A zebrafish model of developmental joint dysplasia: Manipulating the larval mechanical environment to drive the malformation and recovery of joint shape
Developmental dysplasia of the hip (DDH), a malformation of the acetabulum, is a frequent cause of early onset osteoarthritis. The disease encompasses a spectrum of severities, some of which are more amenable to treatment. Embryonic immobilisation significantly impairs the development of joint shape however the impact of this malformation to the function and growth of the joint in the short to medium term is unclear. We developed a novel model of developmental joint dysplasia using the zebrafish jaw joint to identify the mechanisms regulating cellular plasticity and ability to recover joint shape and function. Larval zebrafish were immobilised either pharmacologically or using targeted ablation of jaw muscles to induce an altered joint shape. Following restoration of muscle activity we dynamically monitored the joint shape and function in individuals at cellular resolution impossible in other vertebrate species. Reflecting the variability of the human condition we found a proportion of joints will recover both their shape and function, while others will not; despite coming from a genetically homogenous population. This allowed us to study what controls likelihood of recovery; we identified a number of cellular changes that predict likelihood of functional recovery, including position of precursor cells, and specific patterns of proliferation, migration and differentiation in joints and associated connective tissues. These factors together predict recovery better than severity of malformation alone. Using Finite Element Analysis we studied the mechanics of joints representative of ones that recover and those that fail to identify differences in patterns of strain that could explain the cellular behaviours that underpin likelihood of recovery. Thus, this model would enable the study of the short to long term impact of altered joint shape on function and could help to identify the changes that render an individual more receptive to treatment and therefore may potentially be indicative of long term joint health.