Foxo1 regulates Dbh expression and the activity of the sympathetic nervous system in vivo

Abstract

The transcription factor FoxO1 regulates multiple physiological processes. Here, we show that FoxO1 is highly expressed in neurons of the locus coeruleus and of various sympathetic ganglions, but not in the adrenal medulla. Consistent with this pattern of expression, mice lacking FoxO1 only in sympathetic neurons (FoxO1 Dbh-/-) display a low sympathetic tone without modification of the catecholamine content in the adrenal medulla. As a result, FoxO1 Dbh-/- mice demonstrate an increased insulin secretion, improved glucose tolerance, low energy expenditure, and high bone mass. FoxO1 favors catecholamine synthesis because it is a potent regulator of the expression of Dbh that encodes the initial and rate-limiting enzyme in the synthesis of these neurotransmitters. By identifying FoxO1 as a transcriptional regulator of the sympathetic tone, these results advance our understanding of the control of some aspects of metabolism and of bone mass accrual.

Keywords: FoxO1; Locus coeruleus; Sympathetic tone.

Figure 1

(A) FoxO1 and Dbh expression in cells of the locus coeruleus (LC), adrenal gland (AG), the dorsal root ganglion (DRG), and superior cervical ganglion (SCG). Ct: Adrenal cortex. Me: Adrenal medulla. (B) Norepinephrine contents in FoxO1fl/fl and FoxO1_Dbh−/− adrenal glands. (C) Detection of FoxO1 mutant allele in genomic DNA isolated from tissues from FoxO1fl/fl Dbh-cre (FoxO1_Dbh−/−) male mouse. (D) Immunohistochemistry in the locus coeruleus, arcuate neurons, the dorsal root ganglion, the superior cervical ganglion of FoxO1fl/fl and FoxO1_Dbh−/− mice using anti-FoxO1 antibody. 3V: Third ventricle. ARC: Arcuate nucleus. (E) Norepinephrine content in the brainstem of 36 week-old FoxO1fl/fl and FoxO1_Dbh−/− mice. (F) Ucp1 expression in 36 week-old FoxO1fl/fl and FoxO1_Dbh−/− brown fat. (G) Urinary epinephrine elimination of 36 week-old FoxO1fl/fl and FoxO1_Dbh−/− mice.

Figure 2

(A) Putative FoxO1 binding sites in the Dbh promoter in human, mouse, rat, horse, dog, chicken and zebrafish. (B) Binding of FoxO1 to the Dbh promoter detected by Chromatin immuno-precipitation (ChIP) assay. (C) DNA cotransfections assays in HEK cells using a FoxO1 expression vector and reporter vectors containing fragments of Dbh promoter fused to the Luciferase gene. (D) Dbh expression in FoxO1fl/fl and FoxO1_Dbh−/− brainstem. (E) In situ hybridization analysis of the Dbh expression in the locus coeruleus, adrenal gland, the dorsal root ganglion, and superior cervical ganglion.

Figure 3

(A) Energy expenditure of 36 week-old FoxO1fl/fl and FoxO1_Dbh−/− mice. (B) Food intake of 36 week-old FoxO1fl/fl and FoxO1_Dbh−/− mice. (C) Fat pad weight of 36 week-old FoxO1fl/fl and FoxO1_Dbh−/− mice. (E and F) Glucose-stimulated insulin secretion test (GSIS), glucose tolerance test (GTT), and insulin tolerance test (ITT) of FoxO1fl/fl and FoxO1_Dbh−/− mice.

Figure 4

(A) Bone histomorophometric analysis of 36 week-old FoxO1fl/fl (n = 10) and FoxO1_Dbh−/− (n = 7) mice. BV/TV: Bone volume per tissue volume. Ob.N/B.Pm: Number of osteoblasts per bone perimeter. BFR: Bone formation rate. OcS/BS: Osteoclast surface per bone surface. (B) Serum PINP levels in 36 week-old FoxO1 FoxO1fl/fl and FoxO1_Dbh−/− mice. (C) Cyclin expression in 36 week-old FoxO1fl/fl and FoxO1_Dbh−/− bone. (D) Serum Ctx levels in 36 week-old FoxO1fl/fl and FoxO1_Dbh−/− mice. (E) Rankl expression in 36 week-old FoxO1fl/fl and FoxO1_Dbh−/− bones.