NADPH Oxidase-Mediated Activation of Neutral Sphingomyelinase Is Responsible for Diesel Particulate Extract-Induced Keratinocyte Apoptosis

Euphorbia supina Extracts Block NADPH Oxidase-Mediated, Ceramide-Induced Apoptosis Initiated by Diesel Particulate Matter

Air pollutants contribute to the development of diseases such as asthma, chronic obstructive pulmonary disease (COPD), pulmonary cancer, cardiovascular problems, and some skin diseases. We recently found that a major air pollutant, diesel particulate matter (DPM), induces apoptosis in human keratinocytes by increasing a proapoptotic lipid mediator, ceramide. DPM activates nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX), which stimulates sphingomyelinase, leading to an increased conversion of sphingomyelin to ceramide. Interestingly, we characterized that although NOX is a reactive oxygen species (ROS) generator, the activation of sphingomyelinases by NOX is an ROS-independent mechanism. A Korean weed, prostrate spurge Euphorbia supina Rafin (ESR), has been used for centuries as a folk medicine to treat bronchitis, hepatitis, hemorrhage, and skin inflammation. Flavonoids, terpenes and tannins are enriched in ESR, and although ESR has proven antioxidative activity, its biological activities are largely unknown. Here, we investigate whether and how ESR protects keratinocytes against DPM-mediated apoptosis. We found that ESR-extracts (ESR-Ex) protect keratinocytes from DPM-induced apoptosis by inhibiting NOX activation in keratinocytes in response to DPM. We also demonstrated that ESR-Ex suppresses NOX activation via a blockage of the aryl hydrocarbon receptor (AhR) activation-mediated transcription of neutrophil cytosolic factor 1 (NCF1)/p47phox, a subunit of NOX. Our study reveals previously uncharacterized biological activity of ESR-Ex; i.e., its inhibition of Ahr and NOX activation. Thus, because the inhibition of NOX has already been developed to treat NOX-mediated diseases, including various types of cardiovascular diseases and cancers, initiated by air pollutants and because AhR activation contributes to the development of chronic inflammatory diseases, our study provides further advantages for the medical use of ESR.

Diesel Particulate Extract Accelerates Premature Skin Aging in Human Fibroblasts via Ceramide-1-Phosphate-Mediated Signaling Pathway

Both intrinsic (i.e., an individual’s body clock) and extrinsic factors (i.e., air pollutants and ultraviolet irradiation) accelerate premature aging. Epidemiological studies have shown a correlation between pollutant levels and aging skin symptoms. Diesel particle matter in particular leads to some diseases, including in the skin. Our recent study demonstrates that diesel particulate extract (DPE) increases apoptosis via increases in an anti-mitogenic/pro-apoptotic lipid mediator, ceramide in epidermal keratinocytes. Here, we investigated whether and how DPE accelerates premature skin aging using cultured normal human dermal fibroblasts (HDF). We first demonstrated that DPE increases cell senescence marker β-galactosidase activity in HDF. We then found increases in mRNA and protein levels, along with activity of matrix metalloprotease (MMP)-1 and MMP-3, which are associated with skin aging following DPE exposure. We confirmed increases in collagen degradation in HDF treated with DPE. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) is activated by DPE and results in increased ceramide production by sphingomyelinase activation in HDF. We identified that ceramide-1-phosphate (C1P) (produced from ceramide by ceramide kinase activation) activates MMP-1 and MMP-3 through activation of arachidonate cascade, followed by STAT 1- and STAT 3-dependent transcriptional activation.

Administration of an Acidic Sphingomyelinase (ASMase) Inhibitor, Imipramine, Reduces Hypoglycemia-Induced Hippocampal Neuronal Death

Severe hypoglycemia (below 35 mg/dL) appears most often in diabetes patients who continuously inject insulin. To rapidly cease the hypoglycemic state in this study, glucose reperfusion was conducted, which can induce a secondary neuronal death cascade following hypoglycemia. Acid sphingomyelinase (ASMase) hydrolyzes sphingomyelin into ceramide and phosphorylcholine. ASMase activity can be influenced by cations, pH, redox, lipids, and other proteins in the cells, and there are many changes in these factors in hypoglycemia. Thus, we expect that ASMase is activated excessively after hypoglycemia. Ceramide is known to cause free radical production, excessive inflammation, calcium dysregulation, and lysosomal injury, resulting in apoptosis and the necrosis of neurons. Imipramine is mainly used in the treatment of depression and certain anxiety disorders, and it is particularly known as an ASMase inhibitor. We hypothesized that imipramine could decrease hippocampal neuronal death by reducing ceramide via the inhibition of ASMase after hypoglycemia. In the present study, we confirmed that the administration of imipramine significantly reduced hypoglycemia-induced neuronal death and improved cognitive function. Therefore, we suggest that imipramine may be a promising therapeutic tool for preventing hypoglycemia-induced neuronal death.

N-Palmitoyl Serinol Stimulates Ceramide Production through a CB1-Dependent Mechanism in In Vitro Model of Skin Inflammation

Ceramides, a class of sphingolipids containing a backbone of sphingoid base, are the most important and effective structural component for the formation of the epidermal permeability barrier. While ceramides comprise approximately 50% of the epidermal lipid content by mass, the content is substantially decreased in certain inflammatory skin diseases, such as atopic dermatitis (AD), causing improper barrier function. It is widely accepted that the endocannabinoid system (ECS) can modulate a number of biological responses in the central nerve system, prior studies revealed that activation of endocannabinoid receptor CB1, a key component of ECS, triggers the generation of ceramides that mediate neuronal cell fate. However, as the impact of ECS on the production of epidermal ceramide has not been studied, we here investigated whether the ECS stimulates the generation of epidermal ceramides in an IL-4-treated in vitro model of skin inflammation using N-palmitoyl serinol (PS), an analog of the endocannabinoid N-palmitoyl ethanolamine. Accordingly, an IL-4-mediated decrease in cellular ceramide levels was significantly stimulated in human epidermal keratinocytes (KC) following PS treatment through both de novo ceramide synthesis- and sphingomyelin hydrolysis-pathways. Importantly, PS selectively increases ceramides with long-chain fatty acids (FAs) (C22–C24), which mainly account for the formation of the epidermal barrier, through activation of ceramide synthase (CerS) 2 and Cer3 in IL-4-mediated inflamed KC. Furthermore, blockade of cannabinoid receptor CB1 activation by AM-251 failed to stimulate the production of total ceramide as well as long-chain ceramides in response to PS. These studies demonstrate that an analog of endocannabinoid, PS, stimulates the generation of specific ceramide species as well as the total amount of ceramides via the endocannabinoid receptor CB1-dependent mechanism, thereby resulting in the enhancement of epidermal permeability barrier function.

Integrating proteomic, lipidomic and metabolomic data to construct a global metabolic network of lethal ventricular tachyarrhythmias (LVTA) induced by aconitine

Lethal ventricular tachyarrhythmias (LVTA)-related sudden cardiac death (SCD) is one of the major causes of death worldwide. However, the mechanisms underlying LVTA induced by myocardial ion channel diseases (MICDs) are not yet fully understood. Here, we produced an LVTA rat model induced by aconitine, to mimic MICDs-elicited LVTA, and constructed a global pathway network via integrating proteomic and lipidomic data, and our previously published metabolomic data. Results showed that both proteome and lipidome were disturbed during the LVTA process. Most of the differentially expressed proteins and lipid species were correlated. Proteomic data indicated disturbance of energy metabolism (e.g. fatty acid β-oxidation and the tricarboxylic acid cycle) and activation of the protein kinase C and nicotinamide adenine dinucleotide phosphate (NAPDH) oxidase pathway; these alterations led to lowered ATP and elevated ROS, respectively. Altered levels of the Ca²⁺ handling proteins suggested aberrant intracellular Ca²⁺ homeostasis, which might also be secondary to the shortage of ATP and oxidative stress. Significantly, the disrupted pathways implied by proteomic data were largely confirmed by lipidomic and metabolomic data. Collectively, we have constructed a metabolic pathway network of aconitine-induced LVTA using a multi-omics strategy, which confers great promise for the deeper interpretation of the mechanisms underlying LVTA. SIGNIFICANCE: In this study, we integrated proteomics, lipidomics and metabolomics to explore the pathophysiological processes of LVTA induced by aconitine. It is innovative to try to integrate these three omics in a study exploring the relative mechanisms. Here, based on the DEPs and differentially abundant lipid species (DALPs) between the LVTA groups and the controls, and the different metabolites discovered previously from the same model, we have successfully constructed a global metabolic network. Taken together, the multi-omics integration strategies used in this study show the potential for a new interpretation of the pathophysiological processes of LVTA induced by different conditions and open the possibility to explore deeper and broader mechanisms of other diseases.

Aryl Hydrocarbon Receptor Activation Downregulates IL-33 Expression in Keratinocytes via Ovo-Like 1

Background: IL-33, one of the IL-1 superfamily cytokines, has been shown to be associated with pruritus and inflammation in atopic dermatitis (AD). Furthermore, IL-33 production derived from keratinocytes reportedly has a crucial role in the development of AD; however, the mechanism of IL-33 expression has not been fully understood. Methods: We analyzed IL-33 expression in normal human epidermal keratinocytes (NHEKs) treated with IL-4. Results: IL-4 induced the upregulation of IL-33 expression in NHEKs. Based on the findings 1) that ovo-like 1 (OVOL1), a susceptible gene of AD, upregulates filaggrin (FLG) and loricrin (LOR) expression in NHEKs and 2) that reduced expression of FLG and LOR leads to production of IL-1 superfamily cytokines, we examined the involvement of OVOL1 in IL-33 expression in NHEKs. Knockdown of OVOL1 induced upregulation of IL-33 expression. Moreover, because Glyteer, an activator of aryl hydrocarbon receptor (AHR), reportedly upregulates OVOL1 expression, we examined whether treatment with Glyteer inhibited IL-33 expression in NHEKs. Treatment with Glyteer inhibited IL-4-induced upregulation of IL-33 expression, which was canceled by knockdown of either AHR or OVOL1. Conclusions: Activation of the AHR-OVOL1 axis inhibits IL-4-induced IL-33 expression, which could be beneficial for the treatment of AD.