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Mutations in Alpha-Synuclein Speed Protein Clumping in Familial Parkinson’s and Affect Severity, Study Finds

alpha-synuclein and A53T

A detailed analysis of alpha-synuclein — a key protein involved in Parkinson’s — revealed how variants of this protein change over time, allowing researchers to identify the initial stages of protein aggregation involved in early onset disease.

These findings provide new insights into how genetic mutations — especially the point mutation A53T — can contribute to familial Parkinson’s, and into understanding why this disease form manifests earlier and is often more severe than sporadic (of unknown cause) Parkinson’s.

The study, “Alpha-synuclein stepwise aggregation reveals features of an early onset mutation in Parkinson’s disease,” was published in the journal Communications Biology.

Parkinson’s is largely a sporadic disease, with 15% to 25% of all cases linked to inherited genetic mutations. One of the first genes identified as directly associated with Parkinson’s, leading to early onset disease, was the alpha-synuclein coding gene SNCA.

It is widely accepted that alpha-synuclein is an important element that drives nerve cell death across several human neurodegenerative disorders, including Parkinson’s and dementia with Lewy bodies. Its toxic effect is, at least in part, tied to the formation of abnormal protein aggregates or clumps.

Despite available knowledge of the damaging impact alpha-synuclein clumps have on nerve cells, the process by which alpha-synuclein changes from a single protein structure into an aggregate form remains poorly understood.

Researchers at the Federal University of Rio de Janeiro (UFRJ) in Brazil conducted a series of biochemical, kinetic, and structural studies to address this gap.

They evaluated in detail the behavior of alpha-synuclein — both its normal form as well as mutated versions found in people with familial Parkinson’s — and its ability to form toxic clumps.

“The conversion from one protein stage to the other takes place slowly. The intermediate structures and the amyloid aggregates accumulate over time in the brain. So far, we don’t know which species cause the symptoms and toxicity to cells,” Guilherme A. P. de Oliveira, a professor at UFRJ and the study’s lead author, said in a press release.

“If we understand the protein species forming during the early stages of disease conversion, we can propose new therapies for disease detection before the symptoms appear.”

Results showed that the versions of alpha-synuclein carrying A53T, A30P, or E46K point mutations were able to from small aggregates (known as oligomers) at a much faster rate than a normal version of the protein.

Of note, point mutations are genetic alterations where a single nucleotide — the building blocks of DNA — is changed, inserted, or deleted from a sequence of DNA. If you think of DNA as a Lego train, a point mutation would be the same as changing, adding, or taking out a single piece. 

Next, the researchers used cutting-edge imaging techniques to visualize for the first time, in detail and over time, all the elements involved in the expansion of alpha-synuclein aggregates — their transition from early oligomers to intermediate fibrils to late filaments.

“By (…) acquiring advanced electron microscope images, we are able to better understand these wrong protein associations in their native environment and [potentially find] ways to avoid their formation,” Oliveira said.

This approach showed that the different protein versions give rise to structurally different fibrils.

The expansion of fibrils into long filaments was found to be dependent on the ability of alpha-synuclein to continue to recruit available oligomers.

Interestingly, the A53T point mutated version was able to overcome some of the limits on protein clumping imposed by the surrounding environment, and for which normal alpha-synuclein showed a sensitivity. This suggests that A53T mutations give alpha-synuclein a greater potential to promote aggregation and induce faster spreading of its toxic clumps.

“Our findings place A53T with features that may explain the early onset of familial Parkinson’s disease cases bearing this mutation,” the researchers concluded.

The post Mutations in Alpha-Synuclein Speed Protein Clumping in Familial Parkinson’s and Affect Severity, Study Finds appeared first on Parkinson’s News Today.

Brain Serotonin Changes May Be Early Warning Sign of Parkinson’s, Study Suggests

serotonin early warning

Changes to the serotonin system in the brain occur years before the development of motor symptoms in Parkinson’s — and may be an important early warning signal for the disease, a study suggests.

“Therefore, brain imaging of the serotonin system could become a valuable tool to detect individuals at risk for Parkinson’s disease, monitor their progression and help with the development of new treatments,” Heather Wilson, research associate at King’s College London and the study’s first author, said in a press release.

The study, “Serotonergic pathology and disease burden in the premotor and motor phase of A53T α-synuclein parkinsonism: a cross-sectional study,” was published in The Lancet Neurology.

Parkinson’s is characterized by the progressive death of brain cells that are responsible for producing dopamine, which eventually leads to the development of motor symptoms associated with the disease, including involuntary tremors or muscle contraction.

Studies have suggested that, in addition to changes in the dopaminergic system, Parkinson’s progression and symptoms may be associated with impaired signals from another important neurotransmitter, called serotonin. Serotonin transmits messages between nerve cells, and is thought to be active in constricting smooth muscles.

To further explore the role of serotonin in Parkinson’s progression, a team led by researchers from King’s College evaluated non-symptomatic carriers of an alpha-synuclein (SNCA) gene variant. That variant is an extremely rare mutation, but a well-known cause for hereditary Parkinson’s disease.

Individuals with mutations in the alpha-synuclein gene are almost certain to develop Parkinson’s during their lifetime, which makes them invaluable candidates to study the biological events that result in the development of the disease.

The study recruited 14 individuals who were carriers of the A53T variant in the SNCA gene, as well as 25 patients with idiopathic (of unknown cause) Parkinson’s disease, and 25 healthy matched volunteers who had no history of neurological or psychiatric disorders.

All participants were evaluated by positron emission tomography (PET) scans. PET scans use a specific dye that binds to the serotonin transporter, and evaluates serotonin metabolism in the brain. Participants also underwent several clinical assessments to determine motor and non-motor symptoms. They were evaluated for cognitive status, dopamine metabolism, and brain structural changes.

Among individuals who were SNCA mutation carriers, 50% were still asymptomatic —  at the premotor stage of the disease — and had dopaminergic deficits.

Compared with healthy controls, the premotor SNCA carriers showed reduced serotonin signals in several brain areas. SNCA carriers who still had normal dopamine transporters already showed “an average of 34% loss of serotonin transporters in raphe nuclei and 22% loss in the striatum compared with healthy controls,” the researchers said.

As the name indicates, a serotonin transporter is a protein that binds to and transports serotonin to different areas of the brain. Raphe nuclei are a type of brain receptor that decrease the release of serotonin. The striatum is a critical brain region involved in voluntary movement.

“Parkinson’s disease has traditionally been thought of as occurring due to damage in the dopamine system, but we show that changes to the serotonin system come first, occurring many years before patients begin to show symptoms,” said Marios Politis, MD, PhD, professor at the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) and senior author of the study.

Those who were SNCA carriers but had already been diagnosed with Parkinson’s disease showed more extensive deficits in the serotonin system, affecting even more areas of the brain. There was 48% serotonin transporter loss in the raphe nuclei, and 57%  loss in the striatum areas.

Further analysis revealed that low serotonin signals in the brainstem were associated with increased total scores on the Movement Disorder Score-Unified Parkinson’s Disease Rating Scale (MDS-UPSRS) — indicating higher disease burden. This occurred in all SNCA carriers, and in those with idiopathic Parkinson’s.

“Our findings provide evidence that molecular imaging of serotonin transporters could be used to visualize premotor pathology of Parkinson’s disease in vivo [in the body],” the researchers said.

Future studies should focus on implementing serotonin transporter imaging as “an adjunctive tool for screening and monitoring progression” for those at risk for, or who already have Parkinson’s.

“This is one of the first studies to suggest that changes in serotonin signaling may be an early consequence of Parkinson’s,” said Beckie Port, PhD, research manager at Parkinson’s UK. “Picking up on the condition earlier and being able to monitor its progression would aid the discovery of new and better treatments that could slow the loss of brain cells in Parkinson’s.”

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