A senescence-driven fibroblast-macrophage feed-forward circuit promotes radiation induced cutaneous fibrosis

Therapeutic radiation for superficial tumors may cause cutaneous fibrosis, a late side effect with limited treatment options. Here, we investigated the underlying mechanisms driving radiation-induced cutaneous fibrosis.

C3H/HeN mice received 35 Gy unilateral hind limb irradiation. Cutaneous tissues from irradiated and contralateral unirradiated legs were analyzed by spatial whole transcriptome profiling using the GeoMx Digital Spatial Profiler platform. Beginning at 5 weeks after irradiation, mice received the senolytic agent ABT-263 (50 mg/kg/day) or vehicle (n ≥ 10/group) by oral gavage (5 consecutive days followed by 2-week rest for 3 cycles). Hind limb contracture was assessed at 150 days after irradiation. Senescence and macrophage markers were evaluated by immunohistochemistry and quantitative PCR. Cellular senescence and senescence-associated secretory phenotype (SASP) factors were evaluated in irradiated fibroblasts and their culture media using senescence-associated β-galactosidase activity assays and multiplex immunoassays. The senolytic activity of ABT-263 in irradiated primary fibroblasts and effects of ABT-263 on primary macrophage cultures were evaluated in vitro.

Spatial whole-transcriptomic analysis of irradiated murine dermis identified expression patterns consistent with macrophage activation, extracellular matrix remodeling, and a senescence-associated secretory phenotype (SASP)-rich environment. In vitro studies identified that the irradiated fibroblast-derived SASP induced a senescent phenotype in unirradiated fibroblasts and macrophages. SASP-induced senescent-like macrophages acquired a CD206⁺ profibrotic phenotype and in concert with activated fibroblasts, initiated a feed-forward loop amplifying IL-6 and collagen production. SASP exposure increased expression of Bcl-2 family proteins in macrophages and fibroblasts, rendering both populations susceptible to clearance by the senolytic agent ABT-263. In vivo, ABT-263 effectively mitigated radiation-induced dermal fibrosis, depleted senescent fibroblasts and CD206⁺ macrophages, and reduced IL-6 expression CONCLUSION: Our findings identify senescence-driven reciprocal macrophage-fibroblast interactions as key mediators of cutaneous fibrosis and demonstrate the therapeutic potential of senolytic interventions for treating late radiation-induced skin injury.