Age-related declines in α-Klotho drive progenitor cell mitochondrial dysfunction and impaired muscle regeneration

Skeletal Muscle Complications in Chronic Kidney Disease

PURPOSE OF REVIEW

To provide an overview of the recent literature investigating the pathophysiology of skeletal muscle changes, interventions for skeletal muscle, and effects of exercise in chronic kidney disease (CKD).

RECENT FINDINGS

There are multiple CKD-related changes that negatively impact muscle size and function. However, the variability in the assessment of muscle size, in particular, hinders the ability to truly understand the impact it may have in CKD. Exercise interventions to improve muscle size and function demonstrate inconsistent responses that warrant further investigation to optimize exercise prescription. Despite progress in the field, there are many gaps in the knowledge of the pathophysiology of sarcopenia of CKD. Identifying these gaps will help in the design of interventions that can be tested to target muscle loss and its consequences such as impaired mobility, falls, and poor quality of life in patients with CKD.

Impact of Ninjin’yoeito on frailty and short life in klotho-hypomorphic (kl/kl) mice

With the recent aging of society, the prevention of frailty has become an important issue because people desire both a long and healthy lifespan. Klotho-hypomorphic (kl/kl) mice are known to show phenotypes of premature aging. Ninjin’yoeito (NYT) is a traditional Japanese Kampo medicine used to treat patients with vulnerable constitution, fatigue or physical exhaustion caused by aging and illness. Recent studies have reported the potential efficacy of NYT against frailty. We therefore evaluated the effect of NYT on the gait function, activity, the histopathological status of organs and survival using kl/kl mice as a model of aging-related frailty. Two sets of 28-day-old male kl/kl mice were assigned to the vehicle (non-treated; NT), 3% or 5% NYT dietary groups. One set of groups (NT, n = 18; 3% NYT, n = 11; 5% NYT, n = 11) was subjected to the analysis of free walking, rotarod, and spontaneous activity tests at approximately 58 days old. Thereafter, we measured triceps surae muscles weight and myofiber cross-sectional area (CSA), and quantified its telomere content. In addition, we evaluated bone strength and performed histopathological examinations of organs. Survival was measured in the second set of groups (NT, 3% NYT and 5% NYT group, n = 8 each). In the walking test, several indicators such as gait velocity were improved in the NYT 3% group. Similar results were obtained for the latency to fall in the rotarod test and spontaneous motor activity. Triceps muscle mass, CSA and its telomere content were significantly improved in the NYT 3% group. Bone density, pulmonary alveolus destruction and testicular atrophy were also significantly improved in the NYT 3% group. Survival rate and body weight were both significantly improved in the NYT3% group compared with those in the NT group. Continuous administration of NYT from the early stage of aging improved not only gait performance, but also the survival in the aging-related frailty model. This effect may be associated with the improvements in aging-related organ changes such as muscle atrophy. Intervention with NYT against the progression of frailty may contribute to a longer, healthier life span among the elderly individuals.

A systematic review and meta-analysis demonstrating Klotho as an emerging exerkine

Klotho is an anti-aging protein with several therapeutic roles in the pathophysiology of different organs, such as the skeletal muscle and kidneys. Available evidence suggests that exercise increases Klotho levels, regardless of the condition or intervention, shedding some light on this anti-aging protein as an emergent and promising exerkine. Development of a systematic review and meta-analysis in order to verify the role of different exercise training protocols on the levels of circulating soluble Klotho (S-Klotho) protein. A systematic search of the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE through PubMed, EMBASE, CINAHL, CT.gov, and PEDro. Randomized and quasi-randomized controlled trials that investigated effects of exercise training on S-Klotho levels. We included 12 reports in the analysis, comprising 621 participants with age ranging from 30 to 65 years old. Klotho concentration increased significantly after chronic exercise training (minimum of 12 weeks) (Hedge' g [95%CI] 1.3 [0.69-1.90]; P < 0.0001). Moreover, exercise training increases S-Klotho values regardless of the health condition of the individual or the exercise intervention, with the exception of combined aerobic + resistance training. Furthermore, protocol duration and volume seem to influence S-Klotho concentration, since the effect of the meta-analysis changes when subgrouping these variables. Altogether, circulating S-Klotho protein is altered after chronic exercise training and it might be considered an exerkine. However, this effect may be influenced by different training configurations, including protocol duration, volume, and intensity.

β-Klotho Promotes the Development of Intrauterine Adhesions via the PI3K/AKT Signaling Pathway

Intrauterine adhesion (IUA) refers to injury to the basal layer of the endometrium, which can be caused by various factors. It is often accompanied by clinical symptoms such as abnormal menstruation, infertility, recurrent abortion, and periodic abdominal pain. In recent years, a number of studies have reported the effects of β-Klotho (KLB) on the occurrence and development of human tumors and fibrotic diseases, but its relationship with endometrial fibroblasts and endometrial fibrosis has not been elucidated. In this study, we compared the expression of KLB in endometrial stromal cells (ESCs) from patients with IUA and normal controls. We constructed animal and cell models of IUA and conducted expression verification and functional experiments on KLB. We found that the expression of KLB was significantly increased in the ESCs of IUA patients and rat models compared with the controls. The overexpression of KLB could promote the proliferation and fibrosis of ESCs. In addition, the overexpression of KLB activated the PI3K/AKT signaling pathway in ESCs. Our study shows that KLB protein is highly expressed in the ESCs of patients with IUA and can enhance stromal cell proliferation and cell fibrosis by activating the PI3K/AKT pathway, thus promoting the development of IUA.

Mitochondrial dynamics maintain muscle stem cell regenerative competence throughout adult life by regulating metabolism and mitophagy

Skeletal muscle regeneration depends on the correct expansion of resident quiescent stem cells (satellite cells), a process that becomes less efficient with aging. Here, we show that mitochondrial dynamics are essential for the successful regenerative capacity of satellite cells. The loss of mitochondrial fission in satellite cells-due to aging or genetic impairment-deregulates the mitochondrial electron transport chain (ETC), leading to inefficient oxidative phosphorylation (OXPHOS) metabolism and mitophagy and increased oxidative stress. This state results in muscle regenerative failure, which is caused by the reduced proliferation and functional loss of satellite cells. Regenerative functions can be restored in fission-impaired or aged satellite cells by the re-establishment of mitochondrial dynamics (by activating fission or preventing fusion), OXPHOS, or mitophagy. Thus, mitochondrial shape and physical networking controls stem cell regenerative functions by regulating metabolism and proteostasis. As mitochondrial fission occurs less frequently in the satellite cells in older humans, our findings have implications for regeneration therapies in sarcopenia.

Contribution of muscle satellite cells to sarcopenia

Sarcopenia, a disorder characterized by age-related muscle loss and reduced muscle strength, is associated with decreased individual independence and quality of life, as well as a high risk of death. Skeletal muscle houses a normally mitotically quiescent population of adult stem cells called muscle satellite cells (MuSCs) that are responsible for muscle maintenance, growth, repair, and regeneration throughout the life cycle. Patients with sarcopenia are often exhibit dysregulation of MuSCs homeostasis. In this review, we focus on the etiology, assessment, and treatment of sarcopenia. We also discuss phenotypic and regulatory mechanisms of MuSC quiescence, activation, and aging states, as well as the controversy between MuSC depletion and sarcopenia. Finally, we give a multi-dimensional treatment strategy for sarcopenia based on improving MuSC function.

Integrating Mechanisms of Exacerbated Atrophy and Other Adverse Skeletal Muscle Impact in COPD

The normal decline in skeletal muscle mass that occurs with aging is exacerbated in patients with chronic obstructive pulmonary disease (COPD) and contributes to poor health outcomes, including a greater risk of death. There has been controversy about the causes of this exacerbated muscle atrophy, with considerable debate about the degree to which it reflects the very sedentary nature of COPD patients vs. being precipitated by various aspects of the COPD pathophysiology and its most frequent proximate cause, long-term smoking. Consistent with the latter view, recent evidence suggests that exacerbated aging muscle loss with COPD is likely initiated by decades of smoking-induced stress on the neuromuscular junction that predisposes patients to premature failure of muscle reinnervation capacity, accompanied by various alterations in mitochondrial function. Superimposed upon this are various aspects of COPD pathophysiology, such as hypercapnia, hypoxia, and inflammation, that can also contribute to muscle atrophy. This review will summarize the available knowledge concerning the mechanisms contributing to exacerbated aging muscle affect in COPD, consider the potential role of comorbidities using the specific example of chronic kidney disease, and identify emerging molecular mechanisms of muscle impairment, including mitochondrial permeability transition as a mechanism of muscle atrophy, and chronic activation of the aryl hydrocarbon receptor in driving COPD muscle pathophysiology.

Recombinant Klotho Protein Ameliorates Myocardial Ischemia/Reperfusion Injury by Attenuating Sterile Inflammation

Currently, no effective therapy and potential target have been elucidated for preventing myocardial ischemia and reperfusion injury (I/R). We hypothesized that the administration of recombinant klotho (rKL) protein could attenuate the sterile inflammation in peri-infarct regions by inhibiting the extracellular release of high mobility group box-1 (HMGB1). This hypothesis was examined using a rat coronary artery ligation model. Rats were divided into sham, sham+ rKL, I/R, and I/R+ rKL groups (n = 5/group). Administration of rKL protein reduced infarct volume and attenuated extracellular release of HMGB1 from peri-infarct tissue after myocardial I/R injury. The administration of rKL protein inhibited the expression of pro-inflammatory cytokines in the peri-infarct regions and significantly attenuated apoptosis and production of intracellular reactive oxygen species by myocardial I/R injury. Klotho treatment significantly reduced the increase in the levels of circulating HMGB1 in blood at 4 h after myocardial ischemia. rKL regulated the levels of inflammation-related proteins. This is the first study to suggest that exogenous administration of rKL exerts myocardial protection effects after I/R injury and provides new mechanistic insights into rKL that can provide the theoretical basis for clinical application of new adjunctive modality for critical care of acute myocardial infarction.

The relationship between polycyclic aromatic hydrocarbons exposure and serum klotho among adult population

Background

Klotho is an important factor involving aging process. Recently, polycyclic aromatic hydrocarbons (PAHs) exposure was reported to have adverse impact on DNA methylation associated with aging. The aim of the current study was to determine the relationship between serum klotho and PAHs exposure in an adult population.

Methods

A total of 2597 participants obtained from NHANES 2015–2016 were included in this cross-sectional study. Serum klotho levels were analyzed by enzyme-linked immunosorbent assay (ELISA). PAHs exposure was estimated by urinary sample using liquid chromatography-tandem mass spectrometry. The relationship between serum klotho and exposure to PAHS was analyzed by a multivariable linear regression model.

Results

2-napthol and 3-fluorene were significantly associated with decreased klotho. After fully adjusting pertinent variables, PAH exposure was significantly associated with decreased klotho, particularly in men.

Conclusion

In the present study we highlighted the significant association between PAHs exposure and serum klotho levels. The importance of environmental effect on aging process and age-related disorders should be paid more attention and clinical intervention is necessary.

Extracellular Matrix in Aging Aorta

The aging population is booming all over the world and arterial aging causes various age-associated pathologies such as cardiovascular diseases (CVDs). The aorta is the largest elastic artery, and transforms pulsatile flow generated by the left ventricle into steady flow to maintain circulation in distal tissues and organs. Age-associated structural and functional changes in the aortic wall such as dilation, tortuousness, stiffening and losing elasticity hamper stable peripheral circulation, lead to tissue and organ dysfunctions in aged people. The extracellular matrix (ECM) is a three-dimensional network of macromolecules produced by resident cells. The composition and organization of key ECM components determine the structure-function relationships of the aorta and therefore maintaining their homeostasis is critical for a healthy performance. Age-associated remodeling of the ECM structural components, including fragmentation of elastic fibers and excessive deposition and crosslinking of collagens, is a hallmark of aging and leads to functional stiffening of the aorta. In this mini review, we discuss age-associated alterations of the ECM in the aortic wall and shed light on how understanding the mechanisms of aortic aging can lead to the development of efficient strategy for aortic pathologies and CVDs.

The anti-aging protein Klotho affects early postnatal myogenesis by downregulating Jmjd3 and the canonical Wnt pathway

Modulating the number of muscle stems cells, called satellite cells, during early postnatal development produces long-term effects on muscle growth. We tested the hypothesis that high expression levels of the anti-aging protein Klotho in early postnatal myogenesis increase satellite cell numbers by influencing the epigenetic regulation of genes that regulate myogenesis. Our findings show that elevated klotho expression caused a transient increase in satellite cell numbers and slowed muscle fiber growth, followed by a period of accelerated muscle growth that leads to larger fibers. Klotho also transcriptionally downregulated the H3K27 demethylase Jmjd3, leading to increased H3K27 methylation and decreased expression of genes in the canonical Wnt pathway, which was associated with a delay in muscle differentiation. In addition, Klotho stimulation and Jmjd3 downregulation produced similar but not additive reductions in the expression of Wnt4, Wnt9a, and Wnt10a in myogenic cells, indicating that inhibition occurred through a common pathway. Together, our results identify a novel pathway through which Klotho influences myogenesis by reducing the expression of Jmjd3, leading to reductions in the expression of Wnt genes and inhibition of canonical Wnt signaling.

Renal Klotho and inorganic phosphate are extrinsic factors that antagonistically regulate hematopoietic stem cell maintenance

The composition and origin of extrinsic cues required for hematopoietic stem cell (HSC) maintenance are incompletely understood. Here we identify renal Klotho and inorganic phosphate (Pi) as extrinsic factors that antagonistically regulate HSC maintenance in the bone marrow (BM). Disruption of the Klotho-Pi axis by renal Klotho deficiency or Pi excess causes Pi overload in the BM niche and Pi retention in HSCs, leading to alteration of HSC maintenance. Mechanistically, Pi retention is mediated by soluble carrier family 20 member 1 (SLC20A1) and sensed by diphosphoinositol pentakisphosphate kinase 2 (PPIP5K2) to enhance Akt activation, which then upregulates SLC20A1 to aggravate Pi retention and augments GATA2 activity to drive the expansion and megakaryocyte/myeloid-biased differentiation of HSCs. However, kidney-secreted soluble Klotho directly maintains HSC pool size and differentiation by restraining SLC20A1-mediated Pi absorption of HSCs. These findings uncover a regulatory role of the Klotho-Pi axis orchestrated by the kidneys in BM HSC maintenance.

Actions of Klotho on hippocampal neuronal cells

Klotho gene was originally recognized as a putative aging-suppressor and its prominent age-regulating effects are mostly attributed to the modulation of mineral homeostasis in the kidney. However, recent studies link alterations in hippocampal Klotho expression with cognitive impairment and neurodegenerative diseases. This suggests that hippocampal neurons require Klotho for health and proper functionality. Klotho protects against neuronal dysfunction and regulates several intracellular signaling pathways including oxidative stress response, inflammation, DNA damage, autophagy, endoplasmic reticulum stress response, and multiple types of cell death. Specifically, this chapter covers the current knowledge as to how Klotho protein affects the hippocampal neuronal cells, with special attention paid to underlying molecular mechanisms, and thus influences hippocampal development, hippocampal-dependent cognition, behavior, and motor skills as well as mediates neurodegenerative processes.

Klotho: An Emerging Factor With Ergogenic Potential

Sarcopenia and impaired cardiorespiratory fitness are commonly observed in older individuals and patients with chronic kidney disease (CKD). Declines in skeletal muscle function and aerobic capacity can progress into impaired physical function and inability to perform activities of daily living. Physical function is highly associated with important clinical outcomes such as hospitalization, functional independence, quality of life, and mortality. While lifestyle modifications such as exercise and dietary interventions have been shown to prevent and reverse declines in physical function, the utility of these treatment strategies is limited by poor widespread adoption and adherence due to a wide variety of both perceived and actual barriers to exercise. Therefore, identifying novel treatment targets to manage physical function decline is critically important. Klotho, a remarkable protein with powerful anti-aging properties has recently been investigated for its role in musculoskeletal health and physical function. Klotho is involved in several key processes that regulate skeletal muscle function, such as muscle regeneration, mitochondrial biogenesis, endothelial function, oxidative stress, and inflammation. This is particularly important for older adults and patients with CKD, which are known states of Klotho deficiency. Emerging data support the existence of Klotho-related benefits to exercise and for potential Klotho-based therapeutic interventions for the treatment of sarcopenia and its progression to physical disability. However, significant gaps in our understanding of Klotho must first be overcome before we can consider its potential ergogenic benefits. These advances will be critical to establish the optimal approach to future Klotho-based interventional trials and to determine if Klotho can regulate physical dysfunction.

Association between Soluble α-Klotho Protein and Metabolic Syndrome in the Adult Population

Klotho protein is an anti-aging protein and plays multiple roles in ion-regulation, anti-oxidative stress, and energy metabolism through various pathways. Metabolic syndrome is a combination of multiple conditions that compose of multiple risk factors of cardiovascular disease and type 2 diabetes. Gene regulation and protein expression are discovered associated with metabolic syndrome. We aimed to figure out the correlation between Klotho protein and metabolic syndrome in generally healthy adults. A cross-sectional study of 9976 respondents ≥ 18 years old from the US National Health and Nutrition Examination Survey (2007-2012) by utilizing their soluble Klotho protein concentrations. Multivariate linear regression models were used to analyze the effect of soluble Klotho protein on the prevalence of metabolic syndrome. Soluble Klotho protein concentration was inversely correlated with the presence of metabolic syndromes (p = 0.013) and numbers of components that met the definition of metabolic syndrome (p < 0.05). The concentration of Soluble Klotho protein was negatively associated with abdominal obesity and high triglyceride (TG) in the adjusted model (p < 0.05). Soluble Klotho protein is correlated with changing metabolic syndrome components in adults, especially central obesity and high TG levels. Despite conventional function as co-factor with fibroblast growth factor-23 (FGF23) that regulates phosphate and vitamin D homeostasis, FGF23-independent soluble Klotho protein may act on multiple signal pathways in different organs and tissue in roles of anti-aging and protection from metabolic syndrome.

Standpoints in mitochondrial dysfunction: Underlying mechanisms in search of therapeutic strategies

Mitochondrial dysfunction has been defined as a reduced efficiency of mitochondria to produce ATP given by a loss of mitochondrial membrane potential, alterations in the electron transport chain (ETC) function, with increase in reactive oxygen species (ROS) generation and decrease in oxygen consumption. During the last decades, mitochondrial dysfunction has been the focus of many researchers as a convergent point for the pathophysiology of several diseases. Numerous investigations have demonstrated that mitochondrial dysfunction is detrimental to cells, tissues and organisms, nevertheless, dysfunctional mitochondria can signal in a particular way in response to stress, a characteristic that may be useful to search for new therapeutic strategies with a common feature. The aim of this review addresses mitochondrial dysfunction and stress signaling as a promising target for future drug development.

Stem cell aging in the skeletal muscle: The importance of communication

Adult stem cells sustain tissue homeostasis and regeneration; their functional decline is often linked to aging, which is characterized by the progressive loss of physiological functions across multiple tissues and organs. The resident stem cells in skeletal muscle, termed satellite cells, are normally quiescent but activate upon injury to reconstitute the damaged tissue. In this review, we discuss the current understanding of the molecular processes that contribute to the functional failure of satellite cells during aging. This failure is due not only to intrinsic changes but also to extrinsic factors, most of which are still undefined but originate from the muscle tissue microenvironment of the satellite cells (the niche), or from the systemic environment. We also highlight the emerging applications of the powerful single-cell sequencing technologies in the study of skeletal muscle aging, particularly in the heterogeneity of the satellite cell population and the molecular interaction of satellite cells and other cell types in the niche. An improved understanding of how satellite cells communicate with their environment, and how this communication is perturbed with aging, will be helpful for defining countermeasures against loss of muscle regenerative capacity in sarcopenia.

Serum α-Klotho associated with oral health among a nationally representative sample of US adults

BACKGROUND

Low klotho is associated with aging-related traits. However, no study has assessed the association between klotho and oral health in a large sample of population. This study aimed to explore the association between serum α-klotho and oral health in US Adults.

METHODS

Data were from the National Health and Nutrition Examination Survey. Oral health parameters included periodontitis, self-rated oral health, and tooth loss. Logistic regression and restricted cubic spline models were adopted to evaluate the associations.

RESULTS

A total of 6187 participants were included in the study. The median of the α-klotho level was 815.2 pg/mL. Serum α-Klotho was significantly lower in participants with poor oral health (all P <0.01). Compared with the highest tertile, the lowest tertile of α-klotho was associated with moderate/severe periodontitis, poor-rated oral health, and tooth loss, with OR (95% CI) being 1.21 (1.01, 1.48), 1.26 (1.01, 1.56) and 1.38 (1.05, 1.84), respectively. An increment of per 1 standard deviation in the α-klotho concentration was associated with lower odds of moderate/severe periodontitis (OR: 0.93; 95% CI: 0.87, 0.99). Linear dose-response relationships were found between α-klotho and the odds of moderate/severe periodontitis (P for non-linearity=0.88) and poor-rated oral health (P for non-linearity=0.66). An L-shaped dose-response relationship was found between levels of α-klotho and the odds of tooth loss (P for non-linearity=0.04).

CONCLUSIONS

Serum α-klotho was associated with oral health. Further studies are necessary to clarify the potential mechanisms and demonstrate the predictive ability of klotho in oral diseases.

The Klotho protein supports redox balance and metabolic functions of cardiomyocytes during ischemia/reperfusion injury

BACKGROUND

Acute heart ischemia followed by reperfusion leads to overproduction of reactive oxygen/ /nitrogen species (ROS/RNS), disrupted expression of nitric oxide synthase (NOS) and unbalanced glucose metabolism. Klotho is a membrane-bound or soluble protein that exerts protective activity in many organs. While Klotho is produced mainly in the kidneys and brain, it has been recently proven that Klotho is expressed in the cardiomyocytes as well. This study aimed to show the influence of the Klotho protein on oxidative/nitrosative stress and metabolic function of the cardiomyocytes subjected to ischemia/reperfusion (I/R) injury.

METHODS

Human cardiac myocytes underwent in vitro chemical I/R (with sodium cyanide and 2-deoxyglucose), in the presence or absence of the recombinant human Klotho protein. The present study included an investigation of cell injury markers, level of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX), level of oxidative/nitrosative stress and metabolic processes of the cardiomyocytes.

RESULTS

Administration of Klotho protein resulted in mitigation of injury, decreased level of NOX2 and NOX4, reduced generation of ROS/RNS and hydrogen peroxide (H2O2), decreased expression of inducible NOS and limited production of nitrates/nitrites in cells under I/R. Glucose uptake and lactate production in the cardiomyocytes subjected to I/R were normalized after Klotho supplementation.

CONCLUSIONS

The Klotho protein participates in the regulation of redox balance and supports metabolic homeostasis of the cardiomyocytes and hence, contributes to protection against I/R injury.

Inducing Energetic Switching Using Klotho Improves Vascular Smooth Muscle Cell Phenotype

The cardiovascular disease of atherosclerosis is characterised by aged vascular smooth muscle cells and compromised cell survival. Analysis of human and murine plaques highlights markers of DNA damage such as p53, Ataxia telangiectasia mutated (ATM), and defects in mitochondrial oxidative metabolism as significant observations. The antiageing protein Klotho could prolong VSMC survival in the atherosclerotic plaque and delay the consequences of plaque rupture by improving VSMC phenotype to delay heart attacks and stroke. Comparing wild-type VSMCs from an ApoE model of atherosclerosis with a flox'd Pink1 knockout of inducible mitochondrial dysfunction we show WT Pink1 is essential for normal cell viability, while Klotho mediates energetic switching which may preserve cell survival.

METHODS

Wild-type ApoE VSMCs were screened to identify potential drug candidates that could improve longevity without inducing cytotoxicity. The central regulator of cell metabolism AMP Kinase was used as a readout of energy homeostasis. Functional energetic switching between oxidative and glycolytic metabolism was assessed using XF24 technology. Live cell imaging was then used as a functional readout for the WT drug response, compared with Pink1 (phosphatase-and-tensin-homolog (PTEN)-induced kinase-1) knockout cells.

RESULTS

Candidate drugs were assessed to induce pACC, pAMPK, and pLKB1 before selecting Klotho for its improved ability to perform energetic switching. Klotho mediated an inverse dose-dependent effect and was able to switch between oxidative and glycolytic metabolism. Klotho mediated improved glycolytic energetics in wild-type cells which were not present in Pink1 knockout cells that model mitochondrial dysfunction. Klotho improved WT cell survival and migration, increasing proliferation and decreasing necrosis independent of effects on apoptosis.

CONCLUSIONS

Klotho plays an important role in VSMC energetics which requires Pink1 to mediate energetic switching between oxidative and glycolytic metabolism. Klotho improved VSMC phenotype and, if targeted to the plaque early in the disease, could be a useful strategy to delay the effects of plaque ageing and improve VSMC survival.

Aronia Upregulates Myogenic Differentiation and Augments Muscle Mass and Function Through Muscle Metabolism

Black chokeberry or aronia (the fruit of Aronia melanocarpa) has been reported to having pharmacological activities against metabolic syndrome, such as hypertension, obesity, diabetes, and pro-inflammatory conditions. However, the effects of aronia on myogenic differentiation and muscle homoeostasis are uncharacterized. In this study, we investigated the effects of aronia (black chokeberry) on myogenic differentiation and muscle metabolic functions in young mice. Aronia extract (AR) promotes myogenic differentiation and elevates the formation of multinucleated myotubes through Akt activation. AR protects dexamethasone (DEX)-induced myotube atrophy through inhibition of muscle-specific ubiquitin ligases mediated by Akt activation. The treatment with AR increases muscle mass and strength in mice without cardiac hypertrophy. AR treatment enhances both oxidative and glycolytic myofibers and muscle metabolism with elevated mitochondrial genes and glucose metabolism-related genes. Furthermore, AR-fed muscle fibers display increased levels of total OxPHOS and myoglobin proteins. Taken together, AR enhances myogenic differentiation and improves muscle mass and function, suggesting that AR has a promising potential as a nutraceutical remedy to intervene in muscle weakness and atrophy.

Regulation of aged skeletal muscle regeneration by circulating extracellular vesicles

Heterochronic blood exchange (HBE) has demonstrated that circulating factors restore youthful features to aged tissues. However, the systemic mediators of those rejuvenating effects remain poorly defined. We show here that the beneficial effect of young blood on aged muscle regeneration was diminished when serum was depleted of extracellular vesicles (EVs). Whereas EVs from young animals rejuvenate aged cell bioenergetics and skeletal muscle regeneration, aging shifts EV subpopulation heterogeneity and compromises downstream benefits on recipient cells. Machine learning classifiers revealed that aging shifts the nucleic acid, but not protein, fingerprint of circulating EVs. Alterations in sub-population heterogeneity were accompanied by declines in transcript levels of the pro-longevity protein, α-Klotho, and injection of EVs improved muscle regeneration in a Klotho mRNA-dependent manner. These studies demonstrate that EVs play a key role in the rejuvenating effects of HBE and that Klotho transcripts within EVs phenocopy the effects of young serum on aged skeletal muscle.

Pyruvate Kinase M2 Supports Muscle Progenitor Cell Proliferation but Is Dispensable for Skeletal Muscle Regeneration after Injury

BACKGROUND

Skeletal muscle progenitor cells (MPCs) repair damaged muscle postinjury. Pyruvate kinase M2 (PKM2) is a glycolytic enzyme (canonical activity) that can also interact with other proteins (noncanonical activity) to modify diverse cellular processes. Recent evidence links PKM2 to MPC proliferation.

OBJECTIVES

This study aimed to understand cellular roles for PKM2 in MPCs and the necessity of PKM2 in MPCs for muscle regeneration postinjury.

METHODS

Cultured, proliferating MPCs (C2C12 cells) were treated with a short hairpin RNA targeting PKM2 or small molecules that selectively affect canonical and noncanonical PKM2 activity (shikonin and TEPP-46). Cell number was measured, and RNA-sequencing and metabolic assays were used in follow-up experiments. Immunoprecipitation coupled to proteomics was used to identify binding partners of PKM2. Lastly, an MPC-specific PKM2 knockout mouse was generated and challenged with a muscle injury to determine the impact of PKM2 on regeneration.

RESULTS

When the noncanonical activity of PKM2 was blocked or impaired, there was an increase in reactive oxygen species concentrations (1.6-2.0-fold, P < 0.01). Blocking noncanonical PKM2 activity also increased lactate excretion (1.2-1.6-fold, P < 0.05) and suppressed mitochondrial oxygen consumption (1.3-1.6-fold, P < 0.01). Glutamate dehydrogenase 1 (GLUD1) was identified as a PKM2 binding partner and blocking noncanonical PKM2 activity increased GLUD activity (1.5-1.6-fold, P < 0.05). Mice with an MPC-specific PKM2 deletion did not demonstrate impaired muscle regeneration.

CONCLUSIONS

The results suggest that the noncanonical activity of PKM2 is important for MPC proliferation in vitro and demonstrate GLUD1 as a PKM2 binding partner. Because no impairments in muscle regeneration were detected in a mouse model, the endogenous environment may compensate for loss of PKM2.

Control of satellite cell function in muscle regeneration and its disruption in ageing

Skeletal muscle contains a designated population of adult stem cells, called satellite cells, which are generally quiescent. In homeostasis, satellite cells proliferate only sporadically and usually by asymmetric cell division to replace myofibres damaged by daily activity and maintain the stem cell pool. However, satellite cells can also be robustly activated upon tissue injury, after which they undergo symmetric divisions to generate new stem cells and numerous proliferating myoblasts that later differentiate to muscle cells (myocytes) to rebuild the muscle fibre, thereby supporting skeletal muscle regeneration. Recent discoveries show that satellite cells have a great degree of population heterogeneity, and that their cell fate choices during the regeneration process are dictated by both intrinsic and extrinsic mechanisms. Extrinsic cues come largely from communication with the numerous distinct stromal cell types in their niche, creating a dynamically interactive microenvironment. This Review discusses the role and regulation of satellite cells in skeletal muscle homeostasis and regeneration. In particular, we highlight the cell-intrinsic control of quiescence versus activation, the importance of satellite cell-niche communication, and deregulation of these mechanisms associated with ageing. The increasing understanding of how satellite cells are regulated will help to advance muscle regeneration and rejuvenation therapies.

Female Outperformance in Voluntary Running Persists in Dystrophin-Null and Klotho-Overexpressing Mice

BACKGROUND

Duchenne muscular dystrophy is a degenerative muscle disease that results from impairment of the dystrophin gene. The disease causes progressive loss in muscle mass and function.

OBJECTIVE

The anti-aging protein, α-klotho, has been implicated in the regulation of muscle regeneration. We previously discovered that mice harboring reduced α-klotho levels exhibited a decline in muscle strength and running endurance.

METHOD

To investigate the ability of α-klotho to improve overall endurance in a dystrophin null murine model, we examined the voluntary wheel running performance of dystrophin-null, mdx4cv mice overexpressing an α-klotho transgene.

RESULTS

As expected, compared to wild type, both male and female dystrophic mice exhibited reduced running ability that was characterized by shorter running duration and longer periods of rest between cycles of activity. While our results did not detect an improvement in running performance with α-klotho overexpression, we identified distinct differences in the running patterns between females and males from all mouse strains analyzed (i.e., mdx4cv, mdx4cv overexpressing α-klotho, α-klotho overexpressing, α-klotho hypomorph, and wild type). For all strains, male mice displayed significantly reduced voluntary running ability compared to females. Further analysis of the mdx4cv strains demonstrated that male mice ran for shorter lengths of time and took longer breaks. However, we did not identify gender-associated differences in the actual speed at which mdx4cv mice ran.

CONCLUSION

Our data suggest key differences in the running capabilities of female and male mice, which are of particular relevance to studies of dystrophin-null mice.

Advanced maternal age causes premature placental senescence and malformation via dysregulated α-Klotho expression in trophoblasts

Advanced maternal age (AMA) pregnancy is associated with higher risks of adverse perinatal outcomes, which may result from premature senescence of the placenta. α-Klotho is a well-known antiaging protein; however, its expression and effect on the placenta in AMA pregnancies have not yet been fully elucidated. The expression patterns of α-Klotho in mouse and human placentas from AMA pregnancies were determined by Western blotting and immunohistochemistry (IHC) staining. α-Klotho expression in JAR cells was manipulated to investigate its role in trophoblastic senescence, and transwell assays were performed to assess trophoblast invasion. The downstream genes regulated by α-Klotho in JAR cells were first screened by mRNA sequencing in α-Klotho-knockdown and control JAR cells and then validated. α-Klotho-deficient mice were generated by injecting klotho-interfering adenovirus (Ad-Klotho) via the tail vein on GD8.5. Ablation of α-Klotho resulted in not only a senescent phenotype and loss of invasiveness in JAR cells but also a reduction in the transcription of cell adhesion molecule (CAM) genes. Overexpression of α-Klotho significantly improved invasion but did not alter the expression of senescence biomarkers. α-Klotho-deficient mice exhibited placental malformation and, consequently, lower placental and fetal weights. In conclusion, AMA results in reduced α-Klotho expression in placental trophoblasts, therefore leading to premature senescence and loss of invasion (possibly through the downregulation of CAMs), both of which ultimately result in placental malformation and adverse perinatal outcomes.

Uraemic solutes as therapeutic targets in CKD-associated cardiovascular disease

Chronic kidney disease (CKD) is characterized by the retention of a myriad of solutes termed uraemic (or uremic) toxins, which inflict damage to several organs, including the cardiovascular system. Uraemic toxins can induce hallmarks of cardiovascular disease (CVD), such as atherothrombosis, heart failure, dysrhythmias, vessel calcification and dysregulated angiogenesis. CVD is an important driver of mortality in patients with CKD; however, reliance on conventional approaches to managing CVD risk is insufficient in these patients, underscoring a need to target risk factors that are specific to CKD. Mounting evidence suggests that targeting uraemic toxins and/or pathways induced by uraemic toxins, including tryptophan metabolites and trimethylamine N-oxide (TMAO), can lower the risk of CVD in patients with CKD. Although tangible therapies resulting from our growing knowledge of uraemic toxicity are yet to materialize, a number of pharmacological and non-pharmacological approaches have the potential to abrogate the effects of uraemic toxins, for example, by decreasing the production of uraemic toxins, by modifying metabolic pathways induced by uraemic toxins such as those controlled by aryl hydrocarbon receptor signalling and by augmenting the clearance of uraemic toxins.

Ranking Biomarkers of Aging by Citation Profiling and Effort Scoring

Aging affects most living organisms and includes the processes that reduce health and survival. The chronological and the biological age of individuals can differ remarkably, and there is a lack of reliable biomarkers to monitor the consequences of aging. In this review we give an overview of commonly mentioned and frequently used potential aging-related biomarkers. We were interested in biomarkers of aging in general and in biomarkers related to cellular senescence in particular. To answer the question whether a biological feature is relevant as a potential biomarker of aging or senescence in the scientific community we used the PICO strategy known from evidence-based medicine. We introduced two scoring systems, aimed at reflecting biomarker relevance and measurement effort, which can be used to support study designs in both clinical and research settings.

βKlotho, a direct target of miR-206, contributes to the growth of hepatoblastoma through augmenting PI3K/Akt/mTOR signaling

Hepatoblastoma (HB) is the most frequent pediatric liver malignancy. However, the treatment outcome for patients with advanced-stage HB remains unsatisfactory. Accumulating evidence indicates that βKlotho (KLB) acts as an oncogene or a tumor-suppressor gene in a context-dependent manner. Despite this, the expression profile and effects of KLB on the growth of HB are still elusive. This study aimed to explore the effect of miR-206/KLB axis on HB growth. The expression of KLB was explored in HB cells (HepG2 and HuH6) and tissues using quantitative polymerase chain reaction (qPCR), Western blot analysis, and immunohistochemistry. Besides, miR-206 expression was determined in HB cells and tissues using qPCR and fluorescence in situ hybridization. The prognostic value of KLB or miR-206 in our patients with HB was investigated using the Kaplan-Meier method. The biological effects of KLB or miR-206 on HB cells were identified in vitro. The proliferative effects of KLB on HuH6 cells were also investigated in vivo. Moreover, the mechanical signaling of KLB in HB was determined through bioinformatics analysis followed by experimental validation. The results showed a significant upregulation of KLB in HB tissues and cells. Elevated level of KLB was found to be significantly correlated with the aggressive phenotype and poor overall survival for children with HB. The in vitro function assay demonstrated that KLB knockdown promoted apoptosis and suppressed the proliferation, migration, and invasion of HB cells. Besides, KLB knockdown inhibited the proliferation of HuH6 cells in vivo, while KLB overexpression had the opposite effect. Furthermore, KLB was proved to be the direct target of miR-206. Low level of miR-206 served as an independent risk factor for poor prognosis in children with HB. The overexpression of miR-206 negatively regulated the aggressive biological behaviors of HB cells, which was partially rescued by KLB overexpression. Mechanically, the miR-206/KLB axis played a vital role in HB growth through augmenting the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling. In conclusion, the data demonstrated that the miR-206/KLB axis might serve as an important biomarker/therapeutic target for HB.

The pleiotropic neuroprotective effects of resveratrol in cognitive decline and Alzheimer's disease pathology: From antioxidant to epigenetic therapy

While the elderly segment of the population continues growing in importance, neurodegenerative diseases increase exponentially. Lifestyle factors such as nutrition, exercise, and education, among others, influence ageing progression, throughout life. Notably, the Central Nervous System (CNS) can benefit from nutritional strategies and dietary interventions that prevent signs of senescence, such as cognitive decline or neurodegenerative diseases such as Alzheimer's disease and Parkinson's Disease. The dietary polyphenol Resveratrol (RV) possesses antioxidant and cytoprotective effects, producing neuroprotection in several organisms. The oxidative stress (OS) occurs because of Reactive oxygen species (ROS) accumulation that has been proposed to explain the cause of the ageing. One of the most harmful effects of ROS in the cell is DNA damage. Nevertheless, there is also evidence demonstrating that OS can produce other molecular changes such as mitochondrial dysfunction, inflammation, apoptosis, and epigenetic modifications, among others. Interestingly, the dietary polyphenol RV is a potent antioxidant and possesses pleiotropic actions, exerting its activity through various molecular pathways. In addition, recent evidence has shown that RV mediates epigenetic changes involved in ageing and the function of the CNS that persists across generations. Furthermore, it has been demonstrated that RV interacts with gut microbiota, showing modifications in bacterial composition associated with beneficial effects. In this review, we give a comprehensive overview of the main mechanisms of action of RV in different experimental models, including clinical trials and discuss how the interconnection of these molecular events could explain the neuroprotective effects induced by RV.

Kidney and epigenetic mechanisms of salt-sensitive hypertension

Dietary salt intake increases blood pressure (BP) but the salt sensitivity of BP differs between individuals. The interplay of ageing, genetics and environmental factors, including malnutrition and stress, contributes to BP salt sensitivity. In adults, obesity is often associated with salt-sensitive hypertension. The children of women who experience malnutrition during pregnancy are at increased risk of developing obesity, diabetes and salt-sensitive hypertension as adults. Similarly, the offspring of mice that are fed a low-protein diet during pregnancy develop salt-sensitive hypertension in association with aberrant DNA methylation of the gene encoding type 1A angiotensin II receptor (AT_1AR) in the hypothalamus, leading to upregulation of hypothalamic AT_1AR and renal sympathetic overactivity. Ageing is also associated with salt-sensitive hypertension. In aged mice, promoter methylation leads to reduced kidney production of the anti-ageing factor Klotho and a decrease in circulating soluble Klotho. In the setting of Klotho deficiency, salt-induced activation of the vascular Wnt5a-RhoA pathway leads to ageing-associated salt-sensitive hypertension, potentially as a result of reduced renal blood flow and increased peripheral resistance. Thus, kidney mechanisms and aberrant DNA methylation of certain genes are involved in the development of salt-sensitive hypertension during fetal development and old age. Three distinct paradigms of epigenetic memory operate on different timescales in prenatal malnutrition, obesity and ageing.

The biphasic and age-dependent impact of klotho on hallmarks of aging and skeletal muscle function

Aging is accompanied by disrupted information flow, resulting from accumulation of molecular mistakes. These mistakes ultimately give rise to debilitating disorders including skeletal muscle wasting, or sarcopenia. To derive a global metric of growing 'disorderliness' of aging muscle, we employed a statistical physics approach to estimate the state parameter, entropy, as a function of genes associated with hallmarks of aging. Escalating network entropy reached an inflection point at old age, while structural and functional alterations progressed into oldest-old age. To probe the potential for restoration of molecular 'order' and reversal of the sarcopenic phenotype, we systemically overexpressed the longevity protein, Klotho, via AAV. Klotho overexpression modulated genes representing all hallmarks of aging in old and oldest-old mice, but pathway enrichment revealed directions of changes were, for many genes, age-dependent. Functional improvements were also age-dependent. Klotho improved strength in old mice, but failed to induce benefits beyond the entropic tipping point.

Yoga improves mitochondrial health and reduces severity of autoimmune inflammatory arthritis: A randomized controlled trial

BACKGROUND

Oxidative stress (OS) and mitochondrial alterations have been implicated in the pathogenesis of rheumatoid arthritis (RA). Various environmental triggers like air pollutants, smoking, unhealthy social habits and sedentary lifestyle induce OS, which may compromise mitochondrial integrity. This trial was designed to explore the effect of 8-weeks yoga practice on mitochondrial health and disease severity in an active RA group compared with a usual-care control group.

METHODS

A total of 70 subjects were randomized into two groups: yoga group and non-yoga group. Mitochondrial health was assessed by calculation of mitochondrial DNA copy number (mtDNA-CN), OS markers, mitochondrial activity, mitochondrial membrane potential (ΔΨm), circadian rhythm markers and transcripts associated with mitochondrial integrity: AMPK, TIMP-1, KLOTHO, SIRT-1, and TFAM. Parameters of disease activity and disability quotient were also assessed by disease activity score - erythrocyte sedimentation rate (DAS28-ESR) and health assessment questionnaire-disability index (HAQ-DI), respectively.

RESULTS

In yoga group, there was a significant upregulation of mtDNA-CN, mitochondrial activity markers, ΔΨm, and transcripts that maintain mitochondrial integrity after 8-weeks of yoga. There was optimization of OS markers, and circadian rhythm markers post 8-weeks practice of yoga. Yoga group participants showed significant improvements in DAS28-ESR (p < 0.05) and HAQ-DI (p < 0.05) over the non-yoga group.

CONCLUSION

Adoption of yoga by RA patients holds the key to enhance mitochondrial health, improve circadian rhythm markers, OS marker regulation, upregulation of transcripts that maintain mitochondrial integrity, reduce disease activity and its associated consequences on health outcome and hence can be beneficial as an adjunct therapy.

Regulation of muscle stem cell function

Regeneration of skeletal muscle is a finely tuned process which is depending on muscle stem cells, a population of stem cells in skeletal muscle which is also termed satellite cells. Muscle stem cells are a prerequisite for regeneration of skeletal muscle. Of note, the muscle stem cell population is heterogeneous and subpopulations can be identified depending on gene expression or phenotypic traits. However, all muscle stem cells express the transcription factor Pax7 and their functionality is tightly controlled by intrinsic signaling pathways and extrinsic signals. The latter ones include signals form the stem cell niche as well as circulating factors such as growth factors and hormones. Among them are Wnt proteins, growth factors like IGF-1 or FGF-2 and hormones such as thyroid hormones and the anti-aging hormone Klotho. A highly orchestrated interplay between those factors and muscle stem cells is important for their full functionality and ultimately regeneration of skeletal muscle as outlined here.

Could α-Klotho Unlock the Key Between Depression and Dementia in the Elderly: from Animal to Human Studies

α-Klotho is known for its aging-related functions and is associated with neurodegenerative diseases, accelerated aging, premature morbidity, and mortality. Recent literature suggests that α-Klotho is also involved in the regulation of mental functions, such as cognition and psychosis. While most of studies of α-Klotho are focusing on its anti-aging functions and protective role in dementia, increasing evidence showed many shared symptoms between depression and dementia, while depression has been proposed as the preclinical stage of dementia such as Alzheimer's disease (AD). To see whether and how α-Klotho can be a key biological link between depression and dementia, in this review, we first gathered the evidence on biological distribution and function of α-Klotho in psychiatric functions from animal studies to human clinical investigations with a focus on the regulation of cognition and mood. Then, we discussed and highlighted the potential common underlying mechanisms of α-Klotho between psychiatric diseases and cognitive impairment. Finally, we hypothesized that α-Klotho might serve as a neurobiological link between depression and dementia through the regulation of oxidative stress and inflammation.

Klotho retards renal fibrosis through targeting mitochondrial dysfunction and cellular senescence in renal tubular cells

Chronic kidney disease (CKD) has a high prevalence worldwide and is an intricate issue to whole medical society. Renal fibrosis is the common pathological feature for various kinds of CKD. As an anti-aging protein, Klotho is predominantly expressed in renal tubular epithelial cells. Reports show Klotho could retard age-related renal fibrosis. Mitochondrial dysfunction plays an important role in cellular senescence. However, the role of Klotho in mitochondrial dysfunction in CKD has not yet been determined. In this study, we treated unilateral ischemia-reperfusion (UIRI) mice and cultured human renal tubular epithelial cells (HKC-8) with Klotho. We assessed renal fibrosis, cellular senescence, and Wnt/β-catenin signaling. We also focused on mitochondrial function assessment. In UIRI mice, ectopic expression of Klotho greatly retarded fibrotic lesions and the activation of Wnt/β-catenin signaling. Interestingly, Klotho significantly preserved mitochondrial mass, inhibited mitochondrial reactive oxygen species (ROS) production and restored the expression of mitochondrial respiration chain complex subunits. Consequently, Klotho restrained cellular senescence. In HKC-8 cells, Klotho significantly inhibited Wnt1- and Wnt9a-induced mitochondrial injury, cellular senescence, and fibrotic lesions. These results suggest Klotho has a protective role in renal function through targeted protection on mitochondria. This further broads the understanding of the beneficial efficacies of Klotho in CKD.

Aging of the immune system and impaired muscle regeneration: A failure of immunomodulation of adult myogenesis

Skeletal muscle regeneration that follows acute injury is strongly influenced by interactions with immune cells that invade and proliferate in the damaged tissue. Discoveries over the past 20 years have identified many of the key mechanisms through which myeloid cells, especially macrophages, regulate muscle regeneration. In addition, lymphoid cells that include CD8+ T-cells and regulatory T-cells also significantly affect the course of muscle regeneration. During aging, the regenerative capacity of skeletal muscle declines, which can contribute to progressive loss of muscle mass and function. Those age-related reductions in muscle regeneration are accompanied by systemic, age-related changes in the immune system, that affect many of the myeloid and lymphoid cell populations that can influence muscle regeneration. In this review, we present recent discoveries that indicate that aging of the immune system contributes to the diminished regenerative capacity of aging muscle. Intrinsic, age-related changes in immune cells modify their expression of factors that affect the function of a population of muscle stem cells, called satellite cells, that are necessary for normal muscle regeneration. For example, age-related reductions in the expression of growth differentiation factor-3 (GDF3) or CXCL10 by macrophages negatively affect adult myogenesis, by disrupting regulatory interactions between macrophages and satellite cells. Those changes contribute to a reduction in the numbers and myogenic capacity of satellite cells in old muscle, which reduces their ability to restore damaged muscle. In addition, aging produces changes in the expression of molecules that regulate the inflammatory response to injured muscle, which also contributes to age-related defects in muscle regeneration. For example, age-related increases in the production of osteopontin by macrophages disrupts the normal inflammatory response to muscle injury, resulting in regenerative defects. These nascent findings represent the beginning of a newly-developing field of investigation into mechanisms through which aging of the immune system affects muscle regeneration.

Gene therapy with secreted acid alpha-glucosidase rescues Pompe disease in a novel mouse model with early-onset spinal cord and respiratory defects

Background

Pompe disease (PD) is a neuromuscular disorder caused by deficiency of acidalpha-glucosidase (GAA), leading to motor and respiratory dysfunctions. Available Gaa knock-out (KO) mouse models do not accurately mimic PD, particularly its highly impaired respiratory phenotype.

Methods

Here we developed a new mouse model of PD crossing Gaa KO^B6;129 with DBA2/J mice. We subsequently treated Gaa KO^DBA2/J mice with adeno-associated virus (AAV) vectors expressing a secretable form of GAA (secGAA).

Findings

Male Gaa KO^DBA2/J mice present most of the key features of the human disease, including early lethality, severe respiratory impairment, cardiac hypertrophy and muscle weakness. Transcriptome analyses of Gaa KO^DBA2/J, compared to the parental Gaa KO^B6;129 mice, revealed a profoundly impaired gene signature in the spinal cord and a similarly deregulated gene expression in skeletal muscle. Muscle and spinal cord transcriptome changes, biochemical defects, respiratory and muscle function in the Gaa KO^DBA2/J model were significantly improved upon gene therapy with AAV vectors expressing secGAA.

Interpretation

These data show that the genetic background impacts on the severity of respiratory function and neuroglial spinal cord defects in the Gaa KO mouse model of PD. Our findings have implications for PD prognosis and treatment, show novel molecular pathophysiology mechanisms of the disease and provide a unique model to study PD respiratory defects, which majorly affect patients.

Funding

This work was supported by Genethon, the French Muscular Dystrophy Association (AFM), the European Commission (grant nos. 667751, 617432, and 797144), and Spark Therapeutics.

Restoring aged stem cell functionality: Current progress and future directions

Stem cell dysfunction is a hallmark of aging, associated with the decline of physical and cognitive abilities of humans and other mammals [Cell 2013;153:1194]. Therefore, it has become an active area of research within the aging and stem cell fields, and various techniques have been employed to mitigate the decline of stem cell function both in vitro and in vivo. While some techniques developed in model organisms are not directly translatable to humans, others show promise in becoming clinically relevant to delay or even mitigate negative phenotypes associated with aging. This review focuses on diet, treatment, and small molecule interventions that provide evidence of functional improvement in at least one type of aged adult stem cell.

Arsenic Stimulates Myoblast Mitochondrial Epidermal Growth Factor Receptor to Impair Myogenesis

Arsenic exposure impairs muscle metabolism, maintenance, progenitor cell differentiation, and regeneration following acute injury. Low to moderate arsenic exposures target muscle fiber and progenitor cell mitochondria to epigenetically decrease muscle quality and regeneration. However, the mechanisms for how low levels of arsenic signal for prolonged mitochondrial dysfunction are not known. In this study, arsenic attenuated murine C2C12 myoblasts differentiation and resulted in abnormal undifferentiated myoblast proliferation. Arsenic prolonged ligand-independent phosphorylation of mitochondrially localized epidermal growth factor receptor (EGFR), a major driver of proliferation. Treating cells with a selective EGFR kinase inhibitor, AG-1478, prevented arsenic inhibition of myoblast differentiation. AG-1478 decreased arsenic-induced colocalization of pY845EGFR with mitochondrial cytochrome C oxidase subunit II, as well as arsenic-enhanced mitochondrial membrane potential, reactive oxygen species generation, and cell cycling. All of the arsenic effects on mitochondrial signaling and cell fate were mitigated or reversed by addition of mitochondrially targeted agents that restored mitochondrial integrity and function. Thus, arsenic-driven pathogenesis in skeletal muscle requires sustained mitochondrial EGFR activation that promotes progenitor cell cycling and proliferation at the detriment of proper differentiation. Collectively, these findings suggest that the arsenic-activated mitochondrial EGFR pathway drives pathogenic signaling for impaired myoblast metabolism and function.

Targeting reactive oxygen species (ROS) to combat the age-related loss of muscle mass and function

The loss of muscle mass and function with age, termed sarcopenia, is an inevitable process, which has a significant impact on quality of life. During ageing we observe a progressive loss of total muscle fibres and a reduction in cross-sectional area of the remaining fibres, resulting in a significant reduction in force output. The mechanisms which underpin sarcopenia are complex and poorly understood, ranging from inflammation, dysregulation of protein metabolism and denervation. However, there is significant evidence to demonstrate that modified ROS generation, redox dis-homeostasis and mitochondrial dysfunction may have an important role to play. Based on this, significant interest and research has interrogated potential ROS-targeted therapies, ranging from nutritional-based interventions such as vitamin E/C, polyphenols (resveratrol) and targeted pharmacological compounds, using molecules such as SS-31 and MitoQ. In this review we evaluate these approaches to target aberrant age-related ROS generation and the impact on muscle mass and function.

Daily and seasonal mitochondrial protection: Unraveling common possible mechanisms involving vitamin D and melatonin

From an evolutionary point of view, vitamin D and melatonin appeared very early and share functions related to defense mechanisms. In the current clinical setting, vitamin D is exclusively associated with phosphocalcic metabolism. Meanwhile, melatonin has chronobiological effects and influences the sleep-wake cycle. Scientific evidence, however, has identified new actions of both molecules in different physiological and pathological settings. The biosynthetic pathways of vitamin D and melatonin are inversely related relative to sun exposure. A deficiency of these molecules has been associated with the pathogenesis of cardiovascular diseases, including arterial hypertension, neurodegenerative diseases, sleep disorders, kidney diseases, cancer, psychiatric disorders, bone diseases, metabolic syndrome, and diabetes, among others. During aging, the intake and cutaneous synthesis of vitamin D, as well as the endogenous synthesis of melatonin are remarkably depleted, therefore, producing a state characterized by an increase of oxidative stress, inflammation, and mitochondrial dysfunction. Both molecules are involved in the homeostatic functioning of the mitochondria. Given the presence of specific receptors in the organelle, the antagonism of the renin-angiotensin-aldosterone system (RAAS), the decrease of reactive species of oxygen (ROS), in conjunction with modifications in autophagy and apoptosis, anti-inflammatory properties inter alia, mitochondria emerge as the final common target for melatonin and vitamin D. The primary purpose of this review is to elucidate the common molecular mechanisms by which vitamin D and melatonin might share a synergistic effect in the protection of proper mitochondrial functioning.

Klotho: An Elephant in Aging Research

The year 2017 marked the 20th anniversary of the first publication describing Klotho. This single protein was and is remarkable in that its absence in mice conferred an accelerated aging, or progeroid, phenotype with a dramatically shortened life span. On the other hand, genetic overexpression extended both health span and life span by an impressive 30%. Not only has Klotho deficiency been linked to a number of debilitating age-related illnesses but many subsequent reports have lent credence to the idea that Klotho can compress the period of morbidity and extend the life span of both model organisms and humans. This suggests that Klotho functions as an integrator of organ systems, making it both a promising tool for advancing our understanding of the biology of aging and an intriguing target for interventional studies. In this review, we highlight advances in our understanding of Klotho as well as key challenges that have somewhat limited our view, and thus translational potential, of this potent protein.

Muscle stem cell aging: identifying ways to induce tissue rejuvenation

Aging is characterized by the functional and regenerative decline of tissues and organs. This regenerative decline is a consequence of the numerical and functional loss of adult stem cells, which are the corner stone of tissue homeostasis and repair. A palpable example of this decline is provided by skeletal muscle, a specialized tissue composed of postmitotic myofibers that contract to generate force. Skeletal muscle stem cells (satellite cells) are long-lived and support muscle regeneration throughout life, but at advanced age they fail for largely undefined reasons. Here, we discuss recent advances in the understanding of how satellite cells integrate diverse intrinsic and extrinsic processes to ensure optimal homeostatic function and how this integration is perturbed during aging, causing regenerative failure. With this increased understanding, it is now feasible to design and test interventions that delay satellite cell aging. We discuss the exciting new therapeutic potential of integrating and combining distinct anti-aging strategies for regenerative medicine.

Klotho Pathways, Myelination Disorders, Neurodegenerative Diseases, and Epigenetic Drugs

In this review we outline a rationale for identifying neuroprotectants aimed at inducing endogenous Klotho activity and expression, which is epigenetic action, by definition. Such an approach should promote remyelination and/or stimulate myelin repair by acting on mitochondrial function, thereby heralding a life-saving path forward for patients suffering from neuroinflammatory diseases. Disorders of myelin in the nervous system damage the transmission of signals, resulting in loss of vision, motion, sensation, and other functions depending on the affected nerves, currently with no effective treatment. Klotho genes and their single-pass transmembrane Klotho proteins are powerful governors of the threads of life and death, true to the origin of their name, Fates, in Greek mythology. Among its many important functions, Klotho is an obligatory co-receptor that binds, activates, and/or potentiates critical fibroblast growth factor activity. Since the discovery of Klotho a little over two decades ago, it has become ever more apparent that when Klotho pathways go awry, oxidative stress and mitochondrial dysfunction take over, and age-related chronic disorders are likely to follow. The physiological consequences can be wide ranging, potentially wreaking havoc on the brain, eye, kidney, muscle, and more. Central nervous system disorders, neurodegenerative in nature, and especially those affecting the myelin sheath, represent worthy targets for advancing therapies that act upon Klotho pathways. Current drugs for these diseases, even therapeutics that are disease modifying rather than treating only the symptoms, leave much room for improvement. It is thus no wonder that this topic has caught the attention of biomedical researchers around the world.