Preeti Malladi

Molecular and Cellular Characterization of Mouse Calvarial Osteoblasts Derived from Neural Crest and Paraxial Mesoderm

Background: Cranial skeletogenic mesenchyme is derived from two distinct embryonic sources: mesoderm and cranial neural crest. Previous studies have focused on molecular and cellular differences of juvenile and adult osteoblasts. Methods: To further understand the features of mouse-derived juvenile osteoblasts, the authors separated calvarial osteoblasts by their developmental origins: frontal bone–derived osteoblasts from cranial neural crest, and parietal bone–derived osteoblasts from paraxial mesoderm. Cells were harvested from a total of 120 mice. Results: Interestingly, the authors observed distinct morphologies and proliferation potential of the two populations of osteoblasts. Osteogenic genes such as alkaline phosphatase, osteopontin, collagen I, and Wnt5a, which was recently identified as playing a role in skeletogenesis, were abundantly expressed in parietal bone–derived osteoblasts versus frontal bone–derived osteoblasts. In addition, fibroblast growth factor (FGF) receptor 2, and FGF-18 were more highly expressed in the parietal bone–derived osteoblasts, suggesting a more differentiated phenotype. In contrast, FGF-2, and adhesion molecules osteoblast cadherins and bone morphogenetic protein receptor IB, the bone tissue-specific type receptor were overexpressed in frontal bone–derived osteoblasts compared with parietal bone–derived osteoblasts. Conclusions: The authors observed that although neural crest–derived osteoblasts represented a population of less differentiated, faster growing cells, they formed bone nodules more rapidly than parietal bone–derived osteoblasts. This in vitro study suggests that embryonic tissue derivations influence postnatal in vitro calvarial osteoblast cell biology.

Isolation and characterization of posterofrontal/sagittal suture mesenchymal cells in vitro.

Background: Craniosynostosis, the premature fusion of cranial sutures, affects one in 2500 children. In the mouse, the posterofrontal suture is programed to fuse postnatally, but the adjacent sagittal suture remains patent throughout life. To study the cellular process of suture fusion, the authors isolated and studied suture-derived mesenchymal cells. Methods: Skulls were harvested from 80 mice (2 to 5 days old), and posterofrontal and sagittal sutures were dissected meticulously. Suture mesenchymal tissue was separated from the underlying dura mater and overlying pericranium and cultured in growth media. After the cells migrated from the explant tissues, the morphologies of the two cell populations were studied carefully, and quantitative real-time polymerase chain reaction was performed to evaluate gene expression. Results: Both posterofrontal and sagittal cells exhibited highly heterogeneous morphologies, and the posterofrontal cells migrated faster than the sagittal cells. Accordingly, growth factors such as transforming growth factor-β1 and fibroblast growth factor (FGF)-2 were expressed significantly more highly in posterofrontal compared with sagittal suture mesenchymal cells. In contrast, FGF receptor 2 and FGF-18 were expressed significantly more in sagittal than in posterofrontal suture cells. Importantly, bone morphogenic protein-3, the only osteogenic inhibitor in the bone morphogenic protein family, and noggin, a bone morphogenic protein antagonist, were expressed significantly more in sagittal than in posterofrontal suture cells, suggesting a possible mechanism of suture patency. Conclusions: To the authors’ knowledge, this is the first analysis of mouse suture-derived mesenchymal cells. The authors conclude that isolation of suture-derived mesenchymal cells will provide a useful in vitro system with which to study the mechanisms underlying suture biology.

Adipose-derived Mesenchymal Cells (AMCs): A Promising Future for Skeletal Tissue Engineering

The reconstruction of bony defects due to congenital deficiencies, degenerative skeletal djsease~ cOlllplex post-surgical deficits, osteonlyeJitis, and fracture nonunion represents a substantial biomedical burden. These repairs often require harvesting autogenous bone fr0l11 other anatomic sites, potentially causing donor sile 1110rbidity (Saito et (II., 200 I; Boo et al., 2002; Ikeuchi et af., 2002). AIlcmatively, the ilnplantation of a prosthetic bone substitute is less than optitllal given its lack of physiologic attributes. which can lead to infection, unpredictable graft resorption, structural failure, or unacceptable aesthetic outcomes (Mulliken et (ll., 1980; Pong et al., 2003). We propose that, in the future, cell-based therapies that exploit the regenerative potentia) of adult ITIultipotenl stromal cells (MSCs) win be a substantial inlprovelnent over currently available treattnent Jnodalities for skeletal defects. MSCs are a heterogeneous population of cells defined by an ability to differentiate to various nlesodennal-derived structural tissues such as the osteogenic, chondrogenic. nlyogenic. and adipogenic lineages. These cells have thus far been isolated frol11 several adult tissues such as bone marrow (BM), periosteunl, trabecular bone, synovium, skeletal tl1uscle, deciduous teeth, and adipose tissue (Barry and Murphy, 2004). Recent studies have suggested lhat adipose tissue conlains 1l1ultipotent cells that are sinli1ar to those derived frorn other tissues, such as bone