Fight Aging! Newsletter, February 8th 2021

The older we grow, the weaker our muscles get, riddling old age with frailty and physical disability. Researchers have now looked at the issue through a different angle: the similarities between muscle aging and degenerative muscle diseases. In the study, the scientists identify amyloid-like protein aggregates in aged muscles from different species, from the nematode C. elegans all the way to humans. In addition, they also found that these aggregates also impair mitochondrial function. Although aggregated proteins have been suggested to contribute to brain aging, this is the first time that they have been shown to contribute to muscle aging and to directly damage mitochondria.

But can the formation of the protein aggregates be reversed? To answer this, the researchers fed worms the vitamin nicotinamide riboside and the antitumor agent Olaparib, both of which boost the levels of nicotinamide adenine dinucleotide (NAD+), a biomolecule that is essential for maintaining mitochondrial function, and whose levels decline during aging. In the worms, the two compounds turned on the defense systems of the mitochondria, even when provided at advanced age. Turning on the so-called "mitochondrial quality control system" of mitophagy reduced the age-related amyloid protein aggregates and improved the worms' fitness and lifespan.

The scientists then moved on to human muscle tissue taken from aged subjects. Turning on the same mitochondrial quality control systems produced similar improvements in protein and mitochondrial homeostasis. The encouraging results led the researchers to test nicotinamide riboside in aged mice. The treatment also activated the mitochondrial defense systems and reduced the number and size of amyloid aggregates in different skeletal muscle tissues.

Due to the fact that mitochondrial function and proteostasis are essential to ensure cellular homeostasis, are functionally interconnected, and decline in aging, it is not surprising that mitochondrial dysfunction and abnormal proteostasis are involved in chronic age-associated neuromuscular proteinopathies, such as Alzheimer's disease (AD), and inclusion body myositis (IBM), a debilitating age-associated muscle disease. Although affecting different organs, AD and IBM are both protein aggregation diseases characterized by the accumulation of amyloid protein deposits. IBM is the most common muscle proteinopathy affecting the elderly; however, it is generally considered a rare disorder, with its overall prevalence still under debate. Skeletal muscle decay instead is one of the most prominent features of aging, characterized by loss of muscle mass and function and by a decline in mitochondrial function. In addition, muscle aging is also typified by dysfunctional proteostasis pathways, including altered ubiquitin-proteasome system (UPS) activity and defective autophagy. Currently, the mechanism underlying the collapse of proteostasis in the aging muscle is not fully elucidated, and it is furthermore unclear whether amyloid deposition, a hallmark of IBM, is also at play in the aging muscle.

Here, we report that, during natural aging, muscle tissues accumulate amyloid-like deposits, a process which is evolutionary conserved in C. elegans, in mouse and human muscle cells and tissues, with molecular features recapitulating some aspects of IBM. Moreover, we also discovered the reversible nature of these deposits, which can be reduced by interventions aimed at restoring mitochondrial homeostasis, such as by enhancing nicotinamide adenine dinucleotide (NAD+) metabolism, even at the onset of aging. Importantly, we show that reduction of the accumulation of amyloid-like deposits in aging is sufficient to improve muscle mitochondrial homeostasis.

Cellvie was founded in the US in 2018 and is headquartered close to Zürich, Switzerland. The founders pioneered the approach of mitochondria augmentation and replacement and the team has now set out to leverage the therapeutic potential of mitochondria for a new treatment modality in ischemia-reperfusion injury, aging and beyond. Mitochondria play a crucial role in the aging process, activating factors and metabolic pathways involved in longevity. Their dysfunction impacts on both lifespan and healthspan. "But treating mitochondria has proven to be an arduous challenge. That is why we turned to introducing healthy, viable mitochondria into cells where these organelles are impaired. To great effect. We can sustainably reinvigorate cells' failing energy metabolism."

The potential of therapeutic mitochondrial transfer was recently demonstrated in a clinical investigation at Boston Children's Hospital; paediatric patients on heart-lung-support after suffering a cardiogenic shock received the treatment to revitalise their heart muscle. 80% of these children experienced myocardial recovery, which compares with an expected 29%. "The investment will enable us to pursue the platform broadly, including a first application in aging, where the need for mitochondria-recovery is particularly dear."

To date, Cellvie has focused primarily on ischemia-reperfusion injury (IRI), which manifests itself whenever the blood flow to a part of the body is interrupted and subsequently reintroduced. Well-known medical conditions causing IRI include heart attacks, strokes, and organ transplantation. Cellvie is also pursuing an indication in organ transplantation, for which the FDA awarded orphan drug designation in 2020. The capital injection will be employed for preparing for market, expanding Cellvie's product pipeline and to prepare an IND submission for a clinical study in kidney transplantation.

The virus-Alzheimer's tug of war continues. New data across several studies weaken the proposed, and much-debated, association; its proponents are holding fast. A new epidemiology study reports a weak link between herpes and dementia. Researchers combed through four European population-wide healthcare databases and describe equivocal data. In Denmark and Wales, short-term antiviral drug use came with slightly fewer future dementia cases. Alas, in Germany and Scotland, this association did not hold. The opposite was also true; infected people who were not prescribed an antiviral had a slightly higher risk of dementia - but only in the German cohort. "The results are not very encouraging. Some of these associations held no matter what type of dementia or virus was considered. Because neither dementia subtype nor herpes subtype modified the association, the small but significant decrease in dementia incidence with antiherpetic administration may reflect confounding and misclassification."

Twenty-five years ago, researchers linked herpes simplex virus type 1 (HSV-1) infection with an increased risk of Alzheimer's disease (AD). She later spotted the virus hiding in amyloid plaques in brain tissue, and postulated that it may trigger the deposits. Since then, other connections have emerged. Scientists linked viral DNA in the brain to expression changes of genes involved in amyloid metabolism; others proposed that amyloid acts as an antimicrobial peptide.

Still, compelling evidence that viruses, particularly herpesviruses, cause AD remains elusive, although some researchers believe that the teeny irritants could speed disease along. The debate has taken on a new sense of urgency since reports that COVID-19 causes long-term neurological symptoms in a fraction of people who contract the disease. Scientists are just beginning to study this aspect of the infection. "Heterogeneous results are not terribly surprising given the complex nature of AD etiology and pathogenesis, which, so far, does not exclude an infectious component."

Every major cause of death and disability in the developed world shares a greatest risk factor, and it is probably not what most people would think. Smoking, obesity, a sedentary lifestyle, and drinking too much alcohol all contribute to disease: however, their contributions are small in comparison to the physiological changes that result from aging. Whether biological aging causes the many functional declines that occur with age, or just permits them, is perhaps open for debate, but there is no question that, for most of us, biological aging determines how and when we and our loved ones will get sick and die.

This connection between aging and disease has become particularly consequential during the COVID-19 pandemic, with the vast majority of severe cases and deaths occurring among the elderly. Given this obvious relationship, it is somewhat surprising how slowly the biomedical research community has come to appreciate the importance of biological aging in many of the disease processes under study.

Today, unfortunately, too many scientists study individual diseases without recognizing the impact of aging biology. It is still common, for example, to see research studies in cancer, neuroscience, metabolism, and other fields where young animal models (such as 4-6 month old mice) are used to study disease processes that almost exclusively occur in old people. 'Mice are not people' is a standard refrain when explaining why so many preclinical therapies fail in human trials. Perhaps the mouse isn't the problem. Failing to account for the physiological changes that occur during aging, both in mice and in people, may be a much bigger reason why so much preclinical research fails to translate to the clinic.

Thinking about certain conserved molecular mechanisms as 'hallmarks' or 'pillars' of aging has benefited researchers within the field, and has also allowed scientists outside the field to begin to recognize how aging biology impacts on their own research. Another important advance in aging research has been the development of a concept called geroscience: researchers in this area seek to understand mechanistically how the hallmarks of aging cause age-related disease and functional decline. The growth of the geroscience concept also reflects a recognition that aging research is much closer to clinical application than it was twenty years ago. Numerous interventions have been developed that target one or more of the hallmarks of aging in order to delay, or even reverse, age-related functional declines.

The future of aging research is brighter than ever before, and the pace of discovery is only increasing. We look forward to major breakthroughs over the next few years that will revolutionize the way we think about aging biology and have the potential to significantly impact human healthspan and longevity.

The calorie restriction diet (CRD) innovative approach consists of a chronic reduction in daily caloric intake of about 25-30% compared to the normal caloric intake, without any exclusion of food groups. Although this regimen is not standardized, numerous studies show its effectiveness. The mechanism of action by which caloric restriction prolongs the life span is not fully understood yet. Recent studies have shown that CRD can determine repair of damaged DNA and decrease fat mass, systolic blood pressure (SBP) and diastolic blood pressure (DBP) values, and the production of free radicals. The results obtained from the CRD can occur quickly, but they can mitigate in case of its suspension.

The CRD would seem to exert a beneficial effect against arterial hypertension (AH) and for this reason represents a useful tool for its clinical management. An important study conducted in this regard was the CALERIE (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy). The CALERIE study was a randomized controlled trial with a two-year follow up. This study was divided in two phases: CALERIE-1 and CALERIE-2. CALERIE-1 study was performed to assess the possible effects induced by a reduction of 10-30% of caloric intake on body composition parameters and lipid profile after 6 and 12 months in a population of middle-aged non-obese subjects. CALERIE-1 results showed an improvement in lipid and glycemic profile and a reduction in body weight (BW) and fat mass.

CALERIE-2 was the largest multi-center study on CRD. A total of 220 subjects were enrolled randomly with a 2:1 allocation into two subgroups: 145 in the CRD group and 75 in the ad libitum group. The CRD group followed 25% caloric restriction for two-years. After two years of diet treatment, cardiometabolic risk factors such as low-density lipoprotein cholesterol (LDL-c), total cholesterol / high-density lipoprotein cholesterol (HDL-c) ratio, SBP and DBP decreased. Moreover, serum biomarkers such as C-reactive protein, insulin sensitivity index and metabolic syndrome score were reduced. Moreover, BW was significantly lower in the CRD group when compared to the ad libitum group (average weight loss in CRD group was 7.5 kg vs average BW increase of 0.1 kg in ad libitum group).

This data showed that a period of two-years of CRD was able to decrease cardiometabolic risk factors in middle-aged non-obese subjects. For this reason, it is possible to consider CRD as nutritional therapeutic approach to enhance life expectancy and reduce the onset of chronic non-communicable diseases such as diabetes mellitus, cancer, chronic kidney disease, and AH, among others.

Other studies have been conducted to investigate the role of CRD in the control of AH. In particular, a study performed on caloric restriction (25%), with two years follow-up, evaluated the possible reduction of CV risk factors and insulin resistance in non-obese subjects and whether the results obtained were maintained over time or were limited to the period study. The authors showed a significant weight loss associated to a decrease in SBP and DBP and an improvement in other parameters, such as lipid profile and insulin resistance. These improvements, with the exception of insulin sensitivity, appeared to be maintained over time.

Research has shown that microglial cells are activated in several neurological diseases, such as Alzheimer's disease, Parkinson's disease, and stroke. People who are affected by these conditions also often fall into a negative mood. Other previous research has suggested that inflammatory processes also play a role in the development of depression. This led the researchers behind the new study to examine more closely whether microglial cells are involved in regulating mood during inflammation. "The study showed that animals feel sick and uneasy when we activate the microglial cells. We demonstrate that two signal molecules, interleukin-6 and prostaglandin E2, are particularly important in these processes. It's not surprising that these signal substances are central, but we were a bit surprised that it is the microglial cells that release these molecules."

During inflammation, many processes are initiated in several cell types. One of the challenges in determining the role played by a specific cell type in the body, therefore, is to isolate its effects. In this study, the scientists used a technique known as chemogenetics, which enabled them to switch on the activity specifically in microglial cells in mice. The researchers activated the microglial cells when the mice were being kept in a certain type of surroundings. The mice subsequently avoided this type of surroundings, which the researchers interpret as showing that the animals disliked the experience. The mice also became less interested in a sweet solution, which they normally find very tempting.

In order to investigate whether the microglial cells are an important link between the immune system and mood, the researchers investigated what happened when microglial cells are inhibited. When the microglial cells were not available for activation, the mice did not feel poorly, even when they had inflammation. This reinforces the idea that these cells are necessary for the process. If further research demonstrates that the biological mechanism described in the study functions in the same way in humans, it may be possible in the long run to reduce symptoms of depression by inhibiting this mechanism.

Aging is often perceived as a degenerative process caused by random accrual of cellular damage over time. In spite of this, age can be accurately estimated by epigenetic clocks based on DNA methylation profiles from almost any tissue of the body. Since such pan-tissue epigenetic clocks have been successfully developed for several different species, it is difficult to ignore the likelihood that a defined and shared mechanism instead underlies the aging process.

To address this, we generated 10,000 methylation arrays, each profiling up to 37,000 cytosines in highly-conserved stretches of DNA, from over 59 tissue-types derived from 128 mammalian species. From these, we identified and characterized specific cytosines, whose methylation levels change with age across mammalian species. Genes associated with these cytosines are greatly enriched in mammalian developmental processes and implicated in age-associated diseases.

From the methylation profiles of these age-related cytosines, we successfully constructed three highly accurate universal mammalian clocks for eutherians, and one universal clock for marsupials. The universal clocks for eutherians are similarly accurate for estimating ages of any mammalian species and tissue with a single mathematical formula. Collectively, these new observations support the notion that aging is indeed evolutionarily conserved and coupled to developmental processes across all mammalian species - a notion that was long-debated without the benefit of this new and compelling evidence.

Researchers have presented data showing that the longevity gene mammalian Indy (mINDY) is involved in blood pressure regulation. Reduced expression of mINDY, which is known to extend life span in lower organisms and to prevent from diet induced obesity, fatty liver, and insulin resistance in mice, has now been shown to lower blood pressure and heart rate in rodents.

The authors provided mechanistic insights for the underlying physiological mechanism based on in vivo data in a genetic knock out model as well as microarray and in vitro studies. Furthermore, the hypothesis is supported by confirming critical effects in vitro using a small molecule inhibitor of mINDY. The authors conclude that deletion of mIndy recapitulates beneficial cardiovascular and metabolic responses to caloric restriction, making it an attractive therapeutic target.

mIndy deletion attenuates sympathoadrenal support of blood pressure and reduced arterial blood pressure and heart rate in a murine knockout model. Blood pressure was assessed invasively using intra-arterial pressure probes over several days. Urinary analysis for catecholamines and metanephrines as well as unbiased transcriptomic analysis of adrenal glands identified the affected biosynthetic pathways. Indeed, catecholamine biosynthesis was attenuated in mINDY-knockout adrenals, whereas plasma steroids and steroid hormone synthesis were unaffected.

In vitro studies on an adrenal cell line supported this hypothesis. mIndy codes for a carboxylic acid transporter protein expressed in plasma membrane. Citrate, the main substrate of the mINDY transporter, increased catecholamine content, while pharmacological inhibition of mINDY by a small molecule inhibitor blunted the effect.

The study looked at the role of MOTS-c, one of several recently identified hormones known to mimic the effects of exercise. However, MOTS-c is unique because it is encoded in the small genome of mitochondria rather than the larger genome in a cell's nucleus. The research team tested how injections of MOTS-c affected mice of different ages by measuring physical capacity and performance in young (2 months), middle-aged (12 months), and old (22 months) mice. When the mice were presented with physical challenges - including maintaining balance on a rotating rod and running on an accelerating treadmill - mice of all ages who had received MOTS-c treatment fared significantly better than untreated mice of the same age.

Even groups of mice that had been fed a high-fat diet showed marked physical improvement after MOTS-c treatment and less weight gain than untreated mice. These findings echo previous research on MOTS-c treatment in mice, which also found that it reversed diet-induced obesity and diet- and age-dependent insulin resistance. Additionally, treating the oldest mice nearing the end of their lives with MOTS-c resulted in marked physical improvements. This late-life treatment improved grip strength, gait (measured by stride length) and physical performance, which was assessed with a walking test (running was not possible at this age)."The older mice were the human equivalent of 65 and above and once treated, they doubled their running capacity on the treadmill. They were even able to outrun their middle-aged, untreated cohorts."

To measure the effects of exercise on MOTS-c levels in people, the researchers collected skeletal muscle tissue and plasma from sedentary, healthy young male volunteers who exercised on a stationary bicycle. Samples were collected before, during and after the exercise as well as following a 4-hour rest. In muscle cells, levels of MOTS-c significantly increased nearly 12-fold after exercise and remained partially elevated after a four-hour rest, while MOTS-c levels in blood plasma also increased by approximately 50% during and after exercise and then returned to baseline after the rest period. The findings suggest that the exercise itself induced the expression of the mitochondrial-encoded regulatory peptides.

Ageing is the gradual decline in organismal fitness that occurs over time leading to tissue dysfunction and disease. At the cellular level, ageing is associated with reduced function, altered gene expression and a perturbed epigenome. Somatic cell reprogramming, the process of converting somatic cells to induced pluripotent stem cells (iPSCs), can reverse these age-associated changes. However, during iPSC reprogramming somatic cell identity is lost, and can be difficult to reacquire as re-differentiated iPSCs often resemble foetal rather than mature adult cells. Recent work has demonstrated that the epigenome is already rejuvenated by the maturation phase of reprogramming, which suggests full iPSC reprogramming is not required to reverse ageing of somatic cells.

Here we have developed the first "maturation phase transient reprogramming" (MPTR) method, where reprogramming factors are expressed until this rejuvenation point followed by withdrawal of their induction. Using dermal fibroblasts from middle age donors, we found that cells reacquire their fibroblast identity following MPTR, possibly as a result of persisting epigenetic memory at enhancers. Excitingly, our method resulted in substantial rejuvenation of multiple cellular attributes, including the transcriptome, which was rejuvenated by around 30 years as measured by a novel transcriptome clock. The epigenome, including H3K9me3 histone methylation levels and the DNA methylation ageing clock, was rejuvenated to a similar extent.

The magnitude of rejuvenation instigated by MTPR is substantially greater than that achieved in previous transient reprogramming protocols. MPTR fibroblasts produced youthful levels of collagen proteins, suggesting functional rejuvenation. Overall, our work demonstrates that it is possible to separate rejuvenation from pluripotency reprogramming, which should facilitate the discovery of novel anti-ageing genes and therapies.

Despite being an extremely simple animal, C. elegans has differentiated organs such as nerves, skeletal muscles, and a digestive tract, and many mammalian animal-related genes are conserved. It is very useful for cutting-edge research in fields like genetics and molecular biology. However, while lifespan analysis of this nematode provides a great deal of useful information, previous lifespan studies had many limitations including 1) sensitivity to various stimuli at room temperature, 2) a long experimental time required for daily measurements, 3) a lack of objectivity due to a tendency for results to be dependent on experimental technique, and 4) the small number of samples that can be processed at one time making it unsuitable for simultaneous measurement of many samples.

The researchers attempted to resolve these issues by developing a new healthy lifespan assessment system that maintained the advantages provided by nematodes. They focused on determining the optimal conditions in a live cell imaging system for automatically measuring nematode survival, such as counting the number of nematodes in a sample, incubation temperature, medium thickness, feeding conditions, imaging interval, and survival determination method. This became C. elegans Lifespan Auto-monitoring System (C-LAS), a fully automated lifespan measurement system that can non-invasively measure a large number of samples (currently up to 36 samples). C-LAS uses overlapping images of nematodes to identify those that are moving, meaning they are alive, and those that are not moving, meaning they are dead.

The researchers performed a mini-population analysis of nematode healthy lifespan using a combination of C-HAS and statistical analysis on common nematodes with the same genetic background. They found that about 28% of the population had average lifespans, about 30% had long and healthy lifespans, about 35% had healthy lifespans but died prematurely, and about 7% had a long period of frailty. They also found that activating - either genetically - or through administration of the drug metformin - AMP-activated protein kinase (AMPK), which is closely associated with healthy life expectancy, dramatically increased the population with healthy longevity and reduced the population with long periods of frailty. Metformin is thought to increase healthy life expectancy in humans, and the present study supports this idea. Currently, clinical trials are underway to ascertain its association with healthy longevity.

The Dutch company Cleara Biotech is developing senescence biomarkers for diagnostics and drug targeting. In 2018 it raised a seed round from Apollo Health. Senisca was spun out of Exeter University in 2020 and is dedicated to the development of new approaches to reverse cellular senescence. Senolytic Therapeutics is a Barcelona-based biotech startup founded in 2017 developing novel medicines that target senescent cells. Life Length is a Spanish company founded in 2010 and has developed a technology for measuring telomere length.

Tree Frog Therapeutics is a French stem cell company that develops C-stem, a platform to accelerate the making of self-replicating cells which can form to grow any part of the human body. The UK-US company Juvenescence is creating a network for longevity companies, scientists as well as AI specialists. It has so far invested in approximately 15 startups. The hopes to IPO in the coming year. Eternans is a UK-based biotech startup, founded in 2017, and is developing senolytic agents to selectively kill senescent cells.

Samsara Therapeutics has developed a screening platform that identifies new molecules that extend healthy lifespan across species, and is funded by Apollo Ventures. The Swiss company Rejuveron is a biotech platform company, that together with entrepreneurial scientists, develops and improves therapies and technologies in this space. The UK-US startup Humanity monitors your rate of ageing and helps users understand which actions will slow down the individual's rate of ageing.

Tracked.bio is a Danish biotechnology company that develops fully automated phenotyping and identification systems for model organisms with the use of deep learning. The systems help effectively evaluate the efficacy of ageing interventions. Age Labs is a Norwegian molecular diagnostics company that discovers, develops and commercialises diagnostic tests for the early detection of age-related diseases. The Swiss startup Centaura, founded in 2019, aims to prevent and reverse ageing by using machine learning to analyse the DNA setup in order to develop an ageing profile.

Aging is a physiological process mediated by numerous biological and genetic pathways, which are directly linked to lifespan and are a driving force for all age-related diseases. Human life expectancy has greatly increased in the past few decades, but this has not been accompanied by a similar increase in their healthspan. At present, research on aging biology has focused on elucidating the biochemical and genetic pathways that contribute to aging over time. Several aging mechanisms have been identified, primarily including genomic instability, telomere shortening, and cellular senescence.

Aging is a driving factor of various age-related diseases, including neurodegenerative diseases, cardiovascular diseases, cancer, immune system disorders, and musculoskeletal disorders. Efforts to find drugs that improve the healthspan by targeting the pathogenesis of aging have now become a hot topic in this field. In the present review, the status of aging research and the development of potential drugs for aging-related diseases, such as metformin, rapamycin, resveratrol, senolytics, as well as caloric restriction, are summarized. The feasibility, side effects, and future potential of these treatments are also discussed, which will provide a basis to develop novel anti-aging therapeutics for improving the healthspan and preventing aging-related diseases.

The enzymes needed to digest most dietary fibers are lacking in the human body. Therefore, the microbiota in the intestine is tasked with fermenting dietary fibers. Fermentation results in the production of short-chain fatty acids (SCFAs), which serve several important functions. In the gut, they aid in microbial growth. They are also second messengers that can modulate gene expression and initiate the synthesis of gut peptides and hormones.

One of the major SCFAs is propionate. In addition to fermentation, two other sources of propionate are food and the oral microbiome. In 1984, the Food and Drug Administration (FDA) labeled propionate as generally recognized as safe (GRAS) and approved its use for food preservation. Therefore, most persons are exposed to dietary sources of propionate every day. As for the oral microbiome, oral microbiota can produce propionate. Increased propionate levels are associated with gingivitis and periodontal disease.

Propionate serves important roles in the human body. However, our review of the current literature suggests that under certain conditions, excess levels of propionate may play a role in Alzheimer's disease (AD). The cause of the excessive levels of propionate may be related to the Bacteroidetes phylum, which are the primary producers of propionate in the human gut. Studies have shown that the relative abundance of the Bacteroidetes phylum is significantly increased in older adults. Other studies have shown that levels of the Bacteroidetes phylum are increased in persons with AD.

There is evidence for such a wide array of different mechanisms that excess propionate likely leads to AD by way of a combination of multiple different mechanisms. Probably the most well-studied mechanism of propionate induced neurotoxicity is related to its ability to impair the urea cycle, the principal pathway for nitrogen metabolism. This condition, known as hyperammonemia, occurs in propionic acidemia (PA), an autosomal recessive genetic disease characterized by an abnormal accumulation of propionic acid. The clinical manifestations of chronic, slightly elevated blood ammonia levels have received relatively little research interest within the field of dementia research. However, considering the well-known neurotoxic nature of ammonia, it is reasonable to speculate that chronically elevated levels of ammonia might be associated with the development of AD.

In the present study, we measured 73 inflammatory proteins in both cerebrospinal fluid (CSF) and plasma in a large clinical cohort in order to investigate inflammatory pathway changes in Alzheimer's disease (AD). Our finding that both CSF and plasma proteins were highly predictive of age in amyloid-β negative, cognitively unimpaired individuals (Aβ- CU) individuals adds to the established evidence that the innate immune system changes even during healthy aging. From this basis, we showed that the AD continuum is characterized by accelerated biological aging of the innate immune system such that mild cognitive impairment (MCI) and AD patients have inflammatory proteomes which are akin to healthy individuals who are significantly older. This finding is in line with similar biological aging studies of AD carried out using structural brain imaging (i.e. brain age), for example.

Importantly, the abnormal inflammatory aging we observed in the AD continuum is differentially expressed across specific inflammatory pathways and can even differ depending on whether proteins are measured in CSF or plasma. For instance, our results showing that plasma-based inflammatory aging was elevated in AD patients compared to amyloid-β negative (Aβ-) MCI patients suggest that cross-sectional inflammatory levels as measured in plasma may be more AD-specific at a given point in time compared to those measured in CSF. Since CSF-based inflammatory aging correlated strongly with core AD biomarkers and predicted chronological age better than plasma in the main Aβ- CU group, CSF inflammatory proteins likely track more closely with those brain-based inflammatory changes which occur during normal aging.