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FGF-23-Klotho signaling stimulates proliferation and prevents vitamin D-induced apoptosis.

Medici D, Razzaque MS, Deluca S, Rector TL, Hou B, Kang K, Goetz R, Mohammadi M, Kuro-O M, Olsen BR, Lanske B - J. Cell Biol. (2008)

Bottom Line: Fibroblast growth factor 23 (FGF-23) and Klotho are secretory proteins that regulate mineral-ion metabolism.Because serum levels of active vitamin D are greatly increased upon genetic ablation of Fgf-23 or Klotho, we find that these molecules have a dual role in suppression of apoptotic actions of vitamin D through both negative regulation of 1alpha-hydroxylase expression and phosphoinositide-3 kinase-dependent inhibition of caspase activity.These data provide new insights into the physiological roles of FGF-23 and Klotho.

View Article: PubMed Central - PubMed

Affiliation: Department of Developmental Biology, Harvard School of Dental Medicine, Boston, MA 02115, USA.

ABSTRACT
Fibroblast growth factor 23 (FGF-23) and Klotho are secretory proteins that regulate mineral-ion metabolism. Fgf-23(-/-) or Klotho(-/-) knockout mice exhibit several pathophysiological processes consistent with premature aging including severe atrophy of tissues. We show that the signal transduction pathways initiated by FGF-23-Klotho prevent tissue atrophy by stimulating proliferation and preventing apoptosis caused by excessive systemic vitamin D. Because serum levels of active vitamin D are greatly increased upon genetic ablation of Fgf-23 or Klotho, we find that these molecules have a dual role in suppression of apoptotic actions of vitamin D through both negative regulation of 1alpha-hydroxylase expression and phosphoinositide-3 kinase-dependent inhibition of caspase activity. These data provide new insights into the physiological roles of FGF-23 and Klotho.

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FGF-23–Klotho prevents vitamin D–induced apoptosis. (A) ELISA analysis of 1α-hydroxylase expression showing no significant changes in PTEC cells exposed to FGF-23 or Klotho alone but greatly decreased levels when exposed to both FGF-23 and Klotho. Small molecule inhibitors against Ras and PI3K were sufficient to provide marginal rescue of this decrease in expression. No significant changes were found for treatment of FHs74Int cells. Graphs represent mean ± SD (n = 3). *, P < 0.05. (B) Flow cytometry analysis for TUNEL staining of cells exposed to exogenous vitamin D showing that it caused extremely high levels of apoptosis. Addition of FGF-23 and Klotho was sufficient to rescue most of the vitamin D–induced apoptosis, whereas FGF-23 or Klotho alone did not. PI3K inhibitor prevented this rescue, whereas Ras inhibitor had no effect. (C) ELISA for active caspase-3 levels, showing the same patterns as observed with the TUNEL analysis. Graphs represent mean ± SD (n = 3). *, P < 0.001.
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fig3: FGF-23–Klotho prevents vitamin D–induced apoptosis. (A) ELISA analysis of 1α-hydroxylase expression showing no significant changes in PTEC cells exposed to FGF-23 or Klotho alone but greatly decreased levels when exposed to both FGF-23 and Klotho. Small molecule inhibitors against Ras and PI3K were sufficient to provide marginal rescue of this decrease in expression. No significant changes were found for treatment of FHs74Int cells. Graphs represent mean ± SD (n = 3). *, P < 0.05. (B) Flow cytometry analysis for TUNEL staining of cells exposed to exogenous vitamin D showing that it caused extremely high levels of apoptosis. Addition of FGF-23 and Klotho was sufficient to rescue most of the vitamin D–induced apoptosis, whereas FGF-23 or Klotho alone did not. PI3K inhibitor prevented this rescue, whereas Ras inhibitor had no effect. (C) ELISA for active caspase-3 levels, showing the same patterns as observed with the TUNEL analysis. Graphs represent mean ± SD (n = 3). *, P < 0.001.

Mentions: Because active vitamin D has recently been described to have anti-cancer effects (Johnson et al., 2002, 2006) and serum levels of 1,25(OH)2D3 are excessively high in Fgf-23−/− or Klotho−/− mice (Tsujikawa et al., 2003; Shimada et al., 2004; Sitara et al., 2004), we hypothesized that these elevated levels might promote apoptosis, thus causing the observed atrophy of tissues. We first showed the direct effect of FGF-23–Klotho on expression of 1α-hydroxylase, the enzyme responsible for final synthesis of active vitamin D metabolite. Protein levels of 1α-hydroxylase were observed by ELISA, showing that FGF-23 and Klotho together were able to greatly reduce expression of this enzyme in PTEC cells compared with the control, whereas FGF-23 or Klotho alone had little effect. Addition of Ras and PI3K inhibitors showed significant rescue of 1α-hydroxylase expression, however full restoration was not achieved. These data suggest that other signaling pathways may also be involved in regulation of 1α-hydroxylase expression. Interestingly, no statistically significant changes in expression of 1α-hydroxylase were found with treatment of FHs74Int cells (Fig. 3 A). This is consistent with the fact that PTEC of the kidney are the primary site of 1α-hydroxylase activity for synthesis of active vitamin D (Dardenne et al., 2001) not small intestinal epithelium.


FGF-23-Klotho signaling stimulates proliferation and prevents vitamin D-induced apoptosis.

Medici D, Razzaque MS, Deluca S, Rector TL, Hou B, Kang K, Goetz R, Mohammadi M, Kuro-O M, Olsen BR, Lanske B - J. Cell Biol. (2008)

FGF-23–Klotho prevents vitamin D–induced apoptosis. (A) ELISA analysis of 1α-hydroxylase expression showing no significant changes in PTEC cells exposed to FGF-23 or Klotho alone but greatly decreased levels when exposed to both FGF-23 and Klotho. Small molecule inhibitors against Ras and PI3K were sufficient to provide marginal rescue of this decrease in expression. No significant changes were found for treatment of FHs74Int cells. Graphs represent mean ± SD (n = 3). *, P < 0.05. (B) Flow cytometry analysis for TUNEL staining of cells exposed to exogenous vitamin D showing that it caused extremely high levels of apoptosis. Addition of FGF-23 and Klotho was sufficient to rescue most of the vitamin D–induced apoptosis, whereas FGF-23 or Klotho alone did not. PI3K inhibitor prevented this rescue, whereas Ras inhibitor had no effect. (C) ELISA for active caspase-3 levels, showing the same patterns as observed with the TUNEL analysis. Graphs represent mean ± SD (n = 3). *, P < 0.001.
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fig3: FGF-23–Klotho prevents vitamin D–induced apoptosis. (A) ELISA analysis of 1α-hydroxylase expression showing no significant changes in PTEC cells exposed to FGF-23 or Klotho alone but greatly decreased levels when exposed to both FGF-23 and Klotho. Small molecule inhibitors against Ras and PI3K were sufficient to provide marginal rescue of this decrease in expression. No significant changes were found for treatment of FHs74Int cells. Graphs represent mean ± SD (n = 3). *, P < 0.05. (B) Flow cytometry analysis for TUNEL staining of cells exposed to exogenous vitamin D showing that it caused extremely high levels of apoptosis. Addition of FGF-23 and Klotho was sufficient to rescue most of the vitamin D–induced apoptosis, whereas FGF-23 or Klotho alone did not. PI3K inhibitor prevented this rescue, whereas Ras inhibitor had no effect. (C) ELISA for active caspase-3 levels, showing the same patterns as observed with the TUNEL analysis. Graphs represent mean ± SD (n = 3). *, P < 0.001.
Mentions: Because active vitamin D has recently been described to have anti-cancer effects (Johnson et al., 2002, 2006) and serum levels of 1,25(OH)2D3 are excessively high in Fgf-23−/− or Klotho−/− mice (Tsujikawa et al., 2003; Shimada et al., 2004; Sitara et al., 2004), we hypothesized that these elevated levels might promote apoptosis, thus causing the observed atrophy of tissues. We first showed the direct effect of FGF-23–Klotho on expression of 1α-hydroxylase, the enzyme responsible for final synthesis of active vitamin D metabolite. Protein levels of 1α-hydroxylase were observed by ELISA, showing that FGF-23 and Klotho together were able to greatly reduce expression of this enzyme in PTEC cells compared with the control, whereas FGF-23 or Klotho alone had little effect. Addition of Ras and PI3K inhibitors showed significant rescue of 1α-hydroxylase expression, however full restoration was not achieved. These data suggest that other signaling pathways may also be involved in regulation of 1α-hydroxylase expression. Interestingly, no statistically significant changes in expression of 1α-hydroxylase were found with treatment of FHs74Int cells (Fig. 3 A). This is consistent with the fact that PTEC of the kidney are the primary site of 1α-hydroxylase activity for synthesis of active vitamin D (Dardenne et al., 2001) not small intestinal epithelium.

Bottom Line: Fibroblast growth factor 23 (FGF-23) and Klotho are secretory proteins that regulate mineral-ion metabolism.Because serum levels of active vitamin D are greatly increased upon genetic ablation of Fgf-23 or Klotho, we find that these molecules have a dual role in suppression of apoptotic actions of vitamin D through both negative regulation of 1alpha-hydroxylase expression and phosphoinositide-3 kinase-dependent inhibition of caspase activity.These data provide new insights into the physiological roles of FGF-23 and Klotho.

View Article: PubMed Central - PubMed

Affiliation: Department of Developmental Biology, Harvard School of Dental Medicine, Boston, MA 02115, USA.

ABSTRACT
Fibroblast growth factor 23 (FGF-23) and Klotho are secretory proteins that regulate mineral-ion metabolism. Fgf-23(-/-) or Klotho(-/-) knockout mice exhibit several pathophysiological processes consistent with premature aging including severe atrophy of tissues. We show that the signal transduction pathways initiated by FGF-23-Klotho prevent tissue atrophy by stimulating proliferation and preventing apoptosis caused by excessive systemic vitamin D. Because serum levels of active vitamin D are greatly increased upon genetic ablation of Fgf-23 or Klotho, we find that these molecules have a dual role in suppression of apoptotic actions of vitamin D through both negative regulation of 1alpha-hydroxylase expression and phosphoinositide-3 kinase-dependent inhibition of caspase activity. These data provide new insights into the physiological roles of FGF-23 and Klotho.

Show MeSH
Related in: MedlinePlus