Low bcl-2 expression and increased spontaneous apoptosis in T-lymphocytes from newly-diagnosed IDDM patients

IL-21 limits peripheral lymphocyte numbers through T cell homeostatic mechanisms

Background

IL-21, a member of the common γ-chain utilizing family of cytokines, participates in immune and inflammatory processes. In addition, the cytokine has been linked to autoimmunity in humans and rodents.

Methodology/Principal Findings

To investigate the mechanism whereby IL-21 affects the immune system, we investigated its role in T cell homeostasis and autoimmunity in both non-autoimmune C57BL/6 and autoimmune NOD mice. Our data indicate that IL-21R knockout C57BL/6 and NOD mice show increased size of their lymphocyte population and decreased homeostatic proliferation. In addition, our experimental results demonstrate that IL-21 inhibits T cell survival. These data suggest that IL-21 acts to limit the size of the T cell pool. Furthermore, our data suggest IL-21 may contribute to the development of autoimmunity.

Conclusions/Significance

Taken together, our results suggest that IL-21 plays a global role in regulating T cell homeostasis, promoting the continuous adaptation of the T cell lymphoid space.

At-risk and recent-onset type 1 diabetic subjects have increased apoptosis in the CD4+CD25+ T-cell fraction

Background

In experimental models, Type 1 diabetes T1D can be prevented by adoptive transfer of CD4+CD25+ FoxP3+ suppressor or regulatory T cells. Recent studies have found a suppression defect of CD4+CD25+^high T cells in human disease. In this study we measure apoptosis of CD4+CD25+^high T cells to see if it could contribute to reduced suppressive activity of these cells.

Methods and Findings

T-cell apoptosis was evaluated in children and adolescent 35 females/40 males subjects comprising recent-onset and long-standing T1D subjects and their first-degree relatives, who are at variable risk to develop T1D. YOPRO1/7AAD and intracellular staining of the active form of caspase 3 were used to evaluate apoptosis. Isolated CD4+CD25+^high and CD4+CD25− T cells were co-cultured in a suppression assay to assess the function of the former cells. We found that recent-onset T1D subjects show increased apoptosis of CD4+CD25+^high T cells when compared to both control and long-standing T1D subjects p<0.0001 for both groups. Subjects at high risk for developing T1D 2–3Ab+ve show a similar trend p<0.02 and p<0.01, respectively. On the contrary, in long-standing T1D and T2D subjects, CD4+CD25+^high T cell apoptosis is at the same level as in control subjects p = NS. Simultaneous intracellular staining of the active form of caspase 3 and FoxP3 confirmed recent-onset FoxP3+ve CD4+CD25+^high T cells committed to apoptosis at a higher percentage 15.3±2.2 compared to FoxP3+ve CD4+CD25+^high T cells in control subjects 6.1±1.7 p<0.002. Compared to control subjects, both recent-onset T1D and high at-risk subjects had significantly decreased function of CD4+CD25+^high T cells p = 0.0007 and p = 0.007, respectively.

Conclusions

There is a higher level of ongoing apoptosis in CD4+CD25+^high T cells in recent-onset T1D subjects and in subjects at high risk for the disease. This high level of CD4+CD25+^high T-cell apoptosis could be a contributing factor to markedly decreased suppressive potential of these cells in recent-onset T1D subjects.

IL-15 is elevated in serum patients with type 1 diabetes mellitus

IL-15 is a 14-15 kD cytokine produced by monocytes/macrophages and shares some biological actions with IL-2. The serum concentration of IL-15 in type 1 diabetic patients has not been reported seriously. Our studies were performed on 51 patients (28 women and 23 men) with type 1 diabetes mellitus. Healthy control subjects (n=22, 12 women and 10 men, mean age 29 years, range 24-32 years) were recruited from medical staff. IL-15 serum levels were detected by ELISA (R & D systems, USA). Short-term and long-term metabolic control parameters, lipid profile and C-reactive protein levels were also estimated. There was a statistically significant increase of serum IL-15 in type 1 diabetic patients in comparison to the control subjects (4.4 (1.5-11.8) versus 2.9 (1.5-6.0) pg/ml, p<0.05). Diabetic patients with higher IL-15 serum levels had higher HbA1c values. A correlation was found between IL-15 serum concentration and HbA1c (N(s)=0.31, p=0.029). There was no relation between acute hyperglycaemic episodes and IL-15 serum level. The potential associations between IL-15 serum level and long-term diabetic control lead us to speculate that IL-15 may serve as a target for future treatment in patients with prediabetes and/or for prevention of late diabetic complications.

Type 1 and type 2 diabetic patients display different patterns of cellular microparticles

The development of vasculopathies in diabetes involves multifactorial processes including pathological activation of vascular cells. Release of microparticles by activated cells has been reported in diseases associated with thrombotic risk, but few data are available in diabetes. The aim of the present work was to explore the number and the procoagulant activity of cell-derived microparticles in type 1 and 2 diabetic patients. Compared with age-matched control subjects, type 1 diabetic patients presented significantly higher numbers of platelet and endothelial microparticles (PMP and EMP), total annexin V-positive blood cell microparticles (TMP), and increased levels of TMP-associated procoagulant activity. In type 2 diabetic patients, only TMP levels were significantly higher without concomitant increase of their procoagulant activity. Interestingly, in type 1 diabetic patients, TMP procoagulant activity was correlated with HbA(1c), suggesting that procoagulant activity is associated with glucose imbalance. These results showed that a wide vesiculation process, resulting from activation or apoptosis of several cell types, occurs in diabetes. However, diabetic patients differ by the procoagulant activity and the cellular origin of microparticles. In type 1 diabetic patients, TMP-procoagulant activity could be involved in vascular complications. Moreover, its correlation with HbA(1c) reinforces the importance of an optimal glycemic control in type 1 diabetes.

Gender- and androgen-related influence on the expression of proto-oncogene and apoptotic factor mRNAs in lacrimal glands of autoimmune and non-autoimmune mice

Our previous studies have shown that the mRNA levels of c-myb, c-myc, bcl-2 and p53 are higher, and partial Fas antigen (i.e. exons 1-2) lower, in lacrimal tissues of female, as compared to male, MRL/lpr mice, which are a model of Sjögren's syndrome. We have also found that this gender-related difference in bcl-2 and c-myb expression appears to be due to the influence of androgens. To extend these findings, we sought to determine: first, whether these gender- and/or hormone-associated variations in mRNA content are unique to MRL/lpr mice, or are also present in lacrimal glands of other murine strains, including autoimmune NZB/NZW F1 (F1) and non-obese diabetic (NOD), as well as non-autoimmune C3H/HeJ (C3H) and BALB/c, mice; and second, whether the levels of these apoptotic factor mRNAs are altered in lacrimal tissues of mice (i.e. testicular feminized (Tfm) with dysfunctional androgen receptors, as compared to glandular amounts in their 'normal' controls (i.e. Tabby). Lacrimal tissues were obtained from adult mice, which were either untreated or treated with placebo or testosterone for 21 days. Glands were processed for the analysis of proto-oncogene mRNAs by RT-PCR (at exponential phase of amplification) and data were standardized to the corresponding levels of beta-actin mRNA. Our results demonstrate that Fas antigen, Fas ligand, c-myb, c-myc, bcl-2, Bax and p53 mRNAs are present in lacrimal tissues of F1, NOD, C3H, BALB/c, Tabby and Tfm mice. The relative levels of Fas antigen mRNA are consistently higher in glands of males, whereas amounts of bcl-2 mRNA are greater in tissues of F1, C3H and BALB/c females. Testosterone administration induced a significant increase in the lacrimal gland content of Bax mRNA, but a striking decrease in the lacrimal tissue level of bcl-2 mRNA in F1 and C3H mice. Lacrimal glands of Tfm mice contained elevated amounts of bcl-2 mRNA, as compared to values in tissues of their Tabby controls. In summary, our findings show that fundamental gender-related differences exist in the expression of genes associated with programmed cell death in lacrimal glands of autoimmune and normal mice. In addition, some of these differences may be due, at least in part, to the effect of androgens.

Neurons undergo apoptosis in animal and cell culture models of diabetes

Recent clinical trials indicate that the severity of diabetic neuropathy is correlated with the level of patient glycemic control. In the current study, hyperglycemia induces apoptotic changes in dorsal root ganglion neurons and Schwann cells in vivo both in streptozotocin-treated diabetic rats and in rats made acutely hyperglycemic with infused glucose. Typical apoptotic nuclear and cytoplasmic changes are observed. In addition mitochondrial changes recently reported to occur as part of the apoptotic cascade, such as ballooning of mitochondria and disruption of the internal cristae, are seen in diabetic dorsal root ganglion neurons and Schwann cells. Similar changes have been reported in neurons in the presence of oxidative stress. In order to study the neurotoxic effects of high glucose we developed an in vitro model using rat dorsal root ganglion neurons. In dorsal root ganglion cultured in defined medium, addition of moderate glucose levels results in neurite degeneration and apoptosis. These changes are coupled with activation of caspase-3, dependent on the concentration of glucose. The apoptotic changes observed in vitro are similar to those observed in vivo. In contrast, addition of IGF-I, even at physiological concentrations, prevents activation of caspase-3 and neuronal apoptosis in vitro. We suggest that oxidative stress may promote the mitochondrial changes in diabetic animals and lead to activation of programmed cell death caspase pathways. These results imply a new pathogenetic mechanism for diabetic sensory neuropathy.

Serum from patients with type 2 diabetes with neuropathy induces complement-independent, calcium-dependent apoptosis in cultured neuronal cells

We hypothesized that sera from type 2 diabetic patients with neuropathy contains an autoimmune immunoglobulin that promotes complement-independent, calcium-dependent apoptosis in neuronal cell lines. Neuronal cells were cultured in the presence of complement-inactivated sera obtained from patients with type 2 diabetes with and without neuropathy and healthy adult control patients. Serum from diabetic patients with neuropathy was associated with a significantly greater induction of apoptosis, compared to serum from diabetic patients without neuropathy and controls. In the presence of calcium channel antagonists, induction of apoptosis was reduced by approximately 50%. Pretreatment of neuronal cells with serum from diabetic patients with neuropathy was associated with a significant increase in elevated K+-evoked cytosolic calcium concentration. Serum-induced enhancement in cytosolic calcium and calcium current density was blocked by treatment with trypsin and filtration of the serum using a 100,000-kd molecular weight filter. Treatment with an anti-human IgG antibody was associated with intense fluorescence on the surface of neuronal cells exposed to sera from patients with type 2 diabetes mellitus with neuropathy. We conclude that sera from type 2 diabetic patients with neuropathy contains an autoimmune immunoglobulin that induces complement-independent, calcium-dependent apoptosis in neuronal cells.

Comparison of Sindbis virus-induced pathology in mosquito and vertebrate cell cultures

We have compared Sindbis virus-induced cytopathology in vertebrate and mosquito (Aedes albopictus) cell cultures. It has been shown that vertebrate cells undergo apoptosis when infected by Sindbis virus and this was confirmed here using hamster cells (BHK). The occurrence of cell death in Sindbis virus-infected A. albopictus cells is a cell clone-specific phenomenon and, unlike in BHK cell cultures, mosquito cell death does not correlate with a large induction of apoptosis, as determined by assays testing for DNA fragmentation or reduced cellular DNA content. Cell cycle distribution changes were observed in Sindbis virus-infected BHK and C7-10 cell cultures, and the changes are distinct, both in the time of induction and the types of perturbations. In Sindbis virus-infected BHK cells, the major cell cycle profile change is the early accumulation of cells with sub-G1 DNA content and a corresponding reduction in the proportion of cells in G1 and G2/M. For Sindbis virus-infected C7-10 cells, the major perturbations are an increased proportion of cells showing G2/M or polyploid DNA content and a reduction in the proportion of G1 and S phase cells. These data suggest that the pathology induced in mosquito cell cultures by Sindbis virus infection may be distinct from the pathology which appears in vertebrate cell cultures.

Quantitative analysis of long-term survival and neuritogenesis in vitro: cochleovestibular ganglion of the chick embryo in BDNF, NT-3, NT-4/5, and insulin

The dynamics of survival and growth were examined for cochleovestibular ganglion (CVG) cells maintained in long-term cultures. CVG cells were explanted from chick embryos after 90 h of incubation into a defined-medium containing BDNF, NT-3, or NT-4/5 and an insulin, transferrin, selenium, and progesterone supplement. Explant survival and neuritogenesis was measured for 23 to 24 days in vitro. All three neurotrophins prolonged CVG survival in a dose-dependent manner although insulin acted as a cofactor. In 0.872 microM insulin-containing medium the ED50 for BDNF and NT-3 was 100 pg/ml, whereas the ED50 for NT-4/5 was 600-1200 pg/ml. However, at later ages in vitro, survival decreased with concentrations of BDNF greater than 2 ng/ml. In insulin-free medium, concentrations of 5-200 ng/ml of BDNF or 30-200 ng/ml of NT-4/5 maintained the survival of explants at a rate that was equivalent to or less than the survival rate of cultures treated with insulin but not with neurotrophin. In contrast, NT-3-treated explants in insulin-free medium did not survive the duration of the experiment. Dose-dependent effects of BDNF and NT-3 on explant neuritogenesis were reflected as an initial delay in outgrowth, whereas NT-4/5 had no effect. Insulin regulation of neuritogenesis was suggested when outgrowth decreased in the presence of an antibody to the insulin receptor. These data suggest that while all three of these neurotrophins protect the CVG from death the long-term consequences of cofactors and certain dose levels should be considered when treating CVG cells in vivo.

Autoimmunity and the highway to diabetes

Insulin-dependent diabetes mellitus (IDDM) is an immunopathological condition involving loss of beta cell function, but views of how this arises are confusing and contradictory. For example, studies with non-obese diabetic mice implicate abnormal cytokine production in disease pathogenesis, but give little insight into how this arises. Many genetic and environmental risk factors have been described, but no single factor predicts the development of disease. Moreover, the prevalence of auto-antibodies suggests an autoimmune aetiology, but no antigen is recognized by all individuals. As an aid to understanding how IDDM develops, this review considers the risk factors as distinct starting points on a journey, and reviews current literature in search of the point where the roads from each origin merge into a highway to diabetes.

Apoptosis in the heart: when and why?

Since mammalian cardiac myocytes essentially rely on aerobic energy metabolism, it has been assumed that cardiocytes die in a catastrophic breakdown of cellular homeostasis (i.e. necrosis), if oxygen supply remains below a critical limit. Recent observations, however, indicate that a process of gene-directed cellular suicide (i.e. apoptosis) is activated in terminally differentiated cardiocytes of the adult mammalian heart by ischemia and reperfusion, and by cardiac overload as well. Apoptosis or programmed cell death is an actively regulated process of cellular self destruction, which requires energy and de novo gene expression, and which is directed by an inborn genetic program. The final result of this program is the fragmentation of nuclear DNA into typical 'nucleosomal ladders', while the functional integrity of the cell membrane and of other cellular organelles is still maintained. The critical step in this regulated apoptotic DNA fragmentation is the proteolytic inactivation of poly-[ADP-ribose]-polymerase (PARP) by a group of cysteine proteases with some structural homologies to interleukin-1 beta-converting enzyme (ICE-related proteases [IRPs] such as apopain, yama and others). PARP catalyzes the ADP-ribosylation of nuclear proteins at the sites of spontaneous DNA strand breaks and thereby facilitates the repair of this DNA damage. IRP-mediated destruction of PARP, the 'supervisor of the genome', can be induced by activation of membrane receptors (e.g. FAS or APOI) and other signals, and is inhibited by activation of 'anti-death genes' (e.g. bcl-2). Overload-triggered myocyte apoptosis appears to contribute to the transition to cardiac failure, which can be prevented by therapeutic hemodynamic unloading. In myocardial ischemia, the activation of the apoptotic program in cardiocytes does not exclude their final destiny to catastrophic necrosis with release of cytosolic enzymes, but might be considered as an adaptive process in hypoperfused ventricular zones, sacrificing some jeopardized myocytes to regulated apoptosis, which may be less arrhythmogenic than necrosis with the primary disturbance of membrane function.