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Mitochondrial Transport (mitochondrial + transport)

Distribution by Scientific Domains

Medical Sciences	83%

Selected Abstracts

Sensitivity of the 2-oxoglutarate carrier to alcohol intake contributes to mitochondrial glutathione depletion

HEPATOLOGY, Issue 3 2003
Olga Coll
The mitochondrial pool of reduced glutathione (mGSH) is known to play a protective role against liver injury and cytokine-mediated cell death. However, the identification of the mitochondrial carriers involved in its transport in hepatocellular mitochondria remains unestablished. In this study, we show that the functional expression of the 2-oxoglutarate carrier from HepG2 cells in mitochondria from Xenopus laevis oocytes conferred a reduced glutathione (GSH) transport activity that was inhibited by phenylsuccinate, a specific inhibitor of the carrier. In addition, the mitochondrial transport of GSH and 2-oxoglutarate in isolated mitochondria from rat liver exhibited mutual competition and sensitivity to glutamate and phenylsuccinate. Interestingly, the kinetics of 2-oxoglutarate transport in rat liver mitochondria displayed a single Michaelis-Menten component with a Michaelis constant of 3.1 ± 0.3 mmol/L and maximum velocity of 1.9 ± 0.1 nmol/mg protein/25 seconds. Furthermore, the initial rate of 2-oxoglutarate was reduced in mitochondria from alcohol-fed rat livers, an effect that was not accompanied by an alcohol-induced decrease in the 2-oxoglutarate messenger RNA levels but rather by changes in mitochondrial membrane dynamics induced by alcohol. The fluidization of mitochondria by the fluidizing agent 2-(2-methoxyethoxy)ethyl 8-(cis-2-n-octylcyclopropyl) (A2C) restored the initial transport rate of both GSH and 2-oxoglutarate. Finally, these changes were reproduced in normal liver mitochondria enriched in cholesterol where the fluidization of cholesterol-enriched mitochondria with A2C restored the order membrane parameter and the mitochondrial 2-oxoglutarate uptake. In conclusion, these findings provide unequivocal evidence for 2-oxoglutarate as a GSH carrier and its sensitivity to membrane dynamics perturbation contributes in part to the alcohol-induced mGSH depletion. [source]

Mitochondrial S -Adenosyl- l -Methionine Transport is Insensitive to Alcohol-Mediated Changes in Membrane Dynamics

ALCOHOLISM, Issue 7 2009
Anna Fernández
Background:, Alcohol-induced liver injury is associated with decreased S -adenosyl- l -methionine (SAM)/S -adenosyl- l -homocysteine (SAH) ratio and mitochondrial glutathione (mGSH) depletion, which has been shown to sensitize hepatocytes to tumor necrosis factor (TNF). Aims:, As the effect of alcohol on mitochondrial SAM (mSAM) has been poorly characterized, our aim was to examine the status and transport of mSAM in relation to that of mGSH during alcohol intake. Methods:, Sprague,Dawley rats were pair fed Lieber,DeCarli diets containing alcohol for 1 to 4 weeks and liver fractionated into cytosol and mitochondria to examine the mSAM transport and its sensitivity to membrane dynamics. Results:, We found that cytosol SAM was depleted from the first week of alcohol feeding, with mSAM levels paralleling these changes. Cytosol SAH, however, increased during the first 3 weeks of alcohol intake, whereas its mitochondrial levels remained unchanged. mGSH depletion occurred by 3 to 4 weeks of alcohol intake due to cholesterol-mediated impaired transport from the cytosol. In contrast to this outcome, the transport of SAM into hepatic mitochondria was unaffected by alcohol intake and resistant to cholesterol-mediated perturbations in membrane dynamics; furthermore cytosolic SAH accumulation in primary hepatocytes by SAH hydrolase inhibition reproduced the mSAM depletion by alcohol due to the competition of SAH with SAM for mitochondrial transport. However, alcohol feeding did not potentiate the sensitivity to inhibition by SAH accumulation. Conclusions:, Alcohol-induced mSAM depletion precedes that of mGSH and occurs independently of alcohol-mediated perturbations in membrane dynamics, disproving an inherent defect in the mSAM transport by alcohol. These findings suggest that the early mSAM depletion may contribute to the alterations of mitochondrial membrane dynamics and the subsequent mGSH down-regulation induced by alcohol feeding. [source]

Cannabinoid signalling in the enteric nervous system

NEUROGASTROENTEROLOGY & MOTILITY, Issue 9 2009
J. J. Galligan
Abstract, Cannabinoid signalling is an important mechanism of synaptic modulation in the nervous system. Endogenous cannabinoids (anandamide and 2-arachidonyl-glycerol) are synthesized and released via calcium-activated biosynthetic pathways. Exogenous cannabinoids and endocannabinoids act on CB1 and CB2 receptors. CB1 receptors are neuronal receptors which couple via G-proteins to inhibition of adenylate cyclase or to activation or inhibition of ion channels. CB2 receptors are expressed by immune cells and cannabinoids can suppress immune function. In the central nervous system, the endocannabinoids may function as retrograde signals released by the postsynaptic neuron to inhibit neurotransmitter release from presynaptic nerve terminals. Enteric neurons also express CB receptors. Exogenously applied CB receptor agonists inhibit enteric neuronal activity but it is not clear if endocannabinoids released by enteric neurons can produce similar responses in the enteric nervous system (ENS). In this issue of Neurogastroenterology and Motility, Boesmans et al. show that CB1 receptor activation on myenteric neurons maintained in primary culture can suppress neuronal activity, inhibit synaptic transmission and mitochondrial transport along axons. They also provide initial evidence that myenteric neurons (or other cell types present in the cultures) release endocannabinoids and which activate CB1 receptors constitutively. These data provide new information about targets for cannabinoid signalling in the ENS and highlight the potential importance of CB receptors as drug targets. It is necessary that future work extends these interesting findings to intact tissues and ideally to the in vivo setting. [source]

Cannabinoid receptor 1 signalling dampens activity and mitochondrial transport in networks of enteric neurones

NEUROGASTROENTEROLOGY & MOTILITY, Issue 9 2009
W. Boesmans
Abstract, Cannabinoid (CB) receptors are expressed in the enteric nervous system (ENS) and CB1 receptor activity slows down motility and delays gastric emptying. This receptor system has become an important target for GI-related drug development such as in obesity treatment. The aim of the study was to investigate how CB1 ligands and antagonists affect ongoing activity in enteric neurone networks, modulate synaptic vesicle cycling and influence mitochondrial transport in nerve processes. Primary cultures of guinea-pig myenteric neurones were loaded with different fluorescent markers: Fluo-4 to measure network activity, FM1-43 to image synaptic vesicles and Mitotracker green to label mitochondria. Synaptic vesicle cluster density was assessed by immunohistochemistry and expression of CB1 receptors was confirmed by RT-PCR. Spontaneous network activity, displayed by both excitatory and inhibitory neurones, was significantly increased by CB1 receptor antagonists (AM-251 and SR141716), abolished by CB1 activation (methanandamide, mAEA) and reduced by two different inhibitors (arachidonylamide serotonin, AA-5HT and URB597) of fatty acid amide hydrolase. Antagonists reduced the number of synaptic vesicles that were recycled during an electrical stimulus. CB1 agonists (mAEA and WIN55,212) reduced and antagonists enhanced the fraction of transported mitochondria in enteric nerve fibres. We found immunohistochemical evidence for an enhancement of synaptophysin-positive release sites with SR141716, while WIN55,212 caused a reduction. The opposite effects of agonists and antagonists suggest that enteric nerve signalling is under the permanent control of CB1 receptor activity. Using inhibitors of the endocannabinoid degrading enzyme, we were able to show there is endogenous production of a CB ligand in the ENS. [source]

Trafficking of macromolecules and organelles in cultured Dystonia musculorum sensory neurons is normal

THE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 4 2006
Madeline Pool
Abstract Dystonia musculorum (dt) mice suffer from a recessive neuropathy characterized by the progressive loss of sensory axons. The gene responsible for this disorder, dystonin/Bpag1, encodes several alternatively spliced forms of a cytoskeletal linker protein. Neural isoforms of dystonin/Bpag1 are predicted to link actin filaments to microtubules. Consistent with this, previous observations have demonstrated that the cytoskeleton within sensory neurites of dt mice is perturbed. Also, recent results have indicated that a neural isoform of dystonin/Bpag1 interacts with the dynein motor complex. Because microtubule organization and dynein motor function are essential for trafficking, we hypothesized that this process would be perturbed in dt sensory neurons. Here, we demonstrate that cultured primary dorsal root ganglion (DRG) neurons express dystonin/Bpag1 and that loss of this expression causes an increase in apoptosis and a decrease in average neurite length. In contrast, detailed examination showed that the organization of microtubules is indistinguishable in DRG neuronal cultures from neonatal dt and wild-type mice. In addition, the steady-state distribution of several molecules and organelles is unchanged in these cultures. Furthermore, the speeds of mitochondrial movement in both anterograde and retrograde directions were comparable in dt and wild-type sensory neurons cultured from neonatal mice. Thus, dystonin/Bpag1 is not essential for microtubule network assembly since the microtubule network is intact in short-term cultures of sensory neurons from neonatal mice lacking this protein. In addition, dystonin/Bpag1 is not an essential part of the dynein motor complex for mitochondrial transport since mitochondrial trafficking is normal in cultured sensory neurons from dt mice. J. Comp. Neurol. 494:549,558, 2006. © 2005 Wiley-Liss, Inc. [source]