Is differential regulation of mitochondrial transcripts in Parkinson's disease related to apoptosis?

Mitochondrial dysfunction and apoptosis are attenuated through activation of AMPK/GSK-3β/PP2A pathway in Parkinson's disease

Parkinson's disease (PD) is a common neurological disorder worldwide, characterized by loss of dopaminergic neurons and decrease of dopamine content. Mitochondria plays an important role in the development of PD. Adenosine 5'-monophosphate-activated protein kinase (AMPK), glycogen synthase kinase 3 (GSK-3β) and protein phosphatase 2A (PP2A) are all key proteins that regulate mitochondrial metabolism and apoptosis, and they are involved in a variety of neurodegenerative diseases. Here, we aimed to explore the involvement of mitochondrial dysfunction and apoptosis in 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine hydrochloride (MPTP)-induced PD mice and MPP⁺ iodide-induced PC12 cells. MPTP-induced mice were subjected to behavioral testing to assess PD-like behaviors. Various molecular biological techniques including ELISA, Western blot, TUNEL assay, flow cytometry, and the important instruments Seahorse XF24 Extracellular and high performance liquid chromatography (HPLC), were used to identify the underlying molecular events of mitochondria. Treatment with the AMPK activator GSK621 dramatically ameliorated PD by increasing the levels of dopamine and rescuing the loss of dopaminergic neurons, which is dependent on the mitochondrial pathway. Moreover, regulation of AMPK/GSK-3β/PP2A pathway-related proteins by GSK621 was partially inhibited the development of PD, suggesting a negative feedback loop exists between AMPK action and mitochondrial dysfunction-mediated apoptosis. Our data preliminarily indicated that mitochondrial dysfunction and apoptosis in the pathogenesis of PD might be mediated by AMPK/GSK-3β/PP2A pathway action, which might be a promising new option for future therapy of PD.

Da-Bu-Yin-Wan and Qian-Zheng-San, two traditional Chinese herbal formulas, up-regulate the expression of mitochondrial subunit NADH dehydrogenase 1 synergistically in the mice model of Parkinson's disease

ETHNOPHARMACOLOGICAL RELEVANCE

Da-Bu-Yin-Wan (DBYW) and Qian-Zheng-San (QZS), two traditional Chinese herbal formulas, were clinically employed to treat Parkinson's disease (PD) for decades.

AIM OF THE STUDY

Our previous studies demonstrated neuroprotective effects of DBYW and QZS on mitochondrial function in mice model of PD induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In present research, we aimed to investigate the possible neuroprotective mechanisms of DBYW and QZS.

MATERIALS AND METHODS

The effects of DBYW and QZS on the behavioral changes (pole test), expression of tyrosine hydroxylase (TH) of substantia nigra by immunohistochemistry, monoaminergic contents and activity of striatum by high performance liquid chromatography, neuronal ultrastructure changes by transmission electron microscopy, mitochondrial DNA (mtDNA) damage by long-extension polymerase chain reaction (PCR), and mRNA expression of mitochondrial subunit NADH dehydrogenase 1(ND1) by qualitative real-time PCR were investigated.

RESULTS

Present study demonstrated that DBYW and QZS not only ameliorated the behavior induced by the administration of MPTP and synergistically prevented the decreasing of TH expression, but also increased monoaminergic contents and activity, improved the ultrastructural changes, decreased the mtDNA damage, and synergistically up-regulated the expression of ND1 in mRNA level.

CONCLUSIONS

These results suggest that DBYW and QZS possess anti-parkinsonism and neuroprotective properties.

Anti-apoptotic signaling and failure of apoptosis in the ischemic rat hippocampus

Several anti-apoptotic proteins are induced in CA1 neurons after transient forebrain ischemia (TFI), but fail to protect the majority of these cells from demise. Correlating cell death morphologies (apoptosis-like and necrosis-like death) with immunohistochemistry (IHC), we investigated whether anti-apoptosis contributes to survival, compromises apoptosis effector functions and/or delays death in CA1 neurons 1-7 days after TFI. As surrogate markers for bioenergetic failure, the IHC of respiratory chain complex (RCC) subunits was investigated. Dentate granule cell (DGC) apoptosis following colchicine injection severed as a reference for classical apoptosis. Heat shock protein 70 (Hsp70), neuronal apoptosis inhibitory protein (NAIP) and manganese superoxide dismutase (MnSOD) were upregulated in the majority of intact CA1 neurons paralleling the occurrence of CA1 neuronal death (days 3-7) as well as in a proportion of apoptosis-(<50%) and necrosis-like (<30%) CA1 neurons. Colchicine did not provoke an anti-apoptotic response in DGC at all. In addition, more than 70% of apoptosis- and necrosis-like CA1 neurons had completely lost their RCC subunits suggesting bioenergetic failure; by contrast, following colchicine injection, 88% of all apoptotic DGC presented RCC subunits. Thus, anti-apoptotic proteins may, in a subset of ischemic CA1 neurons, prevent cell death, while in others, affected by pronounced energy failure, they may cause secondary necrosis.

A murine dopamine neuron-specific cDNA library and microarray: increased COX1 expression during methamphetamine neurotoxicity

Due to brain tissue heterogeneity, the molecular genetic profile of any neurotransmitter-specific neuronal subtype is unknown. The purpose of this study was to purify a population of dopamine neurons, construct a cDNA library, and generate an initial gene expression profile and a microarray representative of dopamine neuron transcripts. Ventral mesencephalic dopamine neurons were purified by fluorescent-activated cell sorting from embryonic day 13.5 transgenic mice harboring a 4.5-kb rat tyrosine hydroxylase promoter-lacZ fusion. Nine-hundred sixty dopamine neuron cDNA clones were sequenced and arrayed for use in studies of gene expression changes during methamphetamine neurotoxicity. A neurotoxic dose of methamphetamine produced a greater than twofold up-regulation of the mitochondrial cytochrome c oxidase polypeptide I transcript from adult mouse substantia nigra at 12 h posttreatment. This is the first work to describe a gene expression profile for a neuronal subtype and to identify gene expression changes during methamphetamine neurotoxicity.

Effects of age and GDNF on noradrenergic innervation of the hippocampal formation: studies from intraocular grafts

Recent studies have suggested that factors in the target tissue influence the degree of plasticity and regeneration following aging and/or specific insults. We have investigated whether young or aged targets differ in their noradrenergic innervation from fetal locus coeruleus (LC) neurons, and also if a specific growth factor, glial cell line-derived neurotrophic factor (GDNF) can affect this innervation pattern. Tissue pieces of fetal brainstem and young (3 months) or old (18 months) iris tissue were transplanted simultaneously into the anterior chamber of the eye of adult hosts. We found that aged iris transplants became innervated to a significantly lesser degree by the cografted LC neurons than young iris transplants. Fetal hippocampal tissue was then grafted to adult hosts, and a fetal brainstem graft containing LC neurons was placed adjacent to the first graft, either at 3 or 21 months post-grafting. Thus, old/young chimeras of the noradrenergic coeruleo-hippocampal pathway were created. Aged hippocampal grafts received a much less dense innervation from co-grafted LC neurons than young hippocampal grafts. Tyrosine hydroxylase-positive-immunoreactive innervation was only found in the outskirts of aged grafts, while the young hippocampal grafts contained an even innervation pattern. The innervation density of hippocampal grafts was significantly enhanced by GDNF treatment. These findings demonstrate that target-derived factors may regulate neuronal plasticity, and that the age of the target is more important for innervation properties than the age of the neuron innervating a particular target.

Metabolic enzyme expression in dopaminergic neurons in Parkinson's disease: an in situ hybridization study

To clarify the role of neuronal complex 1 activity in idiopathic Parkinson's disease (IPD), expression of mitochondrial mRNA encoding the ND1 subunit of mitochondrial complex I was examined by semiquantitative in situ hybridization histochemistry in melanized neurons of human substantia nigra in IPD cases and control subjects. Expression of mRNA encoding the glycolytic enzyme, aldolase C, was also examined in substantia nigra and other neurons of the midbrain and brain stem. ND1 mRNA expression was strong in melanized substantia nigra neurons but undetectable in nigral glia. Levels of expression in nigral neurons were higher than in neurons of the red nucleus or cranial nerve nuclei, but similar values were obtained in pontine neurons. ND1 mRNA expression was reduced by about 25% in melanized neurons in IPD. There was no relationship between ND1 expression per cell and disease duration or L-DOPA dosage in the IPD group. No change in ND1 expression was observed in pontine neurons in IPD, and ND1 expression in the locus ceruleus was also unchanged. Melanized nigral neurons expressed lower levels of aldolase C mRNA than other midbrain or brain stem populations in both control and IPD material. These findings suggest that dopamine neurons are more strongly dependent on mitochondrial energy metabolism and oxidative phosphorylation than other brain stem populations. Because mitochondrial complex I activity is significantly reduced in IPD, intrinsically low expression of glycolytic enzymes, together with disease-related reduction in complex I activity, may be a contributory factor predisposing nigral neurons

Does neuronal loss in Parkinson's disease involve programmed cell death?

Recently it has been hypothesized that apoptotic cell death is involved in several neuropathological conditions including Parkinson's disease (PD). Initial morphological studies assessing the presence of apoptosis in Parkinsonian brain tissues yielded mixed results. Based on more recent studies in human PD brains as well in animal and cell culture models of the disease, a picture is emerging, however, that strongly suggests that many of the molecular players thought to participate in this type of neuronal cell death are active in the disease. The task of researchers in the field is now to deduce how these players may be interacting with one another to bring about cell death in PD and to design effective therapies to interfere with these processes.

Ganoderma extract activates MAP kinases and induces the neuronal differentiation of rat pheochromocytoma PC12 cells

The pharmacology and clinical application of traditional Chinese medicine has been extensively documented. We have used an in vitro model system, PC12 cells, to demonstrate the presence of neuroactive compounds in Ganoderma lucidum (lingzhi). Ganoderma extract induced the neuronal differentiation of PC12 cells and prevented nerve growth factor-dependent PC12 neurons from apoptosis. Moreover, these effects of ganoderma might be mediated via the ras/extracellular signal-regulated kinase (Erk) and cAMP-response element binding protein (CREB) signaling pathways, as demonstrated by the phosphorylation of Erk1, Erk2 and CREB. Thus, our data not only present the first evidence of the presence of neuroactive compounds that mediate the neuronal differentiation and neuroprotection of the PC12 cells, but also reveal the potential signaling molecules involved in its action.

Glial cell line-derived neurotrophic factor is essential for postnatal survival of midbrain dopamine neurons

Glial cell line-derived neurotrophic factor (GDNF) is one of the most potent trophic factors that have been identified for midbrain dopamine (DA) neurons. Null mutations for trophic factor genes have been used frequently for studies of the role of these important proteins in brain development. One problem with these studies has been that often only prenatal development can be studied because many of the knockout strains, such as those with GDNF null mutations, will die shortly after birth. In this study, we looked at the continued fate of specific neuronal phenotypes from trophic factor knockout mice beyond the time that these animals die. By transplanting fetal neural tissues from GDNF -/-, GDNF +/-, and wild-type (WT) mice into the brain of adult wild-type mice, we demonstrate that the continued postnatal development of ventral midbrain dopamine neurons is severely disturbed as a result of the GDNF null mutation. Ventral midbrain grafts from -/- fetuses have markedly reduced DA neuron numbers and fiber outgrowth. Moreover, DA neurons in such transplants can be "rescued" by immersion in GDNF before grafting. These findings suggest that postnatal survival and/or phenotypic expression of ventral mesencephalic DA neurons is dependent on GDNF. In addition, we present here a strategy for studies of maturation and even aging of tissues from trophic factor and other knockout animals that do not survive past birth.

GDNF and NT-4 protect midbrain dopaminergic neurons from toxic damage by iron and nitric oxide

Free radical formation is considered to be a major cause of dopaminergic (DAergic) cell death in the substantia nigra leading to Parkinson's disease (PD). In this study we employed several radical donors including iron and sodium nitroprusside to induce toxic effects on DAergic neurons cultured from the embryonic rat midbrain floor. Overall cell survival was assessed by assaying LDH, and DAergic neuron survival was monitored by counting tyrosine hydroxylase-positive cells. Our data suggest that the DAergic neuron population is about fourfold more susceptible to free-radical-mediated damage than the total population of midbrain neurons. Application of the neurotrophic factors GDNF and NT-4, for which DAergic neurons have specific receptors, prior to toxin administration protected these neurons from toxin-mediated death, which, fully or in part, occurs under the signs of apoptosis. These findings underscore the importance of GDNF and NT-4 in designing future therapeutical concepts for PD.

Review of apoptosis vs. necrosis of substantia nigra pars compacta in Parkinson's disease

The discovery that melanized neurons of the pars compacta of substantia nigra (pcSN) degenerate in the midbrain of human Parkinsonians is nearly a century old, but only in this decade have we gained insights into mechanisms underlying this neuronal loss. Although it had long been assumed that pcSN neurons underwent necrosis, recent (1) in vitro studies on isolated neurons, (2) in vivo studies in animals treated with neurotoxins, and (3) postmortem study of human Parkinsonian brain provide strong evidence that pcSN cells may be lost more from apoptosis (i.e., cell suicide) than from necrosis. This paper gives some historical perspective, but focuses primarily on mechanisms involved in both necrosis and apoptosis of neurons, primarily dopaminergic, and reviews the recent literature relating to apoptosis and apoptotic factors now identified in neurons undergoing neurotoxin-induced death and in postmortem human Parkinsonian brain. The weight of evidence in favor of apoptosis and apoptotic factors in these neurons, provides us with tools needed to develop anti-apoptotic factors that can be targeted to proteins on genes, so that it may be possible to decelerate or prevent the progressive neuronal cell loss in human Parkinsonians or in humans with other neurodegenerative disorders.

Recombinant adeno-associated viral vector-mediated glial cell line-derived neurotrophic factor gene transfer protects nigral dopamine neurons after onset of progressive degeneration in a rat model of Parkinson's disease

Previous work has demonstrated that viral vector mediated gene transfer of glial cell line-derived neurotrophic factor (GDNF), when administered prior to a striatal injection of the specific neurotoxin, 6-hydroxydopamine (6-OHDA), can protect nigral dopamine (DA) neurons from cell death. When considering gene therapy for Parkinson's disease (PD), vector delivery prior to the onset of neuropathology is not possible and chronic delivery will likely be necessary in a GDNF-based PD therapy. The present study was undertaken to determine if GDNF delivered via a recombinant adeno-associated viral vector (rAAV) could affect nigral DA cell survival when initiated just after the administration of striatal 6-OHDA. The onset of rAAV-mediated GDNF transgene expression near the substantia nigra was determined to begin somewhere between 1 and 7 days after the 6-OHDA injection and subsequent vector administration. The cell survival data indicate that rAAV-GDNF delivery results in a highly significant sparing of nigral DA neurons. These data indicate that a single delivery of rAAV encoding GDNF is efficacious when delivered after the onset of progressive degeneration in a rat model of PD.

Nerve growth factor inhibits apoptosis induced by tumor necrosis factor in PC12 cells

Tumor necrosis factor-alpha (TNFalpha) may play a role in at least some of the neuronal death that occurs following brain insults or in neurodegenerative diseases. It is therefore important to characterize the mechanism underlying apoptosis induced by TNFalpha in neuronal cells and to identify factors capable of protecting neurons from this death. In the present study, we characterized the apoptotic effect of TNFalpha in PC12 cells, a model system commonly used for studying neuronal apoptosis, and examined the role of Bcl-2 and caspases in this process. We show that TNFalpha induces apoptosis in both naive and primed PC12 cells. The TNFalpha-induced apoptosis was inhibited by nerve growth factor (NGF) but not by insulin. These findings suggest that the apoptotic effect of TNFalpha can be inhibited by trophic factors and that the survival-promoting effect of NGF is mediated by a specific pathway not shared by all tyrosine kinase receptors. The effect of Bcl-2 on TNFalpha-induced apoptosis was examined in PC12 cells overexpressing Bcl-2. These cells were resistant to TNFalpha-induced apoptosis, suggesting that the apoptotic effect of TNFalpha in PC12 cells is mediated via a pathway controlled by Bcl-2. Examination of the role of caspase-3 like activity in TNFalpha-induced apoptosis showed that caspase-3-like proteases are activated, and their substrate, poly (ADP-ribose) polymerase, is cleaved following TNFalpha treatment. In addition, the broad-spectrum inhibitor of caspases, benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (Z-VAD-FMK), was found to inhibit the TNFalpha-induced apoptosis of PC12 cells. These results suggest that caspases are activated following TNFalpha treatment and are needed for TNFalpha-induced apoptosis in PC12 cells.

Cloning of the SCA7 gene reveals a highly unstable CAG repeat expansion

The gene for spinocerebellar ataxia 7 (SCA7) has been mapped to chromosome 3p12-13. By positional cloning, we have identified a new gene of unknown function containing a CAG repeat that is expanded in SCA7 patients. On mutated alleles, CAG repeat size is highly variable, ranging from 38 to 130 repeats, whereas on normal alleles it ranges from 7 to 17 repeats. Gonadal instability in SCA7 is greater than that observed in any of the seven known neuro-degenerative diseases caused by translated CAG repeat expansions, and is markedly associated with paternal transmissions. SCA7 is the first such disorder in which the degenerative process also affects the retina.