Adipose tissue microvascular endothelial cells form a tight vascular barrier that selectively transcytoses fatty acid tracers

In organs with continuous, non-leaky capillaries like white adipose tissue and the heart, microvascular endothelial cells (ECs) serve as a vital barrier, facilitating nutrient delivery to underlying tissues. While capillary heterogeneity between organs is well established, how these vascular layers have adapted their key functions - such as fatty acid transport - to their respective organs remains unclear, largely due to the lack of organotypic endothelial model systems. Here we demonstrate that the vascular barrier in white adipose tissue, a crucial organ for whole-body fatty acid handling, exhibits comparable impermeability to that of heart and muscle. To investigate if the adipose endothelium possesses tissue-specific functions for facilitating fatty acid transport, we developed an in vitro dual tracing-system that allows simultaneous monitoring of barrier integrity and fatty acid transport dynamics by modifying the classic transwell culture. Using this system, we can show human adipose-derived primary ECs selectively transport fluorescent fatty acid tracers while excluding other tracers like dextrans, a phenomenon not observed in other cultured human ECs. Additionally, our findings reveal EC-type specific responses to various transcytosis inhibitors. Our results underscore the unique characteristics of the adipose endothelium and enhances our understanding of how microvascular permeability and transport dynamics have adapted to their specific organ physiology.