Bone material properties and response to teriparatide in osteoporosis due to WNT1 and PLS3 mutations

Abstract

Context: Patients with osteoporosis-associated WNT1 or PLS3 mutations have unique bone histomorphometric features and osteocyte-specific hormone expression patterns.

Objective: To investigate the effects of WNT1 and PLS3 mutations on bone material properties.

Design: Transiliac bone biopsies were evaluated by quantitative backscattered electron imaging, immunohistochemistry, and bone histomorphometry.

Setting: Ambulatory patients.

Patients: Three pediatric and eight adult patients with WNT1 or PLS3 mutations.

Intervention: Bone mineralization density distribution and osteocyte protein expression was evaluated in 11 patients and repeated in six patients who underwent repeat biopsy after 24 months of teriparatide treatment.

Main outcome measure: Bone mineralization density distribution and protein expression.

Results: Children with WNT1 or PLS3 mutations had heterogeneous bone matrix mineralization, consistent with bone modeling during growth. Bone matrix mineralization was homogenous in adults and increased throughout the age spectrum. Teriparatide had very little effect on matrix mineralization or bone formation in patients with WNT1 or PLS3 mutations. However, teriparatide decreased trabecular osteocyte lacunae size and increased trabecular bone FGF23 expression.

Conclusion: The contrast between preserved bone formation with heterogeneous mineralization in children and low bone turnover with homogenous bone mineral content in adults suggests that WNT1 and PLS3 have differential effects on bone modeling and remodeling. The lack of change in matrix mineralization in response to teriparatide, despite clear changes in osteocyte lacunae size and protein expression, suggests that altered WNT1 and PLS3 expression may interfere with coupling of osteocyte, osteoblast, and osteoclast function. Further studies are warranted to determine the mechanism of these changes.

Keywords: Bone mineralization density distribution; FGF23; Histomorphometry; Quantitative backscattered electron microscopy; Teriparatide.