TRIF promotes angiotensin II-induced cross-talk between fibroblasts and macrophages in atrial fibrosis.

AIMS: Atrial fibroblasts and macrophages have long been thought to participate in atrial fibrillation (AF). However, which specific mediator may regulate the interaction between them remains unclear. METHODS AND RESULTS: We provided the evidence for the involvement of Toll/IL-1 receptor domain-containing adaptor inducing IFN-ß (TRIF), an important inflammation-related molecule, in the pathophysiology of AF. Patients with AF showed higher levels of angiotensin II (AngII) and TRIF expression and larger number of macrophages infiltration in left atria appendage than individuals with sinus rhythm (SR). In the cell study, AngII induced chemokines expressions in mouse atrial fibroblasts and AngII-stimulated atrial fibroblasts induced the chemotaxis of macrophages, which were reduced by losartan and TRIF siRNA. Meanwhile, AngII-stimulated atrial fibroblasts proliferation was enhanced by macrophages. CONCLUSIONS: Our data demonstrated that TRIF may be a crucial factor promoting the interaction between atrial fibroblasts and macrophages, leading to atrial fibrosis.

Pioglitazone inhibits angiotensin II-induced atrial fibroblasts proliferation via NF-κB/TGF-ß1/TRIF/TRAF6 pathway.

The exact mechanisms underlying inhibitory effects of pioglitazone (Pio) on Angiotensin II (AngII)-induced atrial fibrosis are complex and remain largely unknown. In the present study, we examined the effect of Pio on AngII-induced mice atrial fibrosis in vivo and atrial fibroblasts proliferation in vitro. In vivo study showed that AngII infusion induced atrial fibrosis and increased expressions of Toll/IL-1 receptor domain-containing adaptor inducing IFN-ß (TRIF) and tumor necrosis factor receptor associated factor 6 (TRAF6) in mice models. However, those effects could be attenuated by Pio (P<0.01). As for in vitro experiment, Pio suppressed AngII-induced atrial fibroblasts proliferation via nuclear factor-κB/transforming growth factor-ß1/TRIF/TRAF6 signaling pathway in primary cultured mice atrial fibroblasts (P<0.01). In conclusion, suppression of Pio on AngII-induced atrial fibrosis might be related to its inhibitory effects on above signaling pathway.

Beneficial effects of pioglitazone on atrial structural and electrical remodeling in vitro cellular models.

It has been demonstrated that atrial remodeling contributes toward atrial fibrillation (AF) maintenance and angiotensin II (AngII) is involved in the pathogenesis of atrial remodeling. Peroxisome proliferator-activated receptor-γ (PPAR-γ) agonists have been shown to inhibit atrial remodeling. However, the underlying mechanisms are poorly understood. In the present study we investigated the regulating effects of PPAR-γ agonist on AngII-induced atrial structural and electrical remodeling in vitro cellular models. The effects of pioglitazone on AngII-induced connective tissue growth factor (CTGF) expression and cell proliferation were assessed in primary-cultured mouse atrial fibroblasts. The influences of pioglitazone on AngII-induced L-type calcium channel (ICa-L) α1c expression and current density were evaluated in atrial myocytes (HL-1). Pioglitazone attenuated AngII-induced CTGF expression and proliferation in atrial fibroblasts, and pioglitazone also inhibited the expression or phosphorylation of AngII-induced transforming growth factor-ß1 (TGF-ß1), tumor necrosis factor receptor associated factor 6 (TRAF6), TGF-ß-associated kinase 1 (TAK1) and Smad2/3. In HL-1 cells, pioglitazone suppressed AngII-induced ICa-L α1c expression and current density as well as CAMP responsive element binding protein (CREB) phosphorylation. Besides, pioglitazone inhibited AngII-induced production of AngII type I receptor (AT1R) and downregulation of PPAR-γ in both atrial fibroblasts and HL-1 cells. In conclusion, Pioglitazone suppresses AngII-induced CTGF expression and proliferation in atrial fibroblasts, which might be at least in part related with its inhibitory effects on TGF-ß1/Smad2/3 and TGF-ß1/TRAF6/TAK1 signaling pathways. Moreover, pioglitazone also attenuates AngII-induced ICa-L remodeling in HL-1 cells, which might be at least in part associated with its inhibitory effect on CREB phosphorylation. It is suggested that PPAR-γ agonist may have potential applications in preventing atrial remodeling.

Angiotensin II increases CTGF expression via MAPKs/TGF-ß1/TRAF6 pathway in atrial fibroblasts.

The activation of transforming growth factor-ß1(TGF-ß1)/Smad signaling pathway and increased expression of connective tissue growth factor (CTGF) induced by angiotensin II (AngII) have been proposed as a mechanism for atrial fibrosis. However, whether TGFß1/non-Smad signaling pathways involved in AngII-induced fibrogenetic factor expression remained unknown. Recently tumor necrosis factor receptor associated factor 6 (TRAF6)/TGFß-associated kinase 1 (TAK1) has been shown to be crucial for the activation of TGF-ß1/non-Smad signaling pathways. In the present study, we explored the role of TGF-ß1/TRAF6 pathway in AngII-induced CTGF expression in cultured adult atrial fibroblasts. AngII (1 µM) provoked the activation of P38 mitogen activated protein kinase (P38 MAPK), extracellular signal-regulated kinase 1/2(ERK1/2) and c-Jun NH(2)-terminal kinase (JNK). AngII (1 µM) also promoted TGFß1, TRAF6, CTGF expression and TAK1 phosphorylation, which were suppressed by angiotensin type I receptor antagonist (Losartan) as well as p38 MAPK inhibitor (SB202190), ERK1/2 inhibitor (PD98059) and JNK inhibitor (SP600125). Meanwhile, both TGFß1 antibody and TRAF6 siRNA decreased the stimulatory effect of AngII on TRAF6, CTGF expression and TAK1 phosphorylation, which also attenuated AngII-induced atrial fibroblasts proliferation. In summary, the MAPKs/TGFß1/TRAF6 pathway is an important signaling pathway in AngII-induced CTGF expression, and inhibition of TRAF6 may therefore represent a new target for reversing Ang II-induced atrial fibrosis.

Suppression of allograft rejection by Tim-1-Fc through cross-linking with a novel Tim-1 binding partner on T cells.

Engagement of T-cell immunoglobulin mucin (Tim)-1 on T cells with its ligand, Tim-4, on antigen presenting cells delivers positive costimulatory signals to T cells. However, the molecular mechanisms for Tim-1-mediated regulation of T-cell activation and differentiation are relatively poorly understood. Here we investigated the role of Tim-1 in T-cell responses and allograft rejection using recombinant human Tim-1 extracellular domain and IgG1-Fc fusion proteins (Tim-1-Fc). In vitro assays confirmed that Tim-1-Fc selectively binds to CD4(+) effector T cells, but not dendritic cells or natural regulatory T cells (nTregs). Tim-1-Fc was able to inhibit the responses of purified CD4(+) T cells that do not express Tim-4 to stimulation by anti-CD3/CD28 mAbs, and this inhibition was associated with reduced AKT and ERK1/2 phosphorylation, but it had no influence on nTregs. Moreover, Tim-1-Fc inhibited the proliferation of CD4(+) T cells stimulated by allogeneic dendritic cells. Treatment of recipient mice with Tim-1-Fc significantly prolonged cardiac allograft survival in a fully MHC-mismatched strain combination, which was associated with impaired Th1 response and preserved Th2 and nTregs function. Importantly, the frequency of Foxp3(+) cells in splenic CD4(+) T cells was increased, thus shifting the balance toward regulators, even though Tim-1-Fc did not induce Foxp3 expression in CD4(+)CD25(-) T cells directly. These results indicate that Tim-1-Fc can inhibit T-cell responses through an unknown Tim-1 binding partner on T cells, and it is a promising immunosuppressive agent for preventing allograft rejection.

[Effects of astilbin on the expression of TNF alpha and IL-10 in liver warm ischemia-reperfusion injury].

OBJECTIVES: To investigate the effects of astilbin on the expressions of TNF alpha and IL-10 during liver warm ischemia-reperfusion injury. METHODS: C57BL/ 6 mice were randomly divided into 4 groups (n = 8): sham-operated group (Sham), model control group(I/R), low dosage of astilbin treatment group (10 mg/kg) and high dosage of astilbin (40 mg/kg) treatment group. The treatment group mice were intraperitoneally injected with 10 or 40 mg/kg astilbin 24 hours and one hour before Ischemia, the hepatic ischemia-reperfusion model were thus established. After jn90 of min ischemia and 6 h reperfusion of the partial hepatic lobe, the expressions of TNF alpha and IL-10 in liver tissues collected from the experimental groups were detected by Western blot and semiquantitative RT-PCR. RESULTS: The expression of TNF alpha protein in liver tissues gradually decreased in treatment groups (low and high dosages of astilbin treatment groups) as compared to the I/R model control group. Similar results were observed in the mRNA expressions of these genes as determined by semiquantitative RT-PCR (P less than 0.05 for low dosage group; P less than 0.01 for high dosage group). Compared with the I/R model control group, the expression of IL-10 was increased in both treatment groups (low dosage group P less than 0.05; large dosage group P less than 0.01). CONCLUSION: Treatment with astilbin decreases TNF alpha expression but induces IL-10 expression in liver during warm ischemia-reperfusion injury.