Recent studies indicate that regulation of cellular oxidative capacity through enhancing mitochondrial biogenesis may be beneficial for neuronal recovery and survival in human neurodegenerative disorders. The peroxisome proliferator-activated receptor ␥ coactivator-1␣ (PGC-1␣) has been shown to be a master regulator of mitochondrial biogenesis and cellular energy metabolism in muscle and liver. The aim of our study was to establish whether PGC-1␣ and PGC-1␤ control mitochondrial density also in neurons and if these coactivators could be up-regulated by deacetylation. The results demonstrate that PGC-1␣ and PGC-1␤ control mitochondrial capacity in an additive and independent manner. This effect was observed in all studied subtypes of neurons, in cortical, midbrain, and cerebellar granule neurons. We also observed that endogenous neuronal PGC-1␣ but not PGC-1␤ could be activated through its repressor domain by suppressing it. Results demonstrate also that overexpression of SIRT1 deacetylase or suppression of GCN5 acetyltransferase activates transcriptional activity of PGC-1␣ in neurons and increases mitochondrial density. These effects were mediated exclusively via PGC-1␣, since overexpression of SIRT1 or suppression of GCN5 was ineffective where PGC-1␣ was suppressed by short hairpin RNA. Moreover, the results demonstrate that overexpression of PGC-1␤ or PGC-1␣ or activation of the latter by SIRT1 protected neurons from mutant ␣-synuclein-or mutant huntingtin-induced mitochondrial loss. These evidences demonstrate that activation or overexpression of the PGC-1 family of coactivators could be used to compensate for neuronal mitochondrial loss and suggest that therapeutic agents activating PGC-1 would be valuable for treating neurodegenerative diseases in which mitochondrial dysfunction and oxidative damage play an important pathogenic role.Previous studies have shown that the PGC-1 family of coactivators, particularly PGC-1␣, are potent stimulators of mitochondrial respiration and gene transcription in liver, heart, and skeletal muscle. It has been shown that PGC-1␣ acts by activating the nuclear respiratory factors NRF1 and NRF2 that in turn regulate expression of Tfam (mitochondrial transcription factor A), essential for replication, maintenance, and transcription of mitochondrial DNA. PGC-1␣ is also important for the expression of nuclear genes encoding respiratory chain subunits and other proteins that are required for proper mitochondrial functions (1-4).Apart from gene expression, the activity of PGC-1␣ is influenced by posttranscriptional regulation by means of protein phosphorylation, acetylation, and methylation. PGC-1␣ is known to be regulated by p38 mitogen-activated protein kinase through the inhibition of the p160 Myb-binding protein (p160 MBP ) 2 in brown fat cells and myotubes (5, 6). AMPK (AMP-activated protein kinase) phosphorylation of PGC-1␣ initiates many of the important gene-regulatory functions of AMPK in skeletal muscle (7). Acetylation status of PGC-1␣ is, on the other hand, regulated by t...

Parkinson disease is characterized by the accumulation of aggregated ␣-synuclein as the major component of the Lewy bodies. ␣-Synuclein accumulation in turn leads to compensatory effects that may include the up-regulation of autophagy. Another common feature of Parkinson disease (PD) is mitochondrial dysfunction. Here, we provide evidence that the overactivation of autophagy may be a link that connects the intracellular accumulation of ␣-synuclein with mitochondrial dysfunction. We found that the activation of macroautophagy in primary cortical neurons that overexpress mutant A53T ␣-synuclein leads to massive mitochondrial destruction and loss, which is associated with a bioenergetic deficit and neuronal degeneration. No mitochondrial removal or net loss was observed when we suppressed the targeting of mitochondria to autophagosomes by silencing Parkin, overexpressing wild-type Mitofusin 2 and dominant negative Dynamin-related protein 1 or blocking autophagy by silencing autophagy-related genes. The inhibition of targeting mitochondria to autophagosomes or autophagy was also partially protective against mutant A53T ␣-synuclein-induced neuronal cell death. These data suggest that overactivated mitochondrial removal could be one of the contributing factors that leads to the mitochondrial loss observed in PD models. Mitochondrial dysfunction is one of the hallmarks of Parkinson disease (PD).2 The link between mitochondrial dysfunction and PD was made after the discovery of mitochondrial complex I deficiency in the substantia nigra (1). This connection has been supported by the finding that the products of several PDrelated genes show mitochondrial localization under certain conditions, including SNCA, Parkin, PINK1, DJ-1, LRRK2, and HTR2A (2), and that the mitochondrial toxins MPTP, rotenone, and acetogenins can cause PD (3). A variety of mechanisms have been proposed to explain mitochondrial dysfunction. Oxidative stress, mitochondrial DNA deletions, pathological mutations in genes encoding mitochondrial proteins, altered mitochondrial morphology, and the interaction of pathogenic proteins with mitochondria can all lead to mitochondrial dysfunction and neuronal demise (4).In this study, we propose an intriguing possibility whereby mitochondrial dysfunction may arise from the loss of mitochondria because of the overactivation of autophagy. Signs of autophagy have been detected in the brains of PD patients, whereas autophagosomes are rarely detected in normal brain (5-6). Moreover, several studies have also demonstrated that the overexpression of mutant A53T ␣-synuclein in PC12 cells, cultured neurons, and nigrostriatal systems activates autophagy (7-10). Here, we provide evidence that shows that the up-regulation of macroautophagy by mutant A53T ␣-synuclein can augment mitochondrial removal, which results in a net mitochondrial loss, energetic failure, and neuronal cell death. EXPERIMENTAL PROCEDURESNeuronal Cultures-Primary cultures of rat cortical cells were prepared from neonatal Wistar rats. Briefly, cortices w...

Deficiency of the protein Wolfram syndrome 1 (WFS1) is associated with multiple neurological and psychiatric abnormalities similar to those observed in pathologies showing alterations in mitochondrial dynamics. The aim of this study was to examine the hypothesis that WFS1 deficiency affects neuronal function via mitochondrial abnormalities. We show that down-regulation of WFS1 in neurons leads to dramatic changes in mitochondrial dynamics (inhibited mitochondrial fusion, altered mitochondrial trafficking, and augmented mitophagy), delaying neuronal development. WFS1 deficiency induces endoplasmic reticulum (ER) stress, leading to inositol 1,4,5-trisphosphate receptor (IP3R) dysfunction and disturbed cytosolic Ca2+ homeostasis, which, in turn, alters mitochondrial dynamics. Importantly, ER stress, impaired Ca2+ homeostasis, altered mitochondrial dynamics, and delayed neuronal development are causatively related events because interventions at all these levels improved the downstream processes. Our data shed light on the mechanisms of neuronal abnormalities in Wolfram syndrome and point out potential therapeutic targets. This work may have broader implications for understanding the role of mitochondrial dynamics in neuropsychiatric diseases.

Dopamine is a neurotransmitter that plays a major role in a variety of brain functions, as well as in disorders such as Parkinson disease and schizophrenia. In cultured astrocytes, we have found that dopamine induces sporadic cytoplasmic calcium ([Ca 2؉ ] c ) signals. Importantly, we show that the dopamine-induced calcium signaling is receptor-independent in midbrain, cortical, and hippocampal astrocytes. We demonstrate that the calcium signal is initiated by the metabolism of dopamine by monoamine oxidase, which produces reactive oxygen species and induces lipid peroxidation. This stimulates the activation of phospholipase C and subsequent release of calcium from the endoplasmic reticulum via the inositol 1,4,5-trisphosphate receptor mechanism. These findings have major implications on the function of astrocytes that are exposed to dopamine and may contribute to understanding the physiological role of dopamine. Dopamine (DA)2 is the predominant catecholamine neurotransmitter in the mammalian brain and controls a variety of functions, including locomotor activity, cognition, emotion, positive reinforcement, food intake, and endocrine regulation. The neurotransmitter DA is a monoamine that is synthesized in dopaminergic neurons in the substantia nigra in the midbrain and transferred to the striatum through very fine C-fibers (1, 2). Dopaminergic terminals constitute ϳ21% of total axon terminals in the striatum and contact mostly dendritic spines and dendritic shafts. The actions of DA are mediated by specific G protein-coupled receptors, which are divided into two major families based on their ability to stimulate (D1-like) or inhibit adenylate cyclase (D2-like). Three human D2-like receptors have been cloned: D2, D3, and D4 (3). Dopamergic receptors are mostly distributed in the striatum and to a lesser degree in other parts of the brain.The signaling pathways of DA in different parts of the brain are of broad clinical and scientific interest. The neurodegenerative disorder, Parkinson disease, is caused by a loss of dopamine-secreting neurons from the midbrain; this leads to rigidity, tremor, and the characteristic slowness of movement. Impairment of DA signaling is thought to play a role not only in Parkinson disease but also Alzheimer disease and psychomotor syndromes such as schizophrenia (4 -6).DA is catabolized by monoamine oxidase (MAO), which breaks down monoamines using FAD, producing aldehydes and hydrogen peroxide. Astrocytes express both forms of MAO: MAO-A and MAO-B (7).Activation of D1 and D2 receptors is believed to modulate intracellular calcium levels by a single mechanism, that is, the stimulation of phosphatidylinositol hydrolysis by phospholipase C, resulting in the production of inositol 1,4,5-trisphosphate (IP 3 ), which mobilizes intracellular calcium stores (2, 3). Other mechanisms of release of Ca 2ϩ from internal stores have also been proposed. DA increases cAMP levels (8 -10). DA appears to affect the activity of calcium channels. In neurons and PC12 cells, DA reduced calcium currents...

During early development, neurons undergo complex morphological rearrangements to assemble into neuronal circuits and propagate signals. Rapid growth requires a large quantity of building materials, efficient intracellular transport and also a considerable amount of energy. To produce this energy, the neuron should first generate new mitochondria because the pre-existing mitochondria are unlikely to provide a sufficient acceleration in ATP production. Here, we demonstrate that mitochondrial biogenesis and ATP production are required for axonal growth and neuronal development in cultured rat cortical neurons. We also demonstrate that growth signals activating the CaMKKβ, LKB1-STRAD or TAK1 pathways also co-activate the AMPK-PGC-1α-NRF1 axis leading to the generation of new mitochondria to ensure energy for upcoming growth. In conclusion, our results suggest that neurons are capable of signalling for upcoming energy requirements. Earlier activation of mitochondrial biogenesis through these pathways will accelerate the generation of new mitochondria, thereby ensuring energy-producing capability for when other factors for axonal growth are synthesized.

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Huntington's disease (HD) is a late manifesting neurodegenerative disorder in humans caused by an expansion of a CAG trinucleotide repeat of more than 39 units in a gene of unknown function. Several mouse models have been reported which show rapid progression of a phenotype leading to death within 3-5 months (transgenic models) resembling the rare juvenile course of HD (Westphal variant) or which do not present with any symptoms (knock-in mice). Owing to the small size of the brain, mice are not suitable for repetitive in vivo imaging studies. Also, rapid progression of the disease in the transgenic models limits their usefulness for neurotransplantation. We therefore generated a rat model transgenic of HD, which carries a truncated huntingtin cDNA fragment with 51 CAG repeats under control of the native rat huntingtin promoter. This is the first transgenic rat model of a neurodegenerative disorder of the brain. These rats exhibit adult-onset neurological phenotypes with reduced anxiety, cognitive impairments, and slowly progressive motor dysfunction as well as typical histopathological alterations in the form of neuronal nuclear inclusions in the brain. As in HD patients, in vivo imaging demonstrates striatal shrinkage in magnetic resonance images and a reduced brain glucose metabolism in high-resolution fluor-deoxy-glucose positron emission tomography studies. This model allows longitudinal in vivo imaging studies and is therefore ideally suited for the evaluation of novel therapeutic approaches such as neurotransplantation.

Glutamate excitotoxicity is responsible for neuronal death in acute neurological disorders including stroke, trauma and neurodegenerative disease. Loss of calcium homeostasis is a key mediator of glutamate-induced cell death. The neurotransmitter dopamine (DA) is known to modulate calcium signalling, and here we show that it can do so in response to physiological concentrations of glutamate. Furthermore, DA is able to protect neurons from glutamate-induced cell death at pathological concentrations of glutamate. We demonstrate that DA has a novel role in preventing delayed calcium deregulation in cortical, hippocampal and midbrain neurons. The effect of DA in abolishing glutamate excitotoxicity can be induced by DA receptor agonists, and is abolished by DA receptor antagonists. Our data indicate that the modulation of glutamate excitotoxicity by DA is receptor-mediated. We postulate that DA has a major physiological function as a safety catch to restrict the glutamate-induced calcium signal, and thereby prevent glutamate-induced cell death in the brain. Signal transduction within the central nervous system (CNS) is mediated by specific neurotransmitters, whose properties have been studied in detail for several decades. Besides their role in signal transduction, neurotransmitters have been implicated in neurotoxicity.Neurotoxicity in the mammalian CNS has been linked to glutamate (e.g. see review by Choi 1 ). Glutamate-induced excitotoxicity has been implicated in neuronal cell death that follows periods of acute neuronal injury as anoxia and reperfusion, and it has been proposed that similar processes may contribute to the neuronal injury in neurodegenerative diseases such as motor neuron disease (for review, see Shaw et al. 2 ) and Alzheimer's disease (e.g. see Schubert and Piasecki 3 ).Neuronal delayed Ca 2 þ accumulation (delayed calcium deregulation, DCD) and mitochondrial membrane depolarization in response to glutamate is a requirement for the progression to cell death 1,4-6 . Exposure of neurons in culture to excitotoxic levels of glutamate results in an initial transient increase in cytosolic calcium concentration [Ca 2 þ ] c followed by a delayed sustained rise in [Ca 2 þ ] c (DCD), which coincides with a profound collapse of mitochondrial membrane potential and is believed to be an initial trigger for neuronal death. 7,8 Exposure of neurons in culture to glutamate causes selective neuronal cell death that can be effectively blocked by application of inhibitors of glutamate receptors. 9 However, glutamate antagonists are significantly less effective against neuronal death in vivo when applied to brain following periods of anoxia and reperfusion and clinical trials of N-methyl-Daspartic acid (NMDA) receptor antagonists remained unsuccessful, suggesting some additional mechanisms apply in the whole brain compared with primary neuronal cultures. 10,11 A possible explanation for this might be an interaction with other neurotransmitters in the brain, modulating glutamate toxicity in vivo.One of the major emer...