טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentSher Ifat
SubjectEngineered Human Skin as a Tool to Study Heparan Sulfate
Proteoglycan Functions; Receptor Binding
Specificity Determinants in FGFs
DepartmentDepartment of Biology
Supervisor Professor Dina Ron


Abstract

Fibroblast growth factors (FGF1-FGF23) control embryonic development and adult tissue homeostasis by activating members of the FGF receptor family (FGFR1-5) to which they bind with overlapping affinities. Receptor binding specificity is an essential element regulating the diverse activities of FGFs. Cellular responses to FGFs are regulated by heparan sulfate proteoglycans (HSPGs). The FGF7 subfamily members are unique among FGFs as they can bind only one FGFR isoform, designated FGFR2IIIb. Here we have employed mutagenesis analysis, molecular modeling as well as crystal structure resolution to identify which domains in FGF7 subfamily members confer this specific interaction. We found that unique interaction between isoform-specific domains in the receptor and residues from the middle and amino-terminus of these FGFs confer specific FGFR2IIIb recognition.  These studies can facilitate future design of FGF7 subfamily analogs for therapeutic applications. In the second part of this work we have used engineered human skin to examine the role of the large HSPG perlecan in epidermis organogenesis. Perturbing perlecan expression in the epidermis, but not in the dermis, prevented the formation of the typical multilayered squamous epithelium. These effects were associated with a dramatic increase in apoptotic rate of basal keratinocytes as well as a block at late differentiation stages. Perlecan deficiency had no effect on basement membrane structure, cell-matrix interactions, or basal keratinocytes proliferation. Exogenous human perlecan restored normal epidermis formation. In contrast, exogenous FGF7 prevented keratinocyte apoptosis but did not restore their differentiation capacity. Collectively, these results reveal novel roles for perlecan in controlling epidermis formation and suggest that perlecan controls the bioavailability of soluble factors involved in skin formation.