Tendon developmental plasticity and functional regeneration

Abstract

Tendons enable movement by transferring force from muscle to bone. They are comprised of a highly organized collagen‐rich extracellular matrix. Disruption to the development and maintenance of tendons can lead to birth defects and result in injury in adults. We currently have an incomplete understanding of how tendons interact with their neighboring tissues to regulate the development and morphogenesis of the musculoskeletal system. In addition, once mature mammalian tendon tissue is formed, it has limited regenerative potential after injury. Central to this challenge is to uncover new mechanisms underlying tendon cell regulation during musculoskeletal development and regeneration. To accomplish this, we have turned to the zebrafish system because it is highly regenerative and amenable to genetic manipulations and live imaging. We have previously demonstrated that zebrafish tendons have molecular, developmental, morphological and biomechanical similarities to mammalian tendons, thereby making them an excellent vertebrate model to study tendon biology. However, no study has investigated their capacity to regenerate their tendons. Using the zebrafish, we developed methods to perform genetic tendon cell ablation, lineage tracing, live imaging, and mechanical testing to determine if developing and adult zebrafish can regenerate their tendon tissues. Following tendon cell ablation in developing zebrafish embryos, we observe defects in tendon gene expression and ECM composition. Cartilage and muscle tissue morphology was also disrupted following tendon cell loss. Tendon cells and the collagen organization returned after 1–2 weeks and 1–2 months, respectively. Interestingly, the pattern of the attachment sites was also restored, indicating the presence of regulatory programs that recruit and/or promote tendon cell proliferation and differentiation at the previous attachment sites. We are currently focused on identifying the developmental origins of the regenerating tendon cells and the pathways restoring the attachment site pattern. In addition to embryonic tendon regeneration, we also found that adult zebrafish appear to regenerate their collagen organization and mechanical properties after an acute physical injury. Together, our work demonstrates robust tendon regeneration at embryonic and adult stages in the zebrafish. These studies also provide a system to examine the morphogenetic and molecular events underlying tendon regeneration and musculoskeletal tissue‐tissue interactions, which has significance for regenerative biology approaches to musculoskeletal injuries.Support or Funding InformationNICHD HD06953, NIDCR DE024771, Charles H. Hood Foundation, HSCI Seed GrantThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.