Clearing the Brain’s Cobwebs: The Role of Autophagy in Neuroprotection

Protein aggregates or inclusion bodies are common hallmarks of age-related neurodegenerative disorders. Why these aggregates form remains unclear. Equally debated is whether they are toxic, protective, or simple by-products. Increasing evidence, however, supports the notion that in general aggregates confer toxicity and disturb neuronal function by hampering axonal transport, synaptic integrity, transcriptional regulation, and mitochondrial function. Thus, neuroscientists in search of effective treatments to slow neural loss during neurodegeneration have long been interested in finding new ways to clear inclusion bodies. Intriguingly, two studies using conditional neuron-specific gene ablations of autophagy regulators in mice revealed that autophagy loss elicits inclusion body formation and a neurodegenerative cascade.Such studies indicate autophagy may be a built-in defense mechanism to clear the nervous system of inclusion bodies.This new finding has implications for our understanding of aging and neurodegeneration and the development of new therapies. First, we discuss the pathways underlying autophagy and its controversial role in cell death and survival regulation.We then discuss the physiological role of autophagy in the aging process of the nervous system. In the final portion of this review, we discuss the therapeutic promise of inducing autophagy and the potential side effects of such treatments

Clearing The Brain\u27S Cobwebs: The Role Of Autophagy In Neuroprotection

Protein aggregates or inclusion bodies are common hallmarks of age-related neurodegenerative disorders. Why these agiplates form remains unclear. Equally debated is whether they are toxic, protective, or simple by-products. Increasing evidence, however, supports the notion that in general aggregates confer toxicity and disturb neuronal function by hampering axonal transport, synaptic integrity, transcriptional regulation, and mitochondrial function. Thus, neuroscientists in search of effective treatments to slow neural loss during neurodegeneration have long been interested in finding new ways to clear inclusion bodies. Intriguingly, two studies using conditional neuron-specific gene ablations of autophagy regulators in mice revealed that autophagy loss elicits inclusion body formation and a neurodegenerative cascade. Such studies indicate autophagy may be a built-in defense mechanism to clear the nervous system of inclusion bodies. This new finding has implications for our understanding of aging and neurodegeneration and the development of new therapies. First, we discuss the pathways underlying autophagy and its controversial role in cell death and survival regulation. We then discuss the physiological role of autophagy in the aging process of the nervous system. In the final portion of this review, we discuss the therapeutic promise of inducing autophagy and the potential side effects of such treatments. © 2008 Bentham Science Publishers Ltd

Mutant Sod1\u3csup\u3eG93A\u3c/sup\u3e Triggers Mitochondrial Fragmentation In Spinal Cord Motor Neurons: Neuroprotection By Sirt3 And Pgc-1Α

Mutations in the Cu/Zn Superoxide Dismutase (SOD1) gene cause an inherited form of ALS with upper and lower motor neuron loss. The mechanism underlying mutant SOD1-mediated motor neuron degeneration remains unclear. While defects in mitochondrial dynamics contribute to neurodegeneration, including ALS, previous reports remain conflicted. Here, we report an improved technique to isolate, transfect, and culture rat spinal cord motor neurons. Using this improved system, we demonstrate that mutant SOD1G93A triggers a significant decrease in mitochondrial length and an accumulation of round fragmented mitochondria. The increase of fragmented mitochondria coincides with an arrest in both anterograde and retrograde axonal transport and increased cell death. In addition, mutant SOD1G93A induces a reduction in neurite length and branching that is accompanied with an abnormal accumulation of round mitochondria in growth cones. Furthermore, restoration of the mitochondrial fission and fusion balance by dominant-negative dynamin-related protein 1 (DRP1) expression rescues the mutant SOD1G93A-induced defects in mitochondrial morphology, dynamics, and cell viability. Interestingly, both SIRT3 and PGC-1α protect against mitochondrial fragmentation and neuronal cell death by mutant SOD1G93A. This data suggests that impairment in mitochondrial dynamics participates in ALS and restoring this defect might provide protection against mutant SOD1G93A-induced neuronal injury. © 2012

Genetic activity along 315 kb of the Drosophila chromosome

Transcripts from different tissues were mapped along a 315 kb segment of the Drosophila chromosome, a region which includes the rosy and Ace loci. Forty-three distinct RNA species were detected, though only 12 recessive lethal complementation groups had been mapped in the interval. The sum of the sizes of the transcripts covers 33% of the genomic DNA. The distribution of transcription units along the walk is very uneven. Sixty-three kb of genomic DNA at the proximal end of the walk encode 18 transcripts, while only seven are found in the next 153 kb. Each tissue exhibits a specific spectrum of transcripts. No clustering was seen among genes expressed coordinately. In salivary glands, the number of transcripts detected corresponds to the number of chromomeric units in the polytene chromosomes of this tissue. Moreover, the density distribution of transcripts along the DNA walk is parallel to the density distribution of chromomeric units

S-Nitrosylation Of Drp1 Does Not Affect Enzymatic Activity And Is Not Specific To Alzheimer\u27S Disease

Mitochondrial dysfunction and synaptic loss are among the earliest events linked to Alzheimer\u27s disease (AD) and might play a causative role in disease onset and progression. The underlying mechanisms of mitochondrial and synaptic dysfunction in AD remain unclear. We previously reported that nitric oxide (NO) triggers persistent mitochondrial fission and causes neuronal cell death. A recent article claimed that S-nitrosylation of dynamin related protein 1 (DRP1) at cysteine 644 causes protein dimerization and increased GTPase activity and is the mechanism responsible for NO-induced mitochondrial fission and neuronal injury in AD, but not in Parkinson\u27s disease (PD). However, this report remains controversial. To resolve the controversy, we investigated the effects of S-nitrosylation on DRP1 structure and function. Contrary to the previous report, S-nitrosylation of DRP1 does not increase GTPase activity or cause dimerization. In fact, DRP1 does not exist as a dimer under native conditions, but rather as a tetramer capable of self-assembly into higher order spiral-and ring-like oligomeric structures after nucleotide binding. S-nitrosylation, as confirmed by the biotin-switch assay, has no impact on DRP1 oligomerization. Importantly, we found no significant difference in S-nitrosylated DRP1 (SNO-DRP1) levels in brains of age-matched normal, AD, or PD patients. We also found that S-nitrosylation is not specific to DRP1 because S-nitrosylated optic atrophy 1 (SNO-OPA1) is present at comparable levels in all human brain samples. Finally, we show that NO triggers DRP1 phosphorylation at serine 616, which results in its activation and recruitment to mitochondria. Our data indicate the mechanism underlying nitrosative stress-induced mitochondrial fragmentation in AD is not DRP1 S-nitrosylation. © 2010 IOS Press and the authors. All rights reserved

Assessing Mitochondrial Morphology And Dynamics Using Fluorescence Wide-Field Microscopy And 3D Image Processing

Mitochondrial morphology and length change during fission and fusion and mitochondrial movement varies dependent upon the cell type and the physiological conditions. Here, we describe fundamental wide-field fluorescence microcopy and 3D imaging techniques to assess mitochondrial shape, number and length in various cell types including cancer cell lines, motor neurons and astrocytes. Furthermore, we illustrate how to assess mitochondrial fission and fusion events by 3D time-lapse imaging and to calculate mitochondrial length and numbers as a function of time. These imaging methods provide useful tools to investigate mitochondrial dynamics in health, aging and disease. © 2008 Elsevier Inc. All rights reserved

Molecular mechanism of DRP1 assembly studied in vitro by cryo-electron microscopy

Mitochondria are dynamic organelles that continually adapt their morphology by fusion andfission events. An imbalance between fusion and fission has been linked to major neurodegenerativediseases, including Huntington's, Alzheimer's, and Parkinson's diseases. Amember of the Dynamin superfamily, dynamin-related protein 1 (DRP1), a dynamin-relatedGTPase, is required for mitochondrial membrane fission. Self-assembly of DRP1 into oligomersin a GTP-dependent manner likely drives the division process. We show here thatDRP1 self-assembles in two ways: i) in the presence of the non-hydrolysable GTP analogGMP-PNP into spiral-like structures of ~36 nm diameter; and ii) in the presence of GTP intorings composed of 13−18 monomers. The most abundant rings were composed of 16 monomersand had an outer and inner ring diameter of ~30 nm and ~20 nm, respectively. Threedimensionalanalysis was performed with rings containing 16 monomers. The single-particlecryo-electron microscopy map of the 16 monomer DRP1 rings suggests a side-by-sideassembly of the monomer with the membrane in a parallel fashion. The inner ring diameterof 20 nm is insufficient to allow four membranes to exist as separate entities. Furthermore,we observed that mitochondria were tubulated upon incubation with DRP1 protein in vitro.The tubes had a diameter of ~ 30nm and were decorated with protein densities. [...

SOD1 Lysine 123 Acetylation in the Adult Central Nervous System

Superoxide dismutase 1 (SOD1) knockout (Sod1-/-) mice exhibit an accelerated aging phenotype. In humans, SOD1 mutations are linked to familial amyotrophic lateral sclerosis (ALS), and post-translational modification (PTM) of wild-type SOD1 has been associated with sporadic ALS. Reversible acetylation regulates many enzymes and proteomic studies have identified SOD1 acetylation at lysine 123 (K123). The function and distribution of K123-acetylated SOD1 (Ac-K123 SOD1) in the nervous system is unknown. Here, we generated polyclonal rabbit antibodies against Ac-K123 SOD1. Sod1 deletion in Sod1-/- mice, K123 mutation, or preabsorption with Ac-K123 peptide all abolished antibody binding. Using immunohistochemistry, we assessed Ac-K123 SOD1 distribution in the normal adult mouse nervous system. In the cerebellum, Ac-K123 SOD1 staining was prominent in cell bodies of the granular cell layer and Purkinje cell dendrites and interneurons of the molecular cell layer. In the hippocampus, Ac-K123 SOD1 staining was strong in the fimbria, subiculum, pyramidal cells, and Schaffer collateral fibers of the cornus ammonis (CA1) region and granule and neuronal progenitor cells of the dentate gyrus. In addition, labeling was observed in the choroid plexus and the ependyma of the brain ventricles and central canal of the spinal cord. In the olfactory bulb, Ac-K123 SOD1 staining was prominent in axons of sensory neurons, in cell bodies of interneurons, and neurites of the mitral and tufted cells. In the retina, labeling was strong in the retinal ganglion cell layer and axons of retinal ganglion cells, the inner nuclear layer, and cone photoreceptors of the outer nuclear layer. In summary, our findings describe Ac-K123 SOD1 distribution to distinct regions and cell types of the normal nervous system

Binding DRP1 to mitochondria in the presence of GMP-PNP by negative-stain EM.

<p>(A) Negative-stain TEM image of mitochondria (red arrows) and mitochondria tubules (blue arrows) in the presence of DRP1-GMP-PNP (Scale bar = 100 nm). (B) TEM image shows three turns of the helices forming the mitochondria tubules (black arrows) (Scale bar = 30 nm). (C) Negative-stain TEM image of mitochondria control (without DRP1). (Scale bar = 100 nm).</p