Defective osteoclast differentiation and function in the osteopetrotic (os) rabbit

Area of Science:

• Skeletal biology
• Cell biology
• Developmental biology

Background:

• Osteopetrosis is a genetic disorder characterized by impaired osteoclast function.
• Osteoclast incompetence in certain rabbit models is resistant to bone marrow transplantation.
• The role of the skeletal microenvironment in osteoclast differentiation is not fully understood.

Purpose of the Study:

• To investigate the competence of the osteopetrotic rabbit skeletal microenvironment for normal osteoclast differentiation.
• To determine if the skeletal environment of osteopetrotic rabbits inhibits osteoclast development.

Main Methods:

• Co-culture of normal osteoclast progenitors with metatarsals from normal and osteopetrotic rabbits.
• Culture of metatarsals with normal liver, spleen, or bone marrow for up to 14 days.
• Assessment of marrow cavity development and osteoclast number and activity (tartrate-resistant acid phosphatase).

Main Results:

• Normal metatarsals developed marrow cavities and functional osteoclasts.
• Osteopetrotic metatarsals failed to develop marrow cavities and showed reduced osteoclast numbers and activity, even when co-cultured with normal tissues.
• A rat model of osteopetrosis, curable by bone marrow transplantation, showed normal development in co-culture.

Conclusions:

• The skeletal microenvironment of osteopetrotic rabbits plays a critical role in osteoclast differentiation and function.
• This environment may contain an inhibitor or lack a necessary promoter for osteoclast development.
• The findings highlight the importance of the local skeletal niche in regulating bone resorption.