Nicotinamide riboside and caffeine partially restore diminished NAD availability but not altered energy metabolism in Alzheimer's disease.

The redox co-factor nicotinamide adenine dinucleotide (NAD) declines with age, and NAD deficits are specifically associated with dysfunctional energy metabolism in late-onset Alzheimer's disease (LOAD). Nicotinamide riboside (NR), a dietary NAD precursor, has been suggested to ameliorate the aging process or neurodegeneration. We assessed whether NR with or without caffeine, which increases nicotinamide mononucleotide transferase subtype 2 (NMNAT2), an essential enzyme in NAD production, modulates bioenergetic functions in LOAD. In LOAD patients-and young or old control individuals-derived dermal fibroblasts as well as in induced pluripotent stem cell-differentiated neural progenitors and astrocytes, NR and caffeine cell type-specifically increased the NAD pool, transiently enhanced mitochondrial respiration or glycolysis and altered the expression of genes in the NAD synthesis or consumption pathways. However, continued treatment led to reversed bioenergetic effects. Importantly, NR and caffeine did not alter the characteristics of a previously documented inherent LOAD-associated bioenergetic phenotype. Thus, although NR and caffeine can partially restore diminished NAD availability, increasing NAD alone may not be sufficient to boost or restore energy metabolism in brain aging or alter aberrant energy management in LOAD. Nicotinamide riboside might still be of value in combination with other agents in preventive or therapeutic intervention strategies to address the aging process or age-associated dementia.

Hypothesis and Theory: Characterizing Abnormalities of Energy Metabolism Using a Cellular Platform as a Personalized Medicine Approach for Alzheimer's Disease.

Sporadic or late-onset Alzheimer's disease (LOAD) is characterized by slowly progressive deterioration and death of CNS neurons. There are currently no substantially disease-modifying therapies. LOAD pathology is closely related to changes with age and include, among others, accumulation of toxic molecules and altered metabolic, microvascular, biochemical and inflammatory processes. In addition, there is growing evidence that cellular energy deficits play a critical role in aging and LOAD pathophysiology. However, the exact mechanisms and causal relationships are largely unknown. In our studies we tested the hypothesis that altered bioenergetic and metabolic cell functions are key elements in LOAD, using a cellular platform consisting of skin fibroblasts derived from LOAD patients and AD-unaffected control individuals and therefrom generated induced pluripotent stem cells that are differentiated to brain-like cells to study LOAD pathogenic processes in context of age, disease, genetic background, cell development, and cell type. This model has revealed that LOAD cells exhibit a multitude of bioenergetic and metabolic alterations, providing evidence for an innate inefficient cellular energy management in LOAD as a prerequisite for the development of neurodegenerative disease with age. We propose that this cellular platform could ultimately be used as a conceptual basis for a personalized medicine tool to predict altered aging and risk for development of dementia, and to test or implement customized therapeutic or disease-preventive intervention strategies.

Brain cells derived from Alzheimer's disease patients have multiple specific innate abnormalities in energy metabolism.

Altered energy metabolism has been implicated both in aging and the pathogenesis of late-onset Alzheimer's disease (LOAD). However, it is unclear which anomalies are acquired phenotypes and which are inherent and predispose to disease. We report that neural progenitor cells and astrocytes differentiated from LOAD patient-derived induced pluripotent stem cells exhibit multiple inter-related bioenergetic alterations including: changes in energy production by mitochondrial respiration versus glycolysis, as a consequence of alterations in bioenergetic substrate processing and transfer of reducing agents, reduced levels of NAD/NADH, diminished glucose uptake and response rates to insulin (INS)/IGF-1 signaling, decreased INS receptor and glucose transporter 1 densities, and changes in the metabolic transcriptome. Our data confirm that LOAD is a "multi-hit" disorder and provide evidence for innate inefficient cellular energy management in LOAD that likely predisposes to neurodegenerative disease with age. These processes may guide the development and testing of diagnostic procedures or therapeutic agents.

HIF-1α-mediated BMP6 down-regulation leads to hyperproliferation and abnormal differentiation of keratinocytes in vitro.

Hypoxia-inducible factor-1α (HIF-1α) has been reported to be up-regulated in psoriatic epidermis, resulting in increased proliferation and abnormal differentiation of human keratinocytes (KCs). However, the role of HIF-1α in psoriatic epidermis, which is mainly composed of KCs, is poorly understood. Here, we show that morphogenic protein 6 (BMP6) is down-regulated when HIF-1α is upregulated in patients with psoriasis skin lesions. HIF-1α overexpression in primary human KCs promoted proliferation and inhibited terminal differentiation. Furthermore, HIF1-α repressed the expression of BMP6 by binding directly to the hypoxia-response element (HRE) in the BMP6 promotor region, which shows that BMP6 is a novel target gene of HIF-1α. We also found that HIF-1α-mediated BMP6 suppression could alter the proliferation status by modulating the expression levels of cell cycle regulatory proteins and also affect the early differentiation of KCs. Therefore, we suggest that HIF-1α-dependent BMP6 suppression has a critical role in the induction of hyper-proliferation and abnormal differentiation in psoriatic KCs.

RIP4 upregulates CCL20 expression through STAT3 signalling in cultured keratinocytes.

The receptor-interacting protein kinase 4 (RIP4), a serine/threonine kinase, is an important modulator of epidermal growth and cutaneous inflammation. We found that RIP4 expression was significantly increased in the lesional skin of psoriasis. However, the role and regulatory mechanism of RIP4 in psoriasis have not been characterized. After treatment with IL-17, RIP4 mRNA and protein levels were increased in HaCaT cells. IL-17 also activated the RIP4 promoter. To understand the functional role of RIP4 in keratinocyte and to investigate the genes regulated by RIP4, RNA-based microarray analysis was performed. Among immune response-related genes, CCL20 expression was significantly changed by RIP4. To identify RIP4-interacting protein, an immunoprecipitation assay was performed. As a result, STAT3 was identified as a new protein that interacts with RIP4. The interaction of RIP4 and STAT3 enhanced STAT3 phosphorylation. In addition, the transcriptional activity of STAT3 induced by RIP4 regulated IL-17-mediated CCL20 expression in HaCaT cells. Taken together, these findings indicate that IL-17 increased RIP4-mediated STAT3 phosphorylation by directly interacting with STAT3. Thus, transcriptional activation of STAT3 promotes the expression of CCL20. Thus, activations of these signalling pathways by RIP4 may contribute to epithermal inflammation in psoriatic keratinocytes.

IL-33 down-regulates CLDN1 expression through the ERK/STAT3 pathway in keratinocytes.

BACKGROUND: Tight junctions (TJs) have important roles in skin barrier function. The TJ protein claudin-1 (CLDN1) is decreased in atopic dermatitis (AD). However, little is known about the mechanism of CLDN1 down-expression. OBJECTIVE: To elucidate the effect of IL-33 on CLDN1 expression in keratinocytes. METHODS: Normal human epidermal keratinocytes (NHEKs) and human skin equivalent models (HSEMs) were cultured in vitro in the presence of IL-33. Production of CLDN1, signal transducer and activator of transcription 3 (STAT3) and Mitogen-activated protein kinases (MAPK) expression were measured by real-time PCR, western blot and immunofluorescence assay. MAPK inhibitors and small interfering RNA were used to confirm the signal pathway of STAT3 and CLDN1. Barrier function was measured by transepithelial electric resistance (TEER) and FITC-dextran flux assays. Electrophoretic Mobility Shift Assay was used to detect STAT3 transcriptional activity. RESULTS: Levels of CLDN1 expression were reduced in the epidermis of AD-model mice overexpressing IL-33. IL-33 down-regulated the expression of CLDN1 mRNA and protein in NHEKs and HSEMs. IL-33 attenuated transepithelial electric resistance and induced FITC-dextran flux in NHEKs. The IL-33 suppressed CLDN1 expression was regulated by an extracellular signal-regulated kinase (ERK) and signal transducer and activator of transcription 3 (STAT3). STAT3 suppressed CLDN1 expression by direct binding to the promoters. CONCLUSION: IL-33 may down-regulate CLDN1 expression through the ERK/STAT3 pathway in keratinocytes.

Late-onset Alzheimer's disease is associated with inherent changes in bioenergetics profiles.

Body-wide changes in bioenergetics, i.e., energy metabolism, occur in normal aging and disturbed bioenergetics may be an important contributing mechanism underlying late-onset Alzheimer's disease (LOAD). We investigated the bioenergetic profiles of fibroblasts from LOAD patients and healthy controls, as a function of age and disease. LOAD cells exhibited an impaired mitochondrial metabolic potential and an abnormal redox potential, associated with reduced nicotinamide adenine dinucleotide metabolism and altered citric acid cycle activity, but not with disease-specific changes in mitochondrial mass, production of reactive oxygen species, transmembrane instability, or DNA deletions. LOAD fibroblasts demonstrated a shift in energy production to glycolysis, despite an inability to increase glucose uptake in response to IGF-1. The increase of glycolysis and the abnormal mitochondrial metabolic potential in LOAD appeared to be inherent, as they were disease- and not age-specific. Our findings support the hypothesis that impairment in multiple interacting components of bioenergetic metabolism may be a key mechanism contributing to the risk and pathophysiology of LOAD.

Intracellular ROS levels determine the apoptotic potential of keratinocyte by Quantum Dot via blockade of AKT Phosphorylation.

Quantum dots (QDs) have shown great potential for biomedical use in a broad range including diagnostic agents. However, the regulatory mechanism of dermal toxicity is poorly understood. In this study, we investigated how QDs-induced apoptosis is regulated in human keratinocytes. We also examined the effect of carboxylic acid-coated QDs (QD 565 and QD 655) on reactive oxygen species (ROS) production and apoptosis-related cellular signalling. The viability of keratinocyte was inhibited by two types of QDs in a concentration-dependent manner. QDs induce ROS production and blockade of AKT phosphorylation. Moreover, the cleavage of AKT-dependent pro-apoptotic proteins such as poly (ADP-ribose) polymerase, caspases-3 and caspases-9 was significantly increased. We also found that a decrease in cellular ROS level by ROS scavenger, N-acetylcysteine (NAC), resulting in the abolishment of QDs-induced AKT de-phosphorylation and cellular apoptosis. Interestingly, QD 655 had a more cytotoxic effect including oxidative stress and AKT-dependent apoptosis than QD 565. In addition, QD 655 had the cytotoxic potential in the human skin equivalent model (HSEM). These data show that QD-induced intracellular ROS levels may be an important parameter in QD-induced apoptosis. These findings from this study indicate that intracellular ROS levels might determine the apoptotic potential of keratinocyte by QD via blockade of AKT phosphorylation.

TSLP Down-Regulates S100A7 and ß-Defensin 2 Via the JAK2/STAT3-Dependent Mechanism.

Elevated T-helper type 2 cytokines in atopic skin, such as IL-4 and IL-13, were thought to be responsible for an impaired expression of antimicrobial proteins, which may contribute to the increased susceptibility to skin infections in patients with atopic dermatitis. In this study, the relationship between thymic stromal lymphopoietin and antimicrobial proteins and the involved molecular pathway was defined in normal human epidermal keratinocytes and human skin equivalent model. Stimulation of normal human epidermal keratinocytes with thymic stromal lymphopoietin decreased both mRNA and levels of S100A7 and human ß-defensin 2 in a dose-dependent manner, and the regulation was JAK2/STAT3-dependent. Thymic stromal lymphopoietin decreased the antimicrobial protein expression, even in the presence of IL-17, which is their strong inducer. STAT3 directly regulated the S100A7 and human ß-defensin 2 promoters in normal human epidermal keratinocytes. Immunohistochemically, lesional atopic skin stained more intensely with phospho-STAT3 compared with healthy control. Our results show that up-regulated thymic stromal lymphopoietin may contribute to the deficiency of antimicrobial proteins in atopic dermatitis, including S100A7 and human ß-defensin 2, by a JAK2/STAT3-dependent mechanism and that STAT3/Sin3a might directly control the transcriptional activity of the antimicrobial protein promoters in normal human epidermal keratinocytes. Taken together, a key role of the JAK2/STAT3/Sin3a signaling pathway in thymic stromal lymphopoietin-mediated immune response in normal human epidermal keratinocytes might give us clues to understanding the pathological signal transductions in atopic dermatitis.

Chloroform upregulates early growth response-1-dependent thymic stromal lymphopoietin expression via the JNK and ERK pathways in human keratinocytes.

BACKGROUND: Exposure to volatile organic compounds (VOCs) in the environment has been reported to exacerbate allergic inflammatory diseases, such as atopic dermatitis (AD). However, the exact mechanism by which VOCs induce an inflammatory response in the skin is poorly understood. Thymic stromal lymphopoietin (TSLP) is known to be an important factor in the initiation and maintenance of allergic inflammatory diseases, including AD. OBJECTIVES: The aim of this work is to define the correlation between VOCs and TSLP. METHODS: The present study demonstrates dose-dependent increases of TSLP protein and mRNA levels in keratinocytes following exposure to chloroform. We further investigated the regulatory mechanisms of chloroform-induced TSLP expression in human keratinocytes. RESULTS: Chloroform induces early growth response-1 (Egr-1) protein expression in human keratinocytes. This process is mediated by the c-JUN N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) signaling pathways. Inhibition of phosphorylated JNK and ERK significantly downregulated Egr-1 expression, which was subsequently associated with reduced TSLP expression in chloroform-exposed human keratinocytes. Moreover, treatment of Egr-1 siRNA abolished chloroform-induced TSLP protein expression and TSLP promoter transcriptional activation. CONCLUSIONS: Taken together, these findings suggest that, in human keratinocytes, the upregulation of TSLP by chloroform is induced through an Egr-1-dependent mechanism that requires the c-JNK and ERK pathways. Our results suggest that exposure to chloroform may aggravate allergic skin diseases such as AD through Egr-1-dependent TSLP regulation.

IL-33 induces Egr-1-dependent TSLP expression via the MAPK pathways in human keratinocytes.

Atopic dermatitis (AD) is a chronic inflammatory skin disease in which T-helper type 2 (Th2)-type immune responses are dominant. Th2 cytokine, interleukin (IL)-33 and thymic stromal lymphopoietin (TSLP) have been suggested to have an important role in AD. IL-33 is highly expressed in AD, but its role in AD has not yet been fully understood. To further identify the role of IL-33 in AD, we investigated the expression of TSLP induced by IL-33 in keratinocytes. This study revealed that IL-33 induced TSLP expression in human keratinocytes. Early growth response protein 1 (Egr)-1, which is an inflammatory transcriptional factor, is induced by IL-33. IL-33-mediated TSLP induction in keratinocytes was suppressed by treatment with mitogen-activated protein kinase (MAPK) inhibitors or small interfering RNA against Egr-1. Chromatin immunoprecipitation (ChIP) assay indicated the direct involvement of Egr-1 in IL-33-mediated TSLP induction. Taken together, these findings indicate that IL-33 may increase TSLP expression through an Egr-1-dependent mechanism via ERK1/2, JNK and p38 activation in keratinocytes. These data suggest that the IL-33-ERK/JNK/p38/Egr-1/TSLP axis is involved in allergic skin Th2 inflammation, and it may be a novel therapeutic target.

Egr-1 is a key regulator of IL-17A-induced psoriasin upregulation in psoriasis.

The early growth response (Egr)-1 is a transcriptional factor which plays an important role in the regulation of cell growth, differentiation, cell survival and immune responses. Emerging evidences including our data demonstrate that the Egr-1 expression is up-regulated in the psoriatic skin lesions. The purpose of this study was to investigate the significance and regulatory mechanism of Egr-1 in the pathogenesis of psoriasis. Through microarray analysis, we found out that psoriasin (S100A7) expression was increased in the Egr-1 overexpressed cells. Our results showed that IL-17A increased Egr-1 expression in the skin of psoriatic patients and cultured human keratinocytes. We then investigated activation of mitogen-activated protein kinase as an upstream signal regulator of Egr-1 expression. IL-17A-induced Egr-1 expression was suppressed by ERK inhibitor. In addition, IL-17A induced psoriasin expression in cultured keratinocytes and the skin of IL-17A intradermally injected mouse. IL-17A-mediated psoriasin upregulation was reduced after treatment of small interfering RNAs against Egr-1. Furthermore, the results of chromatin immunoprecipitation assays demonstrated that Egr-1 directly binds the psoriasin promoter. Our findings present a novel signalling mechanism by which IL-17A can induce the Egr-1-dependent psoriasin expression via the ERK pathway in human keratinocytes. This study suggests that Egr-1 may be a novel and important modulator in IL-17A-mediated immune response in psoriasis.

ZnO nanoparticles induce TNF-α expression via ROS-ERK-Egr-1 pathway in human keratinocytes.

BACKGROUND: The area of nanotechnology continues to expand rapidly and zinc oxide (ZnO) nanoparticles (NPs) are widely being used in cosmetics and sunscreens. Although ZnO-NPs are considered materials that can potentially cause skin inflammation, the underlying mechanisms remain elusive. OBJECTIVE: The aim of this study was to investigate the signaling pathways of a cutaneous inflammatory response induced by ZnO-NPs. ZnO-NPs increased the early growth response-1 (Egr-1) expression, promoter activity and its nuclear translocation in HaCaT cells. METHODS: HaCaT cells and primary keratinocytes were exposed to ZnO NPs over a range of doses and time course. Protein levels and mRNA levels of Egr-1 and mitogen-activated protein kinase (MAPK) were measured by Western blot and ELISA, respectively. As an in vivo study, ZnO-NPs were applicated on mouse skin, and immunohistochemical stain with TNF-α and Egr-1 was done. RESULTS: ZnO-NPs activated extracellular signal-regulated kinase (ERK) of MAPK pathways. The up-regulation of Egr-1 expression by ZnO-NPs stimulation was found to be inhibited by an ERK inhibitor, but by neither c-Jun-N-terminal kinase (JNK) nor p38 inhibitor. Antioxidative N-acetyl-cysteine (NAC) strongly inhibited the level of Egr-1 and phosphorylated ERK expression in ZnO-NPs treated cells. ZnO NPs also increased tumor necrosis factor (TNF)-α expression and secretion, which were inhibited by the blockade of Egr-1 expression. CONCLUSIONS: The present study demonstrated that ZnO-NPs might induce inflammatory response via ROS-ERK-Egr-1 pathway in human keratinocytes.

UVB induces HIF-1α-dependent TSLP expression via the JNK and ERK pathways.

Thymic stromal lymphopoietin (TSLP) may have a key role in the initiation and maintenance of allergic inflammatory diseases, including atopic dermatitis. The present study revealed that UVB radiation exposure could induce TSLP expression in human keratinocytes and a human skin equivalent model. In addition, we investigated the regulatory mechanism of UVB-induced TSLP expression in keratinocytes. TSLP expression was upregulated by transfection with pcDNA3-hypoxia-inducible factor (HIF)-1α (P402A and P564A), which stably expresses HIF-1α protein. UVB-induced TSLP induction in keratinocytes was suppressed in the treatment of mitogen-activated protein kinase inhibitors or small interfering RNAs against HIF-1α. The results of chromatin immunoprecipitation assays indicate the direct involvement of HIF-1α in UVB-mediated TSLP induction. Taken together, these findings indicate that UVB exposure may increase TSLP expression through a HIF-1α-dependent mechanism via the c-JUN N-terminal kinase and extracellular signal-regulated kinase pathways in human keratinocytes. Our data showed that UVB-induced TSLP might increase secretion of the T-helper type 2-attracting chemokine (c-c motif) ligand 17 by human dendritic cells. The present study suggests an important role of HIF-1α in UVB-mediated immune response in keratinocytes.