Yan Xu

Multiple-modulation effects of Oridonin on the production of proinflammatory cytokines and neurotrophic factors in LPS-activated microglia.

Microglial activation has been implicated in many neurological disorders for its inflammatory and/or neurotrophic effects. In this study, we investigated the effects upon activated microglia of Oridonin (Ori), an effective component isolated from Rabdosia rubescens. We pretreated rat primary microglia with or without Ori, then stimulated with lipopolysaccharide (LPS). We found that Ori pretreatment inhibited the release of proinflammatory mediators including nitric oxide (NO), tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1beta) and interleukin-6 (IL-6). Such suppressive effects were accompanied by inhibition of DNA binding activity of the critical transcription factor nuclear factor-kappa B (NF-kappaB). In addition, Ori upregulated the production of the neurotrophic factor, nerve growth factor (NGF). Our findings suggest that Ori may have anti-inflammatory and neuroregulatory effects through modulation of multiple functions of microglia.

γ-Aminobutyric Acid Transporter 1 Negatively Regulates T Cell-Mediated Immune Responses and Ameliorates Autoimmune Inflammation in the CNS

γ-aminobutyric acid (GABA) is the major inhibitory neurotransmitter of the CNS, and GABA transporter 1 (GAT-1) is critical in maintaining a GABA reservoir and associated functions. The wide expression of GAT-1 in the CNS prompted us to explore its role in neuroimmunological disorders. In mice induced with experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis, we found that the expression levels of GAT-1 mRNA and protein in spinal cord were greatly suppressed as compared with those in naive mice and irrelevant Ag-immunized mice. Therefore, we induced EAE in GAT-1−/− mice and found that the disease was significantly aggravated and was accompanied by some nonclassic EAE signs. Mononuclear cells from GAT-1−/− mice with EAE showed much higher Ag-specific proliferative responses. Proinflammatory cytokine production in these mice was also greatly up-regulated. Further studies revealed that GAT-1 deficiency induced vigorous immune responses by enhancing IκB kinase phosphorylation and NF-κB-DNA binding activity, as well as strengthening the T-bet-STAT1 circuit signaling pathway. Finally, we found that GAT-1 was expressed only on activated T cells primed with Ags, but not on B cells or macrophages. These findings indicate that GAT-1 is a critical modulator in T cell-mediated immune responses and in EAE pathogenesis.

Interleukin 10 deficiency exacerbates halothane induced liver injury by increasing interleukin 8 expression and neutrophil infiltration.

The prediction and prevention of drug-induced liver injury (DILI) have been hindered by limited knowledge of the underlying mechanisms, in part the result of a lack of animal models. Using a newly established DILI model induced by halothane, we found increased liver damage susceptibility in interleukin 10 (IL-10) knockout (KO) mice. Extensive neutrophil infiltration and chemoattractant factor interleukin 8 (IL-8) expression in IL-10 KO mice were observed after halothane administration. The elevation of IL-8 expression was NF-kappaB- and P38 MAPK-dependent. In addition, increased signal transducer and activator of transcription factors (STAT) 1 and STAT3 were observed in halothane treated IL-10 KO mice. Exogenous IL-10 treatment protected susceptible mice from halothane induced liver injury (HILI). In conclusion, IL-10 deficiency increases susceptibility to HILI and increased IL-8 expression as well as neutrophil infiltration may be responsible for this phenomenon.

γ-Aminobutyric Acid Transporter 1 Negatively Regulates T Cell Activation and Survival through Protein Kinase C-Dependent Signaling Pathways

γ-aminobutyric acid transporter 1 (GAT-1), as the major regulator in maintaining a γ-aminobutyric acid reservoir in the CNS, plays negative roles in experimental autoimmune encephalomyelitis pathogenesis. Our previous study has revealed that, besides its wide expression in the CNS, GAT-1 expression can be induced on activated T cells triggered by Ag. However, the function of GAT-1 in T cell activation is unclear. In this study, we show that GAT-1 deficiency induces more vigorous cell cycle entry and less cell apoptosis in T cells, thus leading to enhanced cell proliferation. GAT-1 deficiency promotes T cell division and survival by down-regulating cyclin dependent kinase inhibitor p27kip1, differentially regulating the pro- and anti-apoptotic proteins Bcl-2, Bcl-xl, and Bad and activating transcription factor NF-κB through induction of translocation and phosphorylation of protein kinase C (PKC) θ. In addition, our data reveal that GAT-1 expression on T cells is modulated by PKC activation. Taken together, the data show that GAT-1 negatively regulates T cell activation and survival through PKC-dependent signaling pathways.

Stearoyl-CoA desaturase 1 deficiency protects mice from immune-mediated liver injury.

Immunity and metabolism are closely linked. The liver is an important metabolic organ in the body. However, the interactions between hepatocytes and the immune system are poorly understood. In mice developing concanavalin A (ConA)-induced hepatitis (CIH), we found extensive lipid accumulation in hepatocytes. Critical enzyme involved in fat synthesis such as stearoyl-CoA desaturase 1 (SCD1) was upregulated. When we injected ConA to SCD1-deficient mice, we found these mice to be highly resistant to CIH. The mechanisms of the protective effect of SCD1 deficiency might be attributed to the reduced leptin levels in those mice, which modulated critical cytokines and signaling pathways in CIH pathogenesis. In conclusion, our study suggests that SCD1 deficiency protects mice from liver injury in a leptin-dependent manner.

Vasoactive intestinal peptide attenuates concanavalin A-mediated liver injury.

Vasoactive intestinal peptide (VIP) is well characterized as an endogenous anti-inflammatory neuropeptide and has a brand range of biological functions. In this study, we found increased endogenous VIP expression in mice with concanavalin A-induced hepatitis, a widely used experimental model of immune-mediated liver injury. We investigated further the effect of VIP administration on concanavalin A-induced liver injury. Compared with mice pretreated with PBS, mice pretreated with VIP exhibited much lower plasma levels of aminotransferases, less inflammatory infiltration in the liver and hepatocyte apoptosis. Meanwhile, VIP significantly inhibited the release of inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) in concanavalin A-injected mice, but markedly elevated the production of anti-inflammatory cytokine interleukine-10 (IL-10). Further investigation demonstrated increased intracellular cAMP concentration after VIP administration, and showed that the protective effect of VIP on concanavalin A-induced hepatitis was mediated mainly through VIP receptor 1 (VPAC(1)). These results suggest that VIP is capable of attenuating immune-mediated liver injury in vivo. This effect is associated with its downregulation of critical inflammatory mediators and its upregulation of anti-inflammatory cytokine through VPAC(1), possibly via the cAMP-dependent pathway.

STAT3 Mediates Protection From Liver Inflammation After Partial Hepatectomy

Background/Aims: The liver has the unique capacity to restore its mass by hepatocyte proliferation after injury or transplantation. The present study investigated whether the regenerating liver responds to immune stimuli in the same way as the quiescent one. Methods: We performed partial hepatectomy (PHx) in mice, then stimulated the mice with concanavalin A (ConA) to study their immune responses. Plasma Alanine aminotransferase (ALT) and cytokine levels as well as liver inflammatory infiltration were measured to evaluate liver damage. Transcriptional factors were further detected to study the underlining mechanisms. Results: Our results showed that PHx mice were resistant to ConA-induced liver inflammation and injury, as evidenced by both morphological and biochemical observations. Then we went further to study the mechanisms. We found marked signal transducer and activator of transcription 3 (STAT3) activation 48 hours after PHx. When STAT3 activation was blocked with its inhibitor JSI-124, PHx mice also developed severe liver inflammation after ConA stimulation. Conclusion: The regenerating liver is resistant to ConA induced immune assaulting, and STAT3 is the major player in the protection process.