p38MAPK controls fibroblast growth factor 23 (FGF23) synthesis in UMR106-osteoblast-like cells and in IDG-SW3 osteocytes.

BACKGROUND: p38 mitogen-activated protein kinase (p38MAPK) is a serine/threonine kinase activated by cellular stress stimuli including radiation, osmotic shock, and inflammation and influencing apoptosis, cell proliferation, and autophagy. Moreover, p38MAPK induces transcriptional activity of the transcription factor complex NFκB mediating multiple pro-inflammatory cellular responses. Fibroblast growth factor 23 (FGF23) is produced by bone cells, and regulates renal phosphate and vitamin D metabolism as a hormone. FGF23 expression is enhanced by NFκB. Here, we analyzed the relevance of p38MAPK activity for the production of FGF23. METHODS: Fgf23 expression was analyzed by qRT-PCR and FGF23 protein by ELISA in UMR106 osteoblast-like cells and in IDG-SW3 osteocytes. RESULTS: Inhibition of p38MAPK with SB203580 or SB202190 significantly down-regulated Fgf23 expression and FGF23 protein expression. Conversely, p38MAPK activator anisomycin increased the abundance of Fgf23 mRNA. NFκB inhibitors wogonin and withaferin A abrogated the stimulatory effect of anisomycin on Fgf23 gene expression. CONCLUSION: p38MAPK induces FGF23 formation, an effect at least in part dependent on NFκB activity.

Functional significance of glutamate-cysteine ligase modifier for erythrocyte survival in vitro and in vivo.

Erythrocytes endure constant exposure to oxidative stress. The major oxidative stress scavenger in erythrocytes is glutathione. The rate-limiting enzyme for glutathione synthesis is glutamate-cysteine ligase, which consists of a catalytic subunit (GCLC) and a modifier subunit (GCLM). Here, we examined erythrocyte survival in GCLM-deficient (gclm(-/-)) mice. Erythrocytes from gclm(-/-) mice showed greatly reduced intracellular glutathione. Prolonged incubation resulted in complete lysis of gclm(-/-) erythrocytes, which could be reversed by exogenous delivery of the antioxidant Trolox. To test the importance of GCLM in vivo, mice were treated with phenylhydrazine (PHZ; 0.07 mg/g b.w.) to induce oxidative stress. Gclm(-/-) mice showed dramatically increased hemolysis compared with gclm(+/+) controls. In addition, PHZ-treated gclm(-/-) mice displayed markedly larger accumulations of injured erythrocytes in the spleen than gclm(+/+) mice within 24 h of treatment. Iron staining indicated precipitations of the erythrocyte-derived pigment hemosiderin in kidney tubules of gclm(-/-) mice and none in gclm(+/+) controls. In fact, 24 h after treatment, kidney function began to diminish in gclm(-/-) mice as evident from increased serum creatinine and urea. Consequently, while all PHZ-treated gclm(+/+) mice survived, 90% of PHZ-treated gclm(-/-) mice died within 5 days of treatment. In vitro, upon incubation in the absence or presence of additional oxidative stress, gclm(-/-) erythrocytes exposed significantly more phosphatidylserine, a cell death marker, than gclm(+/+) erythrocytes, an effect at least partially due to increased cytosolic Ca(2+) concentration. Under resting conditions, gclm(-/-) mice exhibited reticulocytosis, indicating that the enhanced erythrocyte death was offset by accelerated erythrocyte generation. GCLM is thus indispensable for erythrocyte survival, in vitro and in vivo, during oxidative stress.

SGK1-dependent salt appetite in pregnant mice.

AIM: Pregnancy is typically paralleled by substantial increase in maternal extracellular fluid volume, requiring net accumulation of water and NaCl. The positive water and salt balance is accomplished at least in part by increased uptake of salt secondary to enhanced salt appetite. Little is known about the underlying cellular mechanisms. Stimulation of salt appetite by mineralocorticoids, however, is known to be dependent on the serum- and glucocorticoid-inducible kinase SGK1. METHODS: To test for a role of SGK1 in the stimulation of salt appetite during pregnancy, fluid intake was recorded in pregnant SGK1 knockout mice (sgk1(-/-) ) and their wild type littermates (sgk1(+/+) ). The mice were offered two bottles, one with plain water and the other with isotonic saline. RESULTS: In early pregnancy, i.e. up to 10 days prior to parturition, the sgk1(+/+) mice displayed a significant preference for saline, whereas the sgk1(-/-) mice preferred water. Accordingly, the water intake was significantly smaller and saline intake was significantly larger in sgk1(+/+) mice than in sgk1(-/-) mice and the preference for water was significantly stronger in sgk1(-/-) mice than in sgk1(+/+) mice. Plasma aldosterone levels were higher in sgk1(-/-) mice than in sgk1(+/+) mice, a difference contrasting the enhanced salt appetite of sgk1(+/+) mice. CONCLUSIONS: SGK1 participates in the stimulation of salt appetite during pregnancy.

Akt2/PKBbeta-sensitive regulation of renal phosphate transport.

AIM: The protein kinase B (PKB)/Akt is known to stimulate the cellular uptake of glucose and amino acids. The kinase is expressed in proximal renal tubules. The present study explored the influence of Akt/PKB on renal tubular phosphate transport. METHODS: The renal phosphate transporter NaPi-IIa was expressed in Xenopus oocytes with or without PKB/Akt and Na(+) phosphate cotransport determined using dual electrode voltage clamp. Renal phosphate excretion was determined in Akt2/PKBbeta knockout mice (akt2(-/-)) and corresponding wild-type mice (akt2(+/+)). Transporter protein abundance was determined using Western blotting and phosphate transport by (32)P uptake into brush border membrane vesicles. RESULTS: The phosphate-induced current in NaPi-IIa-expressing Xenopus oocytes was significantly increased by the coexpression of Akt/PKB. Phosphate excretion [micromol per 24 h per g BW] was higher by 91% in akt2(-/-) than in akt2(+/+) mice. The phosphaturia of akt2(-/-) mice occurred despite normal transport activity and expression of the renal phosphate transporters NaPi-IIa, NaPi-IIc and Pit2 in the brush border membrane, a significantly decreased plasma PTH concentration (by 46%) and a significantly enhanced plasma 1,25-dihydroxyvitamin D(3) concentration (by 46%). Moreover, fractional renal Ca(2+) excretion was significantly enhanced (by 53%) and bone density significantly reduced (by 11%) in akt2(-/-) mice. CONCLUSIONS: Akt2/PKBbeta plays a role in the acute regulation of renal phosphate transport and thus contributes to the maintenance of phosphate balance and adequate mineralization of bone.

Participation of leukotriene C(4) in the regulation of suicidal erythrocyte death.

Eryptosis, the suicidal death of erythrocytes, is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine exposure at the erythrocyte surface. Eryptosis is triggered by increase in cytosolic Ca(2+) concentration upon energy depletion. The present study explored the involvement of leukotrienes. Western blotting was employed to detect the cysteinyl-leukotriene receptor cysLT1, competitive immune assay to determine leukotriene release from erythrocytes, Fluo3 fluorescence to estimate cytosolic Ca(2+) concentration, forward scatter to analyse cell volume and annexin V-binding to disclose phosphatidylserine exposure. As a result, erythrocytes expressed the leukotriene receptor CysLT1. Glucose depletion (24 hours) significantly increased the formation of the cysteinyl-leukotrienes C(4)/D(4)/E(4). Leukotriene C(4) (10 nM) increased Ca(2+) entry, decreased forward scatter, activated caspases 3 and 8, and stimulated annexin V-binding. Glucose depletion similarly increased annexin V-binding, an effect significantly blunted in the presence of the leukotriene receptor antagonist cinalukast (1 microM) or the 5-lipoxygenase inhibitor BW B70C (1 microM). In conclusion, upon energy depletion erythrocytes form leukotrienes, which in turn activate cation channels, leading to Ca(2+) entry, cell shrinkage and cell membrane scrambling. Cysteinyl-leukotrienes thus participate in the signaling of eryptosis during energy depletion.

Triggering of suicidal erythrocyte death by radiocontrast agents.

BACKGROUND: According to in vitro observations, gadolinium-containing magnetic resonance (MRT) contrast agents stimulate suicidal cell death or apoptosis. Similar to nucleated cells, erythrocytes may undergo suicidal death or eryptosis, characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine (PS) exposure at the erythrocyte surface. Eryptosis is triggered by increased cytosolic Ca2+-activity. This study explored whether gadolinium-containing MRT contrast agents stimulate eryptosis. MATERIALS AND METHODS: Annexin V-binding reflecting PS exposure and forward scatter reflecting cell volume were determined in erythrocytes within freshly drawn blood from patients (8female symbol, 3male symbol, 29-72 years) prior to and 10 min after administration of gadoterate meglumine (0.1 mmol kg(-1) b.w. Dotarem; six patients) or gadobenate dimeglumine (0.05 mmol kg(-1) bw Multi Hance; five patients). In a separate series, eryptosis was determined prior to and following in vitro incubation of erythrocytes from 16 blood donors for 4 h with gadoterate meglumine (5 mM Dotarem) or gadobenate dimeglumine (5 mM Multi Hance). Finally, eryptosis and Fluo3 fluorescence reflecting cytosolic Ca2+ were determined in vitro following exposure to Gd3+. Data were analysed using paired t-test or anova with Tukey's test as post-test. RESULTS: The MRT contrast agents such as gadoterate meglumine (Dotarem) and gadobenate dimeglumine (Multi Hance) significantly increased the percentage of eryptotic cells. Moreover, in vitro exposure to gadoterate meglumine (5 mM), gadobenate dimeglumine (5 mM) or Gd3+ (1.9 microM) stimulated eryptosis in vitro. The effect of Gd3+ was paralleled by increase in cytosolic Ca2+-activity. CONCLUSIONS: MRT contrast agents may stimulate suicidal erythrocyte death or eryptosis in vitro and in vivo.

Ion channels in cell proliferation and apoptotic cell death.

Cell proliferation and apoptosis are paralleled by altered regulation of ion channels that play an active part in the signaling of those fundamental cellular mechanisms. Cell proliferation must--at some time point--increase cell volume and apoptosis is typically paralleled by cell shrinkage. Cell volume changes require the participation of ion transport across the cell membrane, including appropriate activity of Cl- and K+ channels. Besides regulating cytosolic Cl- activity, osmolyte flux and, thus, cell volume, most Cl- channels allow HCO3- exit and cytosolic acidification, which inhibits cell proliferation and favors apoptosis. K+ exit through K+ channels may decrease intracellular K+ concentration, which in turn favors apoptotic cell death. K+ channel activity further maintains the cell membrane potential, a critical determinant of Ca2+ entry through Ca2+ channels. Cytosolic Ca2+ may trigger mechanisms required for cell proliferation and stimulate enzymes executing apoptosis. The switch between cell proliferation and apoptosis apparently depends on the magnitude and temporal organization of Ca2+ entry and on the functional state of the cell. Due to complex interaction with other signaling pathways, a given ion channel may play a dual role in both cell proliferation and apoptosis. Thus, specific ion channel blockers may abrogate both fundamental cellular mechanisms, depending on cell type, regulatory environment and condition of the cell. Clearly, considerable further experimental effort is required to fully understand the complex interplay between ion channels, cell proliferation and apoptosis.

Interactions between global processes and local health problems. A human ecology approach to health among indigenous groups in the Amazon.

This article deals with methodological issues and how to link global processes - social and ecological - with environmental changes and human health in local communities. The discussion concerns how interdisciplinary approaches can help us find tools to develop new knowledge. Scientific knowledge and local knowledge are not seen as opposite epistemological forms, but as socially and culturally constructed. Power and social legitimacy have to be included when analyzing how to deal with the interaction between global processes and local environmental change and the health/disease interface.

A new approach to interdisciplinary health studies: the Koster Health Project.

The Koster Health Project, initiated in 1987, is an interdisciplinary development project with a focus on human ecology. The objectives are to use relatively simple methods of medical and odontological annual examinations to carry out a 10-year longitudinal study of how life situations and life style factors may direct the development of individual's health in a sparse, geographically rather isolated and socially static, rural population in which it is possible to compare older and younger generations. An investigative model is established on the Koster islands and in this model assessments of given health criteria and other preventive medical, odontological and psychosocial measures may be followed up. Furthermore, the effects of environmental changes may be ascertained. Based on the experiences from the Koster Health Project, national and international seminars are arranged on the islands with emphasis on the impact of environment and life style on human health. The nutritional questions are the centre of specific interest.

A new approach to community health.

This article deals with the local health care among the Shipibo-Conibo in eastern Peru. A project called AMETRA--application of traditional medicine--is functioning in the area. The aim of AMETRA is to give courses and stimulate co-operation between traditional medical practice and Western medicine. The solutions to the health problems are seen in direct relation to the socio-economic structure and to the environmental prerequisites. The aim and purposes of AMETRA are described and analysed. It is proposed that the two medical systems should co-operate in such a manner that their complementary nature is emphasized and fully utilized.