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Cell death can occur by mechanisms such as apoptosis or programmed cell death, in which death occurs by a characteristic sequence of events. Premature or inappropriate cell death in the nervous system is associated with numerous neurodegenerative diseases and following ischemic events such as stroke. Research 24 September Open Access. Research 18 September Open Access. Yamada et al. During cortical development the first wave of oligodendrocyte precursor cells OPCs completely disappear by programmed cell death, so that it is presumed that this OPC population does not play a role at postnatal stages.
In this study, authors use lineage tracing in different transgenic mice to show that a subpopulation of OPCs from the first wave survives at postnatal stages and display a preferential synaptic connectivity with their ontogenetically-related interneurons compared to other OPCs or interneurons. Research 12 September Open Access.
We have developed two new methods to identify apoptotic cells under the microscope. The morphologic analysis of nuclear disintegration has allowed us to test whether cell death is due to production of a toxic factor or due to the loss of a protective factor. Using the new microscopic method to identify apoptosis, the nuclei in the heterokaryons were found to follow the original and distinct fate of the parent cells and not to transfer apoptosis nor viability between nuclei. This new method also allowed us to identify apoptosis as the method of cerebellar granule cell death after MPP treatment in vitro.
This allows us to examine brains of animals undergoing neurodegenerative changes during ischemia, MPTP treatment, and during development. This new method should illuminate the role apoptosis plays during development and during various disease states of the nervous system.
Road to Cell Death More Clearly Identified for Parkinson’s Disease
Toggle navigation. Recent in Grantomics:. A repeat of CAG results in a polyglutamine polyQ tract.
Diseases showing this are known as polyglutamine diseases. Several neurodegenerative diseases are classified as proteopathies as they are associated with the aggregation of misfolded proteins. Parkinson's disease and Huntington's disease are both late-onset and associated with the accumulation of intracellular toxic proteins. Diseases caused by the aggregation of proteins are known as proteinopathies, and they are primarily caused by aggregates in the following structures: . Damage to the membranes of organelles by monomeric or oligomeric proteins could also contribute to these diseases.
Alpha-synuclein can damage membranes by inducing membrane curvature,  and cause extensive tubulation and vesiculation when incubated with artificial phospholipid vesicles. Extensive induction of membrane curvature is deleterious to the cell and would eventually lead to cell death. Apart from tubular structures, alpha-synuclein can also form lipoprotein nanoparticles similar to apolipoproteins. The most common form of cell death in neurodegeneration is through the intrinsic mitochondrial apoptotic pathway. This pathway controls the activation of caspase-9 by regulating the release of cytochrome c from the mitochondrial intermembrane space IMS.
Reactive oxygen species ROS are normal byproducts of mitochondrial respiratory chain activity. ROS concentration is mediated by mitochondrial antioxidants such as manganese superoxide dismutase SOD2 and glutathione peroxidase.
Research improves screening of experimental therapies for neurodegenerative disease
Over production of ROS oxidative stress is a central feature of all neurodegenerative disorders. In addition to the generation of ROS, mitochondria are also involved with life-sustaining functions including calcium homeostasis, PCD, mitochondrial fission and fusion , lipid concentration of the mitochondrial membranes, and the mitochondrial permeability transition. Mitochondrial disease leading to neurodegeneration is likely, at least on some level, to involve all of these functions. There is strong evidence that mitochondrial dysfunction and oxidative stress play a causal role in neurodegenerative disease pathogenesis, including in four of the more well known diseases Alzheimer's , Parkinson's , Huntington's , and Amyotrophic lateral sclerosis.
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Neurons are particularly vulnerable to oxidative damage due to their strong metabolic activity associated with high transcription levels, high oxygen consumption, and weak antioxidant defense. The brain metabolizes as much as a fifth of consumed oxygen, and reactive oxygen species produced by oxidative metabolism are a major source of DNA damage in the brain. The vulnerability of post-mitotic neurons to DNA damage such as oxidative lesions or certain types of DNA strand breaks , coupled with a gradual decline in the activities of repair mechanisms , could lead to accumulation of DNA damage with age and contribute to brain aging and neurodegeneration.
Axonal swelling and spheroids have been observed in many different neurodegenerative diseases. This suggests that defective axons are not only present in diseased neurons, but also that they may cause certain pathological insult due to accumulation of organelles. Axonal transport can be disrupted by a variety of mechanisms including damage to: kinesin and cytoplasmic dynein , microtubules , cargoes, and mitochondria. Programmed cell death PCD is death of a cell in any form, mediated by an intracellular program. Apoptosis is a form of programmed cell death in multicellular organisms.
It is one of the main types of programmed cell death PCD and involves a series of biochemical events leading to a characteristic cell morphology and death. Caspases cysteine-aspartic acid proteases cleave at very specific amino acid residues. There are two types of caspases: initiators and effectors. Initiator caspases cleave inactive forms of effector caspases. This activates the effectors that in turn cleave other proteins resulting in apoptotic initiation.
Autophagy is essentially a form of intracellular phagocytosis in which a cell actively consumes damaged organelles or misfolded proteins by encapsulating them into an autophagosome, which fuses with a lysosome to destroy the contents of the autophagosome. Many neurodegenerative diseases show unusual protein aggregates. This could potentially be a result of underlying autophagic defect common to multiple neurodegenerative diseases. It is important to note that this is a hypothesis, and more research must be done.
The final and least understood PCD mechanism is through non-apoptotic processes. These fall under Type III, or cytoplasmic cell death. Many other forms of PCD are observed but not fully understood or accepted by the scientific community. For example, PCD might be caused by trophotoxicity, or hyperactivation of trophic factor receptors. In addition to this, other cytotoxins that induce PCD at low concentrations act to cause necrosis , or aponecrosis — the combination of apoptosis and necrosis, when in higher concentrations. It is still unclear exactly what combination of apoptosis, non-apoptosis, and necrosis causes different kinds of aponecrosis.
In the above-mentioned neurodegenerative diseases, PCD may be pathogenic. In order to identify the potential of neuroprotective targets in PCD machinery, there were experimental models conducted on these neurodegenerative diseases. These studies showed that the expression of certain components have been altered by genetic and pharmacological means.
Expression of PCD molecular components are said to be controlled by gene and antisense therapy, but this needs further research. Pharmacological approaches involve inhibitors of caspase activity, and caspase inhibition might delay cell death in the different experimental models. Transglutaminases are human enzymes ubiquitously present in the human body and in the brain in particular. The main function of transglutaminases is bind proteins and peptides intra- and intermolecularly, by a type of covalent bonds termed isopeptide bonds , in a reaction termed transamidation or crosslinking.
Transglutaminase binding of these proteins and peptides make them clump together. The resulting structures are turned extremely resistant to chemical and mechanical disruption.
Apoptosis in the Nervous System
Most relevant human neurodegenerative diseases share the property of having abnormal structures made up of proteins and peptides. Each of these neurodegenerative disesases have one or several specific main protein or peptide. In Alzheimer's disease , these are amyloid-beta and tau. Transglutaminase substrates : Amyloid-beta , tau , alpha-synuclein and huntingtin have been proved to be substrates of transglutaminases in vitro or in vivo, that is, they can be bonded by trasglutaminases by covalent bonds to each other and potentially to any other transglutaminase substrate in the brain.
Presence of isopeptide bonds in these structures: The presence of isopeptide bonds the result of the transglutaminase reaction have been detected in the abnormal structures that are characteristic of these neurodegenerative diseases. Co-localization: Co-localization of transglutaminase mediated isopeptide bonds with these abnormal structures has been detected in the autopsy of brains of patients with these diseases. The process of neurodegeneration is not well understood, so the diseases that stem from it have, as yet, no cures.