Fibroblast‐Driven Fibroblast Growth Factor and Fibronectin 1 Signaling Orchestrates Extracellular Matrix Remodeling for Ovine Mammary Lactation Decline

Lactation decline in sheep is accompanied by extensive mammary gland remodeling, primarily involving extracellular matrix (ECM) reorganization. Here, we integrated single-cell RNA sequencing data from peak (PL) and late lactation (LL) stages to delineate the cellular and molecular mechanisms underlying this process. We identified nine immune cell subtypes and observed marked stage-specific changes in their abundance, highlighting a dynamic immune landscape during lactation regression. Notably, fibroblasts emerged as pivotal stromal regulators, exhibiting high expression of ECM-related genes and mediating collagen restructuring. Ligand-receptor interaction analysis revealed that fibroblasts maintained robust communication with endothelial and immune cells via FGF and FN1 signaling pathways, orchestrating ECM remodeling and structural stabilization. Metabolic profiling further implicated fibroblast-driven valine, leucine, and isoleucine degradation in supporting ECM dynamics. Cross-species comparisons revealed conserved transcriptional programs in fibroblasts and endothelial cells between sheep and humans, underscoring their evolutionarily conserved roles in ECM remodeling and angiogenesis. The study uncovers a fibroblast-driven regulatory network governing postpartum ECM remodeling, providing theoretical insights into the development and reconstruction of mammary tissue, and laying a foundation for investigating lactation dynamics and tissue regression across species.