Oxidative Activation of Protein Kinase Cγ through the C1 Domain

H2O2 and PAF mediate Abeta1-42-induced Ca2+ dyshomeostasis that is blocked by EGb761

Calcium (Ca2+) dyshomeostasis may be of pivotal importance in mediating the neurotoxic action of amyloid beta peptide (Abeta), but the mechanism whereby Abeta disrupts Ca2+ homeostasis remains unclear. Using hippocampal neuronal cultures, the present study investigated possible mechanisms underlying Ca2+ dyshomeostasis induced by the oligomeric form of Abeta1-42 and two possible mediators of its toxicity, hydrogen peroxide (H2O2) and platelet-activating factor (PAF). It was found that, both H2O2 and PAF were able to reproduce each of the events induced by oligomeric Abeta1-42, including (a) Ca2+ influx via N-methyl-D-aspartic acid (NMDA) receptors, (b) enhancement of Ca2+ response to NMDA via activation of protein kinase C (PKC), (c) the increase of extracellular concentrations of glutamate and (d) the increase in cytosolic free Ca2+ ([Ca2+]i). Moreover, each of these events could be blocked by Ginkgo biloba extract EGb761, a free radical scavenger with PAF antagonism, and by quercetin, a constituent with well-established free radical scavenging property. In contrast, ginkgolide B, another constituent of EGb761 with well-established PAF-antagonizing activity protected the neurons against Ca2+ dyshomeostasis induced by Abeta1-42 and PAF, but not by H2O2. These results suggested the possibility that Abeta1-42-induced Ca2+ dyshomeostasis might be mediated by formation of toxic mediators such as H2O2 and PAF. Therefore, increased production of toxic mediators such as H2O2 and PAF in the brain may be critical in the pathological mechanism of neurodegenerative diseases, particularly Alzheimer's disease (AD), and may serve as major therapeutic targets for these diseases.

Protein kinase Cgamma in colon cancer cells: expression, Thr514 phosphorylation and sensitivity to butyrate-mediated upregulation as related to the degree of differentiation

Protein kinase C (PKC) isoenzymes are expressed and activated in a cell type-specific manner, and play an essential role in tissue-specific signal transduction. The presence of butyrate at millimolar concentrations in the colon raises the question of whether it affects the expression of PKC isoenzymes in the different cell types of the colonic epithelium. We investigated the protein expression levels of PKCgamma, Thr(514)-phosphorylated PKCgamma (pPKCgamma-Thr(514)), and their subcellular distribution as affected by butyrate in a set of colon cancer cell lines. Thr(514)-phosphorylation of de novo synthesized PKCgamma is the first step in priming of the inactive PKCgamma before its release into the cytoplasm. For immunoblot analysis, we employed three antibodies, one against an unmodified sequence, mapping within 50 amino acids at its C-terminus, a second against pPKCgamma-Thr(514), and a third against pPKCgamma-pan-Thr(514). The antibody against an unmodified C-terminal peptide epitope did not recognize pPKCgamma-Thr(514), suggesting that phosphorylation at this site interferes with the binding of the antibody to the C-terminus. Marked butyrate-induced upregulation of PKCgamma occurred in HT29 cells (model for colonocyte stem cells) and HT29-derived cell lines. However, in Caco2 and IEC-18 cells (models for differentiated intestinal epithelial cells), PKCgamma was insensitive to upregulation, and present exclusively as pPKCgamma-Thr(514). Lovo and SW480 expressed higher levels of PKCgamma. In HT29 cells, butyrate-induced upregulation of the non-phosphorylated PKCgamma was observed in both the membrane and the cytosolic fraction. In Caco2 cells, the Thr(514)-phosphorylated form was present at high levels in both fractions. The presence of unphosphorylated PKCgamma in HT29 cells, and its complete absence in Caco2 cells demonstrates a cell type-dependent differential coupling of Thr(514)-phosphorylation with de novo synthesis of PKCgamma in colon cancer cells.

Lens gap junctions in growth, differentiation, and homeostasis

The cells of most mammalian organs are connected by groups of cell-to-cell channels called gap junctions. Gap junction channels are made from the connexin (Cx) family of proteins. There are at least 20 isoforms of connexins, and most tissues express more than 1 isoform. The lens is no exception, as it expresses three isoforms: Cx43, Cx46, and Cx50. A common role for all gap junctions, regardless of their Cx composition, is to provide a conduit for ion flow between cells, thus creating a syncytial tissue with regard to intracellular voltage and ion concentrations. Given this rather simple role of gap junctions, a persistent question has been: Why are there so many Cx isoforms and why do tissues express more than one isoform? Recent studies of lens Cx knockout (KO) and knock in (KI) lenses have begun to answer these questions. To understand these roles, one must first understand the physiological requirements of the lens. We therefore first review the development and structure of the lens, its numerous transport systems, how these systems are integrated to generate the lens circulation, the roles of the circulation in lens homeostasis, and finally the roles of lens connexins in growth, development, and the lens circulation.

Redox signaling (cross-talk) from and to mitochondria involves mitochondrial pores and reactive oxygen species

This review highlights the important role of redox signaling between mitochondria and NADPH oxidases. Besides the definition and general importance of redox signaling, the cross-talk between mitochondrial and Nox-derived reactive oxygen species (ROS) is discussed on the basis of 4 different examples. In the first model, angiotensin-II is discussed as a trigger for NADPH oxidase activation with subsequent ROS-dependent opening of mitochondrial ATP-sensitive potassium channels leading to depolarization of mitochondrial membrane potential followed by mitochondrial ROS formation and respiratory dysfunction. This concept was supported by observations that ethidium bromide-induced mitochondrial damage suppressed angiotensin-II-dependent increase in Nox1 and oxidative stress. In another example hypoxia was used as a stimulator of mitochondrial ROS formation and by using pharmacological and genetic inhibitors, a role of mitochondrial ROS for the induction of NADPH oxidase via PKCvarepsilon was demonstrated. The third model was based on cell death by serum withdrawal that promotes the production of ROS in human 293T cells by stimulating both the mitochondria and Nox1. By superior molecular biological methods the authors showed that mitochondria were responsible for the fast onset of ROS formation followed by a slower but long-lasting oxidative stress condition based on the activation of an NADPH oxidase (Nox1) in response to the fast mitochondrial ROS formation. Finally, a cross-talk between mitochondria and NADPH oxidases (Nox2) was shown in nitroglycerin-induced tolerance involving the mitochondrial permeability transition pore and ATP-sensitive potassium channels. The use of these redox signaling pathways as pharmacological targets is briefly discussed.

New Insights into Hyperglycemia-induced Molecular Changes in Microvascular Cells

Hyperglycemia is the most prevalent characteristic of diabetes and plays a central role in mediating adverse effects on vascular cells during the progression of diabetic vascular complications. In diabetic microangiopathy, hyperglycemia induces biochemical and molecular changes in microvascular cells that ultimately progress to retinal, renal, and neural complications and extends to other complications, including advanced periodontal disease. In this review, we describe changes involving basement membrane thickening, tissue remodeling, gap junctions, inflammation, cytokines, and transcription factors, and their effects on the pathogenesis of diabetic microvascular complications. The majority of the changes described relate to retinal microangiopathy, since ultrastructural, structural, and biochemical alterations have been well-characterized in this tissue.

Oxidative stress and oxidative damage in carcinogenesis

Carcinogenesis is a multistep process involving mutation and the subsequent selective clonal expansion of the mutated cell. Chemical and physical agents including those that induce reative oxygen species can induce and/or modulate this multistep process. Several modes of action by which carcinogens induce cancer have been identified, including through production of reactive oxygen species (ROS). Oxidative damage to cellular macromolecules can arise through overproduction of ROS and faulty antioxidant and/or DNA repair mechanisms. In addition, ROS can stimulate signal transduction pathways and lead to activation of key transcription factors such as Nrf2 and NF-kappaB. The resultant altered gene expression patterns evoked by ROS contribute to the carcinogenesis process. Recent evidence demonstrates an association between a number of single nucleotide polymorphisms (SNPs) in oxidative DNA repair genes and antioxidant genes with human cancer susceptibility. These aspects of ROS biology will be discussed in the context of their relationship to carcinogenesis.

BRCA1 interacts with Smad3 and regulates Smad3-mediated TGF-beta signaling during oxidative stress responses

Background

BRCA1 is a key regulatory protein participating in cell cycle checkpoint and DNA damage repair networks. BRCA1 plays important roles in protecting numerous cellular processes in response to cell damaging signals. Transforming growth factor-beta (TGF-β) is a potent regulator of growth, apoptosis and invasiveness of tumor cells. TFG-β activates Smad signaling via its two cell surface receptors, the TbetaRII and ALK5/TbetaRI, leading to Smad-mediated transcriptional regulation.

Methodology/Principal Findings

Here, we report an important role of BRCA1 in modulating TGF-β signaling during oxidative stress responses. Wild-type (WT) BRCA1, but not mutated BRCA1 failed to activate TGF-β mediated transactivation of the TGF-β responsive reporter, p3TP-Lux. Further, WT-BRCA1, but not mutated BRCA1 increased the expression of Smad3 protein in a dose-dependent manner, while silencing of WT-BRCA1 by siRNA decreased Smad3 and Smad4 interaction induced by TGF-β in MCF-7 breast cancer cells. BRCA1 interacted with Smad3 upon TGF-β1 stimulation in MCF-7 cells and this interaction was mediated via the domain of 298–436aa of BRCA1 and Smad3 domain of 207–426aa. In addition, H₂O₂ increased the colocalization and the interaction of Smad3 with WT-BRCA1. Interestingly, TGF-β1 induced Smad3 and Smad4 interaction was increased in the presence of H₂O₂ in cells expressing WT-BRCA1, while the TGF-β1 induced interaction between Smad3 and Smad4 was decreased upon H₂O₂ treatment in a dose-dependent manner in HCC1937 breast cancer cells, deficient for endogenous BRCA1. This interaction between Smad3 and Smad4 was increased in reconstituted HCC1937 cells expressing WT-BRCA1 (HCC1937/BRCA1). Further, loss of BRCA1 resulted in H₂O₂ induced nuclear export of phosphor-Smad3 protein to the cytoplasm, resulting decreased of Smad3 and Smad4 interaction induced by TGF-β and in significant decrease in Smad3 and Smad4 transcriptional activities.

Conclusions/Significance

These results strongly suggest that loss or reduction of BRCA1 alters TGF-β growth inhibiting activity via Smad3 during oxidative stress responses.

Protein Kinase C-γ Activation in the Early Streptozotocin Diabetic Rat Lens

PURPOSE

The purpose of this study is to demonstrate the early activation of the protein kinase C-gamma (PKC-gamma) pathway in the streptozotocin (STZ)-induced diabetic rat lens.

METHODS

Twelve-week-old male and female Sprague-Dawley rats were injected with 80 mg/kg (body weight) of STZ (N-[methylnitrosocarbamoyl]-D-glucosamine) intraperitoneally. Very high glucose (VHG) diabetes was defined as a nonfasting blood glucose level of at least 450 mg/dl, confirmed by daily monitoring with Accu-Check Advantage test strips, and occurred about 2 weeks after STZ administration. All assayed lenses were from VHG or age-matched control rats, harvested within 24 hr of VHG detection. PKC-gamma activation was measured by enzyme activity assay and by Western blotting to show autophosphorylation on Thr514. Cellular insulin-like growth factor-1 (IGF-1), PKC-gamma phosphorylation of Cx43 on Ser368, and activation of phospholipase C-gamma 1 (PLC-gamma 1), extracellular signal-regulated kinase (ERK1/2), and caspase-3 were determined by Western blotting. Endogenous diacylglycerol (DAG) levels were measured with a DAG assay kit. Lens gap junction activity was determined by the microinjection/Lucifer yellow dye transfer assay. Electron microscopy was applied to affirm fiber cell damage in the VHG diabetic lenses.

RESULTS

In the lenses of VHG diabetic rats, PKC-gamma enzyme was activated. PKC-gamma could be further activated by 400 nM phorbol-12-myristate-13-acetate (PMA), but the PKC-gamma protein levels remained constant. No elevation of IGF-1 level was observed. Western blots showed that activation of PKC-gamma may be due to activation of PLC-gamma 1, which synthesized endogenous DAG, a native PKC activator. The level of PKC-gamma -catalyzed phosphorylation of Cx43 on Ser368 and resulting inhibition of lens gap junction dye transfer activity was increased in the VHG diabetic lenses. At this early time period, the diabetic lens showed no activation of either caspase-3 or ERK1/2. Only a single fiber cell layer deep within the cortex (approximately 90 cell layers from capsule surface) showed vacuoles and damaged cell connections.

CONCLUSIONS

Early activation of PLC-gamma 1 and elevated DAG were observed within VHG diabetic lenses. These were correlated with activation of PKC-gamma, phosphorylation of Cx43 on Ser368, and inhibition of dye transfer. Abnormal signaling from PKC-gamma to Cx43 in the epithelial cells/early fiber cells, observed within VHG diabetic lenses, may be responsible for fiber cell damage deeper in the lens cortex.

Protein kinase C gamma, a protein causative for dominant ataxia, negatively regulates nuclear import of recessive-ataxia-related aprataxin

Spinocerebellar ataxia type 14 (SCA14) is an autosomal dominant disease caused by mutations in the gene encoding protein kinase C gamma (PKC gamma). We report an SCA14 family with a novel deletion of a termination-codon-containing region, resulting in a missense change and a C-terminal 13-amino-acid extension with increased kinase activity. Notably, one patient with a severe phenotype is the first homozygote for the mutation causing SCA14. We show the novel molecular consequences of increased kinase activities of mutants: aprataxin (APTX), a DNA repair protein causative for autosomal recessive ataxia, was found to be a preferential substrate of mutant PKC gamma, and phosphorylation inhibited its nuclear entry. The phosphorylated residue was Thr111, located adjacent to the nuclear localization signal, and disturbed interactions with importin alpha, a nuclear import adaptor. Decreased nuclear APTX increased oxidative stress-induced DNA damage and cell death. Phosphorylation-resistant APTX, kinase inhibitors, and antioxidants may be therapeutic options for SCA14.

Increased connexin 43 expression as a potential mediator of the neuroprotective activity of the corticotropin-releasing hormone

CRH is a major central stress mediator, but also a potent neuroprotective effector. The mechanisms by which CRH mediates its neuroprotective actions are largely unknown. Here, we describe that the gap junction molecule connexin43 (Cx43) mediates neuroprotective effects of CRH toward experimentally induced oxidative stress. An enhanced gap junction communication has been reported to contribute to neuroprotection after neurotoxic insults. We show that CRH treatment up-regulates Cx43 expression and gap junctional communication in a CRH receptor-dependent manner in IMR32 neuroblastoma cells, primary astrocytes, and organotypic hippocampal slice cultures. MAPKs and protein kinase A-cAMP response element binding protein -coupled pathways are involved in the signaling cascade from CRH to enhanced Cx43 function. Inhibition of CRH-promoted gap junction communication by the gap junction inhibitor carbenoxolone could prevent neuroprotective actions of CRH in cell and tissue culture models suggesting that gap junction molecules are involved in the neuroprotective effects of CRH. The extent of oxidative stress-induced protein carbonylation and cell death inversely correlated with Cx43 protein levels as shown by Cx43 small interfering RNA knockdown experiments. Coculture studies of primary neurons and astrocytes revealed that astrocytic Cx43 likely contributes to the neuroprotective effects of CRH. To our knowledge this is the first description of Cx43 as a potential mediator of the neuroprotective actions of CRH.

Loss of protein kinase Cgamma in knockout mice and increased retinal sensitivity to hyperbaric oxygen

OBJECTIVE

To determine if loss of protein kinase Cgamma (PKCgamma) results in increased structural damage to the retina by hyperbaric oxygen (HBO), a treatment used for several ocular disorders.

METHODS

Six-week-old mice were exposed in vivo to 100% HBO 3 times a week for 8 weeks. Eyes were dissected, fixed, embedded in Epon, sectioned, stained with toluidine blue O, and examined by light microscopy.

RESULTS

The thicknesses of the inner nuclear and ganglion cell layers were increased. Destruction of the outer plexiform layer was observed in the retinas of the PKCgamma-knockout mice relative to control mice. Exposure to HBO caused significant degradation of the retina in knockout mice compared with control mice. Damage to the outer segments of the photoreceptor layer and ganglion cell layer was apparent in central retinas of HBO-treated knockout mice.

CONCLUSIONS

Protein kinase Cgamma-knockout mice had increased retinal sensitivity to HBO. Results demonstrate that PKCgamma protects retinas from HBO damage.

CLINICAL RELEVANCE

Care should be taken in treating patients with HBO, particularly if they have a genetic disease, such as spinocerebellar ataxia type 14, a condition in which the PKCgamma is mutated and nonfunctional.

Connexin-related signaling in cell death: to live or let die?

Evidence is accumulating that some forms of cell death, like apoptosis, are not only governed by the complex interplay between extracellular and intracellular signals but are also strongly influenced by intercellular communicative networks. The latter is provided by arrays of channels consisting of connexin proteins, with gap junctions directly connecting the cytoplasm of neighboring cells and hemichannels positioned as pores that link the cytoplasm to the extracellular environment. The role of gap junctions in cell death communication has received considerable interest and recently hemichannels have joined in as potentially toxic pores adding their part to the cell death process. However, despite a large body of existing evidence, especially for gap junctions, the exact contribution of the connexin channel family still remains controversial, as both gap junctions and hemichannels may furnish cell death as well as cell survival signals. An additional layer of complexity is formed by the fact that connexin proteins as such, beyond their channel function, may influence the cell death process. We here review the current knowledge on connexins and their channels in cell death and specifically address the molecular mechanisms that underlie connexin-related signaling. We also briefly focus on pannexins, a novel set of connexin-like proteins that have been implicated in cellular responses to pathological insults.

Oxidative stress, lens gap junctions, and cataracts

The eye lens is constantly subjected to oxidative stress from radiation and other sources. The lens has several mechanisms to protect its components from oxidative stress and to maintain its redox state, including enzymatic pathways and high concentrations of ascorbate and reduced glutathione. With aging, accumulation of oxidized lens components and decreased efficiency of repair mechanisms can contribute to the development of lens opacities or cataracts. Maintenance of transparency and homeostasis of the avascular lens depend on an extensive network of gap junctions. Communication through gap junction channels allows intercellular passage of molecules (up to 1 kDa) including antioxidants. Lens gap junctions and their constituent proteins, connexins (Cx43, Cx46, and Cx50), are also subject to the effects of oxidative stress. These observations suggest that oxidative stress-induced damage to connexins (and consequent altered intercellular communication) may contribute to cataract formation.

Gap junctions in the control of vascular function

Direct intercellular communication via gap junctions is critical in the control and coordination of vascular function. In the cardiovascular system, gap junctions are made up of one or more of four connexin proteins: Cx37, Cx40, Cx43, and Cx45. The expression of more than one gap-junction protein in the vasculature is not redundant. Rather, vascular connexins work in concert, first during the development of the cardiovascular system, and then in integrating smooth muscle and endothelial cell function, and in coordinating cell function along the length of the vessel wall. In addition, connexin-based channels have emerged as an important signaling pathway in the astrocyte-mediated neurovascular coupling. Direct electrical communication between endothelial cells and vascular smooth muscle cells via gap junctions is thought to play a relevant role in the control of vasomotor tone, providing the signaling pathway known as endothelium-derived hyperpolarizing factor (EDHF). Consistent with the importance of gap junctions in the regulation of vasomotor tone and arterial blood pressure, the expression of connexins is altered in diseases associated with vascular complications. In this review, we discuss the participation of connexin-based channels in the control of vascular function in physiologic and pathologic conditions, with a special emphasis on hypertension and diabetes.

The effects of GPX-1 knockout on membrane transport and intracellular homeostasis in the lens

Glutathione peroxidase-1 (GPX-1) is an enzyme that protects the lens against H2O2-mediated oxidative damage. The purpose of the present study was to determine the effects of GPX-1 knockout (KO) on lens transport and intracellular homeostasis. To investigate these lenses we used (1) whole lens impedance studies to measure membrane conductance, resting voltage and fiber cell gap junction coupling conductance; (2) osmotic swelling of fiber cell membrane vesicles to determine water permeability; and (3) injection of Fura2 and Na+-binding benzofuran isophthalate (SBFI) into fiber cells to measure [Ca2+]i and [Na+]i, respectively, in intact lenses. These approaches were used to compare wild-type (WT) and GPX-1 KO lenses from mice around 2 months of age. There were no significant differences in clarity, size, resting voltage, membrane conductance or fiber cell membrane water permeability between WT and GPX-1 KO lenses. However, in GPX-1 KO lenses, coupling conductance was 72% of normal in the outer shell of differentiating fibers and 45% of normal in the inner core of mature fibers. Quantitative Western blots showed that GPX-1 KO lenses had about 50% as much labeled Cx46 and Cx50 protein as WT, whereas they had equivalent labeled AQP0 protein as WT. Both Ca2+ and Na+ accumulated significantly in the core of GPX-1 KO lenses. In summary, the major effect on lens transport of GPX-1 KO was a reduction in gap junction coupling conductance. This reduction affected the lens normal circulation by causing [Na+]i and [Ca2+]i to increase, which could increase cataract susceptibility in GPX-1 KO lenses.

Loss of Purkinje cells in the PKCgamma H101Y transgenic mouse

Spinocerebellar ataxia type 14 (SCA14) is an autosomal, dominant neurodegenerative disorder caused by mutations in PKCgamma. The objective of this study was to determine effects of PKCgamma H101Y SCA14 mutation on Purkinje cells in the transgenic mouse. Results demonstrated that wild type PKCgamma-like Purkinje cell localization of HA-tagged PKCgamma H101Y mutant proteins, altered morphology and loss of Purkinje cells were observed in the PKCgamma H101Y SCA14 transgenic mouse at four weeks of age. Failure of stereotypical clasping responses in the hind limbs of transgenic mice was also observed. Further, PKCgamma H101Y SCA14 mutation caused lack of total cellular PKCgamma enzyme activity, loss of connexin 57 phosphorylation on serines, and activation of caspase-12 in the PKCgamma H101Y SCA14 transgenic mouse. Results clearly demonstrate a need for PKCgamma control of gap junctions for maintenance of Purkinje cells. This is the first transgenic mouse to our knowledge which models a human SCA14 mutation.

Structural basis of protein kinase C isoform function

Protein kinase C (PKC) isoforms comprise a family of lipid-activated enzymes that have been implicated in a wide range of cellular functions. PKCs are modular enzymes comprised of a regulatory domain (that contains the membrane-targeting motifs that respond to lipid cofactors, and in the case of some PKCs calcium) and a relatively conserved catalytic domain that binds ATP and substrates. These enzymes are coexpressed and respond to similar stimulatory agonists in many cell types. However, there is growing evidence that individual PKC isoforms subserve unique (and in some cases opposing) functions in cells, at least in part as a result of isoform-specific subcellular compartmentalization patterns, protein-protein interactions, and posttranslational modifications that influence catalytic function. This review focuses on the structural basis for differences in lipid cofactor responsiveness for individual PKC isoforms, the regulatory phosphorylations that control the normal maturation, activation, signaling function, and downregulation of these enzymes, and the intra-/intermolecular interactions that control PKC isoform activation and subcellular targeting in cells. A detailed understanding of the unique molecular features that underlie isoform-specific posttranslational modification patterns, protein-protein interactions, and subcellular targeting (i.e., that impart functional specificity) should provide the basis for the design of novel PKC isoform-specific activator or inhibitor compounds that can achieve therapeutically useful changes in PKC signaling in cells.

Hypoxia-regulated activity of PKCepsilon in the lens

PURPOSE

To show that hypoxia is necessary to prevent opacification of the lens. Protein kinase C (PKC)-epsilon serves a role that is distinct from PKC-gamma when both PKC isoforms are expressed in the lens. PKCepsilon serves a very important role in hypoxic conditions, helping to prevent opacification of the lens.

METHODS

Digital image analysis, confocal microscopy, dye transfer assay, coimmunoprecipitation, Western blot analysis, and enzyme activity assays were used, respectively, to study opacification of the lens, intercellular communications, cellular localization of connexin-43 (Cx43), and the interactions between PKCepsilon, PKCgamma, and Cx43 in the lens epithelial cells.

RESULTS

Hypoxic conditions (1%-5% of oxygen) were very important in maintaining clarity of the lenses of wild-type (WT) mice. Normoxic conditions induced opacification of the WT lens. Lenses from the PKCepsilon-knockout mice underwent rapid opacification, even in hypoxic conditions. Hypoxia did not induce apoptosis in the lens epithelial cells, judging by the absence of active caspase-3, and it did not change intercellular communication and did not affect the number and localization of junctional Cx43 plaques in the lens epithelial cell culture. Hypoxia activated PKCepsilon, whereas phorbol ester (TPA), oxidation (H(2)O(2)), and insulin-like growth factor-1 (IGF-1) activated PKCgamma and decreased the activity of PKCepsilon. Hypoxia did not induce the phosphorylation of the Cx43.

CONCLUSIONS

Hypoxia-induced activation of PKCepsilon is very important in surviving hypoxia and maintaining the clarity of the lens. However, PKCgamma is utilized in the control of Cx43 gap junctions.

Reactive oxygen species derived from NOX1/NADPH oxidase enhance inflammatory pain

The involvement of reactive oxygen species (ROS) in an augmented sensitivity to painful stimuli (hyperalgesia) during inflammation has been suggested, yet how and where ROS affect the pain signaling remain unknown. Here we report a novel role for the superoxide-generating NADPH oxidase in the development of hyperalgesia. In mice lacking Nox1 (Nox1(-/Y)), a catalytic subunit of NADPH oxidase, thermal and mechanical hyperalgesia was significantly attenuated, whereas no change in nociceptive responses to heat or mechanical stimuli was observed. In dorsal root ganglia (DRG) neurons of Nox1(+/Y), pretreatment with chemical mediators bradykinin, serotonin, or phorbol 12-myristate 13-acetate (PMA) augmented the capsaicin-induced calcium increase, whereas this increase was significantly attenuated in DRG neurons of Nox1(-/Y). Concomitantly, PMA-induced translocation of PKCepsilon was markedly perturbed in Nox1(-/Y) or Nox1(+/Y) DRG neurons treated with ROS-scavenging agents. In cells transfected with tagged PKCepsilon, hydrogen peroxide induced translocation and a reduction in free sulfhydryls of full-length PKCepsilon but not of the deletion mutant lacking the C1A domain. These findings indicate that NOX1/NADPH oxidase accelerates the translocation of PKCepsilon in DRG neurons, thereby enhancing the TRPV1 activity and the sensitivity to painful stimuli.

Immunohistochemical expression of connexin 43 and occludin in the rat testis after epididymal and vasal ligation

OBJECTIVE

To describe the effects of epididymal and vasal ligation, in an experimental rat model, by using connexin 43 and occludin immunohistochemistry as well as transmission electron microscopy.

DESIGN

Comparative and controlled experimental research study.

SETTING

University animal research and histology laboratories in Turkey.

ANIMAL(S)

Wistar male rats in experimental and control groups.

INTERVENTION(S)

The control group underwent sham operation (n = 7). The first experimental group (n = 7) underwent unilateral epididymal ligation, whereas the second experimental group (n = 7) underwent unilateral vasal ligation to induce experimental epididymal and vasal obstruction models, respectively. All animals were then killed at 90 days.

MAIN OUTCOME MEASURE(S)

Immunohistochemical expression of connexin 43 and occludin for testicular tissues was determined after epididymal and vasal obstruction models. Ultrastructural morphological changes were examined by electron microscopy.

RESULT(S)

Results of the semiquantitative analysis revealed that expressions of both occludin and connexin 43 in the rat testis were decreased in the experimental groups compared with in the sham-operated group. However, changes after vasal ligation were more prominent. Ultrastructural examination confirmed decreased intercellular communication as well as increased cellular degeneration among the ipsilateral and contralateral testicular tissues.

CONCLUSION(S)

Immunohistochemical expression of occludin and connexin 43 were decreased in the testis after vasal and epididymal ligation when compared with the sham-operated group. Ultrastructural changes indicating cell degeneration were more prominent after vasal ligation.

Protection of retinal cells from ischemia by a novel gap junction inhibitor

Retinal cells which become ischemic will pass apoptotic signal to adjacent cells, resulting in the spread of damage. This occurs through open gap junctions. A class of novel drugs, based on primaquine (PQ), was tested for binding to connexin 43 using simulated docking studies. A novel drug has been synthesized and tested for inhibition of gap junction activity using R28 neuro-retinal cells in culture. Four drugs were initially compared to mefloquine, a known gap junction inhibitor. The drug with optimal inhibitory activity, PQ1, was tested for inhibition and was found to inhibit dye transfer by 70% at 10 microM. Retinal ischemia was produced in R28 cells using cobalt chloride as a chemical agent. This resulted in activation of caspase-3 which was prevented by PQ1, the gap junction inhibitor. Results demonstrate that novel gap junction inhibitors may provide a means to prevent retinal damage during ischemia.

Activation of mutant protein kinase Cgamma leads to aberrant sequestration and impairment of its cellular function

Mutations in protein kinase Cgamma (PKCgamma) cause the neurodegenerative disease spinocerebellar ataxia type 14 (SCA14). In this study, expression of an extensive panel of known SCA14-associated PKCgamma mutations as fusion proteins in cell culture led to the consistent formation of cytoplasmic aggregates in response to purinoceptor stimulation. Aggregates co-stained with antibodies to phosphorylated PKCgamma and the early endosome marker EEA1 but failed to redistribute to the cell membrane under conditions of oxidative stress. These studies suggest that Purkinje cell damage in SCA14 may result from a reduction of PKCgamma activity due its aberrant sequestration in the early endosome compartment.

Identification of a PKCε-dependent regulation of myocardial contraction by epicatechin-3-gallate

In this study, the effects of tea catechins and tea theaflavins on myocardial contraction were examined in isolated rat hearts using a Langendorff-perfusion system. We found that both tea catechins and theaflavins had positive inotropic effects on the myocardium. Of the tested chemicals, epicatechin-3-gallate (ECG) and theaflavin-3,3′-digallate (TF4) appear to be the most effective tea catechin and theaflavin, respectively. Further studies of ECG-induced positive inotropy revealed the following insights. First, unlike digitalis drugs, ECG had no effect on intracellular Ca2+ level in cultured adult cardiac myocytes. Second, it activated PKCε, but not PKCα, in the isolated hearts as well as in cultured cells. Neither a phospholipase C (PLC) inhibitor ( U73122) nor the antioxidant N-acetyl cysteine (NAC) affected the ECG-induced activation of PKCε. Third, inhibition of PKCε by either chelerythrine chloride (CHE) or PKCε translocation inhibitor peptide (TIP) caused a partial reduction of ECG-induced increases in myocardial contraction. Moreover, NAC was also effective in reducing the effects of ECG on myocardial contraction. Finally, pretreatment of the heart with both CHE and NAC completely abolished ECG-induced inotropic effects on the heart. Together, these findings indicate that ECG can regulate myocardial contractility via a novel PKCε-dependent signaling pathway.

Coordinating cell proliferation and migration in the lens and cornea

Migration is a complex process for epithelial tissues, because the epithelium must move as an intact sheet to preserve its barrier function. The requirement for structural integrity is met by coupling cell-to-matrix and cell-to-cell adhesion at the cellular level, and by coordinating cell proliferation and cell migration in the tissue as a whole. Proliferation is suppressed at the migrating cell front, allowing cells in this region to remain tightly packed while advancing rapidly. At the same time, proliferation is enhanced in a region behind the advancing cell front to expand the epithelial cell sheet. This review considers the extracellular signals and intracellular signaling pathways that regulate these processes in the lens and corneal epithelium, with emphasis on the commonalities that link these tissues.

Protection from ataxia-linked apoptosis by gap junction inhibitors

Mutations in the protein kinase C gamma (PKCgamma) gene cause spinocerebellar ataxia type 14 (SCA14), a heterogeneous neurodegenerative disorder. Synthetic peptides (C1B1) serve as gap junction inhibitors through activation of PKCgamma control of gap junctions. We investigated the neuroprotective potential of these peptides against SCA14 mutation-induced cell death using neuronal HT22 cells. The C1B1 synthetic peptides completely restored PKCgamma enzyme activity and subsequent control of gap junctions. PKCgamma SCA14 mutant proteins were shown to cause aggregation which initially resulted in endoplasmic reticulum (ER) stress and cell apoptosis as demonstrated by phosphorylation of PERK on Thr981, activation of caspase-12, increases in BiP/GRP78 protein levels, and consequent activation of caspase-3. Pre-incubation with C1B1 peptides completely abolished these SCA14 effects on ER stress and caspase-3 activation, suggesting that C1B1 peptides protect cells from apoptosis through inhibition of gap junctions by restoration of PKCgamma control of gap junctions, which may result in neuroprotection in SCA14.

Genetic and epigenetic mechanisms of gene regulation during lens development

Recent studies demonstrated a number of links between chromatin structure, gene expression, extracellular signaling and cellular differentiation during lens development. Lens progenitor cells originate from a pool of common progenitor cells, the pre-placodal region (PPR) which is formed from a combination of extracellular signaling between the neural plate, naïve ectoderm and mesendoderm. A specific commitment to the lens program over alternate choices such as the formation of olfactory epithelium or the anterior pituitary is manifested by the formation of a thickened surface ectoderm, the lens placode. Mouse lens progenitor cells are characterized by the expression of a complement of lens lineage-specific transcription factors including Pax6, Six3 and Sox2, controlled by FGF and BMP signaling, followed later by c-Maf, Mab21like1, Prox1 and FoxE3. Proliferation of lens progenitors together with their morphogenetic movements results in the formation of the lens vesicle. This transient structure, comprised of lens precursor cells, is polarized with its anterior cells retaining their epithelial morphology and proliferative capacity, whereas the posterior lens precursor cells initiate terminal differentiation forming the primary lens fibers. Lens differentiation is marked by expression and accumulation of crystallins and other structural proteins. The transcriptional control of crystallin genes is characterized by the reiterative use of transcription factors required for the establishment of lens precursors in combination with more ubiquitously expressed factors (e.g. AP-1, AP-2alpha, CREB and USF) and recruitment of histone acetyltransferases (HATs) CBP and p300, and chromatin remodeling complexes SWI/SNF and ISWI. These studies have poised the study of lens development at the forefront of efforts to understand the connections between development, cell signaling, gene transcription and chromatin remodeling.

Various Molecular Species of Diacylglycerol Hydroperoxide Activate Human Neutrophils via PKC Activation

We have proposed that diacylglycerol hydroperoxide-induced unregulated signal transduction causes oxidative stress-related diseases. In this study, we investigated which molecular species of diacylglycerol hydroperoxide activated human peripheral neutrophils. All diacylglycerol hydroperoxides, diacylglycerol hydroxides, and diacyglycerols tested in the present study induced superoxide production by neutrophils. The ability to activate neutrophils among molecular species containing the same fatty acid composition was as follows; diacylglycerol hydroperoxide>diacylglycerol hydroxide>/=diacylglycerol. The diacylglycerol hydroperoxide composed of linoleate was a stronger activator for neutrophils than that composed of arachidonate. 1-Palmitoyl-2-linoleoylglycerol hydroperoxide (PLG-OOH) was the strongest stimulator for neutrophils. We reconfirmed that PLG-OOH activated protein kinase C (PKC) in neutrophils. PLG-OOH induced the phosphorylation of p47(phox), a substrate of PKC and a cytosolic component of NADPH oxidase, in neutrophils, as did N-formyl-methionyl-leucyl-phenylalanine or 4beta-phorbol-12beta-myristate-13alpha-acetate. Moreover, the time course of p47(phox) phosphorylation was comparable to that of superoxide production. These results suggest that PLG-OOH activated intracellular protein kinase C. PLG-OOH, produced via an uncontrolled process, can act as a biological second messenger to cause inflammatory disease from oxidative stress.

Status of caveolin-1 in various membrane domains of the bovine lens

Recent studies of the distribution and relative concentration of caveolin-1 in fractions of bovine lens epithelial and fiber cells have led to the novel concept that caveolin-1 may largely exist as a peripheral membrane protein in some cells. Caveolin-1 is typically viewed as a scaffolding protein for caveolae in plasma membrane. In this study, membrane from cultured bovine lens epithelial cells and bovine lens fiber cells were divided into urea soluble and insoluble fractions. Cytosolic lipid vesicles were also recovered from the lens epithelial cells. Lipid-raft domains were recovered from fiber cells following treatment with detergents and examined for caveolin and lipid content. Aliquots of all fractions were Western blotted for caveolin-1. Fluorescence microscopy and double immunofluorescence labeling were used to examine the distribution of caveolin-1 in cultured epithelial cells. Electron micrographs revealed an abundance of caveolae in plasma membrane of cultured lens epithelial cells. About 60% of the caveolin-1 in the epithelial-crude membrane was soluble in urea, a characteristic of peripheral membrane proteins. About 30% of the total was urea-insoluble membrane protein that likely supports the structure of caveolae. The remaining caveolin was part of cytosolic lipid vesicles. By contrast, most caveolin in the bovine lens fiber cell membrane was identified as intrinsic protein, being present at relatively low concentrations in caveolae-free lipid raft domains enriched in cholesterol and sphingomyelin. We estimate that these domains occupied 25-30% of the fiber cell membrane surface. Thus, the status of caveolin-1 in lens epithelial cells appears markedly different from that in fiber cells.

Modulation of gap-junction-dependent arterial relaxation by ascorbic acid

AIMS

To investigate whether ascorbic acid (AA) can influence endothelium-dependent relaxation by modulating the spread of endothelial hyperpolarization through the arterial wall via gap junctions.

METHODS

Force development and membrane potential were monitored by myography and sharp electrode techniques in isolated rabbit iliac arteries.

RESULTS

AA prevented the ability of the gap junction blocker 2-aminoethoxydiphenyl borate to inhibit endothelium-dependent relaxations and subintimal smooth muscle hyperpolarizations evoked by cyclopiazonic acid in the presence of nitric oxide (NO) synthase and cyclooxygenase blockade. AA also prevented the ability of a connexin-mimetic peptide targeted against Cx37 and Cx40 (37,40Gap 26) to attenuate the transmission of endothelial hyperpolarization to subintimal smooth muscle, and a peptide targeted against Cx43 (43Gap 26) to attenuate the spread of subintimal hyperpolarization to subadventitial smooth muscle and the associated mechanical relaxation. Parallel studies with endothelium-denuded preparations demonstrated that AA and cyclopiazonic acid both depressed relaxation evoked by the NO donor MAHMA NONOate.

CONCLUSIONS

The data suggest that AA can modulate arterial function through a previously unrecognized ability to preserve electrotonic signalling via myoendothelial and homocellular smooth muscle gap junctions under conditions where cell coupling is depressed. Underlying mechanisms do not involve amplification of 'residual' NO activity by AA.

Protein kinase C as a stress sensor

While there are many reviews which examine the group of proteins known as protein kinase C (PKC), the focus of this article is to examine the cellular roles of two PKCs that are important for stress responses in neurological tissues (PKC gamma and epsilon) and in cardiac tissues (PKC epsilon). These two kinases, in particular, seem to have overlapping functions and interact with an identical target, connexin 43 (Cx43), a gap junction protein which is central to proper control of signals in both tissues. While PKC gamma and PKC epsilon both help protect neural tissue from ischemia, PKC epsilon is the primary PKC isoform responsible for responding to decreased oxygen, or ischemia, in the heart. Both do this through Cx43. It is clear that both PKC gamma and PKC epsilon are necessary for protection from ischemia. However, the importance of these kinases has been inferred from preconditioning experiments which demonstrate that brief periods of hypoxia protect neurological and cardiac tissues from future insults, and that this depends on the activation, translocation, or ability for PKC gamma and/or PKC epsilon to interact with distinct cellular targets, especially Cx43. This review summarizes the recent findings which define the roles of PKC gamma and PKC epsilon in cardiac and neurological functions and their relationships to ischemia/reperfusion injury. In addition, a biochemical comparison of PKC gamma and PKC epsilon and a proposed argument for why both forms are present in neurological tissue while only PKC epsilon is present in heart, are discussed. Finally, the biochemistry of PKCs and future directions for the field are discussed, in light of this new information.

Protein kinase C gamma mutations in the C1B domain cause caspase-3-linked apoptosis in lens epithelial cells through gap junctions

Failure to control oxidative stress is closely related to aging and to a diverse range of human diseases. We have reported that protein kinase C gamma (PKCgamma) acts as a primary oxidative stress sensor in the lens. PKCgamma has a Zn-finger C1B stress switch domain, residues 101-150. Mutation, H101Y, in the C1B domain of PKCgamma proteins causes a failure of the PKCgamma oxidative stress response [Lin, D., Takemoto, D.J., 2005. Oxidative activation of protein kinase Cgamma through the C1 domain. Effects on gap junctions. J. Biol. Chem. 280, 13682-13693]. Some human neurodegenerative spinocerebellar ataxia type 14 are caused by mutations in the PKCgamma C1B domain. In the current study we have investigated the effects of these mutations on lens epithelial cell responses to oxidative stress. The results demonstrate that PKCgamma C1B mutants had lower basal enzyme activities and were not activated by H(2)O(2). Furthermore, the PKCgamma mutations caused a failure of endogenous wild type PKCgamma to be activated by H(2)O(2). These PKCgamma mutations abolished the effect of H(2)O(2) on phosphorylation of Cx43 and Cx50 by H(2)O(2) activation of PKCgamma. The cells with PKCgamma C1B mutations had more Cx43 and/or Cx50 gap junction plaques which were not decreased by H(2)O(2). Since open gap junctions could have a bystander effect this could cause apoptosis to occur. H(2)O(2) (100 microM, 3 h) activated a caspase-3 apoptotic pathway in the lens epithelial cells but was more severe in cells expressing PKCgamma mutations. The presence of 18alpha-glycyrrhetinic acid (AGA), an inhibitor of gap junctions, decreased Cx43 and Cx50 protein levels and gap junction plaque number. This reduction in gap junctions by AGA resulted in inhibition of H(2)O(2)-induced apoptosis. Our results demonstrate that there is a dominant negative effect of PKCgamma C1B mutations on endogenous PKCgamma which results in loss of control of gap junctions. Modeled structures suggest that the severity of C1B mutation effects may be related to the extent of loss of C1B structure. Mutations in the C1B domain of PKCgamma result in increased apoptosis in lens epithelial cells. This can be prevented by a gap junction inhibitor. Thus, propagation of apoptosis from cell-to-cell in lens epithelial cells may be through open gap junctions. The control of gap junctions requires PKCgamma.

The signaling mechanism of ROS in tumor progression

Reactive oxygen species (ROS) are recently proposed to be involved in tumor metastasis which is a complicated processes including epithelial-mesenchymal transition (EMT), migration, invasion of the tumor cells and angiogenesis around the tumor lesion. ROS generation may be induced intracellularly, in either NADPH oxidase- or mitochondria-dependent manner, by growth factors and cytokines (such as TGFbeta and HGF) and tumor promoters (such as TPA) capable of triggering cell adhesion, EMT and migration. As a signaling messenger, ROS are able to oxidize the critical target molecules such as PKC and protein tyrosine phosphates (PTPs), which are relevant to tumor cell invasion. PKC contain multiple cysteine residues that can be oxidized and activated by ROS. Inactivation of multiple PTPs by ROS may relieve the tyrosine phosphorylation-dependent signaling. Two of the down-stream molecules regulated by ROS are MAPK and PAK. MAPKs cascades were established to be a major signal pathway for driving tumor cell metastasis, which are mediated by PKC, TGF-beta/Smad and integrin-mediated signaling. PAK is an effector of Rac-mediated cytoskeletal remodeling that is responsible for cell migration and angiogenesis. There are several transcriptional factors such as AP1, Ets, Smad and Snail regulating a lot of genes relevant to metastasis. AP-1 and Smad can be activated by PKC activator and TGF-beta1, respectively, in a ROS dependent manner. On the other hand, Est-1 can be upregulated by H2O2 via an antioxidant response element in the promoter. The ROS-regulated genes relevant to EMT and metastasis include E-cahedrin, integrin and MMP. Comprehensive understanding of the ROS-triggered signaling transduction, transcriptional activation and regulation of gene expressions will help strengthen the critical role of ROS in tumor progression and devising strategy for chemo-therapeutic interventions.

PKCgamma knockout mouse lenses are more susceptible to oxidative stress damage

Cataracts, or lens opacities, are the leading cause of blindness worldwide. Cataracts increase with age and environmental insults, e.g. oxidative stress. Lens homeostasis depends on functional gap junctions. Knockout or missense mutations of lens gap junction proteins, Cx46 or Cx50, result in cataractogenesis in mice. We have previously demonstrated that protein kinase Cgamma (PKCgamma) regulates gap junctions in the lens epithelium and cortex. In the current study, we further determined whether PKCgamma control of gap junctions protects the lens from cataractogenesis induced by oxidative stress in vitro, using PKCgamma knockout and control mice as our models. The results demonstrate that PKCgamma knockout lenses are normal at 2 days post-natal when compared to control. However, cell damage, but not obvious cataract, was observed in the lenses of 6-week-old PKCgamma knockout mice, suggesting that the deletion of PKCgamma causes lenses to be more susceptible to damage. Furthermore, in vitro incubation or lens oxidative stress treatment by H(2)O(2) significantly induced lens opacification (cataract) in the PKCgamma knockout mice when compared to controls. Biochemical and structural results also demonstrated that H(2)O(2) activation of endogenous PKCgamma resulted in phosphorylation of Cx50 and subsequent inhibition of gap junctions in the lenses of control mice, but not in the knockout. Deletion of PKCgamma altered the arrangement of gap junctions on the cortical fiber cell surface, and completely abolished the inhibitory effect of H(2)O(2) on lens gap junctions. Data suggest that activation of PKCgamma is an important mechanism regulating the closure of the communicating pathway mediated by gap junction channels in lens fiber cells. The absence of this regulatory mechanism in the PKCgamma knockout mice may cause those lenses to have increased susceptibility to oxidative damage.

PKC signaling deficits: a mechanistic hypothesis for the origins of Alzheimer's disease

There is strong evidence that protein kinase C (PKC) isozyme signaling pathways are causally involved in associative memory storage. Other observations have indicated that PKC signaling pathways regulate important molecular events in the neurodegenerative pathophysiology of Alzheimer's disease (AD), which is a progressive dementia that is characterized by loss of recent memory. This parallel involvement of PKC signaling in both memory and neurodegeneration indicates a common basis for the origins of both the symptoms and the pathology of AD. Here, we discuss this conceptual framework as a basis for an autopsy-validated peripheral biomarker--and for AD drug design targeting drugs (bryostatin and bryologs) that activate PKC isozymes--that has already demonstrated significant promise for treating both AD neurodegeneration and its symptomatic memory loss.

ZO-1 is required for protein kinase C gamma-driven disassembly of connexin 43

We have previously reported that protein kinase C gamma (PKC-gamma) is activated by phorbol-12-myristate-13-acetate (TPA) and that this causes PKC-gamma translocation to membranes and phosphorylation of the gap junction protein, connexin 43 (Cx43). This phosphorylation, on S368 of Cx43, causes disassembly of Cx43 out of cell junctional plaques resulting in the inhibition of dye transfer. The purpose of this study is to identify the specific role of zonula occludens protein-1 (ZO-1), a tight junction protein with recently established effects on gap junctions, in this PKC-gamma-driven Cx43 disassembly. For this purpose, ZO-1 levels in lens epithelial cells in culture were decreased by up to 70% using specific siRNA. The down-regulation of ZO-1 caused a stable interaction of PKC-gamma with Cx43 even without normal enzyme activation by TPA. However, after TPA activation of the PKC-gamma, the Cx43 did not disassemble out of plaques even though the PKC-gamma enzyme was activated and the Cx43 was phosphorylated on S368. Confocal microscopy demonstrated that the siRNA treatment caused a loss of ZO-1 from borders of large junctional Cx43 cell-to-cell plaques and resulted in the accumulation of Cx43 aggregates inside of cells. Loss of the specific "plaquetosome" arrangement of large Cx43 plaques surrounded by ZO-1 was accompanied by a complete loss of functional dye transfer. These results suggest that ZO-1 is required for Cx43 control, both for dye transfer, and, for the PKC-gamma-driven disassembly response.

Redox control of neural function: background, mechanisms, and significance

The redox environment within neural cells is dependent on a series of redox couples. The glutathione disulfide/ glutathione (GSSG/GSH) redox pair forms the major redox couple in cells and as such plays a critical role in regulating redox-dependent cellular functions. Not only does GSH act as an antioxidant but it also can modulate the activity of a variety of different proteins via S-glutathionylation of cysteine sulfhydryl groups. The thioredoxin system also makes a significant contribution to the redox environment by reducing inter- and intrachain protein disulfide bonds as well as maintaining the activity of important antioxidant enzymes such as peroxiredoxins and methionine sulfoxide reductases. The redox environment affects the activity and function of a number of different protein phosphatases, protein kinases, and transcription factors. The sum of these effects will determine how changes in the redox environment alter overall cellular function, thereby playing a fundamental role in regulating neural cell fate and physiology.

Drugs modulating the biological effects of peroxynitrite and related nitrogen species

The term "reactive nitrogen species" includes nitrogen monoxide, commonly called nitric oxide, and some other remarkable chemical entities (peroxynitrite, nitrosoperoxycarbonate, etc.) formed mostly from nitrogen monoxide itself in biological environments. Regardless of the specific mechanisms implicated in their effects, however, it is clear that an integrated pharmacological approach to peroxynitrite and related species is only just beginning to take shape. The array of affected chemical and pathological processes is extremely broad. One of the most conspicuous mechanisms observed thus far has been the scavenging of the peroxynitrite anion by molecules endowed with antioxidant activity. This discovery has in turn lent great significance to several naturally occurring and synthetic antioxidants, which usually protect not only against oxidative reactions, but also from nitrating ones, both in vitro and in vivo. This has proven to be beneficial in different tissues, especially within the central nervous system. Taking these results and those of other biochemical investigations into account, many research lines are currently in progress to establish the true potential of reactive nitrogen species deactivators in the therapy of neurological diseases, ischemia-reperfusion damage, renal failure, and lung injury, among others.

Gap junctions and cochlear homeostasis

Gap junctions play a critical role in hearing and mutations in connexin genes cause a high incidence of human deafness. Pathogenesis mainly occurs in the cochlea, where gap junctions form extensive networks between non-sensory cells that can be divided into two independent gap junction systems, the epithelial cell gap junction system and the connective tissue cell gap junction system. At least four different connexins have been reported to be present in the mammalian inner ear, and gap junctions are thought to provide a route for recycling potassium ions that pass through the sensory cells during the mechanosensory transduction process back to the endolymph. Here we review the cochlear gap junction networks and their hypothesized role in potassium ion recycling mechanism, pharmacological and physiological gating of cochlear connexins, animal models harboring connexin mutations and functional studies of mutant channels that cause human deafness. These studies elucidate gap junction functions in the cochlea and also provide insight for understanding the pathogenesis of this common hereditary deafness induced by connexin mutations.

Protein kinase C-mediated endothelial barrier regulation is caveolin-1-dependent

Protein kinase C (PKC) is activated in response to various inflammatory mediators and contributes significantly to the endothelial barrier breakdown. However, the mechanisms underlying PKC-mediated permeability regulation are not well understood. We prepared microvascular myocardial endothelial cells from both wild-type (WT) and caveolin-1-deficient mice. Activation of PKC by phorbol myristate acetate (PMA) (100 nM) for 30 min induced intercellular gap formation and fragmentation of VE-cadherin immunoreactivity in WT but not in caveolin-1-deficient monolayers. To test the effect of PKC activation on VE-cadherin-mediated adhesion, we allowed VE-cadherin-coated microbeads to bind to the endothelial cell surface and probed their adhesion by laser tweezers. PMA significantly reduced bead binding to 78+/-6% of controls in WT endothelial cells without any effect in caveolin-1-deficient cells. In WT cells, PMA caused an 86+/-18% increase in FITC-dextran permeability whereas no increase in permeability was observed in caveolin-1-deficient monolayers. Inhibition of PKC by staurosporine (50 nM, 30 min) did not affect barrier functions in both WT and caveolin-1-deficient MyEnd cells. Theses data indicate that PKC activation reduces endothelial barrier functions at least in part by the reduction of VE-cadherin-mediated adhesion and demonstrate that PKC-mediated permeability regulation depends on caveolin-1.