Every textbook written about the condition will tell you that the classical pathological characteristic of Parkinson’s is the loss of dopamine neurons in the midbrain region of the brain. It is the distinguishing feature that pathologists look for in order to provide a postmortem diagnosis of the condition.
But what is meant by the words ‘loss of dopamine neurons’? Do the cells actually die? Recently researchers from Korea have published new data exploring this question.
Interestingly, they found evidence of ‘dormant’ dopamine neurons in postmortem sections of brains from people with Parkinson’s – even those with severe forms of the condition.
In today’s post, we will discuss what a dopamine neuron is, what this new research found, and what it could mean for our understanding of Parkinson’s.
2019 represented the centenary year for an important discovery in Parkinson’s research.
In 1919, the Uzbek neuropathologist Konstantin Tretiakoff (1892-1958) reported his findings regarding an examination of 54 human brains.
Konstantin Tretiakoff. Source: Wikipedia
Six of the postmortem brains had belonged to individuals who had suffered from Parkinson’s and three others had been diagnosed with postencephalitic Parkinsonism. In these brains he noticed something rather striking.
What did he find?
Nuclear receptor related 1 protein (or NURR1) is a protein that has been shown to have a powerful effect on the survival of dopamine neurons – a population of cells in the brain that is severely affected by Parkinson’s.
For a long time researchers have been searching for compounds that would activate NURR1, but the vast majority of those efforts have been unsuccessful, leaving some scientists suggesting that NURR1 is “undruggable” (meaning there is no drug that can activate it).
Recently, however, a research report was published which suggests this “undruggable” protein is druggable, and the activator is derived from a curious source: dopamine
In today’s post, we will discuss what NURR1 is, what the new research suggests, and how this new research could be useful in the development of novel therapeutics for Parkinson’s.
It always seems impossible until it’s done – Nelson Mandela
In 1997, when Nelson Mandela was stepping down as President of the African National Congress, 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.
(Yeah, I know. That is a strange segway, but some of my recent intros have dragged on a bit – so let’s just get down to business)
Dopamine neurons are of the one groups of cells in the brain that are severely affected by Parkinson’s. 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 (on the left) and the other from a person who passed away with Parkinson’s demonstrating a reduction in this cell population (on the right).
The dark pigmented dopamine neurons in the substantia nigra are reduced in the Parkinsonian brain (right). Source:Memorangapp
The researchers in Sweden had made an amazing discovery – they had identified a single gene (a specific region of DNA) that was critical to the survival of dopamine neurons. When they artificially disrupted the section of DNA where this gene lives – an action which resulted in no protein for this gene being produced – it resulted in mice being born with no midbrain 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 independent research groups (Click here and here to see examples)
So what was this amazing gene called?
Nuclear receptor related 1 protein (or NURR1; it is also known as NR4A2 – nuclear receptor subfamily 4, group A, member 2)
And what is NURR1?
In this post I review recently published research describing interesting new gene therapy tools.
“Gene therapy” involved using genetics, rather than medication to treat conditions like Parkinson’s disease. By replacing faulty sections of DNA (or genes) or providing supportive genes, doctors hope to better treat certain diseases.
While we have ample knowledge regarding how to correct or insert genes effectively, the problem has always been delivery: getting the new DNA into the right types of cells while avoiding all of the other cells.
Now, researchers at the California Institute of Technology may be on the verge of solving this issue with specially engineered viruses.
Gene therapy. Source: yourgenome
When you get sick, the usual solution is to visit your doctor. They will prescribe a medication for you to take, and then all things going well (fingers crossed/knock on wood) you will start to feel better. It is a rather simple and straight forward process, and it has largely worked well for most of us for quite some time.
As the overall population has started to live longer, however, we have become more and more exposed to chronic conditions which require long-term treatment regimes. The “long-term” aspect of this means that some people are regularly taking medication as part of their daily lives. In many cases, these medications are taken multiple times per day.
An example of this is Levodopa (also known as Sinemet or Madopar) which is the most common treatment for the chronic condition of Parkinson’s disease. When you swallow your Levodopa pill, it is broken down in the gut, absorbed through the wall of the intestines, transported to the brain via our blood system, where it is converted into the chemical dopamine – the chemical that is lost in Parkinson’s disease. This conversion of Levodopa increases the levels of dopamine in your brain, which helps to alleviate the motor issues associated with Parkinson’s disease.
Levodopa. Source: Drugs
This pill form of treating a disease is only a temporary solution though. People with Parkinson’s disease – like other chronic conditions – need to take multiple tablets of Levodopa every day to keep their motor features under control. And long term this approach can result in other complications, such as Levodopa-induced dyskinesias in the case of Parkinson’s.
Yeah, but is there a better approach?
Some researchers believe there is. But we are not quite there yet with the application of that approach. Let me explain: