Femur Shape Changes in Prg4-Deficient Mice: Morphological Insights Into Joint Well-Being

Area of Science:

• Biomedical Engineering
• Orthopedics
• Molecular Biology

Background:

• Proteoglycan-4 (PRG4), also known as lubricin, is vital for reducing friction and protecting cartilage in joints.
• PRG4 gene disruption in humans and mice results in premature joint failure, synovial hyperplasia, and cartilage fibrillation.
• Previous observations noted variable distal femoral morphology in Prg4 knockout mice compared to wild-types.

Purpose of the Study:

• To quantitatively assess joint element size and shape differences in Prg4 knockout mice.
• To determine if observed distal femoral morphology variations are consistent in a larger sample size.
• To elucidate the impact of PRG4 deficiency on joint morphology and biomechanics.

Main Methods:

• High-resolution X-ray microscopy (XRM) was used to image femora from wild-type (WT) and Prg4 knockout (Prg4-/-) mice (8-36 weeks old).
• Geometric morphometrics were employed to characterize and quantify shape changes in mouse femora.
• Histological analysis correlated shape changes with cross-sectional findings and assessed articular cartilage thickness and biomechanical properties.

Main Results:

• Prg4-/- femora exhibited significant variations in size and shape compared to WT controls.
• Distal femora in Prg4-/- mice were enlarged, extended anteroposteriorly, and narrowed mediolaterally.
• Largest deviations were observed in the trochlear groove, epicondyles, and medial condyle, with altered cartilage thickness and biomechanical properties.

Conclusions:

• PRG4 deficiency leads to distinct alterations in distal femoral morphology.
• These morphological changes are associated with abnormal articular cartilage thickness and biomechanical properties.
• The study concludes that PRG4 loss critically impacts joint morphology beyond its role in joint homeostasis.