Expression of Nox4 in osteoclasts

NOX4-reactive oxygen species axis: critical regulators of bone health and metabolism

Bone marrow stromal cells (BMSCs) play a significant role in bone metabolism as they can differentiate into osteoblasts, bone marrow adipocytes (BMAds), and chondrocytes. BMSCs chronically exposed to nutrient overload undergo adipogenic programming, resulting in bone marrow adipose tissue (BMAT) formation. BMAT is a fat depot transcriptionally, metabolically, and morphologically distinct from peripheral adipose depots. Reactive oxygen species (ROS) are elevated in obesity and serve as important signals directing BMSC fate. ROS produced by the NADPH oxidase (NOX) family of enzymes, such as NOX4, may be responsible for driving BMSC adipogenesis at the expense of osteogenic differentiation. The dual nature of ROS as both cellular signaling mediators and contributors to oxidative stress complicates their effects on bone metabolism. This review discusses the complex interplay between ROS and BMSC differentiation in the context of metabolic bone diseases.Special attention is paid to the role of NOX4-ROS in regulating cellular processes within the bone marrow microenvironment and potential target in metabolic bone diseases.

NADPH Oxidase 3: Beyond the Inner Ear

Reactive oxygen species (ROS) were formerly known as mere byproducts of metabolism with damaging effects on cellular structures. The discovery and description of NADPH oxidases (Nox) as a whole enzyme family that only produce this harmful group of molecules was surprising. After intensive research, seven Nox isoforms were discovered, described and extensively studied. Among them, the NADPH oxidase 3 is the perhaps most underrated Nox isoform, since it was firstly discovered in the inner ear. This stigma of Nox3 as "being only expressed in the inner ear" was also used by me several times. Therefore, the question arose whether this sentence is still valid or even usable. To this end, this review solely focuses on Nox3 and summarizes its discovery, the structural components, the activating and regulating factors, the expression in cells, tissues and organs, as well as the beneficial and detrimental effects of Nox3-mediated ROS production on body functions. Furthermore, the involvement of Nox3-derived ROS in diseases progression and, accordingly, as a potential target for disease treatment, will be discussed.

Nox4 as a novel therapeutic target for diabetic vascular complications

Diabetic vascular complications can affect both microvascular and macrovascular. Diabetic microvascular complications, such as diabetic nephropathy, diabetic retinopathy, diabetic neuropathy, and diabetic cardiomyopathy, are believed to be caused by oxidative stress. The Nox family of NADPH oxidases is a significant source of reactive oxygen species and plays a crucial role in regulating redox signaling, particularly in response to high glucose and diabetes mellitus. This review aims to provide an overview of the current knowledge about the role of Nox4 and its regulatory mechanisms in diabetic microangiopathies. Especially, the latest novel advances in the upregulation of Nox4 that aggravate various cell types within diabetic kidney disease will be highlighted. Interestingly, this review also presents the mechanisms by which Nox4 regulates diabetic microangiopathy from novel perspectives such as epigenetics. Besides, we emphasize Nox4 as a therapeutic target for treating microvascular complications of diabetes and summarize drugs, inhibitors, and dietary components targeting Nox4 as important therapeutic measures in preventing and treating diabetic microangiopathy. Additionally, this review also sums up the evidence related to Nox4 and diabetic macroangiopathy.

Resveratrol-Mediated Reversal of Doxorubicin-Induced Osteoclast Differentiation

Secondary osteoporosis has been associated with cancer patients undertaking Doxorubicin (DOX) chemotherapy. However, the molecular mechanisms behind DOX-induced bone loss have not been elucidated. Molecules that can protect against the adverse effects of DOX are still a challenge in chemotherapeutic treatments. We investigated the effect and mechanism of DOX in osteoclast differentiation and used the Sirt 1 activator resveratrol (RES) to counteract DOX-induced effects. RAW 264.7 cells were differentiated into osteoclasts under cotreatment with DOX and RES, alone or combined. RES treatment inhibited DOX-induced osteoclast differentiation, reduced the expression of osteoclast fusion marker Oc-stamp and osteoclast differentiation markers Rank, Trap, Ctsk and Nfatc1. Conversely, RES induced the upregulation of antioxidant genes Sod 1 and Nrf 2 while DOX significantly reduced the FoxM1 expression, resulting in oxidative stress. Treatment with the antioxidant MitoTEMPO did not influence DOX-induced osteoclast differentiation. DOX-induced osteoclastogenesis was studied using the cathepsin-K zebrafish reporter line (Tg[ctsk:DsRed]). DOX significantly increased ctsk signal, while RES cotreatment resulted in a significant reduction in ctsk positive cells. RES significantly rescued DOX-induced mucositis in this model. Additionally, DOX-exposed zebrafish displayed altered locomotor behavior and locomotory patterns, while RES significantly reversed these effects. Our research shows that RES prevents DOX-induced osteoclast fusion and activation in vitro and in vivo and reduces DOX-induced mucositis, while improving locomotion parameters.

Sexually Dimorphic Increases in Bone Mass Following Tissue-specific Overexpression of Runx1 in Osteoclast Precursors

Many metabolic bone diseases arise as a result excessive osteoclastic bone resorption, which has motivated efforts to identify new molecular targets that can inhibit the formation or activity of these bone-resorbing cells. Mounting evidence indicates that the transcription factor Runx1 acts as a transcriptional repressor of osteoclast formation. Prior studies using a conditional knockout approach suggested that Runx1 in osteoclast precursors acts as an inhibitor of osteoclastogenesis; however, the effects of upregulation of Runx1 on osteoclast formation remain unknown. In this study, we investigated the skeletal effects of conditional overexpression of Runx1 in preosteoclasts by crossing novel Runx1 gain-of-function mice (Rosa26-LSL-Runx1) with LysM-Cre transgenic mice. We observed a sex-dependent effect whereby overexpression of Runx1 in female mice increased trabecular bone microarchitectural indices and improved torsion biomechanical properties. These effects were likely mediated by delayed osteoclastogenesis and decreased bone resorption. Transcriptomics analyses during osteoclastogenesis revealed a distinct transcriptomic profile in the Runx1-overexpressing cells, with enrichment of genes related to redox signaling, apoptosis, osteoclast differentiation, and bone remodeling. These data further confirm the antiosteoclastogenic activities of Runx1 and provide new insight into the molecular targets that may mediate these effects.

Osteomyelitis, Oxidative Stress and Related Biomarkers

Bone is a very dynamic tissue, subject to continuous renewal to maintain homeostasis through bone remodeling, a process promoted by two cell types: osteoblasts, of mesenchymal derivation, are responsible for the deposition of new material, and osteoclasts, which are hematopoietic cells, responsible for bone resorption. Osteomyelitis (OM) is an invasive infectious process, with several etiological agents, the most common being Staphylococcus aureus, affecting bone or bone marrow, and severely impairing bone homeostasis, resulting in osteolysis. One of the characteristic features of OM is a strong state of oxidative stress (OS) with severe consequences on the delicate balance between osteoblastogenesis and osteoclastogenesis. Here we describe this, analyzing the effects of OS in bone remodeling and discussing the need for new, easy-to-measure and widely available OS biomarkers that will provide valid support in the management of the disease.

NOX4 blockade suppresses titanium nanoparticle-induced bone destruction via activation of the Nrf2 signaling pathway

Periprosthetic osteolysis (PPO) triggered by wear particles is the most severe complication of total joint replacement (TJR) surgeries, representing the major cause of implant failure, which is public health concern worldwide. Previous studies have confirmed the specialized role of osteoclast-induced progressive bone destruction in the progression of PPO. Additionally, the reactive oxygen species (ROS) induced by wear particles can promote excessive osteoclastogenesis and bone resorption. Nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4), a cellular enzyme, is considered to be responsible for the production of ROS and the formation of mature osteoclasts. However, NOX4 involvement in PPO has not yet been elucidated. Therefore, we investigated the mechanism by which NOX4 regulates osteoclast differentiation and the therapeutic effects on titanium nanoparticle-induced bone destruction. We found that NOX4 blockade suppressed osteoclastogenesis and enhanced the scavenging of intracellular ROS. Our rescue experiment revealed that nuclear factor-erythroid 2-related factor 2 (Nrf2) silencing reversed the effects of NOX4 blockade on ROS production and osteoclast differentiation. In addition, we found increased expression levels of NOX4 in PPO tissues, while NOX4 inhibition in vivo exerted protective effects on titanium nanoparticle-induced osteolysis through antiosteoclastic and antioxidant effects. Collectively, these findings suggested that NOX4 blockade suppresses titanium nanoparticle-induced bone destruction via activation of the Nrf2 signaling pathway and that NOX4 blockade may be an attractive therapeutic approach for preventing PPO.

Involvement of Rho-kinase/IκB-α/NF-κB activation in IL-1β-induced inflammatory response and oxidative stress in human chondrocytes

It has been clearly indicated that osteoarthritis (OA) is an inflammatory and degenerative disease that could be promoted by Rho-kinase (ROCK); however, little is known about the role of ROCK/inhibitor κB alpha (IκB-α)/nuclear factor-κB (NF-κB) p65 pathway activation in interleukin-1β (IL-1β) induced inflammatory response and oxidative stress in primary human chondrocytes. To test this hypothesis, we focused on determining ROCK-II, IκB-α, p-IκB-α, NF-κB p65, p-NF-κB p65, IL-6, tumor necrosis factor alpha (TNF-α), cyclooxygenase-2 (COX-2), p22phox, and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subtype 4 (NOX4) protein expression, ROCK-II activity, NADPH oxidase levels, and total antioxidant capacity (TAC) in the presence and absence of ROCK-inhibitor fasudil. IL-1β (2 ng·mL-1, 24 h) increased the expression of ROCK-II, p-IκB-α, NF-κB p65, p-NF-κB p65, IL-6, TNF-α, COX-2, and p22phox proteins, and decreased the expression of IκB-α, and the NOX4 protein level did not alter. ROCK activity and NADPH oxidase levels were increased, whereas the TAC was decreased by IL-1β. Fasudil (10-5-10-7 M) reversed all these changes induced by IL-1β. These results demonstrate that ROCK/IκB-α/NF-κB p65 pathway activation contributes to the IL-1β-induced inflammatory response and oxidative stress, and thus, ROCK inhibition might be a beneficial treatment option for OA patients mainly based on its anti-inflammatory and antioxidant effects.

NADPH oxidases in bone and cartilage homeostasis and disease: A promising therapeutic target

Reactive oxygen species (ROS) generated by the NADPH oxidase (Nox) enzymes are important short-range signaling molecules. They have been extensively studied in the physiology and pathophysiology of the cardiovascular system, where they have important roles in vascular inflammation, angiogenesis, hypertension, cardiac injury, stroke, and aging. Increasing evidence demonstrates that ROS and Nox enzymes also affect bone homeostasis and osteoporosis, and more recent studies implicate ROS and Nox enzymes in both inflammatory arthritis and osteoarthritis. Mechanistically, this connection may be through the effects of ROS on signal transduction. ROS affect both transforming growth factor-β/Smad signaling, interleukin-1β/nuclear factor-kappa B signaling, and the resulting changes in matrix metalloproteinase expression. The purpose of this review is to describe the role of Nox enzymes in the physiology and pathobiology of bone and joints and to highlight the potential of therapeutically targeting the Nox enzymes.

Porphyromonas gingivalis adopts intricate and unique molecular mechanisms to survive and persist within the host: a critical update

is an obligate, asaccharolytic, gram-negative bacteria commonly associated with increased periodontal and systemic inflammation. P. gingivalis is known to survive and persist within the host tissues as it modulates the entire ecosystem by either engineering its environment or modifying the host's immune response. It interacts with various host receptors and alters signaling pathways of inflammation, complement system, cell cycle, and apoptosis. P. gingivalis is even known to induce suicidal cell death of the host and other microbes in its vicinity with the emergence of pathobiont species. Recently, new molecular and immunological mechanisms and virulence factors of P. gingivalis that increase its chance of survival and immune evasion within the host have been discovered. Thus, the present paper aims to provide a consolidated update on the new intricate and unique molecular mechanisms and virulence factors of P. gingivalis associated with its survival, persistence, and immune evasion within the host.

Reactive Oxygen Species in Osteoclast Differentiation and Possible Pharmaceutical Targets of ROS-Mediated Osteoclast Diseases

Reactive oxygen species (ROS) and free radicals are essential for transmission of cell signals and other physiological functions. However, excessive amounts of ROS can cause cellular imbalance in reduction–oxidation reactions and disrupt normal biological functions, leading to oxidative stress, a condition known to be responsible for the development of several diseases. The biphasic role of ROS in cellular functions has been a target of pharmacological research. Osteoclasts are derived from hematopoietic progenitors in the bone and are essential for skeletal growth and remodeling, for the maintenance of bone architecture throughout lifespan, and for calcium metabolism during bone homeostasis. ROS, including superoxide ion (O₂⁻) and hydrogen peroxide (H₂O₂), are important components that regulate the differentiation of osteoclasts. Under normal physiological conditions, ROS produced by osteoclasts stimulate and facilitate resorption of bone tissue. Thus, elucidating the effects of ROS during osteoclast differentiation is important when studying diseases associated with bone resorption such as osteoporosis. This review examines the effect of ROS on osteoclast differentiation and the efficacy of novel chemical compounds with therapeutic potential for osteoclast related diseases.

Mammalian NADPH Oxidases

Reactive oxygen species (ROS) are highly reactive oxygen derivatives. Initially, they were considered as metabolic by-products (of mitochondria in particular), which consistently lead to aging and disease. Over the last decades, however, it became increasingly apparent that virtually all eukaryotic cells possess specifically ROS-producing enzymes, namely, NOX NADPH oxidases. In most mammals, there are seven NOX isoforms: three closely related isoforms, NOX1, 2, 3, which are activated by cytoplasmic subunits; NOX4, which appears to be constitutively active; and the EF-hand-containing Ca²⁺-activated isoforms NOX5 and DUOX1 and 2. Loss-of-function mutations in NOX genes can lead to serious human disease. NOX2 deficiency leads to primary immune deficiency, while DUOX2 deficiency presents as congenital hypothyroidism. Nox-deficient mice provide important tools to explore the physiological functions of various NADPH oxidases as a loss of function in Nox2, Nox3, and Duox2 leads to a spontaneous phenotype. The genetic absence of Nox1, Nox4, and Duox1 does not result in an obvious mouse phenotype (the NOX5 gene is absent in rodents and can therefore not be studied using knockout mice). Since the discovery of the NOX family at the turn of the millennium, much progress in understanding the biochemistry and the physiology of NOX has been made; however many questions remain unanswered to date. This chapter is an overview of our present knowledge on mammalian NOX/DUOX enzymes.

Nox2 Activity Is Required in Obesity-Mediated Alteration of Bone Remodeling

Despite increasing evidence suggesting a role for NADPH oxidases (Nox) in bone pathophysiology, whether Nox enzymes contribute to obesity-mediated bone remodeling remains to be clearly elucidated. Nox2 is one of the predominant Nox enzymes expressed in the bone marrow microenvironment and is a major source of ROS generation during inflammatory processes. It is also well recognized that a high-fat diet (HFD) induces obesity, which negatively impacts bone remodeling. In this work, we investigated the effect of Nox2 loss of function on obesity-mediated alteration of bone remodeling using wild-type (WT) and Nox2-knockout (KO) mice fed with a standard lab chow diet (SD) as a control or a HFD as an obesity model. Bone mineral density (BMD) of mice was assessed at the beginning and after 3 months of feeding with SD or HFD. Our results show that HFD increased bone mineral density to a greater extent in KO mice than in WT mice without affecting the total body weight and fat mass. HFD also significantly increased the number of adipocytes in the bone marrow microenvironment of WT mice as compared to KO mice. The bone levels of proinflammatory cytokines and proosteoclastogenic factors were also significantly elevated in WT-HFD mice as compared to KO-HFD mice. Furthermore, the in vitro differentiation of bone marrow cells into osteoclasts was significantly increased when using bone marrow cells from WT-HFD mice as compared to KO-HFD mice. Our data collectively suggest that Nox2 is implicated in HFD-induced deleterious bone remodeling by enhancing bone marrow adipogenesis and osteoclastogenesis.

Eurycoma longifolia, a promising suppressor of RANKL-induced differentiation and activation of osteoclasts: An in vitro mechanistic evaluation

Background

Eurycoma longifolia (E. longifolia) has gained remarkable recognition due to its promising efficacy of stimulating bone formation in androgen-deficient osteoporosis. Numerous in vivo studies have explored the effects of E. longifolia on osteoporosis; however, the in vitro cellular mechanism was not discovered yet.

Objectives

The present study was aimed to investigate the effect of E. longifolia on the proliferation, differentiation and maturation of osteoclasts and the translational mechanism of inhibition of osteoclastogenesis using RAW 264.7 cells as an in vitro osteoclastic model.

Materials and methods

Having assessed cytotoxicity, the cell viability, cell proliferation rate and osteoclastic differentiation capacity of E. longifolia was investigated by evaluating the tartrate-resistant acid phosphatase (TRAP) activity in receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL)-induced osteoclasts. Taken together, the time-mannered expression of osteoclast-related protein biomarkers such as matrix metallopeptidase-9 (MMP-9), cathepsin-K, TRAP, nuclear factor of activated T-cells cytoplasmic 1 (NFATc1), superoxide (free radicals) generation and superoxide dismutase activity were also measured to comprehend the mechanism of osteoclastogenesis.

Results

E. longifolia did not show significant effects on cytotoxicity and cell proliferation of RAW 264.7 cells; however, a significant inhibition of cells differentiation and maturation of osteoclasts was observed. Moreover, a significant down-regulation of RANKL-induced TRAP activity and expression of MMP-9, cathepsin-K, TRAP, NFATc1 and generation of superoxide and enhanced superoxide dismutase activity was observed in E. longifolia treated cell cultures.

Conclusion

We anticipated that E. longifolia that enhances bone regeneration on the one hand and suppresses osteoclast’s maturation on the other hand may have great therapeutic value in treating osteoporosis and other bone-erosive diseases such as rheumatoid arthritis and metastasis associated with bone loss.

NOX4 Deletion in Male Mice Exacerbates the Effect of Ethanol on Trabecular Bone and Osteoblastogenesis

Chronic alcohol consumption increases bone resorption and decreases bone formation. A major component of ethanol (EtOH) pathology in bone is the generation of excess reactive oxygen species (ROS). The ROS-generating NADPH oxidase-4 (NOX4) is proposed to drive much of the EtOH-induced suppression of bone formation. Here, 13-week-old male wild-type (WT) and NOX4^-/- mice were pair fed (PF) a high-fat (35%), Lieber-DeCarli liquid diet with or without EtOH at 30% of their total calories for 12 weeks. Micro-computed tomography analysis demonstrated significant decreases in trabecular bone volume/total volume (BV/TV) percentage and cortical thickness in WT, EtOH-fed mice compared with PF controls. EtOH-fed NOX4^-/- mice also displayed decreased trabecular BV/TV and trabecular number compared with PF (P < 0.05). However, NOX4^-/- mice were protected against EtOH-induced decreases in cortical thickness (P < 0.05) and decreases in collagen1 and osteocalcin mRNA expression in cortical bone (P < 0.05). In WT and NOX4^-/- vertebral bone, EtOH suppressed expression of Wnt signaling components that promote osteoblast maturation. A role for NOX4 in EtOH inhibition of osteoblast differentiation was further demonstrated by protection against EtOH inhibition of osteoblastogenesis in ex vivo bone marrow cultures from NOX4^-/-, but not p47^phox-/- mice lacking active NADPH oxidase-2. However, bone marrow cultures from NOX4^-/- mice formed fewer osteoblastic colonies compared with WT cultures (P < 0.05), suggesting a role for NOX4 in the maintenance of mesenchymal progenitor cell populations. These data suggest that NOX4 deletion is partially protective against EtOH effects on osteoblast differentiation, but may predispose bone to osteogenic impairments.

The Oxygen Paradox, the French Paradox, and age-related diseases

A paradox is a seemingly absurd or impossible concept, proposition, or theory that is often difficult to understand or explain, sometimes apparently self-contradictory, and yet ultimately correct or true. How is it possible, for example, that oxygen "a toxic environmental poison" could be also indispensable for life (Beckman and Ames Physiol Rev 78(2):547-81, 1998; Stadtman and Berlett Chem Res Toxicol 10(5):485-94, 1997)?: the so-called Oxygen Paradox (Davies and Ursini 1995; Davies Biochem Soc Symp 61:1-31, 1995). How can French people apparently disregard the rule that high dietary intakes of cholesterol and saturated fats (e.g., cheese and paté) will result in an early death from cardiovascular diseases (Renaud and de Lorgeril Lancet 339(8808):1523-6, 1992; Catalgol et al. Front Pharmacol 3:141, 2012; Eisenberg et al. Nat Med 22(12):1428-1438, 2016)?: the so-called, French Paradox. Doubtless, the truth is not a duality and epistemological bias probably generates apparently self-contradictory conclusions. Perhaps nowhere in biology are there so many apparently contradictory views, and even experimental results, affecting human physiology and pathology as in the fields of free radicals and oxidative stress, antioxidants, foods and drinks, and dietary recommendations; this is particularly true when issues such as disease-susceptibility or avoidance, "healthspan," "lifespan," and ageing are involved. Consider, for example, the apparently paradoxical observation that treatment with low doses of a substance that is toxic at high concentrations may actually induce transient adaptations that protect against a subsequent exposure to the same (or similar) toxin. This particular paradox is now mechanistically explained as "Adaptive Homeostasis" (Davies Mol Asp Med 49:1-7, 2016; Pomatto et al. 2017a; Lomeli et al. Clin Sci (Lond) 131(21):2573-2599, 2017; Pomatto and Davies 2017); the non-damaging process by which an apparent toxicant can activate biological signal transduction pathways to increase expression of protective genes, by mechanisms that are completely different from those by which the same agent induces toxicity at high concentrations. In this review, we explore the influences and effects of paradoxes such as the Oxygen Paradox and the French Paradox on the etiology, progression, and outcomes of many of the major human age-related diseases, as well as the basic biological phenomenon of ageing itself.

NADPH oxidase gp91phox contributes to RANKL-induced osteoclast differentiation by upregulating NFATc1

Bone-marrow derived monocyte-macrophages (BMMs) differentiate into osteoclasts by M-CSF along subsequent RANKL stimulation possibly in collaboration with many other unknown cytokines released by pre- or mature osteoblasts. The differentiation process requires receptor activator of nuclear factor kappa-B ligand (RANKL)/RANK signaling and reactive oxygen species (ROS) such as superoxide anion (O₂^•−). Gp91^phox, a plasma membrane subunit of NADPH oxidase (Nox), is constitutively expressed in BMMs and plays a major role in superoxide anion production. In this study, we found that mice deficient in gp91^phox (gp91^phox−/−) showed defects in osteoclast differentiation. Femurs of these mice produced osteoclasts at about 70% of the levels seen in femurs from wild-type mice, and accordingly exhibited excessive bone density. This abnormal bone growth in the femurs of gp91^phox−/− mice resulted from impaired osteoclast differentiation. In addition, gp91^phox−/− mice were defective for RANKL-induced expression of nuclear factor of activated T cells c1 (NFATc1). However, H₂O₂ treatment compensated for gp91^phox deficiency in BMMs, almost completely rescuing osteoclast differentiation. Treating wild-type BMMs with antioxidants and superoxide inhibitors resulted in a differentiation defect resembling the phenotype of gp91^phox−/− BMMs. Therefore, our results demonstrate that gp91^phox-derived superoxide is important for promoting efficient osteoclast differentiation by inducing NFATc1 as a downstream signaling mediator of RANK.

Diabetes and Kidney Disease: Role of Oxidative Stress

Intrarenal oxidative stress plays a critical role in the initiation and progression of diabetic kidney disease (DKD). Enhanced oxidative stress results from overproduction of reactive oxygen species (ROS) in the context of concomitant, insufficient antioxidant pathways. Renal ROS production in diabetes is predominantly mediated by various NADPH oxidases (NOXs), but a defective antioxidant system as well as mitochondrial dysfunction may also contribute. Recent Advances: Effective agents targeting the source of ROS generation hold the promise to rescue the kidney from oxidative damage and prevent subsequent progression of DKD. Critical Issues and Future Directions: In the present review, we summarize and critically analyze molecular and cellular mechanisms that have been demonstrated to be involved in NOX-induced renal injury in diabetes, with particular focus on the role of increased glomerular injury, the development of albuminuria, and tubulointerstitial fibrosis, as well as mitochondrial dysfunction. Furthermore, novel agents targeting NOX isoforms are discussed. Antioxid. Redox Signal. 25, 657-684.

Chronic Psychosocial Stress Impairs Bone Homeostasis: A Study in the Social Isolation Reared Rat

Chronic psychosocial stress is a key player in the onset and aggravation of mental diseases, including psychosis. Although a strong association between this psychiatric condition and other medical co-morbidities has been recently demonstrated, few data on the link between psychosis and bone homeostasis are actually available. The aim of this study was to investigate whether chronic psychosocial stress induced by 4 or 7 weeks of social isolation in drug-naïve male Wistar rats could alter bone homeostasis in terms of bone thickness, mineral density and content, as well as markers of bone formation and resorption (sclerostin, cathepsin K, and CTX-I). We found that bone mineral density was increased in rats exposed to 7 weeks of social isolation, while no differences were detected in bone mineral content and area. Moreover, 7 weeks of social isolation lead to increase of femur thickness with respect to controls, suggesting the development of a hyperostosis condition. Isolated rats showed no changes in sclerostin levels, a marker of bone formation, compared to grouped animals. Conversely, bone resorption markers were significantly altered after 7 weeks of social isolation in terms of decrease in cathepsin K and increase of CTX-I. No alterations were found after 4 weeks of isolation rearing. Our observations suggest that chronic psychosocial stress might affect bone homeostasis, more likely independently from drug treatment. Thus, the social isolation model might help to identify possible new therapeutic targets to treat the burden of chronic psychosocial stress and to attempt alternative therapy choices.

IL-1beta mediates MMP secretion and IL-1beta neosynthesis via upregulation of p22(phox) and NOX4 activity in human articular chondrocytes

OBJECTIVES

Osteoarthritis (OA) is characterized by a progressive alteration of the biochemical properties of the articular cartilage. Inflammation plays a major role in OA, particularly through the cytokine Interleukine-1β, promoting reactive oxygen species (ROS) generation and matrix metalloproteinases (MMP) synthesis by the chondrocytes, orchestrating matrix proteolysis. NADPH oxidases (NOX) are membrane enzymes dedicated to the production of ROS. Role of oxidative stress is well established in OA; however, contribution of NOX in this process is still poorly documented. In this study, we addressed the role of NOX in primary human articular chondrocytes (HAC) upon inflammatory conditions--namely IL-1β and OA.

DESIGN

HAC were collected from patients undergoing hip surgery. Chondrocytes were treated with IL-1β and NOX inhibitors Diphenylene Iodonium, GKT136901, Tiron and Heme oxygenase-1 before MMP expression and NOX activity assessment. Finally, NOX4 expression was compared between OA and non OA parts of hip cartilage (n = 14).

RESULTS

This study establishes for the first time in human that NOX4 is the main NOX isoform expressed in chondrocytes. We found a significant upregulation of NOX4 mRNA in OA chondrocytes. Expression of NOX4/p22(phox) as well as ROS production is enhanced by IL-1β. On the other hand, the use of NOX4 inhibitors decreased IL-1β-induced collagenase synthesis by chondrocytes. Moreover, our study support the existence of a redox dependant loop sustaining pro-catabolic pathways induced by IL-1β.

CONCLUSIONS

This study points out NOX4 as a new putative target in OA and suggests that NOX-targeted therapies could be of interest for the causal treatment of the pathology.

Voltage-Gated Proton Channels as Novel Drug Targets: From NADPH Oxidase Regulation to Sperm Biology

SIGNIFICANCE

Voltage-gated proton channels are increasingly implicated in cellular proton homeostasis. Proton currents were originally identified in snail neurons less than 40 years ago, and subsequently shown to play an important auxiliary role in the functioning of reactive oxygen species (ROS)-generating nicotinamide adenine dinucleotide phosphate (NADPH) oxidases. Molecular identification of voltage-gated proton channels was achieved less than 10 years ago. Interestingly, so far, only one gene coding for voltage-gated proton channels has been identified, namely hydrogen voltage-gated channel 1 (HVCN1), which codes for the HV1 proton channel protein. Over the last years, the first picture of putative physiological functions of HV1 has been emerging.

RECENT ADVANCES

The best-studied role remains charge and pH compensation during the respiratory burst of the phagocyte NADPH oxidase (NOX). Strong evidence for a role of HV1 is also emerging in sperm biology, but the relationship with the sperm NOX5 remains unclear. Probably in many instances, HV1 functions independently of NOX: for example in snail neurons, basophils, osteoclasts, and cancer cells.

CRITICAL ISSUES

Generally, ion channels are good drug targets; however, this feature has so far not been exploited for HV1, and hitherto no inhibitors compatible with clinical use exist. However, there are emerging indications for HV1 inhibitors, ranging from diseases with a strong activation of the phagocyte NOX (e.g., stroke) to infertility, osteoporosis, and cancer.

FUTURE DIRECTIONS

Clinically useful HV1-active drugs should be developed and might become interesting drugs of the future.

Reactive oxygen species and oxidative stress in osteoclastogenesis, skeletal aging and bone diseases

Osteoclasts are cells derived from bone marrow macrophages and are important in regulating bone resorption during bone homeostasis. Understanding what drives osteoclast differentiation and activity is important when studying diseases characterized by heightened bone resorption relative to formation, such as osteoporosis. In the last decade, studies have indicated that reactive oxygen species (ROS), including superoxide and hydrogen peroxide, are crucial components that regulate the differentiation process of osteoclasts. However, there are still many unanswered questions that remain. This review will examine the mechanisms by which ROS can be produced in osteoclasts as well as how it may affect osteoclast differentiation and activity through its actions on osteoclastogenesis signaling pathways. In addition, the contribution of ROS to the aging-associated disease of osteoporosis will be addressed and how targeting ROS may lead to the development of novel therapeutic treatment options.

Rosmarinic acid and arbutin suppress osteoclast differentiation by inhibiting superoxide and NFATc1 downregulation in RAW 264.7 cells

The present study investigated the effect of the natural polyphenols, rosmarinic acid and arbutin, on osteoclast differentiation in RAW 264.7 cells. Rosmarinic acid and arbutin suppressed osteoclast differentiation and had no cytotoxic effect on osteoclast precursor cells. Rosmarinic acid and arbutin inhibited superoxide production in a dose-dependent manner. mRNA expression of the master regulator of osteoclastogenesis, nuclear factor of activated T cells cytoplasmic 1 (NFATc1) and the osteoclast marker genes, matrix metalloproteinase-9, tartrate-resistant acid phosphatase and cathepsin-K, decreased following treatments with rosmarinic acid and arbutin. Furthermore, resorption activity decreased with the number of osteoclasts. These results suggest that rosmarinic acid and arbutin may be useful for the prevention and treatment of bone diseases, such as osteoporosis, through mechanisms involving inhibition of superoxide and downregulation of NFATc1.

NADPH oxidases in bone homeostasis and osteoporosis

Bone formation and degradation are perfectly coordinated. In case of an imbalance of these processes diseases occur associated with exaggerated formation of new bone or bone loss as in osteoporosis. Most studies investigating osteoporosis either focus on osteoblast or osteoclast function and differentiation. Both processes have been suggested to be affected by reactive oxygen species (ROS). Besides a potentially harmful role of ROS, these small molecules are important second messengers. The family of NADPH oxidases produces ROS in a controlled and targeted manner, to specifically regulate signal transduction. This review will highlight the role of reactive oxygen species in bone cell differentiation and bone-loss associated disease with a special focus on osteoporosis and NADPH oxidases as specialized sources of ROS.

LPS from P. gingivalis and hypoxia increases oxidative stress in periodontal ligament fibroblasts and contributes to periodontitis

Oxidative stress is characterized by an accumulation of reactive oxygen species (ROS) and plays a key role in the progression of inflammatory diseases. We hypothesize that hypoxic and inflammatory events induce oxidative stress in the periodontal ligament (PDL) by activating NOX4. Human primary PDL fibroblasts were stimulated with lipopolysaccharide from Porphyromonas gingivalis (LPS-PG), a periodontal pathogen bacterium under normoxic and hypoxic conditions. By quantitative PCR, immunoblot, immunostaining, and a specific ROS assay we determined the amount of NOX4, ROS, and several redox systems. Healthy and inflamed periodontal tissues were collected to evaluate NOX4 and redox systems by immunohistochemistry. We found significantly increased NOX4 levels after hypoxic or inflammatory stimulation in PDL cells (P < 0.001) which was even more pronounced after combination of the stimuli. This was accompanied by a significant upregulation of ROS and catalase (P < 0.001). However, prolonged incubation with both stimuli induced a reduction of catalase indicating a collapse of the protective machinery favoring ROS increase and the progression of inflammatory oral diseases. Analysis of inflamed tissues confirmed our hypothesis. In conclusion, we demonstrated that the interplay of NOX4 and redox systems is crucial for ROS formation which plays a pivotal role during oral diseases.

Immunohistochemical localization of Nox1, Nox4 and Mn-SOD in mouse femur during endochondral ossification

Enzymes synthesizing reactive oxygen (Nox family) have recently been identified. Elucidation of the production mechanism has been initiated, and the involvement of reactive oxygen in metabolism, intracellular transport, signal transmission and apoptosis has been reported. We immunohistochemically investigated expression and localization of the Nox family in endochondral ossification using a normal mouse femur. Weakly positive reactions with Nox1, Noxa1, and Noxo1 were observed in the zones of proliferative and prehypertrophic chondrocytes at 3 weeks of age. Nox4 was widely positive from the resting over the hypertrophic cell zone. At 18 weeks of age, none of the Nox types was expressed in chondrocytes as the zones disappeared. On the other hand, positive reactions with Nox1, Noxa1, Noxo1, and Nox4 were observed in osteoblasts in the zone of ossification at 3 weeks of age, and each Nox was also positive in osteoblasts arranged on the bone marrow side in the epiphyseal cartilage at 18 weeks of age. In addition, a reactive oxygen-eliminating enzyme, Mn-SOD, was observed only in prehypertrophic chondrocytes at 3 weeks of age, and not detected in osteoblasts. It was suggested that the Nox family is closely associated with endochondral ossification of the mouse femur, and Nox1 and Nox4 are closely involved in the chondrocyte maturation process and bone matrix formation.

Wild-type and mutant p53 differentially regulate NADPH oxidase 4 in TGF-β-mediated migration of human lung and breast epithelial cells

BACKGROUND

Transforming growth factor-beta (TGF-β) induces the epithelial-to-mesenchymal transition (EMT) leading to increased cell plasticity at the onset of cancer cell invasion and metastasis. Mechanisms involved in TGF-β-mediated EMT and cell motility are unclear. Recent studies showed that p53 affects TGF-β/SMAD3-mediated signalling, cell migration, and tumorigenesis. We previously demonstrated that Nox4, a Nox family NADPH oxidase, is a TGF-β/SMAD3-inducible source of reactive oxygen species (ROS) affecting cell migration and fibronectin expression, an EMT marker, in normal and metastatic breast epithelial cells. Our present study investigates the involvement of p53 in TGF-β-regulated Nox4 expression and cell migration.

METHODS

We investigated the effect of wild-type p53 (WT-p53) and mutant p53 proteins on TGF-β-regulated Nox4 expression and cell migration. Nox4 mRNA and protein, ROS production, cell migration, and focal adhesion kinase (FAK) activation were examined in three different cell models based on their p53 mutational status. H1299, a p53-null lung epithelial cell line, was used for heterologous expression of WT-p53 or mutant p53. In contrast, functional studies using siRNA-mediated knockdown of endogenous p53 were conducted in MDA-MB-231 metastatic breast epithelial cells that express p53-R280K and MCF-10A normal breast cells that have WT-p53.

RESULTS

We found that WT-p53 is a potent suppressor of TGF-β-induced Nox4, ROS production, and cell migration in p53-null lung epithelial (H1299) cells. In contrast, tumour-associated mutant p53 proteins (R175H or R280K) caused enhanced Nox4 expression and cell migration in both TGF-β-dependent and TGF-β-independent pathways. Moreover, knockdown of endogenous mutant p53 (R280K) in TGF-β-treated MDA-MB-231 metastatic breast epithelial cells resulted in decreased Nox4 protein and reduced phosphorylation of FAK, a key regulator of cell motility. Expression of WT-p53 or dominant-negative Nox4 decreased TGF-β-mediated FAK phosphorylation, whereas mutant p53 (R280K) increased phospho-FAK. Furthermore, knockdown of WT-p53 in MCF-10A normal breast epithelial cells increased basal Nox4 expression, whereas p53-R280K could override endogenous WT-p53 repression of Nox4. Remarkably, immunofluorescence analysis revealed MCF-10A cells expressing p53-R280K mutant showed an upregulation of Nox4 in both confluent and migrating cells.

CONCLUSIONS

Collectively, our findings define novel opposing functions for WT-p53 and mutant p53 proteins in regulating Nox4-dependent signalling in TGF-β-mediated cell motility.

NADPH oxidase 4 limits bone mass by promoting osteoclastogenesis

ROS are implicated in bone diseases. NADPH oxidase 4 (NOX4), a constitutively active enzymatic source of ROS, may contribute to the development of such disorders. Therefore, we studied the role of NOX4 in bone homeostasis. Nox4(-/-) mice displayed higher bone density and reduced numbers and markers of osteoclasts. Ex vivo, differentiation of monocytes into osteoclasts with RANKL and M-CSF induced Nox4 expression. Loss of NOX4 activity attenuated osteoclastogenesis, which was accompanied by impaired activation of RANKL-induced NFATc1 and c-JUN. In an in vivo model of murine ovariectomy–induced osteoporosis, pharmacological inhibition or acute genetic knockdown of Nox4 mitigated loss of trabecular bone. Human bone obtained from patients with increased osteoclast activity exhibited increased NOX4 expression. Moreover, a SNP of NOX4 was associated with elevated circulating markers of bone turnover and reduced bone density in women. Thus, NOX4 is involved in bone loss and represents a potential therapeutic target for the treatment of osteoporosis.

Glutathione attenuates ethanol-induced alveolar macrophage oxidative stress and dysfunction by downregulating NADPH oxidases

Chronic alcohol abuse increases lung oxidative stress and susceptibility to respiratory infections by impairing alveolar macrophage (AM) function. NADPH oxidases (Nox) are major sources of reactive oxygen species in AMs. We hypothesized that treatment with the critical antioxidant glutathione (GSH) attenuates chronic alcohol-induced oxidative stress by downregulating Noxes and restores AM phagocytic function. Bronchoalveolar lavage (BAL) fluid and AMs were isolated from male C57BL/6J mice (8-10 wk) treated ± ethanol in drinking water (20% wt/vol, 12 wk) ± orally gavaged GSH in methylcellulose vehicle (300 mg x kg(-1) x day(-1), during week 12). MH-S cells, a mouse AM cell line, were treated ± ethanol (0.08%, 3 days) ± GSH (500 μM, 3 days or last 1 day of ethanol). BAL and AMs were also isolated from ethanol-fed and control mice ± inoculated airway Klebsiella pneumoniae (200 colony-forming units, 28 h) ± orally gavaged GSH (300 mg/kg, 24 h). GSH levels (HPLC), Nox mRNA (quantitative RT-PCR) and protein levels (Western blot and immunostaining), oxidative stress (2',7'-dichlorofluorescein-diacetate and Amplex Red), and phagocytosis (Staphylococcus aureus internalization) were measured. Chronic alcohol decreased GSH levels, increased Nox expression and activity, enhanced oxidative stress, impaired phagocytic function in AMs in vivo and in vitro, and exacerbated K. pneumonia-induced oxidative stress. Although how oral GSH restored GSH pools in ethanol-fed mice is unknown, oral GSH treatments abrogated the detrimental effects of chronic alcohol exposure and improved AM function. These studies provide GSH as a novel therapeutic approach for attenuating alcohol-induced derangements in AM Nox expression, oxidative stress, dysfunction, and risk for pneumonia.

Heme oxygenase-1 regulates matrix metalloproteinase MMP-1 secretion and chondrocyte cell death via Nox4 NADPH oxidase activity in chondrocytes

Interleukin-1β (IL-1β) activates the production of reactive oxygen species (ROS) and secretion of MMPs as well as chondrocyte apoptosis. Those events lead to matrix breakdown and are key features of osteoarthritis (OA). We confirmed that in human C-20/A4 chondrocytes the NADPH oxidase Nox4 is the main source of ROS upon IL-1β stimulation. Since heme molecules are essential for the NADPH oxidase maturation and activity, we therefore investigated the consequences of the modulation of Heme oxygenase-1 (HO-1), the limiting enzyme in heme catabolism, on the IL-1β signaling pathway and more specifically on Nox4 activity. Induction of HO-1 expression decreased dramatically Nox4 activity in C-20/A4 and HEK293 T-REx™ Nox4 cell lines. Unexpectedly, this decrease was not accompanied by any change in the expression, the subcellular localization or the maturation of Nox4. In fact, the inhibition of the heme synthesis by succinylacetone rather than heme catabolism by HO-1, led to a confinement of the Nox4/p22^phox heterodimer in the endoplasmic reticulum with an absence of redox differential spectrum highlighting an incomplete maturation. Therefore, the downregulation of Nox4 activity by HO-1 induction appeared to be mediated by carbon monoxide (CO) generated from the heme degradation process. Interestingly, either HO-1 or CO caused a significant decrease in the expression of MMP-1 and DNA fragmentation of chondrocytes stimulated by IL-1β. These results all together suggest that a modulation of Nox4 activity via heme oxygenase-1 may represent a promising therapeutic tool in osteoarthritis.

Selenium in bone health: roles in antioxidant protection and cell proliferation

Selenium (Se) is an essential trace element for humans and animals, and several findings suggest that dietary Se intake may be necessary for bone health. Such findings may relate to roles of Se in antioxidant protection, enhanced immune surveillance and modulation of cell proliferation. Elucidation of the mechanisms by which Se supports these cellular processes can lead to a better understanding of the role of this nutrient in normal bone metabolism. This article reviews the current knowledge concerning the molecular functions of Se relevant to bone health.

From form to function: the role of Nox4 in the cardiovascular system

The NADPH oxidase (Nox) family of proteins is comprised of seven members, including Noxes1–5 and the Duoxes 1 and 2. Nox4 is readily distinguished from the other Nox isoforms by its high level of expression in cardiovascular tissues and unique enzymatic properties. Nox4 is constitutively active and the amount of reactive oxygen species (ROS) contributed by Nox4 is primarily regulated at the transcriptional level although there is recent evidence for post-translational control. Nox4 emits a different pattern of ROS and its subcellular localizations, tissue distribution and influence over signaling pathways is different from the other Nox enzymes. Previous investigations have revealed that Nox4 is involved in oxygen sensing, vasomotor control, cellular proliferation, differentiation, migration, apoptosis, senescence, fibrosis, and angiogenesis. Elevated expression of Nox4 has been reported in a number of cardiovascular diseases, including atherosclerosis, pulmonary fibrosis, and hypertension, cardiac failure and ischemic stroke. However, many important questions remain regarding the functional significance of Nox4 in health and disease, including the role of Nox4 subcellular localization and its downstream targets. The goal of this review is to summarize the recent literature on the genetic and enzymatic regulation, subcellular localization, signaling pathways, and the role of Nox4 in cardiovascular disease states.

Nox4 involvement in TGF-beta and SMAD3-driven induction of the epithelial-to-mesenchymal transition and migration of breast epithelial cells

The epithelial-to-mesenchymal transition (EMT) is the development of increased cell plasticity that occurs normally during wound healing and embryonic development and can be coopted for cancer invasion and metastasis. TGF-beta induces EMT but the mechanism is unclear. Our studies suggest that Nox4, a member of the NADPH oxidase (Nox) family, is a source of reactive oxygen species (ROS) affecting cell migration and fibronectin expression, an EMT marker, in normal and metastatic breast epithelial cells. We found that TGF-beta induces Nox4 expression (mRNA and protein) and ROS generation in normal (MCF10A) and metastatic (MDA-MB-231) human breast epithelial cells. Conversely, cells expressing a dominant-negative form of Nox4 or Nox4-targeted shRNA showed significantly lower ROS production on TGF-beta treatment. Expression of a constitutively active TGF-beta receptor type I significantly increased Nox4 promoter activity, mRNA and protein expression, and ROS generation. Nox4 transcriptional regulation by TGF-beta was SMAD3 dependent based on the effect of constitutively active SMAD3 increasing Nox4 promoter activity, whereas dominant-negative SMAD3 or SIS3, a SMAD3-specific inhibitor, had the opposite effect. Furthermore, Nox4 knockdown, dominant-negative Nox4 or SMAD3, or SIS3 blunted TGF-beta induced wound healing and cell migration, whereas cell proliferation was not affected. Our experiments further indicate that Nox4 plays a role in TGF-beta regulation of fibronectin mRNA expression, based on the effects of dominant-negative Nox4 in reducing fibronectin mRNA in TGF-beta-treated MDA-MB-231and MCF10A cells. Collectively, these data indicate that Nox4 contributes to NADPH oxidase-dependent ROS production that may be critical for the progression of the EMT in breast epithelial cells, and thereby has therapeutic implications.

Biochemistry, physiology, and pathophysiology of NADPH oxidases in the cardiovascular system

The NADPH oxidase (Nox) enzymes are critical mediators of cardiovascular physiology and pathophysiology. These proteins are expressed in virtually all cardiovascular cells, and regulate such diverse functions as differentiation, proliferation, apoptosis, senescence, inflammatory responses and oxygen sensing. They target a number of important signaling molecules, including kinases, phosphatases, transcription factors, ion channels, and proteins that regulate the cytoskeleton. Nox enzymes have been implicated in many different cardiovascular pathologies: atherosclerosis, hypertension, cardiac hypertrophy and remodeling, angiogenesis and collateral formation, stroke, and heart failure. In this review, we discuss in detail the biochemistry of Nox enzymes expressed in the cardiovascular system (Nox1, 2, 4, and 5), their roles in cardiovascular cell biology, and their contributions to disease development.

Ethanol induces oxidative stress in alveolar macrophages via upregulation of NADPH oxidases

Chronic alcohol abuse is a comorbid variable of acute respiratory distress syndrome. Previous studies showed that, in the lung, chronic alcohol consumption increased oxidative stress and impaired alveolar macrophage (AM) function. NADPH oxidases (Noxes) are the main source of reactive oxygen species in AMs. Therefore, we hypothesized that chronic alcohol consumption increases AM oxidant stress through modulation of Nox1, Nox2, and Nox4 expression. AMs were isolated from male C57BL/6J mice, aged 8-10 wk, which were treated with or without ethanol in drinking water (20% w/v, 12 wk). MH-S cells, a mouse AM cell line, were treated with or without ethanol (0.08%, 3 d) for in vitro studies. Selected cells were treated with apocynin (300 μM), a Nox1 and Nox2 complex formation inhibitor, or were transfected with Nox small interfering RNAs (20-35 nM), before ethanol exposure. Human AMs were isolated from alcoholic and control patients' bronchoalveolar lavage fluid. Nox mRNA levels (quantitative RT-PCR), protein levels (Western blot and immunostaining), oxidative stress (2',7'-dichlorofluorescein-diacetate and Amplex Red analysis), and phagocytosis (Staphylococcus aureus internalization) were measured. Chronic alcohol increased Nox expression and oxidative stress in mouse AMs in vivo and in vitro. Experiments using apocynin and Nox small interfering RNAs demonstrated that ethanol-induced Nox4 expression, oxidative stress, and AM dysfunction were modulated through Nox1 and Nox2 upregulation. Further, Nox1, Nox2, and Nox4 protein levels were augmented in human AMs from alcoholic patients compared with control subjects. Ethanol induces AM oxidative stress initially through upregulation of Nox1 and Nox2 with downstream Nox4 upregulation and subsequent impairment of AM function.

Free radicals and extrinsic skin aging

Human skin is constantly directly exposed to the air, solar radiation, environmental pollutants, or other mechanical and chemical insults, which are capable of inducing the generation of free radicals as well as reactive oxygen species (ROS) of our own metabolism. Extrinsic skin damage develops due to several factors: ionizing radiation, severe physical and psychological stress, alcohol intake, poor nutrition, overeating, environmental pollution, and exposure to UV radiation (UVR). It is estimated that among all these environmental factors, UVR contributes up to 80%. UV-induced generation of ROS in the skin develops oxidative stress, when their formation exceeds the antioxidant defence ability of the target cell. The primary mechanism by which UVR initiates molecular responses in human skin is via photochemical generation of ROS mainly formation of superoxide anion (O₂^−∙), hydrogen peroxide (H₂O₂), hydroxyl radical (OH^∙), and singlet oxygen (¹O₂). The only protection of our skin is in its endogenous protection (melanin and enzymatic antioxidants) and antioxidants we consume from the food (vitamin A, C, E, etc.). The most important strategy to reduce the risk of sun UVR damage is to avoid the sun exposure and the use of sunscreens. The next step is the use of exogenous antioxidants orally or by topical application and interventions in preventing oxidative stress and in enhanced DNA repair.

Platinum nanoparticles suppress osteoclastogenesis through scavenging of reactive oxygen species produced in RAW264.7 cells

Recent research has shown that platinum nanoparticles (nano-Pt) efficiently quench reactive oxygen species (ROS) as a reducing catalyst. ROS have been suggested to regulate receptor activator of NF-κB ligand (RANKL)-stimulated osteoclast differentiation. In the present study, we examined the direct effects of platinum nano-Pt on RANKL-induced osteoclast differentiation of murine pre-osteoclastic RAW 264.7 cells. The effect of the nano-Pt on the number of osteoclasts was measured and their effect on the mRNA expression for osteoclast differentiation was assayed using real-time PCR. Nano-Pt appeared to have a ROS-scavenging activity. Nano-Pt decreased the number of osteoclasts (2+ nuclei) and large osteoclasts (8+ nuclei) in a dose-dependent manner without affecting cell viability. In addition, this agent significantly blocked RANKL-induced mRNA expression of osteoclastic differentiation genes such as c-fms, NFATc1, NFATc2, and DC-STAMP as well as that of osteoclast-specific marker genes including MMP-9, Cath-K, CLC7, ATP6i, CTR, and TRAP. Although nano-Pt attenuated expression of the ROS-producing NOX-family oxidases, Nox1 and Nox4, they up-regulated expression of Nox2, the major Nox enzyme in macrophages. These findings suggest that the nano-Pt inhibit RANKL-stimulated osteoclast differentiation via their ROS scavenging property. The use of nano-Pt as scavengers of ROS that is generated by RANKL may be a novel and innovative therapy for bone diseases.

Novel Nox homologues in the vasculature: focusing on Nox4 and Nox5

The Noxes (NADPH oxidases) are a family of ROS (reactive oxygen species)-generating enzymes. Of the seven family members, four have been identified as important sources of ROS in the vasculature: Nox1, Nox2, Nox4 and Nox5. Although Nox isoforms can be influenced by the same stimulus and co-localize in cellular compartments, their tissue distribution, subcellular regulation, requirement for cofactors and NADPH oxidase subunits and ability to generate specific ROS differ, which may help to understand the multiplicity of biological functions of these oxidases. Nox4 and Nox5 are the newest isoforms identified in the vasculature. Nox4 is the major isoform expressed in renal cells and appear to produce primarily H2O2. The Nox5 isoform produces ROS in response to increased levels of intracellular Ca2+ and does not require the other NADPH oxidase subunits for its activation. The present review focuses on these unique Noxes, Nox4 and Nox5, and provides novel concepts related to the regulation and interaction in the vasculature, and discusses new potential roles for these isoforms in vascular biology.

Ultrastructural analysis and electron microscopic localization of Nox4 in healthy and atherosclerotic human aorta

During diverse pathological conditions, vascular smooth muscle cells (SMCs) characteristically change from a quiescent, contractile phenotype to a proliferative, synthetic state, migrate toward the intima, and synthesize excess extracellular matrix. Although reactive oxygen species (ROS) are generally considered to be toxic to cells, recent evidence suggests that they may also modulate multiple signaling pathways. The vascular system contains several sources of ROS, among which NADPH oxidases (NOXes) have been shown to take an important part in the regulation of cell function, with effects on growth and proliferation. In the present study, the authors investigate the ultrastructural features of SMCs and the expression profile of Nox4 in healthy and atherosclerotic human aorta to explore the possibility of a relationship between Nox4 and SMCs differentiation state. The data extend at the level of immunoelectron microscopy previous observations, demonstrating for the first time the precise distribution and the differential expression of Nox4 in the morphologically distinct SMC types of healthy and diseased human aorta.

Role of mitochondrial reactive oxygen species in osteoclast differentiation

Previously we showed that hypoxia-induced mitochondrial respiratory stress in RAW 264.7 macrophages and other cells caused activation of retrograde signaling (also known as mitochondrial respiratory stress signaling) and the appearance of tartrate-resistant acid phosphatase (TRAP)-positive cells. In the present study, we used N-acetyl cysteine and ascorbate (general antioxidants) and MitoQ, a mitochondria-specific antioxidant, to investigate the role of intracellular reactive oxygen species (ROS) in osteoclast differentiation. Our results show that hypoxia-mediated mitochondrial dysfunction, as tested by disruption of mitochondrial transmembrane potential, was suppressed by MitoQ as well as by the other antioxidants. These agents also suppressed the activation of mitochondrial retrograde signaling. Interestingly, in terms of molar concentrations, MitoQ was more than 1000-fold more effective than general antioxidants in suppressing the receptor activator of nuclear factor-B ligand-induced differentiation of RAW 264.7 cells into multinucleated and TRAP-positive osteoclasts. We propose that mitochondrial function and intramitochondrial ROS play important roles in osteoclastogenesis.

Nox proteins in signal transduction

The NADPH oxidase (Nox) family of superoxide (O(2)(*-)) and hydrogen peroxide (H(2)O(2))-producing proteins has emerged as an important source of reactive oxygen species (ROS) in signal transduction. ROS produced by Nox proteins Nox1-5 and Duox1/2 are now recognized to play essential roles in the physiology of the brain, the immune system, the vasculature, and the digestive tract as well as in hormone synthesis. Nox-derived ROS have been implicated in regulation of cytoskeletal remodeling, gene expression, proliferation, differentiation, migration, and cell death. These processes are tightly controlled and reversible. In this review, we will discuss recent literature on Nox protein tissue distribution, subcellular localization, activation, and the resulting signal transduction mechanisms.

Translation-linked mRNA destabilization accompanying serum-induced Nox4 expression in human endothelial cells

NADPH oxidase is involved in cell signaling, regulating proliferation of vascular cells, especially in endothelium. The Nox4 catalytic subunit has a major role in endothelial cells, but growth arrest of cultured endothelial cells following serum deprivation paradoxically increases mRNA for Nox4. We investigated the relationships between Nox4 mRNA stability and protein expression in human microvascular endothelial cells. Serum starvation increased the steady-state level of Nox4 mRNA but paradoxically diminished Nox4 protein expression. mRNA transcription in the absence of serum is maintained by the p38MAP kinase pathway, for inhibition of p38MAP kinase reduced both Nox4 mRNA and Nox4 promoter activity. In serum-starved cells, reintroduction of serum increased Nox4 protein levels within 30 min and up to 24 h. In contrast, the mRNA decreased equally rapidly after serum stimulation. Inhibition of Nox4 translation by cycloheximide blocked serum-induced mRNA degradation and Nox4 protein synthesis, and actinomycin-D also delayed Nox4 mRNA decay. Therefore, Nox4 mRNA level falls after serum stimulation because of a translation-initiated mRNA destabilization program. Clearly Nox4 mRNA is regulated at both transcriptional and post-transcriptional levels, and the steady state level of Nox4 mRNA does not accurately reflect Nox4 protein abundance and functions, with implications for regulation of cell proliferation and survival.

Receptor activator of nuclear factor-kappaB ligand-induced mouse osteoclast differentiation is associated with switching between NADPH oxidase homologues

Reactive oxygen species (ROS) have been suggested to regulate receptor activator of nuclear factor-kappaB ligand (RANKL)-stimulated osteoclast differentiation. Stimulation of wild-type mouse bone marrow monocyte/macrophage lineage (BMM) cells by RANKL down-regulated NADPH oxidase 2 (Nox2) mRNA expression by half. RANKL reciprocally increased Nox1 mRNA levels and newly induced Nox4 transcript expression. BMM cells from Nox1 knockout (Nox1(-/-)) as well as Nox2(-/-) mice generated ROS in response to RANKL and differentiated into osteoclasts in the same way as wild-type BMM cells, which was assessed by the appearance of tartrate-resistant acid phosphatase-positive, multinucleated cells having the ability to form resorption pits and by the expression of osteoclast marker genes. A small interfering RNA (siRNA) targeting Nox1 or Nox2 failed to inhibit the RANKL-stimulated ROS generation and osteoclast formation in wild-type cells, whereas Nox1 and Nox2 siRNAs significantly suppressed the ROS generation and osteoclast formation in Nox2(-/-) and Nox1(-/-) cells, respectively. We also confirmed that Nox4 siRNA did not affect the RANKL-dependent events in Nox2(-/-) cells, whereas p22(phox) siRNA suppressed the events in both wild-type and Nox1(-/-) cells. Collectively, our results suggest that there may be a flexible compensatory mechanism between Nox1 and Nox2 for RANKL-stimulated ROS generation to facilitate osteoclast differentiation.

NADPH oxidase-derived reactive oxygen species are essential for differentiation of a mouse macrophage cell line (RAW264.7) into osteoclasts

Reactive oxygen species (ROS) derived from NADPH oxidase (Nox) homologues have been suggested to regulate osteoclast differentiation. However, no bone abnormalities have been documented in Nox1 deficient, Nox2 deficient, or Nox3 mutant mice. During receptor activator of nuclear factor-kappaB ligand (RANKL)-stimulated differentiation of a mouse macrophage cell line (RAW264.7) into osteoclasts, mRNA levels of Nox enzymes (Nox1-4) and their adaptor proteins were monitored by real-time reverse transcriptase PCR. RAW264.7 cells constitutively expressed abundant Nox2 mRNA and small amounts of Nox1 and Nox3 transcripts. RANKL markedly attenuated Nox2 mRNA expression in association with reciprocal up-regulation of Nox1 and Nox3 transcripts. Introduction of small interference RNA targeting p67(phox) or p22(phox) into RAW264.7 cells effectively down-regulated ROS generation and significantly suppressed the RANKL-stimulated differentiation, which was assessed by appearance of tartrate resistant acid phosphatase (TRAP)-positive, multinucleated cells having an ability to form resorption pits on calcium phosphate thin film-coated disks, and by expression of osteoclast marker genes (TRAP, cathepsin K, Atp6i, ClC-7, and NFATc1). Our results suggest that RANKL may stimulate switching between Nox homologues during osteoclast differentiation, and Nox-derived ROS may be crucial for RANKL-induced osteoclast differentiation.

Role of NADPH oxidase in formation and function of multinucleated giant cells

Macrophages play essential roles in a wide variety of physiological and pathological processes. One of the unique features of these phagocytic leukocytes is their ability to fuse, forming multinucleated giant cells. Multinucleated giant cells are important mediators of tissue remodeling and repair and are also responsible for removal or sequestration of foreign material, intracellular bacteria and non-phagocytosable pathogens, such as parasites and fungi. Depending on the tissue where fusion occurs and the inflammatory insult, multinucleated giant cells assume distinctly different phenotypes. Nevertheless, the ultimate outcome is the formation of large cells that can resorb bone tissue (osteoclasts) or foreign material and pathogens (giant cells) extracellularly. While progress has been made in recent years, the mechanisms and factors involved in macrophage fusion are still not fully understood. In addition to cytokines and a number of adhesion proteins and receptors, it is becoming increasingly clear that NADPH oxidase-generated reactive oxygen species (ROS) also play an important role in macrophage fusion. In this review, we provide an overview of macrophage multinucleation, with a specific focus on the role of NADPH oxidases and ROS in macrophage fusion and in the function of multinucleated giant cells. In addition, we provide an updated overview of the role of these cells in inflammation and various autoimmune diseases.

Oxidative stress, free radicals and bone remodeling

Reactive oxygen species (ROS) are widely considered to be a causal factor in aging and in a number of pathological conditions, such as atherosclerosis, carcinogenesis and infarction. Their role in bone metabolism is dual, considering their effects under physiological or pathological conditions. Under physiological conditions, the production of ROS by osteoclasts helps accelerate destruction of calcified tissue, thus assisting in bone remodeling. In pathological conditions, when a bone fractures, e.g., radical generation is remarkably high. However, though the increases in osteoclastic activity and ROS production are linked in many skeletal pathologies, it remains to be clarified whether increased ROS production overwhelms antioxidant defenses, leaving the individual open to hyperoxidant stress.

Mitochondrial H2O2 emission and cellular redox state link excess fat intake to insulin resistance in both rodents and humans

High dietary fat intake leads to insulin resistance in skeletal muscle, and this represents a major risk factor for type 2 diabetes and cardiovascular disease. Mitochondrial dysfunction and oxidative stress have been implicated in the disease process, but the underlying mechanisms are still unknown. Here we show that in skeletal muscle of both rodents and humans, a diet high in fat increases the H(2)O(2)-emitting potential of mitochondria, shifts the cellular redox environment to a more oxidized state, and decreases the redox-buffering capacity in the absence of any change in mitochondrial respiratory function. Furthermore, we show that attenuating mitochondrial H(2)O(2) emission, either by treating rats with a mitochondrial-targeted antioxidant or by genetically engineering the overexpression of catalase in mitochondria of muscle in mice, completely preserves insulin sensitivity despite a high-fat diet. These findings place the etiology of insulin resistance in the context of mitochondrial bioenergetics by demonstrating that mitochondrial H(2)O(2) emission serves as both a gauge of energy balance and a regulator of cellular redox environment, linking intracellular metabolic balance to the control of insulin sensitivity.

Enhanced expression of NADPH oxidase Nox4 in human gliomas and its roles in cell proliferation and survival

Reactive oxygen species (ROS) have been attracting attention as mediators of various cell-signaling pathways. Nox-family NADPH oxidases have proven to be a major source of ROS production in various cell types and have crucial roles in various physiological and pathological processes. In this study, we show that Nox4, a member of Nox family, is prominently expressed in various neuroepithelial tumors by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemical studies. We quantified Nox4 mRNA expression by real-time PCR in tumor specimens from 58 patients with astrocytomas and found that the expression levels of Nox4 mRNA in glioblastomas (WHO grade IV) were significantly higher than those in other astrocytomas (WHO grade II and III). In addition, we show that specific knockdown of Nox4 expression by RNA interference results in cell-growth inhibition and enhances induction of apoptosis by chemotherapeutic agents, such as cisplatin, in cultured glioma cell lines. Based on these observations, enhanced expression of Nox4 appears to be involved in cell proliferation and survival in glioma cells.