Effect of age on peptide chain initiation and elongation in preparations from brain, liver, kidney and skeletal muscle of the C57B1/6J mouse

G-quadruplexes and associated proteins in aging and Alzheimer's disease

Aging is a prominent risk factor for many neurodegenerative disorders, such as Alzheimer's disease (AD). Alzheimer's disease is characterized by progressive cognitive decline, memory loss, and neuropsychiatric and behavioral symptoms, accounting for most of the reported dementia cases. This disease is now becoming a major challenge and burden on modern society, especially with the aging population. Over the last few decades, a significant understanding of the pathophysiology of AD has been gained by studying amyloid deposition, hyperphosphorylated tau, synaptic dysfunction, oxidative stress, calcium dysregulation, and neuroinflammation. This review focuses on the role of non-canonical secondary structures of DNA/RNA G-quadruplexes (G4s, G4-DNA, and G4-RNA), G4-binding proteins (G4BPs), and helicases, and their roles in aging and AD. Being critically important for cellular function, G4s are involved in the regulation of DNA and RNA processes, such as replication, transcription, translation, RNA localization, and degradation. Recent studies have also highlighted G4-DNA's roles in inducing DNA double-strand breaks that cause genomic instability and G4-RNA's participation in regulating stress granule formation. This review emphasizes the significance of G4s in aging processes and how their homeostatic imbalance may contribute to the pathophysiology of AD.

Protein translation paradox: Implications in translational regulation of aging

Protein translation is an essential cellular process playing key roles in growth and development. Protein translation declines over the course of age in multiple animal species, including nematodes, fruit flies, mice, rats, and even humans. In all these species, protein translation transiently peaks in early adulthood with a subsequent drop over the course of age. Conversely, lifelong reductions in protein translation have been found to extend lifespan and healthspan in multiple animal models. These findings raise the protein synthesis paradox: age-related declines in protein synthesis should be detrimental, but life-long reductions in protein translation paradoxically slow down aging and prolong lifespan. This article discusses the nature of this paradox and complies an extensive body of work demonstrating protein translation as a modulator of lifespan and healthspan.

Effects of aging on human skeletal muscle myosin heavy-chain mRNA content and protein isoform expression

The purpose of this investigation was to determine the role played by pretranslational events in the decreased rate of myosin heavy-chain (MyHC) protein synthesis in old age. It was hypothesized that the decreased rate of MyHC protein synthesis reported in the elderly population is, at least in part, related to lower MyHC messenger RNA (mRNA) in old age. MyHC protein expression and mRNA levels for the three MyHC isoforms expressed in human muscle, that is, types I, IIa, and IIx/d, were measured in percutaneous vastus lateralis muscle biopsies from 16 young and 16 old healthy men. The MyHC isoform mRNA content was determined by quantitative, real-time reverse transcriptase polymerase chain reaction, and it was normalized to 18S ribosomal RNA; the relative MyHC protein isoform content was measured on silver-stained 7% sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels. The old men demonstrated signs of sarcopenia, such as loss of muscle force, a trend toward a loss in lean body mass, and an increased percentage of body fat. Statistically significant correlations were observed between the isoform expression of different MyHCs at the protein and mRNA levels. However, the expression of the different MyHC isoforms at the mRNA and protein levels did not differ between the young and old men. Thus, the present results do not support the hypothesis that pretranslational events in MyHC protein synthesis are playing a significant role in the development of sarcopenia.

Concentrations of free carnosine (a putative membrane-protective antioxidant) in human muscle biopsies and rat muscles

Carnosine has possible functional effects on skeletal muscle contractility, along with membrane-protective, antioxidant effects. We determined tissue free carnosine concentrations in skeletal muscles from patients with neuromuscular diseases and in skeletal and heart muscles from rats of various ages. The effects of age, gender and diagnostic category on free carnosine levels in patients with neuromuscular diseases were analyzed by a stepwise multiple linear regression model. The age of the patients emerged as a significant negative predictor of carnosine concentrations (R=-0.40, P<0.05). Free carnosine concentrations in rat skeletal muscles also showed a significant negative correlation with the ages of the rats (male rats: R=-0.49, P<0.05; female rats: R=-0.56, P<0.05). Only the diagnostic category amyotrophic lateral sclerosis (ALS) emerged as a significant negative predictor compared to the control group in the stepwise regression model, this was confirmed by Wilcoxon Signed Rank Test (P<0.05). We conclude that the age-related decline in muscle mass, strength and function is associated with decreased tissue concentrations of the putative membrane-protective antioxidant carnosine. In addition we found decreased carnosine tissue concentrations in ALS. The reduction in carnosine content might be caused by progressive denervation processes.

Age effects on serum amino acids in endurance exercise at the aerobic/anaerobic threshold in patients with neuromuscular diseases

We have measured concentrations of 26 serum amino acids in 46 subjects (aged 17-75 years), with the following neurological diseases: amyotrophic lateral sclerosis, n=7; peripheral neuropathy, n=5; muscular dystrophy, n=7; mitochondriopathy, n=3; metabolic myopathy (others), n=2; inflammatory myopathy, n=4; mononeuropathy, n=3; controls (patients with symptoms suggesting neuromuscular system dysfunction without objective evidence of neuromuscular disease), n=15, before and after prolonged muscular effort. Tests were done on a bicycle ergometer at the individual aerobic/anaerobic threshold determined for each subject in preliminary tests. Using a stepwise multiple linear regression model, age emerged as a significant negative predictor (P<0.05) of the post/before ratio of the levels of five amino acids. We conclude that an increase in recovery time and a reduction in training capacity with aging could be linked to these changes. The cause is assumed to be principally a reduction in glycogen storage in muscle with increasing age; this situation could possibly be improved by consumption of carbohydrate before or during exercise, or also during rehabilitation exercise or training in neuromuscular or other diseases.

Tissue concentrations of nerve growth factor in aging rat heart and skeletal muscle

In order to examine the association between adult nerve growth factor (NGF) levels and age-related changes in skeletal and heart muscle mass, we determined NGF concentrations in both tissues. NGF concentrations in rat heart muscle were significantly higher than those in skeletal muscle. NGF concentrations in heart muscle had a significant positive correlation with heart muscle wet weight. A causal association may exist between age-related changes in adult heart muscle mass and tissue NGF levels (in contrast to skeletal muscle). Among the potential clinical implications for skeletal muscle, it appears that age-related delay or deterioration in regeneration processes in neuromuscular diseases, or age-related decline in skeletal muscle mass, are not caused by reduced tissue NGF concentrations.

Polyadenylated RNA, actin mRNA, and myosin heavy chain mRNA in young and old human skeletal muscle

The myofibrillar protein synthesis rate in old human skeletal muscle is slower than that in young adult muscle. To examine whether this difference in protein synthesis rate is explained by reduced availability of the mRNAs that encode the most abundant myofibrillar proteins, we determined relative hybridization signals from probes for actin mRNA, myosin heavy chain mRNA, and total polyadenylated RNA in vastus lateralis muscle biopsies taken from young (22- to 31-yr-old) and old (61- to 74-yr-old) human subjects. The mean fractional rate of myofibrillar synthesis was 38% slower in the older muscles, as determined by incorporation of a stable isotope tracer. Total actin and myosin heavy chain mRNAs, and polyadenylated RNA, were determined using slot-blot assays. Isoform-specific determinations of alpha-actin mRNA, type I myosin heavy chain mRNA, and type IIa myosin heavy chain mRNA were done with ribonuclease protection assays. Hybridization signals were expressed relative to tissue DNA content. There was no difference between age groups in total polyadenylated RNA or in any of the specific mRNAs. We conclude that the slower myofibrillar synthesis rate in older muscle is not caused by reduced mRNA availability.

Myofibrillar protein synthesis in young and old men

We tested the hypothesis that healthy older men (> 60 yr old) have a slower rate of myofibrillar protein synthesis than young men (< 35 yr old). Myofibrillar protein synthesis was determined by the in vivo incorporation of L-[1-13C]leucine into myofibrillar proteins obtained by muscle biopsy. Subjects were eight young (21-31 yr) and eight older (62-81 yr) men, all healthy and moderately active. There was no significant difference in the mean height and weight of the two age groups, but the older group had 12% less lean body mass (determined by 40K counting) and 21% less muscle mass (estimated by urinary creatinine excretion). Upper leg strength was approximately one-third lower in the older subjects according to isokinetic dynamometry. The fractional rate of myofibrillar protein synthesis was 28% slower in the older group (0.039 +/- 0.009 vs. 0.054 +/- 0.010 %/h, mean +/- SD, P < 0.01). Total myofibrillar protein synthesis, estimated as total myofibrillar mass (from creatinine excretion) times the fractional synthesis rate, was 44% slower in the older group (1.4 vs. 2.5 g/h, P < 0.001). Whole body protein synthesis, assessed as the difference between leucine disappearance rate and leucine oxidation, was marginally slower (8%, P = 0.10) in the older group, but not when the data were adjusted for lean body mass. Myofibrillar protein synthesis was a smaller fraction of whole body protein synthesis in the older group (12 vs. 19%). Reduced myofibrillar protein synthesis may be an important mechanism of the muscle atrophy associated with aging.

Protein synthesis and the components of protein synthetic machinery during cellular aging

The slowing down of protein synthesis is a change widely observed during the aging of organisms. It has also been claimed that a decline in the rate of protein synthesis occurs during cellular aging. However, the evidence in favour of this view is not clear-cut, and reliable estimates of rates of protein synthesis during cellular aging have yet to be made. Studies on various components of the protein synthetic machinery during cellular aging have revealed a decline in the efficiency and accuracy of ribosomes, an increase in the levels of rRNA and tRNA, and a decrease in the amounts and activities of elongation factors. Detailed studies on the structure and function of ribosomes, tRNA isoacceptor profiles, activities of aminoacyl-tRNA synthetases, levels and activities of initiation factors, rates of protein elongation, and the accuracy of protein synthesis will be needed before the molecular mechanisms of the regulation of protein synthesis during cellular aging can be understood.

Protein synthesis by liver ribosomes from aged rats

The age-related decrease in protein synthesis by cell-free systems has been traced to a factor which can be obtained by high salt extraction of young polysomes. Such extracts, when added to old ribosomes in young post-ribosomal supernate, stimulate the level of Poly(U)-directed protein synthesis. Extracts of old polysomes have essentially no effect. The deficient factor is not EF-2 and is highly unlikely to be EF-1, as this component resides almost entirely in the post-ribosomal supernates used in the reaction mixture. Since initiation factors are not necessary for Poly(U)-directed protein synthesis and EF-1 and EF-2 do not appear to be involved, the nature of the soluble factor which is deficient in old ribosomes appears to lie outside of proteins which are commonly implicated in the age-related slowing of protein synthesis.

Changes in activity and amount of active elongation factor 1 alpha in aging and immortal human fibroblast cultures

Stoichiometrically estimated amounts of active elongation factor, EF-1 alpha, remain constant in serially passaged Phase II cultures of human fibroblasts, MRC-5, but decrease by 45% towards the end (Phase III) of their lifespan. Catalytic activity of EF-1 alpha is also reduced by 35% in Phase III old cells. The SV40 transformed immortal cell line MRC-5V2 has 30% higher levels of active EF-1 alpha without significant increase in its catalytic activity. Low-serum-associated G1 arrest of normal and transformed cells reduces amounts of active EF-1 alpha by 35% and 20%, respectively. Catalytic activity, however, is reduced rapidly only in G1 arrested normal cells and not in transformed cells. Even though the cell cycle-related changes are reversible both in normal and transformed cells, the age-related decline in amounts of active EF-1 alpha and its activity are irreversible and, most probably, crucial.

Effects of dietary choline on memory and brain chemistry in aged mice

The purpose of this study was to investigate in more detail the characteristics of the age-related extension of the retrograde amnesia gradient previously demonstrated in a passive avoidance task [6]. In Experiment 1, it was found that while 2-3 month old mice were susceptible to the amnesic effects of anisomycin (ANI) only when given prior to 15 min post-training, memory of 14-16 month old mice was susceptible to disruption when ANI was given as late as 20 min post-training, and retention of 17-20 month old mice was impaired when ANI was injected even as late as 30 min after training. Experiment 2 examined whether the age-related change in susceptibility to the effects of ANI could be ameliorated by chronic pretreatment with a choline-enriched diet. Results showed that ANI injected 20 min after training did not induce amnesia in choline treated mice (14.5 month old), but did induce amnesia when injected 15 min post training. Subsequent assay of choline acetyltransferase (ChAT) and tyrosine hydroxylase (TH) activity showed that choline treatment significantly reduced ChAT activity but did not affect TH activity. It appears that dietary choline treatment can render new long-term memories less susceptible to disruption following training.