|M.Sc Student||Kreizman-Shefer Hila|
|Subject||Interrelation between Fibroblast Growth Factor (FGF) and|
Osteoprotegerin (OPG) in Regulation of Skeletal
|Department||Department of Medicine||Supervisors||Dr. Gila Maor|
|Dr. Avner Yayon|
|Full Thesis text|
Achondroplasia (ACH) is the most common innate dwarfism which involves asymmetric limb growth and an impaired endochondral ossification. The etiology of the disease is a point mutation in FGFR3, which causes a constitutive activation of the receptor. However, the precise mechanism involved in ACH is not fully understood, nor there is any efficient treatment currently.
A mouse model that mimics human ACH syndrome is instrumental for better understanding the molecular mechanisms and nature of ACH. Several ACH mouse models have been generated including a 'knock-in' model in which the mouse FGFR3 gene was mutated in the position equivalent to the human Gly375Cys mutation, and closely resemble human ACH by exhibiting many of the severe skeletal malformations of the disease.
RANKL is an osteoclastogenesis factor that activates RANK, a transmembrane signaling receptor located on osteoclast precursor membrane, which is involved in modulating the latter’s differentiation and maturation. Thus, a state of deficiency in RANKL may lead to a decrease in bone resorption rate. The impact of this state was studied using RANKL deficient mice (RANKL+/-) that were cross-bred with ACH mice, and ACH phenotype was examined.
An in vitro model of early chondrogenesis based on neonatal mandibular condyle-derived chondrocytes (MCDC) is a unique model of spontaneously differentiating cartilage producing cells, developed in our laboratory. By applying FGF variants (produced by ProChon Biotech Ltd., Rehovot), that specifically activate certain FGFR, to this cell model, we could mimic ACH physiologic state and follow the specific impacts of this state on chondrogenesis local parameters. FGF2 variant, which is mediated mainly via FGFR1- a mitogenic signal transducer, markedly interfered with normal chondrocytes differentiation. FGF9v, which preferentially binds FGFR3, accelerated chondrogenesis and maturation, resembling local changes taking place in ACH. Following FGF9v -treated MCDC cultures, we could learn the uncoupling between proliferation and differentiation in this ACH-resembling model.
Additional potential ameliorative approach investigated in the current research implicates Osteoprotegerin (OPG), a soluble protein locally produced during endochondral ossification that has been recently found to act as a potent chondrogenic factor. In the current study, we examined the effects of OPG on ACH-derived primary chondrocytes.
Our studies demonstrated that achondroplasia induces a biphasic effect on endochondral ossification: an accelerated proliferation and premature differentiation, as well as blocked ossification. The therapeutic approaches of ACH X RANKL cross breeding and OPG administration seem to moderate initial accelerated chondrogenesis, but fail to reverse the overall growth interference.