Pivotal role of Smad3 in a mouse model of T cell-mediated hepatitis

Abstract

Transforming growth factor beta (TGF␤) promotes hepatocellular apoptosis and suppresses hepatic lymphocyte responses in part through activation of Smad3. The purpose of the current study was to determine the importance of Smad3 signaling in an experimental model of autoimmune hepatitis induced by concanavalin A (ConA), a process involving T cell activation and hepatocellular apoptosis. C57Bl/6 wild-type (Wt) or Smad3-deficient (Smad3 ؊/؊ ) mice were injected intravenously with 15 mg/kg ConA or vehicle. Nine hours post ConA injection, Wt mice presented with severe hepatitis as assessed by increased liver transferases. This injury was associated with eosinophil accumulation and preceded at 3 hours post-injection by significant increases in hepatic T helper 1 (interferon gamma) and T helper 2 (interleukin-4) cytokine production. Absence of Smad3 significantly blunted hepatocellular injury 9 hours post ConA injection, which was associated with reduced early T helper 1 and T helper 2 cytokine production and eosinophil accumulation. Smad3 ؊/؊ livers also showed significant reductions in hepatocellular apoptosis as assessed by terminal UTP nick-end labeling when compared to ConA-treated Wt mice in conjunction with reduced caspase 3 cleavage, which was likely mediated by a Smad3-dependent inhibition of the survival factor extracellular signal-regulated kinase 1/2. In vitro, Smad3 ؊/؊ hepatocytes were resistant to TGF␤-induced apoptosis, and this protection was dependent on extracellular signal-regulated kinase activation. Conclusion: Together, these results show, for the first time, the significance of Smad3 signaling in autoimmune hepatitis, underlining the control of Smad3-dependent TGF␤ signaling on proinflammatory cytokine production, eosinophil recruitment, and hepatocellular apoptosis. Interruption of this pathway could be beneficial clinically to limit acute fulminant liver pathologies. ( The inherent ability of TGF␤ to regulate immune responses is strong evidence for it being an endogenous regulator of T cell function. 2 In fact, TGF␤ exerts great impact on T cells, as is evident in mice with a T cellspecific blockade of TGF␤ signaling, which resulted in the activation of a self-targeted immune response. 3,4 Additionally, recent studies in mice and humans have elucidated an important and complex role for TGF␤ in autoimmune diseases, 5 which are very often mediated by disrupted T cell signaling. 6 Inhibition of TGF␤ is associated with increased susceptibility to different experimental models of autoimmune diseases, including rheumatoid arthritis, insulin-dependent (type 1) diabetes mellitus, and inflammatory bowel disease. 7-9 Surprisingly, the role of TGF␤ in autoimmune hepatitis is not known. Recent work suggests that TGF␤ inhibits the development of immunopathology to self or otherwise nonharmful antigens without compromising immune responses to pathogens. This appears to be achieved by TGF␤-controlled initiation and resolution of inflammatory responses mediated by the regulation of chemotaxis, activation, and...

Notch1 and TGFβ1 cooperatively regulate Foxp3 expression and the maintenance of peripheral regulatory T cells

“…Mice with a conditional knockout of TGF␤RII in CD4 ϩ T cells or a complete knockout of Smad3 are more susceptible to disease induction in a mouse model of autoimmune hepatitis, compared with wild-type controls, and reduced expression of TGF␤RII on peripheral blood mononuclear cells (PBMCs) in patients with autoimmune hepatitis at least partially contributes to disease pathology. [47][48][49] Patients with autoimmune hepatitis also have reduced FOXP3 expression within the T reg pool, and diminished Foxp3 protein expression in murine cells has been associated with the onset of autoimmune disease. 50,51 In summary, this study provides evidence that Foxp3 is a novel downstream target of Notch signaling both in vitro and in vivo.…”

Insulin Resistance and Metabolic Hepatocarcinogenesis with Parent-of-Origin Effects in A×B Mice

“…16 Briefly, murine livers were sequentially perfused in situ with 25 mL of calciumfree EGTA-containing buffer followed by 50 mL of buffered saline containing 0.3 mg/mL of type IV collagenase (Roche Diagnostics Corp, Indianapolis, IN) at 37°C. After perfusion, collagenase-treated livers were dissociated by mincing with scissors followed by passage through a 100-m-pore nylon mesh.…”

Organisation der klinischen Forschung

“…In der Allgemein-und Viszeralchirurgie [3,4], chirurgische Onkologie [5,6], Pankreaschirurgie [7,8,9], minimal-invasive Chirurgie [10,11];…”

“…Aufgrund der beschriebenen Forschungsorganisation der Klinik war es in den vergangenen Jahren möglich, alle genannten klinischen Schwerpunktbereiche sowohl in der Grundlagenforschung [3,4,9,14,16] als auch unter translationalen Aspekten [5,18] und durch klinische Studien zu vertreten [1,8,11,19,20].…”