Increased Leptin Expression in Common Carp (Cyprinus carpio) after Food Intake But Not after Fasting or Feeding to Satiation

Abstract

Leptin is a key factor in the regulation of food intake and is an important factor in the pathophysiology of obesity. However, more than a decade after the discovery of leptin in mouse, information regarding leptin in any nonmammalian species is still scant. We report the identification of duplicate leptin genes in common carp (Cyprinus carpio). The unique gene structure, the conservation of both cysteines that form leptin's single disulfide bridge, and stable clustering in phylogenetic analyses substantiate the unambiguous orthology of mammalian and carp leptins, despite low amino acid identity. The liver is a major yet not the only site of leptin expression. However, neither 6 d nor 6 wk of fasting nor subsequent refeeding affected hepatic leptin expression, although the carp predictably shifted from carbohydrate to lipid metabolism. Animals that were fed to satiation grew twice as fast as controls; however, they did not show increased leptin expression at the termination of the study. Hepatic leptin expression did, however, display an acute and transient postprandial increase that follows the postprandial plasma glucose peak. In summary, leptin mRNA expression in carp changes acutely after food intake, but involvement of leptin in the long-term regulation of food intake and energy metabolism was not evident from fasting for days or weeks or long-term feeding to satiation. These are the first data on the regulation of leptin expression in any nonmammalian species.

Towards Fish Lipid Nutrigenomics: Current State and Prospects for Fin-Fish Aquaculture

“…However, as the gene structure of orthologous cytokines is well conserved, the availability of genome sequences for pufferfish and zebrafish enabled the search for candidate piscine cytokine genes by concentrating searches in areas of the genome flanked by genes which are clearly conserved, at the sequence and positional level in mammals. This genomic synteny approach resulted in the identification of leptin genes in pufferfish (Takifugu rubripes) and common carp (Kurokawa et al 2005;Huising et al 2006a). Unlike in mammals, leptin appears to be mostly expressed in the liver of these two species.…”

“…Due to the exceptionally low sequence similarity between fish and mammalian leptins, these data must be interpreted with caution and repeated with conspecific fish leptin. In common carp, there is a postprandial increase in leptin mRNA expression, but no long-term effects of fasting on leptin mRNA expression was observed despite clear effects on body weight and metabolism (Huising et al 2006a). Data indicate that plasma leptin levels may be positively correlated with plasma PGE 2 levels, but a human leptin immoassay kit was used (Richard et al 2006).…”

Immunolocalisation of leptin in the digestive system of juvenile European sea bass (Dicentrarchus labrax)

“…Leptin amino acid sequence is conserved in mammalian and fish classes even though it seems to show higher diversity within teleosts (Kurokawa et al 2005). Thus recent reports identify additional leptin in several teleosts (leptin-a and leptin-b), such as carp (Cyprinus carpio), zebrafish (Danio rerio) and medaka (Oryzias latipes) (Huising et al 2006;Gorissen et al 2009;Kurokawa & Murashita 2009). Leptin-a shares high primary sequence conservation within zebrafish and carp (61%), whereas leptin-b shares only 25% amino acid identity.…”

“…Leptin has already been demonstrated to be highly conserved among vertebrate evolution (Zhang et al 1994) and to date its gene has been sequenced in birds, amphibians and fish (Doyon et al 2001;Kurokawa et al 2005;Huising et al 2006).…”

“…Leptin was immunodetected in the blood, brain, heart and liver of several bony fish species (Johnson et al 2000), in the enteric epithelium and nervous system of trout (Muruzàbal et al 2002) and in salmon adipocytes (Vegusdal et al 2003). Furthermore, leptin expression has been found in liver, adipose tissue, ovary and pituitary gland (Kurokawa et al 2005;Huising et al 2006;Gorissen et al 2009). No studies are available about the juvenile stages of the species used in aquaculture, including the sea bass.…”