Craniosynostosis, the premature fusion of cranial growth plates, can lead to severe functional and morphologic problems in children. The functional problems include increased intracranial pressure, mental retardation, blindness and death. The morphologic problems may include a severely dysmorphic cranial shape and mid-face hypoplasia. Craniosynostosis represents a substantial biomedical burden with an estimated incidence as high as 1:2000 births. Recent advances have documented an association between fibroblast growth factor receptor mutations and syndromic craniosynostoses. To elucidate the molecular mechanisms underlying suture fusion, we have developed a murine model in which the posterior frontal suture has been shown to undergo programmed sutural fusion shortly after birth. Our preliminary studies have implicated transforming growth factor beta (TGF-beta1) and fibroblast growth factor (FGF) signaling in the regulation of dura mater-suture interaction. These findings have led to the central hypothesis to be tested in this proposal: regional differentiation and growth factor expression by the dura mater directly underlying a cranial suture regulates the fate of the overlying cranial suture. The specific roles of transforming growth factor and fibroblast growth factors in fusing and patent sutures will be examined using adenovirus-mediated gene therapy. Specifically, we will evaluate the ability of adenovirus vectors encoding a dominant negative TGF-beta receptor or a dominant negative FGF receptor (i.e. down-regulation of the biologic activities of TGF-beta or FGF, respectively) to prevent programmed posterior frontal suture fusion. Similarly, the ability of adenovirus vectors capable of increasing TGF-beta1 or FGF-2 biologic activities to cause cranial suture will be evaluated in the normally patent sagittal suture. Sutures will be assessed histologically for temporal and spatial changes in suture fusion/patency and we will assess molecular effects of alterations in TGF-beta or FGF biologic activity by analyzing mRNA and protein expression of extracellular matrix products, TGF-beta isoforms, TGF-beta receptors, FGF-2, and FGF receptors. Finally, cellular proliferation and programmed cell death will be evaluated in experimental and control sutures. This proposal is important and timely because it addresses the basic etiopathogenesis of a common craniofacial disorder. The long-term objective of this work is to understand the mechanisms underlying sutural fusion so we can develop biomolecular strategies to treat or reverse prematurely fused sutures non- surgically.
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