Targeting 14-3-3θ-mediated TDP-43 pathology in mice

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Every day brings its share of scientific articles announcing the imminent arrival of drugs for neurodegenerative diseases.

However, we are unable even to diagnose these diseases with certainty. The diagnosis is made by exclusion and sometimes gives rise to several different diagnoses. We would be better off talking about the spectrum of neurogenerative diseases. The only thing we know for certain is that these diseases are characterized by malformed protein aggregates in inappropriate places in cells.

These diseases are currently differentiated by scientists by the type of protein involved, but in fact, all of these malformed proteins are present to varying degrees in all of these diseases. The recent trend to generalize diagnosis based on molecular markers only recognizes our incompetence and only serves the pharmaceutical industry.

Amyotrophic lateral sclerosis (ALS) and/or frontotemporal dementia (FTD) are most often characterized by the cytoplasmic deposition of nuclear TAR-binding protein 43 (TDP-43). But this is rarely of a rare and deleterious protein form. Although the cytoplasmic localization of TDP-43 aggregates is commonly associated with ALS/FTD, it is unknown what causes the dysfunction, although different hypotheses have been posed such as cellular stress, for example (but not only) due to to a significant change in metabolism.

In a recent article, scientists from Macquarie University in Australia reported their work concerning the interaction between the proteins 14-3-3θ and TDP-43, which regulates the nuclear-cytoplasmic shuttle.

The 14-3-3θ protein, like many other proteins, is associated with several neurodegenerative diseases.

Similar work was carried out in the past (2016) which consisted of creating a peptide by attaching the M1 section of TDP-43 to a TAT peptide which gives a peptide: YGRKKRRQRRRAQFPGACGL, which repatriates the aggregates poorly localized in the nucleus of the cells.

This work does not seem to have given rise to recent developments in the field of neurodegenerative diseases. In any case, this 2016 work did not explain why these aggregates appeared. They only provided a mechanism to get them back into the cell's nucleus. It is not clear how this would have formed them correctly since this happens in a cellular organ called "endoplasmic reticulum" which is located in the cytoplasm.

In addition, forming proteins requires energy, but we know that the cells of many patients are in a state of "hibernation" called the cellular stress response, with activity reduced to the minimum necessary to survive. Furthermore, any genetic therapy only "infects" a fraction of cells, which reduces its interest. And these genetic therapies are not without side effects.

This new article presents a slightly different mechanism but does not further answer the questions above. The 14-3-3θ protein belongs to a family of proteins called 14-3-3, known to regulate other proteins by binding to them and they play a role in various cellular processes, including signaling, survival, and cell differentiation. This family includes more than 200 members. The authors found that neuronal levels of 14-3-3θ were increased in mouse models of ALS and sporadic FTD with TDP-43 pathology. As we already know, 14-3-3θ is associated with several neurodegenerative diseases. Scientists believe that the interaction of deleterious TDP-43 alleles with the 14-3-3θ protein results in cytoplasmic accumulation, insolubility, phosphorylation, and fragmentation of TDP-43, which resembles the pathological changes caused by these diseases in humans. enter image description here What is interesting is that 14-3-3θ seems to interact preferentially with pathogenic TDP-43 versions but not with the usual version of TDP-43. This suggests that reducing the production (or increasing the degradation) of 14-3-3θ would reduce the production of pathogenic TDP-43. Scientists have therefore sought to reduce the amount of this 14-3-3θ protein in cells through genetic therapy.

The authors designed multiple versions of a peptide they called CTx1000, each version of which is tailored to reduce one of these deleterious forms of TDP-43. This reduction is mediated by degron of pathogenic TDP-43. A degron is a part of a protein that plays an important role in regulating protein degradation rates. In mice that underwent this gene therapy, functional deficits and neurodegeneration decreased, including when they were already symptomatic at the time of treatment. This incidentally matches many studies that, contrary to consensus, show that motor neurons do not die in ALS.

The university's press kit is, as usual, dithyrambic and the authors' statements resounding: "This new research is incredibly promising in slowing the progression of MND and FTD for the vast majority of our patients. I'm extremely hopeful that it will soon be available to our patients at the Macquarie University Hospital MND Clinic." This type of press kit is not aimed at patients and their loved ones, but rather at potential investors.

In conclusion, we can think that just as the therapy proposed in 2016 did not allow the development of a drug eight years later, it will probably be the same for this one, because it does not answer basic questions: Quid patients (the majority) who do not present a mutated form of TDP-43? What causes these protein clumps? Where can cells find the energy to be permanently “reactivated” from cellular stress response so that the therapy can do its work? How can we ensure that all of the targeted cells can receive the therapy, without side effects?

A possible breakthrough in ALS and FTD

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There are multiple subtypes of ALS: It could be of genetic origin, for example, an uncommon version of a SOD1, FUS, or C9orf72 genes might under some unknown conditions lead to ALS in aging people. But most people with ALS have no genetic alleles yet they developed ALS, perhaps due to some environmental conditions, like ingesting some toxins. In most cases people with ALS have a biomarker: They have aggregates of a very common protein, TDP-43, which localizes at an unlikely place in the neuron cells.

Some other things that are a bit weird in ALS, if it's of genetic origin why only aged people are striked? Why does it start with a seemingly innocuous muscular problem that soon extends to the whole body, but only for a specific type of muscle? The only therapy up to now, which seems to be a breakthrough is Qalsody, a genetic therapy by Biogen and Ionis. Unfortunately, it aims at a specific variant of the SOD1 gene which is present only in very few ALS patients. SOD1 variants are implicated in only 2% of ALS cases, and there are hundreds of SOD1 variants, while Qalsody targets only one of them.

In 2019 following the arrival of a SMA therapy, I made a plea for a genetic therapy aiming at TDP-43. Many scientists have been working on it in recent years, and it seems that one of those efforts is starting to show some results.

In 2011, Shulin Ju, Gregory A Petsko and colleagues found that hUPF1, a human gene, rescues the toxicity of FUS/TLS in a yeast model of ALS. This does not mean much as indeed there is an abyss between a yeast model of ALS and human beings. Yeasts are very different from mammal cells, but they are cheap so they are convenient for testing a large array of substances. The scientists identified several human genes that, when over-expressed in yeast, can rescue the cell from the toxicity of mislocalized FUS/TLS. This was confirmed again in 2013.

In 2015 the same team progressed pre-clinical trials research by demonstrating that on a rat model of ALS, human UPF1 exerted protective effects. The rat model was based on an over-expression of TDP-43. What was astonishing was that first there was no mortality between rats, second, it would demonstrate action both on FUS repeats and TDP-43 mislocalization which are very different diseases at the molecular level. This was again confirmed in 2015 by the same team while alluding that possible ALS therapy might also be useful for FTD, a type of dementia.

Astonishingly in 2021 another team led by Benjamin L Zaepfel, in the laboratory of well-known ALS scientist Jeffrey D Rothstein, found that UPF1 reduces C9orf72 neurotoxicity in an iPSC model of the disease. This might at the same time look insignificant (an iPSC model) and very significant (a therapy working for FUS/C9orf73/TDP-43).

Some of the scientists involved in this research work in a biotech MeiraGTx. MeiraGTx among other therapies, has designed a gene therapy for amyotrophic lateral sclerosis.

In a presentation on Oct. 27 at the European Society of Cell and Gene Therapy conference in Brussels, MeiraGTx showed that a single treatment with its gene therapy AAV-UPF1 prevented the loss of motor neurons in mouse and rat models with genetic and cellular defects seen in ALS

What is the significance of this? I do not know. UPF1 is a gene that encodes a protein that is part of a post-splicing multiprotein complex, the exon junction complex, involved in both mRNA nuclear export and mRNA surveillance. This has a relation with FUS and C9orf72, but not with TDP-43 versions of the disease. enter image description here Any way at least if it works in human patients with FUS/C9orf72 that would mean one in five ALS patients would benefit from it. This would be much larger than Qualsody benefits.

If it works for TDP-43 it would heal most ALS and FTD cases. This would represent a large number of patients, FTD prevalence is 20/100,000 persons.

This presentation was probably a call to investors such as Biogen, to fund clinical studies. Let's hope it works.

New study on Arimoclomol for ALS and FTD

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The accumulation of toxic protein clumps is a crucial contributor to cell damage in people with ALS (TDP-43), Alzheimer's disease (beta-amyloid), or Parkinson's disease (alpha-synuclein). These aggregates are composed of abnormal proteins that fail to acquire their standard three-dimensional shape. enter image description here In the case of ALS, the clusters of TDP-43 are also located in the cytosol, i.e. where the proteins are produced, before being folded up in the ER and then sent to their place of use by the Golgi apparatus. After shipment, TDP-43 should be in the nucleus.

Arimoclomol is an oral therapy that increases the production of heat shock response proteins (HSPs), which help misfolded proteins to their normal shape. HSPs also direct the removal of abnormal proteins when refolding is not possible.

One would therefore think that if ALS is primarily a problem with folding proteins, therapies that help misfolded proteins acquire their typical configuration should slow the progression of ALS. This has been tested with Arimoclomol. For once a clinical trial would have been launched on a drug that seemed to have a good chance of succeeding (oddly drug targets in most clinical trials in neurodegenerative diseases seem to be based on non-scientific criteria).

Arimoclomol was evaluated in a previous Phase 2/3 clinical trial (NCT00706147) in 36 patients with rapidly worsening ALS due to SOD1 mutations. The choice to select SOD1 patients is quite curious. There are countless SOD1 mutations, with consequences ranging from extremely rapid deterioration (a few months) to extremely slow deterioration (death after 10 years). There are therefore probably multiple mechanisms of action at work.

On the other hand, SOD1 mutations are only present in 5% of ALS cases. But SOD1 mutations were the first mutations discovered in ALS and are by far the most studied for 30 years, yet without significant progress being recorded.

Although this clinical trial did not show statistically significant results, the company Orphazyme managed to find funding for a phase III trial. The Phase 3 ORARIALS-01 trial (NCT03491462) studied arimoclomol in 245 adults with ALS. This clinical trial did not achieve its objectives. Arimoclomol did not prolong the life of patients or even delay the progression of disability in people with the disease. In other words, it was a spectacular failure, like almost all clinical trials in ALS.

Although I am neither a doctor nor a scientist, this made me think that the premises for rationale of arimoclomol in ALS were false. Personally, since that time, I am convinced that ALS is due to a cellular stress response that does not stop and which therefore destroys not only neurons but also muscle cells.

Indeed, the response to cellular stress consists of an almost total shutdown of the cell, this shutdown cannot be permanent. This stop explains very well the loss of muscle mass (which scientists explain by the death of motor neurons, while this loss occurs before motor neurons death).

From this perspective (very personal), any action aimed at increasing the energy expenditure of the cell (it takes energy to fold proteins), is doomed to failure.

Yet the scientists behind arimoclomol in 2004, seem to be back at the lab table. This time they are no longer interested in SOD1 mutations but in VCP mutations. VCP mutations are very rare, less than 1% of ALS cases. They conducted a study of arimoclomol in mice with a mutation in valosin-containing protein (VCP) that causes both ALS and FTD in patients.

Similar to studies of arimoclomol in SOD1 mice, enhancement of the heat shock response ameliorated the ALS/FTD-like phenotype in the spinal cord and brain of VCP mutant mice. Arimoclomol prevents neuronal loss in it. Additionally, in human cell models, the authors demonstrate improvements in pathology in VCP mutant patient fibroblasts and iPSC-derived motor neurons.

The scientists suggest that targeting HSP may have therapeutic potential, not only in non-SOD1 ALS, but also for the treatment of FTD.

Errare humanum perseverare diabolicum

De nouveaux travaux sur Arimoclomol pour la SLA et FTD

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L'accumulation d'amas de protéines toxiques est un contributeur crucial aux dommages cellulaire chez les personnes atteintes de SLA (TDP-43), de la maladie d'Alzheimer (beta amyloïdes) ou de Parkinson (alpha-synuclein). Ces amas sont composés de protéines anormales qui ne parviennent pas à acquérir leur forme tridimensionnelle standard. enter image description here Dans le cas de la SLA, les amas de TDP-43 sont aussi localisés dans le cytosol, c'est à dire là où les protéines sont produites, avant d'être repliées dans l'ER puis expédiées vers leur lieu d'utilisation par l'appareil de Golgi. Après expédition TDP-43 devrait se trouver dans le noyau.

L'arimoclomol est une thérapie orale qui augmente la production de protéines de réponse au choc thermique (HSP), qui stabilisent les protéines mal repliées et les aident à acquérir leur forme normale. Les HSP dirigent également l'élimination des protéines anormales lorsque le repliement n'est pas possible.

On pourrait donc penser que s'il s'agit en premier lieu d'un problème de repliement, les thérapies qui aident les protéines mal repliées à acquérir leur configuration typique devraient ralentir la progression de la SLA. Cela a été testé avec Arimoclomol. Pour une fois un essai clinique aurait été lancé sur un médicament qui semblait avoir une bonne chance de réussir (bizarrement la plupart des essais cliniques dans les maladies neurodégénératives semblent se faire sur des critères non-scientifiques).

L'arimoclomol a été évalué dans un essai clinique de phase 2/3 antérieur (NCT00706147) chez 36 patients atteints d'une SLA s'aggravant rapidement en raison de mutations SOD1. Le choix de sélectionner des patients SOD1 est assez curieux. Il y a d'innombrables mutations de SOD1, avec des conséquences qui vont de la détérioration extrêmenent rapide (quelques mois) à une détérioration extrêmement lente (décès en 10 ans ou plus). Il y a donc probablementde multiples mécanismes d'action à l'oeuvre. D'autre part l'ensemble des mutations de SOD1 n'est présent que dans 5% des cas de SLA. Mais les mutations de SOD1 sont les premières mutations découvertes dans la SLA et sont de très loin les plus étudiés sans que des progrès maanifestes soient enregistrés depuis 30 ans.

Bien que cet essai clinique n'est pas montré de résults statistiquement significatifs, la société Orphazyme a réussi à trouver le financement pour un essai de phase III. L'essai de phase 3 ORARIALS-01 (NCT03491462) a étudié l'arimoclomol chez 245 adultes atteints de SLA. Cet essai clinique n'a pas atteint ses objectifs. L'arimoclomol n'a pas prolongé la vie des patients ni même retardé la progression de l'invalidité chez les personnes atteintes de la maladie. Autrement dit ça a été un raté spectaculaire, comme la quasi totalité des essais cliniques en matière de SLA.

Bien que je ne soit ni médecin, ni scientifique, cela m'a fait penser que les prémisses du raisonnement préconisant Arimoclomol étaient fausses. Personnellement je suis persuadé que la SLA est due à une réaction de type réponse au stress cellulaire qui ne s'arrête pas et qui détruit les neurones, mais aussi les cellules des muscles. En effet le réponse à un stress cellulaire consiste en un arrêt quasi total de la cellule, cet arrêt ne peut être permanent. Cet arrêt explique très bien la perte de masse musculaire (que les scientifiques expliquent par la mort des motoneurones, alors que cette perte arrive avant cette mort).

Dans cette perspective (toute personnelle), toute action visant à accroitre la dépense énergétique de la cellule (il faut de l'énergie pour replier les protéines), est vouée à l'échec.

Pourtant les scientifiques à l'origine de l'arimoclomol en 2004, semblent être de retour à la table de laboratoire. Cette fois ils ne s'intéressent plus aux mutation SOD1, mais aux mutation de VCP. Les mutations de VCP sont très rares, moins de 1% des cas de SLA. Ils ont mené une étude de l'arimoclomol chez des souris présentant une mutation de la protéine contenant de la valosine (VCP) qui provoque à la fois la SLA et la FTD chez les patients.

Comme dans les études d'arimoclomol sur des souris SOD1, l'amplification de la réponse au choc thermique a amélioré le phénotype de type ALS/FTD dans la moelle épinière et le cerveau des souris mutantes VCP. Arimoclomol y prévient la perte neuronale. De plus, dans des modèles de cellules humaines, les auteurs démontrent des améliorations de la pathologie dans des fibroblastes de patients mutants VCP et des motoneurones dérivés d'iPSC.

Les scientifiques suggèrent que le ciblage de la HSP peut avoir un potentiel thérapeutique, non seulement dans la SLA non-SOD1, mais également pour le traitement de la FTD.

Errare humanum perseverare diabolicum


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