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Blocking a protein called PTP sigma led to better nerve survival and motor function in a mouse model of <a href="https://alsnewstoday.com/what-is-als/">amyotrophic lateral sclerosis</a> (ALS) caused by mutations in the C9ORF72 gene — leading the researchers to highlight this strategy for potentially treating this genetic ALS form.
Data from cell models suggest that reducing PTP sigma is protective because it activates a molecular pathway used to transport molecular cargo within nerve cells, which is required to move unwanted proteins to sites of degradation, pointing to this pathway as a possible therapeutic target.
&#8220;These exciting findings highlight the role of [this pathway] in the [disease development of this ALS form], offering a new direction for the therapy development of the disease,&#8221; the scientists wrote in an abstract detailing the research findings.
Zhe Zhang, PhD, a postdoctoral fellow at Johns Hopkins University, in Maryland, presented the findings in a talk titled “<a href="https://www.mdaconference.org/abstract-library/ptp%cf%83-mediated-pi3p-regulation-as-a-therapeutic-strategy-for-c9orf72-als-ftd/">PTP [sigma]-Mediated PI3P Regulation as a Therapeutic Strategy for 9ORF72-ALS/FTD</a>” at the Muscular Dystrophy Association (MDA) 2024 Clinical and Scientific Conference, held last week in Florida and virtually.
[recommended-reading id=86923]
<h3>Seeking treatment strategies for genetic ALS due to C9ORF72 mutations</h3>
Though the <a href="https://alsnewstoday.com/causes-of-als/">causes of ALS</a> are not fully understood, genetic mutations are responsible for some cases of the disease. Mutations in the gene C9ORF72 are the most common genetic cause of ALS.
Disease-causing mutations in C9ORF72 lead to the production of small proteins called dipeptide repeats, or DPRs. These small proteins can cause <a href="https://alsnewstoday.com/news/molecular-traps-may-thwart-als-nerve-damage-from-gene-mutations/">toxic effects in cells</a>, and it’s thought that the toxic impacts of DPRs in nerve cells are the main reason that C9ORF72 mutations cause disease. One of the most toxic C9ORF72-derived DPRs is called poly-GR (poly-glycine-arginine).
With an eye toward identifying potential treatment strategies, Zhang and colleagues set out to find other genes that could modulate the toxic effects of poly-GR. The team conducted a screen in which the scientists basically inactivated random genes in nerve cells, then expressed poly-GR.
The toxic protein killed most, but not all, of the cells, and the researchers looked to see which genes had been inactivated in cells that survived.
&#8220;When you knock down these genes, it can significantly improve [poly]-GR-expressing neuron survival,&#8221; Zhang said.
One of the genes identified by this screen was PTP sigma, which provides instructions for making a protein with the same name. This protein is known to be involved in regulating the development and activity of nerve cells and also activates in a cellular recycling process called autophagy, helping it catch the researchers&#8217; attention.
In further experiments, the team confirmed that reducing PTP sigma protein levels led to better survival in nerve cells expressing toxic poly-GR. Then they set out to identify exactly why this was happening.
The team showed that altering PTP sigma didn&#8217;t affect levels of the toxic poly-GR itself, which Zhang said suggests that &#8220;this rescue effect is not coming from lowering [levels of poly]-GR.&#8221; Instead, the beneficial effect of reducing PTP sigma &#8220;has to be associated with other functions related to PTP sigma,&#8221; Zhang said.
The PTP sigma protein is known to be important for regulating the activity of another protein called PI3P, which is important for coordinating shipments of molecular cargo between different parts of nerve cells. This includes the movement of unwanted or faulty proteins or cellular components into lysosomes, the cell&#8217;s recycling centers — needed to eliminate the toxic protein clumps that build up in ALS.
The scientists found that expressing poly-GR in nerve cells reduced levels of PI3P — but reducing PTP sigma reversed this effect. This suggests that &#8220;maybe PI3P level is important for neuron survival,&#8221; Zhang said.
[recommended-reading id=83790]
<h3>Tests in cell models showed nerve-protecting effects</h3>
Further supporting this idea, the researchers showed that reducing PTP sigma was no longer protective when cells were treated with a PI3P-blocking drug. And conversely, treating cells with a compound that activates PI3P boosted survival in the face of toxic poly-GR.
&#8220;This is showing that the PI3P levels is critical for neuron survival with the presence of [poly]-GR,&#8221; Zhang said.
Additional tests in cell models showed that boosting the early endosomal pathway, which is one of the major molecular pathways that PI3P participates in to help move molecular cargo, had similar nerve-protecting effects to reducing PTP sigma or increasing PI3P.
These findings suggest that it&#8217;s this particular pathway that&#8217;s helping protect cells against poly-GR in these models — pointing to this pathway as a potential treatment target for C9ORF72-related ALS.
The researchers then conducted experiments in mice to see if a drug that blocks PTP sigma could reduce disease activity in animals expressing toxic poly-GR. The results showed that reducing PTP sigma led to less nerve death and less neuroinflammation, as well as better scores on tests of motor function.
Altogether, the scientists concluded, the results suggest a new biological strategy for treating this genetic form of ALS that warrants further study.

MDA 2024: Blocking protein shows promise for genetic form of ALS

Blocking certain inflammatory signaling pathways may be one way to reverse nerve cell alterations that drive the symptoms of <a href="https://alsnewstoday.com/what-is-als/">amyotrophic lateral sclerosis</a> (ALS), according to preclinical research using a mouse model of the disease.
In the mice, an ALS-associated mutation in the FUS gene caused caused motor neurons — the nerve cells involved in motor control — to lose the branches and connections needed to function properly. It also disrupted cellular energy production and caused neuroinflammation, a complex inflammatory response typically seen within the brain or spinal cord.
A blockade of the inflammatory signaling pathway NF-kappa B was shown to reverse these cellular changes and improve motor and cognitive function in these animals.
In addition to further elucidating the role of FUS in driving <a href="https://alsnewstoday.com/symptoms-of-als/">ALS symptoms</a>, the study indicates that &#8220;modulation of the [NF-kappa B] pathway &#8230; is an important therapeutic approach to attenuate disease,&#8221; the researchers wrote.
The study, &#8220;<a href="https://actaneurocomms.biomedcentral.com/articles/10.1186/s40478-023-01671-1">Neuronal dysfunction caused by FUSR521G promotes ALS-associated phenotypes that are attenuated by NF-κB inhibition</a>,&#8221; was published in <a href="https://actaneurocomms.biomedcentral.com/">Acta Neuropathologica Communications</a>.
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<h3>Investigating the impact of FUS gene mutations on motor neurons</h3>
ALS is characterized by the degeneration of motor neurons, the specialized nerve cells involved in motor control. <a href="https://alsnewstoday.com/causes-of-als/#Genetics_of_ALS">Mutations</a> in FUS are thought to underlie the disease in about 5%-10% of people with <a href="https://alsnewstoday.com/forms-of-als-familial-als/">familial ALS</a> and less than 1% of those with <a href="https://alsnewstoday.com/sporadic-als/">sporadic ALS.</a>
These mutations lead to the production of an abnormal version of the FUS protein that toxically accumulates in the wrong part of the cell. While the FUS protein is normally seen in the nucleus — the core of the cell where DNA is housed — ALS-associated FUS instead gathers outside the nucleus in the cytoplasm and disturbs cellular function.
In mouse models, FUS mutations are associated with motor and cognitive deficits, activation of cells that promote inflammation, and structural changes to motor neurons that are also seen in the human condition. Specifically, motor neurons are found to lose dendrites, the branches they use to reach out to and communicate with other cells. The synapses, or connections, made with other cells via structures called dendritic spines also are lost.
Despite this knowledge, gaps still remain in scientists&#8217; understanding of how FUS mutations lead to these neuronal changes and contribute to disease progression.
Now, a team of researchers from Laval University, in Canada, genetically engineered mice to house a human ALS-associated FUS mutation specifically in neurons, using them to further explore the effects of FUS. 
At 1 month old, these mutant mice exhibited cognitive defects and reduced dendritic branching of upper motor neurons — the motor neurons that originate in the brain and travel to the spinal cord.
By 6 months of age, loss of dendritic branches and synapses had spread to affect the lower motor neurons, or those that travel from the spinal cord and innervate the muscles to coordinate movement. This was accompanied by progressive motor impairments.
A number of other cellular alterations also corresponded with the deteriorating cognitive and motor function of the mice. This included mis-localization of mutant FUS to the cytoplasm and signs of dysfunctional mitochondria, which are cells&#8217; energy-producing organelles.
Moreover, activation of <a href="https://alsnewstoday.com/news/astrocytes-microglia-als-friends-foes-amyotrophic-lateral-sclerosis/">astrocytes and microglia</a>, the nerve support cells (glia) that can drive neuroinflammation, was observed in the symptomatic mice.
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<h3>Researchers use compound based on plant used in traditional Indian medicine</h3>
Activation of the NF-kappa B inflammatory signaling pathway — a series of molecular events that cells use to respond to signals of inflammation or infection — is thought to promote glial activation in ALS and other neurodegenerative diseases. That, in turn, has been linked to motor neuron damage and disease progression.
As such, the researchers aimed to investigate whether blocking inflammatory signaling might help restore more normal nerve cell connections and ease symptoms.
To that end, they treated the mice with the NF-kappa B inhibitor IMS-088, a synthetic compound based on the naturally occurring Ashwagandha plant.
That plant has been &#8220;used for thousands of years in traditional Indian medicine,&#8221; Chantelle F. Sephton, PhD, assistant professor at the University of Laval and the study&#8217;s senior author, said in a <a href="https://salledepresse.ulaval.ca/2024/01/10/sla-bloquer-linflammation-pour-reduire-les-symptomes-a:7163fae3-28bf-45c7-ba00-218cd8782b65">press release</a>.
The treatment reversed many of the observed cellular deficits, leading to restored motor neuron dendrites and synapses, reduced glia activation, decreased FUS mis-localization, and increased mitochondrial function. This was accompanied by cognitive and motor improvements.
&#8220;Neurons regenerate without activated immune cells,&#8221; Sephton noted.
&#8220;The dendrites of motor neurons start to grow and make connections again, increasing the number of synapses between motor neurons and muscles,&#8221; Sephton said.
Lab studies of neurons from the mice further indicated that IMS-088 treatment promotes more normal mitochondrial function.
Altogether, the researchers believe the findings demonstrate the key role of neuroinflammation in ALS disease processes.
&#8220;Future studies will examine the mechanistic actions of inhibiting the [NF-kappa B] pathway on FUS function and the dynamic interplay between pro-inflammatory signals and mitochondrial function,&#8221; the team concluded.
The findings likely also have implications for other related diseases, including frontotemporal dementia (FTD), a neurodegenerative disease that has significant clinical and cellular overlap with ALS, as well as other inflammatory neurodegenerative conditions.

Blocking signaling pathways may reverse nerve cell changes in ALS

In most cases of <a href="https://alsnewstoday.com/?page_id=9613">amyotrophic lateral sclerosis</a> (ALS), dysfunction of a protein known as TDP-43 leads to abnormally low levels of another protein, stathmin-2, which is sufficient to drive nerve cell dysfunction, new data suggest.
In an aim to restore stathmin-2 levels, researchers created a designer DNA treatment. Now, that experimental therapy has shown promise in early mouse studies.
Results from the research were shared by Clotide Lagier-Tourenne, MD, PhD, a professor at Massachusetts General Hospital and Harvard Medical School, at the Muscular Dystrophy Association&#8217;s MDA Clinical &amp; Scientific Conference, held March 19-22 in Dallas and virtually. The talk was titled &#8220;Stathmin-2: an emerging therapeutic target in TDP-43 proteinopathies.&#8221;
The data also were detailed in the study, &#8220;<a href="https://www.science.org/doi/10.1126/science.abq5622">Mechanism of STMN2 cryptic splice-polyadenylation and its correction for TDP-43 proteinopathies</a>,&#8221; which was published in <a href="https://www.science.org/journal/science">Science</a>.
&#8220;Our findings lay the foundation for a clinical trial to delay paralysis in ALS by maintaining stathmin-2 protein levels in patients using our designer DNA drug,&#8221; Don Cleveland, PhD, a professor at the University of California San Diego (UCSD) and co-author of the study, said in a <a href="https://today.ucsd.edu/story/dna-treatment-could-delay-paralysis-that-strikes-nearly-all-patients-with-als">university press release</a>.
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<h3>Creating a designer DNA therapy to restore stathmin-2</h3>
Nearly all cases of ALS are characterized by abnormalities with the protein TDP-43. Normally, TDP-43 is located in the nucleus, the cellular compartment that houses DNA, but in ALS, the protein moves outside of the nucleus, disrupting its normal function.
TDP-43 has long been known to be involved in processing messenger RNA (mRNA) — an intermediary molecule made when genes are read to make protein. In particular, TDP-43 plays essential roles in mRNA splicing.
Within a cell&#8217;s DNA, genes contain exons — the parts of the genetic code that have instructions for making proteins — that are interspersed with introns. While introns don&#8217;t provide instructions for making protein, they have other regulatory functions.
When a gene is read, the entire sequence normally is copied over into mRNA, and then the mRNA undergoes splicing to remove all the introns and string the exons together. The final mature mRNA sequence is then sent to the cell&#8217;s protein-making machines, which can read the code to make protein.
&#8220;Now, as a field, we know that TDP-43 binds thousands of targets, and actually leads to hundreds if not thousands of RNA alterations and RNA splicing,&#8221; Lagier-Tourenne said.
In cell experiments, the researchers showed that reducing TDP-43 levels leads to a change in splicing for the gene STMN2, which provides instructions for making the protein stathmin-2. Specifically, the lack of TDP-43 led to the inclusion of an extra sequence called a cryptic exon, which is normally removed from the mature code.
The researchers showed that TDP-43 normally binds to the cryptic exon sequence, preventing it from being included in the mature mRNA. Without TDP-43, the cryptic exon gets included in the mature sequence, but other exons get left out, resulting in a shortened mRNA that cannot be used to produce the stathmin-2 protein. The end result is that dysfunctional TDP-43 leads to reduced levels of stathmin-2.
In their study, the team found high levels of the shortened STMN2 mRNA containing the cryptic exon in spinal cord samples from people with <a href="https://alsnewstoday.com/sporadic-als/">sporadic ALS</a>. However, the abnormal mRNA was not present in people without ALS. Consistently, levels of stathmin-2 protein were decreased in the sporadic ALS patients, but not in spinal cords unaffected by ALS.
The abnormal mRNA also was present in people with ALS caused by mutations in the C9ORF7 gene, which is known to cause TDP-43 abnormalities. However, patients with mutations in the gene SOD1 — a rare genetic form of ALS that typically doesn&#8217;t cause abnormalities with TDP-43 — did not have the abnormal mRNA.
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<h3>Designer DNA drug is similar to therapy for spinal muscular atrophy</h3>
The stathmin-2 protein is known to play roles in providing structural support to nerve cells and axons — the long fibers that nerves use to connect with each other. The researchers showed that motor neuron cells lacking stathmin-2 were unable to regrow after an axon injury. Cells lacking TDP-43 and, consequently, with low stathmin-2 levels, also were not able to regrow.
However, when the researchers engineered cells lacking TDP-43 so that they could express higher levels of stathmin-2 protein, the cells&#8217; ability to regrow was restored.
&#8220;What was very surprising was that, in these motor neurons where we have TDP-43 knock-down, we know there are hundreds if not thousands of [RNA] expression and splicing alterations, and restoring stathmin-2 was sufficient to completely rescue the regeneration ability of these motor neurons,&#8221; Lagier-Tourenne said.
In mice, reducing levels of stathmin-2 in the nervous system led to progressive motor weakness and dysfunction, with poorer connections between nerve and muscle cells. These findings collectively implied that increasing stathmin-2 levels could be therapeutic in ALS.
[quote align=&#8221;center&#8221;]Our findings lay the foundation for a clinical trial to delay paralysis in ALS by maintaining stathmin-2 protein levels in patients using our designer DNA drug.[/quote]
The researchers created a designer DNA drug, called an antisense oligonucleotide, which basically aims to mimic the function of TDP-43, thereby correcting splicing of STMN2 mRNA and restoring production of stathmin-2 protein.
A similar type of therapy is approved in the U.S. and other countries to treat <a href="https://smanewstoday.com/what-is-spinal-muscular-atrophy/">spinal muscular atrophy</a>, a genetic disorder that, like ALS, affects motor neurons.
&#8220;What we have now found is that we can mimic TDP-43 function with a designer DNA drug, thereby restoring correct stathmin-2 RNA and protein level in the mammalian nervous system,&#8221; Cleveland said.
To test the experimental therapy, the researchers used mice engineered to express a version of the human STMN2 gene that lacked sites for TDP-43 to bind — meaning that these mice always produced the abnormal, truncated mRNA, and had low stathmin-2 levels as a result. Treatment with the experimental DNA therapy restored stathmin-2 levels.
&#8220;With mouse models we engineered to misprocess their stathmin-2 encoding RNAs, like in these human diseases, we show that administration of one of these designer DNA drugs into the fluid that surrounds the brain and spinal cord restores normal stathmin-2 levels throughout the nervous system,” Cleveland said.

Tag: mouse model of ALS

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