Tagged: Huntingtin

Making sense of antisense

 

Recent regulator approvals and exciting new preclinical data has refocused attention on a treatment approach for genetic conditions that has travelled a long and winding road towards clinical use.

Antisense oligonucleotides represent a method of altering protein levels at the post transcriptional level – it basically stops certain RNAs from being translated into protein.

And recently, a new clinical trial has been registered which will explore the use of this treatment approach in people with Parkinson’s.

In today’s post, we will look at what antisense oligonucleotides are, how they work, what research has been conducted in the context of Parkinson’s, and some of the limitations of this approach that still exist.

 


Source: Youtube

Spinal muscular atrophy (or SMA) is a genetic disorder that results in the degeneration of motor neurons in the spinal cord. This leads to progressive weakening and atrophy of muscules, ultimately leaving sufferers paralysed. It is caused by loss-of-function mutations in the survival motor neuron 1 (SMN1) gene.

It is a terrible condition that starts in very young children and has an incidence approaching 1:10,000 live births.

Luckily, novel therapies are being developed to deal with this condition, and in 2016, the US FDA approved a new treatment – following rather dramatic clinical trial results – called Nusinersen. This new therapy has caused a great deal of excitement as it basically halted the progression of SMA in many cases.

And a recent long term report highlights some of these very impressive results:

Title: Nusinersen in later-onset spinal muscular atrophy: Long-term results from the phase 1/2 studies.
Authors: Darras BT, Chiriboga CA, Iannaccone ST, Swoboda KJ, Montes J, Mignon L, Xia S, Bennett CF, Bishop KM, Shefner JM, Green AM, Sun P, Bhan I, Gheuens S, Schneider E, Farwell W, De Vivo DC; ISIS-396443-CS2/ISIS-396443-CS12 Study Groups.
Journal: Neurology. 2019 May 21;92(21):e2492-e2506.
PMID: 31019106                (This report is OPEN ACCESS if you would like to read it)

Most importantly, Nusinersen is having real impact on the children who are affected by this condition:

Interesting, but what exactly is Nusinersen?

It is an antisense oligonucleotide.

What are antisense oligonucleotides?

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TRIMming aggregates

 

Novel methods for treating neurodegenerative conditions are being proposed on a weekly (sometimes daily) basis.

Recently researchers from the University of Cambridge have presented an intriguing new method of removing proteins from inside of cells which involves small proteins called antibodies.

Antibodies are an important part of the immune systems response to infection. But their function usually only applies to objects floating around outside of cells. 

In today’s post, we will look at what antibodies are, explain how this new system works, and discuss some of the issues we face with taking this new technique forward.


A brain cell from a person with Alzheimer’s. The red tangles in the yellow cell body are toxic misfolded “TAU” proteins next to the cell’s green nucleus. Source: NPR

Here at the SoPD, we often talk about the clustering (or aggregation) of proteins.

Densely packed aggregates of a protein are a common feature of many neurodegenerative conditions, including Parkinson’s.

In fact, the aggregation of a protein called alpha synuclein are one of the cardinal features of the Parkinsonian brain.

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Aggregated alpha synuclein protein in the Parkinsonian brain (stained in brown). Source: Wikimedia

Researchers have long been devising new ways of trying to reduce the amount of alpha synuclein collecting in the brain cells of people with Parkinson’s.

In most cases, their efforts have focused on utilising the cell’s own waste disposal systems.

How do cells dispose of waste?

There are two major pathways by which the cells in your body degrade and remove rubbish:

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“Three hellos” for Parkinson’s

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.

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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

Alpha-synuclein is actually a very common protein in the brain – it makes up about 1% of the material in neurons (and understand that there are thousands of different proteins in a cell, thus 1% is a huge portion). For some reason, however, in Parkinson’s disease this protein starts to aggregate and ultimately forms into Lewy bodies:

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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.

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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’).

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Tetrabenazine: A strategy for Levodopa-induced dyskinesia?

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For many people diagnosed with Parkinson’s disease, one of the scariest prospects of the condition that they face is the possibility of developing dyskinesias.

Dyskinesias are involuntary movements that can develop after long term use of the primary treatment of Parkinson’s disease: Levodopa

In todays post I discuss one experimental strategy for dealing with this debilitating aspect of Parkinson’s disease.


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Dyskinesia. Source: JAMA Neurology

There is a normal course of events with Parkinson’s disease (and yes, I am grossly generalising here).

First comes the shock of the diagnosis.

This is generally followed by the roller coaster of various emotions (including disbelief, sadness, anger, denial).

Then comes the period during which one will try to familiarise oneself with the condition (reading books, searching online, joining Facebook groups), and this usually leads to awareness of some of the realities of the condition.

One of those realities (especially for people with early onset Parkinson’s disease) are dyskinesias.

What are dyskinesias?

Dyskinesias (from Greek: dys – abnormal; and kinēsis – motion, movement) are simply a category of movement disorders that are characterised by involuntary muscle movements. And they are certainly not specific to Parkinson’s disease.

As I have suggested in the summary at the top, they are associated in Parkinson’s disease with long-term use of Levodopa (also known as Sinemet or Madopar).

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Sinemet is Levodopa. Source: Drugs

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