scholarly journals Endothelial cell death subroutines at physiological and supraphysiological concentrations of calcium phosphate bions

2020 ◽  
pp. 19-30
Author(s):  
В.Е. Маркова ◽  
Д.К. Шишкова ◽  
А.Г. Кутихин
Keyword(s):  
Cell Death ◽  
Calcium Phosphate ◽  
Optical Density ◽  
Caspase 3 ◽  
Considerable Proportion ◽  
Colorimetric Determination ◽  
Apoptosis Pathway ◽  
Caspase Inhibitors ◽  
Regulated Cell Death ◽  
Intrinsic Apoptosis Pathway

Актуальность. Формирующиеся при перенасыщении крови ионами кальция и фосфора и циркулирующие в кровотоке кальций-фосфатные бионы (КФБ) вызывают дисфункцию эндотелия вследствие гибели части артериальных эндотелиальных клеток (ЭК). Цель исследования. Оценить типы гибели первичных артериальных ЭК человека под воздействием физиологических и супрафизиологических концентраций сферических КФБ (СКФБ) и игольчатых КФБ (ИКФБ). Материалы и методы. К конфлюэнтным культурам первичных ЭК коронарной и внутренней грудной артерии человека в 96-луночных планшетах были добавлены равные объемы (10 мкл на лунку) суспензий СКФБ и ИКФБ с оптической плотностью 0,08-0,10 (физиологическая концентрация) или 0,42-0,45 (супрафизиологическая концентрация) на длине волны 650 нм. Во всех экспериментальных группах также производилось селективное ингибирование каспазы-3 (Z-D(OMe)E(OMe)VD(OMe)-FMK, 100 мкмоль/л) или ингибирование всех каспаз (Z-VAD(OMe)-FMK, 100 мкмоль/л) для оценки типа клеточной гибели (регулируемая или моментальная). Жизнеспособность клеток определялась посредством последовательного колориметрического определения их метаболической активности через 4, 24 и 48 часов после добавления КФБ. Результаты. При добавлении супрафизиологических концентраций КФБ уже на первой временной точке большинство (60-85%) эндотелиальных клеток погибало вне зависимости от типа добавленных КФБ и воздействия ингибиторов каспаз, при этом через 24 и 48 часов экспозиции ингибиторы каспаз оказывали некоторое цитопротективное действие на незначительное количество выживших клеток. При добавлении физиологических концентраций КФБ ингибиторы каспаз оказывали выраженное цитопротективное действие через 24 и 48 часов экспозиции, при этом ИКФБ демонстрировали существенно более высокую токсичность для ЭК в сравнении с СКФБ. Независимо от временной точки пан-каспазный ингибитор оказывал значительно более выраженное цитопротективное действие по сравнению с селективным ингибитором каспазы-3, что свидетельствует о кумулятивном эффекте ингибирования каспаз, возникающем, вероятно, вследствие запуска внутреннего пути апоптоза. Заключение. В супрафизиологических концентрациях КФБ вызывают моментальную гибель абсолютного большинства ЭК, однако в физиологических концентрациях ингибиторы каспаз существенно повышают выживаемость ЭК, что свидетельствует о регулируемом направлении их клеточной гибели. Дальнейшие исследования в этом направлении должны расшифровать молекулярные пути регулируемой клеточной гибели ЭК под воздействием физиологических концентраций КФБ. Background. Calcium phosphate bions (CPB) formed and circulating in the blood at its supersaturation with calcium and phosphate provoke endothelial dysfunction by causing the demise of arterial endothelial cells (ECs). Aim. To examine cell death subroutines of human primary arterial ECs exposed to physiological and supraphysiological concentrations of spherical CPB (CPB-S) and needle-shaped CPB (CPB-N). Materials and methods. Equal volumes (10 μL) of CPB-S and CPB-N at physiological concentration (optical density at 650 nm wavelength = 0.08-0.10) or supraphysiological amounts (optical density at 650 nm wavelength = 0.42-0.45) were added to the confluent primary human coronary artery and internal thoracic artery ECs cultured in 96-well plates. In all experimental groups, we selectively inhibited caspase-3 by adding Z-D(OMe)E(OMe)VD(OMe)-FMK (100 μmol/L) or all caspases (Z-VAD(OMe)-FMK, 100 μmol/L) to assess whether the CPB-induced cell death is regulated or accidental. Cell viability was evaluated by sequential colorimetric determination of metabolic activity at 4, 24, and 48 hours of incubation with CPB. Results. At supraphysiological CPB concentrations, the majority (60-85%) of ECs died regardless of CPB type and caspase inhibitors, albeit at 24- and 48-hour time points the latter had minor cytoprotective action. However at physiological CPB levels, caspase inhibitors rescued a considerable proportion of ECs after 24 or 48 hours of exposure, and CPB-N had significantly higher toxicity than CPB-S. Regardless of the time point, the cytoprotective effect of the pan-caspase inhibitor was significantly higher than that of the selective caspase-3 inhibitor indicating a cumulative caspase inhibition and suggesting that cell death was precipitated by an intrinsic apoptosis pathway. Conclusion. At supraphysiological concentrations, CPB cause instant cell death; yet at physiological amounts, caspase inhibitors rescue the majority of ECs testifying to the regulated cell death. Further studies in this field should decipher the molecular pathways of CPB-induced regulated cell death of ECs.

scholarly journals Amphiregulin Regulates Phagocytosis-Induced Cell Death in Monocytes via EGFR and the Bcl-2 Protein Family

2019 ◽  
Vol 2019 ◽  
pp. 1-13 ◽  
Author(s):  
Christopher Platen ◽  
Stephan Dreschers ◽  
Jessica Wappler ◽  
Andreas Ludwig ◽  
Stefan Düsterhöft ◽  
...  
Keyword(s):  
Cell Death ◽  
Bacterial Infections ◽  
Caspase 3 ◽  
Inflammatory Responses ◽  
Inflammatory Diseases ◽  
Dependent Manner ◽  
Intrinsic Apoptosis ◽  
Caspase 9 ◽  
Apoptosis Pathway ◽  
Intrinsic Apoptosis Pathway

Neonates are extremely susceptible to bacterial infections, and evidences suggest that phagocytosis-induced cell death (PICD) is less frequently triggered in neonatal monocytes than in monocytes from adult donors. An insufficient termination of the inflammatory response, leading to a prolonged survival of neonatal monocytes with ongoing proinflammatory cytokine release, could be associated with the progression of various inflammatory diseases in neonates. Our previous data indicate that amphiregulin (AREG) is increasingly expressed on the cell surface of neonatal monocytes, resulting in remarkably higher soluble AREG levels after proteolytic shedding. In this study, we found that E. coli-infected neonatal monocytes show an increased phosphorylation of ERK, increased expression of Bcl-2 and Bcl-XL, and reduced levels of cleaved caspase-3 and caspase-9 compared to adult monocytes. In both cell types, additional stimulation with soluble AREG further increased ERK activation and expression of Bcl-2 and Bcl-XL and reduced levels of cleaved caspase-3 and caspase-9 in an EGFR-dependent manner. These data suggest that reduced PICD of neonatal monocytes could be due to reduced intrinsic apoptosis and that AREG can promote protection against PICD. This reduction of the intrinsic apoptosis pathway in neonatal monocytes could be relevant for severely prolonged inflammatory responses of neonates.

scholarly journals Positive allosteric modulation of P2X7 promotes apoptotic cell death over lytic cell death responses in macrophages

2019 ◽  
Vol 10 (12) ◽  
Author(s):  
Stefan Bidula ◽  
Kshitija Dhuna ◽  
Ray Helliwell ◽  
Leanne Stokes
Keyword(s):  
Cell Death ◽  
Mitochondrial Membrane ◽  
Caspase 3 ◽  
Allosteric Modulation ◽  
Cell Swelling ◽  
Dependent Manner ◽  
Apoptosis Pathway ◽  
Membrane Rupture ◽  
Cell Death Pathways ◽  
Intrinsic Apoptosis Pathway

AbstractP2X7 is an ATP-gated ion channel that is highly expressed by leukocytes, such as macrophages. Here, P2X7 has been demonstrated to be involved in the regulation of various cell death pathways; including apoptosis, pyroptosis, necrosis, and autophagy. However, cell death induction via P2X7 is complex and is reliant upon the nature of the stimulus, the duration of the stimulus, and the cell type investigated. Previous reports state that high extracellular ATP concentrations promote osmotic lysis, but whether positive allosteric modulation of P2X7 in the presence of lower concentrations of ATP condemns cells to the same fate is unknown. In this study, we compared cell death induced by high ATP concentrations, to cell death induced by compound K, a recently identified and potent positive allosteric modulator of P2X7. Based on our observations, we propose that high ATP concentrations induce early cell swelling, loss of mitochondrial membrane potential, plasma membrane rupture, and LDH release. Conversely, positive allosteric modulation of P2X7 primarily promotes an intrinsic apoptosis pathway. This was characterised by an increase in mitochondrial Ca2+, accelerated production of mitochondrial ROS, loss of mitochondrial membrane permeability in a Bax-dependent manner, the potential involvement of caspase-1, and caspase-3, and significantly accelerated kinetics of caspase-3 activation. This study highlights the ability of positive allosteric modulators to calibrate P2X7-dependent cell death pathways and may have important implications in modulating the antimicrobial immune response and in the resolution of inflammation.

scholarly journals AnIn VivoZebrafish Model for Interrogating ROS-Mediated Pancreaticβ-Cell Injury, Response, and Prevention

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Abhishek A. Kulkarni ◽  
Abass M. Conteh ◽  
Cody A. Sorrell ◽  
Anjali Mirmira ◽  
Sarah A. Tersey ◽  
...  
Keyword(s):  
Cell Death ◽  
Caspase 3 ◽  
Cell Injury ◽  
Zebrafish Model ◽  
Chemical Genetic ◽  
Regulated Cell Death ◽  
Specific Manner ◽  
High Doses

It is well known that a chronic state of elevated reactive oxygen species (ROS) in pancreaticβ-cells impairs their ability to release insulin in response to elevated plasma glucose. Moreover, at its extreme, unmitigated ROS drives regulated cell death. This dysfunctional state of ROS buildup can result both from genetic predisposition and environmental factors such as obesity and overnutrition. Importantly, excessive ROS buildup may underlie metabolic pathologies such as type 2 diabetes mellitus. The ability to monitor ROS dynamics inβ-cells in situ and to manipulate it via genetic, pharmacological, and environmental means would accelerate the development of novel therapeutics that could abate this pathology. Currently, there is a lack of models with these attributes that are available to the field. In this study, we use a zebrafish model to demonstrate that ROS can be generated in aβ-cell-specific manner using a hybrid chemical genetic approach. Using a transgenic nitroreductase-expressing zebrafish line,Tg(ins:Flag-NTR)s950, treated with the prodrug metronidazole (MTZ), we found that ROS is rapidly and explicitly generated inβ-cells. Furthermore, the level of ROS generated was proportional to the dosage of prodrug added to the system. At high doses of MTZ, caspase 3 was rapidly cleaved,β-cells underwent regulated cell death, and macrophages were recruited to the islet to phagocytose the debris. Based on our findings, we propose a model for the mechanism of NTR/MTZ action in transgenic eukaryotic cells and demonstrate the robust utility of this system to model ROS-related disease pathology.

scholarly journals Implication of caspases during maedi–visna virus-induced apoptosis

2002 ◽  
Vol 83 (12) ◽  
pp. 3153-3161 ◽  
Author(s):  
R. Duval ◽  
V. Bellet ◽  
S. Delebassée ◽  
C. Bosgiraud
Keyword(s):  
Cell Death ◽  
Caspase 3 ◽  
Specific Cell ◽  
Caspase 9 ◽  
Virus Growth ◽  
Caspase Inhibitors ◽  
Visna Virus ◽  
Maedi Visna Virus ◽  
Cellular Lysis

Maedi–visna virus (MVV) causes encephalitis, pneumonia and arthritis in sheep. In vitro, MVV infection and replication lead to strong cytopathic effects characterized by syncytia formation and subsequent cellular lysis. It was demonstrated previously that MVV infection in vitro induces cell death of sheep choroid plexus cells (SCPC) by a mechanism that can be associated with apoptotic cell death. Here, the relative implication of several caspases during acute infection with MVV is investigated by employing diverse in vitro and in situ strategies. It was demonstrated using specific pairs of caspase substrates and inhibitors that, during in vitro infection of SCPC by MVV, the two major pathways of caspase activation (i.e. intrinsic and extrinsic pathways) were stimulated: significant caspase-9 and -8 activities, as well as caspase-3 activity, were detected. To study the role of caspases during MVV infection in vitro, specific, cell-permeable, caspase inhibitors were used. First, these results showed that both z-DEVD-FMK (a potent inhibitor of caspase-3-like activities) and z-VAD-FMK (a broad spectrum caspase inhibitor) inhibit caspase-9, -8 and -3 activities. Second, both irreversible caspase inhibitors, z-DEVD-FMK and z-VAD-FMK, delayed MVV-induced cellular lysis as well as virus growth. Third, during SCPC in vitro infection by MVV, cells were positively stained with FITC-VAD-FMK, a probe that specifically stains cells containing active caspases. In conclusion, these data suggest that MVV infection in vitro induces SCPC cell death by a mechanism that is strongly dependent on active caspases.

scholarly journals Cell death following the loss of ADAR1 mediated A-to-I RNA editing is not effected by the intrinsic apoptosis pathway

2019 ◽  
Vol 10 (12) ◽  
Author(s):  
Carl R. Walkley ◽  
Benjamin T. Kile
Keyword(s):  
Cell Death ◽  
Rna Editing ◽  
Rna Structure ◽  
Fetal Liver ◽  
Loss Of Function ◽  
Intrinsic Apoptosis ◽  
Triple Mutant ◽  
Apoptosis Pathway ◽  
Mitochondrial Apoptosis Pathway ◽  
Intrinsic Apoptosis Pathway

AbstractModifications of RNA, collectively termed as the epitranscriptome, are widespread, evolutionarily conserved and contribute to gene regulation and protein diversity in healthy and disease states. There are >160 RNA modifications described, greatly exceeding the number of modifications to DNA. Of these, adenosine-to-inosine (A-to-I) RNA editing is one of the most common. There are tens of thousands of A-to-I editing sites in mouse, and millions in humans. Upon translation or sequencing an inosine base is decoded as guanosine, leading to A-to-G mismatches between the RNA and DNA. Inosine has different base pairing properties to adenosine and as a result editing not only alters the RNA code but can also change the RNA structure. In mammals A-to-I editing is performed by ADAR1 and ADAR2. A feature of murine loss of function ADAR1 alleles is cell death and a failure to survive embryogenesis. Adar1−/− and editing deficient (Adar1E861A/E861A) mice die between E11.75–13.5 of failed hematopoiesis. Strikingly this phenotype is rescued by the deletion of the cytosolic dsRNA sensor MDA5 or its downstream adaptor MAVS, a mechanism conserved in human and mouse. Current literature indicates that the loss of ADAR1 leads to cell death via apoptosis, yet this has not been genetically established. We report that blockade of the intrinsic (mitochondrial) apoptosis pathway, through the loss of both BAK and BAX, does not rescue or modify the cellular phenotype of the fetal liver or extend the lifespan of ADAR1 editing deficient embryos. We had anticipated that the loss of BAK and BAX would rescue, or at least significantly extend, the gestational viability of Adar1E861A/E861A embryos. However, the triple mutant Adar1E861A/E861ABak−/−Bax−/− embryos that were recovered at E13.5 were indistinguishable from the Adar1E861A/E861A embryos with BAK and BAX. The results indicate that cell death processes not requiring the intrinsic apoptosis pathway are triggered by MDA5 following the loss of ADAR1.

scholarly journals High expression of anti-apoptotic genes in grade I and II meningiomas

2017 ◽  
Vol 75 (4) ◽  
pp. 209-215 ◽  
Author(s):  
Daniela Pretti da Cunha Tirapelli ◽  
Sarah Bomfim Menezes ◽  
Indira Maynart Franco ◽  
Isis Lacrose Lustosa ◽  
Andressa Romualdo Rodrigues ◽  
...  
Keyword(s):  
Caspase 3 ◽  
Control Group ◽  
Intrinsic Apoptosis ◽  
Extrinsic Pathway ◽  
Apoptosis Pathway ◽  
Intrinsic Apoptosis Pathway ◽  
Apoptosis Pathways ◽  
Genetic Mechanisms ◽  
Apoptotic Genes ◽  
Low Expression

ABSTRACT One of the different genetic mechanisms involved in the carcinogenesis of meningiomas is influenced by interactions between proteins that induce and inhibit apoptosis. Objective To evaluate the expression of c-FLIP, XIAP, Bcl-2, caspase 3, 8 and 9, cytochrome c, APAF 1 and Smac/DIABLO genes related to apoptosis pathways. Methods The gene expression was evaluated in 30 meningiomas (WHO grades I and II) and in 10 normal samples (from arachnoid tissue) through PCR-RT. Results The results showed higher expression of anti-apoptotic genes in meningiomas when compared to the control group, which had a low expression of pro-apoptotic genes. Conclusion There is a possible block in the activation of caspases through the intrinsic apoptosis pathway in meningiomas. c-FLIP modulates caspase 8 and, by inhibiting its activation due to the lack of connection with the receiver, there is a block to the FAS activation of apoptosis by its extrinsic pathway.

Preclinical Evaluation of the Proteasome Inhibitor MLN9708 (MLN2238) In Chronic Lymphocytic Leukemia Cells

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 4634-4634
Author(s):  
Aisha Masood ◽  
Kiersten M Miles ◽  
Nazmul H Khan ◽  
Drusilla Akhtar ◽  
Remi Adelaiye ◽  
...  
Keyword(s):  
Cell Death ◽  
Chronic Lymphocytic Leukemia ◽  
Proteasome Inhibitor ◽  
Active Form ◽  
Lymphocytic Leukemia ◽  
Biologically Active ◽  
Autologous Serum ◽  
Mitochondrial Outer Membrane ◽  
Apoptosis Pathway ◽  
Intrinsic Apoptosis Pathway

Abstract Abstract 4634 The proteasome is an important therapeutic target in multiple hematological malignancies. The proteasome inhibitor bortezomib has demonstrated significant clinical activity in multiple myeloma and mantle cell lymphoma. However, clinically bortezomib has failed to demonstrate efficacy in chronic lymphocytic leukemia (CLL); the exact reason for this remains unknown. MLN9708 (Millennium Pharmaceuticals, Inc., Cambridge, MA) is a proteasome inhibitor which has a shorter proteasome dissociation half life than bortezomib and is currently in Phase I clinical development. Upon exposure to aqueous solutions or plasma, MLN9708 rapidly hydrolyzes to MLN2238, the biologically active form. MLN2238 was used for all of the studies reported here, in which we evaluated the antileukemic effects of MLN2238 in primary CLL cells from 16 patients. MLN 2238 induced a time and dose dependent decrease in CLL cell viability in 12 (75%) patient cells in vitro. Cell death was shown to be due to the induction of apoptosis confirmed by Annexin V staining of CLL cells and cleavage of PARP-1, an indicator of apoptosis. Biochemical analysis showed that caspase 3 and 9 were activated in these cells, indicating that MLN2238 induces cell death through the intrinsic apoptosis pathway. We noted increased mitochondrial outer membrane permeability (MOMP) in the presence of MLN2238, which suggests the engagement of the mitochondria in MLN2238 induced apoptosis in CLL cells. Evaluation of non-responding CLL patient samples demonstrated that increased expression of PSMB5 is associated with lack of sensitivity to MLN2238. Furthermore, incremental addition of autologous serum in responding CLL samples resulted in upregulation of PSMB5 levels, resulting in protection against MLN2238 induced cell death. Our preclinical observations demonstrate for the first time that MLN2238 can induce death in primary CLL cells, and support further investigation in CLL. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Aviculin Isolated from Lespedeza cuneata Induce Apoptosis in Breast Cancer Cells through Mitochondria-Mediated Caspase Activation Pathway

Molecules ◽  
2020 ◽  
Vol 25 (7) ◽  
pp. 1708 ◽  
Author(s):  
Dahae Lee ◽  
Yong Hoon Lee ◽  
Kwang Ho Lee ◽  
Bum Soo Lee ◽  
Akida Alishir ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Cell Death ◽  
Breast Cancer Cells ◽  
Apoptotic Cell ◽  
Underlying Mechanism ◽  
Intrinsic Apoptosis ◽  
Lespedeza Cuneata ◽  
Apoptosis Pathway ◽  
Intrinsic Apoptosis Pathway ◽  
Mcf 7

The global incidence of breast cancer has increased. However, there are many impediments to the development of safe and effective anticancer drugs. The aim of the present study was to evaluate the effect of aviculin isolated from Lespedeza cuneata (Dum. Cours.) G. Don. (Fabaceae) on MCF-7 human breast cancer cells and determine the underlying mechanism. Using the bioassay-guided isolation by water soluble tetrazolium salt (WST-1)-based Ez-Cytox assay, nine compounds (four lignan glycosides (1–4), three flavonoid glycosides (5–7), and two phenolic compounds (8 and 9)) were isolated from the ethyl acetate (EA) fraction of the L. cuneata methanolic extract. Of these, aviculin (2), a lignan glycoside, was the only compound that reduced metabolic activity on MCF-7 cells below 50% (IC50: 75.47 ± 2.23 μM). The underlying mechanism was analyzed using the annexin V Alexa Fluor 488 binding assay and Western blotting. Aviculin (2) was found to induce apoptotic cell death through the intrinsic apoptosis pathway, as indicated by the increased expression of initiator caspase-9, executioner caspase-7, and poly (ADP-ribose) polymerase (PARP). Aviculin (2)-induced apoptotic cell death was accompanied by an increase in the Bax/Bcl-2 ratio. These findings demonstrated that aviculin (2) could induce breast cancer cell apoptosis through the intrinsic apoptosis pathway, and it can therefore be considered an excellent candidate for herbal treatment of breast cancer.

Deletion of Bcl-X in the Megakaryocyte Compartment Results in Profound Thrombocytopenia Caused by Impaired Platelet Production and Survival.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 1495-1495
Author(s):  
Chloé James ◽  
Emma C. Josefsson ◽  
Michael J. White ◽  
Katya J. Henley ◽  
Benjamin T. Kile
Keyword(s):  
Cell Death ◽  
Life Span ◽  
Conflicts Of Interest ◽  
Platelet Factor ◽  
Apoptosis Pathway ◽  
Platelet Production ◽  
Cell Death Pathway ◽  
Platelet Survival ◽  
Intrinsic Apoptosis Pathway ◽  
Megakaryocyte Progenitors

Abstract Abstract 1495 Poster Board I-518 Recent studies have suggested a role for the intrinsic apoptosis pathway in megakaryocytic differentiation and platelet shedding. The intrinsic pathway is regulated by the Bcl-2 family of pro- and anti- cell death proteins. We recently demonstrated that platelet life span is controlled by an intrinsic cell death pathway, whereby the anti-apoptotic protein Bcl-xL constrains the pro-apoptotic activity of Bak to maintain platelet survival. As Bcl-xL is expressed in megakaryocytes, we investigated whether this protein is required for megakaryocyte survival, differentiation and/or platelet shedding. We specifically deleted the Bcl-x gene in the megakaryocyte lineage by crossing mice carrying a floxed allele of Bcl-x with mice carrying a platelet factor 4-regulated Cre transgene. Bcl-xfl/flCre+ mice were profoundly thrombocytopenic (26 ± 5 × 103/μl, n=14) compared with Bcl-xfl/flCre− animals (1157 ± 202 × 103/μl, n=13). Platelet life span in these mice was reduced to only 5 hours, as compared to 5 days in wild type littermates. This result confirmed that Bcl-xL is absolutely required for platelet survival. To determine whether Bcl-x deletion has an impact on platelet production, we analyzed the megakaryocyte compartment in Bcl-xfl/flCre+ and Bcl-xfl/flCre− mice. We observed that the number of megakaryocyte progenitors, and number of megakaryocytes in the bone marrow were increased in Bcl-xfl/flCre+ mice (23 ± 9 megakaryocyte progenitors vs 11 ± 5, and 51 ± 9 megakaryocytes vs 12 ± 1). This result suggested that Bcl-xL is not required for the survival of megakaryocytes or their progenitors. To determine whether Bcl-xL is required for the last step of megakaryocyte differentiation, i.e. platelet shedding, we cultured fetal liver cells with thrombopoietin. Large megakaryocytes were isolated after 3 days of differentiation on discontinuous bovine serum albumin gradient. They were cultured for 3 more days in the same media and the percentage of megakaryocytes displaying proplatelets was determined each day. Interestingly, Bcl-xfl/flCre+ megakaryocytes died much more quickly than Bcl-xfl/flCre− megakaryocytes, and almost none of those that survived were able to form proplatelets. Our study indicates that Bcl-xL is not only essential for platelet survival, but it is also required for the survival of mature megakaryocytes at the stage of platelet shedding. Disclosures: No relevant conflicts of interest to declare.

Platelet Death.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. sci-40-sci-40
Author(s):  
Emma C. Josefsson ◽  
Simone Schoenwaelder ◽  
Michael White ◽  
Matthew Goschnick ◽  
Andrew W. Roberts ◽  
...  
Keyword(s):  
Cell Death ◽  
Cultured Cells ◽  
Preliminary Evidence ◽  
Human Platelets ◽  
Mitochondrial Damage ◽  
Intrinsic Apoptosis ◽  
Apoptosis Pathway ◽  
Intrinsic Apoptosis Pathway

Abstract Human platelets exhibit a circulating lifespan of ~10 days, mouse platelets ~5 days. This finite existence is circumscribed by members of the Bcl-2 family of proteins, which control the intrinsic apoptosis pathway. Pro-survival Bcl-xL is the critical regulator of platelet lifespan, functioning to keep pro-death Bak and Bax in check, thereby maintaining platelet viability. After 5–10 days in the circulation, platelets not consumed in hemostatic processes initiate a Bak and Bax-dependent cell death program and clearance from the bloodstream. Mutations in Bcl-xL reduce platelet lifespan in a dose-dependent fashion, while deletion of Bak and Bax extend it. Studies with the BH3 mimetic compound ABT-737, which inhibits pro-survival Bcl-xL, have shown that platelets induced to undergo cell death in vitro exhibit many of the hallmarks of apoptosis in nucleated cells, including mitochondrial damage, caspase activation and externalization of membrane phosphatidylserine (PS). Whether any of these features occur during physiological platelet clearance remains unclear. Certainly, mitochondrial damage can reduce the recovery of transfused platelets, but whether PS – which is known to promote the pro-coagulant activity of agonist-activated platelets – also acts as a clearance signal for dying platelets in vivo is yet to be established. Conversely, Bak and Bax may play a role in mediating PS exposure triggered by activation. Supporting the idea that there may be crosstalk between classical platelet signaling pathways and the intrinsic apoptosis pathway is recent evidence that platelet agonists can also activate caspases. Intriguingly, elements of the intrinsic pathway may also contribute to the generation of platelets by megakaryocytes. Several groups have demonstrated that megakaryocytes contain activated caspases and that their inhibition can block platelet shedding by cultured cells. Preliminary evidence we have generated suggests that Bcl-2 family proteins may be required for platelet production in vivo. Thus, it appears that there is much to be understood about the role of the intrinsic apoptosis pathway in the regulation of platelet biogenesis, function, and death.

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