Different studies have revealed that the Ca2+-dependent serine/threonine phosphatase calcineurin is involved in the regulation of adipocyte differentiation. Calcineurin acts as a Ca2+-dependent molecular switch that negatively regulates the ability of 3T3-L1 cells to undergo adipocyte differentiation by preventing the expression of critical proadipogenic transcription factors. In this study we investigated the role of interleukin-15 (IL-15), a cytokine previously known to be involved in the control of fat accretion by adipose cells, in the differentiation of the 3T3-L1 preadipose cell line. We found that IL-15 is able to increase α-calcineurin mRNA content in white adipose tissue of rats chronically treated with the cytokine and also in the 3T3-L1 preadipose cell line. Moreover, IL-15 promoted a decrease in both leptin mRNA expression and lipid accumulation, as estimated by Red Oil O staining. Cotreatment with IL-15 and FK506 (a calcineurin inhibitor) resulted in no changes in lipid content compared with the non-treated group. These data suggest that IL-15 directly inhibits adipogenesis, possibly by upregulating α-calcineurin and preventing the induction of adipocyte differentiation.

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