Epidermal growth factor and phorbol myristate acetate increase expression of the mRNA for cytosolic phospholipase A2 in glomerular mesangial cells

We have previously shown that phospholipase A2 (PLA2) activity is rapidly activated by epidermal growth factor (EGF) and phorbol 12-myristate 13-acetate (PMA) in renal mesangial cells and other cell systems in a manner that suggests a covalent modification of the PLA2 enzyme(s). This PLA2 activity is cytosolic (cPLA2) and is distinct from secretory forms of PLA2, which are also stimulated in mesangial cells in response to cytokines and other agonists. However, longer-term regulation of cPLA2 in renal cells may also occur at the level of gene expression. Cultured rat mesangial cells were used as a model system to test the effects of EGF and PMA on the regulation of cPLA2 gene expression. EGF and PMA both produced sustained increases in cPLA2 mRNA levels, with a parallel increase in enzyme activity over time. Inhibition of protein synthesis by cycloheximide increased basal cPLA2 mRNA accumulation in serum-starved mesangial cells, and the combination of EGF and cycloheximide resulted in super-induction of cPLA2 gene expression compared with EGF alone. Actinomycin D treatment entirely abrogated the effect of EGF on cPLA2 mRNA accumulation. These findings suggest that regulation of cPLA2 is achieved by factors controlling gene transcription and possibly mRNA stability, in addition to previously characterized posttranslational modifications.

Native and modified LDL activate extracellular signal-regulated kinases in mesangial cells

Glycation and/or oxidation of LDL may promote diabetic nephropathy. The mitogen-activated protein kinase (MAPK) cascade, which includes extracellular signal-regulated protein kinases (ERKs), modulates cell function. Therefore, we examined the effects of LDL on ERK phosphorylation in cultured rat mesangial cells. In cells exposed to 100 microg/ml native LDL or LDL modified by glycation, and/or mild or marked (copper-mediated) oxidation, ERK activation peaked at 5 min. Five minutes of exposure to 10-100 microg/ml native or modified LDL produced a concentration-dependent (up to sevenfold) increase in ERK activity. Also, 10 microg/ml native LDL and mildly modified LDL (glycated and/or mildly oxidized) produced significantly greater ERK activation than that induced by copper-oxidized LDL +/- glycation (P <0.05). Pretreatment of cells with Src kinase and MAPK kinase inhibitors blocked ERK activation by 50-80% (P <0.05). Native and mildly modified LDL, which are recognized by the native LDL receptor, induced a transient spike of intracellular calcium. Copper-oxidized (+/- glycation) LDL, recognized by the scavenger receptor, induced a sustained rise in intracellular calcium. The intracellular calcium chelator (EGTA/AM) further increased ERK activation by native and mildly modified LDL (P <0.05). These findings demonstrate that native and modified LDL activate ERKs 1 and 2, an early mitogenic signal, in mesangial cells and provide evidence for a potential link between modified LDL and the development of glomerular injury in diabetes.

Cytosolic phospholipase A2 gene expression in rat mesangial cells is regulated post-transcriptionally

Cytosolic phospholipase A2 (cPLA2) is thought to be the rate-limiting enzyme in the arachidonic acid/eicosanoid cascade. The ability of various agonists to increase steady-state cPLA2 mRNA levels has previously been reported. The current study delineates the contributions of transcriptional and post-transcriptional processes to the regulation of cPLA2 gene expression in response to a variety of agonists in cultured rat glomerular mesangial cells. Epidermal growth factor, platelet-derived growth factor, serum and phorbol myristate acetate all increase the half-life of cPLA2 mRNA transcripts, indicating a role for post-transcriptional modulation of gene expression. The presence of three ATTTA motifs in the 3' untranslated region (3'UTR) of the rat cPLA2 cDNA is ascertained. Heterologous expression of chimeric constructs with different 3'UTRs ligated into the 3' end of the luciferase coding region reveals that the presence of the cPLA2 3'UTR results in reduced luciferase activity compared with constructs without the cPLA2 3'UTR. Furthermore, the luciferase activity in the constructs with the cPLA2 3'UTR is increased in response to the same agonists which stabilize endogenous cPLA2 mRNA. A negligible effect of these agonists on transcriptional control of cPLA2 is evident using promoter-reporter constructs expressed in transient and stable transfectants. Taken together, these results indicate predominant post-transcriptional regulation of cPLA2 mRNA levels.

Perceptions of high involvement work practices and burnout: investigating the mediating role of procedural justice and role overload and the moderating role of colleague support

Purpose
The purpose of this paper is to investigate the impact of employees’ perceptions of high involvement work practices (HIWPs) on burnout (emotional exhaustion and depersonalisation) via the mediating role of role overload and procedural justice. Further, perceived colleague support was hypothesised to moderate the effects of role overload and procedural justice on these outcomes.

Design/Methodology
The study was conducted on a random sample of unionised registered nurses (RNs) working in the Canadian public health care sector, stratified by mission and size of the institution to ensure representativeness. Of the 6546 nurses solicited, 2174 returned a completed questionnaire, resulting in a response rate of 33.2%. To test our hypotheses we conducted structural equation modelling (SEM) in Mplus version 6.0 (Muthen and Muthen, 1998 – 2010) with Maximum Likelihood (ML) estimation.

Results
The results showed that procedural justice and role overload fully mediated the influence of HIWPs on burnout. Moreover, colleague support moderated the effects of procedural justice and role overload on emotional exhaustion but not depersonalisation.

Limitations
The study used a cross-sectional research design and is conducted among one occupational group (i.e. nurses).

Research/Practical Implications
The findings question the dark side of HRM in the health care context. They also contribute to the lack of theoretical and empirical work dedicated to understanding the ‘black box’ problem (Castanheira and Chambel, 2010).

Originality/Value
The study employs a well-known theoretical perspective from the occupational health psychology literature to the HR field in order to contribute to the lack of theorising in the HR-well-being link.

Iron Overload Favors the Elimination of Leishmania

Iron plays a central role in host-parasite interactions, since both intervenients need iron for survival and growth, but are sensitive to iron-mediated toxicity. The host’s iron overload is often associated with susceptibility to infection. However, it has been previously reported that iron overload prevented the growth of Leishmania major, an agent of cutaneous leishmaniasis, in BALB/c mice. In order to further clarify the impact of iron modulation on the growth of Leishmania in vivo, we studied the effects of iron supplementation or deprivation on the growth of L. infantum, the causative agent of Mediterranean visceral leishmaniasis, in the mouse model. We found that dietary iron deficiency did not affect the protozoan growth, whereas iron overload decreased its replication in the liver and spleen of a susceptible mouse strain. The fact that the iron-induced inhibitory effect could not be seen in mice deficient in NADPH dependent oxidase or nitric oxide synthase 2 suggests that iron eliminates L. infantum in vivo through the interaction with reactive oxygen and nitrogen species. Iron overload did not significantly alter the mouse adaptive immune response against L. infantum. Furthermore, the inhibitory action of iron towards L. infantum was also observed, in a dose dependent manner, in axenic cultures of promastigotes and amastigotes. Importantly, high iron concentrations were needed to achieve such effects. In conclusion, externally added iron synergizes with the host’s oxidative mechanisms of defense in eliminating L. infantum from mouse tissues. Additionally, the direct toxicity of iron against Leishmania suggests a potential use of this metal as a therapeutic tool or the further exploration of iron anti-parasitic mechanisms for the design of new drugs.

Iron Overload in a Murine Model of Hereditary Hemochromatosis Is Associated with Accelerated Progression of Osteoarthritis Under Mechanical Stress

OBJECTIVE: Hereditary hemochromatosis (HH) is a disease caused by mutations in the Hfe gene characterised by systemic iron overload and associated with an increased prevalence of osteoarthritis (OA) but the role of iron overload in the development of OA is still undefined. To further understand the molecular mechanisms involved we have used a murine model of HH and studied the progression of experimental OA under mechanical stress. DESIGN: OA was surgically induced in the knee joints of 10-week-old C57BL6 (wild-type) mice and Hfe-KO mice. OA progression was assessed using histology, micro CT, gene expression and immunohistochemistry at 8 weeks after surgery. RESULTS: Hfe-KO mice showed a systemic iron overload and an increased iron accumulation in the knee synovial membrane following surgery. The histological OA score was significantly higher in the Hfe-KO mice at 8 weeks after surgery. Micro CT study of the proximal tibia revealed increased subchondral bone volume and increased trabecular thickness. Gene expression and immunohistochemical analysis showed a significant increase in the expression of matrix metallopeptidase 3 (MMP-3) in the joints of Hfe-KO mice compared with control mice at 8 weeks after surgery. CONCLUSIONS: HH was associated with an accelerated development of OA in mice. Our findings suggest that synovial iron overload has a definite role in the progression of HH-related OA

Pro-fibrotic role of ERK3-MK5 during pressure-overload induced cardiac hypertrophy

Il y a 4 isoforme de p38 : α, β, δ, and γ. MK5, à l'origine identifié comme étant un régulateur de PRAK (Regulated/Activated Protein Kinase), est maintenant connu pour être activée par la protéine kinase p38 (qui est un mitogène activé par la protéine kinase, MAPK). Cette dernière est impliquée dans les mécanismes de fibrose et d'apoptose pendant l'hypertrophie cardiaque. De plus, MK5 est également activée par les MAPKs atypiques; ERK3 et ERK4. Bien qu’elles soient fortement exprimées dans le coeur, le rôle physiologique de MK5 et ERK3 demeure inconnu. Par conséquent, nous avons étudié l'effet de la constriction aortique transversale (TAC) – induisant un surcharge chronique de pression chez les souris hétèrozygotes knockout pour MK5 (MK5+/-) ou ERK3 (ERK3+/-) et pour leurs types sauvages (MK5+/+ et ERK3+/+). Deux sem post-TAC; le ratio de poids du coeur/poids corporel a été augmenté chez les 2 souris MK5+/- et MK5+/+. L'échocardiographie de la trans-thoracique démontre que la surcharge de pression a altéré la fonction diastolique du ventricule gauche chez MK5+/+, mais pas chez la souris MK5+/-. De plus, nous avons observé moins de dépôt de collagène, évalué par une coloration au trichrome de Masson, 2 et 3 sem post-TAC chez les souris MK5+/-. Parallèlement, le niveau de l’ARNm de collagène type1 alpha-1 a été significativement diminué dans les coeurs des souris MK5+/-, 2 et 3 sem post-TAC. De même, ERK3, mais pas ERK5 ni p38α, co-IP avec MK5 dans les 2 modèles des coeurs TAC; aigus ou chroniques. En revanche, l’ajout exogénique de GST-MK5 a abaissé ERK4 et p38α, mais pas ERK3 dans les lysâtes de coeur de souris. Par contre, GST-ERK3 et GST-p38α ne démontrent aucune co-IP avec MK5. Ces données suggèrent que dans le coeur seul ERK3, et non ERK4 ou p38α, est capable d’interagir avec, et réguler MK5. A niveau physiologique MK5 interagit entièrement avec ERK3 et par conséquent MK5 n’est pas disponible pour lier les protéines exogéniques. Les souris hétérozygotes pour ERK3 (ERK3+/-) ont également démontré une réduction ou une absence de collagène et une faible expression d’ARNm du collagène type1 alpha1, 3 sem post-TAC. Ces résultats démontrent un important rôle pro-fibrotique de la signalisation MK5-ERK3 pendant une surcharge chronique de pression.Nous avons également démontré 5 variant d'épissage de (MK5.1-5), y compris la forme originale (MK5.1). MK5.2 et MK5.5 subissent une délétion de 6 paires de base dans l’exon 12 : MK5.3 manque l'exon 12 : MK5.4 et MK5.5 manquent les exons 2-6. L'expression des ARNm des différents variant d'épissage a été vérifiée par PCR en temps réel (qPCR). Bien que l’expression est ubiquitaire, l'abondance relative de chaque variant était tissu-spécifique (coeur, rein, pancréas, muscle squelettique, poumon, foie, et cerveau). En plus, l'abondance relative des variant d’épissage varie pendant la surcharge de pression et le développement postnatal du coeur. En outre, l'immunofluorescence a indiqué que MK5.1-5.3 se localise au noyau alors que MK5.4-5.5 est situé au niveau cytoplasmic dans les cellules HEK 293 non stimulées. Suite à une stimulation avec l'anisomycin, un activateur de p38 MAPK, MK5.1-5.3 se translocalise du noyau au cytoplasme alors qu’une petite fraction de MK5.4-5.5 translocalise vers le noyau. Ces variant d'épissage peuvent diversifier la signalisation de MK5-ERK3 dans coeur, mais leur rôle exact oblige des recherches supplémentaires. Excepté l’isoforme δ, toutes les isoformes de p38 sont exprimées dans le coeur et la forme α est considérée comme étant l'isoforme dominante. L’analyse par qPCR et immunobuvardage de type western ont démontré que p38α et p38γ sont les deux isoformes prédominantes alors que p38β et p38δ sont exprimées aux mêmes niveaux dans le coeur de rat adulte. L'immunofluorescence a démontré que p38α et p38γ se trouvent dans le cytoplasme et le noyau. Cependant, suite à la surcharge par TAC, p38γ s'est accumulé dans noyau tandis que la distribution de p38α est demeurée inchangée. Ainsi, l'abondance de p38γ et sa translocalisation nucléaire suite à la surcharge de pression indique un rôle potentiel dans l'expression génique pendant le remodelage cardiaque. En conclusion, nous avons mis en évidence pour la première fois un rôle pro-fibrotique pour la signalisation MK5-ERK3 pendant une surcharge chronique de pression. D'ailleurs, les niveaux comparables d'expression de p38γ avec p38α, et la localisation différentielle de p38γ pendant la surcharge aiguë ou chronique de pression suggèrent différents rôles possibles pour ces isoformes pendant le remodelage hypertrophique cardiaque.