Muscle regeneration in gilthead sea bream: Implications of endocrine and local regulatory factors and the crosstalk with bone

Abstract

Fish muscle regeneration is still a poorly known process. In the present study, an injury was done into the left anterior epaxial skeletal muscle of seventy 15 g gilthead sea bream (Sparus aurata) juveniles to evaluate at days 0, 1, 2, 4, 8, 16 and 30 post-wound, the expression of several muscle genes. Moreover, transcripts' expression in the bone (uninjured tissue) was also analyzed. Histology of the muscle showed the presence of dead tissue the first day after injury and how the damaged fibers were removed and replaced by new muscle fibers by day 16 that kept growing up to day 30. Gene expression results showed in muscle an early upregulation of igf-2 and a downregulation of ghr-1 and igf-1. Proteolytic systems expression increased with capn2 and ctsl peaking at 1 and 2 days post-injury, respectively and mafbx at day 8. A pattern of expression that fitted well with active myogenesis progression 16 days after the injury was then observed, with the recovery of igf-1, pax7, cmet, and cav1 expression; and later on, that of cav3 as well. Furthermore, the first days post-injury, the cytokines il-6 and il-15 were also upregulated confirming the tissue inflammation, while tnfα was only upregulated at days 16 and 30 to induce satellite cells recruitment; overall suggesting a possible role for these molecules as myokines. The results of the bone transcripts showed an upregulation first, of bmp2 and ctsk at days 1 and 2, respectively; then, ogn1 and ocn peaked at day 4 in parallel to mstn2 downregulation, and runx2 and ogn2 increased after 8 days of muscle injury, suggesting a possible tissue crosstalk during the regenerative process. Overall, the present model allows studying the sequential involvement of different regulatory molecules during muscle regeneration, as well as the potential relationship between muscle and other tissues such as bone to control musculoskeletal development and growth, pointing out an interesting new line of research in this group of vertebrates.

Keywords: GH-IGFs axis; bone; crosstalk; injury; myogenesis; proteolytic systems; regeneration; skeletal muscle.