Defective activation of p21ras in peripheral blood mononuclear cells from patients with insulin dependent diabetes mellitus

Single-cell mass cytometry of TCR signaling: amplification of small initial differences results in low ERK activation in NOD mice

Signaling from the T-cell receptor (TCR) conditions T-cell differentiation and activation, requiring exquisite sensitivity and discrimination. Using mass cytometry, a high-dimensional technique that can probe multiple signaling nodes at the single-cell level, we interrogate TCR signaling dynamics in control C57BL/6 and autoimmunity-prone nonobese diabetic (NOD) mice, which show ineffective ERK activation after TCR triggering. By quantitating signals at multiple steps along the signaling cascade and parsing the phosphorylation level of each node as a function of its predecessors, we show that a small impairment in initial pCD3ζ activation resonates farther down the signaling cascade and results in larger defects in activation of the ERK1/2-S6 and IκBα modules. This nonlinear property of TCR signaling networks, which magnifies small initial differences during signal propagation, also applies in cells from B6 mice activated at different levels of intensity. Impairment in pCD3ζ and pSLP76 is not a feedback consequence of a primary deficiency in ERK activation because no proximal signaling defect was observed in Erk2 KO T cells. These defects, which were manifest at all stages of T-cell differentiation from early thymic pre-T cells to memory T cells, may condition the imbalanced immunoregulation and tolerance in NOD T cells. More generally, this amplification of small initial differences in signal intensity may explain how T cells discriminate between closely related ligands and adopt strongly delineated cell fates.

Thymic negative selection is functional in NOD mice

Based on analyses of multiple TCR transgenic (tg) models, the emergence of pathogenic T cells in diabetes-prone NOD mice has been ascribed to a failure to censure autoreactive clones in the thymus. In contrast, using isolated and preselected thymocytes, we show that nonobese diabetic (NOD) genetic variation impairs neither clonal deletion nor downstream transcriptional programs. However, we find that NOD genetic variation influences αβ/γδ-lineage decisions promoted by early expression of tg αβ-TCRs at the double-negative (DN) stage. In B6 and other genetic backgrounds, tg αβ-TCRs behave like γδ-TCRs and commit a large fraction of DNs toward the γδ-lineage, thereby decreasing the size of the double-positive (DP) pool, which is efficiently positively and negatively selected. In NOD DNs, αβ-TCR signalosomes instead behave like pre-TCRs, resulting in high numbers of DPs competing for limited selection niches, and poor positive and negative selection. Once niche effects are neutralized in mixed bone marrow chimeras, positive and negative selection are equally efficient on B6 and NOD backgrounds. Biochemical analysis revealed a selective defect in the activation of Erk1/2 downstream of NOD αβ-TCR signalosomes. Therefore, NOD genetic variation influences αβ/γδ-lineage decisions when the αβ-TCR heterodimer is prematurely expressed, but not the process of negative selection.

Evidence for aberrant regulation of MAP kinase signal transduction pathway in peripheral blood mononuclear cells in patients with active celiac disease

BACKGROUND

Aberrant signaling via the p21/mitogen-activated proteins (MAP) kinase pathway has been described in lymphocytes of patients with various autoimmune diseases. There is little published data about the intracellular mediators and signals that regulate expression and activity of transcription factors and their effect on celiac disease induction and progression.

AIM

To investigate the possible involvement of MAP kinase pathway in peripheral blood mononuclear cells (PBMC) in celiac disease and its correlation with disease activity.

METHODS

Expression of the total and activated forms of two MAP kinases [extracellular response kinase (ERK) and c-Jun amino terminal kinase (JNK)] were studied by Western blots in PBMC of 17 untreated and 19 treated celiac patients, and 17 controls. Seven of these untreated celiac patients were studies before and after 6 months of gluten-free diet.

RESULTS

Phosphorylated ERK of active celiac disease patients was significantly lower compared with controls (P < 0.01) and was increased towards normal after 6 month of gluten-free diet (P < 0.01). Phosphorylated JNK was increased significantly in the untreated celiac group (P < 0.01) and normalized towards the control level after 6 months of gluten-free diet (P < 0.04).

CONCLUSIONS

Aberrant MAP-kinase pathway activity is associated with active celiac disease (CD). Further studies should examine the potential role of this aberration in pathogenesis of CD.

Effect of different antihypertensive treatments on Ras, MAPK and Akt activation in hypertension and diabetes

Ras GTPases function as transducers of extracellular signals regulating many cell functions, and they appear to be involved in the development of hypertension. In the present study, we have investigated whether antihypertensive treatment with ARBs (angiotensin II receptor blockers), ACEi (angiotensin-converting enzyme inhibitors) and diuretics induce changes in Ras activation and in some of its effectors [ERK (extracellular-signal-regulated kinase) and Akt] in lymphocytes from patients with hypertension without or with diabetes. ACEi treatment transiently reduced Ras activation in the first month of treatment, but diuretics induced a sustained increase in Ras activation throughout the 3 months of the study. In patients with hypertension and diabetes, ARB, ACEi and diuretic treatment increased Ras activation only during the first week. ACEi treatment increased phospho-ERK expression during the first week and also in the last 2 months of the study; however, diuretic treatment reduced phospho-ERK expression during the last 2 months of the study. In patients with hypertension and diabetes, antihypertensive treatments did not induce changes in phospho-ERK expression in lymphocytes. ACEi treatment reduced phospho-Akt expression in patients with hypertension and diabetes only in the first month of treatment. In conclusion, these findings show that antihypertensive treatments with ACEi, and diuretics to a lesser extent, modify Ras activation and some of its signalling pathways, although in different directions, whereas ARBs do not appear to have any influence on Ras signalling pathways.

Constitutive up-regulated activity of MAP kinase is associated with down-regulated early p21Ras pathway in lymphocytes of SLE patients

Aberrant expression of the p21Ras proto-oncogene has been reported in lymphoid cells of SLE patients. We previously showed that the expression of the p21Ras stimulatory element, hSOS1, is reduced in PBMC from SLE patients with non-active disease. However, the significance of this finding regarding the regulation and function of the p21Ras pathway and its correlation to disease activity remained unclear. The expression, regulation and function of the p21Ras pathway were determined in 23 ambulatory SLE patients with active and non-active disease and eleven controls. Levels of p21Ras stimulatory element hSOS1 but not p21Ras and its inhibitory element p120GAP were significantly decreased in SLE patients. Early p21Ras signalling was down-regulated in SLE patients with active disease as indicated by the decreased membrane/cytoplasmic (M/C) ratios of the p21Ras regulatory elements hSOS1 and p120GAP and by the non-responsiveness of these ratios to cellular stimulation. Anchorage of p21Ras to the cellular membrane was also significantly decreased in these patients. In contrast, the late p21Ras signalling was up-regulated in SLE patients as indicated by the significantly higher constitutive activity of the p21Ras down stream key regulator enzyme MAP Kinase. Taken together, our data demonstrate for the first time a disease associated functional defect in p21Ras signalling in lymphocytes of SLE patients.

Evidence for aberrant regulation of the p21Ras pathway in PBMCs of patients with chronic idiopathic urticaria

BACKGROUND

Recent data suggest that a subpopulation of patients with chronic urticaria has an autoimmune disorder. Aberrant expression and regulation of the p21Ras pathway has been reported in lymphoid cells in a variety of systemic autoimmune diseases but not in chronic idiopathic urticaria (CIU).

OBJECTIVES

The aim of this study was to examine the expression, regulation, and function of the p21Ras pathway in patients with CIU.

METHODS

Twenty-four patients with CIU and 14 control subjects were enrolled. All patients and 9 control subjects were intradermally injected with autologous serum. PBMCs were isolated, and the p21Ras and its regulatory proteins were studied.

RESULTS

We found increased expression of the p21ras proto-oncogene in patients with CIU. This was associated with a low expression of the p21Ras stimulatory element human son of sevenless (hSOS1) but normally expressed p21Ras inhibitory element p120GTPase-activating protein. The basal nonstimulated membrane/cytoplasmic ratio of hSOS1, which indicates the p21Ras pathway activity, was higher in patients compared with that seen in control subjects. Moreover, after stimulation, both patients and control subjects decreased their hSOS1 membrane/cytoplasmic ratio. The magnitude of this decrease was much higher in patients than in control subjects: 14- and approximately 2-fold, respectively. The basal and stimulated activities of the p21Ras downstream key regulatory enzyme mitogen-activated protein kinase were comparable in patients and control subjects, as was their in vitro mitogen-stimulated lymphocyte proliferation.

CONCLUSION

Our data demonstrate for the first time an aberrant signaling through the p21Ras pathway in lymphocytes of patients with CIU. This finding further supports the autoimmune basis of this disease.

Specific deficiency of p56lck expression in T lymphocytes from type 1 diabetic patients

Peripheral T lymphocyte activation in response to TCR/CD3 stimulation is reduced in type 1 diabetic patients. To explore the basis of this deficiency, a comprehensive analysis of the signal transduction pathway downstream of the TCR/CD3 complex was performed for a cohort of patients (n = 38). The main result of the study shows that T cell hyporesponsiveness is positively correlated with a reduced amount of p56(lck) in resting T lymphocytes. Upon CD3-mediated activation, this defect leads to a hypophosphorylation of the CD3zeta-chain and few other polypeptides without affecting the recruitment of ZAP70. Other downstream effectors of the TCR/CD3 transduction machinery, such as phosphatidylinositol 3-kinase p85alpha, p59(fyn), linker for activation of T cells (LAT), and phospholipase C-gamma1, are not affected. In some patients, the severity of this phenotypic deficit could be linked to low levels of p56(lck) mRNA and resulted in the failure to efficiently induce the expression of the CD69 early activation marker. We propose that a primary deficiency in human type 1 diabetes is a defect in TCR/CD3-mediated T cell activation due to the abnormal expression of the p56(lck) tyrosine kinase.

T cell signaling and autoimmune diabetes

Stimulation of the T-cell lymphocyte surface receptor (TCR) initiates a cascade of intracellular signaling events leading to proliferation, anergy, cytokine secretion, or apoptosis. In prediabetic NOD mice, T cell proliferative hyporesponsiveness has been correlated to decreased TCR-mediated signal transduction along the PKC/p21ras/p42mapk pathway. Limited data regarding T cell signaling defects are available in patients with autoimmune diabetes mellitus. Some but not all investigators have found decreased in vitro proliferative hyporesponsiveness to lectin mitogens or anti-CD3 mAb associated with impaired PKC activation and cytokine production. More recently, defective expression and function of the p21ras cascade was reported in these patients. Taken together, these data suggest that lymphocytes from animals and patients with autoimmune diabetes have defective TCR mediated signaling which may result in aberrant T cell activation and proliferation. This may lead to an imbalance of Th1/Th2 cytokine secretory pattern and thereby promote disease development.