Changes in metal ions essential for the normal function of the brain have long been suspected to play a role in the neurodegeneration that characterises Parkinson’s disease (PD). Now, scientists have investigated changes in copper (Cu) and Cu-associated pathways in the brain of cases of Parkinson’s disease and found that the levels of copper are significantly reduced in the surviving neurons.
These results suggest that copper plays an important role in protecting the health and survival of neurons in areas of the brain affected by this disorder. This research is especially important as it enhances our understanding of Parkinson’s pathology, potentially opening new possibilities for early diagnosis and for the development of new therapies. The international research team was led by Australian neuroscientist, Prof. Kay Double from The University of Sydney and Sylvain Bohic Inserm senior scientist at Grenoble Neurosciences Institute and Grenoble Alpes University, and scientific collaborator at the ESRF's nano-imaging beamline.
Fig. 1: (a) Anatomical location of the human brain nuclei studied. Typical section from the locus coeruleus (lC), substantia nigra pars compacta (SN) and a magnified view of typical neuromelanin (Nm)-containing neurons from healthy human brain analysed by synchrotron radiation X-ray fl uorescence microscopy (SrXFm) (b) experimental set-up for SrXFm. (c) shows representative SRXRf maps for selected elements in a single intact NM-containing neuron of the SN shown in (a). Sulfur (S), iron (Fe) and copper (Cu). Scale bar 5 μm
The team used very powerful X-rays produced by The European Synchrotron (ESRF) to study metal levels inside single neurons in the human brain. “The sensitivity and high resolution available at the ESRF enabled us to study single neurons with an unprecedented level of detail”, says Sylvain Bohic.
Previous research has been limited to studying metal levels within whole tissues, rather than individual cells but recent developments in the area of synchrotron radiation instrumentation now make it possible to measure metal levels inside single brain cells, allowing the study of vulnerable neurons.
Parkinson’s disease (PD) involves the malfunction and death of neurons, the vital nerve cells in the brain. It is a chronic and progressive movement disorder, meaning that symptoms worsen over time. Although symptoms can be treated with medication or surgery, the cause of PD is unknown and there is no cure. A greater understanding of what it is that makes these neurons so vulnerable may help identify novel treatment strategies.
Parkinson's primarily affects neurons in an area of the brain called the substantia nigra. Some of these dying neurons produce dopamine, a chemical that sends messages to the part of the brain that controls movement and coordination. As PD progresses, due to the gradual death of these neurons, the amount of dopamine produced in the brain is not sufficient to allow the patient to control movement in a normal manner and problems with movement develop.
In the healthy brain, copper levels are especially high in the substantia nigra, suggesting that there is a particular need for copper in this region of the brain.
Representative map for copper obtained from single intact neuromelanin-containing neurons in fresh frozen tissue sections of the substantia nigra (SN) of a Parkinson’s disease and control case, by Synchrotron X-ray fluorescence microscopy. This shows intraneuronal copper levels significantly reduced in the Parkinson’s disease SN compared to normal controls.
Today Parkinson’s disease affects more than 5 million people worldwide. It is hard to detect with 90% of cases having no known cause (10% are genetic-related). At the diagnosis stage today, around 60-80% of neurons have already degenerated. “If we can identify the origin of the copper reduction, we could potentially develop a biomarker for PD”, says professor Kay Double.
One question the team now has to answer is whether the reduction of copper found in the cells is a cause or consequence of the brain cell death. The results would suggest that decreased brain copper levels are an early change in the development of Parkinson’s disease which may be increasing the vulnerability of these brain cells to death.
S. Bohic admits that this direction of research was not the one originally targeted. “A lot of people are investigating iron and alpha-synuclein [the protein that forms Lewy bodies in the brains of people with Parkinson’s], but very few are looking at copper in Parkinson’s”, Kath Davies adds.
“When we first conducted pilot studies on the PD brain, we were surprised to see such a large reduction in copper levels in PD,” said S. Bohic
The initial scepticism met from neuroscientists as to the role of biometals forced the team to be rigorously disciplined in their methodology. More than two years of study were necessary, including back-up research to consolidate findings and a solid confirmation of the results. This included collaborative work with the CNRS team from Bordeaux University (Dr. A. Carmona and Dr. R. Ortega) that made use of sophisticated nuclear microprobe (CENBG, AIFIRA platform) and also additional experiments conducted at the Diamond Synchroton light source (T. Geraki, I18 beamline). The samples studied had to be strictly controlled to ensure the findings were not related to outside factors, such as the medication that patients were taking for example. The research was recently published in Neurobiology of Aging – a feat in itself, as this type of research rarely attracts interest from a neuroscience journal.
The research team are now interested to investigate if restoring brain copper levels can slow brain cell death in Parkinson’s disease. While this is a new approach in Parkinson’s disease, restoring brain copper is known to be beneficial in other disorders where brain copper levels are reduced. The team is hopeful that their findings will lead to improved treatments for this common and devastating disorder.
K. M. Davies, S. Bohic et al, Copper pathology in vulnerable brain regions in Parkinson’s disease, Neurobiol Aging. 2014 Apr;35(4):858-66.