DNA strand breaks occurring during apoptosis - their early insitu detection by the terminal deoxynucleotidyl transferase and nick translation assays and prevention by serine protease inhibitors

Elucidating sequence-function relationships in a template-independent polymerase to enable novel DNA recording applications

Harnessing DNA as a high-density storage medium for information storage and molecular recording of signals has been of increasing interest in the biotechnology field. Recently, progress in enzymatic DNA synthesis, DNA digital data storage, and DNA-based molecular recording has been made by leveraging the activity of the template-independent DNA polymerase, terminal deoxynucleotidyl transferase (TdT). TdT adds deoxyribonucleotides to the 3' end of single-stranded DNA, generating random sequences of single-stranded DNA. TdT can use several divalent cations for its enzymatic activity and exhibits shifts in deoxyribonucleotide incorporation frequencies in response to changes in its reaction environment. However, there is limited understanding of sequence-structure-function relationships regarding these properties, which in turn limits our ability to modulate TdT to further advance TdT-based tools. Most TdT literature to-date explores the activity of murine, bovine or human TdTs; studies probing TdT sequence and structure largely focus on strictly conserved residues that are functionally critical to TdT activity. Here, we explore non-conserved TdT sequence space by surveying the natural diversity of TdT. We characterize a diverse set of TdT homologs from different organisms and identify several TdT residues/regions that confer differences in TdT behavior between homologs. The observations in this study can design rules for targeted TdT libraries, in tandem with a screening assay, to modulate TdT properties. Moreover, the data can be useful in guiding further studies of potential residues of interest. Overall, we characterize TdTs that have not been previously studied in the literature, and we provide new insights into TdT sequence-function relationships.

Clinical Utility of Sperm Function Tests in Predicting Male Fertility: A Systematic Review

Routine semen analysis provides considerable information regarding sperm parameters; however, it is not solely adequate to predict male fertility potential. In the past two decades, several advance sperm function tests have been developed. The present systematic review intends to assess the clinical utility of available advance sperm function tests in predicting the male fertility potential. A systematic literature search was conducted as per PRISMA guidelines using PubMed, MEDLINE, Google Scholar, and Cochrane Library. Different keywords either singly or in combination were used to retrieve the relevant articles related to sperm function tests, male fertility, and pregnancy outcomes. A total of 5169 articles were obtained, out of which 110 meeting the selection criteria were included in this review. The majorly investigated sperm function tests are hypo-osmotic swelling test, acrosome reaction test, sperm capacitation test, hemizona binding assay, sperm DNA fragmentation test, seminal reactive oxygen species test, mitochondrial dysfunction tests, antisperm antibody test, nuclear chromatin de-condensation (NCD) test, etc. The different advance sperm function tests analyse different aspects of sperm function. Hence, any one test may not be helpful to appropriately predict the male fertility potential. Currently, the unavailability of high-quality clinical data, robust thresholds, complex protocols, high cost, etc., are the limiting factors and prohibiting current sperm function tests to reach the clinics. Further multi-centric research efforts are required to fulfil the existing lacunas and pave the way for these tests to be introduced into the clinics.

Multifaceted Anticancer Potential of Gnidia glauca (Fresen.) Gilg Leaf Alkaloids: Impact on Multiple Cellular Targets

Gnidia glauca (Fresen.) Gilg has demonstrated significant anticancer potential through multiple mechanisms, including apoptosis induction, as shown by the TUNEL assay against MCF-7 cells, modulation of tubulin polymerization, preservation of mitochondrial function indicated by the JC-1 assay, and inhibition of DNA polymerase α and β activities. Rationale for the present study is to investigate the potential anticancer properties of G. glauca leaf alkaloid extract. Fresh and healthy G. glauca leaves were cleaned, shade-dried, and the powder was defatted, extracted with 10% acetic acid in ethanol, and subjected for alkaloid extraction. The partially purified G. glauca leaf alkaloid extract was evaluated for its effects on tubulin polymerization, DNA polymerase activity, mitochondrial membrane potential, and apoptosis studies using human breast cancer (MCF-7) cells by flow cytometry. The extract was found to affect microtubule assembly in a concentration-dependent manner (15.125-250 μg/mL), indicating presence of alkaloids that function as spindle poison agents. Leaf alkaloid extract of G. glauca was also found to affect the mitochondrial membrane potential with IC50 value 144.51 μg/mL, and inhibited DNA polymerase α and β activities dose dependently, thus potentially interfering with DNA replication and repair processes. Leaf alkaloid extract also showed the potential to induce DNA damage of 53.6%, albeit somewhat less than the standard drug camptothecin (64.94%) as confirmed by the TUNEL assay. Additionally, the GgLAE (IC50 144.51 μg/mL) showed significant inhibition of MCF-7 cells proliferation after 24 h, revealing phase arrests in sub G0/G1, S, and G2/M. These findings suggest that G. glauca leaf alkaloid extract contains alkaloids that possess anticancer properties with multiple targets, making the plant a natural source for a promising phytochemical drug candidates for further evaluation in pre-clinical and clinical studies. Further investigations are warranted to determine the efficacy, safety, identification and characterization of the alkaloids, and evaluate and determine their potential applications in cancer therapy.

Current trends in luminescence-based assessment of apoptosis

Apoptosis, the most extensively studied type of cell death, is known to play a crucial role in numerous processes such as elimination of unwanted cells or cellular debris, growth, control of the immune system, and prevention of malignancies. Defective regulation of apoptosis can trigger various diseases and disorders including cancer, neurological conditions, autoimmune diseases and developmental disorders. Knowing the nuances of the cell death type induced by a compound can help decipher which therapy is more effective for specific diseases. The detection of apoptotic cells using classic methods has brought significant contribution over the years, but innovative methods are quickly emerging and allow more in-depth understanding of the mechanisms, aside from a simple quantification. Due to increased sensitivity, time efficiency, pathway specificity and negligible cytotoxicity, these innovative approaches have great potential for both in vitro and in vivo studies. This review aims to shed light on the importance of developing and using novel nanoscale methods as an alternative to the classic apoptosis detection techniques.

GSK3β Inhibition Is the Molecular Pivot That Underlies the Mir-210-Induced Attenuation of Intrinsic Apoptosis Cascade during Hypoxia

Apoptotic cell death is a deleterious consequence of hypoxia-induced cellular stress. The master hypoxamiR, microRNA-210 (miR-210), is considered the primary driver of the cellular response to hypoxia stress. We have recently demonstrated that miR-210 attenuates hypoxia-induced apoptotic cell death. In this paper, we unveil that the miR-210-induced inhibition of the serine/threonine kinase Glycogen Synthase Kinase 3 beta (GSK3β) in AC-16 cardiomyocytes subjected to hypoxia stress underlies the salutary protective response of miR-210 in mitigating the hypoxia-induced apoptotic cell death. Using transient overexpression vectors to augment miR-210 expression concomitant with the ectopic expression of the constitutive active GSK3β S9A mutant (ca-GSK3β S9A), we exhaustively performed biochemical and molecular assays to determine the status of the hypoxia-induced intrinsic apoptosis cascade. Caspase-3 activity analysis coupled with DNA fragmentation assays cogently demonstrate that the inhibition of GSK3β kinase activity underlies the miR-210-induced attenuation in the hypoxia-driven apoptotic cell death. Further elucidation and delineation of the upstream cellular events unveiled an indispensable role of the inhibition of GSK3β kinase activity in mediating the miR-210-induced mitigation of the hypoxia-driven BAX and BAK insertion into the outer mitochondria membrane (OMM) and the ensuing Cytochrome C release into the cytosol. Our study is the first to unveil that the inhibition of GSK3β kinase activity is indispensable in mediating the miR-210-orchestrated protective cellular response to hypoxia-induced apoptotic cell death.

miR-210 Regulates Apoptotic Cell Death during Cellular Hypoxia and Reoxygenation in a Diametrically Opposite Manner

Apoptotic cell death of cardiomyocytes is a characteristic hallmark of ischemia-reperfusion (I/R) injury. The master hypoxamiR, microRNA-210 (miR-210), is considered the primary driver of the cellular response to hypoxic stress. However, to date, no consensus has emerged with regards to the polarity of the miR-210-elicited cellular response, as miR-210 has been shown to exacerbate as well as attenuate hypoxia-driven apoptotic cell death. Herein, in AC-16 cardiomyocytes subjected to hypoxia-reoxygenation (H-R) stress, we unravel novel facets of miR-210 biology and resolve the biological response mediated by miR-210 into the hypoxia and reoxygenation temporal components. Using transient overexpression and decoy/inhibition vectors to modulate miR-210 expression, we elucidated a Janus role miR-210 in the cellular response to H-R stress, wherein miR-210 mitigated the hypoxia-induced apoptotic cell death but exacerbated apoptotic cell death during cellular reoxygenation. We further delineated the underlying cellular mechanisms that confer this diametrically opposite effect of miR-210 on apoptotic cell death. Our exhaustive biochemical assays cogently demonstrate that miR-210 attenuates the hypoxia-driven intrinsic apoptosis pathway, while significantly augmenting the reoxygenation-induced caspase-8-mediated extrinsic apoptosis pathway. Our study is the first to unveil this Janus role of miR-210 and to substantiate the cellular mechanisms that underlie this functional duality.

β-Cell Death in Diabetes: Past Discoveries, Present Understanding, and Potential Future Advances

β-cell death is regarded as a major event driving loss of insulin secretion and hyperglycemia in both type 1 and type 2 diabetes mellitus. In this review, we explore past, present, and potential future advances in our understanding of the mechanisms that promote β-cell death in diabetes, with a focus on the primary literature. We first review discoveries of insulin insufficiency, β-cell loss, and β-cell death in human diabetes. We discuss findings in humans and mouse models of diabetes related to autoimmune-associated β-cell loss and the roles of autoreactive T cells, B cells, and the β cell itself in this process. We review discoveries of the molecular mechanisms that underlie β-cell death-inducing stimuli, including proinflammatory cytokines, islet amyloid formation, ER stress, oxidative stress, glucotoxicity, and lipotoxicity. Finally, we explore recent perspectives on β-cell death in diabetes, including: (1) the role of the β cell in its own demise, (2) methods and terminology for identifying diverse mechanisms of β-cell death, and (3) whether non-canonical forms of β-cell death, such as regulated necrosis, contribute to islet inflammation and β-cell loss in diabetes. We believe new perspectives on the mechanisms of β-cell death in diabetes will provide a better understanding of this pathological process and may lead to new therapeutic strategies to protect β cells in the setting of diabetes.

Antimelanoma activities of chimeric thiazole-androstenone derivatives

The discovery of chimeric anti-melanoma agents is reported. These molecules are potent growth suppressors of melanoma cells in vitro with growth inhibition of 50% (GI₅₀) values as low as 1.32 µM. Compounds were more toxic to melanoma cells in vitro than commonly used anti-melanoma agent dacarbazine as measured by TUNEL assay. They induced both caspase-independent apoptosis evident by colocalization of TUNEL with endonuclease G (EndoG) and caspase-mediated apoptosis measured by colocalization of TUNEL with caspase-activated DNase (CAD). In addition, compounds 3 and 5 strongly induced oxidative injury to melanoma cells as measured by TUNEL colocalization with heme oxygenase-1 (HO1). Dacarbazine induced only caspase-independent apoptosis, which may explain why it is less cytotoxic to melanoma cells than compounds 3, 4 and 5.

Elevated inflammatory responses and targeted therapeutic intervention in a preclinical mouse model of ataxia-telangiectasia lung disease

Ataxia-telangiectasia (A-T) is an autosomal recessive, multisystem disorder characterized by cerebellar degeneration, cancer predisposition, and immune system defects. A major cause of mortality in A-T patients is severe pulmonary disease; however, the underlying causes of the lung complications are poorly understood, and there are currently no curative therapeutic interventions. In this study, we examined the lung phenotypes caused by ATM-deficient immune cells using a mouse model of A-T pulmonary disease. In response to acute lung injury, ATM-deficiency causes decreased survival, reduced blood oxygen saturation, elevated neutrophil recruitment, exaggerated and prolonged inflammatory responses and excessive lung injury compared to controls. We found that ATM null bone marrow adoptively transferred to WT recipients induces similar phenotypes that culminate in impaired lung function. Moreover, we demonstrated that activated ATM-deficient macrophages exhibit significantly elevated production of harmful reactive oxygen and nitrogen species and pro-inflammatory cytokines. These findings indicate that ATM-deficient immune cells play major roles in causing the lung pathologies in A-T. Based on these results, we examined the impact of inhibiting the aberrant inflammatory responses caused by ATM-deficiency with reparixin, a CXCR1/CXCR2 chemokine receptor antagonist. We demonstrated that reparixin treatment reduces neutrophil recruitment, edema and tissue damage in ATM mutant lungs. Thus, our findings indicate that targeted inhibition of CXCR1/CXCR2 attenuates pulmonary phenotypes caused by ATM-deficiency and suggest that this treatment approach represents a viable therapeutic strategy for A-T lung disease.

TUNEL Assay: A Powerful Tool for Kidney Injury Evaluation

Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay is a long-established assay used to detect cell death-associated DNA fragmentation (3'-OH DNA termini) by endonucleases. Because these enzymes are particularly active in the kidney, TUNEL is widely used to identify and quantify DNA fragmentation and cell death in cultured kidney cells and animal and human kidneys resulting from toxic or hypoxic injury. The early characterization of TUNEL as an apoptotic assay has led to numerous misinterpretations of the mechanisms of kidney cell injury. Nevertheless, TUNEL is becoming increasingly popular for kidney injury assessment because it can be used universally in cultured and tissue cells and for all mechanisms of cell death. Furthermore, it is sensitive, accurate, quantitative, easily linked to particular cells or tissue compartments, and can be combined with immunohistochemistry to allow reliable identification of cell types or likely mechanisms of cell death. Traditionally, TUNEL analysis has been limited to the presence or absence of a TUNEL signal. However, additional information on the mechanism of cell death can be obtained from the analysis of TUNEL patterns.

Using TUNEL Assay to Quantitate p53-Induced Apoptosis in Mouse Tissues

Critical to tumor surveillance in eukaryotic cells is the ability to perceive and respond to DNA damage. p53, fulfills its role as "guardian of the genome" by either arresting cells in the cell cycle in order to allow time for repair of DNA damage or regulating a process of programmed cell death known as apoptosis. This process will eliminate cells that have suffered severe damage from intrinsic or extrinsic factors such as X-ray irradiation or chemotherapeutic drug treatments that include doxorubicin, etoposide, cisplatin, and methotrexate. Assays designed to specifically detect cells undergoing programmed cell death are essential in defining the tissue specific responses to tumor therapy treatment, tissue damage, or degenerative processes. This chapter will delineate the TUNEL (terminal deoxynucleotidyl transferase nick-end labeling) assay that is used for the rapid detection of 3' OH ends of DNA that are generated during apoptosis.

Do TUNEL and Other Apoptosis Assays Detect Cell Death in Preclinical Studies?

The terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay detects DNA breakage by labeling the free 3ʹ-hydroxyl termini. Given that genomic DNA breaks arise during early and late stages of apoptosis, TUNEL staining continues to be widely used as a measure of apoptotic cell death. The advantages of the assay include its relative ease of performance and the broad availability of TUNEL assay kits for various applications, such as single-cell analysis of apoptosis in cell cultures and tissue samples. However, as briefly discussed herein, aside from some concerns relating to the specificity of the TUNEL assay itself, it was demonstrated some twenty years ago that the early stages of apoptosis, detected by TUNEL, can be reversed. More recently, compelling evidence from different biological systems has revealed that cells can recover from even late stage apoptosis through a process called anastasis. Specifically, such recovery has been observed in cells exhibiting caspase activation, genomic DNA breakage, phosphatidylserine externalization, and formation of apoptotic bodies. Furthermore, there is solid evidence demonstrating that apoptotic cells can promote neighboring tumor cell repopulation (e.g., through caspase-3-mediated secretion of prostaglandin E₂) and confer resistance to anticancer therapy. Accordingly, caution should be exercised in the interpretation of results obtained by the TUNEL and other apoptosis assays (e.g., caspase activation) in terms of apoptotic cell demise.

Truncated PPM1D Prevents Apoptosis in the Murine Thymus and Promotes Ionizing Radiation-Induced Lymphoma

Genome integrity is protected by the cell-cycle checkpoints that prevent cell proliferation in the presence of DNA damage and allow time for DNA repair. The transient checkpoint arrest together with cellular senescence represent an intrinsic barrier to tumorigenesis. Tumor suppressor p53 is an integral part of the checkpoints and its inactivating mutations promote cancer growth. Protein phosphatase magnesium-dependent 1 (PPM1D) is a negative regulator of p53. Although its loss impairs recovery from the G2 checkpoint and promotes induction of senescence, amplification of the PPM1D locus or gain-of-function truncating mutations of PPM1D occur in various cancers. Here we used a transgenic mouse model carrying a truncating mutation in exon 6 of PPM1D (Ppm1d^T). As with human cell lines, we found that the truncated PPM1D was present at high levels in the mouse thymus. Truncated PPM1D did not affect differentiation of T-cells in the thymus but it impaired their response to ionizing radiation (IR). Thymocytes in Ppm1d^T/+ mice did not arrest in the checkpoint and continued to proliferate despite the presence of DNA damage. In addition, we observed a decreased level of apoptosis in the thymi of Ppm1d^T/+ mice. Moreover, the frequency of the IR-induced T-cell lymphomas increased in Ppm1d^T/+Trp53^+/- mice resulting in decreased survival. We conclude that truncated PPM1D partially suppresses the p53 pathway in the mouse thymus and potentiates tumor formation under the condition of a partial loss of p53 function.

Δ9-Tetrahydrocannabinol Prevents Mortality from Acute Respiratory Distress Syndrome through the Induction of Apoptosis in Immune Cells, Leading to Cytokine Storm Suppression

Acute Respiratory Distress Syndrome (ARDS) causes up to 40% mortality in humans and is difficult to treat. ARDS is also one of the major triggers of mortality associated with coronavirus-induced disease (COVID-19). We used a mouse model of ARDS induced by Staphylococcal enterotoxin B (SEB), which triggers 100% mortality, to investigate the mechanisms through which Δ9-tetrahydrocannabinol (THC) attenuates ARDS. SEB was used to trigger ARDS in C3H mice. These mice were treated with THC and analyzed for survival, ARDS, cytokine storm, and metabolome. Additionally, cells isolated from the lungs were used to perform single-cell RNA sequencing and transcriptome analysis. A database analysis of human COVID-19 patients was also performed to compare the signaling pathways with SEB-mediated ARDS. The treatment of SEB-mediated ARDS mice with THC led to a 100% survival, decreased lung inflammation, and the suppression of cytokine storm. This was associated with immune cell apoptosis involving the mitochondrial pathway, as suggested by single-cell RNA sequencing. A transcriptomic analysis of immune cells from the lungs revealed an increase in mitochondrial respiratory chain enzymes following THC treatment. In addition, metabolomic analysis revealed elevated serum concentrations of amino acids, lysine, n-acetyl methionine, carnitine, and propionyl L-carnitine in THC-treated mice. THC caused the downregulation of miR-185, which correlated with an increase in the pro-apoptotic gene targets. Interestingly, the gene expression datasets from the bronchoalveolar lavage fluid (BALF) of human COVID-19 patients showed some similarities between cytokine and apoptotic genes with SEB-induced ARDS. Collectively, this study suggests that the activation of cannabinoid receptors may serve as a therapeutic modality to treat ARDS associated with COVID-19.

A selective p38α/β MAPK inhibitor alleviates neuropathology and cognitive impairment, and modulates microglia function in 5XFAD mouse

Background

Chronic neuroinflammation, aggressive amyloid beta (Aβ) deposition, neuronal cell loss, and cognitive impairment are pathological presentations of Alzheimer’s disease (AD). Therefore, resolution of neuroinflammation and inhibition of Aβ-driven pathology have been suggested to be important strategies for AD therapy. Previous efforts to prevent AD progression have identified p38 mitogen-activated protein kinases (MAPKs) as a promising target for AD therapy. Recent studies showed pharmacological inhibition of p38α MAPK improved memory impairment in AD mouse models.

Methods

In this study, we used an AD mouse model, 5XFAD, to explore the therapeutic potential of NJK14047 which is a novel, selective p38α/β MAPK inhibitor. The mice were injected with 2.5 mg/kg NJK14047 or vehicle every other day for 3 months. Morris water maze task and histological imaging analysis were performed. Protein and mRNA expression levels were measured using immunoblotting and qRT-PCR, respectively. In vitro studies were conducted to measure the cytotoxicity of microglia- and astrocyte-conditioned medium on primary neurons using the MTT assay and TUNEL assay.

Results

NJK14047 treatment downregulated phospho-p38 MAPK levels, decreased the amount of Aβ deposits, and reduced spatial learning memory loss in 9-month-old 5XFAD mice. While the pro-inflammatory conditions were decreased, the expression of alternatively activated microglial markers and microglial phagocytic receptors was increased. Furthermore, NJK14047 treatment reduced the number of degenerating neurons labeled with Fluoro-Jade B in the brains of 5XFAD mice. The neuroprotective effect of NJK14047 was further confirmed by in vitro studies.

Conclusion

Taken together, a selective p38α/β MAPK inhibitor NJK14047 successfully showed therapeutic effects for AD in 5XFAD mice. Based on our data, p38 MAPK inhibition is a potential strategy for AD therapy, suggesting NJK14047 as one of the promising candidates for AD therapeutics targeting p38 MAPKs.

STRIDE-a fluorescence method for direct, specific in situ detection of individual single- or double-strand DNA breaks in fixed cells

We here describe a technique termed STRIDE (SensiTive Recognition of Individual DNA Ends), which enables highly sensitive, specific, direct in situ detection of single- or double-strand DNA breaks (sSTRIDE or dSTRIDE), in nuclei of single cells, using fluorescence microscopy. The sensitivity of STRIDE was tested using a specially developed CRISPR/Cas9 DNA damage induction system, capable of inducing small clusters or individual single- or double-strand breaks. STRIDE exhibits significantly higher sensitivity and specificity of detection of DNA breaks than the commonly used terminal deoxynucleotidyl transferase dUTP nick-end labeling assay or methods based on monitoring of recruitment of repair proteins or histone modifications at the damage site (e.g. γH2AX). Even individual genome site-specific DNA double-strand cuts induced by CRISPR/Cas9, as well as individual single-strand DNA scissions induced by the nickase version of Cas9, can be detected by STRIDE and precisely localized within the cell nucleus. We further show that STRIDE can detect low-level spontaneous DNA damage, including age-related DNA lesions, DNA breaks induced by several agents (bleomycin, doxorubicin, topotecan, hydrogen peroxide, UV, photosensitized reactions) and fragmentation of DNA in human spermatozoa. The STRIDE methods are potentially useful in studies of mechanisms of DNA damage induction and repair in cell lines and primary cultures, including cells with impaired repair mechanisms.

Ag(I) and Au(III) Mercaptobenzothiazole complexes induced apoptotic cell death

2-Mercaptobenzothiazole (MBT) complexes of Ag(I) and Au(III) were synthesized by wet chemical method. The structural, optical, 1HNMR, ICP - MS and electrochemical studies of the complexes were carried out. The TUNEL assay studies of Ag(I)MBT and Au(III)MBT complexes on A549 cell line indicated induced apoptosis in the cells. TUNEL assay showed 60% cell viability for Ag(I)MBT whereas 80% for Au(III)MBT. Thus Ag(I)MBT can induce cell apoptosis in cells at a higher rate than Au(III)MBT. Therefore these complexes studied here can be a viable option as anti - proliferating agent.

Early bone tissue aging in human auditory ossicles is accompanied by excessive hypermineralization, osteocyte death and micropetrosis

Within the mineralized bone, osteocytes form a multifunctional mechanosensitive network orchestrating bone remodelling. A preserved osteocyte population is a crucial determinant of bone quality. In human auditory ossicles, the early decrease in osteocyte numbers but maintained integrity remains an unexplained phenomenon that might serve for sound transmission from air to the labyrinth. Here we analysed the frequency, size and composition of osteocyte lacunae in the auditory ossicles of 22 individuals from early postnatal period to old age. Mineralization of the bone matrix was determined using backscattered electron imaging. No signs of bone remodelling were observed above the age of 1 year. We detected characteristics of early bone tissue aging, such as decrease in osteocytes, lower total lacunar density and lacunar area, as well as high matrix mineralization accompanied by distinct accumulation of micropetrotic lacunae and decreased indentation depths. The majority of these changes took place in the first months and years of life, while afterwards only minor reorganization was present. With osteocyte apoptosis potentially being a consequence of low mechanical stimuli, the early loss of osteocytes without initiation of bone remodelling indicates an adaptive response conserving the architecture of the auditory ossicles and ensuring stable sound transmission throughout life.

P2X7 receptor drives Th1 cell differentiation and controls the follicular helper T cell population to protect against Plasmodium chabaudi malaria

A complete understanding of the mechanisms underlying the acquisition of protective immunity is crucial to improve vaccine strategies to eradicate malaria. However, it is still unclear whether recognition of damage signals influences the immune response to Plasmodium infection. Adenosine triphosphate (ATP) accumulates in infected erythrocytes and is released into the extracellular milieu through ion channels in the erythrocyte membrane or upon erythrocyte rupture. The P2X7 receptor senses extracellular ATP and induces CD4 T cell activation and death. Here we show that P2X7 receptor promotes T helper 1 (Th1) cell differentiation to the detriment of follicular T helper (Tfh) cells during blood-stage Plasmodium chabaudi malaria. The P2X7 receptor was activated in CD4 T cells following the rupture of infected erythrocytes and these cells became highly responsive to ATP during acute infection. Moreover, mice lacking the P2X7 receptor had increased susceptibility to infection, which correlated with impaired Th1 cell differentiation. Accordingly, IL-2 and IFNγ secretion, as well as T-bet expression, critically depended on P2X7 signaling in CD4 T cells. Additionally, P2X7 receptor controlled the splenic Tfh cell population in infected mice by promoting apoptotic-like cell death. Finally, the P2X7 receptor was required to generate a balanced Th1/Tfh cell population with an improved ability to transfer parasite protection to CD4-deficient mice. This study provides a new insight into malaria immunology by showing the importance of P2X7 receptor in controlling the fine-tuning between Th1 and Tfh cell differentiation during P. chabaudi infection and thus in disease outcome.

Malaria still causes the death of approximately half a million people yearly despite efforts to develop vaccines. The ability of Plasmodium parasites to survive the immune effector mechanisms indicates how suitable the immune response must be to eliminate the infection. CD4 T cells have a dual role in protection against blood-stage malaria by producing IFNγ and helping B cells to secrete antibodies. Infected erythrocytes release adenosine triphosphate (ATP), a damage signal that can be recognized by purinergic receptors. Among them, the P2X7 receptor senses extracellular ATP and induces CD4 T cell activation and death. Here, we evaluated the role of P2X7 receptor in the CD4 T cell response during blood-stage Plasmodium chabaudi malaria. We observed that the selective expression of P2X7 receptor in CD4 T cells was required for T helper 1 (Th1) cell differentiation, contributing to IFNγ production and parasite control. In contrast, we found an increase in follicular T helper (Tfh) cell population, germinal center reaction and anti-parasite antibody production in the absence of the P2X7 receptor. Our findings provide mechanistic insights into malaria pathogenesis by demonstrating the importance of damage signals for the fine-tuning between Th1 and Tfh cell populations and thus for the outcome of the disease.

Evidence of apoptosis in some cell types due to pentachlorophenol (PCP) in Heteropneustes fossilis

The study aimed to clarify the role of apoptosis in pentachlorophenol (PCP) induced testicular, ovarian and renal cell genotoxicity of Heteropneustes fossilis. It was further intended to find the target germ cell type and assess the cellular and nuclear damage. Treatment of PCP was used for multiduration on the germinal tissues and they were processed to detect structural changes by light and electron microscopic evaluation and kidney cells for subsequent detection of DNA fragmentation by agarose gel electrophoresis. Findings suggest functional and morphological changes in the tissues are due to apoptosis, as evidenced by some biochemical and cytological signs. Histological observation on germinal epithelium reveals cell suicidal symptoms such as vacuolization, liquefied regions in the cytoplasm of oocytes, margination of nuclei, clumping of chromatin, and compaction of cytoplasmic organelle. Biochemical manifestation concurrent to this, is; cleavage of kidney cell DNA into low molecular weight fragments confirming apoptosis. Subsequently, it is further cleaved into nucleosome size fragments or its multiples. Ultra-structural histopathology and DNA studies conclusively lead to the PCP induced apoptosis in the exposed cell types. Results further support the usefulness of this assay in the related studies and its feasibility in generating a base line data.

Effects of temperature shift on cell cycle, apoptosis and nucleotide pools in CHO cell batch cultues

Temperature reduction in CHO cell batch culture may be beneficial in the production of recombinant protein and in maintenance of viability. The effects on cell cycle, apoptosis and nucleotide pools were studied in cultures initiated at 37°C and temperature shifted to 30 °C after 48 hours. In control cultures maintained at 37 °C, viable cells continued to proliferate until the termination of the culture, however, temperature reduction caused a rapid decrease in the percent of cells in S phase and accumulation of cells in G-1. This was accompanied by a concurrent reduction in U ratio (UTO/UDP-GNAc), previously shown to be a sensitive indicator of growth rate. Culture viability was extended following temperature shift, as a result of delayed onset of apoptosis, however, once initiated, the rate and manner of cell death was similar to that observed at 37 °C. All nucleotide pools were similarly degraded at the time of apoptotic cell death. Temperature reduction to 30 °C did not decrease the energy charge of the cells, however, the overall rate of metabolism was reduced. The latter may be sufficient to extend culture viability via a reduction in toxic metabolites and/or limitation of nutrient deprivation. However, the possibility remains that the benefits of temperature reduction in terms of both viability and productivity are more directly associated with cultures spending extended time in G-1.

Apoptosis and beyond: cytometry in studies of programmed cell death

A cell undergoing apoptosis demonstrates multitude of characteristic morphological and biochemical features, which vary depending on the inducer of apoptosis, cell type and the "time window" at which the process of apoptosis is observed. Because the gross majority of apoptotic hallmarks can be revealed by flow and image cytometry, the cytometric methods become a technology of choice in diverse studies of cellular demise. Variety of cytometric methods designed to identify apoptotic cells, detect particular events of apoptosis and probe mechanisms associated with this mode of cell death have been developed during the past two decades. In the present review, we outline commonly used methods that are based on the assessment of mitochondrial transmembrane potential, activation of caspases, DNA fragmentation, and plasma membrane alterations. We also present novel developments in the field such as the use of cyanine SYTO and TO-PRO family of probes. Strategies of selecting the optimal multiparameter approaches, as well as potential difficulties in the experimental procedures, are thoroughly summarized.

Cytometry of DNA replication and RNA synthesis: Historical perspective and recent advances based on "click chemistry"

This review covers progress in the development of cytometric methodologies designed to assess DNA replication and RNA synthesis. The early approaches utilizing autoradiography to detect incorporation of (3) H- or (14) C-labeled thymidine were able to identify the four fundamental phases of the cell cycle G(1) , S, G(2) , and M, and by analysis of the fraction of labeled mitosis (FLM), to precisely define the kinetics of cell progression through these phases. Analysis of (3) H-uridine incorporation and RNA content provided the means to distinguish quiescent G(0) from cycling G(1) cells. Subsequent progress in analysis of DNA replication was based on the use of BrdU as a DNA precursor and its detection by the quenching of the fluorescence intensity of DNA-bound fluorochromes such as Hoechst 33358 or acridine orange as measured by flow cytometry. Several variants of this methodology have been designed and used in studies to detect anticancer drug-induced perturbations of cell cycle kinetics. The next phase of method development, which was particularly useful in studies of the cell cycle in vivo, including clinical applications, relied on immunocytochemical detection of incorporated halogenated DNA or RNA precursors. This approach however was hampered by the need for DNA denaturation, which made it difficult to concurrently detect other cell constituents for multiparametric analysis. The recently introduced "click chemistry" approach has no such limitation and is the method of choice for analysis of DNA replication and RNA synthesis. This method is based on the use of 5-ethynyl-2'deoxyuridine (EdU) as a DNA precursor or 5-ethynyluridine (EU) as an RNA precursor and their detection with fluorochrome-tagged azides utilizing a copper (I) catalyzed [3+2] cycloaddition. Several examples are presented that illustrate incorporation of EdU or EU in cells subjected to DNA damage detected as histone H2AX phosphorylation that have been analyzed by flow or laser scanning cytometry.

Cytometry in cell necrobiology revisited. Recent advances and new vistas

Over a decade has passed since publication of the last review on "Cytometry in cell necrobiology." During these years we have witnessed many substantial developments in the field of cell necrobiology such as remarkable advancements in cytometric technologies and improvements in analytical biochemistry. The latest innovative platforms such as laser scanning cytometry, multispectral imaging cytometry, spectroscopic cytometry, and microfluidic Lab-on-a-Chip solutions rapidly emerge as highly advantageous tools in cell necrobiology studies. Furthermore, we have recently gained substantial knowledge on alternative cell demise modes such as caspase-independent apoptosis-like programmed cell death (PCD), autophagy, necrosis-like PCD, or mitotic catastrophe, all with profound connotations to pathogenesis and treatment. Although detection of classical, caspase-dependent apoptosis is still the major ground for the advancement of cytometric techniques, there is an increasing demand for novel analytical tools to rapidly quantify noncanonical modes of cell death. This review highlights the key developments warranting a renaissance and evolution of cytometric techniques in the field of cell necrobiology.

Induction of differentiation of leukaemic (HL-60) or prostate cancer (LNCaP, JCA-1) cells potentiates apoptosis triggered by onconase

Onconase (Onc) is a ribonuclease from amphibian oocytes that is cytostatic and cytotoxic to many tumour lines. It shows in vivo antitumour activity in mouse tumour models and is currently in Phase III clinical trials. The present study was designed to test whether cytotoxic effects of ONC can be modulated by differentiating agents. Human leukaemic HL-60 and prostate cancer LNCaP and JCA-1 cells were treated with Onc in the absence and presence of several inducers of differentiation and frequency of apoptosis was assessed using three different cytometric methods and confirmed by analysis of cell morphology. A moderate degree of apoptosis observed after 48-72 h incubation of HL-60 cells in the presence of 0.42 microM Onc alone was markedly potentiated by administration of retinoic acid (all trans), sodium butyrate or dimethylsulfoxide at concentrations known to induce differentiation but be minimally cytotoxic. Likewise, the frequency of apoptosis of LNCaP and JCA-1 cells treated with Onc was increased in the cultures to which phenylbutyrate was added. Although cell treatment with Onc alone, with each of the differentiating agents alone or with Onc in combination with the differentiating agents led to an increase in the proportion of G1 cells, no specific cell cycle phase preference in induction of apoptosis was observed. The data suggest that cells undergoing differentiation are particularly vulnerable to Onc; a combination of Onc and differentiating agents should be considered for further in vivo tests to assess its possible usefulness in the clinic.

Protective effect of hyaluronate on oxidative DNA damage in WI-38 and A549 cells

Progressive DNA damage in live cells by oxidants is the key factor contributing to cell aging and preconditioning to neoplastic transformation. The strategies to slow aging or prevent cancer rely on protection of DNA from the damage. Since cells reside within intercellular matrix it is of interest to know whether matrix constituents possess properties of modulating oxidative DNA damage. We explored, therefore, the effect of hyaluronate (HA), the ubiquitous component of the matrix, on extent of DNA damage induced by exogenous and endogenously generated oxidants. WI-38 and A549 cells were exposed to 200 microM H2O2 in the absence or presence of HA and induction of histone H2AX phosphorylation and activation of ATM, the reporters of DNA damage, was assessed by multiparameter cytometry. Also explored was effect of HA on constitutive H2AX phosphorylation that reflects DNA damage caused by endogenous oxidants generated during aerobic metabolism. HA of average MW 5.4 million (high MW) and 2 million (medium MW) at 0.1% (w/v) in culture medium totally prevented the H2O2-induced H2AX phosphorylation in both cell types whereas effect of 60,000 average MW (low MW) HA was somewhat less pronounced. Constitutive H2AX phosphorylation in WI-38 cells growing in the presence of 0.1% HA of low MW and medium MW was reduced by about 35 and 30%, respectively; no reduction was observed in A549 cells. The data indicate that HA protected DNA from damage caused by the exogenous oxidant H2O2. In WI-38 fibroblasts, the cells that express the HA-receptor CD44, HA also protected DNA from damage caused by endogenous oxidants. We postulate that expression of CD44 in some cell types such as stem cells may provide the means to internalize HA by endocytosis and one of the functions of the internalized HA may be protection of DNA from oxidants. The mechanism of protective effect of HA may either: i) involve entrapment of iron ions thereby inhibiting the Fenton's reaction that produces secondary oxidative species, and/or: ii) directly scavenging of primary and secondary ROIs, as an antioxidant, resulting in HA degradation. Since no significant degradation of HA upon its exposure in tissue culture medium to H2O2 was detected the scavenging may occur intracellularly.

Remarkable enhancement of cytotoxicity of onconase and cepharanthine when used in combination on various tumor cell lines

Onconase (Onc), a ribonuclease from oocytes or early embryos of Northern Leopard frog (Rana pipiens), is cytostatic and cytotoxic to a variety of tumor lines in vitro, inhibits growth of tumors in animal in vivo models and is currently in Phase IIIb clinical trials for malignant mesothelioma where it displays antitumor activity with minor overall toxicity to the patient. One of the characteristic features of Onc is a synergism with a variety of other antitumor modalities. Cepharanthine (Cep), a biscoclaurine alkaloid from Stephania cepharantha Hayata, is widely used in Japan to treat variety of ailments. It also shows low toxicity to patients. The aim of the present study was to assess the interaction of these two drugs on different tumor cell lines. When human promyelocytic leukemia HL-60, histiomonocytic lymphoma U937, multiple myeloma RPMI-8228, prostate carcinoma DU 145 and prostate adenocarcinoma LNCaP cells were exposed to relatively low concentrations of Onc or Cep their growth rates were somewhat suppressed but the cells were still able to proliferate. Cell growth, however, was totally abolished in each of these cell lines when treated with Onc and Cep combined. The frequency of apoptosis was also many-fold higher in cultures treated with a combination of Onc and Cep than in respective cultures treated with Onc or Cep alone. The mechanism of the observed synergism is unclear but it may be associated with the Onc activity in targeting microRNAs and/or NFkappaB and Cep activity also targeting NFkappaB. The data suggest that the combination of these two drugs, that individually express a low toxic profile, may have strong antitumor potential.

Analysis of apoptosis by cytometry using TUNEL assay

Activation of endonucleases that cleave chromosomal DNA preferentially at internucleosomal sections is a hallmark of apoptosis. DNA fragmentation revealed by the presence of a multitude of DNA strand breaks, therefore, is considered to be the gold standard for identification apoptotic cells. Several variants of the methodology that is based on fluorochrome-labeling of 3'-OH termini of DNA strand breaks in situ with the use of exogenous terminal deoxynucleotidyl transferase (TdT), commonly defined as the TUNEL assay, have been developed by us. This Chapter describes the variant based on strand breaks labeling with Br-dUTP that is subsequently detected immunocytochemically with Br-dUAb. Compared with other TUNEL variants the Br-dU-labeling assay offers the greatest sensitivity in detecting DNA breaks. Described also are modifications of the protocol that allow one to use other than Br-dUTP fluorochrome-tagged deoxynucleotides to label DNA breaks. Concurrent staining of DNA with propidium or 4',6-diamidino-2-phenylindole (DAPI) and multiparameter analysis of cells by flow- or laser scanning cytometry enables one to correlate induction of apoptosis with the cell cycle phase.

Cytometric assessment of DNA damage by exogenous and endogenous oxidants reports aging-related processes

The ongoing DNA damage caused by reactive oxygen species generated during oxidative metabolism is considered a key factor contributing to cell aging as well as preconditioning cells to neoplastic transformation. We postulated before that a significant fraction of constitutive histone H2AX phosphorylation (CHP) and constitutive activation of ATM (CAA) seen in untreated normal and tumor cells occurs in response to such DNA damage. In the present study, we provide further evidence in support of this postulate. The level of ATM activation and H2AX phosphorylation, detected immunocytochemically, has been monitored in WI-38, A549, and TK6 cells treated with H2O2 as well as growing under conditions known or suspected to affect the level of endogenous oxidants. Thirty- to 60-min exposure of cells to 100 or 200 microM H2O2 led to an increase in the level of H2AX phosphorylation and ATM activation, particularly pronounced (nearly fivefold) in S-phase cells. Cell growth for 24-48 h under hypoxic conditions (3% O2) distinctly lowered the level of CHP and CAA while it had minor effect on cell cycle progression. Treatment (4 h) with 0.1 or 0.3 mM 3-bromopyruvate, an inhibitor of glycolysis and mitochondrial oxidative phosphorylation, reduced the level of CHP (up to fourfold) and also decreased the level of CAA. Growth of WI-38 cells in 2% serum concentration for 48 h led to a 25 and 30% reduction in CHP and CHA, respectively, compared with cells growing in 10% serum. The antioxidant vitamin C (2 mM) reduced CHP and CAA by 20-30% after 24 h of treatment, while the COX-2 inhibitor celecoxib (5 microM) had a minor effect on CHP and CAA, though it decreased the level of H2O2-induced H2AX phosphorylation and ATM activation. In contrast, dichloroacetate known to shift metabolism from anaerobic to oxidative glycolysis through its effect on pyruvate dehydrogenase kinase enhanced the level of CHP and CAA. Our present data and earlier observations strongly support the postulate that a large fraction of CHP and CAA occurs in response to DNA damage caused by metabolically generated oxidants. Cytometric analysis of CHP and CAA provides the means to measure the effectiveness of exogenous factors, which either through lowering aerobic metabolism or neutralizing radicals may protect DNA from such damage.

Cytometry of ATM activation and histone H2AX phosphorylation to estimate extent of DNA damage induced by exogenous agents

This review covers the topic of cytometric assessment of activation of Ataxia telangiectasia mutated (ATM) protein kinase and histone H2AX phosphorylation on Ser139 in response to DNA damage, particularly the damage that involves formation of DNA double-strand breaks. Briefly described are molecular mechanisms associated with activation of ATM and the downstream events that lead to recruitment of DNA repair machinery, engagement of cell cycle checkpoints, and activation of apoptotic pathway. Examples of multiparameter analysis of ATM activation and H2AX phosphorylation vis-a-vis cell cycle phase position and induction of apoptosis that employ flow- and laser scanning-cytometry are provided. They include cells treated with a variety of exogenous genotoxic agents, such as ionizing and UV radiation, DNA topoisomerase I (topotecan) and II (mitoxantrone, etoposide) inhibitors, nitric oxide-releasing aspirin, DNA replication inhibitors (aphidicolin, hydroxyurea, thymidine), and complex environmental carcinogens such as present in tobacco smoke. Also presented is an approach to identify DNA replicating (BrdU incorporating) cells based on selective photolysis of DNA that triggers H2AX phosphorylation. Listed are strategies to distinguish ATM activation and H2AX phosphorylation induced by primary DNA damage by genotoxic agents from those effects triggered by DNA fragmentation that takes place during apoptosis. While we review most published data, recent new findings also are included. Examples of multivariate analysis of ATM activation and H2AX phosphorylation presented in this review illustrate the advantages of cytometric flow- and image-analysis of these events in terms of offering a sensitive and valuable tool in studies of factors that induce DNA damage and/or affect DNA repair and allow one to explore the linkage between DNA damage, cell cycle checkpoints and initiation of apoptosis.

Cytostatic and cytotoxic properties of Amphinase: a novel cytotoxic ribonuclease from Rana pipiens oocytes

Onconase (Onc), is a novel amphibian cytotoxic ribonuclease with antitumor activity, and is currently in a confirmatory phase III clinical trial for the treatment of malignant mesothelioma. It was recently reported that Rana pipiens oocytes contain still another ribonuclease, named Amphinase (Amph). Amph shows 38-40% amino acid sequence identity with onconase, presents as four variants varying between themselves from 87-99% in amino acid sequence identity and has a molecular mass approximately 13,000. In the present study we describe the effects of Amph on growth of several tumor cell lines. All four variants demonstrated cytostatic and cytotoxic activity against human promyelocytic HL-60-, Jurkat T-cell- and U-937 monocytic leukemia cells. The pattern of Amph activity to certain extent resembled that of Onc. Thus, cell proliferation was suppressed at 0.5-10.0 mug/ml (40-80 nM) Amph concentration with distinct accumulation of cells in G(1) phase of the cell cycle. In addition, the cells were undergoing apoptosis, which manifested by DNA fragmentation (presence of "sub-G1" cells, TUNEL-positivity), caspases and serine proteases activation as well as activation of transglutaminase. The cytostatic and cytotoxic effects of Amph required its ribonuclease activity: the enzymatically inactive Amph-2 having histidine at the active site alkylated was ineffective. The effectiveness and cell cycle specificity was generally similar for all four Amph variants and at the equimolar concentrations was somewhat more pronounced than that of Onc. The observed cytostatic and cytotoxic activity of Amph against tumor cell lines suggests that similar to Onc this cytotoxic ribonuclease may have antitumor activity and find an application in clinical oncology.

Constitutive histone H2AX phosphorylation and ATM activation, the reporters of DNA damage by endogenous oxidants

DNA in live cells undergoes continuous oxidative damage caused by metabolically generated endogenous as well as external oxidants and oxidant-inducers. The cumulative oxidative DNA damage is considered the key factor in aging and senescence while the effectiveness of anti-aging agents is often assessed by their ability to reduce such damage. Oxidative DNA damage also preconditions cells to neoplastic transformation. Sensitive reporters of DNA damage, particularly the induction of DNA double-strand breaks (DSBs), are activation of ATM, through its phosphorylation on Ser 1981, and phosphorylation of histone H2AX on Ser 139; the phosphorylated form of H2AX has been named gammaH2AX. We review the observations that constitutive ATM activation (CAA) and H2AX phosphorylation (CHP) take place in normal cells as well in the cells of tumor lines untreated by exogenous genotoxic agents. We postulate that CAA and CHP, which have been measured by multiparameter cytometry in relation to the cell cycle phase, are triggered by oxidative DNA damage. This review also presents the findings on differences in CAA and CHP in various cell lines as well as on the effects of several agents and growth conditions that modulate the extent of these histone and ATM modifications. Specifically, described are effects of the reactive oxygen species (ROS) scavenger N-acetyl-L-cysteine (NAC), and the glutathione synthetase inhibitor buthionine sulfoximine (BSO) as well as suppression of cell metabolism by growth at higher cell density or in the presence of the glucose antimetabolite 2-deoxy-D-glucose. Collectively, the reviewed data indicate that multiparameter cytometric measurement of the level of CHP and/or CAA allows one to estimate the extent of ongoing oxidative DNA damage and to measure the DNA protective-effects of antioxidants or agents that reduce or amplify generation of endogenous ROS.

N-acetylcysteine conjugate of phenethyl isothiocyanate enhances apoptosis in growth-stimulated human lung cells

We previously showed that dietary treatment with the N-acetylcysteine conjugate of phenethyl isothiocyanate (PEITC-NAC) inhibited benzo(a)pyrene-induced lung tumorigenesis in A/J mice, and that tumor inhibition was associated with induction of activator protein-1 (AP-1) activity and stimulation of apoptosis in the lungs of mice. In the present study, we show that PEITC-NAC also induces apoptosis and AP-1 activity in human lung adenocarcinoma A549 cells, and that activation of AP-1 is important in PEITC-NAC induced apoptosis in these cells. PEITC-NAC induced AP-1 binding activity in A549 cells in a dose- and time-dependent manner; peak activity appeared at 10 micromol/L after 24 hours. At that time, flow cytometric analysis showed a sub-G1 peak, indicating that approximately 4.5% of the cells had undergone apoptosis. When wild-type c-jun cDNA was transfected into A549 cells, PEITC-NAC-mediated apoptosis was greatly increased in the c-jun-transfected cells compared with the control vector-transfected cells, based on cell morphology and analysis of DNA fragmentation. Furthermore, cells that were pretreated with 100 nmol/L 12-O-tetradecanoyl phorbol-13-acetate, and then treated with 25 micromol/L PEITC-NAC, underwent enhanced apoptosis compared with cells that were treated with PEITC-NAC alone; cells treated with 12-O-tetradecanoyl phorbol-13-acetate alone showed active cell growth without apoptosis. Bivariate flow cytometric analysis of DNA strand breaks versus DNA content showed that apoptosis induced by PEITC-NAC occurred predominantly in the G2-M phase. These findings suggest that growth-stimulated cells with an elevated basal AP-1 activity, i.e., A549 cells transfected with wild-type c-jun or treated with a tumor promoter, were more sensitive to PEITC-NAC-mediated apoptosis. The observation that PEITC-NAC induces apoptosis predominantly in growth-promoted cells, such as neoplastic cells, suggests a selective mechanism by which PEITC-NAC inhibits lung carcinogenesis.

Cytometric assessment of DNA damage in relation to cell cycle phase and apoptosis

Reviewed are the methods aimed to detect DNA damage in individual cells, estimate its extent and relate it to cell cycle phase and induction of apoptosis. They include the assays that reveal DNA fragmentation during apoptosis, as well as DNA damage induced by genotoxic agents. DNA fragmentation that occurs in the course of apoptosis is detected by selective extraction of degraded DNA. DNA in chromatin of apoptotic cells shows also increased propensity to undergo denaturation. The most common assay of DNA fragmentation relies on labelling DNA strand breaks with fluorochrome-tagged deoxynucleotides. The induction of double-strand DNA breaks (DSBs) by genotoxic agents provides a signal for histone H2AX phosphorylation on Ser139; the phosphorylated H2AX is named gammaH2AX. Also, ATM-kinase is activated through its autophosphorylation on Ser1981. Immunocytochemical detection of gammaH2AX and/or ATM-Ser1981(P) are sensitive probes to reveal induction of DSBs. When used concurrently with analysis of cellular DNA content and caspase-3 activation, they allow one to correlate the extent of DNA damage with the cell cycle phase and with activation of the apoptotic pathway. The presented data reveal cell cycle phase-specific patterns of H2AX phosphorylation and ATM autophosphorylation in response to induction of DSBs by ionizing radiation, topoisomerase I and II inhibitors and carcinogens. Detection of DNA damage in tumour cells during radio- or chemotherapy may provide an early marker predictive of response to treatment.

Cytometric assessment of DNA damage in relation to cell cycle phase and apoptosis

Reviewed are the methods aimed to detect DNA damage in individual cells, estimate its extent and relate it to cell cycle phase and induction of apoptosis. They include the assays that reveal DNA fragmentation during apoptosis, as well as DNA damage induced by genotoxic agents. DNA fragmentation that occurs in the course of apoptosis is detected by selective extraction of degraded DNA. DNA in chromatin of apoptotic cells shows also increased propensity to undergo denaturation. The most common assay of DNA fragmentation relies on labelling DNA strand breaks with fluorochrome-tagged deoxynucleotides. The induction of double-strand DNA breaks (DSBs) by genotoxic agents provides a signal for histone H2AX phosphorylation on Ser139; the phosphorylated H2AX is named gammaH2AX. Also, ATM-kinase is activated through its autophosphorylation on Ser1981. Immunocytochemical detection of gammaH2AX and/or ATM-Ser1981(P) are sensitive probes to reveal induction of DSBs. When used concurrently with analysis of cellular DNA content and caspase-3 activation, they allow one to correlate the extent of DNA damage with the cell cycle phase and with activation of the apoptotic pathway. The presented data reveal cell cycle phase-specific patterns of H2AX phosphorylation and ATM autophosphorylation in response to induction of DSBs by ionizing radiation, topoisomerase I and II inhibitors and carcinogens. Detection of DNA damage in tumour cells during radio- or chemotherapy may provide an early marker predictive of response to treatment.

Degradation of apoptotic cells and fragments in HL-60 suspension cultures after induction of apoptosis by camptothecin and ethanol

Early indicators of apoptosis in mammalian cells are membrane potential breakdown (loss) in mitochondria (MPLM), chromatin condensation, DNA degradation, and phosphatidylserine exposure (PSE) on the outside plasma membrane. One aim of the present study was to determine the kinetics of these characteristics. These changes were measured by flow cytometry using the following methods: membrane potential of mitochondria was analysed using Mito Tracker Green and Red, PSE was analysed using annexin-V-FITC staining simultaneously with propidium iodide (PI) to detect membrane permeability; chromatin condensation was measured using the acid denaturation Acridine Orange (AO) method; DNA degradation was studied by the sub G1 method and the terminal transferase dUTP nick end-labelling (TUNEL) assay (labelling of strand breaks). HL-60 cells were induced to apoptosis by 3% ethanol and 1.5 microM camptothecin (CAM) and the kinetics of the apoptotic cells were measured. The same kinetics were found for chromatin condensation and DNA degradation indicating that these changes appeared at approximately the same time after induction. The MPLM and PSE kinetics showed a considerably later increase indicating that MPLM occurred downstream of DNA degradation and that plasma membrane changes occurred downstream of MPLM. The main aim of the study was to follow the fate of apoptotic cells after the appearance of the initial characteristics. The lifetime of apoptotic cells was studied by chase experiments. The inducing drug was removed after 4 h treatment and the disappearance of apoptoses recorded. An exponential decay was measured with a half life (T(1/2)) of 17.8 h. As a corollary from these experiments, camptothecin was found to induce apoptosis also in G1 and G2 phase cells, however, it took much longer to occur than in S phase cells. Using labelling of the plasma membrane with a fluorescent cell membrane linker, it was possible to show that the majority of apoptotic bodies as well as condensed apoptotic cells contain DNA and membrane. The degradation of these apoptotic bodies follows similar kinetics as those of the condensed apoptotic cells. The membrane remained considerably stable, there was no further loss in the next 7 days, after the first day when the apoptotic characteristics develop. It is concluded that the apoptosis programme is completed within a day and no further steps follow.

Use of fluorescently labeled caspase inhibitors as affinity labels to detect activated caspases

Activation of caspases is the key event of apoptosis and different approaches were developed to assay it. To detect their activation in situ, we applied fluorochrome labeled inhibitors of caspases (FLICA) as affinity labels of active centers of these enzymes. The FLICA ligands are fluorescein or sulforhodamine conjugated peptide-fluoromethyl ketones that covalently bind to enzymatic centers of caspases with 1:1 stoichiometry. The specificity of FLICA towards individual caspases is provided by the peptide sequence of amino acids. Exposure of live cells to FLICA results in uptake of these ligands and their binding to activated caspases; unbound FLICA is removed by cell rinse. Cells labeled with FLICA can be examined by fluorescence microscopy or subjected to quantitative analysis by cytometry. Intracellular binding sites of FLICA are consistent with known localization of caspases. Covalent binding of FLICA allowed us to identify the labeled proteins by immunoblotting: the proteins that bound individual FLICAs had molecular weight between 17 and 22 kDa, which corresponds to large subunits of the caspases. Detection of caspases activation by FLICA can be combined with other markers of apoptosis or cell cycle for multiparametric analysis. Because FLICA are caspase inhibitors they arrest the process of apoptosis preventing cell disintegration. The stathmo-apoptotic method was developed, therefore, that allows one to assay cumulative apoptotic index over long period of time and estimate the rate of cell entry into apoptosis for large cell populations. FLICA offers a rapid and convenient assay of caspases activation and can also be used to accurately estimate the incidence of apoptosis.

Comparison of methods based on annexin-V binding, DNA content or TUNEL for evaluating cell death in HL-60 and adherent MCF-7 cells

HL-60 and MCF-7 cells were treated with 0.15 microM camptothecin (CPT) or with the solvent dimethylsulfoxide (DMSO) for the controls, for 2, 3 and 4 h or for 24, 48 and 72 h, respectively. The apoptotic index (AI) was then evaluated in parallel by the following flow cytometric methods: (1) double staining of unfixed cells with fluoresceinated annexin V and propidium iodide (PI), this after detachment by trypsinization in the case of MCF-7 cultures; (2) prefixation in 70% ethanol, extraction of degraded, low molecular weight DNA with 0.2 M phosphatecitrate buffer and analysis of the DNA content stained with PI; (3) TUNEL, i.e. labelling of DNA strand breaks with biotin-dUTP, followed by staining with streptavidin-fluorescein and counterstaining with PI. In HL-60 cells, the three methods gave similar results for the AI (3-4% in the controls and at 2 h of CPT treatment, and 35-43% at 3 and 4 h after CPT). This indicates that CPT-induced membrane alteration and DNA fragmentation occurred concomitantly in those cells. For MCF-7 cells, CPT-induced apoptosis developed more slowly, the AI, whether based on annexin V or on DNA content, remained unchanged at 24 h, then was increasing to 8% at 48 h and to 25% at 72 h of treatment. In these cells, the TUNEL index did not increase prior to 72 h, and the increase was minor (up to 9% vs. 2-3% in the controls) at 72 h of the treatment. This indicates that in MCF-7 cells DNA strand breaks cannot be effectively labelled, which may be due to inaccessibility of 3'-OH ends in the breaks to exogenous terminal deoxynucleotidyl transferase. The mechanism of endonucleolytic DNA fragmentation thus may be different, depending on the cell type.

Apoptosis -- the story so far

The process of programmed cell death, or apoptosis, has become one of the most intensively studied topics in biological sciences in the last two decades. Apoptosis as a common and universal mechanism of cell death, distinguishable from necrosis, is now a widely accepted concept after the landmark paper by Kerr, Wyllie and Currie in the early seventies [1]. Different components of the death machinery in eukaryotes are discussed in this issue.

Distinct rate and patterns of human CD4+ T-cell depletion in hu-PBL-SCID mice infected with different isolates of the human immunodeficiency virus

The most fundamental question about infection with the human immunodeficiency virus is the mechanism by which infection leads to depletion of CD4+ T lymphocytes, a critical cell type for the regulation of both cellular and humoral immunity. We have studied this issue using a unique small-animal model that is highly susceptible to infection with human immunodeficiency virus. Severe combined immune deficient mice are transplanted with human peripheral blood leukocytes to create hu-PBL-SCID mice, which maintain human T and B lymphocytes and some elements of functional immunity. The hu-PBL-SCID mice respond to human immune deficiency virus infection by the relatively rapid loss of human CD4+ T cells, while other human cells remain unaffected. In this paper, we review evidence showing that different isolates of human immunodeficiency virus-2 cause different rates of CD4+ T-cell depletion and that these rates reflect differences in local spread of infection with lymphoid organs.

Synergistic effect of inhibitors of topoisomerase I and II on chromosome damage and cell killing in cultured Chinese hamster ovary cells

Simultaneous treatment of cultured Chinese hamster ovary cells with the topoisomerase I inhibitor camptothecin and the topoisomerase II inhibitor 4'-(9-acridinylamino)-methanesulfon-m-anisidide results in a clear synergistic effect on both chromosome damage detected at metaphase and loss of colony-forming ability. In contrast, the effect of combined treatment with these topoisomerase inhibitors on sister chromatid exchanges was not significantly different from that expected if the effects were additive. Taken as a whole, these results seem to support the hypothesis that topoisomerase inhibitors can lead to cell death, presumably when DNA replication forks collide with drug-stabilized cleavable complexes. Nevertheless, no evidence of apoptosis was obtained from DNA fragmentation analysis. The possible clinical implications of our findings are discussed.