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| Author(s): |
Erika Yeh
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB) |
| Defense date: | 2011-08-04 |
| Examining board members: |
Maria Rita dos Santos e Passos Bueno;
Hugo Aguirre Armelin;
Andrea Laurato Sertie Santos;
Tatiana Teixeira Torres;
Chao Yun Irene Yan
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| Advisor: | Maria Rita dos Santos e Passos Bueno |
| Abstract | |
The skull is composed of structures that interact with each other forming a complex system, sucha as the bones of the skull that are united by fibrous tissue (suture), which plays important role during the development of the individual until adulthood. The phenomenon of premature fusion of sutures is named as craniosynostosis, which are caused by mutations in the FGFR2 gene in 32% of the cases with molecular diagnosis. The FGF signaling pathway has been implicated in both mitogenic biological processes, regulatory, morphological and endocrine processes. Apert syndrome accounts for 4% of all cases of craniosynostosis and the two most frequent mutations found in these patients, S252W (64%) and P253R (26%), increase the binding affinity in mesenchymal and epithelial isoforms of the receptor for nearly all FGFs and lead to loss of ligand specificity. However, literature concerning the aberrant cellular characteristics caused by Apert syndrome mutations is controversial. Currently, many studies have highlighted the importance of the periosteum (a fibrous tissue rich in cells that covers the bones) in bone regeneration, not only through paracrine signaling, but also as a source of osteoprogenitor cells. In this regard, there are few studies in literature. Our main hypothesis is to verify whether the periosteum contributes to premature and post-surgical fusion of the coronal sutures in Apert syndrome. In this case, we expect that the cells that compose this tissue, such as fibroblasts and mesenchymal stem have abnormal cell functions such as proliferation, migration and differentiation in response to altered intracellular signaling pathways. Our objectives were to verify if the S252W mutation has a similar functional/cellular effect in two different potential osteoprogenitor cells: fibroblasts and mesenchymal stem cells; and to verify whether different ligands to FGFR2, the FGFs, act differently in these cells with S252W mutation. Overall, our results reveal functional differences between fibroblasts and mesenchymal stem cells (MSCs) from patients with Apert syndrome, and that these functions are more impaired in the mutant fibroblasts. Moreover, the S252W fibroblasts have positive effect on the osteogenic differentiation of MSCs (wild-type and mutant) whereas the opposite does not occur. Inhibition of JNK phosphorylation nullifies the effect of atypical osteogenic differentiation of mutant fibroblasts. We also show that FGF2, FGF10 and FGF19 have different influences on the phenotype of mutant cells, which also differs between cell types. The FGF19 is the main factor that interferes with the process of ossification of S252W cells. Our analysis of gene expression profile showed that FGFs modulate different signaling pathways in fibroblasts from Apert syndrome patients: while FGF2 gene is linked to the central nervous system, supported by studies in animal model, FGF10 is associated to immune response and FGF19, to ossification. The study of cells with atypical mutation shows that the ectopic expression of the epithelial isoform of FGFR2 generates the clinical phenotype of Apert syndrome, but also leads to an atypical phenotype associated with epithelial-mesenchymal transition. These results enabled us to infer that the periosteum contributes to the process of suture reossification in Apert syndrome, and that both fibroblast and mesenchymal stem cells may be involved in this process. (AU) | |