The role of the macrophage in apoptosis: hunter, gatherer, and regulator

Effective-mononuclear cell (E-MNC) therapy alleviates salivary gland damage by suppressing lymphocyte infiltration in Sjögren-like disease

Introduction: Sjögren syndrome (SS) is an autoimmune disease characterized by salivary gland (SG) destruction leading to loss of secretory function. A hallmark of the disease is the presence of focal lymphocyte infiltration in SGs, which is predominantly composed of T cells. Currently, there are no effective therapies for SS. Recently, we demonstrated that a newly developed therapy using effective-mononuclear cells (E-MNCs) improved the function of radiation-injured SGs due to anti-inflammatory and regenerative effects. In this study, we investigated whether E-MNCs could ameliorate disease development in non-obese diabetic (NOD) mice as a model for primary SS. Methods: E-MNCs were obtained from peripheral blood mononuclear cells (PBMNCs) cultured for 7 days in serum-free medium supplemented with five specific recombinant proteins (5G culture). The anti-inflammatory characteristics of E-MNCs were then analyzed using a co-culture system with CD3/CD28-stimulated PBMNCs. To evaluate the therapeutic efficacy of E-MNCs against SS onset, E-MNCs were transplanted into SGs of NOD mice. Subsequently, saliva secretion, histological, and gene expression analyses of harvested SG were performed to investigate if E-MNCs therapy delays disease development. Results: First, we characterized that both human and mouse E-MNCs exhibited induction of CD11b/CD206-positive cells (M2 macrophages) and that human E-MNCs could inhibit inflammatory gene expressions in CD3/CD28- stimulated PBMNCs. Further analyses revealed that Msr1-and galectin3-positive macrophages (immunomodulatory M2c phenotype) were specifically induced in E-MNCs of both NOD and MHC class I-matched mice. Transplanted E-MNCs induced M2 macrophages and reduced the expression of T cell-derived chemokine-related and inflammatory genes in SG tissue of NOD mice at SS-onset. Then, E-MNCs suppressed the infiltration of CD4-positive T cells and facilitated the maintenance of saliva secretion for up to 12 weeks after E-MNC administration. Discussion: Thus, the immunomodulatory actions of E-MNCs could be part of a therapeutic strategy targeting the early stage of primary SS.

Interaction of Graphene Oxide Modified with Linear and Branched PEG with Monocytes Isolated from Human Blood

Multiple graphene-based therapeutics have recently been developed, however potential risks related to the interaction between nanomaterials and immune cells are still poorly understood. Therefore, studying the impact of graphene oxide on various populations of immune cells is of importance. In this work, we aimed to investigate the effects of PEGylated graphene oxide on monocytes isolated from human peripheral blood. Graphene oxide nanoparticles with lateral sizes of 100–200 nm and 1–5 μm were modified with linear and branched PEG (GO-PEG). Size, elemental composition, and structure of the resulting nanoparticles were characterized. We confirmed that PEG was successfully attached to the graphene oxide surface. The influence of GO-PEG on the production of reactive oxygen species (ROS), cytokines, phagocytosis, and viability of monocytes was studied. Uptake of GO-PEG by monocytes depends on PEG structure (linear or branched). Branched PEG decreased the number of GO-PEG nanoparticles per monocyte. The viability of monocytes was not altered by co-cultivation with GO-PEG. GO-PEG decreased the phagocytosis of Escherichia coli in a concentration-dependent manner. ROS formation by monocytes was determined by measuring luminol-, lucigenin-, and dichlorodihydrofluorescein-dependent luminescence. GO-PEG decreased luminescent signal probably due to inactivation of ROS, such as hydroxyl and superoxide radicals. Some types of GO-PEG stimulated secretion of IL-10 by monocytes, but this effect did not correlate with their size or PEG structure.

The pan-caspase inhibitor Emricasan (IDN-6556) decreases liver injury and fibrosis in a murine model of non-alcoholic steatohepatitis

BACKGROUND & AIMS

Hepatocyte apoptosis, the hallmark of non-alcoholic steatohepatitis (NASH) contributes to liver injury and fibrosis. Although, both the intrinsic and extrinsic apoptotic pathways are involved in the pathogenesis of NASH, the final common step of apoptosis is executed by a family of cysteine-proteases termed caspases. Thus, our aim was to ascertain if administration of Emricasan, a pan-caspase inhibitor, ameliorates liver injury and fibrosis in a murine model of NASH.

METHODS

C57/BL6J-mice were fed regular chow or high fat diet (HFD) for 20 weeks. All mice were treated with vehicle or Emricasan.

RESULTS

Mice fed a HFD diet demonstrate a five-fold increase in hepatocyte apoptosis by the TUNEL assay and a 1.5-fold and 1.3-fold increase in caspase-3 and-8 activities respectively; this increase in apoptosis was substantially attenuated in mice fed a HFD treated with Emricasan (HFD-Em). Likewise, liver injury and inflammation were reduced in mice fed HFD-Em as compare to HFD by measuring serum aspartate aminotransferase and alanine aminotransferase levels, NAS histological score and IL 1-β, TNF-α, monocyte chemoattractant protein (MCP-1) and C-X-C chemokine ligand-2 (CXCL2) quantitative reverse-transcription polymerase chain reaction (qPCR). These differences could not be attributed to differences in hepatic steatosis as liver triglycerides content were similar in both HFD groups. Hepatic fibrosis was reduced by Emricasan in HFD animals by decreasing αSMA (a marker for hepatic stellate cell activation), fibrosis score, Sirius red staining, hydroxyproline liver content and profibrogenic cytokines by qPCR.

CONCLUSION

In conclusion, these data demonstrate that in a murine model of NASH, liver injury and fibrosis are suppressed by inhibiting hepatocytes apoptosis and suggests that Emricasan may be an attractive antifibrotic therapy in NASH.

Loading of nuclear autoantigens prototypically recognized by systemic lupus erythematosus sera into late apoptotic vesicles requires intact microtubules and myosin light chain kinase activity

Most cases of systemic lupus erythematosus (SLE) are characterized by an impaired clearance of apoptotic cells in various tissues. Non-cleared apoptotic waste is considered an immunogen driving the autoimmune response in patients with SLE. During the execution of apoptosis, membrane blebs are formed and filled with cellular components. Here, we evaluate the cytoskeletal pathway(s) responsible for the loading of SLE prototypic nuclear autoantigens into the apoptotic cell-derived membranous vesicles (ACMV) generated during late phases of apoptosis. HeLa cells expressing a fusion protein of histone H2B with green fluorescent protein (GFP) were irradiated with ultraviolet (UV)-B to induce apoptosis. The appearance and trafficking of chromatin-derived material was monitored by fluorescence microscopy. Specific inhibitors of cytoskeletal pathways were employed to identify the motile elements involved in translocation and trafficking of the nuclear components. We observed that immediately after their appearance the ACMV did not contain histone H2B(GFP) ; in this phase the fluorescence was contained in the nuclear remnants and the cytoplasm. Within consecutive minutes the ACMV were loaded with chromatin-derived material, whereas the loading of simultaneously created ACMV with histone H2B(GFP) was not uniform. Some ACMV were preferentially filled and, consequently, showed a remarkably higher histone H2B(GFP) accumulation. Inhibitors of the cytoskeleton revealed that functional microtubules and myosin light chain kinase are required for nuclear shrinkage and loading of nuclear material into the ACMV, respectively.

Cyclooxygenase-2 promotes hepatocellular apoptosis by interacting with TNF-α and IL-6 in the pathogenesis of nonalcoholic steatohepatitis in rats

BACKGROUND AND PURPOSE

The underlying mechanisms of nonalcoholic steatohepatitis (NASH) are poorly understood, and little is known about hepatocellular apoptosis in NASH. Cyclooxygenase (COX)-2, the key enzyme in eicosanoid metabolism, is highly expressed in NASH. COX-2 can also regulate the release of mediators of inflammation, such as tumor necrosis factor (TNF)-α and interleukin (IL)-6. The aim of our study was to evaluate the effects of COX-2 on hepatocellular apoptosis and the mechanism of the action in the pathogenesis of NASH in rats.

METHODS

Sprague-Dawley rats were fed a high-fat diet (HFD) or standard diet for 8 and 12 weeks. COX-2 and cytokines expression in hepatic tissue and TNF-α and IL-6 levels in serum were measured at 8 and 12 weeks. Moreover, celecoxib (10 mg/kg body weight once a day) was administered to rats for 4 weeks to inhibit the expression of COX-2. Liver pathology was assessed by hematoxylin and eosin (H&E) stain and electron microscopy. Hepatocyte apoptosis was evaluated by TUNEL staining.

RESULTS

COX-2 messenger RNA and protein were highly expressed in livers of HFD rats and were correlated with the severity of steatohepatitis (R = 0.82, p < 0.01). COX-2 upregulation was preceded by increases in TNF-α and IL-6. The level of hepatocellular apoptosis was significantly higher in HFD rats than in the control rats. The hepatocellular apoptosis was suppressed by the inhibition of COX-2.

CONCLUSIONS

COX-2 may promote hepatocellular apoptosis by interacting with TNF-α and IL-6 in NASH in rats.

Baicalein selectively induces apoptosis in activated lymphocytes and ameliorates concanavalin a-induced hepatitis in mice

Background

Insufficient apoptosis in activated lymphocytes contributes to the development of autoimmune hepatitis (AIH). Baicalein (BE), a flavonoid originally isolated from the root of Scutellaria baicalensis Georgi, possesses anti-inflammatory properties. However, whether BE can selectively induce apoptosis in activated lymphocytes and exert therapeutic effect on AIH has not been studied.

Methodology/Principal Findings

The pro-apoptotic properties of BE were evaluated in vitro on different types of immune cells, and in vivo effects of BE were examined in a murine model of Concanavalin A (Con A)-induced hepatitis. In vitro treatment with BE resulted in a higher increase in the level of apoptosis in Con A-stimulated murine splenocytes, Con A-stimulated CD3⁺ splenocytes, lipopolysaccharide (LPS)-stimulated CD19⁺ splenocytes, and phorbol 12-myristate 13-acetate/ionomycin-stimulated Jurkat T cells, compared with that in unstimulated naïve ones. Murine bone marrow-derived dentritic cells, peritoneal macrophages, and RAW264.7 cells, either stimulated with LPS or unstimulated, were all insensitive to the BE-induced apoptosis. BE treatment also led to a loss of mitochondrial membrane potential, an increase of cytochrome c release from mitochondria to the cytosol, a decrease in the ratio of Bcl-2/Bax, and activation of caspase-9,-3 in Con A-stimulated CD3⁺ splenocytes and LPS-stimulated CD19⁺ splenocytes, while showing no impact on Fas/FasL expressions and caspase-8 activation. In vivo administration of BE alleviated Con A-induced liver injury, suppressed serum level of TNF-α and IFN-γ, and reduced liver infiltration of mononuclear cells (MNCs). Furthermore, BE treatment increased the incidences of apoptosis in liver-infiltrating MNCs and splenocytes, as well as in CD3⁺ and CD19⁺ splenocytes. When liver MNCs and splenocytes from BE-treated mice were cultured in vitro for 24 h, they exhibited marked increase in apoptosis compared to vehicle-treated control.

Conclusions/Significance

The present study demonstrates the ability of BE to promote apoptosis in activated lymphocytes through mitochondrial pathway and its potential use in the treatment of AIH.

Effect of culture conditions on the phenotype of THP-1 monocyte cell line

PROBLEM

Macrophage function has many implications in a variety of diseases. Understanding their biology becomes imperative when trying to elucidate immune cell interactions with their environment, and in vitro cell lines allow researchers to manipulate these interactions. A common cell line used is THP-1, a promyeloid cell line suggestive to outside factors, and therefore sensitive to culture conditions. In this study, we describe how culture conditions can alter THP-1 morphology and in turn affect their response to differentiation stimuli.

METHOD OF STUDY

THP-1 cells were cultured in two conditions and treated with phorbol 12-myristate 13-acetate (PMA) or MCSF. CD14 surface expression was determined by flow cytometry and cytokine/chemokine production determined by multiplex analysis.

RESULTS

Culture conditions of THP-1 affect their response to PMA. Highly confluent THP-1 cells differentiate into a heterogeneous population responsive to PMA as seen by an increase in CD14 expression. However, these cells, cultured in low confluence, remain as a homogenous population and do not gain CD14. Additionally, there are major differences in the constitutive cytokine profile.

CONCLUSION

We demonstrate that the culture conditions of THP-1 cells can alter their response PMA. This suggests that culture techniques may account for the discrepancy in the literature of both basal THP-1 phenotype and their response to PMA.

Mechanisms of disease progression in NASH: new paradigms

The incidence of nonalcoholic fatty liver disease is increasing at an astonishing rate in the US population. Although only a small proportion of these patients develop steatohepatitis (NASH), those who do have a greater likelihood of developing end-stage liver disease and complications. Research on liver fibrosis and NASH progression shows that hedgehog (Hh) is reactivated after liver injury to assist in liver repair and regeneration. When the process of tissue repair and regeneration is prolonged or when Hh ligand and related genes are aberrantly regulated and excessive, tissue repair goes awry and NASH progresses to cirrhosis and hepatocellular carcinoma.

Dendritic cells and their role in tumor immunosurveillance

Dendritic cells (DCs) comprise a heterogeneous population of cells that play a key role in initiating, directing and regulating adaptive immune responses, including those critically involved in tumor immunosurveillance. As a riposte to the central role of DCs in the generation of antitumor immune responses, tumors have developed various mechanisms which impair the immunostimulatory functions of DCs or even instruct them to actively contribute to tumor growth and progression. In the first part of this review we discuss general aspects of DC biology, including their origin, subtypes, immature and mature states, and functional plasticity which ensures a delicate balance between active immune response and immune tolerance. In the second part of the review we discuss the complex interactions between DCs and the tumor microenvironment, and point out the challenges faced by DCs during the recognition of tumor Ags. We also discuss the role of DCs in tumor angiogenesis and vasculogenesis.

Toxins-useful biochemical tools for leukocyte research

Leukocytes are a heterogeneous group of cells that display differences in anatomic localization, cell surface phenotype, and function. The different subtypes include e.g., granulocytes, monocytes, dendritic cells, T cells, B cells and NK cells. These different cell types represent the cellular component of innate and adaptive immunity. Using certain toxins such as pertussis toxin, cholera toxin or clostridium difficile toxin, the regulatory functions of Gα_i, Gαs and small GTPases of the Rho family in leukocytes have been reported. A summary of these reports is discussed in this review.

Apoptotic and necrotic cells as sentinels of local tissue stress and inflammation: response pathways initiated in nearby viable cells

Virtually all cells in the body have the capacity to recognize and respond to dead cells. Viable cells discriminate apo from nec targets via distinct cell surface receptors. Engagement of these receptors induces "recognition-dependent" signaling events in viable responding cells that differ for apo vs. nec targets. Although "engulfment-dependent" signaling events also contribute to the response by viable cells, these events do not differ for apo vs. nec targets. While many signaling events are conserved across diverse cell lineages, other signaling events, especially those involving Akt, demonstrate lineage-specific variation. Whereas apo targets activate Akt in MPhi, they inhibit Akt in kidney epithelial cells. Differences in the responses to dead targets by viable migratory cells, such as MPhi, and viable fixed cells, such as kidney epithelial cells, permit cell-specific adaptations to local environmental change or stress. We propose that dead cells (apo and nec) act as sentinels to alert nearby viable cells to local environmental change or stress.

Apoptosis and cytokines in non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD), one of the commonest causes of chronic liver disease in the United States, represents several overlapping clinicopathological states, ranging from simple steatosis to non-alcoholic steatohepatitis (NASH). Although dysregulated lipid accumulation occurs across the spectrum of NAFLD, features of liver cell injury, such as hepatocyte ballooning, cytoskeletal changes (Mallory-Denk bodies), and hepatocyte apoptosis, occur predominantly in NASH and distinguish NASH from simple steatosis. Indeed, NASH is a more serious form of liver damage because cirrhosis and hepatocellular carcinoma are potential outcomes of NASH. Meanwhile, cirrhosis and hepatocellular carcinoma rarely occur in individuals with simple steatosis. Hepatic injury and apoptosis that occur in adults are often dysregulated and accompanied by the accumulation of immune cells, which produce cytokines and growth factors that drive chronic inflammation and may result in fibrosis. This article summarizes the process of apoptosis and roles of putative cytokines in progressive NAFLD.

In vivo99mTc-HYNIC-annexin V imaging of early tumor apoptosis in mice after single dose irradiation

Background

Apoptosis is a major mode of hematological tumor death after radiation. Early detection of apoptosis may be beneficial for cancer adaptive treatment. ^99mTc-HYNIC-annexinV has been reported as a promising agent for in vivo apoptosis imaging. The purpose of this study is to evaluate the feasibility of in vivo^99mTc-HYNIC-annexinV imaging of radiation- induced apoptosis, and to investigate its correlation with radiosensitivity.

Methods

Ten days after inoculation of tumor cells in the right upper limbs, the mice were randomly divided into two groups. The imaging group (4 mice each level, 4 dose levels) was injected with 4-8 MBq ^99mTc-HYNIC-annexinV 24 hours after irradiation and imaged 1 hr post-injection, and the mice were sacrificed immediately after imaging for biodistribution analysis of annexin V. The observation group (4 mice each level, 2 dose levels) was only observed for tumor regression post-radiation. The number of apoptotic cells in a tumor was estimated with TUNEL assay.

Results

The ^99mTc-HYNIC-annexin V uptake in E14 lymphoma significantly increased as the radiation dose escalated from 0 to 8 Gy, and significantly correlated with the number of TUNEL-positive cells (r = 0.892, P < 0.001). The Annexin-V uptake and the number of TUNEL-positive cells in El4 lymphoma were significantly greater than those in S180 sarcoma. With 8 Gy, S180 sarcoma tumor showed scanty apoptosis and less shrinkage while El4 lymphoma showed remarkable apoptosis and complete remission.

Conclusion

⁹⁹mTc-HYNIC-annexinV in vivo imaging is a feasible method to detect early radiation-induced apoptosis in different tumors, and might be predictive for radiation sensitivity.

The phagocytes: neutrophils and monocytes

The production and deployment of phagocytes are central functions of the hematopoietic system. In the 1950s, radioisotopic studies demonstrated the high production rate and short lifespan of neutrophils and allowed researchers to follow the monocytes as they moved from the marrow through the blood to become tissue macrophages, histiocytes, and dendritic cells. Subsequently, the discovery of the colony-stimulating factors greatly improved understanding the regulation of phagocyte production. The discovery of the microbicidal myeloperoxidase-H2O2-halide system and the importance of NADPH oxidase to the generation of H2O2 also stimulated intense interest in phagocyte disorders. More recent research has focused on membrane receptors and the dynamics of the responses of phagocytes to external factors including immunoglobulins, complement proteins, cytokines, chemokines, integrins, and selectins. Phagocytes express toll-like receptors that aid in the clearance of a wide range of microbial pathogens and their products. Phagocytes are also important sources of pro- and anti-inflammatory cytokines, thus participating in host defenses through a variety of mechanisms. Over the last 50 years, many genetic and molecular disorders of phagocytes have been identified, leading to improved diagnosis and treatment of conditions which predispose patients to the risk of recurrent fevers and infectious diseases.

Autoantigens are translocated into small apoptotic bodies during early stages of apoptosis

A dysregulation of apoptosis or an ineffective clearance of apoptotic material is suspected to be involved in the pathogenesis of systemic lupus erythematodes. Subcellular fragments such as apoptotic bodies (ABs) have been recognized as modulators of intercellular communication and immune function. In this context, we have been interested whether nuclear and cytoplasmic antigens are relocated into ABs. In the present study, we characterized ABs isolated from apoptozing lymphoblasts. We found an accumulation of the linker-histone (histone 1) as well as the core-histones (histone 2A, histone 2B, histone 3, histone 4) in ABs. Further, they contained DNA, RNA and the ribonuclear protein La/SSB. Proteins such as cytochrome c, HSP 70, prohibitin, p53, nuclear matrix antigen or lamin B were excluded from ABs. The content of ABs differed from that observed in membrane microparticles isolated from viable cells. Formation of ABs occurred early during apoptosis. It was observed before DNA-degradation or phosphatidylserine exposure was detected. ABs were engulfed by monocyte-derived phagocytes. These findings suggest that immunogenic molecules are actively translocated into ABs followed by a rapid engulfment of the latter by environmental phagocytes. In autoimmune diseases, a defect in the clearance of ABs or AB formation may contribute to the development of autoimmunity.

Roles of the innate immune system in mammary gland remodeling during involution

Mammary gland involution is a period of intensive tissue remodeling. Over the course of a relatively brief period, a large proportion of the mammary gland epithelium undergoes programmed cell death and is removed by phagocytes. In addition, the gland is cleared of residual milk fat globules as well as milk and adipocytes become the predominant cell type. The role of the immune system in this process has not been clearly defined. Professional phagocytes derived from the immune system can participate in the clearance of apoptotic and autophagic cells, the removal of residual milk components, and the prevention of mastitis during mammary gland involution. However, many of these functions can also be performed by non-professional phagocytes (e.g. mammary epithelial cells). This review will discuss the evidence that supports a role for innate immune cells in mammary gland remodeling during involution.

NOD mice exocrinopathy: towards a neuroimmune link

Sjogren's syndrome (SS) is a chronic autoimmune disorder of exocrine glands characterized as an autoimmune exocrinopathy and more specifically as an autoimmune epithelitis. An impaired balance of neuroimmune interactions mediated by vasoactive intestinal peptide (VIP) in the target organ at early stages of disease is explored by means of the nonobese diabetic (NOD) mouse model of SS. We have previously described a reduced salivary secretion and signaling upon VIP stimulation. The effect reflected a differential regulation of the neural isoform of nitric oxide synthase by calcium calmodulin kinase II and occurred prior to the appearance of detectable levels of cytokines in NOD glands. VIP acting on NOD macrophages treated with lipopolysaccharide promoted anti-inflammatory effects by inhibiting nitric oxide synthase induction as well as IL-12 and TNF-alpha production, while stimulating IL-10. Here we present evidence on the ability of apoptotic acinar cells from submandibular glands of NOD mice to stimulate nitric oxide in both peritoneal and glandular macrophage pools to a similar extent as lipopolysaccharide + IFN-gamma. VIP was not effective to prevent nitrite accumulation and modestly increased IL-10 levels in macrophages coincubated with acinar cells. An enhanced nitrite response of NOD glandular macrophages in basal and stimulated conditions compared to peritoneal cells is also shown.

Human macrophages rescue myoblasts and myotubes from apoptosis through a set of adhesion molecular systems

The mechanisms underlying stromal cell supportive functions are incompletely understood but probably implicate a mixture of cytokines, matrix components and cell adhesion molecules. Skeletal muscle uses recruited macrophages to support post-injury regeneration. We and others have previously shown that macrophages secrete mitogenic factors for myogenic cells. Here, we focused on macrophage-elicited survival signals. We demonstrated that: (1) macrophage influx is temporally correlated with the disappearance of TUNEL-positive apoptotic myogenic cells during post-injury muscle regeneration in mice; (2) direct cell-cell contacts between human macrophages and myogenic cells rescue myogenic cells from apoptosis, as assessed by decreased annexin V labelling and caspase-3 activity, and by increased DIOC-6 staining, Bcl-2 expression and phosphorylation of Akt and ERK1/2 survival pathways; (3) four pro-survival cell-cell adhesion molecular systems detected by DNA macroarray are expressed by macrophages and myogenic cells in vitro and in vivo - VCAM-1-VLA-4, ICAM-1-LFA-1, PECAM-1-PECAM-1 and CX3CL1-CX3CR1; (4) macrophages deliver anti-apoptotic signals through all four adhesion systems, as assessed by functional analyses with blocking antibodies; and (5) macrophages more strongly rescue differentiated myotubes, which must achieve adhesion-induced stabilisation of their structure to survive. Macrophages could secure these cells until they establish final association with the matrix.

Gout: Update on Some Pathogenic and Clinical Aspects

Pathogenesis of gout inflammation remains unknown, but recent advances have been made with respect to initiation, amplification, and self-limitation. Direct crystal-cell membrane contact leads to cell activation, involving membrane-associated molecules. Resolution of acute gout inflammation is a mechanism that is controlled by monocyte-macrophage switch, which results in the loss of cytokine production capability and, conversely, the ability to produce anti-inflammatory molecules. MRI and ultrasound findings provide preliminary data that are not yet used in clinical trials. Diagnosis and management recommendations are missing, but this gap will be filled soon with the upcoming European League Against Rheumatism Task Force's recommendations on gout.

Untargeted effects of ionizing radiation: implications for radiation pathology

The dogma that genetic alterations are restricted to directly irradiated cells has been challenged by observations in which effects of ionizing radiation, characteristically associated with the consequences of energy deposition in the cell nucleus, arise in non-irradiated cells. These, so called, untargeted effects are demonstrated in cells that have received damaging signals produced by irradiated cells (radiation-induced bystander effects) or that are the descendants of irradiated cells (radiation-induced genomic instability). Radiation-induced genomic instability is characterized by a number of delayed adverse responses including chromosomal abnormalities, gene mutations and cell death. Similar effects, as well as responses that may be regarded as protective, have been attributed to bystander mechanisms. Whilst the majority of studies to date have used in vitro systems, some adverse non-targeted effects have been demonstrated in vivo. However, at least for haemopoietic tissues, radiation-induced genomic instability in vivo may not necessarily be a reflection of genomically unstable cells. Rather the damage may reflect responses to ongoing production of damaging signals; i.e. bystander responses, but not in the sense used to describe the rapidly induced effects resulting from direct interaction of irradiated and non-irradiated cells. The findings are consistent with a delayed and long-lived tissue reaction to radiation injury characteristic of an inflammatory response with the potential for persisting bystander-mediated damage. An important implication of the findings is that contrary to conventional radiobiological dogma and interpretation of epidemiologically-based risk estimates, ionizing radiation may contribute to malignancy and particularly childhood leukaemia by promoting initiated cells rather than being the initiating agent. Untargeted mechanisms may also contribute to other pathological consequences.

The role of apoptosis in the regulation of trophoblast survival and differentiation during pregnancy

Apoptosis is important for normal placental development, but it may also be involved in the pathophysiology of pregnancy-related diseases. Normal placental development is dependent upon the differentiation and invasion of the trophoblast, the main cellular component of the placenta. Trophoblast apoptosis increases in normal placentas as gestation proceeds, and a greater incidence of trophoblast apoptosis has been observed in pregnancies complicated by preeclampsia or intrauterine growth retardation (IUGR). In response to different stimuli, apoptosis may be initiated extrinsically by the death receptor pathway or intrinsically by the mitochondrial pathway. The central executioners of apoptosis are the caspases, which cleave numerous vital cellular proteins to affect the apoptotic cascade. By inhibiting caspase activation, several endogenous inhibitors, including flice-like inhibitory proteins (FLIPs), inhibitors of apoptosis (IAPs), and antiapoptotic Bcl-2 family members, can prevent further propagation of the death signal. Macrophages present at the maternal-fetal interface may also contribute to trophoblast survival by removing apoptotic cells and producing cytokines and growth factors, which influence the progression of the apoptotic cascade. This review focuses on the role of apoptosis in trophoblast development and differentiation, the molecular mechanisms by which normal trophoblast apoptosis can occur, and how it is regulated to prevent excessive trophoblast apoptosis and possible pregnancy complications.

Radiation and the microenvironment - tumorigenesis and therapy

Radiation rapidly and persistently alters the soluble and insoluble components of the tissue microenvironment. This affects the cell phenotype, tissue composition and the physical interactions and signalling between cells. These alterations in the microenvironment can contribute to carcinogenesis and alter the tissue response to anticancer therapy. Examples of these responses and their implications are discussed with a view to therapeutic intervention.

Mfge8 is critical for mammary gland remodeling during involution

Apoptosis is a critical process in normal mammary gland development and the rapid clearance of apoptotic cells prevents tissue injury associated with the release of intracellular antigens from dying cells. Milk fat globule-EGF-factor 8 (Mfge8) is a milk glycoprotein that is abundantly expressed in the mammary gland epithelium and has been shown to facilitate the clearance of apoptotic lymphocytes by splenic macrophages. We report that mice with disruption of Mfge8 had normal mammary gland development until involution. However, abnormal mammary gland remodeling was observed postlactation in Mfge8 mutant mice. During early involution, Mfge8 mutant mice had increased numbers of apoptotic cells within the mammary gland associated with a delay in alveolar collapse and fat cell repopulation. As involution progressed, Mfge8 mutants developed inflammation as assessed by CD45 and CD11b staining of mammary gland tissue sections. With additional pregnancies, Mfge8 mutant mice developed progressive dilatation of the mammary gland ductal network. These data demonstrate that Mfge8 regulates the clearance of apoptotic epithelial cells during mammary gland involution and that the absence of Mfge8 leads to inflammation and abnormal mammary gland remodeling.

Epithelial cells as phagocytes: apoptotic epithelial cells are engulfed by mammary alveolar epithelial cells and repress inflammatory mediator release

Clearance of apoptotic cells is critical to tissue homeostasis and resolution of inflammatory lesions. Macrophages are known to remove dying cells and release anti-inflammatory mediators in response; however, many cells traditionally thought of as poor phagocytes can mediate this function as well. In the lactating mammary gland following weaning, alveolar epithelial cell death is massive, yet the gland involutes rapidly, attaining its prepregnancy state in a matter of days. We found histologic evidence of apoptotic cell phagocytosis by viable mammary epithelial cells (MEC) in the involuting mouse mammary gland. Cultured MEC were able to engulf apoptotic cells in vitro, utilizing many of the same receptors used by macrophages, including the phosphatidylserine receptor (PSR), CD36, the vitronectin receptor alpha(v)beta3, and CD91. In addition, MEC, like macrophages, produced TGFbeta in response to stimulation of the PSR by apoptotic cells or the anti-PSR ab 217G8E9, and downregulated endotoxin-stimulated proinflammatory cytokine production. These data support the hypothesis that amateur phagocytes play a significant role in apoptotic cell clearance and its regulation of inflammation.

Lung inflammation induced by endotoxin is enhanced in rats depleted of alveolar macrophages with aerosolized clodronate

Clodronate liposomes were given to rats via intratracheal inhalation to investigate the importance of alveolar macrophages (AMs) in inhaled endotoxin-induced lung injury. When AM depletion was maximal (87% to 90%), rats were exposed to lipopolysaccharide (LPS) or saline. Neither clodronate nor saline liposomes induced an influx of neutrophils (PMNs) into the lungs. However, depleted LPS-exposed rats had 5- to 8-fold higher numbers of lavage PMNs and greater lavage cell reactive oxygen species release compared to undepleted rats. Although AM depletion by itself did not significantly increase inflammatory cytokine expression in lung tissue, LPS-induced message levels for interleukin (IL)-1alpha, IL-1beta, IL-6, and tumor necrosis factor (TNF)-alpha were approximately 2-fold higher in AM-depleted rats compared to undepleted rats. These results indicate that cells other than AMs can recruit inflammatory cells into the lungs during acute LPS-induced injury and that AMs play an important suppressive role in the innate pulmonary inflammatory response.

Clearance of apoptotic cells is not impaired in mouse embryos deficient in class A scavenger receptor types I and II (CD204)

Elimination of apoptotic cells is an important mechanism to maintain proper embryonal morphogenesis. The class A scavenger receptor type I, II (CD204), one of the major receptors expressed on macrophages, is a receptor actively involved in recognition and ingestion of apoptotic cells. To clarify the role of CD204 in embryonic morphogenesis, we performed immunohistochemical and immunoelectron microscopic studies using CD204-deficient mouse embryos. In control mice, almost all macrophages expressed CD204 from embryonic day 9.5 (E9.5). Phagocytes engulfing dead cells in the E13.5 interdigit region showed strong expression of CD204, indicating that CD204 was actively involved in apoptotic cell clearance. However, CD204 is not essential for the embryonic clearance of apoptotic cells, because CD204-deficient embryos developed normally without any retardation in footplate remodeling. Up-regulation of CD36 in CD204-deficient fetal macrophages suggested that CD36 substitutes for CD204 function. We also found that mesenchymal cells frequently engulfed apoptotic cells especially in early embryonal stages. These data suggest that CD204 is partially but not essentially involved in apoptotic cell clearance in embryogenesis. During early embryonal development, mesenchymal cells, rather than macrophages, play a major role in apoptotic cell clearance.

Cell targeting by a generic receptor-targeted polymer nanocontainer platform

Nanotechnology promises new avenues to medical diagnosis and treatment. Of special interest are injectable nanovehicles that are programmable towards specific targets, are able to evade the immune defense, and are versatile enough to be suited as carriers of complex functionality. Biotin-functionalized (poly(2-methyloxazoline)-b-poly(dimethylsiloxane)-b-poly(2-methyloxazoline) triblock copolymers were self-assembled to form nanocontainers, and biotinylated targeting ligands were attached by using streptavidin as a coupling agent. Specifically, fluorescence-labeled nanocontainers were targeted against the scavenger receptor A1 from macrophages, an important cell in human disease. In human and transgenic cell lines and in mixed cultures, receptor-specific binding of these generic carriers was followed by vesicular uptake. Low nonspecific binding supported the "stealth" properties of the carrier while cytotoxicity was absent. This versatile carrier appears promising for diagnostic or therapeutic medical use.

Cell and tissue responses to genotoxic stress

Cancers arise as a consequence of the accumulation of multiple genetic mutations in a susceptible cell, resulting in perturbation of regulatory networks that control proliferation, survival, and cellular function. Here, the sources of cellular stress that can cause oncogenic mutations and the responses of cells to DNA damage are reviewed. The role of different repair pathways and the potential for cell- and tissue-specific reliance on individual repair mechanisms are discussed. Evidence for cell- and tissue-specific activation of p53-mediated growth arrest and apoptosis after exposure to an individual genotoxin is assessed and some of the potential mediators of these different responses are provided. These cell- and tissue-specific responses to particular forms of DNA damage are likely to be key determinants of tissue-specific tumour susceptibility, and there is good evidence for genetic variations in these responses. The role that genotoxic agents play in altering the microenvironment to produce indirect effects on tumourigenesis through altered production of free radicals and cytokines that are characteristic of inflammatory-type processes is also evaluated. Changes to the microenvironment as direct or indirect effects of genotoxic stress can be involved in both tumour initiation and progression and may even be a prerequisite for tumourigenesis. Therefore, tumour susceptibility after endogenous or exogenous genotoxic stress represents a balance between cell-intrinsic responses of target cells and changes to the microenvironment. A fuller understanding of cell- and tissue-specific responses, alterations to the microenvironment, and genetic modifiers of these responses could lead to novel prevention and therapeutic strategies for common forms of human malignancy.

The effect of inflammation on the generation of plasma DNA from dead and dying cells in the peritoneum

To assess the effects of inflammation on the generation of circulating DNA from dead and dying cells, plasma DNA levels were determined in BALB/c mice, administered apoptotic or necrotic Jurkat cells following induction of peritonitis by treatment with thioglycollate (TG), peptone (PT), or sodium periodate (NaIO(4)). In mice receiving TG or NaIO(4), plasma DNA levels following intraperitoneal administration of Jurkat cells were significantly reduced compared with controls, whereas they were not affected in mice receiving PT. To determine the basis of these differences, the cellular composition of peritoneal fluids prior to the administration of the dead cells was analyzed. Among agents tested, TG administration led to the largest increase in cells, both neutrophils and monocytes. As shown by flow cytometry, the exudates contained apoptotic neutrophils and macrophages, with the highest levels in the TG-induced exudates. Analysis of DNA and caspase 3 in the fluids also showed differences. TG exudates showed increases in DNA and caspase 3, while NaIO(4)-induced exudates had an increase only in DNA. Fluid from PT-treated mice did not have increases in DNA or caspase 3. Together, these results indicate that prior inflammation can affect the generation of blood DNA from apoptotic or necrotic cells, although this effect may vary depending on the composition of the exudates with respect to cells as well as DNA.

The immune response to cell death in SLE

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease characterized by the production of antinuclear antibodies (ANA). These antibodies target a wide variety of antigens whose presence in an immunologically active form may result from cell death processes that cause their translocation and release from cells. As indicated by in vivo model systems, the release of DNA from cells may not be a simple consequence of cell death but rather may require the intervention of other cell types including macrophages. Thus, in mice, administration of either apoptotic or necrotic cells produces a blood DNA response, whereas mice lacking macrophages fail to show blood DNA under the same conditions. Furthermore, the circulating DNA arising from apoptotic and necrotic cells displays a similar pattern with respect to size distribution, with both showing DNA laddering, a pattern indicating enzymatic cleavage. Since circulating DNA in the form of immune complexes can play a role in lupus pathogenesis, these findings suggest that the generation and clearance of dead cells are important events that may underlie autoimmunity in this disease and may be targeted for therapy.

The imaging of apoptosis with the radiolabeled annexin V: optimal timing for clinical feasibility

In recent years, the imaging of drug-induced apoptosis has become one of the centers of interest in experimental and clinical research. In particular, the accurate monitoring of chemosensitivity as well as the early prediction of chemoresistance in response to various pro-apoptotic interventions are critical requirements for the best management of oncology patients. The use of technetium [(99m)Tc]-labeled annexin V on animal and human models of cancers provides a proof of principle for the feasibility of a non-invasive, in vivo detection of an apoptotic signal and then for the early assessment of tumor response in the course of chemotherapy. Although promising, however, the initial clinical data point out on the technical limitations that are still to be resolved in terms of tumor-to-background ratio and optimal timing for the imaging of apoptosis. In the present review article, we report the results of animal studies aimed to the evaluation of apoptotic peaks following chemotherapy. In the light of these basic research works, we analyze the profiles of radiolabeled annexin V uptake over time as observed in clinical trials. We then discuss possible new imaging strategies designed to optimize the visualization of apoptotic changes within tumor tissues using the [(99m)Tc]-labeled annexin V. We also suggest longer lived forms of radiolabeled annexin V designed to better understand the temporal patterns of apoptotic tumor response, which in turn, may help to capture the best time-window for the imaging of cell death.

Overlapping and independent contributions of MMP2 and MMP9 to lung allergic inflammatory cell egression through decreased CC chemokines

The mechanisms that initiate allergic lung inflammation are relevant to expression of diseases such as asthma, but the factors underlying resolution of inflammation are equally important. Previously, we demonstrated the importance of matrix metalloproteinase 2 (MMP2) for airway egression of lung eosinophils, a critical anti-inflammatory mechanism without which mice are rendered highly susceptible to lethal asphyxiation. Here we show that leukocyte MMP9 is the dominant airway MMP controlling inflammatory cell egression. The allergic lung phenotype of MMP9-/- mice was similar to WT and was not altered by concomitant deletion of the MMP2 gene (double knockout; dko). However, inflammatory cells accumulated aberrantly in the lungs of allergen-challenged MMP9-/- and dko mice and fewer eosinophils and neutrophils were present in bronchoalveolar lavage. These aberrant cellular trafficking patterns were explained by disruption of transepithelial chemokine gradients, in MMP2-/- mice affecting only eotaxin (CCL11), but in MMP9-/- and dko mice involving eotaxin, MARC (CCL7), and TARC (CCL17). Thus, by establishing multiple transepithelial chemokine gradients, MMP9 is broadly implicated in the resolution of allergic inflammation, an essential protective mechanism that overlaps with a more limited role played by MMP2.

Apoptotic cell and phagocyte interplay: recognition and consequences in different cell systems

Cell death by apoptosis is characterized by specific biochemical changes, including the exposure of multiple ligands, expected to tag the dying cell for prompt recognition by phagocytes. In non-pathological conditions, an efficient clearance is assured by the redundant interaction between apoptotic cell ligands and multiple receptor molecules present on the engulfing cell surface. This review concentrates on the molecular interactions operating in mammalian and non-mammalian systems for apoptotic cell recognition, as well as on the consequences of their signaling. Furthermore, some cellular models where the exposure of the phosphatidylserine (PS) phospholipid, a classical hallmark of the apoptotic phenotype, is not followed by cell death will be discussed.

Multi-modality Imaging Identifies Key Times for Annexin V Imaging as an Early Predictor of Therapeutic Outcome

Radiolabeled annexin V may provide an early indication of the success or failure of anticancer therapy on a patient-by-patient basis as an in vivo marker of tumor cell killing. An important question that remains is when, after initiation of treatment, should annexin V imaging be performed. To address this issue, we obtained simultaneous in vivo measurements of tumor burden and uptake of radiolabeled annexin V in the syngeneic orthotopic murine BCL1 lymphoma model using in vivo bioluminescence imaging (BLI) and small animal single-photon emission computed tomography (SPECT). BCL1 cells labeled for fluorescence and bioluminescence assays (BCL1-gfp/luc) were injected into mice at a dose that leads to progressive disease within two to three weeks. Tumor response was followed by BLI and SPECT before and after treatment with a single dose of 10 mg/kg doxorubicin. Biodistribution analyses revealed a biphasic increase of annexin V uptake within the tumor-bearing tissues of mice. An early peak occurring before actual tumor cells loss was observed between 1 and 5 hr after treatment, and a second longer sustained rise from 9 to 24 hr after therapy, which heralds the onset of tumor cell loss as confirmed by BLI. Multimodality imaging revealed the temporal patterns of tumor cell loss and annexin V uptake revealing a better understanding of the timing of radiolabeled annexin V uptake for its development as a marker of therapeutic efficacy.

The caspase inhibitor IDN-6556 attenuates hepatic injury and fibrosis in the bile duct ligated mouse

Liver injury is characterized by hepatocyte apoptosis and collagen-producing activated hepatic stellate cells (HSC). Hepatocyte apoptosis promotes liver injury and fibrosis, whereas activated HSC apoptosis limits hepatic fibrosis. Pharmacological inhibition of liver cell apoptosis may potentially attenuate liver injury and fibrosis by blocking hepatocyte apoptosis or promote fibrosis by permitting accumulation of activated HSCs. To ascertain the net effect of inhibiting liver cell apoptosis on liver injury, inflammation, and hepatic fibrogenesis, we examined the effect of a pancaspase inhibition IDN-6556 on these parameters in the bile duct ligated (BDL) mouse. Hepatocyte apoptosis was assessed by the terminal deoxynucleotidyl transferase dUTP nick-end labeling assay and immunofluorescence for active caspases 3/7, and liver injury by histopathology and serum alanine aminotransferase (ALT) determinations. Real-time polymerase chain reaction was used to measure mRNA transcripts for markers of hepatic inflammation, HSC activation, and fibrosis. Immunohistochemistry for alpha-smooth muscle actin was performed to identify HSC activation. Collagen deposition was quantitated by Sirius red staining and digital imaging techniques. Hepatocyte apoptosis and liver injury (bile infarcts and serum ALT values) were reduced in IDN-6556-treated versus saline-treated 3-day BDL mice. Markers for liver inflammation [chemokine (C-X-C) ligand 1 and macrophage inflammatory protein-2 chemokine expression] and hepatic fibrogenesis (transforming growth factor-beta and collagen I expression) were also attenuated. Consistent with these data, HSC activation as assessed by alpha-smooth muscle actin mRNA expression and immunohistochemistry was markedly reduced in both 3- and 10-day BDL animals. Collectively, these data suggest hepatocyte apoptosis initiates cascades culminating in liver injury and fibrosis. The pan-caspase inhibitor IDN-6556 is a promising agent for cholestatic liver injury.

Kupffer cell engulfment of apoptotic bodies stimulates death ligand and cytokine expression

Hepatocyte apoptosis by death receptors, hepatic inflammation, and fibrosis are prominent features of liver diseases. However, the link between these processes remains unclear. Our aim was to ascertain whether engulfment of apoptotic bodies by Kupffer cells promotes hepatic inflammation and fibrosis. Isolated murine Kupffer cells efficiently engulfed apoptotic bodies generated from UV-treated mouse hepatocytes. Engulfment of the apoptotic bodies, but not latex beads, stimulated Kupffer cell generation of death ligands, including Fas ligand, and tumor necrosis factor alpha (TNF-alpha). Both apoptotic body phagocytosis and death ligand generation were attenuated by gadolinium chloride, a Kupffer cell toxicant. Kupffer cells isolated from 3-day bile duct-ligated (BDL) mice were phenotypically similar to apoptotic body-"fed" Kupffer cells with enhanced death ligand expression; inhibition of hepatocyte apoptosis with a caspase inhibitor prevented this Kupffer cell activation. Consistent with a role for Kupffer cells in liver inflammation and fibrosis, gadolinium chloride attenuated neutrophil infiltration and markers for stellate cell activation. In conclusion, these findings support a model of cholestatic liver injury where Kupffer cell engulfment of apoptotic bodies promotes inflammation and fibrogenesis.

Cell death in MMTV-c-myc transgenic mouse mammary tumors may not be typical apoptosis

Enforced expression of c-myc has been shown to serve as an apoptotic stimulus in cultured cells. Prior studies have also demonstrated that several tissues expressing c-myc transgene display a large number of dead cells, although a morphologic or biochemical verification of apoptosis in these tissues has actually not been presented. In the present study, we examined the morphologic properties of cell death in the mammary tumors developed from MMTV-c-myc transgenic mice. We found that c-myc-expressing mammary tumor cells exhibited malformation of mitochondria, characterized by an amorphous matrix with very few cristae. The mitochondria were also frequently degenerated by lysis of the matrix and cristae. The protein level of cytochrome c was much lower in the areas of c-myc-expressing tumor cells compared with the adjacent tumor foci, which was previously shown to have decreased expression of c-myc, reduced frequencies of cell death, and increased frequencies of proliferating cells. In the c-myc-expressing tumor areas, there were many dying or dead cells organized in clusters, termed "dead cell islands." These cells exhibited shrinkage, DNA breakage as indicated by a positive TUNEL staining, and nuclear localization of apoptosis-inducing factor, but a lack of typical apoptotic morphology, such as nuclear condensation and formation of cell membrane blebs and apoptotic bodies. Many macrophages infiltrated into these dead cell islands, engulfing the dying or dead tumor cells. In the total tumor tissue, the protein level of caspase-3 was very low, and the poly(ADP)-ribose polymerase was present mainly as the unprocessed, inactive form. Collectively, these results suggest that programmed cell death in the c-myc transgenic mammary tumor tissue may not be typical apoptosis and may involve a caspase-independent mechanism.

Cellular and molecular themes in apoptosis

Apoptosis, an active mechanism of cell death, is of central importance in many biological scenarios. Research in this area has the potential to contribute to our understanding of many diseases and raises several potential therapeutic opportunities. Given this potential and the speed with which our understanding of this field has advanced over recent years, it is timely to introduce the clinician to the background on which the clinical implications of this research will be built. This review begins with contrasting apoptosis with the other mechanism of cell death, necrosis, and then outlines the features by which apoptosis may be recognised. With a view to understanding the level at which this process may be involved in disease and therapeutics, it is important to be aware of the basic mechanistic features of the induction and execution of apoptosis. In this, surface molecules such as CD95 (Fas) and the cascade of intracellular enzymes involved at many levels in apoptosis, the caspases, are of central importance. In all this, the mitochondrion is crucial to the induction of apoptosis and the regulation of the whole process. In the last part of this review, we attempt to draw out the clinical relevance of all this information. It is clear that apoptosis has an important role in the pathophysiology of malignancy, particularly with respect to haematological cancers, but also other oncological diseases. Apoptosis is also very important in autoimmune disease and viral infection. Finally, it is clear that apoptosis may be manipulated therapeutically to the benefit of patients in various scenarios. This is clearly an exciting area for future development, but one which clearly depends on a thorough mechanistic understanding.

Development of reduced-intensity hematopoietic stem cell transplantation in the National Cancer Center Hospital, Japan

Reduced-intensity hematopoietic stem cell transplantation (RIST) is a new approach of stem cell transplantation, which has shown promising features as reported in multiple phase I and II studies. Elderly patients, who are not eligible for conventional myeloablative hematopoietic stem cell transplantation (HSCT), are now treatable with RIST. It has also reduced regimen-related toxicity and provided better prognosis in short-term follow-up than that of conventional HSCT. Favorable results have been reported particularly in hematological malignancies, such as chronic myelocytic leukemia and malignant lymphoma. Among solid tumors, metastatic renal cell carcinoma was found to respond well to RIST. Clinical studies are currently being conducted to evaluate the efficacy of RIST in other types of solid tumors. However, the mechanism of graft-versus-host disease and graft-versus-tumor remains unclear. More knowledge on the mechanism is crucial to enhance antitumor effect and to further improve the prognosis.

Do inflammatory cells participate in mammary gland involution?

The processes by which the involuting mammary gland clears residual milk and milk fat, as well as apoptotic cells, have gone largely unstudied in the modern literature. Here we review the evidence for and against the involvement of professional phagocytes of hematopoietic lineage in this process. Additionally we present evidence that mammary epithelial cells themselves are capable of phagocytosis and may be responsible for the majority of apoptotic cell and residual milk clearance during murine involution. In this scheme these cells regulate their cytokine production in response to apoptotic cells in a manner similar to other cells, including macrophages. The ensuing model describes a process of involution that actively suppresses an inflammatory response in the gland, allowing for effective tissue remodeling and damage prevention.