Abstract
The tolerance of fish to fasting offers a model to study the regulatory mechanisms and changes produced when feeding is restored. Gilthead sea bream juveniles were exposed to a 21-days fasting period followed by 2 h to 7-days refeeding. Fasting provoked a decrease in body weight, somatic indexes, and muscle gene expression of members of the Gh/Igf system, signaling molecules (akt, tor and downstream effectors), proliferation marker pcna, myogenic regulatory factors, myostatin, and proteolytic molecules such as cathepsins or calpains, while most ubiquitin-proteasome system members increased or remained stable. In bone, downregulated expression of Gh/Igf members and osteogenic factors was observed, whereas expression of the osteoclastic marker ctsk was increased. Refeeding recovered the expression of Gh/Igf system, myogenic and osteogenic factors in a sequence similar to that of development. Akt and Tor phosphorylation raised at 2 and 5 h post-refeeding, much faster than its gene expression increased, which occurred at day 7. The expression in bone and muscle of the inhibitor myostatin (mstn2) showed an inverse profile suggesting an inter-organ coordination that needs to be further explored in fish. Overall, this study provides new information on the molecules involved in the musculoskeletal system remodeling during the early stages of refeeding in fish.
Highlights
The tolerance of fish to fasting offers a model to study the regulatory mechanisms and changes produced when feeding is restored
The metabolism switches to a catabolic status, resulting in low growth rate, and the following refeeding reverts the situation towards a hyper-anabolic phase when organisms attempt to accelerate the growth rate[6]
The present study continues the previous one already published by Perelló-Amorós and coworkers[27] in which the function of ghrelin during fasting and refeeding was characterized in gilthead sea bream
Summary
The tolerance of fish to fasting offers a model to study the regulatory mechanisms and changes produced when feeding is restored. The muscle mass of fish species is an important tissue that considerably depends during fasting and refeeding on protein degradation and synthesis During these stages of nutritional changes, metabolism and growth are adapted to resist the restrictions and rapidly adjust to the arrival of new nutrients. During fasting and refeeding, proteolytic molecules play a remarkable role to adapt to the changes in amino acids supply This is more important in fish that have a specific and enhanced protein metabolism. The main endogenous proteolytic systems, each one performing specific degradative or regulatory functions according to the nutritional conditions are, calpains, cathepsins and ubiquitin-proteasome, all of which are well-known in fish, especially salmonids[17,18,19], and in gilthead sea bream[20,21,22]
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