Loss of Fibroblast-Derived ECM1 Disturbs Tubular Lipid Metabolism and Aggravates AKI

Background: Growing evidence suggests that fibroblast activation is an early and critical event after AKI. Once activated, these cells rapidly migrate to injured tubular sites and synthesize specific types and amounts of extracellular matrix to support tissue repair. Our preliminary proteomics identified extracellular matrix protein 1 (ECM1) as one of the earliest induced core matrisome components, primarily produced by fibroblasts. However, the functional role of fibroblast-derived ECM1 in AKI remains unknown. Methods: Two strains of tamoxifen-inducible fibroblast-specific ECM1 conditional knockout (cKO) mice were generated by crossing ECM1-floxed mice with Col1α2-Cre or Pdgfrβ-Cre mice. These mice were subjected to 1-day bilateral ischemia-reperfusion injury (bIRI) and 1-day Cisplatin-induced AKI, respectively. Global and phosphoproteomic analyses were employed to profile kidney proteome changes and explore the mechanisms. In vitro and ex vivo experiments were conducted for validation. Results: ECM1 protein was markedly upregulated in AKI kidneys, predominantly localized to fibroblasts. In bIRI and Cisplatin models, both strains of fibroblast-ECM1 cKO mice showed worsened renal function, increased tubular damage, inflammation, and cell death compared to controls. Global proteomics revealed significant upregulation of sterol regulatory element-binding protein cleavage-activating protein (SCAP), a key regulator of cholesterol biosynthesis, in ECM1 cKO kidneys. Consistently, Oil-Red O staining confirmed increased lipid accumulation in tubules. Treatment with the SCAP-specific inhibitor Lycorine reduced lipid deposition and mitigated AKI. In vitro or ex vivo, cultured tubular cells exposed to conditioned medium from ECM1-knockdown fibroblasts or seeded onto ECM1-knockdown decellularized matrix scaffolds under hypoxic stress exhibited increased cell injury, cholesterol synthesis, and SCAP activation. These effects were prevented by SCAP knockdown. Mechanistically, fibroblast loss of ECM1 led to increased secretion of active hypoxia-inducible factor 1α (HIF-1α), which upregulated SCAP in tubules, consistent with our phosphoproteomics findings. Conclusion: Fibroblast-derived ECM1 is essential for maintaining tubular lipid homeostasis during AKI. Its deficiency in fibroblasts leads to HIF-1α-mediated SCAP activation, abnormal cholesterol synthesis, and exacerbated AKI. Funding: NIDDK Support