Evaluating the long-term safety of lentiviral gene therapy in SCA3 mice

Written by Dr. Ambika Tewari Edited by Dr. Hayley McLoughlin

Lentiviral expression of an shRNA against ataxin-3 was well-tolerated and produced no measurable adverse effects in wild-type mice.

Evaluating the safety profile is a necessary and crucial step in qualifying a therapy for use in patients. Gene therapy is an experimental technique that has demonstrated tremendous progress in the treatment or reversal of a disease, specifically monogenic disorders. Carefully investigating the safety and tolerance of gene therapy is important to gauge its suitability for clinical trials. Gene therapy tools can be used in different ways to achieve the same therapeutic effect: the faulty gene can be replaced with a healthy copy, the mutated gene can be repaired, or the mutant copy of the gene can be silenced. You can learn more about gene therapy in this pat SCAsource Snapshot.

Spinocerebellar ataxia type 3 (SCA3) or Machado-Joseph disease (MJD) causes progressive loss of neurons in the spinal cord, and several regions of the brain. This includes the cerebellum, brainstem, striatum and substantia nigra. These neurons have crucial functions. Without these neurons, patients experience motor incoordination, loss of balance, and in severe cases, premature death. While great progress continues to be made in understanding how a mutation in a single gene, Ataxin-3, causes the symptoms of SCA3, there is still no treatment to stop the disease progression. As a monogenic disorder, SCA3, like other Spinocerebellar ataxias (SCA), is a promising candidate for gene therapy. While there are no approved gene therapies for SCA yet, there any several research labs and companies working towards achieving this goal.

An artist's drawing of scientists standing infront of a giant piece of DNA and drugs
This is truly an exciting time for gene therapy, but it is also important to keep the safety of patients a top priority. Photo used under license by Visual Generation/Shutterstock.com.

The researchers in this study have been working on gene therapy for SCA3 since 2008. They have researched how gene therapy could offer protection against further decline, in several cell and mouse models of SCA3. They used an approach where they decreased the levels of the mutant Ataxin-3 gene while leaving the normal Ataxin-3 gene intact. This is known as allele-specific targeting. They demonstrated that using this technique, they could significantly reduce the behavioral and neuropathological changes that occur in SCA3 mice. Mice treated with the gene therapy showed improvements in their balance and motor coordination. 

Gene therapy in its most basic form involves two components, the gene that will replace or remove the diseased gene and a vector that will transport this new gene to its site of action. The most commonly used vectors today are adeno-associated virus (AAVs) followed by retrovirus. These viruses have been specifically engineered to deliver their passenger to the specified location. While both vectors have been through several years of preclinical and clinical testing for numerous gene therapy candidates, there are questions that remain regarding their safety. (1) Does the gene therapy product continue to be expressed in the targeted area long-term; (2) If there is long-term expression does it cause any adverse measurable effects to the targeted area; (3) Does the long-term expression affect the normal functioning of the targeted cells/organ.

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Spotlight: The Zoghbi Lab

Baylor College of Medicine

Principal Investigator: Dr. Huda Zoghbi

Location: Baylor College of Medicine and Texas Children’s Hospital, Houston, TX, USA

Year Founded:  1988

Logo: Texas Children's Hospital. Jan and Dan Duncan Neurological Research Institute

What models and techniques do you use?

Research Focus

What is your research about?

Our laboratory uses multiple methods to explore the underlying causes of different neurodegenerative and neurodevelopmental disorders. Some diseases we study affect children, like Rett Syndrome. Others affect adults, like spinocerebellar ataxia type 1 (SCA1), Alzheimer’s disease (AD) and Parkinson’s disease (PD). We also research how healthy brains grow and develop.

We first seek to understand the mechanism by which a mutant protein causes disease, allowing us to more thoughtfully and effectively develop therapeutic options for the diseases we study. Our work in SCA1 demonstrated that lowering levels of the disease-driving protein is beneficial in the course of disease, informing our approach to the study of other diseases of the brain.  

Why do you do this research?

We do this research to help the patients, families and caregivers affected by the diseases we study. Most of the disorders we study currently have no or very few treatment options available, and we hope to help in changing that.

Our lab began with Dr. Zoghbi seeing patients in the clinic who were diagnosed with Rett Syndrome and SCA1. Work with these patients allowed for the discovery of the genes causing these diseases. Today, we hope to aid in understanding how these diseases work and to develop therapies that can then be brought back to the clinic for patients. Furthermore, we hope our findings and the tools we’ve developed will aid in the study of other neurodevelopmental and neurodegenerative disorders.

A group picture of the Zoghbi Lab
Zoghbi Lab members at Hermann Park in Houston, TX in 2021. Bottom row L-R: Y. Sun, W. Wang, W. Lee, M. Zaghlula, H. Lee, S. Coffin, S. Wu, J. Butts, C. Adamski, H. Zoghbi (PI), Y. Shao, J. Johnson, J. Zhou, A. Tewari, H. Palikarana Tirumala, J. Lopez, Top row L-R: A. Anderson, E. Xhako, E. Villavicencio, Y. Li, S. Bajikar, M. Durham.

Fun Fact

On April 8, 1993, both Dr. Huda Zoghbi and Dr. Harry Orr identified the gene, ATXN1, which when mutated, is responsible for causing SCA1. You can read about this discovery here.

For More Information, check out the Zoghbi Lab website!


Written by Stephanie Coffin, Edited by Celeste Suart

Identifying FDA-approved molecules to treat SCA6

Written by Dr Hannah Shorrock Edited by Dr. Larissa Nitschke

Pastor and colleagues identify FDA-approved small molecules that selectively reduce the toxic polyglutamine-expanded protein in SCA6.

Selectively targeting disease-causing genes without disrupting cellular functions is essential for successful therapy development. In spinocerebellar ataxia type 6 (SCA6), achieving this selectivity is particularly complicated as the disease-causing gene produces two proteins that contain an expanded polyglutamine tract. In this study, Pastor and colleagues identified several Food and Drug Administration (FDA) approved small molecules that selectively reduce the levels of one of these polyglutamine-containing proteins without affecting the levels of the other protein, which is essential for normal brain function. By using drugs already approved by the United States Food and Drug Administration to treat other diseases, referred to as FDA-approved drugs, the team hopes to reduce the time frame for pre-clinical therapy development.

SCA6 is an autosomal dominant ataxia that causes progressive impairment of movement and coordination. This is due to the dysfunction and death of brain cells, including Purkinje neurons in the cerebellum. SCA6 is caused by a CAG repeat expansion in the CACNA1A gene. CACNA1A encodes two proteins: the a1A subunit, the main pore-forming subunit of the P/Q type voltage-gated calcium ion channel, as well as a transcription factor named a1ACT.

The a1A subunit is essential for life. Its function is less affected by the presence of the expanded polyglutamine tract than that of a1ACT. The transcription factor, a1ACT, controls the expression of various genes involved in the development of Purkinje cells. Expressing a1ACT protein containing an expanded polyglutamine tract in mice causes cerebellar atrophy and ataxia. While reducing levels of the a1A subunit may have little effect on SCA6 disease but impact normal brain cell function, reducing levels of a1ACT may improve disease in SCA6. Therefore, Pastor and colleagues decided to test the hypothesis that selectively reducing levels of the a1ACT protein without affecting levels of the a1A protein may be a viable therapeutic approach for SCA6.

Colorful pile of medicines in blister packs which color are White, Yellow, Black and Pink pills.
By using drugs already approved by the FDA, the team hopes to reduce the time frame for pre-clinical therapy development. Photo used under license by Wanchana Phuangwan/Shutterstock.com.
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El BDNF puede revertir la ataxia en ratones SCA1

Escrito por Anna Cook Editado por Dr. David Bushart. Publicado inicialmente en el 19 de Marzo de 2021. Traducción al español fueron hechas por FEDAES y Carlos Barba.

El factor neurotrófico derivado del cerebro -BDNF- puede prevenir la ataxia en ratones SCA1. Una nueva investigación muestra que el tratamiento funciona incluso si se inicia después de que los ratones desarrollan signos de ataxia.

SCA1 es una enfermedad neurodegenerativa causada por una mutación en el gen Ataxin1 . Las personas con SCA1 a menudo desarrollan síntomas alrededor de los 30-40 años, aunque esto puede variar. Los síntomas más comunes incluyen ataxia o problemas de movimiento que dificultan moverse y caminar. Estos síntomas empeoran progresivamente y eventualmente provocan problemas para tragar o hablar. Actualmente no existe cura para SCA1, por lo que es importante que se realicen investigaciones sobre posibles tratamientos.

El laboratorio de la Dra. Marija Cvetanovic de la Universidad de Minnesota ha estado utilizando un modelo de ratón de SCA1 para tratar de identificar nuevos tratamientos. En el pasado, estos investigadores han demostrado que una molécula llamada factor neurotrófico derivado del cerebro (BDNF) podría retrasar la aparición de ataxia en un modelo de ratón de SCA1.

A laboratory mouse sitting on a researcher's hand.
La investigación con ratones SCA1 muestra que el tratamiento con BDNF puede tener un impacto, incluso después de que comienzan a aparecer los síntomas de la ataxia.. Foto utilizada bajo licencia por unoL/Shutterstock.com.

El BDNF es una molécula que se encuentra en el cerebro y es muy importante para el desarrollo saludable del cerebro. Es necesario para que muchos procesos del cerebro funcionen con normalidad. Los investigadores demostraron que los niveles de BDNF se redujeron en los cerebros de los ratones SCA1. Los investigadores inyectaron BDNF en los cerebros de estos ratones para intentar compensar el BDNF perdido. Este tratamiento, antes de que los ratones comenzaran a desarrollar síntomas de ataxia, previno la aparición de problemas motores y la muerte de las células de Purkinje.

Este trabajo anterior fue muy prometedor, pero había un problema. En este estudio, el tratamiento solo se probó antes de que los ratones SCA1 desarrollaran signos de problemas motores o cambios en sus cerebros. En el mundo real, si queremos ayudar a los pacientes con SCA1, necesitamos tratamientos que funcionen incluso una vez que la enfermedad haya comenzado a progresar. Por lo tanto, era importante que los investigadores averiguaran si este tratamiento funcionaría más adelante en la progresión de la enfermedad. Eso es exactamente lo que hicieron a continuación: en diciembre de 2020, el laboratorio de Cvetanovic publicó los resultados de su estudio que probaba el BDNF como tratamiento después de que los ratones habían comenzado a desarrollar signos de SCA1.

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Eliminación de la proteína ataxina-2 agregada como vía terapéutica para SCA2

Escrito por el Dr. Vitaliy Bondar Editado por el Dr. Hayley McLoughlin. Publicado inicialmente en el 5 de febrero de 2021. Traducción al español fueron hechas por FEDAES y Carlos Barba.

Una nueva investigación sugiere que la proteína ataxina-2 mutante abruma a las células en SCA2, lo que lleva a una disminución de la autofagia y la eliminación de las proteínas dañadas.

Se pueden hacer muchas comparaciones entre células y seres humanos. Al igual que los humanos, las células pueden acumular basura y desechos en ciertos momentos y este desorden con el tiempo se vuelve problemático e incluso tóxico. Esto es precisamente lo que Jonathan Henry Wardman y sus colegas de la Universidad de Copenhague decidieron investigar a nivel celular. Preguntaron si la falta de una eliminación adecuada de las proteínas defectuosas de la enfermedad afecta la supervivencia y el bienestar celular.

Los investigadores optaron por estudiar células derivadas de un paciente que tiene ataxia espinocerebelosa tipo 2 (SCA2). La causa de SCA2 es la expansión de la repetición CAG en el gen ATAXIN-2 , que codifica la cadena de aminoácidos de poliglutamina en una proteína de unión al ARN , ataxina-2. Se encuentra que la proteína ATXN2 expandida poliQ defectuosa se agrega dentro de la célula y las horas extraordinarias pueden afectar su supervivencia. La acumulación de productos proteicos agregados derivados de genes mutados es un sello distintivo de muchos tipos de ataxias espinocerebelosas, así como de otras formas de trastornos neurodegenerativos como la enfermedad de Parkinson.

No está claro cómo la agregación de proteínas afecta la supervivencia celular. Sin embargo, se han correlacionado múltiples defectos celulares con la agregación de ataxina-2. Por ejemplo, se ha informado que las mitocondrias que generan energía para una célula funcionan de manera anormal en modelos celulares SCA2. Además, un mecanismo de depuración celular, llamado autofagia , que es responsable de limpiar los compartimentos celulares defectuosos y ciertas proteínas rotas, se muestra menos eficaz en varios modelos de SCA2. Estos mecanismos los autores decidieron investigar en su artículo de investigación recientemente publicado.

scientist using microscope
Una nueva investigación que utiliza células SCA2 arroja luz sobre las causas de los síntomas de la enfermedad. Foto de Chokniti Khongchum en Pexels.com

Los científicos identificaron por primera vez la evidencia de disfunción celular SCA2 mediante la detección de una elevación significativa de los niveles de caspasa-9 y caspasa-8. Son proteínas que indican estrés celular y muerte. Los autores plantearon la hipótesis de que dicha disfunción celular puede deberse a la acumulación de ataxina-2 defectuosa. Para probar esta hipótesis, decidieron bloquear sistemáticamente dos vías celulares que procesan proteínas defectuosas: proteostasis y autofagia.

Continue reading “Eliminación de la proteína ataxina-2 agregada como vía terapéutica para SCA2”