Urokinase plasminogen activator receptor affects bone homeostasis by regulating osteoblast and osteoclast function

Area of Science:

• Bone biology and remodeling
• Cellular and molecular biology
• Biochemistry

Background:

• Urokinase receptor (uPAR) regulates cell functions like proliferation, adhesion, and migration.
• Osteoblasts and osteoclasts, key players in bone remodeling, express uPAR and urokinase (uPA).

Purpose of the Study:

• To investigate the role of uPAR in bone remodeling.
• To elucidate the in vivo function of uPAR in osteoblasts and osteoclasts.

Main Methods:

• Utilized uPAR knockout (KO) and wildtype (WT) mice for in vivo studies.
• Assessed bone mass using pQCT and mechanical testing.
• Characterized osteoblast and osteoclast function through proliferation assays, gene expression analysis (RT-PCR), and in vitro formation studies.

Main Results:

• uPAR-null mice exhibited increased bone mass but reduced bone mechanical strength.
• uPAR KO osteoblasts demonstrated enhanced proliferation, mineralization, and earlier differentiation markers.
• Osteoclast formation was decreased in uPAR KO monocytes, with observed defects in cytoskeletal organization (actin ring formation).

Conclusions:

• uPAR plays a critical role in regulating both osteoblast and osteoclast function in vivo.
• Aberrant transcription factor expression and cytoskeletal organization in uPAR-deficient bone cells highlight uPAR-dependent phenotypes.
• The study demonstrates uPAR's involvement in bone remodeling through its effects on bone cell proliferation, differentiation, and cytoskeletal dynamics.