Reactive Oxygen Species-Induced Necrotic Cell Death

Abstract

Mechanisms of cell death extend beyond the simple apoptosis/necrosis relationship to include regulated modes of cell death that do not readily fit either of the classic descriptors. One such mechanism of cell death involves poly(ADP-ribose)polymerase-1 (PARP-1)-mediated cell death. 2,3,5-Tris(Glutathion-S-yl)-hydroquinone (TGHQ), a reactive oxygen species (ROS) generating nephrotoxic and nephrocarcinogenic metabolite of hydroquinone, causes necrotic renal cell death, the basis for which is unclear. We therefore investigated TGHQ-mediated cell death in human renal proximal tubule epithelial HK-2 cells. TGHQ induced ROS generation, DNA strand breaks, hyperactivation of PARP-1, rapid depletion of nicotinamide adenine dinucleotide (NAD), elevations in intracellular Ca2+ concentrations, loss of mitochondrial membrane potential, and subsequent necrotic cell death. Interestingly, PARP-1 hyperactivation was not accompanied by the translocation of apoptosis-inducing factor (AIF) from mitochondria to the nucleus, a process usually associated with PARP-dependent cell death. Inhibition of PARP-1 with PJ34 blocked TGHQ-mediated accumulation of poly(ADP-ribose) polymers, NAD consumption, and the consequent necrotic cell death. However, HK-2 cell death was only delayed by PJ34, and cell death remained necrotic in nature. In contrast, chelation of intracellular Ca2+ with BAPTA-AM completely abrogated TGHQ-induced necrotic cell death. Ca2+ chelation not only prevented the collapse in the mitochondrial potential but also attenuated PARP-1 hyperactivation. Conversely, inhibition of PARP-1 modulated TGHQ-mediated changes in Ca2+ homeostasis. Moreover, TGHQ caused a sequential oxidation of peroxiredoxin III (PrxIII), a protein considered the primary antioxidant defense within mitochondria. Thus, TGHQ induced two acidic shifts in PrxIII, with both pI shifted spots representing oxidized forms of PrxIII. Transient expression of a dominant negative version of PrxIII resulted in a significant increase in TGHQ-induced cytotoxicity, whereas overexpression of wild-type PrxIII significantly attenuated cytotoxicity. Our studies provide new insights into PARP-1-mediated necrotic cell death. Changes in intracellular Ca2+ concentrations appear to couple PARP-1-hyperactivation to subsequent cell death, but in the absence of AIF release from mitochondria. NAD depletion, mitochondrial membrane depolarization, Ca2+-mediated calpain activation, and PrxIII oxidation, all contribute to TGHQ-driven ROS-mediated necrotic cell death.