Role and mechanism of tetrahedral DNA nanostructures in the repair of urethral injury in rats.

Urethral injury is a common type of traumatic damage to the urinary system, often leading to urethral stricture, fibrosis and dysfunction, which significantly impair physiological function and quality of life. The present study aimed to investigate the therapeutic efficacy of the novel immune‑regulatory molecule tetrahedral DNA nanostructure (TDN) in a rat model of urethral injury and explore the underlying mechanisms of action. A rat model of urethral injury was established through mechanical injury. Animals were divided into four groups: Control, model, model + rapamycin and model + TDN. Therapeutic effects and associated mechanisms were assessed via retrograde urethrography, Masson's trichrome staining, immunohistochemistry, western blotting, reverse transcription‑quantitative PCR (RT‑qPCR) and transcriptomic analysis. The results revealed that TDN markedly alleviated the immune response after urethral injury, reduced immune cell infiltration, downregulated the expression of inflammatory cytokines, including IL‑6, IL‑1β and TNF‑α, and effectively inhibited the progression of fibrosis. Masson's trichrome staining and western blotting provided evidence of reduced collagen deposition and decreased expression of fibrosis markers, including α‑smooth muscle actin, TGF‑β1, collagen I, collagen III and Smad3, after treatment with TDN. Transcriptomic analysis revealed that TDN modulated multiple immune‑related pathways, including the NF‑κB signaling pathway, NOD‑like receptor signaling pathway and cytokine‑cytokine receptor interaction, accompanied by a decrease in immune‑inflammatory responses, such as reduced inflammatory cytokine production and immune cell infiltration. Additionally, the results suggested that TDN may improve cellular metabolism and inhibit cell proliferation by downregulating the expression of cell cycle‑associated genes, as demonstrated by transcriptomic analysis and RT‑qPCR validation of cyclin B1, ribonucleotide reductase regulatory subunit M2, polo‑like kinase 1 and cyclin‑dependent kinase 1. In conclusion, TDN notably promoted tissue repair after urethral injury in rats by regulating the immune response, inhibiting fibrosis and enhancing cellular metabolism. These findings highlight TDN as a promising therapeutic candidate for urethral injury and offer novel insights into immune-regulatory strategies for the treatment of other fibrotic diseases.