M2 macrophage-mediated interleukin-4 signalling induces myofibroblast phenotype during the progression of benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is a progressive disease in elderly men, but potential factors accelerating its progression remain largely unknown. The aim of this study was to elucidate the factors affecting BPH progression by understanding the complex mechanisms causing early- progressed BPH, which progresses rapidly and requires surgical intervention before the age of 50. Three groups of human prostate tissue samples, from patients with early-progressed BPH, age-matched prostate and elderly BPH tissues, were collected (n = 25 each). We compared these tissues to determine the histologic features and molecular mechanisms underlying BPH progression. We found that early-progressed BPH samples were characterised by aberrant stromal hyper-proliferation, collagen deposition and increased M2 macrophage infiltration, compared to those from age-matched prostate and elderly BPH tissues. The M2 macrophage–fibroblast co-culture system demonstrated that the myofibroblast phenotypes were strongly induced only in fibroblasts from the early-progressed BPH samples, while the co-cultured M2 macrophages expressed high levels of pro-fibrotic cytokines, such as IL4 and TGFβ1. M2 macrophage-derived IL4, but not TGFβ1, selectively induced the myofibroblast phenotype through the JAK/STAT6, PI3K/AKT and MAPK/ERK signalling pathways in the early-progressed BPH prostate fibroblasts. Taken together, our results indicate that induction of the myofibroblast phenotype may lead to BPH progression through M2 macrophage-mediated IL4 signalling, and that IL4 may represent a potential therapeutic target, allowing the prevention of M2 macrophage activation and fibroblast-to-myofibroblast differentiation.