(677b) Transendothelial Transport May Determine Adiponectin Oligomer Functions

Adiponectin has exhibited positive effects in regulation of systemic metabolism and insulin sensitivity through tissues such as liver, skeletal muscle, and centrally in the brain. Circulating as oligomers of 90 to 1080kDa, adiponectin must cross the endothelium to have metabolic effects. Our laboratory has reported differential efficacy of these oligomers on insulin sensitivity. Recent data has also demonstrated oligomer size-dependence on adiponectin clearance; only the small trimeric oligomer is found in cerebral spinal fluid. Here, we have produced all oligomers of adiponectin in mammalian cells and used FPLC to fractionate adiponectin by molecular size. We have measured the Stokes radii of adiponectin to be approximately 5, 10, and 25nm for the trimeric, hexameric, and high molecular weight (HMW) forms, respectively. These molecular transport sizes, particularly that of the HMW, present transport limitations across endothelial barriers with low intercellular permeabilities such as in muscle or in the brain. Model murine MS1, bEnd.3, and EOMA endothelial cell lines were used in in vitro transwell permeability studies to determine the relative transport of oligomers across different endothelium. We demonstrate size-dependent exclusion of adiponectin oligomers in pancreatic MS1 cells, and in EOMA cells, a microvascularture model, equivalent transport of trimeric and HMW adiponectin for their diffusive sizes. The bEnd.3 cells, a model of brain endothelium, presented an increased barrier to HMW adiponectin. Each cell type had notable differences in the amount of intracellular adiponectin at the experiments' end. As in each case adiponectin fluxes were less than equivalently-sized dextrans, these findings suggest active adiponectin transport mechanisms. In vivo, increasing vessel permeability reduced the circulatory half-life of adiponectin. These data demonstrate that the effects of different adiponectin oligomers on tissue metabolism may depend on the endothelium in a given tissue.