The fibroblast growth factor (FGF23) plasma level is high in cardiac and renal failure and is associated with poor clinical prognosis of these disorders. Both diseases are paralleled by hyperaldosteronism. Excessive FGF23 levels and hyperaldosteronism are further observed in Klotho-deficient mice. The present study explored a putative aldosterone sensitivity of Fgf23 transcription and secretion the putative involvement of the aldosterone sensitive serum glucocorticoid inducible kinase SGK1, SGK1 sensitive transcription factor NFB and store operated Ca(2+) entry (SOCE). Serum FGF23 levels were determined by ELISA in mice following sham treatment or exposure to deoxycorticosterone acetate (DOCA) or salt depletion. In osteoblastic UMR106 cells transcript levels were quantified by qRT-PCR, cytosolic Ca(2+) concentration utilizing Fura-2-fluorescence, and SOCE from Ca(2+) entry following store depletion by thapsigargin. As a result, DOCA treatment and salt depletion of mice elevated the serum C-terminal FGF23 concentration. In UMR106 cells aldosterone enhanced and spironolactone decreased SOCE. Aldosterone further increased Fgf23 transcript levels in UMR106 cells, an effect reversed by mineralocorticoid receptor blockers spironolactone and eplerenone, SGK1 inhibitor EMD638683, NFB-inhibitor withaferin A, and Ca(2+) channel blocker YM58483. In conclusion, Fgf23 expression is up-regulated by aldosterone, an effect sensitive to SGK1, NFB and store-operated Ca(2+) entry. AbstractThe fibroblast growth factor (FGF23) plasma level is high in cardiac and renal failure and is associated with poor clinical prognosis of these disorders. Both diseases are paralleled with hyperaldosteronism. Excessive FGF23 levels and hyperaldosteronism are further observed in Klotho-deficient mice. The present study explored a putative aldosterone sensitivity of Fgf23 transcription and secretion and the putative involvement of the aldosterone sensitive serum & glucocorticoid inducibe kinase SGK1 and SGK1 sensitive and store operated Ca 2+ entry (SOCE). Serum FGF23 levels were determined by ELISA in mice following sham treatment or exposure to deoxycorticosterone acetate (DOCA) or salt depletion. In osteoblastic UMR106 cells transcript levels were quantified by qRT-PCR, cytosolic Ca 2+ concentration utilizing Fura-2-fluorescence, and SOCE from Ca 2+ entry following store depletion by thapsigargin. As a result, DOCA treatment and salt depletion of mice elevated the serum C-terminal FGF23 concentration. In UMR106 cells aldosterone enhanced and spironolactone decreased SOCE. Aldosterone further increased Fgf23 transcript levels in UMR106 cells, an effect reversed by mineralocorticoid receptor blockers spironolactone and eplerenone, SGK1 inhibitor EMD638683, -inhibitor withaferin A, and Ca 2+ channel blocker YM58483. In conclusion, Fgf23 expression is up-regulated by aldosterone, an effect sensitive to SGK1, and store-operated Ca 2+ entry.

Fibroblast growth factor (FGF23) plasma levels are elevated in cardiac and renal failure and correlate with poor clinical prognosis of those disorders. Both disorders are associated with inflammation and activation of the inflammatory transcription factor NFB. An excessive FGF23 level is further observed in Klotho-deficient mice. The present study explored a putative sensitivity of FGF23 expression to transcription factor NFB, which is known to upregulate Orai1, the Ca(2+) channel accomplishing storeoperated Ca(2+) entry (SOCE). In osteoblastic cells (UMR106) and immortalized primary periosteal (IPO) cells, protein abundance was determined by Western blotting, and in UMR106 cells, transcript levels were quantified by RT-PCR, cytosolic Ca(2+) activity utilizing Fura-2-fluorescence, and SOCE from Ca(2+) entry following store depletion by thapsigargin. As a result, UMR106 and IPO cells expressed Ca(2+) channel Orai1. SOCE was lowered by NFB inhibitor wogonin as well as by Orai1 inhibitors 2-APB and YM58483. UMR106 cell Fgf23 transcripts were increased by stimulation of SOCE and Ca(2+) ionophore ionomycin and decreased by Orai inhibitors 2-APB, YM58483 and SKF96365, by Orai1 silencing, as well as by NFB inhibitors wogonin, withaferin A, and CAS 545380-34-5. In conclusion, Fgf23 expression is upregulated by stimulation of NFB-sensitive, store-operated Ca(2+) entry. KEY MES-SAGES Osteoblast UMR106 and IPO cells express Ca(2+) channel Orai1. Osteoblast store-operated Ca(2+) entry is accomplished by NFB-sensitive Orai1. Osteoblast Fgf23 transcription is upregulated by increase in the cytosolic Ca(2+) activity.

Embryo implantation requires a hospitable uterine environment. A key metabolic change that occurs during the peri-implantation period, and throughout early pregnancy, is the rise in endometrial glycogen content. Glycogen accumulation requires prior cellular uptake of glucose. Here we show that both human and murine endometrial epithelial cells express the high affinity Na+-coupled glucose carrier SGLT1. Ussing chamber experiments revealed electrogenic glucose transport across the endometrium in wild type (Slc5a1 +/+) but not in SGLT1 deficient (Slc5a1 −/−) mice. Endometrial glycogen content, litter size and weight of offspring at birth were significantly lower in Slc5a1 −/− mice. In humans, SLC5A1 expression was upregulated upon decidualization of primary endometrial stromal cells. Endometrial SLC5A1 expression during the implantation window was attenuated in patients with recurrent pregnancy loss when compared with control subjects. Our findings reveal a novel mechanism establishing adequate endometrial glycogen stores for pregnancy. Disruption of this histiotrophic pathway leads to adverse pregnancy outcome.

Putative functions of the heterotrimeric G-protein subunit Gαi2-dependent signaling include ion channel regulation, cell differentiation, proliferation and apoptosis. Erythrocytes may, similar to apoptosis of nucleated cells, undergo eryptosis, characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine (PS) exposure. Eryptosis may be triggered by increased cytosolic Ca2+ activity and ceramide. In the present study, we show that Gαi2 is expressed in both murine and human erythrocytes and further examined the survival of erythrocytes drawn from Gαi2-deficient mice (Gαi2−/−) and corresponding wild-type mice (Gαi2+/+). Our data show that plasma erythropoietin levels, erythrocyte maturation markers, erythrocyte counts, hematocrit and hemoglobin concentration were similar in Gαi2−/− and Gαi2+/+ mice but the mean corpuscular volume was significantly larger in Gαi2−/− mice. Spontaneous PS exposure of circulating Gαi2−/− erythrocytes was significantly lower than that of circulating Gαi2+/+ erythrocytes. PS exposure was significantly lower in Gαi2−/− than in Gαi2+/+ erythrocytes following ex vivo exposure to hyperosmotic shock, bacterial sphingomyelinase or C6 ceramide. Erythrocyte Gαi2 deficiency further attenuated hyperosmotic shock-induced increase of cytosolic Ca2+ activity and cell shrinkage. Moreover, Gαi2−/− erythrocytes were more resistant to osmosensitive hemolysis as compared to Gαi2+/+ erythrocytes. In conclusion, Gαi2 deficiency in erythrocytes confers partial protection against suicidal cell death.

Background/Aims: The WNK-dependent STE20/SPS1-related proline/alanine-rich kinase SPAK participates in the regulation of NaCl and Na⁺,K⁺,2Cl^- cotransport and thus renal salt excretion. The present study explored whether SPAK has similarly the potential to regulate the epithelial Na⁺ channel (ENaC). Methods: ENaC was expressed in Xenopus oocytes with or without additional expression of wild type SPAK, constitutively active ^T233ESPAK, WNK insensitive ^T233ASPAK or catalytically inactive ^D212ASPAK, and ENaC activity estimated from amiloride (50 µM) sensitive current (I_amil) in dual electrode voltage clamp experiments. Moreover, Ussing chamber was employed to determine I_amil in colonic tissue from wild type mice (spak^wt/wt) and from gene targeted mice carrying WNK insensitive SPAK (spak^tg/tg). Results: I_amil was observed in ENaC-expressing oocytes, but not in water-injected oocytes. In ENaC expressing oocytes I_amil was significantly increased following coexpression of wild-type SPAK and ^T233ESPAK, but not following coexpression of ^T233ASPAK or ^D212ASPAK. Colonic I_amil was significantly higher in spak^wt/wt than in spak^tg/tg mice. Conclusion: SPAK has the potential to up-regulate ENaC.