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.

Increased NAD+ levels protect female mouse reproductive system against zearalenone-impaired glycolysis, lipid metabolism, antioxidant capacity and inflammation.

The reproductive system is a primary target organ for zearalenone (ZEN, a widespread fusarium mycotoxin) to exert its toxic effects, including decreased antioxidant capacity and aggravated inflammatory response. These ZEN-induced reproductive abnormalities are partially caused by the declining levels of nicotinamide adenine dinucleotide (NAD+), which results in an imbalance in lipid/glucose metabolism. Accordingly, the present study aimed to investigate whether supplements of nicotinamide mononucleotide (NMN, a NAD+ precursor) in female mice could protect against ZEN-induced reproductive toxicity. In this study, thirty female mice were randomly divided into three groups that were intragastrically administered with i) 0.5% DMSO (the Ctrl group), ii) 3 mg/(kg bw.d) ZEN (the ZEN group), or iii) ZEN + 500 mg/(kg bw.d) NMN (the ZEN/NMN group) for two weeks. The results revealed that, compared with the Ctrl group, animals exposed to ZEN exhibited reproductive toxicity, such as decreased antioxidant capacity and aggravated inflammatory response in reproductive tissues. These effects were strongly correlated with lower activities in key glycolytic enzymes (e.g., ALDOA and PGK), but increased expressions in key lipid-synthesis genes (e.g., LPIN1 and ATGL). These changes contribute to lipid accumulation, specifically for diacylglycerols (DAGs). Furthermore, these ZEN-induced changes were linked with disturbed NAD+ synthesis/degradation, and subsequently decreased NAD+ levels. Notably, NMN supplements in mice protected against these ZEN-induced reproductive abnormalities by boosting NAD+ levels. Herein, the present findings demonstrate that potential strategies to enhance NAD+ levels can protect against ZEN-induced reproductive toxicity.

Adipocyte-derived chemerin rescues lipid overload-induced cardiac dysfunction.

Chemerin, an adipocyte-secreted protein, has been recently suggested to be linked to metabolic syndrome and cardiac function in obese and diabetes mellitus. This study aimed to investigate the potential roles of adipokine chemerin on high fat-induced cardiac dysfunction. Chemerin (Rarres2) knockout mice, which were fed with either a normal diet or a high-fat diet for 20 weeks, were employed to observe whether adipokine chemerin affected lipid metabolism, inflammation, and cardiac function. Firstly, we found normal metabolic substrate inflexibility and cardiac function in Rarres2 -/- mice with a normal diet. Notably, in a high-fat diet, Rarres2 -/- mice showed lipotoxicity, insulin resistance, and inflammation, thus causing metabolic substrate inflexibility and cardiac dysfunction. Furthermore, by using in vitro model of lipid-overload cardiomyocytes, we found chemerin supplementation reversed the lipid-induced abnormalities above. Herein, in the presence of obesity, adipocyte-derived chemerin might function as an endogenous cardioprotective factor against obese-related cardiomyopathy.