COL1A1-Enhanced CD44/SLC7A11 Interaction and Cystine Uptake Result in CD34 + Foam-Like Macrophage Accumulation in Transplant Arteriosclerosis

BACKGROUND: Chronic transplant arteriosclerosis is the primary cause of long-term graft failure. Selectively targeting specific inflammatory macrophage subpopulations is essential for inhibiting the primary triggers of inflammatory and immune responses. Therefore, elucidating the origins and regulatory mechanisms of these macrophages in allograft arteriosclerosis is key for the development of targeted therapies. METHODS: We performed single-cell RNA sequencing and spatial transcriptomics or integrated transcriptomic data from human chronic allograft vasculopathy specimens and mouse vascular allograft models. Flow cytometry and immunofluorescence staining were used to characterize macrophage subpopulations within remodeled allograft arteries. To determine cellular origins, CD34 + lineage tracing and depletion strategies were used. The interactions among COL1A1 (collagen type 1 α1), CD44, and SLC7A11 (solute carrier family 7 member 11) were analyzed using proximity ligation assays and coimmunoprecipitation. Furthermore, metabolic profiles were investigated with ultraperformance liquid chromatography coupled with high-resolution mass spectrometry. To validate the role of cystine transport in macrophage differentiation, we used pharmacologic inhibitors and a genetic approach using myeloid-specific Slc7a11 knockout mice (Lysm- Slc7a11 -KO). The mechanisms identified in vivo were further corroborated through in vitro experiments. RESULTS: We identified a novel proinflammatory foam-like macrophage phenotype in allograft arterial adventitia. These macrophages primarily originated from bone marrow–derived CD34 + lineage cells and exhibit heightened de novo lipogenesis and proinflammatory activity. Their lipogenesis is driven by increased cystine uptake, facilitated by enhanced membrane expression of the CD44–SLC7A11 complex, which activates mTORC1 (mechanistic target of rapamycin complex 1)–HIF-1α (hypoxia-inducible factor 1α) signaling. We also revealed that fibroblast-secreted COL1A1 is essential for anchoring the complex to the cell membrane through its direct interaction with CD44. Blocking COL1A1, CD44, or SLC7A11 effectively attenuated mTORC1–HIF-1α signaling, inflammation, and lipogenesis in macrophages as well as accumulation of foam-like cells and intimal hyperplasia in allograft arteries. CONCLUSIONS: This study has revealed previously uncharacterized foam-like macrophages in transplant arteriosclerosis, with COL1A1-enhanced amino acid metabolism modulating lipogenesis and foamy macrophage formation. This study offers potential therapeutic targets to modulate immune response and enhance transplant outcomes.