Texture quality, histological and extracellular matrix-related molecular changes of the calipash of Chinese soft-shelled turtle Pelodiscus sinensis in response to Aeromonas hydrophila challenge

Chinese soft-shelled turtle Pelodiscus sinensis possesses a distinctively soft and pliable apron around its dorsal carapace termed calipash, which is of great importance to evaluate the nutritional quality in turtle industry. As bacterial infection such as Aeromonas hydrophila often brings severe economic losses to P. sinensis culturing in China, it is necessary to study the response of this most distinctive calipash tissue to bacterial infection, which has not been reported. In this study, the texture quality, histology and extracellular matrix-related molecules of calipash in P. sinensis after A. hydrophila challenge were evaluated. After A. hydrophila infection, calipash tissue samples were subjected to biological evaluation, histological analyses using hematoxylin and eosin staining, Masson trichrome staining, scanning electron microscopy and real-time polymerase chain reaction for measuring mRNA expression of collagen biosynthesis as well as collagen degradation-related genes. Picrosirius red staining was used to reveal the type I collagen distribution. The results showed histologically observable connective tissue disorganization with a notable increase in collagen-characteristic amino acid hydroxyproline level, greater collagen I density and more collagen content in infected turtles when compared to the control. For the infected, significantly decreased mRNA levels of type I collagen and proline-4-hydroxylase coding genes, increased matrix metalloproteinases and lowered tissue inhibitor of metalloproteinase expression were observed. These results suggest that collagen metabolism or mobilization characterized using collagen degradation may play an important role in the maintenance of calipash in response to the A. hydrophila challenge.