Abstract: BACKGROUND: Microglia cells play a major role in maintaining the balance as well as the development and function reconstruction of the central nervous system. As a histone deacetylase inhibitor, Scriptaid can inhibit neuroinflammation and enhance neuroprotection.
OBJECTIVE: To investigate the effect of silk fibroin methacryloyl hydrogel loaded with Scriptaid on the behaviors of microglia cells.
METHODS: Microglia (BV2 cells) were cultured in medium containing different concentrations of Scriptaid (0, 0.1, 0.5, 1, 2, 5, 10 μmol/L). The optimal concentration of Scriptaid was screened by the CCK-8 assay and live/dead cell staining. Silk fibroin methacryloyl hydrogels loaded with or without Scriptaid were prepared using photocuring. The micromorphology, swelling properties, mechanical properties, slow release properties, and hydrophilicity of the hydrogels were characterized. Microglia (BV2 cells) were inoculated in the subventricular region of 24-well Transwell and cultured in five groups. In the control group, the cell culture medium was added to the lower chamber. In the lipopolysaccharide group, Scriptaid group, hydrogel group, and drug-loaded hydrogel group, cell culture media containing lipopolysaccharide were added into the lower chamber. After 24 hours of lipopolysaccharide intervention, in the Scriptaid group, hydrogel group and drug-loaded hydrogel group, Scriptaid, silk fibroin methacryloyl hydrogel, and silk fibroin methacryloyl hydrogel loaded with Scriptaid were added to the upper chamber, respectively. The culture medium was replaced with ordinary culture medium and continued to culture for 24 hours. The cell viability was detected by CCK-8 assay, and the cell phenotype was detected by immunofluorescence staining of induced nitric oxide synthase and arginase 1.
RESULTS AND CONCLUSION: (1) Compared with the group without Scriptaid, the viability and number of BV2 cells were decreased after Scriptaid added. When Scriptaid 2 μmol/L or above was added, the cell viability was lower than the standardized cell viability (70%), and the number of BV2 cells was significantly reduced. Therefore, 1 μmol/L Scriptaid was selected to be loaded into the hydrogel. (2) Characterization experiments showed that the addition of Scriptaid did not affect the microscopic morphology, swelling rate of water absorption, compression modulus and hydrophilicity of silk fibroin methacryloyl hydrogel, and silk fibroin methacryloyl hydrogel had slow release performance. (3) The result of CCK-8 assay showed that compared with the control group, silk fibroin methacryloyl hydrogel significantly increased the viability of BV2 cells (P < 0.001). (4) Immunofluorescence staining showed that compared with the control group, the expression of inducible nitric oxide synthase was increased in the lipopolysaccharide group (P < 0.01); the expression of inducible nitric oxide synthase was decreased (P < 0.01) and the expression of arginase 1 was increased (P < 0.001) in the drug-loaded hydrogel group; the expression of arginase 1 was increased in the Scriptaid group (P < 0.01). (5) The results indicate that Scriptaid-loaded silk fibroin methacryloyl hydrogel is able to promote polarization of microglia to the M2 type after lipopolysaccharide induction. 

Key words: Scriptaid, silk fibroin methacryloyl, hydrogel, microglia, cell polarization