Histomorfologia do reparo tecidual no disco da arraia cururu Potamotrygon wallacei (Chondrichthyes: Potamotrygoninae)

Abstract

This study aimed to describe tissue responses following injury to the pectoral fin (PF) of Potamotrygon wallacei and to evaluate quantitative variations in tissue components after injury, comparing them with the intact fin. To achieve these objectives, juvenile individuals of P. wallacei (n = 12) were collected from Cubá Lake, Barcelos, Amazonas, Brazil. Excisional injuries were performed on the left and right medial portions of the pectoral fin using 8 mm dermatological punches, after anesthetizing the specimens. Early tissue responses (n = 8), consisting of the re-epithelialization, inflammation, and proliferation phases, were assessed through biopsies collected between 24 h and 28 days post-injury. Late responses (n = 4), corresponding to the remodeling phase, were assessed through biopsies collected between 45 and 90 days. Biopsies from the PF underwent routine histological processing and were stained with Hematoxylin and Eosin, Masson’s Trichrome, Periodic Acid-Schiff (PAS), and Alcian blue at pH 1.0 and 2.5 (AB 1.0 and 2.5). Measurements of epidermal thickness, cartilaginous radials, and transverse muscle fibers, as well as counts of epithelial cells, mucous cells, and chondroblasts/chondrocytes, were performed. Data were compared using the nonparametric Kruskal–Wallis test, followed by Dunn’s post hoc test. During the early responses, the increased number of epithelial and mucous cells led to greater epidermal thickness between 24 hours and 7 days post-injury. Mucous cells activated sulfated acidic mucosubstances as a protective mechanism against pathogens during this same period. In the dermis and muscle layer, inflammatory exudate, leukocyte infiltration, granulation tissue formation, and muscle fiber necrosis characterized the intense inflammatory response during the first 4 days post-injury, which gradually decreased until day 21. In the proliferative phase, there was marked fibroblast proliferation, the onset of cartilaginous radial repair at 14 days, and the first record of myofibroblasts contributing to wound contraction in elasmobranchs. In the radial, repair began through the proliferation and differentiation of chondroprogenitor cells into chondroblasts, which initiated the deposition of new cartilaginous matrix, resulting in an increased number of cells. In the muscle tissue, myogenesis likely occurred through satellite cells. Late responses consisted of complete regeneration of the muscle layer and cartilaginous radial, a novel finding for elasmobranchs. The results of this study demonstrate that P. wallacei exhibits an effective regenerative capacity in the main tissues that constitute the PF, including cartilaginous and muscular tissues, and may therefore be considered a promising model for studies on tissue regeneration in vertebrates.