Regulación de la actividad fibrogénica de las células hepáticas por la leucina

Abstract

The amino acid leucine specifically activates signaling pathways leading to the activation of the translational machinery and the increase of total protein synthesis. Regulation of type I collagen production by hepatic stellate cells (HSC) is a multistep process involving transcriptional and post-transcriptional mechanisms. In the present work we studied the effect of leucine on translation regulation of collagen alpha1(I) production in HSC and the signaling pathways involved. Treatment of HSC with leucine did not alter half-life or steady state levels of procollagen alpha1(I) mRNA, but caused an increase in procollagen alpha1(I) protein and changes of components involved in translational regulation. Leucine also induced mTOR, ERK and Akt phosphorylation without affecting p38 and JNK activation, intracellular ROS levels were increased in HSC incubated with leucine and this effect was abolished by pretreatment with the antioxidant glutathione (GSH). Preincubation with GSH also prevented 4E-BP1, eIF4E and Mnk-1 phosphorylation induced by leucine, as its effects on procollagen alpha1(I). Inhibitors for MEK-1 (PD98059), PI3K (wortmannin) or mTOR (rapamycin) did not affect leucine-induced ROS production. However, preincubation with GSH prevented ERK, Akt and mTOR phosphorylation caused by leucine. The mitochondrial electron chain inhibitor rotenone and the NADPH oxidase inhibitor apocynin prevented ROS production caused by leucine. Leucine also induced an increased phosphorylation of IR/IGF-R that was abolished by pretreatment with either rotenone or apocynin.%&/Therefore, leucine exerts on HSC a prooxidant action and these effects mediate the activation of IR/IGF-IR and signaling pathways, finally leading to changes in translational regulation of collagen synthesis.