Limits...
Brain IGF-1 receptors control mammalian growth and lifespan through a neuroendocrine mechanism.

Kappeler L, De Magalhaes Filho C, Dupont J, Leneuve P, Cervera P, Périn L, Loudes C, Blaise A, Klein R, Epelbaum J, Le Bouc Y, Holzenberger M - PLoS Biol. (2008)

Bottom Line: Thus, early changes in neuroendocrine development can durably modify the life trajectory in mammals.The underlying mechanism appears to be an adaptive plasticity of somatotropic functions allowing individuals to decelerate growth and preserve resources, and thereby improve fitness in challenging environments.Our results also suggest that tonic somatotropic signaling entails the risk of shortened lifespan.

View Article: PubMed Central - PubMed

Affiliation: INSERM U893, Hôpital Saint-Antoine, Paris, France.

ABSTRACT
Mutations that decrease insulin-like growth factor (IGF) and growth hormone signaling limit body size and prolong lifespan in mice. In vertebrates, these somatotropic hormones are controlled by the neuroendocrine brain. Hormone-like regulations discovered in nematodes and flies suggest that IGF signals in the nervous system can determine lifespan, but it is unknown whether this applies to higher organisms. Using conditional mutagenesis in the mouse, we show that brain IGF receptors (IGF-1R) efficiently regulate somatotropic development. Partial inactivation of IGF-1R in the embryonic brain selectively inhibited GH and IGF-I pathways after birth. This caused growth retardation, smaller adult size, and metabolic alterations, and led to delayed mortality and longer mean lifespan. Thus, early changes in neuroendocrine development can durably modify the life trajectory in mammals. The underlying mechanism appears to be an adaptive plasticity of somatotropic functions allowing individuals to decelerate growth and preserve resources, and thereby improve fitness in challenging environments. Our results also suggest that tonic somatotropic signaling entails the risk of shortened lifespan.

Show MeSH

Related in: MedlinePlus

Brain-Targeted Inactivation of the Igf1r Gene Using Cre-lox Mutagenesis(A) CNS-specific Cre-lox recombination demonstrated using X-Gal staining (blue) in a sagittal section from a 2-wk-old NesCre+/0 mouse harboring a LacZ reporter (Rosa26R+/0) [33]. NesCre is expressed in neuroepithelium by neuronal and glial precursors. Abbreviations: Br, brain; FT, fat tissue; He, heart; Int, intestine (with bacterial artifacts); Li, liver; OE, olfactory epithelium (red arrow).(B) Southern blot analysis of adult bIGF1RKO+/− tissues revealed complete recombination in the brain (Br) and the intact Igf1rflox allele in all peripheral tissues (left panel). Recombination in peripheral tissues was minimal. The IGF-1R knockout was effective throughout the brain (right panel) and stable through time (unpublished data). The restriction enzymes used were HincII and I-SceI (left blot) and HincII alone (right). Cb, cerebellum, Cx, cortex, Ki, kidney, Lu, lung, M, DNA size marker, M1/M2, skeletal muscle, Ob, olfactory bulb, Po, pons, Sk, skin, Sp, spleen, St, striatum, Th, thalamus, Ts, testis.(C) bIGF1RKO+/− mice had normal IGF-1R levels in peripheral tissues (e.g., muscle) and ∼50% of normal levels in the CNS (here: hypothalamus and cortex), as assessed by western blotting.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2573928&req=5

pbio-0060254-g001: Brain-Targeted Inactivation of the Igf1r Gene Using Cre-lox Mutagenesis(A) CNS-specific Cre-lox recombination demonstrated using X-Gal staining (blue) in a sagittal section from a 2-wk-old NesCre+/0 mouse harboring a LacZ reporter (Rosa26R+/0) [33]. NesCre is expressed in neuroepithelium by neuronal and glial precursors. Abbreviations: Br, brain; FT, fat tissue; He, heart; Int, intestine (with bacterial artifacts); Li, liver; OE, olfactory epithelium (red arrow).(B) Southern blot analysis of adult bIGF1RKO+/− tissues revealed complete recombination in the brain (Br) and the intact Igf1rflox allele in all peripheral tissues (left panel). Recombination in peripheral tissues was minimal. The IGF-1R knockout was effective throughout the brain (right panel) and stable through time (unpublished data). The restriction enzymes used were HincII and I-SceI (left blot) and HincII alone (right). Cb, cerebellum, Cx, cortex, Ki, kidney, Lu, lung, M, DNA size marker, M1/M2, skeletal muscle, Ob, olfactory bulb, Po, pons, Sk, skin, Sp, spleen, St, striatum, Th, thalamus, Ts, testis.(C) bIGF1RKO+/− mice had normal IGF-1R levels in peripheral tissues (e.g., muscle) and ∼50% of normal levels in the CNS (here: hypothalamus and cortex), as assessed by western blotting.

Mentions: To study the role of IGF signaling in the CNS, we generated mice with heterozygous and homozygous brain-specific IGF-1 receptor knockout mutations (bIGF1RKO+/− and bIGF1RKO−/−) by conditional mutagenesis (Figure 1A and 1B). Mutants and their controls were littermates with identical genetic background, and matings were performed such that the Nestin-Cre transgene was always paternally transmitted (see Methods and Text S1 for breeding and genetic background). Homozygous mutants (bIGF1RKO−/−) have no IGF-1R on CNS neurons or glia. They were microcephalic and developed a complex phenotype involving severe growth retardation, infertility, and abnormal behavior (Figure S1). Though very interesting per se, the homozygous bIGF1RKO−/− mice did not show extended lifespan and their adult plasma IGF-I concentration was significantly higher than control values (Figure S1E and S1G). Thus, homozygous mutants were not a suitable model for healthy longevity, which is generally associated with diminished insulin-like signaling [20,21]. We therefore studied the heterozygous mutants (bIGF1RKO+/−), in which the IGF-1R levels in the CNS are half that in the wild-type (Figure 1C). They were healthy and behaved normally (Figure S2). Their body growth, however, though initially normal, was progressively retarded from 20 d of age onwards (Figure 2A). By age 90 d, bIGF1RKO+/− adults weighed about 90% of controls (males, 30.5 ± 0.6 g, n = 12 versus 33.7 ± 0.4 g, −9.6%, n = 19, p < 0.0001; females, 24.1 ± 0.3 g, n = 18 versus 26.2 ± 0.5 g, −7.9%, n = 14, p < 0.001) and were 5% shorter than controls (p < 0.001) (Table S1). bIGF1RKO+/− mice had normal IGF-1R levels in peripheral tissues (see Figure 1C), so we speculated that endocrine growth regulation during development was disturbed. bIGF1RKO+/− pituitaries were indeed small from age 10 d onwards (Figure 2B), and total GH content remained low throughout development (Figure 2C). The GH concentration per milligram protein fell at age 20 d, suggesting that retardation of early postnatal somatotroph differentiation (Figure 2D) started between day 10 and day 20. Plasma IGF-I, which strongly depends on GH, did not show any pubertal increase in bIGF1RKO+/− mice while controls displayed the normal surge (Figure 2E). Moreover, the concentration of the acid labile subunit (ALS), an important regulator of IGF-I stability and itself regulated by GH, was very low in mutants throughout postnatal life (Figure 2F). Importantly, in this model the IGF-1R gene is knocked out in the hypothalamus but not in the pituitary (Figure 3A). Therefore, we suspected that this somatotropic phenotype was caused by alterations in GH-regulatory neurons of the hypothalamus, i.e. arcuate nucleus GHRH neurons and anterior periventricular somatostatin (SRIH) neurons whose endings converge on the external layer of the median eminence (ME). Indeed, hypothalamic GHRH expression in bIGF1RKO+/− mice was significantly low, and GHRH accumulation in the GHRH neuron endings was clearly diminished around age 10 d (Figure 3B and 3C). In contrast, hypophysiotropic SRIH-producing neurons in the hypothalamus exhibited a normal abundance of SRIH at age 10 d, evidence of the cell-specificity of this phenotype (Figure 3B and 3D). Accordingly, Pit-1 expression, which is controlled by GHRH neurons and steers somatotropic cell differentiation, was half normal in mutant pituitaries (Figure 3E).


Brain IGF-1 receptors control mammalian growth and lifespan through a neuroendocrine mechanism.

Kappeler L, De Magalhaes Filho C, Dupont J, Leneuve P, Cervera P, Périn L, Loudes C, Blaise A, Klein R, Epelbaum J, Le Bouc Y, Holzenberger M - PLoS Biol. (2008)

Brain-Targeted Inactivation of the Igf1r Gene Using Cre-lox Mutagenesis(A) CNS-specific Cre-lox recombination demonstrated using X-Gal staining (blue) in a sagittal section from a 2-wk-old NesCre+/0 mouse harboring a LacZ reporter (Rosa26R+/0) [33]. NesCre is expressed in neuroepithelium by neuronal and glial precursors. Abbreviations: Br, brain; FT, fat tissue; He, heart; Int, intestine (with bacterial artifacts); Li, liver; OE, olfactory epithelium (red arrow).(B) Southern blot analysis of adult bIGF1RKO+/− tissues revealed complete recombination in the brain (Br) and the intact Igf1rflox allele in all peripheral tissues (left panel). Recombination in peripheral tissues was minimal. The IGF-1R knockout was effective throughout the brain (right panel) and stable through time (unpublished data). The restriction enzymes used were HincII and I-SceI (left blot) and HincII alone (right). Cb, cerebellum, Cx, cortex, Ki, kidney, Lu, lung, M, DNA size marker, M1/M2, skeletal muscle, Ob, olfactory bulb, Po, pons, Sk, skin, Sp, spleen, St, striatum, Th, thalamus, Ts, testis.(C) bIGF1RKO+/− mice had normal IGF-1R levels in peripheral tissues (e.g., muscle) and ∼50% of normal levels in the CNS (here: hypothalamus and cortex), as assessed by western blotting.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2573928&req=5

pbio-0060254-g001: Brain-Targeted Inactivation of the Igf1r Gene Using Cre-lox Mutagenesis(A) CNS-specific Cre-lox recombination demonstrated using X-Gal staining (blue) in a sagittal section from a 2-wk-old NesCre+/0 mouse harboring a LacZ reporter (Rosa26R+/0) [33]. NesCre is expressed in neuroepithelium by neuronal and glial precursors. Abbreviations: Br, brain; FT, fat tissue; He, heart; Int, intestine (with bacterial artifacts); Li, liver; OE, olfactory epithelium (red arrow).(B) Southern blot analysis of adult bIGF1RKO+/− tissues revealed complete recombination in the brain (Br) and the intact Igf1rflox allele in all peripheral tissues (left panel). Recombination in peripheral tissues was minimal. The IGF-1R knockout was effective throughout the brain (right panel) and stable through time (unpublished data). The restriction enzymes used were HincII and I-SceI (left blot) and HincII alone (right). Cb, cerebellum, Cx, cortex, Ki, kidney, Lu, lung, M, DNA size marker, M1/M2, skeletal muscle, Ob, olfactory bulb, Po, pons, Sk, skin, Sp, spleen, St, striatum, Th, thalamus, Ts, testis.(C) bIGF1RKO+/− mice had normal IGF-1R levels in peripheral tissues (e.g., muscle) and ∼50% of normal levels in the CNS (here: hypothalamus and cortex), as assessed by western blotting.
Mentions: To study the role of IGF signaling in the CNS, we generated mice with heterozygous and homozygous brain-specific IGF-1 receptor knockout mutations (bIGF1RKO+/− and bIGF1RKO−/−) by conditional mutagenesis (Figure 1A and 1B). Mutants and their controls were littermates with identical genetic background, and matings were performed such that the Nestin-Cre transgene was always paternally transmitted (see Methods and Text S1 for breeding and genetic background). Homozygous mutants (bIGF1RKO−/−) have no IGF-1R on CNS neurons or glia. They were microcephalic and developed a complex phenotype involving severe growth retardation, infertility, and abnormal behavior (Figure S1). Though very interesting per se, the homozygous bIGF1RKO−/− mice did not show extended lifespan and their adult plasma IGF-I concentration was significantly higher than control values (Figure S1E and S1G). Thus, homozygous mutants were not a suitable model for healthy longevity, which is generally associated with diminished insulin-like signaling [20,21]. We therefore studied the heterozygous mutants (bIGF1RKO+/−), in which the IGF-1R levels in the CNS are half that in the wild-type (Figure 1C). They were healthy and behaved normally (Figure S2). Their body growth, however, though initially normal, was progressively retarded from 20 d of age onwards (Figure 2A). By age 90 d, bIGF1RKO+/− adults weighed about 90% of controls (males, 30.5 ± 0.6 g, n = 12 versus 33.7 ± 0.4 g, −9.6%, n = 19, p < 0.0001; females, 24.1 ± 0.3 g, n = 18 versus 26.2 ± 0.5 g, −7.9%, n = 14, p < 0.001) and were 5% shorter than controls (p < 0.001) (Table S1). bIGF1RKO+/− mice had normal IGF-1R levels in peripheral tissues (see Figure 1C), so we speculated that endocrine growth regulation during development was disturbed. bIGF1RKO+/− pituitaries were indeed small from age 10 d onwards (Figure 2B), and total GH content remained low throughout development (Figure 2C). The GH concentration per milligram protein fell at age 20 d, suggesting that retardation of early postnatal somatotroph differentiation (Figure 2D) started between day 10 and day 20. Plasma IGF-I, which strongly depends on GH, did not show any pubertal increase in bIGF1RKO+/− mice while controls displayed the normal surge (Figure 2E). Moreover, the concentration of the acid labile subunit (ALS), an important regulator of IGF-I stability and itself regulated by GH, was very low in mutants throughout postnatal life (Figure 2F). Importantly, in this model the IGF-1R gene is knocked out in the hypothalamus but not in the pituitary (Figure 3A). Therefore, we suspected that this somatotropic phenotype was caused by alterations in GH-regulatory neurons of the hypothalamus, i.e. arcuate nucleus GHRH neurons and anterior periventricular somatostatin (SRIH) neurons whose endings converge on the external layer of the median eminence (ME). Indeed, hypothalamic GHRH expression in bIGF1RKO+/− mice was significantly low, and GHRH accumulation in the GHRH neuron endings was clearly diminished around age 10 d (Figure 3B and 3C). In contrast, hypophysiotropic SRIH-producing neurons in the hypothalamus exhibited a normal abundance of SRIH at age 10 d, evidence of the cell-specificity of this phenotype (Figure 3B and 3D). Accordingly, Pit-1 expression, which is controlled by GHRH neurons and steers somatotropic cell differentiation, was half normal in mutant pituitaries (Figure 3E).

Bottom Line: Thus, early changes in neuroendocrine development can durably modify the life trajectory in mammals.The underlying mechanism appears to be an adaptive plasticity of somatotropic functions allowing individuals to decelerate growth and preserve resources, and thereby improve fitness in challenging environments.Our results also suggest that tonic somatotropic signaling entails the risk of shortened lifespan.

View Article: PubMed Central - PubMed

Affiliation: INSERM U893, Hôpital Saint-Antoine, Paris, France.

ABSTRACT
Mutations that decrease insulin-like growth factor (IGF) and growth hormone signaling limit body size and prolong lifespan in mice. In vertebrates, these somatotropic hormones are controlled by the neuroendocrine brain. Hormone-like regulations discovered in nematodes and flies suggest that IGF signals in the nervous system can determine lifespan, but it is unknown whether this applies to higher organisms. Using conditional mutagenesis in the mouse, we show that brain IGF receptors (IGF-1R) efficiently regulate somatotropic development. Partial inactivation of IGF-1R in the embryonic brain selectively inhibited GH and IGF-I pathways after birth. This caused growth retardation, smaller adult size, and metabolic alterations, and led to delayed mortality and longer mean lifespan. Thus, early changes in neuroendocrine development can durably modify the life trajectory in mammals. The underlying mechanism appears to be an adaptive plasticity of somatotropic functions allowing individuals to decelerate growth and preserve resources, and thereby improve fitness in challenging environments. Our results also suggest that tonic somatotropic signaling entails the risk of shortened lifespan.

Show MeSH
Related in: MedlinePlus