The mitochondrial NAD kinase functions as a major metabolic regulator upon increased energy demand

Homeostatic regulation of NAD(H) and NADP(H) in cells

Nicotinamide adenine dinucleotide (NAD+)/reduced NAD+ (NADH) and nicotinamide adenine dinucleotide phosphate (NADP+)/reduced NADP+ (NADPH) are essential metabolites involved in multiple metabolic pathways and cellular processes. NAD+ and NADH redox couple plays a vital role in catabolic redox reactions, while NADPH is crucial for cellular anabolism and antioxidant responses. Maintaining NAD(H) and NADP(H) homeostasis is crucial for normal physiological activity and is tightly regulated through various mechanisms, such as biosynthesis, consumption, recycling, and conversion between NAD(H) and NADP(H). The conversions between NAD(H) and NADP(H) are controlled by NAD kinases (NADKs) and NADP(H) phosphatases [specifically, metazoan SpoT homolog-1 (MESH1) and nocturnin (NOCT)]. NADKs facilitate the synthesis of NADP+ from NAD+, while MESH1 and NOCT convert NADP(H) into NAD(H). In this review, we summarize the physiological roles of NAD(H) and NADP(H) and discuss the regulatory mechanisms governing NAD(H) and NADP(H) homeostasis in three key aspects: the transcriptional and posttranslational regulation of NADKs, the role of MESH1 and NOCT in maintaining NAD(H) and NADP(H) homeostasis, and the influence of the circadian clock on NAD(H) and NADP(H) homeostasis. In conclusion, NADKs, MESH1, and NOCT are integral to various cellular processes, regulating NAD(H) and NADP(H) homeostasis. Dysregulation of these enzymes results in various human diseases, such as cancers and metabolic disorders. Hence, strategies aiming to restore NAD(H) and NADP(H) homeostasis hold promise as novel therapeutic approaches for these diseases.

Insights from homozygous signatures of cervus nippon revealed genetic architecture for components of fitness

This study investigates the genomic landscape of Sika deer populations, emphasizing the detection and characterization of runs of homozygosity (ROH) and their contribution towards components of fitness. Using 85,001 high-confidence SNPs, the investigation into ROH distribution unveiled nuanced patterns of autozygosity across individuals especially in 2 out of the 8 farms, exhibiting elevated ROH levels and mean genome coverage under ROH segments. The prevalence of shorter ROH segments (0.5-4 Mb) suggests historical relatedness and potential selective pressures within these populations. Intriguingly, despite observed variations in ROH profiles, the overall genomic inbreeding coefficient (FROH) remained relatively low across all farms, indicating a discernible degree of genetic exchange and effective mitigation of inbreeding within the studied Sika deer populations. Consensus ROH (cROH) were found to harbor genes for important functions viz., EGFLAM gene which is involved in the vision function of the eye, SKP2 gene which regulates cell cycle, CAPSL involved in adipogenesis, SPEF2 which is essential for sperm flagellar assembly, DCLK3 involved in the heat stress. This first ever study on ROH in Sika deer, to shed light on the adaptive role of genes in these homozygous regions. The insights garnered from this study have broader implications in the management of genetic diversity in this vulnerable species.

Regulation of and challenges in targeting NAD+ metabolism

Nicotinamide adenine dinucleotide, in its oxidized (NAD+) and reduced (NADH) forms, is a reduction-oxidation (redox) co-factor and substrate for signalling enzymes that have essential roles in metabolism. The recognition that NAD+ levels fall in response to stress and can be readily replenished through supplementation has fostered great interest in the potential benefits of increasing or restoring NAD+ levels in humans to prevent or delay diseases and degenerative processes. However, much about the biology of NAD+ and related molecules remains poorly understood. In this Review, we discuss the current knowledge of NAD+ metabolism, including limitations of, assumptions about and unappreciated factors that might influence the success or contribute to risks of NAD+ supplementation. We highlight several ongoing controversies in the field, and discuss the role of the microbiome in modulating the availability of NAD+ precursors such as nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), the presence of multiple cellular compartments that have distinct pools of NAD+ and NADH, and non-canonical NAD+ and NADH degradation pathways. We conclude that a substantial investment in understanding the fundamental biology of NAD+, its detection and its metabolites in specific cells and cellular compartments is needed to support current translational efforts to safely boost NAD+ levels in humans.

A mitochondrial NAD/NADH kinase governs fungal virulence through an oxidative stress response and arginine biosynthesis in Fusarium graminearum

NADP/NADPH plays an indispensable role in cellular metabolism, serving as a pivotal cofactor in numerous enzymatic processes involved in anabolic pathways, antioxidant defense, and the biosynthesis of essential cellular components. NAD/NADH kinases (NADKs) phosphorylate NAD/NADH, constituting the sole de novo synthetic pathway for NADP/NADPH generation. Despite the pivotal role of NADP/NADPH in cellular functions, the physiological role of NADK remains largely unexplored in filamentous fungi. In this study, we identified three putative NADKs in Fusarium graminearum-FgNadk1, FgNadk2, and FgNadk3-responsible for NAD/NADH phosphorylation. NADK-mediated formation of intracellular NADPH proved crucial for vegetative growth, sexual reproduction, and virulence. Specifically, FgNadk2, the mitochondrial NADK, played a role in oxidative stress resistance and the maintenance of mitochondrial reactive oxygen species levels. Moreover, the deletion of FgNADK2 resulted in arginine auxotrophy, contributing to the reduced fungal virulence. These findings underscore the necessity of mitochondrial NADK in fungal virulence in F. graminearum, revealing its involvement in mitochondrial redox homeostasis and the arginine biosynthetic pathway. This study provides critical insights into the interconnectedness of metabolic pathways essential for fungal growth, stress response, and pathogenicity.

NADPH Dynamics: Linking Insulin Resistance and β-Cells Ferroptosis in Diabetes Mellitus

This review offers an in-depth exploration of Nicotinamide Adenine Dinucleotide Phosphate (NADPH) in metabolic health. It delves into how NADPH affects insulin secretion, influences insulin resistance, and plays a role in ferroptosis. NADPH, a critical cofactor in cellular antioxidant systems and lipid synthesis, plays a central role in maintaining metabolic homeostasis. In adipocytes and skeletal muscle, NADPH influences the pathophysiology of insulin resistance, a hallmark of metabolic disorders such as type 2 diabetes and obesity. The review explores the mechanisms by which NADPH contributes to or mitigates insulin resistance, including its role in lipid and reactive oxygen species (ROS) metabolism. Parallelly, the paper investigates the dual nature of NADPH in the context of pancreatic β-cell health, particularly in its relation to ferroptosis, an iron-dependent form of programmed cell death. While NADPH's antioxidative properties are crucial for preventing oxidative damage in β-cells, its involvement in lipid metabolism can potentiate ferroptotic pathways under certain pathological conditions. This complex relationship underscores the delicate balance of NADPH homeostasis in pancreatic health and diabetes pathogenesis. By integrating findings from recent studies, this review aims to illuminate the nuanced roles of NADPH in different tissues and its potential as a therapeutic target. Understanding these dynamics offers vital insights into the development of more effective strategies for managing insulin resistance and preserving pancreatic β-cell function, thereby advancing the treatment of metabolic diseases.

Mitochondrial NAD kinase in health and disease

Nicotinamide adenine dinucleotide phosphate (NADP), a co-enzyme and an electron carrier, plays crucial roles in numerous biological functions, including cellular metabolism and antioxidation. Because NADP is subcellular-membrane impermeable, eukaryotes compartmentalize NAD kinases (NADKs), the NADP biosynthetic enzymes. Mitochondria are fundamental organelles for energy production through oxidative phosphorylation. Ten years after the discovery of the mitochondrial NADK (known as MNADK or NADK2), a significant amount of knowledge has been obtained regarding its functions, mechanism of action, human biology, mouse models, crystal structures, and post-translation modifications. NADK2 phosphorylates NAD(H) to generate mitochondrial NADP(H). NADK2-deficient patients suffered from hyperlysinemia, elevated plasma C10:2-carnitine (due to the inactivity of relevant NADP-dependent enzymes), and neuronal development defects. Nadk2-deficient mice recapitulate key features of NADK2-deficient patients, including metabolic and neuronal abnormalities. Crystal structures of human NADK2 show a dimer, with the NADP⁺-binding site located at the dimer interface. NADK2 activity is highly regulated by post-translational modifications, including S188 phosphorylation, K76 and K304 acetylation, and C193 S-nitrosylation; mutations in each site affect NADK2 activity and function. In mice, hepatic Nadk2 functions as a major metabolic regulator upon increased energy demands by regulating sirtuin 3 activity and fatty acid oxidation. Hopefully, future research on NADK2 will not only elucidate its functional roles in health and disease but will also pave the way for novel therapeutics for both rare and common diseases, including NADK2 deficiency and metabolic syndrome.