A novel murine model of early calcium pyrophosphate deposition disease based on the TNFRSF11B mutation mimics features of the human disease.

Abstract

Objectives: Calcium pyrophosphate deposition (CPPD) disease is a common form of arthritis affecting older individuals. This disease is characterised by high levels of pyrophosphate in articular cartilage, resulting in calcium pyrophosphate crystal formation in humans and inflammatory and degenerative arthritis. A loss-of-function mutation in the TNFRSF11B locus (also known as CCAL1), which encodes osteoprotegerin (OPG) causes familial CPPD. OPG acts as a decoy receptor for RANKL, thereby inhibiting osteoclast differentiation and activity. CPPD currently lacks any animal models. The goal of this study was to develop a murine model of early CPPD by incorporating the TNFRSF11B gene mutation in mice and determining its effects on bones, joints and CPPD biomarkers.

Methods: We used CRISPR/Cas9 editing to generate mice carrying the TNFRSF11B mutation (Opg^mt). Joint and bone phenotypes, bone remodelling biomarkers and key CPPD biomarkers were assessed in wild type (WT; Opg^wt/wt), Opg^wt/mt and Opg^mt/mt mice at 6 and 12 months of age.

Results: Male and female mice carrying Opg^mt displayed osteopenia and high bone remodelling markers at 6 and 12 months of age. This phenotype was concurrent with increased osteoclast numbers and activity. Female Opg^mt/mt mice also displayed significant osteoarthritis features by 12 months of age, including articular cartilage loss in the lateral compartment of the knee based on Mankin structural damage scores. Additionally, biomarkers pathognomonic of CPPD disease, such as pyrophosphate, transforming growth factor (TGF)-β1 levels and ENPP1 activity, were significantly elevated in the joints of both 6- and 12-month-old female mice with OPG^mt.

Conclusions: Mice carrying Opg^mt display bone and joint phenotypes characteristic of early-stage CPPD disease in humans. Opg^mt mice represent a novel preclinical model of early CPPD, ideal for exploring potential therapies targeting the disease prior to the development of major joint damage.