Caracterización de la respuesta de las células estelares hepáticas a la carencia de aminoácidos

Resumen

During amino acid deprivation, GCN2 kinase becomes phosphorylated and inhibits translation factor eIF2α; thus, lowering protein synthesis to allow cell survival under stress conditions. Aim: We hypothesized that amino acid deprivation could modulate the generation of reactive oxygen species (ROS) in hepatic stellate cells (HSC), and as a result, regulate collagen I synthesis and the fibrogenic reponse. Results: Histidine deprivation decreased H2O2 levels in HSC and promoted cell survival. The histidine-dependent decrease in H2O2 levels correlated with phosphorylation of GCN2. Incubation with salubrinal, an inhibitor of the eIF2α phosphatase, demonstrated that eIF2α phosphorylation and H2O2 depletion are independent events, thus suggesting that GCN2 does not function as an eIF2α kinase in this context. Incubation with histidine-free medium caused an increase in superoxide radical levels and down-regulated SOD activity in HSC. Histidine deprivation also decreased intra- and extracellular protein levels collagen I and COL1A1 and COL1A2 mRNA levels. Studies performed in animal models for liver injury using knock out mice for GCN2, showed higher necroinflammatory scores in Gcn2-/- mice treated with CCl4 than in WT mice; greater focal necrosis and portal inflammation as well as enhanced levels of transaminases ALT and AST were also observed. Moreover, Gcn2-/- mice showed a higher deposition of collagen type I even in the absence of CCl4 treatment. Conclusion: These results suggest that GCN2 could play a role in down-regulating H2O2 levels and collagen I synthesis in HSC, which in turn may decrease the fibrogenic response of these cells to liver injury.