Current Molecular Medicine 2008, 8, 207-220 207 1566-5240/08 $55.00+.00 © 2008 Bentham Science Publishers Ltd. Molecular Mechanisms and Pathophysiology of Necrotic Cell Death Nele Vanlangenakker 1,2 , Tom Vanden Berghe 1,2 , Dmitri V. Krysko 1,2 , Nele Festjens 3,4 and Peter Vandenabeele* ,1,2 1 Molecular Signaling and Cell Death Unit, Department for Molecular Biomedical Research, VIB, 9052 Ghent, Belgium 2 Department of Molecular Biology, Ghent University, 9052 Ghent, Belgium 3 Unit for Molecular Glycobiology, Department for Molecular Biomedical Research, VIB, 9052 Ghent, Belgium 4 Department of Biochemistry, Physiology and Microbiology, Laboratory for Protein Biochemistry and Biomo- lecular Engineering, Ghent University, 9052 Ghent, Belgium Abstract: Necrotic cell death has long been considered an accidental and uncontrolled mode of cell death. But recently it has become clear that necrosis is a molecularly regulated event that is associated with pathologies such as ischemia-reperfusion (IR) injury, neurodegeneration and pathogen infection. The serine/threonine ki- nase receptor-interacting protein 1 (RIP1) plays a crucial role during the initiation of necrosis induced by li- gand-receptor interactions. On the other hand, ATP depletion is an initiating factor in ischemia-induced necrotic cell death. Common players in necrotic cell death irrespective of the stimulus are calcium and reactive oxygen species (ROS). During necrosis, elevated cytosolic calcium levels typically lead to mitochondrial calcium over- load, bioenergetics effects, and activation of proteases and phospholipases. ROS initiates damage to lipids, proteins and DNA and consequently results in mitochondrial dysfunction, ion balance deregulation and loss of membrane integrity. Membrane destabilization during necrosis is also mediated by other factors, such as acid- sphingomyelinase (ASM), phospholipase A2 (PLA2) and calpains. Furthermore, necrotic cells release immu- nomodulatory factors that lead to recognition and engulfment by phagocytes and the subsequent immunologi- cal response. The knowledge of the molecular mechanisms involved in necrosis has contributed to our under- standing of necrosis-associated pathologies. In this review we will focus on the intracellular and intercellular signaling events in necrosis induced by different stimuli, such as oxidative stress, cytokines and pathogen- associated molecular patterns (PAMPs), which can be linked to several pathologies such as stroke, cardiac fai- lure, neurodegenerative diseases, and infections. Keywords: Necrosis, RIP1, mitochondrial Ca 2+ overload, ROS, clearance of necrotic cells, phagocyte response, neurodegenerative disorders, ischemia-reperfusion injury. INTRODUCTION Three major morphological types of cell death have been described [1]. Type I or apoptotic cell death is mediated by caspases and characterized by cellular shrinkage, chromatin condensation and DNA degrada- tion (reviewed in [2]). Type II cell death is associated with the formation of autophagic vacuoles inside the dying cell (reviewed in [3]). Type III or necrotic cell death is characterized by cellular swelling, plasma membrane rupture and the subsequent loss of the in- tracellular contents (reviewed in [4]). For a long time necrosis has been considered to be an accidental, un- controlled form of cell death, but evidence is accumula- ting that execution of necrotic cell death may be carried out by a set of signal transduction pathways and exe- cution mechanisms [4]. Some studies have demonstra- ted the occurrence of necrotic cell death in develop- ment and maintenance of homeostasis. For example, Apaf-1-deficient embryos show delayed development of digits, which are formed through the induction of ne- crosis of interdigital cells [5,6]. During homeostasis, *Address correspondence to this author at the Technologiepark 927, B-9052 Zwijnaarde (Ghent), Belgium; Tel: 0032.9.3313760; Fax: 0032.9.3313609, E-mail: Peter.Vandenabeele@dmbr.UGent.be necrosis of chondrocytes facilitates longitudinal growth of bones [7] and necrosis of specific epithelial cells of the human colon supports the turnover of the large in- testine [8]. In general, necrosis is mainly associated with pathologies such as IR injury, neurodegeneration and more recently also with certain pathogen infec- tions. METABOLIC CHANGES DURING NECROSIS Necrotic cell death occurs generally in response to physico-chemical stress, including hypoxia, ischemia, hypoglycemia, extreme temperature changes, and nu- trient deprivation [9,10]. In this paragraph we will focus on metabolic changes that lead to necrotic cell death in IR injury. Ischemia due to obstruction of blood flow to a tissue results in inadequacy of oxygen and nutrient supply, accumulation of metabolic waste products, and consequent impairment of energy metabolism. If pro- longed, this can result in cell death. Restoration of the blood flow, called reperfusion, particularly after prolon- ged ischemia, increases cell death, a phenomenon known as ‘reperfusion injury’. When oxygen supply is limited, oxidative phosphorylation is inhibited and mito- chondrial ATP production is thereby blocked. The im-