Lead and Calcium Produce Rod Photoreceptor Cell Apoptosis by Opening the Mitochondrial Permeability Transition Pore

Abstract

Calcium overload is suggested to play a fundamental role in the process of rod apoptosis in chemical-induced and inherited retinal degenerations. However, this hypothesis has not been tested directly. We developed an in vitro model utilizing isolated rat retinas to determine the mechanisms underlying Ca Apoptosis is an active mode of cell death that is induced by a variety of physiological and pathological stimuli. Convergent evidence suggests that mitochondria and caspases play a central and fundamental role in the effector or executioner phase of apoptosis (1). Early during the effector phase, the mitochondrial permeability transition pore (PTP), 1 a megachannel in the inner mitochondrial membrane, is opened by a variety of apoptotic inducers such as elevated matrix Ca 2ϩ , pro-oxidants, and thiol-reactive agents (1-3). This leads to mitochondrial depolarization (decrease in ⌬⌿ m ) and subsequently to the release of cytochrome c and/or apoptosis-inducing factor from mitochondria to cytosol or nuclei (1, 4, 5). Caspases are activated, which cleave downstream death substrates and activate endonucleases that cleave genomic DNA into fragments resulting in the apoptotic nuclear morphology (6, 7). The opening of the mitochondrial PTP and the apoptotic process can be inhibited by a diverse group of agents such as Bcl-2, Bcl-x L , bongkrekic acid, and CsA (1).Sustained increases in intracellular [Ca 2ϩ ] trigger apoptosis in a diverse array of in vivo and in vitro systems (1, 8). Results from several studies suggest that elevated rod photoreceptor [Ca 2ϩ ] plays a key role in the process of apoptotic rod cell death in humans and animals during inherited retinal degenerations, retinal diseases and injuries, and chemical exposure. These include patients with retinitis pigmentosa and cancer-associated retinopathy (9, 10), lead-exposed rats (11-13), retinal degeneration mice (13,14), rats injected with anti-recoverin monoclonal antibodies (15), rats with hypoxic-ischemic injury (16), and rats with light induced damage (17).Several neurotoxic heavy metals, transition metals, and organometals produce neuronal apoptosis in whole animals and cultured cells (11, 12, 18 -25). For example, low to moderate level Pb 2ϩ exposure produces apoptotic rod and bipolar cell death in developing and adult rats (11,12) and apoptotic neuronal cell death in primary cultured cells (23,24). Similarly, Cu 2ϩ and methyl mercury produce apoptosis in the developing and mature olfactory epithelium and cerebellum, respectively (18,22). Although the molecular mechanisms underlying the apoptosis induced by these different metals are unknown, there are two possible, though not mutually exclusive, triggering mechanisms: one is Ca 2ϩ overload and the other is the generation of ROS. Both in vivo and in vitro lead exposure increase rod and retinal intracellular [Ca 2ϩ ] during cell death (26, 27). Hg 2ϩ , tributyltin, and methyl mercury also cause Ca 2ϩ overload in cultured neuronal cells prior to cell death (19,20,28). Moreover, Hg 2ϩ , Mn 2ϩ , Cu 2ϩ...

The interactions of cobalt(II) with mitochondria from rat liver

“…4), Ca 2+ was not added, but, by operating under conditions similar to those reported in the literature [19,20] (i.e., 0.25 M sucrose, 10 mM Hepes/Mops pH 7.4, 5 lM CaCl 2 ), the addition of small amounts of Co 2+ (around 10 lM) induces a swelling, and the swelling is cyclosporine-sensitive (not shown). The above mentioned evidence appears to indicate similar targets for Co 2+ , Zn 2+ , and Pb 2+ , but in the cases of Zn 2+ and Pb 2+ [19,20] the authors have not proposed a specific action site for these two metals.…”

“…With regard to Zn 2+ [19] and Pb 2+ [20], the opening of the MTP pore has been observed in the presence of micromolar amounts of Ca 2+ . In our experiments (Fig.…”

Intracellular mechanisms of TRAIL: apoptosis through mitochondrial-dependent and -independent pathways

“…However, TRAIL-induced caspase-3 activation is su cient to cause apoptosis without the involvement of mitochondria, as cyclosporin A (CsA) delays, but does not block, caspase-3 activation and apoptosis. In other systems where apoptosis occurs via mitochondrial-dependent pathway, CsA blocks caspase-3 activation and apoptosis (Susin et al, 1998;He et al, 2000). It is not known whether TRAIL induces early response gene.…”

Interactions within the Coiled-coil Domain of RetGC-1 Guanylyl Cyclase Are Optimized for Regulation Rather than for High Affinity

“…Consequently, accelerated Na ϩ /Ca 2ϩ influx would drive the intracellular [Ca 2ϩ ] to higher than normal levels until they are sufficient to inactivate the mutant cyclase. Previous studies have suggested that elevated [Ca 2ϩ ] plays a fundamental role in the process of apoptotic rod cell death in humans and animals during inherited retinal degenerations, retinal diseases, injuries, and chemical exposure (67).…”