Fight Aging! Newsletter, January 15th 2024

Genomic instability and inflammation are distinct hallmarks of aging, but the connection between them is poorly understood. Understanding their interrelationship will help unravel new mechanisms and therapeutic targets of aging and age-associated diseases. Here we report a novel mechanism directly linking genomic instability and inflammation in senescent cells, through a mitochondria-regulated molecular circuit that connects the p53 tumor suppressor and cytoplasmic chromatin fragments (CCF), a driver of inflammation through the cGAS-STING pathway.

Activation or inactivation of p53 by genetic and pharmacologic approaches showed that p53 suppresses CCF accumulation and the downstream inflammatory senescence-associated secretory phenotype (SASP), independent of its effects on cell cycle arrest. p53 activation suppressed CCF formation by promoting DNA repair, reflected in maintenance of genomic integrity, particularly in subtelomeric regions, as shown by single cell genome resequencing. Activation of p53 by pharmacological inhibition of MDM2 in old mice decreased features of SASP in liver, indicating a senomorphic role in vivo. Remarkably, mitochondria in senescent cells suppressed p53 activity by promoting CCF formation and thereby restricting ATM-dependent nuclear DNA damage signaling.

This data provides evidence for a mitochondria-regulated p53-CCF circuit in senescent cells that controls DNA repair, genome integrity and inflammatory SASP, and is a potential target for senomorphic healthy aging interventions.

It is commonly said that "age is just a number," and chronologic age, calculated as the time elapsed from birth, has been the primary way to define an individual's age. However, this method fails to account for the complex and diverse processes of aging. Indeed, a person's genetics along with their diet, lifestyle, and cumulative exposure to risk factors leads to significant heterogeneity in biologic age for persons of the same chronologic age. This creates a problem for cardiovascular risk calculators such as the Pooled Cohort Equation (PCE), because chronologic age is the most heavily weighted variable. Nearly all adults younger than 40 years have a low 10-year predicted risk of atherosclerotic cardiovascular disease (ASCVD), while most men older than 60 and women older than 65 years of age have at least an intermediate 10-year ASCVD risk from 7.5% to 20%, regardless of their traditional risk factor burden.

The shortcomings of chronologic age have led to an increased recognition that other measures are needed to better classify an individual's biologic age and ASCVD risk. Genetic biomarkers of DNA methylation and telomere length have been linked to acceleration of the aging processes, but the cost of testing and expertise needed for interpretation of the results limit their widespread use in clinical practice. Interestingly, even a subjective estimation of an individual's perceived age provides significant insight into their biologic age and survival. More direct quantification of arterial or vascular aging with the use of coronary artery calcium (CAC) scoring or noninvasive markers of arterial stiffness such as pulse-wave velocity (PWV) also better classify biologic age, which in turn improves ASCVD risk stratification relative to models that rely on chronologic age and may provide a more accurate and personalized estimate of ASCVD risk.

Compared with measuring systolic and diastolic blood pressure, measuring PWV provides distinct information on vascular health that is specifically related to vascular compliance and distensibility and is an early marker of poor vascular health, even before the development of hypertension. PWV is also strongly associated with cardiovascular outcomes and improves risk prediction beyond traditional cardiovascular risk factors, with a 30% increased risk for cardiovascular disease (CVD) for every 1 standard deviation higher PWV. As such, PWV is one simple method to improve the measurement of biologic age.

Nuclear factor-erythroid 2 (NFE2)-related factor 1 (Nrf1, encoded by NFE2L1) acts as a transcription factor involved in multiple essential life processes, e.g., redox signaling, cellular metabolism, and proteasomal regulation. Of note, NFE2L1 binds to the promoter regions of its target genes through the antioxidant response elements (AREs), crucially to drive transactivation of those stress-responsive and cytoprotective genes, which are also present in the promoters of genes encoding proteasomal subunits. Further studies revealed that NFE2L1 regulates multiple antioxidant genes, such as HMOX1, SOD1, or GCLC; it has also been verified as a master regulator of the ubiquitin-proteasome system (UPS) by controlling the transcriptional expression of almost all proteasome subunits and relevant co-factors.

Multiple neuroprotective interventions, as aforementioned, rely mainly on increasing NFE2L1 activity in neurons, which enhances the cell survival ability to defend against various stressors. NFE2L1 is essential for the proper functioning of proteasomes, and its lack results in an aberrant accumulation of ubiquitinated proteins through the nervous system. Notably, the knockout of the NFE2L1 gene in animal models brings about a severe pathology that resembles human neurodegenerative diseases. In the postmortem analyses, reduced NFE2L1 levels were found in the substantia nigra region of patients with Parkinson's disease and in the hippocampus of patients with Alzheimer's disease. This presents a strong case of NFE2L1 deficiency involved in the pathogenesis of neurodegenerative diseases.

Therefore, it is plausible that NFE2L1 has significant potential in translational medicine to serve as a therapeutic target for these neurodegenerative diseases. Nevertheless, since NFE2L1 is widely expressed throughout a given organism's whole body, a neuron-specific activation of this transcription factor would be more beneficial to minimize off-target effects.

The proteasome plays key roles in synaptic plasticity and memory by regulating protein turnover, quality control, and elimination of oxidized/misfolded proteins. Here, we investigate proteasome function and localization at synapses in Alzheimer's disease (AD) post-mortem brain tissue and in experimental models.

We found a marked increase in ubiquitinylated proteins in post-mortem human AD hippocampi compared to controls. Using several experimental models, we show that amyloid-β oligomers (AβOs) inhibit synaptic proteasome activity and trigger a reduction in synaptic proteasome content. We further show proteasome inhibition specifically in hippocampal synaptic fractions derived from Alzheimer's model mice.

Reduced synaptic proteasome activity instigated by AβOs is corrected by treatment with rolipram, a phosphodiesterase-4 inhibitor, in mice. Results further show that dynein inhibition blocks AβO-induced reduction in dendritic proteasome content in hippocampal neurons. Finally, proteasome inhibition induces AD-like pathological features, including reactive oxygen species and dendritic spine loss in hippocampal neurons, inhibition of hippocampal mRNA translation, and memory impairment in mice. Results suggest that proteasome inhibition may contribute to synaptic and memory deficits in AD.

Fasting mimicking diets (FMDs) have the potential to enhance the efficacy of a wide variety of cancer treatments, weakening cancer cells by a process we termed differential stress sensitization (DSS) while strengthening normal cells by a response termed differential stress resistance (DSR). The effects of fasting/FMD in inducing DSS in both in vitro and in vivo models were previously shown to be mediated, in part, by the reduction of circulating IGF-1 and glucose levels. In a mouse leukemia model, fasting alone reversed the progression of both B cell and T cell acute lymphoblastic leukemia (ALL) but did not affect acute myeloid leukemia (AML).

Here we show that cycles of FMD induce significant anti-leukemia efficacy and cancer-free survival when combined with vincristine, in part by activating T-cell-dependent anti-cancer effects. Fasting/FMD alone causes a trend for increasing autophagy, but when fasting/FMD is combined with vincristine, a significant and consistent downregulation of autophagy markers is observed. This role of autophagy in the FMD/VC-dependent toxicity to ALL cells is confirmed by the effect of the combination of vincristine with the autophagy inhibitor chloroquine, which also promotes p53 modulation, apoptosis, and cancer-free survival in agreement with the established role of p53 in mediating cell death in AML and in solid malignancies.

Fasting/FMD and other dietary restrictions have also been tested clinically in a number of clinical trials. In a prospective, nonrandomized, controlled trial of 40 patients, the potential benefits of caloric restriction were shown (The Improving Diet and Exercise in ALL (IDEAL)) in the efficacy of chemotherapy in patients newly diagnosed with B-ALL. This intervention resulted in a low minimal residual disease risk, high-circulating adiponectin and low insulin resistance. In a randomized controlled study of 131 patients with HER2-negative early-stage breast cancer, FMD cycles significantly enhanced the effects of neoadjuvant chemotherapy on the radiological and pathological tumor response. A short-term fasting-mimicking diet was also well tolerated during chemotherapy in patients with ovarian cancers and appeared to improve quality of life and fatigue. In conclusion, FMD cycles have high potential to be effective in increasing the toxicity of a range of therapies against ALL and other blood cancers and should be tested in randomized clinical trials, especially in combination with immunotherapy and low toxicity cancer therapies.

In summary, we present a new strategy for improving leukemia treatment by combining FMD with chemotherapy to promote the killing of ALL cells in part by an immune-dependent mechanism. Fasting/FMD has been shown to reduce chemotherapy-associated toxicity in pre-clinical and clinical studies and thus represents a safe and potentially effective treatment adjunct for leukemia patients which should be tested clinically.

Mitochondria power the cell and lysosomes keep the cell tidy. Although damage to these two organelles has been linked to aging, cellular senescence, and many diseases, the regulation and maintenance of these organelles has remained poorly understood. There was evidence that a protein called TFEB is involved in maintaining the function of both organelles, but no targets of this protein were known. By comparing all the genes of the cell that are active under particular conditions, and by using a method called chromatin immunoprecipitation, which can identify the DNA targets of proteins, researchers have shown that the gene encoding HKDC1 is a direct target of TFEB, and that HKDC1 becomes upregulated under conditions of mitochondrial or lysosomal stress.

One way that mitochondria are protected from damage is through the process of "mitophagy", the controlled removal of damaged mitochondria. There are various mitophagy pathways, and the most well-characterized of these depends on proteins called PINK1 and Parkin. "We observed that HKDC1 co-localizes with a protein called TOM20, which is located in the outer membrane of the mitochondria. Through our experiments, we found that HKDC1, and its interaction with TOM20, are critical for PINK1/Parkin-dependent mitophagy."

"HKDC1 is localized to the mitochondria, right? Well, this turns out to also be critical for the process of lysosomal repair. Lysosomes and mitochondria contact each other via proteins called VDACs. Specifically, HKDC1 is responsible for interacting with the VDACs; this protein is essential for mitochondria-lysosome contact, and thus, lysosomal repair." These two diverse functions of HKDC1, with key roles in both the lysosome and the mitochondria, help to prevent cellular senescence by simultaneously maintaining the stability of these two organelles.

Ageing is a complex biological process associated with increased morbidity and mortality. Nine classic, interdependent hallmarks of ageing have been proposed involving genetic and biochemical pathways that collectively influence ageing trajectories and susceptibility to pathology in humans. Ageing skeletal muscle undergoes profound morphological and physiological changes associated with loss of strength, mass, and function, a condition known as sarcopenia. The aetiology of sarcopenia is complex and whilst research in this area is growing rapidly, there is a relative paucity of human studies, particularly in older women.

Here, we evaluate how the nine classic hallmarks of ageing: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication contribute to skeletal muscle ageing and the pathophysiology of sarcopenia. We also highlight five novel hallmarks of particular significance to skeletal muscle ageing: inflammation, neural dysfunction, extracellular matrix (ECM) dysfunction, reduced vascular perfusion, and ionic dyshomeostasis, and discuss how the classic and novel hallmarks are interconnected. Their clinical relevance and translational potential are also considered.

We conclude that there is strong evidence for epigenetic alteration, mitochondrial dysfunction, neural dysfunction, and moderate evidence for inflammation, deregulated nutrient sensing, immunoaging, ECM dysfunction, and reduced vascular perfusion as hallmarks for skeletal muscle ageing, with their relevance for sarcopenia evolving.

Glymphatic clearance dysfunction may play an important role in a variety of neurodegenerative diseases and the progression of ageing. However, in vivo imaging of the glymphatic system is challenging. In this study, we describe an MRI method based on chemical exchange saturation transfer (CEST) of the Angiopep-2 probe to visualize the clearance function of the glymphatic system.

We injected rats with Angiopep-2 via the tail vein and performed in vivo MRI at 7 T to track differences in Angiopep-2 signal changes; we then applied the same principles in a bilateral deep cervical lymph node ligation rat model and in ageing rats. We demonstrated the feasibility of Angiopep-2 CEST for visualizing the clearance function of the glymphatic system. Finally, a pathological assessment was performed. Within the model group, the deep cervical lymph node ligation group and the ageing group showed higher CEST signal than the control group. We conclude that this new MRI method can visualize clearance in the glymphatic system.

Reduced expression of the plasma membrane citrate transporter SLC13A5, also known as INDY, has been linked to increased longevity and mitigated age-related cardiovascular and metabolic diseases. Citrate, a vital component of the tricarboxylic acid cycle, constitutes 1-5% of bone weight, binding to mineral apatite surfaces. Our previous research highlighted osteoblasts' specialized metabolic pathway facilitated by SLC13A5 regulating citrate uptake, production, and deposition within bones. Disrupting this pathway impairs bone mineralization in young mice.

New Mendelian randomization analysis using UK Biobank data indicated that SNPs linked to reduced SLC13A5 function lowered osteoporosis risk. Comparative studies of young (10 weeks) and middle-aged (52 weeks) osteocalcin-cre-driven osteoblast-specific Slc13a5 knockout mice (Slc13a5cKO) showed a sexual dimorphism: while middle-aged females exhibited improved elasticity, middle-aged males demonstrated enhanced bone strength due to reduced SLC13A5 function. These findings suggest reduced SLC13A5 function could attenuate age-related bone fragility, advocating for SLC13A5 inhibition as a potential osteoporosis treatment.

Hearing loss has been suggested as a risk factor for dementia, but there is still a need for high-quality research to better understand the association between these two conditions and the underlying causal mechanisms and treatment benefits using larger cohorts and detailed data. This population-based cohort study was conducted in Southern Denmark between January 2003 and December 2017 and included all residents 50 years and older. We excluded all persons with dementia before baseline as well as those who did not live in the region 5 years before baseline, with incomplete address history, or who had missing covariate information.

The study population comprised 573,088 persons (298,006 women [52%]; mean [SD] age, 60.8 [11.3] years) with 23,023 cases of dementia and mean (SD) follow-up of 8.6 (4.3) years. Having a hearing loss was associated with an increased risk of dementia, with an adjusted hazard ratio (HR) of 1.07 compared with having no hearing loss. Severe hearing loss in the better and worse ear was associated with a higher dementia risk, with an HR of 1.20 and 1.13, respectively, compared with having no hearing loss in the corresponding ear. Compared with people without hearing loss, the risk of dementia was higher among people with hearing loss who were not using hearing aids than those who had hearing loss and were using hearing aids, with HRs of 1.20 and 1.06, respectively.

The results of this cohort study suggest that hearing loss was associated with increased dementia risk, especially among people not using hearing aids, suggesting that hearing aids might prevent or delay the onset and progression of dementia. The risk estimates were lower than in previous studies, highlighting the need for more high-quality longitudinal studies.

The immune system of semi-centenarians and super-centenarians (i.e., the oldest centenarians) is believed to have peculiar characteristics that enable them to reach extreme longevity in a relatively healthy state. Therefore, in previous papers, we investigated, through flow cytometry, variations in the percentages of the main subsets of αβ T cells and γδ T cells in a Sicilian cohort of 28 women and 26 men (age range 19-110 years), including 11 long-living individuals (older than 90 years) and 8 oldest centenarians. These investigations suggested that some observed immunophenotypic changes may contribute to the extreme longevity of the oldest centenarians.

In the present study, to further characterize the immunophenotype of the oldest centenarians, we examined the percentages of Natural Killer (NK) cells identified as CD3-CD56+CD16+ in the previously described Sicilian cohort. We found a highly significant increase in NK cell percentages with age. When stratified by gender, this significant increase with age was maintained in both sexes, with higher significance observed in males.

Our findings on NK cells, together with the previously obtained results, discussed in the context of the literature, suggest that these changes are not unfavourable for centenarians, including the oldest ones, supporting the hypothesis that immune aging should be considered as a differential adaptation rather than a general immune alteration. These adapted immune mechanisms allow the oldest centenarians to successfully adapt to a history of insults and achieve remarkable longevity.

This study used DNA methylation (DNAm)-based aging clocks to measure changes in biological age in response to diverse forms of stress. The researchers began with a laboratory experiment known to produce aged physiology in young mice or restore youthful physiology to old mice by surgically joining young, 3-month-old mice with older, 20-month-old mice, which allowed them to share their blood. At the molecular level, they found that the biological age of the young mice increased when measured with most aging clocks. Once the young mice were separated from the old mice and therefore were no longer experiencing the older mouse physiology, their biological age returned to youthful levels. This finding suggested that biological age is malleable and potentially reversible, and these changes are reported by DNAm aging clocks.

Next, the researchers examined blood samples from people who had recently experienced stressful situations, including surgery (emergency versus elective), pregnancy, or severe COVID-19. Analysis of blood samples from patients who underwent emergency surgery showed their biological age increased the morning after surgery and returned to pre-surgery levels four to seven days later. Elective surgeries, on the other hand, had less impact on biological age, which the authors attribute to pre-operative regimens known to aide recovery. Pregnancy in both mice and humans led to increased biological age at delivery, which reverted to lower biological age following delivery and recovery.

Arterial vascular smooth muscle cells (VSMCs) play a central role in the onset and progression of atherosclerosis. Upon exposure to pathological stimuli, they can take on alternative phenotypes that, among others, have been described as macrophage like, or foam cells. VSMC foam cells make up more than 50% of all arterial foam cells and have been suggested to retain an even higher proportion of the cell stored lipid droplets, further leading to apoptosis, secondary necrosis, and an inflammatory response. However, the mechanism of VSMC foam cell formation is still unclear.

Here, it is identified that mechanical stimulation through hypertensive pressure alone is sufficient for the phenotypic switch. Hyperspectral stimulated Raman scattering imaging demonstrates rapid lipid droplet formation and changes to lipid metabolism and changes are confirmed in ABCA1, KLF4, LDLR, and CD68 expression, cell proliferation, and migration. Further, a mechanosignaling route is identified involving Piezo1, phospholipid, and arachidonic acid signaling, as well as epigenetic regulation, whereby CUT&Tag epigenomic analysis confirms changes in the cells (lipid) metabolism and atherosclerotic pathways.

Overall, the results show for the first time that VSMC foam cell formation can be triggered by mechanical stimulation alone, suggesting modulation of mechanosignaling can be harnessed as potential therapeutic strategy.

It remains controversial whether the long-term use of statins or newer nonstatin drugs has a positive effect on human longevity. Therefore, this study aimed to investigate the genetic associations between different lipid-lowering therapeutic gene targets and human longevity. Two-sample Mendelian randomization analyses were conducted. The exposures comprised genetic variants that proxy nine drug target genes mimicking lipid-lowering effects (LDLR, HMGCR, PCSK9, NPC1L1, APOB, CETP, LPL, APOC3, and ANGPTL3). Two large-scale genome-wide association study (GWAS) summary datasets of human lifespan, including up to 500,193 European individuals, were used as outcomes.

Genetically proxied LDLR variants, which mimic the effects of lowering low-density lipoprotein cholesterol (LDL-C), were associated with extended lifespan. This association was replicated in the validation set and was further confirmed in the eQTL summary data of blood and liver tissues. Mediation analysis revealed that the genetic mimicry of LDLR enhancement extended lifespan by reducing the risk of major coronary heart disease, accounting for 22.8% of the mediation effect. The genetically proxied CETP and APOC3 inhibitions also showed causal effects on increased life expectancy in both outcome datasets. The lipid-lowering variants of HMGCR, PCKS9, LPL, and APOB were associated with longer lifespans but did not causally increase extreme longevity. No statistical evidence was detected to support an association between NPC1L1 and lifespan.

This study suggests that LDLR is a promising genetic target for human longevity. Lipid-related gene targets, such as PCSK9, CETP, and APOC3, might potentially regulate human lifespan, thus offering promising prospects for developing newer nonstatin therapies.

Dentin is a complex mineralized tissue primarily composed of hydroxyapatite crystals, collagen fibers, and a fluid-filled tubular structure that extends from the pulp to the dentino-enamel or dentino-cementum junctions. Dentin is formed by highly specialized cells called odontoblasts, which secrete an extracellular matrix comprising collagen fibers and non-collagen proteins that serve as a scaffold for subsequent mineralization. Odontoblasts deposit dentin throughout the life of a tooth, albeit at a slower rate after early dentinogenesis, contributing to the thickening of dentin and potentially aiding in response of the tooth to external insults.

As a consequence of dentinal injury or decay, tertiary dentinogenesis of two different natures occur to protect and maintain dental pulp integrity. When secretory activities of quiescent odontoblasts are re-activated, reactionary dentin that is structurally and functionally similar to physiologic dentin is formed. On the other hand, newly differentiated odontoblast-like cells form pathologic reparative dentin, which is often less organized and more akin to bone-like tissue rather than dentin at the histological level. Likewise, physiologic dentin regeneration and pathologic dentin repair are two distinct processes aimed at restoring dentin functionality following damage, and re-establish a protective barrier for the pulp, alleviate sensitivity, and prevent further loss.

Physiologic dentin regeneration, in particular, seeks to recreate dentin that closely mimics its original, healthy state. This includes the reconstruction of dentinal tubules that integrate seamlessly with remaining dentin, the restoration of dentin-pulp complex, and the engagement of cellular and molecular pathways that govern dentinogenesis. The unique structure and function of true dentin, characterized by its distinctive tubular architecture housing odontoblasts and nerve endings, not only confers mechanical resilience to the tooth but plays a crucial role in the tooth's immune and sensitivity responses. A number of biological molecules that can direct the odontoblastic differentiation of dental pulp cells have been studied, most of which are part of key signaling pathways regulating dentinogenesis during tooth development. These include TGF-β, BMP, and Wnt/β-catenin signaling known to orchestrate the complex processes of cell differentiation, matrix deposition, and mineralization. The use of bioactive molecules in dentin regeneration has emerged as a promising approach, leveraging the biological cues to promote natural tissue regeneration.