T cell signaling and autoimmune diabetes

Discovery of a novel series of inhibitors of lymphoid tyrosine phosphatase with activity in human T cells

The lymphoid tyrosine phosphatase LYP, encoded by the PTPN22 gene, is a critical regulator of signaling in T cells and recently emerged as a candidate target for therapy of autoimmune diseases. Here, by library screening, we identified a series of noncompetitive inhibitors of LYP that showed activity in primary T cells. Kinetic analysis confirmed that binding of the compounds to the phosphatase is nonmutually exclusive with respect to a known bidentate competitive inhibitor. The mechanism of action of the lead inhibitor compound 4e was studied by a combination of hydrogen/deuterium-exchange mass spectrometry and molecular modeling. The results suggest that the inhibitor interacts critically with a hydrophobic patch located outside the active site of the phosphatase. Targeting of secondary allosteric sites is viewed as a promising yet unexplored approach to develop pharmacological inhibitors of protein tyrosine phosphatases. Our novel scaffold could be a starting point to attempt development of "nonactive site" anti-LYP pharmacological agents.

Experimental diabetes attenuates calcium mobilization and proliferative response in splenic lymphocytes from mice

The present study was conducted to investigate the effects of the diabetic condition on cytosolic free Ca(2+) concentration, [Ca(2+)](i), and the proliferation of splenic lymphocytes from mice. Diabetes was induced in mice by intraperitoneal injection of alloxan. [Ca(2+)](i) and the proliferation ex vivo of splenic lymphocytes isolated from mice were examined using fura-2 and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide, respectively. Diabetes caused a significant increase in resting [Ca(2+)](i) and significantly reduced the ability of concanavalin A (Con A; a T-lymphocyte-selective mitogen) to increase [Ca(2+)](i), but not that of lipopolysaccharide (LPS; a B-lymphocyte-selective mitogen). In addition, diabetes significantly reduced Con A-stimulated but not LPS-stimulated lymphocyte proliferation. Verapamil (an L-type Ca(2+) channel blocker) inhibited Con A-induced increases in [Ca(2+)](i) and proliferation in lymphocytes from control and diabetic mice to a similar extent, respectively. These results suggest that diabetes attenuates Con A-stimulated T-lymphocyte proliferation by decreasing [Ca(2+)](i) via reduction of Ca(2+) entry through L-type Ca(2+) channels.

Lymphoid tyrosine phosphatase and autoimmunity: human genetics rediscovers tyrosine phosphatases

A relatively large number of protein tyrosine phosphatases (PTPs) are known to regulate signaling through the T cell receptor (TCR). Recent human genetics studies have shown that several of these PTPs are encoded by major autoimmunity genes. Here, we will focus on the lymphoid tyrosine phosphatase (LYP), a critical negative modulator of TCR signaling encoded by the PTPN22 gene. The functional analysis of autoimmune-associated PTPN22 genetic variants suggests that genetic variability of TCR signal transduction contributes to the pathogenesis of autoimmunity in humans.

Antibodies to CD1d enhance thymic expression of invariant NKT TCR and increase the presence of NOD thymic invariant NKT cells

Natural Killer T (NKT) cells can effect both T cell development and peripheral immune responses through T(H)1/T(H)2 cytokines. Some humans with Type 1 Diabetes Mellitus (T1DM) have numerical and functional NKT deficiencies that contribute to disease severity. Correcting these deficiencies inhibits diabetes in the non-obese diabetic (NOD) T1DM model, which shares similar deficiencies. Here we show that antibodies to CD1d, when given during early thymic development, induce specific increases in surface TCR of developing NOD and C57BL/6 CD4(+)CD8(+) (DP) invariant NKT (iNKT) cells. However, the addition of anti-CD1d causes distinct strain-specific population changes in response to treatment. These changes include: (1) a dose-dependent increase in NOD iNKT(TCR)(+) cells and, conversely, (2) an inhibition of B6 iNKT(TCR)(+) cell production. The observed NOD iNKT expansions correlated with diabetes inhibition in an in vitro T1DM system, suggesting that intrathymic anti-CD1d treatment may correct NOD numerical iNKT deficiencies through developmental TCR enhancement.

Protein tyrosine phosphatase PTPN22 in human autoimmunity

The discovery that a single-nucleotide polymorphism (SNP) in lymphoid tyrosine phosphatase (LYP), encoded by the PTPN22 gene, is associated with type 1 diabetes (T1D) has now been verified by numerous studies and has been expanded to rheumatoid arthritis, juvenile rheumatoid arthritis (JRA), systemic lupus erythematosus, Graves' disease, generalized vitiligo and other human autoimmune diseases. In this paper, we discuss the association of PTPN22 with autoimmunity, the biochemistry of the PTPN22-encoded phosphatase, and the molecular mechanism(s) by which the disease-predisposing allele contributes to the development of human disease.

Insulin and insulin-like growth factor-1 promote mast cell survival via activation of the phosphatidylinositol-3-kinase pathway

OBJECTIVE

Mast cells (MCs) play central roles for the onset and development of immediate-type and inflammatory allergic reactions. Since the inverse relationship between atopic disorders and diabetes mellitus has been observed in animals and humans, we investigated the effects of insulin (Ins) on MC signaling and biological function.

METHODS

In bone marrow-derived MCs (BMMCs) from wild-type as well as SHIP-deficient mice Ins as well as insulin-like growth factor-1 (IGF-I)-triggered intracellular signaling events and MC effector functions were studied.

RESULTS

We found that the addition of either Ins or IGF-1 to BMMCs triggers the phosphorylation of protein kinase B (PKB) and p38 kinase but not extracellular signal-regulated kinase (Erk). We also found that Ins/IGF-1 stimulates the tyrosine phosphorylation of SHIP1 and, in keeping with this, Ins/IGF-1-induced PKB phosphorylation is higher in SHIP1-/- BMMCs and is inhibited in SHIP+/+ as well as SHIP1-/- BMMCs with inhibitors of phosphatidylinositol-3-kinase (PI3K). Ins/IGF-1, like antigen (Ag), also stimulates the Rac-dependent activation of PAK as well as the production of hydrogen peroxide (H2O2). To elucidate the role of Ins and IGF-1 in MC biology, we studied their effects on Ag-mediated degranulation and MC survival. Although both only slightly enhanced Ag-mediated degranulation, they significantly promoted MC survival in the absence of IL-3 in a PI3K-dependent manner.

CONCLUSION

The promotion of BMMC survival by induction of Ins/IGF-1 signaling may, in part, be responsible for the inverse correlation observed between atopic disorders and diabetes mellitus.

Role of PTPN22 in type 1 diabetes and other autoimmune diseases

We recently discovered that a single-nucleotide polymorphism (SNP) in the lymphoid tyrosine phosphatase (LYP), encoded by the PTPN22 gene on chromosome 1p13, correlates strongly with the incidence of type 1 diabetes (T1D) in two independent populations. This findings has now been verified by numerous studies and it has been expanded to rheumatoid arthritis, juvenile rheumatoid arthritis, systemic lupus erythematosus, Graves' disease, generalized vitiligo and other autoimmune disease. Here we review the genetics of the SNP and its association with autoimmunity, discuss the function of the phosphatase in signaling, the biochemistry of the disease-predisposing allele, and the possible mechanisms by which PTPN22 contributes to the development of human disease.

Signal pathways underlying homocysteine-induced production of MCP-1 and IL-8 in cultured human whole blood

AIM

To elucidate the mechanisms underlying homocysteine (Hcy)-induced chemokine production.

METHODS

Human whole blood was pretreated with inhibitors of calmodulin (CaM), protein kinase C (PKC), protein tyrosine kinase (PTK), mitogen-activated protein kinase (MAPK), and NF-kappaB and activators of PPARgamma for 60 min followed by incubation with Hcy 100 micromol/L for 32 h. The levels of mitogen chemokine protein (MCP)-1 and interleukin-8 (IL-8) were determined by enzyme-linked immunosorbant assay (ELISA).

RESULTS

Inhibitors of PKC (calphostin C, 50-500 nmol/L and RO-31-8220, 10-100 nmol/L), CaM (W7, 28-280 micromol/L), ERK1/2 MAPK (PD 98059, 2-20 micromol/L), p38 MAPK (SB 203580, 0.6-6 micromol/L), JNK MAPK (curcumin, 2-10 micromol/L), and NF-kappaB (PDTC, 10-100 nmol/L) markedly reduced Hcy 100 micromol/L-induced production of MCP-1 and IL-8 in human cultured whole blood, but the inhibitors of PTK (genistein, 2.6-26 micromol/L and tyrphostin, 0.5-5 micromol/L) had no obvious effect on MCP-1 and IL-8 production. PPARgamma activators (ciglitazone 30 micromol/L and troglitazone 10 micromol/L) depressed the Hcy-induced MCP-1 production but not IL-8 production in the cultured whole blood.

CONCLUSION

Hcy-induced MCP-1 and IL-8 production is mediated by activated signaling pathways such as PKC, CaM, MAPK, and NF-kappaB. Our results not only provide clues for the signal transduction pathways mediating Hcy-induced chemokine production, but also offer a plausible explanation for a pathogenic role of hyperhomocysteinemia in these diseases.

Insulin and glucose induced changes in expression level of nucleoside transporters and adenosine transport in rat T lymphocytes

Adenosine is an endogenous agent exerting potent action on the immune system including regulation of lymphocyte functioning. Impaired T lymphocyte functioning is a common feature of diabetes. The aims of this study were to examine the effects of glucose and insulin on nucleoside transporters (NT) expression level and adenosine (Ado) transport in rat T lymphocytes cultured under the defined concentrations of glucose and insulin. Performed experiments revealed that rat T lymphocytes expressed the equilibrative nucleoside transporter type 1 and 2 (rENT1, rENT2) and concentrative nucleoside transporter type 2 (rCNT2). The mRNA levels of rENT2 and rCNT2 were highly dependent on insulin but were not affected by changes in extracellular glucose concentration. Exposition of T cells to 10nM insulin resulted in 73% increase in rENT2 mRNA and 50% decrease in the rCNT2 mRNA level. The level of rENT1 mRNA was sensitive to extracellular glucose concentration but not to insulin. The highest differences among cells cultured in high (20mM) and low (5mM) glucose were observed in equilibrative nitrobenzylthioinosine sensitive adenosine transport, which was lowered by 65% in cells cultured at high glucose. Alterations in adenosine transport were accompanied by changes in adenosine accumulation in the cell. These results indicate that adenosine transport in rat T lymphocytes is independently and differentially regulated by glucose and insulin by means of changes in the nucleoside transporters expression level. Altered adenosine transport has a great impact on its intracellular level. This suggests that under diabetic conditions adenosine action on T lymphocytes might be altered.