Interplay of adiponectin, TNFα and insulin on gene expression, glucose uptake and PPARγ, AKT and TOR pathways in rainbow trout cultured adipocytes.

ABSTRACT

Adipose tissue is being increasingly recognized as an important endocrine organ that produces and releases a variety of factors. In the present study we have evaluated in primary cultures of rainbow trout adipocytes, obtained from visceral adipose tissue, the interplay of the adiponectin system, TNFα and insulin at a transcriptional level and, their effects on the adipogenic transcription factor PPARγ, as well as on the activation of main insulin signaling pathways. Likewise, the implication of these adipokines in the regulation of glucose uptake in the adipocyte and their interactions with insulin or IGF-I were also evaluated. Similarly to the mammalian model, insulin enhanced adiponectin gene expression, while it exerted a negative modulation on adiponectin receptors. TNFα increased the mRNA levels of adiponectin receptor 1, but neither adiponectin nor TNFα modulated each other expression. Therefore, the reciprocal suppressive effect of both adipokines previously reported in mammals was not present in this model. Furthermore, the anti-adipogenic effect of TNFα was revealed by the down-regulation of PPARγ at a protein level, meanwhile adiponectin increased PPARγ expression in insulin-stimulated adipocytes, supporting its insulin-sensitizing role. Both adipokines stimulated glucose uptake without modifying AKT or TOR phosphorylation; however, glucose uptake in insulin-treated adipocytes was enhanced by TNFα but not by adiponectin. All in all, these results contribute to gain knowledge on the role of adipokines in rainbow trout adipose tissue and, to better understand the mechanisms that regulate glucose metabolism in this species.