The global population of individuals over the age of 65 is growing at an unprecedented rate and is expected to reach 1.6 billion by 2050. Most older individuals are affected by multiple chronic ...diseases, leading to complex drug treatments and increased risk of physical and cognitive disability. Improving or preserving the health and quality of life of these individuals is challenging due to a lack of well‐established clinical guidelines. Physicians are often forced to engage in cycles of “trial and error” that are centered on palliative treatment of symptoms rather than the root cause, often resulting in dubious outcomes. Recently, geroscience challenged this view, proposing that the underlying biological mechanisms of aging are central to the global increase in susceptibility to disease and disability that occurs with aging. In fact, strong correlations have recently been revealed between health dimensions and phenotypes that are typical of aging, especially with autophagy, mitochondrial function, cellular senescence, and DNA methylation. Current research focuses on measuring the pace of aging to identify individuals who are “aging faster” to test and develop interventions that could prevent or delay the progression of multimorbidity and disability with aging. Understanding how the underlying biological mechanisms of aging connect to and impact longitudinal changes in health trajectories offers a unique opportunity to identify resilience mechanisms, their dynamic changes, and their impact on stress responses. Harnessing how to evoke and control resilience mechanisms in individuals with successful aging could lead to writing a new chapter in human medicine.
Finding a reference metric for the rate of biological aging is key to understanding the molecular nature of the aging process. Defining and validating this metric in humans opens the door to a new kind of medicine that will overcome the limitation of current disease definitions. We will then be able to approach health in a global perspective and bring life course preventative measures to the center of attention.
Summary
Mitochondrial function in human skeletal muscle declines with age. Most evidence for this decline comes from studies that assessed mitochondrial function indirectly, and the impact of such ...deterioration with respect to physical function has not been clearly delineated. We hypothesized that mitochondrial respiration in permeabilized human muscle fibers declines with age and correlates with phosphocreatine postexercise recovery rate (kPCr), muscle performance, and aerobic fitness. Mitochondrial respiration was assessed by high‐resolution respirometry in saponin‐permeabilized fibers from vastus lateralis muscle biopsies of 38 participants from the Baltimore Longitudinal Study of Aging (BLSA; 21 men, age 24–91 years) who also had available measures of peak oxygen consumption (VO2max) from treadmill tests, gait speed in different tasks, 31P magnetic resonance spectroscopy, isokinetic knee extension, and grip strength. Results indicated a significant reduction in mitochondrial respiration with age (p < .05) that was independent of other potential confounders. Mitochondrial respiratory capacity was also associated with VO2max, muscle strength, kPCr, and time to complete a 400‐m walk (p < .05). A negative trend toward significance (p = .074) was observed between mitochondrial respiration and BMI. Finally, transcriptional profiling revealed a reduced mRNA expression of mitochondrial gene networks with aging (p < .05). Overall, our findings reinforce the notion that mitochondrial function declines with age and may contribute to age‐associated loss of muscle performance and cardiorespiratory fitness.
To characterize the proteomic signature of chronological age, 1,301 proteins were measured in plasma using the SOMAscan assay (SomaLogic, Boulder, CO, USA) in a population of 240 healthy men and ...women, 22–93 years old, who were disease‐ and treatment‐free and had no physical and cognitive impairment. Using a p ≤ 3.83 × 10−5 significance threshold, 197 proteins were positively associated, and 20 proteins were negatively associated with age. Growth differentiation factor 15 (GDF15) had the strongest, positive association with age (GDF15; 0.018 ± 0.001, p = 7.49 × 10−56). In our sample, GDF15 was not associated with other cardiovascular risk factors such as cholesterol or inflammatory markers. The functional pathways enriched in the 217 age‐associated proteins included blood coagulation, chemokine and inflammatory pathways, axon guidance, peptidase activity, and apoptosis. Using elastic net regression models, we created a proteomic signature of age based on relative concentrations of 76 proteins that highly correlated with chronological age (r = 0.94). The generalizability of our findings needs replication in an independent cohort.
Epigenetic reprogramming underlies specification of immune cell lineages, but patterns that uniquely define immune cell types and the mechanisms by which they are established remain unclear. Here, we ...identified lineage-specific DNA methylation signatures of six immune cell types from human peripheral blood and determined their relationship to other epigenetic and transcriptomic patterns. Sites of lineage-specific hypomethylation were associated with distinct combinations of transcription factors in each cell type. By contrast, sites of lineage-specific hypermethylation were restricted mostly to adaptive immune cells. PU.1 binding sites were associated with lineage-specific hypo- and hypermethylation in different cell types, suggesting that it regulates DNA methylation in a context-dependent manner. These observations indicate that innate and adaptive immune lineages are specified by distinct epigenetic mechanisms via combinatorial and context-dependent use of key transcription factors. The cell-specific epigenomics and transcriptional patterns identified serve as a foundation for future studies on immune dysregulation in diseases and aging.
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•Identifies differential DNA methylation signatures of six human immune cell types•Combinations of transcription factor motifs associate with lineage-specific methylation•EBF1 binding coincides with DNA hypomethylated sites in human B cells•Adaptive and innate immune cells show distinct methylation and gene expression patterns
Epigenetic patterns that define immune cell lineages remain unclear. Roy et al. define DNA methylation signatures of six human immune cell types. Sites of cell-specific differential methylation are related to transcription factors, other epigenetic modifications, and gene expression. Their study reveals differences in the relationship of DNA methylation to tissue-selective gene expression in adaptive compared with innate immune cell types.
Background Patients with peripheral artery disease (PAD) undergo frequent episodes of ischemia-reperfusion in lower extremity muscles that may negatively affect mitochondrial health and are ...associated with impaired mobility. We hypothesized that skeletal muscle from PAD patients will show high mitochondrial DNA heteroplasmy, especially in regions more susceptible to oxidative damage, such as the displacement loop, and that the degree of heteroplasmy will be correlated with the severity of ischemia and mobility impairment. Methods and Results Mitochondrial mutations and deletions and their relative abundance were identified by targeted mitochondrial DNA sequencing in biopsy specimens of gastrocnemius muscle from 33 PAD (ankle brachial index <0.9) and 9 non-PAD (ankle brachial index >0.9) subjects aged ≥60 years. The probability of heteroplasmy per DNA base was significantly higher for PAD subjects than non-PAD within each region. In adjusted models, PAD was associated with higher heteroplasmy than non-PAD (
=0.003), but the association was limited to microheteroplasmy, that is heteroplasmy found in 1% to 5% of all mitochondrial genomes (
=0.004). Heteroplasmy in the displacement loop and coding regions were significantly higher for PAD than non-PAD subjects after adjustment for age, sex, race, and diabetes mellitus (
=0.037 and 0.004, respectively). Low mitochondrial damage, defined by both low mitochondrial DNA copy number and low microheteroplasmy, was associated with better walking performance. Conclusions People with PAD have higher "low frequency" heteroplasmy in gastrocnemius muscle compared with people without PAD. Among people with PAD, those who had evidence of least mitochondrial damage, had better walking performance than those with more mitochondrial damage. Registration URL: http://www.clinicaltrials.gov. Unique identifier: NCT02246660.
The association between blood‐based estimates of mitochondrial DNA parameters, mitochondrial DNA copy number (mtDNA‐CN) and heteroplasmy load, with skeletal muscle bioenergetic capacity was evaluated ...in 230 participants of the Baltimore Longitudinal Study of Aging (mean age:74.7 years, 53% women). Participants in the study sample had concurrent data on muscle oxidative capacity (τPCr) assessed by 31P magnetic resonance spectroscopy, and mitochondrial DNA parameters estimated from whole‐genome sequencing data. In multivariable linear regression models, adjusted for age, sex, extent of phosphocreatine (PCr) depletion, autosomal sequencing coverage, white blood cell total, and differential count, as well as platelet count, mtDNA‐CN and heteroplasmy load were not significantly associated with τPCr (both p > 0.05). However, in models evaluating whether the association between mtDNA‐CN and τPCr varied by heteroplasmy load, there was a significant interaction between mtDNA‐CN and heteroplasmy load (p = 0.037). In stratified analysis, higher mtDNA‐CN was significantly associated with lower τPCr among participants with high heteroplasmy load (n = 84, β (SE) = −0.236 (0.115), p‐value = 0.044), but not in those with low heteroplasmy load (n = 146, β (SE) = 0.046 (0.119), p‐value = 0.702). Taken together, mtDNA‐CN and heteroplasmy load provide information on muscle bioenergetics. Thus, mitochondrial DNA parameters may be considered proxy measures of mitochondrial function that can be used in large epidemiological studies, especially when comparing subgroups.
Mitochondrial DNA copy number and heteroplasmy load provide complementary information on mitochondrial oxidative capacity measured in skeletal muscle. The relationship between mitochondrial DNA copy number and muscle bioenergetics is different according to levels of heteroplasmy load. Assessing mitochondrial DNA copy number and heteroplasmy load may provide cost‐effective and accessible insight into muscle mitochondrial function in large epidemiological studies.
The study of age‐related biomarkers from different biofluids and tissues within the same individual might provide a more comprehensive understanding of age‐related changes within and between ...compartments as these changes are likely highly interconnected. Understanding age‐related differences by compartments may shed light on the mechanism of their reciprocal interactions, which may contribute to the phenotypic manifestations of aging. To study such possible interactions, we carried out a targeted metabolomic analysis of plasma, skeletal muscle, and urine collected from healthy participants, age 22–92 years, and identified 92, 34, and 35 age‐associated metabolites, respectively. The metabolic pathways that were identified across compartments included inflammation and cellular senescence, microbial metabolism, mitochondrial health, sphingolipid metabolism, lysosomal membrane permeabilization, vascular aging, and kidney function.
A targeted metabolomic analysis of plasma, skeletal muscle, and urine from healthy participants was carried out to compare and contrast metabolite changes with aging across and within compartments. The metabolic pathways that were identified included inflammation and cellular senescence, microbial metabolism, mitochondrial health, sphingolipid metabolism, lysosomal membrane permeabilization, vascular aging, and kidney function.
Age-related hearing loss (ARHL) is highly prevalent among older adults, but the potential mechanisms and predictive markers for ARHL are lacking. Epigenetic age acceleration has been shown to be ...predictive of many age-associated diseases and mortality. However, the association between epigenetic age acceleration and hearing remains unknown. Our study aims to investigate the relationship between epigenetic age acceleration and audiometric hearing in the Baltimore Longitudinal Study of Aging (BLSA).
Participants with both DNA methylation and audiometric hearing measurements were included. The main independent variables are epigenetic age acceleration measures, including intrinsic epigenetic age acceleration-"IEAA," Hannum age acceleration-"AgeAccelerationResidualHannum," PhenoAge acceleration-"AgeAccelPheno," GrimAge acceleration-"AgeAccelGrim," and methylation-based pace of aging estimation-"DunedinPoAm." The main dependent variable is speech-frequency pure tone average. Linear regression was used to assess the association between epigenetic age acceleration and hearing.
Among the 236 participants (52.5% female), after adjusting for age, sex, race, time difference between measurements, cardiovascular factors, and smoking history, the effect sizes were 0.11 995% CI: (-0.00, 0.23),
= 0.054 for Hannum's clock, 0.08 95% CI: (-0.03, 0.19),
= 0.143 for Horvath's clock, 0.10 95% CI: (-0.01, 0.21),
= 0.089 for PhenoAge, 0.20 95% CI: (0.06, 0.33),
= 0.004 for GrimAge, and 0.21 95% CI: (0.09, 0.33),
= 0.001 for DunedinPoAm.
The present study suggests that some epigenetic age acceleration measurements are associated with hearing. Future research is needed to study the potential subclinical cardiovascular causes of hearing and to investigate the longitudinal relationship between DNA methylation and hearing.
Senescent vascular smooth muscle cells (VSMCs) accumulate in the vasculature with age and tissue damage and secrete factors that promote atherosclerotic plaque vulnerability and disease. Here, we ...report increased levels and activity of dipeptidyl peptidase 4 (DPP4), a serine protease, in senescent VSMCs. Analysis of the conditioned media from senescent VSMCs revealed a unique senescence-associated secretory phenotype (SASP) signature comprising many complement and coagulation factors; silencing or inhibiting DPP4 reduced these factors and increased cell death. Serum samples from persons with high risk for cardiovascular disease contained high levels of DPP4-regulated complement and coagulation factors. Importantly, DPP4 inhibition reduced senescent cell burden and coagulation and improved plaque stability, while single-cell resolution of senescent VSMCs reflected the senomorphic and senolytic effects of DPP4 inhibition in murine atherosclerosis. We propose that DPP4-regulated factors could be exploited therapeutically to reduce senescent cell function, reverse senohemostasis, and improve vascular disease.
There is evidence that the association of protein intake and frailty may depend on the source of dietary protein. The mechanism underlying this association is not clear. In this study, we explore ...circulating metabolites as mediators of the relationship between dietary protein and of frailty in participants of the Baltimore Longitudinal Study of Aging (BLSA). Cross-sectional analyses in 735 BLSA participants of associations between plant and animal protein intake and frailty. Usual protein intake from plant and animal sources were estimated with a Food Frequency Questionnaire (FFQ) and frailty was assessed with a 44-item Frailty Index (FI). Compared with the lowest quartile, higher quartiles of plant, but not animal, protein were associated with lower FI. Twenty-five plasma metabolites were associated with plant protein intake; of these, fifteen, including phosphatidylcholines, cholesterol esters, sphingomyelins, and indole metabolites, mediated the association between plant protein intake and FI. The protective association between plant protein consumption and FI is mediated by lower abundance of lipid metabolites and higher abundance of tryptophan-related metabolites.
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