Maria Sounidaki

Differential effects of the two amino acid sensing systems, the GCN2 kinase and the mTOR complex 1, on primary human alloreactive CD4+ T-cells

Amino acid deprivation activates general control nonderepressible 2 (GCN2) kinase and inhibits mammalian target of rapamycin (mTOR), affecting the immune response. In this study, the effects of GCN2 kinase activation or mTOR inhibition on human alloreactive CD4+ T-cells were evaluated. The mixed lymphocyte reaction, as a model of alloreactivity, the GCN2 kinase activator, tryptophanol (TRP), and the mTOR complex 1 inhibitor, rapamycin (RAP), were used. Both TRP and RAP suppressed cell proliferation and induced cell apoptosis. These events were p53-independent in the case of RAP, but were accompanied by an increase in p53 levels in the case of TRP. TRP decreased the levels of the Th2 signature transcription factor, GATA-3, as RAP did, yet the latter also decreased the levels of the Th1 and Th17 signature transcription factors, T-bet and RORγt, whereas it increased the levels of the Treg signature transcription factor, FoxP3. Accordingly, TRP decreased the production of interleukin (IL)-4, as RAP did, but RAP also decreased the levels of interferon-γ (IFN-γ) and IL-17. Both TRP and RAP increased the levels of IL-10. As regards hypoxia-inducible factor-1α (HIF-1α), which upregulates the Th17/Treg ratio, its levels were decreased by RAP. TRP increased the HIF-1α levels, which however, remained inactive. In conclusion, our findings indicate that, in primary human alloreactive CD4+ T-cells, the two systems that sense amino acid deprivation affect cell proliferation, apoptosis and differentiation in different ways or through different mechanisms. Both mTOR inhibition and GCN2 kinase activation exert immunosuppressive effects, since they inhibit cell proliferation and induce apoptosis. As regards CD4+ T-cell differentiation, mTOR inhibition exerted a more profound effect, since it suppressed differentiation into the Th1, Th2 and Th17 lineages, while it induced Treg differentiation. On the contrary, the activation of GCN2 kinase suppressed only Th2 differentiation.

Restless legs syndrome does not affect 3-year mortality in hemodialysis patients

OBJECTIVE Uremic restless legs syndrome (RLS) has been related to an enhanced mortality of hemodialysis (HD) patients. In the general population studies of this association have yielded inconsistent results. The aim of the present study was to re-evaluate the relationship of RLS and mortality in HD patients. METHODS We recorded the 3-year mortality in 579 HD patients after assessment for RLS symptoms. This population has been previously evaluated for the prevalence of RLS, according to the essential criteria of the International RLS Study Group. Mortality data were acquired from the national end-stage renal disease registry. Survival probability was calculated by the Kaplan-Meier method and analyzed by the log-rank test. For multivariate survival analysis, we implemented a Cox regression model. RESULTS During the 3-year follow-up, we documented 118 deaths. Mortality was 15.6% in patients with RLS and 22.3% in patients without RLS (p =  0.079). According to the Cox regression analysis, there was no significant association between RLS and 3-year mortality, either in an age- and gender-adjusted model (hazard ratio [HR] = 0.772, 95% confidence interval [CI] = 0.488-1.219, p = 0.267) or in a multivariate adjusted model (HR = 0.667, 95% CI = 0.417-1.069, p = 0.092). CONCLUSION Diagnosis of RLS according to the essential criteria of the International RLS Study Group does not seem to influence the 3-year mortality in HD patients. Our findings are in contrast to those in some previous reports, and reinforce the need for further studies of RLS and mortality in HD.

In human alloreactive CD4+ T-cells, dichloroacetate inhibits aerobic glycolysis, induces apoptosis and favors differentiation towards the regulatory T-cell subset instead of effector T-cell subsets

Although kidney transplantation is the best therapy for end-stage renal disease, rejection remains a concern, and currently available immunosuppressive agents contribute to morbidity and mortality. Thus, novel immunosuppressive drugs are required. Dichloroacetate (DCA) is already used in the treatment of congenital lactic acidosis and characterized by limited toxicity. As DCA inhibits aerobic glycolysis, which is a prerequisite for CD4+ T-cell proliferation and differentiation into effector T-cells, its possible immunosuppressive role in mixed lymphocyte reaction (MLR), a model of alloreactivity, was investigated. Glucose and lactate concentrations were measured in the supernatants, and cell proliferation was assessed immunoenzymatically. CD4+ T‑cells were then isolated from the MLRs and the expression of cleaved caspase‑3, various enzymes involved in glycolysis, and the signature transcription factors of CD4+ T‑cell subsets were evaluated by western blotting. In MLRs, DCA decreased glucose consumption and aerobic glycolysis, while it exerted a negligible effect on cell proliferation. In CD4+ T‑cells, DCA induced apoptosis, and decreased the expression of glucose trasporter‑1, hexokinase II, lactate dehydrogenase‑A and phosphorylated pyruvate dehydrogenase, while it increased total pyruvate dehydrogenase. In addition, DCA increased the expression of transcription factor forkhead box P3, whereas it decreased the expression of T‑box transcription factor TBX21, trans‑acting T-cell-specific transcription factor GATA‑3 and retinoic acid receptor related orphan receptor‑γt. In conclusion, in alloreactive CD4+ T‑cells, DCA inhibits aerobic glycolysis, induces apoptosis and favors differentiation towards the regulatory T‑cell subset. These characteristics render it a promising immunosuppressive agent in the field of transplantation.

Indoleamine 2,3‑dioxygenase downregulates T‑cell receptor complex ζ‑chain and c‑Myc, and reduces proliferation, lactate dehydrogenase levels and mitochondrial glutaminase in human T‑cells

Indoleamine 2,3‑dioxygenase (IDO), through L‑tryptophan depletion, activates general control non‑derepressible (GCN) 2 kinase and suppresses T‑cell proliferation, in addition to suppressing aerobic glycolysis and glutaminolysis, which are required for these rapidly proliferating cells. A number of, however not all of these alterations, are partially mediated through IDO‑induced p53 upregulation. In two‑way mixed lymphocyte reactions (MLRs), IDO reduced cellular proliferation. In MLR‑derived T‑cells, IDO induced the expression levels of p53 and p21, however concurrently reduced the levels of ζ‑chain, c‑Myc, lactate dehydrogenase A (LDH‑A) and glutaminase (GLS)2. However, p53 had no effect on the expression of the above proteins. These results were recapitulated in T‑cells activated with anti‑CD2, anti‑CD3 and anti‑CD28 by direct activation of the GCN2 kinase with tryptophanol. In conclusion, IDO, through GCN2 kinase activation, downregulates the levels of TCR‑complex ζ‑chain and c‑Myc, resulting in the suppression of T‑cell proliferation and a reduction in the levels of LDH‑A and GLS2, which are key enzymes involved in aerobic glycolysis and glutaminolysis, respectively.

Tryptophan depletion under conditions that imitate insulin resistance enhances fatty acid oxidation and induces endothelial dysfunction through reactive oxygen species-dependent and independent pathways

In the original publication of the article, last author’s name was misspelt. The correct name is given here.

Uric acid increases cellular and humoral alloimmunity in primary human peripheral blood mononuclear cells

Hyperuricaemia is common among kidney transplant recipients and has been associated with worse graft outcome. Since episodes of acute cellular rejection and chronic humoral rejection contribute to decreased graft survival, in this study the effect of uric acid on cellular and humoral alloimmunity was evaluated.

Preconditioning of primary human renal proximal tubular epithelial cells without tryptophan increases survival under hypoxia by inducing autophagy

PurposeHypoxia plays a significant role in the pathogenesis of acute kidney injury (AKI). Autophagy protects from AKI. Amino acid deprivation induces autophagy. The effect of l-tryptophan depletion on survival and autophagy in cultures of renal proximal tubular epithelial cells (RPTECs) under hypoxia was evaluated.MethodsRPTECs were preconditioned in a medium containing or not tryptophan, following culture under hypoxia and treatment with or without the autophagy inhibitor chloroquine. Cell survival was assessed by cell imaging, the level of certain proteins by western blotting and cellular ATP fluorometrically.ResultsPreconditioning of RPTECs in a medium without tryptophan activated general control nonderepressible 2 kinase and induced changes that favored autophagy and cell survival under hypoxic conditions. Additionally, it increased cellular ATP, while it inhibited apoptosis. Inhibition of autophagy nullified the induced increase in cellular ATP and cell survival by the absence of tryptophan. The absence of tryptophan increased p53, although its effect on p53’s transcriptional targets was heterogeneous. In accordance with the decreased apoptosis, expression of p21 increased, while expression of Bax decreased. The expression of BNIP3L, which may be pro-apoptotic or pro-autophagic, increased. Considering the decreased apoptosis, it is likely that tryptophan depletion enhances autophagy through a p53-mediated increase of BNIP3L.ConclusionPreconditioning of primary human RPTECs in a medium without tryptophan increases their survival under hypoxia by inducing autophagy. Identifying new molecular mechanisms that protect renal tissue from hypoxia could be proved clinically important in the prevention of AKI.

In human cell cultures, everolimus is inferior to tacrolimus in inhibiting cellular alloimmunity, but equally effective as regards humoral alloimmunity

PurposeAcute cellular rejection is the major cause of immune-mediated graft failure early in the course of kidney transplantation, whereas chronic antibody-mediated rejection is a major contributor to graft loss in the late post-transplant phase. Based mainly on the results of short-term studies, the calcineurin inhibitor tacrolimus prevails over the mammalian target of rapamycin (mTOR) inhibitors. However, the toxicity profile of the two drug categories differs, making the interchange between them appealing. In this study, the effect of tacrolimus and of the mTOR inhibitor everolimus on cellular and humoral alloimmunity was evaluated.MethodsCellular alloimmunity was assessed by cell proliferation in two-way mixed lymphocyte reaction (MLR) with human peripheral blood mononuclear cells (PBMC). For assessing humoral alloimmunity, we developed a method in which humoral alloimmunity was induced in a one-way MLR. The de novo production of alloantibodies was measured with an antibody-mediated complement-dependent cytotoxicity assay, in which supernatants from the above MLRs were used against resting PBMC similar to the stimulator cells of the forementioned MLRs. Tacrolimus and everolimus were used at concentrations near their upper recommended trough levels.ResultsIn two-way MLRs, tacrolimus inhibited cell proliferation more than everolimus. In one-way MLRs, tacrolimus and everolimus decreased alloantibody production to the same extent.ConclusionsIn human cell cultures, everolimus is inferior to tacrolimus in inhibiting cellular alloimmunity, but equally effective as regards humoral alloimmunity. Thus, everolimus might be a safe alternative in case of tacrolimus toxicity, particularly after the early period of kidney transplantation.

Urate crystals activate directly T-cell receptor complex and induce T-cell proliferation

Uric acid is a known danger associated molecular pattern molecule able to induce inflammation following internalization of its crystals by cells of the innate immune system. By activating antigen-presenting cells, urate boosts adaptive immunity as well. Furthermore, urate crystals can induce proliferation of isolated T-cells, which are unable to phagocytose crystal particles. In light of the evidence that urate crystals can also activate dendritic cells and macrophages without prior internalization but through sequestration of lipid rafts (and consequently receptors clustering in a non specific manner), the authors evaluated whether such a mechanism is involved in the direct activation of T-cells by urate crystals. In the present study, isolated human T-cells were cultured with or without urate at a concentration above its crystallization level. The expression and phosphorylation state of the T-cell receptor (TCR) complex zeta chain and the expression of the master regulator of cell proliferation c-Myc were assessed by western blotting. T-cell proliferation was measured by bromodeoxyuridine assay. Collectively, the results indicated that urate increased zeta chain phosphorylation indicating that it induces activation of TCR complex directly, since zeta chain phosphorylation takes place at the cell membrane and is a very proximal event in TCR complex-mediated signal transduction. In parallel, urate increased the expression of the transcription factor c-Myc and induced T-cell proliferation. In conclusion, urate crystals directly activate the TCR complex and induce T-cell proliferation.