Caveolin expression and activation in retroperitoneal and subcutaneous adipocytes: influence of a high-fat diet.

The effect of a high-fat diet on the expression of the three main isoforms of caveolins in adipocytes isolated from rat retroperitoneal and subcutaneous white adipose tissue was investigated. Two distinct phases can be distinguished on a time-dependent response in adipocytes from both locations. The early stage affects only to retroperitoneal adipocytes and implies caveolin-1 activation and caveolin-2 inactivation, together with increased expression of insulin signaling intermediaries. This initial response would be aimed to counterbalance the energy overload. Continued exposure to the high-fat diet produces an increase in circulating glucose and insulin levels, inducing a late stage in which adipocytes from both locations are affected. This late stage is characterized by general increased caveolin-1 and caveolin-2 expression; while on the other hand, the insulin signaling intermediaries are downregulated, with the noticeable exception of GLUT-4, whose expression remains high. Therefore, it seems that at this stage caveolins and GLUT-4 are regulated independently of the insulin pathway, through a mechanism that could be mediated by inflammation and oxidative stress associated with obesity. Although this GLUT-4 upregulation suggests a response against the raise in circulating glucose, this might not be the case, since the developing insulin resistance at this stage indicates a prediabetic state. We have also found that the high-fat diet is able to induce the expression of muscle-specific caveolin-3 in retroperitoneal adipocytes since the initial phase. This observation is similar to what we reported previously in skeletal muscle (Gómez-Ruiz et al., 2009, FEBS Lett 583:3259-3264), suggesting a similar regulatory mechanism for this isoform.