Nitric oxide stimulates COX-2 expression in cultured collecting duct cells through MAP kinases and superoxide but not cGMP

Elucidating the roles of SOD3 correlated genes and reactive oxygen species in rare human diseases using a bioinformatic-ontology approach

Superoxide Dismutase 3 (SOD3) scavenges extracellular superoxide giving a hydrogen peroxide metabolite. Both Reactive Oxygen Species diffuse through aquaporins causing oxidative stress and biomolecular damage. SOD3 is differentially expressed in cancer and this research utilises Gene Expression Omnibus data series GSE2109 with 2,158 cancer samples. Genome-wide expression correlation analysis was conducted with SOD3 as the seed gene. Categorical SOD3 Pearson Correlation gene lists incrementing in correlation strength by 0.01 from ρ≥|0.34| to ρ≥|0.41| were extracted from the data. Positively and negatively SOD3 correlated genes were separated for each list and checked for significance against disease overlapping genes in the ClinVar and Orphanet databases via Enrichr. Disease causal genes were added to the relevant gene list and checked against Gene Ontology, Phenotype Ontology, and Elsevier Pathways via Enrichr before the significant ontologies containing causal and non-overlapping genes were reviewed with a literature search for possible disease and oxidative stress associations. 12 significant individually discriminated disorders were identified: Autosomal Dominant Cutis Laxa (p = 6.05x10-7), Renal Tubular Dysgenesis of Genetic Origin (p = 6.05x10-7), Lethal Arteriopathy Syndrome due to Fibulin-4 Deficiency (p = 6.54x10-9), EMILIN-1-related Connective Tissue Disease (p = 6.54x10-9), Holt-Oram Syndrome (p = 7.72x10-10), Multisystemic Smooth Muscle Dysfunction Syndrome (p = 9.95x10-15), Distal Hereditary Motor Neuropathy type 2 (p = 4.48x10-7), Congenital Glaucoma (p = 5.24x210-9), Megacystis-Microcolon-Intestinal Hypoperistalsis Syndrome (p = 3.77x10-16), Classical-like Ehlers-Danlos Syndrome type 1 (p = 3.77x10-16), Retinoblastoma (p = 1.9x10-8), and Lynch Syndrome (p = 5.04x10-9). 35 novel (21 unique) genes across 12 disorders were identified: ADNP, AOC3, CDC42EP2, CHTOP, CNN1, DES, FOXF1, FXR1, HLTF, KCNMB1, MTF2, MYH11, PLN, PNPLA2, REST, SGCA, SORBS1, SYNPO2, TAGLN, WAPL, and ZMYM4. These genes are proffered as potential biomarkers or therapeutic targets for the corresponding rare diseases discussed.

Unravelling bisphenol A-induced hepatotoxicity: Insights into oxidative stress, inflammation, and energy dysregulation

Bisphenol A (BPA), a prevalent plastic monomer and endocrine disruptor, negatively impacts metabolic functions. This study examines the chronic effects of eco-relevant BPA concentrations on hepatotoxicity, focusing on redox balance, inflammatory response, cellular energy sensors, and metabolic homeostasis in male Swiss albino mice. Chronic BPA exposure resulted in reactive oxygen species (ROS) accumulation, altered hepatic antioxidant defense, lipid peroxidation, and NOX4 expression, leading to reduced cell viability. Additionally, BPA exposure significantly upregulated hepatic pro-inflammatory cytokine genes (Tnf-α, Il-1β, Il-6), NOS2, and arginase II, correlating with increased TLR4 expression, NF-κB phosphorylation, and a dose-dependent decrease in IκBα levels. BPA-induced NF-κB nuclear localization and inflammasome activation (NLRP3, cleaved caspase-1, IL-1β) established an inflammatory milieu. Perturbations in hepatic AMPKα phosphorylation, SIRT1, and PGC-1α, along with elevated p38 MAPK phosphorylation and ERα expression, indicated BPA-induced energy dysregulation. Furthermore, increased PLA2G4A, COX1, COX2, and PTGES2 expression in BPA-treated liver correlated with hyperlipidemia, hepatic FASN expression, steatosis, and visceral adiposity, likely due to disrupted energy sensors, oxidative stress, and inflammasome activation. Elevated liver enzymes (ALP, AST, ALT) and apoptotic markers indicated liver damage. Notably, N-acetylcysteine (NAC) priming reversed BPA-induced hepatocellular ROS accumulation, NF-κB-inflammasome activation, and intracellular lipid accumulation, while upregulating cellular energy sensors and attenuating ERα expression, suggesting NAC's protective effects against BPA-induced hepatotoxicity. Pharmacological inhibition of the NF-κB/NLRP3 cascade in BAY11-7082 pretreated, or NLRP3 immunodepleted hepatocytes reversed BPA's negative impact on SIRT1/p-AMPKα/PGC-1α and intracellular lipid accumulation, providing mechanistic insights into BPA-induced metabolic disruption.

Impact of photoperiod on uterine redox/inflammatory and metabolic status of golden hamster, Mesocricetus auratus

Photoperiod modulates reproductive physiology at multiple levels in seasonally breeding animals. Golden hamsters are long-day breeders that diminish their fertility during the short days. Photoperiod is known to regulate hormonal milieu and uterus is a hormone-sensitive dynamic tissue. However, there is lack of molecular insight regarding the impact of photoperiod on uterine physiology with respect to redox and metabolic status in Mesocricetus auratus. We evaluated the impact of photoperiod on circulatory hormonal parameters (triiodothyronine [T3], thyroxin [T4], estradiol [E2], progesterone [P4], melatonin, and insulin), their receptor expressions and key markers associated with redox (SIRT-1/FOXO-1), inflammatory (NFĸB/COX-2) and metabolic (IR/GLUT4) status in uterus. Adult female golden hamsters were exposed to different photoperiodic regimes, that is, short photoperiod (SP; 8L:16D) and long photoperiod (LP; 16L:8D) for 12 weeks. SP drastically decreased peripheral hormone profiles (T3, T4, E2, and P4) and compromised uterine histoarchitecture when compared with LP-exposed hamsters. Further, SP markedly decreased thyroid hormone receptor-α (TRα), insulin receptor, and glucose uptake transporter-4 (GLUT-4) expressions in uterus. We noted enhanced uterine oxidative (increased MDA and decreased SOD/CAT levels), SIRT-1/FOXO-1 expression and inflammatory (NFĸB/COX-2) load in SP condition. Further, elevated levels of circulatory insulin, melatonin, and its receptor (MT-1) expression in uterus was noted under SP condition. Thus, we may suggest that photoperiod might regulate uterine seasonality through modulation of local hormonal and redox/metabolic homeostasis thereby may restrict offspring bearing capacity under short days.

Expression of COX-2 and Nrf2/GPx3 in the anterior vaginal wall tissues of women with pelvic organ prolapse

PURPOSE

To evaluate COX-2 and Nrf2/GPx3 expressions in the lamina propria of the anterior vaginal wall tissues of women with and without pelvic organ prolapse (POP).

METHODS

Tissue samples of anterior vaginal wall were examined using HE staining, immuohistochemical staining and Western blot for the expressions of COX-2/PGE2, Nrf2/GPx3, MMP2, TIMP1, collagen I and collagen III (n = 35, per group).

RESULTS

Compared with control group, collagen fibers of the anterior vaginal wall were disorganized and discontinuous. Expressions of Nrf2, GPx3, TIMP1, collagen I and collagen III were found significantly lower in POP group (P < 0.05); while, expressions of COX-2, PGE2, and MMP2 were found significantly higher in POP group (P < 0.05). Statistically significant correlations of COX-2 and Nrf2/GPx3 were showed (P < 0.01).

CONCLUSION

We found that the interaction between inflammation and oxidative stress was closely related to the development of POP. This study demonstrates that COX-2 and Nrf2 pathways may be involved in pathogenesis of POP, as promising potential therapeutic targets and agents.

The roles of p38 MAPK → COX2 and NF-κB → COX2 signal pathways in age-related testosterone reduction

In our study, we explored changes in the redox status and inflammatory response in the testes of the SAMP8 model of varying ages (2, 4, 8, 10 months old) compared with control mice SAMR1 by the methods of immunohistochemical staining, Western blotting, RT-PCR and Luminex multi-analyte cytokine profiling. We found that as ROS and inflammation levels increased during aging, steroidogenic enzymes (StAR and P450scc) reduced and led to the decline of testosterone production eventually. The pathways of P38 MAPK → COX2 and NF-κB → COX2 were detected by using specific inhibitors of SB203580 and Bay 11-7082 in isolated Leydig cells. These results indicated that activation of both p38 MAPK → COX2 and NF-κB → COX2 signaling pathways are functionally linked to the oxidative stress response and chronic inflammation during aging, and mediate their inhibitory effects on testosterone production.

Getting the Message? Native Reactive Electrophiles Pass Two Out of Three Thresholds to be Bona Fide Signaling Mediators

Precision cell signaling activities of reactive electrophilic species (RES) are arguably among the most poorly-understood means to transmit biological messages. Latest research implicates native RES to be a chemically-distinct subset of endogenous redox signals that influence cell decision making through non-enzyme-assisted modifications of specific proteins. Yet, fundamental questions remain regarding the role of RES as bona fide second messengers. Here, we lay out three sets of criteria we feel need to be met for RES to be considered as true cellular signals that directly mediate information transfer by modifying "first-responding" sensor proteins. We critically assess the available evidence and define the extent to which each criterion has been fulfilled. Finally, we offer some ideas on the future trajectories of the electrophile signaling field taking inspiration from work that has been done to understand canonical signaling mediators. Also see the video abstract here: https://youtu.be/rG7o0clVP0c.

Preconditioning c-Kit-positive Human Cardiac Stem Cells with a Nitric Oxide Donor Enhances Cell Survival through Activation of Survival Signaling Pathways

Cardiac stem cell therapy has shown very promising potential to repair the infarcted heart but is severely limited by the poor survival of donor cells. Nitric oxide (NO) has demonstrated cytoprotective properties in various cells, but its benefits are unknown specifically for human cardiac stem cells (hCSCs). Therefore, we investigated whether pretreatment of hCSCs with a widely used NO donor, diethylenetriamine nitric oxide adduct (DETA-NO), promotes cell survival. Results from lactate dehydrogenase release assays showed a dose- and time-dependent attenuation of cell death induced by oxidative stress after DETA-NO preconditioning; this cytoprotective effect was abolished by the NO scavenger. Concomitant up-regulation of several cell signaling molecules after DETA-NO preconditioning was observed by Western blotting, including elevated phosphorylation of NRF2, NFκB, STAT3, ERK, and AKT, as well as increased protein expression of HO-1 and COX2. Furthermore, pharmaceutical inhibition of ERK, STAT3, and NFκB activities significantly diminished NO-induced cytoprotection against oxidative stress, whereas inhibition of AKT or knockdown of NRF2 only produced a minor effect. Blocking PI3K activity or knocking down COX2 expression did not alter the protective effect of DETA-NO on cell survival. The crucial roles of STAT3 and NFκB in NO-mediated signaling pathways were further confirmed by stable expression of gene-specific shRNAs in hCSCs. Thus, preconditioning hCSCs with DETA-NO promotes cell survival and resistance to oxidative stress by activating multiple cell survival signaling pathways. These results will potentially provide a simple and effective strategy to enhance survival of hCSCs after transplantation and increase their efficacy in repairing infarcted myocardium.

Endogenous flow-induced nitric oxide reduces superoxide-stimulated Na/H exchange activity via PKG in thick ascending limbs

Luminal flow stimulates endogenous nitric oxide (NO) and superoxide (O2 (-)) production by renal thick ascending limbs (TALs). The delicate balance between these two factors regulates Na transport in TALs; NO enhances natriuresis, whereas O2 (-) augments Na absorption. Endogenous, flow-stimulated O2 (-) enhances Na/H exchange (NHE). Flow-stimulated NO reduces flow-induced O2 (-), a process mediated by cGMP-dependent protein kinase (PKG). However, whether flow-stimulated, endogenously-produced NO diminishes O2 (-)-stimulated NHE activity and the signaling pathway involved are unknown. We hypothesized that flow-induced NO reduces the stimulation of NHE activity caused by flow-induced O2 (-) via PKG in TALs. Intracellular pH recovery after an acid load was measured as an indicator of NHE activity in isolated, perfused rat TALs. l-Arginine, the NO synthase substrate, decreased NHE activity by 34 ± 5% (n = 5; P < 0.04). The O2 (-) scavenger tempol decreased NHE activity by 46 ± 8% (n = 6; P < 0.004) in the absence of NO. In the presence of l-arginine, the inhibitory effect of tempol on NHE activity was reduced to -19 ± 6% (n = 6; P < 0.03). The soluble guanylate cyclase inhibitor LY-83583 blocked the effect of l-arginine thus restoring tempol's effect on NHE activity to -42 ± 4% (n = 6; P < 0.0005). The PKG inhibitor KT-5823 also inhibited l-arginine's effect on tempol-reduced NHE activity (-43 ± 5%; n = 5; P < 0.03). We conclude that flow-induced NO reduces the stimulatory effect of endogenous, flow-induced O2 (-) on NHE activity in TALs via an increase in cGMP and PKG activation.

Renal medullary cyclooxygenase-2 and (pro)renin receptor expression during angiotensin II-dependent hypertension

The (pro)renin receptor [(P)RR] upregulates cyclooxygenase-2 (COX-2) in inner medullary collecting duct (IMCD) cells through ERK1/2. Intrarenal COX-2 and (P)RR are upregulated during chronic ANG II infusion. However, the duration of COX-2 and (P)RR upregulation has not been determined. We hypothesized that during the early phase of ANG II-dependent hypertension, membrane-bound (P)RR and COX-2 are augmented in the renal medulla, serving to buffer the hypertensinogenic and vasoconstricting effects of ANG II. In Sprague-Dawley rats infused with ANG II (0.4 μg·min(-1)·kg(-1)), systolic blood pressure (BP) increased by day 7 (162 ± 5 vs. 114 ± 10 mmHg) and continued to increase by day 14 (198 ± 15 vs. 115 ± 13 mmHg). Membrane-bound (P)RR was augmented at day 3 coincident with phospho-ERK1/2 levels, COX-2 expression, and PGE2 in the renal medulla. In contrast, membrane-bound (P)RR was reduced and COX-2 protein levels were not different from controls by day 14. In cultured IMCD cells, ANG II increased secretion of the soluble (P)RR. In anesthetized rats, COX-2 inhibition decreased the glomerular filtration rate (GFR) and renal blood flow (RBF) during the early phase of ANG II infusion without altering BP. However, at 14 days of ANG II infusions, COX-2 inhibition decreased mean arterial BP (MABP), RBF, and GFR. Thus, during the early phase of ANG II-dependent hypertension, the increased (P)RR and COX-2 expression in the renal medulla may contribute to attenuate the vasoconstrictor effects of ANG II on renal hemodynamics. In contrast, at 14 days the reductions in RBF and GFR caused by COX-2 inhibition paralleled the reduced MABP, suggesting that vasoconstrictor COX-2 metabolites contribute to ANG II hypertension.

Cyclooxygenase metabolites in the kidney

In the mammalian kidney, prostaglandins (PGs) are important mediators of physiologic processes, including modulation of vascular tone and salt and water. PGs arise from enzymatic metabolism of free arachidonic acid (AA), which is cleaved from membrane phospholipids by phospholipase A2 activity. The cyclooxygenase (COX) enzyme system is a major pathway for metabolism of AA in the kidney. COX are the enzymes responsible for the initial conversion of AA to PGG2 and subsequently to PGH2, which serves as the precursor for subsequent metabolism by PG and thromboxane synthases. In addition to high levels of expression of the "constitutive" rate-limiting enzyme responsible for prostanoid production, COX-1, the "inducible" isoform of cyclooxygenase, COX-2, is also constitutively expressed in the kidney and is highly regulated in response to alterations in intravascular volume. PGs and thromboxane A2 exert their biological functions predominantly through activation of specific 7-transmembrane G-protein-coupled receptors. COX metabolites have been shown to exert important physiologic functions in maintenance of renal blood flow, mediation of renin release and regulation of sodium excretion. In addition to physiologic regulation of prostanoid production in the kidney, increases in prostanoid production are also seen in a variety of inflammatory renal injuries, and COX metabolites may serve as mediators of inflammatory injury in renal disease.

Angiotensin II-independent upregulation of cyclooxygenase-2 by activation of the (Pro)renin receptor in rat renal inner medullary cells

During renin-angiotensin system activation, cyclooxygenase-2 (COX-2)-derived prostaglandins attenuate the pressor and antinatriuretic effects of angiotensin II (AngII) in the renal medulla. The (pro)renin receptor (PRR) is abundantly expressed in the collecting ducts (CD) and its expression is augmented by AngII. PRR overexpression upregulates COX-2 via mitogen-activated kinases/extracellular regulated kinases 1/2 in renal tissues; however, it is not clear whether this effect occurs independently or in concert with AngII type 1 receptor (AT1R) activation. We hypothesized that PRR activation stimulates COX-2 expression independently of AT(1)R in primary cultures of rat renal inner medullary cells. The use of different cell-specific immunomarkers (aquaporin-2 for principal cells, anion exchanger type 1 for intercalated type-A cells, and tenascin C for interstitial cells) and costaining for AT(1)R, COX-2, and PRR revealed that PRR and COX-2 were colocalized in intercalated and interstitial cells whereas principal cells did not express PRR or COX-2. In normal rat kidney sections, PRR and COX-2 were colocalized in intercalated and interstitial cells. In rat renal inner medullary cultured cells, treatment with AngII (100 nmol/L) increased COX-2 expression via AT(1)R. In addition, AngII and rat recombinant prorenin (100 nmol/L) treatments increased extracellular regulated kinases 1/2 phosphorylation, independently. Importantly, rat recombinant prorenin upregulated COX-2 expression in the presence of AT(1)R blockade. Inhibition of mitogen-activated kinases/extracellular regulated kinases 1/2 suppressed COX-2 upregulation mediated by either AngII or rat recombinant prorenin. Furthermore, PRR knockdown using PRR-short hairpin RNA blunted the rat recombinant prorenin-mediated upregulation of COX-2. These results indicate that COX-2 expression is upregulated by activation of either PRR or AT(1)R via mitogen-activated kinases/extracellular regulated kinases 1/2 in rat renal inner medullary cells.

Pendrin protein abundance in the kidney is regulated by nitric oxide and cAMP

Pendrin is a Cl(-)/HCO(3)(-) exchanger, expressed in the apical regions of some intercalated cell subtypes, and is critical in the pressor response to angiotensin II. Since angiotensin type 1 receptor inhibitors reduce renal pendrin protein abundance in mice in vivo through a mechanism that is dependent on nitric oxide (NO), we asked if NO modulates renal pendrin expression in vitro and explored the mechanism by which it occurs. Thus we quantified pendrin protein abundance by confocal fluorescent microscopy in cultured mouse cortical collecting ducts (CCDs) and connecting tubules (CNTs). After overnight culture, CCDs maintain their tubular structure and maintain a solute gradient when perfused in vitro. Pendrin protein abundance increased 67% in CNT and 53% in CCD when NO synthase was inhibited (N(G)-nitro-L-arginine methyl ester, 100 μM), while NO donor (DETA NONOate, 200 μM) application reduced pendrin protein by ∼33% in the CCD and CNT. When CNTs were cultured in the presence of the guanylyl cyclase inhibitor 1H-[1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (10 μM), NO donors did not alter pendrin abundance. Conversely, pendrin protein abundance rose when cAMP content was increased by the application of an adenylyl cyclase agonist (forskolin, 10 μM), a cAMP analog (8-bromo-cAMP, 1 mM), or a phosphodiesterase inhibitor (BAY60-7550, 50 μM). Since NO reduces cellular cAMP in the CNT, we asked if NO reduces pendrin abundance by reducing cAMP. With blockade of cGMP-stimulated phosphodiesterase II, NO did not alter pendrin protein abundance. We conclude that NO acts through cAMP to reduce pendrin total protein abundance by enhancing cAMP degradation.

Renal interstitial hyaluronan: functional aspects during normal and pathological conditions

The glycosaminoglycan (GAG) hyaluronan (HA) is recognized as an important structural component of the extracellular matrix, but it also interacts with cells during embryonic development, wound healing, inflammation, and cancer; i.e., important features in normal and pathological conditions. The specific physicochemical properties of HA enable a unique hydration capacity, and in the last decade it was revealed that in the interstitium of the renal medulla, where the HA content is very high, it changes rapidly depending on the body hydration status while the HA content of the cortex remains unchanged at very low amounts. The kidney, which regulates fluid balance, uses HA dynamically for the regulation of whole body fluid homeostasis. Renomedullary HA elevation occurs in response to hydration and during dehydration the opposite occurs. The HA-induced alterations in the physicochemical characteristics of the interstitial space affects fluid flux; i.e., reabsorption. Antidiuretic hormone, nitric oxide, angiotensin II, and prostaglandins are classical hormones/compounds involved in renal fluid handling and are important regulators of HA turnover during variations in hydration status. One major producer of HA in the kidney is the renomedullary interstitial cell, which displays receptors and/or synthesis enzymes for the hormones mentioned above. During several kidney disease states, such as ischemia-reperfusion injury, tubulointerstitial inflammation, renal transplant rejection, diabetes, and kidney stone formation, HA is upregulated, which contributes to an abnormal phenotype. In these situations, cytokines and other growth factors are important stimulators. The immunosuppressant agent cyclosporine A is nephrotoxic and induces HA accumulation, which could be involved in graft rejection and edema formation. The use of hyaluronidase to reduce pathologically overexpressed levels of tissue HA is a potential therapeutic tool since diuretics are less efficient in removing water bound to HA in the interstitium. Although the majority of data describing the role of HA originate from animal and cell studies, the available data from humans demonstrate that an upregulation of HA also occurs in diabetic kidneys, in transplant-rejected kidneys, and during acute tubular necrosis. This review summarizes the current knowledge regarding interstitial HA in the role of regulating kidney function during normal and pathological conditions. It encompasses mechanistic insights into the background of the heterogeneous intrarenal distribution of HA; i.e., late nephrogenesis, its regulation during variations in hydration status, and its involvement during several pathological conditions. Changes in hyaluronan synthases, hyaluronidases, and binding receptor expression are discussed in parallel.

Roles of reactive oxygen and nitrogen species in pain

Peroxynitrite (PN; ONOO⁻) and its reactive oxygen precursor superoxide (SO; O₂•⁻) are critically important in the development of pain of several etiologies including pain associated with chronic use of opiates such as morphine (also known as opiate-induced hyperalgesia and antinociceptive tolerance). This is now an emerging field in which considerable progress has been made in terms of understanding the relative contributions of SO, PN, and nitroxidative stress in pain signaling at the molecular and biochemical levels. Aggressive research in this area is poised to provide the pharmacological basis for development of novel nonnarcotic analgesics that are based upon the unique ability to selectively eliminate SO and/or PN. As we have a better understanding of the roles of SO and PN in pathophysiological settings, targeting PN may be a better therapeutic strategy than targeting SO. This is because, unlike PN, which has no currently known beneficial role, SO may play a significant role in learning and memory. Thus, the best approach may be to spare SO while directly targeting its downstream product, PN. Over the past 15 years, our team has spearheaded research concerning the roles of SO and PN in pain and these results are currently leading to the development of solid therapeutic strategies in this important area.

Effect of glutathione redox state on Leydig cell susceptibility to acute oxidative stress

The free radical, or oxidative stress, theory posits that imbalance in cells between prooxidants and antioxidants results in an altered redox state and, over time, an accumulation of oxidative damage. We hypothesized herein that cells with an increasingly prooxidant intracellular environment also might be particularly susceptible to acute oxidative stress. To test this hypothesis, MA-10 cells were used as a model because of their well-defined, measurable function, namely progesterone production. We first experimentally altered the redox environment of the cells by their incubation with buthionine sulfoximine (BSO) or diethyl maleate (DEM) so as to deplete glutathione (GSH), and then exposed the GSH-depleted cells acutely to the prooxidant tert-butyl hydroperoxide (t-BuOOH). Neither BSO nor DEM by themselves affected progesterone production. However, when the GSH-depleted cells subsequently were exposed acutely to t-BuOOH, intracellular reactive oxygen species concentration was significantly increased, and this was accompanied by significant reductions in progesterone production. In striking contrast, treatment of control cells with t-BuOOH had no effect. Depletion of GSH and subsequent treatment of the cells with t-BuOOH-induced the phosphorylation of each of ERK1/2, JNK and p38, members of the MAPK family. Inhibition of p38 phosphorylation largely prevented the t-BuOOH-induced down-regulation of progesterone production in GSH-depleted cells. These results suggest that, as hypothesized, alteration of the intracellular GSH redox environment results in the increased sensitivity of MA-10 cells to oxidative stress, and that this is mediated by activation of one or more redox-sensitive MAPK members.

Reactive nitroxidative species and nociceptive processing: determining the roles for nitric oxide, superoxide, and peroxynitrite in pain

Pain is a multidimensional perception and is modified at distinct regions of the neuroaxis. During enhanced pain, neuroplastic changes occur in the spinal and supraspinal nociceptive modulating centers and may result in a hypersensitive state termed central sensitization, which is thought to contribute to chronic pain states. Central sensitization culminates in hyperexcitability of dorsal horn nociceptive neurons resulting in increased nociceptive transmission and pain perception. This state is associated with enhanced nociceptive signaling, spinal glutamate-mediated N-methyl-D: -aspartate receptor activation, neuroimmune activation, nitroxidative stress, and supraspinal descending facilitation. The nitroxidative species considered for their role in nociception and central sensitization include nitric oxide (NO), superoxide ([Formula: see text]), and peroxynitrite (ONOO(-)). Nitroxidative species are implicated during persistent but not normal nociceptive processing. This review examines the role of nitroxidative species in pain through a discussion of their contributions to central sensitization and the underlying mechanisms. Future directions for nitroxidative pain research are also addressed. As more selective pharmacologic agents are developed to target nitroxidative species, the exact role of nitroxidative species in pain states will be better characterized and should offer promising alternatives to available pain management options.

Leydig cells: From stem cells to aging

Leydig cells are the testosterone-producing cells of the testis. The adult Leydig cell population ultimately develops from undifferentiated mesenchymal-like stem cells present in the interstitial compartment of the neonatal testis. Four distinct stages of adult Leydig cell development have been identified and characterized: stem Leydig cells, progenitor Leydig cells, immature Leydig cells and adult Leydig cells. The stem Leydig cells are undifferentiated cells that are capable of indefinite self-renewal, differentiation, and replenishment of the Leydig cell niche. Progenitor Leydig cells are derived from the stem Leydig cells. These spindle-shaped cells are luteinizing hormone (LH) receptor positive, have high mitotic activity, and produce little testosterone but rather testosterone metabolites. The progenitor Leydig cells give rise to immature Leydig cells which are round, contain large amounts of smooth endoplasmic reticulum, and produce some testosterone but also very high levels of testosterone metabolites. A single division of these cells produces adult Leydig cells, which are terminally differentiated cells that produce high levels of testosterone. As men age, serum testosterone levels decline, and this is associated with alterations in body composition, energy level, muscle strength, physical, sexual and cognitive functions, and mood. In the Brown Norway rat, used extensively as a model for male reproductive aging, age-related reductions in serum testosterone result from significant decline in the ability of aged Leydig cells to produce testosterone in response to LH stimulation. This review describes Leydig cell development and aging. Additionally, the molecular mechanisms by which testosterone synthesis declines with aging are discussed.

Leydig cell aging and the mechanisms of reduced testosterone synthesis

In males, serum testosterone levels decline with advancing age. Though part of a complex process, this age-related decline in testosterone appears to occur, in part, due to a significant decline in the ability of aged Leydig cells to produce testosterone maximally in response to luteinizing hormone (LH). The structure of the molecular machinery responsible for the synthesis of testosterone is described, and placed in the context of Leydig cell biology. Multiple parameters related to the synthesis of testosterone by the Leydig cell have been observed to change with age. Relationships among these changes are reviewed. A discussion of potential causes of the age-related decline in Leydig cell steroidogenic capacity presents a model in which the inability of aged cells to adequately respond to hormonal stimulation results in cellular regression with concomitant decline in maximal testosterone output.

Exogenous nitric oxide regulates cyclooxygenase-2 expression and prostaglandin D(2) generation through p38 MAPK in mouse bone marrow-derived mast cells

Nitric oxide (NO) is an important signaling molecule that regulates MC function. However, the involvement of NO in an important lipid mediator, prostaglandin (PG) D(2) production by MC, is unclear. The role of NO in cyclooxygenase (COX)-2 expression and PGD(2) generation as well as IL-6 production in mouse bone marrow-derived MC (BMMC) was investigated using NO donors. Exogenous NO augmented COX-2 protein expression and increased COX-2-dependent PGD(2) generation in response to SCF, IL-10, and IL-1beta, or antigen activation in combination with IL-10 and IL-1beta after sensitization with IgE. The increased expression of COX-2 by NO donors was inhibited by hemoglobin. Moreover it was not affected by soluble guanylyl cyclase inhibitor, but reduced by the p38 MAPK inhibitor, SB202190. Downstream of p38 MAPK, NO donors augmented not only COX-2 mRNA transcription but also its stability. Exogenous NO also augmented IL-6 production by SCF, IL-10, and IL-1beta. These results show that exogenous NO can increase COX-2-dependent PGD(2) and IL-6 production by MC in inflammatory environments through the p38 MAPK pathway. Therefore, our novel observations suggest that the effect of NO on MC is not limited to the suppression of their activation as has been the emphasis previously, but can also augment certain MC responses.

Nitric oxide decreases expression of osmoprotective genes via direct inhibition of TonEBP transcriptional activity

During antidiuresis, renal medullary cells adapt to the hyperosmotic interstitial environment by increased expression of osmoprotective genes, which is driven by a common transcriptional activator, tonicity-responsive enhancer binding protein (TonEBP). Because nitric oxide (NO) is abundantly produced in the renal medulla, the present studies addressed the effect of NO on expression of osmoprotective genes and TonEBP activation in MDCK cells. Several structurally unrelated NO donors blunted tonicity-induced up-regulation of TonEBP target genes involved in intracellular accumulation of organic osmolytes. These effects were mediated by reduced transcriptional activity of TonEBP, as assessed by tonicity-responsive elements- and aldose reductase promoter-driven reporter constructs. Neither total TonEBP abundance nor nuclear translocation of TonEBP was affected by NO. Furthermore, 8-bromo-cGMP and peroxynitrite failed to reproduce the inhibitory effect of NO, indicating that NO acts directly on TonEBP rather than through classical NO signaling pathways. In support of this notion, electrophoretic mobility shift assays showed reduced binding of TonEBP to its target sequence in nuclear extracts prepared from MDCK cells treated with NO in vivo and in nuclear extracts exposed to NO in vitro. Furthermore, immunoprecipitation of S-nitrosylated proteins and the biotin-switch method identified TonEBP as a target for S-nitrosylation, which correlates with reduced DNA binding and transcriptional activity. These observations disclose a novel direct inhibitory effect of NO on TonEBP, a phenomenon that may be relevant for regulation of osmoprotective genes in the renal medulla.

Cyclooxygenases 1 and 2 contribute to peroxynitrite-mediated inflammatory pain hypersensitivity

Peroxynitrite (ONOO(-)), the reaction product of the interaction between superoxide (O(2)(*-)) and nitric oxide (*NO), is a potent proinflammatory and cytotoxic nitrooxidative species. Its role as a mediator of hyperalgesia (clinically defined as an augmented sensitivity to painful stimuli) is not known. In light of the known proinflammatory properties of ONOO(-), our study addressed its potential involvement in the development of hyperalgesia associated with tissue damage and inflammation. Intraplantar injection in rats of the ONOO(-) precursor O(2)(*-) (1 microM) led to the development of thermal hyperalgesia associated with a profound localized inflammatory response. Both events were blocked by L-NAME (N(G)-nitro-L-arginine methyl ester, 3-30 mg/kg), a nitric oxide synthase inhibitor, or by FeTM-4-PyP(5+) [Fe(III)5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin, 3-30 mg/kg], an ONOO(-) decomposition catalyst. These results suggested that locally synthesized ONOO(-) produced in situ by O(2)(*-) and *NO is key in the development of inflammatory hyperalgesia. The direct link between ONOO(-) and hyperalgesia was further supported by demonstrating that intraplantar injection of soluble ONOO(-) itself (1 microM) similarly led to inflammatory hyperalgesia. ONOO(-) generated by the interaction between exogenous administration of O(2)(*-) and endogenous *NO, or provided by direct injection of ONOO(-), activated the transcription factor NF-kappaB in paw tissues, enhancing expression of the inducible but not the constitutive cyclooxygenase enzyme (COX-2 and COX-1, respectively). ONOO(-)-mediated hyperalgesia was blocked in a dose-dependent manner by intraperitoneal injections of indomethacin (10 mg/kg), a nonselective COX-1/COX-2 inhibitor, or NS398 [N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide; 10 mg/kg] a selective COX-2 inhibitor, as well as by an anti-prostaglandin (PG) E(2) antibody (200 microg). In another established model of inflammation-related hyperalgesia by intraplantar injection of carrageenan in rats, inhibition of ONOO(-) with FeTM-4-PyP(5+) (3-30 mg/kg) inhibited the development of hyperalgesia and the release of PGE(2) in paw tissue exudates. Furthermore, FeTM-4-PyP(5+) synergized with indomethacin and NS397 (1-10 mg/kg) to block both hyperalgesia and edema. Taken together, these data show for the first time that ONOO(-) is a potent mediator of inflammation-derived hyperalgesia operating via the COX-to-PGE(2) pathway. These results provide a pharmacological rationale for the development of inhibitors of peroxynitrite biosynthesis as novel nonnarcotic analgesics. The broad implications of our study are that dual inhibition of both ONOO(-) formation and COX activity may provide an alternative therapeutic approach to the management of pain: effective analgesia with reduced side-effects typically associated with the use of COX inhibitors.

Different effects of 26-week dietary intake of rapeseed oil and soybean oil on plasma lipid levels, glucose-6-phosphate dehydrogenase activity and cyclooxygenase-2 expression in spontaneously hypertensive rats

We intended to determine whether or not dietary canola oil (CO) elevates plasma lipids and oxidative stress, since both of these are, possibly, related to the CO-induced life shortening through exacerbation of hypertension-associated vascular lesions found in stroke-prone spontaneously hypertensive rats (SHRSP). Spontaneously hypertensive rats (SHR) were used in this study to avoid a potential bias in the results due to the irregular death by stroke seen in SHRSP. SHR were fed for 26 weeks on a chow containing either, 10 wt/wt% of CO or soybean oil (SO), i.e., the control. Elevated plasma lipids and glucose-6-phosphate dehydrogenase (G6PD) activation in the liver and erythrocyte were found in SHR fed CO compared to that fed SO, while anti-oxidative enzymes other than G6PD were not activated. The CO diet brought about significant vascular lesions in the kidney, in which abundant cyclooxygenase-2 (COX-2) positive foci were immunochemically located in the juxtaglomerular apparatus. These results suggest that dietary CO induces a hyperlipidemic condition, in which G6PD may serve as an NADPH provider, and aggravates genetic diseases in SHR (also, probably, in SHRSP). The increased COX-2 expression indicates a role of renin-angiotensin-aldosterone system activation in the increased vascular lesions, whereas the effects of oxidative stress remain unclear.

Evidence that age-related changes in p38 MAP kinase contribute to the decreased steroid production by the adrenocortical cells from old rats

The current studies were initiated to investigate whether excessive oxidative stress exerts its antisteroidogenic action through modulation of oxidant-sensitive mitogen-activated protein kinase (MAPK) signaling pathways. Western blot analysis indicated that aging caused increased phosphorylation and activation of rat adrenal p38 MAPK, but not the ERK1/2 or JNK1/2. Lipid peroxidation measurements (an index of cellular oxidative stress) indicated that adrenal membranes from young animals contained only minimal levels of endogenous thiobarbituric acid-reactive substances (TBARS), and exposure of membranes to enzymatic and non-enzymatic pro-oxidants enhanced TBARS formation approximately 12- and 20-fold, respectively. The adrenal membranes from old animals showed much more susceptibility to lipid peroxidation and exhibited roughly 4- to 6-fold higher TBARS formation than young controls both under basal conditions and in response to pro-oxidants. Qualitatively similar results were obtained when lipid peroxide formation was measured using a sensitive FOXRS (ferrous oxidation-xylenol orange-reactive substances) technique. We next tested whether aging-induced excessive oxidative insult alters steroidogenesis through modulation of MAPK signaling pathway. Treatment of adrenocortical cells from old rats with specific p38 MAPK inhibitors restored Bt(2)cAMP-stimulated steroidogenesis approximately 60-70% of the value seen in cells of young animals. Likewise, pretreatment of cells with reactive oxygen species (ROS) scavengers MnTMPyP and N-acetyl cysteine also partially rescued age-induced loss of steroid production. In contrast, simultaneous treatment of cells with ROS scavengers and p38 MAPK inhibitor did not produce any additional effect suggesting that both types of inhibitors exert their stimulatory action through inhibition of p38 MAPK activation. Collectively, these results indicate that p38 MAPK functions as a signaling effector in oxidative stress-induced inhibition of steroidogenesis during aging.

Ectodomain shedding of pro-TGF-alpha is required for COX-2 induction and cell survival in renal medullary cells exposed to osmotic stress

In the renal medulla, cyclooxygenase (COX)-2 is induced by osmotic stress as present in this kidney region during antidiuresis. Increasing evidence suggests that EGF receptor (EGFR) signaling is involved in this process. The aim of the present study was to examine the mechanisms responsible for COX-2 expression and PGE(2) production during hypertonic conditions and to identify potential autocrine/paracrine EGFR ligands. Immunohistochemisty and Western blot analysis revealed abundant expression of the pro-EGFR ligand pro-transforming growth factor (TGF)-alpha in renal medullary cells in vivo and in cultured Madin-Darby canine kidney cells. In Madin-Darby canine kidney cells, hypertonicity rapidly increased TNF-alpha converting enzyme (TACE)-dependent ectodomain shedding of pro-TGF-alpha; phosphorylation of EGFR, p38, and ERK1/2; expression of COX-2; and production of PGE(2). Conversely, TACE inhibition prevented TGF-alpha release; EGFR, p38, and ERK1/2 activation; and COX-2 expression. Furthermore, cell survival was reduced substantially, a response that could be reversed by the addition of PGE(2). Simultaneous addition of recombinant TGF-alpha during TACE inhibition restored EGFR and MAPK phosphorylation, COX-2 expression, PGE(2) production, and cell survival during osmotic stress. These results indicate that hypertonicity induces TACE-mediated ectodomain shedding of pro-TGF-alpha, which subsequently activates COX-2 expression in an autocrine/paracrine fashion, via EGFR and MAPKs. We conclude that tonicity-induced TGF-alpha release is required for COX-2 expression, PGE(2) synthesis, and survival of renal medullary cells during osmotic stress.

Altered collecting duct adenylyl cyclase content in collecting duct endothelin-1 knockout mice

Background

Endothelin-1 (ET-1) inhibition of vasopressin (AVP)-stimulated water reabsorption by the inner medullary collecting duct (IMCD) is associated with reduced cAMP accumulation. To determine the effect of ET-1 deficiency, AVP-stimulated cAMP responsiveness was assessed in IMCD from mice with collecting duct-specific deletion of ET-1 (CD ET-1 KO) and from control animals.

Methods

Cyclic AMP production, adenylyl cyclase (AC) mRNA, and AC protein were measured in acutely isolated IMCD.

Results

CD ET-1 KO IMCD had enhanced AVP-stimulated cAMP accumulation. Inhibition of calcium-stimulated AC using BAPTA did not prevent enhanced AVP responsiveness in CD ET-1 KO IMCD. Factors known to be modified by ET-1, including nitric oxide, cyclooxygenase metabolites, and superoxide did not affect the increased AVP responsiveness of CD ET-1 KO IMCD. Differential V2 receptor or G-protein activity was not involved since CD ET-1 KO IMCD had increased cAMP accumulation in response to forskolin and/or cholera toxin. CD ET-1 KO did not affect mRNA or protein levels of AC3, one of the major known collecting duct AC isoforms. However, the other known major collecting duct AC isoform (AC5/6) did have increased protein levels in CD ET-1 KO IMCD, although AC5 (weak signal) and 6 mRNA levels were unchanged.

Conclusion

ET-1 deficiency increases IMCD AC5/6 content, an effect that may synergize with acute ET-1 inhibition of AVP-stimulated cAMP accumulation.

Microsomal prostaglandin E synthase-1 and blood pressure regulation

Prostaglandin E (PGE)(2) is a major arachidonic acid metabolite in a wide variety of tissues and is implicated in the control of inflammatory as well as physiological responses. At least three major forms of PGE synthase (PGES) have recently been cloned and characterized: membrane-associated PGES (mPGES)-1, mPGES-2, and cytosolic PGES (cPGES). Among them, mPGES-1 is highly inducible by cytokine and is critically involved in pain and inflammatory responses. Emerging evidence suggests that mPGES-1 may also participate in blood pressure (BP) regulation through an impact on renal and vascular functions. Within the kidney, mPGES-1 predominates in the distal nephron where its expression is highly inducible by salt loading. Mice lacking mPGES-1 exhibit blunted natriuretic response paralleled with remarkably suppressed nitric oxide production, leading to salt-sensitive hypertension. These mice also exhibit an exaggerated hypertensive response to angiotensin II infusion. Together, these results suggest that mPGES-1 may be an important physiological regulator of BP.