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1.  Bioenergetics of neurons inhibit the translocation response of Parkin following rapid mitochondrial depolarization 
Human Molecular Genetics  2010;20(5):927-940.
Recent studies delineate a pathway involving familial Parkinson's disease (PD)-related proteins PINK1 and Parkin, in which PINK1-dependent mitochondrial accumulation of Parkin targets depolarized mitochondria towards degradation through mitophagy. The pathway has been primarily characterized in cells less dependent on mitochondria for energy production than neurons. Here we report that in neurons, unlike other cells, mitochondrial depolarization by carbonyl cyanide m-chlorophenyl hydrazone did not induce Parkin translocation to mitochondria or mitophagy. PINK1 overexpression increased basal Parkin accumulation on neuronal mitochondria, but did not sensitize them to depolarization-induced Parkin translocation. Our data suggest that bioenergetic differences between neurons and cultured cell lines contribute to these different responses. In HeLa cells utilizing usual glycolytic metabolism, mitochondrial depolarization robustly triggered Parkin–mitochondrial translocation, but this did not occur in HeLa cells forced into dependence on mitochondrial respiration. Declining ATP levels after mitochondrial depolarization correlated with the absence of induced Parkin–mitochondrial translocation in both HeLa cells and neurons. However, intervention allowing neurons to maintain ATP levels after mitochondrial depolarization only modestly increased Parkin recruitment to mitochondria, without evidence of increased mitophagy. These data suggest that changes in ATP levels are not the sole determinant of the different responses between neurons and other cell types, and imply that additional mechanisms regulate mitophagy in neurons. Since the Parkin–mitophagy pathway is heavily dependent on bioenergetic status, the unique metabolic properties of neurons likely influence the function of this pathway in the pathogenesis of PD.
doi:10.1093/hmg/ddq531
PMCID: PMC3033183  PMID: 21147754
2.  Integrating multiple aspects of mitochondrial dynamics in neurons: Age-related differences and dynamic changes in a chronic rotenone model 
Neurobiology of disease  2010;41(1):189-200.
Changes in dynamic properties of mitochondria are increasingly implicated in neurodegenerative diseases, particularly Parkinson’s disease (PD). Static changes in mitochondrial morphology, often under acutely toxic conditions, are commonly utilized as indicators of changes in mitochondrial fission and fusion. However, in neurons, mitochondrial fission and fusion occur in a dynamic system of axonal/dendritic transport, biogenesis and degradation, and thus, likely interact and change over time. We sought to explore this using a chronic neuronal model (nonlethal low-concentration rotenone over several weeks), examining distal neurites, which may give insight into the earliest changes occurring in PD. Using this model, in live primary neurons, we directly quantified mitochondrial fission, fusion, and transport over time and integrated multiple aspects of mitochondrial dynamics, including morphology and growth/mitophagy. We found that rates of mitochondrial fission and fusion change as neurons age. In addition, we found that chronic rotenone exposure initially increased the ratio of fusion to fission, but later, this was reversed. Surprisingly, despite changes in rates of fission and fusion, mitochondrial morphology was minimally affected, demonstrating that morphology can be an inaccurate indicator of fission/fusion changes. In addition, we found evidence of subcellular compartmentalization of compensatory changes, as mitochondrial density increased in distal neurites first, which may be important in PD, where pathology may begin distally. We propose that rotenone-induced early changes such as in mitochondrial fusion are compensatory, accompanied later by detrimental fission. As evidence, in a dopaminergic neuronal model, in which chronic rotenone caused loss of neurites before cell death (like PD pathology), inhibiting fission protected against the neurite loss. This suggests that aberrant mitochondrial dynamics may contribute to the earliest neuropathologic mechanisms in PD. These data also emphasize that mitochondrial fission and fusion do not occur in isolation, and highlight the importance of analysis and integration of multiple mitochondrial dynamic functions in neurons.
doi:10.1016/j.nbd.2010.09.006
PMCID: PMC3021420  PMID: 20850532
mitochondria; mitochondrial; fission; fusion; transport; Parkinson’s disease; dynamics; mitophagy; neurodegenerative; neuron; neurodegeneration
3.  Characterization of Notch1 Antibodies That Inhibit Signaling of Both Normal and Mutated Notch1 Receptors 
PLoS ONE  2010;5(2):e9094.
Background
Notch receptors normally play a key role in guiding a variety of cell fate decisions during development and differentiation of metazoan organisms. On the other hand, dysregulation of Notch1 signaling is associated with many different types of cancer as well as tumor angiogenesis, making Notch1 a potential therapeutic target.
Principal Findings
Here we report the in vitro activities of inhibitory Notch1 monoclonal antibodies derived from cell-based and solid-phase screening of a phage display library. Two classes of antibodies were found, one directed against the EGF-repeat region that encompasses the ligand-binding domain (LBD), and the second directed against the activation switch of the receptor, the Notch negative regulatory region (NRR). The antibodies are selective for Notch1, inhibiting Jag2-dependent signaling by Notch1 but not by Notch 2 and 3 in reporter gene assays, with EC50 values as low as 5±3 nM and 0.13±0.09 nM for the LBD and NRR antibodies, respectively, and fail to recognize Notch4. While more potent, NRR antibodies are incomplete antagonists of Notch1 signaling. The antagonistic activity of LBD, but not NRR, antibodies is strongly dependent on the activating ligand. Both LBD and NRR antibodies bind to Notch1 on human tumor cell lines and inhibit the expression of sentinel Notch target genes, including HES1, HES5, and DTX1. NRR antibodies also strongly inhibit ligand-independent signaling in heterologous cells transiently expressing Notch1 receptors with diverse NRR “class I” point mutations, the most common type of mutation found in human T-cell acute lymphoblastic leukemia (T-ALL). In contrast, NRR antibodies failed to antagonize Notch1 receptors bearing rare “class II” or “class III” mutations, in which amino acid insertions generate a duplicated or constitutively sensitive metalloprotease cleavage site. Signaling in T-ALL cell lines bearing class I mutations is partially refractory to inhibitory antibodies as compared to cell-penetrating gamma-secretase inhibitors.
Conclusions/Significance
Antibodies that compete with Notch1 ligand binding or that bind to the negative regulatory region can act as potent inhibitors of Notch1 signaling. These antibodies may have clinical utility for conditions in which inhibition of signaling by wild-type Notch1 is desired, but are likely to be of limited value for treatment of T-ALLs associated with aberrant Notch1 activation.
doi:10.1371/journal.pone.0009094
PMCID: PMC2817004  PMID: 20161710
4.  Bcl-xL increases mitochondrial fission, fusion, and biomass in neurons 
The Journal of Cell Biology  2009;184(5):707-719.
Mitochondrial fission and fusion are linked to synaptic activity in healthy neurons and are implicated in the regulation of apoptotic cell death in many cell types. We developed fluorescence microscopy and computational strategies to directly measure mitochondrial fission and fusion frequencies and their effects on mitochondrial morphology in cultured neurons. We found that the rate of fission exceeds the rate of fusion in healthy neuronal processes, and, therefore, the fission/fusion ratio alone is insufficient to explain mitochondrial morphology at steady state. This imbalance between fission and fusion is compensated by growth of mitochondrial organelles. Bcl-xL increases the rates of both fusion and fission, but more important for explaining the longer organelle morphology induced by Bcl-xL is its ability to increase mitochondrial biomass. Deficits in these Bcl-xL–dependent mechanisms may be critical in neuronal dysfunction during the earliest phases of neurodegeneration, long before commitment to cell death.
doi:10.1083/jcb.200809060
PMCID: PMC2686401  PMID: 19255249

Results 1-4 (4)