Mutations that cause constitutive activation of fibroblast growth factor receptor 3 (FGFR3) result in skeletal disorders that are characterized by short-limbed dwarfism and premature closure of cranial sutures. In previous work, it was shown that congenital deficiency of FGFR3 led to skeletal overgrowth. Using a combination of imaging, classic histology and molecular cell biology we now show that young adult FGFR3(-/-) mice are osteopenic due to reduced cortical bone thickness and defective trabecular bone mineralization. The reduction in mineralized bone and lack of trabecular connectivity observed by micro-computed tomography were confirmed in histological and histomorphometric analyses, which revealed a significant decrease in calcein labelling of mineralizing surfaces and a significant increase in osteoid in the long bones of 4-month-old FGFR3(-/-) mice. These alterations were associated with increased staining for recognized markers of differentiated osteoblasts and increased numbers of tartrate-resistant acid phsophatase postitive osteoclasts. Primary cultures of adherent bone marrow-derived cells from FGFR3(-/-) mice expressed markers of differentiated osteoblasts but developed fewer mineralized nodules than FGFR3(+/+) cultures of the same age. Our observations reveal a role for FGFR3 in post-natal bone growth and remodelling, which identifies it as a potential therapeutic target for osteopenic disorders and those associated with defective bone mineralization.
Fibroblast growth factor (FGF) receptor 3 has been identified as a key regulator of endochondral bone development and of post-natal bone metabolism through its action on growth plate chondrocytes and osteoblasts, respectively. It has also been shown to promote chondrogenesis and cartilage production by cultured pre-chondrogenic cells in response to FGF18. In the current studies, we show that the absence of signaling through Fgfr3 in the joints of Fgfr3(-/-) mice leads to premature cartilage degeneration and early arthritis. Degenerative changes in cartilage matrix included excessive proteolysis of aggrecan core protein and type II collagen, as measured by neo-epitope immunoreactivity. These changes were accompanied by increased expression of metalloproteinase MMP13, type X collagen, cellular hypertrophy and loss of proteoglycan at the articular surface. Using a novel micro-mechanical indentation protocol, it was shown that articular cartilage in the humeral head of 4-month-old Fgfr3(-/-) mice was less resistant to compressive force and less stiff than that of littermate controls. These results identify Fgfr3 signaling as a potential target for intervention in degenerative disorders of cartilage metabolism.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.