Expression of fatty acid binding proteins in mesenteric adipose tissue

Adipose is a complex tissue comprised of adipocytes, immune cells, endothelial and progenitor stem cells. In humans, there are at least nine defined adipose depots, each containing variable numbers of genetically identified adipocyte clusters suggesting remarkable heterogeneity and potential functionality in each depot with respect to lipid metabolism. Although subcutaneous and visceral depots are commonly analyzed for biochemical and molecular functions, the mesenteric depot has been overlooked yet strongly implicated in lipid mediated immune surveillance. Since fatty acid binding proteins (FABPs) are primary cellular conduits to lipid trafficking, we evaluated the expression patterns for four major fatty acid binding proteins (FABP1, FABP3, FABP4 and FABP5) using a combination of gene expression, immunoblotting, and immunofluorescence in mesenteric fat from both young and old, male and female C57Bl/6J mice. All four FABPs were expressed at the mRNA and protein level in murine mesenteric adipose tissue. While there was no statistical change in expression of mesenteric FABP isoforms with sex or age, the expression of mesenteric FABP1 was increased, and FABP4 decreased, in both males and females as compared to perigonadal and inguinal depots. Surprisingly, immunofluorescence staining revealed that compared to subcutaneous or perigonadal depots, mesenteric fat expresses FABP3, but little FABP5, in adipocytes. These results highlight the diversity in adipose tissue and the importance of evaluating the mesenteric depot in the context of lipid transport and metabolism.