A zebrafish model of developmental joint dysplasia: Manipulating the larval mechanical environment to drive the malformation and recovery of joint shape

Abstract

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.

The mechanical impact ofcol11a2loss on joints;col11a2mutant zebrafish show changes to joint development and function, which leads to early-onset osteoarthritis

“…Meshes were generated of wt and mutant larvae at 7 dpf (meshes shown in electronic supplementary material, figure S5 b ). We applied muscle forces as per Roddy et al [ 55 ] and used the material properties established from AFM ( figure 3 b ).…”

“…Meshes were generated of wt and mutant larvae at 7 dpf (meshes shown in electronic supplementary material, figure S5b). We applied muscle forces as per Roddy et al [55] and used the material properties established from AFM (figure 3b). We first modelled the wt and the mutant jaw shapes using the material properties established from each genotype and modelled a two-step process for jaw movement with step 1 denoting jaw closure and step 2 jaw opening (as per [43,55]) and visualized the maximum principal (E Max ) and minimum principal (E Min ) strains for jaw opening (figure 4) and closure (electronic supplementary material, figure S6).…”

“…We applied muscle forces as per Roddy et al [55] and used the material properties established from AFM (figure 3b). We first modelled the wt and the mutant jaw shapes using the material properties established from each genotype and modelled a two-step process for jaw movement with step 1 denoting jaw closure and step 2 jaw opening (as per [43,55]) and visualized the maximum principal (E Max ) and minimum principal (E Min ) strains for jaw opening (figure 4) and closure (electronic supplementary material, figure S6). In the wt model, tensional strains (E Max ) are located laterally around the joint and either side of the Meckel's symphysis, focused on the muscle insertion points with the strain spreading widely through the element.…”

The mechanical impact of col11a2 loss on joints; col11a2 mutant zebrafish show changes to joint development and function, which leads to early onset osteoarthritis

“…Meshes were generated of wt and mutant larvae at 7dpf (meshes shown in Supplementary Figure 4). We applied muscle forces as per Roddy et al (45) and used the material properties established from AFM ( Figure 1C).…”

“…We first modelled the wt and the mutant jaw shapes using the material properties established from each genotype and modelled a 2 step process for jaw movement with Step 1 denoting jaw closure and Step 2 jaw opening (as per (39,45)) and…”