Activation of cardiac Nmnat/NAD+/SIR2 pathways mediates endurance exercise resistance to lipotoxic cardiomyopathy in aging Drosophila

Glycolysis-Mediated Activation of v-ATPase by Nicotinamide Mononucleotide Ameliorates Lipid-Induced Cardiomyopathy by Repressing the CD36-TLR4 Axis

BACKGROUND

Chronic overconsumption of lipids followed by their excessive accumulation in the heart leads to cardiomyopathy. The cause of lipid-induced cardiomyopathy involves a pivotal role for the proton-pump vacuolar-type H+-ATPase (v-ATPase), which acidifies endosomes, and for lipid-transporter CD36, which is stored in acidified endosomes. During lipid overexposure, an increased influx of lipids into cardiomyocytes is sensed by v-ATPase, which then disassembles, causing endosomal de-acidification and expulsion of stored CD36 from the endosomes toward the sarcolemma. Once at the sarcolemma, CD36 not only increases lipid uptake but also interacts with inflammatory receptor TLR4 (Toll-like receptor 4), together resulting in lipid-induced insulin resistance, inflammation, fibrosis, and cardiac dysfunction. Strategies inducing v-ATPase reassembly, that is, to achieve CD36 reinternalization, may correct these maladaptive alterations. For this, we used NAD+ (nicotinamide adenine dinucleotide)-precursor nicotinamide mononucleotide (NMN), inducing v-ATPase reassembly by stimulating glycolytic enzymes to bind to v-ATPase.

METHODS

Rats/mice on cardiomyopathy-inducing high-fat diets were supplemented with NMN and for comparison with a cocktail of lysine/leucine/arginine (mTORC1 [mechanistic target of rapamycin complex 1]-mediated v-ATPase reassembly). We used the following methods: RNA sequencing, mRNA/protein expression analysis, immunofluorescence microscopy, (co)immunoprecipitation/proximity ligation assay (v-ATPase assembly), myocellular uptake of [3H]chloroquine (endosomal pH), and [14C]palmitate, targeted lipidomics, and echocardiography. To confirm the involvement of v-ATPase in the beneficial effects of both supplementations, mTORC1/v-ATPase inhibitors (rapamycin/bafilomycin A1) were administered. Additionally, 2 heart-specific v-ATPase-knockout mouse models (subunits V1G1/V0d2) were subjected to these measurements. Mechanisms were confirmed in pharmacologically/genetically manipulated cardiomyocyte models of lipid overload.

RESULTS

NMN successfully preserved endosomal acidification during myocardial lipid overload by maintaining v-ATPase activity and subsequently prevented CD36-mediated lipid accumulation, CD36-TLR4 interaction toward inflammation, fibrosis, cardiac dysfunction, and whole-body insulin resistance. Lipidomics revealed C18:1-enriched diacylglycerols as lipid class prominently increased by high-fat diet and subsequently reversed/preserved by lysine/leucine/arginine/NMN treatment. Studies with mTORC1/v-ATPase inhibitors and heart-specific v-ATPase-knockout mice further confirmed the pivotal roles of v-ATPase in these beneficial actions.

CONCLUSION

NMN preserves heart function during lipid overload by preventing v-ATPase disassembly.

Physical exercise ameliorates age-related deterioration of skeletal muscle and mortality by activating Pten-related pathways in Drosophila on a high-salt diet

The phosphatase and tensin congeners (Pten) gene affects cell growth, cell proliferation, and rearrangement of connections, and it is closely related to cellular senescence, but it remains unclear the role of muscle-Pten gene in exercise against age-related deterioration in skeletal muscle and mortality induced by a high-salt diet (HSD). In here, overexpression and knockdown of muscle Pten gene were constructed by building MhcGAL4 /PtenUAS-overexpression and MhcGAL4 /PtenUAS-RNAi system in flies, and flies were given exercise training and a HSD for 2 weeks. The results showed that muscle Pten knockdown significantly reduced the climbing speed, climbing endurance, GPX activity, and the expression of Pten, Sirt1, PGC-1α genes, and it significantly increased the expression of Akt and ROS level, and impaired myofibril and mitochondria of aged skeletal muscle. Pten knockdown prevented exercise from countering the HSD-induced age-related deterioration of skeletal muscle. Pten overexpression has the opposite effect on skeletal muscle aging when compared to it knockdown, and it promoted exercise against HSD-induced age-related deterioration of skeletal muscle. Pten overexpression significantly increased lifespan, but its knockdown significantly decreased lifespan of flies. Thus, current results confirmed that differential expression of muscle Pten gene played an important role in regulating skeletal muscle aging and lifespan, and it also affected the adaptability of aging skeletal muscle to physical exercise since it determined the activity of muscle Pten/Akt pathway and Pten/Sirt1/PGC-1α pathway.

Muscle-specific overexpression of Atg2 gene and endurance exercise delay age-related deteriorations of skeletal muscle and heart function via activating the AMPK/Sirt1/PGC-1α pathway in male Drosophila

Atg2 is a key gene in autophagy formation and plays an important role in regulating aging progress. Exercise is an important tool to resist oxidative stress in cells and delay muscle aging. However, the relationship between exercise and the muscle Atg2 gene in regulating skeletal muscle aging remains unclear. Here, overexpression or knockdown of muscle Atg2 gene was achieved by constructing the AtgUAS/MhcGal4 system in Drosophila, and these flies were also subjected to an exercise intervention for 2 weeks. The results showed that both overexpression of Atg2 and exercise significantly increased the climbing speed, climbing endurance, cardiac function, and lifespan of aging flies. They also significantly up-regulated the expression of muscle Atg2, AMPK, Sirt1, and PGC-1α genes, and they significantly reduced muscle malondialdehyde and triglyceride. These positive benefits were even more pronounced when the two were combined. However, the effects of Atg2 knockdown on skeletal muscle, heart, and lifespan were reversed compared to its overexpression. Importantly, exercise ameliorated age-related changes induced by Atg2 knockdown. Therefore, current results confirmed that both overexpression of muscle Atg2 and exercise delayed age-related deteriorations of skeletal muscle, the heart function, and lifespan, and exercise could also reverse age-related changes induced by Atg2 knockdown. The molecular mechanism is related to the overexpression of the Atg2 gene and exercise, which increase the activity of the AMPK/Sirt1/PGC-1α pathway, oxidation and antioxidant balance, and lipid metabolism in aging muscle.

Diet supplementation with egg yolk powder fattens the beetle Tribolium castaneum

Insects have become essential models in studying human metabolic diseases, mainly due to their low maintenance cost and available tools. Both mutations and modified diets induce metabolic states similar to human obesity and diabetes. Here, we explore the effect of a high-calorie, high-fat diet on the metabolism of the beetle Tribolium castaneum. Supplementation of the wheat flour diet with powdered egg yolk for 3 weeks increased the total triacylglycerol and accelerated larval development. In addition, this diet increased the triacylglycerol levels of adult beetles. However, this egg yolk supplementation did not alter the larvae's total glucose levels or lipogenic capacity and ATP citrate lyase activity. The diet also did not change the expression profile of several lipid and carbohydrate metabolism genes and insulin-like peptides. Thus, we conclude that the diet supplemented with egg yolk induces increased fat without causing diabetes phenotypes, as seen in other hypercaloric diets in insects.

Regular Exercise in Drosophila Prevents Age-Related Cardiac Dysfunction Caused by High Fat and Heart-Specific Knockdown of skd

Skuld (skd) is a subunit of the Mediator complex subunit complex. In the heart, skd controls systemic obesity, is involved in systemic energy metabolism, and is closely linked to cardiac function and aging. However, it is unclear whether the effect of cardiac skd on cardiac energy metabolism affects cardiac function. We found that cardiac-specific knockdown of skd showed impaired cardiac function, metabolic impairment, and premature aging. Drosophila was subjected to an exercise and high-fat diet (HFD) intervention to explore the effects of exercise on cardiac skd expression and cardiac function in HFD Drosophila. We found that Hand-Gal4>skd RNAi (KC) Drosophila had impaired cardiac function, metabolic impairment, and premature aging. Regular exercise significantly improved cardiac function and metabolism and delayed aging in HFD KC Drosophila. Thus, our study found that the effect of skd on cardiac energy metabolism in the heart affected cardiac function. Exercise may counteract age-related cardiac dysfunction and metabolic disturbances caused by HFD and heart-specific knockdown of skd. Skd may be a potential therapeutic target for heart disease.

Regular Exercise Rescues Heart Function Defects and Shortens the Lifespan of Drosophila Caused by dMnM Downregulation

Although studies have shown that myomesin 2 (MYOM2) mutations can lead to hypertrophic cardiomyopathy (HCM), a common cardiovascular disease that has a serious impact on human life, the effect of MYOM2 on cardiac function and lifespan in humans is unknown. In this study, dMnM (MYOM2 homologs) knockdown in cardiomyocytes resulted in diastolic cardiac defects (diastolic dysfunction and arrhythmias) and increased cardiac oxidative stress. Furthermore, the knockdown of dMnM in indirect flight muscle (IFM) reduced climbing ability and shortened lifespan. However, regular exercise significantly ameliorated diastolic cardiac dysfunction, arrhythmias, and oxidative stress triggered by dMnM knockdown in cardiac myocytes and also reversed the reduction in climbing ability and shortening of lifespan caused by dMnM knockdown in Drosophila IFM. In conclusion, these results suggest that Drosophila cardiomyocyte dMnM knockdown leads to cardiac functional defects, while dMnM knockdown in IFM affects climbing ability and lifespan. Furthermore, regular exercise effectively upregulates cardiomyocyte dMnM expression levels and ameliorates cardiac functional defects caused by Drosophila cardiomyocyte dMnM knockdown by increasing cardiac antioxidant capacity. Importantly, regular exercise ameliorates the shortened lifespan caused by dMnM knockdown in IFM.

Early life exercise training and inhibition of apoLpp mRNA expression to improve age-related arrhythmias and prolong the average lifespan in Drosophila melanogaster

Cardiovascular disease (CVD) places a heavy burden on older patients and the global healthcare system. A large body of evidence suggests that exercise training is essential in preventing and treating cardiovascular disease, but the underlying mechanisms are not well understood. Here, we used the Drosophila melanogaster animal model to study the effects of early-life exercise training (Exercise) on the aging heart and lifespan. We found in flies that age-induced arrhythmias are conserved across different genetic backgrounds. The fat body is the primary source of circulating lipoproteins in flies. Inhibition of fat body apoLpp (Drosophila apoB homolog) demonstrated that low expression of apoLpp reduced the development of arrhythmias in aged flies but did not affect average lifespan. At the same time, exercise can also reduce the expression of apoLpp mRNA in aged flies and have a protective effect on the heart, which is similar to the inhibition of apoLpp mRNA. Although treatment of UAS-apoLpp^RNAi and exercise alone had no significant effect on lifespan, the combination of UAS-apoLpp^RNAi and exercise extended the average lifespan of flies. Therefore, we conclude that UAS-apoLpp^RNAi and exercise are sufficient to resist age-induced arrhythmias, which may be related to the decreased expression of apoLpp mRNA, and that UAS-apoLpp^RNAi and exercise have a combined effect on prolonging the average lifespan.

Drosophila exercise, an emerging model bridging the fields of exercise and aging in human

Exercise is one of the most effective treatments for the diseases of aging. In recent years, a growing number of researchers have used Drosophila melanogaster to study the broad benefits of regular exercise in aging individuals. With the widespread use of Drosophila exercise models and the upgrading of the Drosophila exercise apparatus, we should carefully examine the differential contribution of regular exercise in the aging process to facilitate more detailed quantitative measurements and assessment of the exercise phenotype. In this paper, we review some of the resources available for Drosophila exercise models. The focus is on the impact of regular exercise or exercise adaptation in the aging process in Drosophila and highlights the great potential and current challenges faced by this model in the field of anti-aging research.

Therapeutic Potential of Emerging NAD+-Increasing Strategies for Cardiovascular Diseases

Cardiovascular diseases are the leading cause of death worldwide. Aging and/or metabolic stress directly impact the cardiovascular system. Over the last few years, the contributions of altered nicotinamide adenine dinucleotide (NAD+) metabolism to aging and other pathological conditions closely related to cardiovascular diseases have been intensively investigated. NAD+ bioavailability decreases with age and cardiometabolic conditions in several mammalian tissues. Compelling data suggest that declining tissue NAD+ is commonly related to mitochondrial dysfunction and might be considered as a therapeutic target. Thus, NAD+ replenishment by either genetic or natural dietary NAD+-increasing strategies has been recently demonstrated to be effective for improving the pathophysiology of cardiac and vascular health in different experimental models, as well as human health, to a lesser extent. Here, we review and discuss recent experimental evidence illustrating that increasing NAD+ bioavailability, particularly by the use of natural NAD+ precursors, may offer hope for new therapeutic strategies to prevent and treat cardiovascular diseases.