Ovarian steroids reduce apoptosis induced by trophic insufficiency in nerve growth factor-differentiated PC12 cells and axotomized rat facial motoneurons.

Previous studies have demonstrated that ovarian steroids exert neuroprotective effects in a variety of in vitro and in vivo systems. The mechanisms underlying these effects remain poorly understood. In the present study, the neuroprotective effects of estradiol (E(2)) and progesterone (P) were examined in two models of apoptosis induced by growth factor insufficiency: partially nerve growth factor (NGF)-differentiated PC12 cells, after serum and NGF withdrawal; and axotomized immature rat facial motor motoneurons. E(2) and P both increased the survival of trophically withdrawn NGF-differentiated PC12 cells, at physiologically relevant concentrations. However, neither steroid had a significant effect on the survival of PC12 cells that had not been NGF treated. Exposure to NGF had no effect on the expression of estrogen receptor (ER)beta, but markedly increased the levels of ERalpha and altered the expression of the progesterone receptor (PR) from predominantly PR-B in NGF naive cells, to predominantly PR-A after NGF. The survival promoting effects of E(2) and P were blocked by the specific steroid receptor antagonists Faslodex (ICI 182780) and onapristone (ZK98299), respectively. Inhibitors of RNA (actinomycin D) or protein (cycloheximide) synthesis also abrogated the protective effects of both steroids. In immature rats, E(2) and P both significantly increased the numbers of surviving facial motor neurons at 21 days after axotomy. These data demonstrate significant protective effects of E(2) and P in two well-characterized models of apoptosis induced by trophic withdrawal and suggest that, at least in PC12 cells, the effects of the steroids are mediated via interaction with nuclear steroid receptor systems. The lack of steroid responsiveness in NGF-naive PC12 cells despite the presence of abundant ERbeta and PR-B are consistent with the view that ERalpha and PR-A may be particularly important as mediators of the neuroprotective effects of their corresponding hormonal ligands.

Propargylamines induce antiapoptotic new protein synthesis in serum- and nerve growth factor (NGF)-withdrawn, NGF-differentiated PC-12 cells.

(-)-Deprenyl and structurally related propargylamines increase neuronal survival independently of monoamine oxidase B (MAO-B) inhibition, in part by decreasing apoptosis. We found that deprenyl and two other propargylamines, one of which does not inhibit monoamine oxidase B, increased survival in trophically withdrawn 6-day nerve growth factor (NGF)- and 9-day NGF-differentiated PC-12 cells but not in NGF naive or 3-day NGF-differentiated PC-12 cells. Four days of prior NGF exposure were required for the propargylamine-mediated antiapoptosis. Studies using actinomycin D, cycloheximide, and camptothecin revealed that the maintenance of both transcription and translation, particularly between 2 and 6 h after trophic withdrawal, was required for propargylamine-mediated antiapoptosis. Metabolic labeling of newly synthesized proteins for two-dimensional protein gel autoradiography and scintillation counting showed that the propargylamines either increased or reduced the levels of new synthesis or induced de novo synthesis of a number of different proteins, most notably proteins in the mitochondrial and nuclear subfractions. Western blotting for whole cell or subcellular fraction lysates showed that the timing of new protein synthesis changes or subcellular redistribution of apoptosis-related proteins induced by the propargylamines were appropriate to antiapoptosis. The apoptosis-related proteins included superoxide dismutases (SOD1 and SOD2), glutathione peroxidase, c-JUN, and glyceraldehyde-3-phosphate dehydrogenase. Most notable were the prevention of apoptotic decreases in BCL-2 levels and increases in mitochondrial BAX levels. In general, (-)-deprenyl-related propargylamines appear to reduce apoptosis by altering the levels or subcellular localization of proteins that affect mitochondrial membrane permeability, scavenge oxidative radicals, or participate in specific apoptosis signaling pathways.

Apoptosis and anti-apoptosis signalling in glaucomatous retinopathy.

PURPOSE: Recent studies in the post-mortem human retina have suggested that apoptosis contributes to retinal ganglion cell (RGC) loss in glaucoma. If apoptosis contributes significantly to glaucomatous RGC loss, and if the specific apoptosis signalling pathways for glaucomatous apoptosis can be determined, agents that interrupt or oppose the signalling have the potential to slow the progression of glaucoma. METHODS: Recent data in animal models indicate that mitochondrially-dependent apoptosis contributes to RGC loss in glaucoma. Mitochondrially-dependent apoptosis involves proteins like BAX that increase mitochondrial membrane permeability and promote apoptosis and proteins like BCL-2 that decrease mitochondrial membrane permeability and reduce apoptosis. New protein synthesis induced by the alpha-2 agonist, brimonidine, prevents decreases in the levels of BCL-2 and thereby reduces mitochondrially-dependent apoptosis. CONCLUSIONS: Brimonidine appears to maintain BCL-2 levels by supporting the activity of an intrinsic anti-apoptosis signalling system that involves phosphorylation of protein kinase B. Phosphorylated protein kinase B appears to counteract the apoptosis signalling mechanisms which operate in glaucomatous retina.

Mitochondrial membrane potential in aging cells.

Decreased mitochondrial membrane potential (DeltaPsi(M)) has been found in a variety of aging cell types from several mammalian species. The physiological significance and mechanisms of the decreased DeltaPsi(M) in aging are not well understood. This review considers the generation of DeltaPsi(M) and its role in ATP generation together with factors that modify DeltaPsi(M) with emphasis on mitochondrial membrane permeability, particularly the role of a multiprotein membrane megapore, the mitochondrial permeability transition pore complex (PTPC). Previous data showing decreased DeltaPsi(M) in aged cells is considered in relation to the methods available to estimate DeltaPsi(M). In the past the majority of studies used whole cell rhodamine 123 fluorescence to estimate DeltaPsi(M) in lymphocytes from mice or rats. Imaging of DeltaPsi(M) in living, in situ mitochondria using laser confocal scanning microscopy offers advantages over whole cell measurements or those from isolated mitochondria, particularly if several different potentiometric dyes are employed. Furthermore, high resolution imaging of the newer fixable potentiometric dyes allows immunocytochemistry for specific proteins and DeltaPsi(M) to be examined in the same cells or even the same mitochondria. We found that decreased DeltaPsi(M) in p53 overexpression-induced or naturally occurring senescence is associated with decreased responsiveness of the PTPC to agents that induce either its opening or closing. The decreased PTPC responsiveness seems to reflect, at least in part, decreased levels of a key PTPC protein, the adenine nucleotide translocase. We also consider the possible basis for decreased DeltaPsi(M) in fibroblasts from patients with Parkinson's disease, an age-related neurodegenerative disease. Finally, we speculate on the mechanisms and functional significance of decreased DeltaPsi(M) in aging.

Maintaining mitochondrial membrane impermeability. an opportunity for new therapy in glaucoma?

Apoptosis may contribute to retinal ganglion cell loss in glaucoma and glaucoma models. Recent research has suggested that mitochondrially dependent apoptosis signaling may contribute to apoptosis in a rat model of glaucoma involving chronic increases in intraocular pressure. In some forms of apoptosis, mitochondrially dependent signaling involves increases in mitochondrial membrane permeability and the mitochondrial release of factors that signal for cell degradation. Opening of a multi-protein, mitochondrial megapore is one factor that contributes to the increased permeability and some anti-apoptotic proteins, particularly BCL-2 and BCL-X(L), bind at the megapore and facilitate megapore closure and reduce increases in mitochondrial membrane permeability. Phosphorylated protein kinase B (Akt) serves as an integrator for cellular survival signals and facilitates the megapore actions of BCL-2 and BCL-X(L), which could protect retinal ganglion cells against insults that induce apoptosis. Several anti-apoptotic agents are being evaluated for use in glaucoma, including brimonidine and propargylamines, which oppose mitochondrially dependent apoptosis through pathways involving phosphorylated Akt.

Retinal damage after 3 to 4 months of elevated intraocular pressure in a rat glaucoma model.

PURPOSE: To characterize a long-term elevated intraocular pressure (IOP) glaucoma model in the rat with respect to electroretinographic (ERG) changes and the pattern and mechanism of retinal ganglion cell (RGC) death. METHODS; An approximate doubling of IOP was induced in one eye (G) of female Wistar rats (150-180 g) by cautery of 3 episcleral/limbal veins. At intervals over 3 to 4 months, measurements of IOP and ERG changes (contact-lens electrode) were made in both the G and contralateral normal (N) eyes. At the end of 3 to 4 months of elevated IOP, RGCs were fluorescently labeled with Fluorogold (retrogradely from the superior colliculus), or retinas were labeled by intravitreal injection of a mitochondrial potential indicator dye and stained for apoptotic nuclei with a DNA dye. Flatmounts of fixed, dye-labeled retinas were examined by epifluorescence, confocal, or interference contrast microscopy. RESULTS: Elevated IOP was consistently maintained for up to 4 months in G eyes, but ERG a- and b-waves showed a statistically significant decline, of 30% to 40% in amplitude, after 3 months. Loss of RGCs in G retinas was primarily focal with no statistically significant loss demonstrable outside of the focal areas when assessed by an area sampling method for counting RGCs, which totaled 2% to 3% of the entire retinal area. Mitochondrial membrane potential of cells in the RGC layer was reduced by 17.5% (P: < 0.05) in regions surrounding areas of focal loss compared with comparable locations in control N eyes. After 3.5 months' elevated IOP the G retinas showed cell nuclei at various stages of apoptosis, from initial DNA condensation to fragmentation. CONCLUSIONS: The three-vein episcleral/limbal vein occlusion model for inducing glaucomatous pathology in the rat eye gives a consistent long-term elevation of IOP. After 3 to 4 months of approximately 100% increased IOP, the ERG responses begin to decline, there is a variable focal loss of RGCs, and some of the remaining RGCs show characteristics of stress and apoptosis. These changes seem consistent with retinal damage in human glaucoma (focal field defects), and this rat model appears to mimic some features of primary open-angle glaucoma.

Motor cortical potentials precede long-latency EMG activity evoked by imposed displacements of the human wrist.

Rapid angular displacements of the wrist evoke cerebral potentials that precede the onset of the long-latency electromyographic (EMG) activity generated in muscles stretched by the displacement. The initial segment of the long-latency EMG activity (termed the M2 response) is thought to be mediated by a transcortical reflex. We used dipole source analysis to examine the source generators of the early components of the cerebral potentials and their relationship to the timing and magnitude of the M2 response. Subjects (n=10) were presented with instructions to either actively flex or extend the wrist in response to a torque motor-imposed extensor displacement or allow the wrist to be passively extended. Electroencephalographic (EEG) recordings were obtained from 32 scalp-surface electrodes, and EMG was recorded from the wrist flexors and extensors. For all three tasks, the M2 response was preceded by cerebral potentials that could be explained by a three-dipole model. One source generator localised to deep within the cerebrum, and the other two localised to the region of the contralateral sensorimotor cortex. We used the P20-N20 dipole evoked by electrical stimulation of the median nerve at the wrist, corresponding to synaptic activity within cortical area 3b, as a local spatial reference to examine the contributions of the pre- and postcentral cortex. This analysis showed that one of the sensorimotor dipoles was consistently located anterior to the P20-N20 dipole at a displacement (average 11.5 mm) appropriate for a generator originating within the deep layers of area 4 on the anterior bank of the central sulcus. The orientation of this dipole was also consistent with a precentral generator and not a reversal of the potentials generated by input to area 3b. The time course of the area-4 dipole moment (onset =35 ms, peak =54 ms) was appropriate to reflect synaptic activity onto corticospinal neurons whose descending volleys mediate the M2 response. Comparisons across tasks showed that the magnitude of the M2 was modulated with task instruction, being largest with active and smallest with passive resistance. In contrast, the magnitude of the early evoked potentials (up to 75 ms) did not grade across tasks. We interpret these results as suggesting that instruction-dependent modulation of the M2 response occurs downstream from inputs to the primary motor cortex.

Reduced apoptosis after nerve growth factor and serum withdrawal: conversion of tetrameric glyceraldehyde-3-phosphate dehydrogenase to a dimer.

Antisense oligonucleotides against the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) are able to reduce some forms of apoptosis. In those forms, overall GAPDH levels increase and the enzyme accumulates in the nucleus. The monoamine oxidase B (MAO-B) inhibitor, (-)-deprenyl (DEP), its metabolite (-)-desmethyldeprenyl, and a tricyclic DEP analog, CGP3466, can reduce apoptosis independently of MAO-B inhibition and have been found to bind to GAPDH. We used neuronally differentiated PC12 cells to show that DEP, DES, and CGP3466 reduce apoptosis caused by serum and nerve growth factor withdrawal over the concentration range of 10(-) to 10(-13) M. We provide evidence that the DEP-like compounds bind to GAPDH in the PC12 cells and that they prevent both the apoptotic increases in GAPDH levels and nuclear accumulation of GAPDH. In vitro, the compounds enhanced the conversion of NAD(+) to NADH by GAPDH in the presence of AUUUA-rich RNA and converted GAPDH from its usual tetrameric form to a dimeric form. Using cell lysates, we found a marked increase in rates of NAD(+) to NADH conversion in early apoptosis, which was returned toward control values by the DEP-like compounds. Accordingly, the DEP-like compounds appear to decrease glycolysis by preventing the GAPDH increases in early apoptosis. GAPDH dimer may not have the capacity to contribute to apoptosis in a similar manner to the tetramer, which might account for the antiapoptotic capacity of the compounds. These actions on GAPDH, rather than MAO-B inhibition, may contribute to the improvements in Parkinson's and Huntington's diseases found with DEP treatment.

Neurorescuing effects of the GAPDH ligand CGP 3466B.

(-)-Deprenyl, used for the treatment of Parkinson's disease, was reported to possess neurorescuing/antiapoptotic effects independent of its MAO-B inhibiting properties. It is metabolized to (-)-desmethyldeprenyl, which seems to be the active principle, and further to (-)-amphetamine and (-)-methamphetamine, which antagonize its rescuing effects. These complications may explain the limited neurorescuing potential of (-)-deprenyl observed clinically. CGP 3466 (dibenzo[b,f]oxepin-10-ylmethyl-methyl-prop-2-ynyl-amine), structurally related to (-)-deprenyl, exhibits virtually no MAO-B nor MAO-A inhibiting properties and is not metabolized to amphetamines. It was shown to bind to glyceraldehyde-3-phosphate dehydrogenase, a glycolytic enzyme with multiple other functions including an involvement in apoptosis, and shows neurorescuing properties qualitatively similar to, but about 100-fold more potent than those of (-)-deprenyl in several in vitro and in vivo paradigms. In concentrations ranging from 10(-13)-10(-5) M, it rescues partially differentiated PC12 cells from apoptosis induced by trophic withdrawal, cerebellar granule cells from apoptosis induced by cytosine arabinoside, rat embryonic mesencephalic dopaminergic cells from death caused by MPP+, and PAJU human neuroblastoma cells from death caused by rotenone. However, it did not affect apoptosis elicited by a variety of agents in rapidly proliferating cells from thymus or skin or in liver or kidney cells. In vivo, it rescued facial motor neuron cell bodies in rat pups after axotomy, rat hippocampal CA1 neurons after transient ischemia/hypoxia, and mouse nigral dopaminergic cell bodies from death induced by MPTP, in doses ranging between 0.0003 and 0.1 mg/kg p.o. or s.c., depending on the model. It also partially prevented the loss of tyrosine hydroxylase immunoreactivity in the substantia nigra of 6-OHDA-lesioned rats and improved motor function in these animals. Moreover, it prolonged the life-span of progressive motor neuronopathy (pmn) mice (a model for ALS), preserved their body weight and improved their motor performance. This was accompanied by a decreased loss of motor neurons and motor neuron fibers, and protection of mitochondria. The active concentration- or dose-ranges in the different in vitro and in vivo paradigms were remarkably similar. In several paradigms, bell-shaped dose-response curves were observed, the rescuing effect being lost above about 1 mg/kg, a fact that must be considered in clinical investigations.

Glyceraldehyde-3-phosphate dehydrogenase in neurodegeneration and apoptosis signaling.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a well-studied glycolytic enzyme that plays a key role in energy metabolism. GAPDH catalyzes the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate in the glycolytic pathway. As part of the conversion, GAPDH converts NAD+ to the high-energy electron carrier NADH. GAPDH has been referred to as a "housekeeping" protein and based on the view that GAPDH gene expression remains constant under changing cellular conditions, the levels of GAPDH mRNA have frequently been used to normalize northern blots. In recent years, that view has changed since GAPDH is now known to contribute to a number of diverse cellular functions unrelated to glycolysis. Normative functions of GAPDH now include nuclear RNA export, DNA replication, DNA repair, exocytotic membrane fusion, cytoskeletal organization and phosphotransferase activity. Pathologically, GAPDH has been implicated in apoptosis, neurodegenerative disease, prostate cancer and viral pathogenesis (see Sirover (1999) for a recent review of GAPDH functions). Most recently, it has been shown that GAPDH is a target for deprenyl related compounds (Carlile et al., 2000; Kragten et al., 1998) and may contribute to the neuroprotection offered by those compounds.

Arsenic trioxide selectively induces acute promyelocytic leukemia cell apoptosis via a hydrogen peroxide-dependent pathway.

Low concentrations of As(2)O(3) (

Reduced mitochondrial membrane potential and altered responsiveness of a mitochondrial membrane megachannel in p53-induced senescence.

There is accumulating evidence that mitochondrial membrane potential (DeltaPsi(M)) is reduced in aged cells. In addition, a decrease of DeltaPsi(M) has been shown to be an early event in many forms of apoptosis. Here we use a mitochondrial potentiometric dye with in situ laser scanning confocal microscopic (LSCM) imaging to demonstrate that DeltaPsi(M) is dramatically decreased in both the p53-overexpressing, senescent EJ tumor cells and in pre-apoptotic PC12 cells compared to controls. Treatment with cyclosporin A (CSA), which facilitates closure of the mitochondrial permeability transition pore (PTP), was able to reverse the decrease in DeltaPsi(M) in pre-apoptotic PC12 cells but not in the senescent EJ-p53 cells. The capacity to prevent dissipation of DeltaPsi(M) in response to agents that facilitate PTP closure may differentiate cells entering apoptosis from those participating in senescence. Therefore, regulation of the closure of the mitochondrial PTP in the presence of decreased DeltaPsi(M) may be a decisional checkpoint in distinguishing between growth arrest pathways.

Apoptotic mechanisms in neurodegeneration: possible relevance to glaucoma.

Deprenyl, a monoamine oxidase inhibitor used in the treatment of Parkinson's disease, along with its primary metabolite desmethyldeprenyl (DES) have been shown to reduce neuronal apoptosis by a mechanism that requires gene transcription and involves the maintenance of mitochondrial membrane potential. This review article explores the mechanisms by which DES maintains mitochondrial membrane potential. Mediated by GAPDH binding, DES increases mitochondrial BCL-2 and BCL-xL levels and decreases BAX levels thereby preventing the permeability transition pore (PTP) form opening and preventing apoptotic degradation. The favorable effects of deprenyl on neuronal apoptosis suggests the therapeutic potential of designing compounds with the capacity to alter the configurations of pro-apoptosis or anti-apoptotic proteins.

Nuclear translocation of GAPDH-GFP fusion protein during apoptosis.

Increased expression and nuclear accumulation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) are early, critical events in several forms of apoptosis. In order to investigate the subcellular trafficking of GAPDH in vivo, the localization of a GAPDH-green fluorescent protein (GFP) fusion was studied in PC12, HEK 293 and COS-1 cells. In control cells, fusion protein autofluorescence was largely restricted to the cytoplasm, rather than the nuclear concentration favored by GFP alone. In contrast, as early as 30 min after an insult, nuclear fluorescence increased in all cell lines studied. The fusion protein redistribution paralleled the dynamics of endogenous GAPDH. These data suggest that some nuclear GAPDH observed during apoptosis represents protein previously resident in the cytosol. This construct provides an in vivo monitor for an early change in apoptosis.

Glucose protection from MPP+-induced apoptosis depends on mitochondrial membrane potential and ATP synthase.

MPP+ inhibits mitochondrial complex I and alpha-ketoglutarate dehydrogenase causing necrosis or apoptosis of catecholaminergic neurons. Low glucose levels or glycolytic blockade has been shown to potentiate MPP+ toxicity. We found that MPP+ caused concentration-dependent apoptosis of neuronally differentiated PC12 cells and that glucose, but not pyruvate, supplementation reduced apoptosis. Oligomycin concentrations sufficient to inhibit ATP synthase blocked the decreased apoptosis afforded by glucose supplementation. Laser-scanning confocal microscope imaging of chloromethyl-tetramethylrosamine methyl ester fluorescence to estimate DeltaPsiM showed that MPP+ and atractyloside reduced DeltaPsiM, while cyclosporin A (CSA) and glucose supplementation reversed decreases in DeltaPsiM caused by MPP+. Oligomycin blocked the effect of glucose supplementation on DeltaPsiM. These findings show that (i) MPP+-induced and atractyloside-induced apoptosis are associated with reduced DeltaPsiM; (ii) CSA maintains DeltaPsiM and reduces MPP+-induced apoptosis; and (iii) glucose supplementation maintains DeltaPsiM, likely by glycolytic ATP-dependent proton pumping at ATP synthase and reduces MPP+-induced apoptosis.

Etiology and pathogenesis of Parkinson's disease.

Parkinson's disease (PD) is an age-related neurodegenerative disorder that affects approximately 1 million persons in the United States. It is characterized by resting tremor, rigidity, bradykinesia or slowness, gait disturbance, and postural instability. Pathological features include degeneration of dopaminergic neurons in the substantia nigra pars compacta coupled with intracytoplasmic inclusions known as Lewy bodies. Neurodegeneration and Lewy bodies can also be found in the locus ceruleus, nucleus basalis, hypothalamus, cerebral cortex, cranial nerve motor nuclei, and central and peripheral components of the autonomic nervous system. Current treatment consists of a dopamine replacement strategy using primarily the dopamine precursor levodopa. While levodopa provides benefit to virtually all PD patients, after 5-10 years of treatment the majority of patients develop adverse events in the form of dyskinesia (involuntary movements) and fluctuations in motor response. Further, disease progression is associated with the development of dementia, autonomic dysfunction, and postural instability, which do not respond to levodopa therapy. Accordingly, research efforts have been directed toward understanding the etiology and pathogenesis of PD in the hope of developing a more effective therapy that will slow or halt the natural progression of PD. This paper reviews recent advances.

Apoptosis in neurodegenerative diseases: the role of mitochondria.

Nerve cell death is the central feature of the human neurodegenerative diseases. It has long been thought that nerve cell death in these disorders occurs by way of necrosis, a process characterized by massive transmembrane ion currents, compromise of mitochondrial ATP production, and the formation of high levels of reactive oxygen species combining to induce rapid disruption of organelles, cell swelling, and plasma membrane rupture with a secondary inflammatory response. Nuclear DNA is relatively preserved. Recent evidence now indicates that the process of apoptosis rather than necrosis primarily contributes to nerve cell death in neurodegeneration. This has opened up new avenues for understanding the pathogenesis of neurodegeneration and may lead to new and more effective therapeutic approaches to these diseases.

Mitochondrial abnormalities in neuroectodermal cells stably expressing human amyloid precursor protein (hAPP751).

Metabolic hypofunction is a common finding in a number of neurodegenerative diseases, including Alzheimer's disease (AD). The strong linkage between the amyloid precursor protein (APP) and AD led us to examine whether over-expression of this protein in CNS-type cells had an effect on mitochondria. We found abnormal morphology in mitochondria of the neuroectodermal progeny of P19 cells stably transfected with human APP751. In addition, the mitochondria of APP-transfected clones had a decreased mitochondrial membrane potential. These changes were independent of Abeta toxicity and distinct from complex I inhibition. Our results have important implications for the earliest events in the pathophysiology of AD and, by extrapolation, for intervention therapies.

Mitochondrial permeability in neuronal death: possible relevance to the pathogenesis of Parkinson's disease.

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes catecholaminergic nerve cell loss and a syndrome similar to Parkinson's disease (PD). The metabolite of MPTP, MPP(+) (1-methyl-4-phenylpyridinium), decreases mitochondrial complex I activity similar to that in the PD nigra. Opening of a multi-protein, mitochondrial membrane pore constitutes a critical decisional event in some forms of apoptosis. We review recent findings showing that the permeability transition pore (PTP) opening caused by a decrease in the mitochondrial membrane potential (DeltaPsi(M)) contributes to MPP(+)-induced apoptosis. The reduction in DeltaPsi(M) appears to result from decreased proton pumping at complex I and therefore decreased complex I activity may also contribute to apoptosis in PD.