C29-22 Cell Type-specific Regulation of Lipidomic Reprogramming by Stearoyl-coa Desaturase Governs Pulmonary Fibrosis

Abstract Rationale Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive lung disease characterized by irreversible scarring of the parenchyma. Current therapies for IPF remain limited and largely ineffective at halting disease progression, in part due to an incomplete understanding of the underlying molecular mechanisms. Dysregulated lipid metabolism has been implicated in IPF pathogenesis, however, the cell type-specific mechanisms governing this process remain poorly defined. Methods We utilized the bleomycin-induced model of pulmonary fibrosis. Mice expressing surfactant protein C (SFTPC)-eGFP enabled identification and isolation of alveolar type II epithelial cells (AT2s), overcoming limitations associated with surface-marker or bead-based selection. Direct infusion mass spectrometry (“shotgun lipidomics”) was performed on FACS-purified AT2 and alveolar macrophage (AM) populations. To mechanistically dissect the de novo lipogenesis (DNL) pathway on a cell type-specific basis, we generated a series of loss-of-function murine models using LysM-Cre or SFTPC-Cre to target macrophages and AT2 cells, respectively. Endpoint analyses included histopathology, collagen quantification, flow cytometry, scRNA-seq, and lipidomics. CRISPR activation (CRISPRa) technology was used to overexpress SCD in PBMC-derived macrophages. Results Shotgun lipidomics revealed unique, cell type-specific lipid metabolic signatures in AT2s and AMs following bleomycin-induced lung injury. AT2s exhibited a reduction in total lipid content, whereas AMs displayed increased lipid biomass. Subclass analysis demonstrated a global shift toward monounsaturated fatty acid (MUFA)-containing species. Parallel bulk RNA-seq identified a similarly divergent transcriptional response between AT2s and AMs, particularly in lipid metabolic enzymes. Stearoyl-CoA desaturase (SCD), the rate-limiting enzyme in MUFA biosynthesis, was increased in AM populations but decreased in AT2s, in response to bleomycin. Human scRNA-seq datasets and multiplex immunofluorescence of IPF patient samples confirmed these findings. Targeted deletion of myeloid SCD (LysM-Cre) unexpectedly exacerbated fibrosis and inflammation, indicating that enforced synthesis of MUFAs in AMs is protective response. Conversely, SCD deletion in AT2s (SFTPC-Cre) modestly reduced fibrosis and improved survival, highlighting a cell-type specific role for this enzyme. Mechanistically, SCD loss altered the desaturation index of the AM lipidome and induced aberrant inflammatory and wound-repair programs. Lastly, SCD overexpression via CRISPRa increased MUFA flux, reduced saturated lipid accumulation, and attenuated profibrotic and proinflammatory gene signatures in human macrophages. Conclusions Together, these data demonstrate unique and divergent lipid metabolic and transcriptomic responses of AT2s and AMs during pulmonary fibrosis. Furthermore, these studies establish SCD as a critical metabolic node in AM programming during fibrogenesis and identify a previously unrecognized therapeutic strategy whereby enforcing MUFA biosynthetic flux can regulate macrophage effector function. This abstract is funded by: NIH