Optogenetic-induced muscle loading leads to mechanical adaptation of the Achilles tendon enthesis in mice

Editorial summary

The investigators used optogenetically stimulated muscle contraction to study how increased loading affects the Achilles tendon–bone attachment in growing and adult mice. Repeated loading was followed by structural, mechanical and gene-expression analyses. Growing animals developed changes in calcaneal shape and a weaker attachment with greater collagen damage, whereas adult animals showed comparatively limited changes. Gene-expression results implicated several pathways involved in tissue adaptation. The study demonstrates that the response of the enthesis to added muscle loading depends on developmental stage. Mechanical failure testing was performed on harvested specimens after the loading intervention.