Yearly Archives: 2017

Little is known about the role of the brain’s immune system in Alzheimer’s disease. But researchers have now found an early immune response in individuals with a genetic predisposition to Alzheimer’s: their brains showed abnormal immune reactions as early as about seven years before the expected onset of dementia.

These results demonstrate that in cases of Alzheimer’s, inflammatory processes in the brain evolve dynamically and are precursors of dementia. These immune responses can be detected by means of a protein in the cerebrospinal fluid, offering physicians the possibility to trace the progression of the disease. The study results are published in the journal Science Translational Medicine.

The researchers were able to detect increasing immune activity of the brain by measuring levels of the protein “TREM2” in the cerebrospinal fluid. TREM2 is segregated by certain immune cells of the brain – called microglia – and thus reflects their activity. In cases of the inherited form of Alzheimer’s disease, the timing for the onset of dementia can be precisely predicted. The researchers were therefore able to monitor the rise of TREM2 levels years before the expected occurrence of dementia symptoms.

In total, 127 individuals with a genetic predisposition to Alzheimer’s participated in the study. They were on average 40 years old. The vast majority showed no symptoms of dementia or had only minor cognitive impairments. The study was conducted as part of the so-called DIAN project (Dominantly Inherited Alzheimer Network), a worldwide network for research into the inherited form of Alzheimer’s disease.

Paper: "Early changes in CSF sTREM2 in dominantly inherited Alzheimer’s disease occur after amyloid deposition and neuronal injury"
Reprinted from materials provided by DZNE.

People with Parkinson’s disease and cognitive impairment have disruptions in their brain networks that can be seen on a type of MRI, according to a study appearing online in the journal Radiology.

Parkinson’s disease (PD) is a progressive disorder of the central nervous system characterized by tremors or trembling and stiffness in the limbs, impaired balance and coordination. It affects about 10 million people worldwide. As PD progresses, many patients develop mild cognitive impairment (MCI), a decline in cognitive abilities, including thinking, memory and language. MCI can be identified in approximately 25 percent of newly diagnosed PD patients, and patients with MCI progress to dementia more frequently than those with normal cognitive performance.

For the new study, researchers used an MRI technique called diffusion tractography to look for differences in the neural networks of PD patients with and without MCI.

Increasingly, the human brain is understood as an integrated network, or connectome, that has both a structural and functional component. By applying an analytical tool called graph analysis to the imaging results, researchers can measure the relationships among highly connected and complex data like the network of connections in the human brain.

The study group was made up of 170 PD patients, including 54 with MCI and 116 without, and 41 healthy controls. Analysis of imaging results showed that only PD patients with MCI had significant alterations at the brain network level. Measurements of the movement and diffusion of water in the brain, an indicator of the condition of the brain’s signal-carrying white matter, differentiated PD patients with MCI from healthy controls and non-MCI PD patients with a good accuracy. Researchers said the results show that cognitive impairment in PD is likely the consequence of a disruption of complex structural brain networks rather than degeneration of individual white matter bundles.

The results may offer markers to differentiate PD patients with and without cognitive deficits, according to researchers.

Paper: "Structural Brain Connectome and Cognitive Impairment in Parkinson Disease"
Reprinted from materials provided by the Radiological Society of North America.

People who live close to high-traffic roadways face a higher risk of developing dementia than those who live further away, new research has found.

The study, published in The Lancet, found that people who lived within 50 metres of high-traffic roads had a seven per cent higher likelihood of developing dementia compared to those who lived more than 300 meters away from busy roads.

The researchers examined records of more than 6.5 million Ontario, Canada, residents aged 20-85 to investigate the correlation between living close to major roads and dementia, Parkinson's disease and multiple sclerosis.

Scientists identified 243,611 cases of dementia, 31,577 cases of Parkinson's disease, and 9,247 cases of multiple sclerosis in Ontario between 2001 and 2012. In addition, they mapped individuals' proximity to major roadways using the postal code of their residence. The findings indicate that living close to major roads increased the risk of developing dementia, but not Parkinson's disease or multiple sclerosis, two other major neurological disorders.

As urban centres become more densely populated and more congested with vehicles on major roads, the researchers suggest the findings of this paper could be used to help inform municipal land use decisions as well as building design to take into account air pollution factors and the impact on residents.

Paper: "Living near major roads and the incidence of dementia, Parkinson's disease, and multiple sclerosis: a population-based cohort study"
Source: Public Health Ontario
 

A new study suggests that a key to Parkinson's disease may lie in the mitochondria, the powerhouses of the cell.

The results were published in Nature Communications.

Mitochondria, it seems, are not able to adapt to the effects of aging in people who get Parkinson's disease. Mitochondria contain their own DNA, which tell them how to build their power generators. In this study, researchers compared brain cells from healthy aged persons to those of individuals with Parkinson's disease.

The researchers discovered that brain cells of healthy persons are able to compensate for the age-induced damage by producing more DNA in their mitochondria. This protective mechanism is weakened in individuals with Parkinson's disease, leading to a loss of the mitochondria's healthy DNA population.

"I believe we have discovered an essential biological mechanism that normally preserves and protects the brain from aging related damage. Intriguingly, this mechanism appears to fail in persons with Parkinson's disease, rendering their brain more vulnerable to the effects of aging," said neurologist Dr Charalampos Tzoulis, who directed the study.

Paper: "Defective mitochondrial DNA homeostasis in the substantia nigra in Parkinson disease"
Reprinted from materials provided by the University of Bergen.

Patients who had a diagnosis of Parkinson's disease (PD) with dementia (PDD) or dementia with Lewy bodies (DLB) and had higher levels of Alzheimer's disease (AD) pathology in their donated post-mortem brains also had more severe symptoms of these Lewy body diseases (LBD) during their lives, compared to those whose brains had less AD pathology, according to new research. In particular, the degree of abnormal tau protein aggregations, indicative of AD, most strongly matched the clinical course of the LBD patients who showed evidence of dementia prior to their deaths, according to the study, which was published in The Lancet Neurology.

The team used post-mortem brain tissue donated by 213 patients with LBD and associated dementia, which was confirmed during autopsies to have alpha-synuclein pathology. They paired the tissue analysis with the patients' detailed medical records. This unique study combined data from eight academic memory or movement disorder centers.

LBD is a family of related brain disorders made up of the clinical syndromes of PD, without or with dementia or DLB. LBD is associated with clumps of misshapened alpha-synuclein proteins. On the other hand, AD pathology is made up of clusters of the protein beta-amyloid called plaques and twisted strands of the protein tau, called tangles. Patients with LBD may have varying amounts of AD pathology, in addition to alpha-synuclein pathology.

Treatments directed at tau and amyloid-beta proteins are currently being tested in patients with Alzheimer's disease. This study could help in selecting appropriate patients for trials of emerging therapies targeting these proteins singly or in combination with emerging therapies targeting alpha-synuclein protein in LBD.

The study suggests that Lewy body pathology may be the primary driver of disease seen in the patients; whereas, AD pathology has an impact on the overall course of disease.

None of the LBD patients had a clinical diagnosis of AD, but their post-mortem brain tissue revealed varying amounts of AD neuropathology. Post-mortem analysis of five brain regions per patient showed that they fell into one of four categories of AD pathology: 23 percent negligible or no AD, 26 percent had low-level, 21 percent intermediate, and 30 percent had high-level.

Increasing severity of AD pathology correlated with a shortened time from motor symptoms to the onset of dementia and death, with the most significant trends seen in the intermediate- and high-level AD groups compared to the low-level and no AD groups. Tau pathology, in particular, was the strongest predictor of a shorter time to dementia and death. AD pathology was also higher in patients who were older at the time of onset of motor symptoms and dementia.

The team also found that two relevant genetic variants in sequences of the patients' DNA samples correlated with the amount of AD pathology. The frequency of a genetic variant in a gene coding for a protein involved in cholesterol metabolism (APOE, the most common risk factor for AD) was more frequent in patients who were in the intermediate or high AD pathology group compared to those in the low-level or no AD group. Interestingly, a variation in the gene for the protein GBA (a risk factor for LBD) was more frequent in patients without significant AD pathology. This gene is associated with LBD overall but not the subgroup with AD pathology.

In the brain, the enzyme GBA normally aids in the breakdown of worn out and misshapened proteins, such as alpha-synuclein. Together these findings suggest that genetic risk factors could influence the amount of AD pathology in LBD. Further understanding of the relationships between genetic risk factors and AD and alpha-synuclein pathology will help improve treatments for these disorders.

Paper: "Neuropathological and genetic correlates of survival and dementia onset in synucleinopathies: a retrospective analysis"
Reprinted from materials provided by the Perelman School of Medicine at the University of Pennsylvania.
 

Researchers have identified a naturally occurring molecule that has the potential for preserving sites of communication between nerves and muscles in amyotrophic lateral sclerosis (ALS) and over the course of aging — as well as a molecule that interferes with this helpful process.

The discovery in mice has implications for patients with ALS, also known as Lou Gehrig's disease.

Published in The Journal of Neuroscience, the research team describes a growth factor called FGFBP1, which is secreted by muscle fibers and maintains neuromuscular junctions — a critical type of synapse that allows the spinal cord to communicate with muscles, sending signals from the central nervous system to create movements.

In mouse models of ALS, a growth factor associated with the immune system, called TGF-beta, emerges and prevents muscles from secreting factors needed to maintain their connections with neurons.

"TGF-beta is upregulated in ALS and in turn blocks expression of FGFBP1, which is released by muscle fibers to preserve the integrity of the neuromuscular junction," said Gregorio Valdez, who led the study. "The body is trying to help itself by generating more TGF-beta. Unfortunately, TGF-beta accumulates at the synapse where it blocks expression of FGFBP1, accelerating degeneration of the neuromuscular junction."

FGFBP1 also gradually decreases during aging, but more precipitously in ALS, because TGF-beta accumulates at the synapse, according to the researchers.

Paper: “Muscle fibers secrete FGFBP1 to slow degeneration of neuromuscular synapses during aging and progression of ALS”
Reprinted from materials provided by Virginia Tech.

Researchers have discovered that mice with Huntington’s disease (HD) suffer defects in muscle maturation that may explain some symptoms of the disorder. The study, which was published in The Journal of General Physiology, suggests that HD is a disease of muscle tissue as well as a neurodegenerative disorder and that therapies targeting skeletal muscle may improve patients’ motor function.

HD is a progressive, and ultimately fatal, disorder caused by a mutation in the huntingtin gene that results in the production of defective huntingtin RNA and protein molecules that disrupt various cellular processes. The cognitive and psychiatric disturbances associated with HD, including memory loss and mood swings, are thought to result from the death of neurons in the striatum and cerebral cortex. But some of the disease’s motor symptoms, such as involuntary movements and muscle rigidity, could arise from the effects of mutant huntingtin in skeletal muscle.

The researchers previously found that mice with an early-onset form of HD showed skeletal muscle defects at late stages of the disease, particularly a decrease in the function of a protein called ClC-1, which conducts chloride ions into the cell. This appeared to be caused by defective processing of the messenger RNA encoding ClC-1 and contributed to muscle hyperexcitability, potentially causing some of the motor symptoms associated with HD. But the loss of ClC-1 function could simply be a late response to the death of neurons innervating skeletal muscle; whether the chloride channel is affected during the onset and progression of HD remained unclear.

In the new study, the researchers examined their HD model mice throughout the course of the disease. They found that the RNA encoding ClC-1 was misprocessed in both HD and control mice when they were young, but, as they grew older, only healthy animals were able to start correctly processing the RNA to produce functional ClC-1. Thus, even before their motor symptoms began to appear, ClC-1 function was reduced in the skeletal muscle of HD mice compared with healthy control animals.

This suggested that muscle maturation might be disrupted in HD mice. The reseachers found that HD mice expressed a form of the muscle motor protein myosin that is usually only produced in newborn mouse muscle. Moreover, they identified similar defects in muscle maturation in a different strain of mice with adult-onset HD.

The researchers say that their results could provide a new opportunity to improve patient care by targeting skeletal muscle tissue. In addition, researchers and clinicians may be able to use the skeletal muscle defects as biomarkers to track the progress of HD, a much easier task than examining patients’ brain tissue.