Mitogen-activated protein kinase phosphatase-1 - a potential therapeutic target in metabolic disease

Role of Mitogen-Activated Protein (MAP) Kinase Pathways in Metabolic Diseases

Physiological processes that govern the normal functioning of mammalian cells are regulated by a myriad of signalling pathways. Mammalian mitogen-activated protein (MAP) kinases constitute one of the major signalling arms and have been broadly classified into four groups that include extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), p38, and ERK5. Each signalling cascade is governed by a wide array of external and cellular stimuli, which play a critical part in mammalian cells in the regulation of various key responses, such as mitogenic growth, differentiation, stress responses, as well as inflammation. This evolutionarily conserved MAP kinase signalling arm is also important for metabolic maintenance, which is tightly coordinated via complicated mechanisms that include the intricate interaction of scaffold proteins, recognition through cognate motifs, action of phosphatases, distinct subcellular localisation, and even post-translational modifications. Aberration in the signalling pathway itself or their regulation has been implicated in the disruption of metabolic homeostasis, which provides a pathophysiological foundation in the development of metabolic syndrome. Metabolic syndrome is an umbrella term that usually includes a group of closely associated metabolic diseases such as hyperglycaemia, hyperlipidaemia, and hypertension. These risk factors exacerbate the development of obesity, diabetes, atherosclerosis, cardiovascular diseases, and hepatic diseases, which have accounted for an increase in the worldwide morbidity and mortality rate. This review aims to summarise recent findings that have implicated MAP kinase signalling in the development of metabolic diseases, highlighting the potential therapeutic targets of this pathway to be investigated further for the attenuation of these diseases.

CGRP physiology, pharmacology, and therapeutic targets: migraine and beyond

Calcitonin gene-related peptide (CGRP) is a neuropeptide with diverse physiological functions. Its two isoforms (α and β) are widely expressed throughout the body in sensory neurons as well as in other cell types, such as motor neurons and neuroendocrine cells. CGRP acts via at least two G protein-coupled receptors that form unusual complexes with receptor activity-modifying proteins. These are the CGRP receptor and the AMY1 receptor; in rodents, additional receptors come into play. Although CGRP is known to produce many effects, the precise molecular identity of the receptor(s) that mediates CGRP effects is seldom clear. Despite the many enigmas still in CGRP biology, therapeutics that target the CGRP axis to treat or prevent migraine are a bench-to-bedside success story. This review provides a contextual background on the regulation and sites of CGRP expression and CGRP receptor pharmacology. The physiological actions of CGRP in the nervous system are discussed, along with updates on CGRP actions in the cardiovascular, pulmonary, gastrointestinal, immune, hematopoietic, and reproductive systems and metabolic effects of CGRP in muscle and adipose tissues. We cover how CGRP in these systems is associated with disease states, most notably migraine. In this context, we discuss how CGRP actions in both the peripheral and central nervous systems provide a basis for therapeutic targeting of CGRP in migraine. Finally, we highlight potentially fertile ground for the development of additional therapeutics and combinatorial strategies that could be designed to modulate CGRP signaling for migraine and other diseases.

MAP kinase phosphatase MKP-1 regulates p-ERK1/2 signaling pathway with fluoride treatment

Dental fluorosis is characterized by hypomineralization of tooth enamel caused by ingestion of excessive fluoride during enamel formation. Excess fluoride could have effects on the ERK signaling, which is essential for the ameloblasts differentiation and tooth development. MAP kinase phosphatase-1 (MKP-1) plays a critical role in regulating ERK related kinases. However, the role of MKP-1 in ameloblast and the mechanisms of MKP-1/ERK signaling in the pathogenesis of dental fluorosis are incompletely understood. Here, we adopted an in vitro fluorosis cell model using murine ameloblasts-like LS8 cells by employing sodium fluoride (NaF) as inducer. Using this system, we demonstrated that fluoride exposure led to an inhibition of p-MEK and p-ERK1/2 with a subsequent increase in MKP-1 expression in a dose-dependent manner. We further identified, under high dose fluoride, MKP-1 acted as a negative regulator of the fluoride-induced p-ERK1/2 signaling, leading to downregulation of CREB, c-myc, and Elk-1. Our results identify a novel MKP-1/ERK signaling mechanism that regulates dental fluorosis and provide a framework for studying the molecular mechanisms of intervention and fluorosis remodeling under normal and pathological conditions. MKP-1 inhibitors may prove to be a benefit therapeutic strategy for dental fluorosis treatment.

SIRT2 is involved in cisplatin-induced acute kidney injury through regulation of mitogen-activated protein kinase phosphatase-1

BACKGROUND

Activation of mitogen-activated protein kinase phosphatase-1 (MKP-1), a dual-specificity protein phosphatase, regulates mitogen-activated protein kinase signaling. C-Jun N-terminal kinase (JNK) and p38 are activated in cisplatin-induced renal injury. However, the change of MKP-1 expression in cisplatin-induced renal injury and the regulatory effect of sirtuin 2 (SIRT2), a nicotinamide adenine dinucleotide-dependent deacetylase, on MKP-1 remains unknown.

METHODS

To address these issues, we used constitutional Sirt2 knockout (KO) mice, transgenic (TG) mice with increased expression of SIRT2 specifically in proximal tubular epithelial cellsand wild-type (WT) mice. Cisplatin nephrotoxicity was induced by intraperitoneal injection of cisplatin.

RESULTS

MKP-1 expression in the kidney was decreased after cisplatin treatment. Cisplatin-induced downregulation of MKP-1 was reversed in Sirt2 KO mice kidney and further decreased in Sirt2 TG mice kidney. We observed similar phenomenon with SIRT2-knockdown or SIRT2-overexpressed tubular epithelial cells. Phosphorylation of p38 and JNK, a downstream signal pathway of MKP-1, increased in WT mice kidney following treatment with cisplatin. A decrease in SIRT2 suppressed cisplatin-induced phosphorylation of p38 and JNK in kidney and tubular epithelial cells. Overexpression of SIRT2 further increased phosphorylation of p38 and JNK in kidney and tubular epithelial cells. Acetylation of MKP-1 was significantly increased in SIRT2-knockdown cells and decreased in SIRT2-overexpressed cells after cisplatin stimulation. Sirt2 KO mice and Sirt2 TG mice showed amelioration and aggravation of renal injury, apoptosis, necroptosis and inflammation induced by cisplatin.

CONCLUSION

Our data show that SIRT2 is associated with cisplatin-induced renal injury through regulation of MKP-1 expression.

Downregulation of mitogen-activated protein kinases (MAPKs) in chronic ethanol-induced fatty liver

Mitogen-activated protein kinases (MAPKs) are versatile proteins that have been suggested to be involved in the regulation of lipid metabolism. This study was designed to investigate the responses of MAPK signaling to chronic ethanol exposure in vivo and in vitro, and try to explore its role in the pathogenesis of alcoholic fatty liver (AFL). Mice were fed with Lieber-Decarli liquid diet (5% ethanol, w/v) for 4 weeks to induce fatty liver, and the chronological changes of MAPK phosphorylation were measured using western blotting. We found that chronic ethanol feeding led to accumulation of triglyceride (TG), decreased phosphorylation of MAPKs, decreased protein level of peroxisomal proliferator activation receptor α (PPARα), and increased protein expression of cytochrome P4502E1 (CYP2E1) in mice liver. In vitro study showed that overexpression of CYP2E1 blunted the response of MAPKs to ethanol, and MAPK phosphatase 1 (MKP-1) knockdown by siRNA led to upregulation of PPARα protein level. Lastly, epidermal growth factor (EGF), a well-known MAPK activator, significantly suppressed chronic ethanol-induced hepatic fat accumulation and decline of PPARα expression in mice liver. Collectively, MAPK suppression, possibly due to the activation of hepatic CYP2E1, may be involved in chronic ethanol-induced hepatic steatosis.

Improving Obesity and Insulin Resistance by Targeting Skeletal Muscle MKP-1

Obesity has reached a global epidemic and it predisposes to the development of insulin resistance, type 2 diabetes and related metabolic diseases. Current interventions against obesity and/or type 2 diabetes such as calorie restriction, exercise, genetic manipulations or established pharmacological treatments have not been successful for many patients with obesity and/or type 2 diabetes. There is an urgent need for new strategies to treat insulin resistance, T2D and obesity. Increased activity of stress-responsive pathways has been linked to the pathogenesis of insulin resistance in obesity. In this commentary, we argue that chronic upregulation of MKP-1 in skeletal muscle is part of a stress response that contributes to the development of insulin resistance, T2D and obesity. Therefore, inhibition of MKP-1 in skeletal muscle is a potential strategy for the treatment of T2D and obesity. We highlight therapeutic strategies for potential targeting of MKP-1 in skeletal muscle for the treatment of metabolic diseases as well as other diseases of skeletal muscle.

Role of Alcohol Oxidative Metabolism in Its Cardiovascular and Autonomic Effects

Several review articles have been published on the neurobehavioral actions of acetaldehyde and other ethanol metabolites as well as in major alcohol-related disorders such as cancer and liver and lung disease. However, very few reviews dealt with the role of alcohol metabolism in the adverse cardiac and autonomic effects of alcohol and their potential underlying mechanisms, particularly in vulnerable populations. In this chapter, following a brief overview of the dose-related favorable and adverse cardiovascular effects of alcohol, we discuss the role of ethanol metabolism in its adverse effects in the brainstem and heart. Notably, current knowledge dismisses a major role for acetaldehyde in the adverse autonomic and cardiac effects of alcohol because of its low tissue level in vivo. Contrary to these findings in men and male rodents, women and hypertensive individuals are more sensitive to the adverse cardiac effects of similar amounts of alcohol. To understand this discrepancy, we discuss the autonomic and cardiac effects of alcohol and its metabolite acetaldehyde in a model of hypertension, the spontaneously hypertensive rat (SHR) and female rats. We present evidence that enhanced catalase activity, which contributes to cardioprotection in hypertension (compensatory) and in the presence of estrogen (inherent), becomes detrimental due to catalase catalysis of alcohol metabolism to acetaldehyde. Noteworthy, studies in SHRs and in estrogen deprived or replete normotensive rats implicate acetaldehyde in triggering oxidative stress in autonomic nuclei and the heart via (i) the Akt/extracellular signal-regulated kinases (ERK)/nitric oxide synthase (NOS) cascade and (ii) estrogen receptor-alpha (ERα) mediation of the higher catalase activity, which generates higher ethanol-derived acetaldehyde in female heart. The latter is supported by the ability of ERα blockade or catalase inhibition to attenuate alcohol-evoked myocardial oxidative stress and dysfunction. More mechanistic studies are needed to further understand the mechanisms of this public health problem.

A review of brain insulin signaling in mood disorders: From biomarker to clinical target

Patients with mood disorders are at increased risk for metabolic dysfunction. Co-occurrence of the two conditions is typically associated with a more severe disease course and poorer treatment outcomes. The specific pathophysiological mechanisms underlying this bidirectional relationship between mood and metabolic dysfunction remains poorly understood. However, it is likely that impairment of metabolic processes within the brain play a critical role. The insulin signaling pathway mediates metabolic homeostasis and is important in the regulation of neurotrophic and synaptic plasticity processes, including those involved in neurodegenerative diseases like Alzheimer's. Thus, insulin signaling in the brain may serve to link metabolic function and mood. Central insulin signaling is mediated through locally secreted insulin and widespread insulin receptor expression. Here we review the preclinical and clinical data addressing the relationships between central insulin signaling, cellular metabolism, neurotrophic processes, and mood regulation, including key points of mechanistic overlap. These relationships have important implications for developing biomarker-based diagnostics and precision medicine approaches to treat severe mood disorders.

A Single Bout of Electroacupuncture Remodels Epigenetic and Transcriptional Changes in Adipose Tissue in Polycystic Ovary Syndrome

A single bout of electroacupuncture results in muscle contractions and increased whole body glucose uptake in women with polycystic ovary syndrome (PCOS). Women with PCOS have transcriptional and epigenetic alterations in the adipose tissue and we hypothesized that electroacupuncture induces epigenetic and transcriptional changes to restore metabolic alterations. Twenty-one women with PCOS received a single bout of electroacupuncture, which increased the whole body glucose uptake. In subcutaneous adipose tissue biopsies, we identified treatment-induced expression changes of 2369 genes (Q < 0.05) and DNA methylation changes of 7055 individual genes (Q = 0.11). The largest increase in expression was observed for FOSB (2405%), and the largest decrease for LOC100128899 (54%). The most enriched pathways included Acute phase response signaling and LXR/RXR activation. The DNA methylation changes ranged from 1-16%, and 407 methylation sites correlated with gene expression. Among genes known to be differentially expressed in PCOS, electroacupuncture reversed the expression of 80 genes, including PPARγ and ADIPOR2. Changes in the expression of Nr4a2 and Junb are reversed by adrenergic blockers in rats demonstrating that changes in gene expression, in part, is due to activation of the sympathetic nervous system. In conclusion, low-frequency electroacupuncture with muscle contractions remodels epigenetic and transcriptional changes that elicit metabolic improvement.

Circadian clock regulates hepatic polyploidy by modulating Mkp1-Erk1/2 signaling pathway

Liver metabolism undergoes robust circadian oscillations in gene expression and enzymatic activity essential for liver homeostasis, but whether the circadian clock controls homeostatic self-renewal of hepatocytes is unknown. Here we show that hepatocyte polyploidization is markedly accelerated around the central vein, the site of permanent cell self-renewal, in mice deficient in circadian Period genes. In these mice, a massive accumulation of hyperpolyploid mononuclear and binuclear hepatocytes occurs due to impaired mitogen-activated protein kinase phosphatase 1 (Mkp1)-mediated circadian modulation of the extracellular signal-regulated kinase (Erk1/2) activity. Time-lapse imaging of hepatocytes suggests that the reduced activity of Erk1/2 in the midbody during cytokinesis results in abscission failure, leading to polyploidization. Manipulation of Mkp1 phosphatase activity is sufficient to change the ploidy level of hepatocytes. These data provide clear evidence that the Period genes not only orchestrate dynamic changes in metabolic activity, but also regulate homeostatic self-renewal of hepatocytes through Mkp1-Erk1/2 signaling pathway.

Circadian clock regulates hepatic gene expression and functions. Here Chao et al. show that alteration of circadian clock genes by Period deletion induces polyploidy in hepatocytes due to impaired regulation of Erk signaling by mitogen-activated protein kinase phosphatase 1.

Caffeic acid methyl and ethyl esters exert potential antidiabetic effects on glucose and lipid metabolism in cultured murine insulin-sensitive cells through mechanisms implicating activation of AMPK

CONTEXT

Caffeic acid methyl (CAME) and ethyl (CAEE) esters stimulate glucose uptake and AMP-activated protein kinase (AMPK) in C2C12 myocytes (ATCC^® CRL-1772^TM).

OBJECTIVE

Effects of CAME and CAEE were now assessed on myocyte glucose transporter GLUT4 activity and expression, on hepatic gluconeogenesis and on adipogenesis as well as major underlying signaling pathways.

MATERIALS AND METHODS

GLUT4 protein translocation was studied in L6 GLUT4myc cells, glucose-6-phospatase (G6Pase) in H4IIE hepatocytes and adipogenesis in 3T3-L1 adipocytes. Key modulators were measured using western immunoblot. Cells were treated for 18 h with either CAME or CAEE at various concentrations (12.5-100 μM).

RESULTS

Myocyte glucose uptake rose from 10.1 ± 0.5 to 18.7 ± 0.8 and 21.9 ± 1.0 pmol/min/mg protein in DMSO-, CAME- and CAEE-stimulated cells, respectively, similar to insulin (17.7 ± 1.2 pmol/min/mg protein), while GLUT4myc translocation increased significantly by 1.70 ± 0.18, by 1.73 ± 0.18- and by 1.95 ± 0.30-fold (relative to DMSO), following insulin, CAME and CAEE stimulation, respectively. CAME and CAEE suppressed hepatocyte G6Pase by 62.0 ± 6.9% and 62.7 ± 6.0% with IC₅₀ of 45.93 and 22.64 μM, respectively, comparable to insulin (70.7 ± 2.3% inhibition). Finally, CAME and CAEE almost abrogated adipogenesis (83.3 ± 7.2% and 97.3 ± 3.0% at 100 μM; IC₅₀ of 13.8 and 12.9 μM, respectively). The compounds inhibited adipogenic factors C/EBP-β and PPAR-γ and stimulated AMPK activity in the three cell-lines.

DISCUSSION AND CONCLUSIONS

CAME and CAEE exerted antidiabetic activities in insulin-responsive cells through insulin-independent mechanisms involving AMPK and adipogenic factors.

Acid-sensing ion channel 1a mediates acid-induced inhibition of matrix metabolism of rat articular chondrocytes via the MAPK signaling pathway

The acid-sensing ion channel 1a (ASIC1a), which is activated by extracellular acid, contributes to the pathogenesis of rheumatoid arthritis. However, it remains unclear whether ASIC1a mediates acid-induced matrix metabolism in rat articular chondrocytes via activation of the MAPK signaling pathway. In the current study, we found that extracellular acidification (pH 6.0) inhibited proliferation and induced apoptosis of articular chondrocytes in a dose-dependent manner, while the expression of phosphorylated ERK1/2 and P38 MAPK increased, but, this effect was blocked by the Ca²⁺ chelator BAPTA-AM and the ASIC1a-specific blocker PcTx-1. In addition, extracellular acidification increased the expression of c-fos, GAG, HYP, and TIM1/2. These effects were inhibited by the Ca²⁺ chelator BAPTA-AM, ERK1/2 inhibitor PD98059, and ASIC1a-specific blocker PcTx-1, but not the P38 MAPK inhibitor SB203580. Finally, extracellular acidification increased the expression of c-jun and MMP-2/9, and these effects were blocked by the Ca²⁺ chelator BAPTA-AM, P38 MAPK inhibitor SB203580, and ASIC1a-specific blocker PcTx-1, but not the ERK1/2 inhibitor PD98059. In conclusion, ASIC1a inhibits the expression of MMP-2/9, GAG, HYP, and TIMP-1/2 by the Ca²⁺-dependent P38 MAPK/c-jun and ERK/c-fos signaling pathways.

ERK1 and ERK2 activation modulates diet-induced obesity in mice

Obesity is a worldwide problem, and dietary lipids play an important role in its pathogenesis. Recently, Erk1 knock-out (ERK1^-/-) mice have been shown to exhibit low preference for dietary fatty acids. Hence, we maintained Erk1^-/- mice on a high-fat diet (HFD) to assess the implication of this mitogen-activated protein (MAP) kinase in obesity. The Erk1^-/- mice, fed the HFD, were more obese than wild-type (WT) animals, fed the same diet. Erk1^-/- obese mice gained more fat and liver mass than WT obese animals. No difference was observed in daily food and energy intake in HFD-fed both group of animals. However, feed efficiency was higher in Erk1^-/- than WT animals. Blood cholesterol, triglyceride and insulin concentrations were higher in Erk1^-/- obese mice compared to WT obese animals. Accordingly, homeostatic model assessment of insulin resistance (HOMA-IR) value was higher in Erk1^-/- obese mice compared to WT obese animals. Interestingly, only Erk1^-/- obese mice, but not WT-obese animals, exhibited high degree of phosphorylation of liver MEK, the upstream regulator of ERK1/2. This phenomenon was associated with high liver ERK2 phosphorylation in Erk1^-/- obese mice which also had high liver acetyl-CoA carboxylase 1 (ACC1) and fatty acid synthase (FAS) mRNA expression, suggesting high lipogenesis in these animals. The Erk1^-/- obese mice also had low PPAR-α and CPT1β mRNA, indicating low fatty acid oxidation. Our observations suggest that ERK1 and ERK2 might play key roles in the regulation of obesity.

MAP kinase phosphatase DUSP1 is overexpressed in obese humans and modulated by physical exercise

Chronic low-grade inflammation and dysregulation of the stress defense system are cardinal features of obesity, a major risk factor for the development of insulin resistance and diabetes. Dual-specificity protein phosphatase 1 (DUSP1), known also as MAP kinase phosphatase 1 (MKP1), is implicated in metabolism and energy expenditure. Mice lacking DUSP1 are resistant to high-fat diet-induced obesity. However, the expression of DUSP1 has not been investigated in human obesity. In the current study, we compared the expression pattern of DUSP1 between lean and obese nondiabetic human subjects using subcutaneous adipose tissue (SAT) and peripheral blood mononuclear cells (PBMCs). The levels of DUSP1 mRNA and protein were significantly increased in obese subjects with concomitant decrease in the phosphorylation of p38 MAPK (p-p38 MAPK) and PGC-1α and an increase in the levels of phospho-JNK (p-JNK) and phospho-ERK (p-ERK). Moreover, obese subjects had higher levels of circulating DUSP1 protein that correlated positively with various obesity indicators, triglycerides, glucagon, insulin, leptin, and PAI-1 (P < 0.05) but negatively with V̇O(2max) and high-density lipoprotein (P < 0.05). The observation that DUSP1 was overexpressed in obese subjects prompted us to investigate whether physical exercise could reduce its expression. In this study, we report for the first time that physical exercise significantly attenuated the expression of DUSP1 in both the SAT and PBMCs, with a parallel increase in the expression of PGC-1α and a reduction in the levels of p-JNK and p-ERK along with attenuated inflammatory response. Collectively, our data suggest that DUSP1 upregulation is strongly linked to adiposity and that physical exercise modulates its expression. This gives further evidence that exercise might be useful as a strategy for managing obesity and preventing its associated complications.

Natural product agonists of peroxisome proliferator-activated receptor gamma (PPARγ): a review

Agonists of the nuclear receptor PPARγ are therapeutically used to combat hyperglycaemia associated with the metabolic syndrome and type 2 diabetes. In spite of being effective in normalization of blood glucose levels, the currently used PPARγ agonists from the thiazolidinedione type have serious side effects, making the discovery of novel ligands highly relevant.

Natural products have proven historically to be a promising pool of structures for drug discovery, and a significant research effort has recently been undertaken to explore the PPARγ-activating potential of a wide range of natural products originating from traditionally used medicinal plants or dietary sources. The majority of identified compounds are selective PPARγ modulators (SPPARMs), transactivating the expression of PPARγ-dependent reporter genes as partial agonists. Those natural PPARγ ligands have different binding modes to the receptor in comparison to the full thiazolidinedione agonists, and on some occasions activate in addition PPARα (e.g. genistein, biochanin A, sargaquinoic acid, sargahydroquinoic acid, resveratrol, amorphastilbol) or the PPARγ-dimer partner retinoid X receptor (RXR; e.g. the neolignans magnolol and honokiol). A number of in vivo studies suggest that some of the natural product activators of PPARγ (e.g. honokiol, amorfrutin 1, amorfrutin B, amorphastilbol) improve metabolic parameters in diabetic animal models, partly with reduced side effects in comparison to full thiazolidinedione agonists. The bioactivity pattern as well as the dietary use of several of the identified active compounds and plant extracts warrants future research regarding their therapeutic potential and the possibility to modulate PPARγ activation by dietary interventions or food supplements.

Role of rostral ventrolateral medullary ERK/JNK/p38 MAPK signaling in the pressor effects of ethanol and its oxidative product acetaldehyde

BACKGROUND

We tested the hypothesis that alterations of the phosphorylation/dephosphorylation profile of mitogen-activated protein kinases (MAPKs) in the rostral ventrolateral medulla (RVLM) underlie the pressor response elicited by ethanol (EtOH) microinjection into the RVLM of spontaneously hypertensive rats (SHRs). The studies were extended to determine whether acetaldehyde (ACA), the primary oxidative product of EtOH, replicates the molecular effects of EtOH within the RVLM and the consequent pressor response.

METHODS

Effects of EtOH or ACA on blood pressure (BP) were evaluated in the absence or presence of selective JNK (SP600125), ERK (PD98059), p38 (SB203580), or ser/thr phosphatases (okadaic acid [OKA]) inhibitor.

RESULTS

Intra-RVLM EtOH (10 μg/rat) or ACA (2 μg/rat) caused a similar ERK2-dependent pressor response because EtOH or ACA-evoked increases in BP and in RVLM p-ERK2 level were abolished after pharmacologic inhibition of ERK phosphorylation. SP600125 abrogated the pressor action of EtOH, but not ACA, thus implicating JNK in EtOH action on BP. Despite EtOH enhancement of p38 phosphorylation, pharmacological studies argued against a causal role for this kinase in EtOH-evoked pressor response. RVLM phosphatase catalytic activity was not influenced by EtOH or ACA. Interestingly, pharmacologic phosphatase inhibition (OKA), which increased RVLM p-ERK2 and BP, abrogated the pressor effect of subsequently administered EtOH or ACA.

CONCLUSIONS

Enhancement of RVLM ERK2 phosphorylation constitutes a major molecular mechanism for the pressor response elicited by intra-RVLM EtOH or its metabolite, ACA, in conscious SHRs. Further, RVLM kinases dephosphorylation does not contribute to intra-RVLM EtOH- or ACA-evoked pressor response.

The brain Renin-Angiotensin system and mitochondrial function: influence on blood pressure and baroreflex in transgenic rat strains

Mitochondrial dysfunction is implicated in many cardiovascular diseases, including hypertension, and may be associated with an overactive renin-angiotensin system (RAS). Angiotensin (Ang) II, a potent vasoconstrictor hormone of the RAS, also impairs baroreflex and mitochondrial function. Most deleterious cardiovascular actions of Ang II are thought to be mediated by NADPH-oxidase- (NOX-) derived reactive oxygen species (ROS) that may also stimulate mitochondrial oxidant release and alter redox-sensitive signaling pathways in the brain. Within the RAS, the actions of Ang II are counterbalanced by Ang-(1–7), a vasodilatory peptide known to mitigate against increased oxidant stress. A balance between Ang II and Ang-(1–7) within the brain dorsal medulla contributes to maintenance of normal blood pressure and proper functioning of the arterial baroreceptor reflex for control of heart rate. We propose that Ang-(1–7) may negatively regulate the redox signaling pathways activated by Ang II to maintain normal blood pressure, baroreflex, and mitochondrial function through attenuating ROS (NOX-generated and/or mitochondrial).

The mitogen-activated protein kinase phosphatase-1 (MKP-1) gene is a potential methylation biomarker for malignancy of breast cancer

The mitogen-activated protein kinase (MAPK) phosphatase- 1 (MKP-1) belongs to the MAPK cascades which are central to cell proliferation and apoptosis. The carcinogenic role of MKP-1 has been reported in many types of cancer but it has rarely been investigated in breast cancer. The present study was designed to evaluate the MKP-1 mRNA expression and its possible regulation by methylation of MKP-1 promoter in the model of several breast cancer cell lines and tissues as well as controls. Our data demonstrate MKP-1 mRNA expression significantly decreased in five breast cancer cell lines compared to breast controls (P<0.01). Using the methylation-specific PCR (MSP) analysis, the unmethylated reaction (U) is dominant in both normal cell lines and benign breast tumors (100% vs. 86.2%), whereas the methylated reaction (M) is dominant in both breast cancer cell lines and invasive breast tumors (100% vs. 57.2%). In terms of methylation ratio (M/M+U), methylation level in MKP-1 promoter is significantly higher in the invasive breast tumor tissues (n = 152) than in benign breast tumor tissues (n = 29) (P<0.0001). Assessing the methylation ratio of the promoter of MKP-1 gene to diagnose the breast malignancy (invasive vs. benign), the area under the receiver- operating characteristic (ROC) curve was 0.809 (95% CI: 0.711-0.906, P<0.001). The best performance for this prediction has a sensitivity of 76.32% and a specificity of 82.76% at the cutoff value of 0.38. Taken together, we firstly demonstrated that the promoter methylation of MKP-1 gene is a potential breast cancer biomarker for breast malignancy.

NADPH oxidase 4 mediates insulin-stimulated HIF-1α and VEGF expression, and angiogenesis in vitro

Acute intensive insulin therapy causes a transient worsening of diabetic retinopathy in type 1 diabetes patients and is related to VEGF expression. Reactive oxygen species (ROS) have been shown to be involved in HIF-1α and VEGF expression induced by insulin, but the role of specific ROS sources has not been fully elucidated. In this study we examined the role of NADPH oxidase subunit 4 (Nox4) in insulin-stimulated HIF-1α and VEGF expression, and angiogenic responses in human microvascular endothelial cells (HMVECs). Here we demonstrate that knockdown of Nox4 by siRNA reduced insulin-stimulated ROS generation, the tyrosine phosphorylation of IR-β and IRS-1, but did not change the serine phosphorylation of IRS-1. Nox4 gene silencing had a much greater inhibitory effect on insulin-induced AKT activation than ERK1/2 activation, whereas it had little effect on the expression of the phosphatases such as MKP-1 and SHIP. Inhibition of Nox4 expression inhibited the transcriptional activity of VEGF through HIF-1. Overexpression of wild-type Nox4 was sufficient to increase VEGF transcriptional activity, and further enhanced insulin-stimulated the activation of VEGF. Downregulation of Nox4 expression decreased insulin-stimulated mRNA and protein expression of HIF-1α, but did not change the rate of HIF-1α degradation. Inhibition of Nox4 impaired insulin-stimulated VEGF expression, cell migration, cell proliferation, and tube formation in HMVECs. Our data indicate that Nox4-derived ROS are essential for HIF-1α-dependent VEGF expression, and angiogenesis in vitro induced by insulin. Nox4 may be an attractive therapeutic target for diabetic retinopathy caused by intensive insulin treatment.

MKP-1 is essential for canonical vitamin D-induced signaling through nuclear import and regulates RANKL expression and function

Vitamin D(3,) and its most active form, 1,25(OH)(2)D(3), are well known to stimulate osteoclastogenesis through stromal cell induction of the receptor activator of nuclear factor-κB ligand (RANKL). MAPK phosphatase-1 (MKP-1) is a phosphatase classically known to negatively regulate the innate immune response through dephosphorylation of p38, ERK, and c-Jun N-terminal kinase activity. This paper describes a new function of MKP-1 in permitting genomic 1,25(OH)(2)D(3) signaling and downstream osteoclastogenesis through RANKL. Initially, quantitative RT-PCR (qRT-PCR) and immunoblot analysis comparing bone marrow stromal cells (BMSC) revealed that 1,25(OH)(2)D(3)-induced vitamin D receptor (VDR), cytochrome P 45024a1, and RANKL mRNA expression and protein were significantly attenuated or absent in MKP-1(-/-) BMSC. Immunoblot analysis from cellular fractions of wild type and MKP-1(-/-) BMSC stimulated with 10(-7) m 1,25(OH)(2)D(3) revealed retinoid X receptor (RXR)α nuclear import was impaired in MKP-1(-/-) BMSC, whereas VDR import was not. Proximity ligation assays revealed that baseline VDR-RXRα heterodimer translocation was unchanged, yet 1,25(OH)(2)D(3)-induced nuclear translocation of VDR-RXRα heterodimers was reduced in MKP-1(-/-) BMSC. A functional consequence was observed as BMSC from MKP-1(-/-) mice treated with 1,25(OH)(2)D(3) and cocultured with RAW 264.7 cells had a 91% decrease in osteoclastogenesis and a 94.5% decrease in mineralized matrix resorption compared with wild-type cocultures (P < 0.01). These results reveal an unexpected, permissive role for MKP-1 in canonical 1,25(OH)(2)D(3) signaling via VDR-RXRα heterodimer nuclear import and downstream osteoclastogenesis through stromal cell RANKL expression.