Enhanced and accelerated lymphoproliferation in Fas-null mice

Necroptosis and autoimmunity

Autoimmunity is a normal physiological state that requires immunological homeostasis and surveillance, whereas necroptosis is a type of inflammatory cell death. When necroptosis occurs, various immune system cells must perform their appropriate duties to preserve immunological homeostasis, whether the consequence is expanding or limiting the inflammatory response and the pathological condition is cleared or progresses to the autoimmune disease stage. This article discusses necroptosis based on RIP homotypic interaction motif (RHIM) interaction under various physiological and pathological situations, with the RIPK1-RIPK3-MLKL necrosome serving as the regulatory core. In addition, the cell biology of necroptosis involved in autoimmunity and its application in autoimmune diseases were also reviewed.

Rare SH2B3 coding variants in lupus patients impair B cell tolerance and predispose to autoimmunity

Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune disease with a clear genetic component. While most SLE patients carry rare gene variants in lupus risk genes, little is known about their contribution to disease pathogenesis. Amongst them, SH2B3-a negative regulator of cytokine and growth factor receptor signaling-harbors rare coding variants in over 5% of SLE patients. Here, we show that unlike the variant found exclusively in healthy controls, SH2B3 rare variants found in lupus patients are predominantly hypomorphic alleles, failing to suppress IFNGR signaling via JAK2-STAT1. The generation of two mouse lines carrying patients' variants revealed that SH2B3 is important in limiting the number of immature and transitional B cells. Furthermore, hypomorphic SH2B3 was shown to impair the negative selection of immature/transitional self-reactive B cells and accelerate autoimmunity in sensitized mice, at least in part due to increased IL-4R signaling and BAFF-R expression. This work identifies a previously unappreciated role for SH2B3 in human B cell tolerance and lupus risk.

Antibody-Targeted TNFRSF Activation for Cancer Immunotherapy: The Role of FcγRIIB Cross-Linking

Co-stimulation signaling in various types of immune cells modulates immune responses in physiology and disease. Tumor necrosis factor receptor superfamily (TNFRSF) members such as CD40, OX40 and CD137/4-1BB are expressed on myeloid cells and/or lymphocytes, and they regulate antigen presentation and adaptive immune activities. TNFRSF agonistic antibodies have been evaluated extensively in preclinical models, and the robust antitumor immune responses and efficacy have encouraged continued clinical investigations for the last two decades. However, balancing the toxicities and efficacy of TNFRSF agonistic antibodies remains a major challenge in the clinical development. Insights into the co-stimulation signaling biology, antibody structural roles and their functionality in immuno-oncology are guiding new advancement of this field. Leveraging the interactions between antibodies and the inhibitory Fc receptor FcγRIIB to optimize co-stimulation agonistic activities dependent on FcγRIIB cross-linking selectively in tumor microenvironment represents the current frontier, which also includes cross-linking through tumor antigen binding with bispecific antibodies. In this review, we will summarize the immunological roles of TNFRSF members and current clinical studies of TNFRSF agonistic antibodies. We will also cover the contribution of different IgG structure domains to these agonistic activities, with a focus on the role of FcγRIIB in TNFRSF cross-linking and clustering bridged by agonistic antibodies. We will review and discuss several Fc-engineering approaches to optimize Fc binding ability to FcγRIIB in the context of proper Fab and the epitope, including a cross-linking antibody (xLinkAb) model and its application in developing TNFRSF agonistic antibodies with improved efficacy and safety for cancer immunotherapy.

The genetic landscape of the FAS pathway deficiencies

Dysfunction of the FAS-FASLG pathway causes a lymphoproliferative disorder with autoimmunity called Autoimmune lymphoproliferative syndrome (ALPS) mainly caused by FAS mutations. The goal of this review is to describe the genetic bases of the autoimmune lymphoproliferative syndrome and to underline their genetic complexity with the contribution of both germline and somatic events accounting for the variable clinical penetrance of the FAS mutations. Starting from the cohort of patients studied in the French cohort (>165 cases), we also reviewed the literature cases in order to depict a full description of the mutations affecting the FAS-FASLG pathway involved in the outcome of this rare non-malignant and non-infectious pediatric lymphoproliferative disease. We also discussed the variable clinical penetrance associated with mutations affecting the extracellular domain of the protein. Such non-penetrant germline mutations are frequently associated with an additional somatic event impacting the second allele of FAS. Moreover, the uncomplete clinical penetrance associated with mutations affecting the intracellular domain of FAS, in patient lacking additional FAS somatic event, suggested a potential digenic inheritance with a FAS mutation accompanied by a genetic modifier possibly impacting another player of the lymphocytes homeostasis (affecting the survival, activation or apoptosis of the peripheral leukocytes).

Mechanisms of Apoptosis Resistance to NK Cell-Mediated Cytotoxicity in Cancer

Natural killer (NK) cells are major contributors to immunosurveillance and control of tumor development by inducing apoptosis of malignant cells. Among the main mechanisms involved in NK cell-mediated cytotoxicity, the death receptor pathway and the release of granules containing perforin/granzymes stand out due to their efficacy in eliminating tumor cells. However, accumulated evidence suggest a profound immune suppression in the context of tumor progression affecting effector cells, such as NK cells, leading to decreased cytotoxicity. This diminished capability, together with the development of resistance to apoptosis by cancer cells, favor the loss of immunogenicity and promote immunosuppression, thus partially inducing NK cell-mediated killing resistance. Altered expression patterns of pro- and anti-apoptotic proteins along with genetic background comprise the main mechanisms of resistance to NK cell-related apoptosis. Herein, we summarize the main effector cytotoxic mechanisms against tumor cells, as well as the major resistance strategies acquired by tumor cells that hamper the extrinsic and intrinsic apoptotic pathways related to NK cell-mediated killing.

Naringenin mitigates autoimmune features in lupus-prone mice by modulation of T-cell subsets and cytokines profile

Naringenin is flavonoid mainly found in citrus fruits which has shown several biological properties. In this work, we evaluated the therapeutic potential of the flavonoid Naringenin. Five-month-old B6.MRL-Faslpr/J lupus-prone mice were administered daily orally with Naringenin for seven months. We showed that Naringenin treatment at 50 or 100 mg/kg inhibited the splenomegaly and decreased the levels of anti-nuclear and anti-dsDNA autoantibodies. Furthermore, a reduction in serum concentration of TNF-α, IFN-γ and IL-6 was observed in the mice provided with Naringenin. Interestingly, serum levels of IL-10 increased. Naringenin decreased the frequency and absolute numbers of splenic effector memory T cells. Additionally, in order to be able to evaluate whether Naringenin prevented kidney damage, twelve-week-old MRL/MpJ-Faslpr/J mice, an accelerated lupus model, were orally administered with Naringenin at 100 mg/kg for six weeks. Surprisingly, Naringenin treatment prevented kidney damage and reduced the development of fibrosis similar to cyclophosphamide group. Moreover, Naringenin treatment increased the percentage of regulatory T cells in this aggressive model of lupus. Together, these results suggest a potential ability of Naringenin to reduce the autoimmunity in lupus-prone mice by modulation of T-cell subsets and cytokines profile that mitigate the development of important lupus clinical manifestations.

T cells instruct myeloid cells to produce inflammasome-independent IL-1β and cause autoimmunity

The cytokine interleukin (IL)-1β is a key mediator of antimicrobial immunity as well as autoimmune inflammation. Production of IL-1β requires transcription by innate immune receptor signaling and maturational cleavage by inflammasomes. Whether this mechanism applies to IL-1β production seen in T cell-driven autoimmune diseases remains unclear. Here, we describe an inflammasome-independent pathway of IL-1β production that was triggered upon cognate interactions between effector CD4+ T cells and mononuclear phagocytes (MPs). The cytokine TNF produced by activated CD4+ T cells engaged its receptor TNFR on MPs, leading to pro-IL-1β synthesis. Membrane-bound FasL, expressed by CD4+ T cells, activated death receptor Fas signaling in MPs, resulting in caspase-8-dependent pro-IL-1β cleavage. The T cell-instructed IL-1β resulted in systemic inflammation, whereas absence of TNFR or Fas signaling protected mice from CD4+ T cell-driven autoimmunity. The TNFR-Fas-caspase-8-dependent pathway provides a mechanistic explanation for IL-1β production and its consequences in CD4+ T cell-driven autoimmune pathology.

FAS and RAS related Apoptosis defects: From autoimmunity to leukemia

The human adaptive immune system recognizes almost all the pathogens that we encounter and all the tumor antigens that may arise during our lifetime. Primary immunodeficiencies affecting lymphocyte development or function therefore lead to severe infections and tumor susceptibility. Furthermore, the fact that autoimmunity is a frequent feature of primary immunodeficiencies reveals a third function of the adaptive immune system: its self-regulation. Indeed, the generation of a broad repertoire of antigen receptors (via a unique strategy of random somatic rearrangements of gene segments in T cell and B cell receptor loci) inevitably creates receptors with specificity for self-antigens and thus leads to the presence of autoreactive lymphocytes. There are many different mechanisms for controlling the emergence or action of autoreactive lymphocytes, including clonal deletion in the primary lymphoid organs, receptor editing, anergy, suppression of effector lymphocytes by regulatory lymphocytes, and programmed cell death. Here, we review the genetic defects affecting lymphocyte apoptosis and that are associated with lymphoproliferation and autoimmunity, together with the role of somatic mutations and their potential involvement in more common autoimmune diseases.

Disruption of the FasL/Fas axis protects against inflammation-derived tumorigenesis in chronic liver disease

Fas Ligand (FasL) and Fas (APO-1/CD95) are members of the TNFR superfamily and may trigger apoptosis. Here, we aimed to elucidate the functional role of Fas signaling in an experimental model of chronic liver disease, the hepatocyte-specific NEMO knockout (NEMO^Δhepa) mice. We generated NEMO^Δhepa /Fas^lpr mice, while NEMO^Δhepa, NEMO^f/f as well as Fas^lpranimals were used as controls, and characterized their phenotype during liver disease progression. Liver damage was evaluated by serum transaminases, histological, immunofluorescence procedures, and biochemical and molecular biology techniques. Proteins were detected by western Blot, expression of mRNA by RT-PCR, and infiltration of inflammatory cells was determined by FACs analysis, respectively. Fas^lpr mutation in NEMO^Δhepa mice resulted in overall decreased liver injury, enhanced hepatocyte survival, and reduced proliferation at 8 weeks of age compared with NEMO^Δhepa mice. Moreover, NEMO^Δhepa/Fas^lpr animals elicited significantly decreased parameters of liver fibrosis, such as Collagen IA1, MMP2, and TIMP1, and reduced proinflammatory macrophages and cytokine expression. At 52 weeks of age, NEMO^Δhepa/Fas^lpr exhibited less malignant growth as evidenced by reduced HCC burden associated with a significantly decreased number of nodules and LW/BW ratio and decreased myeloid populations. Deletion of TNFR1 further reduced tumor load of 52-weeks-old NEMO^Δhepa/Fas^lpr mice. The functionality of FasL/Fas might affect inflammation-driven tumorigenesis in an experimental model of chronic liver disease. These results help to develop alternative therapeutic approaches and extend the limitations of tumor therapy against HCC.

Fas receptor induces apoptosis of synovial bone and cartilage progenitor populations and promotes bone loss in antigen-induced arthritis

Rheumatoid arthritis (RA) is an inflammatory joint disease that eventually leads to permanent bone and cartilage destruction. Fas has already been established as the regulator of inflammation in RA, but its role in bone formation under arthritic conditions is not completely defined. The aim of this study was to assess the effect of Fas inactivation on the bone damage during murine antigen-induced arthritis. Subchondral bone of wild-type (WT) and Fas-knockout (Fas^-/-) mice was evaluated by histomorphometry and microcomputerized tomography. Proportions of synovial bone and cartilage progenitors were assessed by flow cytometry. Synovial bone and cartilage progenitors were purified by fluorescence-activated cell sorting and expression of Fas and Fas-induced apoptosis were analyzed in vitro. Results showed that Fas^-/- mice developed attenuated arthritis characterized by preserved epiphyseal bone and cartilage. A proportion of the earliest CD200⁺ bone and cartilage progenitors was reduced in WT mice with arthritis and was unaltered in Fas^-/- mice. During osteoblastic differentiation in vitro, CD200⁺ cells express the highest levels of Fas and are removed by Fas ligation. These results suggest that Fas-induced apoptosis of early CD200⁺ osteoprogenitor population represents potential mechanism underlying the impaired bone formation in arthritis, so their preservation may represent the bone-protective mechanism during arthritis.-Lazić Mosler, E., Lukač, N., Flegar, D., Fadljević, M., Radanović, I., Cvija, H., Kelava, T., Ivčević, S., Šućur, A., Markotić, A., Katavić, V., Marušić, A., Grčević, D., Kovačić, N. Fas receptor induces apoptosis of synovial bone and cartilage progenitor populations and promotes bone loss in antigen-induced arthritis.

The Autoimmune Lymphoproliferative Syndrome with Defective FAS or FAS-Ligand Functions

The autoimmune lymphoproliferative syndrome (ALPS) is a non-malignant and non-infectious uncontrolled proliferation of lymphocytes accompanied by autoimmune cytopenia. The genetic etiology of the ALPS was described in 1995 by the discovery of the FAS gene mutations. The related apoptosis defect accounts for the accumulation of autoreactive lymphocytes as well as for specific clinical and biological features that distinguish the ALPS-FAS from other monogenic defects of this apoptosis pathway, such as FADD and CASPASE 8 deficiencies. The ALPS-FAS was the first description of a monogenic cause of autoimmunity, but its non-Mendelian expression remained elusive until the description of somatic and germline mutations in ALPS patients. The recognition of these genetic diseases brought new information on the role of this apoptotic pathway in controlling the adaptive immune response in humans.

Role of Lgals9 Deficiency in Attenuating Nephritis and Arthritis in BALB/c Mice in a Pristane-Induced Lupus Model

OBJECTIVE

In systemic lupus erythematosus (SLE), an autoimmune disease associated with multiple organ involvement, the development of lupus nephritis determines prognosis, and arthritis impairs quality of life. Galectin 9 (Gal-9, Lgals9) is a β-galactoside-binding lectin that has been used for clinical application in autoimmune diseases, since recombinant Gal-9, as a ligand for T cell immunoglobulin and mucin domain-containing protein 3 (TIM-3), induces apoptosis of activated CD4+TIM-3+ Th1 cells. This study was undertaken to investigate whether deficiency of Lgals9 has beneficial or deleterious effects on lupus in a murine model.

METHODS

Gal-9^+/+ and Gal-9^-/- female BALB/c mice were injected with pristane, and the severity of arthritis, proteinuria, and levels of autoantibody production were assessed at several time points immediately following injection. At 7 months after pristane injection, renal pathologic features, the severity of joint inflammation, and formation of lipogranulomas were evaluated. Subsets of inflammatory cells in the spleen and peritoneal lavage were characterized, and expression levels of cytokines from peritoneal macrophages were analyzed.

RESULTS

Lgals9 deficiency protected against the development of immune complex glomerulonephritis, arthritis, and peritoneal lipogranuloma formation in BALB/c mice in this murine model of pristane-induced lupus. The populations of T cell subsets and B cells in the spleen and peritoneum were not altered by Lgals9 deficiency in pristane-injected BALB/c mice. Furthermore, Lgals9 deficiency protected against pristane-induced lupus without altering the Toll-like receptor 7-type I interferon pathway.

CONCLUSION

Gal-9 is required for the induction and development of lupus nephritis and arthritis in this murine model of SLE. The results of the current investigation provide a potential new strategy in which antagonism of Gal-9 may be beneficial for the treatment of nephritis and arthritis in patients with SLE through targeting of activated macrophages.

Rescue of autophagy and lysosome defects in salivary glands of MRL/lpr mice by a therapeutic phosphopeptide

Sjögren's syndrome is a multifactorial systemic autoimmune disorder characterized by lymphocytic infiltrates in exocrine organs. Patients present with sicca symptoms, such as extensive dry eyes and dry mouth, and parotid enlargement. Other serious complications include profound fatigue, chronic pain, major organ involvement, neuropathies and lymphomas. Current treatments only focus on relieving symptoms and do not target the origin of the disease, which is largely unknown. The question we addressed here was whether some defects exist in autophagy processes in Sjögren's syndrome and if they can be corrected or minimized using an appropriate mechanism-driven treatment targeting this central survival pathway. Using a recognized murine model of secondary Sjögren's syndrome, we identified molecular alterations of autophagy occurring in the salivary glands of MRL/lpr mice, and discovered that opposite (up- or down-regulated) autophagy events can arise in distinct organs of the same mouse strain, here in lymphoid organs and salivary glands. We showed further that the therapeutic P140 peptide, known to directly act on chaperone-mediated autophagy, rescued MRL/lpr mice from cellular infiltration and autophagy defects occurring in salivary glands. Our findings provide a proof-of-concept that targeting autophagy might represent a promising therapeutic strategy for treating patients with Sjögren's syndrome.

Daxx plays a novel role in T cell survival but is dispensable in Fas-induced apoptosis

Daxx was originally isolated as a Fas-binding protein. However, the in vivo function of Daxx in Fas-induced apoptosis has remained enigmatic. Fas plays an important role in homeostasis in the immune system. Fas gene mutations lead to autoimmune-lymphoproliferation (lpr) diseases characterized by hyperplasia of secondary lymphoid organs. It is well established that the FADD adaptor binds to Fas, and recruits/activates caspase 8. However, additional proteins including Daxx have also been indicated to associate with Fas. It was proposed that Daxx mediates a parallel apoptotic pathway that is independent of FADD and caspase 8, but signals through ASK1-mediated apoptotic pathway. However, because the deletion of Daxx leads to embryonic lethality, the in vivo function of Daxx has not been properly analyzed. In the current study, analysis was performed using a conditional mutant mouse in which Daxx was deleted specifically in T cells. The data show that Daxx^-/- T cells were able to undergo normal Fas-induced apoptosis. While containing normal thymocyte populations, the T cell-specific Daxx^-/- mice have a reduced peripheral T cell pool. Importantly, Daxx-deficient T cells displayed increased death responses upon activation through TCR stimulation. These results unequivocally demonstrated that Daxx does not mediate Fas-induced apoptosis, but rather that it plays a critical role in survival responses in primary mature T cells.

Necroptosis: Mechanisms and Relevance to Disease

Necroptosis is a form of regulated cell death that critically depends on receptor-interacting serine-threonine kinase 3 (RIPK3) and mixed lineage kinase domain-like (MLKL) and generally manifests with morphological features of necrosis. The molecular mechanisms that underlie distinct instances of necroptosis have just begun to emerge. Nonetheless, it has already been shown that necroptosis contributes to cellular demise in various pathophysiological conditions, including viral infection, acute kidney injury, and cardiac ischemia/reperfusion. Moreover, human tumors appear to obtain an advantage from the downregulation of key components of the molecular machinery for necroptosis. Although such an advantage may stem from an increased resistance to adverse microenvironmental conditions, accumulating evidence indicates that necroptosis-deficient cancer cells are poorly immunogenic and hence escape natural and therapy-elicited immunosurveillance. Here, we discuss the molecular mechanisms and relevance to disease of necroptosis.

Efficient analysis of mouse genome sequences reveal many nonsense variants

Genetic polymorphisms in coding genes play an important role when using mouse inbred strains as research models. They have been shown to influence research results, explain phenotypical differences between inbred strains, and increase the amount of interesting gene variants present in the many available inbred lines. SPRET/Ei is an inbred strain derived from Mus spretus that has ∼1% sequence difference with the C57BL/6J reference genome. We obtained a listing of all SNPs and insertions/deletions (indels) present in SPRET/Ei from the Mouse Genomes Project (Wellcome Trust Sanger Institute) and processed these data to obtain an overview of all transcripts having nonsynonymous coding sequence variants. We identified 8,883 unique variants affecting 10,096 different transcripts from 6,328 protein-coding genes, which is about 28% of all coding genes. Because only a subset of these variants results in drastic changes in proteins, we focused on variations that are nonsense mutations that ultimately resulted in a gain of a stop codon. These genes were identified by in silico changing the C57BL/6J coding sequences to the SPRET/Ei sequences, converting them to amino acid (AA) sequences, and comparing the AA sequences. All variants and transcripts affected were also stored in a database, which can be browsed using a SPRET/Ei M. spretus variants web tool (www.spretus.org), including a manual. We validated the tool by demonstrating the loss of function of three proteins predicted to be severely truncated, namely Fas, IRAK2, and IFNγR1.

The importance of p53 pathway genetics in inherited and somatic cancer genomes

Decades of research have shown that mutations in the p53 stress response pathway affect the incidence of diverse cancers more than mutations in other pathways. However, most evidence is limited to somatic mutations and rare inherited mutations. Using newly abundant genomic data, we demonstrate that commonly inherited genetic variants in the p53 pathway also affect the incidence of a broad range of cancers more than variants in other pathways. The cancer-associated single nucleotide polymorphisms (SNPs) of the p53 pathway have strikingly similar genetic characteristics to well-studied p53 pathway cancer-causing somatic mutations. Our results enable insights into p53-mediated tumour suppression in humans and into p53 pathway-based cancer surveillance and treatment strategies.

Fas Ligand Deficiency Impairs Tumor Immunity by Promoting an Accumulation of Monocytic Myeloid-Derived Suppressor Cells

The Fas receptor ligand FasL regulates immune cell levels by inducing apoptosis of Fas receptor-positive cells. Here, we studied the impact of host FasL on tumor development in mice. Genetically targeting FasL in naïve mice increased myeloid cell populations, but, in marked contrast, it reduced the levels of myeloid-derived suppressor cells (MDSC) in mice bearing Lewis lung carcinoma tumors. Analysis of the MDSC subset distribution revealed that FasL deficiency skewed cell populations toward the M-MDSC subset, which displays a highly immunosuppressive activity. Furthermore, tumor-bearing mice that were FasL-deficient displayed an enhanced proportion of tumor-associated macrophages and regulatory T cells. Overall, the immunosuppressive environment produced by FasL targeting correlated with reduced survival of tumor-bearing mice. These results disclose a new role for FasL in modulating immunosuppressive cells.

A BTLA-mediated bait and switch strategy permits Listeria expansion in CD8α(+) DCs to promote long-term T cell responses

Listeria monocytogenes infected CD8α(+) DCs in the spleen are essential for CD8(+) T cell generation. CD8α(+) DCs are also necessary for Listeria expansion and dissemination within the host. The mechanisms that regulate CD8α(+) DCs to allow Listeria expansion are unclear. We find that activating the B and T lymphocyte attenuator (BTLA), a coinhibitory receptor for T cells, suppresses, while blocking BTLA enhances, both the primary and memory CD8 T cell responses against Listeria. Btla(-/-) mice have lower effector and memory CD8(+) T cells while paradoxically also being more resistant to Listeria. Although bacterial entry into Btla(-/-) CD8α(+) DCs is unaffected, Listeria fails to expand within these cells. BTLA signaling limits Fas/FasL-mediated suppression of Listeria expansion within CD8α(+) DCs to more effectively alert adaptive immune cells. This study uncovers a BTLA-mediated strategy used by the host that permits Listeria proliferation to enable increasing T cell responses for long-term protection.

Infiltration of circulating myeloid cells through CD95L contributes to neurodegeneration in mice

Gao et al. report that genetic or pharmacological blockade of CD95 ligand prevents infiltration of peripheral myeloid cells and thereby averts toxin-induced neurodegeneration in mice.

Neuroinflammation is increasingly recognized as a hallmark of neurodegeneration. Activated central nervous system–resident microglia and infiltrating immune cells contribute to the degeneration of dopaminergic neurons (DNs). However, how the inflammatory process leads to neuron loss and whether blocking this response would be beneficial to disease progression remains largely unknown. CD95 is a mediator of inflammation that has also been proposed as an apoptosis inducer in DNs, but previous studies using ubiquitous deletion of CD95 or CD95L in mouse models of neurodegeneration have generated conflicting results. Here we examine the role of CD95 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridin (MPTP)–induced neurodegeneration using tissue-specific deletion of CD95 or CD95L. We show that DN death is not mediated by CD95-induced apoptosis because deletion of CD95 in DNs does not influence MPTP-induced neurodegeneration. In contrast, deletion of CD95L in peripheral myeloid cells significantly protects against MPTP neurotoxicity and preserves striatal dopamine levels. Systemic pharmacological inhibition of CD95L dampens the peripheral innate response, reduces the accumulation of infiltrating myeloid cells, and efficiently prevents MPTP-induced DN death. Altogether, this study emphasizes the role of the peripheral innate immune response in neurodegeneration and identifies CD95 as potential pharmacological target for neurodegenerative disease.

Deletion of receptor for advanced glycation end products exacerbates lymphoproliferative syndrome and lupus nephritis in B6-MRL Fas lpr/j mice

The receptor for advanced glycation end products (RAGE) is a pattern recognition receptor that interacts with advanced glycation end products, but also with C3a, CpG DNA oligonucleotides, and alarmin molecules such as HMGB1 to initiate a proinflammatory reaction. Systemic lupus erythematosus is an autoimmune disorder associated with the accumulation of RAGE ligands. We generated mice invalidated for RAGE in the lupus-prone B6-MRL Fas lpr/j background to determine the role of RAGE in the pathogenesis of systemic lupus erythematosus. We compared the phenotype of these mice with that of their wild-type and B6-MRL Fas lpr/j littermates. Lymphoproliferative syndrome, production of anti-dsDNA Abs, lupus nephritis, and accumulation of CD3(+)B220(+)CD4(-)CD8(-) autoreactive T cells (in the peripheral blood and the spleen) were significantly increased in B6-MRL Fas lpr/j RAGE(-/-) mice compared with B6-MRL Fas lpr/j mice (respectively p < 0.005, p < 0.05, p < 0.001, and p < 0.001). A large proportion of autoreactive T cells from B6-MRL Fas lpr/j mice expressed RAGE at their surface. Time course studies of annexin V expression revealed that autoreactive T cells in the spleen of B6-MRL Fas lpr/j-RAGE(-/-) mice exhibited a delay in apoptosis and expressed significantly less activated caspase 3 (39.5 ± 4.3%) than T cells in B6-MRL Fas lpr/j mice (65.5 ± 5.2%) or wild-type mice (75.3 ± 2.64%) (p = 0.02). We conclude that the deletion of RAGE in B6-MRL Fas lpr/j mice promotes the accumulation of autoreactive CD3(+)B220(+)CD4(-)CD8(-) T cells, therefore exacerbating lymphoproliferative syndrome, autoimmunity, and organ injury. This suggests that RAGE rescues the apoptosis of T lymphocytes when the death receptor Fas/CD95 is dysfunctional.

A novel function of RIP1 in postnatal development and immune homeostasis by protecting against RIP3-dependent necroptosis and FADD-mediated apoptosis

RIP1 is an adaptor kinase originally identified as being able to associate with TNFR1 and Fas, and is later shown to be involved in signaling induced by TLRs. Major signaling pathways regulated by RIP1 include necroptosis, apoptosis, and pro-survival/inflammation NF-κB activation. Previous studies show that RIP1 deficiency has no effect on mouse embryogenesis, but blocks postnatal development. This phenotype could not readily be explained, since mice lacking TNFR1, Fas, or TLRs show no apparent developmental defect. Certain types of RIP1-deficient cells are hypersensitive to TNF-induced apoptosis. However, in our previous study, deletion of the apoptotic adaptor protein, FADD, provides marginal improvement of postnatal development of rip1^−/− mice. Remarkably, the current data shows that haploid insufficiency of RIP3, a known mediator of necroptosis, allowed survival of rip1^−/−fadd^−/− mice beyond weaning age, although the resulting rip1^−/−fadd^−/− rip3^+/− mice were significant smaller in size and weight. Moreover, complete absence of RIP3 further improved postnatal development of the resulting rip1^−/−fadd^−/−rip3^−/− mice, which display normal size and weight. In such triple knockout (TKO) mice, lymphocytes underwent normal development, but progressively accumulated as mice age. This lymphoproliferative (lpr) disease in TKO mice is, however, less severe than that of fadd^−/−rip3^−/− double knockout mice. In total, the data show that the postnatal developmental defect in rip1^−/− mice is due in part to FADD-mediated apoptosis as well as RIP3-dependent necroptosis. Moreover, the function of RIP1 contributes to development of lpr diseases.

Lymphoid hyperplasia and lymphoma in KSHV K1 transgenic mice

Growing evidence supports the involvement of human herpervirus 8, Kaposi's sarcoma associated herpesvirus (KSHV), in the pathology of primary effusion lymphoma, multicentric Castleman's disease, and Kaposi's sarcoma, but the exact mechanism of KSHV contribution to the oncogenic process remains elusive. We studied transgenic mice expressing the ORF K1 of KSHV, whose position in the KSHV genome corresponds to known lymphoproliferative genes of other herpesviruses. K1 protein was previously shown to contain a constitutively active ITAM domain, involved in activation of Akt and pro-survival signaling, and to inhibit Fas-mediated apoptosis by interfering with binding of FasL. All this pointed to a possible role of K1 in the pathogenesis of KSHV-associated cancers. K1 transgenic mice (80-90%) developed lymphoid hyperplasia and splenomegaly at 8 and 10 months of age, 25% had confirmed diagnosis of lymphoma, and 50% developed abdominal and/or hepatic tumors by 18 months of age. Histological examination showed loss of splenic architecture and increased cellularity. Lymph nodes showed disrupted architecture with effaced follicles and other pathological changes, including signs of angiofollicular lymphoid hyperplasia. One of the livers showed signs of angiosarcoma. In summary, our histology results revealed pathological changes in K1 transgenic mice similar to lymphoma, Castleman's disease, and angiosarcoma, suggesting that K1 may contribute to the development of KSHV-associated cancers.

Loss of the death receptor CD95 (Fas) expression by dendritic cells protects from a chronic viral infection

Chronic viral infections incapacitate adaptive immune responses by "exhausting" virus-specific T cells, inducing their deletion and reducing productive T-cell memory. Viral infection rapidly induces death receptor CD95 (Fas) expression by dendritic cells (DCs), making them susceptible to elimination by the immune response. Lymphocytic choriomeningitis virus (LCMV) clone 13, which normally establishes a chronic infection, is rapidly cleared in C57Black6/J mice with conditional deletion of Fas in DCs. The immune response to LCMV is characterized by an extended survival of virus-specific effector T cells. Moreover, transfer of Fas-negative DCs from noninfected mice to preinfected animals results in either complete clearance of the virus or a significant reduction of viral titers. Thus, DC-specific Fas expression plays a role in regulation of antiviral responses and suggests a strategy for stimulation of T cells in chronically infected animals and humans to achieve the clearance of persistent viruses.

Cyclic GMP catabolism up-regulation in MRL/lpr lupus-prone mice is associated with organ remodeling

Production of high titer of antibodies against nuclear components is a hallmark of systemic lupus erythematosus, an autoimmune disease characterized by the progressive chronic inflammation of multiple joints and organs. Organ damage and dysfunction such as renal failure are typical clinical features in lupus. Cell hypermetabolism and hypertrophy can accelerate organ dysfunction. In this study we focus on a specific murine model of lupus, the MRL/lpr strain, and investigated the role of cyclic guanosine monophosphate (cGMP) catabolism in organ remodeling of main target tissues (kidney, spleen and liver) in comparison with age-matched control mice. In MRL/lpr-prone mice, the cGMP-phosphodiesterase (PDE) activities were significantly increased in the kidney (3-fold, P<0.001), spleen (2-fold, P<0.001) and liver (1.6-fold, P<0.05). These raised activity levels were paralleled by both an increased activity of PDE1 in the kidney (associated with nephromegaly) and in the liver, and PDE2 in the spleen of lupus-prone mice. The up-regulation of PDE1 and PDE2 activities were associated with a decrease in intracellular cGMP levels. This underlines an alteration of cGMP-PDE signaling in the kidney, spleen and liver targeting different PDEs according to organs. In good agreement with these findings, a single intravenous administration to MRL/lpr mice of nimodipine (PDE1 inhibitor) but not of EHNA (PDE2 inhibitor) was able to significantly lower peripheral hypercellularity (P=0.0401), a characteristic feature of this strain of lupus-prone mice. Collectively, our findings are important for generating personalized strategies to prevent certain forms of the lupus disease as well as for understanding the role of PDEs and cGMP in the pathophysiology of lupus.

Trim27-deficient mice are susceptible to streptozotocin-induced diabetes

Tumor necrosis factor α (TNF-α) plays an important role in cell proliferation and apoptosis, and defects in TNF-α-induced apoptosis are associated with various diseases. TRIM27 is a tripartite motif (TRIM) protein containing RING finger, B-box, and coiled-coil domains. We recently reported that TRIM27 positively regulates TNF-α-induced apoptosis through deubiquitination of receptor-interacting protein 1 (RIP1). Multiple studies have suggested a link between TNF-α pathway and various diseases, such as diabetes and colitis. Here, we report that Trim27-deficient mice were susceptible to streptozotocin (STZ)-induced diabetes, a mouse model of diabetes. Infiltration of T cells and cleaved caspase-3 signals were enhanced, and β-cell mass was decreased in Trim27-deficient islets compared to wild-type islets. On the other hand, Trim27-mutation did not affect the dextran sodium sulphate (DSS)-induced colitis. These data support the idea that the TRIM27 mutation is responsible for the development of certain types of diseases.

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Trim27-deficient mice are susceptible to streptozotocin-induced diabetes.

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Infiltration of T cells is enhanced in Trim27-deficient islets.

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Beta-cell mass was decreased in Trim27-deficient islets.

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Trim27-deficient mice are not susceptible to dextran sodium sulphate-induced colitis.

Interferon-γ excess leads to pathogenic accumulation of follicular helper T cells and germinal centers

Overactivity of the germinal center (GC) pathway resulting from accumulation of follicular helper T (Tfh) cells causes autoimmunity, underscoring the need to understand the factors that control Tfh cell homeostasis. Here we have identifed posttranscriptional repression of interferon-γ (Ifng) mRNA as a mechanism to limit Tfh cell formation. By using the sanroque lupus model, we have shown that decreased Ifng mRNA decay caused excessive IFN-γ signaling in T cells and led to accumulation of Tfh cells, spontaneous GC, autoantibody formation, and nephritis. Unlike ICOS and T-bet deficiency that failed to rescue several autoimmune manifestations, interferon-γ receptor (IFN-γR) deficiency prevented lupus development. IFN-γ blockade reduced Tfh cells and autoantibodies, demonstrating that IFN-γ overproduction was required to sustain lupus-associated pathology. Increased IFN-γR signaling caused Bcl-6 overexpression in Tfh cells and their precursors. This link between IFN-γ and aberrant Tfh cell formation provides a rationale for IFN-γ blockade in lupus patients with an overactive Tfh cell-associated pathway.

TLR9-mediated signals rescue B-cells from Fas-induced apoptosis via inactivation of caspases

The death receptor, CD95/Fas, serves to eliminate potentially dangerous, self-reactive B cells. Engagement of B-cell receptors (BCR) on mature B-cells mediates the escape from cell death resulting in the activation and expansion of antigen specific clones. In addition to the antigen receptors, the receptors of B-cell activating factor belong to the tumor necrosis factor (TNF) family (BAFFR); moreover, the pattern recognition receptor, TLR9 may also deliver survival signals inhibiting Fas-mediated death of B-cells. Our aim was to compare the mechanism of BCR-induced and the BAFFR- or TLR9-stimulated rescue of B-cells from CD95/Fas-mediated apoptosis. We have found that BAFFR and TLR9 collaborate with BCR to protect B-cells from Fas-induced elimination and the rescue is independent of protein synthesis. The results revealed that the TLR9- and BCR-triggered rescue signals are transmitted through partially overlapping pathways; the protein kinase C (PKC) and the abl kinase induced phosphorylation may inactivate caspases in both CpG and anti-IgG stimulated cells. However, PI3-K activation is crucial upon the BCR driven anti-apoptotic effect, while p38 MAPK-mediated inactivation of caspases seems to play essential role in TLR9-mediated protection against Fas-induced programmed cell death.

Increased levels of prolactin receptor expression correlate with the early onset of lupus symptoms and increased numbers of transitional-1 B cells after prolactin treatment

Background

Prolactin is secreted from the pituitary gland and other organs, as well as by cells such as lymphocytes. Prolactin has an immunostimulatory effect and is associated with autoimmune diseases that are characterised by abnormal B cell activation, such as systemic lupus erythematosus (SLE). Our aim was to determine if different splenic B cell subsets express the prolactin receptor and if the presence of prolactin influences these B cell subsets and correlates with development of lupus.

Results

Using real-time PCR and flow cytometry, we found that different subsets of immature (transitional) and mature (follicular, marginal zone) B cells express different levels of the prolactin receptor and are differentially affected by hyperprolactinaemia. We found that transitional B cells express the prolactin receptor at higher levels compared to mature B cells in C57BL/6 mice and the lupus-prone MRL/lpr and MRL mouse strains. Transitional-1 (T1) B cells showed a higher level of prolactin receptor expression in both MRL/lpr and MRL mice compared to C57BL/6 mice. Hyperprolactinaemia was induced using metoclopramide, which resulted in the development of early symptoms of SLE. We found that T1 B cells are the main targets of prolactin and that prolactin augments the absolute number of T1 B cells, which reflects the finding that this B cell subpopulation expresses the highest level of the prolactin receptor.

Conclusions

We found that all B cell subsets express the prolactin receptor but that transitional B cells showed the highest prolactin receptor expression levels. Hyperprolactinaemia in mice susceptible to lupus accelerated the disease and increased the absolute numbers of T1 and T3 B cells but not of mature B cells, suggesting a primary effect of prolactin on the early stages of B cell maturation in the spleen and a role of prolactin in B cell differentiation, contributing to SLE onset.

CD95 death receptor and epidermal growth factor receptor (EGFR) in liver cell apoptosis and regeneration

Recent evidence suggests that signaling pathways towards cell proliferation and cell death are much more interconnected than previously thought. Whereas not only death receptors such as CD95 (Fas, APO-1) can couple to both, cell death and proliferation, also growth factor receptors such as the epidermal growth factor receptor (EGFR) are involved in these opposing kinds of cell fate. EGFR is briefly discussed as a growth factor receptor involved in liver cell proliferation during liver regeneration. Then the role of EGFR in activating CD95 death receptor in liver parenchymal cells (PC) and hepatic stellate cells (HSC), which represent a liver stem/progenitor cell compartment, is described summarizing different ways of CD95- and EGFR-dependent signaling in the liver. Here, depending on the hepatic cell type (PC vs. HSC) and the respective signaling context (sustained vs. transient JNK activation) CD95-/EGFR-mediated signaling ends up in either liver cell apoptosis or cell proliferation.

Deconstructing p53 transcriptional networks in tumor suppression

p53 is a pivotal tumor suppressor that induces apoptosis, cell-cycle arrest and senescence in response to stress signals. Although p53 transcriptional activation is important for these responses, the mechanisms underlying tumor suppression have been elusive. To date, no single or compound mouse knockout of specific p53 target genes has recapitulated the dramatic tumor predisposition that characterizes p53-null mice. Recently, however, analysis of knock-in mice expressing p53 transactivation domain mutants has revealed a group of primarily novel direct p53 target genes that may mediate tumor suppression in vivo. We present here an overview of well-known p53 target genes and the tumor phenotypes of the cognate knockout mice, and address the recent identification of new p53 transcriptional targets and how they enhance our understanding of p53 transcriptional networks central for tumor suppression.

Hematopoietic Fas deficiency does not affect experimental atherosclerotic lesion formation despite inducing a proatherogenic state

The Fas death receptor (CD95) is expressed on macrophages, smooth muscle cells, and T cells within atherosclerotic lesions. Given the dual roles of Fas in both apoptotic and nonapoptotic signaling, the aim of the present study was to test the effect of hematopoietic Fas deficiency on experimental atherosclerosis in low-density lipoprotein receptor-null mice (Ldlr(-/-)). Bone marrow from Fas(-/-) mice was used to reconstitute irradiated Ldlr(-/-) mice as a model for atherosclerosis. After 16 weeks on an 0.5% cholesterol diet, no differences were noted in brachiocephalic artery lesion size, cellularity, or vessel wall apoptosis. However, Ldlr(-/-) mice reconstituted with Fas(-/-) hematopoietic cells had elevated hyperlipidemia [80% increase, relative to wild-type (WT) controls; P < 0.001] and showed marked elevation of plasma levels of CXCL1/KC, CCL2/MCP-1, IL-6, IL-10, IL-12 subunit p70, and soluble Fas ligand (P < 0.01), as well as systemic microvascular inflammation. It was not possible to assess later stages of atherosclerosis because of increased mortality in Fas(-/-) bone marrow recipients. Our data indicate that hematopoietic Fas deficiency does not affect early atherosclerotic lesion development in Ldlr(-/-) mice.

Defining the antigen receptor-dependent regulatory network that induces arrest of cycling immature B-lymphocytes

Background

Engagement of the antigen receptor on immature B-lymphocytes leads to cell cycle arrest, and subsequent apoptosis. This is an essential process for eliminating self reactive B cells during its different stages of development. However, the mechanism by which it is achieved is not completely understood.

Results

Here we employed a systems biology approach that combined extensive experimentation with in silico methodologies to chart the network of receptor-activated pathways that mediated the arrest of immature B cells in the G1 phase of the cell cycle. Interestingly, we found that only a sparse network of signaling intermediates was recruited upon engagement of the antigen receptor. This then led to the activation of a restricted subset of transcription factors, with the consequent induction of genes primarily involved in the cell death pathway. Subsequent experiments revealed that the weak initiation of intracellular signaling pathways derived from desensitization of the receptor-proximal protein tyrosine kinase Lyn, to receptor-dependent activation. Intriguingly, the desensitization was a result of the constitutive activation of this kinase in unstimulated cells, which was likely maintained through a regulatory feedback loop involving the p38 MAP kinase. The high basal activity then attenuated the ability of the antigen receptor to recruit Lyn, and thereby also the downstream signaling intermediates. Finally, integration of these results into a mathematical model provided further substantiation to the novel finding that the ground state of the intracellular signaling machinery constitutes an important determinant of the outcome of receptor-induced cellular responses.

Conclusions

Our results identify the global events leading to the G1 arrest and subsequent apoptosis in immature B cells upon receptor activation.

FADD deficiency impairs early hematopoiesis in the bone marrow

Signal transduction mediated by Fas-associated death domain protein (FADD) represents a paradigm of coregulation of apoptosis and cellular proliferation. During apoptotic signaling induced by death receptors including Fas, FADD is required for the recruitment and activation of caspase 8. In addition, a death receptor-independent function of FADD is essential for embryogenesis. In previous studies, FADD deficiency in embryonic stem cells resulted in a complete lack of B cells and dramatically reduced T cell numbers, as shown by Rag1(-/-) blastocyst complementation assays. However, T-specific FADD-deficient mice contained normal numbers of thymocytes and slightly reduced peripheral T cell numbers, whereas B cell-specific deletion of FADD led to increased peripheral B cell numbers. It remains undetermined what impact an FADD deficiency has on hematopoietic stem cells and progenitors. The current study analyzed the effect of simultaneous deletion of FADD in multiple cell types, including bone marrow cells, by using the IFN-inducible Mx1-cre transgene. The resulting FADD mutant mice did not develop lymphoproliferation diseases, unlike Fas-deficient mice. Instead, a time-dependent depletion of peripheral FADD-deficient lymphocytes was observed. In the bone marrow, a lack of FADD led to a dramatic decrease in the hematopoietic stem cells and progenitor-enriched population. Furthermore, FADD-deficient bone marrow cells were defective in their ability to generate lymphoid, myeloid, and erythroid cells. Thus, the results revealed a temporal requirement for FADD. Although dispensable during lymphopoiesis post lineage commitment, FADD plays a critical role in early hematopoietic stages in the bone marrow.

Cutting edge: Lymphoproliferation caused by Fas deficiency is dependent on the transcription factor eomesodermin

A hallmark of autoimmune lymphoproliferative syndrome (ALPS), caused by mutation of the Fas death receptor, is massive lymphadenopathy from aberrant expansion of CD4(-)CD8(-) (double-negative [DN]) T cells. Eomesodermin (Eomes) is a member of the T-box family of transcription factors and plays critical roles in effector cell function and memory cell fitness of CD8(+) T lymphocytes. We provide evidence in this study that DN T cells exhibit dysregulated expression of Eomes in humans and mice with ALPS. We also find that T cell-specific deletion of Eomes prevents lymphoid hypertrophy and accumulation of DN T cells in Fas-mutant mice. Although Eomes has critical physiological roles in the function and homeostasis of CD8(+) T cells, overexpression of Eomes appears to enable pathological induction or expansion of unusual CD8-related T cell subsets. Thus, antagonism of Eomes emerges as a therapeutic target for DN T cell ablation in ALPS.

Extreme lymphoproliferative disease and fatal autoimmune thrombocytopenia in FasL and TRAIL double-deficient mice

To delineate the relative roles of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and Fas ligand in lymphocyte biology and lymphoproliferative disease, we generated mice defective in both molecules. B6.GT mice develop severe polyclonal lymphoproliferative disease because of accumulating CD3(+)CD4(-)CD8(-)B220(+) T cells, CD4(+) and CD8(+) T cells, and follicular B cells, and mice die prematurely from extreme lymphocytosis, thrombocytopenia, and hemorrhage. Accumulating lymphocytes resembled antigen-experienced lymphocytes, consistent with the maximal resistance of B6.GT CD4(+) and CD8(+) T cell to activation-induced cell death. More specifically, we show that TRAIL contributes to Fas ligand-mediated activation-induced cell death and controls lymphocyte apoptosis in the presence of interferon-gamma once antigen stimulation is removed. Furthermore, dysregulated lymphocyte homeostasis results in the production of anti-DNA and rheumatoid factor autoantibodies, as well as antiplatelet IgM and IgG causing thrombocytopenia. Thus, B6.GT mice reveal new roles for TRAIL in lymphocyte homeostasis and autoimmune lymphoproliferative syndromes and are a model of spontaneous idiopathic thrombocytopenia purpura secondary to lymphoproliferative disease.

T follicular helper cells during immunity and tolerance

Helper T cells are required for the generation of a potent immune response to foreign antigens. Amongst them, T follicular helper (Tfh) cells are specialized in promoting protective, long-lived antibody responses that arise from germinal centers. Within these structures, the specificity of B cell receptors may change, due to the process of random somatic hypermutation aimed at increasing the overall affinity of the antibody response. The danger of emerging self-reactive specificities is offset by a stringent selection mechanism delegated in great part to Tfh cells. Only those B cells receiving survival signals from Tfh cells can exit the germinal centers to join the long-lived pools of memory B cells and bone marrow-homing plasma cells. Thus, a crucial immune tolerance checkpoint to prevent long-term autoantibody production lies in the ability to tolerize Tfh cells and to control positive and negative selection signals delivered by this subset. This review tackles the known mechanisms that ensure Tfh tolerance, many of them shared by other T helper subsets during thymic development and priming, but others unique to Tfh cells. Amongst the latter are checkpoints at the stages of Tfh differentiation, follicular migration, growth, longevity, and quality control of selection signals. Finally, we also discuss the consequences of a breakdown in Tfh tolerance.

Prevention of autoimmunity and control of recall response to exogenous antigen by Fas death receptor ligand expression on T cells

Mice with mutations in the gene encoding Fas ligand (FasL) develop lymphoproliferation and systemic autoimmune diseases. However, the cellular subset responsible for the prevention of autoimmunity in FasL-deficient mice remains undetermined. Here, we show that mice with FasL loss on either B or T cells had identical life span as littermates, and both genotypes developed signs of autoimmunity. In addition, we show that T cell-dependent death was vital for the elimination of aberrant T cells and for controlling the numbers of B cells and dendritic cells that dampen autoimmune responses. Furthermore, we show that the loss of FasL on T cells affected the follicular dentritic cell network in the germinal centers, leading to an impaired recall response to exogenous antigen. These results disclose the distinct roles of cellular subsets in FasL-dependent control of autoimmunity and provide further insight into the role of FasL in humoral immunity.

MicroRNAs: key players in the immune system, differentiation, tumorigenesis and cell death

Micro (mi)RNAs are small, highly conserved noncoding RNAs that control gene expression post-transcriptionally either via the degradation of target mRNAs or the inhibition of protein translation. Each miRNA is believed to regulate the expression of multiple mRNA targets, and many miRNAs have been linked to the initiation and progression of human cancer. miRNAs control various activities of the immune system and different stages of hematopoietic development, and their misexpression is the cause of various blood malignancies. Certain miRNAs have oncogenic activities, whereas others have the potential to act as tumor suppressors. Because they control fundamental processes such as differentiation, cell growth and cell death, the study of the role of miRNAs in human neoplasms holds great promise for novel forms of therapy. Here, we summarize the role of miRNAs and their targets in contributing to human cancers and their function as regulators of apoptotic pathways and the immune system.

[Could apoptotic markers help the exploration of male infertility?]

Apoptosis is a cell death program involved in different steps of spermatogenesis, first at puberty, at the beginning of spermatogenesis, then in adult testicles by controlling normal spermatogenesis. As a result, apoptosis deregulation can affect spermatogenesis. Many studies have provided evidence that apoptosis deregulation in germinal cells resulted in male infertility. In addition, apoptosis detection in ejaculated spermatozoa arouses a growing interest in research as a reliable marker of spermatozoon quality. The aim of this review is to summarize our knowledge on physiological apoptosis during spermatogenesis, and then analyse the possibility of using apoptotic markers as selective markers of spermatozoon quality to optimize the rate of success of in vitro fertilization.

Cellular and molecular mechanisms of liver injury

Derangements in apoptosis of liver cells are mechanistically important in the pathogenesis of end-stage liver disease. Vulnerable hepatocytes can undergo apoptosis via an extrinsic, death receptor-mediated pathway, or alternatively intracellular stress can activate the intrinsic pathway of apoptosis. Both pathways converge on mitochondria, and mitochondrial dysfunction is a prerequisite for hepatocyte apoptosis. Persistent apoptosis is a feature of chronic liver diseases, and massive apoptosis is a feature of acute liver diseases. Fibrogenesis is stimulated by ongoing hepatocyte apoptosis, eventually resulting in cirrhosis of the liver in chronic liver diseases. Endothelial cell apoptosis occurs in ischemia-reperfusion injury. Natural killer and natural killer T cells remove virus-infected hepatocytes by death receptor-mediated fibrosis. Lastly, activated stellate cell apoptosis leads to slowing and resolution of apoptosis. This review summarizes recent cellular and molecular advances in the understanding of the injury mechanisms leading to end-stage liver disease.

Apoptosis signaling pathways and lymphocyte homeostasis

It has been almost three decades since the term "apoptosis" was first coined to describe a unique form of cell death that involves orderly, gene-dependent cell disintegration. It is now well accepted that apoptosis is an essential life process for metazoan animals and is critical for the formation and function of tissues and organs. In the adult mammalian body, apoptosis is especially important for proper functioning of the immune system. In recent years, along with the rapid advancement of molecular and cellular biology, great progress has been made in understanding the mechanisms leading to apoptosis. It is generally accepted that there are two major pathways of apoptotic cell death induction: extrinsic signaling through death receptors that leads to the formation of the death-inducing signaling complex (DISC), and intrinsic signaling mainly through mitochondria which leads to the formation of the apoptosome. Formation of the DISC or apoptosome, respectively, activates initiator and common effector caspases that execute the apoptosis process. In the immune system, both pathways operate; however, it is not known whether they are sufficient to maintain lymphocyte homeostasis. Recently, new apoptotic mechanisms including caspase-independent pathways and granzyme-initiated pathways have been shown to exist in lymphocytes. This review will summarize our understanding of the mechanisms that control the homeostasis of various lymphocyte populations.

Long-term exposure to superantigen induces p27Kip1 and Bcl-2 expression in effector memory CD4+ T cells

The long-term exposure of mice to superantigen SEA using a mini-osmotic pump (SEA pump) induced a long-lasting expansion of Vbeta3+ CD4+ T cells with T helper (Th) 2 cell-type properties. Removal of the SEA pump 10 days after pump implantation did not significantly alter the level of Vbeta3+ CD4+ T cell expansion/maintenance. Furthermore, CFSE-labeled CD4+ T cells failed to divide when transferred to post-implantation day 15 mice. Thus, CD4+ T cells appeared to survive for at least 30 days in the absence of a sufficient amount of antigen to trigger cell division. STAT6 deficient mice, in which Th2 cell development is largely impaired, also exhibited a protracted cell expansion, similar to that observed in normal mice, suggesting that the Th2 cell property is dispensable for the maintenance of Vbeta3+ CD4+ T cell expansion. The expanded CD4+ T cells on post-implantation day 26 were arrested in the G0/G1 phase of the cell cycle and showed a lower level of cell division upon restimulation. The Cdk inhibitor p27(Kip1) was highly expressed, and Cdk2 was downregulated. Moreover, the CD4+ T cells were resistant to in vitro apoptosis induction in parallel with their level of Bcl-2 expression. Collectively, the Vbeta3+ CD4+ T cells appeared to develop into long-lived memory T cells with cell cycle arrest upon long-term exposure to SEA.

T cell recognition and immunity in the fetus and mother

All multi-cellular organisms protect themselves from invasion by allogeneic organisms and cells by mounting immune responses. While protective, allogeneic immune responses present a threat to successful reproduction in eutherian mammals in which the maternal immune system is exposed to the semi-allogeneic fetus. Thus, successful reproduction in eutherian mammals depends on mechanisms that control the potentially hostile maternal immune system without hindering immune responses to potentially deadly infectious organisms. Three general mechanisms have been proposed to explain successful reproduction in mammals: (i) the formation of an anatomical barrier between mother and fetus; (ii) expression of allogeneic antigens at a very low level by the fetus; and (iii) hindrance of the maternal immune system responding to fetal antigens. These mechanisms explain in part how the fetus evades the maternal immune system; however, they do not explain fully the survival of the fetus. We hypothesize that site-specific immune suppression may play an important role in successful eutherian reproduction in conjunction with other mechanisms. Site-specific immune suppression at the fetal-maternal interface would protect the fetus while allowing peripheral maternal immune responses to continue unabated.

Exposure to inorganic mercury in vivo attenuates extrinsic apoptotic signaling in Staphylococcal aureus enterotoxin B stimulated T-cells

The heavy metal mercury (Hg) is known to have immunomodulatory properties affecting lymphocyte signal transduction, death receptor signaling and autoimmunity. In this study we tested the hypothesis that Hg exposure would attenuate T-cell activation and caspase 8 and 3 activity in response to antigenic stimuli. To test this hypothesis, BALB/cJ mice were exposed to 10 mg/l mercuric chloride (HgCl(2)) in their drinking water for 2 weeks followed by injection with 20 microg of the Staphylococcal aureus enterotoxin B (SEB) superantigen. Eighteen hours after SEB challenge, there was a statistically significant reduction in caspase 8 and caspase 3 enzyme activity in the SEB reactive Vbeta8+ T-cells. The attenuated caspase activity in Hg-exposed mice persisted for 48 h after exposure. Moreover, activation of caspase 8 and caspase 3 was reduced by more than 60% in CD95 deficient MRL/MpJ-Fas(lpr) mice demonstrating that caspase 8 and 3 activation in response to SEB is CD95 dependent. In addition to the effects of Hg on caspase activity, expression of the T-cell activation marker CD69 was also attenuated in SEB reactive Vbeta8 T-cells in Hg-exposed mice. Moreover, CD69 expression in MRL/MpJ-Fas(lpr) mice was also reduced. Taken together the caspase and CD69 data support a role for CD95 in promoting a proapoptotic and activated state in SEB responsive T-lymphocytes and this state is attenuated by the autoimmune potentiating environmental agent mercury.

OBF-1 is essential for the generation of antibody-secreting cells and the development of autoimmunity in MRL-lpr mice

As reported previously, the lack of the transcriptional co-activator OBF-1 prevented development of autoimmunity in Aiolos knockout mice. To further investigate the role and mechanism of OBF-1 in autoimmunity, we crossed OBF-1 null mice with MRL-lpr mice and generated OBF-1-deficent MRL-lpr mice. OBF-1 deletion abrogated all autoantibodies in the MRL-lpr mice, including anti-dsDNA Ab and anti-Sm Ab. The failure to produce autoantibodies was not related to development of immature or mature B cells, but correlated with severely reduced antibody-secreting cells (ASCs). The loss of OBF-1 protected against hypergammaglobulinemia, immune complex deposition, glomerulonephritis, and early mortality in MRL-lpr mice. In addition, accumulation of CD4(-)CD8(-)B220(+)CD3(+) T cells that characteristically develop in Fas mutation mice were markedly reduced in MRL-lpr mice without OBF-1. These results identify OBF-1 as a critical gene in the development of autoantibodies and reveal an essential role for OBF-1 in the generation of antibody/autoantibody-secreting cells in vivo.

Treatment of autoimmune diseases in MRL/lpr mice by allogenic bone marrow transplantation plus adult thymus transplantation

MRL/lpr mice (H-2(k)) with Fas gene mutation develop severe autoimmune diseases, and their haematolymphoid cells such as bone marrow and spleen cells showed a low apoptotic activity by irradiation. Therefore, conventional bone marrow transplantation (BMT) cannot be used to treat autoimmune diseases in these mice (chimeric resistance). In the present study, we examine the effects of additional adult thymus transplantation (TT) from the same donor on successful BMT. When the MRL/lpr mice were lethally irradiated (9 x 5Gy) and reconstituted with 3 x 10(7) of C57BL/6 mouse (H-2b) bone marrow cells (BMCs) in conjunction with TT, the mice significantly survived long term and showed a high donor-derived chimerism in comparison with those treated with BMT alone. Interestingly, the numbers of not only donor-derived T cells but also B cells increased significantly in the mice treated with BMT plus TT, even at the early phase of BMT. The number of aberrant CD3+B220+ cells decreased significantly, and the numbers of lymphocyte subsets were also normalized 4 weeks after the treatment. Finally, the autoimmune diseases in MRL/lpr mice could be cured by BMT with TT. These results indicate that the combination of BMT plus TT can overcome the chimeric resistance and treat the autoimmune diseases in MRL/lpr mice.