Trehalose is a small molecule – nutritionally equivalent to glucose – that helps to prevent protein from aggregating (that is, clustering together in a bad way).
Parkinson’s disease is a neurodegenerative condition that is characterised by protein aggregating, or clustering together in a bad way.
Is anyone else thinking what I’m thinking?
In today’s post we will look at what trelahose is, review some of the research has been done in the context of Parkinson’s disease, and discuss how we should be thinking about assessing this molecule clinically.
Neuropathologists examining a section of brain tissue. Source: Imperial
When a neuropathologist makes an examination of the brain of a person who passed away with Parkinson’s, there are two characteristic hallmarks that they will be looking for in order to provide a definitively postmortem diagnosis of the condition:
1. The loss of dopamine producing neurons in a region of the brain called the substantia nigra.
The dark pigmented dopamine neurons in the substantia nigra are reduced in the Parkinson’s disease brain (right). Source:Memorangapp
2. The clustering (or ‘aggregation’) of a protein called alpha synuclein. Specifically, they will be looking for dense circular aggregates of the protein within cells, which are referred to as Lewy bodies.
A Lewy body inside of a neuron. Source: Neuropathology-web
A cartoon of a neuron, with the Lewy body indicated within the cell body. Source: Alzheimer’s news
In addition to Lewy bodies, the neuropathologist may also see alpha synuclein clustering in other parts of affected cells. For example, aggregated alpha synuclein can be seen in the branches of cells (these clusterings are called ‘Lewy neurites‘ – see the image below where alpha synuclein has been stained brown on a section of brain from a person with Parkinson’s disease.
Examples of Lewy neurites (indicated by arrows). Source: Wikimedia
Given these two distinctive features of the Parkinsonian brain (the loss of dopamine neurons and the aggregation of alpha synuclein), a great deal of research has focused on A.) neuroprotective agents to protect the remaining dopamine-producing neurons in the substantia nigra, and B.) compounds that stop the aggregation of alpha synuclein.
In today’s post, we will look at the research that has been conducted on one particular compounds that appears to stop the aggregation of alpha synuclein.
It is call Trehalose (pronounces ‘tray-hellos’).
Nuclear receptor related 1 protein (or NURR1) is a protein that is critical to the development and survival of dopamine neurons – the cells in the brain that are affected in Parkinson’s disease.
Given the importance of this protein for the survival of these cells, a lot of research has been conducted on finding activators of NURR1.
In today’s post we will look at this research, discuss the results, and consider issues with regards to using these activators in Parkinson’s disease.
Comet Hale–Bopp. Source: Physics.smu.edu
Back in 1997, 10 days after Comet Hale–Bopp passed perihelion (April 1, 1997 – no joke; perihelion being the the point in the orbit of a comet when it is nearest to the sun) and just two days before golfer Tiger Woods won his first Masters Tournament, some researchers in Stockholm (Sweden) published the results of a study that would have a major impact on our understanding of how to keep dopamine neurons alive.
Dopamine neurons are one group of cells in the brain that are severely affected by Parkinson’s disease. By the time a person begins to exhibit the movement symptoms of the condition, they will have lost 40-60% of the dopamine neurons in a region called the substantia nigra. In the image below, there are two sections of brain – cut on a horizontal plane through the midbrain at the level of the substantia nigra – one displaying a normal compliment of dopamine neurons and the other from a person who passed away with Parkinson’s demonstrating a reduction in this cell population.
The dark pigmented dopamine neurons in the substantia nigra are reduced in the Parkinson’s disease brain (right). Source:Memorangapp
The researchers in Sweden had made an amazing discovery – they had identified a single gene that was critical to the survival of dopamine neurons. When they artificially mutated the section of DNA where this gene lives – an action which resulted in no protein for this gene being produced – they generated genetically engineered mice with no dopamine neurons:
Title: Dopamine neuron agenesis in Nurr1-deficient mice
Authors: Zetterström RH, Solomin L, Jansson L, Hoffer BJ, Olson L, Perlmann T.
Journal: Science. 1997 Apr 11;276(5310):248-50.
The researchers who conducted this study found that the mice with no NURR1 protein exhibited very little movement and did not survive long after birth. And this result was very quickly replicated by other research groups (Click here and here to see examples)
So what was this amazing gene called?
This week a biotech company called Voyager Therapeutics announced the results of their ongoing phase Ib clinical trial. The trial is investigating a gene therapy approach for people with severe Parkinson’s disease.
Gene therapy is a technique that involves inserting new DNA into a cell using a virus. The DNA can help the cell to produce beneficial proteins that go on help to alleviate the motor features of Parkinson’s disease.
In today’s post we will discuss gene therapy, review the new results and consider what they mean for the Parkinson’s community.
On 25th August 2012, the Voyager 1 space craft became the first human-made object to exit our solar system.
After 35 years and 11 billion miles of travel, this explorer has finally left the heliosphere (which encompasses our solar system) and it has crossed into the a region of space called the heliosheath – the boundary area that separates our solar system from interstellar space. Next stop on the journey of Voyager 1 will be the Oort cloud, which it will reach in approximately 300 years and it will take the tiny craft about 30,000 years to pass through it.
Where is Voyager 1? Source: Tampabay
Where is Voyager actually going? Well, eventually it will pass within 1 light year of a star called AC +79 3888 (also known as Gliese 445), which lies 17.6 light-years from Earth. It will achieve this goal on a Tuesday afternoon in 40,000 years time.
Gliese 445 (circled). Source: Wikipedia
Remarkably, the Gliese 445 star itself is actually coming towards us. Rather rapidly as well. It is approaching with a current velocity of 119 km/sec – nearly 7 times as fast as Voyager 1 is travelling towards it (the current speed of the craft is 38,000 mph (61,000 km/h).
Interesting, but what does any of that have to do with Parkinson’s disease?
Well closer to home, another ‘Voyager’ is also ‘going boldly where no man has gone before’ (sort of).
Last year – two years after actor Robin Williams died – his wife Susan Schneider Williams wrote an essay entitled The terrorist inside my husband’s head, published in the journal Neurology.
It is a heartfelt/heartbreaking insight into the actor’s final years. It also highlights the plight of many who are diagnosed with Parkinson’s disease, but experience an array of additional symptoms that leave them feeling that something else is actually wrong.
Today’s post is all about Dementia with Lewy bodies (or DLB). In particular, we will review the latest refinements and recommendations of the Dementia with Lewy Bodies Consortium, regarding the clinical and pathologic diagnosis of DLB.
Robin Williams. Source: Quotesgram
On the 28th May of 2014, the actor Robin Williams was diagnosed with Parkinson’s disease.
At the time, he had a slight tremor in his left hand, a slow shuffling gait and mask-like face – some of the classical features of Parkinson’s disease.
According to his wife, the diagnosis gave the symptoms Robin had been experiencing a name. And this brought her a sense of relief and comfort. Now they could do something about the problem. Better to know what you are dealing with rather than be left unsure and asking questions.
But Mr Williams sensed that something else was wrong, and he was left unsure and asking questions. While filming the movie Night at the Museum 3, Williams experienced panic attacks and regularly forgot his lines. He kept asking the doctors “Do I have Alzheimer’s? Dementia? Am I schizophrenic?”
Williams took his own life on the 11th August 2014, and the world mourned the tragic loss of a uniquely talented performer.
When the autopsy report came back from the coroner, however, it indicated that the actor had been misdiagnosed.
He didn’t have Parkinson’s disease.
What he actually had was Dementia with Lewy bodies (or DLB).
What is Dementia with Lewy bodies?
In this post we discuss several recently published research reports suggesting that Parkinson’s disease may be an autoimmune condition. “Autoimmunity” occurs when the defence system of the body starts attacks the body itself.
This new research does not explain what causes of Parkinson’s disease, but it could explain why certain brain cells are being lost in some people with Parkinson’s disease. And such information could point us towards novel therapeutic strategies.
The first issue of Nature. Source: SimpleWikipedia
The journal Nature was first published on 4th November 1869, by Alexander MacMillan. It hoped to “provide cultivated readers with an accessible forum for reading about advances in scientific knowledge.” It has subsequently become one of the most prestigious scientific journals in the world, with an online readership of approximately 3 million unique readers per month (almost as much as we have here at the SoPD).
Each Wednesday afternoon, researchers around the world await the weekly outpouring of new research from Nature. And this week a research report was published in Nature that could be big for the world of Parkinson’s disease. Really big!
On the 21st June, this report was published:
Title: T cells from patients with Parkinson’s disease recognize α-synuclein peptides
Authors: Sulzer D, Alcalay RN, Garretti F, Cote L, Kanter E, Agin-Liebes J, Liong C, McMurtrey C, Hildebrand WH, Mao X, Dawson VL, Dawson TM, Oseroff C, Pham J, Sidney J, Dillon MB, Carpenter C, Weiskopf D, Phillips E, Mallal S, Peters B, Frazier A, Lindestam Arlehamn CS, Sette A
Journal: Nature. 2017 Jun 21. doi: 10.1038/nature22815.
In their study, the investigators collected blood samples from 67 people with Parkinson’s disease and from 36 healthy patients (which were used as control samples). They then exposed the blood samples to fragments of proteins found in brain cells, including fragments of alpha synuclein – this is the protein that is so closely associated with Parkinson’s disease (it makes regular appearances on this blog).
What happened next was rather startling: the blood from the Parkinson’s patients had a strong reaction to two specific fragments of alpha synuclein, while the blood from the control subjects hardly reacted at all to these fragments.
In the image below, you will see the fragments listed along the bottom of the graph (protein fragments are labelled with combinations of alphabetical letters). The grey band on the plot indicates the two fragments that elicited a strong reaction from the blood cells – note the number of black dots (indicating PD samples) within the band, compared to the number of white dots (control samples). The numbers on the left side of the graph indicate the number of reacting cells per 100,000 blood cells.
The investigators concluded from this experiment that these alpha synuclein fragments may be acting as antigenic epitopes, which would drive immune responses in people with Parkinson’s disease and they decided to investigate this further.
Please excuse our use of UK slang in the title of this post, but a group of Australian researchers have recently discovered something really interesting about Parkinson’s disease.
And being a patriotic kiwi, it takes something REALLY interesting for me to even acknowledge that other South Pacific nation. This new finding, however, could be big.
In today’s post, we will review new research dealing with a protein called SOD1, and discuss what it could mean for the Parkinson’s community.
The number of dark pigmented dopamine cells in the substantia nigra are reduced in the Parkinson’s disease brain (right). Source: Adaptd from Memorangapp
Every Parkinson’s-associated website and every Parkinson’s disease researchers will tell you exactly the same thing when describing the two cardinal features in the brain of a person who died with Parkinson’s disease:
- The loss of certain types of cells (such as the dopamine producing cells of the substantia nigra region of the brain – see the image above)
- The clustering (or aggregation) of a protein called Alpha synuclein in tightly packed, circular deposits, called Lewy bodies (see image below).
A Lewy body inside a cell. Source: Adapted from Neuropathology-web
The clustered alpha synuclein protein, however, is not limited to just the Lewy bodies. In the affected areas of the brain, aggregated alpha synuclein can be seen in the branches of cells – see the image below where alpha synuclein has been stained brown on a section of brain from a person with Parkinson’s disease.
Examples of Lewy neurites (indicated by arrows). Source: Wikimedia
Now, one of the problems with our understanding of Parkinson’s disease is disparity between the widespread presence of clustered alpha synuclein and very selective pattern of cell loss. Alpha synuclein aggregation can be seen distributed widely around the affected areas of the brain, but the cell loss will be limited to specific populations of cells.
If the disease is killing a particular population of cells, why is alpha synuclein clustering so wide spread?
So why is there a difference?
We don’t know.
It could be that the cells that die have a lower threshold for alpha synuclein toxicity (we discussed this is a previous post – click here?).
But this question regarding the difference between these two features has left many researchers wondering if there may be some other protein or agent that is actually killing off the cells and then disappearing quickly, leaving poor old alpha synuclein looking rather guilty.
Poor little Mr “A Synuclein” got the blame, but his older brother actually did it! Source: Youtube
And this is a very serious discussion point.
This year of 2017 represents the 200th anniversary of James Parkinson’s first description of Parkinson’s disease, but it also represents the 20th anniversary since the association between alpha synuclein and PD was first established. We have produced almost 7,000 research reports on the topic of alpha synuclein and PD during that time, and we currently have ongoing clinical trials targetting alpha synuclein.
But what if our basic premise – that alpha synuclein is the bad guy – is actually wrong?
Is there any evidence to suggest this?
We are just speculating here, but yes there is.
For example, in a study of 904 brains, alpha synuclein deposits were observed in 11.3% of the brains (or 106 cases), but of those cases only 32 had been diagnosed with a neurodegenerative disorder (Click here to read more on this). The remaining 74 cases had demonstrated none of the clinical features of Parkinson’s disease.
So what else could be causing the cell death?
Well, this week some scientists from sunny Sydney (Australia) reported a protein that could fit the bill.
Sydney. Source: Vagabond
The interesting part of their finding is that the protein is also associated with another neurodegenerative condition: Amyotrophic lateral sclerosis.
Remind me again, what is Amyotrophic lateral sclerosis?
Parkinson’s disease and Amyotrophic lateral sclerosis (ALS) are the second and third most common adult-onset neurodegenerative conditions (respectively) after Alzheimer’s disease. We recently discussed ALS in a previous post (Click here to read that post).
ALS, also known as Lou Gehrig’s disease and motor neuron disease, is a neurodegenerative condition in which the neurons that control voluntary muscle movement die. The condition affects 2 people in every 100,000 each year, and those individuals have an average survival time of two to four years.
You may have heard of ALS due to it’s association with the internet ‘Ice bucket challenge‘ craze that went viral in 2014-15.
The Ice bucket challenge. Source: Forbes
What is the protein associated with ALS?
In 1993, scientists discovered that mutations in the gene called SOD1 were associated with familial forms of ALS (Click here to read more about this). We now know that mutations in the SOD1 gene are associated with around 20% of familial cases of ALS and 5% of sporadic ALS.
The SOD1 gene produces an enzyme called Cu-Zn superoxide dismutase.
This enzyme is a very powerful antioxidant that protects the body from damage caused by toxic free radical generated in the mitochondria.
SOD1 protein structure. Source: Wikipedia
One important note here regarding ALS: the genetic mutations in the SOD1 gene do not cause ALS by affecting SOD1’s antioxidant properties (Click here to read more about this). Rather, researchers believe that the cell death seen in SOD1-associated forms of ALS is the consequences of some kind of toxic effect caused by the mutant protein.
So what did the Aussie researchers find about SOD1 in Parkinson’s disease?
This week, the Aussie researchers published this research report:
Title: Amyotrophic lateral sclerosis-like superoxide dismutase 1 proteinopathy is associated withneuronal loss in Parkinson’s disease brain.
Authors: Trist BG, Davies KM, Cottam V, Genoud S, Ortega R, Roudeau S, Carmona A, De Silva K, Wasinger V, Lewis SJG, Sachdev P, Smith B, Troakes C, Vance C, Shaw C, Al-Sarraj S, Ball HJ, Halliday GM, Hare DJ, Double KL.
Journal: Acta Neuropathol. 2017 May 19. doi: 10.1007/s00401-017-1726-6.
Given that oxidative stress is a major feature of Parkinson’s disease, the Aussie researchers wanted to investigate the role of the anti-oxidant enzyme, SOD1 in this condition. And what they found surprised them.
Heck, it surprised us!
Two areas affected by Parkinson’s disease – the substantia nigra (where the dopamine neurons reside; SNc in the image below) and the locus coeruleus (an area in the brain stem that is involved with physiological responses to stress; LC in the image below) – exhibited little or no SOD1 protein in the control brains.
But in the Parkinsonian brains, there was a great deal of SOD1 protein (see image below).
SO1 staining in PD brain and Control brains. Source: Springer
In the image above, you can see yellowish-brown stained patches in both the PD and control images. This a chemical called neuromelanin and it can be used to identify the dopamine-producing cells in the SNc and LC. The grey staining in the PD images (top) are cells that contain SOD1. Note the lack of SOD1 (grey staining) in the control images (bottom).
Approximately 90% of Lewy bodies in the Parkinson’s affected brains contained SOD1 protein. The investigators did report that the levels of SOD1 protein varied between Lewy bodies. But the clustered (or ‘aggregated’) SOD1 protein was not just present with alpha synuclein, often it was found by itself in the degenerating regions.
The researchers occasional saw SOD1 aggregation in regions of age-matched control brains, and they concluded that a very low level of SOD1 must be inherent to the normal ageing process.
But the density of SOD1 clustering was (on average) 8x higher in the SNc and 4x higher in the LC in the Parkinsonian brain compared to age-matched controls. In addition, the SOD1 clustering was significantly greater in these regions than all of the non-degenerating regions of the same Parkinson’s disease brains.
The investigators concluded that these data suggest an association between SOD1 aggregation and neuronal loss in Parkinson’s disease. Importantly, the presence of SOD1 aggregations “closely reflected the regional pattern of neuronal loss”.
They also demonstrated that the SOD1 protein in the Parkinsonian brain was not folded correctly, a similar characteristic to alpha synuclein. A protein must fold properly to be able to do it’s assigned jobs. By not folding into the correct configuration, the SOD1 protein could not do it’s various functions – and the investigators observed a 66% reduction in SOD1 specific activity in the SNc of the Parkinson’s disease brains.
Interestingly, when the researchers looked at the SNc and LC of brains from people with ALS, they identified SOD1 aggregates matching the SOD1 clusters they had seen in these regions of the Parkinson’s disease brain.
Is this the first time SOD1 has been associated with Parkinson’s disease?
No, but it is the first major analysis of postmortem Parkinsonian brains. SOD1 protein in Lewy bodies has been reported before:
Title: Cu/Zn superoxide dismutase-like immunoreactivity is present in Lewy bodies from Parkinson disease: a light and electron microscopic immunocytochemical study
Authors: Nishiyama K, Murayama S, Shimizu J, Ohya Y, Kwak S, Asayama K, Kanazawa I.
Journal: Acta Neuropathol. 1995;89(6):471-4.
The investigators behind this study reported SOD1 protein was present in Lewy bodies, in the substantia nigra and locus coeruleus of brains from five people with Parkinson’s disease. Interestingly, they showed that SOD1 is present in the periphery of the Lewy body, similar to alpha synuclein. Both of these protein are present on the outside of the Lewy body, as opposed to another Parkinson’s associated protein, Ubiquitin, which is mainly present in the centre (or the core) of Lewy bodies (see image below).
A more recent study also demonstrated SOD1 protein in the Parkinsonian brain, including direct interaction between SOD1 and alpha synuclein:
Title: α-synuclein interacts with SOD1 and promotes its oligomerization
Authors: Helferich AM, Ruf WP, Grozdanov V, Freischmidt A, Feiler MS, Zondler L, Ludolph AC, McLean PJ, Weishaupt JH, Danzer KM.
Journal: Mol Neurodegener. 2015 Dec 8;10:66.
PMID: 26643113 (This article is OPEN ACCESS if you would like to read it)
These researchers found that alpha synuclein and SOD1 interact directly, and they noted that Parkinson’s disease related mutations in alpha synuclein (A30P, A53T) and ALS associated mutation in SOD1 (G85R, G93A) modify the binding of the two proteins to each other. They also reported that alpha synuclein accelerates SOD1 aggregation in cell culture. This same group of researchers published another research report last year in which they noted that aggregated alpha synuclein increases SOD1 clustering in a mouse model of ALS (Click here for more on this).
Are there any genetic mutations in the SOD1 gene that are associated with Parkinson’s disease?
Two studies have addressed this question:
Title: Sequence of the superoxide dismutase 1 (SOD 1) gene in familial Parkinson’s disease.
Authors: Bandmann O, Davis MB, Marsden CD, Harding AE.
Journal: J Neurol Neurosurg Psychiatry. 1995 Jul;59(1):90-1.
PMID: 7608718 (This article is OPEN ACCESS if you would like to read it)
And then in 2001, a second analysis:
Title: Genetic polymorphisms of superoxide dismutase in Parkinson’s disease.
Authors: Farin FM, Hitosis Y, Hallagan SE, Kushleika J, Woods JS, Janssen PS, Smith-Weller T, Franklin GM, Swanson PD, Checkoway H.
Journal: Mov Disord. 2001 Jul;16(4):705-7.
Both studies found no genetic variations in the SOD1 gene that were more frequent in the Parkinson’s affected community than the general population. So, no, there are no SOD1 genetic mutations that are associated with Parkinson’s disease.
Are there any treatments targeting SOD1 that could be tested in Parkinson’s disease?
Great question. Yes there are. And they have already been tested in models of PD:
Title: The hypoxia imaging agent CuII(atsm) is neuroprotective and improves motor and cognitive functions in multiple animal models of Parkinson’s disease.
Authors: Hung LW, Villemagne VL, Cheng L, Sherratt NA, Ayton S, White AR, Crouch PJ, Lim S, Leong SL, Wilkins S, George J, Roberts BR, Pham CL, Liu X, Chiu FC, Shackleford DM, Powell AK, Masters CL, Bush AI, O’Keefe G, Culvenor JG, Cappai R, Cherny RA, Donnelly PS, Hill AF, Finkelstein DI, Barnham KJ.
Title: J Exp Med. 2012 Apr 9;209(4):837-54.
PMID: 22473957 (This article is OPEN ACCESS if you would like to read it)
CuII(atsm) is a drug that is currently under clinical investigation as a brain imaging agent for detecting hypoxia (damage caused by lack of oxygen – Click here to read more about this).
The researchers conducting this study, however, were interested in this compound for other reasons: CuII(atsm) is also a highly effective scavenger of a chemical called ONOO, which can be very toxic. CuII(atsm) not only inhibits this toxicity, but it also blocks the clustering of alpha synuclein. And given that CuII(atsm) is capable of crossing the blood–brain barrier, these investigators wanted to assess the drug for its ability to rescue model of Parkinson’s disease.
And guess what? It did!
And not just in one model of Parkinson’s disease, but FOUR!
The investigators even waited three days after giving the neurotoxins to the mice before giving the CuII(atsm) drug, and it still demonstrated neuroprotection. It also improved the behavioural features of these models of Parkinson’s disease.
Is CuII(atsm) being tested for anything else in Clinical trials?
Yes, there is a clinical trial ongoing for ALS in Australia.
The Phase I study, being run by Collaborative Medicinal Development Pty Limited, is a dose escalating study of Cu(II)ATSM to determine if this drug is safe for use in ALS (Click here for more on this study).
Cu(II)ATSM is an orally administered drug that inhibits the activity of misfolded SOD1 protein. It has been shown to paradoxically increase mutant SOD1 protein in a mouse model of ALS, but it also provides neuroprotection and improves the outcome for these mice (Click here to read more on this).
If this trial is successful, it would be interesting to test this drug on a cohort of people with Parkinson’s disease. Determining which subgroup of the Parkinson’s affected community would most benefit from this treatment is still to be determined. There is some evidence published last year that suggests people with genetic mutations in the Parkinson’s associated gene PARK2 could benefit from the approach (Click here to read more on this). More research, however, is needed in this area.
So what does it all mean?
Right, so summing up, a group of Australian researchers have reported that the ALS associated protein SOD1 is closely associated with the cell death that we observe in the brains of people with Parkinson’s disease.
They suggest that this could highlight a common mechanisms of toxic SOD1 aggregation in both Parkinson’s disease and ALS. Individuals within the Parkinson’s affected community do not appear to have any genetic mutations in the SOD1 gene, which makes this finding is very interesting.
What remains to be determined is whether SOD1 aggregation is a “primary pathological event”, or if it is secondary to some other disease causing agent. We are also waiting to see if a clinical trial targeting SOD1 in ALS is successful. If it is, there may be good reasons for targeting SOD1 as a novel treatment for Parkinson’s disease.
The banner for today’s post was sourced from Pinterest
Exciting new last week from a small biotech company called Voyager Therapeutics which is using gene therapy to treat neurodegenerative disease. Their primary product (VY-AADC01) is focused on Parkinson’s disease and the initial results look very positive.
The press release has indicates that the treatment is well tolerated and has beneficial effects on the subject’s motor functions. This last part is very interesting as the trial is being conducted on people with advanced Parkinson’s disease.
In today’s post, we’ll review the technology and what the results mean.
Gene therapy. Source: HuffingtonPost
In Parkinson’s disease, we often talk about the loss of the dopamine neurons in the midbrain as a cardinal feature of the disease. When people are diagnosed with Parkinson’s disease, they have usually lost approximately 50-60% of the dopamine neurons in an area of the brain called the substantia nigra.
The dark pigmented dopamine neurons in the substantia nigra are reduced in the Parkinson’s disease brain (right). Source: Memorangapp
The midbrain is – as the label suggests – in the middle of the brain, just above the brainstem (see image below). The substantia nigra dopamine neurons reside there.
Location of the substantia nigra in the midbrain. Source: Memorylossonline
The dopamine neurons of the substantia nigra generate dopamine and release that chemical in different areas of the brain. The primary regions of that release are areas of the brain called the putamen and the Caudate nucleus. The dopamine neurons of the substantia nigra have long projections (or axons) that extend a long way across the brain to the putamen and caudate nucleus, so that dopamine can be released there.
The projections of the substantia nigra dopamine neurons. Source: MyBrainNotes
In Parkinson’s disease, these ‘axon’ extensions that project to the putamen and caudate nucleus gradually disappear as the dopamine neurons of the substantia nigra are lost. When one looks at brain sections of the putamen after the axons have been labelled with a dark staining technique, this reduction in axons is very apparent over time, especially when compared to a healthy control brain.
The putamen in Parkinson’s disease (across time). Source: Brain
Previously we have discussed replacing the loss dopamine by transplanting dopamine producing cells into the putamen (click here to read that post), but some researchers now believe that this is not necessary. Instead they have proposed using gene therapy for Parkinson’s disease.
What is gene therapy?
The gene therapy involves inducing cells to produce proteins that they usually do not. This is usually done using genetically modified viruses which have had all the disease causing component removed, allowing us to use the virus as an efficient delivery system. Viruses by their very nature are very good at infecting cells, so if we remove the disease causing components, what is left is a very effective delivery system. Taking this approach one step further, we could next take genes involved with dopamine synthesis and insert them into our empty virus. By then injecting this virus into the brain, we could produce dopamine in any infected cells (it’s slightly more complicated than that, but you get the basic idea).
Gene therapy for Parkinson’s disease. Source: Wiki.Epfl
This approach demonstrated amazing results in preclinical studies in the lab, but the transition to the clinic has not been easy (click here for a good review of the field).
What has been done in the clinic for gene therapy and Parkinson’s disease?
The first clinical attempt at gene therapy for Parkinson’s disease involved injecting a virus containing a gene called glutamic acid decarboxylase (GAD), which is an enzyme involved in the production of a chemical called GABA. The virus was injected into an area of the brain called the subthalamic nucleus, which becomes over-active in Parkinson’s disease. By ectopically producing GAD in the subthalamic nucleus, researchers were able to reduce the level of activity (this is similar to deep brain stimulation in Parkinson’s disease which modulates the activity of the subthalamic nucleus). The clinical trials for GAD produced modest results. The virus was well tolerated, but the clinical effect was limited.
Another clinical trial attempted to cause cells in the putamen to produce a chemical called neurturin (which is very similar to GDNF – we have previously written about GDNF, click here to read that post). The goal of the study was to prove neuroprotection and regeneration to the remaining dopamine neurons, by releasing neurturin in the putamen. Subjects were injected in the putamen with the virus and then the participants were followed for 15 months. Unfortunately, this study failed to demonstrate any meaningful improvement in subjects with Parkinson’s disease.
So what were the results of the trial?
Voyager Therapeutics‘s gene therapy product, VY-AADC01 is an adeno associated virus that carries a gene called Aromatic L-amino acid decarboxylase (or AADC).
AAV Viruses. Source: HuffingtonPost
Yeah, I know: what is AADC?
AADC is the enzyme that converts L-dopa into dopamine. L-dopa can be naturally produced in the brain from Tyrosine that is absorbed from the blood. It is also the basic component of many treatments for Parkinson’s disease.
The production of dopamine. Source: Slideplayer
By injecting VY-AADC01 into the putamen of people with advanced Parkinson’s disease, Voyager is hoping to alleviate the motor features of the condition by allowing the brain to produce a constant supply of dopamine in the exact location that is missing the dopamine (remember, the putamen is where dopamine is released). This approach will not cure the disease, but it may make life a lot easier for those affected by it.
The phase 1b clinical trial was designed to assess whether the virus had any negative side effects in humans. After the subjects were injected in the brain with VY-AADC01, they were assessed at six and twelve months after the surgery. The results suggest that the virus was well tolerated and resulted in increased AADC enzyme activity, enhanced response to L-dopa treatment, and clinically meaningful improvements in various measures of patients’ motor function (44% improvement in ‘off medication’ measures and 55% improvement in ‘on medication’ measures).
The company currently has 2 groups of subjects injected with the virus (two different concentrations) and they are looking to have a third group injected in early 2017. Phase 2 trials are planned to begin in late 2017.
What does it all mean?
They are also interesting results because the subjects involved in the study all have advanced Parkinson’s disease (the average time since diagnosis in the subject was 10 years). So it is very positive news to see beneficial effects in later stage subjects.
Our ability to delivery of genes to different locations is a symbol of how far we have come with our understanding of biology. The fact that this knowledge is now having a positive impact in the medical world is very exciting. Gene therapy is one treatment approach that we here at SoPD are very excited about and watching very closely.
The banner for today’s post was sourced from Voyager Therapeutics
It is very closely associated with Parkinson’s disease, given that people with genetic mutations in the alpha synuclein gene are more vulnerable to the condition, AND the protein is a key component in the disease-related circular aggregations (called ‘Lewy bodies’) in the brain. Recently researchers have identified proteins that may be involved with the transfer of Alpha Synuclein between cells – the method by which the disease is believed to be spreading. By blocking or removing these proteins, the researchers have been able to block the transfer of alpha synuclein.
In this post, we will review the research and discuss what this could mean for Parkinson’s disease.
Science conference. Source: JPL
At the recent annual Society for Neuroscience conference in sunny San Diego, Dr Ravindran Kumaran, a neuroscientist in the laboratory of Professor Mark Cookson (at the National Institute on Aging in Bethesda, Maryland) stood up and presented data about an interesting protein that few people in the audience had ever heard of.
Title: High-content siRNA screen identifies cellular modifiers of pre-formed alpha-synuclein fibril uptake
Authors: Kumarani R, Fernandez D, Werner-Allen JW, Buehler E, Bax A, Lai-Nag M, Cookson MR.
Source: Click here to see the full abstract
Dr Kumaran and his colleagues had systematically removed the function of each gene – one by one – in cell cultures of human cancer cells, and then measured the efficiency of the cells to absorb (or ‘take up’) the Parkinson’s related protein, alpha synuclein. An absolutely laborious task (remember there are over 20,000+ genes), but when they turned off a gene called TM9SF2, something amazing happened:
The cells absorbed 75% less of the free floating alpha synuclein than normal health cells.
This caused a bit of excitement in the Parkinson’s research community. Here was a potential method of blocking the spreading of alpha synuclein.
The funny thing is: few people had ever heard of TM9SF2, and yet Dr Kumaran then showed that TM9SF2 is in the top 3% of all proteins present in the brain. In fact, the highest concentrations of TM9SF2 are in the substantia nigra and other brain regions that are most affected by Parkinson’s disease.
So you can hopefully understand why some people in the Parkinson’s research community thought that this was a wee bit exciting.
Plus, this data presentation came on the back of another study that was published in September which presented another protein (called Lag3) that exhibited a similar ability to reduce the absorption of alpha synuclein:
Title: Pathological α-synuclein transmission initiated by binding lymphocyte-activation gene 3.
Authors: Mao X, Ou MT, Karuppagounder SS, Kam TI, Yin X, Xiong Y, Ge P, Umanah GE, Brahmachari S, Shin JH, Kang HC, Zhang J, Xu J, Chen R, Park H, Andrabi SA, Kang SU, Gonçalves RA, Liang Y, Zhang S, Qi C, Lam S, Keiler JA, Tyson J, Kim D, Panicker N, Yun SP, Workman CJ, Vignali DA, Dawson VL, Ko HS, Dawson TM.
Journal: Science. 2016 Sep 30;353(6307).
In this study, the researchers conducted a screen of 352 proteins that sit on the membrane of cells. They were measuring the level of alpha synuclein binding. They identified three interesting candidates for further investigation, include lymphocyte-activation gene 3 (LAG3), neurexin 1β, and amyloid β precursor-like protein 1 (APLP1).
When the researchers compared the three, they found that by removing LAG3 less alpha synuclein was taken into the cell (by endocytosis) than the other two proteins. In addition, when they increased the amount of LAG3 that a cell produces, they observed a similar increase in the amount of alpha synuclein absorbed by cells.
Next the researchers investigated the transmission of alpha synuclein between brain cells in both normal cells and cells that had no LAG3, and they found not only that LAG3 is required for the transmission, but the absence of LAG3 reduces the damage caused by the transmission.
Finally the researchers used small proteins (antibodies) to bind to and block LAG3, and they observed less transmission and damage caused by alpha synuclein. In their conclusions, the authors pointed out that LAG3 is not the only protein involved with the transmission of alpha synclein – there will be others – but it represents a potential future target for therapeutic intervention in Parkinson’s disease.
So what does this mean?
If the theory of alpha synuclein – that this protein is passed between cells, causing the spread of the disease – is correct, then any agent that can block that transmission should slow down or halt Parkinson’s disease. We have previously talked about vacines and antibodies against alpha synuclein being tested in the clinic (Click here, here and here for more on this), but blocking TM9SF2 and LAG3 represent a new method of preventing the transmission of alpha synuclein. This is very exciting. The more angles of attack that we have for designing a treatment the better our options.
Schematic of how LAG3 may be working. Source: Science
We will be watching the field very closely and will keep you posted as new information comes to hand.
The banner for today’s post is sourced from Keepcalm-o-matic
The classical clinical motor features of Parkinson’s disease (slowness of movement, rigidity and a resting tremor in one of the limbs) are associated with the loss 60% of the dopamine neurons in the midbrain.
What does this mean?
The midbrain is a structure at the top of the spinal cord – just as you enter the brain proper – and dopamine is a chemical that is produced in the brain. The dopamine neurons in the midbrain form connections with different areas of the brain, and are involved in many basic neurological functions, such as movement, motivation and addiction.
Sections of the human midbrain from a healthy individual (left) and a person who had Parkinson’s disease (right). The dopamine cells in the control subject can be seen on both sides of the brain with the eye because they produce a chemical (neuromelanin) that makes them black. These cells are noticeably absent in the Parkinsonian brain. Source: Springer
Not all midbrain dopamine neurons are affected in the same way in Parkinson’s disease though.
There are three basic groupings of dopamine neurons in the midbrain region:
- The substantia nigra pars compacta (or SNC)
- The ventral tegmental area (or VTA)
- The retrorubral fields (this is a very small group compared with the VTA and SNC)
As the image above illustrates the SNC is divided into two regions – a dorsal layer and a ventral layer.
It has been acknowledged for a long time that the dopamine neurons in the SNC are more vulnerable in Parkinson’s disease than dopamine neurons in the VTA. We have no idea why this specific vulnerability exists. A great deal of attention has been focused on the SNC as a result.
The vulnerability of the SNC dopamine neurons when compared to the VTA, however, is not as clear as many researchers would believe.
In an interesting study published last year, some researchers from the University of Iowa, reviewed previous studies of postmortem analysis of the brains of people with Parkinson’s disease, in particular, focusing on the studies that had counted the number of dopamine neurons in the VTA and the SNC. The results were very interesting:
Title: The Vulnerable Ventral Tegmental Area in Parkinson’s Disease.
Authors: Alberico SL, Cassell MD, Narayanan NS.
Journal: Basal Ganglia. 2015 Aug 1;5(2-3):51-55.
In essence, the study was very simple: the researchers compared the percentage of VTA and SNC dopamine neurons lost in Parkinson’s disease as determined by eight previous studies. They then conducted their own postmortem analysis and compared the results.
In their review of the previous studies, the researchers found that while the SNC was more vulnerable in Parkinson’s disease (approximately 70% of the dopamine neurons are lost), the VTA region still lost 50% of it’s dopamine neurons (see table below).
Curiously, the researcher’s own postmortem analysis found that the VTA was actually more vulnerable than the SNC. Their analysis, however, was based on only 3 brains. In addition, questions can be raised as to how the previous studies defined the borders of the SNC and VTA. Difference exist in those delineations of borders, which may impact on the number of dopamine neurons counted in each region.
The important message, however, is that the VTA is also badly affected in Parkinson’s disease. And given that the VTA is a region involved in mood and motivation, acknowledging its involvement in the disease will help to focus more research attention on to those areas of functioning in Parkinson’s.