Nell-1-Induced Bone Regeneration in Calvarial Defects

Abstract

Many craniofacial birth defects contain skeletal components requiring bone grafting. We previously identified the novel secreted osteogenic molecule NELL-1, first noted to be overexpressed during premature bone formation in calvarial sutures of craniosynostosis patients. Nell-1 overexpression significantly increases differentiation and mineralization selectively in osteoblasts, while newborn Nell-1 transgenic mice significantly increase premature bone formation in calvarial sutures. In the current study, cultured calvarial explants isolated from Nell-1 transgenic newborn mice (with mild sagittal synostosis) demonstrated continuous bone growth and overlapping sagittal sutures. Further investigation into gene expression cascades revealed that fibroblast growth factor-2 and transforming growth factor-beta1 stimulated Nell-1 expression, whereas bone morphogenetic protein (BMP)-2 had no direct effect. Additionally, Nell-1-induced osteogenesis in MC3T3-E1 osteoblasts through reduction in the expression of early up-regulated osteogenic regulators (OSX and ALP) but induction of later markers (OPN and OCN). Grafting Nell-1 protein-coated PLGA scaffolds into rat calvarial defects revealed the osteogenic potential of Nell-1 to induce bone regeneration equivalent to BMP-2, whereas immunohistochemistry indicated that Nell-1 reduced osterix-producing cells and increased bone sialoprotein, osteocalcin, and BMP-7 expression. Insights into Nell-1-regulated osteogenesis coupled with its ability to stimulate bone regeneration revealed a potential therapeutic role and an alternative to the currently accepted techniques for bone regeneration.

Involvement of MAPK signaling molecules and Runx2 in the NELL1‐induced osteoblastic differentiation

“…On the other hand, the NELL1-deficient mice had reduced levels of extracellular matrix (ECM) proteins, thereby causing skeletal defects in the vertebral column and ribcage [7]. These observations have facilitated recent attempts to examine the therapeutic effects of NELL1 protein on bone defects in animal models [8,9]. However, it has not been elucidated how NELL1 protein evokes the intracellular signaling cascade in osteoblasts.…”

Delivery of Phenamil Enhances BMP-2-Induced Osteogenic Differentiation of Adipose-Derived Stem Cells and Bone Formation in Calvarial Defects

“…Calvaria of male 2-month-old CD-1 nude mice were exposed to a trephine drill under constant irrigation and 3-mm full-thickness craniotomy defects were created in each parietal bone with care to avoid injury to the underlying dura mater as previously described. 26 Each defect was syringed with sterile saline solution to remove bone debris and then implanted with scaffolds containing phenamil or/and BMP-2 (n = 8-12). Phenamil was applied to Ap-PLGA scaffolds at final concentrations of 100, 300, 600, 1000, and 1500 mM as described above.…”

Realizing the potential of gene-based molecular therapies in bone repair

“…(146,147) NEL-like molecule-1 (Nell-1) is another molecule under investigation for its osteogenic properties in repair of large segmental defects. (148)(149)(150) Nell-1 was shown to be as effective as BMP-2 in repair of critical-size defect (151) and also works synergistically with BMPs (129) that are endogenously expressed at the defect site. These proteins and, their combinations, are expected to provide further leads in aiding or even replacing BMPs in functional bone regeneration.…”