Novel model of restricted mobility induced osteopenia in zebrafish

Immobilization, such as prolonged bed rest, is a risk factor for bone loss in humans. Motivated by the emerging utility of zebrafish (Danio rerio) as an animal of choice for the study of musculoskeletal disease, here we report a model of restricted-mobility-induced osteopenia in adult zebrafish. Aquatic tanks with small cubical compartments to restrict the movement and locomotion of single fish were designed and fabricated for this study. Adult zebrafish were divided into two groups, i.e. normal control (CONT) and restricted mobility group (RMG) (18 fish/group). Six fish from each group were euthanized on day 14, 21, and 35 of the movement restriction. By using microcomputed tomography (micro-CT), we assessed bone volume/tissue volume (BV/TV) and bone density in the whole skeleton of the fish. Further, we assessed skeletal shape in the vertebrae (radius, length, volume, neural and haemal AAAs, neural and haemal arch angle and thickness of the intervertebral space), single vertebra bone volume and bone density. Movement restriction significantly decreased vertebral skeletal parameters such as radius, length, volume, arch aperture areas and angles as well as the thickness of the intervertebral space in RMG. Further, restricted mobility significantly (p < 0.001) decreased BV/TV and bone density as compared to CONT group, starting as early as 14 days. By analysing zebrafish from CONT and RMG, we show that micro-CT imaging is a sensitive method to quantify distinct skeletal properties in zebrafish. We further defined the micro-CT parameters which can be used to examine the effects of restricted mobility on the skeleton of the fish. Our findings propose a rapid and effective osteopenia "stabulation" model, which could be used widely for osteoporosis drug screening. SIGNIFICANCE STATEMENT: Bone loss and fragility are regarded as a public health problem and necessitate new treatments and prevention strategies. Zebrafish serves as a reliable model-organism system, faithfully resembling the phenotype of osteopenia. We propose a rapid and effective zebrafish model, which could be used widely for osteoporosis drug screening, as well as studying etiology of immobilization-related musculoskeletal conditions.