Poly(ADP-ribose)glycohydrolase is an upstream regulator of Ca2+ fluxes in oxidative cell death

Oxidative DNA damage to cells activates poly(ADP-ribose)polymerase-1 (PARP-1) and the poly(ADP-ribose) formed is rapidly degraded to ADP-ribose by poly(ADP-ribose)glycohydrolase (PARG). Here we show that PARP-1 and PARG control extracellular Ca2+ fluxes through melastatin-like transient receptor potential 2 channels (TRPM2) in a cell death signaling pathway. TRPM2 activation accounts for essentially the entire Ca2+ influx into the cytosol, activating caspases and causing the translocation of apoptosis inducing factor (AIF) from the inner mitochondrial membrane to the nucleus followed by cell death. Abrogation of PARP-1 or PARG function disrupts these signals and reduces cell death. ADP-ribose-loading of cells induces Ca2+ fluxes in the absence of oxidative damage, suggesting that ADP-ribose is the key metabolite of the PARP-1/PARG system regulating TRPM2. We conclude that PARP-1/PARG control a cell death signal pathway that operates between five different cell compartments and communicates via three types of chemical messengers: a nucleotide, a cation, and proteins

Free radicals and the pancreatic acinar cells: role in physiology and pathology

Reactive oxygen and nitrogen species (ROS and RNS) play an important role in signal transduction and cell injury processes. Nitric oxide synthase (NOS)—the key enzyme producing nitric oxide (NO)—is found in neuronal structures, vascular endothelium and, possibly, in acinar and ductal epithelial cells in the pancreas. NO is known to regulate cell homeostasis, and its effects on the acinar cells are reviewed here. ROS are implicated in the early events within the acinar cells, leading to the development of acute pancreatitis. The available data on ROS/RNS involvement in the apoptotic and necrotic death of pancreatic acinar cells will be discussed

Hydrogen peroxide mobilizes Ca2+ through two distinct mechanisms in rat hepatocytes

AIM: Hydrogen peroxide (H(2)O(2)) is produced during liver transplantation. Ischemia/reperfusion induces oxidation and causes intracellular Ca(2+) overload, which harms liver cells. Our goal was to determine the precise mechanisms of these processes. METHODS: Hepatocytes were extracted from rats. Intracellular Ca(2+) concentrations ([Ca(2+)](i)), inner mitochondrial membrane potentials and NAD(P)H levels were measured using fluorescence imaging. Phospholipase C (PLC) activity was detected using exogenous PIP(2). ATP concentrations were measured using the luciferin-luciferase method. Patch-clamp recordings were performed to evaluate membrane currents. RESULTS: H(2)O(2) increased intracellular Ca(2+) concentrations ([Ca(2+)](i)) across two kinetic phases. A low concentration (400 μmol/L) of H(2)O(2) induced a sustained elevation of [Ca(2+)](i) that was reversed by removing extracellular Ca(2+). H(2)O(2) increased membrane currents consistent with intracellular ATP concentrations. The non-selective ATP-sensitive cation channel blocker amiloride inhibited H(2)O(2)-induced membrane current increases and [Ca(2+)](i) elevation. A high concentration (1 mmol/L) of H(2)O(2) induced an additional transient elevation of [Ca(2+)](i), which was abolished by the specific PLC blocker U73122 but was not eliminated by removal of extracellular Ca(2+). PLC activity was increased by 1 mmol/L H(2)O(2) but not by 400 μmol/L H(2)O(2). CONCLUSION: H(2)O(2) mobilizes Ca(2+) through two distinct mechanisms. In one, 400 μmol/L H(2)O(2)-induced sustained [Ca(2+)](i) elevation is mediated via a Ca(2+) influx mechanism, under which H(2)O(2) impairs mitochondrial function via oxidative stress, reduces intracellular ATP production, and in turn opens ATP-sensitive, non-specific cation channels, leading to Ca(2+) influx. In contrast, 1 mmol/L H(2)O(2)-induced transient elevation of [Ca(2+)](i) is mediated via activation of the PLC signaling pathway and subsequently, by mobilization of Ca(2+) from intracellular Ca(2+) stores