FOXO1 orchestrates the bone-suppressing function of gut-derived serotonin
Aruna Kode, … , X. Edward Guo, Stavroula Kousteni
Aruna Kode, … , X. Edward Guo, Stavroula Kousteni
Published September 4, 2012
Citation Information: J Clin Invest. 2012;122(10):3490-3503. https://doi.org/10.1172/JCI64906.
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Research Article Bone biology

FOXO1 orchestrates the bone-suppressing function of gut-derived serotonin

Abstract

Serotonin is a critical regulator of bone mass, fulfilling different functions depending on its site of synthesis. Brain-derived serotonin promotes osteoblast proliferation, whereas duodenal-derived serotonin suppresses it. To understand the molecular mechanisms of duodenal-derived serotonin action on osteoblasts, we explored its transcriptional mediation in mice. We found that the transcription factor FOXO1 is a crucial determinant of the effects of duodenum-derived serotonin on bone formation We identified two key FOXO1 complexes in osteoblasts, one with the transcription factor cAMP-responsive element–binding protein 1 (CREB) and another with activating transcription factor 4 (ATF4). Under normal levels of circulating serotonin, the proliferative activity of FOXO1 was promoted by a balance between its interaction with CREB and ATF4. However, high circulating serotonin levels prevented the association of FOXO1 with CREB, resulting in suppressed osteoblast proliferation. These observations identify FOXO1 as the molecular node of an intricate transcriptional machinery that confers the signal of duodenal-derived serotonin to inhibit bone formation.

Authors

Aruna Kode, Ioanna Mosialou, Barbara C. Silva, Marie-Therese Rached, Bin Zhou, Ji Wang, Tim M. Townes, Rene Hen, Ronald A. DePinho, X. Edward Guo, Stavroula Kousteni

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Figure 4

Serotonin regulates a FOXO1-CREB interaction.

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Serotonin regulates a FOXO1-CREB interaction. (A and B) Phosphorylation ...
(A and B) Phosphorylation status of (A) ATF4 and (B) CREB in OB-6 cells treated with serotonin (100 μM). (C) OB-6 cells transfected with expression plasmids for PKA, the active domain of CREB fused to GAL4, and a construct with GAL4-binding sites upstream of the luciferase gene and treated with 100 μM serotonin for 24 hours (n = 3). *P < 0.05 versus PKA plasmid vehicle. (D and E) Immunoprecipitation and immunoblotting in OB-6 cells treated with serotonin (100 μM) for 1 hour. Blots were representative of 3 experiments. ND, not detected. (F) Binding of GST-FOXO1 fragments and His-CREB for mapping the FOXO1 interaction domain. (G) Binding of GST-FOXO1 (aa 290–655) and His-CREB fragments for mapping the CREB interaction domain. (H) Calvaria cells transfected with indicated plasmids and treated with vehicle or serotonin (100 μM) for 24 hours (n = 3). *P < 0.05 versus EV vehicle; #P < 0.05 versus respective vehicle. (I) Serum serotonin levels, (J) SOD2 activity in tibial lysates, and (K and L) immunoprecipitation and immunoblotting in femoral lysates from WT and Lrp5–/– mice (n = 3–4 mice/group). *P < 0.05 versus WT.