Lrp5 and Lrp6 exert overlapping functions in osteoblasts during postnatal bone acquisition

Area of Science:

• Skeletal Biology
• Molecular Biology
• Genetics

Background:

• The Wnt signaling pathway is crucial for bone development and maintenance.
• The specific roles of Wnt co-receptors Lrp5 and Lrp6 in osteoblasts are not fully understood.

Purpose of the Study:

• To investigate the individual and combined roles of Lrp5 and Lrp6 in mature osteoblasts for postnatal bone acquisition and function.
• To elucidate the contribution of these co-receptors to bone architecture and osteoblast differentiation.

Main Methods:

• Utilized Cre-loxP recombination driven by the human osteocalcin promoter to generate mice lacking Lrp5 or Lrp6 selectively in mature osteoblasts.
• Analyzed bone mineral density, bone architecture via microCT, and in vitro osteoblast differentiation.
• Examined calvarial cells doubly deficient for Lrp5 and Lrp6.

Main Results:

• Mice lacking Lrp5 or Lrp6 in osteoblasts showed reduced bone mineral density and altered bone structure.
• Lrp6 deficiency primarily affected trabecular bone accumulation, while Lrp5 deficiency led to age-dependent bone loss.
• In vitro differentiation was impaired in both single mutants, more severely in Lrp6 null cells.
• Double mutants exhibited severe osteopenia and a chondrocyte-like phenotype in calvarial cells, indicating a critical role for both co-receptors.

Conclusions:

• Both Lrp5 and Lrp6 are required in mature osteoblasts for normal postnatal bone development and maintenance.
• These co-receptors play distinct yet cooperative roles in regulating bone acquisition, architecture, and osteoblast differentiation.