Oxidative damage to myelin proteins accompanies peripheral nerve motor dysfunction in aging C57BL/6 male mice

Neuronal ageing is promoted by the decay of the microtubule cytoskeleton

Natural ageing is accompanied by a decline in motor, sensory, and cognitive functions, all impacting quality of life. Ageing is also the predominant risk factor for many neurodegenerative diseases, including Parkinson's disease and Alzheimer's disease. We need to therefore gain a better understanding of the cellular and physiological processes underlying age-related neuronal decay. However, gaining this understanding is a slow process due to the large amount of time required to age mammalian or vertebrate animal models. Here, we introduce a new cellular model within the Drosophila brain, in which we report classical ageing hallmarks previously observed in the primate brain. These hallmarks include axonal swellings, cytoskeletal decay, a reduction in axonal calibre, and morphological changes arising at synaptic terminals. In the fly brain, these changes begin to occur within a few weeks, ideal to study the underlying mechanisms of ageing. We discovered that the decay of the neuronal microtubule (MT) cytoskeleton precedes the onset of other ageing hallmarks. We showed that the MT-binding factors Tau, EB1, and Shot/MACF1, are necessary for MT maintenance in axons and synapses, and that their functional loss during ageing triggers MT bundle decay, followed by a decline in axons and synaptic terminals. Furthermore, genetic manipulations that improve MT networks slowed down the onset of neuronal ageing hallmarks and confer aged specimens the ability to outperform age-matched controls. Our work suggests that MT networks are a key lesion site in ageing neurons and therefore the MT cytoskeleton offers a promising target to improve neuronal decay in advanced age.

Analysis of the Effects of Ninjin’yoeito on Physical Frailty in Mice

Physical frailty is an aging-related clinical syndrome involving decreases in body weight, mobility, activity, and walking speed that occurs in individuals with sarcopenia and is accelerated by increased oxidative stress. Ninjin’yoeito, a traditional Japanese Kampo medicine, is used for treating conditions, including anemia and physical weakness. Here, we investigated whether ninjin’yoeito could improve physical frailty by controlling oxidative stress in the senescence-accelerated mouse prone 8 (SAMP8) model. First, SAMP8 mice were divided into two groups, ninjin’yoeito treated and untreated, with the former consuming a diet containing 3% ninjin’yoeito from 3 months of age. At 7 months of age, body weight, motor function, locomotor activity, and mean walking speed were measured. Subsequently, mice were euthanized and measured for muscle weight, 8-hydroxy-2′-deoxyguanosine levels in muscle and brain, and cleaved caspase-3 expression in brain. The results showed reductions in weight, locomotor function, locomotion, and average walking speed in the untreated group, which were significantly improved by ninjin’yoeito. Furthermore, 8-hydroxy-2′-deoxyguanosine levels were reduced in muscle and brain from ninjin’yoeito-treated mice, compared with the levels in untreated mice; cleaved caspase-3 expression was similarly reduced in brain from the treated mice, indicating reduced apoptosis. Our findings suggest that ninjin’yoeito inhibits sarcopenia-based physical frailty through its antioxidant effects.

Four Seasons for Schwann Cell Biology, Revisiting Key Periods: Development, Homeostasis, Repair, and Aging

Like the seasons of the year, all natural things happen in stages, going through adaptations when challenged, and Schwann cells are a great example of that. During maturation, these cells regulate several steps in peripheral nervous system development. The Spring of the cell means the rise and bloom through organized stages defined by time-dependent regulation of factors and microenvironmental influences. Once matured, the Summer of the cell begins: a high energy stage focused on maintaining adult homeostasis. The Schwann cell provides many neuron-glia communications resulting in the maintenance of synapses. In the peripheral nervous system, Schwann cells are pivotal after injuries, balancing degeneration and regeneration, similarly to when Autumn comes. Their ability to acquire a repair phenotype brings the potential to reconnect axons to targets and regain function. Finally, Schwann cells age, not only by growing old, but also by imposed environmental cues, like loss of function induced by pathologies. The Winter of the cell presents as reduced activity, especially regarding their role in repair; this reflects on the regenerative potential of older/less healthy individuals. This review gathers essential information about Schwann cells in different stages, summarizing important participation of this intriguing cell in many functions throughout its lifetime.

The Impact of Milk Fat Globule Membrane with Exercise on Age-Related Degeneration of Neuromuscular Junctions

Morphological changes in neuromuscular junctions (NMJs), which are synapses formed between α-motor neurons and skeletal muscle fibers, are considered to be important in age-related motor dysfunction. We have previously shown that the intake of dietary milk fat globule membrane (MFGM) combined with exercise attenuates age-related NMJ alterations in the early phase of aging. However, it is unclear whether the effect of MFGM with exercise on age-related NMJ alterations persists into old age, and whether intervention from old age is still effective when age-related changes in NMJs have already occurred. In this study, 6- or 18-month-old mice were treated with a 1% MFGM diet and daily running wheel exercise until 23 or 24 months of age, respectively. MFGM treatment with exercise was effective in suppressing the progression of age-related NMJ alterations in old age, and even after age-related changes in NMJs had already occurred. Moreover, the effect of MFGM intake with exercise was not restricted to NMJs but extended to the structure and function of peripheral nerves. This study demonstrates that MFGM intake with exercise may be a novel approach for improving motor function in the elderly by suppressing age-related NMJ alterations.

Protective mechanism against age-associated changes in the peripheral nerves

AIMS

Senescence is the normal decline in physiological functions due to aging that results in cell dysfunction. However, age-associated changes in peripheral nerves have not been elucidated. We observed histological changes in the sciatic nerves of young and older mice to investigate how peripheral nerves changed with age, and we evaluated protective mechanisms of peripheral nerves against aging.

MAIN METHODS

Sciatic nerves were collected from female C57BL/6 mice at the ages of 8 weeks (young group) and 78 weeks (aged group) and examined histologically. Using hematoxylin and eosin staining, the number and density of sciatic nerve axons were evaluated. Through immunofluorescence staining, the expression of nerve-specific proteins, oxidative stress markers, and a neuronal aging marker (REST/NRSF) were investigated, and the intensity of fluorescence was quantified. The differences between the groups were assessed, and age-associated peripheral nerve changes were evaluated. Statistical analysis was performed using the Mann-Whitney U test.

KEY FINDINGS

Although the number and density of axons did not differ significantly between the groups, they were lower in the aged group than in the young group. In addition, the fluorescence intensity of each marker did not differ significantly between the groups, but the expression of REST/NRSF alone was significantly higher in the aged group than in the young group (p < 0.05).

SIGNIFICANCE

This study suggested that peripheral nerve functions are preserved by the expression of REST/NRSF, which increases with age. Because oxidative stress did not change, the protective effects of REST/NRSF are considered to be related to oxidative stress.

Decoding the relationship between ageing and amyotrophic lateral sclerosis: a cellular perspective

With an ageing population comes an inevitable increase in the prevalence of age-associated neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS), a relentlessly progressive and universally fatal disease characterized by the degeneration of upper and lower motor neurons within the brain and spinal cord. Indeed, the physiological process of ageing causes a variety of molecular and cellular phenotypes. With dysfunction at the neuromuscular junction implicated as a key pathological mechanism in ALS, and each lower motor unit cell type vulnerable to its own set of age-related phenotypes, the effects of ageing might in fact prove a prerequisite to ALS, rendering the cells susceptible to disease-specific mechanisms. Moreover, we discuss evidence for overlap between age and ALS-associated hallmarks, potentially implicating cell type-specific ageing as a key contributor to this multifactorial and complex disease. With a dearth of disease-modifying therapy currently available for ALS patients and a substantial failure in bench to bedside translation of other potential therapies, the unification of research in ageing and ALS requires high fidelity models to better recapitulate age-related human disease and will ultimately yield more reliable candidate therapeutics for patients, with the aim of enhancing healthspan and life expectancy.

Magnetic Resonance Imaging as a Biomarker in Rodent Peripheral Nerve Injury Models Reveals an Age-Related Impairment of Nerve Regeneration

Assessment of myelin integrity in peripheral nerve injuries and pathologies has largely been limited to post-mortem analysis owing to the difficulty in obtaining biopsies without affecting nerve function. This is further encumbered  by the small size of the tissue and its location. Therefore, the development of robust, non-invasive methods is highly attractive. In this study, we used magnetic resonance imaging (MRI) techniques, including magnetization transfer ratio (MTR), to longitudinally and non-invasively characterize both the sciatic nerve crush and lysolecithin (LCP) demyelination models of peripheral nerve injury in rodents. Electrophysiological, gene expression and histological assessments complemented the extensive MRI analyses in young and aged animals. In the nerve crush model, MTR analysis indicated a slower recovery in regions distal to the site of injury in aged animals, as well as incomplete recovery at six weeks post-crush when analyzing across the entire nerve surface. Similar regional impairments were also found in the LCP demyelination model. This research underlines the power of MTR for the study of peripheral nerve injury in small tissues such as the sciatic nerve of rodents and contributes new knowledge to the effect of aging on recovery after injury. A particular advantage of the approach is the translational potential to human neuropathies.

The effects of dietary methionine restriction on the function and metabolic reprogramming in the liver and brain - implications for longevity

Methionine is an essential sulphur-containing amino acid involved in protein synthesis, regulation of protein function and methylation reactions. Dietary methionine restriction (0.12-0.17% methionine in food) extends the life span of various animal species and delays the onset of aging-associated diseases and cancers. In the liver, methionine restriction attenuates steatosis and delays the development of non-alcoholic steatohepatitis due to antioxidative action and metabolic reprogramming. The limited intake of methionine stimulates the fatty acid oxidation in the liver and the export of lipoproteins as well as inhibits de novo lipogenesis. These effects are mediated by various signaling pathways and effector molecules, including sirtuins, growth hormone/insulin-like growth factor-1 axis, sterol regulatory element binding proteins, adenosine monophosphate-dependent kinase and general control nonderepressible 2 pathway. Additionally, methionine restriction stimulates the synthesis of fibroblast growth factor-21 in the liver, which increases the insulin sensitivity of peripheral tissues. In the brain, methionine restriction delays the onset of neurodegenerative diseases and increases the resistance to various forms of stress through antioxidative effects and alterations in lipid composition. This review aimed to summarize the morphological, functional and molecular changes in the liver and brain caused by the methionine restriction, with possible implications in the prolongation of maximal life span.

Axonal Degeneration during Aging and Its Functional Role in Neurodegenerative Disorders

Aging constitutes the main risk factor for the development of neurodegenerative diseases. This represents a major health issue worldwide that is only expected to escalate due to the ever-increasing life expectancy of the population. Interestingly, axonal degeneration, which occurs at early stages of neurodegenerative disorders (ND) such as Alzheimer's disease, Amyotrophic lateral sclerosis, and Parkinson's disease, also takes place as a consequence of normal aging. Moreover, the alteration of several cellular processes such as proteostasis, response to cellular stress and mitochondrial homeostasis, which have been described to occur in the aging brain, can also contribute to axonal pathology. Compelling evidence indicate that the degeneration of axons precedes clinical symptoms in NDs and occurs before cell body loss, constituting an early event in the pathological process and providing a potential therapeutic target to treat neurodegeneration before neuronal cell death. Although, normal aging and the development of neurodegeneration are two processes that are closely linked, the molecular basis of the switch that triggers the transition from healthy aging to neurodegeneration remains unrevealed. In this review we discuss the potential role of axonal degeneration in this transition and provide a detailed overview of the literature and current advances in the molecular understanding of the cellular changes that occur during aging that promote axonal degeneration and then discuss this in the context of ND.

Effects of calorie restriction on the lifespan and healthspan of POLG mitochondrial mutator mice

Mitochondrial DNA (mtDNA) mutations are thought to have a causative role in age-related pathologies. We have shown previously that mitochondrial mutator mice (Polg^D257A/D257A), harboring a proofreading-deficient version of the mtDNA polymerase gamma (POLG), accumulate mtDNA mutations in multiple tissues and display several features of accelerated aging. Calorie restriction (CR) is known to delay the onset of age-related diseases and to extend the lifespan of a variety of species, including rodents. In the current study we investigated the effects of CR on the lifespan and healthspan of mitochondrial mutator mice. Long-term CR did not increase the median or maximum lifespan of Polg^D257A/D257A mice. Furthermore, CR did not reduce mtDNA deletions in the heart and muscle, accelerated sarcopenia, testicular atrophy, nor improve the alterations in cardiac parameters that are present in aged mitochondrial mutator mice. Therefore, our findings suggest that accumulation of mtDNA mutations may interfere with the beneficial action of CR in aging retardation.