The IGF/IGFBP system in rainbow trout (Oncorhynchus mykiss) adipose tissue: expression related to regional localization and cell type.

While in mammals, the IGF/IGFBP system is known to be involved in adipose tissue growth, the presence of such a system in fish is as yet undetermined. The present work aimed at investigating the influence of regional localization of adipose tissues and cell types on the expression of this system. Using quantitative real-time PCR (qPCR), the presence of IGFs, IGFBPs, IGFBP-rPs, and IGFR I (insulin-like growth factors, IGF-binding proteins, IGFBP-related proteins, type I IGF receptor) was studied in crude subcutaneous and visceral fat depots as well as in isolated stromal vascular (SV) cells and mature adipocytes from the latter depot in the prepubescent female rainbow trout. In adipose tissues, no differences were observed in the transcript expressions of IGFs and IGFBPs (1-6) and rP1 relative to their regional localization. On the other hand, the two paralogues of IGFR I were more strongly expressed in visceral than in subcutaneous depots which could be related to a differential receptivity to IGF between fat depots. The amount of IGF-I and IGFR Ia transcripts is larger in mature adipocytes than in SV cells, while a similar level of expression was observed for IGF-II and IGFR Ib. IGFBP-1, -2a, -4, -5, -6, and -rP1 were more strongly expressed in the SV cells than in adipocytes, while IGFBP-2b displayed comparable expression. These results indicate that the IGF/IGFBP system is expressed in rainbow trout fat depots, whatever their regional origin, and that cell types, i.e., SV cells or mature adipocytes, influence its expression.