Granulin+ Macrophages Promote Lineage Plasticity in Prostate Cancer Through Paracrine Signaling Loops.

While lineage plasticity is a well-established driver of therapy resistance in prostate cancer, the role of tumor-infiltrating immune cells in mediating phenotype switching remains poorly understood. Here, we employed single-cell multi-omics to systematically characterize immune infiltration dynamics, transcriptional reprogramming, and intercellular communication networks during prostate cancer progression. Our analysis revealed that granulin (GRN)-expressing macrophages orchestrate the transition from adenocarcinoma (Adeno) to a therapy-resistant multilineage state exhibiting vimentin (VIM)+ mesenchymal and stem-like features through GRN/ tumor necrosis factor receptor superfamily member 1A (TNFRSF1A) interaction and the subsequent activation of the nuclear factor kappa-B (NF-κB) pathway. Intriguingly, these plastic tumor subclones reciprocally enhanced GRN expression in macrophages via colony stimulating factor 1 (CSF1) and CSF1 receptor (CSF1R) receptor-ligand axis, establishing a feedforward signaling loop that sustains lineage plasticity. Functional validation demonstrated GRN's critical role in driving epithelial-mesenchymal transition in vitro and conferring resistance to enzalutamide (ENZ) in patient-derived organoids. Therapeutic intervention studies in transgenic Adeno of the mouse prostate (TRAMP) models showed that CSF1R inhibition disrupted this vicious cycle, reducing GRN  + macrophages and suppressing multilineage subclone emergence. Spatial mapping revealed direct physical interactions between VIM  + tumor cells and GRN  + macrophages, while single-cell proteomics in castration-resistant patients confirmed the clinical relevance of this axis. Furthermore, we identified three novel stromal populations [decorin (DCN)+ endothelial cells, C-C motif chemokine ligand 7 (CCL7)+ fibroblasts, and interferon-induced protein with tetratricopeptide repeats 1 (IFIT1)+ neutrophils associated with disease relapse. These findings illuminate the tumor-immune crosstalk underlying treatment resistance and unveil promising therapeutic targets for overcoming lineage plasticity-driven resistance in advanced prostate cancer.