2022 journal article
Evidence for a leptin-insulin axis in a fish, the tilapia (Oreochromis mossambicus)
JOURNAL OF ENDOCRINOLOGY, 253(1), 13–25.
author keywords: leptin; insulin; glucagon; Brockmann bodies; tilapia
MeSH headings : Animals; Blood Glucose / metabolism; Cells, Cultured; Fish Proteins / genetics; Fish Proteins / metabolism; Gene Expression Regulation; Glucagon / genetics; Glucagon / metabolism; Glucose / metabolism; Hepatocytes / metabolism; Insulin / genetics; Insulin / metabolism; Insulin Secretion; Leptin / genetics; Leptin / metabolism; Male; RNA, Messenger / genetics; RNA, Messenger / metabolism; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction / genetics; Tilapia / genetics; Tilapia / metabolism; Time Factors
TL;DR:
Data indicate that a leptin-insulin axis may be conserved among vertebrates and is thus essential for regulating nutrient balance but that the relationship is likely much more dynamic in teleosts as glycaemia is not as tightly regulated as it is in mammals.
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Added: July 11, 2022
Leptin, insulin, and glucagon are involved in regulating glycaemia in vertebrates and play a role in the progression of obesity and type 2 diabetes. While mammals possess an ‘adipoinsular axis’ whereby insulin stimulates leptin release from adipocytes and leptin in turn feeds back on the pancreas to inhibit further insulin secretion, evidence of such an axis in non-mammalian vertebrates is unknown. We investigated the interactions between these glycaemic hormones and provide evidence for a leptin–insulin axis in a teleost fish, the tilapia. In the first study, we exposed hepatocytes to various concentrations of either insulin or glucagon to determine effects on leptin a (lepa) and then examined this in vivo with i.p. injections of both hormones. We also exposed isolated Brockmann bodies (pancreatic islets) to recombinant tilapia leptin A (rtLepA) and again followed this up with an i.p. injection to examine changes in insulin a and glucagon b. We found that glucagon increases lepa in vitroand in vivo, with the latter being 18-fold higher than saline-injected controls; however, the effects of rtLepA on glub were more variable. Insulin increased lepa by 2.5-fold in vitro and 70-fold in vivo, while rtLepA decreased insa at basal and increased it at high glucose concentrations. These data indicate that a leptin–insulin axis may be conserved among vertebrates and is thus essential for regulating nutrient balance but that the relationship is likely much more dynamic in teleosts as glycaemia is not as tightly regulated as it is in mammals.