Stocker une vie dans un cerveau

Comment le cerveau stocke t-il l'immense quantité d'informations auxquelles nous sommes confrontés dans un volume relativement restreint comme celui de l'hippocampe, constitue l'une des plus grandes énigmes des neurosciences. Comment le cerveau accède-t-il, sépare-t-il et organise-t-il des millions de souvenirs sans qu'ils ne se mélangent en un amas inutilisable? Et comment se fait-il que des malades d'Alzheimer oublie le nom de leur conjoint ou de leurs enfants, mais pas leur enfance?

La réponse réside dans un stockage hiérarchique et distribué par regroupement fonctionnel dynamique, où les souvenirs sont encodés non pas dans des neurones spécifiques, mais dans de vastes ensembles de neurones par le renforcement et la stabilisation dynamiques des circuits fonctionnels.

Le rôle des assemblages neuronal et du centre CA2

Le cerveau organise l'information en interconnectant des groupes fonctionnels de neurones via leurs synapses, ce que l'on appelle engrammes, qui agissent comme des « étiquettes » organisationnelles.

1. Ce contenu est distribué : Le contenu d’un souvenir (par exemple, les caractéristiques visuelles, la voix, les faits sémantiques) est distribué dans plusieurs aires corticales spécialisées.

2. L'hippocampe est une sorte de carte ou index de ces zones : L’hippocampe agit comme un index rapide et temporaire, reliant ces aires corticales distribuées pour former un souvenir cohérent.

Pour la mémoire sociale en particulier, un index crucial se situe dans une partie spécialisée de l’hippocampe appelée CA2. La région CA2 constitue le centre principal de la reconnaissance sociale dans le cerveau, encodant et maintenant la distinction entre les personnes familières et inconnues. Lorsque vous vous souvenez d’un membre de votre famille, le réseau neuronal spécifique qui représente cette personne est activé, guidé par l’index CA2.

Réseaux péri-neuronaux : Stabilisation du code social

La capacité à maintenir la netteté et la distinction de ces schémas de mémoire sociale uniques dépend fortement d’un composant structurel appelé réseau péri-neuronal.

Le réseau péri-neuronal est une structure spécialisée, dense et réticulaire, composée de la matrice extracellulaire (MEC) qui entoure les corps cellulaires et les dendrites proximales de certains neurones matures, notamment les interneurones inhibiteurs à parvalbumine (PV) à décharge rapide.

Le réseau péri-neuronal agit comme un frein moléculaire sur la plasticité synaptique, une fonction essentielle au maintien de la mémoire:

• Consolidation des codes mémoriels : En se formant autour des interneurones PV dans la région CA2, les réseaux péri-neuronaux stabilisent la force synaptique des circuits qui encodent la mémoire de reconnaissance sociale. Ceci garantit la rétention à long terme de la familiarité.

• Prévention des interférences : Les interneurones PV sont essentiels à l’inhibition ; ils suppriment l’activité des neurones environnants. En stabilisant ces cellules inhibitrices, les réseaux périneuronaux empêchent les interférences et maintiennent des frontières nettes et distinctes nécessaires au stockage de la mémoire.

Le lien avec la maladie d'Alzheimer

Il y a un lien connu depuis quelque temps entre les réseaux péri-neuronaux et la maladie d'Alzheimer.

L'un des symptômes les plus précoces et les plus dévastateurs de la maladie d'Alzheimer est la perte de la mémoire de reconnaissance sociale, soit la difficulté extrême à reconnaître les membres de sa famille et ses proches. La recherche a montré que ce déficit cognitif spécifique est souvent corrélé à la dégradation et à la perte des réseaux péri-neuronaux, notamment dans la région CA2 de l'hippocampe.

La théorie suggère que, lorsque les réseaux péri-neuronaux se dégradent, les interneurones PV inhibiteurs deviennent dysfonctionnels. Le « frein » moléculaire est relâché, entraînant la déstabilisation des circuits CA2. Les assemblages neuronaux distincts associés aux individus familiers ne peuvent plus être maintenus, ce qui provoque une interférence et un brouillage des codes de la mémoire sociale, rendant impossible la distinction entre les visages familiers et inconnus.

Par conséquent, le réseau péri-neuronal n'est pas un simple spectateur ; il constitue un élément clé de l'intégrité structurelle nécessaire au maintien des souvenirs spécifiques, catégorisés et vastes de notre monde social.

Réseaux péri-neuronaux ou plaques amyloïdes

De façon intéressante, certaines découvertes récentes suggèrent que la dégradation des réseaux péri-neuronaux, en particulier dans la région CA2, pourrait être un événement précoce et critique, indépendant de la formation locale de plaques amyloïdes. Ces recherches proposent que la perte de mémoire sociale dans la maladie d'Alzheimer pourrait être une conséquence directe de la dégradation des réseaux péri-neuronaux dans la région CA2, déstabilisant les circuits de la mémoire sociale, avant ou indépendamment du dépôt local et massif de plaques d'amyloïdes.

Ce point de vue complexifie la situation, suggérant que les réseaux péri-neuronaux résistent protègent les neurones qu’elles entourent des pathologies liées aux plaques, mais qu’ils finissent par être dégradées par certains processus pathologiques, ce qui entraîne une déficience cognitive importante et une progression des plaques amyloïdes.

Vers un ralentissement de la progression de la maladie Lata Chaunsali et ses collègues de Virginia School of Medicine ont utilisé le modèle murin 5XFAD de la maladie d'Alzheimer pour étudier le rôle des réseaux périneuronaux autour des neurones CA2 de l'hippocampe dans les troubles de la mémoire sociale associée à la maladie d'Alzheimer.

Les souris atteintes de la maladie d'Alzheimer présentaient une perturbation importante des réseaux péri-neuronauxs de la région CA2, associée à une altération de la mémoire sociale. L'inactivation génétique ou enzymatique des réseaux péri-neuronaux de la région CA2 chez les souris saines reproduisait ces altérations. L'analyse transcriptomique révèle une surexpression des métalloprotéinases matricielles (MMP) clivant les réseaux péri-neuronaux chez les souris atteintes de la maladie d'Alzheimer, induisant un déséquilibre entre la synthèse et le remodelage des réseaux péri-neuronaux.

Les auteurs ont alors testé si les inhibiteurs de MMP — une classe de médicaments déjà étudiée pour leur potentiel dans le traitement du cancer et de l'arthrite — pouvaient prévenir la perte des réseaux périneuronaux. L'ilomastat (code de développement GM6001 et nom commercial Galardin) est un inhibiteur de métalloprotéinases matricielles à large spectre.

Le traitement s'est avéré plutôt efficace, empêchant d'autres lésions et aidant les souris à conserver leurs souvenirs les unes des autres. L'inhibition de l'activité des métalloprotéinases matricielles (MMP) par le GM6001 a prévenu la perturbation des réseaux péri-neuronaux et protègé contre les déficits de mémoire sociale dans ce modèle murin de maladie d'Alzheimer. Évidemment il s'agit là d'une avancée vers un médicament qui ralentirait la progression de la maladie, mais les dégâts étant déjà présents, il est impossible de restaurer les souvenirs disparus.

Une interrogation demeure sur la cause de la destruction des réseaux péri-neuronaux par les métalloprotéinases. En général cela arrive à la suite d’évènements stressants imposant un remodelage des tissus. La recherche a donc des pistes intéressantes à creuser.

Globalement, cette étude fournit également des éléments convaincants que l'inhibition pharmacologique de la protéolyse du réseau péri-neuronal peut prévenir la perte de mémoire sociale, suggérant que les réseaux péri-neuronaux constituent une cible thérapeutique potentielle.

ApoE Isoforms, Glucose and Lipid Metabolism, and PPARα in Neurodegenerative Diseases

Apolipoprotein E (apoE) is essential for lipid transport and neuronal repair in the central nervous system. Of its three main forms—apoE2, apoE3, and apoE4—apoE3 is considered the “neutral” variant, supporting normal lipid balance and synaptic stability. In contrast, apoE4 is a major genetic risk factor for late-onset Alzheimer’s disease and several other neurodegenerative disorders.

Structural differences between apoE3 and apoE4 change how they bind lipids and trigger a cascade of metabolic and inflammatory disturbances that weaken neurons over time.

A key part of this vulnerability lies in energy metabolism. Neurons rely heavily on glucose, but in aging or disease, glucose uptake and utilization often decline. ApoE4 has been linked to reduced glucose transport and impaired mitochondrial efficiency, leading to energy shortages and oxidative stress.

The peroxisome proliferator-activated receptor alpha (PPARα), a nuclear receptor regulating genes involved in fatty acid oxidation and lipid balance, plays a protective role in this context.

Together, apoE isoforms, glucose metabolism, lipid regulation, and PPARα signaling form a tightly linked metabolic network that shapes the progression of neurodegenerative diseases.

The New Study: Sortilin, ApoE, and Neuronal Energy Metabolism

A recent study explored how sortilin, a neuronal receptor, interacts with apoE3 and apoE4 to regulate how neurons use fatty acids for energy. Sortilin is known to participate in brain lipid metabolism and is thought to cooperate with apoE3 to maintain healthy neuronal lipid processing. The authors hypothesized that this partnership fails when sortilin is absent or when apoE4 replaces apoE3.

Experimental Models

Researchers examined four types of genetically modified mice:

• E3WT: human apoE3, sortilin present
• E3KO: human apoE3, sortilin knockout
• E4WT: human apoE4, sortilin present (but functionally impaired)
• E4KO: human apoE4, sortilin knockout

Key Findings

Only the E3WT neurons displayed high mitochondrial respiration (oxygen consumption). All other groups—E3KO, E4WT, and E4KO—showed lower respiration, even though their mitochondria were structurally normal. ➡️ Interpretation: Sortilin–apoE3 interaction is required for neurons to reach full mitochondrial energy capacity.

To identify which energy pathways were affected, the researchers blocked specific fuel routes:

UK5099 blocked glucose-derived pyruvate entry into mitochondria.

Etomoxir blocked long-chain fatty acid (LCFA) import via CPT1A.

They found that the defect was specific to long-chain fatty acid metabolism. Neurons could still metabolize medium- and short-chain fatty acids, which enter mitochondria independently of the carnitine transport system.

Human Cell Models

Using human induced pluripotent stem cells (iPSCs) carrying the same genetic combinations, the team generated astrocytes and neurons. All appeared normal structurally, but only E3WT neurons used both glucose and LCFAs for energy. The others (E3KO, E4WT, E4KO) relied exclusively on glucose, mirroring the mouse results.

When E4 neurons were cultured in medium from E3 astrocytes, their ability to use LCFAs returned. ➡️ Interpretation: ApoE4 disrupts sortilin’s metabolic function, but factors secreted by apoE3 astrocytes can restore it.

Neuronal Activity

Electrical recordings showed that under normal glucose conditions, E3WT and E3KO neurons fired similarly. When glucose was scarce, E3WT neurons maintained their activity by switching to fatty acid metabolism, while E3KO neurons did not. ➡️ Interpretation: Sortilin enables neurons to use fatty acids as an alternative fuel, a key mechanism for metabolic resilience during glucose shortage.

Pharmacological Rescue

Treatment with bezafibrate, a PPARα agonist, restored PPARα activity and increased expression of CPT1A in E3KO and E4 neurons. This also reinstated their sensitivity to etomoxir, indicating that fatty acid oxidation had resumed. ➡️ Interpretation: Activating PPARα can compensate for metabolic defects caused by apoE4 or loss of sortilin.

Conceptual Model

According to the authors, sortilin and apoE3 work together to import and metabolize lipids (especially polyunsaturated and long-chain fatty acids) and to activate PPARα-dependent genes for energy production and neuroprotection.

ApoE4, by binding sortilin abnormally, mimics a loss of sortilin function. Without this partnership, neurons lose their ability to oxidize long-chain fatty acids, leading to reduced mitochondrial respiration, lower levels of protective lipids, and weaker PPARα activation — ultimately impairing neuronal energy resilience.

Translational Outlook

These results are mechanistically insightful but not yet directly applicable to humans. The models reveal how apoE4 and sortilin influence neuronal metabolism, yet human validation remains essential before any clinical translation.

In neurodegenerative diseases, timing is critical. Because neurons in the adult brain do not divide and have very limited regenerative capacity, much of the damage is already irreversible once symptoms appear. Consequently, such studies are most valuable for developing preventive or early interventions, rather than curative therapies.

Current research, therefore, focuses on:

identifying individuals at risk (e.g., through APOE genotyping or early metabolic biomarkers),

and evaluating whether long-term activation of protective pathways — such as PPARα or mitochondrial support mechanisms — could maintain neuronal energy balance and delay disease onset.

Even if started later in life, treatments that restore lipid metabolism or support mitochondrial function might still preserve remaining neurons and slow disease progression.

A recent study analyzed the plasma proteomes of over 2,000 participants to identify proteins and biological pathways associated with Alzheimer's disease and related disorders. https://www.nature.com/articles/s43587-025-00965-4

The widely held hypothesis among scientists is that sticky amyloid plaques in the brain are a hallmark of Alzheimer's disease. With the announcement that the initial work on this hypothesis was fraudulent, along with hundreds of unsuccessful clinical trials, a growing number of scientists suggest that other processes must be at play.

This new study suggests that factors outside the brain, such as processes in the blood and other organs, may contribute to the disease. The authors show that several biological processes, including those related to the extracellular matrix, proteostasis, the immune system, and metabolism, play an important role in Alzheimer's disease. This means that what happens in the rest of the body could influence the brain and how quickly Alzheimer's disease progresses. The study also highlights the strong influence of the APOE ε4 genotype and lipoprotein biology.

Extracellular matrix (ECM):

The ECM is closely linked to cerebral β-amyloid (Aβ) deposition and cognitive decline. Some ECM proteins, such as SMOC1 and SPON1, are elevated in both plasma and the brains of patients with Alzheimer’s, while others, like HTRA1, show opposite trends in the two compartments. Changes in the ECM could impact cognitive function independently of β-amyloid buildup and may be connected to vascular integrity loss.

ECM proteins are found throughout the body and provide structural and biochemical support to cells and tissues. They are produced by various cell types, with fibroblasts being the most common source in connective tissues. Other cells, such as cartilage chondrocytes and kidney mesangial cells, also produce ECM components.

Proteostasis:

This process, involving protein synthesis and clearance, is linked to both Aβ plaques and cognitive function. Increased protein synthesis correlates with better cognition, while enhanced protein degradation links to poorer cognitive performance. Further research is needed to understand how these processes interact in the brain and peripheral tissues.

The proteostasis network, which manages protein synthesis, folding, and degradation, operates across multiple cell compartments in all tissues. As a result, proteins involved in this process originate from organs like the liver, muscle, and adipose tissue.

Immune system:

Activation of the immune response in the blood is strongly associated with declines in cognitive function, even after accounting for Aβ plaques. This suggests that peripheral immune responses may contribute significantly to cognitive impairment.

Proteins involved in immune processes are primarily produced by immune cells like leukocytes (white blood cells) and by other cells in immune-related organs such as the bone marrow, spleen, and thymus.

Synaptic proteins:

The synaptic protein NPTXR was the only protein consistently associated with cognitive performance across all examined groups; higher NPTXR levels correlated with better cognition. However, the study found mixed associations for other neuronal proteins—some indicated healthy brain function, while others signaled neuronal damage.

Metabolism:

Unlike in the brain and cerebrospinal fluid, where increased metabolic proteins associate with cognitive decline, plasma proteins related to metabolism show the opposite trend. This inverse relationship suggests that these proteins may originate from peripheral non-neuronal sources or that their transport across the blood-brain barrier is tightly regulated.

Metabolic proteins participate in processes like glycolysis and energy production. They are produced by cells in tissues such as skeletal muscle, fat, and the liver, which is central to metabolic regulation.

Lipoproteins and APOE ε4:

Lipoprotein biology is closely linked to Aβ buildup in the brain and cognitive function. Lower plasma levels of lipoprotein proteins, including APOE, associate with higher brain Aβ levels. The study also confirms the widespread effects of the APOE ε4 genotype, influencing multiple pathways such as cell division and microtubule functions, potentially connecting Aβ and tau pathologies.

The liver mainly produces and regulates lipoproteins like VLDL and HDL, which are crucial for lipid transport in the bloodstream.

Conclusion:

The study showed that some biological pathways, including the extracellular matrix, are similar across blood, cerebrospinal fluid, and brain, but others, like metabolism and synaptic pathways, differ significantly. These findings emphasize the importance of studying proteins in multiple body compartments to fully understand their role in Alzheimer’s.

The researchers note several limitations, such as incomplete data on factors like medication use, the absence of long-term follow-up data, and limited information on neurofibrillary tangle (NFT) burden in most groups.

In summary, the study illustrates that the complex processes underlying Alzheimer's disease can be detected in blood plasma, identifying potential targets for future therapies and biomarkers. It also supports the idea of using blood tests as a less invasive, more accessible way to study and monitor the disease progression.

Most disease research involves inactivating or deleting biological entities like genes, proteins, or RNA. It's hard to imagine, in principle, how deleting an entity shaped by millions of years of evolution could benefit an organism. It's counterintuitive, yet sometimes it works due to a high level of redundancy in biological functions. What's more interesting, in my opinion, is research that aims to heal from disease by restoring health to a malfunctioning biological system.

Some scientists argue that neurodegenerative diseases are primarily age-related, so strategies to rejuvenate may help. Young plasma or bone marrow can rejuvenate aged animals, but these strategies have drawbacks.

A new study tested whether induced pluripotent stem cell–derived mononuclear phagocytes (iMPs) can offer similar regenerative effects in Alzheimer’s disease.

iPSCs are adult cells reprogrammed back into a stem-cell-like state. From iPSCs, researchers can generate various cell types, in this case, mononuclear phagocytes. It's a group that includes macrophages and microglia-like cells, which are key immune cells in both the body and the brain. The IMP treatment involves injecting these iPSC-derived phagocytes into middle-aged mice (11–12 months). They don’t cross the blood–brain barrier but instead release factors that influence the brain indirectly—for example, by modifying inflammation, supporting microglia, or affecting mossy cells.

What specific, observable results did the authors find? Regarding cognition and behavior, they observed that iMP-treated aging mice performed similarly to young mice in several tasks. In a test called "novel object location," iMPs fully reversed age-related deficits in some models. Most of us, as we age, would benefit from therapy in this area! The effects lasted up to 10 weeks of treatment. These findings were consistent across different mouse models, including immune-deficient NSG, wild-type BALB/c, and AD-prone 5xFAD. However, in Alzheimer’s model mice (5xFAD), iMPs improved memory tasks but did not reduce amyloid plaque load.

The authors found that some cell types benefited from the iMP therapy, but the effects weren’t due to overall neurogenesis. iMPs likely exert their effects via secreted factors. The authors also did not study how sex differences might influence the therapy’s effectiveness.

Overall, I find this article promising, but it has some shortcomings. Induced pluripotent stem cells (iPSCs) often retain an “epigenetic memory” of their tissue of origin. For example, skin-derived iPSCs might still carry subtle molecular traces that bias them toward skin-like fates. This raises questions about the mechanism of action; however, the reprogramming process may have reset many age-related cellular features.

As usual, more studies are needed, including investigations into gender differences. It’s clear that mice are not humans, so this article does not prove that this therapy might work in humans. Nonetheless, the principle behind this therapy appears promising, as it parallels the effects seen with young bone marrow transplants but does not require donor tissue. Additionally, iMPs can be generated autologously, reducing the risk of immune rejection.

A Rare Gene Mutation Offers Clues to Combating Alzheimer’s and Cancer

The human immune system is not only our first line of defense against infectious threats, but it also plays an essential role in regulating how our bodies respond to internal dangers like cancer and neurodegenerative diseases.

One of the immune system’s tools is a molecular pathway known as cGAS-STING. This pathway functions as a sensor, detecting misplaced DNA in cells — a common feature in viral infections, cancer transformations, and some brain disorders.

A rare genetic mutation, first observed in 2019 in a woman with a strong inherited risk for Alzheimer’s disease, may help us better understand and even treat conditions such as Alzheimer’s, cancer, and autoimmune disorders. This woman, who carried a high-risk PSEN1 mutation that usually causes early-onset Alzheimer’s, remained cognitively intact into her seventies. Postmortem analysis revealed extensive amyloid plaques in her brain (a hallmark of Alzheimer’s) but very low tau pathology, which is more closely linked to memory loss and cognitive decline.

Genetic testing showed she carried two copies of a rare variant of the APOE3 gene: R136S, also known as the Christchurch mutation. APOE is a gene long known to influence Alzheimer’s risk, with different variants (APOE2, APOE3, and APOE4) conferring varying levels of protection or susceptibility.

What roles does the cGAS-STING pathway play? Under normal conditions, our cells keep their DNA tightly stored in the nucleus. But sometimes, DNA ends up in the wrong place — floating in the cytoplasm, the main body of the cell. This can happen due to viral infection, cellular stress, or genetic damage. The immune system interprets this misplaced DNA as a danger signal.

cGAS acts as a sensor activated primarily in two pathological contexts: microbial invasion by DNA viruses, bacteria, or retroviruses that introduce exogenous DNA into the cytoplasm, and aberrant leakage of nuclear or mitochondrial self-DNA into the cytosol. When cGAS detects double-stranded DNA in the cytoplasm, it produces a signaling molecule called cGAMP. This molecule then binds to a protein called STING (stimulator of interferon genes), activating a cascade that results in the production of type I interferons and inflammatory cytokines. These signals alert the immune system to potential threats and mobilize a defensive response. Interestingly, TDP-43, which is involved in several degenerative diseases, also has roles in protecting against DNA damage and viruses such as HIV.

While this response is critical for fighting infections and catching early-stage tumors, it can also become problematic when overactive. Persistent or misdirected cGAS-STING activity has been linked to autoimmune diseases, chronic inflammation, and cellular aging (senescence).

New Insights from Mouse Models To explore how exactly the R136S mutation offers protection, researchers engineered mice with human APOE3 or APOE3-R136S genes and introduced a tauopathy-causing mutation (P301S) mimicking key features of Alzheimer’s and frontotemporal dementia.

The findings were compelling: Mice carrying the R136S mutation showed less tau buildup, fewer signs of synaptic and myelin loss, and better brain activity patterns (theta and gamma oscillations important for learning and memory).

At the molecular level, the R136S mutation suppressed the cGAS-STING pathway in microglia, the brain’s resident immune cells.

When researchers treated APOE3 mice (a model of Alzheimer's) with a cGAS inhibitor, these animals exhibited many of the same benefits seen in people who are R136S carriers, including protection from tau-induced synaptic damage and similar gene expression changes across multiple brain cell types.

cGAS-STING: From Immunity to Neurodegeneration This research highlights a key insight: overactivation of cGAS-STING in microglia plays a damaging role in tau-driven neurodegeneration. Misfolded tau proteins can cause inflammation and disrupt brain networks, and microglia that respond too strongly—especially by ramping up interferon signaling through cGAS-STING—may inadvertently worsen the damage.

By reducing this response, the R136S mutation appears to create a more balanced immune environment in the brain. Instead of amplifying harmful inflammation, microglia can more effectively process and break down tau.

The discoveries related to R136S and the cGAS-STING pathway have broad implications:

• Cancer Immunotherapy: The same pathway that detects misplaced DNA in Alzheimer’s also helps identify cancer cells. Modulating cGAS-STING could improve immune responses against tumors or reduce chronic inflammation that promotes their growth.
• Autoimmune Disorders: Conditions like Aicardi–Goutières syndrome involve constant activation of the cGAS-STING pathway, leading the body to attack itself. Understanding how mutations like R136S impact this response may aid in developing treatments that dial down harmful immune activity without compromising protective responses.
• Healthy Aging and Senescence: The cGAS-STING pathway is also involved in cellular aging and the development of the senescence-associated secretory phenotype (SASP). Inhibiting this pathway could delay age-related degeneration and lessen age-related inflammation.

Looking Forward: From Mutation to Medicine

As discussed above, reducing cGAS-STING activity carries risks, including the potential to increase cancer susceptibility in older adults. Additionally, effects may vary across different cell types, benefiting the brain while impairing other vital organs. There are multiple schools of thought about what causes Alzheimer's disease; some incriminate the tau protein, but a majority of researchers are working on mitigating amyloid plaques. Another consideration —though obvious but not often explicitly stated— is that this research provides a preventive tool against Alzheimer's disease. In its early stages, it may slow the disease's progression, but it cannot cure someone who experiences the full impact of the disease.

In conclusion, the cGAS-STING pathway is a crucial sensor of misplaced DNA and a regulator of immune responses. A rare mutation in APOE3 (R136S) has been shown to suppress this pathway in brain immune cells, protecting against tau-related damage in Alzheimer’s models. This discovery opens new avenues for treating neurodegenerative diseases, autoimmune disorders, and cancer through precise modulation of our immune system’s ancient alarm system.

Recent research continues to highlight the complex relationship between cardiovascular health and brain aging. For instance, vascular dementia is one type of dementia. Furthermore, universities are encouraging their teams to identify useful biomarkers for neurodegenerative diseases, as they believe they can generate revenue from potential patents. One quick and inexpensive method to conduct a study is to utilize databases available online.

The Framingham Study is a long-term epidemiological study (since 1948) that initially focused on cardiovascular disease. We owe much of our knowledge about cardiovascular disease to the Framingham Study, particularly regarding the identification of cardiovascular risk factors, including the effects of smoking and diet. Thus, the recognition of high blood pressure as a risk factor for heart disease dates back to 1957, for neurological diseases to 1967, and heart failure to 1971. By Manu5 - http://www.scientificanimations.com/wiki-images/

At the same time, the Framingham Study focused on a relatively affluent population of European origin, meaning the conclusions drawn from it may not necessarily apply to other populations. Furthermore, marker values vary depending on the data collection devices and methods (some values date back to 1948!), so an a priori analysis must consider these difficulties, which is rarely addressed in rapid studies.

The authors of the article discussed in this post selected 822 elderly individuals (mean age: approximately 72 years) from the database who were not suffering from dementia at the time of their first blood test with the Framingham Study. Participants were monitored for Alzheimer's disease until 2020. Over a median follow-up period of 12.5 years, 128 of these individuals developed Alzheimer's disease.

The article authors measured levels of high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), small dense LDL cholesterol (sdLDL-C), lipoprotein a (Lp(a)), apolipoprotein B (ApoB), and the ApoB48 isoform of ApoB in the blood samples collected from 1985 to 1988 by the Framingham Study.

It has long been acknowledged that, although the mechanism is not fully understood, elevated levels of apolipoprotein B (ApoB) are associated with higher concentrations of LDL particles and are the primary driver of plaques that cause vascular disease (atherosclerosis), which typically first manifests as obvious symptoms such as heart disease, stroke, and various other body-wide complications after decades of progression.

Furthermore, the causes of Alzheimer's disease remain poorly understood, but the most significant genetic risk factor arises from an allele of apolipoprotein E. Other risk factors include a history of head trauma, clinical depression, and high blood pressure. The progression of the disease is largely characterized by the accumulation of malformed protein deposits in the cerebral cortex, known as amyloid plaques and neurofibrillary tangles.

Therefore, there is a possible link between dementia and cardiovascular risk, and the Framingham Study database allows us to statistically compare heart health and the risk of developing comorbidities.

The article authors considered a wide range of cholesterol-related markers:

• HDL-C: "Good" cholesterol

• LDL-C: "Bad" cholesterol

• sdLDL-C: Small, dense particles of LDL cholesterol

• ApoB and ApoB48: Proteins involved in cholesterol transport

• Lp(a): A lipoprotein linked to the risk of heart disease

The researchers examined the relationship between these markers, standardized by their standard deviation units (SDUs), and the future risk of Alzheimer's disease.

** sdLDL-C ** They found that high sdLDL-C levels correlate with an increased risk of developing Alzheimer's disease. This result has also been observed by other teams, including a recent one that examined a database in Finland:

SdLDL-C stands for "small dense low-density lipoprotein cholesterol." It is a subclass of LDL particles that are smaller and denser than conventional LDL and more likely to penetrate blood vessel walls. This cholesterol subtype is rarely tested. sdLDL is regarded as a more atherogenic lipoprotein due to its higher retention rate in the arterial wall, better penetration, lower binding affinity to the LDL receptor, lower resistance to oxidative stress, and longer plasma half-life. In addition to being associated with a heightened risk of cardiovascular disease, sdLDL, particularly sdLDL-C levels, have been linked to type 2 diabetes mellitus, metabolic syndrome, obesity, and low-grade inflammation.

** ApoB48 ** Conversely, elevated ApoB48 levels are linked to a reduced risk of Alzheimer's disease. This finding was previously known.

** HDL-C ** However, the authors uncovered surprising results regarding HDL-C, often referred to as "good cholesterol". Numerous epidemiological studies have indicated that high circulating HDL levels are associated with a reduced risk of Alzheimer's disease. Yet, this new study's authors found that participants with the lowest HDL-C levels had a 44% reduced risk of developing Alzheimer's disease compared to those with higher HDL-C levels.

Because HDL-C is generally considered protective, this team's findings may reflect other age-related changes, such as metabolic status or weight loss, that occur before the onset of dementia.

Un article semble démontrer de façon inattendue que certains médicaments contre le VIH et l'hépatite pourraient contribuer à réduire le risque de maladie d'Alzheimer. La maladie d'Alzheimer (MA) reste l'une des maladies les plus complexes de la médecine moderne, tant en termes de traitement que de prévention. Mais des recherches par une équipe de l'université de Virginie menée par Joseph Magagnoli et Meenakshi Ambati, pointent vers un allié potentiel inattendu : une classe de médicaments antiviraux initialement développés pour traiter le VIH et l'hépatite B.

On sait que réduire l'inflammation induite par NLRP3 peut réduire l'impact de la maladie d'Alzheimer. Les inhibiteurs nucléosidiques de la transcriptase inverse (NRTI), sont approuvés par la Food and Drug Administration (FDA) des États-Unis pour traiter les infections par le virus de l'immunodéficience humaine (VIH) et l'hépatite B. L'équipe de Joseph Magagnoli et Meenakshi Ambati avait montré antérieurement des NRTI inhibent également l'activation de l'inflammasome indépendamment de leur activité antirétrovirale. D'autres groupes ont par la suite confirmé cette observation.

Cependant il s'agit là des études pré-cliniques, il y en a des dizaines de milliers chaque année pour la maladie d'Alzheimer et elles ne suffisent pas à convaincre un investisseur de financer une étude clinique qui en phase III coûte au minimum une vingtaine de millions de Dollars. Il faut donc des indications qu'un tel médicament pourrait bénéficier à de spatients humains. Plusieurs moyens peuvent être employés, mais si l'on veut prouver qu'un médicament déjà commercialisé est utile dans une autre maladie, il est intéressant d'étudier les bases de données historiques qui analyse l'évolution d'une cohorte sur une longue période.

Les chercheurs ont analysé deux importantes bases de données de santé américaines afin de répondre à une question simple, mais essentielle : les personnes prenant des inhibiteurs nucléosidiques de la transcriptase inverse (NRTI), un groupe de médicaments antiviraux, présentent-elles un risque moindre de développer la maladie d'Alzheimer ?

Les chercheurs ont examiné plus de 270 000 patients dans deux bases de données : - Administration de la santé des anciens combattants (VA) – 72 193 patients entre 2000 et 2024 - MarketScan (assurance privée) – 199 005 patients entre 2006 et 2020

L’étude a porté sur des personnes âgées de 50 ans ou plus, atteintes du VIH ou d’hépatite B, mais sans diagnostic préalable de maladie d’Alzheimer. L’étude a permis de déterminer les personnes à qui des NRTI étaient prescrits et la durée de leur prise.

L’analyse a pris en compte un large éventail de facteurs susceptibles d’influencer le risque de maladie d’Alzheimer, notamment l’âge, le sexe, l’origine ethnique, les maladies cardiaques, le diabète, la dépression, les lésions cérébrales, etc. Les chercheurs ont également réalisé une analyse spécifique (appelée appariement par score de propension) afin de s’assurer de comparer des groupes de personnes similaires : celles qui prenaient des NRTI et celles qui n’en prenaient pas. Ils ont confirmé qu'une exposition prolongée aux NRTI était associée à un risque moindre de développer la maladie d’Alzheimer. - D’après les données du VA, chaque année supplémentaire de traitement par NRTI était associée à une réduction de 4 à 6 % du risque de maladie d’Alzheimer. - D’après les données de MarketScan, la réduction était encore plus marquée : de 10 à 13 % par année d’utilisation.

Au total il semblerait que la prise d’un NRTI soit associée à une réduction de 32 à 37 % du risque de maladie d’Alzheimer. Attention il s'agit bien de réduction du rique de développer cette maladie, il ne s'agit pas d'un médicament qui guérirait de cette maladie. Une question importante est alors (si ce médicament est autorisé) sur quels critères devrait-on prescrire ce médicament à des personnes apparement saines?

Il s’agit d’une étude observationnelle et non d’un essai clinique ; elle ne prouve donc pas que les NRTI préviennent la maladie d’Alzheimer. Mais la concordance des résultats obtenus sur deux grandes populations, avec des ajustements importants pour d'autres facteurs de santé, rend ces conclusions remarquables.

Ce qui est particulièrement intriguant, c'est que les NRTI sont déjà approuvés et utilisés, ce qui signifie qu'ils pourraient être réutilisés plus rapidement que des médicaments entièrement nouveaux. Et comme la maladie d'Alzheimer est une maladie aux options thérapeutiques limitées, même de petites avancées en matière de prévention pourraient faire une différence significative.

Des essais contrôlés randomisés, sont nécessaires pour confirmer si ces médicaments ont réellement un effet protecteur contre la maladie d'Alzheimer et si ce bénéfice l'emporte sur les risques, en particulier chez les personnes non atteintes du VIH ou de l'hépatite B. Néanmoins, cette recherche ouvre une voie prometteuse.

Researchers are currently very interested in finding biomarkers for the early detection of many neurodegenerative diseases. The market for these technologies is likely to be quite large. Detecting weakened cerebral rigidity before the onset of irreversible damage could pave the way for early intervention in Alzheimer's disease and related disorders. This could be achieved using a device that has now become relatively common: MRI. The hippocampus, a small, seahorse-shaped structure buried deep within the brain, is best known for its role in memory formation and learning. It is an exceptionally vulnerable structure, with perfusion deficits often observed in diseases related to learning and memory. However, a brain affected by Alzheimer's disease tends to exhibit at least moderate cortical atrophy, including in the precuneus and posterior cingulate gyrus. It should be noted that the posterior cingulate gyrus is adjacent to the hippocampus.

A recent study shows a relationship between blood flow and mechanical stiffness (an MRI concept) of the hippocampus. Researchers sought to understand how these physical properties interact in a healthy brain and what this might reveal about early brain changes in neurodegenerative diseases. The researchers used two advanced MRI techniques—magnetic resonance elastography (MRE) and arterial spin labeling (ASL).

Using these tools, the researchers measured: * Tissue stiffness (the resistance of an area to physical deformation) * Perfusion (blood flow at the tissue level)

Seventeen healthy adults were examined by the researchers at two different MRI intensities (3T and 7T), allowing for a cross-comparison between the two magnetic field strengths. They found that the hippocampus had the highest blood flow among the deep gray matter structures, followed closely by the caudate nucleus and putamen.

A strong positive correlation was observed between blood flow and stiffness in the hippocampus, but not in the caudate nucleus, although both regions are highly vascularized. This indicates that good brain health appears to be linked to good blood flow, manifested by the good stability (stiffness) of the tissue.

In a subgroup of ten subjects, it was found that higher blood flow resulted in larger tissue pulsations, suggesting that the dynamics of blood supply physically influence the hippocampus.

These results suggest a previously underestimated link between the physical characteristics of well-perfused brain tissue and its metabolic needs. This connection is not entirely surprising, as the macroscopic characteristics of tissue depend on the well-being of its constituent cells.

Although not mentioned in the article, one might wonder about the relationship between this mechanical property—rigidity—and beta-amyloid (Aβ), the signature protein implicated in Alzheimer's disease.

Beta-amyloid plaques begin to accumulate in the brain well before the onset of symptoms. These plaques can form: * Extracellularly: outside neurons, interfering with cell-to-cell communication and nutrient supply; * Intracellularly: inside neurons and other nerve cells, disrupting protein production.

Based on current knowledge, beta-amyloid likely appears before physical changes in tissues. It emerges early, sometimes decades before cognitive symptoms, triggering a cascade of tissue changes. Mechanical stiffness, as measured by MRE, is more likely a result of these changes than a cause.

Interestingly, numerous MRE studies have observed brain softening, particularly in the hippocampus and cortex, in Alzheimer's patients and those with mild cognitive impairment. This supports the perspective that stiffness decreases due to beta-amyloid pathology and its effects on brain tissue structure.

As fascinating as these findings are, it is important to acknowledge the limitations of the study, which suggest future research directions.

With only 17 participants, the study lacks statistical power, making it vulnerable to false positives or exaggerated effect sizes.

All subjects were young adults (22–35 years old) who were generally healthy, limiting the relevance of the results to aging populations or those at risk for Alzheimer's disease.

The sample did not include key groups, either clinical or high-risk individuals, such as APOE4 gene carriers or those with mild cognitive impairment (MCI).

The study was cross-sectional, capturing a single snapshot in time. We do not yet know how stiffness or perfusion might change over time or in response to pathology.

No cognitive data were collected; therefore, the relationship between hippocampal mechanics and actual memory performance remains unexplored.

There are considerable interpretation challenges: Stiffness, measured by magnetic resonance elastography (MRE), reflects a complex array of biological factors: neuronal density, inflammation, vascular integrity, etc. It is a valuable signal, but not biologically specific. Indeed, perfusion can vary depending on common physiological factors (e.g., hydration, stress).

Because the study did not include beta-amyloid PET scans or fluid biomarkers, the link between mechanical findings and Alzheimer's pathology remains hypothetical.

The analysis focused on the hippocampus and a few other deep gray matter structures. Key cortical regions involved in Alzheimer's disease (such as the entorhinal cortex or precuneus) were not examined.

The emerging link between perfusion and mechanics, and how this relationship deteriorates in the presence of beta-amyloid, could help us uncover subtle clues that precede cognitive decline. Ultimately, measuring something as simple as brain "firmness" could help us identify those at risk and determine when to act.