Polyhedrin microcrystals embedded with bFGF promote wound healing

Growth factors play a critical role in wound healing, and finding a suitable biosustained-release system has always been a research hotspot. Bombyx mori cypovirus (BmCPV) is an insect virus, which produces polyhedra that encapsulate progeny virions. In this study, we found that the viral structural protein VP7 encoded by the BmCPV genomic dsRNAs S7 segment can interact with polyhedrin (Polh) encoded by the BmCPV genomic dsRNAs S10 segment. We also confirmed that the amino acid sequence at position 331-360 (VP7-tag) of VP7 is needed to interact with Polh. We found that VP7-tag can be used as an immobilization signal to direct the incorporation of foreign proteins into polyhedra. Furthermore, we constructed polyhedra (bFGF-polyhedra) containing basic fibroblast growth factor (bFGF) using a baculovirus expression system co-expressing Polh and bFGF-VP7 (fusion of VP7-tag to C-terminus of bFGF). We found that bFGF-VP7 embedded into polyhedra was difficult to degrade in the natural environment, and bFGF-VP7 was continuously released from the polyhedra, enhancing cell proliferation and migration. The animal model was used to assess the effect of bFGF-polyhedra spray on the healing of full-thickness wounds. bFGF-polyhedra promoted the expression of TGF-beta 1, alpha-SMA, and PCNA, inhibited the expression of proinflammatory factors NF-kappa B and COX-2, promoted the proliferation and differentiation of fibroblasts, enhanced collagen production and epidermal regeneration, and improved wound healing. These results indicated that bFGF-polyhedra has a promising potential for accelerating wound healing.