Early exercise disrupts a pro-repair extracellular matrix program during zebrafish fin regeneration
Understanding how mechanical stimulation affects cellular behaviors during tissue regeneration offers valuable insight into the mechanisms that regulate injury repair. We incorporated a swim tunnel exercise regimen during zebrafish caudal fin regeneration to explore exercise loading impacts on a robust model of tissue regeneration. Early exercise loading, initiated before or during blastema formation, resulted in reduced regenerative outcomes. Long-term tracking of fluorescently labeled cell lineages showed exercise loading disrupted blastemal mesenchyme formation. Transcriptomic profiling and section staining indicated loading reduced an extracellular matrix (ECM) gene expression program, including for hyaluronic acid (HA) synthesis. Like exercise loading, HA synthesis inhibition or blastemal HA depletion disrupted blastema formation. We considered if injury-upregulated HA establishes a pro-regenerative environment facilitating mechanotransduction.  HA density across the blastema correlated with nuclear localization of the mechanotransducer Yes-associated protein (Yap). Further, exercise loading or HA depletion decreased nuclear Yap and Proliferative Cell Nuclear Antigen staining. We conclude early loading during fin regeneration disrupts expression of an HA-rich ECM supporting blastema expansion. Our study of mechanical loading during fin regeneration reveals a stage-dependent response similar to that seen in mammalian skeletal repair, where early exercise—applied during blastema establishment—impairs regeneration, while delayed loading during outgrowth does not, suggesting a conserved sensitivity to the timing and intensity of mechanical stimuli in regenerative processes. Overall design: RNAseq profiling of 3 day post amputation fin regenerate blastema tissue following either swimming exercise (exp) or unexercised controls (control)