Intrahepatic stem/progenitor cells and cytotoxic CD8+ T cells (CD8+ T cells) in the cirrhotic liver undergo apoptosis, which potentially facilitates progression to cancer. Here, we report that hepatocyte growth factor (HGF) signaling plays an important role in promoting normal and damaged liver CD8+ T cell Fas-mediated apoptosis through its only receptor, c-Met. In addition to binding with HGF, c-Met also binds to Fas to form a complex. Using a diethylnitrosamine (DEN)-induced liver fibrosis/cirrhosis mouse model, immunostaining, and terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) staining, we found that HGF secretion was significantly higher at 10 weeks post-DEN, the liver cirrhotic phase (LCP), than at 3 weeks post-DEN, the liver fibrotic phase (LFP). Correspondingly, differences in CD8+ T cell proliferation and apoptosis were noted between the two phases. Interestingly, staining and TUNEL assays revealed lower smooth muscle actin (α-SMA)+ cell apoptosis, a marker for hepatic stellate cells (HSCs), in the LFP group than in the LCP group, which suggested a beneficial correlation among HGF, CD8+ T cells and HSCs in improving the fibrotic load during damaged liver repair. In cultures, when met different concentrations of recombinant HGF (rHGF), phytohemagglutinin (PHA)-stimulated naive mouse splenic CD8+ T cells (pn-msCD8+ T cells) responded differently; as increases in rHGF increased were associated with decreases in the clonal numbers of pn-msCD8+ T cells, and when the rHGF dose was greater than 200 ng/mL, the clonal numbers significantly decreased. In the presence of 400 ng/mL rHGF, the death-inducing signaling complex (DISC) can be directly activated in both nsCD8+ T cells and healthy human peripheral blood CD8+ T cells (hp-CD8+ T cells), as indicated by recruitment of FADD and caspase-8 because DISC forms via the recruitment of FADD and caspase-8, among others. These findings suggest that Fas-mediated apoptosis, may also indicate a regulatory role of HGF signaling in hepatic homeostasis.

Intrahepatic stem/progenitor cells and cytotoxic CD8+ T cells (CD8+ T cells) in the cirrhotic liver undergo apoptosis potentially facilitating progression to cancer. Here, we report that hepatocyte growth factor (HGF) signaling plays an important role in promoting normal and damaged liver CD8+ T cell Fas-mediated apoptotosis through its only receptor c-Met. In addition to binding with HGF, c-Met also binds to Fas as a complex. Using a diethylnitrosamine (DEN)-induced liver fibrosis/cirrhosis mouse model, immunofluostaining and terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) staining, we identified significantly increased HGF secretion at 10 weeks post-DEN, the liver cirrhotic phase (LCP), compared to it at 3 weeks post-DEN, the liver fibrotic phase (LFP). Correspondingly, difference CD8+ T cell proliferation and apoptosis were noted in the two phases, Interestingly, staining and TUNEL identified that higher smooth muscle actin (α-SMA)+ cell apoptosis, a marker for hepatic stellate cell (HSC) in the LFP compared to their in the LCP, suggesting that beneficial correlation of HGF, CD8+ T cells and HSC in improving fibrotic load during damaged liver repair. In cultures, up to 200 ng/mL amounts of recombinant HGF the naive mouse splenic CD8+ T cells (n-msCD8+ T cells) death, 400 ng/mL rHGF show directly activated death-inducing signaling complex (DISC) to recruit FADD and caspase-8 in both nsCD8+ T cells and healthy human peripheral blood CD8+ T cells (hp-CD8+ T cells), suggesting Fas-mediated apoptosis, may suggest the regulating role of HGF signaling in hepatic homeostasis.

Allostimulated CD8+ T cells (aCD8+ T cells), as the main mediators of acute liver rejection (ARJ), are hyposensitive to apoptosis due to the inactivation of death receptor FAS-mediated pathways and fail to allow tolerance induction, eventually leading to acute graft rejection. Although tacrolimus (FK506), the most commonly used immunosuppressant (IS) in the clinic, allows tolerance induction, its use is limited because its target immune cells are unknown and it is associated with increased incidences of malignancy, infection, and nephrotoxicity, which substantially impact long-term liver transplantation (LTx) outcomes. The dark agouti (DA)-to-Lewis rat LTx model is a well-known ARJ model and was hence chosen for the present study. We show that both hepatocyte growth factor (HGF) (cHGF, containing the main form of promoting HGF production) and recombinant HGF (h-rHGF) exert immunoregulatory effects mainly on allogeneic aCD8+ T cell suppression through FAS-mediated apoptotic pathways by inhibiting cMet to FAS antagonism and Fas trimerization, leading to acute tolerance induction. We also showed that such inhibition can be abrogated by treatment with neutralizing antibodies against cMet (HGF-only receptor). In contrast, we did not observe these effects in rats treated with FK506. However, we observed that the effect of anti-rejection by FK506 was mainly on allostimulated CD4+ T cell (aCD4+ T cell) suppression and regulatory T cell (Treg) promotion, in contrast to the mechanism of HGF. In addition, the protective mechanism of HGF in FK506-mediated nephrotoxicity was addressed. Therefore, HGF as a tolerance inducer, whether used in combination with FK506 or as monotherapy, may have good clinical value. Additional roles of these T-cell subpopulations in other biological systems and studies in these fields will also be meaningful.