Apoptosis and progression of hepatic fibrosis in liver diseases

RESUMO

Apoptosis is a Greek term that means "the fall of the old leaves of the autumn trees". This term describes the process by which undesirable, damaged or old cells are eliminated from the multicellular organisms. Apoptosis differs from cellular necrosis, because it is actively controlled and the membrane integrity is maintained, avoiding extravasations of intracellular material and inflammatory response. The apoptotic process can occur by two mechanisms: death receptor (DR) or extrinsic mechanism and mitochondrial or intrinsic mechanism. The liver cells express different death receptors: hepatocytes express Fas, TNF-R1, TRAIL-R1, TRAIL-R2, Stellate Cell (HSC) express Fas and TRAIL when activated; cholangiocytes seem to be type II cells (in which the mitochondrial mechanism to apoptosis is essential) regarding signaling of Fas endothelial cells from rat livers express Fas, and their activation may lead to apoptosis of murine endothelial cells from hepatic sinusoids. Apoptosis mediated by these receptors has a major role in a variety of biological processes as tissue injury, protection against pathogenic microorganisms, and the role on hepatic injury and posterior progession to fibrosis has been well established in different hepatic diseases