FK506 and cyclosporin A each inhibit antigen-specific signaling in the T cell line 171 in the absence of a calcium signal

Targeting CaN/NFAT in Alzheimer's brain degeneration

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive loss of cognitive functions. While the exact causes of this debilitating disorder remain elusive, numerous investigations have characterized its two core pathologies: the presence of β-amyloid plaques and tau tangles. Additionally, multiple studies of postmortem brain tissue, as well as results from AD preclinical models, have consistently demonstrated the presence of a sustained inflammatory response. As the persistent immune response is associated with neurodegeneration, it became clear that it may also exacerbate other AD pathologies, providing a link between the initial deposition of β-amyloid plaques and the later development of neurofibrillary tangles. Initially discovered in T cells, the nuclear factor of activated T-cells (NFAT) is one of the main transcription factors driving the expression of inflammatory genes and thus regulating immune responses. NFAT-dependent production of inflammatory mediators is controlled by Ca2+-dependent protein phosphatase calcineurin (CaN), which dephosphorylates NFAT and promotes its transcriptional activity. A substantial body of evidence has demonstrated that aberrant CaN/NFAT signaling is linked to several pathologies observed in AD, including neuronal apoptosis, synaptic deficits, and glia activation. In view of this, the role of NFAT isoforms in AD has been linked to disease progression at different stages, some of which are paralleled to diminished cognitive status. The use of classical inhibitors of CaN/NFAT signaling, such as tacrolimus or cyclosporine, or adeno-associated viruses to specifically inhibit astrocytic NFAT activation, has alleviated some symptoms of AD by diminishing β-amyloid neurotoxicity and neuroinflammation. In this article, we discuss the recent findings related to the contribution of CaN/NFAT signaling to the progression of AD and highlight the possible benefits of targeting this pathway in AD treatment.

Calcineurin-NFAT signalling in myeloid leucocytes: new prospects and pitfalls in immunosuppressive therapy

Myeloid leucocytes mediate host protection against infection and critically regulate inflammatory responses in body tissues. Pattern recognition receptor signalling is crucial for myeloid cell responses to pathogens, but growing evidence suggests an equally potent role for Calcineurin–NFAT signalling in control of myeloid cell function. All major subsets of myeloid leucocytes employ Calcineurin–NFAT signalling during immune responses to pathogens and/or tissue damage, but the influence this pathway exerts on pathogen clearance and host susceptibility to infection is not fully understood. Recent data from experimental models indicate that Calcineurin‐NFAT signalling is essential for infection control, and calcineurin inhibitors used in transplantation medicine (including cyclosporine A and tacrolimus) are now being tested for efficacy in a diverse range of inflammatory conditions and autoimmune pathologies. Efforts to repurpose calcineurin inhibitor drugs for new therapeutic applications may yield rapid improvements in clinical outcomes, but the potential impact of these compounds on myeloid cell function in treated patients is largely unknown. Here we discuss Calcineurin–NFAT control of myeloid leucocyte function in the context of recent therapeutic developments and ongoing clinical studies.

Cyclophilin A as a target in the treatment of cytomegalovirus infections

BACKGROUND

Viruses are obligate parasites that depend on the cellular machinery of the host to regenerate and manufacture their proteins. Most antiviral drugs on the market today target viral proteins. However, the more recent strategies involve targeting the host cell proteins or pathways that mediate viral replication. This new approach would be effective for most viruses while minimizing drug resistance and toxicity.

METHODS

Cytomegalovirus replication, latency, and immune response are mediated by the intermediate early protein 2, the main protein that determines the effectiveness of drugs in cytomegalovirus inhibition. This review explains how intermediate early protein 2 can modify the action of cyclosporin A, an immunosuppressive, and antiviral drug. It also links all the pathways mediated by cyclosporin A, cytomegalovirus replication, and its encoded proteins.

RESULTS

Intermediate early protein 2 can influence the cellular cyclophilin A pathway, affecting cyclosporin A as a mediator of viral replication or anti-cytomegalovirus drug.

CONCLUSION

Cyclosporin A has a dual function in cytomegalovirus pathogenesis. It has the immunosuppressive effect that establishes virus replication through the inhibition of T-cell function. It also has an anti-cytomegalovirus effect mediated by intermediate early protein 2. Both of these functions involve cyclophilin A pathway.

PKC θ-mediated Ca2+/NF-AT signalling pathway may be involved in T-cell immunosuppression in coal-burning arsenic-poisoned population

Arsenic poisoning is a worldwide endemic disease that affects thousands of people. Growing evidence from animal, cell, and human studies indicates that arsenic has deleterious effects on the immune system. The present investigation is a population-based study that observed changes in the proliferation of human T-cells and IL-2 and INF-γ mRNA expression. Our results show that coal-burning arsenic can cause T-cell immunosuppression in the population, and participates in the occurrence and development of arsenic poisoning. In addition, we analyzed the intracellular calcium index, expression of protein kinase C theta (PKC θ) and phosphorylated PKC θ, and the DNA-binding activity of NF-AT in peripheral blood mononuclear cells (PBMCs). Our analysis demonstrates that the PKC θ-mediated Ca²⁺/NF-AT signalling pathway may be involved in the T-cell immunosuppression of coal-burning arsenic-poisoned population. This study provides important data for a mechanistic understanding of endemic arsenic poisoning.

Using genetic and clinical factors to predict tacrolimus dose in renal transplant recipients

AIMS

Tacrolimus has a narrow therapeutic window and shows significant interindividual difference in dose requirement. In this study we aim to first identify genetic factors that impact tacrolimus dose using a candidate gene association approach, and then generate a personalized algorithm combining identified genetic and clinical factors to predict individualized tacrolimus dose.

MATERIALS & METHODS

We screened 768 SNPs in 15 candidate genes in metabolism, transport and calcineurin inhibition pathways of tacrolimus, for association with tacrolimus dose in a discovery cohort of 96 patients.

RESULTS

Four polymorphisms in CYP3A5 and one polymorphism in CYP3A4 were identified to be significantly associated with tacrolimus stable dose (p < 8.46 × 10(-5)). The same SNPs were identified when dose-normalized trough tacrolimus concentration was analyzed. The CYP3A5*1 allele was associated with significantly higher stable dose, bigger dose increase, higher risk of being underdosed and lower incidence of post-transplant hyperlipidemia. ABCB1 polymorphisms were not associated with stable dose. No significant difference was found between CYP3A5 expressers and nonexpressers in incidence of acute rejection and time to first rejection. Age, ethnicity and CYP3A inhibitor use could predict 30% of tacrolimus dosing variability. Adding the identified genetic polymorphisms to the algorithm increased the predictability to 58%. In two validation cohorts of 77 and 64 patients, the algorithm containing both genetic and clinical factors produced correlation coefficients of 0.63 and 0.42, respectively. This algorithm gave a prediction of the stable doses closer to the actual doses when compared with another algorithm based only on the CYP3A5 genotype.

CONCLUSION

CYP3A5 genotype is the most significant genetic factor that impacts tacrolimus dose among the genes studied. This study generated the first pharmacogenomics model that predicts tacrolimus stable dose based on age, ethnicity, genotype and comedication use. Our results highlight the importance of incorporating both genetic and clinical, demographic factors into dose prediction.

Long-Term Cell Monitoring of Kidney Recipients After an Antilymphocyte Globulin Induction With and Without Steroids

BACKGROUND

Because of several side effects, the corticosteroid usage has been minimized in kidney transplantation. The increased acute rejection episodes associated with their withdrawal may counterbalance with induction treatment using polyclonal antilymphocyte globulin (ALG). The effects of ALG on blood cell phenotype have already been the subject of several reports. However, to date, no data are available concerning the comparison of blood phenotype when ALG is given with or without steroids and no gene profiling study has been performed.

METHODS

We report here on a longitudinal blood cell analysis of a selected cohort of kidney recipients enrolled in a randomized study of steroid avoidance or withdrawal (during 6 months) during ALG induction.

RESULTS

In the two groups, ALG quickly and massively depleted all the T cells and natural killer cells, but not B cells. Interestingly, the lymphopenia-driven homeostatic proliferation of CD4 and CD8T cells strongly differed with persistent low CD4 (including CD25CD4) T-cell counts. Effector memory CD8T cells reappeared rapidly. ALG induced apoptosis-associated molecules and increased myeloid cell genes. However, few genes were found differentially expressed with a low fold ratio between the two groups during and at distance of corticotherapy.

CONCLUSION

Thus initial steroid avoidance or withdrawal associated with ALG induction has a weak influence on phenotype and transcriptional pattern of blood leukocytes. In contrast, ALG therapy induces an early and strong depletion of all T-cell subsets with contrasted long-lasting homeostatic regulation.

Contrasting CD25hiCD4+T cells/FOXP3 patterns in chronic rejection and operational drug-free tolerance

BACKGROUND

Although immunosuppression withdrawal in kidney recipients usually leads to rejection, in some patients it does not, leading to a state of clinical operational tolerance.

METHODS

We compared these highly contrasted situations by analyzing blood cell phenotype and transcriptional patterns in drug-free spontaneously tolerant kidney recipients, recipients with chronic rejection, recipients with stable graft function under standard or minimal immunosuppression and healthy individuals

RESULTS

The blood cell phenotype of clinically tolerant patients did not differ from that of healthy individuals. In contrast, recipients with chronic rejection had significantly less CD25hiCD4+T cells and lower levels of FOXP3 transcripts compared with clinically tolerant recipients. Patients with chronic rejection also displayed CD25-CD4+T cells expressing NKG2D+CD94+ and CD57+CD27-CD28- cytotoxic-associated markers (P<0.05).

CONCLUSION

These data show that whereas clinically tolerant recipients displayed normal levels of CD25hiCD4+T cells and FOXP3 transcripts, chronic rejection is associated with a decrease in CD25hiCD4+T cells and FOXP3 transcripts, suggesting that clinically "operational tolerance" may be due to a maintained phenomenon of natural tolerance that is lacking in patients with chronic rejection.

Cardiac transplant experience with cyclosporine

The advent of cyclosporine 20 years ago was a major advance in the field of solid organ transplantation. Its use enabled directed immunosuppression with a consequent decrease in the incidence of graft failure, acute rejection, and systemic infection. The early oil-based preparation, however, was difficult to administer and had limited bioavailability and unpredictable pharmacokinetics. The drug also has a fairly narrow therapeutic window with major long-term side effects, which include nephrotoxicity, malignancy, hyperlipidemia, and hypertension. The introduction of a microemulsion preparation (Neoral) with improved bioavailability has been associated with lower rates of rejection and comparable tolerability, therefore allowing the use of lower doses. Traditionally cyclosporine toxicity has been minimized by monitoring trough levels. Monitoring of levels 2 hours after dosing may provide a more accurate determination of cyclosporine exposure. The next phase in cardiac transplantation immunosuppression will most likely see a significantly diminished role for cyclosporine with the introduction of newer, more potent immunosuppressive agents with more favorable side-effect profiles. These agents, which include mycophenolate mofetil, sirolimus, and everolimus, also hold the promise of having a major impact on the development of transplant vasculopathy, which up to now has been an important determinant of limiting long-term allograft survival.

Pharmacology of calcineurin antagonists

Cyclosporine and tacrolimus share the same pharmacodynamic property of activated T-cell suppression via inhibition of calcineurin. The introduction of these drugs to the immunosuppressive repertoire of transplant management has greatly improved the outcomes in organ transplantation and constitutes arguably one of the major breakthroughs in modern medicine. To this date, calcineurin inhibitors are the mainstay of prevention of allograft rejection. The experience gained from the laboratory and clinical use of cyclosporine and tacrolimus has greatly advanced our knowledge about the nature of many aspects of immune response. However, the clinical practice still struggles with the shortcomings of these drugs: the significant inter- and intraindividual variability of their pharmacokinetics, the unpredictability of their pharmacodynamic effects, as well as complexity of interactions with other agents in transplant recipients. This article briefly reviews the pharmacological aspects of calcineurin antagonists as they relate to the mode of action and pharmacokinetics as well as drug interactions and monitoring.

Modulation of the electrophoretic mobility of the linker for activation of T cells (LAT) by the calcineurin inhibitors CsA and FK506: LAT is a potential substrate for PKC and calcineurin signaling pathways

The linker for activation of T cells (LAT) is essential for T cell activation. Cyclosporin A (CsA) and FK506, inhibitors of T cell proliferation, have been very useful for preventing autoimmune and inflammatory disease and graft rejection. However, both compounds are associated with side effects. We show that TCR ligation in the presence of FK506 or CsA induced rapid modifications in LAT that modulate the electrophoretic mobility of the molecule in SDS-PAGE. Calcineurin, a target for CsA and FK506, dephosphorylated LAT in vitro and restored its electrophoretic mobility. Stimulating T cells with the protein kinase C (PKC) activator PMA induced a shift in the mobility of LAT, whereas inhibitors of PKC blocked the effect of PMA. Thus, manipulating calcineurin or PKC activation alters the electrophoretic mobility of LAT. These results shed light on the molecular actions of CsA and FK506 in T cells and implicate LAT in mediating the drugs' actions.

Calcineurin inhibitors and sirolimus: mechanisms of action and applications in dermatology

Controlled trials and clinical experience indicate that systemic cyclosporin A and tacrolimus are effective treatments for psoriasis, and that cyclosporin A also improves atopic eczema. A variety of other inflammatory and non-inflammatory skin diseases are probably also responsive to these drugs. However, the widespread and longer-term use of cyclosporin A and tacrolimus are limited by side effects. The molecular mechanisms of action of cyclosporin A, tacrolimus and a related drug, sirolimus, have been well defined in T cells and involve inhibition of critical signalling pathways that regulate T cell activation. For example cyclosporin and tacrolimus inhibit calcineurin phosphatase activity and thereby inhibit activation of the transcription factor NFAT. The therapeutic efficacy of topical calcineurin inhibitors in atopic eczema have restimulated interest in the mechanism of action of these drugs in skin disease. Recently the expression pattern of calcineurin and NFAT has been defined in non-immune tissues including the akin. The relevance of this to the mechanism of action of systemic and topical calcineurin inhibitors and sirolimus in skin disorders is discussed.

Mechanisms of action of cyclosporine

Cyclosporine (cyclosporin A, CsA) has potent immunosuppressive properties, reflecting its ability to block the transcription of cytokine genes in activated T cells. It is well established that CsA through formation of a complex with cyclophilin inhibits the phosphatase activity of calcineurin, which regulates nuclear translocation and subsequent activation of NFAT transcription factors. In addition to the calcineurin/NFAT pathway, recent studies indicate that CsA also blocks the activation of JNK and p38 signaling pathways triggered by antigen recognition, making CsA a highly specific inhibitor of T cell activation. Here we discuss the action of CsA on JNK and p38 activation pathways. We also argue the potential of CsA and its natural counterparts as pharmacological probes.

Amplification of natural regulatory immune mechanisms for transplantation tolerance

There is a need to derive donor-specific tolerance in clinical organ transplantation, where potential benefits remain overshadowed by chronic rejection and side effects of continual immunosuppressive therapy. It is known that the mature immune system in mice can be reprogrammed to accept a foreign graft as if it were "self." Here we show that, once generated, this state of operational tolerance becomes self-sustaining, imposing itself on new cohorts of lymphocytes as they arise. These new cohorts retain specificity for the tolerizing antigen and can be selectively amplified to tolerate new antigens that have linked expression with the original tolerogen. Regulation is critically dependent upon the continuous presence of tolerizing antigen and is mediated by the CD4+ lymphocyte population. We propose that such natural mechanisms of immune regulation may eventually be exploited for transplantation tolerance, even in fully immune-competent recipients.

T cell responses in calcineurin A alpha-deficient mice

We have created embryonic stem (ES) cells and mice lacking the predominant isoform (alpha) of the calcineurin A subunit (CNA alpha) to study the role of this serine/threonine phosphatase in the immune system. T and B cell maturation appeared to be normal in CNA alpha -/- mice. CNA alpha -/- T cells responded normally to mitogenic stimulation (i.e., PMA plus ionomycin, concanavalin A, and anti-CD3 epsilon antibody). However, CNA alpha -/- mice generated defective antigen-specific T cell responses in vivo. Mice produced from CNA alpha -/- ES cells injected into RAG-2-deficient blastocysts had a similar defective T cell response, indicating that CNA alpha is required for T cell function per se, rather than for an activity of other cell types involved in the immune response. CNA alpha -/- T cells remained sensitive to both cyclosporin A and FK506, suggesting that CNA beta or another CNA-like molecule can mediate the action of these immunosuppressive drugs. CNA alpha -/- mice provide an animal model for dissecting the physiologic functions of calcineurin as well as the effects of FK506 and CsA.