Mast cell activation in vivo impairs the macrophage reverse cholesterol transport pathway in the mouse

Chymase released by activated mast cells degrades high-density lipoproteins. We evaluated whether local activation of mast cells would attenuate cholesterol efflux from neighboring macrophage foam cells, thereby disrupting the entire in vivo pathway of macrophage-specific reverse cholesterol transport (RCT).

C57Bl/6J mice received intraperitoneal injections of the mast cell-degranulating compound 48/80 to induce peritoneal mast cell activation, human apolipoprotein A-I (apoA-I) to stimulate RCT, and [(3)H]cholesterol-labeled J774 macrophages for measurement of the rate of RCT. After 3 hours, (3)H-radioactivity was measured in the intestinal lumen contents. Activation of mast cells in the peritoneal cavity depleted human apoA-I pre-β-migrating species, impairing the ability of the peritoneal fluid to efficiently promote cholesterol efflux from cultured macrophages. Moreover, intact but not chymase-treated (proteolyzed) apoA-I accelerated the transfer of macrophage-derived (3)H- radioactivity to the intestinal contents. Importantly, stimulation of RCT by human apoA-I was fully blocked by 48/80 in mast cell-competent wild-type C57Bl/6J mice but not in mast cell-deficient W-sash c-kit mutant mice. The ability of intraperitoneally administered phospholipid vesicles to promote RCT in wild-type mice was not blocked by 48/80, supporting the notion that mast cell-dependent proteolysis of the intraperitoneally administered apoA-I was responsible for RCT inhibition.

Overall, our results suggest that tissue-specific activation of mast cells with ensuing release of chymase is able to proteolytically inactivate apoA-I in the microenvironment of the activated mast cells, thus locally impairing the initiation of macrophage RCT in vivo.