Protein kinase C activates NAD kinase in human neutrophils

Anti-inflammatory and antioxidative effects of Perilla frutescens-derived extracellular vesicles: Insights from Zebrafish models

Plant-derived extracellular vesicles have recently been extracted and recognized as promising bioactive molecules, owing to their distinctive biological properties and inherent therapeutic activities. In this study, we investigated the physicochemical characteristics, bioactive properties, and therapeutic potential of Perilla frutescens-derived exosome-like nanoparticles (PELNs). Transmission electron microscopy (TEM) revealed that PELNs exhibited a cup-shaped morphology, with a lipid bilayer and a size distribution ranging from 40 to 200 nm (mean: 68.4 ± 13.0 nm). The cargoes in PELNs were analyzed through multi-omics and small RNA sequencing. In vivo studies on zebrafish demonstrated that PELNs are non-toxic at experimental concentrations. A reduction in neutrophil migration to injured fins evidenced the anti-inflammatory properties of PELNs. Furthermore, a meta-analysis of transcriptomic data identified hundreds of differentially expressed genes (DEGs) across 12 samples of three experimental groups. These DEGs were annotated into three categories following gene ontology (GO) enrichment analysis. Additionally, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that these DEGs were involved in immune-related pathways, including complement and coagulation cascades, systemic lupus erythematosus, PPAR signaling pathways, and antigen processing and presentation. Twelve selected DEGs were validated by quantitative real-time PCR (qRT-PCR), with particular confirmation of the mpx and lcp1 genes via in situ hybridization. Furthermore, PELNs demonstrated antioxidative effects by mitigating reactive oxygen species (ROS) levels, as evidenced by measurements of four oxidative stress (OS) indicators (i.e., SOD, CAT, GSH, and MDA) in zebrafish larvae subjected to H2O2-induced OS. In summary, PELNs exhibit substantial anti-inflammatory and antioxidant properties, underscoring their potential as therapeutic agents for treating various inflammatory diseases.

Cryo-EM structure and regulation of human NAD kinase

Reduced nicotinamide adenine dinucleotide phosphate (NADPH) is a crucial reducing cofactor for reductive biosynthesis and protection from oxidative stress. To fulfill their heightened anabolic and reductive power demands, cancer cells must boost their NADPH production. Progrowth and mitogenic protein kinases promote the activity of cytosolic NAD kinase (NADK), which produces NADP+, a limiting NADPH precursor. However, the molecular architecture and mechanistic regulation of human NADK remain undescribed. Here, we report the cryo-electron microscopy structure of human NADK, both in its apo-form and in complex with its substrate NAD+ (nicotinamide adenine dinucleotide), revealing a tetrameric organization with distinct structural features. We discover that the amino (N)- and carboxyl (C)-terminal tails of NADK have opposing effects on its enzymatic activity and cellular NADP(H) levels. Specifically, the C-terminal region is critical for NADK activity, whereas the N-terminal region exhibits an inhibitory role. This study highlights molecular insights into the regulation of a vital enzyme governing NADP(H) production.

Effects of the pan-caspase inhibitor Q-VD-OPh on human neutrophil lifespan and function

Human neutrophils are abundant, short-lived leukocytes that turn over at a rate of approximately 1011 cells/day via a constitutive apoptosis program. Certain growth factors, inflammatory mediators and infectious agents can delay apoptosis or induce neutrophils to die by other mechanisms. Nonetheless, a large body of data demonstrates that apoptosis of untreated neutrophils typically ensues within 24 hours of cell isolation and in vitro culture. At the molecular level apoptosis is driven by executioner caspase-3, and during this process cell proinflammatory capacity and host defense functions are downregulated. We undertook the current study to determine the extent to which human neutrophil viability and function could be prolonged by treatment with the non-toxic, irreversible, pan-caspase inhibitor Q-VD-OPh. Our data demonstrate that a single 10 μM dose of this drug was sufficient to markedly prolong cell lifespan. Specifically, we show that apoptosis was prevented for at least 5 days as indicated by analysis of nuclear morphology, DNA fragmentation, and phosphatidylserine externalization together with measurements of procaspase-3 processing and caspase activity. Conversely, mitochondrial depolarization declined despite abundant Myeloid Cell Leukemia 1 (MCL-1). At the same time, glutathione levels were maintained and Q-VD-OPh prevented age-associated increases mitochondrial oxidative stress. Regarding functional capacity, we show that phagocytosis, NADPH oxidase activity, chemotaxis, and degranulation were maintained following Q-VD-OPh treatment, albeit to somewhat different extents. Thus, a single 10 μM dose of Q-VD-OPh can sustain human neutrophil viability and function for at least 5 days.

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.

G-protein-coupled estrogen receptor 1 promotes peritoneal metastasis of gastric cancer through nicotinamide adenine dinucleotide kinase 1-mediated redox modulation

Adipose tissue is the second most important site of estrogen production, where androgens are converted into estrogen by aromatase. While gastric cancer patients often develop adipocyte-rich peritoneal metastasis, the underlying mechanism remains unclear. In this study, we identified the G-protein-coupled estrogen receptor (GPER1) as a promoter of gastric cancer peritoneal metastasis. Functional in vitro studies revealed that β-Estradiol (E2) or the GPER1 agonist G1 inhibited anoikis in gastric cancer cells. Additionally, genetic overexpression or knockout of GPER1 significantly inhibited or enhanced gastric cancer cell anoikis in vitro and peritoneal metastasis in vivo, respectively. Mechanically, GPER1 knockout disrupted the NADPH pool and increased reactive oxygen species (ROS) generation. Conversely, overexpression of GPER1 had the opposite effects. GPER1 suppressed nicotinamide adenine dinucleotide kinase 1(NADK1) ubiquitination and promoted its phosphorylation, which were responsible for the elevated expression of NADK1 at protein levels and activity, respectively. Moreover, genetic inhibition of NADK1 disrupted NADPH and redox homeostasis, leading to high levels of ROS and significant anoikis, which inhibited lung and peritoneal metastasis in cell-based xenograft models. In summary, our study suggests that inhibiting GPER1-mediated NADK1 activity and its ubiquitination may be a promising therapeutic strategy for peritoneal metastasis of gastric cancer.

PVB exerts anti-inflammatory effects by inhibiting the activation of MAPK and NF-κB signaling pathways and ROS generation in neutrophils

Pinaverium bromide (PVB) has been shown to protect mice against sepsis, which is predominantly attributed to PVB-mediated anti-inflammatory effects by inhibiting primed neutrophils to produce proinflammatory cytokines. However, the underlying mechanism(s) by which PVB affects neutrophils remains unknown. In this study, we report that treatment with PVB either before or after LPS stimulation attenuated IL-1β and TNF-α expression at both mRNA and protein levels in LPS-activated murine neutrophils. Further experiments revealed that PVB inhibited the phosphorylation of ERK, JNK, and IκBα in LPS-stimulated murine neutrophils. Moreover, PVB reduced reactive oxygen species (ROS) levels via regulating NADPH oxidase 2 (NOX2) activity, as represented by inhibiting p47phox translocation from the cytoplasm to the cellular membrane. Importantly, PVB significantly attenuated IL-1β, TNF-α, IL-6, CXCL1 production in both LPS-stimulated low density neutrophils (LDNs) and normal density neutrophils (NDNs) isolated from septic patients. Collectively, we demonstrated that PVB exerts anti-inflammatory effect by attenuating ROS generation and suppressing the activation of MAPK and NF-κB signaling pathways, suggesting that PVB may act as a potential therapeutic agent for sepsis by inhibiting neutrophil priming and activation.

Regulation of nucleotide metabolism in cancers and immune disorders

Nucleotides are the foundational elements of life. Proliferative cells acquire nutrients for energy production and the synthesis of macromolecules, including proteins, lipids, and nucleic acids. Nucleotides are continuously replenished through the activation of the nucleotide synthesis pathways. Despite the importance of nucleotides in cell physiology, there is still much to learn about how the purine and pyrimidine synthesis pathways are regulated in response to intracellular and exogenous signals. Over the past decade, evidence has emerged that several signaling pathways [Akt, mechanistic target of rapamycin complex I (mTORC1), RAS, TP53, and Hippo-Yes-associated protein (YAP) signaling] alter nucleotide synthesis activity and influence cell function. Here, we examine the mechanisms by which these signaling networks affect de novo nucleotide synthesis in mammalian cells. We also discuss how these molecular links can be targeted in diseases such as cancers and immune disorders.

Excessive neutrophil extracellular trap formation induced by Porphyromonas gingivalis lipopolysaccharide exacerbates inflammatory responses in high glucose microenvironment

Introduction

Neutrophil extracellular trap (NET) is a novel defense strategy of neutrophils and found to be induced by Porphyromonas gingivalis (P. gingivalis) lipopolysaccharide (LPS) or high glucose. The aim of this study was to investigate the roles and mechanisms of NET formation in high glucose inflammatory microenvironment.

Methods

NETs induced by 1 μg/ml P. gingivalis LPS and/or 25 mM glucose were visualized using a fluorescence microscopy and the levels of extracellular DNA were determined by a microplate reader. The bactericidal efficiency of NETs was assessed by quantifying the survival P. gingivalis in neutrophils. The levels of NLRP3 and IL-1β in THP-1 derived-macrophages, and the expressions of p-PKC βII, p-MEK1/2, p-ERK1/2, ORAI1 and ORAI2 in neutrophils were detected by Western blot. Moreover, levels of intracellular Ca2+ and reactive oxygen species (ROS) in neutrophils were explored by flow cytometry.

Results

P. gingivalis LPS enhanced the formation of NETs and increased the levels of extracellular DNA in high glucose microenvironment (p < 0.05). Compared with normal glucose inflammatory microenvironment, quantities of extra- and intracellular viable P. gingivalis in neutrophils exposed to NETs induced in high glucose inflammatory one were increased (p < 0.05) and the expressions of NLRP3 and IL-1β were dramatically increased in macrophages co-cultured with NETs from high glucose inflammatory microenvironment (p < 0.05). In addition, levels of ROS, intracellular Ca²⁺, p-PKC βII, p-MEK1/2, p-ERK1/2, ORAI1 and ORAI2 were increased in neutrophils stimulated with both high glucose and P. gingivalis LPS compared with the single stimulus groups (p < 0.05).

Discussion

In high glucose inflammatory microenvironment, formation of NETs was enhanced via oxidative stress, which failed to reverse the decreased bactericidal capacity in high glucose microenvironment, and instead aggravated the subsequent inflammatory responses.

Molecular properties and regulation of NAD+ kinase (NADK)

Nicotinamide adenine dinucleotide (NAD⁺) kinase (NADK) phosphorylates NAD⁺, thereby producing nicotinamide adenine dinucleotide phosphate (NADP). Both NADK genes and the NADP(H)-producing mechanism are evolutionarily conserved among archaea, bacteria, plants and mammals. In mammals, NADK is activated by phosphorylation and protein-protein interaction. Recent studies conducted using genetically altered models validate the essential role of NADK in cellular redox homeostasis and metabolism in multicellular organisms. Here, we describe the evolutionary conservation, molecular properties, and signaling mechanisms and discuss the pathophysiological significance of NADK.

Neutrophil Activated by the Famous and Potent PMA (Phorbol Myristate Acetate)

This review will briefly outline the major signaling pathways in PMA-activated neutrophils. PMA is widely used to understand neutrophil pathways and formation of NETs. PMA activates PKC; however, we highlight some isoforms that contribute to specific functions. PKC α, β and δ contribute to ROS production while PKC βII and PKC ζ are involved in cytoskeleton remodeling. Actin polymerization is important for the chemotaxis of neutrophils and its remodeling is connected to ROS balance. We suggest that, although ROS and production of NETs are usually observed together in PMA-activated neutrophils, there might be a regulatory mechanism balancing both. Interestingly, we suggest that serine proteases might determine the PAD4 action. PAD4 could be responsible for the activation of the NF-κB pathway that leads to IL-1β release, triggering the cleavage of gasdermin D by serine proteases such as elastase, leading to pore formation contributing to release of NETs. On the other hand, when serine proteases are inhibited, NETs are formed by citrullination through the PAD4 pathway. This review puts together results from the last 31 years of research on the effects of PMA on the neutrophil and proposes new insights on their interpretation.

Crystal structure of human NADK2 reveals a dimeric organization and active site occlusion by lysine acetylation

NAD⁺ kinases (NADKs) are metabolite kinases that phosphorylate NAD⁺ molecules to make NADP⁺, a limiting substrate for the generation of reducing power NADPH. NADK2 sustains mitochondrial NADPH production that enables proline biosynthesis and antioxidant defense. However, its molecular architecture and mechanistic regulation remain undescribed. Here, we report the crystal structure of human NADK2, revealing a substrate-driven mode of activation. We find that NADK2 presents an unexpected dimeric organization instead of the typical tetrameric assemblage observed for other NADKs. A specific extended segment (aa 325-365) is crucial for NADK2 dimerization and activity. Moreover, we characterize numerous acetylation events, including those on Lys76 and Lys304, which reside near the active site and inhibit NADK2 activity without disrupting dimerization, thereby reducing mitochondrial NADP(H) production, proline synthesis, and cell growth. These findings reveal important molecular insight into the structure and regulation of a vital enzyme in mitochondrial NADPH and proline metabolism.

Switching to the cyclic pentose phosphate pathway powers the oxidative burst in activated neutrophils

Neutrophils are cells at the frontline of innate immunity that can quickly activate effector functions to eliminate pathogens upon stimulation. However, little is known about the metabolic adaptations that power these functions. Here we show rapid metabolic alterations in neutrophils upon activation, particularly drastic reconfiguration around the pentose phosphate pathway, which is specifically and quantitatively coupled to an oxidative burst. During this oxidative burst, neutrophils switch from glycolysis-dominant metabolism to a unique metabolic mode termed 'pentose cycle', where all glucose-6-phosphate is diverted into oxidative pentose phosphate pathway and net flux through upper glycolysis is reversed to allow substantial recycling of pentose phosphates. This reconfiguration maximizes NADPH yield to fuel superoxide production via NADPH oxidase. Disruptions of pentose cycle greatly suppress oxidative burst, the release of neutrophil extracellular traps and pathogen killing by neutrophils. Together, these results demonstrate the remarkable metabolic flexibility of neutrophils, which is essential for their functions as the first responders in innate immunity.

Redox Dysregulation in Aging and COPD: Role of NOX Enzymes and Implications for Antioxidant Strategies

With a rapidly growing elderly human population, the incidence of age-related lung diseases such as chronic obstructive pulmonary disease (COPD) continues to rise. It is widely believed that reactive oxygen species (ROS) play an important role in ageing and in age-related disease, and approaches of antioxidant supplementation have been touted as useful strategies to mitigate age-related disease progression, although success of such strategies has been very limited to date. Involvement of ROS in ageing is largely attributed to mitochondrial dysfunction and impaired adaptive antioxidant responses. NADPH oxidase (NOX) enzymes represent an important enzyme family that generates ROS in a regulated fashion for purposes of oxidative host defense and redox-based signalling, however, the associations of NOX enzymes with lung ageing or age-related lung disease have to date only been minimally addressed. The present review will focus on our current understanding of the impact of ageing on NOX biology and its consequences for age-related lung disease, particularly COPD, and will also discuss the implications of altered NOX biology for current and future antioxidant-based strategies aimed at treating these diseases.