2 minuti di Scienza: Cosa sono I nucleotidi antisenso?

I nucleotidi anti-senso (anche noti come ASOs o AON, dall’inglese Antisense oligonucleotides) sono piccole molecole che possono essere usate per prevenire o alterare la produzione di proteine. Le proteine sono la forza lavoro della cellula, e dirigono la maggior parte dei processi cellulari. Le proteine sono prodotte in due fasi: nella prima un gene che codifica per una proteina viene convertito in una molecola che contiene specifiche istruzioni, l’RNA messaggero (mRNA). L’ mRNA trasferisce l’informazione contenuta nei geni al compartimento che assembla le proteine. Qui, l’mRNA è infine trasformato in proteina. Gli ASOs sono corte sequenze di DNA a singolo filamento, complementari alla sequenza di uno specifico mRNA. In base a diversi tipi di modifiche chimiche della loro sequenza, gli ASOs possono determinare due tipi di effetti sull’ mRNA complementare. Alcune modifiche fanno si che gli ASO distruggano l’mRNA e, di conseguenza, causano la perdita della proteina corrispondente. Altre modifiche, invece, permettono agli ASO di mascherare certi tratti dell’mRNA bersaglio, causando la produzione di una versione alterata della proteina.

Come funzionano gli ASO nel corpo umano. Autore della figura Larissa Nitschke, creato con BioRender.

La maggior parte delle Atassie spinocerebellari (dall’inglese Spinocerebellar Ataxias, SCAs) sono causate dall’accumulazione di una proteina tossica in una specifica regione del cervello. Per questo motivo, il principale obiettivo del trattamento delle SCAs con gli ASOs è inibire la produzione della proteina tossica. Un esempio di questa applicazione degli ASO è il lavoro del Prof. Harry Orr all’ Università del Minnesota. Il suo gruppo di ricerca studia l’Atassia spinocerebellare di tipo 1 (SCA1), causata dall’accumulo tossico della proteina Ataxina-1. Iniezioni di ASOs in modelli animali di SCA1 riducono i livelli di Ataxina-1 e migliorano l’incoordinazione motoria tipica della SCA1. Un altro modo di usare gli ASOs per il trattamento delle SCAs è la modifica dell’informazione trasmessa dall’mRNA per produrre una versione alterata della proteina. Questo approccio è stato testato nel caso della Atassia spinocerebellare di tipo 3 (SCA3), nella quale un’espansione nel gene Atxn3 rende la proteina Ataxina 3 tossica. Il gruppo del Dr. van Roon-Mom, in Olanda, per esempio, ha usato gli ASOs per rimuovere esclusivamente la porzione espansa della proteina Atxn3, lasciando intatta il resto della struttura proteica e la sua funzione.

Entrambi gli studi, così come altri studi portati avanti per altre SCAs, hanno evidenziato il potenziale uso degli ASOs come strumenti terapeutici per le SCAs. Mentre la ricerca sugli ASOs per le SCAs è per lo più nella fase preclinica, il trattamento con gli ASO per altre malattie, come la Distrofia Muscolare di Duchenne e l’atrofia muscolare spinale, è stato già approvato dall’ente statunitense Food and Drug Administration. Ulteriori studi clinici saranno necessari per misurare il beneficio terapeutico degli ASOs in pazienti di SCAs.

Per saperne di più sugli oligonucleotidi antisenso, leggi questo articolo alla pagina  HDBuzz sugli ASOs in via di sviluppo per la malattia di Huntington.

“2 minuti di Scienza” scritto da Dr. Larissa Nitschke, revisionato da Dr. Hayley McLoughli, tradotto in italiano da Dr. Antonia De Maio. Pubblicato per la prima volta il 31 Maggio 2019.

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).

Continue reading “A new molecule identified that controls cerebellar communication”

Spotlight: The Neuro-D lab Leiden

Principal Investigator: Dr. Willeke van Roon-Mom

Location: Leiden University Medical Centre, Leiden, The Netherlands

Year Founded: 1995

What disease areas do you research?

What models and techniques do you use?

A group photo of members of the Neuro-D lab Leiden standing outside on a patio.
This is a group picture taken during our brainstorm day last June. From left to right: Boyd Kenkhuis, Elena Daoutsali, Tom Metz, Ronald Buijsen, Willeke van Roon-Mom (PI), David Parfitt, Hannah Bakels, Barry Pepers, Linda van der Graaf and Elsa Kuijper. Image courtesy of Ronald Buijsen.

Research Focus

What is your research about?

The Neuro-D research group studies how diseases develop and progress at the molecular level in several neurodegenerative diseases. They focus on diseases that have protein aggregation, where the disease proteins clump up into bundles in the brain and don’t work correctly.

We focus strongly on translational research, meaning we try to bridge the gap between research happening in the laboratory to what is happening in medical clinics. To do this we use more “traditional” research models like animal and cell models. But we also use donated patient tissues and induced pluripotent stem cell (iPSC) models, which is closer to what is seen in medical clinics.

Our aim is to unravel what is going wrong in these diseases, then discover and test potential novel drug targets and therapies.

One thing we are doing to work towards this goal is identifying biomarkers to measure how diseases progress over time. To do this, we use sequencing technology and other techniques to look at new and past data from patients.

Why do you do this research?

So far there are no therapies to stop the progression of ataxia. If we can understand what is happening in diseases in individual cells, we can develop therapies that can halt or maybe even reverse disease progression.

Identifying biomarkers is also important, because it will help us figure out the best time to treat patients when we eventually have a therapy to test.

Stylized logo for the Dutch Center for RNA Therapeutics
The Neuro-D lab Leiden is part of the Dutch Center for RNA Therapeutics, which focuses on RNA therapies like antisense oligonucleotides. Logo designed by Justus Kuijer (VormMorgen), as 29 year old patient with Duchenne muscular dystrophy.

Are you recruiting human participants for research?

Yes, we are! We are looking for participants for a SCA1 natural history study and biomarker study. More information can be found here. Please note that information about this study is only available in Dutch.

Fun Fact

All our fridges and freezers have funny names like walrus, seal, snow grouse and snowflake.

For More Information, check out the Neuro-D lab Leiden website!


Written by Dr. Ronald Buijsen, Edited by Celeste Suart

Fishing for a solution to SCA38 – are omega-3 fatty acids the key to symptom relief?

Written by Dr. Siddharth Nath Edited by Dr. Sriram Jayabal

SCA38 results in a deficiency of an omega-3-fatty acid called docosahexaenoic acid (DHA). Scientists from Italy had shown previously that short-term DHA supplementation reduces disease symptoms. Now, new research from the same group finds that this impact continues with long-term DHA supplementation.

What is SCA38?

One of the rarer forms of ataxia, SCA38 is an autosomal dominant SCA that occurs as a result of mutations in the ELOVL5 gene. This gene contains the recipe for the protein called elongase. It is responsible for building long-chain fatty acids in the brain, including docosahexaenoic acid (DHA), a process key for normal cellular function. Importantly, this protein is found mostly in Purkinje cells, a special type of neuron found within the cerebellum of the brain.

In SCA38, mutant elongase is found primarily in a part of the cell called the Golgi apparatus, which is responsible for packaging proteins and finalizing production, similar to a quality-control technician in an assembly line. Normally, elongase is found at the endoplasmic reticulum, which is further up the assembly line, more akin to the fabrication section.

This mislocation of the protein may explain why it is unable to produce sufficient amounts of long-chain fatty acids to support healthy Purkinje cell function. Deficiencies in DHA resulting from mutations in elongase are detectable by blood tests.

spilled bottle of yellow capsule pills
Photo by Pixabay on Pexels.com

Docosahexa-what?

You’ve probably heard of omega-3-fatty acids. Omega-3 fatty acids are part of a larger group of molecules called polyunsaturated fatty acids to which the omega-6 fatty acids also belong. DHA is a type of omega-3 fatty acid. Omega-3 fatty acids and omega-6 fatty acids are often touted as a key component of a healthy diet.

Omega-3-fatty acids are important building blocks of the cellular membrane, which is part of all cells in the body. Humans aren’t able to make omega-3-fatty acids ourselves, we need to get them from our diet. That is why many food guides have recommended intakes of omega-3 and omega-6 fatty acids from oily fish and nuts. Vegetarians can also supplement their diet with flaxseed or algae capsules to get these fatty acids in their diet.

DHA is just one of many omega-3-fatty acids and it is most prevalent in the membranes of brain cells, where it plays a key role in normal brain function. Thus, when there is a disturbance or deficiency in the level of DHA, we can expect brain function to become impaired, as is the case in SCA38.

Continue reading “Fishing for a solution to SCA38 – are omega-3 fatty acids the key to symptom relief?”

Snapshot: What are Intrathecal Injections?

Drug delivery into the body can be achieved in several ways, from applying a medicated cream on the skin, to swallowing a pill, to injecting into a muscle or vein. Each route of delivery should at least achieve one thing – getting the drug to the part of the body where it can be helpful. Delivering therapeutic drugs into the brain, however, can be more difficult. Intrathecal injections are used to overcome this challenge.

Cartoon drawing of a woman's back, her hand resting on her lower back.
How do you get drugs to the brain? Through the back!

When a drug enters the body, it travels through the bloodstream until it reaches the target organs. But when a drug is destined to reach the brain, it needs to pass through a unique security feature known as the blood-brain barrier. The blood-brain barrier is important for keeping harmful and unknown substances out of the brain. It turns out that the majority of drugs injected into the body cannot pass this barrier. This poses a challenge for researchers and doctors for delivering important drug treatments to the brain.

One way that drugs can be delivered to the brain via the blood is by modifying their chemical nature slightly. This can help with entry through the blood-brain barrier. A more straightforward route of delivery is by injecting drugs into the brain space directly. Your brain inside your head and spinal cord along your back are bathed in and float in a liquid called cerebrospinal fluid (CSF).

CSF is a clear, colourless fluid that protects the brain from injury by absorbing shock, and it helps bring waste products out of the brain. Importantly, as CSF flows, it helps distribute substances around the brain. Injecting a drug directly in the CSF allows that drug to bypass the blood-brain barrier. One of the less invasive ways to access the CSF space is via injection through the thecal sac, the cushiony layer containing CSF that surrounds the spinal cord. This type of injection is therefore known as an “intrathecal injection”.

Intrathecal injections are injected into the cerebrospinal fluid around the spinal cord around the thacal sac (mid-back area). The injected drug then travels up the back to the brain.
A diagram of how intrathecal injections work. Image by Claudia Hung.

Intrathecal injections can be very helpful. They are used during surgeries to manage pain (spinal anaesthesia) and to deliver chemotherapeutic agents to target brain cancers. Intrathecal injections becoming an increasingly important route of administration for drugs investigated in neurodegenerative diseases, such as Huntington’s disease, Alzheimer’s disease, ALS, spinal muscular atrophy (SMA), and spinocerebellar ataxias (SCAs). These drugs include antisense oligonucleotides that can be delivered directly to the brain.

However, there are still a few challenges in giving medication through intrathecal injections:

  • Medication delivered by intrathecal injections may need to be given quite often. Since the CSF is replenished regularly, the substances are cleared quickly out of the brain and spinal cavity.
  • Intrathecal injections involve a needle being inserted into the spine. So they are more invasive and painful than a typical shot or swallowing a pill. This is especially true if multiple injections are needed.

Therefore, researchers and doctors are constantly trying to learn more about how drugs enter the brain. By studying this, they will make improvements in how medication is delivered to patients. Despite these challenges though, intrathecal injections are a clever and important way for delivering critical drugs to the brain to treat a wide range of diseases.

If you would like to learn more about intrathecal injections, take a look at these resources by the Allina Health and Cancer Research UK.

Snapshot written by Claudia Hung and edited by Judit M. Pérez Ortiz