IGFBP-1 as a potential marker of environmental stress in fish

Insulin-like growth factors have diverse roles in growth and metabolism that are regulated by a family of IGF-binding proteins (IGFBPs). IGFBP-1 is an important inhibitor of IGF action. In mammals hepatic IGFBP-1 in inhibited by insulin, and stimulated by glucocorticoids and other stress-related factors. In zebrafish there are two IGFBP-1 genes and we have shown that expression of each is suppressed in vivo by feeding. We have developed a liver explant culture system to study the direct regulation of Igfbp1a and Igfbp1b in vitro. A 2-h exposure to a maximally effective concentration of dexamethasone stimulated Igfbp1a 44-fold (p<0.001) and Igfbp1b 24-fold (p<0.001), in the presence and absence of inhibition by insulin. A maximally inhibitory concentration of insulin was more effective at short incubation times (15min). Oestrogen stimulated IGFBP-1, particularly at long incubation times (24h). It is speculated that IGFBP-1 expression is a marker of environmental stress in fish.