Posts tagged alzheimer's disease

Neurodegenerative diseases are not all alike. Two individuals suffering from the same disease may experience very different age of onset, symptoms, severity, and constellation of impairments, as well as different rates of disease progression. Researchers in the Perelman School of Medicine at the University of Pennsylvania have shown one disease protein can morph into different strains and promote misfolding of other disease proteins commonly found in Alzheimer’s, Parkinson’s and other related neurodegenerative diseases.

Virginia M.Y. Lee, PhD, MBA, professor of Pathology and Laboratory Medicine and director of the Center for Neurodegenerative Disease Research, with co-director, John Q. Trojanowski MD, PhD, postdoctoral fellow Jing L. Guo, PhD, and colleagues, discovered that alpha-synuclein, a protein that forms sticky clumps in the neurons of Parkinson’s disease patients, can exist in at least two different structural shapes, or “strains,” when it clumps into fibrils, despite having precisely the same chemical composition.

These two strains differ in their ability to promote fibril formation of normal alpha-synuclein, as well as the protein tau, which forms neurofibrillary tangles in individuals with Alzheimer’s disease.

Importantly, these alpha-synuclein strains are not static; they somehow evolve, such that fibrils that initially cannot promote tau tangles acquire that ability after multiple rounds of “seeded” fibril formation in test tubes.

The findings appear in the July 3rd issue of Cell.

Morphed Misfolding Proteins Found In Overlapping Neurodegenerative Diseases
Tau and alpha-synuclein protein clumps are hallmarks of separate diseases – Alzheimer’s and Parkinson’s, respectively. Yet these two proteins are often found entangled in diseased brains of patients who may manifest symptoms of both disorders.

One possible explanation for this convergence of Alzheimer’s and Parkinson’s disease pathology in the same patient is a global disruption in protein folding. But, Guo and Lee showed that one strain of alpha-synuclein fibrils which cannot promote tau fibrillization actually evolved into another strain that could efficiently cause tau to fibrillize in cultured neurons, although both strains are identical at the amino acid sequence level. Guo and Lee called the starting conformation “Strain A,” and the evolved conformation, “Strain B.”

To figure out how A and B differ, Guo showed that the two strains folded into different shapes, as indicated by their differential reactivity to antibodies and sensitivity to protein-degrading enzymes. The two strains also differed in their ability to promote tau fibrillization and pathology in mouse brains, mimicking the results from cultured cells. When analyzing post-mortem brains of Parkinson’s patients, the team found at least two distinct forms of pathological alpha-synuclein.

Lee and her team speculate that in humans, alpha-synuclein aggregates may shift their shapes as they pass from cell to cell (much like a cube of silly putty being re-shaped to form a sphere), possibly developing the ability to entangle other proteins such as tau along the way. That process, in turn, could theoretically yield distinct types of alpha-synuclein pathologies that are observed in different brain regions of Parkinson’s disease patients.

While further research is needed to confirm and extend these findings, they have potentially significant implications for patients afflicted with Parkinson’s and other neurodegenerative diseases. For example, Lee explains, they could account for some of the heterogeneity observed in Parkinson’s disease. Different strains of pathological alpha-synuclein may promote formation of distinct types of alpha-synuclein aggregates that may or may not induce tau pathology in different brain regions and in different patients. That, in turn, could explain why some Parkinson’s patients, for example, experience only motor impairments while others ultimately develop cognitive impairments.

The findings also have potential therapeutic implications, Lee says. By recognizing that pathological alpha-synuclein can exist in different forms that are linked with different impairments, researchers can now selectively target one or the other, or both, for instance with strain-selective antibodies.

“What we’ve found opens up new areas for developing therapies, and particularly immunotherapies, for Parkinson’s and other neurodegenerative diseases,” Lee says.

(Source: uphs.upenn.edu)

The results of the study may bear significance in the treatment of Alzheimer’s disease and cancer

Dysfunction of the ubiquitin-proteasome system is related to many severe neurodegenerative diseases, such as Alzheimer’s and Parkinson’s diseases, and certain types of cancer. Such dysfunction is also believed to be related to some degenerative muscle diseases.

The proteasome is a large protein complex that maintains cellular protein balance by degrading and destroying damaged or expired proteins. The ubiquitin is a small protein that labels proteins for destruction for the proteasome. If the system does not work effectively enough, expired and damaged proteins accumulate in the cell. If the system is overly active, it destroys necessary proteins in addition to unnecessary ones. In both cases, cell function is disturbed, and the cell may even die.

Proteasome activity is believed to decrease with ageing. However, not much is yet known about how proteasome activity is regulated in an aging multicellular organism. The research team of Academy Research Fellow, Docent Carina Holmberg-Still has discovered an important proteasome regulatory mechanism. The study was published in Cell Reports, a highly esteemed scientific journal.

"We examined whether proteasome activity is affected by insulin/IGF-1 signalling [IIS], which regulates aging in many organisms. The results show that decreased IIS increases proteasome activity," says Holmberg-Still.

Proteasome activity was studied in C. elegans, a free-living roundworm. Decreased IIS increases proteasome activity through the FOXO transcription factor DAF-16 and the UBH-4 enzyme. DAF-16 represses the expression of ubh-4 in certain cell types. The ubh-4 enzyme slows proteasome activity, which means that its repression accelerates proteasome activity.

"Using a cell culture model, we proved that the same mechanism works in human cells," says Holmberg-Still. When the expression of the uchl5 enzyme – the human equivalent of ubh-4 – was decreased, proteasome activity and the degradation of harmful proteins increased.

"Our study shows that the effect of ageing and the related signalling pathway on proteasome activity is tissue-specific. This was a new and interesting discovery that bears great significance in terms of treatment opportunities," says researcher Olli Matilainen, who prepared his dissertation in Holmberg-Still’s research team.

The identification of proteins that regulate proteasome activity and an understanding of the regulatory mechanism offer new opportunities in treating diseases that involve proteasome dysfunction. According to Holmberg-Still, proteins that regulate proteasome activity are particularly interesting in terms of medicine development.

"An ability to accelerate proteasome activity could be beneficial in the treatment of neurodegenerative diseases. Targeted proteasome inhibitors would be useful in the treatment of cancer – general proteasome inhibitors are already used as cancer medication to some extent, but they often have harmful side effects, because they cannot be targeted to a specific tissue."

Holmberg-Still’s team continues to investigate tissue-specific mechanisms that regulate proteasome activity. The team collaborates with clinical researchers to confirm whether its research results can be refined for clinical use.

(Source: eurekalert.org)

Identification of a protein that appears to play an important role in the immune system’s removal of amyloid beta (A-beta) protein from the brain could lead to a new treatment strategy for Alzheimer’s disease. The report from researchers at Massachusetts General Hospital (MGH) has been published online in Nature Communications.

"We identified a receptor protein that mediates clearance from the brain of soluble A-beta by cells of the innate immune system," says Joseph El Khoury, MD, of the Center for Immunology and Inflammatory Diseases in the MGH Division of Infectious Diseases, co-corresponding author of the report. "We also found that deficiency of this receptor in a mouse model of Alzheimer’s disease leads to greater A-beta deposition and accelerated death, while upregulating its expression enhanced A-beta clearance from the brain."

The brain’s immune system – which includes cells like microglia, monocytes and macrophages that engulf and remove foreign materials – appears to play a dual role in neurodegenerative disorders like Alzheimer’s disease. At early stages, these cells mount a response against the buildup of A-beta, the primary component of the toxic plaques found in the brains of patients with the devastating neurological disorder. But as the disease progresses and A-beta plaques become larger, not only do these cells lose their ability to take up A-beta, they also release inflammatory chemicals that cause further damage to brain tissue.

In their investigation of factors that may underlie the breakdown of the immune system’s clearance of A-beta, El Khoury’s team with the hypothesis that, in addition to recognizing and binding to the insoluble form of A-beta found in amyloid plaques, the brain’s immune cells might also interact with soluble forms of A-beta that could begin accumulating in the brain before plaques appear. The researchers first examined a group of receptor proteins known to be used by microglia, monocytes and macrophages to interact with insoluble A-beta. Although any role for these proteins in Alzheimer’s disease has not been known, the MGH investigators previously found that their expression in a mouse model of the disease dropped as the animals aged.

After they first identified the involvement of a receptor called Scara1 in the uptake of soluble A-beta by monocytes and macrophages, the researchers then confirmed that Scara1 appears to be the major receptor for recognition and clearance of A-beta by the innate immune system, the body’s first line of defense. In a mouse model of Alzheimer’s, animals that were missing one or both copies of the Scara1 gene died several months earlier than did those with two functioning copies. By the age of 8 months, Alzheimer’s mice with no functioning Scara1 genes had double the A-beta in their brains as did a control group of Alzheimer’s mice, while normal mice had virtually none.

To investigate possible therapeutic application of the role of Scara1 in A-beta clearance, the MGH team treated cultured immune cells with Protollin, a compound that has been used to enhance the immune response to certain vaccines. Application of Protollin to immune cells tripled their expression of Scara1 and also increased levels of a protein that attracts other immune cells. Adding Protollin-stimulated microglia to brain samples from Alzheimer’s mice reduced the size and number of A-beta deposits in the hippocampus, an area particularly damaged by the disease, but that reduction was significantly less when microglia from Scara1-deficient mice were used.

El Khoury notes that previous research showed that Protollin treatment reduced A-beta deposits in Alzheimer’s mice and the current study reveals the probable mechanism behind that finding. “Upregulating Scara1 expression is a promising approach to treating Alzheimer’s disease,” he says. “First we need to duplicate these studies using human cells and identify new classes of molecules that can safely increase Scara1 expression or activity. That could potentially lead to ways of harnessing the immune system to delay the progression of this disease.” El Khoury is an associate professor of Medicine at Harvard Medical School.

(Source: massgeneral.org)

Scientists using sophisticated imaging techniques have observed a molecular protein folding process that may help medical researchers understand and treat diseases such as Alzheimer’s, Lou Gehrig’s and cancer.

The study, reported this month in the journal Cell, verifies a process that scientists knew existed but with a mechanism they had never been able to observe, according to Dr. Hays Rye, Texas A&M AgriLife Research biochemist.

“This is a step in the direction of understanding how to modulate systems to prevent diseases like Alzheimer’s. We needed to understand the cell’s folding machines and how they interact with each other in a complicated network,” said Rye, who also is associate professor of biochemistry and biophysics at Texas A&M.

Rye explained that individual amino acids get linked together like beads on a string as a protein is made in the cell.

“But that linear sequence of amino acids is not functional,” he explained. “It’s like an origami structure that has to fold up into a three-dimensional shape to do what it has to do.”

Rye said researchers have been trying to understand this process for more than 50 years, but in a living cell the process is complicated by the presence of many proteins in a concentrated environment.

"The constraints on getting that protein to fold up into a good ‘origami’ structure are a lot more demanding,” he said. “So, there are special protein machines, known as molecular chaperones, in the cell that help proteins fold.”

But how the molecular chaperones help protein fold when it isn’t folding well by itself has been the nagging question for researchers.

“Molecular chaperones are like little machines, because they have levers and gears and power sources. They go through turning over cycles and just sort of buzz along inside a cell, driving a protein folding reaction every few seconds,” Rye said.

The many chemical reactions that are essential to life rely on the exact three-dimensional shape of folded proteins, he said. In the cell, enzymes, for example, are specialized proteins that help speed biological processes along by binding molecules and bringing them together in just the right way.

“They are bound together like a three-dimensional jigsaw puzzle,” Rye explained.  “And the proteins — those little beads on the string that are designed to fold up like origami — are folded to position all these beads in three-dimensional space to perfectly wrap around those molecules and do those chemical reactions.

“If that doesn’t happen — if the protein doesn’t get folded up right – the chemical reaction can’t be done. And if it’s essential, the cell dies because it can’t convert food into power needed to build the other structures in the cell that are needed. Chemical reactions are the structural underpinning of how cells are put together, and all of that depends on the proteins being folded in the right way.”

When a protein doesn’t fold or folds incorrectly it turns into an “aggregate,” which Rye described as “white goo that looks kind of like a mayonnaise, like crud in the test tube.

“You’re dead; the cell dies,” he said.

Over the past 20 years, he said, researchers have linked that aggregation process “pretty convincingly” to the development of diseases — Alzheimer’s disease, Lou Gehrig’s disease, Huntington’s disease, to name a few. There’s evidence that diabetes and cancer also are linked to protein folding disorders.

“One of the main roles for the molecular chaperones is preventing those protein misfolding events that lead to aggregation and not letting a cell get poisoned by badly folded or aggregated proteins,” he said.

Rye’s team focused on a key molecular chaperone — the HSP60.

“They’re called HSP for ‘heat shock protein’ because when the cell is stressed with heat, the proteins get unstable and start to fall apart and unfold,” Rye said. “The cell is built to respond by making more of the chaperones to try and fix the problem.

“This particular chaperone takes unfolded protein and goes through a chemical reaction to bind the unfolded protein and literally puts it inside a little ‘box,’” Rye said.

He added that the mystery had long been how the folding worked because, while researchers could see evidence of that happening, no one had ever seen precisely how it happened.

Rye and the team zeroed in on a chemically modified mutant that in other experiments had seemed to stall at an important step in the process that the “machine” goes through to start the folding action. This clued the researchers that this stalling might make it easier to watch.

They then used cryo-electron microscopy to capture hundreds of thousands of images of the process at very high resolutions which allowed them to reconstruct from two-dimensional flat images a three-dimensional model. A highly sophisticated computer algorithm aligns the images and classifies them in subcategories.

“If you have enough of them you can actually reconstruct and view a structure as a three-dimensional model,” Rye said.

What the team saw was this: The HSP60 chaperone is designed to recognize proteins that are not folded from the ones that are. It binds them and then has a separate co-chaperone that puts a “lid” on top of the box to keep the folding intermediate in the box. They could see the box move, and parts of the molecule moved to peel the chaperone box away from the bound protein — or “gift” in the box. But the bound protein was kept inside the package where it could then initiate a folding reaction. They saw tiny tentacles, “like a little octopus in the bottom of the box rising up and grabbing hold of the substrate protein and helping hold it inside the cavity.”

"The first thing we saw was a large amount of an unfolded protein inside of this cavity,” he said. “Even though we knew from lots and lots of other studies that it had to go in there, nobody had ever seen it like this before. We can also see the non-native protein interacting with parts of the box that no one had ever seen before. It was exciting to see all of this for the first time. I think we got a glimpse of a protein in the process of folding, which we actually can compare to other structures.”

“By understanding the mechanism of these machines, the hope is that one of the things we can learn to do is turn them up or turn them off when we need to, like for a patient who has one of the protein folding diseases,” he said.

(Source: today.agrilife.org)

A protein secreted with insulin travels through the bloodstream and accumulates in the brains of individuals with type 2 diabetes and dementia, in the same manner as the amyloid beta (Αβ) plaques that are associated with Alzheimer’s disease, a study by researchers with the UC Davis Alzheimer’s Disease Center has found.

The study is the first to identify deposits of the protein, called amylin, in the brains of people with Alzheimer’s disease, as well as combined deposits of amylin and Aβ plaques, suggesting that amylin is a second amyloid as well as a new biomarker for age-related dementia and Alzheimer’s.

“We’ve known for a long time that diabetes hurts the brain, and there has been a lot of speculation about why that occurs, but there has been no conclusive evidence until now,” said UC Davis Alzheimer’s Disease Center Director Charles DeCarli.

“This research is the first to provide clear evidence that amylin gets into the brain itself and that it forms plaques that are just like the amyloid beta that has been thought to be the cause of Alzheimer’s disease,” DeCarli said. “In fact, the amylin looks like the amyloid beta protein, and they both interact. That’s why we’re calling it the second amyloid of Alzheimer’s disease.”

 ”Amylin deposition in the brain: A second amyloid in Alzheimer’s disease?” is published online today in the Annals of Neurology.

Type 2 diabetes is a chronic metabolic disorder that increases the risk for cerebrovascular disease and dementia, a risk that develops years before the onset of clinically apparent diabetes. Its incidence is far greater among people who are obese and insulin resistant.

Amylin, or islet amyloid polypeptide, is a hormone produced by the pancreas that circulates in the bloodstream with insulin and plays a critical role in glycemic regulation by slowing gastric emptying, promoting satiety and preventing post-prandial spikes in blood glucose levels. Its deposition in the pancreas is a hallmark of type 2 diabetes.

When over-secreted, some proteins have a higher propensity to stick to one another, forming small aggregates, called oligomers, fibrils and amyloids. These types of proteins are called amyloidogenic and include amylin and Aβ. There are about 28 amyloidogenic proteins, each of which is associated with diseases.                

The study was conducted by examining brain tissue from individuals who fell into three groups: those who had both diabetes and dementia from cerebrovascular or Alzheimer’s disease; those with Alzheimer’s disease without diabetes; and age-matched healthy individuals who served as controls.

The research found numerous amylin deposits in the gray matter of the diabetic patients with dementia, as well as in the walls of the blood vessels in their brains, suggesting amylin influx from blood circulation. Surprisingly, the researchers also found amylin in the brain tissue of individuals with Alzheimer’s who had not been diagnosed with diabetes; they postulate that these individuals may have had undiagnosed insulin resistance. They did not find amylin deposits in the brains of the healthy control subjects.

“We found that the amylin deposits in the brains of people with dementia are both independent of and co-located with the Aβ, which is the suspected cause of Alzheimer’s disease,” said Florin Despa, assistant professor-in-residence in the UC Davis Department of Pharmacology. “It is both in the walls of the blood vessels of the brain and also in areas remote from the blood vessels.

“It is accumulating in the brain and we found signs that amylin is killing neurons similar to Aβ,” he continued. “And that might be the answer to the question of ‘What makes obese and type 2 diabetes patients more prone to developing dementia?’”

The researchers undertook the investigation after Despa and his colleagues found that amylin accumulates in the blood vessels and muscle of the heart. From this evidence, he hypothesized that the same thing might be happening in the brain. To test the hypothesis he received a pilot research grant through the Alzheimer’s Disease Center.

The research was conducted using tissue from the brains of individuals over 65 donated to the UC Davis Alzheimer’s Disease Center: 15 patients with Alzheimer’s disease and type 2 diabetes; 14 Alzheimer’s disease patients without diabetes; and 13 healthy controls. A series of tests, including Western blot, immunohistochemistry and ELISA (enzyme-linked immunosorbent assay) were used to test amylin accumulation in specimens from the temporal cortex.

In contrast with the healthy brains, the brain tissue infiltrated with amylin showed increased interstitial spaces, cavities within the tissue, sponginess, and blood vessels bent around amylin accumulation sites.

Despa said that the finding may offer a therapeutic target for drug development, either by increasing the rate of amylin elimination through the kidneys, or by decreasing its rate of oligomerization and deposition in diabetic patients.

"If we’re smart about the treatment of pre-diabetes, a condition that promotes increased amylin secretion, we might be able to reduce the risk of complications, including Alzheimer’s and dementia,” Despa said.

(Source: ucdmc.ucdavis.edu)

In a perspective piece appearing today in the journal Science, researchers at University of Rochester Medical Center (URMC) point to a newly discovered system by which the brain removes waste as a potentially powerful new tool to treat neurological disorders like Alzheimer’s disease. In fact, scientists believe that some of these conditions may arise when the system is not doing its job properly. 

“Essentially all neurodegenerative diseases are associated with the accumulation of cellular waste products,” said Maiken Nedergaard, M.D., D.M.Sc., co-director of the URMC Center for Translational Neuromedicine and author of the article. “Understanding and ultimately discovering how to modulate the brain’s system for removing toxic waste could point to new ways to treat these diseases.”   

The body defends the brain like a fortress and rings it with a complex system of gateways that control which molecules can enter and exit. While this “blood-brain barrier” was first described in the late 1800s, scientists are only now just beginning to understand the dynamics of how these mechanisms function. In fact, the complex network of waste removal, which researchers have dubbed the glymphatic system, was only first disclosed by URMC scientists last August in the journal Science Translational Medicine.  

The removal of waste is an essential biological function and the lymphatic system – a circulatory network of organs and vessels – performs this task in most of the body. However, the lymphatic system does not extend to the brain and, consequently, researchers have never fully understood what the brain does its own waste. Some scientists have even speculated that these byproducts of cellular function where somehow being “recycled” by the brain’s cells.  

One of the reasons why the glymphatic system had long eluded comprehension is that it cannot be detected in samples of brain tissue. The key to discovering and understanding the system was the advent of a new imaging technology called two-photon microscopy which enables scientists to peer deep within the living brain. Using this technology on mice, whose brains are remarkably similar to humans, Nedergaard and her colleagues were able to observe and document what amounts to an extensive, and heretofore unknown, plumbing system responsible for flushing waste from throughout the brain. 

The brain is surrounded by a membrane called the arachnoid and bathed in cerebral spinal fluid (CSF). CSF flows into the interior of the brain through the same pathways as the arteries that carry blood. This parallel system is akin to a donut shaped pipe within a pipe, with the inner ring carrying blood and the outer ring carrying CSF. The CSF is draw into brain tissue via a system of conduits that are controlled by a type support cells in the brain known as glia, in this case astrocytes. The term glymphatic was coined by combining the words glia and lymphatic.

The CSF is flushed through the brain tissue at a high speed sweeping excess proteins and other waste along with it. The fluid and waste are exchanged with a similar system that parallels veins which carries the waste out of the brain and down the spine where it is eventually transferred to the lymphatic system and from there to the liver, where it is ultimately broken down.

While the discovery of the glymphatic system solved a mystery that had long baffled the scientific community, understanding how the brain removes waste – both effectively and what happens when this system breaks down – has significant implications for the treatment of neurological disorders.

One of the hallmarks of Alzheimer’s disease is the accumulation in the brain of the protein beta amyloid. In fact, over time these proteins amass with such density that they can be observed as plaques on scans of the brain. Understanding what role the glymphatic system plays in the brain’s inability to break down and remove beta amyloid could point the way to new treatments. Specifically, whether certainly key ‘players’ in the glymphatic system, such as astrocytes, can be manipulated to ramp up the removal of waste.

“The idea that ‘dirty brain’ diseases like Alzheimer may result from a slowing down of the glymphatic system as we age is a completely new way to think about neurological disorders,” said Nedergaard. “It also presents us with a new set of targets to potentially increase the efficiency of glymphatic clearance and, ultimately, change the course of these conditions.”