[Apoptosis and progression of hepatic fibrosis in liver diseases]

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. Pathologic cell death in the liver has traditionally been referred to as necrosis, but pathophysiologic process in the liver can lead to cell injury and death by apoptosis as well by necrosis. The first differs from the second, because it is actively controlled and the membrane integrity is maintained, avoiding extravasations of intracellular material and inflammatory response. Apoptosis can occur by two mechanisms: death receptor (DR) or extrinsic mechanism and mitochondrial or intrinsic mechanism. Liver cells express different death receptors: hepatocytes express Fas, TNF-R1, TRAIL-R1, TRAIL-R2; Stellate Cell (HCS) express Fas and TRAIL when is activated into myofibroblast-like phenotype and undergo apoptosis during resolution of liver injury in vivo. Cholangiocytes seem to be type II cells (in which the mitochondrial mechanism to apoptotic is essential) regarding signaling of Fas endothelial cells from rat livers express Fas, and their activation may lead to apoptosis of endothelial cells from hepatic sinusoids. Apoptosis mediated by these receptors have a major role in a variety of biological processes as tissue injury, protection against pathogenic microorganisms, and the role on hepatic injury and posterior progression to fibrosis has been well established in different hepatic diseases. Apoptosis may occur in the absence of significant transaminase elevations as happen in cellular necrosis. This paper is a review of this process.