title: Control of leptin by metabolic state and its regulatory interactions with pituitary growth hormone and hepatic growth hormone receptors and insulin like growth factors in the tilapia (Oreochromis mossambicus).
abstract: Leptin is an important cytokine for regulating energy homeostasis, however, relatively little is known about its function and control in teleost fishes or other ectotherms, particularly with regard to interactions with the growth hormone (GH)/insulin-like growth factors (IGFs) growth regulatory axis. Here we assessed the regulation of LepA, the dominant paralog in tilapia (Oreochromis mossambicus) and other teleosts under altered nutritional state, and evaluated how LepA might alter pituitary growth hormone (GH) and hepatic insulin-like growth factors (IGFs) that are known to be disparately regulated by metabolic state. Circulating LepA, and lepa and lepr gene expression increased after 3-weeks fasting and declined to control levels 10days following refeeding. This pattern of leptin regulation by metabolic state is similar to that previously observed for pituitary GH and opposite that of hepatic GHR and/or IGF dynamics in tilapia and other fishes. We therefore evaluated if LepA might differentially regulate pituitary GH, and hepatic GH receptors (GHRs) and IGFs. Recombinant tilapia LepA (rtLepA) increased hepatic gene expression of igf-1, igf-2, ghr-1, and ghr-2 from isolated hepatocytes following 24h incubation. Intraperitoneal rtLepA injection, on the other hand, stimulated hepatic igf-1, but had little effect on hepatic igf-2, ghr1, or ghr2 mRNA abundance. LepA suppressed GH accumulation and gh mRNA in pituitaries in vitro, but had no effect on GH release. We next sought to test if abolition of pituitary GH via hypophysectomy (Hx) affects the expression of hepatic lepa and lepr. Hypophysectomy significantly increases hepatic lepa mRNA abundance, while GH replacement in Hx fish restores lepa mRNA levels to that of sham controls. Leptin receptor (lepr) mRNA was unchanged by Hx. In in vitro hepatocyte incubations, GH inhibits lepa and lepr mRNA expression at low concentrations, while higher concentration stimulates lepa expression. Taken together, these findings indicate LepA gene expression and secretion increases with fasting, consistent with the hormones function in promoting energy expenditure during catabolic stress. It would also appear that LepA might play an important role in stimulating GHR and IGFs to potentially spare declines in these factors during catabolism. Evidence also suggests for the first time in teleosts that GH may exert important regulatory effects on hepatic LepA production, insofar as physiological levels (0.05-1 nM) suppresse lepa mRNA accumulation. Leptin A, may in turn exert negative feedback effects on basal GH mRNA abundance, but not secretion.
authors.affiliation: Department of Biological Sciences, North Carolina State University, Raleigh, NC 27695-7617, United States.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Douros
authors.affiliation: Department of Biological Sciences, North Carolina State University, Raleigh, NC 27695-7617, United States.
authors.forename: David A
authors.initials: DA
authors.lastname: Baltzegar
authors.affiliation: Department of Biological Sciences, North Carolina State University, Raleigh, NC 27695-7617, United States.
authors.forename: Jamie
authors.initials: J
authors.lastname: Mankiewicz
authors.affiliation: Department of Biological Sciences, North Carolina State University, Raleigh, NC 27695-7617, United States.
authors.forename: Jordan
authors.initials: J
authors.lastname: Taylor
authors.affiliation: Hawaii Institute of Marine Biology, University of Hawaii, Kaneohe, HI 96744, United States.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Yamaguchi
authors.affiliation: Hawaii Institute of Marine Biology, University of Hawaii, Kaneohe, HI 96744, United States.
authors.forename: Darren T
authors.initials: DT
authors.lastname: Lerner
authors.affiliation: Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa, Honolulu, HI 96822, United States.
authors.forename: Andre P
authors.initials: AP
authors.lastname: Seale
authors.affiliation: Hawaii Institute of Marine Biology, University of Hawaii, Kaneohe, HI 96744, United States.
authors.forename: E Gordon
authors.initials: EG
authors.lastname: Grau
authors.affiliation: Department of Biology, Skidmore College, Saratoga Springs, NY 12866, United States.
authors.forename: Jason P
authors.initials: JP
authors.lastname: Breves
authors.affiliation: Department of Biological Sciences, North Carolina State University, Raleigh, NC 27695-7617, United States. Electronic address: russell_borski@ncsu.edu.
authors.forename: Russell J
authors.initials: RJ
authors.lastname: Borski
mesh_terms: D000818:Animals; D001835:Body Weight / Q000187:drug effects; D005215:Fasting; D005247:Feeding Behavior / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D013006:Growth Hormone / Q000378:metabolism*; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D007016:Hypophysectomy; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism*; D020738:Leptin / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D011986:Receptors, Somatotropin / Q000235:genetics / Q000378:metabolism*; D017210:Tilapia / Q000378:metabolism*
chemical_list: D020738:Leptin; D012333:RNA, Messenger; D011986:Receptors, Somatotropin; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D013006:Growth Hormone
keywords: Growth hormone; Growth hormone receptor; Insulin-like growth factors; Leptin; Metabolic stress; Teleost fishes