Dysregulation of SIRT-1 in aging mice increases skeletal muscle fatigue by a PARP-1-dependent mechanism

TRIM16 facilitates SIRT-1-dependent regulation of antioxidant response to alleviate age-related sarcopenia

BACKGROUND

Age-related sarcopenia, characterized by reduced skeletal muscle mass and function, significantly affects the health of the elderly individuals. Oxidative stress plays a crucial role in the development of sarcopenia. Tripartite motif containing 16 (TRIM16) is implicated in orchestrating antioxidant responses to mitigate oxidative stress, yet its regulatory role in skeletal muscle remains unclear. This study aims to elucidate the impact of TRIM16 on enhancing antioxidant response through SIRT-1, consequently mitigating age-related oxidative stress, and ameliorating muscle atrophy.

METHODS

Aged mouse models were established utilizing male mice at 18 months with D-galactose (D-gal, 200 mg/kg) intervention and at 24 months with natural aging, while 3-month-old young mice served as controls. Muscle cell senescence was induced in C2C12 myoblasts using 30 g/L D-gal. TRIM16 was overexpressed in the skeletal muscle of aged mice and silenced/overexpressed in C2C12 myoblasts. The effects of TRIM16 on skeletal muscle mass, grip strength, morphological changes, myotube formation, myogenic differentiation, and muscle atrophy indicators were evaluated. Reactive oxygen species (ROS) levels and oxidative stress-related parameters were measured. The SIRT-1 inhibitor EX-527 was employed to elucidate the protective role of TRIM16 mediated through SIRT-1.

RESULTS

Aged mice displayed significant reductions in lean mass (-11.58%; -14.47% vs. young, P < 0.05), hindlimb lean mass (-17.38%; -15.95% vs. young, P < 0.05), and grip strength (-22.29%; -31.45% vs. young, P < 0.01). Skeletal muscle fibre cross-sectional area (CSA) decreased (-29.30%; -24.12% vs. young, P < 0.05). TRIM16 expression significantly decreased in aging skeletal muscle (-56.82%; -66.27% vs. young, P < 0.001) and senescent muscle cells (-46.53% vs. control, P < 0.001). ROS levels increased (+69.83% vs. control, P < 0.001), and myotube formation decreased in senescent muscle cells (-56.68% vs. control, P < 0.001). Expression of myogenic differentiation and antioxidant indicators decreased, while muscle atrophy markers increased in vivo and in vitro (all P < 0.05). Silencing TRIM16 in myoblasts induced oxidative stress and myotube atrophy, while TRIM16 overexpression partially mitigated aging effects on skeletal muscle. TRIM16 activation enhanced SIRT-1 expression (+75.38% vs. control, P < 0.001). SIRT-1 inhibitor EX-527 (100 μM) suppressed TRIM16's antioxidant response and mitigating muscle atrophy, offsetting the protective effect of TRIM16 on senescent muscle cells.

CONCLUSIONS

This study elucidates TRIM16's role in mitigating oxidative stress and ameliorating muscle atrophy through the activation of SIRT-1-dependent antioxidant effects. TRIM16 emerges as a potential therapeutic target for age-related sarcopenia.

Bone-organ axes: bidirectional crosstalk

In addition to its recognized role in providing structural support, bone plays a crucial role in maintaining the functionality and balance of various organs by secreting specific cytokines (also known as osteokines). This reciprocal influence extends to these organs modulating bone homeostasis and development, although this aspect has yet to be systematically reviewed. This review aims to elucidate this bidirectional crosstalk, with a particular focus on the role of osteokines. Additionally, it presents a unique compilation of evidence highlighting the critical function of extracellular vesicles (EVs) within bone-organ axes for the first time. Moreover, it explores the implications of this crosstalk for designing and implementing bone-on-chips and assembloids, underscoring the importance of comprehending these interactions for advancing physiologically relevant in vitro models. Consequently, this review establishes a robust theoretical foundation for preventing, diagnosing, and treating diseases related to the bone-organ axis from the perspective of cytokines, EVs, hormones, and metabolites.

Biological basis and treatment of frailty and sarcopenia

In an ageing society, the importance of maintaining healthy life expectancy has been emphasized. As a result of age-related decline in functional reserve, frailty is a state of increased vulnerability and susceptibility to adverse health outcomes with a serious impact on healthy life expectancy. The decline in skeletal muscle mass and function, also known as sarcopenia, is key in the development of physical frailty. Both frailty and sarcopenia are highly prevalent in patients not only with advanced age but also in patients with illnesses that exacerbate their progression like heart failure (HF), cancer, or dementia, with the prevalence of frailty and sarcopenia in HF patients reaching up to 50-75% and 19.5-47.3%, respectively, resulting in 1.5-3 times higher 1-year mortality. The biological mechanisms of frailty and sarcopenia are multifactorial, complex, and not yet fully elucidated, ranging from DNA damage, proteostasis impairment, and epigenetic changes to mitochondrial dysfunction, cellular senescence, and environmental factors, many of which are further linked to cardiac disease. Currently, there is no gold standard for the treatment of frailty and sarcopenia, however, growing evidence supports that a combination of exercise training and nutritional supplement improves skeletal muscle function and frailty, with a variety of other therapies being devised based on the underlying pathophysiology. In this review, we address the involvement of frailty and sarcopenia in cardiac disease and describe the latest insights into their biological mechanisms as well as the potential for intervention through exercise, diet, and specific therapies.

Biomarkers of frailty

Several biomarkers have been proposed to identify frailty, a multisystemic age-related syndrome. However, the complex pathophysiology and the absence of a consensus on a comprehensive and universal definition make it challenging to pinpoint a singular biomarker or set of biomarkers that conclusively characterize frailty. This review delves into the main laboratory biomarkers, placing special emphasis on those associated with various pathways closely tied to the frailty condition, such as inflammation, oxidative stress, mitochondrial dysfunction, metabolic and endocrine alterations and microRNA. Additionally, we provide a summary of different clinical biomarkers encompassing different tools that have been proposed to assess frailty. We further address various imaging biomarkers such as Dual Energy X-ray Absorptiometry, Bioelectrical Impedance analysis, Computed Tomography and Magnetic Resonance Imaging, Ultrasound and D3 Creatine dilution. Intervention to treat frailty, including non-pharmacological ones, especially those involving physical exercise and nutrition, and pharmacological interventions, that include those targeting specific mechanisms such as myostatin inhibitors, insulin sensitizer metformin and with special relevance for hormonal treatments are mentioned. We further address the levels of different biomarkers in monitoring the potential positive effects of some of these interventions. Despite the availability of numerous biomarkers, their performance and usefulness in the clinical arena are far from being satisfactory. Considering the multicausality of frailty, there is an increasing need to assess the role of sets of biomarkers and the combination between laboratory, clinical and image biomarkers, in terms of sensitivity, specificity and predictive values for the diagnosis and prognosis of the different outcomes of frailty to improve detection and monitoring of older people with frailty or at risk of developing it, being this a need in the everyday clinical practice.

Tankyrase-1 regulates RBP-mediated mRNA turnover to promote muscle fiber formation

Poly(ADP-ribosylation) (PARylation) is a post-translational modification mediated by a subset of ADP-ribosyl transferases (ARTs). Although PARylation-inhibition based therapies are considered as an avenue to combat debilitating diseases such as cancer and myopathies, the role of this modification in physiological processes such as cell differentiation remains unclear. Here, we show that Tankyrase1 (TNKS1), a PARylating ART, plays a major role in myogenesis, a vital process known to drive muscle fiber formation and regeneration. Although all bona fide PARPs are expressed in muscle cells, experiments using siRNA-mediated knockdown or pharmacological inhibition show that TNKS1 is the enzyme responsible of catalyzing PARylation during myogenesis. Via this activity, TNKS1 controls the turnover of mRNAs encoding myogenic regulatory factors such as nucleophosmin (NPM) and myogenin. TNKS1 mediates these effects by targeting RNA-binding proteins such as Human Antigen R (HuR). HuR harbors a conserved TNKS-binding motif (TBM), the mutation of which not only prevents the association of HuR with TNKS1 and its PARylation, but also precludes HuR from regulating the turnover of NPM and myogenin mRNAs as well as from promoting myogenesis. Therefore, our data uncover a new role for TNKS1 as a key modulator of RBP-mediated post-transcriptional events required for vital processes such as myogenesis.

Oxidative stress and metabolism meet epigenetic modulation in physical exercise

Physical exercise is established as an important factor of health and generally is recommended for its positive effects on several tissues, organs, and systems. These positive effects come from metabolic adaptations that also include oxidative eustress, in which physical activity increases ROS production and antioxidant mechanisms, although this depends on the intensity of the exercise. Muscle metabolism through mechanisms such as aerobic and anaerobic glycolysis, tricarboxylic acid cycle, and oxidative lipid metabolism can produce metabolites and co-factors which directly impact the epigenetic machinery. In this review, we clearly reinforce the evidence that exercise regulates several epigenetic mechanisms and explain how these mechanisms can be regulated by metabolic products and co-factors produced during exercise. In fact, recent evidence has demonstrated the importance of epigenetics in the gene expression changes implicated in metabolic adaptation after exercise. Importantly, intermediates of the metabolism generated by continuous, acute, moderate, or strenuous exercise control the activity of epigenetic enzymes, therefore turning on or turning off the gene expression of specific programs which can lead to physiological adaptations after exercise.

Impact of Exercise Training on Survival Rate and Neural Cell Death in Sepsis Through the Maintenance of Redox Equilibrium

PURPOSE

Sepsis-related deaths occur during both the early proinflammatory and the late immunosuppressive phases of the condition. The balance of pro- and anti-inflammatory responses is influenced by damaged cells that die via either proinflammatory necroptosis or anti-inflammatory apoptosis. Both forms of cell death may be mediated by reactive oxygen species (ROS) generated during the proinflammatory response. Recent evidence suggests that exercise training boosts antioxidative capacity and could offer protection against sepsis. Given these findings, we aimed to examine the impact of exercise training on neural cell death in the context of sepsis.

METHODS

We assessed the effectiveness of exercise in reducing ROS production and the inflammatory response using a cecal ligation and puncture (CLP)-induced sepsis model. Forty C57BL/6N male mice were randomly divided into 2 groups: control (CLP-Con; n=20) and experimental (CLP-Ex; n=20). Before the induction of sepsis by CLP, the CLP-Ex mice underwent interval training on a treadmill 3 days per week for 8 weeks. Each day involved 10 cycles of 2 minutes at 8 m/min and 2 minutes at 15 m/min. After the CLP procedure, we monitored the survival of 10 mice from each group over a 30-hour period.

RESULTS

The findings indicated that exercise training increased the survival rate among mice with CLP-induced sepsis by enhancing antioxidative capacity and delaying the transition from a hyperdynamic to an immunosuppressive state.

CONCLUSION

Exercise training may delay the progression from the hyperdynamic state to the hypodynamic phase of sepsis by increasing antioxidant capacity and reducing apoptotic cell death.

The Impact of 8 Weeks of Combined Physical Exercise Training on SIRT3 and mTOR in Lymphocytes, and on Lipid Peroxidation

The sirtuins (SIRT) protein family and the mechanistic/mammalian target of rapamycin (mTOR) are intracellular molecules that have been involved in the regulation of several biological processes, as well as in various aging-related processes. This pilot study, in small scale, aimed to analyze the effects of an 8-week physical exercise program on SIRT3 and mTOR levels in lymphocytes, as well as on lipid peroxidation in middle aged and older men. A total of 9 participants aged between 56 and 73 years were enrolled in an 8-week physical exercise program comprising cardiovascular and high-intensity interval training. The program involved three sessions per week, each lasting 45-60 min, conducted on non-consecutive days. Tests were conducted before and after the experimental period (pre- and post-training). Assessments included a vertical jump, 20 m velocity, ball throwing, and an aerobic capacity test. Lipid peroxidation (MDA) was measured in plasma as an oxidative stress biomarker. Additionally, sirtuin 3 (SIRT3/β-actin) and mTOR (mTOR/β-actin) levels were measured in isolated lymphocytes extracted from venous blood. Following the exercise training period, our results demonstrated a significant improvement in aerobic capacity (pre-training: 615.4 ± 45.3 m; post-training: 687.2 ± 34.6 m; t = -2.521; p = 0.012) and 20 m velocity (pre-training: 4.6 ± 0.5 s; post-training: 4.3 ± 0.3 s; t = -2.023; p = 0.04). Concerning blood variables, there was a significant decrease in mTOR levels (pre-training: 0.857 ± 0.593; post-training: 0.214 ± 0.097; t = -2.547; p = 0.011), while no changes were observed in SIRT3 (pre-training: 0.608 ± 0.404; post-training: 0.516 ± 0.390; t = 0.533; p = 0.594) and MDA (pre-training: 8420 ± 4615; post-training: 8800 ± 3163; t = -0.533; p = 0.594). The notable reduction in mTOR levels in lymphocytes following the 8-week physical exercise program suggests a potential role of exercise in modulating immune cell dynamics, particularly in middle-aged and older individuals. Furthermore, the exercise regimen resulted in improvements in physical function, including enhanced aerobic capacity and walking velocity.

Epithelial NAD+ depletion drives mitochondrial dysfunction and contributes to intestinal inflammation

Introduction

We have previously demonstrated that a pathologic downregulation of peroxisome proliferator-activated receptor-gamma coactivator 1-alpha (PGC1α) within the intestinal epithelium contributes to the pathogenesis of inflammatory bowel disease (IBD). However, the mechanism underlying downregulation of PGC1α expression and activity during IBD is not yet clear.

Methods

Mice (male; C57Bl/6, Villincre/+;Pgc1afl/fl mice, and Pgc1afl/fl) were subjected to experimental colitis and treated with nicotinamide riboside. Western blot, high-resolution respirometry, nicotinamide adenine dinucleotide (NAD+) quantification, and immunoprecipitation were used to in this study.

Results

We demonstrate a significant depletion in the NAD+ levels within the intestinal epithelium of mice undergoing experimental colitis, as well as humans with ulcerative colitis. While we found no decrease in the levels of NAD+-synthesizing enzymes within the intestinal epithelium of mice undergoing experimental colitis, we did find an increase in the mRNA level, as well as the enzymatic activity, of the NAD+-consuming enzyme poly(ADP-ribose) polymerase-1 (PARP1). Treatment of mice undergoing experimental colitis with an NAD+ precursor reduced the severity of colitis, restored mitochondrial function, and increased active PGC1α levels; however, NAD+ repletion did not benefit transgenic mice that lack PGC1α within the intestinal epithelium, suggesting that the therapeutic effects require an intact PGC1α axis.

Discussion

Our results emphasize the importance of PGC1α expression to both mitochondrial health and homeostasis within the intestinal epithelium and suggest a novel therapeutic approach for disease management. These findings also provide a mechanistic basis for clinical trials of nicotinamide riboside in IBD patients.

PARP1 mediated PARylation contributes to myogenic progression and glucocorticoid transcriptional response

The ADP-ribosyltransferase, PARP1 enzymatically generates and applies the post-translational modification, ADP-Ribose (ADPR). PARP1 roles in genome maintenance are well described, but recent work highlights roles in many fundamental processes including cellular identity and energy homeostasis. Herein, we show in both mouse and human skeletal muscle cells that PARP1-mediated PARylation is a regulator of the myogenic program and the muscle transcriptional response to steroid hormones. Chemical PARP1 modulation impacts the expression of major myocellular proteins, including troponins, key in dictating muscle contractile force. Whilst PARP1 in absence of DNA damage is often assumed to be basally inactive, we show PARylation to be acutely sensitive to extracellular glucose concentrations and the steroid hormone class, glucocorticoids which exert considerable authority over muscle tissue mass. Specifically, we find during myogenesis, a transient and significant rise in PAR. This early-stage differentiation event, if blocked with PARP1 inhibition, reduced the abundance of important muscle proteins in the fully differentiated myotubes. This suggests that PAR targets during early-stage differentiation are central to the proper development of the muscle contractile unit. We also show that reduced PARP1 in myoblasts impacts a variety of metabolic pathways in line with the recorded actions of glucocorticoids. Currently, as both regulators of myogenesis and muscle mass loss, glucocorticoids represent a clinical conundrum. Our work goes on to identify that PARP1 influences transcriptional activation by glucocorticoids of a subset of genes critical to human skeletal muscle pathology. These genes may therefore signify a regulatory battery of targets through which selective glucocorticoid modulation could be achieved. Collectively, our data provide clear links between PARP1-mediated PARylation and skeletal muscle homeostatic mechanisms crucial to tissue mass maintenance and endocrine response.

Tissue-specific effects of exercise as NAD+ -boosting strategy: Current knowledge and future perspectives

Nicotinamide adenine dinucleotide (NAD⁺ ) is an evolutionarily highly conserved coenzyme with multi-faceted cell functions, including energy metabolism, molecular signaling processes, epigenetic regulation, and DNA repair. Since the discovery that lower NAD⁺ levels are a shared characteristic of various diseases and aging per se, several NAD⁺ -boosting strategies have emerged. Other than pharmacological and nutritional approaches, exercise is thought to restore NAD⁺ homeostasis through metabolic adaption to chronically recurring states of increased energy demand. In this review we discuss the impact of acute exercise and exercise training on tissue-specific NAD⁺ metabolism of rodents and humans to highlight the potential value as NAD⁺ -boosting strategy. By interconnecting results from different investigations, we aim to draw attention to tissue-specific alterations in NAD⁺ metabolism and the associated implications for whole-body NAD⁺ homeostasis. Acute exercise led to profound alterations of intracellular NAD⁺ metabolism in various investigations, with the magnitude and direction of changes being strongly dependent on the applied exercise modality, cell type, and investigated animal model or human population. Exercise training elevated NAD⁺ levels and NAD⁺ metabolism enzymes in various tissues. Based on these results, we discuss molecular mechanisms that might connect acute exercise-induced disruptions of NAD⁺ /NADH homeostasis to chronic exercise adaptions in NAD⁺ metabolism. Taking this hypothesis-driven approach, we hope to inspire future research on the molecular mechanisms of exercise as NAD⁺ -modifying lifestyle intervention, thereby elucidating the potential therapeutic value in NAD⁺ -related pathologies.

The Role of Sirtuins in Sarcopenia and Frailty

The population of older individuals is increasing rapidly, but only a small fraction among them is able to experiences a healthy life. Due to lack of physical exercise and oxidative stress, aging leads to sarcopenia and finally end up with frailty. Sarcopenia is a component of the frailty and described as age related degenerative changes in the skeletal muscle mass, strength and quality. Though the loss of muscle strength and mass gradually seem inevitable during aging, it can be partially prevented or overcome by a deeper insight into the pathogenesis. Sirtuin protein leads to longevity across different organisms ranging from worms to mammals. Expression of sirtuin protein increases during physical exercise and thus strengthens muscle mass. Satellite cells leads to muscle repair in a SIRT1 dependent manner. In addition, SIRT1 improves insulin sensitivity and induces autophagy in the aged mice. The current paper discussed the putative role of sirtuins in sarcopenia and frailty. Moreover, it highlighted the pathways by which sirtuins can inhibit ROS production, inflammation and mitochondrial dysfunctions and therefore confers a protective role against frailty and sarcopenia. The critical role of sirtuins in the sarcopenia and frailty pathogenesis can eventually fuel the development of novel interventions by targeting sirtuins.

Mitochondria transplant therapy improves regeneration and restoration of injured skeletal muscle

BACKGROUND

Injection of exogenous mitochondria has been shown to improve the ischaemia-damaged myocardium, but the effect of mitochondrial transplant therapy (MTT) to restore skeletal muscle mass and function has not been tested following neuromuscular injury. Therefore, we tested the hypothesis that MTT would improve the restoration of muscle function after injury.

METHODS

BaCl₂ was injected into the gastrocnemius muscle of one limb of 8-12-week-old C57BL/6 mice to induce damage without injury to the resident stem cells. The contralateral gastrocnemius muscle was injected with phosphate-buffered saline (PBS) and served as the non-injured intra-animal control. Mitochondria were isolated from donor mice. Donor mitochondria were suspended in PBS or PBS without mitochondria (sham treatment) and injected into the tail vein of BaCl₂ injured mice 24 h after the initial injury. Muscle repair was examined 7, 14 and 21 days after injury.

RESULTS

MTT did not increase systemic inflammation in mice. Muscle mass 7 days following injury was 21.9 ± 2.1% and 17.4 ± 1.9% lower (P < 0.05) in injured as compared with non-injured intra-animal control muscles in phosphate-buffered saline (PBS)- and MTT-treated animals, respectively. Maximal plantar flexor muscle force was significantly lower in injured as compared with uninjured muscles of PBS-treated (-43.4 ± 4.2%, P < 0.05) and MTT-treated mice (-47.7 ± 7.3%, P < 0.05), but the reduction in force was not different between the experimental groups. The percentage of collagen and other non-contractile tissue in histological muscle cross sections, was significantly greater in injured muscles of PBS-treated mice (33.2 ± 0.2%) compared with MTT-treated mice (26.5 ± 0.2%) 7 days after injury. Muscle wet weight and maximal muscle force from injured MTT-treated mice had recovered to control levels by 14 days after the injury. However, muscle mass and force had not improved in PBS-treated animals by 14 days after injury. The non-contractile composition of the gastrocnemius muscle tissue cross sections was not different between control, repaired PBS-treated and repaired MTT-treated mice 14 days after injury. By 21 days following injury, PBS-treated mice had fully restored gastrocnemius muscle mass of the injured muscle to that of the uninjured muscle, although maximal plantar flexion force was still 19.4 ± 3.7% (P < 0.05) lower in injured/repaired gastrocnemius as compared with uninjured intra-animal control muscles.

CONCLUSIONS

Our results suggest that systemic mitochondria delivery can enhance the rate of muscle regeneration and restoration of muscle function following injury.

Post-translational Modifications: The Signals at the Intersection of Exercise, Glucose Uptake, and Insulin Sensitivity

Diabetes is a global epidemic, of which type 2 diabetes makes up the majority of cases. Nonetheless, for some individuals, type 2 diabetes is eminently preventable and treatable via lifestyle interventions. Glucose uptake into skeletal muscle increases during and in recovery from exercise, with exercise effective at controlling glucose homeostasis in individuals with type 2 diabetes. Furthermore, acute and chronic exercise sensitizes skeletal muscle to insulin. A complex network of signals converge and interact to regulate glucose metabolism and insulin sensitivity in response to exercise. Numerous forms of post-translational modifications (eg, phosphorylation, ubiquitination, acetylation, ribosylation, and more) are regulated by exercise. Here we review the current state of the art of the role of post-translational modifications in transducing exercise-induced signals to modulate glucose uptake and insulin sensitivity within skeletal muscle. Furthermore, we consider emerging evidence for noncanonical signaling in the control of glucose homeostasis and the potential for regulation by exercise. While exercise is clearly an effective intervention to reduce glycemia and improve insulin sensitivity, the insulin- and exercise-sensitive signaling networks orchestrating this biology are not fully clarified. Elucidation of the complex proteome-wide interactions between post-translational modifications and the associated functional implications will identify mechanisms by which exercise regulates glucose homeostasis and insulin sensitivity. In doing so, this knowledge should illuminate novel therapeutic targets to enhance insulin sensitivity for the clinical management of type 2 diabetes.

Attenuation of Muscle Damage, Structural Abnormalities, and Physical Activity in Respiratory and Limb Muscles following Treatment with Rucaparib in Lung Cancer Cachexia Mice

Simple Summary

Muscle wasting and cachexia are common in patients with cancer. Several mechanisms underlie muscle physiological and structural alterations in cancer-induced cachexia. Poly (ADPribose) polymerases (PARPs) are involved in muscle metabolism and in cancer. Selective inhibitors of PARP activity improve muscle function and structure. This study sought to investigate whether rucaparib (PARP inhibitor) may attenuate muscle damage in a mouse model of lung-cancer-induced cachexia. Rucaparib was administered to cancer-cachectic mice. Physiological and biological parameters were determined in the respiratory and limb muscles of the animals. In cancer cachexia mice compared to non-cachexia controls, body weight and body weight gain, muscle weight, limb strength, physical activity, and muscle fiber size significantly declined, while levels of PARP activity, plasma troponin I, muscle damage, and proteolytic and autophagy markers increased. Treatment with rucaparib elicited a significant improvement in body weight gain, tumor size and weight, physical activity, muscle damage, troponin I, and proteolytic and autophagy levels.

Abstract

Overactivation of poly (ADPribose) polymerases (PARPs) is involved in cancer-induced cachexia. We hypothesized that the PARP inhibitor rucaparib may improve muscle mass and reduce damage in cancer cachexia mice. In mouse diaphragm and gastrocnemius (LP07 lung adenocarcinoma) treated with PARP inhibitor (rucaparib,150 mg/kg body weight/24 h for 20 days) and in non-tumor control animals, body, muscle, and tumor weights; tumor area; limb muscle strength; physical activity; muscle structural abnormalities, damage, and phenotype; PARP activity; and proteolytic and autophagy markers were quantified. In cancer cachexia mice compared to non-cachexia controls, body weight and body weight gain, muscle weight, limb strength, physical activity, and muscle fiber size significantly declined, while levels of PARP activity, plasma troponin I, muscle damage, and proteolytic and autophagy markers increased. Treatment with the PARP inhibitor rucaparib elicited a significant improvement in body weight gain, tumor size and weight, physical activity, muscle damage, troponin I, and proteolytic and autophagy levels. PARP pharmacological inhibition did not exert any significant improvements in muscle weight, fiber size, or limb muscle strength. Treatment with rucaparib, however, improved muscle damage and structural abnormalities and physical activity in cancer cachexia mice. These findings suggest that rucaparib exerts its beneficial effects on cancer cachexia performance through the restoration of muscle structure.

NAD+ centric mechanisms and molecular determinants of skeletal muscle disease and aging

The nicotinamide adenine dinucleotide (NAD+) is an essential redox cofactor, involved in various physiological and molecular processes, including energy metabolism, epigenetics, aging, and metabolic diseases. NAD+ repletion ameliorates muscular dystrophy and improves the mitochondrial and muscle stem cell function and thereby increase lifespan in mice. Accordingly, NAD+ is considered as an anti-oxidant and anti-aging molecule. NAD+ plays a central role in energy metabolism and the energy produced is used for movements, thermoregulation, and defense against foreign bodies. The dietary precursors of NAD+ synthesis is targeted to improve NAD+ biosynthesis; however, studies have revealed conflicting results regarding skeletal muscle-specific effects. Recent advances in the activation of nicotinamide phosphoribosyltransferase in the NAD+ salvage pathway and supplementation of NAD+ precursors have led to beneficial effects in skeletal muscle pathophysiology and function during aging and associated metabolic diseases. NAD+ is also involved in the epigenetic regulation and post-translational modifications of proteins that are involved in various cellular processes to maintain tissue homeostasis. This review provides detailed insights into the roles of NAD+ along with molecular mechanisms during aging and disease conditions, such as the impacts of age-related NAD+ deficiencies on NAD+-dependent enzymes, including poly (ADP-ribose) polymerase (PARPs), CD38, and sirtuins within skeletal muscle, and the most recent studies on the potential of nutritional supplementation and distinct modes of exercise to replenish the NAD+ pool.

Resveratrol ameliorates muscle atrophy in chronic kidney disease via the axis of SIRT1/FoxO1

Chronic kidney disease (CKD) is often associated with muscle atrophy. However, the underlying molecular mechanisms are still not well understood. Here, we treated 5/6-nephrectomized (5/6Nx) rats with resveratrol and found that this treatment greatly improves renal function as evidenced by reduced proteinuria and cystatin C. Moreover, resveratrol ameliorates renal fibrosis by reducing transforming growth factor β (TGF-β) and connective tissue growth factor (CTGF). Meanwhile, muscle atrophy in these 5/6Nx rats was largely attenuated by resveratrol. Immunoprecipitation revealed that SIRT1 physically interacts with FoxO1 in muscle, and this interaction was weakened in 5/6Nx rats. As a consequence, acetylated FoxO1 was increased in muscle of 5/6Nx rats. The application of resveratrol markedly reverses this trend. These data point out that SIRT1 is a key factor for linking renal disease and muscle atrophy. Indeed, both renal dysfunction and muscle atrophy were further aggravated by 5/6Nx in Sirt1^+/- mice. Taken together, our data indicate that SIRT1 plays a pivotal role in muscle atrophy in CKD, and FoxO1 might be a substrate of SIRT1 in this process. Furthermore, resveratrol, together with other agonists of SIRT1, may hold great therapeutic potentials for treating CKD and its related muscle atrophy.

CYB5R3 overexpression preserves skeletal muscle mitochondria and autophagic signaling in aged transgenic mice

Cytochrome b₅ reductase 3 (CYB5R3) overexpression activates respiratory metabolism and exerts prolongevity effects in transgenic mice, mimicking some of the salutary effects of calorie restriction. The aim of our study was to understand how CYB5R3 overexpression targets key pathways that modulate the rate of aging in skeletal muscle, a postmitotic tissue with a greater contribution to resting energy expenditure. Mitochondrial function, autophagy and mitophagy markers were evaluated in mouse hind limb skeletal muscles from young-adult (7 months old) and old (24 months old) males of wild-type and CYB5R3-overexpressing genotypes. Ultrastructure of subsarcolemmal and intermyofibrillar mitochondria was studied by electron microscopy in red gastrocnemius. CYB5R3, which was efficiently overexpressed and targeted to skeletal muscle mitochondria regardless of age, increased the abundance of complexes I, II, and IV in old mice and prevented the age-related decrease of complexes I, III, IV, and V and the mitofusin MFN-2. ATP was significantly decreased by aging, which was prevented by CYB5R3 overexpression. Coenzyme Q and the mitochondrial biogenesis markers TFAM and NRF-1 were also significantly diminished by aging, but CYB5R3 overexpression did not protect against these declines. Both aging and CYB5R3 overexpression upregulated SIRT3 and the mitochondrial fission markers FIS1 and DRP-1, although with different outcomes on mitochondrial ultrastructure: old wild-type mice exhibited mitochondrial fragmentation whereas CYB5R3 overexpression increased mitochondrial size in old transgenic mice concomitant with an improvement of autophagic recycling. Interventions aimed at stimulating CYB5R3 could represent a valuable strategy to counteract the deleterious effects of aging in skeletal muscle.

Maintenance of NAD+ Homeostasis in Skeletal Muscle during Aging and Exercise

Nicotinamide adenine dinucleotide (NAD) is a versatile chemical compound serving as a coenzyme in metabolic pathways and as a substrate to support the enzymatic functions of sirtuins (SIRTs), poly (ADP-ribose) polymerase-1 (PARP-1), and cyclic ADP ribose hydrolase (CD38). Under normal physiological conditions, NAD+ consumption is matched by its synthesis primarily via the salvage pathway catalyzed by nicotinamide phosphoribosyltransferase (NAMPT). However, aging and muscular contraction enhance NAD+ utilization, whereas NAD+ replenishment is limited by cellular sources of NAD+ precursors and/or enzyme expression. This paper will briefly review NAD+ metabolic functions, its roles in regulating cell signaling, mechanisms of its degradation and biosynthesis, and major challenges to maintaining its cellular level in skeletal muscle. The effects of aging, physical exercise, and dietary supplementation on NAD+ homeostasis will be highlighted based on recent literature.

Divergent serum metabolomic, skeletal muscle signaling, transcriptomic, and performance adaptations to fasted versus whey protein-fed sprint interval training

Sprint interval training (SIT) is a time-efficient alternative to endurance exercise, conferring beneficial skeletal muscle metabolic adaptations. Current literature has investigated the nutritional regulation of acute and chronic exercise-induced metabolic adaptations in muscle following endurance exercise, principally comparing the impact of training in fasted and carbohydrate-fed (CHO) conditions. Alternative strategies such as exercising in low CHO, protein-fed conditions remain poorly characterized, specifically pertaining to adaptations associated with SIT. Thus, this study aimed to compare the metabolic and performance adaptations to acute and short-term SIT in the fasted state with preexercise hydrolyzed (WPH) or concentrated (WPC) whey protein supplementation. In healthy males, preexercise protein ingestion did not alter exercise-induced increases in PGC-1α, PDK4, SIRT1, and PPAR-δ mRNA expression following acute SIT. However, supplementation of WPH beneficially altered acute exercise-induced CD36 mRNA expression. Preexercise protein ingestion attenuated acute exercise-induced increases in muscle pan-acetylation and PARP1 protein content compared with fasted SIT. Acute serum metabolomic differences confirmed greater preexercise amino acid delivery in protein-fed compared with fasted conditions. Following 3 wk of SIT, training-induced increases in mitochondrial enzymatic activity and exercise performance were similar across nutritional groups. Interestingly, resting muscle acetylation status was downregulated in WPH conditions following training. Such findings suggest preexercise WPC and WPH ingestion positively influences metabolic adaptations to SIT compared with fasted training, resulting in either similar or enhanced performance adaptations. Future studies investigating nutritional modulation of metabolic adaptations to exercise are warranted to build upon these novel findings.NEW & NOTEWORTHY These are the first data to show the influence of preexercise protein on serum and skeletal muscle metabolic adaptations to acute and short-term sprint interval training (SIT). Preexercise whey protein concentrate (WPC) or hydrolysate (WPH) feeding acutely affected the serum metabolome, which differentially influenced acute and chronic changes in mitochondrial gene expression, intracellular signaling (acetylation and PARylation) resulting in either similar or enhanced performance outcomes when compared with fasted training.

PARPs in lipid metabolism and related diseases

PARPs and tankyrases (TNKS) represent a family of 17 proteins. PARPs and tankyrases were originally identified as DNA repair factors, nevertheless, recent advances have shed light on their role in lipid metabolism. To date, PARP1, PARP2, PARP3, tankyrases, PARP9, PARP10, PARP14 were reported to have multi-pronged connections to lipid metabolism. The activity of PARP enzymes is fine-tuned by a set of cholesterol-based compounds as oxidized cholesterol derivatives, steroid hormones or bile acids. In turn, PARPs modulate several key processes of lipid homeostasis (lipotoxicity, fatty acid and steroid biosynthesis, lipoprotein homeostasis, fatty acid oxidation, etc.). PARPs are also cofactors of lipid-responsive nuclear receptors and transcription factors through which PARPs regulate lipid metabolism and lipid homeostasis. PARP activation often represents a disruptive signal to (lipid) metabolism, and PARP-dependent changes to lipid metabolism have pathophysiological role in the development of hyperlipidemia, obesity, alcoholic and non-alcoholic fatty liver disease, type II diabetes and its complications, atherosclerosis, cardiovascular aging and skin pathologies, just to name a few. In this synopsis we will review the evidence supporting the beneficial effects of pharmacological PARP inhibitors in these diseases/pathologies and propose repurposing PARP inhibitors already available for the treatment of various malignancies.

Skeletal Muscle Gene Expression Profile in Response to Caloric Restriction and Aging: A Role for SirT1

SirT1 plays a crucial role in the regulation of some of the caloric restriction (CR) responsive biological pathways. Aging suppresses SirT1 gene expression in skeletal muscle, suggesting that aging may affect the role of CR in muscle. To determine the role of SirT1 in the regulation of CR regulated pathways in skeletal muscle, we performed high-throughput RNA sequencing using total RNA isolated from the skeletal muscles of young and aged wild-type (WT), SirT1 knockout (SirT1-KO), and SirT1 overexpression (SirT1-OE) mice fed to 20 wk ad libitum (AL) or 40% CR diet. Our data show that aging repressed the global gene expression profile, which was restored by CR via upregulating transcriptional and translational process-related pathways. CR inhibits pathways linked to the extracellular matrix and cytoskeletal proteins regardless of aging. Mitochondrial function and muscle contraction-related pathways are upregulated in aged SirT1 KO mice following CR. SirT1 OE did not affect whole-body energy expenditure or augment skeletal muscle insulin sensitivity associated pathways, regardless of aging or diet. Overall, our RNA-seq data showed that SirT1 and CR have different functions and activation of SirT1 by its activator or exercise may enhance SirT1 activity that, along with CR, likely have a better functional role in aging muscle.

Skeletal Aging and Osteoporosis: Mechanisms and Therapeutics

Bone is a dynamic organ maintained by tightly regulated mechanisms. With old age, bone homeostasis, which is maintained by an intricate balance between bone formation and bone resorption, undergoes deregulation. Oxidative stress-induced DNA damage, cellular apoptosis, and cellular senescence are all responsible for this tissue dysfunction and the imbalance in the bone homeostasis. These cellular mechanisms have become a target for therapeutics to treat age-related osteoporosis. Genetic mouse models have shown the importance of senescent cell clearance in alleviating age-related osteoporosis. Furthermore, we and others have shown that targeting cellular senescence pharmacologically was an effective tool to alleviate age- and radiation-induced osteoporosis. Senescent cells also have an altered secretome known as the senescence associated secretory phenotype (SASP), which may have autocrine, paracrine, or endocrine function. The current review discusses the current and potential pathways which lead to a senescence profile in an aged skeleton and how bone homeostasis is affected during age-related osteoporosis. The review has also discussed existing therapeutics for the treatment of osteoporosis and rationalizes for novel therapeutic options based on cellular senescence and the SASP as an underlying pathogenesis of an aging bone.

FGF19 protects skeletal muscle against obesity-induced muscle atrophy, metabolic derangement and abnormal irisin levels via the AMPK/SIRT-1/PGC-α pathway

Obesity is associated with biological dysfunction in skeletal muscle. As a condition of obesity accompanied by muscle mass loss and physical dysfunction, sarcopenic obesity (SO) has become a novel public health problem. Human fibroblast growth factor 19 (FGF19) plays a therapeutic role in metabolic diseases. However, the protective effects of FGF19 on skeletal muscle in obesity and SO are still not completely understood. Our results showed that FGF19 administration improved muscle loss and grip strength in young and aged mice fed a high‐fat diet (HFD). Increases in muscle atrophy markers (FOXO‐3, Atrogin‐1, MuRF‐1) were abrogated by FGF19 in palmitic acid (PA)‐treated C2C12 myotubes and in the skeletal muscle of HFD‐fed mice. FGF19 not only reduced HFD‐induced body weight gain, excessive lipid accumulation and hyperlipidaemia but also promoted energy expenditure (PGC‐1α, UCP‐1, PPAR‐γ) in brown adipose tissue (BAT). FGF19 treatment restored PA‐ and HFD‐induced hyperglycaemia, impaired glucose tolerance and insulin resistance (IRS‐1, GLUT‐4) and mitigated the PA‐ and HFD‐induced decrease in FNDC‐5/irisin expression. However, these beneficial effects of FGF19 on skeletal muscle were abolished by inhibiting AMPK, SIRT‐1 and PGC‐1α expression. Taken together, this study suggests that FGF19 protects skeletal muscle against obesity‐induced muscle atrophy, metabolic derangement and abnormal irisin secretion partially through the AMPK/SIRT‐1/PGC‐α signalling pathway, which might be a potential therapeutic target for obesity and SO.

Exogenous NAD+ Postpones the D-Gal-Induced Senescence of Bone Marrow-Derived Mesenchymal Stem Cells via Sirt1 Signaling

Cell senescence is accompanied by decreased nicotinamide adenine dinucleotide (NAD⁺) levels; however, whether exogenous NAD⁺ affects bone marrow-derived mesenchymal stem cells (BMSCs) senescence and the involved mechanisms is still unclear. Here, we find that exogenous NAD⁺ replenishment significantly postpones BMSC senescence induced by D-galactose (D-gal). It is also shown that exogenous NAD⁺ leads to increased intracellular NAD⁺ levels and reduced intracellular reactive oxygen species in senescent BMSCs here. Further investigation showed that exogenous NAD⁺ weakened BMSC senescence by increasing Sirtuin 1 (Sirt1) expression. Moreover, exogenous NAD⁺ reduced senescence-associated-β-galactosidase activity, and downregulated poly (ADP-ribose) polymerase 1 expression. In addition, the reduced expression of Sirt1 by small interfering RNA abolished the beneficial effects of exogenous NAD⁺ in terms of postponing BMSCs senescence induced by D-gal. Taken together, our results indicate that exogenous NAD⁺ could postpone D-gal-induced BMSC senescence through Sirt1 signaling, providing a potential method for obtaining high quality BMSCs to support their research and clinical application.

Poly (ADP-ribose) polymerase 1 and Parkinson's disease: A study in post-mortem human brain

Poly (ADP-ribose) polymerase 1 (PARP1) is crucial in both maintenance of genome integrity and cell death. PARP1 activation has been very recently linked to Parkinson's disease (PD) and its role in inducing the pathologic accumulation of α-Synuclein demonstrated in a PD mouse model. The objective of this study was to investigate the presence and localization of PARP1 in PD brain. PARP1 localization was assessed by immunostaining and confocal microscopy in post-mortem human brains obtained from PD patients (Braak stage VI) compared to controls. PARP1 positive nuclei in substantia nigra, mainly in dopaminergic neurons but also in astrocytes and oligodendrocytes, were decreased in PD. The same alteration was observed in several areas that are affected in PD pathology, namely the dorsal motor nucleus of vagus, frontal and cingulate cortex, whereas no changes in PARP1 staining were detectable in the inferior olivary nucleus that is unaffected in PD. In addition, PARP1 co-localizes with α-Synuclein that is accumulated in the cytoplasm and in Lewy bodies of PD tissue sections. Our data reveal previously unknown changes of PARP1 localization in the brain of PD patients, in both neurons and glia, supporting its widespread involvement in this pathology and its potential use as a therapeutic target.

PARP-1 and SIRT-1 are Interacted in Diabetic Nephropathy by Activating AMPK/PGC-1α Signaling Pathway

INTRODUCTION

Diabetic nephropathy (DN) is a metabolic disorder characterized by the accumulation of extracellular matrix (ECM). This study aims to investigate whether exists an interplay between poly (ADP-ribose) polymerase 1 (PARP-1) and sirtuin 1 (SIRT-1) in DN via AMP-activated protein kinase (AMPK)/peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α) signaling pathway.

METHODS

Eight-week-old male obese leptin-resistant (db/db) mice and nondiabetic control male C57BLKs/J (db/m) mice were used in this study. Body weight and blood glucose were evaluated after 6 h of fasting, which continues for 4 weeks. The kidney tissues were dissected for Western blot, immunofluorescence (IF) assay. Besides, PARP activity assay, MTT assay, NAD⁺ qualification, Western blot and IF were also performed to detect the level and relation of PARP-1 and SIRT-1 in mouse mesangial cells (MCs) with or without high glucose followed by inhibiting or elevating PARP-1 and SIRT-1, respectively.

RESULTS

Western blotting shows PARP-1 and ECM marker fibronectin (FN) are upregulated while SIRT-1 is downregulated in db/db mice (p<0.05) or in mouse MCs with high glucose (p<0.05), which are significantly restored by PARP-1 inhibitor (PJ34) (p<0.05) and SIRT-1 lentiviral transfected treatment (p<0.05), or worsened by SIRT-1 inhibitor EX527 (p<0.05). PJ34 treatment (p < 0.05) or SIRT-1 overexpression (p < 0.05) could increase PGC-1α and p-AMPK levels, concomitant with down expression of FN, however, were reversed in the presence of EX527 (p<0.05).

DISCUSSION

Our results suggest an important relationship between PARP-1 and SIRT-1 through AMPK-PGC-1α pathway, indicating a potential therapeutic method for DN.

The Paradoxical Effect of PARP Inhibitor BGP-15 on Irinotecan-Induced Cachexia and Skeletal Muscle Dysfunction

Simple Summary

Both cancer and the chemotherapy used to treat it are drivers of cachexia, a life-threatening body-wasting condition which complicates cancer treatment. Poly-(ADP-ribose) polymerase (PARP) inhibitors are currently being investigated as a treatment against cancer. Here, we present paradoxical evidence that they might also be useful for mitigating the skeletal muscle specific side-effects of anti-cancer chemotherapy or exacerbate them. BGP-15 is a small molecule PARP inhibitor which protected against irinotecan (IRI)-induced cachexia and loss of skeletal muscle mass and dysfunction in our study. However, peculiarly, BGP-15 adjuvant therapy reduced protein synthesis rates and the expression of key cytoskeletal proteins associated with the dystrophin-associated protein complex and increased matrix metalloproteinase activity, while it increased the propensity for fast-twitch muscles to tear during fatiguing contraction. Our data suggest that both IRI and BGP-15 cause structural remodeling involving proteins associated with the contractile apparatus, cytoskeleton and/or the extracellular matrix which may be only transient and ultimately beneficial or may paradoxically onset a muscular dystrophy phenotype and be detrimental if more permanent.

Abstract

Chemotherapy-induced muscle wasting and dysfunction is a contributing factor to cachexia alongside cancer and increases the risk of morbidity and mortality. Here, we investigate the effects of the chemotherapeutic agent irinotecan (IRI) on skeletal muscle mass and function and whether BGP-15 (a poly-(ADP-ribose) polymerase-1 (PARP-1) inhibitor and heat shock protein co-inducer) adjuvant therapy could protect against IRI-induced skeletal myopathy. Healthy 6-week-old male Balb/C mice (n = 24; 8/group) were treated with six intraperitoneal injections of either vehicle, IRI (30 mg/kg) or BGP-15 adjuvant therapy (IRI+BGP; 15 mg/kg) over two weeks. IRI reduced lean and tibialis anterior mass, which were attenuated by IRI+BGP treatment. Remarkably, IRI reduced muscle protein synthesis, while IRI+BGP reduced protein synthesis further. These changes occurred in the absence of a change in crude markers of mammalian/mechanistic target of rapamycin (mTOR) Complex 1 (mTORC1) signaling and protein degradation. Interestingly, the cytoskeletal protein dystrophin was reduced in both IRI- and IRI+BGP-treated mice, while IRI+BGP treatment also decreased β-dystroglycan, suggesting significant remodeling of the cytoskeleton. IRI reduced absolute force production of the soleus and extensor digitorum longus (EDL) muscles, while IRI+BGP rescued absolute force production of the soleus and strongly trended to rescue force output of the EDL (p = 0.06), which was associated with improvements in mass. During the fatiguing stimulation, IRI+BGP-treated EDL muscles were somewhat susceptible to rupture at the musculotendinous junction, likely due to BGP-15’s capacity to maintain the rate of force development within a weakened environment characterized by significant structural remodeling. Our paradoxical data highlight that BGP-15 has some therapeutic advantage by attenuating IRI-induced skeletal myopathy; however, its effects on the remodeling of the cytoskeleton and extracellular matrix, which appear to make fast-twitch muscles more prone to tearing during contraction, could suggest the induction of muscular dystrophy and, thus, require further characterization.

Bone and Muscle Crosstalk in Aging

Osteoporosis and sarcopenia are two age-related diseases that affect the quality of life in the elderly. Initially, they were thought to be two independent diseases; however, recently, increasing basic and clinical data suggest that skeletal muscle and bone are both spatially and metabolically connected. The term "osteosarcopenia" is used to define a condition of synergy of low bone mineral density with muscle atrophy and hypofunction. Bone and muscle cells secrete several factors, such as cytokines, myokines, and osteokines, into the circulation to influence the biological and pathological activities in local and distant organs and cells. Recent studies reveal that extracellular vesicles containing microRNAs derived from senescent skeletal muscle and bone cells can also be transported and aid in regulating bone-muscle crosstalk. In this review, we summarize the age-related changes in the secretome and extracellular vesicle-microRNAs secreted by the muscle and bone, and discuss their interactions between muscle and bone cells during aging.

Sarcopenia in aging, obesity, and cancer

Sarcopenia, defined as loss of muscle mass, strength and physical performance, is a hallmark of aging and is invariably associated with perturbation of amino acid metabolism, increased muscle protein catabolism relative to anabolism, and loss of muscle fibers. Sarcopenia may be associated with general loss of body mass, or it may also occur along with obesity [sarcopenic obesity (SO)]. Although sarcopenia is associated with multiple comorbidities in older adults, its effects may even be more severe in patients with malignant disease where it has been shown to contribute to poor surgical outcomes, increased chemotherapy toxicity associated with both cytotoxic and targeted agents, as well as adversely impacting survival. While development of sarcopenia is a common age-related phenomenon, the associated catabolic processes appear to be promoted by physical inactivity, inadequate nutrition, and systemic low-grade inflammation, as well as intrinsic muscle and molecular changes, including mitochondrial dysfunction and impaired muscle stem cell regenerative capacity. Increased physical activity and adequate protein intake can reduce incidence and severity of sarcopenia in cancer patients, but many older cancer patients do not meet physical activity and nutrition recommendations, and cancer treatment can make it more difficult to make favorable lifestyle changes. Sarcopenia is discussed in terms of its adverse clinical consequences in older subjects and particularly, in older patients with cancer. Contributions of lifestyle, molecular, and cellular factors are likewise reviewed with suggestions for interventions to improve sarcopenia and its comorbid sequalae.

The Effects of Calcium-β-Hydroxy-β-Methylbutyrate on Aging-Associated Apoptotic Signaling and Muscle Mass and Function in Unloaded but Nonatrophied Extensor Digitorum Longus Muscles of Aged Rats

Beta-hydroxy-beta-methylbutyrate (HMB), a naturally occurring leucine metabolite, has been shown to attenuate plantar flexor muscle loss and increase myogenic stem cell activation during reloading after a period of significant muscle wasting by disuse in old rodents. However, it was less clear if HMB would alter dorsiflexor muscle response to unloading or reloading when there was no significant atrophy that was induced by unloading. In this study, we tested if calcium HMB (Ca-HMB) would improve muscle function and alter apoptotic signaling in the extensor digitorum longus (EDL) of aged animals that were unloaded but did not undergo atrophy. The EDL muscle was unloaded for 14 days by hindlimb suspension (HS) in aged (34-36 mo.) male Fisher 344 × Brown Norway rats. The rats were removed from HS and allowed normal cage ambulation for 14 days of reloading (R). Throughout the study, the rats were gavaged daily with 170 mg of Ca-HMB or water 7 days prior to HS, then throughout 14 days of HS and 14 days of recovery after removing HS. The animals' body weights were significantly reduced by ~18% after 14 days of HS and continued to decline by ~22% during R as compared to control conditions; however, despite unloading, EDL did not atrophy by HS, nor did it increase in mass after R. No changes were observed in EDL twitch contraction time, force production, fatigue resistance, fiber cross-sectional area, or markers of nuclear apoptosis (myonuclei + satellite cells) after HS or R. While HS and R increased the proapoptotic Bax protein abundance, BCL-2 abundance was also increased as was the frequency of TUNEL-positive myonuclei and satellite cells, yet muscle mass and fiber cross-sectional area did not change and Ca-HMB treatment had no effect reducing apoptotic signaling. These data indicate that (i) increased apoptotic signaling preceded muscle atrophy or occurred without significant EDL atrophy and (ii) that Ca-HMB treatment did not improve EDL signaling, muscle mass, or muscle function in aged rats, when HS and R did not impact mass or function.

Muscle-specific sirtuin1 gain-of-function ameliorates skeletal muscle atrophy in a pre-clinical mouse model of cerebral ischemic stroke

Stroke causes severe long-term disability in patients due to the induction of skeletal muscle atrophy and weakness, but the molecular mechanisms remain elusive. Using a preclinical mouse model of cerebral ischemic stroke, we show that stroke robustly induced atrophy and significantly decreased SirT1 gene expression in the PTA (paralytic tibialis anterior) muscle. Muscle-specific SirT1 gain-of-function mice are resistant to stroke-induced muscle atrophy and this protective effect requires its deacetylase activity. Although SirT1 counteracts the stroke-induced up-regulation of atrogin1, MuRF1 and ZNF216 genes, we found a mechanism that regulates the ZNF216 gene transcription in post-stroke muscle. Stroke increased the expression of the ZNF216 gene in PTA muscle by activating PARP-1, which binds on the ZNF216 promoter. The SirT1 gain-of-function or SirT1 activator, resveratrol, reversed the PARP-1-mediated up-regulation of ZNF216 expression at the promoter level, suggesting a contradicted role for SirT1 and PARP-1 in the regulation of ZNF216 gene. Overall, our study for the first-time demonstrated that (a) stroke causes muscle atrophy, in part, through the SirT1/PARP-1/ZNF216 signaling mechanism; (b) SirT1 can block muscle atrophy in response to different types of atrophic signals via different signaling mechanisms; and (c) SirT1 is a critical regulator of post-stroke muscle mass.

Role of PARP-1 in mitochondrial homeostasis

BACKGROUND

Nuclear poly(ADP-ribose) polymerase-1 (PARP-1) is a well characterised protein that accounts for the majority of PARylation reactions using NAD⁺ as a substrate, regulating diverse cellular functions. In addition to its nuclear functions, several recent studies have identified localization of PARP-1 in mitochondria and emphasized its possible role in maintaining mitochondrial homeostasis. Various reports suggest that nuclear PARP-1 has been implicated in diverse mitochondria-specific communication processes.

SCOPE OF REVIEW

The present review emphasizes on the potential role of PARP-1 in mitochondrial processes such as bioenergetics, mtDNA maintenance, cell death and mitophagy.

MAJOR CONCLUSIONS

The origin of mitochondrial PARP-1 is still an enigma; however researchers are trying to establish the cross-talk between nuclear and mitochondrial PARP-1 and how these PARP-1 pools modulate mitochondrial activity.

GENERAL SIGNIFICANCE

A better understanding of the possible role of PARP-1 in mitochondrial homeostasis helps us to explore the potential therapeutic targets to protect mitochondrial dysfunctions.

Nicotinamide riboside-A missing piece in the puzzle of exercise therapy for older adults?

Maintaining physical mobility is important for preventing age-related comorbidities in older adults. Endurance and resistance training prevent mobility loss in aging, but exercise alone does not always achieve the expected improvements in physical and cardiopulmonary function. Recent preclinical evidence suggests that a reason for the variability in exercise training responses may be the age-related dysregulation of the nicotinamide adenine dinucleotide (NAD+) metabolome. NAD+ is an essential enzymatic cofactor in energetic and signaling pathways. Endogenous NAD+ pool is lower in several chronic and degenerative diseases (e.g., cardiovascular diseases, Alzheimer's and Parkinson's diseases, muscular dystrophies), and also in aging. Exercise requires a higher energy expenditure than a resting state, thus a state of NAD+ insufficiency with reduced energy metabolism, could result in an inadequate exercise response. Recently, the NAD+ precursor nicotinamide riboside (NR), a vitamin B3 derivate, showed an ability to improve NAD+ metabolome homeostasis, restoring energy metabolism and cellular function in various organs in animals. NR has also been tested in older humans and is considered safe, but the effects of NR supplementation alone on physical performance are unclear. The purpose of this review is to examine the preclinical and clinical evidence on the effect of NR supplementation strategies alone and in combination with physical activity on mobility and skeletal muscle and cardiovascular function.

The systemic role of SIRT1 in exercise mediated adaptation

Cellular energy demands are readily changed during physical exercise resulting in adaptive responses by signaling proteins of metabolic processes, including the NAD⁺ dependent lysine deacetylase SIRT1. Regular exercise results in systemic adaptation that restores the level of SIRT1 in the kidney, liver, and brain in patients with neurodegenerative diseases, and thereby normalizes cellular metabolic processes to attenuate the severity of these diseases. In skeletal muscle, over-expression of SIRT1 results in enhanced numbers of myonuclei improves the repair process after injury and is actively involved in muscle hypertrophy by up-regulating anabolic and downregulating catabolic processes. The present review discusses the different views of SIRT1 dependent deacetylation of PGC-α.

NAD+ homeostasis in health and disease

The conceptual evolution of nicotinamide adenine dinucleotide (NAD⁺) from being seen as a simple metabolic cofactor to a pivotal cosubstrate for proteins regulating metabolism and longevity, including the sirtuin family of protein deacylases, has led to a new wave of scientific interest in NAD⁺. NAD⁺ levels decline during ageing, and alterations in NAD⁺ homeostasis can be found in virtually all age-related diseases, including neurodegeneration, diabetes and cancer. In preclinical settings, various strategies to increase NAD⁺ levels have shown beneficial effects, thus starting a competitive race to discover marketable NAD⁺ boosters to improve healthspan and lifespan. Here, we review the basics of NAD⁺ biochemistry and metabolism, and its roles in health and disease, and we discuss current challenges and the future translational potential of NAD⁺ research.

Switch of NAD Salvage to de novo Biosynthesis Sustains SIRT1-RelB-Dependent Inflammatory Tolerance

A typical inflammatory response sequentially progresses from pro-inflammatory, immune suppressive to inflammatory repairing phases. Although the physiological inflammatory response resolves in time, severe acute inflammation usually sustains immune tolerance and leads to high mortality, yet the underlying mechanism is not completely understood. Here, using the leukemia-derived THP-1 human monocytes, healthy and septic human peripheral blood mononuclear cells (PBMC), we report that endotoxin dose-dependent switch of nicotinamide adenine dinucleotide (NAD) biosynthesis pathways sustain immune tolerant status. Low dose endotoxin triggered nicotinamide phosphoribosyltransferase (NAMPT)-dependent NAD salvage activity to adapt pro-inflammation. In contrast, high dose endotoxin drove a shift of NAD synthesis pathway from early NAMPT-dependent NAD salvage to late indoleamine 2,3-dioxygenase-1 (IDO1)-dependent NAD de novo biosynthesis, leading to persistent immune suppression. This is resulted from the IDO1-dependent expansion of nuclear NAD pool and nuclear NAD-dependent prolongation of sirtuin1 (SIRT1)-directed epigenetics of immune tolerance. Inhibition of IDO1 activity predominantly decreased nuclear NAD level, which promoted sequential dissociations of immunosuppressive SIRT1 and RelB from the promoter of pro-inflammatory TNF-α gene and broke endotoxin tolerance. Thus, NAMPT-NAD-SIRT1 axis adapts pro-inflammation, but IDO1-NAD-SIRT1-RelB axis sustains endotoxin tolerance during acute inflammatory response. Remarkably, in contrast to the prevention of sepsis death of animal model by IDO1 inhibition before sepsis initiation, we demonstrated that the combination therapy of IDO1 inhibition by 1-methyl-D-tryptophan (1-MT) and tryptophan supplementation rather than 1-MT administration alone after sepsis onset rescued sepsis animals, highlighting the translational significance of tryptophan restoration in IDO1 targeting therapy of severe inflammatory diseases like sepsis.

The role of SIRT1 in skeletal muscle function and repair of older mice

BACKGROUND

Sirtuin 1 (SIRT1) is a NAD+ sensitive deacetylase that has been linked to longevity and has been suggested to confer beneficial effects that counter aging-associated deterioration. Muscle repair is dependent upon satellite cell function, which is reported to be reduced with aging; however, it is not known if this is linked to an aging-suppression of SIRT1. This study tested the hypothesis that Sirtuin 1 (SIRT1) overexpression would increase the extent of muscle repair and muscle function in older mice.

METHODS

We examined satellite cell dependent repair in tibialis anterior, gastrocnemius, and soleus muscles of 13 young wild-type mice (20-30 weeks) and 49 older (80+ weeks) mice that were controls (n = 13), overexpressed SIRT1 in skeletal muscle (n = 14), and had a skeletal muscle SIRT1 knockout (n = 12) or a satellite cell SIRT1 knockout (n = 10). Acute muscle injury was induced by injection of cardiotoxin (CTX), and phosphate-buffered saline was used as a vector control. Plantarflexor muscle force and fatigue were evaluated before or 21 days after CTX injection. Satellite cell proliferation and mitochondrial function were also evaluated in undamaged muscles.

RESULTS

Maximal muscle force was significantly lower in control muscles of older satellite cell knockout SIRT1 mice compared to young adult wild-type (YWT) mice (P < 0.001). Mean contraction force at 40 Hz stimulation was significantly greater after recovery from CTX injury in older mice that overexpressed muscle SIRT1 than age-matched SIRT1 knockout mice (P < 0.05). SIRT1 muscle knockout models (P < 0.05) had greater levels of p53 (P < 0.05 MKO, P < 0.001 OE) in CTX-damaged tissues as compared to YWT CTX mice. SIRT1 overexpression with co-expression of p53 was associated with increased fatigue resistance and increased force potentiation during repeated contractions as compared to wild-type or SIRT1 knockout models (P < 0.001). Muscle structure and mitochondrial function were not different between the groups, but proliferation of satellite cells was significantly greater in older mice with SIRT1 muscle knockout (P < 0.05), but not older SIRT1 satellite cell knockout models, in vitro, although this effect was attenuated in vivo after 21 days of recovery.

CONCLUSIONS

The data suggest skeletal muscle structure, function, and recovery after CTX-induced injury are not significantly influenced by gain or loss of SIRT1 abundance alone in skeletal muscle; however, muscle function is impaired by ablation of SIRT1 in satellite cells. SIRT1 appears to interact with p53 to improve muscle fatigue resistance after repair from muscle injury.

PJ34, a PARP1 inhibitor, promotes endothelial repair in a rabbit model of high fat diet-induced atherosclerosis

Objective: Atherosclerosis involves endothelial injury caused by oxidative stress. Endothelial progenitor cells (EPCs) play important roles in preventing the early stages of atherosclerosis. Meanwhile, poly (ADP-ribose) polymerase 1 (PARP1) utilizes nicotinamide adenine dinucleotide (NAD⁺) to repair DNA damage. PARP1 overactivation results in excessive NAD⁺ consumption in the presence of pathological DNA damage. PJ34 is a PARP1 inhibitor that attenuates cellular NAD+ depletion and can prevent endothelial dysfunction. However, few studies have been conducted on its effects on EPCs. In this study, we tried to elucidate the action of PJ34 in rabbit EPCs and tested its effectiveness in rabbit atherosclerosis. Methods: We analyzed the effect of PJ34 supplementation by inducing oxidative damage by H₂O₂ in vitro and using a rabbit atherosclerosis model induced by a high-fat-diet in vivo. Transwell, immunofluorescence, Matrigel, and western blot analyses, as well as adenoviral vector transfection were used to quantify the levels of reactive oxygen species, proteins, and NAD⁺. Results: The effects of PJ34 were dependent on SIRT1 levels. In vitro results showed that when oxidative damage attenuated cellular function, PJ34 treatment restored partial functionality. In vivo results confirmed that PJ34 can prevent atherosclerosis in a rabbit model.

Muscle-derived miR-34a increases with age in circulating extracellular vesicles and induces senescence of bone marrow stem cells

Extracellular vesicles (EVs) are known to play important roles in cell-cell communication. Here we investigated the role of muscle-derived EVs and their microRNAs in the loss of bone stem cell populations with age. Aging in male and female C57BL6 mice was associated with a significant increase in expression of the senescence-associated microRNA miR-34a-5p (miR-34a) in skeletal muscle and in serum -derived EVs. Muscle-derived, alpha-sarcoglycan positive, EVs isolated from serum samples also showed a significant increase in miR-34a with age. EVs were isolated from conditioned medium of C2C12 mouse myoblasts and primary human myotubes after cells were treated with hydrogen peroxide to simulate oxidative stress. These EVs were shown to have elevated levels of miR-34a, and these EVs decreased viability of bone marrow mesenchymal (stromal) cells (BMSCs) and increased BMSC senescence. A lentiviral vector system was used to overexpress miR-34a in C2C12 cells, and EVs isolated from these transfected cells were observed to home to bone in vivo and to induce senescence and decrease Sirt1 expression of primary bone marrow cells ex vivo. These findings suggest that aged skeletal muscle is a potential source of circulating, senescence-associated EVs that may directly impact stem cell populations in tissues such as bone via their microRNA cargo.

Role of miRNAs in skeletal muscle aging

Purpose

The aim of this study was to explore the role of miRNAs in the process of skeletal muscle aging.

Materials and methods

We analyzed the miRNA microarray datasets from 19 young and 17 old skeletal muscle samples by bioinformatic analysis. Differentially expressed miRNAs were identified, followed by function and pathway enrichment analysis. The expression of miRNAs were validated by real-time quantitative PCR (RT-qPCR) analysis.

Results

A total of 23 miRNAs were found to be differentially expressed in old muscle samples based on two platforms. Gene targets of upregulated miRNAs were significantly enriched in the oxytocin signaling pathway, AMP-activated protein kinase (AMPK) signaling pathway, and Notch signaling pathway. The target genes of downregulated miRNAs were significantly related to gap junction, salivary secretion, and estrogen signaling pathway. has-miR-19a and hsa-miR-34a were significant nodes in the miRNA regulatory network. has-miR-19a was closely related to the AMPK signaling pathway. hsa-miR-34a was closely related to cellular senescence and mitogen-activated protein kinase (MAPK) signaling pathway. PCR analysis showed that the expression of has-miR-34a-5p and has-miR-449b-5p was significantly higher in the patient group than in the control group, while no significant difference was observed in the expression of has-miR-19a-3p and has-miR-144-3p between the two groups. Furthermore, the expression of key target genes involved in cellular senescence (sirtuin 1 [SITRI]), MAPK signaling pathway (vascular endothelial growth factor A [VEGFA]), and AMPK signaling pathway (protein kinase AMP-activated catalytic subunit alpha 1 [PRKAA1] and 6-phosphofructo-2-kinase/fructose-2-,6-biphosphatase 3 [PFKFB3]) were significantly increased in patients with sarcopenia.

Conclusion

has-miR-19a and hsa-miR-34a may play regulatory roles in the aging process of skeletal muscles and may be candidate targets to prevent muscle aging. Further experimental validations are warranted.

Effects of hindlimb suspension and reloading on gastrocnemius and soleus muscle mass and function in geriatric mice

Reloading of atrophied muscles after hindlimb suspension (HLS) can induce muscle injury and prolong recovery after disuse in old rats, especially in fast contracting muscles. Less is known about the responses in mice and whether fast and slow muscles from geriatric mice will respond in a similar fashion to HLS unloading and recovery (HLS + R). Furthermore, while slow muscles undergo atrophy with disuse, they typically are more resistant to sarcopenia than fast contracting muscles. Geriatric (28 mo. of age) male C57BL/6 mice were randomly placed into 3 groups. These included HLS for 14 days n = 9, and HLS followed by 14 days of reloading recovery (HLS + R; n = 9), or normal ambulatory cage controls (n = 9). Control mice were not exposed to unloading. Electrically evoked maximal muscle function was assessed in vivo in anesthetized mice at baseline, after 14 days of HLS or HLS + R. As expected, HLS significantly reduced body weight, wet weight of gastrocnemius and soleus muscles and in vivo maximal force. There were no differences in vivo fatigability of the plantar flexor muscles and overall fiber size. There were only minor fiber type distribution and frequency distribution of fiber sizes that differ between HLS + R and control gastrocnemius and soleus muscles. Soleus muscle wet weight had recovered to control levels after reloading, but type I/IIA fibers in the soleus muscles were significantly smaller after HLS + R than control muscles. In contrast, gastrocnemius muscle wet weight did not recover to control levels after reloading. Plantar flexion muscle force (primarily influenced by the gastrocnemius muscles) did not recover in HLS + R conditions as compared to HLS conditions and both were lower than control force production signaling for apoptosis, autophagy and anabolic markers were not different between control and HLS + R gastrocnemius and soleus muscles in geriatric mice. These results suggest that molecular signaling does not explain attenuated ability to regain muscle wet weight, fiber size or muscle force production after HLS in geriatric mice. It is possible that fluid shifts, reduced blood flow, or shortened muscle fibers which failed to regain control lengths contributed to the attenuation of muscle wet weight after HLS and reloading and this affected force production. Further work is needed to determine if altered/loss of neural activity contributed to the inability of geriatric mice to regain gastrocnemius muscle weight and function after HLS and reloading.

PARP1 inhibitor (PJ34) improves the function of aging-induced endothelial progenitor cells by preserving intracellular NAD+ levels and increasing SIRT1 activity

Background

Nicotinamide adenine dinucleotide (NAD⁺) is a critical molecule involved in various biological functions. Poly (ADP-ribose) polymerase 1 (PARP1) and sirtuin 1 (SIRT1) affect cellular NAD⁺ levels and play essential roles in regulating metabolism. However, there has been little research on the effects of PARP1 and SIRT1 crosstalk during senescence.

Methods

We isolated endothelial progenitor cells (EPCs) from human umbilical cord blood and treated them with a PARP1 inhibitor (PJ34).

Results

Using a stress-induced premature aging model built by H₂O₂, transfection with adenoviral vectors, and Western blot analysis, we observed that PJ34 treatment preserved intracellular NAD⁺ levels, increased SIRT1 activity, decreased p53 acetylation, and improved the function of stress-induced premature aging EPCs.

Conclusions

Our results suggest that PJ34 improves the function of aging-induced EPCs and may contribute to cellular therapies for atherosclerosis.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0961-7) contains supplementary material, which is available to authorized users.

Does the Poly (ADP-Ribose) Polymerase Inhibitor Veliparib Merit Further Study for Cancer-Associated Weight Loss? Observations and Conclusions from Sixty Prospectively Treated Patients

BACKGROUND

More than 80% of patients with advanced cancer develop weight loss. Because preclinical data suggest poly (ADP-ribose) polymerase (PARP) inhibitors can treat this weight loss, this study was undertaken to explore the PARP inhibitor veliparib for this indication.

OBJECTIVE

The current study was undertaken to analyze prospectively gathered data on weight in cancer patients on PARP inhibitors.

DESIGN/SETTING

The current study relied on a previously published, prospectively conducted phase 1 single institution trial that combined veliparib and topotecan (NCT01012817) as antineoplastic therapy for advanced cancer patients. Serial weight data and, when available and clinically relevant, computerized tomography scans were also examined.

MEASUREMENTS

The primary endpoint was 10% or greater weight gain from trial enrollment.

RESULTS

Nearly all 60 patients lost weight over time. Only one patient manifested a 10% or greater gain in weight. However, review of computerized tomography L3 images showed this weight gain was a manifestation of ascites. Four other patients gained 5% of their baseline weight. However, findings in two patients with available radiographs showed no evidence of muscle augmentation.

CONCLUSIONS

The addition of the PARP inhibitor veliparib to chemotherapy does not appear to result in notable weight gain or in weight maintenance in patients with advanced cancer. Interventions other than PARP inhibitors should be considered for the palliation/treatment of cancer-associated weight loss.

The variable role of SIRT1 in the maintenance and differentiation of mesenchymal stem cells

SIRT1 is an NAD+-dependent deacetylase that acts as a nutrient sensitive regulator of longevity. SIRT1 also acts as a key regulator of mesenchymal stem cells (MSCs), adult stem cells that give rise to tissues such as bone, fat, muscle and cartilage. This review focuses on how SIRT1 regulates the self-renewal, multipotency and differentiation of MSCs. The variable role of SIRT1 in promoting the differentiation of MSCs towards certain lineages, while repressing others, will be examined within the broader context of aging, calorie restriction, and regenerative medicine. Finally, recent animal and human studies will be highlighted which paint an overall salutary role for SIRT1 in protecting MSCs (and resulting tissues) from age-related atrophy and dysfunction.

A need for NAD+ in muscle development, homeostasis, and aging

Skeletal muscle enables posture, breathing, and locomotion. Skeletal muscle also impacts systemic processes such as metabolism, thermoregulation, and immunity. Skeletal muscle is energetically expensive and is a major consumer of glucose and fatty acids. Metabolism of fatty acids and glucose requires NAD+ function as a hydrogen/electron transfer molecule. Therefore, NAD+ plays a vital role in energy production. In addition, NAD+ also functions as a cosubstrate for post-translational modifications such as deacetylation and ADP-ribosylation. Therefore, NAD+ levels influence a myriad of cellular processes including mitochondrial biogenesis, transcription, and organization of the extracellular matrix. Clearly, NAD+ is a major player in skeletal muscle development, regeneration, aging, and disease. The vast majority of studies indicate that lower NAD+ levels are deleterious for muscle health and higher NAD+ levels augment muscle health. However, the downstream mechanisms of NAD+ function throughout different cellular compartments are not well understood. The purpose of this review is to highlight recent studies investigating NAD+ function in muscle development, homeostasis, disease, and regeneration. Emerging research areas include elucidating roles for NAD+ in muscle lysosome function and calcium mobilization, mechanisms controlling fluctuations in NAD+ levels during muscle development and regeneration, and interactions between targets of NAD+ signaling (especially mitochondria and the extracellular matrix). This knowledge should facilitate identification of more precise pharmacological and activity-based interventions to raise NAD+ levels in skeletal muscle, thereby promoting human health and function in normal and disease states.