein Bcl-xL, but not pharmacological blockade of outward potassium currents, inhibited staurosporine-induced hyperpolarization and apoptosis. Dissipation of mitochondrial potassium and proton gradients by valinomycin or carbonyl cyanide p-trifluoromethoxy-phenylhydrazone also potently inhibited staurosporine-induced hyperpolarization, cytochrome c release, and caspase activation. This effect was not attributable to changes in cellular ATP levels. Prolonged exposure to valinomycin induced significant matrix swelling, and per se also caused release of cytochrome c from mitochondria. In contrast to staurosporine, however, valinomycin-induced cytochrome c release and cell death were not associated with caspase-3 activation and insensitive to Bcl-xL overexpression. Our data suggest two distinct mechanisms for mitochondrial cytochrome c release: (1) active cytochrome c release associated with early mitochondrial hyperpolarization, leading to neuronal apoptosis, and (2) passive cytochrome c release secondary to mitochondrial depolarization and matrix swelling.

Up-regulation of Bcl-xL in response to subtoxic beta-amyloid: role in neuronal resistance against apoptotic and oxidative injury

Neuron death in Alzheimer's disease is believed to be triggered by an increased production of amyloidogenic beta-amyloid peptides, involving both increased oxidative stress and activation of a conserved death program. Bcl-xL, an anti-apoptotic protein of the Bcl-2 family, is expressed at high levels in the adult nervous system. Exposure of neuronal cultures to subtoxic concentrations of beta-amyloid peptide 1-40 (1-10microM) or the fragment 25-35 (1-10microM) up-regulated both bcl-xL mRNA and Bcl-xL protein levels, determined by reverse transcriptase-polymerase chain reaction and western blot analysis. Bcl-xL protein was also up-regulated during oxidative stress induced by exposure to hydrogen peroxide (3-100microM) or ferric ions (1-10microM). In contrast, apoptotic stimuli (exposure to staurosporine or serum withdrawal) actually decreased neuronal Bcl-xL expression. To investigate the role of Bcl-xL in cell death relevant to Alzheimer's disease, we stably overexpressed Bcl-xL in human SH-SY5Y neuroblastoma cells. Cells overexpressing Bcl-xL were significantly protected from beta-amyloid neurotoxicity and staurosporine-induced apoptosis compared to vector-transfected controls. In contrast, Bcl-xL overexpression only conferred a mild protection against oxidative injury induced by hydrogen peroxide. We conclude that up-regulation of Bcl-xL expression in response to subtoxic concentrations of beta-amyloid is a stress response that increases the resistance of neurons to beta-amyloid neurotoxicity primarily by inhibiting apoptotic processes.

The DAP kinase family of pro-apoptotic proteins: novel players in the apoptotic game

The DAP (Death Associated Protein) kinase family is a novel subfamily of pro-apoptotic serine/threonine kinases. All five DAP kinase family members identified to date are ubiquitously expressed in various tissues and are capable of inducing apoptosis. The sequence homology of the five kinases is largely restricted to the N-terminal kinase domain. In contrast, the adjacent C-terminal regions are very diverse and link individual family members to specific signal transduction pathways. There is increasing evidence that DAP kinase family members are involved in both extrinsic and intrinsic pathways of apoptosis and may play a role in tumor progression. This review will focus on structural composition and subcellular localization of DAP kinase family members and on signal transduction pathways leading to their activation. Potential mechanisms of DAP kinase family-mediated apoptosis will be discussed. BioEssays 23:352-358, 2001.

Activation of nuclear factor kappaB and Bcl-x survival gene expression by nerve growth factor requires tyrosine phosphorylation of IkappaBalpha

NGF has been shown to support neuron survival by activating the transcription factor nuclear factor-kappaB (NFkappaB). We investigated the effect of NGF on the expression of Bcl-xL, an anti-apoptotic Bcl-2 family protein. Treatment of rat pheochromocytoma PC12 cells, human neuroblastoma SH-SY5Y cells, or primary rat hippocampal neurons with NGF (0.1-10 ng/ml) increased the expression of bcl-xL mRNA and protein. Reporter gene analysis revealed a significant increase in NFkappaB activity after treatment with NGF that was associated with increased nuclear translocation of the active NFkappaB p65 subunit. NGF-induced NFkappaB activity and Bcl-xL expression were inhibited in cells overexpressing the NFkappaB inhibitor, IkappaBalpha. Unlike tumor necrosis factor-alpha (TNF-alpha), however, NGF-induced NFkappaB activation occurred without significant degradation of IkappaBs determined by Western blot analysis and time-lapse imaging of neurons expressing green fluorescent protein-tagged IkappaBalpha. Moreover, in contrast to TNF-alpha, NGF failed to phosphorylate IkappaBalpha at serine residue 32, but instead caused significant tyrosine phosphorylation. Overexpression of a Y42F mutant of IkappaBalpha potently suppressed NFG-, but not TNF-alpha-induced NFkappaB activation. Conversely, overexpression of a dominant negative mutant of TNF receptor-associated factor-6 blocked TNF-alpha-, but not NGF-induced NFkappaB activation. We conclude that NGF and TNF-alpha induce different signaling pathways in neurons to activate NFkappaB and bcl-x gene expression.

Delayed mitochondrial dysfunction in excitotoxic neuron death: cytochrome c release and a secondary increase in superoxide production

An increased production of superoxide has been shown to mediate glutamate-induced neuron death. We monitored intracellular superoxide production of hippocampal neurons during and after exposure to the glutamate receptor agonist NMDA (300 microm). During a 30 min NMDA exposure, intracellular superoxide production increased significantly and remained elevated for several hours after wash-out of NMDA. After a 5 min exposure, superoxide production remained elevated for 10 min, but then rapidly returned to baseline. Mitochondrial membrane potential also recovered after wash-out of NMDA. However, recovery of mitochondria was transient and followed by delayed mitochondrial depolarization, loss of cytochrome c, and a secondary rise in superoxide production 4-8 hr after NMDA exposure. Treatment with a superoxide dismutase mimetic before the secondary rise conferred the same protection against cell death as a treatment before the first. The secondary rise could be inhibited by the complex I inhibitor rotenone (in combination with oligomycin) and mimicked by the complex III inhibitor antimycin A. To investigate the relationship between cytochrome c release and superoxide production, human D283 medulloblastoma cells deficient in mitochondrial respiration (rho(-) cells) were exposed to the apoptosis-inducing agent staurosporine. Treatment with staurosporine induced mitochondrial release of cytochrome c, caspase activation, and cell death in control and rho(-) cells. However, a delayed increase in superoxide production was only observed in control cells. Our data suggest that the delayed superoxide production in excitotoxicity and apoptosis occurs secondary to a defect in mitochondrial electron transport and that mitochondrial cytochrome c release occurs upstream of this defect.

Activation of calpain I converts excitotoxic neuron death into a caspase-independent cell death

Glutamate receptor overactivation contributes to neuron death after stroke, trauma, and epileptic seizures. Exposure of cultured rat hippocampal neurons to the selective glutamate receptor agonist N-methyl-d-aspartate (300 microm, 5 min) or to the apoptosis-inducing protein kinase inhibitor staurosporine (300 nm) induced a delayed neuron death. In both cases, neuron death was preceded by the mitochondrial release of the pro-apoptotic factor cytochrome c. Unlike staurosporine, the N-methyl-d-aspartate-induced release of cytochrome c did not lead to significant activation of caspase-3, the main caspase involved in the execution of neuronal apoptosis. In contrast, activation of the Ca(2+)-activated neutral protease calpain I was readily detectable after the exposure to N-methyl-d-aspartate. In a neuronal cell-free apoptosis system, calpain I prevented the ability of cytochrome c to activate the caspase cascade by inhibiting the processing of procaspase-3 and -9 into their active subunits. In the hippocampal neuron cultures, the inhibition of calpain activity restored caspase-3-like protease activity after an exposure to N-methyl-d-aspartate. Our data demonstrate the existence of signal transduction pathways that prevent the entry of cells into a caspase-dependent cell death program after the mitochondrial release of cytochrome c.

Mitochondrial depolarization is not required for neuronal apoptosis

Mitochondria are sites of cellular energy production but may also influence life and death decisions by initiating or inhibiting cell death. Mitochondrial depolarization and the subsequent release of pro-apoptotic factors have been suggested to be required for the activation of a cell death program in some forms of neuronal apoptosis. We induced apoptosis in cultured rat hippocampal neurons by exposure to the protein kinase inhibitor staurosporine (STS) (300 nM). The time course of mitochondrial membrane potential (DeltaPsi(m)) during apoptosis was examined using the probe tetramethylrhodamine ethyl ester (TMRE). Cells exhibited no decrease in TMRE fluorescence, indicative of mitochondrial depolarization, up to 8 hr after STS exposure. Rather, baseline TMRE fluorescence remained unchanged up to 2 hr and thereafter actually increased significantly. Throughout this time period, the mitochondria could also be depolarized with the protonophore carbonyl cyanide p-trifluoromethoxy-phenylhydrazone (FCCP, 0.1 microM), exhibiting the same relative magnitude of fluorescence release (unquenching) as controls. Even after 16 hr of staurosporine treatment, neurons that showed signs of nuclear apoptosis maintained DeltaPsi(m) and could be depolarized with FCCP. In contrast, caspase-3-like activity had increased roughly sevenfold by 2 hr and >20-fold by 8 hr. Double-labeling of hippocampal neurons with the potential-sensitive probe Mitotracker Red Chloromethyl X-Rosamine and an antibody to cytochrome c demonstrated at the subcellular level that mitochondrial cytochrome c release also occurred in the absence of mitochondrial depolarization. These data suggest that mitochondrial depolarization is not a decisive event in neuronal apoptosis.

The beta2-adrenoceptor agonist clenbuterol modulates Bcl-2, Bcl-xl and Bax protein expression following transient forebrain ischemia

It is well known that proteins encoded by the Bcl-2 gene family play a major role in the regulation of apoptosis. We have demonstrated previously that neuronal apoptosis can be induced in the hippocampus and striatum after global ischemia. Clenbuterol, a beta2-adrenoceptor agonist, showed considerable activity against neuronal apoptosis. In the present study, we attempted to find out whether the members of the Bcl-2 family are induced after ischemia, and whether expression of these genes could be altered by clenbuterol. Transient forebrain ischemia was performed in male Wistar rats by clamping both common carotid arteries and reducing the blood pressure to 40 mmHg for 10 min. Clenbuterol (0.5 mg/kg, i.p.) or vehicle were injected 3 h before onset of ischemia or in non-ischemic rats. The hippocampus and striatum were taken from non-ischemic rats 3, 6 and 24 h after injection of clenbuterol, as well as from drug-treated and untreated rats 6 and 24 h after ischemia. Eighty micrograms/lane total protein were loaded on a 15% sodium dodecyl sulfate-polyacrylamide gel for western blotting. Bcl-2, Bax and Bcl-xl proteins were detectable in the non-ischemic hippocampus and the striatum. Clenbuterol up-regulated the expression of Bcl-2 protein at 3, 6 and 24 h after administration. Enhanced Bcl-xl signals were found in the non-ischemic striatum 3, 6 and 24 h after clenbuterol treatment, but no change of Bcl-xl expression by clenbuterol was seen in the non-ischemic hippocampus. Bax expression was not altered by clenbuterol in the non-ischemic hippocampus and striatum. Bcl-2 was up-regulated in both detected regions at 24 h after ischemia, while the increase in Bax and Bcl-xl protein expression had appeared already at 6 h and also 24 h after ischemia. Clenbuterol further increased the expression of Bcl-2 at 6 and 24 h after ischemia. In contrast, Bax protein level was down-regulated by clenbuterol at 6 and 24 h after ischemia. Clenbuterol also increased Bcl-xl level in the ischemic striatum. The results suggest that global ischemia induces proto-oncogenes which are associated with apoptosis. Clenbuterol not only increased Bcl-2 expression in the non-ischemic hippocampus and striatum, but also up-regulated Bcl-2 and down-regulated Bax expression in the ischemic hippocampus and striatum. The increase in the ratio of Bcl-2 and Bax may contribute to the anti-apoptotic effect of clenbuterol. The present study indicates that pharmacological modulation of Bcl-2 family member expression could become a new strategy to interfere with neuronal damage.

Staurosporine-induced apoptosis of cultured rat hippocampal neurons involves caspase-1-like proteases as upstream initiators and increased production of superoxide as a main downstream effector

We induced apoptosis in cultured rat hippocampal neurons by exposure to the protein kinase inhibitor staurosporine (30 nM, 24 hr). Treatment with the antioxidant (+/-)-alpha-tocopherol (100 microM) or the superoxide dismutase-mimetic manganese tetrakis (4-benzoyl acid) porphyrin (1 microM) significantly reduced staurosporine-induced cell death. Using hydroethidine-based digital videomicroscopy, we observed a significant increase in intracellular superoxide production that peaked 6-8 hr into the staurosporine exposure. This increase occurred in the absence of gross mitochondrial depolarization monitored with the voltage-sensitive probe tetramethylrhodamine ethyl ester. We then prepared extracts from staurosporine-treated hippocampal neurons and monitored cleavage of acetyl-Tyr-Val-Ala-Asp-aminomethyl-coumarin and acetyl-Asp-Glu-Val-Asp-AMC, fluorogenic substrates for caspase-1-like and caspase-3-like proteases, respectively. Staurosporine caused a significant increase in caspase-1-like activity that preceded intracellular superoxide production and reached a maximum after 30 min. Caspase-3-like activity paralleled intracellular superoxide production, with peak activity seen after 8 hr. Treatment with the corresponding caspase-3-like protease inhibitor acetyl-Asp-Glu-Val-Asp-aldehyde (10 microM) prevented the increase in caspase-3-like activity and staurosporine-induced nuclear fragmentation, but failed to prevent the rise in superoxide production and subsequent cell death. In contrast, treatment with caspase-1-like protease inhibitors reduced both superoxide production and cell death. Of note, antioxidants prevented superoxide production, caspase-3-like protease activity, and cell death even when added 4 hr after the onset of the staurosporine exposure. These results suggest a scenario of an early, caspase-1-like activity followed by a delayed intracellular superoxide production that mediates staurosporine-induced cell death of cultured rat hippocampal neurons.

NMDA-induced superoxide production and neurotoxicity in cultured rat hippocampal neurons: role of mitochondria

Excitotoxic mechanisms are believed to be involved in the death of neurons after trauma, epileptic seizures and cerebral ischaemia. We investigated the role of mitochondrial superoxide production in excitotoxic cell death of cultured rat hippocampal neurons. Brief exposure to the selective glutamate agonist N-methyl-D-aspartate (NMDA; 100-300 microM, 10 min) induced significant neuronal death, which was sensitive to cycloheximide (1 microM) and the caspase-1 inhibitor, acetyl-Tyr-Val-Ala-Asp-chloromethylketone (10 microM). Intracellular superoxide production was monitored semiquantitatively on sister cultures from the same platings using the oxidation-sensitive probe, hydroethidine. Brief exposures to toxic NMDA concentrations induced significant increases in superoxide production which correlated with the degree of neuronal injury. However, subtoxic NMDA exposures also produced moderate, yet statistically significant increases in superoxide production. Both NMDA-induced superoxide production and neurotoxicity were reduced by inhibition of mitochondrial electron transport using either sodium cyanide (1 mM), or a combination of rotenone (2 microM) and oligomycin (2 microM). The mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxy-phenylhydrazone (FCCP, 1 microM) mimicked the effect of NMDA on mitochondrial superoxide production. Both NMDA-induced superoxide production and neurotoxicity were potentiated by FCCP (1 microM). Exposure to FCCP alone (1-10 microM, 10 min), however, failed to produce any toxicity. Our data suggest that mitochondrial superoxide production per se is not sufficient to trigger the degeneration of cultured hippocampal neurons, but that manipulation of mitochondrial activity alters NMDA-induced superoxide production and neurotoxicity.

Mitochondrial transmembrane potential and free radical production in excitotoxic neurodegeneration

Excitotoxic cell death is involved in many forms of acute and chronic neurodegeneration. We induced excitotoxic cell death in cultured rat hippocampal neurons by brief exposure to two selective glutamate receptor agonists with different neurotoxic potencies, N-methyl-D-aspartate (NMDA) and kainate (KA). Digital video imaging was performed during exposure to the agonists to monitor free radical production and changes in mitochondrial transmembrane potential, psi(m). Brief exposure to NMDA (10 min) induced significant cell death in the hippocampal neurons reaching a maximum at a concentration of 300 microM (57.2+/-2.6% cell death; P<0.001). In parallel imaging experiments we found that exposure to NMDA (300 microM, 10 min) induced a significant increase in superoxide production monitored with the oxidation-sensitive probe, hydroethidine (increase of 280+/-33% above baseline; P<0.001). Rhodamine-123-based imaging revealed a loss of psi(m) in 70.1+/-10.1 % of the hippocampal neurons during the exposure to NMDA. In contrast to NMDA, brief exposure to KA (10 min) produced limited neurotoxicity reaching a maximum at a concentration of 100 microM (10.2+/-4.0% cell death; P<0.05). Exposure to KA (100 microM, 10 min) also caused a significant increase in superoxide production. This increase, however, was significantly less pronounced than that produced by NMDA (increase of 94+/-17% above baseline; P<0.001 compared to controls or NMDA-exposed cultures). Moreover, rhodamine-123-based imaging revealed that KA (100 microM) caused a collapse of psi(m) in only 13.5+/-1.4% of the hippocampal neurons. In conclusion, the present study demonstrates that early changes in intracellular superoxide production and psi(m) relate to neuronal survival outcome in excitotoxic cell death.

Ca2+ and reactive oxygen species in staurosporine-induced neuronal apoptosis

Staurosporine (0.03-0.5 microM) induced a dose-dependent, apoptotic degeneration in cultured rat hippocampal neurons that was sensitive to 24-h pretreatments with the protein synthesis inhibitor cycloheximide (1 microM) or the cell cycle inhibitor mimosine (100 microM). To investigate the role of Ca2+ and reactive oxygen species in staurosporine-induced neuronal apoptosis, we overexpressed calbindin D28K, a Ca2+ binding protein, and Cu/ Zn superoxide dismutase, an antioxidative enzyme, in the hippocampal neurons using adenovirus-mediated gene transfer. Infection of the cultures with the recombinant adenoviruses (100 multiplicity of infection) resulted in a stable expression of the respective proteins assessed 48 h later. Overexpression of both calbindin D28K and Cu/Zn superoxide dismutase significantly reduced staurosporine neurotoxicity compared with control cultures infected with a beta-galactosidase overexpressing adenovirus. Staurosporine-induced neuronal apoptosis was also significantly reduced when the culture medium was supplemented with 10 or 30 mM K+, suggesting that Ca2+ influx via voltage-sensitive Ca2+ channels reduces this apoptotic cell death. In contrast, neither the glutamate receptor agonist NMDA (1-10 microM) nor the NMDA receptor antagonist dizocilpine (MK-801; 1 microM) was able to reduce staurosporine neurotoxicity. Cultures treated with the antioxidants U-74500A (1-10 microM) and N-acetylcysteine (100 microM) also demonstrated reduced staurosporine neurotoxicity. These results suggest a fundamental role for both Ca2+ and reactive oxygen species in staurosprine-induced neuronal apoptosis.

Activation of ATP-sensitive potassium channels decreases neuronal injury caused by chemical hypoxia

Cerebral ischemia is known to induce endogenous adaptive mechanisms such as the activation of ATP-sensitive potassium channels that can prevent or delay neuronal injury. This process can be therapeutically mimicked by treatment with potassium channel openers. Primary neuronal cell cultures were derived from embryonic chick telencephalon and were exposed to chemical hypoxia (1 mM cyanide) or excitotoxic injury (1 mM L-glutamate). While treatments with the potassium channel openers bimakalim (1-10 microM) and EMD 57283 (0.1-10 microM) were clearly able to maintain neuronal viability after chemical hypoxia, similar concentrations of the drugs had negligible effects on glutamate-induced neurotoxicity. In contrast, both types of neuronal injury were sensitive to the protective action of the glutamate receptor antagonist dizocilpine (MK-801; 0.1-1 microM). The neuroprotective effect of bimakalim against chemically induced hypoxic injury was reversed by tolbutamide (1 microM), an ATP-sensitive potassium channel blocker. These experiments demonstrate neuroprotective effects of potassium channel openers that could be related to inhibition of neurotransmitter release.

p53 expression induces apoptosis in hippocampal pyramidal neuron cultures

The tumor suppressor gene p53 has been implicated in the induction of apoptosis in dividing cells. We now show that overexpression of p53 using an adenoviral vector in cultured rat hippocampal pyramidal neurons causes widespread neuronal death with features typical of apoptosis. p53 overexpression did not induce p21, bax, or mdm2 in neurons. X-irradiation of hippocampal neurons induced p53 immunoreactivity and cell death associated with features typical of apoptosis. Overexpression of a constitutively active nonphosphorylatable form of the retinoblastoma gene product blocked x-irradiation-induced neuronal death. However, overexpression of the cyclin-dependent kinase inhibitor p21 did not. Treatment of neurons with transforming growth factor-beta1 protected them from x-irradiation. These results are consistent with a role for p53 in nerve cell death that is distinct from its actions relating to cell cycle arrest.

TGF-beta 1 protects hippocampal neurons against degeneration caused by transient global ischemia. Dose-response relationship and potential neuroprotective mechanisms

BACKGROUND AND PURPOSE

Transforming growth factor-beta 1 (TGF-beta 1) has been shown to rescue cultured neurons from excitotoxic and hypoxic cell death and to reduce infarct size after focal cerebral ischemia in mice and rabbits. The present study investigated the effects of TGF-beta 1 in a different pathophysiological setting and the delayed neuronal death of hippocampal pyramidal cells after transient global ischemia in rats, and evaluated the potential mechanisms of the neuroprotective activity of TGF-beta 1.

METHODS

Transient forebrain ischemia was induced in male adult Wistar rats with bilateral occlusion of both common carotid arteries combined with systemic hypotension for 10 minutes. Seven days after ischemia, brains were perfusion-fixed and stained for histological evaluation. TGF-beta 1 or vehicle was injected intracerebroventricularly (ICV; 0.5, 4, and 50 ng) or intrahippocampally (4 ng) 1 hour before ischemia. For in vitro studies, hippocampal neurons were derived from E17 rat embryos and cultured for 10 to 14 days. Cells were exposed to (1) S-nitrosocysteine (SNOC; 30 mumol/L) to induce nitric oxide-induced oxidative injury and (2) staurosporine (0.03 mumol/L) to induce apoptotic cell death.

RESULTS

Transient forebrain ischemia caused extensive degeneration of CA1 hippocampal pyramidal cells in vehicle-treated control animals. Ischemic injury was not significantly reduced after ICV administration of 0.5 ng TGF-beta 1 (71 +/- 7% damaged neurons versus 84 +/- 3% in vehicle-treated controls: n = 9 and 11, respectively; P = .07, Mann-Whitney U test). Administration of 4 ng TGF-beta 1 reduced the percentage of damaged CA1 pyramidal cells from 71 +/- 10% in controls to 52 +/- 7% in TGF-beta 1-treated animals (n = 11 and 12, respectively; P = .04). TGF-beta 1 (4 ng) also produced significant protection when injected directly into the hippocampal tissue. In contrast, ICV administration of 50 ng TGF-beta 1 failed to show a protective effect in two separate sets of experiments. In vitro, a 24-hour pretreatment of the cultured hippocampal neurons with TGF-beta 1 (0.1 to 10 ng/mL) significantly inhibited both nitric oxide and staurosporine neurotoxicity. Posttreatment with TGF-beta 1 (10 ng/mL) also inhibited staurosporine neurotoxicity but actually potentiated nitric oxide-induced neuronal injury.

CONCLUSIONS

We demonstrated that TGF-beta 1 in a surprisingly low dose range has the capacity to reduce injury to CA1 hippocampal neurons caused by transient global ischemia in rats. This protective action could well be associated with the antioxidative and antiapoptotic effects of TGF-beta 1 demonstrated in vitro.

Marked diversity in the action of growth factors on N-methyl-D-aspartate-induced neuronal degeneration

Neuronal degeneration was induced in cultured rat hippocampal neurons by a 20-min exposure to the glutamatergic agonist, N-methyl-D-aspartate (NMDA; 100 microM), and the neuroprotective activity of a set growth factors and cytokines was compared. During the early stages of degeneration, NMDA induced changes that were characteristic of neuronal necrosis, including swelling and darkening of the neuronal soma and swelling of neurites, leading to the formation of beaded varicosities ('blebs'). These changes were followed by nuclear pyknosis, formation of double-stranded DNA breaks and loss of membrane integrity. Only transforming growth factor-beta 1 (TGF-beta 1; 1-10 ng/ml) and tumor necrosis factor-alpha (TNF-alpha; 30 ng/ml) protected the hippocampal neurons against NMDA neurotoxicity after short-term (60 min) pre-treatments. Interleukin-1 beta (10-100 ng/ml) and fibroblast growth factor-2 (FGF-2; 50 ng/ml) were clearly effective when administered 24 h prior to the NMDA exposure, but not when given 60 min before the insult. Interestingly, the protective effect of interleukin-1 beta was significantly reduced in the presence of a neutralizing antibody to TGF-beta. Of note, short-term pre-treatment with brain-derived neurotrophic factor (BDNF; 5-50 ng/ml) significantly potentiated NMDA-induced neurodegeneration. These experiments demonstrate marked diversity in the actions of growth factors on NMDA-induced neuronal degeneration.

Opposite effects of TGF-beta 1 on rapidly- and slowly-triggered excitotoxic injury

Transforming growth factor-beta (TGF-beta) has been shown to protect central neurons against diverse metabolic and excitotoxic challenges. We induced different types of excitotoxic injury on cultured rat hippocampal neurons and investigated TGF-beta 1 for its protective activity. TGF-beta 1 (0.3-10 ng/ml) effectively blocked excitotoxic injury of cultured rat hippocampal neurons induced by short-term exposure to the selective agonist N-methyl-D-aspartate (NMDA; 100 microM, 20 min). Excitotoxic injury caused by long-term exposure to the non-NMDA agonists kainate (50 microM, 24 hr) or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA; 10 microM, 24 hr) caused a similar reduction in neuronal viability. However, treatments with TGF-beta 1 (0.1-10 ng/ml) actually potentiated this slowly-triggered excitotoxic injury. Cultures of rat cerebellar neurons enriched for Purkinje cells have been shown to express AMPA/kainate receptors with significant permeability to Ca2+ and to be uniquely sensitive to non-NMDA receptor-mediated neurotoxicity. In this culture system, short-term exposure to kainate (100 microM; 30 min) in Na(+)-free extracellular solution caused a pronounced decrease in neuronal viability, and this toxicity was also significantly reduced in cultures treated with TGF-beta 1 (10 ng/ml). These results suggest that TGF-beta 1 has the capacity to protect neurons against rapidly-triggered, Ca(2+)-mediated excitotoxic injury, but significantly potentiates slowly-triggered types of excitotoxic injury. This complex action of TGF-beta 1 could have important implications for the use of TGF-beta s and related growth factors in the treatment of neurodegenerative diseases.

Protective effect of transforming growth factor-beta 1 on beta-amyloid neurotoxicity in rat hippocampal neurons

Neurodegeneration associated with Alzheimer's disease is believed to involve toxicity to beta-amyloid (A beta) and related peptides. Treatment of cultured rat hippocampal neurons with A beta 1-40 (1 microM) or the active fragment A beta 25-35 (1 microM) for 5 days led to a approximately 40-50% decrease in neuronal viability. The hydrophilic antioxidant ascorbic acid (300 microM) and the lipophilic antioxidant 2-mercaptoethanol (10 microM) both protected significantly against A beta neurotoxicity. Despite the protective effects of these antioxidants, both acute and chronic treatments with A beta 25-35 did not increase production of superoxide anions, as monitored with the fluorescent probe hydroethidine. Similarly, overexpression of Cu/Zn-superoxide dismutase using adenovirus-mediated gene transfer did not protect against A beta neurotoxicity. A beta neurotoxicity, however, was prevented in cultures infected with a recombinant, replication-defective adenovirus overexpressing the Ca2+ binding protein calbindin D28k. Transforming growth factor-beta 1 (TGF-beta 1) has been shown to protect neurons against both Ca(2+)- and free radical-mediated neuronal degeneration. We found that A beta neurotoxicity was significantly attenuated by single treatments with TGF-beta 1 (0.1-10 ng/ml) and prevented by repetitive treatments (10 ng/ml/day). The protective effects of TGF-beta 1 were associated with a preservation of mitochondrial potential and function, as determined with rhodamine-123-based microfluorimetry. Because both increased oxidative stress and pathophysiological Ca2+ fluxes can impair mitochondrial function, preservation of mitochondrial potential by TGF-beta 1 could be directly associated with its protection against A beta neurotoxicity. The ability of TGF-beta 1 to increase the expression of the anti-apoptotic proteins Bcl-2 and Bcl-XL is discussed in this context.

Expression of human copper/zinc-superoxide dismutase inhibits the death of rat sympathetic neurons caused by withdrawal of nerve growth factor

Rat superior cervical ganglion neurons require the presence of nerve growth factor (NGF) to develop and survive in culture. If NGF is removed from the culture medium, then the neurons die of programmed cell death. We investigated the potential role of Ca2+ and reactive oxygen species in this process. We found that overexpression of human wild-type copper/zinc-superoxide dismutase in cultured superior cervical ganglion neurons, using an adenovirus-based vector, substantially protected the cells from the effects of NGF withdrawal, although overexpression of the Ca(2+)-binding protein calbindin D28k or the enzyme beta-galactosidase did not. We also observed that treatment of the cells with the cytokine transforming growth factor-beta 1, which has been shown to protect neurons against oxidative injury, delayed cell death produced by NGF withdrawal. These data suggest a role for reactive oxygen species in triggering programmed cell death of rat sympathetic neurons upon growth factor withdrawal.

Are NMDA or AMPA/kainate receptor antagonists more efficacious in the delayed treatment of excitotoxic neuronal injury?

At which time-point and to what extent do N-methyl-D-aspartate (NMDA) receptors, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptors and L-type voltage-sensitive Ca2+ channels (VSCC) contribute to glutamate-induced neuronal injury? To address this question, we induced glutamate neurotoxicity in two neuronal culture systems, chick telencephalic neurons and rat hippocampal neurons, and tested selective antagonists for their neuroprotective activity when administered either during the excitotoxic insult (acute treatment) or during the recovery period (posttreatment). In cultured chick telencephalic neurons exposed to 1 mM L-glutamate for 60 min, both the NMDA receptor antagonist dizocilpine (MK-801; 0.1 microM) and the AMPA/kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 1 microM) completely blocked glutamate-induced neuronal injury when applied concomitantly with glutamate. If the antagonists were applied during the recovery period, dizocilpine at concentrations up to 10 microM only moderately increased cell viability, whereas CNQX showed a neuroprotective activity comparable to that observed in the case of the acute treatment. In cultured rat hippocampal neurons, excitotoxic injury was induced by a 30-min exposure to 1 microM glutamate. Treatment with dizocilpine during the glutamate exposure could rescue the hippocampal neurons from the excitotoxic insult, whereas acute treatment with the AMPA/kainate receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)-quinoxaline (NBQX) or the L-type VSCC blocker nimodipine showed no protection. In contrast, all three drugs showed neuroprotective activity when applied 30, 60 or 120 min after the glutamate exposure. Surprisingly, when the onset of the treatment was delayed for even 240 min, only NBQX and nimodipine led to a reduction in excitotoxic neuronal injury. We conclude that activation of AMPA/kainate receptors and L-type VSCC is critically involved in a late stage of glutamate neurotoxicity, thereby allowing pharmacological intervention at a time when blockade of NMDA receptors becomes less efficacious.

Regulation of neuronal Bcl2 protein expression and calcium homeostasis by transforming growth factor type beta confers wide-ranging protection on rat hippocampal neurons

Excessive activation of glutamate receptors accompanied by Ca2+ overloading is thought to be responsible for the death of neurons in various conditions including stroke and epilepsy. Neurons also die if deprived of important growth factors and trophic influences, conditions sensitive to certain oncogene products such as the Bcl2 protein. We now demonstrate that transforming growth factor type beta (TGF-beta) prevents neuronal Ca2+ overloading of rat hippocampal neurons in response to the glutamatergic agonist N-methyl-D-aspartate or the Ca2+ ionophore 4-Br-A23187 and, in addition, leads to a substantial increase in neuronal Bcl2 protein expression. Parallel cytotoxicity experiments demonstrate that treatment with TGF-beta protects rat hippocampal neurons from death induced by excitotoxicity, trophic factor removal, and oxidative injury. Thus, TGF-beta may protect against a wide range of toxic insults by regulating two factors with great importance for neuronal viability.

Opposing effects of transforming growth factor-beta 1 on glutamate neurotoxicity

Activation of microglia has been emphasized as a critical step in the pathophysiology of degenerative and inflammatory processes of the CNS. Activated microglia release low molecular weight compounds, such as excitatory amino acids, that are directly toxic to neurons. Here we demonstrate that a microglia-derived cytokine, transforming growth factor-beta 1, directly alters the susceptibility of neurons to glutamate-induced cell damage. Transforming growth factor-beta 1 acts as a neuroprotectant following short-term exposure to glutamate, whereas, following chronic exposure to glutamate, similar concentrations of transforming growth factor-beta 1 actually potentiate excitotoxic cell death. This complex interaction may play an important role in determining the extent of local tissue damage.

Protective effects of 5-HT1A receptor agonists against neuronal damage demonstrated in vivo and in vitro

The aim of the present study was to evaluate the neuroprotective effect of the 5-hydroxytryptamine1A (5-HT1A) agonists, CM 57493 and urapidil, in vivo and in vitro, respectively. In vivo permanent occlusion of the middle cerebral artery (MCA) was performed in male Wistar rats. Forty-eight hours after electrocoagulation of the MCA the infarct volume was determined. Pretreatment of the rat with the 5-HT1A agonist urapidil significantly reduced infarct development. The neuroprotective effect of the agent was restricted to the cortical area; the striatal damage was not influenced. As the stimulation of the 5-HT1A receptor by serotonin is supposed to induce inhibitory, hyperpolarizing effects by opening of a Ca(2+)-independent neuronal K+ ionophore, the efficacy of agonistic drugs directly on the neuron was investigated in vitro. Cyanide-induced cytotoxic hypoxia as well as glutamate-induced excitotoxicity were performed using primary neuronal cell cultures from chick embryo cerebral hemispheres. Treatment with the 5-HT1A agonists urapidil and CM 57493 significantly increased protein content of hypoxic cultures. CM 57493 added to the culture medium (1-10 microM) during and up to 24 h after glutamate exposure ameliorated viability of the neurons. The results demonstrate neuroprotective potency of the 5-HT1A agonists, urapidil and CM 57493, when applied under hypoxic, excitotoxic and ischemic conditions in vivo and in vitro, respectively. Both, presynaptically induced inhibition of glutamate release as well as postsynaptically induced inhibition of neuronal excitability could be discussed as possible mechanisms of action of the 5-HT1A receptor agonism.

Effects of serotonergic drugs in experimental brain ischemia: evidence for a protective role of serotonin in cerebral ischemia

We have examined the significance of the serotonergic system in the pathophysiology of ischemic brain damage. Permanent occlusion of the middle cerebral artery (MCA) was performed in male NMRI mice. After 48 h, the animals received a transcardiac injection of carbon black. The area of ischemia was restricted to the neocortex and its size was determined planimetrically by means of an image analyzing system. In control experiments, the NMDA antagonist dizocilpine (MK-801), the AMPA/kainate antagonist NBQX (2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)-quinoxaline) and the L-type calcium channel blocker nimodipine all produced a significant reduction in ischemic injury of the mouse neocortex. Interestingly, all of the 5-HT1A agonists tested (ipsapirone, CM 57493 [4-(3-trifluoromethylphenyl)-1-(2-cyanoethyl)-1,2,3,6-tetrahydropyridine ] and urapidil) were equally efficacious in reducing ischemic injury. On the other hand, the 5-HT2 antagonist naftidrofuryl failed to protect the brain tissue significantly against ischemic brain damage. Roxindole, a 5-HT1A agonist and 5-HT uptake inhibitor, was the most potent serotonergic compound tested. In order to examine the effects of 5-HT1A receptor activation in a different context, 10 min of forebrain ischemia was induced in male Wistar rats by a bilateral occlusion of the common carotid arteries combined with systemic hypotension. Administration of the 5-HT1A agonist CM 57493 reduced the neuronal damage within the ventral hippocampus and the entorhinal cortex as assessed histologically 7 days after ischemia. Finally, we found that 5-HT1A agonists are capable of reducing neuronal damage of cultured neocortical and hippocampal neurons subjected to a chemical hypoxia or glutamate in a dose dependent manner. These data suggest that 5-HT, released during ischemia, may have protective effects in the pathophysiology of ischemic brain damage through a direct action on neurons mediated via the inhibitory 5-HT1A receptor subtype. The results obtained from different in vivo and in vitro models indicate that 5-HT1A agonists are promising agents for the treatment of ischemic brain disorders.

Transforming growth factor-beta 1 prevents glutamate neurotoxicity in rat neocortical cultures and protects mouse neocortex from ischemic injury in vivo

Transforming growth factor-beta 1 (TGF-beta 1) has been shown to be an injury-related peptide growth factor within the mammalian central nervous system. We tested whether TGF-beta 1 has the capacity to protect rat neocortical neurons against excitotoxic damage in vitro and mouse neocortex against ischemic injury in vivo. After 14 days in vitro, cultured neurons from rat cerebral cortex were exposed to 1 mM L-glutamate in serum-free culture medium. The cultures received TGF-beta 1 immediately after the addition of glutamate. Eighteen hours later, the cell viability of the cultures was determined using trypan blue exclusion. TGF-beta 1 (1-10 ng/ml) significantly reduced the excitotoxic neuronal damage in a concentration-dependent manner. In vivo, male NMRI mice were subjected to a permanent occlusion of the left middle cerebral artery by microbipolar electrocoagulation. After 48 h, the animals received a transcardiac injection of carbon black. The area of ischemia (devoid of carbon) was restricted to the neocortex and its size was determined planimetrically by means of an image-analyzing system. The treatment with TGF-beta 1 (1 microgram/kg i.c.v.) at 6, 4, or 2 h prior to vessel occlusion reduced the area of ischemia by 5.3, 10.0, and 9.6%, respectively. The effect of the treatment with TGF-beta 1 was statistically significant (p < 0.05 by two-way ANOVA). The present in vitro and in vivo data suggest that TGF-beta 1 has the capacity to diminish the deleterious consequences of an excitotoxic or ischemic insult.

Isoform-specific effects of transforming growth factors-beta on degeneration of primary neuronal cultures induced by cytotoxic hypoxia or glutamate

The transforming growth factors-beta (TGFs-beta) are multifunctional peptide growth factors that have been localized in neuronal and glial cells of the CNS of mice, rats, and chick embryos. We tested the TGF-beta isoforms 1, 2, and 3 for their protective effects against neuronal degeneration caused by cytotoxic hypoxia or by the excitatory amino acid L-glutamate. A cytotoxic hypoxia was induced in cultured chick embryo telencephalic neurons by adding 1 mM sodium cyanide to the culture medium for a period of 30 min. Treatment with TGF-beta 1 (1-30 ng/ml) led to a statistically significant increase in cell viability, neuronal ATP levels, and protein content of the cultures assessed 72 h after the toxic insult. TGF-beta 3 was able to reduce the cyanide-induced neuronal damage at concentrations of 0.3 and 1 ng/ml, whereas TGF-beta 2 only showed neuroprotective activity at concentrations of 30 and 50 ng/ml. Both pre- and post-treatment with TGF-beta 1 also prevented the degeneration of cultured chick embryo telencephalic neurons that had been exposed to 1 mM L-glutamate in a buffered salt solution for a period of 60 min. Furthermore, TGF-beta 1 (0.3-3 ng/ml), and to a lesser extent TGF-beta 3 (0.1-1 ng/ml), significantly reduced excitotoxic injury of cultured neurons from rat cerebral cortex that had been exposed to serum-free culture medium supplemented with 1 mM L-glutamate. These results demonstrate that the TGFs-beta are able to prevent the degeneration of primary neuronal cultures, which was caused by energy depletion and activation of glutamate receptors, in an isoform-specific manner.

Platelet-activating factor antagonists reduce excitotoxic damage in cultured neurons from embryonic chick telencephalon and protect the rat hippocampus and neocortex from ischemic injury in vivo

The neuroprotective effects of the platelet-activating factor (PAF) antagonists BN 52020 and BN 52021 were determined in a temperature-controlled model of transient forebrain ischemia in the rat (occlusion of both common carotid arteries combined with lowering of the mean arterial blood pressure to 40 mm Hg for 10 min). After 7 days of recirculation, the ischemic neuronal damage was evaluated histologically within the hippocampus and neocortex. Combined pre- and post-treatment with the PAF antagonists (2 x 25 mg/kg, s.c.) significantly reduced the resulting neuronal damage of the CA1 and CA3 hippocampal subfields and of the occipital and parietal cerebral cortex. The two PAF antagonists were also tested for their neuroprotective activity in primary neuronal cultures isolated from embryonic chick telencephalon. Since an excessive activation of excitatory amino acid receptors is discussed to be of importance for the ischemic brain damage, the cultured neurons were exposed to the excitatory amino acid L-glutamate (1 mM) for a period of 60 min. Twenty hours after the excitotoxic insult, BN 52020- and BN 52021-treated cultures (1-100 microM) showed both a better preserved morphology, as well as a dose-dependent increase in cell viability and protein content compared to the control cultures. Our results demonstrate that the PAF antagonists BN 52020 and BN 52021 have the capacity to protect brain tissue against ischemic neuronal damage independent of hypothermic effects and are also capable of reducing excitotoxic damage of telencephalic neurons from chick embryos cultured in the absence of glial or endothelial cells. We thus propose that PAF plays an important role in the pathophysiology of ischemic/excitotoxic neuronal injury via a direct action on neurons.

Dihydrolipoate reduces neuronal injury after cerebral ischemia

It has been shown in vitro that dihydrolipoate (DL-6,8-dithioloctanoic acid) has antioxidant activity against microsomal lipid peroxidation. We tested dihydrolipoate for its neuroprotective activity using models of hypoxic and excitotoxic neuronal damage in vitro and rodent models of cerebral ischemia in vivo. In vitro, neuronal damage was induced in primary neuronal cultures derived form 7-day-old chick embryo telencephalon by adding either 1 mM cyanide or 1 mM glutamate to the cultures. Cyanide-exposed and dihydrolipoate-treated (10(-9)-10(-7) M) cultures showed an increased protein and ATP content compared with controls. The glutamate-exposed cultures treated with dihydrolipoate (10(-7)-10(-5) M) showed a decreased number of damaged neurons. In vivo, dihydrolipoate treatment (50 and 100 mg/kg) reduced brain infarction after permanent middle cerebral artery occlusion in mice and rats. Dihydrolipoate treatment (50 and 100 mg/kg) could not ameliorate neuronal damage in the rat hippocampus or cortex caused by 10 min of forebrain ischemia. A comparable neuroprotection was obtained by using dimethylthiourea, both in vitro (10(-7) and 10(-6) M) and at a dose of 750 mg/kg in the focal ischemia models. Lipoate, the oxidized form of dihydrolipoate, failed to reduce neuronal injury in any model tested. We conclude that dihydrolipoate, similarly to dimethylthiourea, is able to protect neurons against ischemic damage by diminishing the accumulation of reactive oxygen species within the cerebral tissue.