X-linked hypophosphataemia (XLH) is the most common form of inherited rickets that leads to deformities in the lower limbs, poor tooth and skeletal mineralization, and disproportionate short stature in children. In adults, it is often complicated by enthesopathy, an abnormal mineralization of the tendon-bone attachment. Enthesopathy causes pain and stiffness in affected joints, particularly in the knee, hip, and ankle joints. Enthesopathy is reported as one of the most debilitating symptoms in XLH patients. Previous studies showed that entheses from mice with XLH (Hyp) are characterized by enhanced Bone morphogenic protein (BMP) and Indian hedgehog (IHH) signaling. This study aims to investigate the role of GDF5 in the development of enthesopathy in the Hyp mice. The study has two specific aims: (1) to determine if deleting GDF5 in enthesis (scleraxis-expressing (Scx+)) cells affects BMP/IHH signaling in entheses and (2) to determine if deleting GDF5 in Scx+ cells of Hyp mice attenuates XLH enthesopathy. The study hopes to gain a better understanding of role of GDF5 in enthesis maturation and XLH enthesopathy development. This study finds that deleting GDF5 in wild-type mice does not change normal enthesis maturation. However, deleting GDF5 in Hyp mice attenuates enthesopathy as indicated by decreased BMP/IHH signaling in Hyp entheses. / 2026-03-19T00:00:00Z

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

La mutagenèse chimique aléatoire par l’Ethyl-Nitroso-Urée (ENU), dont la puissance a été largement démontrée au cours de ces dernières décennies dans la création de modèles murins constitue un outil remarquable et essentiel en génomique fonctionnelle. Cette approche est en effet d’un apport considérable pour la compréhension de la fonction des gènes et de leur régulation et constitue un accélérateur pour identifier des éléments clés dans une voie de signalisation. Cette approche systématique, basée sur le criblage simultané d’un grand nombre de souris ne nécessite aucune connaissance préalable sur l’identité et la fonction des gènes étudiés. Les mutants sont identifiés au travers de cribles phénotypiques spécifiques, hiérarchisés et non-invasifs. L’identification du gène et de la mutation causale responsable du phénotype sont réalisés par un travail de cartographie génique en utilisant une série de marqueurs polymorphes ou par séquençage nouvelle génération. L’objectif de ma thèse a été de caractériser au niveau phénotypique et moléculaire, 3 lignées murines indépendantes issues de deux cribles ENU, un crible récessif et un crible dominant sensibilisé. Le premier crible visait à développer des modèles de pathologies humaines, à partir duquel a été isolée la lignée vdb, qui présente des défauts du système vestibulaire dus à une mutation dans le gène otog codant pour l’otogeline, et constitue un modèle de surdité chez l’homme. Le deuxième crible avait été mis en place dans le but d’approfondir nos connaissances fondamentales sur le développement du système squeletto-musculaire chez les mammifères, plus particulièrement chez l’homme et le bovin. Les analyses de deux lignées issues de ce crible, GMA24 et GMA06, ont permis d’identifier la mutation dans le gène Phex pour les souris GMA24 qui présentent un retard de croissance et constituent un modèle pour la maladie XLH (X-Linked Hypophosphatemic Rickets) chez l’homme. Pour les souris GMA06 présentant une hypermusculature, la mutation a été localisée sur le chromosome 2 et son identification est en cours. Ces trois modèles murins constituent des outils intéressants qui peuvent s’ajouter aux modèles déjà existants pour la surdité, la maladie XLH et les maladies type myopathies pour mieux appréhender les mécanismes moléculaires impliqués dans ces pathologies et les interactions génétiques mises en jeu dans l’objectif de tester de nouvelles thérapies. / The random chemical mutagenesis with the Ethyl-Nitroso-Urea (ENU), whose power has been widely demonstrated during these last decades in the murine models creation, is a remarkable and essential tool in functional genomics. This approach is indeed a significant contribution to the understanding of the genes’ function and regulation; it also establishes an accelerator to identify the key elements in a signaling pathway. This systematic approach, based on the simultaneous screening of a large number of mice, requires no prior knowledge on the identity and the function of the studied genes. The mutants are identified through specific, hierarchical and non-invasive phenotypic screens. The identification of the gene and the causal mutation responsible for the mutant phenotype are achieved by gene mapping by using a series of polymorphic markers or by new generation sequencing. The objective of my thesis has been to characterize at the phenotypic and molecular level 3 independent murine lines from two ENU screens, a recessive and a sensitized dominant one. The first screen aimed to develop models for human diseases, from which has been isolated the vbd murine line, presenting vestibular system defects due to a mutation in the Otog gene coding for the otogelin. This mouse line presents a model for human deafness. The second screen had been established in order to deepen our fundamental knowledge on the skeletto-muscular system development in mammals, more particularly in humans and cattle. Analyzes of two lines from this screen, GMA24 and GMA06, have allowed to identify the mutation in Phex gene for GMA24 mice showing a growth retardation and modeling XLH (X-linked Hypophosphatemic rickets) disease in humans. For the GMA06 mice presenting an increase muscle mass, the mutation has been localized on chromosome 2 and its identification is in progress. These three murine models are interesting added tools to the existing models for deafness, XLH and myopathies diseases for a better understanding of the molecular mechanisms and genetic interactions involved in these pathologies and so testing new therapies.

<p>The regulation of serum phosphate (Pi) concentrations is a complex process and our current models are far from complete. Due to major advancements in biotechnology and the development of more powerful research tools, recent advances in the field of genetics has led to the identification of several candidates for the long sought-after phosphatonin(s), or Pi regulating hormones. One of these candidates is fibroblast growth factor 23 (FGF-23) and this thesis is based upon studies of the role of FGF-23 in Pi homeostasis. We demonstrate that FGF-23 is a secreted protein which is highly expressed in tumors giving rise to oncogenic hypophosphatemic osteomalacia (OOM). Furthermore, we have developed a two-site enzyme-linked immunosorbent assay for the detection of circulating FGF-23 and established that FGF-23 is present in the circulation of healthy individuals. Also, FGF-23 serum levels are elevated in patients with disturbances in Pi homeostasis such as OOM, X-linked hypophosphatemic rickets (XLH) and chronic kidney disease and are likely to play an important role in the pathogenesis of these disorders. A transgenic mouse model that express human FGF-23 under the control of the α1(I) collagen promoter exhibit similar clinical and biochemical characteristics as do patients with OOM, XLH and autosomal dominant hypophosphatemic rickets indicating that FGF-23 is an important determinant of Pi homeostasis, vitamin D metabolism and bone mineralization.</p>

The regulation of serum phosphate (Pi) concentrations is a complex process and our current models are far from complete. Due to major advancements in biotechnology and the development of more powerful research tools, recent advances in the field of genetics has led to the identification of several candidates for the long sought-after phosphatonin(s), or Pi regulating hormones. One of these candidates is fibroblast growth factor 23 (FGF-23) and this thesis is based upon studies of the role of FGF-23 in Pi homeostasis. We demonstrate that FGF-23 is a secreted protein which is highly expressed in tumors giving rise to oncogenic hypophosphatemic osteomalacia (OOM). Furthermore, we have developed a two-site enzyme-linked immunosorbent assay for the detection of circulating FGF-23 and established that FGF-23 is present in the circulation of healthy individuals. Also, FGF-23 serum levels are elevated in patients with disturbances in Pi homeostasis such as OOM, X-linked hypophosphatemic rickets (XLH) and chronic kidney disease and are likely to play an important role in the pathogenesis of these disorders. A transgenic mouse model that express human FGF-23 under the control of the α1(I) collagen promoter exhibit similar clinical and biochemical characteristics as do patients with OOM, XLH and autosomal dominant hypophosphatemic rickets indicating that FGF-23 is an important determinant of Pi homeostasis, vitamin D metabolism and bone mineralization.