Graduate Student SUNY Upstate Med. Univ., United States
Disclosure(s):
Julia Drolet: No financial relationships to disclose
Introduction/Rationale: Macrophages resolve inflammation to maintain tissue homeostasis by clearing apoptotic cells, a process known as efferocytosis. Immune–metabolic interactions are proposed to regulate macrophage functions; however, the role of one-carbon (1C) metabolism metabolites—serine, glycine, and methionine— in resolution remains unclear. Levels of 1C metabolites are reduced in diabetes, a condition that induces non-resolution after wound injury.
Methods: Mouse bone marrow derived macrophages (BMDMs) were cultured in physiological media supplemented with 1C metabolites. Efferocytosis using live cell imaging, lipid droplet (LD) accumulation, and gene/protein expression were analyzed. Diabetic (db/db) mice after dorsal skin biopsy were studied as a model of 1C deficiency and non-resolution.
Results: Supplementing BMDMs with 1C metabolites—serine and methionine—enhanced efferocytosis specifically in an inflammatory environment, which exhibited reduced efferocytosis compared to normal or anti-inflammatory environments. Enhanced efferocytosis by 1C was accompanied by decreased LD formation. Pharmacological manipulation identified that the amino acid–sensing mTORC1 and methylation through S-adenosylmethionine were required for 1C-induced lipid metabolism and efferocytosis. RNA-seq revealed that 1C induced-resolution reprogramming included LD dynamics, lipid metabolism, and efferocytosis as well as upregulated cell cycle genes and downregulated inflammatory response, highlighting a role in methylation-dependent gene regulation in macrophages. In vivo, wound macrophages in the inflammatory phase accumulated LD, which was inhibited by serine supplementation. Systemic but not topical serine supplementation promoted wound closure in db/db mice.
Conclusion: 1C metabolism promotes pro-resolution programming in macrophages in inflammatory environments through amino acid sensing and methylation-dependent gene regulation. Serine supplementation may induce such programming in wound macrophages to promote wound healing.
