| Summary: | Bone morphogenetic proteins (BMPs) can induce osteoblast differentiation during bone formation and repair. BMP-2 is currently the most used BMP in delivery systems (DSs) for growth factors. Approved by the US Food and Drug Administration, BMP-2 and type I collagen are already used in orthopaedic clinical applications. Recently, studies demontrated that BMP-9 has a higher osteogenic potential than BMP-2. However, high purification costs of BMPs limit their use. So, alternatives such as peptides derived from BMPs are studied. We have developped a peptide derived from the knuckle epitope of human BMP-9 (pBMP-9) which inhibits the proliferation of murine preosteoblasts MC3T3-E1 and increases their differentiation when used at 400 ng/mL. This study first compares in vitro the effects of equimolar concentrations (1.92 nM) of BMP-2, BMP-9 or pBMP-9 on the differentiation of MC3T3-E1 in serum-free medium. Like BMP-2, BMP-9 and pBMP-9 both activate Smads signaling pathway within 1h. In contrary to BMP-2, the Smad phosphorylation induced by BMP-9 and pBMP-9 is not prevented by noggin, an extracellular antagonist of BMP-2. Moreover, BMP-9 and pBMP-9 increase dose dependently alkaline phosphatase activity, an early marker of osteoblast differentiation within 1 day. Quantitative real-time polymerase chain reaction (qPCR) analysis demonstrates that BMP-2, BMP-9 and pBMP-9 all activate the transcription of Runx2, Osterix, type I collagen a1 chain and Osteocalcin within 6 days. Osteocalcin is the only truly osteoblast-specific gene that encodes for a protein required for Ca[superscript 2+] deposition in the extracellular matrix and subsequent mineralization. The peptide pBMP-9 allows a slight deposition of calcium ions (Ca[superscript 2+]) in the extracellular matrix of cells within 18 days. To favor efficiency of these molecules, DSs for BMP-9 or pBMP-9 using type I collagen gel or chitosan matrix have been studied. Collagen and chitosan DSs release in vitro within 1h about 35% and 80% of the initial dose of BMP-9 respectively. A slower release of pBMP-9 is observed in both DSs. The release of BMP-9 and pBMP-9 from both DSs follows Korsmeyer-Peppas kinetics. Collagen DS containing 3.84 nM BMP-2, BMP-9 or pBMP-9 activates in vitro the expression of osteogenic genes in MC3T3-E1 cells within 6 days. 6.35 [micro]g BMP-9 or 100 [micro]g pBMP-9 incorporated into chitosan DS can induce in vivo bone formation in C57BL/6 mouse quadriceps muscles within 24 days. Furthermore, collagen DS is less efficient than chitosan DS. Since BMPs can also influence adipogenic cell lineages, the effects of 3.84 nM BMP-2, BMP-9 or pBMP-9 have been studied on human white preadipocytes (HWP). pBMP-9 dose dependently reduces the proliferation of HWP without affecting the number of apoptotic cells. Incubation for 1h with BMPs or pBMP-9 activates the Smad pathway. These molecules also enhance the levels of the mRNA of the adipogenic markers aP2 and adipoQ and increase the number of lipid vesicles within 7 days in adipogenic differentiation (AD) serum-free medium containing ciglitazone. Thus, pBMP-9 seems a promising replacement for costly BMP in tissue engineering applications since this molecule can favor osteogenic differentiation of preosteoblasts and adipogenic differentiation of preadipocytes in serum-free medium.
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