This is a short post about this publication with an interesting title.

I thought it was about the acute anxiety of carers when their loved one could not eat anymore, actually, it is about how doctors in British hospitals manage patients who could not take their medication orally.

The alternatives are either a soluble medication, a topical patch, or a nasogastric tube.

I wonder if there is not a more urgent problem for patients that could not swallow, than taking their medication.

For once, we are going to talk about an article about Huntington's disease. Huntington's disease (sometimes called Huntington's chorea) is a rare hereditary disease that results in neurological degeneration causing significant motor, cognitive, and psychiatric disorders, and progressing to the loss of autonomy and then death. This disease occurs in adults aged between 35 and 50 on average. The progression of the disease follows a rhythm and a form that varies greatly from one individual to another.

The genetic abnormality that causes Huntington's disease is a greater than normal increase (20 times) of the repetition of three nucleotides (C, A, and G - called the CAG codon or triplet) within the HTT gene encoding the huntingtin protein. This blog focuses on three neurodegenerative diseases, ALS (sometimes called Charcot's disease or Lou Gehrig's disease), Parkinson's disease, or Alzheimer's disease. But in fact, it is only in books that these diseases are clearly categorized, in reality, we distinguish multiple subtypes to each of these categorizations and moreover, these diseases share characteristics both between themselves and with other neurodegenerative diseases.

A variant of ALS (C9orf72) closely resembles Huntington's disease in some aspects because it too is characterized by repeat expansions of a gene, C9orf72. Repeat expansions of the C9orf72 gene are responsible for about 40% of genetic ALS and 25% of genetic FTD.

The article we are discussing today focuses on the genetic and molecular mechanisms underlying Huntington's disease (HD), with a particular emphasis on the dynamics of CAG repeat expansions in the huntingtin (HTT) gene.

It explores the implications for the pathogenesis and therapeutics of HD. Although ALS is not cited by the authors, this paper has implications for that disease as well as for about 30 others.

An expansion of CAG triplet causes Huntington's disease repeats in the HTT gene. Normal alleles have 15 to 30 CAGs; disease-causing alleles have 36 or more. Longer CAG repeats correlate with earlier onset.

Scientists identified the progression of CAG repeat expansion with age by analyzing somatic mosaicism, or the variability in CAG repeat lengths between different cells within an individual. This variability increases over time, and the progression of CAG repeat length has been linked to cell-specific processes that cause expansions as individuals age.

The authors found that HTT alleles are not inherently toxic, but become harmful after somatic expansion exceeds approximately 150 repeats. This toxicity results in asynchronous and rapid neuronal decline, challenging the understanding of Huntington’s disease as a slowly progressive disease. They measured somatic repeat expansion over time in individual neurons from donors of different ages. They found that early-phase expansions (e.g., from 40 to 80 CAG repeats) were slow and stochastic, taking decades, while later expansions (e.g., from 80 to 150 repeats) occurred more rapidly. They then analyzed genetic markers and DNA repair mechanisms associated with repeat instability, such as those involving DNA mismatch repair (MMR) proteins (e.g., MSH3, PMS1). Variants in these genes have been shown to influence the rate of somatic instability. The progression of CAG repeat expansion is driven by errors in DNA replication, repair, and maintenance, particularly in neurons. Key mechanisms include:

Striatal projection neurons, the cells most affected by Huntington’s disease, exhibit higher levels of somatic instability than other cell types. This may be due to their unique transcriptional and metabolic profiles, which make them more susceptible to DNA damage and inefficient repair.

Expansion dynamics have been categorized into phases: - Phase A (36–80 repeats): Slow and stochastic over decades. - Phase B (80–150 repeats): Faster and more predictable. - Phase C (>150 repeats): Gene expression changes begin, leading to cellular dysfunction. Toxicity threshold: Neurons derepress other genes (e.g., CDKN2A/B) and eventually die.

These findings highlight how somatic mosaicism and age-related repeat expansions are central to the pathogenesis of Huntington’s disease and provide a framework for understanding similar processes in other repeat expansion disorders.

The somatic expansion mechanism may extend to other repeat expansion disorders, such as myotonic dystrophy or some forms of spinocerebellar ataxia.

The C9orf72 variant in ALS involves a hexanucleotide repeat expansion (GGGGCC) in a noncoding gene region. Although distinct from the CAG repeats in the Huntington’s disease coding region, there are notable parallels. As in Huntington’s disease, somatic instability of the repeat expansion has been observed in ALS C9orf72. The degree of mosaicism may influence disease onset and progression. C9orf72 expansions lead to toxic RNA foci and dipeptide repeat (DPR) proteins, leading to neuronal dysfunction and death. This reflects Huntington’s disease idea that toxicity only occurs after substantial repeat expansion. In ALS, motor neurons are selectively vulnerable. As in Huntington’s disease, the specific cell types affected may result from unique somatic instability dynamics.

Therapeutic potential: This work in Huntington’s disease suggests that modulation of DNA repair pathways (e.g., MSH3) may stabilize nucleotide repeats, thereby delaying toxicity.

It's a bit sad that scientists studying FTD think of themself as "dementia scientists" while scientists studying ALS or Parkinson's disease think they belong to a motor disorders category and motor neurons specialists for ALS scientists, while many neurodegenerative diseases share a lot of molecular and physiologic characteristics. At least these cases are often those of aged people and they involve mislocated and misfolded protein aggregates.

So many scientists from the Memory and Aging Center at the University of California, were motivated to study the impact of age on neurodegenerative diseases:

• They tell that age is the biggest risk factor for dementia, which is a way to present aging as a cause of neurodegenerative diseases, not simply a comorbidity.
• Most dementia cases (>75%) involve multiple types of brain pathologies, which implies again that those pathologies are not diseases in the same sense as communicable diseases where usually there is a single pathogen and removing this pathogen more or less (not always) restore health.
• Previous animal experiments showed that exchanging blood between young and old animals could affect brain aging (called "heterochronic blood experiments"). This is a controversial topic as some ultra-rich people already buy young blood of unclear origin. Identifying the detrimental substances and those that are beneficial would help human society as a whole.
• While individual blood factors had been identified in animal studies, their relevance to human disease wasn't well understood

This study involved the direct examination of persons in two cohorts: A longitudinal study of people with genetic frontotemporal dementia (FTD) and healthy controls. A cross-sectional study of people with sporadic Alzheimer's disease and controls.

• Discovery Cohort (ALLFTD Study): 119 people with FTD genetic mutations (37 MAPT, 33 GRN, 49 C9orf72) 78 healthy controls without mutations This was a longitudinal study (participants were followed over time) Participants had on average 3 annual evaluations (ranging from 1-7 visits) About half (52) of the mutation carriers were asymptomatic at the beginning of the study.

• Replication Cohort (Stanford ADRC): 35 people with Alzheimer's disease 56 clinically normal older adults This was a cross-sectional study (participants were NOT followed over time)

For both groups, the scientists collected: - Cerebrospinal fluid (CSF) through lumbar punctures - Comprehensive cognitive tests - Functional assessments (rated by caregivers) - Blood or CSF samples for NfL (a marker of neurodegeneration)

The scientists identified five specific proteins from previous animal studies: - Could cross the blood-brain barrier - Were measurable in human samples - Had shown effects on brain aging

These proteins included: Three "pro-aging" factors: CCL11, CCL2, B2M Two "pro-youthful" factors: CSF2 and BGLAP

They found that people with FTD mutations had lower levels of "rejuvenation proteins". Higher levels of these proteins were associated with slower disease progression The protective effect was seen across multiple cognitive domains. The effect was similar regardless of which specific FTD mutation people had

Similar protective associations were found in Alzheimer's disease. Higher levels of these proteins were associated with better cognitive performance and functional status. The effect was particularly strong for memory performance.

• CCL11 is a small cytokine belonging to the CC chemokine family. CCL11 selectively recruits eosinophils by inducing their chemotaxis, and therefore, is implicated in allergic responses. Increased CCL11 levels in blood plasma are associated with aging. Exposing young mice to CCL11 or the blood plasma of older mice decreases their neurogenesis and cognitive performance on behavioral tasks.
• CCL2, another cytokine, is implicated in pathogeneses of several diseases characterized by monocytes (a type of leukocyte or white blood cell) infiltrates, such as psoriasis, rheumatoid arthritis, and atherosclerosis
• B2M is a component of MHC class I molecules. MHC class I function is to display peptide fragments of proteins from within the cell to cytotoxic T cells. Systemic B2M accumulating in aging blood promotes age-related cognitive dysfunction and impaired neurogenesis. In addition, it promotes beta-amyloid aggregation and neurotoxicity in models of Alzheimer’s disease.
• CSF2 is a monomeric glycoprotein secreted by macrophages, T cells, mast cells, natural killer cells, endothelial cells, and fibroblasts, that functions as a cytokine.
• Osteocalcin, also known as (BGLAP), is a protein hormone found in bone. Numerous recent studies have revealed bidirectional crosstalk between the brain (and Alzheimer's disease) and bone health.

The publication does not mechanistically explain these "pro-aging" and "pro-youthful" factors. It may suggest that it pays to have a low inflammation level and to be physically active. The results appear relatively reliable because the scientists found similar effects in two different types of dementia. The effects were seen across multiple measures (cognitive, functional, and biological markers).

This research could impact drug development in several ways: - It suggests targeting multiple proteins simultaneously might be more effective than single-target approaches - It identifies specific proteins that could be therapeutic targets - It demonstrates these effects in humans, making it more likely to translate into effective treatments - The proteins are measurable in the blood, which could make treatment monitoring easier and safer than the very intrusive CSF sampling.

While not directly studied, this research could be relevant to ALS because ALS shares some biological mechanisms with FTD (they're often considered part of the same disease spectrum).

The research suggests a new paradigm for treating neurodegenerative diseases by targeting multiple age-related factors simultaneously, rather than focusing on single disease-specific pathologies. This could be particularly relevant for diseases like ALS where multiple mechanisms contribute to disease progression.

Preclinical studies are performed on a number of organisms, which scientists call "animal models of the disease." This concept is very vague and can involve everything from immortalized cancer cells to nematodes or fish. The most serious work is done on several standardized and commercial mouse models. This makes it possible in theory to compare work between laboratories, although this remains difficult in practice. However, commercial mouse models of disease are expensive and are almost useless for diseases like ALS, because the nervous system of mice is very different from the human nervous system. However, in preclinical studies, scientists look for clues that a drug might be useful, but it is not yet possible to prove that a drug will be effective in humans. One of the best things they can do at this stage is to show that a drug has a positive effect on several unrelated commercial animal models. The endoplasmic reticulum (ER) is an important organelle in cells that is involved in protein conformation. This step occurs after protein synthesis by ribosomes and after conformation, the new protein will be sent to its final destination by the Golgi apparatus. Protein conformation requires energy, so when disease occurs, the ER may not be able to properly conform the new proteins.

The accumulation of unfolded proteins leads to ER stress, followed by an adaptive response via activation of the unfolded protein response (UPR). Since folded proteins require energy, the unfolded protein response significantly slows down the production of new proteins. This is a way to cope with temporary stressful events, but it is not sustainable, as a cell that does not produce proteins is in a kind of stasis and will die quickly. Indeed, prolonged cellular stress activates apoptosis signaling leading to cell death.

Several studies have shown that impaired endoplasmic reticulum (ER) proteostasis is a pathogenic feature of ALS/FTD. Several drugs targeting the UPR in ALS have been proposed (GSK2606414, ISRIB, Guanabenz, Sephin1, Trazodone, KIRA), but none seem to be effective in ALS at this point.

There are different strategies, one is to stop the prolonged deleterious UPR in the hope that somehow the stressor has disappeared and the cell is healthy again. Another, on the contrary, tries to force an unfolded protein response state on all cells in the hope that the cell will be able to clear the backlog of accumulated misfolded proteins. However, the involvement of the UPR and the mechanisms by which ER stress contributes to pathogenesis are not entirely clear and can have contrasting or even opposing effects. Contributing to this complexity is that the UPR is actually several mechanisms.

The transcription factor XBP1s has several roles, one of them being that of regulator of the unfolded protein response. In a new publication, scientists provide evidence of suboptimal activation of the UPR in mouse models of ALS/FTD under experimental ER stress.

They designed a genetic therapy so that nervous system cells in ALS/FTD mouse models express the active form of XBP1 (XBP1s). XBP1s expression improved motor performance and extended lifespan in SOD1 mutant mice, associated with reduced protein aggregation.

It is important to note that AAV-XBP1 administration also attenuated disease progression in mouse models of TDP-43 and C9orf72 pathogenesis. As noted at the beginning of this text, most preclinical work in a single animal model is a bit suspect, especially when the animal model is not standardized but performed by administering a chemical that affects the nervous system.

ALS SOD1 disease is probably very different from TDP-43 and C9orf72 diseases. As SOD1 is an anti-oxidant, a mutated SOD1 protein probably protect less neurons from metabolism by-products. TDP-43 protein has many roles but one is to repair DNA in pluripotent stem cell-derived motor neurons. Most ALS patients have misfolded, aggregated fragments of TDP-43 in cell's cytosol which is weird as normally TDP-43 should be in cell's nucleus where it could repair DNA. C9orf72 is different again, in this disease the cellular ribosomes produce the wrong proteins from correct RNA, a so-called frameshift effect.

It is not clear how an XBP1s drug could benefit these three variants of ALS. However, if this is confirmed in humans, it would be good news because today, only one drug benefits ALS patients (Tofersen), but it benefits less than 1% of them. Having a drug that would benefit most patients would be extraordinary.

But we are not there yet, a first step would be to understand the mechanism of action of this drug in ALS

We decided to use a new post format in 2025. It would propose aggregated short news instead of dedicating a post per publication.

Scientists who publish on neurodegenerative diseases often ignore the fact that neuron-type cells comprise only half of cells in the central nervous system. So it's fresh air to read a review on Schwann cells involvement in ALS. Yet conceptually associating Schwann cells and ALS is not common, ALS is a disease of the central nervous system (upper motor neurons in the brain and spine) while Schwann cells are located in the peripheral nervous system (lower motor neurons with their bodies from the spine and terminating in muscles). This does not mean there are no relations between the two types of cells, and it's a common view now that neurons are not independent, self-sufficient entities and that they are cared for by a large number of other cell types.

In a similar vein, Uruguayan scientists were interested in astrocytes' health. Astrocytes are the main kind of motor neuron supportive cells, if they ill behave, motor neurons die and it happens that they can switch between several behaviors. The scientists thought that metabolic reprogramming could occur in astrocytes following damage, and it significantly influences the progression of ALS pathology. Metabolic reprogramming, which involves changes in mitochondrial activity, within glial cells may provide valuable insights for developing innovative therapeutic approaches to mitigate neuronal damage.

It's no new but another study finds common molecular features between ALS and Parkinson's diseases. This reinforces the idea that sporadic neurodegenerative diseases are not clearly delineated diseases as in medical books. On the contrary, these medical classifications just describe symptoms belonging to a spectrum shared by many sporadic neurodegenerative diseases and aging.

Scientists in Taiwan studied the effects of isofraxidin on motor performance changes in chemically induced (lipopolysaccharide) Parkinson's disease in mice.

Isofraxidin is isolated from Eleutherococcus senticosus. Eleutherococcus senticosus, as many berries, is itself loaded with chemical components and provokes adverse effects in some people. What makes them study this plant is not disclosed. Still, as often it's probably because it is used in traditional medicine, and there were some interesting scientific studies on its effects on neurological disease. Isofraxidin pre-treatment significantly improved lipopolysaccharide-induced motor dysfunction, as evidenced by better performance in the rotarod, pole-climbing, and beam-walking tests. Does this prove anything? I am not sure, there are many articles that isofraxidin protects against lipopolysaccharide-induced diseases, the scientists most probably knew that when they planned their experiment.

It's 2025, Happy New Year!

Since late 2018 this blog has comments on research on ALS, Parkinson's, and Alzheimer's diseases. My goal initially was to write a post every two days, with newly published research on Pubmed as input. This goal was impossible to reach because there is an immense activity but little valuable research on these topics.

Most articles are produced with an optic where quality is not important as long it's obscured by jargon. As publishing an article cost anywhere between $1000 and $4000, this is an incredible waste of money. Another aspect is that the articles about drugs' effects on immortalized cells, worms, or fishes, do not provide any hint that a drug might be useful for humans.

At a minimum such research to apply to humans must use animal models that are as large as humans and with a similar central nervous system. Only upper primates fit these requirements and the cost and ethics aspects are that kind of research almost never happen.

So I will try for a few months to write posts that briefly talk about publications that I feel have some merit.

Let's go!

• A medical case report recounts that an ALS patient was given a GLP1-inhibitor (a category of drugs including Ozempic). Indeed the "case" deteriorated quickly. Sometimes patients make bad encounters in white coats.

• Some good news came for ALS patients with a familial form. More than half of familial ALS cases are due to a nasty dysfunction in the mechanism that produces proteins. This study explores a novel approach to combat C9ORF72-linked amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) using a CRISPR-Cas13-based RNA-targeting system. C9ORF72 mutations contribute to those diseases through three mechanisms: loss of C9ORF72 protein function, RNA toxicity from repeat-containing transcripts, and toxicity from dipeptide repeat (DPR) proteins. Current therapies, such as antisense oligonucleotides (ASOs) and miRNAs, face limitations, including transient effects and suboptimal targeting. The researchers developed RfxCas13d, a compact CRISPR-Cas13 variant, to target and degrade the pathogenic G4C2 repeat RNA in cellular and animal models. When delivered to the brain of a transgenic rodent model, this Cas13-based platform curbed the expression of the G4C2 repeats without affecting normal C9ORF72 levels.

• Another study demonstrates the potential of a CRISPR-CasRx-based approach for targeting both sense and antisense C9orf72 repeat transcripts. ASOs for the G4C2 repeat RNA developed by Wave Life Sciences and Ionis Pharmaceuticals and Biogen failed to show a benefit in human trials. Though the exact reason for this remains unknown, these ASOs targeted only the G4C2 (sense) repeat RNA and were thus presumed to not affect the G2C4 (antisense) transcript. This last study has the same overall goal as the first one but it targets both sense and antisense C9orf72 repeat transcripts. Yet the First study's RfxCas13d is a multiplexable enzyme. Thus, it has also the capacity to simultaneously target both the G4C2 (sense) and G2C4 (antisense) repeat RNAs from a single vector. Indeed there is a long road to transform these findings into efficient drugs, but it's a step in the right direction.

• In younger, healthy cells, the "normal" metabolic process is typically oxidative phosphorylation (OXPHOS), which occurs in the mitochondria. Healthy cells maintain a slightly alkaline intracellular pH (around 7.2 in the cytoplasm). However, during aging, cells may shift towards glycolysis (a process common in senescent cells), where the cytoplasm, not mitochondria consumes glucose to produce ATP with lactic acid as a side product. As neurodegenerative diseases are, in most cases, diseases of aged people, one layperson would expect that the cell shift in metabolism from mitochondria to cytoplasm and subsequent acidification are of the utmost importance. Unfortunately, it is not, and as usual, when scientists have no idea about something, they tell that this shift in aging metabolism is due to a combination of multiple factors. Joyal Xavier and colleagues wanted to understand the mechanisms associated with TDP-43 aggregation. TDP-43 expressing cell lines were exposed to either an acidic environment, a neutral environment, or sodium arsenate. Asparaginyl endopeptidase (AEP) has been implicated in the misfolding and aggregation of TDP-43 and other proteins implicated in neurodegenerative diseases because it is an enzyme that can cleave proteins in toxic fragments. They have observed the localization of TDP-43 in the mitochondria under normal pH conditions. However, under acidic conditions and after sodium arsenate exposure, they observed an increase in TDP43 levels in the mitochondria and nucleus. Alternatively, they observed a decrease in TDP43 in the mitochondria and nucleus following treatment with an asparaginyl endopeptidase inhibitor. My conclusion is that not much has been learned, yet it is a neglected research avenue that has some potential.