Targeted disruption of the adipocyte lipid-binding protein (aP2 protein) gene impairs fat cell lipolysis and increases cellular fatty acid levels.

The availability of mice containing an adipocyte lipid-binding protein (ALBP/aP2) gene disruption allowed for a direct examination of the presumed role of lipid-binding proteins in the mobilization and trafficking of intracellular fatty acids. Total body and epididymal fat pad weights, as well as adipose cell morphology, were unaltered in male ALBP/aP2 disrupted mice when compared to their wild-type littermates. Analysis of adipocytes isolated from wild-type and ALBP/aP2 null mice revealed that a selective 40- and 13-fold increase in the level of the keratinocyte lipid-binding protein (KLBP) mRNA and protein, respectively, accompanied the ALBP/aP2 gene disruption. Although KLBP protein was significantly up-regulated, the total lipid-binding protein level decreased 8 -fold as a consequence of the disruption. There was no appreciable difference in the rate of fatty acid influx or esterification in adipocytes of wild-type and ALBP/aP2 null animals. To the contrary, basal lipolysis decreased approximately 40% in ALBP/aP2 nulls as compared to wild-type littermates. The glycerol release from isproterenol-stimulated ALBP/aP2 null fat cells was similarly reduced by approximately 35%. Consistent with a decrease in basal efflux, the non-esterified fatty acid (NEFA) level was nearly 3-fold greater in adipocytes from ALBP/aP2 nulls as compared to wild-type animals. The significant decrease in both basal and isoproterenol-stimulated lipolysis in adipose tissue of ALBP/aP2 null mice supports the model whereby intracellular lipid-binding proteins function as lipid chaperones, facilitating the movement of fatty acids out of the fat cell.