AIM: To explore the dynamic expression of high mobility group box 1(HMGB1)in scar tissues after glaucoma drainage valve implantation, and to further reveal the role and possible mechanism of HMGB1 in scarring after glaucoma surgery.METHODS: A total of 60 New Zealand white rabbits were randomly divided into control group(n=20), model group(n=20, silicone implantation under conjunctival sac)and model with drug administration group(n=20, silicone implantation under conjunctival sac combined with 5-fluorouracil injection). The conjunctival tissues were collected at 4 and 8 wk after surgery. HE staining and Masson staining were used to detect the proliferation and distribution of fibroblasts and collagen fibers in conjunctival tissues. Immunohistochemistry was utilized to detect the distribution and changes of HMGB1, transforming growth factor(TGF)-β1, Smad3 and α-smooth muscle actin(SMA)in conjunctival tissues. RT-PCR and Western blot were adopted to detect the mRNA and protein expression of HMGB1, TGF-β1, Smad3 and α-SMA in conjunctival tissues.RESULTS: HE staining and Masson staining showed that the proliferation of inflammatory cells, fibroblasts and collagen fibers in the model group was significantly higher than that in the control group at both 4 and 8 wk. Meanwhile, the proliferation of fibroblasts and collagen fibers in the model with drug administration group was significantly lower than that in the model group. Immunohistochemical staining showed that the expression of HMGB1, TGF-β1, Smad3 and α-SMA protein was observed in the conjunctival tissues of the model group both 4 and 8 wk, with brown and significantly deeper staining of the model group at 8 wk. Meanwhile, the positive staining in the model with drug administration group at both 4 and 8 wk was significantly lower than that in the model group. There was positive correlations between the number of fibroblasts stained with HE and the expression of HMGB1 in the conjunctival tissue of the model group at both 4 and 8 wk(r=0.602, 0.703, all P<0.05). RT-PCR and Western blot revealed that the mRNA and protein expression levels of HMGB1, TGF-β1, Smad3 and α-SMA in the model group were significantly higher than those in the control group at both 4 and 8 wk(all P<0.05). Meanwhile, the mRNA and protein expression levels of HMGB1, TGF-β1, Smad3 and α-SMA in the model with drug administration group were significantly lower than those in the model group(all P<0.05). There was positive correlations between mRNA expressions of HMGB1 and TGF-β1, Smad3 in the model group and the model with drug administration group(all P<0.05).CONCLUSION: The expression of HMGB1 increased at a time-dependent manner after glaucoma valve implantation. HMGB1 acts an indispensable role in the initiation and progression of scar formation after glaucoma surgery, which may be involved in the regulation of TGF-β/Smad signaling pathway.