Characteristics and Possible Role of Bovine Sperm Head-to-Head Agglutination

Although sperm head-to-head agglutination has been reported in many mammalian species, the biological significance of this unique sperm–sperm interaction remains largely unknown. Here, we aimed to examine the functional characteristics of agglutinated bovine sperm to determine the possible role of sperm agglutination in the fertilization process. We initially examined temporal changes to the degree of head-to-head agglutination in culture, and found that bovine sperm agglutinated despite the lack of sperm agglutination inducers in medium. Sperm viability and motility were evaluated by SYBR14/PI and JC-1 staining, respectively, to identify the relationship between sperm agglutination and fertilizing ability. Agglutinated sperm had increased motility, viability, and intact mitochondrial function compared with unagglutinated sperm. Furthermore, we found that heparin significantly increased the percentage of unagglutinated sperm, but did not affect viability of both agglutinated and unagglutinated sperm, suggesting that sperm agglutination dictated the viability. In conclusion, agglutinated bovine sperm maintained viability and motility for a longer time than unagglutinated sperm. Thus, we propose that the head-to-head agglutination is a crucial sperm–sperm interaction to ensure the fertilizing ability of sperm.

Effective activation of antioxidant system by immune-relevant factors reversely correlates with apoptosis of Eisenia andrei coelomocytes

Oxidative stress is harmful to the microbes but also to the host, and may result in bystander damage or death. Because of this, respiratory burst triggered in phagocytes by pathogens is counteracted by production of antioxidative factors. The aim of this work was to examine effectiveness of the latter system in earthworms Eisenia andrei by induction of reactive oxygen species, lipofuscin and phenoloxidase by natural (LPS, zymosan, Micrococus luteus) and synthetic (phorbol ester, PMA) stimulants. The compounds impaired numbers, viability (increased apoptosis) and composition of coelomocytes, and triggered the antioxidant activity of catalase and selenium-dependent glutathione peroxidase. The natural pathogenic compounds, unlike PMA, strongly activated antioxidative responses that diminished cell apoptosis. Moreover, repeated exposure to the same or different pathogenic compounds did not induce respiratory burst exhausted phenotype showing that coelomocytes are constantly at bay to withstand numerous infections. The current study reveals importance and efficiency of the oxidative-antioxidative systems in annelids but also confirms its evolutionary conservatism and complexity even in lower taxa of the animal kingdom.

Influenza A virus protein PB1-F2 translocates into mitochondria via Tom40 channels and impairs innate immunity

Mitochondria contribute to cellular innate immunity against RNA viruses. Mitochondrial-mediated innate immunity is regulated by signalling molecules that are recruited to the mitochondrial membrane, and depends on the mitochondrial inner membrane potential (Δψm). Here we examine the physiological relevance of Δψm and the mitochondrial-associating influenza A viral protein PB1-F2 in innate immunity. When expressed in host cells, PB1-F2 completely translocates into the mitochondrial inner membrane space via Tom40 channels, and its accumulation accelerates mitochondrial fragmentation due to reduced Δψm. By contrast, PB1-F2 variants lacking a C-terminal polypeptide, which is frequently found in low pathogenic subtypes, do not affect mitochondrial function. PB1-F2-mediated attenuation of Δψm suppresses the RIG-I signalling pathway and activation of NLRP3 inflammasomes. PB1-F2 translocation into mitochondria strongly correlates with impaired cellular innate immunity, making this translocation event a potential therapeutic target.

Ganglioside GD2 in reception and transduction of cell death signal in tumor cells

BACKGROUND

Ganglioside GD2 is expressed on plasma membranes of various types of malignant cells. One of the most promising approaches for cancer immunotherapy is the treatment with monoclonal antibodies recognizing tumor-associated markers such as ganglioside GD2. It is considered that major mechanisms of anticancer activity of anti-GD2 antibodies are complement-dependent cytotoxicity and/or antibody-mediated cellular cytotoxicity. At the same time, several studies suggested that anti-GD2 antibodies are capable of direct induction of cell death of number of tumor cell lines, but it has not been investigated in details. In this study we investigated the functional role of ganglioside GD2 in the induction of cell death of multiple tumor cell lines by using GD2-specific monoclonal antibodies.

METHODS

Expression of GD2 on different tumor cell lines was analyzed by flow cytometry using anti-GD2 antibodies. By using HPTLC followed by densitometric analysis we measured the amount of ganglioside GD2 in total ganglioside fractions isolated from tumor cell lines. An MTT assay was performed to assess viability of GD2-positive and -negative tumor cell lines treated with anti-GD2 mAbs. Cross-reactivity of anti-GD2 mAbs with other gangliosides or other surface molecules was investigated by ELISA and flow cytometry. Inhibition of GD2 expression was achieved by using of inhibitor for ganglioside synthesis PDMP and/or siRNA for GM2/GD2 and GD3 synthases.

RESULTS

Anti-GD2 mAbs effectively induced non-classical cell death that combined features of both apoptosis and necrosis in GD2-positive tumor cells and did not affect GD2-negative tumors. Anti-GD2 mAbs directly induced cell death, which included alteration of mitochondrial membrane potential, induction of apoptotic volume decrease and cell membrane permeability. This cytotoxic effect was mediated exclusively by specific binding of anti-GD2 antibodies with ganglioside GD2 but not with other molecules. Moreover, the level of GD2 expression correlated with susceptibility of tumor cell lines to cytotoxic effect of anti-GD2 antibodies.

CONCLUSIONS

Results of this study demonstrate that anti-GD2 antibodies not only passively bind to the surface of tumor cells but also directly induce rapid cell death after the incubation with GD2-positive tumor cells. These results suggest a new role of GD2 as a receptor that actively transduces death signal in malignant cells.

Necroptosis takes place in human immunodeficiency virus type-1 (HIV-1)-infected CD4+ T lymphocytes

Human immunodeficiency virus type 1 (HIV-1) infection is characterized by progressive depletion of CD4+ T lymphocytes and dysfunction of the immune system. The numbers of CD4+ T lymphocytes in the human body are maintained constantly by homeostatic mechanisms that failed during HIV-1 infection, resulting in progressive loss of CD4+ T cells mainly via apoptosis. Recently, a non-apoptotic form of necrotic programmed cell death, named necroptosis, has been investigated in many biological and pathological processes. We then determine whether HIV-1-infected cells also undergo necroptosis. In this report, we demonstrate that HIV-1 not only induces apoptosis, but also mediates necroptosis in the infected primary CD4+ T lymphocytes and CD4+ T-cell lines. Necroptosis-dependent cytopathic effects are significantly increased in HIV-1-infected Jurkat cells that is lack of Fas-associated protein-containing death domain (FADD), indicating that necroptosis occurs as an alternative cell death mechanism in the absence of apoptosis. Unlike apoptosis, necroptosis mainly occurs in HIV-infected cells and spares bystander damage. Treatment with necrostatin-1(Nec-1), a RIP1 inhibitor that specifically blocks the necroptosis pathway, potently restrains HIV-1-induced cytopathic effect and interestingly, inhibits the formation of HIV-induced syncytia in CD4+ T-cell lines. This suggests that syncytia formation is mediated, at least partially, by necroptosis-related processes. Furthermore, we also found that the HIV-1 infection-augmented tumor necrosis factor-alpha (TNF-α) plays a key role in inducing necroptosis and HIV-1 Envelope and Tat proteins function as its co-factors. Taken together,necroptosis can function as an alternative cell death pathway in lieu of apoptosis during HIV-1 infection, thereby also contributing to HIV-1-induced cytopathic effects. Our results reveal that in addition to apoptosis, necroptosis also plays an important role in HIV-1-induced pathogenesis.

Mitochondrial physiology and gene expression analyses reveal metabolic and translational dysregulation in oocyte-induced somatic nuclear reprogramming

While reprogramming a foreign nucleus after somatic cell nuclear transfer (SCNT), the enucleated oocyte (ooplasm) must signal that biomass and cellular requirements changed compared to the nucleus donor cell. Using cells expressing nuclear-encoded but mitochondria-targeted EGFP, a strategy was developed to directly distinguish maternal and embryonic products, testing ooplasm demands on transcriptional and post-transcriptional activity during reprogramming. Specifically, we compared transcript and protein levels for EGFP and other products in pre-implantation SCNT embryos, side-by-side to fertilized controls (embryos produced from the same oocyte pool, by intracytoplasmic injection of sperm containing the EGFP transgene). We observed that while EGFP transcript abundance is not different, protein levels are significantly lower in SCNT compared to fertilized blastocysts. This was not observed for Gapdh and Actb, whose protein reflected mRNA. This transcript-protein relationship indicates that the somatic nucleus can keep up with ooplasm transcript demands, whilst transcription and translation mismatch occurs after SCNT for certain mRNAs. We further detected metabolic disturbances after SCNT, suggesting a place among forces regulating post-transcriptional changes during reprogramming. Our observations ascribe oocyte-induced reprogramming with previously unsuspected regulatory dimensions, in that presence of functional proteins may no longer be inferred from mRNA, but rather depend on post-transcriptional regulation possibly modulated through metabolism.

Combination anti-CD74 (milatuzumab) and anti-CD20 (rituximab) monoclonal antibody therapy has in vitro and in vivo activity in mantle cell lymphoma

Mantle cell lymphoma (MCL) is an aggressive B-cell malignancy with a median survival of 3 years despite chemoimmunotherapy. Rituximab, a chimeric anti-CD20 monoclonal antibody (mAb), has shown only modest activity as single agent in MCL. The humanized mAb milatuzumab targets CD74, an integral membrane protein linked with promotion of B-cell growth and survival, and has shown preclinical activity against B-cell malignancies. Because rituximab and milatuzumab target distinct antigens and potentially signal through different pathways, we explored a preclinical combination strategy in MCL. Treatment of MCL cell lines and primary tumor cells with immobilized milatuzumab and rituximab resulted in rapid cell death, radical oxygen species generation, and loss of mitochondrial membrane potential. Cytoskeletal distrupting agents significantly reduced formation of CD20/CD74 aggregates, cell adhesion, and cell death, highlighting the importance of actin microfilaments in rituximab/milatuzumab-mediated cell death. Cell death was independent of caspase activation, Bcl-2 family proteins or modulation of autophagy. Maximal inhibition of p65 nuclear translocation was observed with combination treatment, indicating disruption of the NF-κB pathway. Significant in vivo therapeutic activity of combination rituximab and milatuzumab was demonstrated in a preclinical model of MCL. These data support clinical evaluation of combination milatuzumab and rituximab therapy in MCL.

The Marsupenaeus japonicus voltage-dependent anion channel (MjVDAC) protein is involved in white spot syndrome virus (WSSV) pathogenesis

Voltage-dependent anion channel (VDAC) proteins abound in the outer membrane of mitochondria. They play an important role in mitochondrial membrane permeabilization (MMP), which can lead to stress-induced cellular apoptosis and necrosis. Several pathogens regulate this MMP in their host cells to benefit their replication cycle, while in other cases, the host can use the same mechanism to combat pathogenesis. In this study, the first shrimp VDAC gene was identified and characterized from Marsupenaeus japonicus (MjVDAC). Its open reading frame (ORF) contained 849 bp encoding 282 amino acids. The deduced MjVDAC protein includes the 4-element eukaryotic porin signature motif, the conserved ATP binding motif (the GLK motif) and a VKAKV-like sequence known in other organisms to be involved in the protein's incorporation in the mitochondrial outer membrane. Tissue tropism analysis indicated that MjVDAC is abundant in the heart, muscle, stomach and pleopod. MjVDAC proteins colocalized with mitochondria in transiently transfected Sf9 cells and in shrimp hemocytes. dsRNA silencing of shrimp VDAC delayed white spot syndrome virus (WSSV) infection by 1 day in different shrimp organs. Taken together, these findings suggest that MjVDAC is likely to be involved in WSSV pathogenesis.

Saikosaponin a inhibits the proliferation and activation of T cells through cell cycle arrest and induction of apoptosis

In the present study, we aimed at examining the immunosuppressive activity of saikosaponin a, a triterpene saponin derived from Bupleurum falcatum L. (Umbelliferae), and the underlying mechanisms. Saikosaponin a significantly inhibited the proliferation and activation of T cells activated by concanavalin A (Con A) in a concentration-dependent manner. Additionally, it potently suppressed Con A-stimulated IL-2, IFN-gamma and TNF-alpha production in mouse T cells. Saikosaponin a also caused G0/G1 arrest of activated T cells through down-regulating the protein levels of CDK6 and Cyclin D3 and up-regulating the protein level of p27(kip). Furthermore, the compound dose-dependently induced apoptosis of Con A-activated T cells rather than those non-activated, as determined by Annexin V/PI staining. Besides, it induced a remarkable collapse of mitochondrial membrane potential and caused significant release of cytochrome c from mitochondria to cytosol. In summary, these results suggest that the G0/G1 arrest as well as the induction of apoptosis via mitochondrial pathway are involved in the immunosuppressive activity of saikosaponin a against activated T cells. This may herald a novel approach for further studies of saikosaponin a as a candidate for the treatment of inflammatory and autoimmune diseases.

[Effect of ryanodine receptor 2 gene silencing on ischemia-reperfusion injury of rat myocardial cells]

OBJECTIVES

To block the synthesis of ryanodine receptor 2 (RyR2) in myocardial cells by RNA interference and to investigate its biological impact on ischemia-reperfusion (I/R) in rat myocardial cells.

METHODS

Rat myocardial cells were isolated and cultured for an I/R model in vitro. RNA interference technique was used to block the synthesis of RyR2 in myocardial cells. Changes of LDH level, apoptosis, RyR2 mRNA expression and cytosolic Ca(2+) concentration were analyzed accordingly.

RESULTS

Myocardial cells after I/R manipolation were severely injuried (LDH leakage, 125 IU/L vs 12 IU/L, P < 0.05), apoptosis (60.1% vs 5.5%, P < 0.05), significant cytosolic Ca(2+) overload (21.2 vs 7.6, P < 0.05) and remarkable mitochondrial membrane potential loss (37.2 vs 85.1, P < 0.05). However, no visible change of RyR2 was observed (20.1 vs 22.7, P > 0.05). Pre-treatment with RyR2 specified siRNA demonstrated suppressed expression of RyR2 (6.8 vs 20.1, P < 0.05), increased mitochondrial membrane potential (55.8 vs 37.2, P < 0.05), attenuated cytosolic Ca(2+) overload (8.6 vs 21.2) and cellular apoptosis (31.2% vs 60.1%, P < 0.05).

CONCLUSION

RyR2 gene silencing enables to protect myocardial cells from I/R injury in vitro.

Mitochondria play a role in the development of non-apoptotic programmed cell death of neutrophils induced by ONO-AE-248

We previously reported that ONO-AE-248, a selective EP3 receptor agonist, has been shown to cause neutrophil death without the typical features of apoptosis and necrosis. However, the mechanism of the neutrophil death is unclear. By using Western blotting, flow cytometry (FACS) and confocal laser scanning microscopy (CLSM), we investigated the cellular signal transduction pathways of the neutrophil death. The research results showed that the neutrophil death induced by ONO-AE-248 did not show the morphologic changes of apoptosis and was not associated with the activity of caspase-3, caspase-8, and phosphorylation of p38-MAPK. However, impairment of mitochondria transmembrane potential has been found during the process of cell death. These findings suggested that ONO-AE-248 induced a non-apoptotic programmed cell death of neutrophils through partially mitochondria signaling transduction pathway.

Enhanced sensitivity to CD95-induced apoptosis in ob/ob mice

Hepatocyte apoptosis was recently described for NASH patients. The pathomechanisms are incompletely understood, but upregulation of the death receptor Fas was detectable on hepatocytes of NASH patients. We analyzed the sensitivity of fatty liver against CD95/Fas-mediated apoptotic cell death by injection of agonistic anti-Fas antibody (Jo2) in obese ob/ob mice and lean control animals. Ob/ob mice died within 12 hrs, whereas control animals survived. Liver enzymes were significantly increased compared to those in control mice (P < 0.001). Histological analysis and also TUNEL assay of liver sections from ob/ob mice exhibited massive liver injury. Activity of caspase 3 was significantly more enhanced in livers of ob/ob mice after Jo2 challenge. The increased sensitivity was confirmed in vitro by using ob/ob-derived primary hepatocytes. CD95 expression was similar in ob/ob and control mice. However, hepatocytes from ob/ob mice revealed a decreased mitochondrial membrane potential, suggesting that mitochondria play a potential role in this increased susceptibility.

Aspirin-Triggered Lipoxins Override the Apoptosis-Delaying Action of Serum Amyloid A in Human Neutrophils: A Novel Mechanism for Resolution of Inflammation

Elevated plasma levels of the acute-phase reactant serum amyloid A (SAA) have been used as a marker and predictor of inflammatory diseases. SAA regulates leukocyte activation; however, it is not known whether it also modulates neutrophil apoptosis, which is critical to the optimal expression and resolution of inflammation. Culture of human neutrophils with SAA (0.1-20 microg/ml) markedly prolonged neutrophil longevity by delaying constitutive apoptosis. SAA evoked concurrent activation of the ERK and PI3K/Akt signaling pathways, leading to phosphorylation of BAD at Ser(112) and Ser(136), respectively, and to prevention of collapse of mitochondrial transmembrane potential, cytochrome c release, and caspase-3 activation. These actions were abrogated by pharmacological inhibition of the formyl peptide receptor, ERK or PI3K. Furthermore, aspirin-triggered 15-epi-lipoxin A(4) (15-epi-LXA(4)) and its stable analog 15-epi-16-p-fluorophenoxy-LXA(4), which binds to the same receptor as SAA, effectively overrode the antiapoptosis signal from SAA even when neutrophils were treated with 15-epi-LXA(4) at either 1 or 4 h postculture with SAA. 15-Epi-LXA(4) itself did not affect neutrophil survival and apoptosis. Our results indicate that SAA at clinically relevant concentrations promotes neutrophil survival by suppressing the apoptotic machinery, an effect that can be opposed by 15-epi-LXA(4). The opposing actions of SAA and aspirin-triggered 15-epi-LXA(4) may contribute to the local regulation of exacerbation and resolution of inflammation, respectively.

Heat shock protein 75 (TRAP1) antagonizes reactive oxygen species generation and protects cells from granzyme M-mediated apoptosis

Natural killer (NK) cells play an important role in innate immunity against virally infected or transformed cells as the first defense line. Granzyme M (GzmM) is an orphan granzyme that is constitutively highly expressed in NK cells and is consistent with NK cell-mediated cytolysis. We recently demonstrated that GzmM induces caspase-dependent apoptosis with DNA fragmentation through direct cleavage of inhibitor of caspase-activated DNase (ICAD). However, the molecular mechanisms for GzmM-induced apoptosis are unclear. We found GzmM causes mitochondrial swelling and loss of mitochondrial transmembrane potential. Moreover, GzmM initiates reactive oxygen species (ROS) generation and cytochrome c release. Heat shock protein 75 (HSP75, also known as TRAP1) acts as an antagonist of ROS and protects cells from GzmM-mediated apoptosis. GzmM cleaves TRAP1 and abolishes its antagonistic function to ROS, resulting in ROS accumulation. Silencing TRAP1 through RNA interference increases ROS accumulation, whereas TRAP1 overexpression attenuates ROS production. ROS accumulation is in accordance with the release of cytochrome c from mitochondria and enhances GzmM-mediated apoptosis.

Ligation of centrocyte/centroblast marker 1 on Epstein-Barr virus--transformed B lymphocytes induces cell death in a reactive oxygen species--dependent manner

After primary infection of B cells with Epstein-Barr virus (EBV), infected B cells express several viral homologs of human genes that promote activation (LMP1 and CD40) or survival (BHRF and BCL2). EBV-infected B cells also express germinal center phenotype markers, such as CD77, PNA, CD95, and CD38. This transformation of B cells by EBV infection resembles normal B-cell activation and differentiation arising in the germinal center. In the present study, we found that EBV-transformed B cells expressed centrocyte/centroblast marker 1 (CM1), a possible marker of GC B cells and an inducer of their apoptosis. Moreover, ligation of CM1 on EBV-transformed B cells by immobilized anti-CM1 monoclonal antibody induced cell death. The ligation of CM1 immediately increased the generation of intracellular reactive oxygen species (ROS) and disrupted the mitochondrial membrane potential. Pretreatment with N-acetyl cystein (an ROS inhibitor) almost completely blocked this cell death, but Z-VAD-fmk (a caspase inhibitor) did not. We further investigated whether apoptosis-inducing factor (AIF) and endonuclease G (EndoG), which are both related to caspase-independent cell death, would be translocated to the nucleus during the ligation of CM1. We found that AIF and EndoG were released to the cytosplam but not translocated to the nucleus. Moreover, cytochalasin D, a cytoskeleton disruptor, rescued the cells from CM1-mediated cell death and blocked ROS generation. Therefore, it is conceivable that CM1 signaling might provoke cytoskeleton polymerization and trigger ROS generation. Taking these observations together, we conclude that the ligation of CM1 on EBV-transformed B cells can cause cell death via the ROS produced by F-actin polymerization in a caspase-independent manner, although this cell death might be unrelated to AIF and EndoG release from the mitochondria.

Interleukin-10 induces apoptosis in developing mast cells and macrophages

Interleukin (IL)-10 is a potent immunoregulatory cytokine capable of inhibiting the inflammatory response. As mast cells and macrophages are central effectors of inflammation, we investigated the effects of IL-10 on mast cell and macrophage development from mouse bone marrow progenitors. Bone marrow cells were cultured in IL-3 + stem cell factor (SCF), giving rise to mixed populations of mast cells and macrophages. The addition of IL-10 greatly decreased the expansion of bone marrow progenitor cells through a mechanism requiring signal tranducer and activator of transcription-3 expression. The inhibitory effects were a result of the induction of apoptosis, which occurred with caspase-3 activation and reduced mitochondrial membrane potential. Supporting a role for the mitochondrion, bone marrow cells from p53-deficient or Bcl-2 transgenic mice were partly resistant to the effects of IL-10. Further, IL-10 decreased Kit receptor expression and inhibited survival signaling by SCF or IL-3. These data indicate that IL-10 induces an intrinsic, mitochondrial apoptosis cascade in developing mast cells and macrophages through mechanisms involving blockade of growth factor receptor function. The ability of IL-10 to inhibit survival could support immune homeostasis by dampening inflammatory responses and preventing chronic inflammation.