(OR04-01-25) The Role of Extracellular Vesicles in Vitamin A Secretion in Macrophages

Objectives: Vitamin A plays an important role in the regulation of the immune system by impacting cell differentiation and proliferation. Previous research in our lab and in others suggests that macrophages can release vitamin A to signal the phenotype of other immune cells. However, the mechanisms by which this process occurs remain unclear. We hypothesize that extracellular vesicles are responsible for vitamin A secretion from macrophages.

Methods: We exposed murine bone marrow derived macrophages to serum enriched with vitamin A for 24 hours. After this incubation time, we washed the cells twice and exposed them to vitamin A-free medium for 6 hours to quantify the amount of vitamin A (retinol and retinyl esters) in cell lysates and media by high performance liquid chromatography. Using these experimental settings, we tested the impact of Y27632 and GW4869, which inhibit microvesicle and exosome secretion, respectively. We complemented these studies with extracellular vesicle isolation and purification to measure their retinoid content.

Results: HPLC analysis showed that the retinoid content of the cells and media mostly consisted of retinyl esters, with low levels of retinol. Our findings demonstrate that Y27632 does not have an impact on vitamin A secretion compared to a vehicle control (p=0.406), however, the inhibition of exosome formation causes a significant reduction in vitamin A secretion in macrophages, both alone or in combination with Y27632 (p=0.006 and p=0.009, respectively). Further supporting this, when analyzing exosomes isolated from macrophages treated with vitamin A, they showed elevated retinoid levels compared to a control group not exposed to vitamin A (p=0.0198).

Conclusions: These results suggest that macrophages release vitamin A through the exosomal pathway. This could have applications for targeted therapy using exosomes as a vehicle for vitamin A signaling between macrophages and other immune cells.

Funding Sources: Funding for this research was provided by the NIH and the USDA. Additional funding was granted by the University of Illinois at Urbana-Champaign Division of Nutritional Sciences.