MAO-A-induced mitogenic signaling is mediated by reactive oxygen species, MMP-2, and the sphingolipid pathway

Alcohol-exacerbates post-traumatic stress psychiatric behavior and its neuropathological sequalae in experimental mice: preventive effects of morin

Posttraumatic stress disorder (PTSD) and alcohol use disorder (AUD) are very prevalent and co-occurring. It is unclear how alcohol exacerbates PTSD predicaments owing to less characterized pathophysiological mechanisms. Also, studies on pharmacological agents that can effectively reverse PTSD-AUD comorbidity have, to date, been scarce. Hence, we designed a methodological approach to investigate the pathophysiological mechanisms and pharmacological outcomes of morin, a neuroprotective flavonoid in mice. After 7 days of PTSD following single-prolonged stress (SPS) induction in mice, the PTSD mice were exposed to intermittent binge ethanol administration using ethanol (2g/kg, oral gavage) every other day, alongside daily morin (50 and 100mg/kg) or fluoxetine (10mg/kg) from days 8-21. The consequences of PTSD-AUD behavior, hypothalamic-pituitary-adrenal-axis (HPA-axis) dysfunction, neurochemistry, oxidative/nitrergic stress, and inflammation were evaluated in the prefrontal-cortex (PFC), striatum, and hippocampus of mice. The exacerbated anxiety-like behavior, and spatial/non-spatial memory deficits, with general depressive phenotypes and social stress susceptibility by SPS-ethanol interaction, were alleviated by morin and fluoxetine, evidenced by reduced corticosterone release and adrenal hypertrophy. SPS-ethanol exacerbates dopamine, serotonin, and glutamic acid decarboxylase alterations, and monoamine oxidase-B and acetylcholinesterase hyperactivities in the striatum, PFC, and hippocampus, respectively, which were prevented by morin. Compared to SPS-ethanol aggravation, morin prevented TNF-α, and IL-6 release, malondialdehyde and nitrite levels, with improved antioxidant (glutathione, superoxide-dismutase, catalase) levels in the hippocampus, PFC, and striatum. Overall, these findings suggest that AUD exacerbated PTSD might be primarily connected, among other mechanisms, with aggravated HPA-axis dysfunction, upregulated neurochemical degradative enzymes, enhancement of oxidative/nitrergic stress and neuroinflammation, stereo-selectively in the mice brains, which morin abated via the preventive mechanisms.

α-Viniferin, a dietary phytochemical, inhibits Monoamine oxidase and alleviates Parkinson's disease associated behavioral deficits in a mice model

Parkinson's disease (PD) is one of the most prevalent age-related neurodegenerative disorders. Behavioral complexities worsen over time due to progressive dopaminergic (DArgic) neuronal loss at substantia nigra region of brain. Available treatments typically aim to increase dopamine (DA) levels at striatum. DA is degraded by Monoamine oxidase (MAO), thus dietary phytochemicals with MAO inhibitory properties can contribute to elevate DA levels and reduce the ailment. Characterization of naturally occurring dietary MAO inhibitors is inadequate. Based on available knowledge, we selected different classes of molecules and conducted a screening process to assess their potential as MAO inhibitors. The compounds mostly derived from food sources, broadly belonging to triterpenoids (ursane, oleanane and hopane), alkaloid, polyphenolics, monoterpenoids, alkylbenzene, phenylpropanoid and aromatic alcohol classes. Among all the molecules, highest level of MAO inhibition is offered by α-viniferin, a resveratrol trimer. Cell viability, mitochondrial morphology and reactive oxygen species (ROS) generation remained unaltered by 50 μM α-viniferin treatment in-vitro. Toxicity studies in Drosophila showed unchanged gross neuronal morphology, ROS level, motor activity or long-term survival. α-Viniferin inhibited MAO in mice brain and elevated striatal DA levels. PD-related akinesia and cataleptic behavior were attenuated by α-viniferin due to increase in striatal DA. Our study implies that α-viniferin can be used as an adjunct phytotherapeutic agent for mitigating PD-related behavioral deterioration.

Formononetin ameliorates isoproterenol induced cardiac fibrosis through improving mitochondrial dysfunction

Formononetin, an isoflavone compound, has been extensively researched due to its various biological activities, including a potent protective effect on the cardiovascular system. However, the impact of formononetin on cardiac fibrosis has not been investigated. In this study, C57BL/6 mice were used to establish cardiac fibrosis animal models by subcutaneous injecting of isoproterenol (ISO) and formononetin was orally administrated. The results showed that formononetin reversed ISO-induced heart stiffness revealed by early-to-atrial wave ratio (E/A ratio). Masson staining, western blot, immunohistochemistry and real-time PCR exhibited that the cardiac fibrosis and fibrosis-related proteins (collage III, fibronectin, TGF-β1, α-SMA, and vimentin) and genes (Col1a1, Col3a1, Acta2 and Tgfb1) induced by ISO were significantly suppressed by formononetin. Furthermore, by combining metabolomics and network pharmacology, we found three important targets (ALDH2, HADH, and MAOB), which are associated with mitochondrial function, were involved in the beneficial effect of formononetin. Further validation revealed that these three genes were more abundance in cardiomyocyte than in cardiac fibroblast. The mRNA expression of ALDH2 and HADH were decreased, while MOAB was increased in cardiomyocyte upon ISO treatment and these phenomena were reversed by formononetin. In addition, we investigated mitochondrial membrane potential and ROS production in cardiomyocytes, the results showed that formononetin effectively improved mitochondrial dysfunction induced by ISO. In summary, we demonstrated that formononetin via regulating the expressions of ALDH2, HADH, and MAOB in cardiomyocyte to improve mitochondrial dysfunction and alleviate β-adrenergic activation cardiac fibrosis.

Recent advances on the role of monoamine oxidases in cardiac pathophysiology

Numerous physiological and pathological roles have been attributed to the formation of mitochondrial reactive oxygen species (ROS). However, the individual contribution of different mitochondrial processes independently of bioenergetics remains elusive and clinical treatments unavailable. A notable exception to this complexity is found in the case of monoamine oxidases (MAOs). Unlike other ROS-producing enzymes, especially within mitochondria, MAOs possess a distinct combination of defined molecular structure, substrate specificity, and clinically accessible inhibitors. Another significant aspect of MAO activity is the simultaneous generation of hydrogen peroxide alongside highly reactive aldehydes and ammonia. These three products synergistically impair mitochondrial function at various levels, ultimately jeopardizing cellular metabolic integrity and viability. This pathological condition arises from exacerbated MAO activity, observed in many cardiovascular diseases, thus justifying the exploration of MAO inhibitors as effective cardioprotective strategy. In this context, we not only summarize the deleterious roles of MAOs in cardiac pathologies and the positive effects resulting from genetic or pharmacological MAO inhibition, but also discuss recent findings that expand our understanding on the role of MAO in gene expression and cardiac development.

Serotonin system is partially involved in immunomodulation of Nile tilapia (Oreochromis niloticus) immune cells

Serotonin (5-hydroxytryptamine) is a well-known neurotransmitter affecting emotion, behavior, and cognition. Additionally, numerous immunomodulatory functions of serotonin have been discovered in mammals. However, the regulatory role of the serotonin system in fish immunity remains unclear. In this study, various serotonergic markers in Nile tilapia (Oreochromis niloticus) were identified and characterized. The involvement of the serotonin system during bacterial infection was investigated. Moreover, the expression characteristics and specific functions of serotonergic markers within Nile tilapia immune cells were also assessed. Overall, 22 evolutionarily conserved serotonergic marker genes in Nile tilapia were cloned and characterized. Transcriptional levels of these molecules were most abundant in the brain, and their transcripts were induced during Streptococcus agalactiae infection. Nevertheless, few serotonergic markers exist on Nile tilapia immune cells, and no distinct immunomodulation effect was observed during an immune response. The present study lays a theoretical foundation for further investigation of the immunological mechanisms in fish as well as the evolution of the serotonin system in animals.

Monoamine Oxidase (MAO) as a Potential Target for Anticancer Drug Design and Development

Monoamine oxidases (MAOs) are oxidative enzymes that catalyze the conversion of biogenic amines into their corresponding aldehydes and ketones through oxidative deamination. Owing to the crucial role of MAOs in maintaining functional levels of neurotransmitters, the implications of its distorted activity have been associated with numerous neurological diseases. Recently, an unanticipated role of MAOs in tumor progression and metastasis has been reported. The chemical inhibition of MAOs might be a valuable therapeutic approach for cancer treatment. In this review, we reported computational approaches exploited in the design and development of selective MAO inhibitors accompanied by their biological activities. Additionally, we generated a pharmacophore model for MAO-A active inhibitors to identify the structural motifs to invoke an activity.

Increased MAO-A Activity Promotes Progression of Pulmonary Arterial Hypertension

Monoamine oxidases (MAOs), a class of enzymes bound to the outer mitochondrial membrane, are important sources of reactive oxygen species. Increased MAO-A activity in endothelial cells and cardiomyocytes contributes to vascular dysfunction and progression of left heart failure. We hypothesized that inhibition of MAO-A can be used to treat pulmonary arterial hypertension (PAH) and right ventricular (RV) failure. MAO-A levels in lung and RV samples from patients with PAH were compared with levels in samples from donors without PAH. Experimental PAH was induced in male Sprague-Dawley rats by using Sugen 5416 and hypoxia (SuHx), and RV failure was induced in male Wistar rats by using pulmonary trunk banding (PTB). Animals were randomized to receive either saline or the MAO-A inhibitor clorgyline at 10 mg/kg. Echocardiography and RV catheterization were performed, and heart and lung tissues were collected for further analysis. We found increased MAO-A expression in the pulmonary vasculature of patients with PAH and in experimental experimental PAH induced by SuHx. Cardiac MAO-A expression and activity was increased in SuHx- and PTB-induced RV failure. Clorgyline treatment reduced RV afterload and pulmonary vascular remodeling in SuHx rats through reduced pulmonary vascular proliferation and oxidative stress. Moreover, clorgyline improved RV stiffness and relaxation and reversed RV hypertrophy in SuHx rats. In PTB rats, clorgyline had no direct clorgyline had no direct effect on the right ventricle effect. Our study reveals the role of MAO-A in the progression of PAH. Collectively, these findings indicated that MAO-A may be involved in pulmonary vascular remodeling and consecutive RV failure.

Monoamine oxidase A inhibition protects the myocardium after experimental acute volume overload

Objective:

The molecular pathway leading to myocardial cellular destruction after acute volume overload (AVO) may include monoamine oxidases. The aim of the present study was to investigate whether moclobemide (Mo), a monoamine oxidase inhibitor, protects the myocardium after AVO.

Methods:

Sixty syngeneic Fischer rats underwent surgical abdominal aortocaval fistula to induce AVO. Eighteen rats were treated with Mo 10 mg/kg/day and were compared with 42 untreated rats with AVO without treatment. Myocardial recovery was analyzed using quantitative reverse transcription polymerase chain reaction for hypoxia-inducible factor 1-alpha, inducible nitric oxide synthase, interleukin 6, E-selectin, atrial natriuretic peptide (ANP), brain natriuretic peptide, vascular endothelial growth factor-alpha, matrix metalloproteinase 9, chitinase 3-like protein (YKL-40), and transforming growth factor-beta.

Results:

After 3 days, the relative number of ischemic intramyocardial arteries in the left ventricle was lower in AVO treated with Mo than in without [0.04 (0.02–0.07) vs. 0.09 (0.07–0.14), point score unit]. After 1 day, ANP was lower in AVO treated with Mo than in without [0.95 (0.37–1.84) vs. 2.40 (1.33–3.09), fold changes from the baseline (FC), p=0.044], whereas after 1 and 3 days, YKL-40 was higher in AVO treated with Mo than in without [22.66 (14.05–28.83) vs. 10.06 (6.23–15.02), FC, p=0.006 and 6.03 (4.72–7.18) vs. 3.70 (2.62–5.35), FC, p=0.025].

Conclusion:

Mo decreases intramyocardial arterial ischemia of the left ventricle after AVO while increases YKL-40, reflecting cellular protection during early cardiac remodeling. In the future, adding Mo may be a simple means for myocardial protection after AVO. (Anatol J Cardiol 2019; 21: 39-45)

Regulation of monoamine oxidase A (MAO-A) expression, activity, and function in IL-13-stimulated monocytes and A549 lung carcinoma cells

Monoamine oxidase A (MAO-A) is a mitochondrial flavoenzyme implicated in the pathogenesis of atherosclerosis and inflammation and also in many neurological disorders. MAO-A also has been reported as a potential therapeutic target in prostate cancer. However, the regulatory mechanisms controlling cytokine-induced MAO-A expression in immune or cancer cells remain to be identified. Here, we show that MAO-A expression is co-induced with 15-lipoxygenase (15-LO) in interleukin 13 (IL-13)-activated primary human monocytes and A549 non-small cell lung carcinoma cells. We present evidence that MAO-A gene expression and activity are regulated by signal transducer and activator of transcription 1, 3, and 6 (STAT1, STAT3, and STAT6), early growth response 1 (EGR1), and cAMP-responsive element-binding protein (CREB), the same transcription factors that control IL-13-dependent 15-LO expression. We further established that in both primary monocytes and in A549 cells, IL-13-stimulated MAO-A expression, activity, and function are directly governed by 15-LO. In contrast, IL-13-driven expression and activity of MAO-A was 15-LO-independent in U937 promonocytic cells. Furthermore, we demonstrate that the 15-LO-dependent transcriptional regulation of MAO-A in response to IL-13 stimulation in monocytes and in A549 cells is mediated by peroxisome proliferator-activated receptor γ (PPARγ) and that signal transducer and activator of transcription 6 (STAT6) plays a crucial role in facilitating the transcriptional activity of PPARγ. We further report that the IL-13-STAT6-15-LO-PPARγ axis is critical for MAO-A expression, activity, and function, including migration and reactive oxygen species generation. Altogether, these results have major implications for the resolution of inflammation and indicate that MAO-A may promote metastatic potential in lung cancer cells.

Differential expression of IL-6/IL-6R and MAO-A regulates invasion/angiogenesis in breast cancer

Background

Monoamine oxidases (MAO) are mitochondrial enzymes functioning in oxidative metabolism of monoamines. The action of MAO-A has been typically described in neuro-pharmacological domains. Here, we have established a co-relation between IL-6/IL-6R and MAO-A and their regulation in hypoxia induced invasion/angiogenesis.

Methods

We employed various in-vitro and in-vivo techniques and clinical samples.

Results

We studied a co-relation among MAO-A and IL-6/IL-6R and tumour angiogenesis/invasion in hypoxic environment in breast cancer model. Activation of IL-6/IL-6R and its downstream was found in hypoxic cancer cells. This elevation of IL-6/IL-6R caused sustained inhibition of MAO-A in hypoxic environment. Inhibition of IL-6R signalling or IL-6R siRNA increased MAO-A activity and inhibited tumour angiogenesis and invasion significantly in different models. Further, elevation of MAO-A with 5-azacytidine (5-Aza) modulated IL-6 mediated angiogenesis and invasive signatures including VEGF, MMPs and EMT in hypoxic breast cancer. High grade invasive ductal carcinoma (IDC) clinical specimen displayed elevated level of IL-6R and depleted MAO-A expression. Expression of VEGF and HIF-1α was unregulated and loss of E-Cadherin was observed in high grade IDC tissue specimen.

Conclusions

Suppression of MAO-A by IL-6/IL-6R activation promotes tumour angiogenesis and invasion in hypoxic breast cancer environment.

Alzheimer's Disease: The Role of Microglia in Brain Homeostasis and Proteopathy

Brain aging is central to late-onset Alzheimer's disease (LOAD), although the mechanisms by which it occurs at protein or cellular levels are not fully understood. Alzheimer's disease is the most common proteopathy and is characterized by two unique pathologies: senile plaques and neurofibrillary tangles, the former accumulating earlier than the latter. Aging alters the proteostasis of amyloid-β peptides and microtubule-associated protein tau, which are regulated in both autonomous and non-autonomous manners. Microglia, the resident phagocytes of the central nervous system, play a major role in the non-autonomous clearance of protein aggregates. Their function is significantly altered by aging and neurodegeneration. This is genetically supported by the association of microglia-specific genes, TREM2 and CD33, and late onset Alzheimer's disease. Here, we propose that the functional characterization of microglia, and their contribution to proteopathy, will lead to a new therapeutic direction in Alzheimer's disease research.

Emerging role of monoamine oxidase as a therapeutic target for cardiovascular disease

In the past decade, accumulating evidence highlighted the role of monoamine oxidases (MAOs) in cardiovascular disease (CVD). MAOs are flavoenzymes located in the outer mitochondrial membrane, responsible for the degradation of neurotransmitters and biogenic amines. During this process they generate hydrogen peroxide, aldehydes and ammonia, species that can target mitochondria and induce mitochondrial dysfunction and cardiomyocyte death. Indeed, MAO inhibition affords cardioprotection in several models of CVD, such as ischemia/reperfusion, heart failure and diabetes. Importantly, a few studies provided encouraging results suggesting that MAO inhibition might be beneficial also in patients with CVD. Thus, selective and reversible MAO inhibitors, currently used as therapy for depression and neurodegenerative disorders, might be considered as candidate drugs for the treatment of CVD.

Inhibition of monoamine oxidase A increases recovery after experimental cardiac arrest

OBJECTIVES

Perioperative myocardial infarction (MI) with ischaemia-reperfusion injury (IRI) is a devastating entity occurring in 1-2% of patients after cardiac surgery. The molecular pathway leading to myocardial cellular destruction after MI may include monoamine oxidases. We experimentally investigated whether moclobemide, a monoamine oxidase inhibitor, enhances myocardial recovery after cardiac arrest and MI.

METHODS

Fifty-six syngeneic Fischer rats underwent heterotopic cardiac transplantation to induce reversible IRI after cardiac arrest. Twenty-eight rats also underwent permanent ligation of the left anterior descending coronary artery to induce MI after cardiac arrest. Twenty-eight rats with or without MI were treated with subcutaneous moclobemide 10 mg/kg/day. Methods used to study myocardial recovery were microdialysis for intramyocardial metabolism, histology and quantitative reverse-transcription polymerase chain reaction for high-mobility group box-1 (HMGB1), haeme oxygenase-1 (HO-1), interleukin-6, hypoxia-inducible factor 1α and macrophages (CD68).

RESULTS

Pyruvate increased in MI treated with moclobemide versus IRI with moclobemide (29.19 ± 7.64 vs 13.86 ± 8.49 µM, P = 0.028), reflecting metabolic activity after cardiac arrest and reperfusion. Myocardial inflammation increased in MI compared with IRI after 1 h (0.80 ± 0.56 vs 0, point score units [PSUs], P = 0.003), but decreased after 5 days in MI treated with moclobemide versus MI alone (0.80 ± 0.83 vs 2.00 ± 0.70, PSU, P = 0.033). Expressions of HMGB1, CD68 and HO-1 decreased in MI treated with moclobemide versus MI alone (1.33 ± 0.20 vs 1.75 ± 0.24, fold changes [FCs], P = 0.028; 5.15 ± 1.10 vs 9.59 ± 2.75, FC, P = 0.050; 10.41 ± 4.17 vs 21.28 ± 10.01, FC, P = 0.047), indicating myocardial recovery and increased cellularity of remote intramyocardial arteries.

CONCLUSIONS

Moclobemide enhances myocardial recovery after cardiac arrest and MI; inhibition of remote myocardial changes may be achieved by targeting treatment against monoamine oxidase.

Ileal neuroendocrine tumors and heart: not only valvular consequences

Ileal neuroendocrine tumors (NETs) often progress slowly, but because of their generally nonspecific symptoms, they have often metastasized to local lymph nodes and to the liver by the time the patient presents. Biochemically, most of these patients have increased levels of whole blood serotonin, urinary 5-hydroxyindoleacetic acid, and chromogranin A. Imaging work-up generally comprises computed tomography or magnetic resonance imaging and somatostatin receptor scintigraphy, or in recent years positron emission tomography with 68Ga-labeled somatostatin analogs, allowing for detection of even sub-cm lesions. Carcinoid heart disease with affected leaflets, mainly to the right side of the heart, is a well-known complication and patients routinely undergo echocardiography to diagnose and monitor this. Multitasking surgery is currently recognized as first-line treatment for ileal NETs with metastases and carcinoid heart disease. Open heart surgery and valve replacement are advocated in patients with valvular disease and progressive heart failure. When valvulopathy in the tricuspid valve results in right-sided heart failure, a sequential approach, performing valve replacement first before intra-abdominal tumor-reductive procedures are conducted, reduces the risk of bleeding. Metastases to the myocardium from ileal NETs are seen in <1-4.3% of patients, depending partly on the imaging technique used, and are generally discovered in those affected with widespread disease. Systemic treatment with somatostatin analogs, and sometimes alpha interferon, is first-line medical therapy in metastatic disease to relieve hormonal symptoms and stabilize the tumor. This treatment is also indicated when heart metastases are detected, with the addition of diuretics and fluid restriction in cases of heart failure. Myocardial metastases are rarely treated by surgical resection.

Annexin II-dependent actin remodelling evoked by hydrogen peroxide requires the metalloproteinase/sphingolipid pathway

Actin remodeling is a dynamic process associated with cell shape modification occurring during cell cycle and proliferation. Oxidative stress plays a role in actin reorganization via various systems including p38MAPK. Beside, the mitogenic response evoked by hydrogen peroxide (H₂O₂) in fibroblasts and smooth muscle cells (SMC) involves the metalloproteinase (MMPs)/sphingomyelinase 2 (nSMase2) signaling pathway. The aim of this work was to investigate whether this system plays a role in actin remodeling induced by H₂O₂.

Low H₂O₂ dose (5 µM) rapidly triggered a signaling cascade leading to nSMase2 activation, src and annexin 2 (AnxA2) phosphorylation, and actin remodeling, in fibroblasts and SMC. These events were blocked by pharmacological inhibitors of MMPs (Ro28-2653) and p38MAPK (SB203580), and were lacking in MMP2^−/− and in nSMase2-mutant (fro) fibroblasts. Likewise, H₂O₂ was unable to induce actin remodeling in fro and MMP2^−/− fibroblasts or in cells pretreated with p38MAPK, or MMP inhibitors. Finally we show that nSMase2 activation by H₂O₂, depends on MMP2 and p38MAPK, and is required for the src-dependent phosphorylation of AnxA2, and actin remodeling.

Taken together, these findings indicate for the first time that AnxA2 phosphorylation and actin remodeling evoked by oxidative stress depend on the sphingolipid pathway, via MMP2 and p38MAPK.

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Low concentration of H₂O₂ activates matrix metalloproteinases MMP-2.

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MMP-2 activates p38MAPK, type 2 neutral sphingomyelinase.

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This signaling pathway induces annexin II phosphorylation via src.

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This pathway is involved in actin remodeling due to H₂O₂ stimulation.

Monoamine oxidase A (MAO-A): a signature marker of alternatively activated monocytes/macrophages

Monocytes/macrophages are versatile cells centrally involved in host defense and immunity. Th1 cytokines induce a classical activation program in monocytes/macrophages leading to a proinflammatory M1 macrophage phenotype while Th2 cytokines IL-4 and IL-13 promote monocyte differentiation into an alternatively activated, anti-inflammatory M2 macrophage phenotype. Although monoamine oxidase A (MAO-A) is primarily known for its action in the nervous system, several recent studies have identified MAO-A as a signature marker of alternative activation of monocytes/macrophages. In this brief review we explore the signaling pathways/molecules that regulate MAO-A expression in alternatively activated monocytes/macrophages. We further discuss the contribution of MAO-A to the resolution of inflammation and identify potential therapeutic targets for controlling inflammation. Altogether this review provides deeper insight into the role of MAO-A in alternative activation of monocytes/macrophages and their participation in the inflammatory response.

Monoamine oxidases as sources of oxidants in the heart

Oxidative stress can be generated at several sites within the mitochondria. Among these, monoamine oxidase (MAO) has been described as a prominent source. MAOs are mitochondrial flavoenzymes responsible for the oxidative deamination of catecholamines, serotonin and biogenic amines, and during this process they generate H2O2 and aldehyde intermediates. The role of MAO in cardiovascular pathophysiology has only recently gathered some attention since it has been demonstrated that both H2O2 and aldehydes may target mitochondrial function and consequently affect function and viability of the myocardium. In the present review, we will discuss the role of MAO in catecholamine and serotonin clearance and cycling in relation to cardiac structure and function. The relevant contribution of each MAO isoform (MAO-A or -B) will be discussed in relation to mitochondrial dysfunction and myocardial injury. Finally, we will examine both beneficial effects of their pharmacological or genetic inhibition along with potential adverse effects observed at baseline in MAO knockout mice, as well as the deleterious effects following their over-expression specifically at cardiomyocyte level. This article is part of a Special Issue entitled "Redox Signalling in the Cardiovascular System".

A signaling cascade mediated by ceramide, src and PDGFRβ coordinates the activation of the redox-sensitive neutral sphingomyelinase-2 and sphingosine kinase-1

Stress-inducing agents, including oxidative stress, generate the sphingolipid mediators ceramide (Cer) and sphingosine-1-phosphate (S1P) that are involved in stress-induced cellular responses. The two redox-sensitive neutral sphingomyelinase-2 (nSMase2) and sphingosine kinase-1 (SK1) participate in transducing stress signaling to ceramide and S1P, respectively; however, whether these key enzymes are coordinately regulated is not known. We investigated whether a signaling link coordinates nSMase2 and SK1 activation by H2O2. In mesenchymal cells, H2O2 elicits a dose-dependent biphasic effect, mitogenic at low concentration (5μM), and anti-proliferative and toxic at high concentration (100μM). Low H2O2 concentration triggered activation of nSMase2 and SK1 through a nSMase2/Cer-dependent signaling pathway that acted upstream of activation of SK1. Further results implicated src and the trans-activation of PDGFRβ, as supported by the blocking effect of specific siRNAs, pharmacological inhibitors, and genetically deficient cells for nSMase2, src and SK1. The H2O2-induced src/PDGFRβ/SK1 signaling cascade was impaired in nSMase2-deficient fro/fro cells and was rescued by exogenous C2Cer that activated src/PDGFRβ/SK1. Thus, the results define a nSMase2/SK1 signaling pathway implicated in the mitogenic response to low oxidative stress. On the other hand, high oxidative stress induced inhibition of SK1. The results also showed that the toxicity of high H2O2 concentration was comparable in control and nSMase2-deficient cells. Taken together the results identify a tightly coordinated nSMase2/SK1 pathway that mediates the mitogenic effects of H2O2 and may sense the degree of oxidative stress.

IL-4 and IL-13 employ discrete signaling pathways for target gene expression in alternatively activated monocytes/macrophages

Monocytes/macrophages are innate immune cells that play a crucial role in the resolution of inflammation. In the presence of the Th2 cytokines interleukin-4 (IL-4) and interleukin-13 (IL-13), they display an anti-inflammatory profile and this activation pathway is known as alternative activation. In this study we compare and differentiate pathways mediated by IL-4 and IL-13 activation of human monocytes/macrophages. Here we report differential regulation of IL-4 and IL-13 signaling in monocytes/macrophages starting from IL-4/IL-13 cytokine receptors to Jak/Stat-mediated signaling pathways that ultimately control expression of several inflammatory genes. Our data demonstrate that although the receptor-associated tyrosine kinases Jak2 and Tyk2 are activated after the recruitment of IL-13 to its receptor (containing IL-4Rα and IL-13Rα1), IL-4 stimulates Jak1 activation. We further show that Jak2 is upstream of Stat3 activation and Tyk2 controls Stat1 and Stat6 activation in response to IL-13 stimulation. In contrast, Jak1 regulates Stat3 and Stat6 activation in IL-4-induced monocytes. Our results further reveal that although IL-13 utilizes both IL-4Rα/Jak2/Stat3 and IL-13Rα1/Tyk2/Stat1/Stat6 signaling pathways, IL-4 can use only the IL-4Rα/Jak1/Stat3/Stat6 cascade to regulate the expression of some critical inflammatory genes, including 15-lipoxygenase, monoamine oxidase A (MAO-A), and the scavenger receptor CD36. Moreover, we demonstrate here that IL-13 and IL-4 can uniquely affect the expression of particular genes such as dual-specificity phosphatase 1 and tissue inhibitor of metalloprotease-3 and do so through different Jaks. As evidence of differential regulation of gene function by IL-4 and IL-13, we further report that MAO-A-mediated reactive oxygen species generation is influenced by different Jaks. Collectively, these results have major implications for understanding the mechanism and function of alternatively activated monocytes/macrophages by IL-4 and IL-13 and add novel insights into the pathogenesis and potential treatment of various inflammatory diseases.

A key role for matrix metalloproteinases and neutral sphingomyelinase-2 in transplant vasculopathy triggered by anti-HLA antibody

BACKGROUND

Outcomes for organ transplantation are constantly improving because of advances in organ preservation, surgical techniques, immune clinical monitoring, and immunosuppressive treatment preventing acute transplant rejection. However, chronic rejection including transplant vasculopathy still limits long-term patient survival. Transplant vasculopathy is characterized by progressive neointimal hyperplasia leading to arterial stenosis and ischemic failure of the allograft. This work sought to decipher the manner in which the humoral immune response, mimicked by W6/32 anti-HLA antibody, contributes to transplant vasculopathy.

METHODS AND RESULTS

Studies were performed in vitro on cultured human smooth muscle cells, ex vivo on human arterial segments, and in vivo in a model consisting of human arterial segments grafted into severe combined immunodeficiency/beige mice injected weekly with anti-HLA antibodies. We report that anti-HLA antibodies are mitogenic for smooth muscle cells through a signaling mechanism implicating matrix metalloproteinases (MMPs) (membrane type 1 MMP and MMP2) and neutral sphingomyelinase-2. This mitogenic signaling and subsequent DNA synthesis are blocked in smooth muscle cells silenced for MMP2 or for neutral sphingomyelinase-2 by small interfering RNAs, in smooth muscle cells transfected with a vector coding for a dominant-negative form of membrane type 1 MMP, and after treatment by pharmacological inhibitors of MMPs (Ro28-2653) or neutral sphingomyelinase-2 (GW4869). In vivo, Ro28-2653 and GW4869 reduced the intimal thickening induced by anti-HLA antibodies in human mesenteric arteries grafted into severe combined immunodeficiency/beige mice.

CONCLUSIONS

These data highlight a crucial role for MMP2 and neutral sphingomyelinase-2 in vasculopathy triggered by a humoral immune response and open new perspectives for preventing transplant vasculopathy with the use of MMP and neutral sphingomyelinase inhibitors, in addition to conventional immunosuppression.

Personality traits of aggression-submissiveness and perfectionism associate with ABO blood groups through catecholamine activities

Personality trait research has shown associations with many genes, prominently those of the catecholamine metabolism such as dopamine beta hydroxylase (DBH), catechol-O-methyltransferase (COMT), and monoamine oxidase A (MAOA). Because DBH gene is in linkage disequilibrium with ABO gene, there is reason to think that other catecholamine genes using the same substrate as DBH may also have associations with ABO blood groups, and this paper demonstrates how this may be so. Reasons include similarities in hapmap population frequency distributions, similarities in illness risks between ABO blood groups and DBH activities as well as between ABO blood groups and COMT activities and between ABO blood groups and MAOA activities. If ABO blood groups can be demonstrated to associate with all these catecholamine genes, then the catecholamine personality trait research can be applied to ABO blood groups and tested for confirmation. ABO blood typing is widely available and affords ability to test this hypothesis and thus confirm the possible joint association of personality traits of aggression-submissiveness and perfectionism to catecholamine genes and to ABO blood groups. Clinical applications and implications are discussed.

Monoamine Oxidase and Semicarbazide-Sensitive Amine Oxidase Kinetic Analysis in Mesenteric Arteries of Patients With Type 2 Diabetes

Monoamine oxidase (MAO, type A and B) and semicarbazide-sensitive amine oxidase (SSAO) metabolize biogenic amines, however, the impact of these enzymes in arteries from patients with type 2 diabetes remains poorly understood. We investigated the kinetic parameters of the enzymes to establish putative correlations with noradrenaline (NA) content and patient age in human mesenteric arteries from type 2 diabetic patients. The kinetic parameters were evaluated by radiochemical assay and NA content by high-performance liquid chromatography (HPLC). The activity of MAO-A and SSAO in type 2 diabetic vascular tissues was significantly lower compared to the activity obtained in non-diabetic tissues. In the correlation between MAO-A (Km) and NA content, we found a positive correlation for both the diabetic and non-diabetic group, but no correlation was established for patient age. In both groups, MAO-B (Vmax) showed a negative correlation with age. The results show that MAO-A and SSAO activities and NA content of type 2 diabetic tissues are lower compared to the non-diabetic tissues, while MAO-B activity remained unchanged. These remarks suggest that MAO-A and SSAO may play an important role in vascular tissue as well as in the vascular pathophysiology of type 2 diabetes.

Monoamine oxidases (MAO) in the pathogenesis of heart failure and ischemia/reperfusion injury

Recent evidence highlights monoamine oxidases (MAO) as another prominent source of oxidative stress. MAO are a class of enzymes located in the outer mitochondrial membrane, deputed to the oxidative breakdown of key neurotransmitters such as norepinephrine, epinephrine and dopamine, and in the process generate H(2)O(2). All these monoamines are endowed with potent modulatory effects on myocardial function. Thus, when the heart is subjected to chronic neuro-hormonal and/or peripheral hemodynamic stress, the abundance of circulating/tissue monoamines can make MAO-derived H(2)O(2) production particularly prominent. This is the case of acute cardiac damage due to ischemia/reperfusion injury or, on a more chronic stand, of the transition from compensated hypertrophy to overt ventricular dilation/pump failure. Here, we will first briefly discuss mitochondrial status and contribution to acute and chronic cardiac disorders. We will illustrate possible mechanisms by which MAO activity affects cardiac biology and function, along with a discussion as to their role as a prominent source of reactive oxygen species. Finally, we will speculate on why MAO inhibition might have a therapeutic value for treating cardiac affections of ischemic and non-ischemic origin. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.

Personality and illness: genetic connections?

Illness is strongly influenced by genetics. Personality traits are influenced by genetics and have linkages with, at least, affective illness. Because genetics influences both personality and illness, we studied by literature review the genes that illness and personality traits share and, by office assessment, our patient population's illnesses and personality traits. This led to the following hypothesis: illness is related to more Submissive than Dominant personality trait and thus to lower norepinephrine activity. Patient affect and personality are often noted to be subdued in chronic illness, but whether from cause or effect is difficult to determine. After reviewing the literature on wellness, personality and genes, we endeavored to explore and better delineate our impressions of illness and personality relationships and to set the stage for a genetic hypothesis by using an online personality test in an ob-gyn practice to determine which traits could be used as proxies for personality trait genes. We thus confirmed our clinical impression that women with psychiatric and/or medical illness have more Submissive personality. The medical literature on gene markers shared by Submissive personality and illness in our population suggests the hypothesis that this relationship could be mediated by genetically lower neurotransmitter activity. Both norepinephrine activity and monoamine oxidase A, the enzyme controlling its catabolism, are in concert to blunt neuronal activity in such diverse states as depression, asthma, obesity, autoimmune illness, and in smokers. Conversely, norepinephrine activity is enhanced in breastfeeders and in other settings known to be related to good health. A point for possible divergence from the hypothesis is that African-Americans have enhanced norepinephrine activity yet poorer health outcomes although the effect of environmental risk factors in African-Americans is considered prominent by researchers. The possible importance of this hypothesis is that it changes emphasis slightly from one of splitting diagnoses to one of grouping them to achieve fresh insight. If we assess what is found in common in diverse illnesses of mind and body, we have yet another tool to assess causation. Although this hypothesis is offered somewhat in a boldness of spirit to take a new look at our many perplexing clinical problems, it is also offered with humility in light of the complexity with which we deal in patient care.

Role of protein transamidation in serotonin-induced proliferation and migration of pulmonary artery smooth muscle cells

Pulmonary hypertension is characterized by elevated pulmonary artery pressure and pulmonary artery smooth muscle cell (SMC) proliferation and migration. Clinical and experimental evidence suggests that serotonin (5-HT) is important in these responses. We previously demonstrated the participation of the 5-HT transporter and intracellular 5-HT (5-HTi) in the pulmonary vascular SMC-proliferative response to 5-HT. However, the mechanism underlying the intracellular actions of 5-HT is unknown. We speculated that 5-HTi activates SMC growth by post-translational transamidation of proteins via transglutaminase (TGase) activity, a process referred to as serotonylation. To test this hypothesis, serotonylation of pulmonary artery SMC proteins, and their role in 5-HT-induced proliferative and migratory responses, were assessed. 5-HT caused dose- and time-dependent increase in serotonylation of multiple proteins in both bovine and rat pulmonary artery SMCs. Inhibition of TGase with dansylcadaverin blocked this activity, as well as SMC-proliferative and migratory responses to 5-HT. Serotonylation of proteins also was blocked by 5-HT transporter inhibitors, and was enhanced by inhibition of monoamine oxidase, an enzyme known to degrade 5-HTi, indicating that 5-HTi levels regulate serotonylation. Immunoprecipitation assays and HPLC-mass spectral peptide sequencing revealed that a major protein serotonylated by TGase was fibronectin (FN). 5-HT-stimulated SMC serotonylation and proliferation were blocked by FN small interfering (si) RNA. These findings, together with previous observations that FN expression in the lung strongly correlates with the progression of pulmonary hypertension in both experimental animals and humans, suggest an important role of FN serotonylation in the pathogenesis of this disease.

Stress-induced sphingolipid signaling: role of type-2 neutral sphingomyelinase in murine cell apoptosis and proliferation

Background

Sphingomyelin hydrolysis in response to stress-inducing agents, and subsequent ceramide generation, are implicated in various cellular responses, including apoptosis, inflammation and proliferation, depending on the nature of the different acidic or neutral sphingomyelinases. This study was carried out to investigate whether the neutral Mg²⁺-dependent neutral sphingomyelinase-2 (nSMase2) plays a role in the cellular signaling evoked by TNFalpha and oxidized LDLs, two stress-inducing agents, which are mitogenic at low concentrations and proapoptotic at higher concentrations.

Methodology and Principal Findings

For this purpose, we used nSMase2-deficient cells from homozygous fro/fro (fragilitas ossium) mice and nSMase2-deficient cells reconstituted with a V5-tagged nSMase2. We report that the genetic defect of nSMase2 (in fibroblasts from fro/fro mice) does not alter the TNFalpha and oxidized LDLs-mediated apoptotic response. Likewise, the hepatic toxicity of TNFalpha is similar in wild type and fro mice, thus is independent of nSMase2 activation. In contrast, the mitogenic response elicited by low concentrations of TNFalpha and oxidized LDLs (but not fetal calf serum) requires nSMase2 activation.

Conclusion and Significance

nSMase2 activation is not involved in apoptosis mediated by TNFalpha and oxidized LDLs in murine fibroblasts, and in the hepatotoxicity of TNFalpha in mice, but is required for the mitogenic response to stress-inducing agents.

Monoamine oxidase A-mediated enhanced catabolism of norepinephrine contributes to adverse remodeling and pump failure in hearts with pressure overload

RATIONALE

Monoamine oxidases (MAOs) are mitochondrial enzymes that catabolize prohypertrophic neurotransmitters, such as norepinephrine and serotonin, generating hydrogen peroxide. Because excess reactive oxygen species and catecholamines are major contributors to the pathophysiology of congestive heart failure, MAOs could play an important role in this process.

OBJECTIVE

Here, we investigated the role of MAO-A in maladaptive hypertrophy and heart failure.

METHODS AND RESULTS

We report that MAO-A activity is triggered in isolated neonatal and adult myocytes on stimulation with norepinephrine, followed by increase in cell size, reactive oxygen species production, and signs of maladaptive hypertrophy. All of these in vitro changes occur, in part, independently from alpha- and beta-adrenergic receptor-operated signaling and are inhibited by the specific MAO-A inhibitor clorgyline. In mice with left ventricular dilation and pump failure attributable to pressure overload, norepinephrine catabolism by MAO-A is increased accompanied by exacerbated oxidative stress. MAO-A inhibition prevents these changes, and also reverses fetal gene reprogramming, metalloproteinase and caspase-3 activation, as well as myocardial apoptosis. The specific role of MAO-A was further tested in mice expressing a dominant-negative MAO-A (MAO-A(neo)), which were more protected against pressure overload than their wild-type littermates.

CONCLUSIONS

In addition to adrenergic receptor-dependent mechanisms, enhanced MAO-A activity coupled with increased intramyocardial norepinephrine availability results in augmented reactive oxygen species generation, contributing to maladaptive remodeling and left ventricular dysfunction in hearts subjected to chronic stress.

Serotonin produces monoamine oxidase-dependent oxidative stress in human heart valves

Heart valve disease and pulmonary hypertension, in patients with carcinoid tumors and people who used the fenfluramine-phentermine combination for weight control, have been associated with high levels of serotonin in blood. The mechanism by which serotonin induces valvular changes is not well understood. We recently reported that increased oxidative stress is associated with valvular changes in aortic valve stenosis in humans and mice. In this study, we tested the hypothesis that serotonin induces oxidative stress in human heart valves, and examined mechanisms by which serotonin may increase reactive oxygen species. Superoxide (O2*.-) was measured in heart valves from explanted human hearts that were not used for transplantation. (O2*.-) levels (lucigenin-enhanced chemoluminescence) were increased in homogenates of cardiac valves and blood vessels after incubation with serotonin. A nonspecific inhibitor of flavin-oxidases (diphenyliodonium), or inhibitors of monoamine oxidase [MAO (tranylcypromine and clorgyline)], prevented the serotonin-induced increase in (O2*.-). Dopamine, another MAO substrate that is increased in patients with carcinoid syndrome, also increased (O2*.-) levels in heart valves, and this effect was attenuated by clorgyline. Apocynin [an inhibitor of NAD(P)H oxidase] did not prevent increases in (O2*.-) during serotonin treatment. Addition of serotonin to recombinant human MAO-A generated (O2*.-), and this effect was prevented by an MAO inhibitor. In conclusion, we have identified a novel mechanism whereby MAO-A can contribute to increased oxidative stress in human heart valves and pulmonary artery exposed to serotonin and dopamine.

Mitochondria and vascular pathology

Functional and structural changes in mitochondria are caused by the opening of the mitochondrial permeability transition pore (PTP) and by the mitochondrial generation of reactive oxygen species (ROS). These two processes are linked in a vicious cycle that has been extensively documented in ischemia/reperfusion injuries of the heart, and the same processes likely contribute to vascular pathology. For instance, the opening of the PTP causes cell death in isolated endothelial and vascular smooth muscle cells. Indeed, atherosclerosis is exacerbated when mitochondrial antioxidant defenses are hampered, but a decrease in mitochondrial ROS formation reduces atherogenesis. Determining the exact location of ROS generation in mitochondria is a relevant and still unanswered question. The respiratory chain is generally believed to be a main site of ROS formation. However, several other mitochondrial components likely contribute to ROS generation. Recent reports highlight the relevance of monoamine oxidases (MAO) and p66(Shc). For example, the absence of p66(Shc) in hypercholesterolemic mice has been reported to reduce the occurrence of foam cells and early atherogenic lesions. On the other hand, MAO inhibition has been shown to reduce oxidative stress in many cell types eliciting significant protection from myocardial ischemia. In conclusion, evidence will be presented to demonstrate that (i) mitochondria are major sites of ROS formation; (ii) an increase in mitochondrial ROS formation and/or a decrease in mitochondrial antioxidant defenses exacerbate atherosclerosis; and (iii) mitochondrial dysfunction is likely a relevant mechanism underlying several risk factors (i.e., diabetes, hyperlipidemia, hypertension) associated with atherosclerosis.

Mitochondrial pathways for ROS formation and myocardial injury: the relevance of p66(Shc) and monoamine oxidase

Although mitochondria are considered the most relevant site for the formation of reactive oxygen species (ROS) in cardiac myocytes, a major and unsolved issue is where ROS are generated in mitochondria. Respiratory chain is generally indicated as a main site for ROS formation. However, other mitochondrial components are likely to contribute to ROS generation. Recent reports highlight the relevance of monoamine oxidases (MAO) and p66(Shc). The importance of these systems in the irreversibility of ischemic heart injury will be discussed along with the cardioprotective effects elicited by both MAO inhibition and p66(Shc) knockout. Finally, recent evidence will be reviewed that highlight the relevance of mitochondrial ROS formation also in myocardial failure and atherosclerosis.

Sphingomyelinases: their regulation and roles in cardiovascular pathophysiology

Sphingomyelinases (SMases) hydrolyse sphingomyelin, releasing ceramide and creating a cascade of bioactive lipids. These lipids include sphingosine and sphingosine-1-phosphate, all of which have a specific signalling capacity. Sphingomyelinase activation occurs in different cardiovascular system cell types, namely cardiac myocytes, endothelial and vascular smooth muscle cells, mediating cell proliferation, cell death, and contraction of cardiac and vascular myocytes. Three main types of SMases contribute to cardiovascular physiology: the lysosomal and secreted acidic SMases (L- and S-ASMases, respectively) and the membrane neutral SMase (NSMase). These three enzymes have common activators, including ischaemia/reperfusion stress and proinflammatory cytokines, but they differ in their enzymatic properties and subcellular locations that determine the final effect of enzyme activation. This review focuses on the recent advances in the understanding of ASMase and NSMase pathways and their specific contribution to cardiovascular pathophysiology. Current knowledge indicates that the inhibitors of the different SMase types are potential tools for the treatment of cardiovascular diseases. Acid SMase inhibitors could be tools against post-ischaemia reperfusion injury and in the treatment of atherosclerosis. Neutral SMase inhibitors could be tools for the treatment of atherosclerosis, heart failure, and age-related decline in vasomotion. However, the design of bioavailable and more specific SMase-type inhibitors remains a challenge.

Hypoxia-induced modifications in plasma membranes and lipid microdomains in A549 cells and primary human alveolar cells

We evaluated the response to mild hypoxia exposure of A549 alveolar human cells and of a continuous alveolar cell line from human excised lungs (A30) exposed to 5% O(2) for 5 and 24 h. No signs of increased peroxidation and of early apoptosis were detected. After 24 h of hypoxia total cell proteins/DNA ratio decreased significantly by about 20%. Similarly, we found a decrease in membrane phospholipid and cholesterol content. The membrane fluidity assessed by fluorescence anisotropy measurements was unchanged. We also prepared the detergent resistant membrane fraction (DRM) to analyze the distribution of the two types of lipid microdomains, caveolae and lipid rafts. The DRM content of Cav-1, marker of caveolae, was decreased, while CD55, marker of lipid rafts, increased in both cell lines. Total content of these markers in the membranes was unchanged indicating remodelling of their distribution between detergent-resistant and detergent-soluble fraction of the cellular membrane. The changes in protein markers distribution did not imply changes in the corresponding mRNA, except in the case of Cav-1 for A30 line. In the latter case we found a parallel decrease in Cav-1 and in the corresponding mRNA. We conclude that an exposure to a mild degree of hypoxia triggers a significant remodelling of the lipid microdomains expression, confirming that they are highly dynamic structures providing a prompt signalling platform to changes of the pericellular microenvironment.

Comparing the relative toxicity of malathion and malaoxon in blue catfish Ictalurus furcatus

Malathion inhibits the critical body enzyme, acetylcholinesterase (AChE). This capability requires that malathion should first be converted to malaoxon to become an active anticholinesterase agent. Conversion can be caused by oxidation in mammals, insects, plants, and in sunlight. In this study, the effects of malathion and malaoxon on catfish Ictalurus furcatus were evaluated. After 96-h exposures, the LC(50) (concentration that causes 50% mortality) and IC(50) (concentration that causes 50% enzyme inhibition) for malaoxon were lower than corresponding values for malathion. The overall mean 96-h LC(50) is 17.0 ppm for malathion and 3.1 ppm for malaoxon. IC(50) values for malathion are 8.5 ppm for brain, 10.3 ppm for liver, and 16.6 ppm for muscle. Corresponding values for malaoxon are 2.3, 3.7, and 6.8 ppm, respectively. All the AChE activities in malathion- and malaoxon-exposed catfish brain showed significant inhibition. The oxidation product malaoxon demonstrated higher inhibition on AChE activity than did malathion. Moreover, malaoxon showed significant inhibition on butyrylcholinesterase (BChE) in the liver if the concentrations were increased to more than 1 ppm. Malathion showed no difference between treatment group and control group. Compared with malathion, malaoxon showed higher inhibition on monoamine activity than that of malathion. The results indicated that the oxidative product malaoxon is more toxic than the parent compound malathion. AChE, BChE, and monoamine activities are confirmed as bioindicators of malathion exposure in blue catfish, I. furcatus.