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.
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.
Aging is characterized by rising susceptibility to development of multiple chronic diseases and, therefore, represents the major risk factor for multimorbidity. From a gerontological perspective, the ...progressive accumulation of multiple diseases, which significantly accelerates at older ages, is a milestone for progressive loss of resilience and age-related multisystem homeostatic dysregulation. Because it is most likely that the same mechanisms that drive aging also drive multiple age-related chronic diseases, addressing those mechanisms may reduce the development of multimorbidity. According to this vision, studying multimorbidity may help to understand the biology of aging and, at the same time, understanding the underpinnings of aging may help to develop strategies to prevent or delay the burden of multimorbidity. As a consequence, we believe that it is time to build connections and dialogue between the clinical experience of general practitioners and geriatricians and the scientists who study aging, so as to stimulate innovative research projects to improve the management and the treatment of older patients with multiple morbidities.
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.
Skeletal muscle is a large organ that accounts for up to half the total mass of the human body. A progressive decline in muscle mass and strength occurs with ageing and in some individuals configures ...the syndrome of ‘sarcopenia’, a condition that impairs mobility, challenges autonomy, and is a risk factor for mortality. The mechanisms leading to sarcopenia as well as myopathies are still little understood. The Human Skeletal Muscle Proteome Project was initiated with the aim to characterize muscle proteins and how they change with ageing and disease. We conducted an extensive review of the literature and analysed publically available protein databases. A systematic search of peer‐reviewed studies was performed using PubMed. Search terms included ‘human’, ‘skeletal muscle’, ‘proteome’, ‘proteomic(s)’, and ‘mass spectrometry’, ‘liquid chromatography‐mass spectrometry (LC‐MS/MS)’. A catalogue of 5431 non‐redundant muscle proteins identified by mass spectrometry‐based proteomics from 38 peer‐reviewed scientific publications from 2002 to November 2015 was created. We also developed a nosology system for the classification of muscle proteins based on localization and function. Such inventory of proteins should serve as a useful background reference for future research on changes in muscle proteome assessed by quantitative mass spectrometry‐based proteomic approaches that occur with ageing and diseases. This classification and compilation of the human skeletal muscle proteome can be used for the identification and quantification of proteins in skeletal muscle to discover new mechanisms for sarcopenia and specific muscle diseases that can be targeted for the prevention and treatment.
The decrease in skeletal muscle mitochondrial oxidative capacity with age adversely affects muscle strength and physical performance. Factors that are associated with this decrease have not been well ...characterized. Low plasma lysophosphatidylcholines (LPC), a major class of systemic bioactive lipids, are predictive of aging phenotypes such as cognitive impairment and decline of gait speed in older adults. Therefore, we tested the hypothesis that low plasma LPC are associated with impaired skeletal muscle mitochondrial oxidative capacity. Skeletal muscle mitochondrial oxidative capacity was measured using in vivo phosphorus magnetic resonance spectroscopy (31P‐MRS) in 385 participants (256 women, 129 men), aged 24–97 years (mean 72.5) in the Baltimore Longitudinal Study of Aging. Postexercise recovery rate of phosphocreatine (PCr), kPCr, was used as a biomarker of mitochondrial oxidative capacity. Plasma LPC were measured using liquid chromatography–tandem mass spectrometry. Adults in the highest quartile of kPCr had higher plasma LPC 16:0 (p = 0.04), 16:1 (p = 0.004), 17:0 (p = 0.01), 18:1 (p = 0.0002), 18:2 (p = 0.002), and 20:3 (p = 0.0007), but not 18:0 (p = 0.07), 20:4 (p = 0.09) compared with those in the lower three quartiles in multivariable linear regression models adjusting for age, sex, and height. Multiple machine‐learning algorithms showed an area under the receiver operating characteristic curve of 0.638 (95% confidence interval, 0.554, 0.723) comparing six LPC in adults in the lower three quartiles of kPCr with the highest quartile. Low plasma LPC are associated with impaired mitochondrial oxidative capacity in adults.
ABSTRACTSarcopenic obesity, the combination of skeletal muscle mass and function loss with an increase in body fat, is associated with physical limitations, cardiovascular diseases, metabolic stress, ...and increased risk of mortality. Cannabinoid receptor type 1 (CB1R) plays a critical role in the regulation of whole‐body energy metabolism because of its involvement in controlling appetite, fuel distribution, and utilization. Inhibition of CB1R improves insulin secretion and insulin sensitivity in pancreatic β‐cells and hepatocytes. We have now developed a skeletal muscle–specific CB1R‐knockout (Skm‐CB1R−/−) mouse to study the specific role of CB1R in muscle. Muscle‐CB1R ablation prevented diet‐induced and age‐induced insulin resistance by increasing IR signaling. Moreover, muscle‐CB1R ablation enhanced AKT signaling, reducing myostatin expression and increasing IL‐6 secretion. Subsequently, muscle‐CB1R ablation increased myogenesis through its action on MAPK‐mediated myogenic gene expression. Consequently, Skm‐CB1R−/− mice had increased muscle mass and whole‐body lean/fat ratio in obesity and aging. Muscle‐CB1R ablation improved mitochondrial performance, leading to increased whole‐body muscle energy expenditure and improved physical endurance, with no change in body weight. These results collectively show that CB1R in muscle is sufficient to regulate whole‐body metabolism and physical performance and is a novel target for the treatment of sarcopenic obesity. —González‐Mariscal, I., Montoro, R. A., O'Connell, J. F., Kim, Y., Gonzalez‐Freire, M., Liu, Q.‐R., Alfaras, I., Carlson, O. D., Lehrmann, E., Zhang, Y., Becker, K. G., Hardivillé, S., Ghosh, P., Egan, J. M. Muscle cannabinoid 1 receptor regulates Il‐6 and myostatin expression, governing physical performance and whole‐body metabolism. FASEB J. 33, 5850–5863 (2019). www.fasebj.org
Sarcopenia, the age‐related loss of muscle mass and strength, is linked to a range of adverse outcomes, such as impaired physical performance, cognitive function, and mortality. Preventing sarcopenia ...may reduce the burden of functional decline with aging and its impact on physiological and economic well‐being in older adults. Mitochondria in muscle cells lose their intrinsic efficiency and capacity to produce energy during aging, and it has been hypothesized that such a decline is the main driver of sarcopenia. Oxidative phosphorylation becomes impaired with aging, affecting muscle performance, and contributing to an age‐associated decline in mobility. However, it is unclear whether this deterioration is due to a reduced mitochondria population, decreased mitochondrial energetic efficiency, or a reduced capacity to dynamically transport oxygen and nutrients into the mitochondria, and addressing these questions is an active area of research. Further research in humans will require use of new “omics” technologies, progress in neuroimaging techniques that permit energy production assessment, and visualization of molecules critical for energetic metabolism, as well as proxy biomarkers of muscle perfusion.
Background
Muscle quality (MQ) or strength‐to‐mass ratio declines with aging, but the rate of MQ change with aging is highly heterogeneous across individuals. The identification of risk factors for ...accelerated MQ decline may offer clues to identity the underpinning physiological mechanisms and indicate targets for prevention and treatment. Using data from the Baltimore Longitudinal Study of Aging, we tested whether measures of body mass and body composition are associated with differential rates of changes in MQ with aging.
Methods
Participants included 511 men and women, aged 50 years or older, followed for an average of 4 years (range: 1–8). MQ was operationalized as ratio between knee‐extension isokinetic strength and CT‐thigh muscle cross‐sectional area. Predictors included body mass and body composition measures: weight (kg), body mass index (BMI, kg/m2), dual‐energy x‐ray absorptiometry‐measured total body fat mass (TFM, kg) and lean mass (TLM, kg), and body fatness (TFM/weight). Covariates were baseline age, sex, race, and body height.
Results
Muscle quality showed a significant linear decline over the time of the follow up (average rate of decline 0.02 Nm/cm2 per year, P < .001). Independent of covariates, neither baseline body weight (P = .756) nor BMI (P = .777) was predictive of longitudinal rate of decline in MQ. Instead, higher TFM and lower TLM at baseline predicted steeper longitudinal decline in MQ (P = .036 and P < .001, respectively). In particular, participants with both high TFM and low TLM at baseline experienced the most dramatic decline compared with those with low TFM and high TLM (about 3% per year vs. 0.5% per year, respectively). Participants in the higher tertile of baseline body fatness presented a significantly faster decline of MQ than the rest of the population (P = .021). Similar results were observed when body mass, TFM, and TLM were modeled as time‐dependent predictors.
Conclusions
Body composition, but not weight nor BMI, is associated with future MQ decline, suggesting that preventive strategies aimed at maintaining good MQ with aging should specifically target body composition features.
Age‐related macular degeneration (AMD) is a leading cause of visual loss among older adults. Two variants in the complement factor H (CFH) gene, Y402H and I62V, are strongly associated with risk of ...AMD. CFH is encoded in regulator of complement activation gene cluster in chromosome 1q32, which includes complement factor related (CFHR) proteins, CFHR1 to CFHR5, with high amino acid sequence homology to CFH. Our goal was to build a SRM assay to measure plasma concentrations of CFH variants Y402, H402, I62, and V62, and CFHR1‐5. The final assay consisted of 24 peptides and 72 interference‐free SRM transition ion pairs. Most peptides showed good linearity over 0.3–200 fmol/μL concentration range. Plasma concentrations of CFH variants and CFHR1‐5 were measured using the SRM assay in 344 adults. Plasma CFH concentrations (mean, SE in μg/mL) by inferred genotype were: YY402, II62 (170.1, 31.4), YY402, VV62 (188.8, 38.5), HH402, VV62 (144.0, 37.0), HY402, VV62 (164.2, 42.3), YY402, IV62 (194.8, 36.8), HY402, IV62 (181.3, 44.7). Mean (SE) plasma concentrations of CFHR1‐5 were 1.63 (0.04), 3.64 (1.20), 0.020 (0.001), 2.42 (0.18), and 5.49 (1.55) μg/mL, respectively. This SRM assay should facilitate the study of the role of systemic complement and risk of AMD.
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