PTH stimulates bone formation in mice deficient in Lrp5

Area of Science:

• Bone biology and endocrinology
• Skeletal tissue remodeling
• Wnt signaling pathway

Background:

• Low-density lipoprotein receptor-related protein 5 (Lrp5) is crucial for osteoblast function and bone mass.
• Lrp5 acts as a co-receptor in the canonical Wnt signaling pathway.
• Understanding Lrp5's role is vital for developing bone anabolic therapies.

Purpose of the Study:

• To investigate the role of Lrp5 in mediating the bone anabolic effects of parathyroid hormone (PTH).
• To evaluate the response of Lrp5-deficient mice to intermittent PTH treatment.

Main Methods:

• Adult wildtype and Lrp5 knockout mice were treated with PTH or vehicle for 6 weeks.
• Bone mineral content, density, and architecture were assessed using DXA and microCT.
• Quantitative bone histomorphometry was performed on lumbar vertebrae.

Main Results:

• Lrp5 deficiency significantly decreased cancellous and cortical bone mass, associated with reduced osteoblast surface and bone formation rate.
• PTH treatment increased osteoblast surface and cortical thickness in both wildtype and Lrp5 knockout mice.
• PTH did not augment cancellous bone volume in either genotype, indicating Lrp5 is not required for this effect.

Conclusions:

• Lrp5 deficiency leads to reduced bone mass due to impaired bone formation.
• Lrp5 is not essential for the bone anabolic effects of PTH on cancellous and cortical bone.
• These findings suggest PTH may act through Lrp5-independent pathways to stimulate bone formation.