Initiation of caspase‐independent death in mouse mesangial cells by Cd²⁺: Involvement of p38 kinase and CaMK‐II

Abstract

Cadmium (Cd) is a toxic metal with multiple effects on cell signaling and cell death. We studied the effects of Cd(2+) on quiescent mouse mesangial cells in serum-free conditions. Cadmium induces cell death over 6 h through annexin V+ states without or with causing uptake of propidium iodide, termed apoptotic and apoptosis-like death, respectively. Little or no necrosis is observed, and cell death is caspase-independent and associated with nuclear translocation of the apoptosis-inducing factor, AIF. We previously showed that Cd(2+) increased phosphorylation of Erk and CaMK-II, and CaMK-II activation increased cell death in an Erk-independent manner. Here we demonstrate that Cd(2+) increases Jnk and p38 kinase phosphorylation, and inhibition of p38-but not of Jnk-increases cell viability by suppressing apoptosis in preference to apoptosis-like death. Neither p38 kinase nor CaMK-II inhibition protects against a decrease in mitochondrial membrane potential, psi, indicating that kinase-mediated death is either independent of, or involves events downstream of a mitochondrial pathway. However, both the antioxidant N-acetyl cysteine (NAC) and the mitochondrial membrane-stabilizing agent cyclosporine A (CsA) partially preserve psi, suppress activation of p38 kinase, and partially protect the cells from Cd(2+)-induced death. Whereas the effect of CsA is on apoptosis, NAC acts on apoptosis-like death. Inhibition of glutathione synthesis exacerbates a Cd(2+)-dependent increase in cellular peroxides and favors apoptosis-like death over apoptosis. The caspase-independence of these modes of cell death is not due to an absence of this machinery in the mesangial cells: when they are exposed to Cd(2+) for longer periods in the presence of serum, procaspase-3 and PARP are cleaved and caspase inhibition is protective. We conclude that Cd(2+) can kill mesangial cells by multiple pathways, including caspase-dependent and -independent apoptotic and apoptosis-like death. Necrosis is not prominent. Activation of p38 kinase and of CaMK-II by Cd(2+) are associated with caspase-independent apoptosis that is not dependent on mitochondrial destabilization.

Cadmium Renal Toxicity <i>via</i> Apoptotic Pathways

“…In kidney proximal tubule cells, cadmium can induce both caspase-9 and -3 activity, which suggests that mitochondria-and caspase-mediated apoptosis pathways are also related to cadmium-induced renal toxicity. 43) In contrast, in rat proximal tubule WKPT-0293 Cl. 2 cells and mouse renal mesangial cells, cadmium can stimulate the release of proapoptotic factors, i.e., endonuclease apoptosis-inducing factor (AIF) from the mitochondria, which indicates that cadmium activates not only a caspase-dependent pathway but also caspase-independent pathways against mitochondria.…”

“…2 cells and mouse renal mesangial cells, cadmium can stimulate the release of proapoptotic factors, i.e., endonuclease apoptosis-inducing factor (AIF) from the mitochondria, which indicates that cadmium activates not only a caspase-dependent pathway but also caspase-independent pathways against mitochondria. 43,44) Moreover, using the mitochondria isolated from the kidney cell, cadmium has been shown to have direct effects against mitochondria because cadmium induces mitochondria swelling and subsequent Cyt c release. 45,46) Possible pathways for cadmium-induced mitochondria-mediated apoptosis are illustrated in Fig.…”

“…5,6) Apoptosis disorders induce a disruption of tissue homeostasis and functions and are associated with many diseases, such as cancer, neurodegenerative disease and toxin-induced disease. 7) Cadmium can induce apoptosis in various tissues and cultured cells, including mouse liver, 8) rat kidney and testis, [9][10][11][12][13] human T cell line (CEM-C12 cells), lymphoma U937 cells, normal hepatocytes, liver L-02 cells, fetal lung fibroblast MRC-5 cells and prostate epithelial cells, [14][15][16][17][18][19] mouse mesangial cells, 20) rat lung epithelial cells, cortical neurons and renal tubular epithelial cells, [21][22][23] and porcine kidney LLC-PK 1 cells. 24) These observations indicate that cell death of the proximal tubule cells in the kidney through apoptotic pathways is one of the key events in cadmium-induced renal toxicity.…”

Effects of Oxidative Stress on the Electrophysiological Function of Neuronal Membranes

“…Overactivation of these enzymes results in the breakdown of proteins and phospholipids and initiates several cascades that damage cells (Lee et al, 1999). It has been described that elevation in cytoplasmic Ca 2+ levels activates the mitogen-activated protein kinase (MAPK) cascade (Liu & Templeton, 2008; and the phosphatidylinositol 3′-kinase (PI3K)-Akt pathway (Cheng et al, 2003). ROS produce cell damage through multiple mechanisms, including excitotoxicity, metabolic dysfunction and disturbance of intracellular homeostasis of Ca 2+ (Halliwell & Gutteridge, 1984;Del Maestro et al, 1980;Bracci, 1992).…”

Resveratrol inhibits cadmium induced neuronal apoptosis by modulating calcium signalling pathway via regulation of MAPK/mTOR network

“…disturbs many signalling cascades (Liu and Templeton, 2008). Ca 2+ levels are critical for activation of mammalian target of rapamycin (mTOR) (Gulati et al, 2008).…”