Improvement in the delivery system of bone morphogenetic protein-2: a new approach to promote bone formation.

Much research has been focused on developing bone morphogenetic protein-2(BMP-2) delivery systems to enhance bone formation in bone defect repair and bone tissue engineering. However, many of these current systems have several drawbacks associated with low loading efficiencies and reduced biological activities after release. Collagen scaffolds can be used as in delivery systems because of their biocompatibility. However, growth factors have naturally low affinity to collagen, which is disadvantageous for maintaining a sufficient growth factor concentration at the delivery sites. To enhance BMP-2 binding to collagen scaffolds, we chose a porous collagen scaffold that was chemically modified using Traut's reagent. The modified collagen scaffold allows cross-linking of the collagen fibers and is able to immobilize more BMP-2 after treatment with Sulfo-SMCC. We demonstrated that cross-linking led to a slower release rate of BMP-2, but did not reduce its biological activity. Moreover, more ectopic bone formation was induced by subcutaneous implants of cross-linked collagen treated with BMP-2. We concluded that collagen scaffolds chemically conjugated with BMP-2 using Traut's reagent and Sulfo-SMCC was an effective delivery system for use in bone defect repair and in bone tissue engineering.

[Generation of bone morphogenetic protein 4 conditional RNA interference mice].

To explore bone morphogenetic protein 4 (BMP4) function in the developing bone, a BMP4 conditional RNA interference (CRNAi) vector was constructed based on the pBSK/U6 vector with a LoxPneo cassette. The transgene fragment targeting bmp4 was obtained by Kpn and Afl double digestion and was purified before being microinjected into fertilized eggs from FVB/NJ mice. BMP4CRNAi transgenic mice were genotyped by PCR. And the PCR positive mice were crossed with Col2a1-Cre transgenic mice, whose Cre recombinase was specifically expressed in osteo-chondro-progenitor cells. Bmp4 mRNA expression in primary chondrocytes were examined by semi-quantitive RT-PCR to determine RNA interference efficiency. Results showed that BMP4(CRNAi) mice and BMP4 (Col2a1-CRNAi) mice were produced successfully, and bmp4 knockdown efficiency in primary chondrocytes of BMP4 Col2a1-CRNAi mice was 81%. This transgenic mouse line provides excellent model for studying the role of BMP4 in chondrocyte development, and BMP4CRNAi mouse may be a good model for studying the role of BMP4 in different cells, tissues and organs through crossing with different Cre transgenic mice.