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Health News and ResearchAlzheimer’s Disease Linked to Mitochondrial DamageInvestigators at the Burnham Institute for Medical Research (Burnham) have demonstrated that attacks on the mitochondrial protein Drp1 by the free radical nitric oxide—which causes a chemical reaction called S-nitrosylation—mediates neurodegeneration associated with Alzheimer’s disease. Prior to this study, the mechanism by which beta-amyloid protein caused synaptic damage to neurons in Alzheimer’s disease was unknown. These findings suggest that preventing S-nitrosylation of Drp1 may reduce or even prevent neurodegeneration in Alzheimer’s patients. The paper was published in the April 3 issue of the journal Science. The team of scientists, led by neuroscientist and clinical neurologist Stuart A. Lipton, M.D., Ph.D., director of the Del E. Webb Center for Neuroscience, Aging and Stem Cell Research, showed that S-nitrosylated Drp1 (SNO-Drp1) facilitates mitochondrial fragmentation, damaging regions of nerve cell communication called synapses. Mitochondria are the energy storehouses of the cell, and their compromise by excessive fragmentation causes synaptic injury and eventual nerve cell death. Synapses are critical for learning and memory and their impairment leads to the dementia seen in Alzheimer’s patients. “We now have a better understanding of the mechanism by which beta-amyloid protein causes neurodegeneration in Alzheimer’s disease,” said Dr. Lipton. “We found that beta-amyloid can generate nitric oxide that reacts with Drp1. By identifying Drp1 as the protein responsible for synaptic injury, we now have a new target for developing drugs that may slow or stop the progression of Alzheimer’s.” Drp1 is an enzyme that mediates fission or fragmentation of mitochondria. The Burnham researchers showed that excessive production of nitric oxide caused S-nitrosylation of Drp1 and induced excessive fragmentation of mitochondria in cultured nerve cells or neurons. The scientists also showed that beta-amyloid protein multimers, which had been previously implicated in Alzheimer’s disease, induced formation of SNO-Drp1. Importantly, elevated SNO-Drp1 levels were also found in human brains of Alzheimer’s patients, but not in those with Parkinson’s disease or controls who didn’t have neurodegenerative diseases. Molecular modeling performed by the team suggested that S-nitrosylation
of Drp1 causes dimerization of the protein and activation of
enzymatic activity that induces mitochondrial fragmentation. To
confirm this hypothesis, the scientists showed that RNA
interference to knock down Drp1 or a mutation that prevented
Drp1 activity inhibited excess mitochondrial fragmentation and
protected the neurons. Finally, the researchers showed that a
mutated Drp1, lacking the nitrosylation site, did not induce
mitochondrial fragmentation and also prevented neuronal damage.
Taken together, these findings suggest that multimers of beta-amyloid
protein induce generation of nitric oxide, which reacts with
Drp1 to cause excessive mitochondrial fragmentation and in turn
neuronal damage. AbstractMitochondria continuously undergo two opposing processes,
fission and fusion. The disruption of this dynamic equilibrium
may herald cell injury or death and may contribute to
developmental and neurodegenerative disorders. Nitric oxide
functions as a signaling molecule, but in excess it mediates
neuronal injury, in part via mitochondrial fission or
fragmentation. However, the underlying mechanism for nitric
oxide-induced pathological fission remains unclear. We found
that nitric oxide produced in response to beta-amyloid protein,
thought to be a key mediator of Alzheimer's disease, triggered
mitochondrial fission, synaptic loss, and neuronal damage, in
part via S-nitrosylation of dynamin-related protein 1 (forming
SNO-Drp1). Preventing nitrosylation of Drp1 by cysteine mutation
abrogated these neurotoxic events. SNO-Drp1 is increased in
brains of human Alzheimer's disease patients and may thus
contribute to the pathogenesis of neurodegeneration. SourceCho DH, Nakamura T, Fang J, Cieplak P, Godzik A, Gu Z, Lipton SA. S-nitrosylation of Drp1 mediates beta-amyloid-related mitochondrial fission and neuronal injury. Science. 2009 Apr 3;324(5923):102-5. Key concepts: mitochondrial function, Alzheimer's Disease |
