Weight cycling may induce lipid handling in mast cells

Abstract Weight cycling worsens diabetes risk in both humans and mice. We recently found that weight loss and weight cycling induce many immunological changes in the adipose tissue of mice by single cell RNA-sequencing. We also found a substantial increase in adipose mast cells with weight cycling, but not weight loss. The purpose of this study was to confirm and characterize the changes in mast cells with weight cycling. However, using flow cytometry (cKit+FcER1+) and Toluidine blue staining, we found that adipose mast cells are greatest in the weight loss group, in contrast to our prior study using single cell RNA-sequencing. Upon further analysis, we found two unique mast cell populations in our single cell sequencing dataset: one that we consider traditional mast cells and one with lower expression of mast cell surface and protease genes and elevated expression of lipid handling and antigen presentation genes. The second fraction appeared similar to lipid-associated macrophages and accounted for most of the mast cells in the weight cycled group. By flow cytometry, we confirmed the %CD9+, MHCII (I-A/I-E)+, and CD74+ mast cells were highest in weight cycled mice. We also found two mast cell populations in human subcutaneous adipose tissue that appear similar to the murine populations in our dataset, with one population significantly correlating with weight variability. Together, these data suggest that weight cycling may induce a population of lipid-associated mast cells. We next aim to to induce lipid handling in bone marrow derived mast cells by repeated exposure to adipose conditioned media in order to understand the mechanisms which induce lipid handling. This project was funded by a Veterans Affairs Merit Award 5I01BX002195 to AHH. AHH is also supported by a Career Scientist Award from the Veterans Affairs (IK6 BX005649). HLC was funded by an American Heart Association Postdoctoral Fellowship (20POST35120547), MAC was funded by an NIH F31 Predoctoral Fellowship (1F31DK123881), and both were previously supported by the Molecular Endocrinology Training Program (T32 DK07563). Additionally, the human mast cell work was funded by VICTR grants to HLC and MM. The Vanderbilt Institute for Clinical and Translational Research (VICTR) is funded by the National Center for Advancing Translational Sciences (NCATS) Clinical Translational Science Award (CTSA) Program, Award Number 5UL1TR002243-03.