Pharmacological Inhibition of poly(ADP-ribose) polymerases improves fitness and mitochondrial function in skeletal muscle

Nanodrug Delivery Systems for Myasthenia Gravis: Advances and Perspectives

Myasthenia gravis (MG) is a rare chronic autoimmune disease caused by the production of autoantibodies against the postsynaptic membrane receptors present at the neuromuscular junction. This condition is characterized by fatigue and muscle weakness, including diplopia, ptosis, and systemic impairment. Emerging evidence suggests that in addition to immune dysregulation, the pathogenesis of MG may involve mitochondrial damage and ferroptosis. Mitochondria are the primary site of energy production, and the reactive oxygen species (ROS) generated due to mitochondrial dysfunction can induce ferroptosis. Nanomedicines have been extensively employed to treat various disorders due to their modifiability and good biocompatibility, but their application in MG management has been rather limited. Nevertheless, nanodrug delivery systems that carry immunomodulatory agents, anti-oxidants, or ferroptosis inhibitors could be effective for the treatment of MG. Therefore, this review focuses on various nanoplatforms aimed at attenuating immune dysregulation, restoring mitochondrial function, and inhibiting ferroptosis that could potentially serve as promising agents for targeted MG therapy.

Body composition and inflammation variables as the potential prognostic factors in epithelial ovarian cancer treated with Olaparib

Background

Epithelial ovarian cancer (EOC) is a significant cause of mortality among gynecological cancers. While Olaparib, a PARP inhibitor, has demonstrated efficacy in EOC maintenance therapy, individual responses vary. This study aims to assess the prognostic significance of body composition and systemic inflammation markers in EOC patients undergoing initial Olaparib treatment.

Methods

A retrospective analysis was conducted on 133 EOC patients initiating Olaparib therapy. Progression-free survival (PFS) was assessed through Kaplan-Meier analysis and Cox proportional hazards regression. Pre-treatment computed tomography images were utilized to evaluate body composition parameters including subcutaneous adipose tissue index (SATI), visceral adipose tissue index (VATI), skeletal muscle area index (SMI), and body mineral density (BMD). Inflammatory markers, such as neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), serum albumin, and hemoglobin levels, were also measured.

Results

The median follow-up duration was 16 months (range: 5-49 months). Survival analysis indicated that high SATI, high VATI, high SMI, high BMD, low NLR, and low PLR were associated with decreased risk of disease progression (all p < 0.05). Multivariate analysis identified several factors independently associated with poor PFS, including second or further lines of therapy (HR = 2.16; 95% CI = 1.09-4.27, p = 0.027), low VATI (HR = 3.79; 95% CI = 1.48-9.70, p = 0.005), low SMI (HR = 2.52; 95% CI = 1.11-5.72, p = 0.027), low BMD (HR = 2.36; 95% CI = 1.22-4.54, p = 0.010), and high NLR (HR = 0.31; 95% CI = 0.14-0.69, p = 0.004). Subgroup analysis in serous adenocarcinoma patients revealed distinct prognostic capabilities of SATI, VATI, SMI, PLR, and NLR.

Conclusion

Body composition and inflammation variables hold promise as predictors of therapeutic response to Olaparib in EOC patients. Understanding their prognostic significance could facilitate tailored treatment strategies, potentially improving patient outcomes.

Poly(ADP-Ribose) Polymerases-Inhibitor Talazoparib Inhibits Muscle Atrophy and Fatty Infiltration in a Tendon Release Infraspinatus Sheep Model: A Pilot Study

Structural muscle changes, including muscle atrophy and fatty infiltration, follow rotator cuff tendon tear and are associated with a high repair failure rate. Despite extensive research efforts, no pharmacological therapy is available to successfully prevent both muscle atrophy and fatty infiltration after tenotomy of tendomuscular unit without surgical repair. Poly(ADP-ribose) polymerases (PARPs) are identified as a key transcription factors involved in the maintenance of cellular homeostasis. PARP inhibitors have been shown to influence muscle degeneration, including mitochondrial hemostasis, oxidative stress, inflammation and metabolic activity, and reduced degenerative changes in a knockout mouse model. Tenotomized infraspinatus were assessed for muscle degeneration for 16 weeks using a Swiss Alpine sheep model (n = 6). All sheep received daily oral administration of 0.5 mg Talazoparib. Due to animal ethics, the treatment group was compared with three different controls from prior studies of our institution. To mitigate potential batch heterogeneity, PARP-I was evaluated in comparison with three distinct control groups (n = 6 per control group) using the same protocol without treatment. The control sheep were treated with an identical study protocol without Talazoparib treatment. Muscle atrophy and fatty infiltration were evaluated at 0, 6 and 16 weeks post-tenotomy using DIXON-MRI. The controls and PARP-I showed a significant (control p < 0.001, PARP-I p = 0.01) decrease in muscle volume after 6 weeks. However, significantly less (p = 0.01) atrophy was observed in PARP-I after 6 weeks (control 1: 76.6 ± 8.7%; control 2: 80.3 ± 9.3%, control 3: 73.8 ± 6.7% vs. PARP-I: 90.8 ± 5.1% of the original volume) and 16 weeks (control 1: 75.7 ± 9.9; control 2: 74.2 ± 5.6%; control 3: 75.3 ± 7.4% vs. PARP-I 93.3 ± 10.6% of the original volume). All experimental groups exhibited a statistically significant (p < 0.001) augmentation in fatty infiltration following a 16-week period when compared to the initial timepoint. However, the PARP-I showed significantly less fatty infiltration (p < 0.003) compared to all controls (control 1: 55.6 ± 6.7%, control 2: 53.4 ± 9.4%, control 3: 52.0 ± 12.8% vs. PARP-I: 33.5 ± 8.4%). Finally, a significantly (p < 0.04) higher proportion and size of fast myosin heavy chain-II fiber type was observed in the treatment group. This study shows that PARP-inhibition with Talazoparib inhibits the progression of both muscle atrophy and fatty infiltration over 16 weeks in retracted sheep musculotendinous units.

Genome Instability and DNA Repair in Somatic and Reproductive Aging

Genetic material is constantly subjected to genotoxic insults and is critically dependent on DNA repair. Genome maintenance mechanisms differ in somatic and germ cells as the soma only requires maintenance during an individual's lifespan, while the germline indefinitely perpetuates its genetic information. DNA lesions are recognized and repaired by mechanistically highly diverse repair machineries. The DNA damage response impinges on a vast array of homeostatic processes and can ultimately result in cell fate changes such as apoptosis or cellular senescence. DNA damage causally contributes to the aging process and aging-associated diseases, most prominently cancer. By causing mutations, DNA damage in germ cells can lead to genetic diseases and impact the evolutionary trajectory of a species. The mechanisms ensuring tight control of germline DNA repair could be highly instructive in defining strategies for improved somatic DNA repair. They may provide future interventions to maintain health and prevent disease during aging.

Physical exercise elicits UPRmt in the skeletal muscle: The role of c-Jun N-terminal kinase

OBJECTIVE

The mitochondrial unfolded protein response (UPRmt) is an adaptive cellular response to stress to ensure mitochondrial proteostasis and function. Here we explore the capacity of physical exercise to induce UPRmt in the skeletal muscle.

METHODS

Therefore, we combined mouse models of exercise (swimming and treadmill running), pharmacological intervention, and bioinformatics analyses.

RESULTS

Firstly, RNA sequencing and Western blotting analysis revealed that an acute aerobic session stimulated several mitostress-related genes and protein content in muscle, including the UPRmt markers. Conversely, using a large panel of isogenic strains of BXD mice, we identified that BXD73a and 73b strains displayed low levels of several UPRmt-related genes in the skeletal muscle, and this genotypic feature was accompanied by body weight gain, lower locomotor activity, and aerobic capacity. Finally, we identified that c-Jun N-terminal kinase (JNK) activation was critical in exercise-induced UPRmt in the skeletal muscle since pharmacological JNK pathway inhibition blunted exercise-induced UPRmt markers in mice muscle.

CONCLUSION

Our findings provide new insights into how exercise triggers mitostress signals toward the oxidative capacity in the skeletal muscle.

NAD+ regulates nucleotide metabolism and genomic DNA replication

The intricate orchestration of enzymatic activities involving nicotinamide adenine dinucleotide (NAD+) is essential for maintaining metabolic homeostasis and preserving genomic integrity. As a co-enzyme, NAD+ plays a key role in regulating metabolic pathways, such as glycolysis and Kreb's cycle. ADP-ribosyltransferases (PARPs) and sirtuins rely on NAD+ to mediate post-translational modifications of target proteins. The activation of PARP1 in response to DNA breaks leads to rapid depletion of cellular NAD+ compromising cell viability. Therefore, the levels of NAD+ must be tightly regulated. Here we show that exogenous NAD+, but not its precursors, has a direct effect on mitochondrial activity. Short-term incubation with NAD+ boosts Kreb's cycle and the electron transport chain and enhances pyrimidine biosynthesis. Extended incubation with NAD+ results in depletion of pyrimidines, accumulation of purines, activation of the replication stress response and cell cycle arrest. Moreover, a combination of NAD+ and 5-fluorouridine selectively kills cancer cells that rely on de novo pyrimidine synthesis. We propose an integrated model of how NAD+ regulates nucleotide metabolism, with relevance to healthspan, ageing and cancer therapy.

Age Is Just a Number: Progress and Obstacles in the Discovery of New Candidate Drugs for Sarcopenia

Sarcopenia is a disease characterized by the progressive loss of skeletal muscle mass and function that occurs with aging. The progression of sarcopenia is correlated with the onset of physical disability, the inability to live independently, and increased mortality. Due to global increases in lifespan and demographic aging in developed countries, sarcopenia has become a major socioeconomic burden. Clinical therapies for sarcopenia are based on physical therapy and nutritional support, although these may suffer from low adherence and variable outcomes. There are currently no clinically approved drugs for sarcopenia. Consequently, there is a large amount of pre-clinical research focusing on discovering new candidate drugs and novel targets. In this review, recent progress in this research will be discussed, along with the challenges that may preclude successful translational research in the clinic. The types of drugs examined include mitochondria-targeting compounds, anti-diabetes agents, small molecules that target non-coding RNAs, protein therapeutics, natural products, and repositioning candidates. In light of the large number of drugs and targets being reported, it can be envisioned that clinically approved pharmaceuticals to prevent the progression or even mitigate sarcopenia may be within reach.

Nicotinamide Adenine Dinucleotide in Aging Biology: Potential Applications and Many Unknowns

Recent research has unveiled an expansive role of NAD+ in cellular energy generation, redox reactions, and as a substrate or cosubstrate in signaling pathways that regulate health span and aging. This review provides a critical appraisal of the clinical pharmacology and the preclinical and clinical evidence for therapeutic effects of NAD+ precursors for age-related conditions, with a particular focus on cardiometabolic disorders, and discusses gaps in current knowledge. NAD+ levels decrease throughout life; age-related decline in NAD+ bioavailability has been postulated to be a contributor to many age-related diseases. Raising NAD+ levels in model organisms by administration of NAD+ precursors improves glucose and lipid metabolism; attenuates diet-induced weight gain, diabetes, diabetic kidney disease, and hepatic steatosis; reduces endothelial dysfunction; protects heart from ischemic injury; improves left ventricular function in models of heart failure; attenuates cerebrovascular and neurodegenerative disorders; and increases health span. Early human studies show that NAD+ levels can be raised safely in blood and some tissues by oral NAD+ precursors and suggest benefit in preventing nonmelanotic skin cancer, modestly reducing blood pressure and improving lipid profile in older adults with obesity or overweight; preventing kidney injury in at-risk patients; and suppressing inflammation in Parkinson disease and SARS-CoV-2 infection. Clinical pharmacology, metabolism, and therapeutic mechanisms of NAD+ precursors remain incompletely understood. We suggest that these early findings provide the rationale for adequately powered randomized trials to evaluate the efficacy of NAD+ augmentation as a therapeutic strategy to prevent and treat metabolic disorders and age-related conditions.

Tweaking host immune responses for novel therapeutic approaches against Mycobacterium tuberculosis

In TB, combat between the human host and Mycobacterium tuberculosis involves intricate interactions with immune cells. M. tuberculosis has evolved a complex evasion system to circumvent immune cells, leading to persistence and limiting its clearance by the host. Host-directed therapies are emerging approaches to modulate host responses, including inflammatory responses, cytokine responses, and autophagy, by using small molecules to curb mycobacterial infections. Targeting host immune pathways reduces the chances of antibiotic resistance to M. tuberculosis because, unlike antibiotics, this approach acts directly on the cells of the host. In this review, we discuss the role of immune cells during M. tuberculosis proliferation, provide a updated understanding of immunopathogenesis, and explore the range of host-modulating options for the clearance of this pathogen.

Mitochondrial protein import and UPRmt in skeletal muscle remodeling and adaptation

The biogenesis of mitochondria requires the coordinated expression of the nuclear and the mitochondrial genomes. However, the vast majority of gene products within the organelle are encoded in the nucleus, synthesized in the cytosol, and imported into mitochondria via the protein import machinery, which permit the entry of proteins to expand the mitochondrial network. Once inside, proteins undergo a maturation and folding process brought about by enzymes comprising the unfolded protein response (UPR^mt). Protein import and UPR^mt activity must be synchronized and matched with mtDNA-encoded subunit synthesis for proper assembly of electron transport chain complexes to avoid proteotoxicity. This review discusses the functions of the import and UPR^mt systems in mammalian skeletal muscle, as well as how exercise alters the equilibrium of these pathways in a time-dependent manner, leading to a new steady state of mitochondrial content resulting in enhanced oxidative capacity and improved muscle health.

Transient changes to metabolic homeostasis initiate mitochondrial adaptation to endurance exercise

Endurance exercise is well established to increase mitochondrial content and function in skeletal muscle, a process termed mitochondrial biogenesis. Current understanding is that exercise initiates skeletal muscle mitochondrial remodeling via modulation of cellular nutrient, energetic and contractile stress pathways. These subtle changes in the cellular milieu are sensed by numerous transduction pathways that serve to initiate and coordinate an increase in mitochondrial gene transcription and translation. The result of these acute signaling events is the promotion of growth and assembly of mitochondria, coupled to a greater capacity for aerobic ATP provision in skeletal muscle. The aim of this review is to highlight the acute metabolic events induced by endurance exercise and the subsequent molecular pathways that sense this transient change in cellular homeostasis to drive mitochondrial adaptation and remodeling.

Nicotinamide Adenine Dinucleotide Augmentation in Overweight or Obese Middle-Aged and Older Adults: A Physiologic Study

CONTEXT

Nicotinamide adenine dinucleotide (NAD) levels decline with aging and age-related decline in NAD has been postulated to contribute to age-related diseases.

OBJECTIVE

We evaluated the safety and physiologic effects of NAD augmentation by administering its precursor, β-nicotinamide mononucleotide (MIB-626, Metro International Biotech, Worcester, MA), in adults at risk for age-related conditions.

METHODS

Thirty overweight or obese adults, ≥ 45 years, were randomized in a 2:1 ratio to 2 MIB-626 tablets each containing 500 mg of microcrystalline β-nicotinamide mononucleotide or placebo twice daily for 28 days. Study outcomes included safety; NAD and its metabolome; body weight; liver, muscle, and intra-abdominal fat; insulin sensitivity; blood pressure; lipids; physical performance, and muscle bioenergetics.

RESULTS

Adverse events were similar between groups. MIB-626 treatment substantially increased circulating concentrations of NAD and its metabolites. Body weight (difference -1.9 [-3.3, -0.5] kg, P = .008); diastolic blood pressure (difference -7.01 [-13.44, -0.59] mmHg, P = .034); total cholesterol (difference -26.89 [-44.34, -9.44] mg/dL, P = .004), low-density lipoprotein (LDL) cholesterol (-18.73 [-31.85, -5.60] mg/dL, P = .007), and nonhigh-density lipoprotein cholesterol decreased significantly more in the MIB-626 group than placebo. Changes in muscle strength, muscle fatigability, aerobic capacity, and stair-climbing power did not differ significantly between groups. Insulin sensitivity and hepatic and intra-abdominal fat did not change in either group.

CONCLUSIONS

MIB-626 administration in overweight or obese, middle-aged and older adults safely increased circulating NAD levels, and significantly reduced total LDL and non-HDL cholesterol, body weight, and diastolic blood pressure. These data provide the rationale for larger trials to assess the efficacy of NAD augmentation in improving cardiometabolic outcomes in older adults.

Biochemical Targets and Molecular Mechanism of Matrine against Aging

The aim of this study is to explore the potential targets and molecular mechanism of matrine (MAT) against aging. Bioinformatic-based network pharmacology was used to investigate the aging-related targets and MAT-treated targets. A total of 193 potential genes of MAT against aging were obtained and then the top 10 key genes (cyclin D1, cyclin-dependent kinase 1, Cyclin A2, androgen receptor, Poly [ADP-ribose] polymerase-1 (PARP1), histone-lysine N-methyltransferase, albumin, mammalian target of rapamycin, histone deacetylase 2, and matrix metalloproteinase 9) were filtered by the molecular complex detection, maximal clique centrality (MMC) algorithm, and degree. The Metascape tool was used for analyzing biological processes and pathways of the top 10 key genes. The main biological processes were response to an inorganic substance and cellular response to chemical stress (including cellular response to oxidative stress). The major pathways were involved in cellular senescence and the cell cycle. After an analysis of major biological processes and pathways, it appears that PARP1/nicotinamide adenine dinucleotide (NAD⁺)-mediated cellular senescence may play an important role in MAT against aging. Molecular docking, molecular dynamics simulation, and in vivo study were used for further investigation. MAT could interact with the cavity of the PARP1 protein with the binding energy at -8.5 kcal/mol. Results from molecular dynamics simulations showed that the PARP1-MAT complex was more stable than PARP1 alone and that the binding-free energy of the PARP1-MAT complex was -15.962 kcal/mol. The in vivo study showed that MAT could significantly increase the NAD⁺ level of the liver of d-gal-induced aging mice. Therefore, MAT could interfere with aging through the PARP1/NAD⁺-mediated cellular senescence signaling pathway.

NAD+ Metabolism and Immune Regulation: New Approaches to Inflammatory Bowel Disease Therapies

Inflammatory bowel disease (IBD), which includes Crohn's disease (CD) and ulcerative colitis (UC), is a multifactorial systemic inflammatory immune response. Nicotinamide adenine dinucleotide (NAD⁺) is a co-enzyme involved in cell signaling and energy metabolism. Calcium homeostasis, gene transcription, DNA repair, and cell communication involve NAD⁺ and its degradation products. There is a growing recognition of the intricate relationship between inflammatory diseases and NAD⁺ metabolism. In the case of IBD, the maintenance of intestinal homeostasis relies on a delicate balance between NAD⁺ biosynthesis and consumption. Consequently, therapeutics designed to target the NAD⁺ pathway are promising for the management of IBD. This review discusses the metabolic and immunoregulatory processes of NAD⁺ in IBD to examine the molecular biology and pathophysiology of the immune regulation of IBD and to provide evidence and theoretical support for the clinical use of NAD⁺ in IBD.

NAD+ metabolism-based immunoregulation and therapeutic potential

Nicotinamide adenine dinucleotide (NAD⁺) is a critical metabolite that acts as a cofactor in energy metabolism, and serves as a cosubstrate for non-redox NAD⁺-dependent enzymes, including sirtuins, CD38 and poly(ADP-ribose) polymerases. NAD⁺ metabolism can regulate functionality attributes of innate and adaptive immune cells and contribute to inflammatory responses. Thus, the manipulation of NAD⁺ bioavailability can reshape the courses of immunological diseases. Here, we review the basics of NAD⁺ biochemistry and its roles in the immune response, and discuss current challenges and the future translational potential of NAD⁺ research in the development of therapeutics for inflammatory diseases, such as COVID-19.

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.

Effects of short-term endurance and strength exercise in the molecular regulation of skeletal muscle in hyperinsulinemic and hyperglycemic Slc2a4+/- mice

OBJECTIVE

Intriguingly, hyperinsulinemia, and hyperglycemia can predispose insulin resistance, obesity, and type 2 diabetes, leading to metabolic disturbances. Conversely, physical exercise stimulates skeletal muscle glucose uptake, improving whole-body glucose homeostasis. Therefore, we investigated the impact of short-term physical activity in a mouse model (Slc2a4+/-) that spontaneously develops hyperinsulinemia and hyperglycemia even when fed on a chow diet.

METHODS

Slc2a4+/- mice were used, that performed 5 days of endurance or strength exercise training. Further analysis included physiological tests (GTT and ITT), skeletal muscle glucose uptake, skeletal muscle RNA-sequencing, mitochondrial function, and experiments with C2C12 cell line.

RESULTS

When Slc2a4+/- mice were submitted to the endurance or strength training protocol, improvements were observed in the skeletal muscle glucose uptake and glucose metabolism, associated with broad transcriptomic modulation, that was, in part, related to mitochondrial adaptations. The endurance training, but not the strength protocol, was effective in improving skeletal muscle mitochondrial activity and unfolded protein response markers (UPRmt). Moreover, experiments with C2C12 cells indicated that insulin or glucose levels could contribute to these mitochondrial adaptations in skeletal muscle.

CONCLUSIONS

Both short-term exercise protocols were efficient in whole-body glucose homeostasis and insulin resistance. While endurance exercise plays an important role in transcriptome and mitochondrial activity, strength exercise mostly affects post-translational mechanisms and protein synthesis in skeletal muscle. Thus, the performance of both types of physical exercise proved to be a very effective way to mitigate the impacts of hyperglycemia and hyperinsulinemia in the Slc2a4+/- mouse model.

Muscle PARP1 inhibition extends lifespan through AMPKα PARylation and activation in Drosophila

Poly(ADP-ribose) polymerase-1 (PARP1) has been reported to play an important role in longevity. Here, we showed that the knockdown of the PARP1 extended the lifespan of Drosophila, with particular emphasis on the skeletal muscle. The muscle-specific mutant Drosophila exhibited resistance to starvation and oxidative stress, as well as an increased ability to climb, with enhanced mitochondrial biogenesis and activity at an older age. Mechanistically, the inhibition of PARP1 increases the activity of AMP-activated protein kinase alpha (AMPKα) and mitochondrial turnover. PARP1 could interact with AMPKα and then regulate it via poly(ADP ribosyl)ation (PARylation) at residues E155 and E195. Double knockdown of PARP1 and AMPKα, specifically in muscle, could counteract the effects of PARP1 inhibition in Drosophila. Finally, we showed that increasing lifespan via maintaining mitochondrial network homeostasis required intact PTEN induced kinase 1 (PINK1). Taken together, these data indicate that the interplay between PARP1 and AMPKα can manipulate mitochondrial turnover, and be targeted to promote longevity.

Effect of PARP-1 Inhibition on Rotator Cuff Healing: A Feasibility Study Using Veliparib in a Rat Model of Acute Rotator Cuff Repair

BACKGROUND

PARP-1 (poly[ADP-ribose]) was shown to influence the inflammatory response after rotator cuff tear, leading to fibrosis, muscular atrophy, and fatty infiltration in mouse rotator cuff degeneration. So far, it is not known how PARP-1 influences enthesis healing after rotator cuff tear repair.

HYPOTHESIS/PURPOSE

This study aimed to examine the feasibility of oral PARP-1 inhibition and investigate its influence on rat supraspinatus enthesis and muscle healing after rotator cuff repair. The hypothesis was that oral PARP-1 inhibition would improve enthesis healing after acute rotator cuff repair in a rat model.

STUDY DESIGN

Controlled laboratory study.

METHODS

In 24 Sprague-Dawley rats, the supraspinatus tendon was sharply detached and immediately repaired with a single transosseous suture. The rats were randomly allocated into 2 groups, with the rats in the inhibitor group receiving veliparib with a target dose of 12.5 mg/kg/d via drinking water during the postoperative recovery period. The animals were sacrificed 8 weeks after surgery. For the analysis, macroscopic, biomechanical, and histologic methods were used.

RESULTS

Oral veliparib was safe for the rats, with no adverse effects observed. In total, the inhibitor group had a significantly better histologic grading of the enthesis with less scar tissue formation. The macroscopic cross-sectional area of the supraspinatus muscles was 10.5% higher (P = .034) in the inhibitor group, which was in agreement with an 8.7% higher microscopic muscle fiber diameter on histologic sections (P < .0001). There were no statistically significant differences in the biomechanical properties between the groups.

CONCLUSION

This study is the first to investigate the influence of PARP-1 inhibition on healing enthesis. On the basis of these findings, we conclude that oral veliparib, which was previously shown to inhibit PARP-1 effectively, is safe to apply and has beneficial effects on morphologic enthesis healing and muscle fiber size.

CLINICAL RELEVANCE

Modulating the inflammatory response through PARP-1 inhibition during the postoperative healing period is a promising approach to improve enthesis healing and reduce rotator cuff retearing. With substances already approved by the Food and Drug Administration, PARP-1 inhibition bears high potential for future translation into clinical application.

Adult patient diagnosed with NADSYN1 associated congenital NAD deficiency and analysis of NAD levels to be published in: European Journal of Medical Genetics

INTRODUCTION

Nicotinamide adenine dinucleotide (NAD) is an essential cosubstrate/coenzyme in multiple cellular redox processes and a substrate in several non-redox reactions. NADSYN1 encodes NAD synthetase 1, an enzyme in the NAD de novo synthesis pathway and the Preiss-Handler pathway, and biallelic pathogenic variants causes NAD deficiency associated with vertebral, cardiac, renal and limb defects. Szot et al. and Kortbawi et al. have reported a total of seven patients with NADSYN1 associated congenital NAD deficiency disorder with the oldest patient being seven years old.

PATIENT DATA

We present a male patient age 30 with a height of 130 cm and numerous skeletal malformations including segmentation defects of the spine, rib anomalies and unequal leg length as well as bilateral ptosis, cleft palate and asymmetric dysmorphic facial features. The patient underwent surgery for an aortic stenosis due to a bicuspid valve. No malformations of the kidneys or urinary tract were identified.

RESULTS

Trio exome sequencing revealed a homozygous missense variant in NADSYN1 c.1717G > A (p.Ala573Thr). Both parents were unaffected carriers of the variant. Analysis of NAD levels showed that the patient had a lower NAD pool compared to his unaffected siblings. The NAD pool rose approximately 25% after supplementation with nicotinamide, a NAD precursor for the salvage pathway.

CONCLUSION

The variant was previously reported in four patients and functional analyses by Szot et al. support the pathogenicity of the variant. We report an adult patient with NADSYN1 associated congenital NAD deficiency disorder and expand the phenotypic spectrum. We also present analysis of the NAD levels before and after supplementation with nicotinamide.

The TAS1R2 sweet taste receptor regulates skeletal muscle mass and fitness

Muscle fitness and mass deteriorate under the conditions of obesity and aging for reasons yet to be fully elucidated. Herein, we describe a novel pathway linking peripheral nutrient sensing and skeletal muscle function through the sweet taste receptor TAS1R2 and the involvement of ERK2-PARP1-NAD signaling axis. Muscle-specific deletion of TAS1R2 (mKO) in mice produced elevated NAD levels due to suppressed PARP1 activity, improved mitochondrial function, increased muscle mass and strength, and prolonged running endurance. Deletion of TAS1R2 in obese or aged mice also ameliorated the decline in muscle mass and fitness arising from these conditions. Remarkably, partial loss-of-function of TAS1R2 (rs35874116) in older, obese humans recapitulated the healthier muscle phenotype displayed by mKO mice in response to exercise training. Our findings show that inhibition of the TAS1R2 signaling in skeletal muscle is a promising therapeutic approach to preserve muscle mass and function.

NAD+ Homeostasis and NAD+-Consuming Enzymes: Implications for Vascular Health

Nicotinamide adenine dinucleotide (NAD⁺) is a ubiquitous metabolite that takes part in many key redox reactions. NAD⁺ biosynthesis and NAD⁺-consuming enzymes have been attracting markedly increasing interest since they have been demonstrated to be involved in several crucial biological pathways, impacting genes transcription, cellular signaling, and cell cycle regulation. As a consequence, many pathological conditions are associated with an impairment of intracellular NAD⁺ levels, directly or indirectly, which include cardiovascular diseases, obesity, neurodegenerative diseases, cancer, and aging. In this review, we describe the general pathways involved in the NAD⁺ biosynthesis starting from the different precursors, analyzing the actual state-of-art of the administration of NAD⁺ precursors or blocking NAD⁺-dependent enzymes as strategies to increase the intracellular NAD⁺ levels or to counteract the decline in NAD⁺ levels associated with ageing. Subsequently, we focus on the disease-related and age-related alterations of NAD⁺ homeostasis and NAD⁺-dependent enzymes in endothelium and the consequent vascular dysfunction, which significantly contributes to a wide group of pathological disorders.

The Central Role of the NAD+ Molecule in the Development of Aging and the Prevention of Chronic Age-Related Diseases: Strategies for NAD+ Modulation

The molecule NAD+ is a coenzyme for enzymes catalyzing cellular redox reactions in several metabolic pathways, encompassing glycolysis, TCA cycle, and oxidative phosphorylation, and is a substrate for NAD+-dependent enzymes. In addition to a hydride and electron transfer in redox reactions, NAD+ is a substrate for sirtuins and poly(adenosine diphosphate-ribose) polymerases and even moderate decreases in its cellular concentrations modify signaling of NAD+-consuming enzymes. Age-related reduction in cellular NAD+ concentrations results in metabolic and aging-associated disorders, while the consequences of increased NAD+ production or decreased degradation seem beneficial. This article reviews the NAD+ molecule in the development of aging and the prevention of chronic age-related diseases and discusses the strategies of NAD+ modulation for healthy aging and longevity.

Trends in mitochondrial unfolded protein response research from 2004 to 2022: A bibliometric analysis

The mitochondrial unfolded protein response (UPR^mt) is a stress response pathway that regulates the expression of mitochondrial chaperones, proteases, and other proteins involved in protein folding and degradation, thereby ensuring proper mitochondrial function. In addition to this critical function, the UPR^mt also plays a role in other cellular processes such as mitochondrial biogenesis, energy metabolism, and cellular signaling. Moreover, the UPR^mt is strongly associated with various diseases. From 2004 to 2022, there has been a lot of interest in UPR^mt. The present study aims to utilized bibliometric tools to assess the genesis, current areas of focus, and research trends pertaining to UPR^mt, thereby highlighting avenues for future research. There were 442 papers discovered to be related to UPR^mt, with the overall number of publications rising yearly. International Journal of Molecular Sciences was the most prominent journal in this field. 2421 authors from 1,402 institutions in 184 nations published studies on UPR^mt. The United States was the most productive country (197 documents). The top three authors were Johan Auwerx, Cole M Haynes, and Dongryeol Ryu. The early focus of UPR^mt is "protein." And then the UPR^mt research shifted from Caenorhabditis elegans back to mammals, and its close link to aging and various diseases. The top emerging research hotspots are neurodegenerative diseases and metabolic diseases. These findings provide the trends and frontiers in the field of UPR^mt, and valuable information for clinicians and scientists to identify new perspectives with potential collaborators and cooperative countries.

Importance of NAD+ Anabolism in Metabolic, Cardiovascular and Neurodegenerative Disorders

The role of nicotinamide adenine dinucleotide (NAD+) in ageing has emerged as a critical factor in understanding links to a wide range of chronic diseases. Depletion of NAD+, a central redox cofactor and substrate of numerous metabolic enzymes, has been detected in many major age-related diseases. However, the mechanisms behind age-associated NAD+ decline remains poorly understood. Despite limited conclusive evidence, supplements aimed at increasing NAD+ levels are becoming increasingly popular. This review provides renewed insights regarding the clinical utility and benefits of NAD+ precursors, namely nicotinamide (NAM), nicotinic acid (NA), nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), in attenuating NAD+ decline and phenotypic characterization of age-related disorders, including metabolic, cardiovascular and neurodegenerative diseases. While it is anticipated that NAD+ precursors can play beneficial protective roles in several conditions, they vary in their ability to promote NAD+ anabolism with differing adverse effects. Careful evaluation of the role of NAD⁺, whether friend or foe in ageing, should be considered.

Methods to Assess the Role of PARPs in Regulating Mitochondrial Oxidative Function

PARP enzymes are involved in metabolic regulation and impact on a plethora of cellular metabolic pathways, among them, mitochondrial oxidative metabolism. The detrimental effects of PARP1 overactivation upon oxidative stress on mitochondrial oxidative metabolism was discovered in 1998. Since then, there was an enormous blooming in the understanding of the interplay between PARPs and mitochondria. Mitochondrial activity can be assessed by a comprehensive set of methods that we aim to introduce here.

Sphingolipids accumulate in aged muscle, and their reduction counteracts sarcopenia

Age-related muscle dysfunction and sarcopenia are major causes of physical incapacitation in older adults and currently lack viable treatment strategies. Here we find that sphingolipids accumulate in mouse skeletal muscle upon aging and that both genetic and pharmacological inhibition of sphingolipid synthesis prevent age-related decline in muscle mass while enhancing strength and exercise capacity. Inhibition of sphingolipid synthesis confers increased myogenic potential and promotes protein synthesis. Within the sphingolipid pathway, we show that accumulation of dihydroceramides is the culprit disturbing myofibrillar homeostasis. The relevance of sphingolipid pathways in human aging is demonstrated in two cohorts, the UK Biobank and Helsinki Birth Cohort Study in which gene expression-reducing variants of SPTLC1 and DEGS1 are associated with improved and reduced fitness of older individuals, respectively. These findings identify sphingolipid synthesis inhibition as an attractive therapeutic strategy for age-related sarcopenia and co-occurring pathologies.

Muscle Delivery of Mitochondria-Targeted Drugs for the Treatment of Sarcopenia: Rationale and Perspectives

An impairment in mitochondrial homeostasis plays a crucial role in the process of aging and contributes to the incidence of age-related diseases, including sarcopenia, which is defined as an age-dependent loss of muscle mass and strength. Mitochondrial dysfunction exerts a negative impact on several cellular activities, including bioenergetics, metabolism, and apoptosis. In sarcopenia, mitochondria homeostasis is disrupted because of reduced oxidative phosphorylation and ATP generation, the enhanced production of reactive species, and impaired antioxidant defense. This review re-establishes the most recent evidence on mitochondrial defects that are thought to be relevant in the pathogenesis of sarcopenia and that may represent promising therapeutic targets for its prevention/treatment. Furthermore, we describe mechanisms of action and translational potential of promising mitochondria-targeted drug delivery systems, including molecules able to boost the metabolism and bioenergetics, counteract apoptosis, antioxidants to scavenge reactive species and decrease oxidative stress, and target mitophagy. Even though these mitochondria-delivered strategies demonstrate to be promising in preclinical models, their use needs to be promoted for clinical studies. Therefore, there is a compelling demand to further understand the mechanisms modulating mitochondrial homeostasis, to characterize powerful compounds that target muscle mitochondria to prevent sarcopenia in aged people.

Current Uncertainties and Future Challenges Regarding NAD+ Boosting Strategies

Precursors of nicotinamide adenine dinucleotide (NAD+), modulators of enzymes of the NAD+ biosynthesis pathways and inhibitors of NAD+ consuming enzymes, are the main boosters of NAD+. Increasing public awareness and interest in anti-ageing strategies and health-promoting lifestyles have grown the interest in the use of NAD+ boosters as dietary supplements, both in scientific circles and among the general population. Here, we discuss the current trends in NAD+ precursor usage as well as the uncertainties in dosage, timing, safety, and side effects. There are many unknowns regarding pharmacokinetics and pharmacodynamics, particularly bioavailability, metabolism, and tissue specificity of NAD+ boosters. Given the lack of long-term safety studies, there is a need for more clinical trials to determine the proper dose of NAD+ boosters and treatment duration for aging prevention and as disease therapy. Further research will also need to address the long-term consequences of increased NAD+ and the best approaches and combinations to increase NAD+ levels. The answers to the above questions will contribute to the more efficient and safer use of NAD+ boosters.

Progress in Research on Antitumor Drugs and Dynamic Changes in Skeletal Muscles

Objective: To review the research progress of reltionship between antitumor drugs and the dynamic changes of the skeletal muscles during treatment phase.

Background: Sarcopenia is a common disease in patients with tumors, and it has been agreed that patients with tumors and sarcopenia experience more serious adverse reactions and have a shorter long-term survival after antitumor therapy than patients without sarcopenia. Antitumor drugs whilst beneficial for tumor regression, interferes and synergizes with cancer-induced muscle wasting/sarcopenia, induced myodemia or intramuscular fat and the two conditions often overlap making it difficult to drive conclusions. In recent years, increasing attention has been paid to the dynamic changes in skeletal muscles during antitumor drug therapy. Dynamic changes refer not only measurement skeletal muscle quantity at baseline level, but give more emphasis on the increasing or decreasing level during or end of the whole treatment course.

Methods: We retrievaled published English-language original research articles via pubmed, those studies mainly focused on repeated measurements of skeletal muscle index using computed tomography (CT) in cancer patients who received antitumor drug treatment but not received interventions that produced muscle mass change (such as exercise and nutritional interventions).

Conclusion: This article will summarize the research progress to date. Most of antineoplastic drug cause skeletal muscle loss during the treatment course, loss of L3 skeletal muscle index is always associated with poor clinical outcomes.

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.

CEST-2.2 overexpression alters lipid metabolism and extends longevity of mitochondrial mutants

Mitochondrial dysfunction can either extend or decrease Caenorhabditis elegans lifespan, depending on whether transcriptionally regulated responses can elicit durable stress adaptation to otherwise detrimental lesions. Here, we test the hypothesis that enhanced metabolic flexibility is sufficient to circumvent bioenergetic abnormalities associated with the phenotypic threshold effect, thereby transforming short‐lived mitochondrial mutants into long‐lived ones. We find that CEST‐2.2, a carboxylesterase mainly localizes in the intestine, may stimulate the survival of mitochondrial deficient animals. We report that genetic manipulation of cest‐2.2 expression has a minor lifespan impact on wild‐type nematodes, whereas its overexpression markedly extends the lifespan of complex I‐deficient gas‐1(fc21) mutants. We profile the transcriptome and lipidome of cest‐2.2 overexpressing animals and show that CEST‐2.2 stimulates lipid metabolism and fatty acid beta‐oxidation, thereby enhancing mitochondrial respiratory capacity through complex II and LET‐721/ETFDH, despite the inherited genetic lesion of complex I. Together, our findings unveil a metabolic pathway that, through the tissue‐specific mobilization of lipid deposits, may influence the longevity of mitochondrial mutant C. elegans.

Sesamol counteracts on metabolic disorders of middle-aged alimentary obese mice through regulating skeletal muscle glucose and lipid metabolism

Background

Globally, obesity is a significant public problem, especially when aging. Sesamol, a phenolic lignan present in sesame seeds, might have a positive effect on high-fat diet (HFD)-induced obesity associated with aging.

Objective

The purpose of current research study was to explore salutary effects and mechanisms of sesamol in treating alimentary obesity and associated metabolic syndrome in middle-aged mice.

Methods

C57BL/6J mice aged 4–6 weeks and 6–8 months were assigned to the young normal diet group, middle-aged normal diet group, middle-aged HFD group, and middle-aged HFD + sesamol group. At the end of experiment, glucose tolerance test and insulin tolerance test were performed; the levels of lipids and oxidative stress-related factors in the serum and skeletal muscle were detected using chemistry reagent kits; lipid accumulation in skeletal muscle was observed by oil red O staining; the expressions of muscular glucose and lipid metabolism associated proteins were measured by Western blotting.

Results

Sesamol decreased the body weight and alleviated obesity-associated metabolism syndrome in middle-aged mice, such as glucose intolerance, insulin resistance, dyslipidemia, and oxidative stress. Moreover, muscular metabolic disorders were attenuated after treatment with sesamol. It increased the expression of glucose transporter type-4 and down-regulated the protein levels of pyruvate dehydrogenase kinase isozyme 4, implying the increase of glucose uptake and oxidation. Meanwhile, sesamol decreased the expression of sterol regulatory element binding protein 1c and up-regulated the phosphorylation of hormone-sensitive lipase and the level of carnitine palmityl transferase 1α, which led to the declined lipogenesis and the increased lipolysis and lipid oxidation. In addition, the SIRT1/AMPK signaling pathway was triggered by sesamol, from which it is understood how sesamol enhances glucose and lipid metabolism.

Conclusions

Sesamol counteracts on metabolic disorders of middle-aged alimentary obese mice through regulating skeletal muscle glucose and lipid metabolism, which might be associated with the stimulation of the SIRT1/AMPK pathway.

C. elegans as a model organism to study female reproductive health

Female reproductive health has been historically understudied and underfunded. Here, we present the advantages of using a free-living nematode, Caenorhabditis elegans, as an animal system to study fundamental aspects of female reproductive health. C. elegans is a powerful high-throughput model organism that shares key genetic and physiological similarities with humans. In this review, we highlight areas of pressing medical and biological importance in the 21st century within the context of female reproductive health. These include the decline in female reproductive capacity with increasing chronological age, reproductive dysfunction arising from toxic environmental insults, and cancers of the reproductive system. C. elegans has been instrumental in uncovering mechanistic insights underlying these processes, and has been valuable for developing and testing therapeutics to combat them. Adopting a convenient model organism such as C. elegans for studying reproductive health will encourage further research into this field, and broaden opportunities for making advancements into evolutionarily conserved mechanisms that control reproductive function.

Translational therapy from preclinical animal models for muscle degeneration after rotator cuff injury

Chronic rotator cuff tears are debilitating diseases which significantly affect patients’ quality of life and pose substantial financial burden to the society. The intraoperative reparability of injured tendon and postoperative probability of tendon retear are highly associated with the quality of torn muscles, specifically, the severity of muscle atrophy and fatty infiltration. Animal models that reproduce the characteristic muscle pathology after rotator cuff injury have been developed and used to provide insight into the underlying biology and pathophysiology. In this review, we briefly summarize the current information obtained from preclinical animal studies regarding the degenerative change of cuff muscle subsequent to tendon release and/or suprascapular nerve denervation. Importantly, we focus on the potential translational therapeutic targets or agents for the prevention or reversal of muscle atrophy and fatty infiltration. While further studies are warranted to assess the safety and efficacy of novel therapies derived from these preclinical animal research, we believe that their clinical translation for the treatment of rotator cuff disorders is on the horizon.

The Translational potential of this article

Novel therapeutic strategies described in this review from preclinical animal studies hold a great translational potential for preventing or reversing rotator cuff muscle pathology, while further assessments on their safety and efficacy are warranted.

Pleiotropic effects of mitochondria in aging

Aging is typified by a progressive decline in mitochondrial activity and stress resilience. Here, we review how mitochondrial stress pathways have pleiotropic effects on cellular and systemic homeostasis, which can comprise protective or detrimental responses during aging. We describe recent evidence arguing that defects in these conserved adaptive pathways contribute to aging and age-related diseases. Signaling pathways regulating the mitochondrial unfolded protein response, mitochondrial membrane dynamics, and mitophagy are discussed, emphasizing how their failure contributes to heteroplasmy and de-regulation of key metabolites. Our current understanding of how these processes are controlled and interconnected explains how mitochondria can widely impact fundamental aspects of aging.

The CD38 glycohydrolase and the NAD sink: implications for pathological conditions

Nicotinamide adenine dinucleotide (NAD) acts as a cofactor in several oxidation-reduction (redox) reactions and is a substrate for a number of nonredox enzymes. NAD is fundamental to a variety of cellular processes including energy metabolism, cell signaling, and epigenetics. NAD homeostasis appears to be of paramount importance to health span and longevity, and its dysregulation is associated with multiple diseases. NAD metabolism is dynamic and maintained by synthesis and degradation. The enzyme CD38, one of the main NAD-consuming enzymes, is a key component of NAD homeostasis. The majority of CD38 is localized in the plasma membrane with its catalytic domain facing the extracellular environment, likely for the purpose of controlling systemic levels of NAD. Several cell types express CD38, but its expression predominates on endothelial cells and immune cells capable of infiltrating organs and tissues. Here we review potential roles of CD38 in health and disease and postulate ways in which CD38 dysregulation causes changes in NAD homeostasis and contributes to the pathophysiology of multiple conditions. Indeed, in animal models the development of infectious diseases, autoimmune disorders, fibrosis, metabolic diseases, and age-associated diseases including cancer, heart disease, and neurodegeneration are associated with altered CD38 enzymatic activity. Many of these conditions are modified in CD38-deficient mice or by blocking CD38 NADase activity. In diseases in which CD38 appears to play a role, CD38-dependent NAD decline is often a common denominator of pathophysiology. Thus, understanding dysregulation of NAD homeostasis by CD38 may open new avenues for the treatment of human diseases.

Elucidating exercise-induced skeletal muscle signaling pathways and applying relevant findings to preemptive therapy for lifestyle-related diseases

While it is well recognized that exercise represents a radical preventive and therapeutic measure for lifestyle-related diseases, it is clear that contemporary lifestyles abound with situations where exercise may be found difficult to implement on a continuous basis. Indeed, this has led to global expectations for elucidation of the exercise-activated skeletal muscle signaling pathways as well as for development of exercise mimics that effectively activate such pathways. It is shown that exercise activates the transcriptional coactivator PGC-1α via AMPK/SIRT1 in muscle, thereby not only enhancing mitochondrial function and muscle endurance but upregulating energy metabolism. Further, adipocyte-derived adiponectin is also shown to activate AMPK/SIRT1/PGC-1α via its receptor AdipoR1 in skeletal muscles. Thus, adiponectin/AdipoR1 signaling is thought to constitute exercise-mimicking signaling. Indeed, it has become clear that AMPK, SIRT1 and AdipoR activators act as exercise mimetics. With the crystal structures of AdipoR elucidated and humanized AdipoR mice generated toward optimization of candidate AdipoR-activators for human use, expectations are mounting for the clinical application in the near future of AdipoR activators as exercise mimetics in humans. This review provides an overview of molecules activated by exercise and compounds activating these molecules, with a focus on the therapeutic potential of AdipoR activators as exercise mimetics.

Evolution of a histone variant involved in compartmental regulation of NAD metabolism

NAD metabolism is essential for all forms of life. Compartmental regulation of NAD⁺ consumption, especially between the nucleus and the mitochondria, is required for energy homeostasis. However, how compartmental regulation evolved remains unclear. In the present study, we investigated the evolution of the macrodomain-containing histone variant macroH2A1.1, an integral chromatin component that limits nuclear NAD⁺ consumption by inhibiting poly(ADP-ribose) polymerase 1 in vertebrate cells. We found that macroH2A originated in premetazoan protists. The crystal structure of the macroH2A macrodomain from the protist Capsaspora owczarzaki allowed us to identify highly conserved principles of ligand binding and pinpoint key residue substitutions, selected for during the evolution of the vertebrate stem lineage. Metabolic characterization of the Capsaspora lifecycle suggested that the metabolic function of macroH2A was associated with nonproliferative stages. Taken together, we provide insight into the evolution of a chromatin element involved in compartmental NAD regulation, relevant for understanding its metabolism and potential therapeutic applications.

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.

BST1 regulates nicotinamide riboside metabolism via its glycohydrolase and base-exchange activities

Nicotinamide riboside (NR) is one of the orally bioavailable NAD⁺ precursors and has been demonstrated to exhibit beneficial effects against aging and aging-associated diseases. However, the metabolic pathway of NR in vivo is not yet fully understood. Here, we demonstrate that orally administered NR increases NAD⁺ level via two different pathways. In the early phase, NR was directly absorbed and contributed to NAD⁺ generation through the NR salvage pathway, while in the late phase, NR was hydrolyzed to nicotinamide (NAM) by bone marrow stromal cell antigen 1 (BST1), and was further metabolized by the gut microbiota to nicotinic acid, contributing to generate NAD⁺ through the Preiss-Handler pathway. Furthermore, we report BST1 has a base-exchange activity against both NR and nicotinic acid riboside (NAR) to generate NAR and NR, respectively, connecting amidated and deamidated pathways. Thus, we conclude that BST1 plays a dual role as glycohydrolase and base-exchange enzyme during oral NR supplementation.

The multifaceted regulation of mitophagy by endogenous metabolites

Owing to the dominant functions of mitochondria in multiple cellular metabolisms and distinct types of regulated cell death, maintaining a functional mitochondrial network is fundamental for the cellular homeostasis and body fitness in response to physiological adaptations and stressed conditions. The process of mitophagy, in which the dysfunctional or superfluous mitochondria are selectively engulfed by autophagosome and subsequently degraded in lysosome, has been well formulated as one of the major mechanisms for mitochondrial quality control. To date, the PINK1-PRKN-dependent and receptors (including proteins and lipids)-dependent pathways have been characterized to determine the mitophagy in mammalian cells. The mitophagy is highly responsive to the dynamics of endogenous metabolites, including iron-, calcium-, glycolysis-TCA-, NAD⁺-, amino acids-, fatty acids-, and cAMP-associated metabolites. Herein, we summarize the recent advances toward the molecular details of mitophagy regulation in mammalian cells. We also highlight the key regulations of mammalian mitophagy by endogenous metabolites, shed new light on the bidirectional interplay between mitophagy and cellular metabolisms, with attempting to provide a perspective insight into the nutritional intervention of metabolic disorders with mitophagy deficit.Abbreviations: acetyl-CoA: acetyl-coenzyme A; ACO1: aconitase 1; ADCYs: adenylate cyclases; AMPK: AMP-activated protein kinase; ATM: ATM serine/threonine kinase; BCL2L1: BCL2 like 1; BCL2L13: BCL2 like 13; BNIP3: BCL2 interacting protein 3; BNIP3L: BCL2 interacting protein 3 like; Ca²⁺: calcium ion; CALCOCO2: calcium binding and coiled-coil domain 2; CANX: calnexin; CO: carbon monoxide; CYCS: cytochrome c, somatic; DFP: deferiprone; DNM1L: dynamin 1 like; ER: endoplasmic reticulum; FKBP8: FKBP prolyl isomerase 8; FOXO3: forkhead box O3; FTMT: ferritin mitochondrial; FUNDC1: FUN14 domain containing 1; GABA: γ-aminobutyric acid; GSH: glutathione; HIF1A: hypoxia inducible factor 1 subunit alpha; IMMT: inner membrane mitochondrial protein; IRP1: iron regulatory protein 1; ISC: iron-sulfur cluster; ITPR2: inositol 1,4,5-trisphosphate type 2 receptor; KMO: kynurenine 3-monooxygenase; LIR: LC3 interacting region; MAM: mitochondria-associated membrane; MAP1LC3: microtubule associated protein 1 light chain 3; MFNs: mitofusins; mitophagy: mitochondrial autophagy; mPTP: mitochondrial permeability transition pore; MTOR: mechanistic target of rapamycin kinase; NAD⁺: nicotinamide adenine dinucleotide; NAM: nicotinamide; NMN: nicotinamide mononucleotide; NO: nitric oxide; NPA: Niemann-Pick type A; NR: nicotinamide riboside; NR4A1: nuclear receptor subfamily 4 group A member 1; NRF1: nuclear respiratory factor 1; OPA1: OPA1 mitochondrial dynamin like GTPase; OPTN: optineurin; PARL: presenilin associated rhomboid like; PARPs: poly(ADP-ribose) polymerases; PC: phosphatidylcholine; PHB2: prohibitin 2; PINK1: PTEN induced kinase 1; PPARG: peroxisome proliferator activated receptor gamma; PPARGC1A: PPARG coactivator 1 alpha; PRKA: protein kinase AMP-activated; PRKDC: protein kinase, DNA-activated, catalytic subunit; PRKN: parkin RBR E3 ubiquitin protein ligase; RHOT: ras homolog family member T; ROS: reactive oxygen species; SIRTs: sirtuins; STK11: serine/threonine kinase 11; TCA: tricarboxylic acid; TP53: tumor protein p53; ULK1: unc-51 like autophagy activating kinase 1; VDAC1: voltage dependent anion channel 1.

The balance between NAD+ biosynthesis and consumption in ageing

Nicotinamide adenine dinucleotide (NAD⁺) is a vital coenzyme in redox reactions. NAD⁺ is also important in cellular signalling as it is consumed by PARPs, SARM1, sirtuins and CD38. Cellular NAD⁺ levels regulate several essential processes including DNA repair, immune cell function, senescence, and chromatin remodelling. Maintenance of these cellular processes is important for healthy ageing and lifespan. Interestingly, the levels of NAD⁺ decline during ageing in several organisms, including humans. Declining NAD⁺ levels have been linked to several age-related diseases including various metabolic diseases and cognitive decline. Decreasing tissue NAD⁺ concentrations have been ascribed to an imbalance between biosynthesis and consumption of the dinucleotide, resulting from, for instance, reduced levels of the rate limiting enzyme NAMPT along with an increased activation state of the NAD⁺-consuming enzymes PARPs and CD38. The progression of some age-related diseases can be halted or reversed by therapeutic augmentation of NAD⁺ levels. NAD⁺ metabolism has therefore emerged as a potential target to ameliorate age-related diseases. The present review explores how ageing affects NAD⁺ metabolism and current approaches to reverse the age-dependent decline of NAD⁺.

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.

NAD+ in Alzheimer's Disease: Molecular Mechanisms and Systematic Therapeutic Evidence Obtained in vivo

Mitochondria in neurons generate adenosine triphosphate (ATP) to provide the necessary energy required for constant activity. Nicotinamide adenine dinucleotide (NAD⁺) is a vital intermediate metabolite involved in cellular bioenergetics, ATP production, mitochondrial homeostasis, and adaptive stress responses. Exploration of the biological functions of NAD⁺ has been gaining momentum, providing many crucial insights into the pathophysiology of age-associated functional decline and diseases, such as Alzheimer’s disease (AD). Here, we systematically review the key roles of NAD⁺ precursors and related metabolites in AD models and show how NAD⁺ affects the pathological hallmarks of AD and the potential mechanisms of action. Advances in understanding the molecular roles of NAD⁺-based neuronal resilience will result in novel approaches for the treatment of AD and set the stage for determining whether the results of exciting preclinical trials can be translated into the clinic to improve AD patients’ phenotypes.

Nicotinamide mononucleotide supplementation enhances aerobic capacity in amateur runners: a randomized, double-blind study

BACKGROUND

Recent studies in rodents indicate that a combination of exercise training and supplementation with nicotinamide adenine dinucleotide (NAD⁺) precursors has synergistic effects. However, there are currently no human clinical trials analyzing this.

OBJECTIVE

This study investigates the effects of a combination of exercise training and supplementation with nicotinamide mononucleotide (NMN), the immediate precursor of NAD⁺, on cardiovascular fitness in healthy amateur runners.

METHODS

A six-week randomized, double-blind, placebo-controlled, four-arm clinical trial including 48 young and middle-aged recreationally trained runners of the Guangzhou Pearl River running team was conducted. The participants were randomized into four groups: the low dosage group (300 mg/day NMN), the medium dosage group (600 mg/day NMN), the high dosage group (1200 mg/day NMN), and the control group (placebo). Each group consisted of ten male participants and two female participants. Each training session was 40-60 min, and the runners trained 5-6 times each week. Cardiopulmonary exercise testing was performed at baseline and after the intervention, at 6 weeks, to assess the aerobic capacity of the runners.

RESULTS

Analysis of covariance of the change from baseline over the 6 week treatment showed that the oxygen uptake (VO₂), percentages of maximum oxygen uptake (VO_2max), power at first ventilatory threshold, and power at second ventilatory threshold increased to a higher degree in the medium and high dosage groups compared with the control group. However, there was no difference in VO_2max, O₂-pulse, VO₂ related to work rate, and peak power after the 6 week treatment from baseline in any of these groups.

CONCLUSION

NMN increases the aerobic capacity of humans during exercise training, and the improvement is likely the result of enhanced O₂ utilization of the skeletal muscle.

TRIAL REGISTRATION NUMBER

ChiCTR2000035138 .

NAD+ homeostasis in human health and disease

Depletion of nicotinamide adenine dinucleotide (NAD+ ), a central redox cofactor and the substrate of key metabolic enzymes, is the causative factor of a number of inherited and acquired diseases in humans. Primary deficiencies of NAD+ homeostasis are the result of impaired biosynthesis, while secondary deficiencies can arise due to other factors affecting NAD+ homeostasis, such as increased NAD+ consumption or dietary deficiency of its vitamin B3 precursors. NAD+ depletion can manifest in a wide variety of pathological phenotypes, ranging from rare inherited defects, characterized by congenital malformations, retinal degeneration, and/or encephalopathy, to more common multifactorial, often age-related, diseases. Here, we discuss NAD+ biochemistry and metabolism and provide an overview of the etiology and pathological consequences of alterations of the NAD+ metabolism in humans. Finally, we discuss the state of the art of the potential therapeutic implications of NAD+ repletion for boosting health as well as treating rare and common diseases, and the possibilities to achieve this by means of the different NAD+ -enhancing agents.

Silencing of Poly(ADP-Ribose) Polymerase-2 Induces Mitochondrial Reactive Species Production and Mitochondrial Fragmentation

PARP2 is a DNA repair protein. The deletion of PARP2 induces mitochondrial biogenesis and mitochondrial activity by increasing NAD⁺ levels and inducing SIRT1 activity. We show that the silencing of PARP2 causes mitochondrial fragmentation in myoblasts. We assessed multiple pathways that can lead to mitochondrial fragmentation and ruled out the involvement of mitophagy, the fusion-fission machinery, SIRT1, and mitochondrial unfolded protein response. Nevertheless, mitochondrial fragmentation was reversed by treatment with strong reductants, such as reduced glutathione (GSH), N-acetyl-cysteine (NAC), and a mitochondria-specific antioxidant MitoTEMPO. The effect of MitoTEMPO on mitochondrial morphology indicates the production of reactive oxygen species of mitochondrial origin. Elimination of reactive oxygen species reversed mitochondrial fragmentation in PARP2-silenced cells.