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...

Dietary restriction (DR) has been shown to increase life span, delay or prevent age-associated diseases, and improve functional and metabolic cardiovascular risk factors in rodents and other species. To investigate the effects of DR on beat-to-beat heart rate and diastolic blood pressure variability (HRV and DPV) in male Sprague-Dawley rats, we implanted telemetric transmitters and animals were maintained on either intermittent fasting (every other day feeding) or calorie-restricted (40% caloric reduction) diets. Using power spectral analysis, we evaluated the temporal profiles of the low- and high-frequency oscillatory components in heart rate and diastolic blood pressure signals to assess cardiac autonomic activity. Body weight, heart rate, and systolic and diastolic blood pressure were all found to decrease in response to DR. Both methods of DR produced decreases in the low-frequency component of DPV spectra, a marker for sympathetic tone, and the high-frequency component of HRV spectra, a marker for parasympathetic activity, was increased. These parameters required at least 1 month to become maximal, but returned toward baseline values rapidly once rats resumed ad libitum diets. These results suggest an additional cardiovascular benefit of DR that merits further studies of this potential effect in humans.

SummaryMitochondrial fusion-fission dynamics play a crucial role in many important cell processes. These dynamics control mitochondrial morphology, which in turn influences several important mitochondrial properties including mitochondrial bioenergetics and quality control, and they appear to be affected in several neurodegenerative diseases. However, an integrated and quantitative understanding of how fusion-fission dynamics control mitochondrial morphology has not yet been described. Here, we took advantage of modern visualisation techniques to provide a clear explanation of how fusion and fission correlate with mitochondrial length and motility in neurons. Our main findings demonstrate that: (1) the probability of a single mitochondrion splitting is determined by its length; (2) the probability of a single mitochondrion fusing is determined primarily by its motility; (3) the fusion and fission cycle is driven by changes in mitochondrial length and deviations from this cycle serves as a corrective mechanism to avoid extreme mitochondrial length; (4) impaired mitochondrial motility in neurons overexpressing 120Q Htt or Tau suppresses mitochondrial fusion and leads to mitochondrial shortening whereas stimulation of mitochondrial motility by overexpressing Miro-1 restores mitochondrial fusion rates and sizes. Taken together, our results provide a novel insight into the complex crosstalk between different processes involved in mitochondrial dynamics. This knowledge will increase understanding of the dynamic mitochondrial functions in cells and in particular, the pathogenesis of mitochondrial-related neurodegenerative diseases.

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.

The preservation of the replicative life span of memory CD8+ T cells is vital for long-term immune protection. Although IL-15 plays a key role in the homeostasis of memory CD8+ T cells, it is unknown whether IL-15 regulates the replicative life span of memory CD8+ T cells. In this study, we report an analysis of telomerase expression and telomere length in human memory phenotype CD8+ T cells maintained by IL-15 in vitro. We demonstrate that IL-15 is capable of activating telomerase in memory CD8+ T cells via Jak3 and PI3K signaling pathways. Furthermore, IL-15 induces a sustained level of telomerase activity over long periods of time, and in turn minimizes telomere loss in memory CD8+ T cells after substantial cell divisions. These findings suggest that IL-15 activates stable telomerase expression and compensates telomere loss in memory phenotype CD8+ T cells, and that telomerase may play an important role in memory CD8+ T cell homeostasis.

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In this study we wanted to determine whether changes in antioxidant profile could follow the catabolic effects of glucocorticoids. We also wanted to compare resistance to glucocorticoid overload in young and old rats. To address these questions, whole body catabolism was induced by the administration of dexamethasone (Dex) at either 2 mg/kg bodyweight/day to young (6 weeks old) or 0.5 mg/kg body-weight/day to old (94 weeks old) rats. Bodyweight loss of pair-fed rats not given Dex was only 2% in the young rats and 8% in the old rats, whereas in Dex-treated rats the decrease in bodyweight was 22% in the young rats and 13% in the old rats after 5 days of treatment. Spleen weight decreased by 65% in the young rats and by 52% in the old rats. Additionally, in the young rats there was a 46% reduction in glutathione (GSH) in erythrocytes as well as a 36% reduction in GSH/tissue wet weight in the soleus muscle. The corresponding figures for the old rats were 35 and 26%, respectively. Taken together, these results suggest that Dex directly and/or indirectly impaired the antioxidant reactions. This was further confirmed by a significant (50%) decline in Cu-Zn superoxide dismutase (SOD-1) activity in erythrocytes isolated from the young rats treated with Dex but not the old rats as they showed a significant elevation in SOD-1 activity (by 101%). Thiobarbituric acid reactant substances were significantly higher in both young and old rats. Activity of blood plasma creatine kinase increased by 73% in the young rats and by 307% in the old rats treated with Dex. Although both the young and the old rats could recover from oxidative stress, the old rats in contrast to the young rats remained catabolic until the end of the experiment. In conclusion, we suggest that old rats are more vulnerable to the catabolic action of Dex, whereas young rats are more susceptible to the oxidative stress induced by Dex.