BDNF can reverse ataxia in SCA1 mice, even after symptom onset

Written by Anna Cook Edited by Dr. David Bushart

Brain-derived neurotrophic factor can prevent ataxia in SCA1 mice. New research shows that the treatment works even if it’s started after mice develop signs of ataxia.

SCA1 is a neurodegenerative disease caused by a mutation in the Ataxin1 gene. People with SCA1 often develop symptoms around 30-40 years old, although this can vary. The most common symptoms include ataxia, or movement problems that make it difficult to move and walk. These symptoms get progressively worse, eventually leading to problems with swallowing or speaking. There is currently no cure for SCA1 so it is important that research is conducted into potential treatments.

The lab of Dr. Marija Cvetanovic at the University of Minnesota has been using a mouse model of SCA1 to try to identify new treatments. In the past, these researchers have shown that a molecule called brain-derived neurotrophic factor (BDNF) could delay the onset of ataxia in a mouse model of SCA1.

A laboratory mouse sitting on a researcher's hand.
Research using SCA1 mice shows that BDNF treatment can have an impact, even after ataxia symptoms begin showing. Photo used under license by unoL/Shutterstock.com.

BDNF is a molecule found in the brain that is very important for healthy brain development. It is needed to keep many processes in the brain working normally. The researchers showed that levels of BDNF were reduced in the brains of SCA1 mice. The researchers injected BDNF into the brains of these mice to try to make up for the lost BDNF. This treatment, before the mice had begun to develop symptoms of ataxia, prevented the onset of motor problems and Purkinje cell death. You can read more about those findings in this past SCASource article.

This previous work was very promising, but there was one problem. In this study, the treatment was only tested before the SCA1 mice developed signs of motor problems or changes in their brains. In the real world, if we want to help SCA1 patients, we need treatments that will work even once the disease has started to progress. It was therefore important for the researchers to find out whether this treatment would work later in disease progression. That is exactly what they did next: In December 2020, the Cvetanovic lab published the results from their study testing BDNF as a treatment after mice had started to develop signs of SCA1.

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A new molecule identified that controls cerebellar communication

Written by Dr. Ambika Tewari Edited by Dr. Sriram Jayabal

Targeting phosphatases in the cerebellum can correct miscommunication in multiple models of ataxia.

The cerebellum is essential for motor coordination and consists of the coordinated activity of different types of cells. Purkinje cells are one of the most fascinating cell types in the cerebellum. They have an elaborate network of branches called dendrites, where a neuron receives communication from other neurons. It is one of the most complex branching systems seen across all neurons in the entire brain. Each one of these branches has many points of contact with other branches called axons. Each axon is part of a neuronal structure that allow communication between neurons. These axons are from different cell types and allow information to be transferred to Purkinje cells.

Colourful illustration of a human brain
Targeting phosphatases in the brain could improve communication between neurons, reducing ataxia symptoms.

Due to this branching complexity, Purkinje cells receive many messages or inputs. This represents different pieces of sensory information to ensure that movements are precisely timed. Purkinje cells must integrate and process this information. This produces motor behaviors like walking, writing, playing a musical instrument, and many more. Any alteration to the processing of this information will result in cerebellum dysfunction; in fact, Purkinje cells have gained attention because they undergo progressive deterioration in most ataxias. 

Neurons, including Purkinje cells, communicate with other neurons using electrical signals known as action potentials or spikes. Firing rate, defined as the number of spikes within a defined period of time, is thought to be an important feature of this communication, which is critical for coordinating muscle movements. Therefore, a lower firing rate in Purkinje cells would signal a faulty communication between Purkinje cells and their targets. This has devastating consequences as seen in many ataxias.

For instance, in an earlier study, a group of authors found that the firing rate of Purkinje cells was decreased in mouse models of three different Spinocerebellar ataxias (SCAs): SCA1, SCA2, and SCA5. They further explored whether there was a common reason underlying the decreased firing rate. They found that a protein named Missing in Metastasis (MTSS1), was important for Purkinje cells to effectively communicate with each other. Mice engineered to have no MTSS1 protein had a decreased firing rate and difficulty walking and maintaining their balance.

In every cell in the body, including brain cells, there are numerous proteins that perform different functions. The concerted effort of all are needed for the cell to perform its intended duty. Some of these proteins are maintained in the cell in an inactive form and are activated when they are required in the cell and inhibited when they are not. This highly regulated system aims to maintain precise levels of proteins in each cell, while simultaneously conserving energy. Each cell has many ways of activating/inactivating a protein. A specialized group of proteins known as kinases and phosphatases, adds and removes phosphate groups to and from proteins respectively, thereby altering their active/inactive forms which then changes their interactions with other proteins. MTSS1 is one such protein that inhibits the activity of a group of kinases known as Src family of non-receptor tyrosine kinases (SFKs).

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Mutated ataxin-1 protein forms harmful, doughnut-shaped aggregates that are not easily destroyed

Written by Brenda Toscano Marquez   Edited by Marija Cvetanovic

Insoluble clumps of mutated ataxin-1 capture essential proteins and trigger the creation of toxic reactive oxygen species.

All proteins produced by our cells consist of long chains of amino acids that are coiled and bent into a particular 3D structure. Changes in that structure can cause serious issues in a cell’s function, sometimes resulting in disease. Spinocerebellar ataxia type 1 (SCA1) is thought to be the result of one such structural change. The cause of SCA1 is a mutation that makes a repeating section of the ATXIN1 gene abnormally long. This repeated genetic code, “CAG,” is what encodes the amino acid glutamine in the resulting ataxin-1 protein. Therefore, in the cells of patients with SCA1, the Ataxin-1 protein is produced with an expanded string of glutamines, one after the other. This polyglutamine expansion makes the mutated ataxin-1 protein form clumps in many different types of cells – most notably, though, in the cells most affected in SCA1: the brain’s Purkinje cells.

Recent research suggests that these clumps, or “aggregates,” not only take up space in the cell, but that the act of ataxin-1 proteins clustering together might even be beneficial in early stages of disease (it’s possible that the proteins wreak less havoc when they’re in large clumps, rather than all floating around individually). However, another line of research suggests that ataxin-1 aggregates might also be toxic, triggering signals that lead to the cell’s death. As such, how exactly these aggregates affect the deterioration of cells has remained an important question in SCA1 research.

n a search for answers, an international team led by Stamatia Laidou designed a unique cell model of SCA1 to track the development of ataxin-1 aggregates. Their study, published in a recent paper, made use of normal human mesenchymal stem cells that had been engineered to make a modified version of the ataxin-1 protein. In these cells, ataxin-1 was produced not only with the SCA1-causing expansion, but also with a marker protein attached to its end. This marker, known as “green fluorescent protein” (GFP), is used extensively in biological research because it glows under fluorescent light.

doughnut with white and pink sprinkles
Laidou and colleagues have observed mutated ataxin-1 clumps that cause cell stress. Photo by Tim Gouw on Pexels.com

Using this to their advantage, Laidou and her team used a fluorescent microscope to follow the formation of ataxin-1 aggregates over the course of 10 days. The abnormal protein first started accumulating in the nucleus as small dots. As time went on, these dots started blending together, increasing in size. By ten days, the ataxin-1 aggregates had grown even more, forming a doughnut-shaped structure that occupied most of the cell’s nucleus – a crucial structure that houses the cell’s genetic information. These results were intriguing, since the accumulation of normal, non-expanded Ataxin-1 protein does not result in an aggregate with a doughnut shape.

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Spotlight: The Watt Lab

Watt lab logo of a neuron

Principal Investigator: Dr. Alanna Watt

Location: McGill University, Montreal, Canada

Year Founded: 2011

What disease areas do you research?

What models and techniques do you use?

Research Focus

What is your research about?

We are interested in how the cerebellum influences motor coordination in both the healthy brain and in models of disease and aging. By identifying changes in the cerebellum underlying ataxias and aging, we hope to discover new treatments for patients.

Why do you do this research?

We want to understand how the cerebellum works and use this knowledge to understand the changes in the cerebellum that lead to ataxia. As a lab, we are particularly interested in studying rare disorders like SCA6 and ARSACS.

These disorders have limited treatment options. We hope that by understanding how the cerebellum works differently in these disorders, we will be able to identify new treatments to help ataxia patients.

We are also interested in identifying common changes between different types of ataxia, to find out whether treatments identified in one form of ataxia might also help other ataxia patients.

Six slippers with a variety of designs, includes brain cells and mice

Fun Lab Fact

We got together and made our own slippers to keep cozy in our office. If you look at the picture closely you might be able to spot some cells from the cerebellum on some of them!

Image courtesy of Anna Cook.

For More Information, check out the Watt Lab Website!


Written by The Watt Lab, Edited by Celeste Suart

A New Use for Old Drugs

Written by Dr. Amy Smith-Dijak Edited by Logan Morrison

Basic biology helps identify a new treatment for ataxia

Drug design doesn’t always have to start with a blank slate. Sometimes understanding how existing drugs work can help researchers to design new ones, or even to recombine old drugs in new and more effective ways. That’s what the researchers behind this paper did. They investigated the basic biology of three existing drugs: chlorzoxazone, baclofen, and SKA-31.

Two of these – chlorzoxazone and baclofen – are already FDA-approved for use as muscle relaxants, and chlorzoxazone had previously been found to have a positive effect on eye movements in spinocerebellar ataxia type 6. Looking at the results of their experiments, they realized that a combination of chlorzoxazone and baclofen would probably be an effective treatment for ataxia over a long period. They offered this drug combination to patients, who had few adverse effects and showed improvement in their diseasesymptoms. Based on these findings, the researchers recommended that larger trials of this drug combination should be conducted and that people trying to design new drugs to treat ataxia should try to interact with the same targets as chlorzoxazone.

mutliple types of drugs in pill form scattered ac
Can old drugs have potential for new types of treatment? Photo by Anna Shvets on Pexels.com.

When this paper’s authors started their research, they wanted to know more about how ataxia changes the way that brain cells communicate with each other. Brain cells do this using a code made up of pulses of electricity. They create these pulses by controlling the movement of electrically charged atoms known as ions. The main ions that brain cells use are potassium, sodium, calcium and chloride. Cells control their movement through proteins on their surface called ion channels which allow specific types of ions to travel into or out of the cell at specific times. Different types of cells use different combinations of ion channels, which causes different types of ions to move into and out of the cell more or less easily and under different conditions. This affects how these cells communicate with each other.

For example, a cell’s “excitability” is a measure of how easy it is for that cell to send out electrical pulses. Creating these pulses depends on the right ions entering and exiting the cell at the right time in order to create one of these pulses. Multiple types of spinocerebellar ataxia seem to make it difficult for Purkinje cells, which send information out of the cerebellum, to properly control the pattern of electrical signals that they send out. This would interfere with the cerebellum’s ability to communicate with the rest of the brain. The cerebellum plays an important roll in balance, posture and general motor coordination, so miscommunication between it and the rest of the brain would account for many of the symptoms of spinocerebellar ataxias.

Earlier research had found a link between this disrupted communication and a decrease in the amount of some types of ion channels that let potassium ions into Purkinje cells. Thus, this paper’s authors wanted to see if drugs that made the remaining potassium channels work better would improve Purkinje cell communication.

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