Role of cathepsin G in the activation of CD4+ T lymphocytes in mice with type 1 diabetes

Abstract

Objective To identify whether regulation of Cathepsin G (CatG) expression can influence CD4+ T lymphocytes (T cells) activation in non-obese diabetic (NOD) mice, and to demonstrate the role of CatG inhibition in prevention and treatment for type 1 diabetes mellitus (T1DM). Methods A total of 36 female NOD mice (6 weeks old) were randomly divided into 3 groups according to the duration and blood glucose: normal control group, pre-diabetes (pre-DM) group, and diabetes (DM) group. CatG gene expression and CD4+ T cells activation were examined in these three groups of NOD mice (12 mice in each group). After modelling, CatG small interfering RNA (siRNA) was administrated to treat the other pre-diabetic NOD mice, and CatG inhibitor was administrated to treat diabetic NOD mice (12 mice in each intervention group) . Also control groups (12 mice in each group) were respectively set. After 8 weeks, all the mice were executed and histological analysis were performed. The effect of CatG inhibitor was investigated in NOD mice on CD4+ T cells activation, islet β cell function, and islet inflammation. Furthermore, NOD mice were injected with CatG siRNA in early stage to observe the effect of CatG knockdown on CD4+ T cells activation status and on diabetes progression. The data of three groups were analyzed with single factor analysis of variance, and the data of two groups were compared with independent samples t test. Results (1) The gene level of CatG of the 3 groups was 0.42±0.21, 0.60±0.33, 0.94±0.45, respectively (F=12.89, P<0.05). The gene level of CatG in pre-DM group and DM group was significantly higher than that in normal control group. Meanwhile, compared with normal control group, the CD4+ T cells in spleen and peripheral blood were gradually activated in pre-DM group and DM group, resulting in more T helper (Th)1 cells and fewer Th2 and regulatory T(Treg) cells (F=11.85-21.36, all P<0.01). (2) After administration with CatG inhibitor, the level of blood glucose was decreased (t=11.26-12.45, all P<0.01) and insulin was increased (t=11.89-13.78, all P<0.01);Meanwhile, the activation of CD4+ T cells was decreased, and the difference was statistically significant (all P<0.05) . (3) Compared with the control group, after early application of CatG siRNA, the percentage of Th1 cells was decreased [peripheral blood: (5.1±1.4)% vs (2.4±0.3)%, spleen: (10.6±2.0) % vs (6.3±1.5) %, t=20.78, 27.96, all P<0.05]. The percentage of Th2 and Treg cells was increased (t=20.59-30.25, all P<0.05). Meanwhile, the mice could maintain in normal glucose status or pre-DM status, and the insulin level could be enhanced significantly in CatG siRNA group (t=31.69-33.98, all P<0.01). Conclusion CatG is the major effector protease in CD4+ T cells activation in the pathogenesis of T1DM. Targeted inhibition of CatG may delay or block T1DM progression through alleviating CD4+ T cells activation. Key words: Diabetes mellitus, type 1; Cathepsin G; Antigens, CD4; Mice, inbred NOD