Biomedical subjects

Gordon L Rintoul

Publications and source records attributed to Gordon L Rintoul.

8 recordsLinked to original sources

PubMed2006

Nitric oxide inhibits mitochondrial movement in forebrain neurons associated with disruption of mitochondrial membrane potential.

Nitric oxide (NO) has a number of physiological and pathophysiological effects in the nervous system. One target of NO is the mitochondrion, where it inhibits respiration and ATP synthesis, which may contribute to NO-mediated neuronal injury. Our recent studies suggested that impaired mitochondrial function impairs mitochondrial trafficking, which could also contribute to neuronal injury. Here, we studied the effects of NO on mitochondrial movement and morphology in primary cultures of forebrain neurons using a mitochondrially targeted enhanced yellow fluorescent protein. NO produced by two NO donors, papa non-oate and diethylamine/NO complex, caused a rapid cessation of mitochondrial movement but did not alter morphology. Movement recovered after removal of NO. The effects of NO on movement were associated with dissipation of the mitochondrial membrane potential. Increasing cGMP levels using 8-bromoguanosine 3',5'-cyclic monophosphate, did not mimic the effects on mitochondrial movement. Furthermore, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), an inhibitor of NO-induced activation of soluble guanylate cyclase, did not block the effects of NO. Thus, neither increasing nor decreasing cGMP levels had an effect on mitochondrial movement. Based on these data, we conclude that NO is a novel modulator of mitochondrial trafficking in neurons, which may act through the inhibition of mitochondrial function.

Animals↗

PubMed2006

Mutant huntingtin aggregates impair mitochondrial movement and trafficking in cortical neurons.

Huntington's disease (HD) is a neurodegenerative disorder caused by a polyglutamine repeat in the huntingtin gene (Htt). Mitochondrial defects and protein aggregates are characteristic of affected neurons. Recent studies suggest that these aggregates impair cellular transport mechanisms by interacting with cytoskeletal components and molecular motors. Here, we investigated whether mutant Htt alters mitochondrial trafficking and morphology in primary cortical neurons. We demonstrate that full-length mutant Htt was more effective than N-terminal mutant Htt in blocking mitochondrial movement, an effect that correlated with its heightened expression in the cytosolic compartment. Aggregates impaired the passage of mitochondria along neuronal processes, causing mitochondria to accumulate adjacent to aggregates and become immobilized. Furthermore, mitochondrial trafficking was reduced specifically at sites of aggregates while remaining unaltered in regions lacking aggregates. We conclude that in cortical neurons, an early event in HD pathophysiology is the aberrant mobility and trafficking of mitochondria caused by cytosolic Htt aggregates.

Animals↗

PubMed2005

Zn2+ inhibits mitochondrial movement in neurons by phosphatidylinositol 3-kinase activation.

Mitochondria have been identified as targets of the neurotoxic actions of zinc, possibly through decreased mitochondrial energy production and increased reactive oxygen species accumulation. It has been hypothesized that impairment of mitochondrial trafficking may be a mechanism of neuronal injury. Here, we report that elevated intraneuronal zinc impairs mitochondrial trafficking. At concentrations just sufficient to cause injury, zinc rapidly inhibited mitochondrial movement without altering morphology. Zinc chelation initially restored movement, but the actions of zinc became insensitive to chelator in <10 min. A search for downstream signaling events revealed that inhibitors of phosphatidylinositol (PI) 3-kinase prevented this zinc effect on movement. Moreover, transient inhibition of PI 3-kinase afforded neuroprotection against zinc-mediated toxicity. These data illustrate a novel mechanism that regulates mitochondrial trafficking in neurons and also suggest that mitochondrial trafficking may be closely coupled to neuronal viability.

Animals↗

PubMed2004

Mitochondrial stop and go: signals that regulate organelle movement.

In order to satisfy the metabolic and ion homeostasis demands of neurons, mitochondria must be transported to appropriate locations within cells. Although it is well established that much of this trafficking occurs on microtubules and, to a lesser extent, actin, the mechanisms by which the trafficking of mitochondria is controlled are poorly understood. A recent study by Chada and Hollenbeck shows that nerve growth factor halts the movement of mitochondria in axons by means of a mechanism that depends on activation of phosphatidylinositol 3-kinase. These studies provide important new insights into the mechanisms that regulate mitochondrial movement and control mitochondrial docking. These insights are critical to the understanding of the factors that control the distribution, location, and function of mitochondria in both healthy and injured neurons.

Humans↗

PubMed2004

Mitochondrial trafficking in neurons: a key variable in neurodegeneration?

Mitochondria are the proximate target of a number of different neurotoxins. Typically, impairing of the key bioenergetic function of mitochondria by toxins is considered as the main mechanism of action. However, the effective maintenance of energy generation in neurons depends on the biogenesis, trafficking, and degradation of mitochondria in addition to the traditional bioenergetic functions. We have recently demonstrated that glutamate alters both the trafficking and morphology of mitochondria in primary neurons. In addition, several other potential neurotoxins, including nitric oxide and zinc, inhibit mitochondrial movement and, in some cases, alter morphology too. This suggests that some part of the action of neurotoxins might include the impairment of mitochondrial trafficking in neurons, with the resultant failure of local ATP delivery.

Animals↗

PubMed2003

Glutamate decreases mitochondrial size and movement in primary forebrain neurons.

Mitochondria are essential to maintain neuronal viability. In addition to the generation of ATP and maintenance of calcium homeostasis, the effective delivery of mitochondria to the appropriate location within neurons is also likely to influence their function. In this study we examined mitochondrial movement and morphology in primary cultures of rat forebrain using a mitochondrially targeted enhanced yellow fluorescent protein (mt-eYFP). Mt-eYFP-labeled mitochondria display a characteristic elongated phenotype and also move extensively. Application of glutamate to cultures results in a rapid diminution of movement and also an alteration from elongated to rounded morphology. This effect required the entry of calcium and was mediated by activation of the NMDA subtype of glutamate receptor. Treatment of cultures with an uncoupler or blocking ATP synthesis with oligomycin also stopped movement but did not alter morphology. Interestingly, application of glutamate together with the uncoupler did not prevent the changes in movement or shape but facilitated recovery after washout of the stimuli. This suggests that the critical target for calcium in this paradigm is cytosolic. These studies demonstrate that in addition to altering the bioenergetic properties of mitochondria, neurotoxins can also alter mitochondrial movement and morphology. We speculate that neurotoxin-mediated impairment of mitochondrial delivery may contribute to the injurious effects of neurotoxins.

Animals↗

PubMed2003

Effects of calcium buffers and calbindin-D28k upon histamine-induced calcium oscillations and calcium waves in HeLa cells.

The effects of the artificial Ca(2+) buffers EGTA and BAPTA upon histamine-induced Ca(2+) oscillations and calcium waves were studied in HeLa cells. These events were also examined in HeLa cell lines transfected with the intracellular calcium-binding protein calbindin-D28k (CaBP; HeLa-CaBP) or the pCINeo vector alone (HeLa-pCINeo). High concentrations of the Ca(2+) indicators fluo-3 and fura-2 significantly influenced the oscillatory pattern of intracellular Ca(2+) in HeLa-pCINeo cells exposed to 1 microM histamine. Loading cells with low concentrations of the cell-permeant esters of the artificial Ca(2+)-buffers EGTA or BAPTA, resulted in fewer cells with a distinct "baseline" oscillatory pattern, and loading with higher concentrations of BAPTA almost completely abolished them. In HeLa-CaBP cells, stimulation with 1 microM histamine resulted in individual Ca(2+) spikes that had a flattened profile when compared to control cells; peak [Ca(2+)](i) was lowered, the rate of increase in [Ca(2+)](i) was slower and transients were prolonged. When compared to HeLa-pCINeo cells, loading with EGTA or BAPTA, or transfection of CaBP, significantly reduced the propagation velocity (by up to 60%) of Ca(2+) waves induced by exposure to 100 microM histamine. We conclude that intracellular Ca(2+) buffering exerts a significant influence on global Ca(2+) responses in HeLa cells and the propagation of Ca(2+) waves that underlie them. The relative effectiveness of different Ca(2+) buffers, including CaBP, appears to be particularly dependent upon the rapidity of their binding kinetics, with BAPTA being the most effective.

Aniline Compounds↗

PubMed2003

New perspectives on mitochondrial morphology in cell function.

Mitochondria are a node of integration for intracellular signaling pathways and their morphology changes seem to be tightly associated with their function. New data show that morphology is one of the parameters involved in mitochondria's choice between promoting cell death and protecting cells against general metabolic jeopardy.

Animals↗