Katelyn Donahue, PhD
Pfizer
Persistent Fibrotic Niche Characterized by SPP1+ Macrophages and Type 3 Immunity Following Injury Resolution
While most antifibrotic therapies target the source of hepatic injury, scar regression is rare. Fibrosis results from activated fibroblasts and SPP1+ macrophages forming a stable pro-fibrotic niche. Murine models of hepatic scar regression also highlight macrophages as essential for scar clearance, emphasizing the functional diversity of this cell type. Thus, further understanding of macrophage regulation and function during injury resolution would inform therapeutic repolarization of the fibrotic niche. We induced liver fibrosis in mice using high-fat diet and carbon tetrachloride (HFD/CCl4). After 10 weeks, mice remained on HFD/CCl4 (progression) or reverted to a control diet (resolution). Samples were collected longitudinally for 8 weeks following peak injury and profiled using high parameter techniques (spectral flow cytometry, scRNA/ATAC-Seq, spatial transcriptomics, multiplex tissue staining). Despite improvement of liver damage, scarring persisted across resolution cohorts, mirroring clinical observations. Resolution livers maintained high levels of pro-fibrotic cytokines (IL17/IL22/GM-CSF) after 8 weeks without injury. A unique population of SPP1+ macrophages expressing the tissue-residency marker TIM4 was common across progression and resolution cohorts and abundant in the fibrotic niche. We are continuing to investigate the ontogeny and function of the TIM4+ SPP1+ macrophage phenotype to promote scar clearance.
While most antifibrotic therapies target the source of hepatic injury, scar regression is rare. Fibrosis results from activated fibroblasts and SPP1+ macrophages forming a stable pro-fibrotic niche. Murine models of hepatic scar regression also highlight macrophages as essential for scar clearance, emphasizing the functional diversity of this cell type. Thus, further understanding of macrophage regulation and function during injury resolution would inform therapeutic repolarization of the fibrotic niche. We induced liver fibrosis in mice using high-fat diet and carbon tetrachloride (HFD/CCl4). After 10 weeks, mice remained on HFD/CCl4 (progression) or reverted to a control diet (resolution). Samples were collected longitudinally for 8 weeks following peak injury and profiled using high parameter techniques (spectral flow cytometry, scRNA/ATAC-Seq, spatial transcriptomics, multiplex tissue staining). Despite improvement of liver damage, scarring persisted across resolution cohorts, mirroring clinical observations. Resolution livers maintained high levels of pro-fibrotic cytokines (IL17/IL22/GM-CSF) after 8 weeks without injury. A unique population of SPP1+ macrophages expressing the tissue-residency marker TIM4 was common across progression and resolution cohorts and abundant in the fibrotic niche. We are continuing to investigate the ontogeny and function of the TIM4+ SPP1+ macrophage phenotype to promote scar clearance.
