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A Genetic Screen Identifies Hypothalamic Fgf15 as a Regulator of Glucagon Secretion

View Article: PubMed Central - PubMed

ABSTRACT

The counterregulatory response to hypoglycemia, which restores normal blood glucose levels to ensure sufficient provision of glucose to the brain, is critical for survival. To discover underlying brain regulatory systems, we performed a genetic screen in recombinant inbred mice for quantitative trait loci (QTL) controlling glucagon secretion in response to neuroglucopenia. We identified a QTL on the distal part of chromosome 7 and combined this genetic information with transcriptomic analysis of hypothalami. This revealed Fgf15 as the strongest candidate to control the glucagon response. Fgf15 was expressed by neurons of the dorsomedial hypothalamus and the perifornical area. Intracerebroventricular injection of FGF19, the human ortholog of Fgf15, reduced activation by neuroglucopenia of dorsal vagal complex neurons, of the parasympathetic nerve, and lowered glucagon secretion. In contrast, silencing Fgf15 in the dorsomedial hypothalamus increased neuroglucopenia-induced glucagon secretion. These data identify hypothalamic Fgf15 as a regulator of glucagon secretion.

No MeSH data available.


Related in: MedlinePlus

FGF19 Blunts 2DG-Induced Parasympathetic Nerve Activity(A) Parasympathetic nerve firing rate in the basal state and following i.p. 2DG injection in mice previously treated with i.c.v. aCSF or FGF19 (top: representative trace and bottom: quantification of the firing activity) (n = 6–7).(B) Sympathetic nerve firing rate in the basal state and following i.p. 2DG injection in mice previously treated with i.c.v. aCSF or FGF19 (top: representative trace and bottom: quantification of the firing activity) (n = 7).(C) Representative micrographs of pERK1/2 positive cells in the ARC 30 min after i.c.v. injection of aCSF or FGF19.(D) Quantification of pERK1/2 positive cells in the ARC 30 min after i.c.v. injection of aCSF or FGF19. (n = 5–7).(E) Representative micrographs of c-fos positive cells in NTS and DMNX at bregma −7.56 mm of mice that received i.c.v. aCSF and 60 min later i.p. NaCl (upper), i.c.v. aCSF and 60 min later i.p. 2DG (mid), or i.c.v FGF19 and 60 in later i.p. 2DG (lower). area postrema, AP; central canal, CC; nucleus of the solitary tract, NTS; DMNX.(F) Quantification of c-fos positive cells in NTS and DMNX of mice treated as in (E). The scale bar represents 50 μm.Two-way ANOVA followed by Bonferroni post hoc test (A and B). Student’s t test (D). One-way ANOVA followed by Bonferroni post hoc test (F). ∗p ≤ 0.05; ∗∗p ≤ 0.01; and ∗∗∗p ≤ 0.001.Data are mean ± SEM.
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fig5: FGF19 Blunts 2DG-Induced Parasympathetic Nerve Activity(A) Parasympathetic nerve firing rate in the basal state and following i.p. 2DG injection in mice previously treated with i.c.v. aCSF or FGF19 (top: representative trace and bottom: quantification of the firing activity) (n = 6–7).(B) Sympathetic nerve firing rate in the basal state and following i.p. 2DG injection in mice previously treated with i.c.v. aCSF or FGF19 (top: representative trace and bottom: quantification of the firing activity) (n = 7).(C) Representative micrographs of pERK1/2 positive cells in the ARC 30 min after i.c.v. injection of aCSF or FGF19.(D) Quantification of pERK1/2 positive cells in the ARC 30 min after i.c.v. injection of aCSF or FGF19. (n = 5–7).(E) Representative micrographs of c-fos positive cells in NTS and DMNX at bregma −7.56 mm of mice that received i.c.v. aCSF and 60 min later i.p. NaCl (upper), i.c.v. aCSF and 60 min later i.p. 2DG (mid), or i.c.v FGF19 and 60 in later i.p. 2DG (lower). area postrema, AP; central canal, CC; nucleus of the solitary tract, NTS; DMNX.(F) Quantification of c-fos positive cells in NTS and DMNX of mice treated as in (E). The scale bar represents 50 μm.Two-way ANOVA followed by Bonferroni post hoc test (A and B). Student’s t test (D). One-way ANOVA followed by Bonferroni post hoc test (F). ∗p ≤ 0.05; ∗∗p ≤ 0.01; and ∗∗∗p ≤ 0.001.Data are mean ± SEM.

Mentions: Glucagon secretion during hypoglycemia is triggered by the activation of both parasympathetic and sympathetic branches of the autonomic nervous system (ANS) (Taborsky and Mundinger, 2012). As i.c.v. FGF19 decreased the glucagon response to 2DG-induced neuroglucopenia, but had no effect in non-injected or i.p. saline injected mice, we measured sympathetic and parasympathetic nerve activities in response to i.p. 2DG in mice, which had previously received i.c.v. aCSF or FGF19. Parasympathetic nerve activity showed no differences between groups in the basal state (Figure 5A). After 2DG injection, its activity increased 2-fold in mice pre-treated with aCSF, but remained unchanged in mice pre-treated with FGF19 (Figure 5A). Sympathetic nerve activity showed no differences between the groups in the basal state or following 2DG injections (Figure 5B). Thus, i.c.v. injection of FGF19 inhibits 2DG-induced parasympathetic, but not sympathetic nervous activity.


A Genetic Screen Identifies Hypothalamic Fgf15 as a Regulator of Glucagon Secretion
FGF19 Blunts 2DG-Induced Parasympathetic Nerve Activity(A) Parasympathetic nerve firing rate in the basal state and following i.p. 2DG injection in mice previously treated with i.c.v. aCSF or FGF19 (top: representative trace and bottom: quantification of the firing activity) (n = 6–7).(B) Sympathetic nerve firing rate in the basal state and following i.p. 2DG injection in mice previously treated with i.c.v. aCSF or FGF19 (top: representative trace and bottom: quantification of the firing activity) (n = 7).(C) Representative micrographs of pERK1/2 positive cells in the ARC 30 min after i.c.v. injection of aCSF or FGF19.(D) Quantification of pERK1/2 positive cells in the ARC 30 min after i.c.v. injection of aCSF or FGF19. (n = 5–7).(E) Representative micrographs of c-fos positive cells in NTS and DMNX at bregma −7.56 mm of mice that received i.c.v. aCSF and 60 min later i.p. NaCl (upper), i.c.v. aCSF and 60 min later i.p. 2DG (mid), or i.c.v FGF19 and 60 in later i.p. 2DG (lower). area postrema, AP; central canal, CC; nucleus of the solitary tract, NTS; DMNX.(F) Quantification of c-fos positive cells in NTS and DMNX of mice treated as in (E). The scale bar represents 50 μm.Two-way ANOVA followed by Bonferroni post hoc test (A and B). Student’s t test (D). One-way ANOVA followed by Bonferroni post hoc test (F). ∗p ≤ 0.05; ∗∗p ≤ 0.01; and ∗∗∗p ≤ 0.001.Data are mean ± SEM.
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fig5: FGF19 Blunts 2DG-Induced Parasympathetic Nerve Activity(A) Parasympathetic nerve firing rate in the basal state and following i.p. 2DG injection in mice previously treated with i.c.v. aCSF or FGF19 (top: representative trace and bottom: quantification of the firing activity) (n = 6–7).(B) Sympathetic nerve firing rate in the basal state and following i.p. 2DG injection in mice previously treated with i.c.v. aCSF or FGF19 (top: representative trace and bottom: quantification of the firing activity) (n = 7).(C) Representative micrographs of pERK1/2 positive cells in the ARC 30 min after i.c.v. injection of aCSF or FGF19.(D) Quantification of pERK1/2 positive cells in the ARC 30 min after i.c.v. injection of aCSF or FGF19. (n = 5–7).(E) Representative micrographs of c-fos positive cells in NTS and DMNX at bregma −7.56 mm of mice that received i.c.v. aCSF and 60 min later i.p. NaCl (upper), i.c.v. aCSF and 60 min later i.p. 2DG (mid), or i.c.v FGF19 and 60 in later i.p. 2DG (lower). area postrema, AP; central canal, CC; nucleus of the solitary tract, NTS; DMNX.(F) Quantification of c-fos positive cells in NTS and DMNX of mice treated as in (E). The scale bar represents 50 μm.Two-way ANOVA followed by Bonferroni post hoc test (A and B). Student’s t test (D). One-way ANOVA followed by Bonferroni post hoc test (F). ∗p ≤ 0.05; ∗∗p ≤ 0.01; and ∗∗∗p ≤ 0.001.Data are mean ± SEM.
Mentions: Glucagon secretion during hypoglycemia is triggered by the activation of both parasympathetic and sympathetic branches of the autonomic nervous system (ANS) (Taborsky and Mundinger, 2012). As i.c.v. FGF19 decreased the glucagon response to 2DG-induced neuroglucopenia, but had no effect in non-injected or i.p. saline injected mice, we measured sympathetic and parasympathetic nerve activities in response to i.p. 2DG in mice, which had previously received i.c.v. aCSF or FGF19. Parasympathetic nerve activity showed no differences between groups in the basal state (Figure 5A). After 2DG injection, its activity increased 2-fold in mice pre-treated with aCSF, but remained unchanged in mice pre-treated with FGF19 (Figure 5A). Sympathetic nerve activity showed no differences between the groups in the basal state or following 2DG injections (Figure 5B). Thus, i.c.v. injection of FGF19 inhibits 2DG-induced parasympathetic, but not sympathetic nervous activity.

View Article: PubMed Central - PubMed

ABSTRACT

The counterregulatory response to hypoglycemia, which restores normal blood glucose levels to ensure sufficient provision of glucose to the brain, is critical for survival. To discover underlying brain regulatory systems, we performed a genetic screen in recombinant inbred mice for quantitative trait loci (QTL) controlling glucagon secretion in response to neuroglucopenia. We identified a QTL on the distal part of chromosome 7 and combined this genetic information with transcriptomic analysis of hypothalami. This revealed Fgf15 as the strongest candidate to control the glucagon response. Fgf15 was expressed by neurons of the dorsomedial hypothalamus and the perifornical area. Intracerebroventricular injection of FGF19, the human ortholog of Fgf15, reduced activation by neuroglucopenia of dorsal vagal complex neurons, of the parasympathetic nerve, and lowered glucagon secretion. In contrast, silencing Fgf15 in the dorsomedial hypothalamus increased neuroglucopenia-induced glucagon secretion. These data identify hypothalamic Fgf15 as a regulator of glucagon secretion.

No MeSH data available.


Related in: MedlinePlus