Limits...
Leptin in teleost fishes: an argument for comparative study.

Copeland DL, Duff RJ, Liu Q, Prokop J, Londraville RL - Front Physiol (2011)

Bottom Line: Indeed, for animals to make favorable decisions about when to grow, eat, or reproduce, they must integrate signals among the systems responsible for energy acquisition, storage, and demand.We make the argument that leptin signaling is a likely candidate for an integrating system.Great progress has been made understanding the leptin system in mammals, however our understanding in fishes has been hampered by difficulty in cloning fish orthologs of mammalian proteins and (we assert), underutilization of the comparative approach.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Akron Akron, OH, USA.

ABSTRACT
All organisms face tradeoffs with regard to how limited energy resources should be invested. When is it most favorable to grow, to reproduce, how much lipid should be allocated to storage in preparation for a period of limited resources (e.g., winter), instead of being used for growth or maturation? These are a few of the high consequence fitness "decisions" that represent the balance between energy acquisition and allocation. Indeed, for animals to make favorable decisions about when to grow, eat, or reproduce, they must integrate signals among the systems responsible for energy acquisition, storage, and demand. We make the argument that leptin signaling is a likely candidate for an integrating system. Great progress has been made understanding the leptin system in mammals, however our understanding in fishes has been hampered by difficulty in cloning fish orthologs of mammalian proteins and (we assert), underutilization of the comparative approach.

No MeSH data available.


(A) The effects of various peptides/hormones on leptin expression/secretion in mammals. (B) The effect of leptin on the expression/secretion of various peptide/hormones. The + and − indicate stimulatory and inhibitory effects respectively. Findings are reviewed in Rayner and Trayhurn (2001) and Reidy and Weber (2000).
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Figure 1: (A) The effects of various peptides/hormones on leptin expression/secretion in mammals. (B) The effect of leptin on the expression/secretion of various peptide/hormones. The + and − indicate stimulatory and inhibitory effects respectively. Findings are reviewed in Rayner and Trayhurn (2001) and Reidy and Weber (2000).

Mentions: In mammals, leptin is synthesized by adipose tissue and secreted into the blood. As adipose stores grow, leptin expression and serum concentrations increase in proportion to total fat stores (Maffei et al., 1995; Considine et al., 1996), although different types of adipose tissue differ in their signaling amplitude (Cnop et al., 2002). Leptin binds to leptin receptors in the hypothalamus, which signal through JAK–STAT pathways to alter transcription and affect phenotype (Tartaglia, 1997). When adipose stores are depleted, circulating leptin titer drops and the effect on phenotype is reversed (e.g., high leptin attenuates appetite and low leptin stimulates appetite; Zhang et al., 1994). Ahima and Flier (2000) proposed that leptin evolved as a starvation signal; low lipid reserves lead to low leptin titers, which communicates to the central nervous system that energy is unavailable for processes that are not life sustaining (e.g., low body fat human females can become infertile, which can be successfully treated with recombinant leptin; LaMarca and Volpe, 2004). The earlier an organism can sense the starvation event, the more energy it can save by ramping down leptin-stimulated functions, and the better its chances for surviving the event. In concordance with its ability to affect such a diversity of processes, leptin interacts with a diversity of hormones and signaling peptides (Figure 1). It appears that chronic stimulation of leptin secretion is mediated by molecules such as glucose, insulin, sex steroids, and glucocorticoids (Larsson and Ahren, 1996; Elbers et al., 1997; Newcomer et al., 1998; Moreno-Aliaga et al., 2001), suggesting that these hormones may be involved in directly regulating serum leptin concentrations (Figure 1; Laferrere et al., 2002; Lee and Fried, 2009).


Leptin in teleost fishes: an argument for comparative study.

Copeland DL, Duff RJ, Liu Q, Prokop J, Londraville RL - Front Physiol (2011)

(A) The effects of various peptides/hormones on leptin expression/secretion in mammals. (B) The effect of leptin on the expression/secretion of various peptide/hormones. The + and − indicate stimulatory and inhibitory effects respectively. Findings are reviewed in Rayner and Trayhurn (2001) and Reidy and Weber (2000).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3117194&req=5

Figure 1: (A) The effects of various peptides/hormones on leptin expression/secretion in mammals. (B) The effect of leptin on the expression/secretion of various peptide/hormones. The + and − indicate stimulatory and inhibitory effects respectively. Findings are reviewed in Rayner and Trayhurn (2001) and Reidy and Weber (2000).
Mentions: In mammals, leptin is synthesized by adipose tissue and secreted into the blood. As adipose stores grow, leptin expression and serum concentrations increase in proportion to total fat stores (Maffei et al., 1995; Considine et al., 1996), although different types of adipose tissue differ in their signaling amplitude (Cnop et al., 2002). Leptin binds to leptin receptors in the hypothalamus, which signal through JAK–STAT pathways to alter transcription and affect phenotype (Tartaglia, 1997). When adipose stores are depleted, circulating leptin titer drops and the effect on phenotype is reversed (e.g., high leptin attenuates appetite and low leptin stimulates appetite; Zhang et al., 1994). Ahima and Flier (2000) proposed that leptin evolved as a starvation signal; low lipid reserves lead to low leptin titers, which communicates to the central nervous system that energy is unavailable for processes that are not life sustaining (e.g., low body fat human females can become infertile, which can be successfully treated with recombinant leptin; LaMarca and Volpe, 2004). The earlier an organism can sense the starvation event, the more energy it can save by ramping down leptin-stimulated functions, and the better its chances for surviving the event. In concordance with its ability to affect such a diversity of processes, leptin interacts with a diversity of hormones and signaling peptides (Figure 1). It appears that chronic stimulation of leptin secretion is mediated by molecules such as glucose, insulin, sex steroids, and glucocorticoids (Larsson and Ahren, 1996; Elbers et al., 1997; Newcomer et al., 1998; Moreno-Aliaga et al., 2001), suggesting that these hormones may be involved in directly regulating serum leptin concentrations (Figure 1; Laferrere et al., 2002; Lee and Fried, 2009).

Bottom Line: Indeed, for animals to make favorable decisions about when to grow, eat, or reproduce, they must integrate signals among the systems responsible for energy acquisition, storage, and demand.We make the argument that leptin signaling is a likely candidate for an integrating system.Great progress has been made understanding the leptin system in mammals, however our understanding in fishes has been hampered by difficulty in cloning fish orthologs of mammalian proteins and (we assert), underutilization of the comparative approach.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Akron Akron, OH, USA.

ABSTRACT
All organisms face tradeoffs with regard to how limited energy resources should be invested. When is it most favorable to grow, to reproduce, how much lipid should be allocated to storage in preparation for a period of limited resources (e.g., winter), instead of being used for growth or maturation? These are a few of the high consequence fitness "decisions" that represent the balance between energy acquisition and allocation. Indeed, for animals to make favorable decisions about when to grow, eat, or reproduce, they must integrate signals among the systems responsible for energy acquisition, storage, and demand. We make the argument that leptin signaling is a likely candidate for an integrating system. Great progress has been made understanding the leptin system in mammals, however our understanding in fishes has been hampered by difficulty in cloning fish orthologs of mammalian proteins and (we assert), underutilization of the comparative approach.

No MeSH data available.